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Potentiometric SensingClick to copy article linkArticle link copied!
- Elena Zdrachek*Elena Zdrachek*E-mail: [email protected]Department of Inorganic and Analytical Chemistry, University of Geneva, Quai Ernest-Ansermet 30, CH-1211 Geneva, SwitzerlandMore by Elena Zdrachek
- Eric Bakker*Eric Bakker*E-mail: [email protected]Department of Inorganic and Analytical Chemistry, University of Geneva, Quai Ernest-Ansermet 30, CH-1211 Geneva, SwitzerlandMore by Eric Bakker
Analytical Chemistry
Cite this: Anal. Chem. 2019, 91, 1, 2–26
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Copyright © 2018 American Chemical Society
SPECIAL ISSUE
This article is part of the
This Review describes, with 187 references, progress in the field of potentiometric sensing in the period between January 2016 and August 2018. January 2016 was when the last fundamental review covering the topic of potentiometric sensors appeared in the special issue of Analytical Chemistry and was set as the start date.
The contributions were sourced from the scientific citation indexing service Web of Science by searching for relevant keywords and author names of recognized experts in the field. We also manually screened the tables of contents of selected journals known for publishing quality work related to electroanalytical chemistry. Owing to the significant number of contributions that are published in the field of potentiometric sensing, we may have overlooked some of them or otherwise chosen not to report on it. This contribution should therefore be appreciated as an opinion piece that gives our view on the current state of the field. It is not a comprehensive discussion of all contributions that deal with potentiometric sensors. We would like to apologize if someone feels that his or her contribution was unfairly discarded.
The field of potentiometric sensors is experiencing solid growth. It is inspiring to see how research blurs the boundaries between the disciplines and explores new readout principles for traditional potentiometric sensors. Progress in material science offers researchers new ion-to-electron transducing materials that bring the field ever closer to robust, calibration-free, and miniature sensors. The application scope of potentiometry is constantly broadening by combining it with bioassays, corrosion monitoring, in situ environmental analysis, and clinical diagnostics. The idea of developing affordable, scalable, and disposable sensors for point-of-care and in-field applications stimulates important research activity in the domain of paper-based potentiometric sensors. The combination of potentiometric sensors with wearable technologies has become a new important trend in the field.
The authors aimed to briefly describe the content of the cited works and to underline their strong and weak points. Our goal was not to offend anyone with these comments but, on the contrary, to raise important questions for critical discussion and to stimulate future progress in the field.
This Review starts with a description of progress in the development and improvement of reference electrodes, which represent an indispensable part of any electrochemical cell and has a particularly important influence on the accuracy of potentiometric measurements. It continues with an overview of recent achievements and discoveries in the domain of solid-contact ion-selective electrodes. This section was structured mainly by the type of ion-to-electron transducing material discussed. Next, insights into modern theory of potentiometry is given, describing the use of numerical simulation to predict time-dependent potential changes at ion-selective membranes as well as new protocols for determining the selectivity coefficient. Subsequently, new and nonclassical readout principles for ion-selective electrodes are presented. It is followed by a section dedicated to new materials exploited for ion-selective electrodes (ISEs), including membrane materials, ion-exchange nanopores, room temperature ionic liquids, molecular imprinted polymers, and new ionophores. Recent developments in the area of miniaturized ISEs, including paper-based devices, wearable sensors, miniaturized pH sensors, ion-selective microelectrodes, and ion-selective field effect transistors (ISFET), are discussed in the next section. The review ends with a discussion of some analytical applications for potentiometric sensors, including polyion detection and environmental, clinical, and surfactant analysis.
We mention relevant reviews published in the announced time period in the sections dedicated to the corresponding topic. However, we refer here to a recently published encyclopedia chapter on the fundamentals of potentiometric sensing (1) that may be specifically useful for readers new in the field to gain basic knowledge about the technique.
Reference Electrodes
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The reference electrode is an essential element for any potentiometric measurements. Historically, scientists have been mostly focused on improving the performance of the ISEs because the established Ag/AgCl or Hg/Hg2Cl2 reference electrodes usually provided a stable and reliable potential response during measurement. However, these reference electrodes are rigid and bulky and suffer from a need for bulky electrolyte solutions. With the growing demand to develop miniaturized electrochemical systems such as lab-on-chips and wearable sensors, it has become even more important to develop miniature solid-state reference electrodes. Some examples of implementing previously developed solid-state liquid-junction free reference electrodes into small portable and/or disposable potentiometric devices are also discussed in the section dedicated to miniaturized ion-selective electrodes. One may broadly distinguish truly novel reference electrode concepts that make use of conducting polymers, ionic liquids or other materials, and more traditional Ag/AgCl elements in contact with a salt solution. Bühlmann and co-workers published a review discussing all-solid-state ISEs and reference electrodes and discussed important aspects that should be considered when designing such sensors for specific applications. (2) Another review published by Sophocleous and Atkinson describes various attempts to produce functionally more traditional but screen printed Ag/AgCl reference electrodes. (3) The paper provides an overview of details of the electrode’s construction and an analytical comparison of its performance.
Bühlmann’s group built on an innovative approach introduced originally by Kakiuchi that made use of the self-partitioning of ionic liquids between two phases to realize a novel class of reference electrodes. Here, the ionic liquid-based reference electrodes were fabricated by polymerization-induced microphase separation, (4) which gives, in a single step approach, self-supported and mechanically and thermally robust reference electrodes. During the polymerization, the ionic liquid partitions into a compatible phase, poly(methyl methacrylate) (PMMA). A simultaneous cross-linking by added styrene and divinylbenzene develops a framework of nanochannels into which the former phase is kinetically trapped. The resulting reference electrodes demonstrated potentials that varied by less than 3 mV over almost five orders of KCl concentration. The authors also tested the 24 h potential stability of their electrodes in deionized water. While the initial potential changed by up to 6 mV over 1 h, the subsequent potential drift was on the order of 1.5 mV/h.
Other reports were conceptually more conservative and were based on electrodes of the second kind, typically of the Ag/AgX type. Lewenstam and co-workers described a solid-contact reference electrode with Ag nanoparticles, AgBr, and KBr suspended in a tetrahydrofuran solution of polyvinyl chloride (PVC) and bis(2-ethylhexyl) sebacate (DOS) and deposited on a silver electrode or another substrate covered with Ag, by drop casting. (5) An insensitivity of the developed reference electrode to repeated changes in the sample composition, pH, and the presence of redox species was found. The role of the PVC coating is not perfectly clear, but it may be assumed that it functions as a diffusion barrier and therefore effectively traps the added KBr.
Zhao et al. presented a flexible Ag/AgCl microreference electrode with an internal electrolyte reservoir based on a rather traditional design. (6) The reference electrode was less than 20 mm long and based on a microfabricated parylene tube structure, which was filled with saturated KCl solution in contact with Ag/AgCl element. The distal end of the tube was filled with KCl saturated agarose gel. The potential drift over a 10-h period was found to be less than 2 mV. The total operation time of the device has exceeded 100 h, but this is expected to depend on the solution composition. An IrOx pH indicating electrode was monolithically integrated on top of this reference electrode to complete a miniaturized combination pH probe.
Li et al. built an all-solid-state ISFET pH sensing system using solid-state thin-film reference electrodes fabricated on a plastic substrate. The Ti/Au/Ag/AgCl multilayer structure is covered with a polyvinyl butyral membrane containing a high concentration of NaCl to maintain a constant concentration of chloride. (7) The achieved potential drift of this reference element was reported to be less than 1.7 mV per hour.
Mechaour et al. studied the effect of the Ag wire diameter and the surface morphology of deposited AgCl on the stability of the resulting microscale Ag/AgCl elements. (8) Bühlmann’s group had shown earlier that the permselective properties of nanoporous glass junction materials called Vycor may result in large errors upon contact with dilute electrolyte solutions. They continued this work by investigating different available liquid junction materials such as Teflon, polyethylene, and two porous glasses sold under the brand names CoralPor and Electroporous KT. (9) It was shown that materials with larger pore sizes of >10 nm are not affected by electrostatic ion screening and exhibit more modest potential changes as a function of sample composition (less than 10 mV). However, the increase of the pores size also accelerates the flow through the junction material, which can cause significant contamination of the sample by the reference electrolyte. The authors also emphasized difficulties related to the wetting of the polymeric frits during electrode fabrication and use that are caused by the hydrophobic nature of these materials.
Solid-Contact Ion-Selective Electrodes
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The development of new solid-contact materials for ISEs remains consistently one of the most active topics in the field of potentiometric sensors. The realization of all-solid-state indicator electrodes with liquid and polymeric membranes is indeed very attractive for a range of applications and promises to simplify electrode design. Conceptually, a solid contact requires an ion to electron transducing layer between ion-selective membrane and electron conductor that gives operationally stable potentials. The quality of such materials is typically evaluated with drift measurements, water layer tests, impedance analysis, and galvanostatic perturbations.
Solid-Contact Based on Conducting Polymers
The conducting polymers poly(3,4-ethylenedioxythiophene) (PEDOT), polypyrrole, and poly(3-octylthiophene) (POT) represent the oldest group of the solid-contact materials. As they are still widely used for potentiometric applications, progress with these materials is discussed first. Chemical derivatives of these materials with improve characteristics have also been reported.
Poly(3,4-ethylenedioxythiophene) (PEDOT)
Lindner’s group focused their attention on the rate determining processes during the equilibration of ISEs based on poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT(PSS)). (10) The influence of the thicknesses of conducting polymer film and electrode substrates (Au, GC, and Pt) was investigated by recording potential–time transients upon first contact with aqueous solution. It was possible to minimize the conditioning time of the ISEs at first use, which is important for disposable sensor systems, by optimizing the thicknesses of the solid contact layer and overlaying membrane. K+-SE based on PEDOT(PSS) deposited on Au or Pt electrodes exhibited different equilibration times, which was studied by electrochemical quartz crystal microbalance. Under the otherwise same conditions, the rate of PEDOT(PSS) polymer growth was found to be significantly faster on Au compared to Pt, resulting in a thicker deposited polymer film. (11) The same group later explored a highly hydrophobic derivative of PEDOT, namely, PEDOT-C14, as a solid contact for H+, Na+, and K+-SEs. (12) All electrodes demonstrated exceptional performance characteristics, including a theoretical response slope, short equilibration time, and excellent potential stability. The superhydrophobic properties of this polymer were confirmed by contact angle measurements (136 ± 5°), which should prevent the accumulation of an aqueous film between membrane and solid contact. The authors emphasized that recording the potential drifts of solid-contact ISEs with pH-sensitive membranes in samples containing different CO2 levels may be a faster and more reliable protocol for detecting the presence of a water layer between ion-selective membrane and solid contact than the one that is widely used today (see Figure 1). (12)
Figure 1
Figure 1. Lindner’s test for the presence of a water layer between an H+-selective membrane and the transducer layer. (12) If a water layer is present, an increasing CO2 sample concentration results in diffusive transport through the membrane and into the water layer. This will result in a pH change at the backside of the membrane and a significant negative potential drift.
Plawinska et al. found that PEDOT layers exhibited a reduced capacitance when they were covered with polymeric sensing membrane. (13) This was ascribed to the low amount of transferable ions across the solid contact/membrane interface. Some procedures and pretreatment methods were proposed to minimize the effect. The groups of Gyurcsanyi and Bobacka synthesized a 3D nanostructured PEDOT(PSS) film with 750 nm-diameter interconnected pores by means of 3D nanosphere lithography and electrosynthesis. (14) The authors aimed to combine the beneficial properties of a large surface area capacitive material with that of molecular redox probes. The voids in the conducting polymer film were loaded with a moderately lipophilic redox mediator (1,1-dimethylferrocene), and the resulting material gave a reduced variation in the standard potential for a series of silver-selective electrodes to within ±4 mV, which is however still not the best in class. Also, this approach may be used only with a low diffusivity silicone rubber matrix as the extraction of redox mediator into the plasticized PVC-based ion-selective membrane was found to greatly deteriorate the slope and selectivity of the sensor.
Polypyrrole
The groups of Lindfors, Höfler, and Gyurcsanyi reported on solid-contact ISEs with excellent potential reproducibility (standard deviation of E0 of only ±0.7 mV) based on polypyrrole. (15) This was achieved by the incorporation of a highly hydrophobic perfluorinated anion (perfluorooctanesulfonate, PFOS–) as doping anion. Moreover, before applying the ion-selective membrane, the oxidation state of the electrodeposited polypyrrole was adjusted by polarization to the value of the open-circuit potential of the solid contact in 0.1 M KCl determined in advance. The obtained standard deviation of E0 is the smallest value reported up to now for conducting polymers. However, the authors conceded in an interlaboratory study that the variation increases with different batches of electrodes.
Michalska’s group synthesized polypyrrole nanospheres (about 40 nm) from poly(n-butyl acrylate) microspheres to deliver the monomer (pyrrole) to the oxidant (iron(III) nitrate) aqueous solution. (16) Ultimately, polypyrrole films were obtained by drop casting aqueous dispersions of these nanoparticles. Cyclic voltammetry and electrochemical impedance spectroscopy experiments demonstrated a high charge transfer reaction rate compared with electrochemically grown polypyrrole. The resulting solid contact in K+-selective electrodes demonstrated reasonably stable Nernstian response. Later, Michalska and co-workers investigated the influence of the doping ion (nitrate or sulfate), and the manner releasing the pyrrole monomer was released on the electrochemical properties of the resulting nanospheres. (17) Besides the enhanced electrochemical activity, the polypyrrole nanoparticles can be easily applied even on nonconductive supports such as paper because the polypyrrole nanoparticles serve as electrical lead and ion-to-electron transducer. Disposable, K+-selective electrodes on paper support were prepared by painting with a polypyrrole nanoparticle suspension and covered by the ion-selective membrane. The analytical parameters (slope, detection limit) were found to be comparable to those of classical ion-selective electrodes. (18)
Bobacka and co-workers explored the possibility of using polypyrrole/zeolite composites as solid contact material in K+-ISEs. (19) The anionic groups on the zeolite framework served as counterions for the electrochemically synthesized polypyrrole. The zeolite endowed the polypyrrole with higher hydrophobicity and gave lower detection limits after conditioning for 1 week, while the electrochemical characteristics were found to be otherwise similar to that of chloride-doped polypyrrole.
Poly(3-octylthiophene) (POT)
POT is often used in potentiometric sensors as a solid contact material by virtue of its high hydrophobicity and ease of its deposition on the electrode surface (drop casting from solution or electrosynthesis). Lindner’s group pointed out ambiguous drifts and poor potential reproducibilities of POT-based ISEs sometimes described in literature and analyzed possible reasons for these contradicting results. (20) To further improve the potential stability of POT-based K+-SEs, the authors doped the POT film with a 7,7,8,8-tetracyanoquinodimethane (TCNQ/TCNQ–) redox couple, imposing a 1:1 molar ratio of TCNQ/TCNQ– by potentiostatic control. This pretreatment resulted in a decrease of the long-term potential drift from −1.4 to −0.1 mV/h but did not improve the sensor-to-sensor potential reproducibility.
Bakker’s group presented for the first time a solid contact ion-selective electrode for the sequential sensing of cations (tetrabutylammonium) and anions (hexafluorophosphate), achieved by electrochemical switching on POT-based solid-contact membrane electrodes. (21) This became possible with a reduced thickness of the sensing membrane (about 200 nm) and the redox properties of the underlying POT film. The switchable ISE was based on plasticized polyurethane membrane containing a cation exchanger and lipophilic electrolyte (ETH 500). The ISE was formulated to naturally respond to cations. The conversion of POT into POT+ during an oxidative current treatment removed the cation exchanger from the membrane to pair with POT+, resulting in an anion-responsive membrane. A reductive current pulse restored the original cationic response. This is a potentially promising approach, but alternative ion to electron transducing layer may be more advantageous for this concept because POT-based solid contact ISEs are known to not be optimal for the detection of anionic species.
Michalska and co-workers reported on an experimental approach for the visualization and quantitation of spontaneous POT partitioning into the ion-selective membrane phase. (22) The approach is based on fluorescence microscopy as well as recording the absorption and emission spectra for membranes that were peeled from the electrode surface and subsequently dissolved in THF. Absorbance estimates total POT concentration while fluorescence emission quantifies the reduced (semiconducting) form of POT. This combination of techniques allowed the authors to quantify the change in the molar ratio between oxidized and reduced forms of POT while ISEs are in use. Fluorescence microscopic imaging suggested that POT is distributed throughout the membrane and at a relative high level of 0.5 wt %.
Polyaniline (PANI) and Other Polymers
Liu et al. demonstrated the significant improvement in the analytical characteristics of solid-contact Pb2+-SE by using electrospun PANI/PMMA microfibers as a transducer layer. (23) The electrodes prepared with electrospun microfibers did not have evidence of water layer formation, presumably due to the enhanced adhesion between the PVC membrane and PMMA containing transducer layer. The detection limit was improved by 1 order of magnitude (6.3 × 10–10 M) in comparison with the electrodes based on drop-cast PANI/PMMA film. The reproducibility of E0 values of the prepared ISEs was unfortunately not given. Abramova et al. reported on a PANI derivative doped with methacrylamide groups as a new solid contact material that can be subsequently copolymerized with polyurethane acrylate membrane matrix upon exposure to UV light. (24) The material was tested for ionophore based-Ca2+-SEs providing enhanced sensor stability (standard potential drift of less than 2 mV/day) and lifetime (up to 3 months of constant contact with calcium solution) and a reduced pH sensitivity (no response to pH change in the range of 4–9) in comparison with conventional PANI. Other sensor characteristics (sensitivity, detection limit, and selectivity) were comparable to the ones reported earlier for similar membrane composition. No evidence of an aqueous layer between membrane and solid contact was observed. The group of Lindfors introduced a composite of a few-layer exfoliated graphene and electrically conducting PANI as a solid contact in Ca2+-selective solid-contact electrodes with a silicone rubber membrane. (25) The transducer layer was deposited by drop casting from a graphene-PANI dispersion in N-methylpyrrolidone. The presence of graphene significantly improved the reproducibility of the standard potential of the electrodes compared to the neat PANI-based electrodes (±4 mV vs ±24 mV (n = 3) in the best case) and increased the hydrophobicity of the solid contact material (ca. 30° higher water contact angle). The achieved detection limit was 5 × 10–8 M.
The groups of Lindfors and Gyurcsanyi characterized lipophilic polyazulene as a solid contact film for K+-SEs suitable for clinical applications. (26) The authors performed a polarization of polyazulene before coating with plasticized poly(vinyl chloride) sensing membrane to increase the reproducibility of the E0 values of ISEs. Unfortunately, the achieved standard deviation value of ±7.9 mV (n = 4) was still worse than the state of art. Nevertheless, the prepared K+-SEs showed a good detection limit (0.7 nM), selectivity, and a close to Nernstian slope. The absence of the aqueous layer between solid contact and sensing membrane was also confirmed. The K+-SEs gave an accurate estimation of potassium levels in serum.
Solid-Contact Based on Other Materials
Carbon Materials
Carbon materials such as graphene, graphene oxide, and carbon nanotubes (CNTs) are widely used as a solid contact material in potentiometric sensors owing to their high lipophilicity and high capacitance value. Cuartero et al. gave the first direct spectroscopic evidence for capacitive charging of CNTs-based solid contact ISEs using synchrotron radiation-X-ray photoelectron spectroscopy and synchrotron radiation valence band spectroscopy. (27) Michalska and co-workers studied the dispersing agent used to prepare CNTs-based solid contact layer for ISEs. (28) The authors tested two such commonly used reagents, an anionic (dodecylbenzenesulfonate) and cationic (cetyltrimetylammonium chloride) surfactant. Thorough washing (about 30 min in excess of deionized water) of the CNT films after deposition increased their hydrophobicity (contact angle measurements) and improved the K+-SEs characteristics significantly in terms of slope and detection limit. The impedance spectra of these electrodes were however changing with time, presumably caused by detachment of the sensing membrane from the solid contact. To avoid these problems, the authors proposed carboxymethylcellulose as alternative polymeric dispersing agent. This resulted in potentiometric sensors with good analytical characteristics, improved potential reproducibility (±2 mV) compared to the other reagents, and no evidence of membrane detachment.
Qin and co-workers presented a CNT-based potentiometric solid-contact sensor for the detection of bisphenol A and explained the analytical signal by a change of surface charge. (29) The proposed sensor was prepared by layer-by-layer assembly of carboxylated multiwall carbon nanotubes, the polycationic poly(diallyldimethylammonium chloride), and the polyanionic aptamer on the electrode surface. Bisphenol A was thought to induce a detachment of the aptamer from the electrode surface, resulting in a change of surface charge (from negative to positive) that presumably resulted in the potential change. We note that earlier work with alternating polyelectrolyte layers on ion-selective membranes gave no measurable potential change as a function of surface charge, rendering this explanation potentially problematic. Bisphenol A was shown to be measured in the concentration range from 3.2 × 10–8 to 1.0 × 10–6 M with a detection limit of 1.0 × 10–8 M.
Yin et al. developed a solid-contact Ca2+-SE with good analytical characteristics (sensitivity, lower detection limit, and potential stability) based on hydrophobic octadecylamine-functionalized graphene oxide uniformly dispersed in the membrane phase. (30) The authors suggested that functionalized graphene oxide not only acts as a transducer layer but also immobilizes the ionophore through hydrophobic interactions, as evidenced by FT-IR spectroscopy. Paczosa-Bator et al. reported on a drop cast graphene supporting platinum nanoparticle layer used as a solid contact material for K+-SEs. (31) The resulting electrodes showed predictable Nernstian slope and a micromolar level detection limit but also attractive potential drifts (10.8 μV/h within 96 h) and excellent reproducibility of the standard potential values (±1.5 mV (n = 3)). Li et al. synthesized a three-dimensional graphene-mesoporous platinum nanoparticle composite and used it as a solid contact material for Cd2+-SE. (32) The transducer layer was drop-cast on the electrode surface from aqueous solution. The achieved detection limit value was 10–8.8 M. A good reproducibility of the standard potential values of ±2.5 mV (n = 3) was demonstrated.
The group of Niu proposed monolayer protected gold clusters as ion-to-electron transducer. (33,34) Gold clusters formed a separate layer by drop casting from solution on the electrode surface (33) or were directly incorporated into the membrane cocktail. (34) The obvious advantage of this material is its hydrophobicity, large capacitance, and good solubility in the membrane matrix. The mechanism of the potential stabilization at the membrane/glassy carbon electrode was, however, not clarified. Nevertheless, the prepared K+-selective electrodes showed reasonably stable Nernstian responses and typical detection limit and selectivity coefficients. Additional studies on the standard potential reproducibility for the electrodes from different batches would be advisable.
Yin et al. developed an interesting approach for the preparation of solid-contact ISEs with reduced graphene oxide as transducer layer, avoiding drop casting from solution. (35) It is based on physical adsorption of the graphene oxide powder modified with Fe3O4 to a magnetic gold electrode. The amount of graphene oxide self-assembled on the electrode surface was controlled by mass. The ion-selective membrane was glued on top of the transducer layer with a PVC/THF slurry. The resulting electrode gave comparable potential stabilities to other graphene-based solid contact ISEs. At the same time, He et al. developed an inkjet-printing process with postprint thermal annealing for graphene deposition to serve as a solid contact for ISEs. (36) The group of Kounaves reported on solid-contact ISEs suitable for measurements at high pressure (about 100 bar). (37) They were fabricated using robust microporous carbon as the ion-to-electron transducer, which was impregnated with an ionophore/additive cocktail before covering it with a PVC membrane to prevent premature sensor aging.
Molecular Redox Couples
The incorporation of a redox couple at the back side of the membrane is a well-known approach for increasing stability of SC ISEs. The group of Paczosa-Bator reported on a graphene-tetrathiafulvalene/tetrathiafulvalene cation (TTF/TTF+) nanocomposite as a promising transducing layer for solid-contact ISEs. The improved potential stability and reproducibility of nitrate-selective electrodes were found to relate to the high double layer capacitance of graphene and the presence of the TTF/TTF+ redox couple. (38) Later, the same group used a similar approach by combining carbon nanomaterials with TCNQ and its sodium salt to prepare an ion-to-electron transducer for solid-contact ISEs. (39) The possibility to improve the Na+-SEs sensitivity, linear range, and detection limit, by changing the NaTCNQ/TCNQ ratio was demonstrated in this work. Paczosa-Bator and co-workers also showed that reproducible standard potentials and low detection limits could be achieved for K+- and NO3–-SEs using the well-known charge transfer salt TTF-TCNQ as ion-to-electron transducer. (40)
The group of Michalska and Paolesse presented what appears to be a redox buffer in the absence of a molecular redox couple. A mixture of cobalt(II) porphyrin and cobalt(III) corrole together with CNTs, drop cast from solution, appears to be a promising transducer layer for solid-contact ISEs. (41) Although the cobalt complexes have different oxidation states, they cannot be electrochemically driven one to another, and so, their function is not immediately evident. The transducer layer was tested on K+-SEs and revealed a significant improvement of the analytical performance of the sensors (linear response range, detection limit, and selectivity) with increased amounts of the porphyrinoid compounds. The potential stabilizing effect was attributed to the spontaneous partitioning of cobalt(II) porphyrin and cobalt(III) corrole into the buried half of the membrane, as corroborated by laser ablation ICPMS. The sensors showed an excellent reproducibility of the E0 values with a standard deviation of just ±0.7 mV (n = 4) between different sensor batches.
Intercalating Compounds
The group of Schuhmann explored an interesting approach to achieve a well-defined interfacial potential between the solid-contact material and the ion-selective membrane by using an intercalation compound as a transducer layer. (42) The authors applied lithium iron phosphate, LiFePO4, as a solid contact for Li+-SEs. LiFePO4 can reversibly intercalate and deintercalate Li+ ions upon electrochemical reduction and oxidation of the Fe(II)/Fe(III) redox centers. In this configuration, one would expect the membrane potential to depend on the difference in the activities of the analyte ions in the sample solution and intercalating material, but since the activity of ions of interest in the intercalating material is assumed to be constant if it is chemically stable, the membrane potential would be a function of the ion activity in the sample solution only. Lithium iron phosphate was applied on the electrode surface as a slurry prepared by mixing it with an electron conductor (graphite powder), a binding polymer, and N-methyl-2-pyrrolidone as a solvent. A potential value drift of just −1.1 μV/h was reported, with a standard deviation of E0 of just ±2.0 mV (n = 3) while the achieved standard deviation of the potential measured in 10–1 M LiCl during 42 days was only ±1.5 mV. Komaba et al. demonstrated the efficiency of this approach by using different intercalating compounds, namely, Na0.33MnO2 and KxMnO2·nH2O, as a transducer layer for solid-contact Na+- and K+-SEs. (43) Lately, Schuhmann’s group also presented a family of Prussian Blue analogues as a promising transducer layer for solid-contact ISEs owing to their known capability to intercalate different ions. (44) It was shown that potassium nickel hexacyanoferrate, sodium nickel hexacyanoferrate, and calcium nickel hexacyanoferrate can be used as solid contact materials for K+-, Na+-, and Ca2+-SEs, correspondingly. All electrodes had similar analytical characteristics (slope, detection limit, selectivity coefficients, and standard potential reproducibility) as their counterparts with inner reference solution. The electrodes provided stable reproducible potentials for at least 2–3 months.
Other Materials
The group of Qin proposed to use molybdenum oxide (MoO2) microspheres (45) and three-dimensional molybdenum sulfide (MoS2) nanoflowers (46) as ion-to-electron transducers for solid contact ISEs. Both materials were applied by drop-casting from THF solution. The authors suggested that the transduction mechanism of these materials is based on forming an electrical double layer at the interface between the polymer membrane and MoO2 or MoS2. The lower detection limit of the resulting K+-SEs was similar to the values typically achieved for this membrane composition. No evidence of water layer formation was found. Unfortunately, the reproducibility of the standard potential of the electrodes was not reported.
Theory of Potentiometric Response
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The use of numerical simulation, typically by finite element analysis, is an established way to predict time-dependent concentration and associated potential changes at ion-selective membranes. The aspect unique to such membranes is the formulation of the jump condition at the sample–membrane interface, which is typically treated by a local ion-exchange equilibrium treatment. A popular approach was based on Morf’s work, but two independent research groups have identified some weakness and put forward conceptual improvement to overcome them. Egorov’s group used finite difference analysis based on the diffusion layer model to compare methods recommended by IUPAC for the determination of selectivity coefficients. (47−49) It was found that in some cases the earlier model shows principal limitations that may lead to failure of the calculations. (47) The authors studied the influence of the boundary conditions and simulation parameters to find a solution for this problem. (48) The reason for the failure is that mass transport does not account for concentration changes at both sides of the phase boundary, just at one. This means that the model allowed for ions to be generated (or lost) out of nowhere, which is chemically implausible. This group proposed to modify the established calculation protocol and termed it an interface equilibria-triggered time-dependent diffusion model. (49) It postulates that the concentration gradients in both membrane and sample solution phases determine the diffusion of the components inside the corresponding phases but not the transfer across the interface. Transfer of the components across the interface at any time is determined by the corresponding local interphase equilibria. Independent of Egorov’s group, Bakker’s group found the same type of failures and used the super-Nernstian potential jump for a membrane initially void of analyte ion as an illustrative example. (50) Here, the authors overcame the problem by treating the two boundary elements, one at either side of the sample–membrane interface, as a combined entity for mass transport purposes. While these two elements are linked by an equilibrium treatment, mass transport into and out of the combined entity is correctly described. Both Egorov’s and Bakker’s approaches are conceptually similar, give a good correlation to experimental data, and make the calculations much more robust than the original model.
Sanders et al. used a rigorous Nernst–Planck–Poisson (NPP) model, where assumption of local equilibrium across the interface is not required, to simulate the behavior of ion sensors with blocked interfaces, such as coated-wire electrodes and ion-selective field effect transistors (ISFETs). (51) This work demonstrates the first application of the NPP model to predict the response of AlGaN/GaN ISFETs with ionophore-doped membranes.
Zdrachek and Bakker revisited an old problem of describing the potential response of ion-selective electrodes in solutions containing competing ions of different charge. It is well established that the Nikolsky-Eisenman equation does not adequately describe this case. The authors compared and analyzed five different approaches to describe this problem. (52) It included the Nikolsky-Eisenman equation and its permutated form, the most rigorous self-consistent model, which is however mathematically complex, and two different approximations valid for cases of low level of interference. One of these approximations was introduced for the first time. An interesting outcome of the study was that the mathematical average of the Nikolsky-Eisenman equation and its permutated form give reasonably accurate results and might be practically useful because a single equation can be used to treat any number of charge combinations (see Figure 2).
Figure 2
Figure 2. Simplified ion-selective electrode selectivity theory for ions of different charge. The two traces show the calculated fraction of primary ion remaining in the membrane phase after ion exchange as a function of sample composition, calculated according to the self-consistent equilibrium model and by a simpler, averaged Nikolsky-Eisenman equation. Top: monovalent primary and divalent interfering ion. Bottom: divalent primary and monovalent interfering ion. (52) To average, the second Nikolsky-Eisenman equation is written to treat the interfering ion as the primary one as vice versa. This averaged Nikolsky-Eisenman equation provides results that are in excellent agreement with the values predicted by the most rigorous model for the entire range of ion exchange.
The new approximation mentioned above was used by the same authors to develop a time-dependent extrapolation method for the determination of unbiased low selectivity coefficients for two of the most prevalent cases of multivalent ions (zi = 2, zj = 1 and zi = 1, zj = 2). (53) This method is based on eliminating the primary ion concentration near the membrane by extrapolating the linearized time dependencies of selectivity coefficients determined by the separate solutions method as a function of t–1/3 or t–1/6, depending on the charge combination of the two ions, to infinite time. The approach is an extension of earlier work by Egorov’s group that only treated equally charged ions. Jasielec et al. used the NPP model to confirm the validity and limits of the method proposed by Egorov and co-workers. (54) The calculations showed that this method works well in the range of medium selectivity coefficients values, provided that the primary ion contamination of the sample (for example, from the impurities in the interfering ion salts) can be avoided. Unfortunately, for very high selectivity coefficients values (Log KijPot < −7.0), the extrapolation gives negative results, and other methods should be used.
Mikhelson’s group presented a simple theoretical model that can describe quantitatively the entire response range of ISEs including the domains of lower and upper detection limits by taking into account the coextraction processes from the inner reference solution and/or sample solution. (55) This is a simplified model; thus, it allows one to predict the potential values of ISEs only for an arbitrarily chosen time. The same group studied the increase in the bulk resistance of ionophore-based ISEs observed with decreasing analyte concentration in the sample. (56) It was suggested that the observed change in the bulk resistance originates from the difference in the membrane water uptake determined by the sample composition.
The groups of Chumbimuni-Torres and Radu suggested that the conditioning step of ISEs can be eliminated by loading the membrane cocktail directly with primary ion solution. (57) The applicability of this approach was confirmed for I–-, Ag+-, and Na+-SEs yielding functional electrodes with submicromolar detection limits.
New and Nonclassical Readout Principles for Ion-Selective Electrodes
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Recent research has demonstrated that the applicability of ISEs can be significantly expanded by interrogating them by other electrochemical (amperometry, coulometry, chronopotentiometry, ion-transfer voltammetry) or optical methodologies. This may allow one to obtain additional analytical information and/or to improve the system’s robustness and performance characteristics, such as operational reversibility, sensitivity, and selectivity.
Amperometry and Coulometry
Bobacka’s group developed an interesting new coulometric readout principle for solid-contact ISEs (see Figure 3). (58) Here, the electrochemical cell is held at constant potential. Any change of the indicator electrode potential must now be compensated by an opposite potential change at a transducing element, which happens to be a capacitive conducting polymer layer, PEDOT(PSS). This results in a transient current response until a new equilibrium state is reached. The accumulated charge is proportional to the logarithmic primary ion activity change. The authors showed that the analytical signal could be significantly amplified by increasing the PEDOT(PSS) film capacitance, which however is at the cost of increased response time. The same group studied the influence of the electrode geometry on the coulometric analytical signal of PEDOT PSS-based K+-SEs. (59) Here, glassy carbon electrodes of different surface area were covered with PEDOT layers of the same capacitance, which was controlled by keeping the polymerization charge constant. The thickness of the covering K+-selective membrane was also kept constant, giving lower membrane resistance with increasing electrode area. The response time significantly decreased with increasing electrode area. In collaboration between Bakker’s and Bobacka’s groups, the application of a coulometric readout mode was extended to the detection of anions using PEDOT doped with chloride ions as the ion-to-electron transducer. (60) As part of the work, a theoretical model was proposed to predict the coulometric response and correlated with impedance analysis. The model showed good correlation with experimental data obtained for Cl–-SE and provided explicit explanations for the previously observed influences of the transducer layer capacitance or membrane resistance on coulometric response. This coulometric readout principle could be very useful in applications where very small concentration changes (down to 0.2%) should be detected which is rather challenging with direct potentiometry.
Figure 3
Figure 3. Coulometric readout principle for solid-contact ISEs with a capacitive layer as a transducer material between electrode surface and ion-selective membrane. (58) The electrochemical cell is held at a constant potential. Any potential change at the sample–membrane interface that is driven by a change in primary ion sample activity is compensated by an opposite potential change at the transducing layer. As shown on the right, this results in a transient current response until a new equilibrium state is reached. A linear relationship between accumulated charge and the logarithmic primary ion activity change is observed and serves as the analytical signal.
Höfler and co-workers proposed an amperometric detection mode in order to enhance selectivity and detection limit of traditional ISEs. (61) The cell is divided with separate ion-selective membranes into three isolated compartments. The measurement principle is based on detecting a current flow between two Ag/AgCl elements that are placed in the outer compartments of the cell, imposed by an asymmetry in the phase-boundary potential change of two ion-selective membranes with and without an ionophore upon their contact with a sample solution in the middle compartment. In some analogy to the coulometric readout principle outlined above, this amperometric mode may sense much smaller concentration changes than conventional potentiometry. The results were corroborated by NPP finite element simulations. It should be noted here that the use of membranes without ionophore may not be practical for the measurement of variable and unknown samples because they exhibit limited selectivity.
Chronopotentiometry
Chronopotentiometry remains a popular readout mode for conventional ISEs. The group of Qin in particular has developed a number of bioassays exploiting chronopotentiometry as a readout mode of polymer based-ISEs. (62,63) The principle is based on the polarization of the polymeric membrane doped with lipophilic electrolyte (i.e., tetradodecylammonium tetrakis(4-chlorophenyl)borate) triggered by oxidation/reduction of underlying PEDOT(PSS) film. The authors recently demonstrated the sequential detection of two oppositely charged biomolecules using a single electrode with this readout mode. (63) The same group applied this electrochemical protocol by combining it with surface imprinting. (64) The recognition reaction between the imprinted polymer surface and bioanalyte molecule is thought to block the flux of an indicating (reference) ion to the membrane, thereby modulating its response. Afshar et al. developed a chronopotentiometric protocol for the detection of a wide range of different analytes (calcium, chloride, alkalinity, acidity, and protamine) by polymer membrane based-ISEs in continuous flow conditions without requiring one to stop the flow. (65) In this work, a nonpolarizable Donnan exclusion anion-exchanger membrane served as a separator to the reference/counter electrode. Such membranes sustain high current densities and exhibit stable potential values in electrolyte solutions. The power of chronopotentiometric readout mode for providing important information on chemical speciation was demonstrated by Jansod et al. for the ionizable drug phenytoin. (66) Zero current potentiometry with membranes doped with an anion exchanger can sense only the ionized form of the analyte but chronopotentiometry allows one to estimate the total amount of analyte present in the solution by the imposed ion flux. A sequential operation allows one to measure both with the same membrane electrode. An elegant approach for tackling speciation analysis was also reported by Jansod et al. for the potentiometric detection of free and total carbonate. (67) In this work, the total carbonate concentration was obtained as a result of the electrochemically triggered alkalinization of a thin layer sample (about 100 μm) formed as a restricted volume between a pH responsive polymer membrane electrode (so-called “proton sink”) and the carbonate-selective membrane electrode. Alkalinization was achieved by potentiostatic polarization of the pH-SE based on polymer membrane, removing hydrogen ions from the sample, and increasing the solution pH to the desired value.
Ion-Transfer Voltammetry
Another readout technique for ISEs that has been widely used over the last three years is ion-transfer voltammetry, which can today be applied at solid contact ISEs. The readout mode is based on the oxidation/reduction of a conducting polymer (POT or PEDOT) transducer layer in solid contact ISEs that initiates ion-transfer processes across the overlaid membrane/sample interface (see Figure 4).
Figure 4
Figure 4. Ion transfer at the membrane–solution interface resulting from the oxidation/reduction of a redox probe in the transducing layer as an analytical tool for ion sensing. (68−77) On the right, two response regimes are identified depending on the analyte concentration range. At low sample concentrations, the peak current linearly depends on concentration (diffusion limitation) while at high concentration the peak position exhibits a Nernstian shift with analyte activity change.
Bakker’s group focused their attention on POT as a transducer layer for these experiments. (68−72) It was shown that a single thin (only 200 nm) polymer membrane doped with up to three different ionophores and deposited on the top of a POT layer allows one to achieve the simultaneous detection of three different hydrophilic cations (lithium, potassium, and sodium) when interrogated by cyclic voltammetry. (68) Peak position serves here as the analytical signal, resulting in response curves that are in analogy to potentiometry. The simultaneous detection of several ions with a single membrane is of course a significant advantage of such a voltammetric readout mode compared to potentiometry. The ion-transfer charge in this configuration is chemically limited by the quantity of added ion exchanger; its concentration should therefore be carefully optimized. While the first ion-transfer experiments with this principle used conventional plasticized PVC membranes, further studies showed that this polymer matrix suffers from a significant deterioration of the signal after rinsing the electrode surface, apparently due to chemical loss of the membrane components and some physical detachment of the membrane. Bakker’s group performed a comparative study of different polymer matrices and found that plasticized polyurethane is a much more suited material. (69) Further experiments showed that one of the limiting conditions for ion-transfer voltammetry experiments is the thickness of the POT layer, as an increase of the conducting polymer film completely suppresses the ion-transfer process. (70) The mechanism of the POT thickness/POT surface roughness dependence on the ion-transfer reaction was elucidated by cyclic voltammetry, electrochemical impedance spectroscopy, ellipsometry, scanning electron microscopy, atomic force microscopy, and synchrotron radiation-X-ray photoelectron spectroscopy.
Ion-transfer at the membrane–solution interface can be exploited for ion sensing in two principal regimes: (1) peak current linearly depends on concentration or (2) the peak position describes a Nernstian shift with increasing ion activity (see Figure 4). The applicability of these two regimes depends on the analyte concentration range. Yuan et al. presented a detailed model that allows one to predict the voltammetric current and peak position for a wide concentration range of analyte by considering diffusional mass transport at the membrane–solution interface. (71,72) Using this model, one can readily estimate the limit of detection of the technique as well as the concentration level at which the switching between the two mentioned sensing regimes will be observed.
Amemiya’s group explored the use of PEDOT films to trigger the ion transfer across the thin plasticized PVC membranes doped with ionophores and lipophilic electrolyte (tetradodecylammonium tetrakis(pentafluorophenyl)borate). They reported on a multiion voltammetric detection with a membrane doped only with one ionophore and reinforced it with a theoretical model and calculations. (73) In contrast to the independent ion-transfer mechanism described above where ionophores give rise to selectivity, the mechanism of the secondary ion detection here is different. Once an ionophore becomes exhaustively depleted upon transfer of the most favorable ion, a less favorite one can be extracted at more extreme potentials. One of course may question the selectivity for this secondary extraction. In other work, Amemiya demonstrated a significant kinetic improvement of ISE selectivity (up to 7 orders of magnitude) exploited in a voltammetric readout mode in comparison to potentiometry where selectivity tends to be given by ion-exchange equilibria. (74) This principle was put forward for Na+ and Li+-ionophore-based membranes. It was shown that the ionophore-facilitated transport across the membrane/water interface of more hydrophilic alkaline earth metal cations (like Ca2+, Sr2+, and Ba2+) is significantly slower than in case of the corresponding primary ions (Na+ or Li+), which is manifested by the negative peak potential shift and increased peak separation. The selectivity coefficients calculated according to the peak positions observed in separate solutions turn out to be smaller. The observed kinetically hindered transport for more hydrophilic ions was intuitively explained by their partial dehydration with the formation of the adduct with a “water finger” prior to complexation with an ionophore at the membrane/water interface. Unfortunately, the concept was not demonstrated in real world samples containing a mixture of ions.
The group of Bakker introduced new molecular redox probes for the ion-transfer voltammetry sensing mode of ISEs, which was originally limited to the use of POT and PEDOT. They can be dissolved in the membrane phase and mediate the ion transfer across the interface upon their reduction or oxidation. (75−77) Jansod et al. (75) demonstrated the applicability of the dinonyl bipyridyl Os(II)/Os(III) complex for mediation of ion transfer for its oxidation/reduction process. The ratio between the concentrations of added cation exchanger and redox probe was found to determine the voltammetric anion or cation response of this system. Cationic diaza, azaoxa, and dioxa[6]helicenes and their derivatives were introduced as another family of molecular redox probes for voltammetric cation (76) and anion (77) detection by Jarolimova et al. Cationic diaza[6]helicene functionalized with two bromine atoms was identified as the most promising candidate. The reduction of [6]helicene cation to [6]helicene radical triggers ion transfer. For cation transfer, the membrane should be doped with a cation exchanger (76) while for anion transfer the presence of lipophilic electrolyte ETH500 (tetradodecylammonium tetrakis(4-chlorophenyl)borate) is necessary. (77) Unfortunately, it was found that the ionophore-based cation-selective membrane was losing its sensitivity with time, presumably owing to an ion exchange between the [6]helicene and analyte cations, which reduces the scope of possible applications. Additional optimization of the molecular structures of the proposed redox probes is needed to obtain a stable analytical response and to decrease the concentration of the redox probes in the membrane phase.
Cuartero et al. rationalized the mechanism of the previously observed irreversible electrochemical behavior followed by complete loss of redox reactivity of ferrocene-based redox probes in thin polymer films. (78) It was shown that the chloride anion is linked to this irreversible ferrocene electrochemistry owing to the conversion of ferrocene into nonlabile and nonreducible FeCl4– species at the glassy carbon/membrane buried interface. This process would affect the behavior of thin membrane films more than for thicker ones as a result of the limited amount of available ferrocene. The explanation was strongly supported by synchrotron radiation-X-ray photoelectron spectroscopy and near edge X-ray absorption fine structure measurements. Cuartero et al. also studied redox molecule valence states implicated in the electron hopping mechanism of ethynylferrocene in unplasticized poly(methyl methacrylate)–poly(decyl methacrylate) membranes using synchrotron radiation-valence band spectroscopy. (79) The authors found Fe 3d valence states at high concentrations of ethynylferrocene that can be explained by electron hopping between ferrocene moieties of neighboring redox molecules.
Optical Readout
A new principle that converts potential changes at ISEs into a color change was recently reported by Bakker’s group (see Figure 5). (80) It was achieved with a closed bipolar electrode at a constant applied potential where the ion-selective component is confined to one end of the electrode while color is generated at the opposite pole in a thin layer compartment. The bipolar electrode configuration allows one to physically separate the sample compartment from the detection compartment. If an electric potential is imposed across the bipolar electrode, the potentiometric signal change at the sample side results in an opposite potential change at the detection side, which is coupled to the turnover of a redox indicator and subsequently a color change. The validity of this approach was confirmed in separate experiments with a chloride responsive Ag/AgCl element and a liquid membrane-based calcium-selective membrane electrode, using the redox indicator ferroin in the detection compartment. This is a promising direction that widens the area of potentiometric sensor applications and paves the way for optical ion sensing in colored and turbid solutions.
Figure 5
Figure 5. Potential change of a potentiometric sensing probe can be visualized by the color change of redox indicator using a closed bipolar electrode configuration. (80) If a constant potential is applied across the bipolar electrode, the potentiometric signal change at the sample side results in an opposite potential change at the detection side, which imposes a new concentration ratio of the redox indicator that results in a visible color change. A colorimetric calibration curve of the bipolar electrode is shown on the right. Reproduced from Jansod, S.; Cuartero, M.; Cherubini, T.; Bakker, E. Anal. Chem., 2018, 90, 6376–6379 (ref (80)). Copyright 2018 American Chemical Society.
Ding et al. reported on another optical ion sensing platform utilizing ISEs. (81) In this work, a fixed potential difference was applied between glassy carbon electrode modified with an iron-alginate-horseradish peroxidase and conventional ISE which are placed in separate compartments of the cell connected with a salt bridge. The change in analyte concentration in the sample compartment results in a potential change of the ISE, which induces the enzyme release and subsequent color change in the detection compartment. The application of this optical ion sensing platform for detecting both cations and anions was successfully demonstrated.
Sensor Materials
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Membrane Materials
Polymeric membrane ISEs are traditionally prepared with PVC as sensing matrix. To enhance the robustness and analytical characteristics of potentiometric sensors, scientists have been looking for an appropriate replacement for PVC for many years. Fluorous liquid membranes are particularly promising because their poor solvent properties can translate into dramatically enhanced selectivity (up to 16 orders of magnitude for an ion-exchange membrane vs 8 orders usually obtained for PVC membranes) and chemical robustness. As an example, Bühlmann’s group recently demonstrated the stability of pH electrodes made of ionophore-doped fluorous membranes (Teflon AF2400) by exposing them to harsh on site cleaning protocols used in many industrial processes. (82) To mimic this type of treatment, the electrodes were repeatedly exposed for 30 min to a 3.0% NaOH solution at 90 °C. The application of fluorous liquids that have to be infused into a porous Teflon disc as a mechanical support to prepare the membrane is only compatible with fluorophilic ionophores and ion exchangers. Carey et al. reported on newly synthesized semifluorinated polymers suitable for ISEs membrane fabrication. (83) It was found that ion-exchange membranes based on these semifluorinated polymers provide a smaller selectivity range (about 8 orders of magnitude) in comparison with fluorous liquids. However, their advantage is that they can be doped both with fluorophilic ionophores and traditional lipophilic ionophores. Moreover, the membranes prepared with cross-linked semifluorinated polymers can be cast and used in the same way as conventional PVC membranes. This material also exhibits superior thermal stability: a Nernstian response was maintained after exposure to a boiling aqueous solution for 10 h.
Bühlmann and co-workers focused their attention on the application of hydrophilic ion-exchange membranes for potentiometric sensing and compared the performance of ISEs based on this material with their hydrophobic counterparts doped with an ionophore and/or an ion exchanger. (84) It was shown that owing to the high concentration of exchangeable ions hydrophilic ion-exchange membranes exhibit an excellent resistance to Donnan failure (the co-ion transfer into the sensing membrane resulting in the upper detection limit) in comparison with traditionally used hydrophobic membranes. The ion-exchange selectivity of such ion-exchange membranes is otherwise rather limited.
Michalska and co-workers introduced the concept of so-called potentiometric bilayer membranes. Authors described the bilayer membranes as a sequence of poly(hexyl acrylate) and/or poly(lauryl acrylate) layers characterized by different ionic mobilities. (85) It was found that careful tailoring of such membrane architecture allows one to compensate the spontaneous ion fluxes across the membrane phase and improve the lower detection limit of ISEs.
Ion-Exchange Nanopore Membranes
Nanopores represent a versatile sensing platform that has been known for a number of years. The principle of their response is based on the selective alteration of the flux of ions passing through preconditioned pores by the chemical and physical properties of the interior pore surface. While the majority of nanopore-based sensors are used to pass ionic current as an analytical signal, an alternative potentiometric readout mode has recently captured some attention. A potentiometric readout allows for simpler instrumentation and higher signal to background noise ratio. The potentiometric response of nanopores can be understood using the concept of permselectivity in some analogy to conventional polymer membrane ISEs. The membranes with charged nanopores exhibit permselectivity behavior by rejecting ions of the same charge sign and transporting those of opposite charge (see Figure 6). The selectivity of this ion transport can be enhanced by using a selective complexing agent (ionophore), together with ion-exchanger sites, grafted to the surface of the nanopore. Gyurcsanyi’s group made significant contributions to the development of potentiometric nanopores using solid-state gold nanopore structures. (86,87) The group presented a new potentiometric method for the selective detection of nucleic acids, (86) which is based on a charge inversion in the sensing zone of a nanopore that is triggered by the selective binding of negatively charged microRNA strands to positively charged complementary peptide-nucleic acid (PNA) modified nanopores. The initial anionic permselectivity of PNA-modified nanopores is gradually changed to cationic permselectivity, which is detected by measuring the potential across the nanoporous membrane. The same group developed a Cu2+-selective potentiometric sensor based on a 5 nm diameter gold nanopore modified with a glycine–glycine–histidine peptide. (87) This is a very hydrophilic ionophore that would normally not be functional in conventional ISEs as it would not be compatible with the sensing matrix and likely leach out of the membrane. In this nanopore application, the problem was solved by modifying the complexing tripeptide with a terminal cysteine and a glycine spacer and attaching it to the gold surface. This approach allowed one to construct ISEs with an extraordinary Cu2+ selectivity. This should pave the way for the use of hydrophilic ionophores for ion sensing that were not appropriate thus far.
Figure 6
Figure 6. Representation of permselectivity properties of solid-state modified gold nanopores. (86,87) The gold surface may be modified with thiol terminated compounds that contain ion-exchanger groups. As a result, ions of the same charge sign are rejected and those of opposite charge are being readily transported. Further chemical functionalization endows the sensing probe with desired chemical selectivity.
Ionic Liquids
Room temperature ionic liquids (ILs) are promising materials for potentiometric sensors, even though their role in potentiometric sensors is not yet fully understood: they have been promoted as inert plasticizers and/or nonspecific ion exchangers and even as ionophores. Radu’s group investigated the effect of trihexyl(tetradecyl) phosphonium-based ILs as plasticizers for PVC membranes doped with anion exchanger. (88) The response characteristics toward ten different anions were evaluated for membranes prepared with six phosphonium-based ILs. The results were compared with membranes based on two classical plasticizers: bis(2-ethylhexyl) sebacate (DOS) and 2-nitrophenyl octyl ether (NPOE). Deviations of the observed selectivity coefficients from the well-known Hofmeister series were found, suggesting binding functionalities of the IL. (88) Schazmann et al. reported on a solid-contact anion-SE based on the family of imidazolium salts covalently linked to PVC. (89) Here, the IL, with chloride as a counterion, served as an anion exchanger and a salt bridge, stabilizing the interfacial potential between the Ag/AgCl electrode substrate and the membrane. The resulting electrodes exhibited close to Nernstian slopes and stable and reproducible signals to different inorganic anions. The handling protocols of these sensors can be significantly simplified since it takes only 1 h to condition them and they can be stored dry between measurements. Rzhevskaia et al. demonstrated the use of low-melting ionic liquids based on the cationic 1,3-dihexadecylimidazolium and a range of counteranions such as chloride, iodide, and thiocyanate for the fabrication of screen-printed solid-state electrodes for the detection of the corresponding anions. (90) The ILs were drop cast in a molten state on the surface of a carbon working electrode and quickly solidified to form a robust layer on the surface. All sensors exhibited slopes close to Nernstian and good selectivity. The applicability of the developed electrodes for the potentiometric determination of iodide in pharmaceutical formulations and thiocyanate in human saliva was demonstrated. Mendecki et al. reported on the development of a novel solid-contact iodide-SE based on covalently attached 1,2,3 triazole-based IL with iodide as a counterion. (91) The iodide-SE was prepared by casting a triazole-based IL copolymerized with lauryl methacrylate on top of POT used as an ion-to-electron transducer. The IL was assumed to play the role of an iodide ionophore. The electrodes exhibited high selectivity toward iodide anions over a number of inorganic anions and near-Nernstian behavior in a wide concentration range with a lower detection limit of 8 ppb. The inherent presence of the iodide in the membrane reduces the need for electrode conditioning. The sensor was used to determine iodide concentration in human urine, but the calculated concentration was 50% lower than the one evaluated by ICPMS. The possible reasons for this discrepancy were unfortunately not discussed.
Molecular Imprinted Polymers (MIP)
Molecular imprinted polymers (MIPs) are tailor-made materials with selective recognition properties toward the compound of interest. The preparation of MIPs is based on the polymerization of a functional monomer and a molecule used as a template in the presence of a cross-linking agent, which is followed by the removal of a template molecule before use.
MIPs have shown to be useful in different analytical applications and became recently rather popular as recognition elements incorporated in the polymer membranes of ISE. MIPs were used for the potentiometric detection of the insecticide dinotefuran, (92) 1-hexyl-3-methylimidazolium, (93) acetylcholine, (94) lactic acid, (95) 2-naphthoic acid, (96) taurine, (97) bisphenol S, (98) and bisphenol AF. (99) Unfortunately, it appears that the authors sometimes overestimate the sensing power of MIP materials and tend to disregard some fundamental principles of potentiometry. For example, it is surprising to see reports on MIP-based potentiometric sensors without any ion exchanger in their membrane composition. The phase boundary potential is determined by the ratio of analyte ion activity in the aqueous and membrane phases. To observe a correlation between measured phase boundary potential and the concentration in the membrane phase, one needs to keep the analyte ion activity in the organic phase constant, which is usually achieved by incorporating a lipophilic ion exchanger into the organic phase.
Abdel-Ghany at al. explored the possibility of using MIPs synthesized with acrylamide or methacrylic acid (MAA) as a functional monomer and ethylene glycol dimethacrylate (EGDMA) as a cross-linker for the potentiometric determination of the insecticide dinotefuran. (92) The authors claimed that the developed sensors exhibited a close to Nernstian response slope with an appealing detection limit of 0.35 μg L–1, but the proposed membrane composition did not include any cation exchanger. Thus, one is left to wonder about the origin of the observed response. Zhuo and co-workers reported on a potentiometric sensor based on MIPs for determination of the cationic 1-hexyl-3-methylimidazolium. (93) The authors prepared the MIP material using MAA and EGDMA as the functional monomers and cross-linking agent. Surprisingly, it was concluded that the optimal membrane composition should be the one without added anionic lipophilic sites since membranes with added sodium tetraphenylborate were found to give a higher detection limit. Nevertheless, this membrane gave a Nernstian slope (58.9 mV) and a detection limit of 2.8 × 10–7 mol kg–1. One might question the role of the MIP in this sensor since ISEs based on a nonimprinted polymer also demonstrated a rather high response slope of 48–52 mV.
The group of Sales used MIPs for acetylcholine detection that was synthesized by bulk polymerization in a composite matrix of multiwalled carbon nanotubes (MWCNTs) and aniline. (94) Unfortunately, the technical quality of this work was rather low and the authors even tried to estimate the selectivity coefficients of the sensor over some neutral species like glucose, which is not possible. A strong pH influence on the performance characteristics was found that might be caused by the pH sensitivity of the polyaniline material. Unexpectedly, the authors came to the conclusion that pH 4.0 provides the best operating characteristics for the sensor with a super Nernstian slope of 84 mV while the same electrode exhibited a slope of 49 mV at pH 6.0. Acetylcholine detection in spiked artificial serum samples was demonstrated.
Alizadeh et al. introduced a MIP-based sensor for lactic acid sensing in dairy products. (95) MIP was synthesized using allyl amine and EGDMA as functional monomer and cross-linker. The sensor exhibited a Nernstian slope of 30.3 mV in the concentration range of 10–1–10–6 M with detection limit of 7.3 × 10–7 M. It was successfully used to estimate lactate anion concentration in samples of milk and yogurt.
Li et al. reported on the development of a screen-printed potentiometric sensor for determination of 2-naphthoic acid using MIPs and a reduced graphene-oxide as a transducer layer. (96) MIP nanobeads were prepared from acrylamide as a functional monomer, methyl methacrylate as a comonomer, and divinylbenzene and trimethylolpropanetrimethacrylate as cross-linkers. The proposed sensor exhibited a Nernstian response of 59.0 mV over the concentration range of 1.0 × 10–5–3.0 × 10–4 M with a detection limit of 2.2 μM. To satisfy the needs of trace-level analysis, the authors aimed to enhance the sensitivity of the ISE by exploiting a nonequilibrium super-Nernstian response, also known as the Hulanicki effect. Under these conditions, a linear concentration range of 1.0 × 10–10–5.0 × 10–9 M with a detection limit of 6.9 × 10–11 M was achieved. As these are transient conditions, the authors should have specified in detail the specific measurement conditions used, such as time interval and stirring conditions. Qin and co-workers also developed an all-solid-state MIP-based potentiometric sensor for determination of bisphenol S by using a nanoporous gold film as a solid contact. (98) The ISE was characterized with close to Nernstian response (28.8 mV) toward dianion of bisphenol S in the concentration range of 3 × 10–3 to 1 × 10–5 M and the detection limit of 3 × 10–6 M at pH 10.2. The authors proposed a way to improve the sensitivity of the sensor based on previously reported super Nernstian anionic potential responses of polymeric membranes doped with quaternary ammonium salt generated in the presence of electrically neutral phenols. The sensing mechanism is thought to be based on the extraction of neutral phenol ArOH into the membrane phase, accompanied by the formation of Q+X–·ArOH complex and subsequent proton dissociation of the complexed ArOH with ejection of acid HX into the aqueous phase. The authors used the potential difference between the baseline potential values and those measured at a fixed time of 250 s after bisphenol S addition at pH 5.0 for quantitation. It was shown that with this protocol the sensor has a linear concentration range from 0.1 to 2 μM with a detection limit of 0.04 μM.
It is well-known that owing to the rigid and highly cross-linked structure MIPs cannot be easily dissolved in the membrane phase. For this reason, they are normally dispersed in the membrane matrix to form a heterogeneous mixture. This heterogeneity may result in a decrease of the amount of the available binding sites as well as the increase of the membrane impedance in comparison with the homogeneous membranes. The group of Qin introduced for the first time a soluble MIP as a receptor for bisphenol AF. (99) The plasticized PVC soluble MIP was prepared by swelling the traditional MIP (synthesized from MAA as a functional monomer and divinylbenzene as cross-linker) in 1,2,4-trichlorobenzene at a high temperature. The same protocol as described above was used for sensing neutral bisphenol AF. The sensor exhibited a linear response in the narrow concentration range of 0.1 to 1 μM with a detection limit of 60 nM at pH 6.0, but the detected potential differences were very small (4.93 mV/μM), which may result in an increased error. Nevertheless, it was demonstrated that the sensor based on a soluble MIP exhibits an improved sensitivity toward bisphenol AF compared to the conventional MIP-based sensor. The selectivity gain over other phenols was also observed in the case of a soluble MIP.
Kupis-Rozmyslowicz et al. reported on MIP materials for potentiometric sensing with electrodeposited films. A molecularly imprinted conducting polymer film for taurine detection was electrodeposited from an aqueous solution containing 3,4-ethylenedioxythiophene, acetic acid thiophene, flavin mononucleotide, and taurine. (97) After removal of the template, the sensor showed close to Nernstian response slope (53.8 mV) toward the protonated form of taurine in the concentration range of 10–4 to 10–2 M.
Ionophores
Anion-Selective Ionophores
Pankratova et al. examined a series of fluorinated tripodal compounds as potential ionophores for the fabrication of ISEs for chloride analysis in serum samples. (100) It was found that ISEs based on tren tris-urea bis(CF3)[C33H27F18N7O3] exhibit the best selectivity for chloride over major lipophilic anions such as salicylate and thiocyanate that are commonly present in biological fluids. This electrode was successfully applied for chloride determination in undiluted human serum while the slope of the linear calibration in a relevant background of interfering ions was close to Nernstian (49.8 mV). Nuclear magnetic resonance titrations, potentiometric sandwich membrane experiments, and computational studies were performed to determine the binding constants and complexation stoichiometry for the new ionophore with chloride ions. Yagi at al. used a zirconium(IV) complex with octaethylporphin as a charged carrier exhibiting high selectivity to triphosphate against other hydrophilic anions including diphosphate and phosphate. (101) In this work, the HP3O104– species was apparently detected at pH 1.5. The structure of the complex was suggested as [Zr(octaethylporphin)2+]4 [HP3O104–]2 where each HP3O104– is neutralized by two Zr(octaethylporphin)2+ units. In this supramolecular organization, the remaining proton of the triphosphate ion is utilized for the intermolecular hydrogen bonding of two units to make the porphyrin rings serve as a lipophilic shell for triphosphate. The group of Bachas presented a pentagonal macrocyclic compound with an electropositive cavity, so-called cyanostar, which is able to bind anions by CH-based hydrogen bonding. (102) The size of the cyanostar’s cavity and its planarity favor the formation of a 2:1 sandwich complex with larger anions, like perchlorate, discriminating the smaller ones like chloride. ISEs of optimized membrane composition demonstrated a response to ClO4– with a slope of −57.0 mV and a detection limit of 50 nM, but unfortunately, complex formation constants were not reported. It is apparent that altering the size of the central cavity and its functionalization might result in the design of new various anion-selective ionophores. Shehab and Mansour introduced a Co(III) complex of (1H-benzimidazol-2-ylmethyl)-N-(2-chloro-phenyl)-amine as a new ionophore for salicylate sensing. (103) ISEs based on this neutral carrier exhibited good selectivity over the range of different inorganic anions, close to Nernstian response slope, and a detection limit of 0.4 μM, but no complex formation constants were reported. The applicability of the sensors was tested for determination of salicylate ions in human plasma and pharmaceutical formulations.
Abdel-Haleem et al. synthesized two new Mn(III)– and Mn(IV)–salophen complexes and used them as charged carrier for thiocyanate. (104) Both sensors exhibited very good selectivity toward thiocyanate, as the logarithmic selectivity coefficients over the very lipophilic perchlorate were about −2. The values of the binding constants of the ionophore with thiocyanate in the polymeric membrane were estimated as 1014.1 and 1012.5 for Mn(III)– and Mn(IV)–salophen complexes, respectively. The analytical application of the sensor was successfully demonstrated in saliva samples.
Cyclodextrin derivatives possessing a cage-like supramolecular structure remain very popular in chemical sensing and have been explored as possible ionophores for anion sensing. Lenik and Nieszporek reported on the use of heptakis (2,3,6-tri-O-benzoyl)-beta-cyclodextrin as an ionophore for ibuprofen (2-(4-isobutylphenyl)propionic acid) detection. (105) The electrode exhibited a Nernstian slope of 59.9 mV but in a rather modest concentration range from 10–5 to 10–2 M. Although authors reported good selectivity, the small electrode slopes for interfering ions suggest a significant experimental bias in the data.
Cation-Selective Ionophores
Porphyrins have been used as ionophores in potentiometry for a long time. The free base porphyrins are known to be cation-selective while metalloporphyrins are normally anion-selective. Lisak et al. studied porphyrin dimers as ionophores for anion and cation sensing and discovered that porphyrin dimers carrying both metal and freebase porphyrin units can exhibit either anion or cation sensitivity with respect to adding either liopophilic anion or cation exchanger to the membrane. (106) Perchlorate and silver were chosen as primary ions for this selectivity study. With cation-sensitive sensors, the selectivity was significantly improved with porphyrin dimers instead of single porphyrin molecules. The selectivity coefficient values depended on the order of porphyrin units in the dimer. These interesting discoveries will likely stimulate the application of complex porphyrin systems with more than one porphyrin unit.
Juarez-Gomez et al. presented a new Hg2+ ionophore, O,O′-(2,2′-biphenylene)dithiophosphate methyl. (107) An ISE based on this neutral carrier exhibited a Nernstian response of 29.8 mV and an attractive detection limit of 9.1 × 10–10 M. While the authors demonstrated a stable potential in the pH range from 0 to 6.0, they chose rather surprisingly an extreme pH of 0 as being optimal for further measurements. The reported logarithmic selectivity coefficients measured by the fixed interference method over Pb2+ and Cu2+ were remarkably good (−6.9 and −5.3, respectively). The sensor was successfully used as an indicating electrode during potentiometric mercury titration with EDTA. Said et al. used bis[1-benzyl-benzimidazoliumethyl]-4-methylbenzenesufonamide bromide as Ag+ ionophore, (108) but the calculated selectivity coefficients of the prepared sensor were very modest and resulted in an unattractive detection limit of 2 × 10–6 M. Omran et al. reported on another Ag+ ionophore, p-tert-butylthiacalix[4]arene with two triazole rings. (109) An ISE based on this carrier exhibited a close to Nernstian response slope in the concentration range from 7.0 × 10–6 to 8.0 × 10–3 M and a very modest detection limit of 3.9 × 10–6 M. Unfortunately, the proposed modification of the calix[4]arene structure did not result in a significant improvement of the selectivity toward Ag+, and the worst selectivity was observed over potassium and sodium.
A family of four Cu2+ ionophores based on [14]tetraazaannulene derivatives was synthesized and characterized in ion-selective membranes by Kawakami and co-workers. (110) A Nernstian response was observed in a rather narrow concentration range between 10–6 and 10–4 M. For the best membrane composition, the logarithmic selectivity coefficients were about −3.5 over Pb2+ and Cd2+ and about −4.5 over Zn2+ and Ni2+. While the ionophores were considered to be neutral carriers, it is not clear why the incorporation of anionic lipophilic sites into the membrane composition deteriorated the ISE response.
Kumar et al. reported on an Fe2+-selective electrode based on (E)-3-((2-aminoethylimino) methyl)-4H-chromen-4-one as a neutral carrier. (111) The sensor exhibited close to Nernstian slope of 27 mV and a good detection limit of 2.5 × 10–8 M but rather modest selectivity. Pb2+, Ni2+, and Ag+ were found to be the most interfering ions with logarithmic selectivity coefficients of about −2. Rezayi et al. explored the use of methylcalix[4]resorcinarene as an ionophore for Ti3+ sensing in its predominant form TiOH2+ in the pH range of 1.0–2.5. (112) The detection limit of ISE with optimized membrane composition was 8.9 × 10–7 M. The reported logarithmic selectivity coefficients estimated for a wide range of different cations ranged from −4.6 to −1.6. The selectivity coefficients were measured with the matched potential method, which cannot directly be compared to data obtained by other protocols.
Zahran et al. showed that the incorporation of cyclosporine A into polymer membrane gave ISEs with a pronounced selectivity toward calcium ions. (113) The selectivity gain over sodium, potassium, and magnesium ions was up to about 3 orders of magnitude in comparison with an ion-exchange membrane without ionophore, which is modest compared to the current state of the art. The authors also demonstrated electrospray ionization mass spectrometry for obtaining data about the distribution of complexed species in a mixture of ionophores and ions. Using these data, one can estimate the efficiency of ion binding for a number of different ionophores in a short period of time, which can be very useful for the screening of new molecules. Mass spectrometry produced data that was consistent with potentiometric selectivity.
The groups of Andrade and Ballester reported on a synthetic receptor, aryl-substituted calix[4] pyrrole with a monophosphonate bridge, for sensing the cationic creatininium ion. (114,115) The receptor works by including the creatininium cation in its deep and polar aromatic cavity and establishing directional interactions in three dimensions. The logarithmic binding constant of the ionophore with creatininium in the polymeric membrane was estimated as 6.60. (115) Creatininium-selective electrode exhibited a close to Nernstian slope with a linear range from 1 μM to 10 mM and detection limit of 10–6.2 M. (114) The operating pH range of the sensor is rather narrow from 2.8 to 3.8. (115) The developed potentiometric sensor demonstrated an improved selectivity over Na+ (log KCreatininium, Na+Pot = −3.7) and K+ (log KCreatininium, K+Pot = −2.5) which may allow its use for the analysis of biological liquids. (114,115) The authors validated this application for diluted urea and plasma samples. Khaled et al. showed that calix[4]arene could be a promising ionophore for gentamicin detection. (116) The proposed sensor demonstrated Nernstian slope of 30.5 mV and detection limit of 7.5 × 10–8 M.
Bliem et al. developed a serotonin-selective electrode incorporating an ion-pair complex of protonated serotonin cation and a carborane anion [Co(1,2-C2B9H11)2]− into plasticized PVC membrane. (117) The ISE exhibited a near Nernstian response in the concentration range from 2.25 × 10–5 to 1.00 × 10–2 M and a micromolar detection limit. Unfortunately, the very modest selectivity of this sensor over Na+ and K+ results in an increase of the observed detection limit to the level of 10–4 M in the artificial biological liquid sample while serotonin concentration in body fluids ranges from 0.3 to 0.7 μM. This fact makes the real-world application of this ISE very difficult.
Miniaturized Ion-Selective Electrodes
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Paper-Based and Microfluidic Potentiometric Devices
Paper has recently become increasingly popular as a substrate for sensor fabrication. Its simplicity, affordability, and ease of scaling and fabrication make a disposable paper-based potentiometric sensor an attractive choice for low-cost point-of-care and in-field testing applications.
Bühlmann’s group reported on a disposable planar paper-based potentiometric ion-sensing platform. (118) It contained an ISE and a reference electrode embedded into the paper substrate. Clinical applications were demonstrated with Cl– and K+ selective membranes. A commercial hydrophilic high-capacity anion-exchange membrane and valinomicyn-doped PVC membrane were used for Cl– and K+ detection. The reference membrane was doped with ionic liquid. Sensing and reference membranes were facing each other and separated the sample and reference solution zones. In complete analogy to a traditional ISE, the authors used a stencil-printed Ag/AgCl in contact with 0.1 M KCl for inner and reference electrolytes to finalize the electrochemical cell. The aqueous channels were formed by depositing polyurethane-based hydrophobic barriers. The required sample volume was just 20 μL. While the sensors worked well even in blood serum and exhibited only a few millivolts variation in their E0 values, the lower detection limit was unusually high (10–3 M) for both membranes. Further improvements are required to achieve calibration-free ion sensing.
Ding et al. developed a three-dimensional origami paper-based device for potentiometric biosensing of organophosphate pesticides (see Figure 7). (119) The bioassay is based on the known ability of organophosphate pesticides to inhibit the activity of butyrylcholinesterase. The device exhibited a test pad containing ISE and reference electrodes and three folding pads: a sampling zone pad, a pad with an immobilized enzyme, and one containing substrate reagents. The ISE for butyrylcholine was fabricated by casting the membrane doped with heptakis(2,3,6-tri-o-methyl)-β-cyclodextrin ionophore on top of a layer of carbon ink. The reference electrode membrane was composed of poly(methyl methacrylate-co-butyl methacrylate) doped with KCl on top of an Ag/AgCl layer. The sample was added to the sampling pad, and the device was folded along the fold-lines following the specific sequence to allow for the monitoring of the EMF change. The origami paper-based device exhibited a 0.06 nM detection limit for methyl parathion.
Figure 7
Figure 7. Three-dimensional origami paper-based device for potentiometric biosensing of organophosphate pesticides. (119) Left: The device consists of one test pad with electrodes and three folding pads, each for the deposition of sample, enzyme, and substrate reagents, respectively. The folding sequence is identified as Steps I, II, and III. Right: The EMF difference observed between samples with and without analyte resulting from the ability of organophosphate pesticides to inhibit the activity of the enzyme is used to calculate analyte concentration.
Radu’s group proposed an alternative approach for the fabrication of paper-based electrodes by preparing an electron conductive layer by mechanical abrasion of household pencil onto a modified acetate sheet. (120) The applicability of this approach was tested for sodium-, nitrate-, and ammonium-selective electrodes and a solid-contact reference electrode by covering a graphite layer with POT and the corresponding ion selective/reference electrode membrane. A PVC-based membrane doped with tetrabutylammonium tetrabutylborate was used as the reference electrode. The ISEs exhibited a wide dynamic response range, fast response time, and satisfactory long-term stability. The same methodology was used to prepare a single strip device consisting of a reference electrode and a series of nitrate- and ammonium-selective electrodes. This device was tested for the analysis of natural water samples and gave results that corresponded well to the data obtained with other traditionally used techniques.
Sjörberg et al. reported on a paper-based planar electrode platform where working and reference electrodes were printed using ink based on a stable suspension of gold nanoparticles. (121) These electrodes were subsequently covered with PEDOT(PSS) layer as solid contact by inkjet printing, giving conducting polymer films with comparable characteristics as electropolymerized or drop-casted ones. The reference electrode was prepared by covering the PEDOT layer with a plasticized PVC membrane doped again with tetrabutylammonium tetrabutylborate. The indicator electrode was a K+-selective valinomycin based-membrane. The analytical characteristics were promising, but the sensors were unfortunately not tested in complex real world samples.
The group of Chumbimuni-Torres developed a single strip paper-based ion sensing platform based on solid-contact working and reference electrodes. (122) The paper-based substrate was prepared by coating it with a suspension of single-walled carbon nanotubes. At the bottom of each paper sheet, a 0.5 cm diameter orifice was spluttered with gold and covered with POT and polymer membrane by drop-casting. The reference electrode membrane consisted of methyl methacrylate-co-decyl methacrylate and ionic liquids ethyl-3-methylimidazolium bis(trifluoromethane sulfonyl)amide in the ratio of 50:50. Na+,- K+-, and I–-selective PVC-based membranes were used as indicator electrodes. The single-strip sensor exhibited a Nernstian response toward all tested ions with submicromolar limits of detection. The possibility of exploiting this platform for multiplexed ion analysis was demonstrated for simultaneous detection of K+ and I–.
Andrade’s group recently reported on the interesting potentiometric hydrogen peroxide detection with Pt electrodes. It was found that Nafion not only can serve as an effective permselective barrier for some charged interfering species, such as ascorbate, but also can significantly enhance the sensitivity to hydrogen peroxide in solutions of high ionic strength. (123) Pt electrodes covered with Nafion membrane were found to exhibit a linear dependence with logarithmic concentration of H2O2 in the 10 μM to 1 mM concentration range with a slope of −125.1 mV, more than 4 times the value predicted by the Nernst equation. The origin of this high response was not clearly understood. The authors suggested that the coupling between the redox potential on the Pt electrode and the Donnan potential of the Nafion membrane may play a role. The approach was put to work by developing a potentiometric paper-based device for detecting glucose in biological liquids (124) where hydrogen peroxide is generated as a result of the enzymatic reaction. The working electrode was built using a platinized filter paper coated with a Nafion membrane that entrapped the glucose oxidase. The reference electrode was fabricated by casting a polyvinylbutyral/NaCl composite onto a conductive paper. The device was equipped with a sampling module that allowed one to perform the analysis in a single drop of blood. Under optimum conditions, a sensitivity of −95.9 mV/dec in the range of 0.3–3 mM was achieved in artificial serum samples. A good correlation between glucose concentration measured by the potentiometric paper-based platform and a commercial glucometer or colorimetric method used in clinical laboratories was demonstrated. Because the linear response range of the sensor was narrower than the physiological range of interest, a 10-fold dilution of the sample was unfortunately required.
The same group presented a modified paper-based biosensor for monitoring glucose levels in beverages. (125) In complete analogy with the previous approach, the sensing principle was based on the potentiometric detection of the hydrogen peroxide generated by an enzymatic reaction, but the working electrode was constructed by covering a platinized paper substrate first with Nafion membrane and subsequently with a polymeric membrane made of a mixture of poly(vinyl alcohol) and chitosan containing glucose oxidase. This approach appeared to facilitate enzyme immobilization and was found to increase the stability of the sensor over time. A commercial double junction reference electrode was used for measurements. The results of glucose determination in commercial orange juices were demonstrated and validated with an alternative analytical technique.
The group of Citterio developed a fully inkjet-printed disposable paper-based device for potentiometric Na+ or K+ sensing. (126) Ion selective electrodes were fabricated by using ink containing PEDOT(PSS)/graphite composite as the solid-state contact and overprinting it with the corresponding ion selective ionophore-based membrane ink. A pseudoreference Ag/AgCl electrode was prepared first by printing a layer of Ag nanoparticle ink followed by covering it with a printed layer of FeCl3 solution and reference membrane. A plasticized PVC membrane containing tetrabutylammonium tetrabutylborate was used as a reference electrode membrane. In order to make the potential of the reference electrode stable upon exposure to chloride solutions with different concentration, the authors overprinted the reference electrode membrane with 3 M KCl. The device exhibited a close to Nernstian response slope toward both Na+ (62.5 mV/dec) and K+ ions (62.9 mV/dec) with a detection limit of 32 and 101 μM, respectively. A rather small standard deviation of the E0 values of a few millivolts was achieved. A separate paper-based device was used for each measurement without any electrode preconditioning step. The device was successfully used for human urine analysis and required a 20 μL sample volume.
Nery and Kubota reported on a paper-based potentiometric electronic tongue system for analysis of beer and wine samples. (127) The system was composed of ionophore-based sodium-, calcium-, ammonium-, and potassium-selective electrodes and simpler ion-exchanger-based electrodes. The electrodes were prepared by painting a paper substrate with conductive silver paint and covering it with the corresponding membrane composition. Ag/AgCl served as a reference electrode and was prepared by oxidizing the underlying Ag electrode with sodium hypochlorite. A set of five electrodes was fixed on laminated foil and applied to the analysis of 34 beer and 11 wine samples. The sample volume could be reduced to 40 μL by placing a small piece of paper impregnated with the analyzed solution on top of the electrodes.
Paper can be used not only as a sensor substrate but also as a versatile sampling and separation platform. Ding et al. developed a paper-based microfluidic sampling and separation device for chloride sensing in the presence of interfering salicylate ions. (128) The device was fabricated by combining two pieces of paper of different pore size (12–25 μm for detection zone and 2 μm for separation zone). The piece of filter paper used for the separation was modified with Fe3+ as a complexing agent for salicylate ions. Two pieces of paper were joined together, and a sample of 150 μL was added to the separation zone. The complex formation rendered salicylate ions less mobile whereas chloride ions were easily wicked into the detection zone. A solid-contact Cl–-selective electrode and a commercial single junction Ag/AgCl reference electrode were pressed against the filter paper in the detecting zone to measure the EMF values.
Farzbod and Moon presented a digital microfluidic platform with an ion-selective electrode array. (129) The novelty of this work was the demonstration of on-chip electrode fabrication, sampling, and measurement using electrowetting-on-dielectric droplet-based microfluidics. The on-chip fabrication of ion-selective electrodes included electroplating of Ag followed by its chemical oxidation to form an AgCl layer and the deposition of a thin layer of polymeric ion selective membrane. Ag/AgCl served as a pseudoreference electrode. The fabricated potassium-selective electrode exhibited a Nernstian slope of 58 mV down to 5 μM.
Gosselin et al. proposed a microfluidic potentiometric device for monitoring DNA amplification, using pH change as analytical signal. (130) Screen-printed polyaniline-based indicator electrodes, applied by drop-casting, and Ag/AgCl chloride reference electrodes were used. A linear response to pH was observed, with a slope of −83 mV/pH. When monitoring loop-mediated isothermal amplification reaction, the device was found to give comparable results to fluorescence measurements.
Wearable Sensors
The development of wearable sensors recently became a very active research field owing to society’s need for personalized healthcare (see Figure 8). Electrochemical sensors are an attractive choice for wearable sensing platforms primarily owing to their ease of miniaturization and their low energy consumption. Sweat is the most popular sample substrate for wearable sensors as its composition is linked to various physiological processes that makes it suitable for the diagnostics of health status and sports performance. Sweat analysis is also noninvasive.
Figure 8
Figure 8. Wearable potentiometric sensors for the real-time monitoring of electrolyte level in sweat have become an important direction of research.
Zhang’s group developed a wearable sweatband sensor platform for Na+ detection. (131) The authors used a gold nanodendrite as a solid contact for PVC-based Na+-selective electrode, which was motivated by their high surface area and high double layer capacitance. The gold nanodendrite array was fabricated on a microwell patterned chip by one-step electrodeposition. Increased surface area of the gold nanodendrite material gave improved potential stability. The lowest potential drift (0.22 mV h–1) was achieved for a surface area of 7.23 cm2. The sensors exhibited stable and reproducible calibration curves for at least two months. The solid-state reference electrode consisted of a poly(vinyl acetate)/KCl composite membrane on top of Ag/AgCl. The developed sweatband sensor platform was used for a real-time monitoring of sodium in sweat during indoor exercise.
Andrade’s group reported on the use of commercial carbon fibers for the fabrication of wearable potentiometric sensors for monitoring of Na+ levels in sweat. (132) Carbon fibers were used to build both working and reference electrodes. The Na+-SE was fabricated by dipping the fiber into a PVC-based membrane cocktail while the reference electrode carbon fiber was first covered with Ag/AgCl ink and subsequently with polyvinyl butyral/NaCl composite. The integrated sensing platform exhibited a close to Nernstian slope in the concentration range from 10–3 to 10–1 M in artificial sweat samples. The system demonstrated good potential stability within 4.5 h (drift of −0.4 ± 0.3 mV/h). This material is very attractive for wearable applications as such fibers and can easily be integrated into textile materials.
Diamond’s group presented a potentiometric microfluidic chip for detecting sodium concentration in sweat. (133) The sensing platform consisted of a solid-state Na+-selective electrode and reference electrode fabricated as screen-printed disposable strips. Different PEDOT films were tested as solid-contact material for Na+-SE, paying attention to sensitivity, linear response range, and within-batch reproducibility. Electrochemically deposited PEDOT from monomer solution in pure 1-ethyl-3-methylimidazolium bis(trifuoromethanesulfonyl) imide offered the best the potential stability (−0.04 mV/min drift within 4 h) and a standard potential reproducibility of a few millivolts. The sensing platform was tested during a real-time exercise session but unfortunately not cross-correlated with any other technique. The same group reported on a new platform design that allows one to harvest sweat samples more efficiently. (134) After entering the device, the sweat sample was passed over the solid-state sodium-selective and reference electrodes and was collected in a storage area containing an adsorbent material. Fluid transport through the system was driven by capillary forces arising in the absorbent material. This configuration allows one to control the flow rate through the device, and the sweat stored during analysis can be used to report the harvested sweat volume, which is valuable for validation. Moreover, the electrodes and the high capacity adsorbent material can be easily replaced. The electrode fabrication process was very similar to the previous work, but it is surprising that the authors used PEDOT electrochemically deposited from the monomer solution in pure 1-ethyl-3-methylimidazolium tris(pentafluoroethyl) trifluorophosphate as solid-contact, while they previously had shown that this material deteriorates the response characteristics (response slope and linear response range).
Roy et al. reported on the development of a wearable sensor based on the CNT electrodes array for monitoring Na+ concentration in sweat. (135) Solid-state Na+-SEs were fabricated by drop casting plasticized PVC doped with ionophore and ion exchanger on CNT electrodes. The authors claimed that CNT electrodes provided stronger attachment of the sensing membrane in comparison with Au, Pt, or carbon electrodes, which renders the sensor more robust and reliable. Reference electrodes were prepared by coating CNT electrodes with a colloidal dispersion of Ag/AgCl, agarose hydrogel with 0.5 M NaCl, and a passivation layer of PVC doped with NaCl. This configuration ensured low sensitivity (−1.7 mV/dec) toward the NaCl solution and high repeatability of the reference electrode.
While the sensitivity and selectivity of the sensors seem to satisfy the requirements, the key challenges for wearable sensor developments may be insufficient mechanical resistance and large-scale fabrication. The groups of Andrade and Wang reported on a highly stretchable and printable textile-based potentiometric sensor array for the simultaneous Na+ and K+ detection in sweat. (136) Na+- and K+-selective electrodes were fabricated by applying Ag/AgCl and MWCNTs inks and subsequently covering them with polyurethane ionophore-based membranes. The reference electrode was prepared by covering Ag/AgCl ink with a polyvinyl butyral layer containing a NaCl dispersion. An implemented serpentine sensor design and Ecoflex cover layer further rendered the sensors stretchable. Mechanical deformation by up to 100%, crumpling, or prolonged washing did not influence the potentiometric response. This sensing platform can be easily printed onto conventional textiles such as underwear, watch straps, and elastic bands. The performance of the potentiometric sensor array printed on different substrates was close to Nernstian from 10–3 to 10–1 M for both Na+ and K+.
Choi et al. developed a wearable potentiometric chloride sensor for sweat analysis with two Ag/AgCl wires inserted into PDMS housing as reference and working electrodes. (137) The reference element was immersed into the closed chamber and connected to the sample area through a salt bridge, both of which contained 1 M KCl. An increase of the length of the salt bridge and a decrease of its diameter was found to reduce equilibration time. One may wonder why the authors decided to use a chloride containing electrolyte for the salt bridge as it will likely cause sample contamination.
Zoerner et al. developed a portable device for the analysis of ammonium in human sweat. (138) They used screen-printed NH4+-selective and reference electrodes connected to an evaluation board for data acquisition and transfer. The NH4+-selective membrane contained PVC, dibutyl sebacate, ion exchanger, and nonactine as an ionophore. The reference electrode was composed of Ag/AgCl covered with polyvinyl butyral/NaCl composite. The accuracy of the calculated ammonium concentration was validated using an enzymatic assay with glutamate dehydrogenase available with a commercial analyzer. It was shown that the sensor should be calibrated in artificial sweat solutions in order to eliminate errors resulting from interfering ions, primarily Na+ and K+. The lower detection limit observed in artificial sweat samples was 0.3 mM. Real sweat samples were measured only ex situ by putting a drop of collected sweat sample onto the sensor.
Andrade’s group demonstrated a miniature disposable paper-based electrochemical cell for monitoring total electrolyte level in sweat. (139) A Nafion membrane cast on a paper coated with carbon-ink was used as a working electrode while polyvinyl butyral/NaCl composite cast on a paper coated with Ag/AgCl-ink served as a reference electrode. The established empirical relationship between EMF signal and the measured logarithm of conductivity for a series of artificial sweat dilutions was used for analysis. The authors faced an unusual potential drift in calibration and sample solutions for some sensors. The conductivity values obtained by the device in real sweat samples were in a good correspondence with the ones obtained with a conductivity meter, but larger discrepancies between the values were observed during on-body monitoring.
Miniaturized pH Sensors
Conventional glass electrodes are known to be rather bulky and resistive, which hinders their application in small sample volumes and motivates the development of alternative miniaturized potentiometric pH sensors. Metal oxide pH sensors remain one of the most attractive alternatives owing to their solid-state configuration and ease of miniaturization. Unfortunately, the response of such pH sensors can be affected by other redox species in solution.
Uria et al. produced miniaturized pH probes on a silicon chip by depositing thin layers of IrOx or Ta2O5 on a platinum metal contact. (140) Two different methods were used for metal oxide deposition, electrodeposition for IrOx and e-beam sputtering for Ta2O5. To finalize the device, a reference Ag/AgCl thick film electrode was screen-printed on the chip. The reference electrode potential was kept indifferent by a constant concentration of chloride ions in all measurements. Ta2O5-based pH sensors exhibited a Nernstian slope in the pH range of 4 to 7.5 while the IrOx-based sensor showed a super-Nernstian slope of 72 mV. The sample volume could be reduced down to 50 μL. The application of the fabricated pH sensors for the detection and quantification of bacterium Escherichia coli (E. coli) was demonstrated, exploiting the fact that the metabolic activity of microorganisms can result in pH changes of the culture medium. Salazar et al. developed a metal oxide pH sensor based on an amorphous nanocolumnar porous thin film of WO3 deposited by reactive magnetron sputtering in an oblique angle configuration onto indium tin oxide (ITO) or gold screen printed electrodes. (141) To fabricate a combination solid-state pH sensor, the authors used an Ag/AgCl electrode covered with polypyrrole as reference electrode. This solid-state pH sensor exhibited a Nernstian behavior in the pH range of 1.0 to 12.0. Manjakkal et al. reported on a miniaturized potentiometric pH sensing platform based on a thick film RuO2–Ta2O5 sensing electrode and Ag/AgCl/KCl reference electrode screen printed on an alumina substrate. (142) The device was fabricated using thick film and so-called low temperature cofired ceramics technology. The sensor was found to exhibit a close to Nernstian response slope in the pH range of 2 to 12, and the electrode remained functional after 1 year. Lonsdale et al. found that pH sensors based on RuO2 thin-film sputtered on mesoporous carbon required less conditioning time and exhibited higher accuracy than their counterparts employing Pt and carbon as contact layers. (143) Later, the same group studied the influence of RuO2 material thickness and discovered that in order to obtain a pH sensor with 0.01 pH units of precision the electrode should be covered with the RuO2 film of at least 500 nm thicknesses. (144)
Jovic et al. adopted a layer-by-layer inkjet printing methodology for the fabrication of a miniaturized pH sensor on a flexible ITO/PET substrate. (145) The electrode was fabricated by printing alternating layers of positively charged polydiallyldimethylammonium and negatively charged IrOx citrate-stabilized nanoparticles. Five printed bilayers were found to give the best performance characteristics with a slope of 58.4 mV in the pH range of 3–10.
Inkjet-printing technology was also used by Pol et al. (146) to prepare miniaturized sulfide-selective electrode of the second kind. The sensor fabrication involved printing a silver electrode over the PEN substrate and electrochemically depositing sulfide from Na2S solution by applying a constant current pulse. The Ag/Ag2S electrode exhibited a Nernstian slope in the concentration range of S2– from 20 μM to 50 mM. The sensor could be used for analysis of river/sea-spiked environmental samples and samples from a bioreactor for reduction of sulfate to sulfide.
Ion-Selective Microelectrodes
Originally introduced by life scientists, ion-selective microelectrodes have become an indispensable tool for the in situ visualization of highly localized ion concentration changes, not only in living cells and tissues but also at the solid/liquid interface in many technical systems (i.e., metal corrosion).
Toczylowska-Maminska et al. reported on an all-solid-state potentiometric sensor array for the simultaneous measurement of four physiologically important ions (K+, Na+, H+, and Cl–) in cells and tissues. (147) The ISEs studied in this work were prepared with plasticized polyurethane-based membranes doped with appropriate ionophores and ion exchangers. The membrane cocktails were deposited directly on the surface of an Ag/AgCl transducer. The reference electrode was fabricated by covering Ag/AgCl with a plasticized polyurethane matrix doped with ionic liquid (1-dodecyl-3-methylimidazolium) chloride, which likely responds to chloride. The sensor array exhibited a close to Nernstian response slope in the concentration range of 10–4–10–1.5 M for Na+, K+, and Cl– and a pH range of 5.5–7.5 for the pH probe. The standard potential reproducibility was a rather modest ±11 mV. One would expect that the use of an appropriate solid-contact transducer layer between ion selective membrane and Ag metal contact would improve this value. The system was successfully applied for ion flux studies in a human colon epithelium Caco-2 cell line. Addressing a similar problem, Lewenstam’s group developed a flat multimicroelectrode platform for monitoring sodium, potassium, hydrogen, and chloride ions. (148) With a diameter of 12 mm, it could operate with a sample volume as small as 10 μL. The miniaturized ISEs were prepared rather conventionally by applying an appropriate PVC-based membrane cocktail on the top of the electrode body and filling it with an inner filling solution composed of 1% agar, 5% glycerine, and the electrolyte of choice. All electrodes exhibited a close to Nernstian response slope in a concentration range suitable for biological studies. The authors showed that by applying two platforms one can study the simultaneous transport of four ions across a layer of epithelial cells.
Church et al. developed a solid contact Zn2+-selective microelectrode to monitor in situ zinc transport in sour orange seedlings using a microelectrode ion flux estimation technique. (149) The authors constructed two types of microelectrodes with a commercially available micropipette tip (tip size of 540 μm) or a borosilicate glass micropipette (of 40 μm) as a support. To fabricate the electrodes, a gold wire coated with POT was fixed inside the corresponding micropipette and the PVC-based membrane cocktail doped with ionophore was inserted through capillary action, forming a phase boundary at the end of the tip. Both sensors exhibited a close to Nernstian response slope with micromolar detection limit. To perform the measurements, the microelectrode tip was moved perpendicularly to the leaf surface and the results measured at different height above the surface were compared. One could observe the decrease of the zinc concentration when approaching the surface if ions were taken up by living cells.
Ma et al. used a Pb2+-selective microelectrode for in situ monitoring of lead leaching from a galvanic joint in a prepared chlorinated drinking water environment. (150) To fabricate the microelectrode, a glass micropipette was backfilled with an internal solution and the Pb(II) PVC-based cocktail was inserted into the front tip by capillary force. The response slope of Pb2+-selective microelectrode was close to Nernstian (22 mV/dec) in the concentration range from 10–6 to 10–3 M. In this work, the authors demonstrated a substantial nonuniform increase of Pb2+ concentration across the lead anode surface which was dependent on the local surface pH.
Mao’s group proposed a carbon fiber-based H+-selective microelectrode (tip size of 20 μm) with a high antifouling property for in vivo monitoring of pH in the central nervous system. (151) The electrodes were fabricated by covering carbon fiber microelectrodes with a plasticized PVC-based H+-selective membrane doped with ionophore and an ion exchanger. The carbon fiber microelectrodes were carefully immersed and rolled into a droplet of membrane cocktail in THF until the solvent was evaporated. The sensor exhibited a Nernstian response slope in the evaluated pH range of 6.0 to 8.0 and a fast response time of less than 1 s. This sensor provided a stable and reproducible response in the vivo monitoring of pH change in the live brain of rats.
Moon et al. proposed a dual amperometric/potentiometric microsensor (428 μm diameter) for sensing nitric oxide (NO) and potassium ion. (152) The dual microsensor was prepared using Pt and Ag microwires inserted into a theta-type glass capillary. The Pt electrode was used for amperometric detection of NO while the Ag electrode partially oxidized to AgCl and covered with K+-selective membrane served for potentiometric potassium detection. The dual sensor exhibited a close to Nernstian response slope (51.6 mV/dec) to K+ from 10–5 to 10–1 M. The authors demonstrated the simultaneous monitoring of NO and K+ in a living rat brain.
Filotas et al. reported on a dual potentiometric microsensor probe for the simultaneous detection of Zn2+ and pH to study localized corrosion processes by scanning electrochemical microscopy (SECM). (153) The dual sensor was fabricated using two intertwined borosilicate capillaries. A PEDOT coated carbon fiber was inserted into one capillary, which was filled with Zn2+-selective cocktail containing PVC, plasticizer, ionophore, and ion exchanger. The second capillary was used to prepare an antimony pH electrode. The distance between the two tips in the final configuration was about 10–15 μm. Both sensors exhibited Nernstian behavior in a wide concentration range, namely, pZn 2–5 for the Zn2+-selective electrode and pH 4–10 for the pH probe. The data obtained with the dual sensor for a model galvanic Fe–Zn system corresponded well to previous results observed with separate single probes.
Ummadi et al. developed a solid-state carbon-based Ca2+-selective microelectrode (25 μm in diameter) that can be used both as an amperometric sensor (to build an approach curve) and as a potentiometric sensor (to map the ion distribution on the surface) in SECM. (154) This is an interesting approach, although the dual amperometric/potentiometric function appears not to be completely understood and optimized at this stage. The membrane cocktail containing ionophore, ion exchanger, PVC, plasticizer, and Vulcan carbon powder was pushed into the capillary tip. The back end of capillary was filled with Vulcan carbon/DOS composite to make the contact with an inserted copper wire. The Ca2+-selective microelectrode was found to have a close to Nernstian response slope of 28 mV/dec in the concentration range from 5 μM to 200 mM with a detection limit of 1 μM. The logarithmic selectivity coefficients were about −6 over Mg2+, Na+, and K+. The authors used the developed sensor to map the process of Ca2+ leaching from bioactive glass.
Zhu et al. reported on an all-solid-state pH microelectrode fabricated by anodic electrodeposition of an iridium oxide film onto a 10 μm platinum ultramicroelectrode. (155) The sensor exhibited a response slope of 61 mV in a wide pH range and remained functional for at least 110 days. This sensor was successfully applied to study the localized pH distribution during the corrosion of stainless steel in NaCl solution by SECM. The same group proposed a dual solid-state microelectrode that can be used in both amperometric and potentiometric SECM modes. (156) As above, the amperometric mode allows one to control tip–substrate distance while the potentiometric mode provides information on ion distribution. The sensor consisted of two 25 μm diameter Pt wires placed in a borosilicate theta capillary. One of the two Pt wires was modified with iridium oxide film to serve as a pH potentiometric sensor, while the other Pt remained unmodified and was used as amperometric sensor.
Freeman et al. demonstrated the feasibility of potentiometric redox measurements in subnanoliter solution droplets (between 280 and 1400 pL) using a nanoporous gold electrode. (157) It was prepared by dealloying gold leaf with concentrated nitric acid followed by its chemisorption to a standard microscope coverslip with (3-mercaptopropyl)trimethoxysilane. The gold was further modified with 1-hexanethiol to improve its hydrophobicity. The close to Nernstian behavior was confirmed with different redox couples (potassium ferricyanide/ferrocyanide, ferrous/ferric ammonium sulfate, benzoquinone/hydroquinone), and the system was also tested for only one form of the redox couple present in appreciable concentrations (potassium ferricyanide and ascorbic acid). Small volumes allowed for faster equilibration and reducing analysis time. Shortening the contact of the electrode surface to the sample solution can also be beneficial in complex samples for preventing electrode surface passivation by other species.
Ion-Selective Field Effect Transistors
Asadnia et al. developed an ISFET based on AlGaN/GaN high electron mobility transistor with the gate area covered with a PVC-based membrane for Ca2+ detection. (158) The proposed AlGaN/GaN-based device was claimed not to require a reference electrode, but a constant background of 10–2 M KCl or NaCl was used for the device to exhibit a close to Nernstian response in the concentration range of Ca2+ from 10–7 to 10–2 M. The selectivity coefficients of the sensor were determined by simply fitting the response curves measured in a background of interfering ion with the Nikolsky-Eisenmann equation. Unfortunately, the selectivity coefficient values obtained for all tested ions were several orders of magnitude higher than the one reported previously for the same basic membrane composition. The use of one of the protocols recommended by IUPAC for selectivity estimation of the sensor would be advisable. To avoid the effects of light, all measurements had to be performed in a dark environment, which may not always be practical. Using ISFET technology, Kaisti et al. developed a hand-held multiplexed discrete transistor-based sensing system that can be coupled wirelessly to a smartphone. (159) The performance of the developed system was tested with a K+-selective membrane. A close to Nernstian slope to potassium with a detection limit of 10–4.8 M was observed. To improve the stability of potential over time with the solid contact electrodes, polyaniline doped with dinonylnaphtalene sulfonic acid was used as a inner transducer layer. Briggs et al. reported on an ISFET-based sensing platform for the reagent-less simultaneous measurement of pH and total alkalinity. (160) The authors combined an ISFET-based pH sensor with one presented earlier and commercialized by Orion for the diffusive titration coupled to electrolytic titrant generation, also known as flash titration. The device was shown to perform a nanoliter-scale acid–base titration in less than 40 s. The authors demonstrated the applicability of the sensing platform for seawater analysis. Andrianova et al. developed an n-channel ISFET based on phosphotriesterase enzyme for organophosphorus pesticide detection. (161) Phosphotriesterase caused the cleavage of the pesticide molecules and was immobilized on the surface of the transistor, resulting in detectable pH changes. The device was coupled to a microfluidic system for analyte delivery and was successfully applied for the detection of paraoxon, parathion, and methyl parathion with detection limits of 0.1, 0.5, and 0.5 μM, respectively. Melzer et al. reported on the direct simultaneous detection of two products of enzymatic urea conversion (NH4+ and H+) using a sensor array based on spray-coated carbon nanotube field-effect transistors. (162) The direct simultaneous detection of both products of the enzymatic reaction was possible owing to the immobilization of urease enzyme on the sensor surface and modification of the corresponding active interfaces with polymeric NH4+- and H+-selective membranes. A detection limit for urea of less than 50 μM in dilute phosphate buffer was reported.
Analytical Applications and Methodologies
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Environmental Analysis
Potentiometric sensors can be easily miniaturized and exhibit reasonably fast response times, simple operation, and low energy consumption. For this reason, they may be attractive as sensing components in ex situ and in situ environmental monitoring systems. Cuartero and Bakker published a critical review that highlights recent examples of membrane electrode applications in water analysis. (163)
The complex composition of environmental water samples may make it difficult to deploy potentiometric sensors directly. With a pH range between 6.5 and 8.5, hydroxide interference may be a significant concern with ionophore-based anion sensors. In seawater samples, the high NaCl content acts as a potentially important interfering agent. To suppress hydroxide and chloride interferences, additional sample acidification and chloride removal steps are sometimes required before analysis. Bakker’s group reported on three different approaches to locally acidify the sample at the electrode surface during measurement. (164) In the first approach, 1 M acetic acid solution was used as an inner filling solution of the PVC-based membrane indicating electrode, which resulted in a significant acid gradient across the membrane and in the desired decrease of pH at the electrode surface. In the second approach, the passive acid diffusion was across a second membrane placed in front of the anion selective electrode. This arrangement formed a thin layer gap where acidification occurred and allowed one to tune both membrane materials to their respective tasks. An ISE with fast diffusive doped polypropylene membrane and a concentrated acetic acid inner solution served as the external proton source. The third approach exhibited a similar configuration, but the protons were released from the external proton source by electrochemical control, applying a potentiostatic pulse. It was demonstrated that all three protocols allowed one to successfully suppress the hydroxide interference and improve the limit of detection of nitrite and dihydrogen phosphate by more than 2 orders of magnitude. Nonetheless, the efficiency of the principles may not be sufficiently high in strongly buffered samples. The same group later proposed an in-line sample acidification approach based on cation exchange/counterdiffusion across an ion-exchange Donnan exclusion membrane. (165) Alkali metal ions from the sample are exchanged with hydrogen ions across the membrane, in analogy to an ion suppressor in ion chromatography. Natural water samples with millimolar sodium chloride levels (freshwater, drinking water, and aquarium water, as well as dechloridized seawater) were modified to about pH 5, depending on experimental condition.
In situ measurements are most attractive for the study of biogeochemical processes as they can provide real-time concentration profiles with the desired spatial and temporal resolution. Cuartero et al. described a new submersible probe that is fully autonomous during the deployment and provides data storage and computer visualization of the data in real time (see Figure 9). (166,167) The probe was explored for marine monitoring in two configurations: (1) simultaneous detection of nitrate, nitrite, and chloride; (166) (2) simultaneous detection of carbonate, calcium, and pH. (167) Potentiometric detection was performed in a custom-made flow cell with all-solid-contact membrane electrodes using functionalized multiwalled carbon nanotubes (f-MWCNTs) as a solid contact. The detection of nitrate and nitrite was accomplished after suppressing hydroxide, as described above, and chloride interferences. Chloride concentration was drastically reduced by addition of a microfluidic desalination module that consisted of two plated silver sheets that served as working and counter electrodes. Electrochemical oxidation of the silver electrode in contact with the sample film removed chloride as plated AgCl while the sodium counterions were transported away from the sample across the cation-exchange membrane to the reference solution. This decreased the chloride concentration in seawater down to millimolar levels. The electrochemical protocol allowed one to also use the desalination cell as a coulometric, calibration-free electrochemical sensor for chloride/salinity detection. The in situ measurement data were validated using on site and ex situ techniques. In some cases, the correlation was difficult. Re-equilibration with atmospheric CO2 after sampling can introduce errors, as can be the use of apparent thermodynamic constants for speciation calculations.
Figure 9
Figure 9. Submersible probes containing ion-selective sensing probes are deployed in marine environments for the in situ potentiometric monitoring of macronutrients (166) and species relevant to the carbon cycle. (167) The probes were integrated in a titanium cage containing pumps, electronics, sensors, and an additional multiparameter CTD module for simultaneous conductivity, temperature, and depth measurements.
Athavale et al. reported on the application of solid contact ammonium and pH selective electrodes for the in situ vertical high-resolution profiling in a eutrophic freshwater lake, (168) using f-MWCNTs as a solid contact. The sensors were found to be insensitive to strong redox changes, high sulfide concentrations, and bright daylight conditions during application in the lake. Ding et al. presented a solid-contact potentiometric sensor for detection of total ammonia nitrogen (free ammonia plus the ammonium ion) in seawater. (169) In this system, a POT-based polymeric membrane ammonium-selective electrode was combined with a poly(vinyl alcohol) hydrogel buffer film of pH 7.0 and a gas-permeable membrane. The proposed sensor exhibited a detection limit of 6.4 × 10–7 M and was successfully applied to the ex situ detection in seawater.
Chango et al. proposed a potentiometric chip-based multipumping flow system for the simultaneous determination of fluoride, chloride, pH, and redox potential in water samples with commercially available reference and sensing electrodes. (170) The system was equipped with a set of four solenoid micropumps to deliver solutions to the electrode surface. One of the pumps supplied a total ionic strength adjusting buffer. The system was applied for the analysis of water samples from wells and pools, giving a satisfactory correlation for chloride and fluoride concentrations between ISE and ion chromatography. Shen and co-workers demonstrated that the accuracy of fluoride determination by ion-selective electrodes is significantly affected by the aggregation of humic substances that are representative of natural organic matter in water. (171) The authors reported on a negative error of detected fluoride concentration up to 19% in the presence of humic substance aggregates. The authors supposed that the formed aggregates act as “open cages”, where fluoride ions can be trapped apparently without restriction of electrostatic attraction or site binding. The process is reversible and was shown to be eliminated by a centrifugation pretreatment of the sample.
Clinical Analysis
Machado et al. described a potentiometric flow injection method for iodide and iodate in urine samples with a commercially available combination iodide-selective electrode. (172) This was achieved by the sequential determination of iodide and the sum of iodate and iodide, after iodate conversion to iodide with a reducing agent in a separate flow channel. The detection limits were around 1 μM. Lindner’s group developed and validated a protocol for the measurement of urinary CO2 of septic shock patients using a Severinghaus-type CO2 probe. (173) The protocol included: (1) sampling urine from a Foley catheter in an intensive care unit setting, (2) storing samples until analysis at a separate facility, (3) calibration of the Severinghaus-type CO2 sensor, and (4) measuring urinary CO2 levels. It was shown that pH does not significantly influence the accuracy of the results so that the measurements can be performed without sample pH adjustment. Nevertheless, the use of the urinary catheter equipped with an in-line thermometer was recommended to correct for the differences in bladder temperature and the equilibration temperature used for the preparation of the standards.
The groups of Meyerhoff and Malinowska presented a potentiometric approach for monitoring the release rate of nitric oxide from NO donor-doped polymer films and electrochemical NO generating systems used as parts of medical devices. (174) The proposed approach is based on the conversion of NO into nitrate in the presence of oxyhemoglobin with subsequent nitrate detection with a polymeric membrane anion-selective electrode. To minimize the interference of oxyhemoglobin on the detection of nitrate, the membrane was prepared using asymmetric cellulose triacetate instead of PVC. Unfortunately, the potentiometrically measured NO concentration values and the ones from the reference chemiluminescence method gave significant discrepancies. A possible reason was assumed to be the low reaction efficiency for the purged NO with the oxyhemoglobin to form nitrate. A correction was performed with empirically estimated reaction efficiencies based on the results of the chemiluminescence analysis. As reaction efficiencies may depend on experimental conditions (temperature or purge rate of NO), the implementation of this approach is likely difficult.
Ortuño’s group described a potentiometric approach for monitoring enzymatic reactions. (175) Potentiometry possesses a number of advantages over traditionally used spectrophotometric methods, such as the use of the enzymes’ natural substrates and the possibility of doing measurements under physiological conditions. As a proof-of-concept, kinetic and inhibition studies were performed using electrodes selective to ionic substrate involved in the enzymatic reaction catalyzed by acetylcholinesterase and butyrylcholinesterase.
Urbanowicz et al. reported on a miniature multisensor platform (10 mm in diameter) based on solid contact ion-selective electrodes for the detection of Na+, K+, Ca2+, Mg2+, and Cl– in fresh, unstimulated, and stimulated human saliva samples. (176) PEDOT(PSS) was used as a transducer layer for the corresponding ionophore-based electrodes. An Ag/AgCl electrode in contact with KCl dispersed in polyvinyl acetate was used as a reference electrode. The concentrations determined by the multisensor platform corresponded well to the ones obtained by separately measured ion-selective electrodes.
Biofouling of ion-selective membranes owing to protein adsorption is a known limitation for the long-term application of potentiometric sensors in complex biological samples such as blood, serum, or urine. Biofouling often results in an increase of signal noise or loss of signal. Goda et al. studied the influence of the adsorption of bovine serum albumin on the performance characteristics of several ion-selective microelectrodes. (177) An Ag/AgCl electrode with protein adsorbed lost sensitivity for chloride concentrations lower than 10–2 M. However, this work indicated that Ir/IrOx microelectrodes are promising for local pH measurements in complex samples containing biomolecules as they maintained adequate pH response in the pH range from 4 to 9. Lisak et al. proposed a way to monitor the kinetics of biofouling of ion-selective membranes by combining in situ potentiometry and null ellipsometry. (178) The authors used their approach to monitor the adsorption of bovine serum albumin at the surface of the custom-made solid-contact K+-SEs with 6-(ferrocenyl)-hexanethiol attached to a gold surface as a transducer layer.
Polyion Sensing
Polyanions are widely used in medicine (e.g., heparin and protamine), food (e.g., carrageenan), and cosmetics (e.g., polyquaterniums). The first polyion potentiometric sensor was a heparin-selective electrode developed in the early 1990s. Meyerhoff’s group recently published a thorough review about key accomplishments in electrochemical and optical sensing of polyions over the past 25 years. (179) The authors discussed the basic sensing principles of single-use and fully reversible polymeric membrane-type potentiometric polyion sensors, voltammetric polyion-sensitive electrodes, and single-use polyion-sensitive optodes. In the last two years, the same group significantly contributed to the development of the analytical protocols for the quantification of polyquaterniums (PQs), polymeric quaternary ammonium salts. (180−182) They are found to be widely used in cosmetics but may be toxic for certain aquatic species. The detection of the quaternized hydroxyethylcellulose compound, PQ-10, was demonstrated using titration with dextran sulfate monitored by polyanion-sensitive polymeric membrane-based electrodes. (180) In this method, once all of the PQ-10 species have been bound by the titrant, the excess polyanion will be extracted into the plasticized PVC membrane and exchange with the Cl–. As a result, the observed equivalence point is directly proportional to the amount of PQ-10 in the sample. The method was shown to detect PQ-10 down to 20 μg mL–1. It was also shown that sodium lauryl sulfate, which is often present in cosmetic samples together with PQ-10, can be readily separated using an anion-exchange resin (the amount of which may need to be adjusted depending on the sample). The authors also discovered that the increase of pH results in a change of the shape of the titration curve. The pH of the sample solution should therefore be closely monitored, especially after pretreatment with anion-exchange resin. In subsequent work in buffered samples, the authors showed that various quaternary ammonium salts (PQ-2, PQ-6, PQ-10, and poly(2-methacryloxy-ethyltrimethylammonium) chloride) can be titrated with the same titrant, dextran sulfate. (181) Here, a syringe pump was used to deliver the titrant at a fixed rate. (181) The direct potentiometric detection of the analytes was also demonstrated using polycation sensitive membrane electrodes. (181) In this case, one measures the change of the phase boundary potential resulting from the extraction of polycationic analyte into the membrane accompanied by the ejection of Na+ ions into the aqueous phase. It was found that the recorded change of the phase boundary potential can also yield the information about the charge density of different analytes.
Reversible potentiometric polyion sensors, also known as “pulstrodes”, were presented for the first time by Bakker’s group in 2003. Meyerhoff’s group adopted this principle for the detection of four polyquaterniums mentioned above. (182) A plasticized PVC membrane was doped with a salt of two oppositely charged lipophilic ions. A short (1 s) galvanostatic pulse polarized the membrane, allowing the polyion analyte to be extracted into the membrane yielding a detectable phase boundary potential change. In a second step, a long (15 s) potentiostatic pulse resulted in the ejection of the polyion back into the sample phase. Meyerhoff’s group developed “pulstrode” protocols for polyquaternium detection by exploiting direct and indirect potentiometric (titration) measurements in the beaker. The possibility of performing measurements in a flow injection analysis system was also demonstrated.
Potentiometric polyion sensors can be also used for the indirect detection of biomolecules and biological species. Gemene’s group used a polyion-selective electrode to determine the activity of a proteolytic enzyme thrombin. (183) It was achieved with a synthetic polypeptide substrate and a flash chronopotentiometry protocol. An applied cathodic current caused the extraction of polypeptides into the membrane while the square root of the transition time at which the depletion of the polypeptides at the membrane–sample interface occurs was found to be proportional to its concentration. The addition of thrombin resulted in proteolysis of the polypeptide substrate and a shortening of the transition times. Qin’s group reported on the potentiometric aptasensing detection of a marine bacterium Vibrio alginolyticus using again a polyion sensor. (184) In the presence of the target, the aptamer on the DNA nanostructure-modified magnetic beads specifically binds to the target and results in a disassembly of the DNA nanostructures. The resulting magnetic beads were then incubated with protamine, and after magnetic separation, the unreacted protamine was detected using the “pulstrode” protocol.
Surfactant Analysis
Surfactants contain a hydrophilic headgroup and hydrophobic chain (tail) and are commonly used in everyday items (soap, toothpaste, washing liquid, laundry detergents) and many industrial processes. The development and improvement of analytic tools for their control and monitoring remains an active research field, and potentiometric sensors are often used in the titrimetric determinations of surfactants. The titration of ionic surfactants is based on the reaction of two oppositely charged large lipophilic ions resulting in the formation of a sparingly soluble ion-associate that becomes extractable into the membrane. Mikysek et al. reported on a low resistive (10 Ω) coated-wire ion-selective electrode for the potentiometric detection of anionic surfactants. (185) The electrode was prepared by dipping an Al conductor into a homogenized mixture of the graphite powder, PVC, and NPOE in THF. In this work, didecyldimethylammonium chloride was used as a cationic titrant to provide titration curves with a larger potential jump than ones obtained with conventionally used titrants. Galovic et al. presented a new all-solid-state membrane ISE for the determination of anionic surfactants. (186) The membrane was applied on the screen-printed electrode based on carbon by drop-casting. The membrane composition included the dimethyldioctadecylammonium–tetraphenylborate ion pair, a graphene nanopowder, PVC, and NPOE. The sensor exhibited close to Nernstian responses for dodecylbenzenesulfonate and dodecyl sulfate in the concentration range of 2.5 × 10–7–4.5 × 10–3 M with detection limits of 1.5 × 10–7 and 2.5 × 10–7 M, respectively. One may wonder about the role of the ion pair incorporated into the membrane phase here as the ion-pair complex does not have ions in common neither with the analyzed anionic surfactants nor with the titrant. As this compound is composed of a hydrophobic cation and anion, it does not seem to possess ion-exchanger properties and so its function is unclear, other than decreasing the resistance of the membrane phase. Khaled et al. demonstrated an enzymatic approach for surfactant analysis. (187) As the surfactants are known to inhibit the activity of some cholinesterase enzymes, the authors used this characteristic to determine the surfactant concentration. The enzymatic activity of acetylcholinesterase was measured by monitoring the hydrolysis of acetylcholine with a disposable acetylcholine potentiometric sensor. The inhibition degree of the enzyme was found to be proportional to surfactant concentration. This method was shown to be applicable to the analysis cationic, anionic, and nonionic surfactants.
Author Information
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- Eric Bakker - Department of Inorganic and Analytical Chemistry, University of Geneva, Quai Ernest-Ansermet 30, CH-1211 Geneva, Switzerland;
http://orcid.org/0000-0001-8970-4343;
Biographies
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Elena Zdrachek
Elena Zdrachek was born in Belarus and studied at Belarusian State University in Minsk, where she obtained her Bachelor degree in Chemistry in 2010. She received her Ph.D. in Analytical Chemistry from the Belarusian State University in 2015 under the guidance of Prof. Vladimir V. Egorov. She then worked as a Senior Research Fellow at the Research Institute for Physical Chemical Problems of the Belarusian State University. In 2016, she moved to Switzerland for a postdoctoral stay at the University of Geneva in the group of Prof. Eric Bakker. E.Z.’s main research interests are in the development and theory of electrochemical sensors. In particular, she focuses on the influence of equilibria at the membrane/solution interface on electrode response and the theory of selectivity.
Eric Bakker
Eric Bakker pursued his doctoral studies with Wilhelm Simon at the Swiss Federal Institute of Technology (ETH) in Zurich (1990–1993) and spent two years at the University of Michigan before starting his independent career at Auburn University (1995–2005) where he eventually rose to the rank of full professor. In 2005–2007, he spent time at Purdue University (West Lafayette, IN), and in 2007–2010, he was at Curtin University (Perth, Western Australia) before coming back to Switzerland in 2010 as a chair of Analytical Chemistry at the University of Geneva. His research interests are in analytical chemistry, chemical sensors, ion sensors, membrane electrodes, and their bioanalytical and environmental applications.
Acknowledgments
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The authors thank the Swiss National Science Foundation for supporting research in this field.
References
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This article references 187 other publications.
- 1Bakker, E. In Reference Module in Chemistry, Molecular Sciences and Chemical Engineering; Elsevier: New York, 2018.Google ScholarThere is no corresponding record for this reference.
- 2Hu, J. B.; Stein, A.; Bühlmann, P. Rational design of all-solid-state ion-selective electrodes and reference electrodes. TrAC, Trends Anal. Chem. 2016, 76, 102– 114, DOI: 10.1016/j.trac.2015.11.004Google Scholar2https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXitVSqu7fK&md5=e1d8f838c3c01cfa4c121ae10edd283cRational design of all-solid-state ion-selective electrodes and reference electrodesHu, Jinbo; Stein, Andreas; Buhlmann, PhilippeTrAC, Trends in Analytical Chemistry (2016), 76 (), 102-114CODEN: TTAEDJ; ISSN:0165-9936. (Elsevier B. V.)A review. Potentiometric sensing, which requires the use of ion-selective electrodes (ISEs) and ref. electrodes, is used to det. electrochem. the concn. of target ions in a variety of chem. environments. In view of the need for more affordable and portable anal. devices with small sample vols., all-solid-state ISEs and ref. electrodes, in which a solid contact is used as ion-to-electron transducer, are highly desirable. This review describes how all-solid-state ISEs and ref. electrodes function and presents important aspects that should be considered when designing such sensors for specific applications. Approaches to improving reproducibility, the stability of the emf response, lowering detection limits, and novel sensor designs are discussed along with specific examples from the recent literature. Emphasis is placed on the ion-to-electron transduction mechanism and the development of new solid contact materials, with a particular view to miniaturized ion-sensing devices with low cost and calibration-free sensing.
- 3Sophocleous, M.; Atkinson, J. K. A review of screen-printed silver/silver chloride (Ag/AgCl) reference electrodes potentially suitable for environmental potentiometric sensors. Sens. Actuators, A 2017, 267, 106– 120, DOI: 10.1016/j.sna.2017.10.013Google Scholar3https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhs1GqtbrE&md5=1ca943d88e6ed33070ba96f1b65397dbA review of screen-printed silver/silver chloride (Ag/AgCl) reference electrodes potentially suitable for environmental potentiometric sensorsSophocleous, Marios; Atkinson, John K.Sensors and Actuators, A: Physical (2017), 267 (), 106-120CODEN: SAAPEB; ISSN:0924-4247. (Elsevier B.V.)A review. The screen-printed (SP), ref. electrode (RE) has been shown to be a crucial element of potentiometric sensors but it is also the stumbling block for reliable and accurate SP sensors. The easiest, most common and most environmentally friendly, type of RE is the Silver/Silver Chloride (Ag/AgCl) RE. Unfortunately, until now the only reliable RE of this kind is the conventional, liq. or gel-filled type. However, for most environmental and soil applications the use of the conventional RE is not an option, which raises the demand for a robust, rugged and low-cost version to replace the conventional RE. This paper presents a review of the various attempts to produce reliable, SP, Ag/AgCl REs, and explain why almost all of them never reach the commercialisation stage. The paper provides an overview of the main challenges that need to be overcome, details of the electrode's construction, an anal. comparison of their performance in terms of chloride susceptibility, cross-sensitivity and lifetime, and their suitability in different applications depending on their performance characteristics.
- 4Chopade, S. A.; Anderson, E. L.; Schmidt, P. W.; Lodge, T. P.; Hillmyer, M. A.; Bühlmann, P. Self-Supporting, Hydrophobic, Ionic Liquid-Based Reference Electrodes Prepared by Polymerization-Induced Microphase Separation. ACS Sens. 2017, 2, 1498– 1504, DOI: 10.1021/acssensors.7b00512Google Scholar4https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsFCjsrbL&md5=00d264a16f9c6854295a93e3b580eedaSelf-Supporting, Hydrophobic, Ionic Liquid-Based Reference Electrodes Prepared by Polymerization-Induced Microphase SeparationChopade, Sujay A.; Anderson, Evan L.; Schmidt, Peter W.; Lodge, Timothy P.; Hillmyer, Marc A.; Buhlmann, PhilippeACS Sensors (2017), 2 (10), 1498-1504CODEN: ASCEFJ; ISSN:2379-3694. (American Chemical Society)Interfaces of ionic liqs. and aq. solns. exhibit stable elec. potentials over a wide range of aq. electrolyte concns. This makes ionic liqs. suitable as bridge materials that sep. in electroanal. measurements the ref. electrode from samples with low and/or unknown ionic strengths. However, methods for the prepn. of ionic liq.-based ref. electrodes were not explored widely. The authors have designed a convenient and reliable synthesis of ionic liq.-based ref. electrodes by polymn.-induced microphase sepn. This technique allows for a facile, single-pot synthesis of ready-to-use ref. electrodes that incorporate ion conducting nanochannels filled with either 1-octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide or 1-dodecyl-3-methylimidazolium bis(trifluoromethyl sulfonyl)imide as ionic liq., supported by a mech. robust cross-linked polystyrene phase. This synthesis procedure allows for the straightforward design of various ref. electrode geometries. These ref. electrodes exhibit a low resistance as well as good ref. potential stability and reproducibility when immersed into aq. solns. varying from deionized, purified H2O to 100 mM KCl, while requiring no correction for liq. junction potentials.
- 5Lewenstam, A.; Blaz, T.; Migdalski, J. Anal. Chem. 2017, 89, 1068– 1072, DOI: 10.1021/acs.analchem.6b02762Google Scholar5https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XitVKqtb%252FE&md5=d3be840a0968d0c29a15d5eb4a89fe60All-Solid-State Reference Electrode with Heterogeneous MembraneLewenstam, Andrzej; Blaz, Teresa; Migdalski, JanAnalytical Chemistry (Washington, DC, United States) (2017), 89 (2), 1068-1072CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Novel ref. electrodes with a solid contact coated by a heterogeneous polymer membrane are described. The electrodes were obtained using Ag nanoparticles, AgBr, KBr suspended in THF soln. of PVC and DOS and deposited on Ag substrate, or another substrate covered with Ag, by drop casting. After a short period of soaking in a KBr soln., stable and reproducible formal potentials of -157 ± 2 mV (vs. Ag/AgCl/3 M KCl) were obsd., and the solid-contact ref. electrodes were ready to use. The described ref. electrodes are relatively insensitive to the changes in the sample matrix, the concns. of ions, the pH and the redox potential. These electrodes can also be fabricated in miniaturized form, and thus used to produce miniaturized multielectrode probes.
- 6Zhao, Z. G.; Tu, H. G.; Kim, E. G. R.; Sloane, B. F.; Xu, Y. A flexible Ag/AgCl micro reference electrode based on a parylene tube structure. Sens. Actuators, B 2017, 247, 92– 97, DOI: 10.1016/j.snb.2017.02.135Google Scholar6https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXksVChtrs%253D&md5=bc9f5b8a7e1508ae456f15d66864e25aA flexible Ag/AgCl micro reference electrode based on a parylene tube structureZhao, Zhiguo; Tu, Hongen; Kim, Eric G. R.; Sloane, Bonnie F.; Xu, YongSensors and Actuators, B: Chemical (2017), 247 (), 92-97CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)In the effort of developing micro-electrochem. sensors, the miniaturization of ref. electrodes has been a challenging task. In this paper, a flexible micro ref. electrode with an internal electrolyte reservoir is reported. This new device is based on a unique microfabricated parylene tube structure, which is filled with Cl- rich electrolyte, into which a 50μm diam. silver (Ag) wire covered with a 7.4μm thick silver chloride (AgCl) layer is inserted. The distal end of the tube is filled with potassium chloride (KCl) satd. agarose gel. The Ag wire, thick AgCl layer, and internal electrolyte reservoir lead to a long operation time and a stable ref. voltage. The drift over a 10-h period has been found to be less than 2 mV. The total operation time of the device has exceeded 100 h. Furthermore, the compatibility with microfabrication allows the integration of other components, leading to truly miniaturized electrochem. sensors or sensing systems. To prove this, we demonstrated a pH sensor by combining the ref. electrode and an iridium oxide electrode monolithically integrated on the surface of the parylene tube.
- 7Li, Q. F.; Tang, W.; Su, Y. Z.; Huang, Y. K.; Peng, S.; Zhuo, B. G.; Qiu, S.; Ding, L.; Li, Y. Z.; Guo, X. J. Stable Thin-Film Reference Electrode on Plastic Substrate for All-Solid-State Ion-Sensitive Field-Effect Transistor Sensing System. IEEE Electron Device Lett. 2017, 38, 1469– 1472, DOI: 10.1109/LED.2017.2732352Google Scholar7https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXitV2jurvF&md5=a3c3ba0ab8731e5f8648a43ad16ff7c2Stable thin-film reference electrode on plastic substrate for all-solid-state ion-sensitive field-effect transistor sensing systemLi, Qiaofeng; Tang, Wei; Su, Yuezeng; Huang, Yukun; Peng, Sai; Zhuo, Bengang; Qiu, Shi; Ding, Li; Li, Yuanzhe; Guo, XiaojunIEEE Electron Device Letters (2017), 38 (10), 1469-1472CODEN: EDLEDZ; ISSN:1558-0563. (Institute of Electrical and Electronics Engineers)Solid-state thin-film ref. electrodes (REs) were fabricated on plastic substrate based on a titanium/gold/silver/silver chloride (Ti/Au/Ag/AgCl) multi-layer metal structure for ion-sensitive field-effect transistor (ISFET)-based sensing systems. A porous structure polyvinyl butyral membrane was formed on top to maintain a const. concn. of chloride as well as acting as a bridge between the electrolyte inside the membrane and the test soln. Excellent measurement stability was achieved with the fabricated RE, with a small drift rate of the open circuit potential less than 1.7 mV per h. An all-solid-state ISFET sensing system was thus able to be built using the RE for pH measurement, showing excellent reproducibility. The system was finally applied for measuring different beverages, and the measurement results agreed well with those obtained with a com. pH meter.
- 8Mechaour, S. S.; Derardja, A.; Oulmi, K.; Deen, M. J. Effect of the Wire Diameter on the Stability of Micro-Scale Ag/AgCl Reference Electrode. J. Electrochem. Soc. 2017, 164, E560– E564, DOI: 10.1149/2.1211714jesGoogle Scholar8https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXkslWrtQ%253D%253D&md5=0c0e084190c116852df3c43ec98f765bEffect of the Wire Diameter on the Stability of Micro-Scale Ag/AgCl Reference ElectrodeMechaour, S. Seghir; Derardja, A.; Oulmi, K.; Deen, M. J.Journal of the Electrochemical Society (2017), 164 (14), E560-E564CODEN: JESOAN; ISSN:0013-4651. (Electrochemical Society)Ag chloride that is commonly used as a ref. electrode in many chem. sensors is stable when its dimensions are relatively large. However, its use in sensors, esp. in nanosensors, requires that its size be reduced significantly. The authors report that the stability of very small Ag chloride electrodes could be obtained if a specific potential is applied. The AgCl wires produced by electrodeposition were studied by the chronoamperometry technique. SEM was used to study the properties of the surface of the fabricated wires surface obtained. The stability depends on the Ag chloride surface morphol. Indeed, the Ag/AgCl wire provided a more stable potential when its surface morphol. is like nanosheets. It seems that this surface morphol. obtained for Ag/AgCl wire with a micrometric diam. is a promising element that could be used to measure a variety of biol. parameters such as membrane potential, intracellular free ion concns. and cell-to-cell communication.
- 9Mousavi, M. P. S.; Saba, S. A.; Anderson, E. L.; Hillmyer, M. A.; Bühlmann, P. Avoiding Errors in Electrochemical Measurements: Effect of Frit Material on the Performance of Reference Electrodes with Porous Frit Junctions. Anal. Chem. 2016, 88, 8706– 8713, DOI: 10.1021/acs.analchem.6b02025Google Scholar9https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xht1CltrfN&md5=8347f1c3872feb03091a7efacf53c4abAvoiding Errors in Electrochemical Measurements: Effect of Frit Material on the Performance of Reference Electrodes with Porous Frit JunctionsMousavi, Maral P. S.; Saba, Stacey A.; Anderson, Evan L.; Hillmyer, Marc A.; Buhlmann, PhilippeAnalytical Chemistry (Washington, DC, United States) (2016), 88 (17), 8706-8713CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)In many com. available and inhouse-prepd. ref. electrodes, nanoporous glass frits (often of the brand named Vycor) contain the electrolyte soln. that forms a salt bridge between the sample and the ref. soln. Recently, in samples with low ionic strength, the half-cell potentials of ref. electrodes comprising nanoporous Vycor frits are affected by the sample and can shift in response to the sample compn. by >50 mV (which can cause up to 900% error in potentiometric measurements). The large potential variations result from electrostatic screening of ion transfer through the frit due to the neg. charged surfaces of the glass nanopores. Since the com. prodn. of porous Vycor glass was recently discontinued, new materials were used lately as porous frits in com. available ref. electrodes, frits made of Teflon, polyethylene, or one of two porous glasses sold under the brand names CoralPor and Electro-porous KT. The authors studied the effect of the frit characteristics on the performance of ref. electrodes, and show that the unwanted changes in the ref. potential are not unique to electrodes with Vycor frits. Increasing the pore size in the glass frits from the <10 nm into the 1 μm range or switching to polymeric frits with pores in the 1 to 10 μm range nearly eliminates the potential variations caused by electrostatic screening of ion transport through the frit pores. Unfortunately, bigger frit pores result in larger flow rates of the ref. soln. through the pores, which can result in the contamination of test solns.
- 10Guzinski, M.; Jarvis, J. M.; Perez, F.; Pendley, B. D.; Lindner, E.; De Marco, R.; Crespo, G. A.; Acres, R. G.; Walker, R.; Bishop, J. PEDOT(PSS) as Solid Contact for Ion-Selective Electrodes: The Influence of the PEDOT(PSS) Film Thickness on the Equilibration Times. Anal. Chem. 2017, 89, 3508– 3516, DOI: 10.1021/acs.analchem.6b04625Google Scholar10https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXis1yiu7k%253D&md5=fcf88a16e72e65fba548b22f0336afedPEDOT(PSS) as Solid Contact for Ion-Selective Electrodes: The Influence of the PEDOT(PSS) Film Thickness on the Equilibration TimesGuzinski, Marcin; Jarvis, Jennifer M.; Perez, Felio; Pendley, Bradford D.; Lindner, Erno; De Marco, Roland; Crespo, Gaston A.; Acres, Robert G.; Walker, Raymart; Bishop, JosiahAnalytical Chemistry (Washington, DC, United States) (2017), 89 (6), 3508-3516CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)To understand the rate detg. processes during the equilibration of poly(3,4-ethylenedioxythiophene):polystyrenesulfonate-based (PEDOT(PSS)-based) solid contact (SC) ion-selective electrodes (ISEs), the surfaces of Pt, Au, and GC electrodes were coated with 0.1, 1.0, 2.0, and 4.0 μm thick galvanostatically deposited PEDOT(PSS) films. Next, potential vs. time transients were recorded with these electrodes, with and without an addnl. K ion-selective membrane (ISM) coating, following their 1st contact with 0.1M KCl solns. The transients were significantly different when the multilayered sensor structures were assembled on Au or GC compared to Pt. The differences in the rate of equilibration were interpreted as a consequence of differences in the hydrophilicity of PEDOT(PSS) in contact with the substrate electrode surfaces based on XPS and synchrotron radiation-XPS (SR-XPS) anal. of 10-100 nm thick PEDOT(PSS) films. The influence of the layer thickness of the electrochem. deposited PEDOT(PSS)-films on the hydrophilicity of these films was documented by contact angle measurements over PEDOT(PSS)-coated Au, GC, and Pt electrode surfaces. It is possible to minimize the equilibration (conditioning) time of SC ISEs with aq. solns. before usage by optimizing the thickness of the SC layer with a controlled ISM thickness. PEDOT(PSS)-coated Au and GC electrodes exhibit a significant neg. potential drift during their equilibration in an aq. soln. By coating the PEDOT(PSS) surface with an ISM, the neg. potential drift is compensated by a pos. potential drift related to the hydration of the ISM and activity changes at the PEDOT(PSS)|ISM interface. The potential drifts related to activity changes in the ISM were detd. by a novel adaptation of the sandwich membrane method.
- 11Jarvis, J. M.; Guzinski, M.; Perez, F.; Pendley, B. D.; Lindner, E. Differences in Electrochemically Deposited PEDOT(PSS) Films on Au and Pt Substrate Electrodes: A Quartz Crystal Microbalance Study. Electroanalysis 2018, 30, 710– 715, DOI: 10.1002/elan.201700699Google Scholar11https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhs1KktQ%253D%253D&md5=348cc448fda55d1e3a88c33217373aa2Differences in Electrochemically Deposited PEDOT(PSS) Films on Au and Pt Substrate Electrodes: a Quartz Crystal Microbalance StudyJarvis, Jennifer M.; Guzinski, Marcin; Perez, Felio; Pendley, Bradford D.; Lindner, ErnoElectroanalysis (2018), 30 (4), 710-715CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)Studying the responses of K ion-selective electrodes with poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate), PEDOT(PSS), as solid contact (SC) revealed significant differences in the equilibration times and std. potentials of the electrodes fabricated on Au or Pt as substrate electrodes. To trace the source of these differences, PEDOT(PSS) films were deposited under the same conditions onto Au and Pt electrodes on the surface of 10 MHz quartz crystals. During the galvanostatic polymn., the frequency decrease of the quartz crystal was monitored by an electrochem. quartz crystal microbalance (EQCM). In the initial 15 s of the electrochem. deposition, the rate of PEDOT(PSS) polymer growth was significantly faster on Au compared to Pt although the c.d. used for the deposition was the same. Consequently, the total frequency change after a given electrolysis time was always larger on Au compared to Pt, indicating a larger deposited mass or PEDOT(PSS) layer thickness. The differences in the thicknesses of the PEDOT(PSS) films on Au and Pt could be quant. confirmed by XPS etching studies. SEM anal. of PEDOT(PSS) films on Au and Pt also showed characteristic differences.
- 12Guzinski, M.; Jarvis, J. M.; D’Orazio, P.; Izadyar, A.; Pendley, B. D.; Lindner, E. Solid-Contact pH Sensor without CO2 Interference with a Superhydrophobic PEDOT-C-14 as Solid Contact: The Ultimate ″Water Layer″ Test. Anal. Chem. 2017, 89, 8468– 8475, DOI: 10.1021/acs.analchem.7b02009Google Scholar12https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtFChsLrP&md5=b8d022e3431810bd9fa7cab8dcf6d539Solid-Contact pH Sensor without CO2 Interference with a Superhydrophobic PEDOT-C14 as Solid Contact: The Ultimate "Water Layer" TestGuzinski, Marcin; Jarvis, Jennifer M.; DOrazio, Paul; Izadyar, Anahita; Pendley, Bradford D.; Lindner, ErnoAnalytical Chemistry (Washington, DC, United States) (2017), 89 (16), 8468-8475CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)The aim of this study was to find a conducting polymer-based solid contact (SC) for ion-selective electrodes (ISEs) that could become the ultimate, generally applicable SC, which in combination with all kinds of ion-selective membranes (ISMs) would match the performance characteristics of conventional ISEs. The authors present data collected with electrodes using PEDOT-C14, a highly hydrophobic deriv. of poly(3,4-ethylenedioxythiophene) (PEDOT), as SC and compare its performance characteristics with PEDOT-based SC ISEs. PEDOT-C14 has not been used in SC ISEs previously. The PEDOT-C14-based solid contact (SC) ion-selective electrodes (ISEs) (H+, K+, and Na+) have outstanding performance characteristics (theor. response slope, short equilibration time, excellent potential stability, etc.). Most importantly, PEDOT-C14-based SC pH sensors have no CO2 interference, an essential pH sensors property when aimed for whole-blood anal. The superhydrophobic properties (water contact angle: 136 ± 5°) of the PEDOT-C14 SC prevent the detachment of the ion-selective membrane (ISM) from its SC and the accumulation of an aq. film between the ISM and the SC. The accumulation of an aq. film between the ISM and its SC has a detrimental effect on the sensor performance. Although there is a test for the presence of an undesirable water layer, if the conditions for this test are not selected properly, it does not provide an unambiguous answer. However, recording the potential drifts of SC electrodes with pH-sensitive membranes in samples with different CO2 levels can effectively prove the presence or absence of a water layer in a short time period.
- 13Plawinska, Z.; Michalska, A.; Maksymiuk, K. Optimization of capacitance of conducting polymer solid contact in ion-selective electrodes. Electrochim. Acta 2016, 187, 397– 405, DOI: 10.1016/j.electacta.2015.11.050Google Scholar13https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhvFWit7zJ&md5=37f06a65ddc8ae40bfb7bf223f9ec8e3Optimization of capacitance of conducting polymer solid contact in ion-selective electrodesPlawinska, Zaneta; Michalska, Agata; Maksymiuk, KrzysztofElectrochimica Acta (2016), 187 (), 397-405CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Ltd.)All-solid-state ion-selective electrodes with conducting polymer solid contact represent good anal. parameters, comparable with those of classical sensors with internal filling soln. One of parameters characterizing quality of the solid contact, related to ion-to-electron transduction, is the elec. capacitance. However, in many cases this capacitance is lower than for the solid contact only, in the absence of ion-selective membrane. This effect can be disadvantageous, particularly for sensors working under polarization conditions, in galvanostatic mode. The capacitance redn. effect was studied on example of model systems of anion- and cation-selective electrodes with poly(3,4-ethylenedioxythiophene) solid contact with anion- or cation-exchange properties. Basing on results obtained for these membranes and contacts as well as some model calcns., the reasons of reduced capacitance were ascribed to low amt. of ions transferrable across the solid contact/membrane interface. This effect can result from low concn. of mobile ions in the conducting polymer contact or concn. polarization effects. Procedures or pretreatment methods probably minimize the effect of capacitance decrease.
- 14Szucs, J.; Lindfors, T.; Bobacka, J.; Gyurcsanyi, R. E. Ion-selective Electrodes with 3D Nanostructured Conducting Polymer Solid Contact. Electroanalysis 2016, 28, 778– 786, DOI: 10.1002/elan.201500465Google Scholar14https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhslOnsbzM&md5=df2a9d820958401f052e6a690a854c69Ion-selective Electrodes with 3D Nanostructured Conducting Polymer Solid ContactSzucs, Julia; Lindfors, Tom; Bobacka, Johan; Gyurcsanyi, Robert E.Electroanalysis (2016), 28 (4), 778-786CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)Until now both ion-to-electron transducers as well as large surface area nanostructured conducting materials were successfully used as solid contacts for polymer-based ion-selective electrodes. We were interested to explore the combination of these two approaches by fabricating ordered elec. conducting polymer (ECP) nanostructures using 3D nanosphere lithog. and electrosynthesis to provide a high surface area and capacitive interface for solid contact ion-selective electrodes (SC-ISEs). For these studies we used poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT(PSS)) films with 750 nm diam. interconnected pores as the intermediate layer between a glassy carbon electrode and a Ag+ -selective polymeric membrane. We also investigated the feasibility of loading the voids created in the polymer film with a lipophilic redox mediator (1,1'-dimethylferrocene) to provide the resp. ISEs with well-defined/controllable E0 values. These expectations were fulfilled as the std. deviation of E0 values were reduced with almost an order of magnitude for 3D nanostructured SC-ISEs filled with the redox mediator as compared to their redox mediator-free analogs. The detrimental effect of the redox mediator extn. into the plasticized PVC-based ion-selective membrane (ISM) was efficiently suppressed by replacing the PVC-based ISMs with a low diffusivity silicone rubber matrix.
- 15He, N.; Papp, S.; Lindfors, T.; Höfler, L.; Latonen, R. M.; Gyurcsanyi, R. E. Pre-Polarized Hydrophobic Conducting Polymer Solid-Contact Ion Selective Electrodes with Improved Potential Reproducibility. Anal. Chem. 2017, 89, 2598– 2605, DOI: 10.1021/acs.analchem.6b04885Google Scholar15https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsFGitb0%253D&md5=22e50a2763833c564c25fbf246b66935Pre-Polarized Hydrophobic Conducting Polymer Solid-Contact Ion-Selective Electrodes with Improved Potential ReproducibilityHe, Ning; Papp, Soma; Lindfors, Tom; Hofler, Lajos; Latonen, Rose-Marie; Gyurcsanyi, Robert E.Analytical Chemistry (Washington, DC, United States) (2017), 89 (4), 2598-2605CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Elec. conducting polymers (ECPs) are one of the most popular types of materials to interface ion-selective membranes (ISMs) with electron-conducting substrates to construct solid-contact ion-selective electrodes (SCISEs). For optimal ion-to-electron transduction and potential stability, the p-doped ECPs with low oxidn. potentials such as PPy need to be generally in their conducting form along with providing a sufficiently hydrophobic interface to counteract the aq. layer formation. The 1st criterion requires that the ECPs are in their oxidized state, but the high charge d. of this state is detrimental for the prevention of the aq. layer formation. The authors offer here a soln. to this paradox by implementing a highly hydrophobic perfluorinated anion (perfluorooctanesulfonate, PFOS-) as doping ion by which the oxidized form of the ECP becomes hydrophobic. The proof of concept is shown by using polypyrrole (PPy) films doped with PFOS- (PPy-PFOS) as the solid contact in K+-selective SCISEs (K+-SCISE). Prior to applying the plasticized poly(vinyl chloride) ISM, the oxidn. state of the electrodeposited PPy-PFOS was adjusted by polarization to the known open-circuit potential of the solid contact in 0.1M KCl. The prepolarization results in a hydrophobic PPy-PFOS film with a H2O contact angle of 97 ± 5°, which effectively prevents the aq. layer formation under the ISM. Under optimal conditions the K+-SCISEs had a very low std. deviation of E0 of only 501.0 ± 0.7 mV that is the best E0 reproducibility reported for ECP-based SCISEs.
- 16Jaworska, E.; Michalska, A.; Maksymiuk, K. Polypyrrole Nanospheres - Electrochemical Properties and Application as a Solid Contact in Ion-selective Electrodes. Electroanalysis 2017, 29, 123– 130, DOI: 10.1002/elan.201600554Google Scholar16https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhslCnsbbF&md5=12331ab6e61cebeaa54d50ad07fece18Polypyrrole Nanospheres - Electrochemical Properties and Application as a Solid Contact in Ion-selective ElectrodesJaworska, Ewa; Michalska, Agata; Maksymiuk, KrzysztofElectroanalysis (2017), 29 (1), 123-130CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)Polypyrrole nanospheres of uniform size, close to 40 nm, of highly active and unblocked surface were obtained. The novel synthetic approach applied used poly(Bu acrylate) microspheres to deliver the monomer (pyrrole) to the oxidant (iron(III) nitrate) aq. soln. Small portions of dispersion of these nanoparticles were coated on glassy carbon electrodes, yielding stable films suitable for electrochem. studies. Electrochem. expts.: Cyclic voltammetry and electrochem. impedance spectroscopy revealed high transport rate of ions inside the polymer and high charge transfer reactions rate, manifested in highly capacitive characteristics of such layers. These properties are different from those of classical electrochem. obtained polypyrrole. Due to their capacitive properties, polypyrrole nanospheres layers were applied as a solid contact in ion-selective electrodes, on example of a potassium-selective potentiometric sensor. Although the capacitance of the conducting polymer was much lower than in the absence of the ion-selective membrane, it was sufficiently high to obtain sensors with stable potentiometric signals.
- 17Jaworska, E.; Kisiel, A.; Michalska, A.; Maksymiuk, K. Electrochemical Properties of Polypyrrole Nanoparticles - The Role of Doping Ions and Synthesis Medium. Electroanalysis 2018, 30, 716– 726, DOI: 10.1002/elan.201700685Google Scholar17https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhs1KktA%253D%253D&md5=87ee32a283d6037ee69115ad33055526Electrochemical Properties of Polypyrrole Nanoparticles - The Role of Doping Ions and Synthesis MediumJaworska, Ewa; Kisiel, Anna; Michalska, Agata; Maksymiuk, KrzysztofElectroanalysis (2018), 30 (4), 716-726CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)Electrochem. properties of polypyrrole nanoparticles coated on glassy C electrodes were studied. The nanoparticles were obtained in a chem. polymn. step using a novel templateless procedure - oxidn. of pyrrole released either from poly(Bu acrylate) microspheres or from micelles of crosslinked alternating polymer (poly(maleic anhydride-alt-1-octadecene)). Voltammetric measurements confirmed high ion transport rate inside the polymer and minor influence of the kind of doping ion and electrolyte ions present in the soln. However, electrochem. impedance spectroscopy measurements revealed a significant difference in the properties of polypyrrole nanoparticles, depending on the synthesis conditions. In case of polypyrrole synthesized in the presence of poly(Bu acrylate) microspheres EIS spectra were almost independent of kind of electrolyte ions and doping anion, pointing to exposed bulk capacitive properties. However, polypyrrole nanoparticles obtained in the presence of alternating polymer micelles represent a typical const. phase element behavior with impedance significantly dependent on the kind of oxidizing (doping) anion. Due to their capacitive properties polypyrrole nanoparticles obtained in the presence of poly(Bu acrylate) microspheres were applied as solid contacts in ion-selective electrodes.
- 18Jaworska, E.; Gniadek, M.; Maksymiuk, K.; Michalska, A. Polypyrrole Nanoparticles Based Disposable Potentiometric Sensors. Electroanalysis 2017, 29, 2766– 2772, DOI: 10.1002/elan.201700441Google Scholar18https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsFOisLjN&md5=b2c28580f95984b11b46942028138e04Polypyrrole Nanoparticles Based Disposable Potentiometric SensorsJaworska, Ewa; Gniadek, Marianna; Maksymiuk, Krzysztof; Michalska, AgataElectroanalysis (2017), 29 (12), 2766-2772CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)In this work polypyrrole nanoparticles of high electrochem. activity were used to prep. disposable, potentiometric sensors with a paper support. The paper support modified with polypyrrole nanoparticles served as elec. lead and ion-to-electron transducer and it was covered by a typical poly(vinyl chloride) based ion-selective membrane. The properties of this arrangement were tested on example of potassium-selective electrodes. The sensors prepd. benefited from the properties of conducting polymer nanostructures: high elec. cond. and electroactivity as well as absence of suspension stabilizing agent. The obtained electrodes were characterized with anal. parameters well comparable with those of classical ion-selective electrodes.
- 19Yu, K.; He, N.; Kumar, N.; Wang, N. X.; Bobacka, J.; Ivaska, A. Electrosynthesized polypyrrole/zeolite composites as solid contact in potassium ion-selective electrode. Electrochim. Acta 2017, 228, 66– 75, DOI: 10.1016/j.electacta.2017.01.009Google Scholar19https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtVKrsLY%253D&md5=ff6cf8f65f9a798c8a9505183a0fe4e7Electrosynthesized polypyrrole/zeolite composites as solid contact in potassium ion-selective electrodeYu, Kai; He, Ning; Kumar, Narendra; Wang, Nian Xing; Bobacka, Johan; Ivaska, AriElectrochimica Acta (2017), 228 (), 66-75CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Ltd.)Polypyrrole/zeolite composites were studied as solid contact material in potassium ion-selective electrodes (K+-ISEs). Proton-exchanged Zeolite Socony Mobil-5 (H-ZSM-5) with SiO2/Al2O3 ratios of 23, 80 and 280 were electrochem. synthesized with polypyrrole (PPy). The anionic groups on the zeolite framework functioned as the counterions for PPy during the reaction. H-ZSM-5 particles were obsd. on the surface as well as inside the composite films. PPy/H-ZSM-5 composites gave a similar cyclic voltammogram as PPy doped with chloride, PPy(Cl-). The hydrophobicity of the composites decreased in the order PPy/H-ZSM-5-23 > PPy/H-ZSM-5-80 > PPy/H-ZSM-5-280. The redox capacitance of the composite was better used than that of PPy(Cl-) after they were coated with a plasticized PVC membrane. PPy/H-ZSM-5 composite-based K+-ISEs exhibited similar potential stability as the PPy(Cl-)-based K+-ISE. However, when compared with the PPy(Cl-)-based K+-ISE, the detection limit of PPy/H-ZSM-5 composite-based K+-ISEs was enhanced after a long-term conditioning.
- 20Jarvis, J. M.; Guzinski, M.; Pendley, B. D.; Lindner, E. Poly(3-octylthiophene) as solid contact for ion-selective electrodes: contradictions and possibilities. J. Solid State Electrochem. 2016, 20, 3033– 3041, DOI: 10.1007/s10008-016-3340-2Google Scholar20https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xht1yqt7nE&md5=76caeae349b41310c5da8c7f5909fc00Poly(3-octylthiophene) as solid contact for ion-selective electrodes: contradictions and possibilitiesJarvis, Jennifer M.; Guzinski, Marcin; Pendley, Bradford D.; Lindner, ErnoJournal of Solid State Electrochemistry (2016), 20 (11), 3033-3041CODEN: JSSEFS; ISSN:1432-8488. (Springer)The hydrophobic conductive polymer, poly(3-octylthiophene) (POT), is considered as uniquely suited to be used as an ion-to-electron transducer in solid contact (SC) ion-selective electrodes (ISEs).the reports on the performance characteristics of POT-based SC ISEs are quite conflicting. the potential sources of the contradicting results on the ambiguous drift and poor potential reproducibility of POT-based ISEs are compiled, and different approaches to minimize the drift and the differences in the std. potentials of POT-based SC ISEs are shown. To set the potential of the POT film, it has been loaded with a 7,7,8,8-tetracyanoquinodimethane (TCNQ/TCNQ·-) redox couple. It is hypothesized that once the POT film has a stable, highly reproducible redox potential, it will provide similarly stable and reproducible interfacial potentials between the POT film and the electron-conducting substrate and result in SC ISEs with excellent reproducibility and potential stability. the potentials of Au, GC, and Pt electrodes with drop-cast POT film coatings were recorded in KCl solns. as a function of time.Some of the POT films were loaded with TCNQ and coated with a K+-selective membrane. The improvement in the potential stabilities and sensor-to-sensor reproducibility as a consequence of the incorporation of TCNQ in the POT film and the potentiostatic control of the TCNQ/TCNQ·-ratio is reported.
- 21Zdrachek, E.; Bakker, E. Electrochemically Switchable Polymeric Membrane Ion-Selective Electrodes. Anal. Chem. 2018, 90, 7591– 7599, DOI: 10.1021/acs.analchem.8b01282Google Scholar21https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhtVWntL7I&md5=96edae264dcac3ae4a4b446b71d85433Electrochemically Switchable Polymeric Membrane Ion-Selective ElectrodesZdrachek, Elena; Bakker, EricAnalytical Chemistry (Washington, DC, United States) (2018), 90 (12), 7591-7599CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)We present here for the first time a solid contact ion-selective electrode suitable for the simultaneous sensing of cations (tetrabutylammonium) and anions (hexafluorophosphate), achieved by electrochem. switching. The membrane is based on a thin plasticized polyurethane membrane deposited on poly(3-octylthiophene) (POT) and contains a cation exchanger and lipophilic electrolyte (ETH 500). The cation exchanger is initially in excess; the ion-selective electrode exhibits an initial potentiometric response to cations. During an oxidative current pulse, POT is converted into POT+, which results in the expulsion of cations from the membrane followed by the extn. of anions from the sample soln. to fulfill the electroneutrality condition. This creates a defined excess of lipophilic cation in the membrane, resulting in a potentiometric anion response. A reductive current pulse restores the original cation response by triggering the conversion of POT+ back into POT, which is accompanied by the expulsion of anions from the membrane and the extn. of cations from the sample soln. Various current pulse magnitudes and durations are explored, and the best results in terms of response slope values and signal stability were obsd. with an oxidn. current pulse of 140 μA cm-2 applied for 8 s and a redn. current pulse of -71 μA cm-2 applied for 8 s.
- 22Jaworska, E.; Mazur, M.; Maksymiuk, K.; Michalska, A. Fate of Poly(3-octylthiophene) Transducer in Solid Contact Ion-Selective Electrodes. Anal. Chem. 2018, 90, 2625– 2630, DOI: 10.1021/acs.analchem.7b04233Google Scholar22https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXnvVGgsw%253D%253D&md5=d2d76871224b3f5edb3c64d7c05b4acdFate of Poly(3-octylthiophene) Transducer in Solid Contact Ion-Selective ElectrodesJaworska, Ewa; Mazur, Maciej; Maksymiuk, Krzysztof; Michalska, AgataAnalytical Chemistry (Washington, DC, United States) (2018), 90 (4), 2625-2630CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)An exptl. approach allowing visualization and quantification of underestimated spontaneous process of partition of conducting polymer transducer material to the ion-selective membrane phase is proposed. The approach proposed is based on optical properties of the transducer material applied, using polythiophene as a model system. It is shown that this process occurs not only during sensor prepn. step but also during pretreatment of the sensor before use. As shown, this uncontrolled partition of the transducer to the receptor leads to conducting polymer contents in the membrane phase reaching 0.5 % wt./wt.; this process is accompanied by a partial spontaneous change of the oxidn. state of polythiophene. The conducting polymer present in the membrane participates to some extent in the overall response of the sensor, which can be obsd. as a change in the polythiophene optical emission spectra. Fluorescence microscopic images obtained clearly show that the conducting polymer is distributed throughout the membrane thickness, being present also at the membrane / soln. interface. The exptl. results presented were obtained for K+-selective sensors using poly(3-octylthiophene) as a model transducer, however, the proposed approach is also applicable for other systems.
- 23Liu, C. C.; Jiang, X. H.; Zhao, Y. Y.; Jiang, W. W.; Zhang, Z. M.; Yu, L. M. A solid-contact Pb2+- selective electrode based on electrospun polyaniline microfibers film as ion-to-electron transducer. Electrochim. Acta 2017, 231, 53– 60, DOI: 10.1016/j.electacta.2017.01.162Google Scholar23https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXivVKmtrw%253D&md5=d47f164b0d06e38bcf5d32ea60800510A solid-contact Pb2+- selective electrode based on electrospun polyaniline microfibers film as ion-to-electron transducerLiu, Chenchen; Jiang, Xiaohui; Zhao, Yunyan; Jiang, Wenwen; Zhang, Zhiming; Yu, LiangminElectrochimica Acta (2017), 231 (), 53-60CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Ltd.)Electrospun polyaniline (PANI) microfibers are applied as ion-to-electron transducer in solid contact Pb2+-ion-selective electrode (GC/s-PANI/Pb2+-ISE). The corresponding electrode shows a Nernstian slope of 28.4 mV/decade, and a detection limit of 6.3 × 10-10 M can be acquired within a range of 10-9-10-3M Pb(NO3)2, with a response time shorter than 10s. The GC/s-PANI/Pb2+-ISE performs higher capacitance and lower impedance than the drop-coating GC/d-PANI/Pb2+-ISE measured by CV and EIS, demonstrating faster ion-to-electron transportation. Addnl., in the H2O layer test, interfacial H2O film is eliminated in the GC/s-PANI/Pb2+-ISE. The developed electrode is applied to the detn. of lead in real tap H2O, and the corresponding results are in compliance with those detd. by at. absorption spectrometry (AAS) method. This study targeted at PANI microfibers demonstrates a novel strategy of boosting potential stability and decreasing detection limit for solid contact ion-selective electrodes.
- 24Abramova, N.; Moral-Vico, J.; Soley, J.; Ocana, C.; Bratov, A. Solid contact ion sensor with conducting polymer layer copolymerized with the ion-selective membrane for determination of calcium in blood serum. Anal. Chim. Acta 2016, 943, 50– 57, DOI: 10.1016/j.aca.2016.09.017Google Scholar24https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhsFKmtrbJ&md5=7b6653163c4ad7ad60631cb74496fdafSolid contact ion sensor with conducting polymer layer copolymerized with the ion-selective membrane for determination of calcium in blood serumAbramova, Natalia; Moral-Vico, Javier; Soley, Jordi; Ocana, Cristina; Bratov, AndreyAnalytica Chimica Acta (2016), 943 (), 50-57CODEN: ACACAM; ISSN:0003-2670. (Elsevier B.V.)A new solid contact ion selective electrode with intermediate conducting polymer (CP) layer formed by electropolymn. on a gold electrode of a bifunctional monomer, n-phenyl-ethylenediamine-methacrylamide (NPEDMA), which contains a methacrylamide group attached to aniline, is presented. The conducting polymer was studied by means of optical spectroscopy, cyclic voltammetry and potentiometric measurements. Ca2+-ion-selective membrane based on acrylated urethane polymer was shown to co-polymerize with the CP forming highly adhesive boundary that prevents formation of water layers between the CP and membrane, thus enhancing the stability and life-time of the sensor. The designed ion-selective electrode was successfully used for detn. of total calcium ion concn. in blood serum samples.
- 25Boeva, Z. A.; Lindfors, T. Few-layer graphene and polyaniline composite as ion-to-electron transducer in silicone rubber solid-contact ion-selective electrodes. Sens. Actuators, B 2016, 224, 624– 631, DOI: 10.1016/j.snb.2015.10.054Google Scholar25https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhvVSlurbJ&md5=b002bed47df0ad36308ba56e8ae2ea41Few-layer graphene and polyaniline composite as ion-to-electron transducer in silicone rubber solid-contact ion-selective electrodesBoeva, Zhanna A.; Lindfors, TomSensors and Actuators, B: Chemical (2016), 224 (), 624-631CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)We have used for the first time a composite consisting of few-layer exfoliated graphene and elec. conducting polyaniline (PANI) as the ion-to-electron transducer (solid-contact) in Ca2+-selective solid-contact electrodes (CaSCISEs). The drop cast transducer deposited from the graphene-PANI dispersion in N-methylpyrrolidone makes use of the synergistic effect of these two materials. It maintains the ion-to-electron transduction which is characteristic for the elec. conducting polymers (ECP), but in addn., graphene improves the reproducibility of the std. potential of the SCISEs compared to the neat PANI based electrodes and increases the hydrophobicity of the transducer (ca. 30° higher water contact angle) which counteracts the water layer formation. Our results reveal that the incorporation of few-layer graphene in the transducer layer improved also the initial potential stability and the response characteristics of the CaSCISEs due to the electrocatalytic effect of the graphene-ECP composite, which facilitates the electron transfer at the transducer/substrate interface. We obtained a potential reproducibility of only ±4 mV (n = 3) for the CaSCISEs having graphene-PANI as the solid-contact. The CaSCISEs in this study had a detection limit of 5 × 10-8 M Ca2+, which was obtained without any sophisticated pre-treatment protocols.
- 26He, N.; Gyurcsanyi, R. E.; Lindfors, T. Electropolymerized hydrophobic polyazulene as solid-contacts in potassium-selective electrodes. Analyst 2016, 141, 2990– 2997, DOI: 10.1039/C5AN02664DGoogle Scholar26https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xkt1Wrsb8%253D&md5=1a356a1c115bf510deb31f7eab217cd8Electropolymerized hydrophobic polyazulene as solid-contacts in potassium-selective electrodesHe, Ning; Gyurcsanyi, Robert E.; Lindfors, TomAnalyst (Cambridge, United Kingdom) (2016), 141 (10), 2990-2997CODEN: ANALAO; ISSN:0003-2654. (Royal Society of Chemistry)Electropolymd. hydrophobic polyazulene (PAz) based solid-state potassium ion-selective electrodes (SC-ISEs) have been characterized in terms of their suitability for clin. application. Polarization of the PAz solid contact before applying the plasticized poly(vinyl chloride) based K+-selective membrane was implemented as a convenient approach to address the general problem of the irreproducible std. potential (E0) of SC-ISEs. Using this method, the E0 reproducibility among different electrodes was, in the worst case, ±7.9 mV (n = 4). The effectiveness of the redox buffer-free approach presented here in stabilizing E0 is strengthened by the absence of light, oxygen and carbon dioxide sensitivity of the PAz SC-ISEs. No evidence was found for the formation of an aq. layer for the PAz-based SC-ISEs. Thus the hydrophobic carbon structure of PAz having a water contact angle of 98 ± 11°, which is slightly higher than that for graphene, can apparently efficiently counteract the aq. layer formation. In terms of the specific application, the PAz solid contact ISEs were found to show a remarkably good potential stability at their first contact with an aq. sample. We also confirmed that the PAz-based SC-ISEs can be used for the accurate detn. of the K+ concn. in serum solns. Overall, the PAz solid contact shows significant advantages as compared to the state-of-the-art of elec. conducting polymer based SC-ISEs.
- 27Cuartero, M.; Bishop, J.; Walker, R.; Acres, R. G.; Bakker, E.; De Marco, R.; Crespo, G. A. Evidence of double layer/capacitive charging in carbon nanomaterial-based solid contact polymeric ion-selective electrodes. Chem. Commun. 2016, 52, 9703– 9706, DOI: 10.1039/C6CC04876EGoogle Scholar27https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhtFSitLbE&md5=6d69f20c07c48f538c1a802da1a20c06Evidence of double layer/capacitive charging in carbon nanomaterial-based solid contact polymeric ion-selective electrodesCuartero, Maria; Bishop, Josiah; Walker, Raymart; Acres, Robert G.; Bakker, Eric; De Marco, Roland; Crespo, Gaston A.Chemical Communications (Cambridge, United Kingdom) (2016), 52 (62), 9703-9706CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)This paper presents the first direct spectroscopic evidence for double layer or capacitive charging of carbon nanomaterial-based solid contacts in all-solid-state polymeric ion-selective electrodes (ISEs). Here, we used synchrotron radiation-XPS (SR-XPS) and SR valence band (VB) spectroscopy in the elucidation of the charging mechanism of the SCs.
- 28Jaworska, E.; Maksymiuk, K.; Michalska, A. Optimizing Carbon Nanotubes Dispersing Agents from the Point of View of Ion-selective Membrane Based Sensors Performance - Introducing Carboxymethylcellulose as Dispersing Agent for Carbon Nanotubes Based Solid Contacts. Electroanalysis 2016, 28, 947– 953, DOI: 10.1002/elan.201500609Google Scholar28https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhvFemsb%252FM&md5=0ce7e436e291b433fd6163939ffc948cOptimizing carbon nanotubes dispersing agents from the point of view of ion-selective membrane based sensors performance-introducing carboxymethylcellulose as dispersing agent for carbon nanotubes based solid contactsJaworska, Ewa; Maksymiuk, Krzysztof; Michalska, AgataElectroanalysis (2016), 28 (5), 947-953CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)The influence of dispersing agent used to prep. carbon nanotubes solid-contact on the performance of all-solid state ion-selective electrodes was evaluated. Excess of surfactant dispersing agent is leading to deterioration of sensor performance, however, removal of dispersing agent - a typically applied approach - is resulting in substantial change of transducer layer phys. properties, which can influence sensor performance. As remedy the authors propose application of a polymeric dispersing agent - CM-cellulose. Thus obtained ion-selective electrodes were characterized by high potential readings stability both within day and between days.
- 29Lv, E. G.; Ding, J. W.; Qin, W. Potentiometric aptasensing of small molecules based on surface charge change. Sens. Actuators, B 2018, 259, 463– 466, DOI: 10.1016/j.snb.2017.12.067Google Scholar29https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXitVWlsbzN&md5=777c768d56d027a4def722951b50a41aPotentiometric aptasensing of small molecules based on surface charge changeLv, Enguang; Ding, Jiawang; Qin, WeiSensors and Actuators, B: Chemical (2018), 259 (), 463-466CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)Solid-state potentiometric sensors based on surface charge change are well-established tools for measuring ions and biol. species. However, their use for detection of small mols. with high sensitivity and good selectivity is still elusive. In this work, a novel potentiometric aptasensing platform for small mols. is presented, using bisphenol A (BPA) as a model. The proposed sensor can be prepd. by layer-by-layer assembling of carboxylated multiwall carbon nanotubes, poly(diallyldimethylammonium chloride) (polycation), and aptamer (polyanion) on the electrode surface. The presence of BPA induces the conformational change and detachment of the aptamer at the surface of the modified electrode, which leads to a variation of the surface charge (neg. to pos.) and therefore a potential change. The introduction of polyions can cause substantial charge change on the electrode surface, thus improving the sensitivity of the sensor. The morphol. and electron-transfer properties of the electrode have been characterized. Under optimum conditions, the present sensor shows a stable response to BPA in the concn. range from 3.2 × 10-8 to 1.0 × 10-6 M with a detection limit of 1.0 × 10-8 M. The proposed methodol. can be used for sensitive potentiometric sensing of other small mols. involved in aptamer/target binding events.
- 30Yin, T. J.; Li, J. H.; Qin, W. An All-solid-state Polymeric Membrane Ca2+-selective Electrode Based on Hydrophobic Alkyl-chain-functionalized Graphene Oxide. Electroanalysis 2017, 29, 821– 827, DOI: 10.1002/elan.201600383Google Scholar30https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xhslygu7vL&md5=81725aa3a2a0ccef36108b1e03a30052An All-solid-state Polymeric Membrane Ca2+-selective Electrode Based on Hydrophobic Alkyl-chain-functionalized Graphene OxideYin, Tanji; Li, Jinghui; Qin, WeiElectroanalysis (2017), 29 (3), 821-827CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)An all-solid-state polymeric membrane Ca2+-selective electrode based on hydrophobic octadecylamine-functionalized graphene oxide has been developed. The hydrophobic composite in the ion-selective membrane not only acts as a transduction element to improve the potential stability for the all-solid-state Ca2+-selective electrode, but also is used to immobilize Ca2+ ionophore with lipophilic side chains through hydrophobic interactions. The developed all-solid-state Ca2+-selective electrode shows a stable potential response in the linear range of 3.0×10-7-1.0×10-3 M with a slope of 24.7±0.3 mV/dec, and the detection limit is (1.6±0.2 )×10-7 M (n=3). Addnl., due to the hydrophobicity and elec. cond. of the composite, the proposed all-solid-state ion-selective electrode exhibits an improved stability with the absence of water layer between the ion-selective membrane and the underlying glassy carbon electrode. This work provides a simple, efficient and low-cost methodol. for developing stable and robust all-solid-state ion-selective electrode with ionophore immobilization.
- 31Paczosa-Bator, B.; Piech, R.; Wardak, C.; Cabaj, L. Application of graphene supporting platinum nanoparticles layer in electrochemical sensors with potentiometric and voltammetric detection. Ionics 2018, 24, 2455– 2464, DOI: 10.1007/s11581-017-2356-7Google Scholar31https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhvVKltbbO&md5=94397cb97b7a5f3fd5d2dfb8f916c0ecApplication of graphene supporting platinum nanoparticles layer in electrochemical sensors with potentiometric and voltammetric detectionPaczosa-Bator, Beata; Piech, Robert; Wardak, Cecylia; Cabaj, LeszekIonics (2018), 24 (8), 2455-2464CODEN: IONIFA; ISSN:0947-7047. (Springer)The present work reports a possibility of using a layer made of graphene supporting platinum nanoparticles (PtNPs-GR) in electrochem. sensors as active and intermediate layer. New sensors with greatly improved both potentiometric and voltammetric signals were prepd. by using a simple and effective drop casting method and characterized by a cyclic voltammetry and a electrochem. impedance spectroscopy. The performance of the new potentiometric sensor was evaluated by the use an ion-selective membrane with well-known valinomycin ion carrier. Potassium electrodes had a Nernstian slope (59.10 mV/pK), high stability and reproducibility of the std. potential values, and a very small drift potential. Under optimized operating conditions, the voltammetric sensor with PtNPs-GR responded to paracetamol concn. in the range from 20 nM to 2.2 μM with the detection limit of 8 nM.
- 32Li, J. H.; Yin, T. J.; Qin, W. An effective solid contact for an all-solid-state polymeric membrane Cd2+-selective electrode: Three-dimensional porous graphene-mesoporous platinum nanoparticle composite. Sens. Actuators, B 2017, 239, 438– 446, DOI: 10.1016/j.snb.2016.08.008Google Scholar32https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhtlehurrL&md5=57f1602b9a8c864f8bfbc9034b438146An effective solid contact for an all-solid-state polymeric membrane Cd2+-selective electrode: Three-dimensional porous graphene-mesoporous platinum nanoparticle compositeLi, Jinghui; Yin, Tanji; Qin, WeiSensors and Actuators, B: Chemical (2017), 239 (), 438-446CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)The three-dimensional porous graphene-mesoporous platinum nanoparticle (3D PGR-MPN) composite is used as solid contact for developing an all-solid-state polymeric membrane Cd2+ ion-selective electrode (Cd2+-ISE). The 3D PGR with MPNs as crosslinking sites can be synthesized by a facile hydrothermal co-assembly method. The obtained 3D PGR-MPN composite is promising for acting as solid contact due to its unique characteristics such as high interfacial area, superior double layer capacitance, excellent cond. and high hydrophobicity. The ISE exhibits a stable Nernstian response in the range of 10-8-10-4 M and the detection limit is 10-8.8 M. The 3D PGR-MPN-based Cd2+-ISE shows good potential response and no water layer exists between the polymeric membrane and the 3D PGR-MPN layer. Addnl., the proposed Cd2+-ISE is robust to O2, CO2 and light interferences. This work provides a versatile method for prepg. an effective solid contact to develop a stable and reliable all-solid-state ISE.
- 33Xu, J. A.; Jia, F.; Li, F. H.; An, Q. B.; Gan, S. Y.; Zhang, Q. X.; Ivaska, A.; Niu, L. Simple and Efficient Synthesis of Gold Nanoclusters and Their Performance as Solid Contact of Ion Selective Electrode. Electrochim. Acta 2016, 222, 1007– 1012, DOI: 10.1016/j.electacta.2016.11.069Google Scholar33https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhvFegur%252FJ&md5=a5ad4edf36dea7efcac74a295282c06dSimple and Efficient Synthesis of Gold Nanoclusters and Their Performance as Solid Contact of Ion Selective ElectrodeXu, Jianan; Jia, Fei; Li, Fenghua; An, Qingbo; Gan, Shiyu; Zhang, Qixian; Ivaska, Ari; Niu, LiElectrochimica Acta (2016), 222 (), 1007-1012CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Ltd.)Gold nanoclusters are ideal materials as solid transducer in all-solid-state ion-selective electrodes (ISEs) due to their high hydrophobicity, excellent ion-to-electron transduction, high specific capacitance and outstanding chem. stability. In this paper, monolayer-protected gold nanoclusters (MPCs) were synthesized by a simple one-phase method requiring a relatively short reaction time with high yield (60%). Transmittance electronic microscopy (TEM) and at.-force microscopy (AFM) were used to characterize the morphol. of MPCs. The compn. of MPCs was studied by UV-vis spectrometry, Matrix-assisted laser desorption ionization (MALDI) mass spectrometry, X-ray diffraction (XRD) measurement and XPS measurements. The performance of MPCs based ISEs was thoroughly characterized by electrochem. impedance, emf. and chronopotentiometry measurement. Comparison with the performance of ISE with other signal transducing materials such as conductive polymer, carbon nanotube, graphene and fullerene, the MPCs based ISEs have higher potential st ability and reproducibility, lower detection limit, longer operating life (one year) and higher anti-interference ability.
- 34An, Q. B.; Jiao, L. S.; Jia, F.; Ye, J. J.; Li, F. H.; Gan, S. Y.; Zhang, Q. X.; Ivaska, A.; Niu, L. Robust single-piece all-solid-state potassium-selective electrode with monolayer-protected Au clusters. J. Electroanal. Chem. 2016, 781, 272– 277, DOI: 10.1016/j.jelechem.2016.10.053Google Scholar34https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhslGqtrbN&md5=14d5565790cbae23c01d68396ae8538eRobust single-piece all-solid-state potassium-selective electrode with monolayer-protected Au clustersAn, Qingbo; Jiao, Liansheng; Jia, Fei; Ye, Junjin; Li, Fenghua; Gan, Shiyu; Zhang, Qixian; Ivaska, Ari; Niu, LiJournal of Electroanalytical Chemistry (2016), 781 (), 272-277CODEN: JECHES; ISSN:1873-2569. (Elsevier B.V.)High stability of the signal and simplicity in fabrication of the device are the two important requirements in development of potentiometric sensors. A robust single-piece all-solid-state potassium-selective electrode (K-SPE) was developed by incorporating monolayer-protected Au clusters (MPCs) as advanced ion-to-electron transducers into a conventional ion-selective membrane (ISM). The extraordinary properties of MPCs such as high soly., profound hydrophobicity and large capacitance make them quite suitable to be used in fabrication of single-piece electrodes (SPEs) with advanced performance. The developed KSPEs contg. small amt. of MPCs in the membrane showed a significant increase in the potential stability (12.9 μV/h), lower detection limit (10-6.1 M) and prolonged life time (high performance still after 3 wk). The multi-valence MPCs in the membrane facilitated the ion-to-electron transduction and fast establishment of the potential equil. resulting in fast response time in potential measurements. The inserted MPCs did not cause any interference either in the potential formation process or in the selectivity of the ion-selective membrane.
- 35Yin, T. J.; Jiang, X. J.; Qin, W. A magnetic field-directed self-assembly solid contact for construction of an all-solid-state polymeric membrane Ca2+- selective electrode. Anal. Chim. Acta 2017, 989, 15– 20, DOI: 10.1016/j.aca.2017.08.015Google Scholar35https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtl2rsLvE&md5=1d56c31935f4f95a946da9d97160d462A magnetic field-directed self-assembly solid contact for construction of an all-solid-state polymeric membrane Ca2+-selective electrodeYin, Tanji; Jiang, Xiaojing; Qin, WeiAnalytica Chimica Acta (2017), 989 (), 15-20CODEN: ACACAM; ISSN:0003-2670. (Elsevier B.V.)A magnetic field-directed self-assembly solid contact has been proposed for developing an all-solid-state polymeric membrane Ca2+-selective electrode. The solid contact was prepd. by phys. adsorbing magnetic graphene powder on a magnetic gold electrode under the direction of the magnetic field. The proposed method for prepg. solid contact avoids using the aq. solns. and is simple, fast and general as compared to the multilayer drop-casting and electrodeposition methods. The all-solid-state Ca2+-selective electrode based on magnetic graphene as solid contact shows a stable potential response in the linear range of 1.0 × 10-6-1.0 × 10-3 M with a slope of 28.2 mV/decade, and the detection limit is ∼4.0 × 10-7 M. Addnl., the magnetic graphene-based electrode shows a comparable potential stability performance to other graphene-based all-solid-state ion-selective electrodes, such as a reduced undesirable water layer and being insensitive to the interferences of O2, CO2 and light. This work provides a favorable way to prep. solid contact for use in the field of all-solid-state ion-selective electrodes.
- 36He, Q.; Das, S. R.; Garland, N. T.; Jing, D. P.; Hondred, J. A.; Cargill, A. A.; Ding, S. W.; Karunakaran, C.; Claussen, J. C. Enabling Inkjet Printed Graphene for Ion Selective Electrodes with Postprint Thermal Annealing. ACS Appl. Mater. Interfaces 2017, 9, 12719– 12727, DOI: 10.1021/acsami.7b00092Google Scholar36https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXivVOisLw%253D&md5=bda54e91f82a089ecd7e32f355bce1e9Enabling Inkjet Printed Graphene for Ion Selective Electrodes with Postprint Thermal AnnealingHe, Qing; Das, Suprem R.; Garland, Nathaniel T.; Jing, Dapeng; Hondred, John A.; Cargill, Allison A.; Ding, Shaowei; Karunakaran, Chandran; Claussen, Jonathan C.ACS Applied Materials & Interfaces (2017), 9 (14), 12719-12727CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)Inkjet printed graphene (IPG) has recently shown tremendous promise in reducing the cost and complexity of graphene circuit fabrication. Herein we demonstrate, for the first time, the fabrication of an ion selective electrode (ISE) with IPG. A thermal annealing process in a nitrogen ambient environment converts the IPG into a highly conductive electrode (sheet resistance changes from 52.8 ± 7.4 MΩ/for unannealed graphene to 172.7 ± 33.3Ω/for graphene annealed at 950°C). Raman spectroscopy and field emission SEM (FESEM) anal. reveals that the printed graphene flakes begin to smooth at an annealing temp. of 500 °C and then become more porous and more elec. conductive when annealed at temps. of 650 °C and above. The resultant thermally annealed, IPG electrodes are converted into potassium ISEs via functionalization with a polyvinyl chloride (PVC) membrane and valinomycin ionophore. The developed potassium ISE displays a wide linear sensing range (0.01mM to 100 mM), a low detection limit (7 μM), minimal drift (8.6 10-6 V/s), and a negligible interference during electrochem. potassium sensing against the backdrop of interfering ions [i.e., sodium (Na), magnesium (Mg), and calcium (Ca)] and artificial eccrine perspiration. Thus, the IPG ISE shows potential for potassium detection in a wide variety of human fluids including plasma, serum, and sweat.
- 37Weber, A. W.; O’Neil, G. D.; Kounaves, S. P. Solid Contact Ion-Selective Electrodes for in Situ Measurements at High Pressure. Anal. Chem. 2017, 89, 4803– 4807, DOI: 10.1021/acs.analchem.7b00366Google Scholar37https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXlvVGqsr0%253D&md5=6be68464dacd04c826d7e48c1f09f81cSolid Contact Ion-Selective Electrodes for in Situ Measurements at High PressureWeber, Andrew W.; O'Neil, Glen D.; Kounaves, Samuel P.Analytical Chemistry (Washington, DC, United States) (2017), 89 (9), 4803-4807CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Solid contact polymeric ion-selective electrodes (SC-ISEs) have been fabricated using microporous carbon (μPC) as the ion-to-electron transducer, loaded with a liq. membrane cocktail contg. both ionophore and additive dissolved in plasticizer. These SC-ISEs were characterized and are suitable for anal. in aq. environments at pressures of 100 bar. Potassium ISEs, prepd. in this manner, showed excellent performance at both atm. and elevated pressures, as evaluated by their response slopes and potential stability. These novel SC-ISEs are capable of measuring K+ at pressures under which traditional liq.-filled ISEs fail. Furthermore, the effect of pressure on the response of these sensors had little or no effect on potential, sensitivity, or limit of detection. High pressure sensor calibrations were performed in std. solns. as well as simulated seawater samples to demonstrate their usefulness as sensors in a deep-sea environment. These novel SC-ISE sensors show promise of providing the ability to make in situ real-time measurements of ion-fluxes near deep-ocean geothermal vents.
- 38Piek, M.; Piech, R.; Paczosa-Bator, B. All-solid-state nitrate selective electrode with graphene/tetrathiafulvalene nanocomposite as high redox and double layer capacitance solid contact. Electrochim. Acta 2016, 210, 407– 414, DOI: 10.1016/j.electacta.2016.05.170Google Scholar38https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XpsVygsrc%253D&md5=9c3e4d35dffbc51575b2aababf9b5f9eAll-solid-state nitrate selective electrode with graphene/tetrathiafulvalene nanocomposite as high redox and double layer capacitance solid contactPiek, Magdalena; Piech, Robert; Paczosa-Bator, BeataElectrochimica Acta (2016), 210 (), 407-414CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Ltd.)Electrodes with graphene-tetrathiafulvalene nanocomposite intermediate layer between a glassy C disk electrode and an ionophore-doped solvent polymeric membrane were made as a new type of all-solid-state ion-selective electrodes. The proposed interlayers prepd. in a quite simple drop casting method exhibited a high redox and double layer capacitance resulting from the use of both, tetrathiafulvalene (TTF/TTF+) as redox-reaction based transducer and graphene (GR) as C material with a large surface area forming high elec. double layer at the ion-selective membrane and the solid contact interface. The influence of the used solid-contact compn. on metrol. parameters of studied electrodes was characterized by electrochem. measurements. The graphene-TTF/TTF+ solid contact layer capacitance detd. applying a current 5 nA was 1.18 mF and potential drift was only 4.26 μV s-1. The GR-TTF/TTF+-modified electrodes exhibited a good Nernstian response with a slope of -59.14 mV/dec at 10-6-10-1 M nitrate ions.
- 39Piek, M.; Piech, R.; Paczosa-Bator, B. The Complex Crystal of NaTCNQ-TCNQ Supported on Different Carbon Materials as Ion-to-Electron Transducer in All-Solid-State Sodium-Selective Electrode. J. Electrochem. Soc. 2016, 163, B573– B579, DOI: 10.1149/2.0341613jesGoogle Scholar39https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXpslentLk%253D&md5=0114dce2f6774666e7d38026adce8172The complex crystal of NaTCNQ-TCNQ supported on different carbon materials as ion-to-electron transducer in all-solid-state sodium-selective electrodePiek, Magdalena; Piech, Robert; Paczosa-Bator, BeataJournal of the Electrochemical Society (2016), 163 (13), B573-B579CODEN: JESOAN; ISSN:0013-4651. (Electrochemical Society)This work demonstrates the application of conductive org. crystals (7,7,8,8-tetracyanoquinodimethane (TCNQ) and its Na salt (NaTCNQ)) supported on C nanomaterials (CNMs) as solid contact layer in all-solid-state ion-selective electrodes (ASS-ISEs). As ion-to-electron transducer between the ionically conducting membrane and the electronically conducting glassy C new layers based on a high capacity of charge transfer and a redox TCNQ/TCNQ- reaction are proposed. Developed CNM-NaTCNQ- TCNQ-contacted sensors provided a near to Nernstian response to Na and excellent elec. parameters. The highest electrode capacitance was 2.15 mF, as the potential drift (and electrodes resistance) are significantly reduced due to the presence in solid contact combination of materials having ionic or electron cond. Also, the introduction of NaTCNQ in Na-selective electrodes improves their selectivity toward to interfering cations. C nanomaterials type used in the interlayer affects, in the different way, the anal. and elec. parameters of proposed ASS-ISEs. The possibility of improving the electrodes sensitivity, linear range and detection limit, by changing the NaTCQ:TCNQ ratio, is also presented.
- 40Piek, M.; Piech, R.; Paczosa-Bator, B. TTF-TCNQ Solid Contact Layer in All-Solid-State Ion-Selective Electrodes for Potassium or Nitrate Determination. J. Electrochem. Soc. 2018, 165, B60– B65, DOI: 10.1149/2.0161803jesGoogle Scholar40https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXjtlKjs7k%253D&md5=2f7c68e318020ea5ed8fc5b2d96c8b50TTF-TCNQ Solid Contact Layer in All-Solid-State Ion-Selective Electrodes for Potassium or Nitrate DeterminationPiek, Magdalena; Piech, Robert; Paczosa-Bator, BeataJournal of the Electrochemical Society (2018), 165 (2), B60-B65CODEN: JESOAN; ISSN:0013-4651. (Electrochemical Society)Nowadays, org. donor-acceptor mols. have attracted a lot of scientific attention because of their unique properties and potential applications in various fields. Although tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) is well known charge transfer salt for a long time, the first application of this material as ion-to-electron transducer in ion-selective electrodes is presented. As a proof of concept, potassium-selective and nitrate-selective solid-state electrodes were constructed. Moreover, TTF-TCNQ intermediate layers were fabricated using two org. solvents. Developed potassium sensors displayed a good Nernstian response with a slope of 58.52 mV/decade (10-6-10-1 M K+), whereas the nitrate-selective electrodes showed a sensitivity of -58.47 mV/decade (10-5-10-1 M NO-3). Reproducible std. potentials and low detection limits were obsd. Potential stability of studied electrodes was evaluated using current-reversal chronopotentiometry. The capacitance of TTF-TCNQ-contacted electrodes is 255 μF and 629 μF for K+ and NO-3 sensors. The results of measurements conducted reveal that TTF-TCNQ has an appropriate effect on potentiometric sensors performance.
- 41Jaworska, E.; Naitana, M. L.; Stelmach, E.; Pomarico, G.; Wojciechowski, M.; Bulska, E.; Maksymiuk, K.; Paolesse, R.; Michalska, A. Introducing Cobalt(II) Porphyrin/Cobalt(III) Corrole Containing Transducers for Improved Potential Reproducibility and Performance of All-Solid-State Ion-Selective Electrodes. Anal. Chem. 2017, 89, 7107– 7114, DOI: 10.1021/acs.analchem.7b01027Google Scholar41https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXpvVSltbk%253D&md5=524ffa437fc229842608dd57287baca9Introducing Cobalt(II) Porphyrin/Cobalt(III) Corrole Containing Transducers for Improved Potential Reproducibility and Performance of All-Solid-State Ion-Selective ElectrodesJaworska, Ewa; Naitana, Mario L.; Stelmach, Emilia; Pomarico, Giuseppe; Wojciechowski, Marcin; Bulska, Ewa; Maksymiuk, Krzysztof; Paolesse, Roberto; Michalska, AgataAnalytical Chemistry (Washington, DC, United States) (2017), 89 (13), 7107-7114CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)A novel solid contact type for all-solid-state ion-selective electrodes is introduced, yielding high stability and reproducibility of potential readings between sensors as well as improved anal. performance. The transducer phase herein proposed takes advantage of the presence of porphyrinoids contg. the same metal ion at different oxidn. states. In contrast to the traditional approach, the compds. of choice are not a redox pair; although they have different oxidn. states, they cannot be electrochem. driven one to another. The compds. of choice were cobalt(II) porphyrin and cobalt(III) corrole, both characterized by a high stability of the coordinated metal ions in their resp. redox states and elec. neutrality, as well as relatively high lipophilicity. The porphyrinoids were used together with carbon nanotubes to yield transducer layers for ion-selective electrodes. As a result, the authors obtained a high stability of potential readings of the resulting ion-selective electrodes together with good reproducibility between different sensor batches. Moreover, advantageously the presence of porphyrinoids in the transducer phase results in improvement of the anal. performance of the sensors: linear response range and selectivity due to interactions with membrane components, resulting in tailoring of ion fluxes through the membrane phase. Thus, carbon nanotubes with the cobalt(II) porphyrin/cobalt(III) corrole system are promising alternatives for existing transducer systems for potentiometric sensors.
- 42Ishige, Y.; Klink, S.; Schuhmann, W. Intercalation Compounds as Inner Reference Electrodes for Reproducible and Robust Solid-Contact Ion-Selective Electrodes. Angew. Chem., Int. Ed. 2016, 55, 4831– 4835, DOI: 10.1002/anie.201600111Google Scholar42https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XktFGktbg%253D&md5=0c3309e479f473f8a6c748f58f4861d1Intercalation Compounds as Inner Reference Electrodes for Reproducible and Robust Solid-Contact Ion-Selective ElectrodesIshige, Yu; Klink, Stefan; Schuhmann, WolfgangAngewandte Chemie, International Edition (2016), 55 (15), 4831-4835CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)With billions of assays performed every year, ion-selective electrodes (ISEs) provide a simple and fast technique for clin. anal. of blood electrolytes. The development of cheap, miniaturized solid-contact (SC-)ISEs for integrated systems, however, remains a difficult balancing act between size, robustness, and reproducibility, because the defined interface potentials between the ion-selective membrane and the inner ref. electrode (iRE) are often compromised. Target cation-sensitive intercalation compds., such as partially charged Li Fe phosphate (LFP), can be applied as iREs of the quasi-first kind for ISEs. The sym. response of the interface potentials towards target cations ultimately results in ISEs with high robustness towards the inner filling (∼5 mV dec-1 conc.) as well as robust and miniaturized SC-ISEs. They have a predictable and stable potential derived from the LiFePO4/FePO4 redox couple (97.0 ± 1.5 mV after 42 days).
- 43Komaba, S.; Akatsuka, T.; Ohura, K.; Suzuki, C.; Yabuuchi, N.; Kanazawa, S.; Tsuchiya, K.; Hasegawa, T. All-solid-state ion-selective electrodes with redox-active lithium, sodium, and potassium insertion materials as the inner solid-contact layer. Analyst 2017, 142, 3857– 3866, DOI: 10.1039/C7AN01068KGoogle Scholar43https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsVejtbfK&md5=1ce57189145e07d57885747f68c71cbeAll-solid-state ion-selective electrodes with redox-active lithium, sodium, and potassium insertion materials as the inner solid-contact layerKomaba, Shinichi; Akatsuka, Tatsuya; Ohura, Kohei; Suzuki, Chihiro; Yabuuchi, Naoaki; Kanazawa, Shintaro; Tsuchiya, Kazuhiko; Hasegawa, TakuAnalyst (Cambridge, United Kingdom) (2017), 142 (20), 3857-3866CODEN: ANALAO; ISSN:0003-2654. (Royal Society of Chemistry)All-solid-state ion-selective electrodes as potentiometric ion sensors for Li, Na, and K were demonstrated by installing a composite layer contg. a powder of alkali insertion materials, LixFePO4, Na0.33MnO2, and KxMnO2·nH2O, resp., as an inner solid-contact layer between the electrode substrate and plasticized poly(vinyl chloride) (PVC)-based ion-sensitive membrane contg. the corresponding ionophores for Li+, Na+, and K+ ions. These double-layer ion-selective electrodes, consisting of the composite and PVC layers prepd. by a simple drop cast method, exhibit a quick potential response (<5 s) to each alkali-metal ion with sufficient Nernstian slopes of calibration curves, ∼59 mV per decade. The installation of the insertion materials as the inner solid-contact layers is highly efficient for the stabilization of membrane potential, resulting in a prompt response to the alkali ion activity in the analyte, compared to those of the electrodes without the alkali insertion materials. From a.c. impedance measurements for the electrodes, the inner layer of the installed alkali insertion materials drastically reduces the impedance of the membrane/electrode interface, leading to an improvement in their ion-sensing performance.
- 44Klink, S.; Ishige, Y.; Schuhmann, W. Prussian Blue Analogues: A Versatile Framework for Solid-Contact Ion-Selective Electrodes with Tunable Potentials. ChemElectroChem 2017, 4, 490– 494, DOI: 10.1002/celc.201700091Google Scholar44https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXitlClsbw%253D&md5=2f313bf2b5bc81572fae2397aa58d5daPrussian Blue Analogues: A Versatile Framework for Solid-Contact Ion-Selective Electrodes with Tunable PotentialsKlink, Stefan; Ishige, Yu; Schuhmann, WolfgangChemElectroChem (2017), 4 (3), 490-494CODEN: CHEMRA; ISSN:2196-0216. (Wiley-VCH Verlag GmbH & Co. KGaA)The development of solid-contact ion-selective electrodes (SC-ISEs) (e.g. for point-of-care sensors) requires simple inner ref. electrodes (iREs) with predictable and reproducible potentials. Intercalation compds. fulfill these requirements, as they respond to target ions present in the ion-selective membrane. Their applicability, however, is limited by the availability of intercalation frameworks capable to intercalate the target ion of interest. We report that Prussian Blue analogs (PBAs) can serve as versatile iREs for a range of target ions of clin. interest, such as Na+, K+, or Ca2+. Combining target-ion intercalated PBAs with ion-selective membranes results in a family of all-solid SC-ISEs, which are capable as ISEs with an inner filling, yet cheap and suitable for mass-prodn. The SC-ISEs' std. potential is predictable and can be tuned by altering the PBAs' redox-active transition metal or by changing its state of charge.
- 45Zeng, X. Z.; Qin, W. A solid-contact potassium-selective electrode with MoO2 microspheres as ion-to-electron transducer. Anal. Chim. Acta 2017, 982, 72– 77, DOI: 10.1016/j.aca.2017.05.032Google Scholar45https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtVGnsbrL&md5=f42660f9463012fbc1c63f77171e80b3A solid-contact potassium-selective electrode with MoO2 microspheres as ion-to-electron transducerZeng, Xianzhong; Qin, WeiAnalytica Chimica Acta (2017), 982 (), 72-77CODEN: ACACAM; ISSN:0003-2670. (Elsevier B.V.)A solid-contact ion-selective electrode (SC-ISE) for potassium with MoO2 microspheres as ion-to-electron transducer is described. MoO2 microsphers can be synthesized via the redn. of MoO3 nanobelts in an isopropanol solvent with a mild process, and the obtained MoO2 microspheres were characterized by x-ray diffraction and field-emission SEM. With the application of MoO2 microspheres, the newly fabricated SC-ISE for K+ exhibits a stable and rapid potential response. A near Nernstian slope of 55 mV/decade to potassium activities in the range of 10-5 - 10-3 M is found and the detection limit is 10-5.5 M. Impedance spectra and chronopotentiometry results show that a smaller resistance together with a larger double layer capacitance is guaranteed due to the introduction of the intermediate layer of MoO2 microspheres. Addnl., light, O2 and CO2 do not induce significant influences to the present SC-ISE, and a reduced water layer between the ion selective membrane and the underlying conductor is formed. Thus, MoO2 microspheres, as metallic analogs, can be used as a good candidate for the new type of transducing layer in SC-ISEs.
- 46Zeng, X. Z.; Yu, S. Y.; Yuan, Q.; Qin, W. Solid-contact K+-selective electrode based on three-dimensional molybdenum sulfide nanoflowers as ion-to-electron transducer. Sens. Actuators, B 2016, 234, 80– 83, DOI: 10.1016/j.snb.2016.04.153Google Scholar46https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XntFymtL4%253D&md5=43235ed5ded9161f1424ec62e990cfbaSolid-contact K+-selective electrode based on three-dimensional molybdenum sulfide nanoflowers as ion-to-electron transducerZeng, Xianzhong; Yu, Shunyang; Yuan, Qun; Qin, WeiSensors and Actuators, B: Chemical (2016), 234 (), 80-83CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)Three-dimensional (3D) molybdenum sulfide (MoS2) nanoflowers have been synthesized via a novel hydrothermal method and applied as ion-to-electron transducer for solid-contact ion-selective electrodes (SC-ISEs). The morphol. and elemental compn. of the prepd. nanomaterials have been characterized. The performance of the developed K+-SC-ISE has been demonstrated by detg. K+ in soln. with a polymeric membrane contg. valinomycin as the ionophore. A Nernstian slope of 55.8 mV/decade with a detection limit of 10-5.5 M can be obtained. Using the 3D flowerlike MoS2 as solid contact, the fabricated K+-SC-ISE exhibits a smaller impedance and more stable potential response than the coated-wire electrode. In addn., the novel SC-ISE behaves well in the water layer test and shows good resistance to interferences from light, O2 and CO2. It is believed that the 3D MoS2 nanoflowers can be a good alternative as solid contact in SC-ISEs.
- 47Egorov, V. V.; Novakovskii, A. D.; Zdrachek, E. A. Modeling of the effect of diffusion processes on the response of ion-selective electrodes by the finite difference technique: Comparison of theory with experiment and critical evaluation. J. Anal. Chem. 2017, 72, 793– 802, DOI: 10.1134/S1061934817070048Google Scholar47https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtFaqsLvP&md5=7f3eb3b035a723103b70eea1ca34946aModeling of the effect of diffusion processes on the response of ion-selective electrodes by the finite difference technique: Comparison of theory with experiment and critical evaluationEgorov, V. V.; Novakovskii, A. D.; Zdrachek, E. A.Journal of Analytical Chemistry (2017), 72 (7), 793-802CODEN: JACTE2; ISSN:1061-9348. (Pleiades Publishing, Ltd.)Exptl. data are compared with the results of calcns. by the finite difference technique within the dynamic diffusion model of the interphase potential on an example of a picrate-selective electrode in real scenarios corresponding to the conditions of the detn. of selectivity coeffs. by the methods recommended by IUPAC. In the majority of the considered cases, the calcd. values of the potential and selectivity coeffs. and also the dynamics of potential change at particular steps well agree with the exptl. data. The model has principal restrictions, leading the failure of calcns., when the concn. of potential-detg. ions in the near-electrode layer of the soln. performed is low according to the algorithm of measurements, whereas the instant increase in its concn. in the surface membrane layer due to the replacement of the sample soln. induces a flux of these ions from the surface deep into of the membrane.
- 48Egorov, V. V.; Novakovskii, A. D.; Zdrachek, E. A. A Simple Dynamic Diffusion Model of the Response of Highly Selective Electrodes: The Effect of Simulation Parameters and Boundary Conditions on the Results of Calculations. Russ. J. Electrochem. 2018, 54, 381– 390, DOI: 10.1134/S1023193518040031Google Scholar48https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXotF2nt70%253D&md5=efd97478de852d068c082bb4850d52e5A Simple Dynamic Diffusion Model of the Response of Highly Selective Electrodes: The Effect of Simulation Parameters and Boundary Conditions on the Results of CalculationsEgorov, V. V.; Novakovskii, A. D.; Zdrachek, E. A.Russian Journal of Electrochemistry (2018), 54 (4), 381-390CODEN: RJELE3; ISSN:1023-1935. (Pleiades Publishing, Ltd.)For a tetrabutylammonium-selective electrode with a ion-exchange membrane, in the real-work scenario corresponding to the detn. of selectivity coeffs. by the IUPAC-recommended method of sep. solns., it is shown that of the results of calcns. obtained within the framework of the dynamic diffusion model based on the use of the finite-difference technique substantially depend on of the chosen boundary conditions and the values of arbitrarily set simulation parameters. The key parameter that dets. the quality of simulation results is the thickness of the elementary layer in the membrane phase, esp. for low diffusion coeffs. It is found that the use of thin elementary layers in membranes and thick elementary layers in the aq. phase makes it possible to combine the high quality with the high calcn. rate. In simulating the long-term expts., account should be taken of the accumulation of the potential-detg. ion in the aq. soln. vol. as a result of its displacement by a foreign ion from the membrane. A good correspondence between calcn. data and exptl. results is demonstrated.
- 49Egorov, V. V.; Novakovskii, A. D.; Zdrachek, E. A. An Interface Equilibria-Triggered Time-Dependent Diffusion Model of the Boundary Potential and Its Application for the Numerical Simulation of the Ion-Selective Electrode Response in Real Systems. Anal. Chem. 2018, 90, 1309– 1316, DOI: 10.1021/acs.analchem.7b04134Google Scholar49https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhvFGjtr3L&md5=7a477189564d3cde5f4859d1f5fafad7An Interface Equilibria-Triggered Time-Dependent Diffusion Model of the Boundary Potential and Its Application for the Numerical Simulation of the Ion-Selective Electrode Response in Real SystemsEgorov, Vladimir V.; Novakovskii, Andrei D.; Zdrachek, Elena A.Analytical Chemistry (Washington, DC, United States) (2018), 90 (2), 1309-1316CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)A simple dynamic model of the phase boundary potential of ion-selective electrodes is presented. The model is based on the calcns. of the concn. profiles of the components in membrane and sample soln. phases by finite difference method. The fundamental idea behind the discussed model is that the concn. gradients in membrane and sample soln. phases det. only the diffusion of the components inside corresponding phases, but not the transfer across the interface. The transfer of the components across the interface at any instant of time is detd. by the corresponding local interphase equil. According to the presented model, each new calcn. cycle begins with the correction of the components concns. in the near-boundary (1st) layers of the membrane and soln., based on the consts. of the interphase equil. and the concns. established at a given time as a result of diffusion. The cor. concns. of the components in the boundary layers every time give a start to a new cycle of the diffusion processes calcns. inside each phase from the 1st layer to the 2nd one etc. In contrast to the known Morf's model, the above-mentioned layers do not comprise an imaginary part and they are entirely localized in the corresponding phases, and this allows performing the equil. concns. calcns. taking into account material balance for each component. The model remains operational for any realistic scenarios of the electrode functioning. The efficiency and predictive ability of the proposed model are confirmed by comparing the results of calcns. with the exptl. data on the dynamics of the potential change of a picrate-selective electrode in nitrate solns. when detg. the selectivity coeffs. using the methods recommended by IUPAC.
- 50Yuan, D. J.; Bakker, E. Overcoming Pitfalls in Boundary Elements Calculations with Computer Simulations of Ion Selective Membrane Electrodes. Anal. Chem. 2017, 89, 7828– 7831, DOI: 10.1021/acs.analchem.7b01777Google Scholar50https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtFGnsLfK&md5=b2ec2a0682aae7c9a86a457683739734Overcoming Pitfalls in Boundary Elements Calculations with Computer Simulations of Ion Selective Membrane ElectrodesYuan, Dajing; Bakker, EricAnalytical Chemistry (Washington, DC, United States) (2017), 89 (15), 7828-7831CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Finite difference anal. of ion-selective membranes is a valuable tool for understanding a range of time dependent phenomena such as response times, long and medium term potential drifts, detn. of selectivity, and (re)conditioning kinetics. It is here shown that an established approach based on the diffusion layer model applied to an ion-exchange membrane fails to use mass transport to account for concn. changes at the membrane side of the phase boundary. Instead, such concns. are imposed by the ion-exchange equil. condition, without taking into account the source of these ions. The limitation is illustrated with a super-Nernstian potential jump, where a membrane initially void of analyte ion is exposed to incremental concns. of analyte in the sample. To overcome this limitation, the two boundary elements, one at either side of the sample-membrane interface, are treated here as a combined entity and its total concn. change is dictated by diffusional fluxes into and out of the interface. For each time step, the concn. distribution between the two boundary elements is then computed by ion-exchange theory. The resulting finite difference simulation is much more robust than the earlier model and gives a good correlation to expts.
- 51Sanders, T. M.; Myers, M.; Asadnia, M.; Umana-Membreno, G. A.; Baker, M.; Fowkes, N.; Parish, G.; Nener, B. Description of ionophore-doped membranes with a blocked interface. Sens. Actuators, B 2017, 250, 499– 508, DOI: 10.1016/j.snb.2017.04.143Google Scholar51https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXns1aiu7c%253D&md5=358f2c76b9118a0bc7290d55f4e02c7cDescription of ionophore-doped membranes with a blocked interfaceSanders, Tarun M.; Myers, Matthew; Asadnia, Mohsen; Umana-Membreno, Gilberto A.; Baker, Murray; Fowkes, Neville; Parish, Giacinta; Nener, BrettSensors and Actuators, B: Chemical (2017), 250 (), 499-508CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)Ion sensors with blocked interfaces, such as coated-wire electrodes (CWEs) and ion-selective field effect transistors (ISFETs), are increasingly being used as alternatives to traditional ion-selective electrodes (ISEs). This work provides insights into the behavior of ionophore-doped membranes in soln., where one side completely blocks ion transfer, using the Nernst-Planck-Poisson (NPP) model, including reaction terms. Extensive investigations were conducted, demonstrating that the NPP model provides reasonable predictions, as well as insight into the interplay between interfacial kinetics, complexation, diffusion and elec. processes. Model validation is achieved through its application to and anal of exptl results obtained for AlGaN/GaN ISFETs with ionophore-doped membranes.
- 52Zdrachek, E.; Bakker, E. Describing Ion Exchange at Membrane Electrodes for Ions of Different Charge. Electroanalysis 2018, 30, 633– 640, DOI: 10.1002/elan.201700700Google Scholar52https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhvFegs73M&md5=d89d42b84212f7ddab34ef28ce2a9b27Describing Ion Exchange at Membrane Electrodes for Ions of Different ChargeZdrachek, Elena; Bakker, EricElectroanalysis (2018), 30 (4), 633-640CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)It is well-documented in the literature that the Nikolsky-Eisenman equation cannot accurately describe the equil. of ion exchange at membrane electrodes for ions of different charge. Despite this, unfortunately, it is still widely used owing to the complexity of the more rigorous formalism developed by Bakker et al. in 1994. Here, different available approaches are presented in a unified manner and compared. This includes two different approxns. that are equally appropriate for cases of low level of interference where the extent of ion-exchange is comparatively small, one of which is introduced here for the 1st time. The comparison also considers the permutated form of the Nikolsky-Eisenman equation, where the primary ion is treated as the interfering ion and vice versa. As the permutated form gives a deviation from the thermodn. model that is opposite that of the regular Nikolsky-Eisenman equation, the two can be combined to give a semi-empirical equation that is surprisingly close to the thermodn. model and that comprises a single equation for any charge combination. The different choices presented here may be helpful to solve more complex theor. problems, as for example in the modeling of the time dependence of the electrode response by numerical simulation where the interfacial step condition is a unique and difficult feature of the calcn.
- 53Zdrachek, E.; Bakker, E. Time-Dependent Determination of Unbiased Selectivity Coefficients of Ion-Selective Electrodes for Multivalent Ions. Anal. Chem. 2017, 89, 13441– 13448, DOI: 10.1021/acs.analchem.7b03726Google Scholar53https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhvVSjurnK&md5=4c25593b04c680159bc5295704c4197aTime-Dependent Determination of Unbiased Selectivity Coefficients of Ion-Selective Electrodes for Multivalent IonsZdrachek, Elena; Bakker, EricAnalytical Chemistry (Washington, DC, United States) (2017), 89 (24), 13441-13448CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)A method for the detn. of unbiased low selectivity coeffs. for two of the most prevalent cases of multivalent ions (zi = 2, zj = 1 and zi = 1, zj = 2) was theor. and exptl. substantiated. The method is based on eliminating the primary ion concn. near the membrane by extrapolating the linearized time dependencies of selectivity coeffs. detd. by the sep. solns. method KPotij(SSM) as a function of t-1/3 or t-1/6, depending on the charge combination of the two ions, to infinite time. The applicability of the method is demonstrated for ionophore-based Mg2+-, Ca2+-, and Na+-selective electrodes. The high level of primary ion impurities in the salts of interfering ions can significantly limit the efficiency of the technique, as demonstrated with salts of different purity levels.
- 54Jasielec, J. J.; Mousavi, Z.; Granholm, K.; Sokalski, T.; Lewenstam, A. Anal. Chem. 2018, 90, 9644– 9649, DOI: 10.1021/acs.analchem.8b02659Google Scholar54https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhtFyqur7P&md5=3eec1fc653c580c308745aada89d0d99Sensitivity and Selectivity of Ion-Selective Electrodes Interpreted Using the Nernst-Planck-Poisson ModelJasielec, Jerzy J.; Mousavi, Zekra; Granholm, Kim; Sokalski, Tomasz; Lewenstam, AndrzejAnalytical Chemistry (Washington, DC, United States) (2018), 90 (15), 9644-9649CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)The Nernst-Planck-Poisson model is used for modeling the sensitivity and selectivity of ion-selective electrodes (ISEs) with plastic membranes. Two pivotal parameters characterizing ISE response are in focus: sensitivity and selectivity. An interpretation of sensitivity, which considers the concurrent influence of anions and cations on the ISE slope, is presented. The interpretation of selectivity shows the validity and limits of approaches hitherto taken to measure the true (unbiased) selectivity coeff. The validity of more idealized interpretations by the diffusion-layer model is conceived.
- 55Ivanova, A. D.; Koltashova, E. S.; Solovyeva, E. V.; Peshkova, M. A.; Mikhelson, K. N. Impact of the Electrolyte Co-Extraction to the Response of the Ionophore-based Ion-Selective Electrodes. Electrochim. Acta 2016, 213, 439– 446, DOI: 10.1016/j.electacta.2016.07.142Google Scholar55https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xht1OrsrbJ&md5=baccf0ad1039de78ed2d3dab6bb37a2dImpact of the Electrolyte Co-Extraction to the Response of the Ionophore-based Ion-Selective ElectrodesIvanova, Anastasiya D.; Koltashova, Evgeniya S.; Solovyeva, Elena V.; Peshkova, Maria A.; Mikhelson, Konstantin N.Electrochimica Acta (2016), 213 (), 439-446CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Ltd.)The impact of the aq. electrolyte coextn. to the potentiometric response of ionophore-based ion-selective electrodes (ISEs) was studied theor. and exptl. A simple theor. model is developed to describe quant. how coextn. of electrolytes influences the lower and the upper detection limits of ISEs. The theory is successfully verified with valinomycin-based K+-ISE as a model system, using potentiometric, chronopotentiometric, impedance and UV-visible measurements. A special (sym.) setup of the galvanic cell is proposed which clearly demonstrates how coextn. from the internal soln. dets. the lower detection limit of ISEs. The values of the partition coeffs. of K salts used in the study are consistent with the resp. Gibbs energies of anion transfer from H2O to org. phase. The model also gives a hint why the slope of real ISEs is typically slightly sub-Nernstian.
- 56Kondratyeva, Y. O.; Solovyeva, E. V.; Khripoun, G. A.; Mikhelson, K. N. Non-constancy of the bulk resistance of ionophore-based ion-selective electrode: A result of electrolyte co-extraction or of something else?. Electrochim. Acta 2018, 259, 458– 465, DOI: 10.1016/j.electacta.2017.10.176Google Scholar56https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhslOisLnE&md5=f8186ad6cf0a2e5075ed57b89b10bb7eNon-constancy of the bulk resistance of ionophore-based ion-selective electrode: A result of electrolyte co-extraction or of something else?Kondratyeva, Yevgeniya O.; Solovyeva, Elena V.; Khripoun, Galina A.; Mikhelson, Konstantin N.Electrochimica Acta (2018), 259 (), 458-465CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Ltd.)The bulk resistance of ionophore-based ion-selective electrodes (ISEs) was studied by chronopotentiometry and electrochem. impedance using Ca2+-ISEs with PVC membranes contg. ETH 1001 as a model system. The membrane bulk resistance is roughly the same within the range of CaCl2 concns. from 0.3 to 10-3 M, and increases significantly when the concn. is decreased to 10-4 and 10-5 M, although the potentiometric response of the ISEs is Nernstian in all these solns. This increase of the resistance when 10-3 M CaCl2 is further deleted is larger than the decrease of the resistance when CaCl2 is replaced with Ca(SCN)2 and Ca(ClO4)2. Probably the non-constancy of the ISE bulk resistance is not caused by coextn. of CaCl2 and therefore is not in conflict with the Nernstian behavior of the IESs potentials. The effect is tentatively ascribed to the regularities of H2O uptake by ISE membranes.
- 57Rich, M.; Mendecki, L.; Mensah, S. T.; Blanco-Martinez, E.; Armas, S.; Calvo-Marzal, P.; Radu, A.; Chumbimuni-Torres, K. Y. Circumventing Traditional Conditioning Protocols in Polymer Membrane-Based Ion-Selective Electrodes. Anal. Chem. 2016, 88, 8404– 8408, DOI: 10.1021/acs.analchem.6b01542Google Scholar57https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xhtleiu77E&md5=17ab64fbc68666f6c9ea9816c6fcf308Circumventing Traditional Conditioning Protocols in Polymer Membrane-Based Ion-Selective ElectrodesRich, Michelle; Mendecki, Lukasz; Mensah, Samantha T.; Blanco-Martinez, Enrique; Armas, Stephanie; Calvo-Marzal, Percy; Radu, Aleksandar; Chumbimuni-Torres, Karin Y.Analytical Chemistry (Washington, DC, United States) (2016), 88 (17), 8404-8408CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Prepn. of ion-selective electrodes (ISEs) often requires long and complicated conditioning protocols limiting their application as tools for in-field measurements. Herein, the authors eliminated the need for electrode conditioning by loading the membrane cocktail directly with primary ion soln. This proof of concept expt. was performed with iodide, silver, and sodium selective electrodes. The proposed methodol. significantly shortened the prepn. time of ISEs, yielding functional electrodes with submicromolar detection limits. Also, it is anticipated that this approach may form the basis for the development of miniaturized all-solid-state ion-selective electrodes for in situ measurements.
- 58Vanamo, U.; Hupa, E.; Yrjana, V.; Bobacka, J. New Signal Readout Principle for Solid-Contact Ion-Selective Electrodes. Anal. Chem. 2016, 88, 4369– 4374, DOI: 10.1021/acs.analchem.5b04800Google Scholar58https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XkvVOqt7c%253D&md5=5be5a1912490c7cf909b05514f5d45ceNew Signal Readout Principle for Solid-Contact Ion-Selective ElectrodesVanamo, Ulriika; Hupa, Elisa; Yrjana, Ville; Bobacka, JohanAnalytical Chemistry (Washington, DC, United States) (2016), 88 (8), 4369-4374CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)A novel approach to signal transduction concerning solid-contact ion-selective electrodes (SC-ISE) with a conducting polymer (CP) as the solid contact was studied. The method presented here is based on const. potential coulometry, where the potential of the SC-ISE vs. the ref. electrode is kept const. using a potentiostat. The change in the potential at the interface between the ion-selective membrane (ISM) and the sample soln., due to the change in the activity of the primary ion, is compensated with a corresponding but opposite change in the potential of the CP solid contact. This enforced change in the potential of the solid contact results in a transient reducing/oxidizing current flow through the SC-ISE. By measuring and integrating the current needed to transfer the CP to a new state of equil., the total cumulated charge that is linearly proportional to the change of the logarithm of the primary ion activity was obtained. Different thicknesses of poly(3,4-ethylenedioxythiophene) (PEDOT) doped with poly(styrenesulfonate) (PSS) were used as solid contact. Also, coated wire electrodes (CWEs) were included in the study to show the general validity of the new approach. The ISM employed was selective for K+ ions, and the selectivity of the membrane under implementation of the presented transduction mechanism was confirmed by measurements performed with a const. background concn. of Na+ ions. A unique feature of this signal readout principle is that it allows amplification of the anal. signal by increasing the capacitance (film thickness) of the solid contact of the SC-ISE.
- 59Han, T. T.; Vanamo, U.; Bobacka, J. Influence of Electrode Geometry on the Response of Solid-Contact Ion-Selective Electrodes when Utilizing a New Coulometric Signal Readout Method. ChemElectroChem 2016, 3, 2071– 2077, DOI: 10.1002/celc.201600575Google Scholar59https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhvVygt7rP&md5=dd43d9822aad047bd840372854f6b1d9Influence of Electrode Geometry on the Response of Solid-Contact Ion-Selective Electrodes when Utilizing a New Coulometric Signal Readout MethodHan, Tingting; Vanamo, Ulriika; Bobacka, JohanChemElectroChem (2016), 3 (12), 2071-2077CODEN: CHEMRA; ISSN:2196-0216. (Wiley-VCH Verlag GmbH & Co. KGaA)This article describes the influence of electrode geometry on the response of solid-contact ion-selective electrodes (SC-ISE) with a conducting polymer (CP) as solid contact, when using a recently reported signal readout method based on const. potential coulometry. Poly(3,4-ethylenedioxythiophene) (PEDOT) doped with poly(styrenesulfonate) (PSS) was electropolymd. on glassy carbon disk electrodes with areas ranging from 0.031 cm2 to 0.79 cm2. The polymn. charge was kept const. (1 mC) for all electrodes, meaning that the redox capacitance of PEDOT was const. for all electrodes while the PEDOT thickness decreased with increasing electrode area. The thickness of the K+-selective membrane covering the CP was kept const., so that the total resistance of the K+-selective membrane decreased with increasing electrode area. When utilizing the coulometric signal readout method, the response time of the SC-ISEs was significantly shortened by increasing the electrode area.
- 60Jarolimova, Z.; Han, T. T.; Mattinen, U.; Bobacka, J.; Bakker, E. Capacitive Model for Coulometric Readout of Ion-Selective Electrodes. Anal. Chem. 2018, 90, 8700– 8707, DOI: 10.1021/acs.analchem.8b02145Google Scholar60https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhtFeqs7rI&md5=5c62bad2d285e911da9c66a34829266eCapacitive Model for Coulometric Readout of Ion-Selective ElectrodesJarolimova, Zdenka; Han, Tingting; Mattinen, Ulriika; Bobacka, Johan; Bakker, EricAnalytical Chemistry (Washington, DC, United States) (2018), 90 (14), 8700-8707CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)We present here a capacitive model for the coulometric signal transduction readout of solid-contact ion-selective membrane electrodes (SC-ISE) with a conducting polymer (CP) as an intermediate layer for the detection of anions. The capacitive model correlates well with exptl. data obtained for chloride-selective SC-ISEs utilizing poly(3,4-ethylenedioxythiophene) (PEDOT) doped with chloride as the ion-to-electron transducer. Addnl., Prussian blue is used as a simple sodium capacitor to further demonstrate the role of the transduction layer. The influence of different thicknesses of PEDOT as a conducting polymer transducer, different thicknesses of the overlaying ion-selective membranes deposited by drop casting and spin coating, and different compns. of the chloride-selective membrane are explored. The responses are evaluated in terms of current-time, charge-time, and charge-chloride activity relationships. The utility of the sensor with coulometric readout is illustrated by the monitoring of very small concn. changes in soln.
- 61Nagy, X.; Höfler, L. Lowering Detection Limits Toward Target Ions Using Quasi-Symmetric Polymeric Ion-Selective Membranes Combined with Amperometric Measurements. Anal. Chem. 2016, 88, 9850– 9855, DOI: 10.1021/acs.analchem.6b03043Google Scholar61https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhsFWqtrbF&md5=b0fcee2bfc5a767ea3745686904d256cLowering Detection Limits Toward Target Ions Using Quasi-Symmetric Polymeric Ion-Selective Membranes Combined with Amperometric MeasurementsNagy, Xenia; Hofler, LajosAnalytical Chemistry (Washington, DC, United States) (2016), 88 (19), 9850-9855CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)An amperometric method is reported that compensates for the interference from marginally discriminated interfering ions when using traditional polymeric ion-selective membrane (ISM) electrodes. The concept involves using two ISMs in a three-compartment electrochem. cell configuration. The two ISMs are identical in compn. except for the addn. of an ionophore to one of the membranes. Initially, all three compartments contain the same concn. of interfering ion and the membrane does not contain primary ions. Ref. electrodes are placed into each of the two outer compartments. At this point, there is no p.d. between the two ref. electrodes. The authors show exptl. and theor. that, when the concn. of an interfering species is increased in the sample compartment, the phase-boundary potentials of both sample soln.|ISMs change similarly. However, when the primary ion is added to the sample, an asymmetry will emerge, and the membrane with the ionophore will exhibit a larger phase-boundary potential change. At low concns., the difference in membrane potentials can be too small for reliable potentiometric detection. Current, which can be routinely measured on pA levels, can be used instead to detect the small primary ion concn. changes with a significant lowering of detection limits. The theory of this method is described by Nernst-Planck-Poisson finite element simulations, and both amperometric and potentiometric exptl. verification is demonstrated using ammonium ISM. Amperometric measurements enable 200 nM ammonium to be detected in the presence of 0.1 mM of K, detection capability that is not possible via conventional potentiometry.
- 62Yu, N. N.; Ding, J. W.; Wang, W. W.; Wang, X. D.; Qin, W. Pulsed galvanostatic control of a solid-contact ion-selective electrode for potentiometric biosensing of microcystin-LR. Sens. Actuators, B 2016, 230, 785– 790, DOI: 10.1016/j.snb.2016.02.121Google Scholar62https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xjslyqtb0%253D&md5=dbdd05c0e778b7924a77e93124eda02cPulsed galvanostatic control of a solid-contact ion-selective electrode for potentiometric biosensing of microcystin-LRYu, Nana; Ding, Jiawang; Wang, Wenwei; Wang, Xuedong; Qin, WeiSensors and Actuators, B: Chemical (2016), 230 (), 785-790CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)We report here on the development of a chronopotentiometric assay for microcystin-LR based on enzymic inhibition. The inhibition of protein phosphatase by microcystin-LR can be sensed potentiometrically by using 4-nitrophenyl phosphate as an enzyme substrate. A solid-contact ion-selective electrode (ISE) with poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) as a transduction layer has been designed for potentiometric biosensing using the pulsed galvanastatic technique. By applying an anodic current, the enzymic generated p-nitrophenol can be extd. into the polymeric membrane with tetradodecylammonium tetrakis(4-chlorophenyl)- borate to produce the chronopotentiometric signal. Meanwhile, a controlled voltage was applied to refresh the membrane for multiple consecutive measurements. The proposed potentiometric assay showed a linear response for microcystin-LR in the range 1-100 μg/L with a detection limit of 0.5 μg/L (3s). We believe that the proposed method can be employed for sensitive, rapid and reliable detn. of analytes involved in enzyme inhibition.
- 63Ding, J.; Yu, N.; Wang, X.; Qin, W. Anal. Chem. 2018, 90, 1734– 1739, DOI: 10.1021/acs.analchem.7b03522Google Scholar63https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhtVarurs%253D&md5=02be456215669b3c18a8914ee3ad0477Sequential and Selective Detection of Two Molecules with a Single Solid-Contact Chronopotentiometric Ion-Selective ElectrodeDing, Jiawang; Yu, Nana; Wang, Xuedong; Qin, WeiAnalytical Chemistry (Washington, DC, United States) (2018), 90 (3), 1734-1739CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)A polymeric membrane ion-selective electrode (ISE) is typically designed for the detn. of one specific ion using a conventional method. In this work, we demonstrate a simple, versatile, and sensitive platform for simultaneous detection of two mols. with a single ISE. Under a series of periodic galvanostatic polarization, a solid-contact ISE without ion exchanger properties under zero-current conditions has been successfully used for simultaneous detection of two opposite charged ions with high sensitivity, good selectivity, and fast reversibility. By integration of biorecognition elements with the potentiometric measurement, highly sensitive and selective detection of a broad range of different mol. targets can be predicted. As a proof of concept, a potentiometric genosensor based on magnetic beads-enzyme sandwich assay has been designed for sensitive and selective detection of pathogenic bacteria Escherichia coli O157:H7 and Staphylococcus aureus. Under optimal conditions, two bacteria nucleic acid sequences can be detected simultaneously with high sensitivity and good selectivity by using a single solid-contact potentiometric ISE. The detection limits of Escherichia coli O157:H7 DNA and Staphylococcus aureus DNA are 120 and 54 fM (3σ), resp. Because of its simplicity, this potentiometric technique based on ISE can be an attractive tool or detector to perform two analyte measurements.
- 64Liang, R. N.; Ding, J. W.; Gao, S. S.; Qin, W. Mussel-Inspired Surface-Imprinted Sensors for Potentiometric Label-Free Detection of Biological Species. Angew. Chem., Int. Ed. 2017, 56, 6833– 6837, DOI: 10.1002/anie.201701892Google Scholar64https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXntlyls7k%253D&md5=b6dd46b0b4038bd6336a690d9f8016d8Mussel-Inspired Surface-Imprinted Sensors for Potentiometric Label-Free Detection of Biological SpeciesLiang, Rongning; Ding, Jiawang; Gao, Shengshuai; Qin, WeiAngewandte Chemie, International Edition (2017), 56 (24), 6833-6837CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)Using sensors to quantify clin. relevant biol. species has emerged as a fascinating research field due to their potential to revolutionize clin. diagnosis and therapeutic monitoring. Taking advantage of the wide utility in clin. anal. and low cost of potentiometric ion sensors, the authors demonstrate a method to use such ion sensors to quantify bioanalytes without chem. labels. This is achieved by combination of chronopotentiometry with a mussel-inspired surface imprinting technique. The biomimetic sensing method is based on a blocking mechanism by which the recognition reaction between the surface imprinted polymer and a bioanalyte can block the current-induced ion transfer of an indicator ion, thus causing a potential change. The present method offers high sensitivity and excellent selectivity for detection of biol. analytes. As models, trypsin and yeast cells can be measured at levels down to 0.03 U mL-1 and 50 CFU mL-1, resp.
- 65Afshar, M. G.; Crespo, G. A.; Bakker, E. Flow Chronopotentiometry with Ion-Selective Membranes for Cation, Anion, and Polyion Detection. Anal. Chem. 2016, 88, 3945– 3952, DOI: 10.1021/acs.analchem.6b00141Google ScholarThere is no corresponding record for this reference.
- 66Jansod, S.; Afshar, M. G.; Crespo, G. A.; Bakker, E. Phenytoin speciation with potentiometric and chronopotentiometric ion-selective membrane electrodes. Biosens. Bioelectron. 2016, 79, 114– 120, DOI: 10.1016/j.bios.2015.12.011Google Scholar66https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXitVems7nK&md5=6aaf5af33b2daf1ed4c6a725c159a955Phenytoin speciation with potentiometric and chronopotentiometric ion-selective membrane electrodesJansod, Sutida; Afshar, Majid Ghahraman; Crespo, Gaston A.; Bakker, EricBiosensors & Bioelectronics (2016), 79 (), 114-120CODEN: BBIOE4; ISSN:0956-5663. (Elsevier B.V.)We report on an electrochem. protocol based on perm-selective membranes to provide valuable information about the speciation of ionizable drugs, with phenytoin as a model example. Membranes contg. varying amts. of tetradodecylammonium chloride (TDDA) were read out at zero current (potentiometry) and with applied current techniques (chronopotentiometry). Potentiometry allows one to assess the ionized form of phenytoin (pKa∼8.2) that corresponds to a neg. monocharged ion. A careful optimization of the membrane components resulted in a lower limit of detection (∼1.6 μM) than previous reports. Once the pH (from 9 to 10) or the concn. of albumin is varied in the sample (from 0 to 30 g L-1), the potentiometric signal changes abruptly as a result of reducing/increasing the ionized concn. of phenytoin. Therefore, potentiometry as a single technique is by itself not sufficient to obtain information about the concn. and speciation of the drug in the system. For this reason, a tandem configuration with chronopotentiometry as addnl. readout principle was used to det. the total and ionized concn. of phenytoin. In samples contg. excess albumin the rate-limiting step for the chronopotentiometry readout appears to be the diffusion of ionized phenytoin preceded by comparatively rapid deprotonation and decomplexation reactions. This protocol was applied to measure phenytoin in pharmaceutical tables (100 mg per tablet). This tandem approach can likely be extended to more ionizable drugs and may eventually be utilized in view of pharmacol. monitoring of drugs during the delivery process.
- 67Jansod, S.; Afshar, M. G.; Crespo, G. A.; Bakker, E. Alkalinization of Thin Layer Samples with a Selective Proton Sink Membrane Electrode for Detecting Carbonate by Carbonate-Selective Electrodes. Anal. Chem. 2016, 88, 3444– 3448, DOI: 10.1021/acs.analchem.6b00346Google Scholar67https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XktFaqu7Y%253D&md5=0fccaeb9bcd3fbb548a9f9db36bf0f66Alkalinization of Thin Layer Samples with a Selective Proton Sink Membrane Electrode for Detecting Carbonate by Carbonate-Selective ElectrodesJansod, Sutida; Ghahraman Afshar, Majid; Crespo, Gaston A.; Bakker, EricAnalytical Chemistry (Washington, DC, United States) (2016), 88 (7), 3444-3448CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Potentiometry is known to be sensitive to so-called free ion activity and is a potentially valuable tool in environmental speciation anal. Here, the direct detection of free and total carbonate is demonstrated by alkalinization of a thin layer sample (∼100 μm), which is electrochem. triggered at a pH responsive membrane placed opposite a carbonate-selective membrane electrode. The concept may serve as a promising future methodol. for in situ environmental sensing applications where traditional sampling and pretreatment steps are no longer required. The possibility of increasing the pH of the sample was demonstrated 1st with a proton selective membrane (pH readout at zero current) placed opposite the thin layer gap. An optimal applied potential (600 mV) for 300 s resulted in a pH increase of 4 units in an artificial sample, with a relative std. deviation (RSD) of ∼2%. The pH probe was subsequently replaced by a solid contact carbonate selective electrode for the detn. of carbonate species (4.17μM) in a sample of 1mM NaHCO3. Increasing the pH to 12.1 by the electrochem. controlled proton sink allowed one to convert bicarbonate to the detectable carbonate species. Initial bicarbonate concn. (∼1 mM) was obtained as the difference between the converted bicarbonate and the initial carbonate concn. An initial application of this concept was illustrated by the speciation anal. of an unfiltered sample from the Arve River (12.3±0.2μM and 22.5±0.3mM carbonate and bicarbonate, resp.). The values were confirmed by volumetric titrn.
- 68Cuartero, M.; Crespo, G. A.; Bakker, E. Ionophore-Based Voltammetric Ion Activity Sensing with Thin Layer Membranes. Anal. Chem. 2016, 88, 1654– 1660, DOI: 10.1021/acs.analchem.5b03611Google Scholar68https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXitV2ntr%252FO&md5=fc1a1919bd579e1e69a5fc6e773d616bIonophore-Based Voltammetric Ion Activity Sensing with Thin Layer MembranesCuartero, Maria; Crespo, Gaston A.; Bakker, EricAnalytical Chemistry (Washington, DC, United States) (2016), 88 (3), 1654-1660CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)As shown in recent work, thin layer ion-selective multi-ionophore membranes can be interrogated by cyclic voltammetry to detect the ion activity of multiple species simultaneously and selectively. Addnl. fundamental evidence is put forward on ion discrimination with thin multi-ionophore-based membranes with thicknesses of 200 ± 25 nm and backside contacted with poly-3-octylthiophene (POT). An anodic potential scan partially oxidizes the POT film (to POT+), thereby initiating the release of hydrophilic cations from the membrane phase to the sample soln. at a characteristic potential. Varying concn. of added cation-exhanger demonstrates that it limits the ion transfer charge and not the deposited POT film. Voltammograms with multiple peaks are obsd. with each assocd. with the transfer of one type of ion (lithium, potassium, and sodium). Exptl. conditions (thickness and compn. of the membrane and concn. of the sample) are chosen that allow one to describe the system by a thermodn. rather than kinetic model. As a consequence, apparent stability consts. for sodium, potassium, and lithium (assuming 1:1 stoichiometry) with their resp. ionophores are calcd. and agree well with the values obtained by the potentiometric sandwich membrane technique. As an anal. application, a membrane contg. three ionophores was used to det. lithium, sodium, and potassium in artificial samples at the same location and within a single voltammetric scan. Lithium and potassium were also detd. in undiluted human plasma in the therapeutic concn. range.
- 69Cuartero, M.; Crespo, G. A.; Bakker, E. Polyurethane Ionophore-Based Thin Layer Membranes for Voltammetric Ion Activity Sensing. Anal. Chem. 2016, 88, 5649– 5654, DOI: 10.1021/acs.analchem.6b01085Google Scholar69https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XnvFKiurc%253D&md5=4e4ec5ef3b915fe9cb6035a2fd1d96ddPolyurethane Ionophore-Based Thin Layer Membranes for Voltammetric Ion Activity SensingCuartero, Maria; Crespo, Gaston A.; Bakker, EricAnalytical Chemistry (Washington, DC, United States) (2016), 88 (11), 5649-5654CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)We report on a plasticized polyurethane ionophore-based thin film material (of hundreds of nanometer thickness) for simultaneous voltammetric multianalyte ion activity detection triggered by the oxidn./redn. of an underlying poly(3-octylthiophene) film. This material provides excellent mech., phys., and chem. robustness compared to other polymers. Polyurethane films did not exhibit leaching of lipophilic additives after rinsing with a direct water jet and exhibited resistance to detachment from the underlying electrode surface, resulting in a voltammetric current response with less than <1.5% RSD variation (n = 50). In contrast, plasticized poly(vinyl chloride), polystyrene, and poly(acrylate) ionophore-based membranes of the same thickness and compn. exhibited a significant deterioration of the signal after identical treatment. While previously reported works emphasized fundamental advancement of multi-ion detection with multi-ionophore-based thin films, polyurethane thin membranes allow one to achieve real world measurements without sacrificing anal. performance. Indeed, polyurethane membranes are demonstrated to be useful for the simultaneous detn. of potassium and lithium in undiluted human serum and blood with attractive precision.
- 70Cuartero, M.; Acres, R. G.; De Marco, R.; Bakker, E.; Crespo, G. A. Electrochemical Ion Transfer with Thin Films of Poly(3-octylthiophene). Anal. Chem. 2016, 88, 6939– 6946, DOI: 10.1021/acs.analchem.6b01800Google Scholar70https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XpsVOgt7g%253D&md5=2bc6e8fcd24419f4c53a6cfdd16c9d40Electrochemical ion transfer with thin films of poly(3-octylthiophene)Cuartero, Maria; Acres, Robert G.; De Marco, Roland; Bakker, Eric; Crespo, Gaston A.Analytical Chemistry (Washington, DC, United States) (2016), 88 (13), 6939-6946CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)We report on the limiting conditions for ion-transfer voltammetry between an ion-exchanger doped and plasticized poly(vinyl chloride) (PVC) membrane and an electrolyte soln. that was triggered via the oxidn. of a poly(3-octylthiophene) (POT) solid-contact (SC), which was unexpectedly related to the thickness of the POT SC. An electropolymd. 60 nm thick film of POT coated with a plasticized PVC membrane exhibited a significant sodium transfer voltammetric signal whereas a thicker film (180 nm) did not display a measurable level of ion transfer due to a lack of oxidn. of thick POT beneath the membrane film. In contrast, this peculiar phenomenon was not obsd. when the POT film was in direct contact with an org. solvent-based electrolyte. This evidence is indicative of three key points: (i) the coated membrane imposes a degree of rigidity to the system, which restricts the swelling of the POT film and its concomitant p-doping; (ii) this phenomenon is exacerbated with thicker POT films due to an initial morphol. (rougher comprising a network of large POT nanoparticles), which gives rise to a diminished surface area and electrochem. reactivity in the POT SC; (iii) the rate of sodium transfer is higher with a thin POT film due to a smoother surface morphol. made up of a network of smaller POT nanoparticles with an increased surface area and electrochem. reactivity. A variety of techniques including cyclic voltammetry (CV), electrochem. impedance spectroscopy (EIS), ellipsometry, SEM (SEM), at. force microscopy (AFM), and synchrotron radiation-XPS (SR-XPS) were used to elucidate the mechanism of the POT thickness/POT surface roughness dependency on the electrochem. reactivity of the PVC/POT SC system.
- 71Yuan, D. J.; Cuartero, M.; Crespo, G. A.; Bakker, E. Voltammetric Thin-Layer lonophore-Based Films: Part 1. Experimental Evidence and Numerical Simulations. Anal. Chem. 2017, 89, 586– 594, DOI: 10.1021/acs.analchem.6b03354Google Scholar71https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhvFKns7rO&md5=736b18423f8b6620d591990a719be73eVoltammetric Thin-Layer Ionophore-Based Films: Part 1. Experimental Evidence and Numerical SimulationsYuan, Dajing; Cuartero, Maria; Crespo, Gaston A.; Bakker, EricAnalytical Chemistry (Washington, DC, United States) (2017), 89 (1), 586-594CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Voltammetric thin layer (∼200 nm) ionophore-based polymeric films of defined ion-exchange capacity have recently emerged as a promising approach to acquire multi-ion information about the sample, in analogy to performing multiple potentiometric measurements with individual membranes. They behave under two different regimes that are dependent on the ion concn. A thin layer control (no mass transport limitation of the polymer film or soln.) is identified for ion concns. of >10 μM, in which case the peak potential serves as the readout signal, in analogy to a potentiometric sensor. However, ion transfer at lower concns. is chiefly controlled by diffusional mass transport from the soln. to the sensing film, resulting in an increase of peak current with ion concn. This concn. range is suitable for electrochem. ion transfer stripping anal. Here, the transition between the two mentioned scenarios is explored exptl., using a highly Ag-selective membrane as a proof-of-concept under different conditions (variation of ion concn. in the sample from 0.1 μM to 1 mM, scan rate from 25 mV s-1 to 200 mV s-1, and angular frequency from 100 rpm to 6400 rpm). Apart from exptl. evidence, a numerical simulation is developed that considers an idealized conducting polymer behavior and permits one to predict exptl. behavior under diffusion or thin-layer control.
- 72Yuan, D. J.; Cuartero, M.; Crespo, G. A.; Bakker, E. Voltammetric Thin-Layer Ionophore-Based Films: Part 2. Semi-Empirical Treatment. Anal. Chem. 2017, 89, 595– 602, DOI: 10.1021/acs.analchem.6b03355Google Scholar72https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhvFKnsL3K&md5=eddb144ef4d5a7c00c788e60fed56779Voltammetric Thin-Layer Ionophore-Based Films: Part 2. Semi-Empirical TreatmentYuan, Dajing; Cuartero, Maria; Crespo, Gaston A.; Bakker, EricAnalytical Chemistry (Washington, DC, United States) (2017), 89 (1), 595-602CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)This work reports on a semiempirical treatment that allows one to rationalize and predict exptl. conditions for thin-layer ionophore-based films with cation-exchange capacity read out with cyclic voltammetry. The transition between diffusional mass transport and thin-layer regime is described with a parameter (α), which depends on membrane compn., diffusion coeff., scan rate, and electrode rotating speed. Once the thin-layer regime is fulfilled (α = 1), the membrane behaves in some analogy to a potentiometric sensor with a second discrimination variable (the applied potential) that allows one to operate such electrodes in a multianalyte detection mode owing to the variable applied ion-transfer potentials. The limit of detection of this regime is defined with a second parameter (β = 2) and is chosen in analogy to the definition of the detection limit for potentiometric sensors provided by the IUPAC. The anal. equations were validated through the simulation of the resp. cyclic voltammograms under the same exptl. conditions. While simulations of high complexity and better accuracy satisfactorily reproduced the exptl. voltammograms during the forward and backward potential sweeps (companion paper 1), the semiempirical treatment here, while less accurate, is of low complexity and allows one to quite easily predict relevant exptl. conditions for this emergent methodol.
- 73Greenawalt, P. J.; Amemiya, S. Voltammetric Mechanism of Multiion Detection with Thin lonophore-Based Polymeric Membrane. Anal. Chem. 2016, 88, 5827– 5834, DOI: 10.1021/acs.analchem.6b00397Google Scholar73https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XmsFOmsL4%253D&md5=a2463c6f31911d9a94238f34517098a6Voltammetric Mechanism of Multiion Detection with Thin Ionophore-Based Polymeric MembraneGreenawalt, Peter J.; Amemiya, ShigeruAnalytical Chemistry (Washington, DC, United States) (2016), 88 (11), 5827-5834CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)The capability to detect multianalyte ions in their mixed soln. is an important advantage of voltammetry with an ionophore-based polymeric membrane against the potentiometric and optical counterparts. This advanced capability is highly attractive for the anal. of physiol. ions at millimolar concns. in biol. and biomedical samples. Herein, we report on the comprehensive response mechanisms based on the voltammetric exchange and transfer of millimolar multiions at a thin polymeric membrane, where an ionophore is exhaustively depleted upon the transfer of the most favorable primary ion, IzI. With a new voltammetric ion-exchange mechanism, the primary ion is exchanged with the secondary favorable ion, JzJ, at more extreme potentials to transfer a net charge of |zJ|/nJ - |zI|/nI for each ionophore mol., which forms 1:nI and 1:nJ complexes with the resp. ions. Alternatively, an ion-transfer mechanism utilizes the second ionophore that independently transfers the secondary ion without ion exchange. Exptl., a membrane is doped with a Na+- or Li+-selective ionophore to detect not only the primary ion, but also the secondary alk. earth ion, based on the ion-exchange mechanism, where both ions form 1:1 complexes with the ionophores to transfer a net charge of +1. Interestingly, the resultant peak potentials of the secondary divalent ion vary with its sample activity to yield an apparently super-Nernstian slope as predicted theor. By contrast, the voltammetric exchange of calcium ion (nI = 3) with lithium ion (nJ = 1) by a Ca2+-selective ionophore is thermodynamically unfavorable, thereby requiring a Li+-selective ionophore for the ion-transfer mechanism.
- 74Amemiya, S. Voltammetric Ion Selectivity of Thin Ionophore-Based Polymeric Membranes: Kinetic Effect of Ion Hydrophilicity. Anal. Chem. 2016, 88, 8893– 8901, DOI: 10.1021/acs.analchem.6b02551Google Scholar74https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xhtlehs7zP&md5=dc86043c1594ca1609000e4876ce3d31Voltammetric Ion Selectivity of Thin Ionophore-Based Polymeric Membranes: Kinetic Effect of Ion HydrophilicityAmemiya, ShigeruAnalytical Chemistry (Washington, DC, United States) (2016), 88 (17), 8893-8901CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)The high ion selectivity of potentiometric and optical sensors based on ionophore-based polymeric membranes is thermodynamically limited. Here, the authors report that the voltammetric selectivity of thin ionophore-based polymeric membranes can be kinetically improved by several orders of magnitude in comparison with their thermodn. selectivity. The kinetic improvement of voltammetric selectivity is evaluated quant. by newly introducing a voltammetric selectivity coeff. in addn. to a thermodn. selectivity coeff. Exptl., both voltammetric and thermodn. selectivity coeffs. are detd. from cyclic voltammograms of excess amts. of analyte and interfering ions with respect to the amt. of a Na+- or Li+-selective ionophore in thin polymeric membranes. The authors reveal the slower ionophore-facilitated transfer of a smaller alk. earth metal cation with higher hydrophilicity across the membrane/water interface, thereby kinetically improving voltammetric Na+ selectivity against calcium, strontium, and barium ions by 3, 2, and 1 order of magnitude, resp., in sep. solns. Remarkably, voltammetric Na+ and Li+ selectivity against calcium and magnesium ions in mixed solns. is improved by 4 and >7 orders of magnitude, resp., owing to both thermodn. and kinetic effects in comparison with thermodn. selectivity in sep. solns. Advantageously, the simultaneous detection of sodium and calcium ions is enabled voltammetrically in contrast to the potentiometric and optical counterparts. Mechanistically, the authors propose a new hypothetical model that the slower transfer of a more hydrophilic ion is controlled by its partial dehydration during the formation of the adduct with a water finger prior to complexation with an ionophore at the membrane/water interface.
- 75Jansod, S.; Wang, L.; Cuartero, M.; Bakker, E. Electrochemical ion transfer mediated by a lipophilic Os(II)/Os(III) dinonyl bipyridyl probe incorporated in thin film membranes. Chem. Commun. 2017, 53, 10757– 10760, DOI: 10.1039/C7CC05908FGoogle Scholar75https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsVKgsb3E&md5=41b2c890ee1a8ce2232d4e2852dd1967Electrochemical ion transfer mediated by a lipophilic Os(II)/Os(III) dinonyl bipyridyl probe incorporated in thin film membranesJansod, Sutida; Wang, Lu; Cuartero, Maria; Bakker, EricChemical Communications (Cambridge, United Kingdom) (2017), 53 (78), 10757-10760CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)A new lipophilic dinonyl bipyridyl Os(II)/Os(III) complex successfully mediates ion transfer processes across voltammetric thin membranes. An added lipophilic cation-exchanger may impose voltammetric anion or cation transfer waves of Gaussian shape that are reversible and repeatable. The peak potential is found to shift with the ion concn. in agreement with the Nernst equation. The addn. of tridodecylmethylammonium nitrate to the polymeric film dramatically reduces the peak sepn. from 240 mV to 65 mV, and the peak width to a near-theor. value of 85 mV, which agrees with a surface confined process. Probably the cationic additive serves as a phase transfer catalyst.
- 76Jarolimova, Z.; Bosson, J.; Labrador, G. M.; Lacour, J.; Bakker, E. Ion Transfer Voltammetry at Thin Films Based on Functionalized Cationic [6]Helicenes. Electroanalysis 2018, 30, 650– 657, DOI: 10.1002/elan.201700669Google Scholar76https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhvFegs7zL&md5=9127c91365f959af7605e6ed9250223cIon Transfer Voltammetry at Thin Films Based on Functionalized Cationic [6]HelicenesJarolimova, Zdenka; Bosson, Johann; Labrador, Geraldine M.; Lacour, Jerome; Bakker, EricElectroanalysis (2018), 30 (4), 650-657CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)The authors describe a new family of mol. ion-to-electron redox probes based on cationic diaza, azaoxa, and dioxa [6]helicenes and their derivs. Their unique structure combines, in a single framework, two privileged families of mols. - helicenes and triaryl Me carbenium moieties. These cationic [6]helicenes exhibit reversible and reproducible oxidn./redn. behavior and facilitate the ion transfer into thin layer sensing films composed of bis(2-ethylhexyl)sebacate (DOS), polyurethane (PU), sodium tetrakis 3.5-bis(trifluoromethyl)phenyl borate, sodium ionophore X and diaza+(C8)2Br2 for cation transfer. Cyclic voltammetry was used to interrogate the thin films. The cationic response can be tuned by adjusting the membrane loading. Addn. of lipophilic cation exchanger into the membrane film results in transfer waves of Gaussian shape for cations. A peak sepn. of 60 mV and peak width of 110 mV are near the theor. values for a surface confined process. While Nernstian shifts of the peak potentials with analyte concn. was obtained for membranes based on cationic [6]helicenes and doped with sodium-selective ionophore X, this ionophore was found to promote a gradual loss of redox active species from the ionophore-based membranes into the sample soln.
- 77Jarolimova, Z.; Bosson, J.; Labrador, G. M.; Lacour, J.; Bakker, E. Ion Transfer Voltammetry in Polyurethane Thin Films Based on Functionalised Cationic [6]Helicenes for Carbonate Detection. Electroanalysis 2018, 30, 1378– 1385, DOI: 10.1002/elan.201800080Google Scholar77https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXkt1Gmtb4%253D&md5=53534d8adb8288c2394c2d591454ccccIon Transfer Voltammetry in Polyurethane Thin Films Based on Functionalised Cationic [6]Helicenes for Carbonate DetectionJarolimova, Zdenka; Bosson, Johann; Labrador, Geraldine M.; Lacour, Jerome; Bakker, EricElectroanalysis (2018), 30 (7), 1378-1385CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)We explore here mol. ion-to-electron redox probes based on cationic diaza, azaoxa, and dioxa [6]helicenes and their derivs. as ion-to-electron transducers for the electrochem. detection of anions. These cationic [6]helicenes exhibit reversible and reproducible oxidn./redn. behavior and facilitate the anion transfer of Gaussian shape into polymeric thin layer sensing films. Films composed of bis(2-ethylhexyl) sebacate (DOS), polyurethane (PU), tetrakis(4-chlorophenyl)borate tetradodecylammonium salt (ETH 500) and [6]helicenes were interrogated by cyclic voltammetry. Even though the peak sepn. of 90 mV is larger than ideal, the obsd. peak width at half max. of 130 mV and the linear relationship between current and scan rate are near theor. values, confirming a surface confined process. A Nernstian shift of the peaks with increasing carbonate concn. is obtained in the presence of carbonate ionophore VII incorporated into the thin sensing film. The concn. of carbonate was detd. in an unfiltered sample of the Arve river (flowing from Chamonix to Geneva) and compared to a ref. method (automatic titrator with potentiometric detection). The results suggested that cationic diaza [6]helicene functionalized with two bromine atoms is an attractive mol. ion-to-electron transducer for anion-selective electrodes.
- 78Cuartero, M.; Acres, R. G.; Bradley, J.; Jarolimova, Z.; Wang, L.; Bakker, E.; Crespo, G. A.; De Marco, R. Electrochemical Mechanism of Ferrocene-Based Redox Molecules in Thin Film Membrane Electrodes. Electrochim. Acta 2017, 238, 357– 367, DOI: 10.1016/j.electacta.2017.04.047Google Scholar78https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXmtVyqs7g%253D&md5=9080ee64d0549e572b4b1523c6380813Electrochemical Mechanism of Ferrocene-Based Redox Molecules in Thin Film Membrane ElectrodesCuartero, Maria; Acres, Robert G.; Bradley, John; Jarolimova, Zdenka; Wang, Lu; Bakker, Eric; Crespo, Gaston A.; De Marco, RolandElectrochimica Acta (2017), 238 (), 357-367CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Ltd.)Cyclic voltammetry (CV) in chloride-based aq. electrolytes of ferrocene mol. doped thin membranes (∼200 nm in thickness) on glassy carbon (GC) substrate electrodes, both plasticized poly(vinyl chloride) (PVC) and unplasticized poly(Me methacrylate)/poly(decyl methacrylate) (PMMA-PDMA) membranes, has shown that the electrochem. oxidn. behavior is irreversible due most likely to degrdn. of ferrocene at the buried interface (GC|membrane). Furthermore, CV of the ferrocene mols. at GC electrodes in org. solvents employing chloride-based and chloride-free org. electrolytes has demonstrated that the chloride anion is inextricably linked to this irreversible ferrocene oxidn. electrochem. Accordingly, we have explored the electrochem. oxidn. mechanism of ferrocene-based redox mols. in thin film plasticized and unplasticized polymeric membrane electrodes by coupling synchrotron radiation-XPS (SR-XPS) and near edge X-ray absorption fine structure (NEXAFS) with argon ion sputtering to depth profile the electrochem. oxidized thin membrane systems. With the PVC depth profiling studies, it was not possible to precisely study the influence of chloride on the ferrocene reactivity due to the high at. ratio of chloride in the PVC membrane; however, the depth profiling results obtained with a chlorine-free polymer (PMMA-PDMA) provided irrefutable evidence for the formation of a chloride-based iron product at the GC|PMMA-PDMA interface. Finally, we have identified conditions that prevent the irreversible conversion of ferrocene by utilizing a high loading of redox active reagent and/or an ionic liq. (IL) membrane plasticizer with high ionicity that suppresses the mass transfer of chloride.
- 79Cuartero, M.; Acres, R. G.; Jarolimova, Z.; Bakker, E.; Crespo, G. A.; De Marco, R. Electron Hopping between Fe 3d States in Ethynylferrocene-doped Poly(Methyl Methacrylate)-poly(Decyl Methacrylate) Copolymer Membranes. Electroanalysis 2018, 30, 596– 601, DOI: 10.1002/elan.201700510Google Scholar79https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhs1CitLbM&md5=d2fb8c79d2538d25cd72eb2c8d62608eElectron Hopping Between Fe 3 d States in Ethynylferrocene-doped Poly(Methyl Methacrylate)-poly(Decyl Methacrylate) Copolymer MembranesCuartero, Maria; Acres, Robert G.; Jarolimova, Zdenka; Bakker, Eric; Crespo, Gaston A.; De Marco, RolandElectroanalysis (2018), 30 (4), 596-601CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)Synchrotron radiation-valence band spectroscopy (SR-VBS) was used in a study of redox mol. valence states implicated in the electron hopping mechanism of ethynylferrocene in unplasticized poly(Me methacrylate)-poly(decyl methacrylate) [PMMA-PDMA] membranes. At high concns. of ethynylferrocene, there are observable Fe 3d valence states that are likely linked to electron hopping between ferrocene moieties of neighboring redox mols. Also, electrochem. induced stratification of ethynylferrocene in an oxidized PMMA-PDMA membrane produces a gradient of Fe 3d states toward the buried interface at the glassy C/PMMA-PDMA membrane enabling electron hopping and electrochem. reactivity of dissolved ethynylferrocene across this buried film.
- 80Jansod, S.; Cuartero, M.; Cherubini, T.; Bakker, E. Colorimetric Readout for Potentiometric Sensors with Closed Bipolar Electrodes. Anal. Chem. 2018, 90, 6376– 6379, DOI: 10.1021/acs.analchem.8b01585Google Scholar80https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXpvVejtLs%253D&md5=9b8baf19fade2f0723427e4fb7e385b7Colorimetric Readout for Potentiometric Sensors with Closed Bipolar ElectrodesJansod, Sutida; Cuartero, Maria; Cherubini, Thomas; Bakker, EricAnalytical Chemistry (Washington, DC, United States) (2018), 90 (11), 6376-6379CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)We present here a general strategy to translate potential change at a potentiometric probe into a tunable color readout. It is achieved with a closed bipolar electrode where the ion-selective component is confined to one end of the electrode while color is generated at the opposite pole, allowing one to phys. sep. the detection compartment from the sample. An elec. potential is imposed across the bipolar electrode by soln. contact such that the potentiometric signal change at the sample side modulates the potential at the detection side. This triggers the turnover of a redox indicator in the thin detection layer until a new equil. state is established. The approach is demonstrated in sep. expts. with a chloride responsive Ag/AgCl element and a liq. membrane based calcium-selective membrane electrode, using the redox indicator ferroin in the detection compartment. The principle can be readily extended to other ion detection materials and optical readout principles.
- 81Ding, J. W.; Lv, E. G.; Zhu, L. Y.; Qin, W. Optical Ion Sensing Platform Based on Potential-Modulated Release of Enzyme. Anal. Chem. 2017, 89, 3235– 3239, DOI: 10.1021/acs.analchem.7b00072Google Scholar81https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXjs1KmtbY%253D&md5=90a4323d4025182b07b06fc3e1a8c35aOptical Ion Sensing Platform Based on Potential-Modulated Release of EnzymeDing, Jiawang; Lv, Enguang; Zhu, Liyan; Qin, WeiAnalytical Chemistry (Washington, DC, United States) (2017), 89 (6), 3235-3239CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)The authors report here on an optical ion sensing platform, in which a polymeric membrane ion-selective electrode (ISE) serves as not only a potentiometric transducer for ion activities in the sample soln. but also a ref. electrode for the potential-modulated release of enzyme from an iron-alginate-horseradish peroxidase (HRP) thin film modified working electrode. The ISE and working electrode are phys. sepd. by a salt bridge. The dissoln. of the HRP-embedded thin film can be triggered by the redn. of Fe3+, which is modulated by the potential response of the ISE to the target ion in the sample. The released enzyme induces the oxidn. of its substrate mediated by H2O2 to produce a visual color change. With this setup, an optical ion sensing platform for both cations (e.g., NH4+) and anions (e.g., Cl-) can be obtained. The proposed platform provides a general and versatile visual-sensing strategy for ions and allows optical ion sensing in colored and turbid solns.
- 82Lugert-Thom, E. C.; Gladysz, J. A.; Rabai, J.; Bühlmann, P. Cleaning of pH Selective Electrodes with Ionophore-doped Fluorous Membranes in NaOH Solution at 90 degrees C. Electroanalysis 2018, 30, 611– 618, DOI: 10.1002/elan.201700228Google Scholar82https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXht1Sgs7nF&md5=ca1389c542434b8c0dcffab94c41dbf0Cleaning of pH Selective Electrodes with Ionophore-Doped Fluorous Membranes in NaOH Solution at 90 °CLugert-Thom, Elizabeth C.; Gladysz, John A.; Rabai, Jozsef; Buehlmann, PhilippeElectroanalysis (2018), 30 (4), 611-618CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)This work demonstrates the remarkable stability of fluorous ion-selective electrode (ISE) membranes by exposing them to cleaning-in-place treatments (CIP) as they were used in many industrial processes. The sensing membranes consisted of Teflon AF2400 plasticized with a linear perfluoropolyether and doped with ionic sites and a H+ ionophore (i.e., tris[3-(perfluorooctyl)propyl]amine, 1, or tris[3-(perfluorooctyl)pentyl]amine, 2). To mimic a typical CIP treatment, the electrodes were repeatedly exposed for 30 min to a 3.0% NaOH soln. at 90° (pH 12.7). ISE membranes doped with the less strongly H+ binding ionophore 1 started to show reduced potentiometric response slopes and increased resistances after one exposure for 30 min to hot 3.0% NaOH soln. No decompn. of the ionic sites and ionophore 1 at 90° was evident by 1H NMR spectroscopy, suggesting that the performance of membranes doped with 1 was compromised primarily by leaching of the neg. charged ionic sites along with H+ into the hot caustic soln. In contrast, even after ten exposures to hot 3.0% NaOH for a cumulative 5 h at 90°, the fluorous sensing membranes doped with the more strongly H+ binding ionophore 2 still showed the ability to respond with a theor. (Nernstian) slope up to pH 12. Addn. of the fluorophilic electrolyte salt methyltris[3-(perfluorooctyl)propyl]ammonium tetrakis[3,5-bis(perfluorohexyl)phenyl]borate reduced the membrane resistance by an order of magnitude.
- 83Carey, J. L.; Hirao, A.; Sugiyama, K.; Buhlmann, P. Semifluorinated Polymers as Ion-selective Electrode Membrane Matrixes. Electroanalysis 2017, 29, 739– 747, DOI: 10.1002/elan.201600586Google Scholar83https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xhsl2ht7nJ&md5=2d29037de8190f5b0699fde5d6e81c16Semifluorinated Polymers as Ion-selective Electrode Membrane MatrixesCarey, Jesse L. III; Hirao, Akira; Sugiyama, Kenji; Buehlmann, PhilippeElectroanalysis (2017), 29 (3), 739-747CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)Most com. available fluorous polymers are ill suited for the fabrication of ion-selective electrode (ISE) membranes. Therefore, we synthesized semifluorinated polymers for this purpose. Ionophore-free ion-exchanger electrodes made with these polymers show a selectivity range (≈14 orders of magnitude) that is nearly as wide as found previously for liq. fluorous ion-exchanger electrodes. These polymers were also used to construct ISE membranes doped with fluorophilic silver ionophores. While the resulting ISEs were somewhat less selective than their fluorous counterparts, the semifluorinated polymers offer the advantage that they can be doped both with fluorophilic ionophores and traditional lipophilic ionophores, such as the silver ionophore Cu(II)-I (o-xylylenebis[N,N-diisobutyldithiocarbamate]). We also cross-linked these polymers, producing very durable membranes that retained broad selectivity ranges. K+ ISEs made with the cross-linked semifluorinated polymer and the ionophore valinomycin showed selectivities similar to those of PVC membrane ISEs but with a superior thermal stability, the majority of the electrodes still giving a theor. (Nernstian) response after exposure to a boiling aq. soln. for 10 h.
- 84Ogawara, S.; Carey, J. L.; Zou, X. U.; Bühlmann, P. Donnan Failure of Ion-Selective Electrodes with Hydrophilic High-Capacity Ion-Exchanger Membranes. ACS Sens. 2016, 1, 95– 101, DOI: 10.1021/acssensors.5b00128Google Scholar84https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhvVarsbvF&md5=53db0365ffd9ae1601bb66871bda34c2Donnan Failure of Ion-Selective Electrodes with Hydrophilic High-Capacity Ion-Exchanger MembranesOgawara, Shogo; Carey, Jesse L.; Zou, Xu U.; Buhlmann, PhilippeACS Sensors (2016), 1 (1), 95-101CODEN: ASCEFJ; ISSN:2379-3694. (American Chemical Society)Hydrophilic ion-exchanger membranes with a high ion-exchange capacity not only find numerous applications in ion sepns., but also have interesting properties when used as sensing membranes of ion-selective electrodes (ISEs). As pointed out in the literature, the hydrophilic nature of these membranes may reduce biofouling of ISE sensing membranes as caused by elec. neutral, hydrophobic interferents. This work shows that hydrophilic high-capacity ion-exchanger membranes are more resistant to Donnan failure (i.e., the limitation of the upper detection limit by co-ion transfer into the sensing membrane) than both hydrophobic ionophore-doped and hydrophobic ionophore-free ion-exchanger membranes. Nernstian responses of hydrophilic anion-exchanger membranes were found for anions as large as 2.0 nm, in spite of the cross-linked nature of the anion exchanger that was used. This shows that the high resistance of hydrophilic anion-exchangers to Donnan failure caused by cations such as tetrabutylammonium is not the result of size exclusion. For typical ions, the hydrophilicity of the anion exchanger does not play a decisive factor either. Instead, the excellent resistance to Donnan failure exhibited by hydrophilic ion exchange membranes is primarily caused by the high activity of exchangeable ions in the ion exchanger phase, which disfavors partitioning of ions of opposite charge (along with target ions) from samples into these sensing membranes. The absence of Donnan failure caused by hydrophobic co-ions may be of substantial benefit for measurements in biol. samples.
- 85Kisiel, A.; Michalska, A.; Maksymiuk, K. Bilayer membranes for ion-selective electrodes. J. Electroanal. Chem. 2016, 766, 128– 134, DOI: 10.1016/j.jelechem.2016.01.040Google Scholar85https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XisFyhsL4%253D&md5=52fafbcde3f336270f0e53f412e39d2fBilayer membranes for ion-selective electrodesKisiel, Anna; Michalska, Agata; Maksymiuk, KrzysztofJournal of Electroanalytical Chemistry (2016), 766 (), 128-134CODEN: JECHES; ISSN:1873-2569. (Elsevier B.V.)In most cases described so far a potentiometric ion-selective membrane is made of one polymer (or one copolymer) used with ion-exchanger, ionophore and with a plasticizer of choice. A concept of potentiometric bilayer membranes is introduced and their benefits from both theor. and practical point of view are presented. They are related to response mechanism interpretation and to detection limit lowering of ion-selective electrodes. The novel structurized bilayer potentiometric membranes represent a sequence of polyacrylate polymers with ion-exchangers (the same or different), the polymers applied were either poly(hexyl acrylate) or poly(lauryl acrylate) characterized by different ionic mobilities. Tailoring of the polymer material for the component layers, kind of ion-exchanger and the layer thickness can result in significantly improved anal. performance represented by wide linear response range and low detection limit, as shown in example of K-selective electrode. This effect was achieved due to controlled compensation of spontaneous ion fluxes in bilayer system. The exptl. data were supplemented by digital simulation results explaining the role of the thickness of the internal layer on the ion fluxes and thus on the detection limit.
- 86Makra, I.; Brajnovits, A.; Jagerszki, G.; Furjes, P.; Gyurcsanyi, R. E. Potentiometric sensing of nucleic acids using chemically modified nanopores. Nanoscale 2017, 9, 739– 747, DOI: 10.1039/C6NR05886HGoogle Scholar86https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhvFKjt7vP&md5=c5dda159f0e4c79dfec35f82e7d21732Potentiometric sensing of nucleic acids using chemically modified nanoporesMakra, Istvan; Brajnovits, Alexandra; Jagerszki, Gyula; Furjes, Peter; Gyurcsanyi, Robert E.Nanoscale (2017), 9 (2), 739-747CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)Unlike the overwhelming majority of nanopore sensors that are based on the measurement of a transpore ionic current, here we introduce a potentiometric sensing scheme and demonstrate its application for the selective detection of nucleic acids. The sensing concept uses the charge inversion that occurs in the sensing zone of a nanopore upon binding of neg. charged microRNA strands to pos. charged peptide-nucleic acid (PNA) modified nanopores. The initial anionic permselectivity of PNA-modified nanopores is thus gradually changed to cationic permselectivity, which can be detected simply by measuring the nanoporous membrane potential. A quant. theor. treatment of the potentiometric microRNA response is provided based on the Nernst-Planck/Poisson model for the nanopore system assuming first order kinetics for the nucleic acid hybridization. An excellent correlation between the theor. and exptl. results was obsd., which revealed that the binding process is focused at the nanopore entrance with contributions from both in pore and out of pore sections of the nanoporous membrane. The theor. treatment is able to give clear guidelines for further optimization of potentiometric nanopore-based nucleic acid sensors by predicting the effect of the most important exptl. parameters on the potential response.
- 87Papp, S.; Jagerszki, G.; Gyurcsanyi, R. E. Ion-Selective Electrodes Based on Hydrophilic Ionophore-Modified Nanopores. Angew. Chem., Int. Ed. 2018, 57, 4752– 4755, DOI: 10.1002/anie.201800954Google Scholar87https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXkt1Gqu7c%253D&md5=a7ea53acc9cdceca82fdd22362083472Ion-Selective Electrodes Based on Hydrophilic Ionophore-Modified NanoporesPapp, Soma; Jagerszki, Gyula; Gyurcsanyi, Robert E.Angewandte Chemie, International Edition (2018), 57 (17), 4752-4755CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)We report the synthesis and anal. application of the first Cu2+-selective synthetic ion channel based on peptide-modified gold nanopores. A Cu2+-binding peptide motif (Gly-Gly-His) along with two addnl. functional thiol derivs. inferring cation-permselectivity and hydrophobicity was self-assembled on the surface of gold nanoporous membranes comprising of about 5 nm diam. pores. These membranes were used to construct ion-selective electrodes (ISEs) with extraordinary Cu2+ selectivities, approaching six orders of magnitude over certain ions. Since all constituents are immobilized to a supporting nanoporous membrane, their leaching, that is a ubiquitous problem of conventional ionophore-based ISEs was effectively suppressed.
- 88Mendecki, L.; Callan, N.; Ahern, M.; Schazmann, B.; Radu, A. Influence of Ionic Liquids on the Selectivity of Ion Exchange-Based Polymer Membrane Sensing Layers. Sensors 2016, 16, 1106, DOI: 10.3390/s16071106Google Scholar88https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsVOnsrbJ&md5=7e2d3544da0f75504899fee78b84cd2dInfluence of ionic liquids on the selectivity of ion exchange-based polymer membrane sensing layersMendecki, Lukasz; Callan, Nicole; Ahern, Meghan; Schazmann, Benjamin; Radu, AleksandarSensors (2016), 16 (7), 1106/1-1106/11CODEN: SENSC9; ISSN:1424-8220. (MDPI AG)The applicability of ion exchange membranes is mainly defined by their permselectivity towards specific ions. For instance, the needed selectivity can be sought by modifying some of the components required for the prepn. of such membranes. In this study, a new class of materials-trihexyl(tetradecyl)phosphonium based ionic liqs. (ILs) were used to modify the properties of ion exchange membranes. We detd. selectivity coeffs. for iodide as model ion utilizing six phosphonium-based ILs and compared the selectivity with two classical plasticizers. The dielec. properties of membranes plasticized with ionic liqs. and their response characteristics towards ten different anions were investigated using potentiometric and impedance measurements. In this large set of data, deviations of obtained selectivity coeffs. from the well-established Hofmeister series were obsd. on many occasions thus indicating a multitude of applications for these ion-exchanging systems.
- 89Schazmann, B.; Demey, S.; Ali, Z. W.; Plissart, M. S.; Brennan, E.; Radu, A. Robust, Bridge-less Ion-selective Electrodes with Significantly Reduced Need for Pre- and Post-application Handling. Electroanalysis 2018, 30, 740– 747, DOI: 10.1002/elan.201700716Google Scholar89https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXit1WnsbY%253D&md5=81516de86b416c50eceb92b470b9095fRobust, Bridge-Less Ion-Selective Electrodes with Significantly Reduced Need for Pre- and Post-Application HandlingSchazmann, B.; Demey, S.; Ali, Z. Waqar; Plissart, M.-S.; Brennan, E.; Radu, A.Electroanalysis (2018), 30 (4), 740-747CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)We are demonstrating robust, single-layer ion-selective electrode (ISE) utilizing simple Ag/AgCl electrode as solid support without the need for intermediate polymer layer. We have created and chem. linked a family of imidazolium ionic liqs. (ILs) with poly (vinyl chloride) (PVC) using click chem., resulting in hybrid materials with tunable characteristics. The resultant material inherently contains chloride ion thus offering the ability to stabilize interfacial potential. This allowed us to construct very simple, single-layer membranes with significantly reduced need for conditioning as an added bonus compared to traditional sensors. Chem. immobilization of ISE membrane components also led to extended lifetime as the potential for material loss is reduced and detection limits are lowered. In our characterization we focused on perchlorate as a model ion. It's levels of around 10-7 M could be repeatedly quantified over a 100 day period despite const. exposure of ISEs to aq. soln. over this time. Most importantly, the electrodes exhibited stable and reproducible signal with significantly simplified pre- and post-operation handling protocols. This offers potential for in situ applications as well as to advanced fabrication techniques and miniaturization. Simplicity of construction and operation, and low cost of the solid substrate allows for disposable ISE formats.
- 90Rzhevskaia, A. V.; Shvedene, N. V.; Pletnev, I. V. Anion-selective electrodes based on solidified 1,3-dihexadecylimidazolium ionic liquids with halide and pseudohalide anions. J. Electroanal. Chem. 2016, 783, 274– 279, DOI: 10.1016/j.jelechem.2016.11.009Google Scholar90https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhvVGgtb3O&md5=439aa5be157e2bca3eaf5a4cacb97e8dAnion-selective electrodes based on solidified 1,3-dihexadecylimidazolium ionic liquids with halide and pseudohalide anionsRzhevskaia, A. V.; Shvedene, N. V.; Pletnev, I. V.Journal of Electroanalytical Chemistry (2016), 783 (), 274-279CODEN: JECHES; ISSN:1873-2569. (Elsevier B.V.)In this study screen-printed solid-state electrodes using low-melting ionic liqs. with cation of 1,3-dihexadecylimidazolium and such anions as chloride, iodide, and thiocyanate were developed. Potentiometric response and electrochem. characteristics of ion-selective electrodes in KCl, KI, and KSCN solns. were studied. All sensors exhibited sensitivity toward the corresponding anions, the slopes close to Nernstian ones, low detection limits (3.0 • 10-6 M for SCN-), and high selectivity in the presence of the extraneous anions. Operation time of the sensors was not less than one year. The applicability of the developed electrodes for the potentiometric detn. of iodide in pharmaceuticals and thiocyanate in human saliva was demonstrated.
- 91Mendecki, L.; Chen, X. R.; Callan, N.; Thompson, D. F.; Schazmann, B.; Granados-Focil, S.; Radu, A. Simple, Robust, and Plasticizer-Free Iodide-Selective Sensor Based on Copolymerized Triazole-Based Ionic Liquid. Anal. Chem. 2016, 88, 4311– 4317, DOI: 10.1021/acs.analchem.5b04461Google Scholar91https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XjvFyrsbw%253D&md5=53ae8f2644b3a8a7fa5afa9d72af21aaSimple, Robust, and Plasticizer-Free Iodide-Selective Sensor Based on Copolymerized Triazole-Based Ionic LiquidMendecki, Lukasz; Chen, Xiaorui; Callan, Nicole; Thompson, David F.; Schazmann, Benjamin; Granados-Focil, Sergio; Radu, AleksandarAnalytical Chemistry (Washington, DC, United States) (2016), 88 (8), 4311-4317CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Novel solid-contact iodide-selective electrodes based on covalently attached 1,2,3 triazole ionic liq. (IL) were prepd. and investigated in this study. Triazole-based IL moieties were synthesized using click chem. and were further copolymd. with lauryl methacrylate via a simple one-step free radical polymn. to produce a "self-plasticized" copolymer. The mech. properties of the copolymer are suitable for the fabrication of plasticizer-free ion-selective membrane electrodes. We demonstrate that covalently attached IL moieties provide adequate functionality to the ion-selective membrane, thus achieving a very simple, one-component sensing membrane. We also demonstrate that the presence of iodide as the counterion in the triazole moiety has direct influence on the membrane's functionality. Potentiometric expts. revealed that each electrode displays high selectivity toward iodide anions over a no. of inorg. anions. Moreover, the inherent presence of the iodide in the membrane reduces the need for conditioning. The nonconditioned electrodes show strikingly similar response characteristics compared to the conditioned ones. The electrodes exhibited a near Nernstian behavior with a slope of -56.1 mV per decade across a large concn. range with lower detection limits found at approx. 6.3 × 10-8 M or 8 ppb. These all-solid-state sensors were utilized for the selective potentiometric detn. of iodide ions in artificial urine samples in the nanomolar concn. range.
- 92Abdel-Ghany, M. F.; Hussein, L. A.; El Azab, N. F. Novel potentiometric sensors for the determination of the dinotefuran insecticide residue levels in cucumber and soil samples. Talanta 2017, 164, 518– 528, DOI: 10.1016/j.talanta.2016.12.019Google Scholar92https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XitV2ls7zO&md5=3d2434d6dfe05d1a6d7e8ea89b8ed02fNovel potentiometric sensors for the determination of the dinotefuran insecticide residue levels in cucumber and soil samplesAbdel-Ghany, Maha F.; Hussein, Lobna A.; El Azab, Noha F.Talanta (2017), 164 (), 518-528CODEN: TLNTA2; ISSN:0039-9140. (Elsevier B.V.)Five new potentiometric membrane sensors for the detn. of the dinotefuran levels in cucumber and soil samples have been developed. Four of these sensors were based on a newly designed molecularly imprinted polymer (MIP) material consisting of acrylamide or methacrylic acid as a functional monomer in a plasticized PVC (polyvinyl chloride) membrane before and after elution of the template. A fifth sensor, a carboxylated PVC-based sensor plasticized with dioctyl phthalate, was also prepd. and tested. Sensor 1 (acrylamide washed) and sensor 3 (methacrylic acid washed) exhibited significantly enhanced responses towards dinotefuran over the concn. range of 10-7-10-2 mol L-1. The limit of detection (LOD) for both sensors was 0.35 μg L-1. The response was near-Nernstian, with av. slopes of 66.3 and 50.8 mV/decade for sensors 1 and 3 resp. Sensors 2 (acrylamide non-washed), 4 (methacrylic acid non-washed) and 5 (carboxylated-PVC) exhibited non-Nernstian responses over the concn. range of 10-7-10-3 mol L-1, with LODs of 10.07, 6.90, and 4.30 μg L-1, resp., as well as av. slopes of 39.1, 27.2 and 33 mV/decade, resp. The application of the proposed sensors to the detn. of the dinotefuran levels in spiked soil and cucumber samples was demonstrated. The av. recoveries from the cucumber samples were from 7.93% to 106.43%, with a std. deviation of less than 13.73%, and recoveries from soil samples were from 97.46% to 108.71%, with a std. deviation of less than 10.66%. The sensors were applied successfully to the detn. of the dinotefuran residue, its rate of disappearance and its half-life in cucumbers in soil in which a safety pre-harvest interval for dinotefuran was suggested.
- 93Zhuo, K. L.; Ma, X. L.; Chen, Y. J.; Wang, C. Y.; Li, A. Q.; Yan, C. L. Molecularly imprinted polymer based potentiometric sensor for the determination of 1-hexyl-3-methylimidazolium cation in aqueous solution. Ionics 2016, 22, 1947– 1955, DOI: 10.1007/s11581-016-1708-zGoogle Scholar93https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xmt1Smur8%253D&md5=ce88df34395b37653db0d1ff9606d18aMolecularly imprinted polymer based potentiometric sensor for the determination of 1-hexyl-3-methylimidazolium cation in aqueous solutionZhuo, Kelei; Ma, Xueli; Chen, Yujuan; Wang, Congyue; Li, Aoqi; Yan, ChanglingIonics (2016), 22 (10), 1947-1955CODEN: IONIFA; ISSN:0947-7047. (Springer)The mol. imprinting technique is powerful to prep. functional materials with mol. recognition properties. In this work, a potentiometric sensor was fabricated by dispersing molecularly imprinted polymers (MIPs) into plasticized PVC matrix and used for the detn. of 1-hexyl-3-methylimidazolium cation ([C6mim]+) in aq. soln. The MIPs were synthesized by pptn. polymn. using 1-hexyl-3-methylimidazolium chloride ([C6mim]Cl) as the template mol., methacrylic acid (MAA) and ethylene glycol dimethacrylate (EGDMA) as the functional monomers, and EGDMA also as the crosslinking agent. The as-prepd. electrode exhibited a Nernstian response (58.87 ± 0.3 mV per decade) to [C6mim]+ in a concn. range from 1.0 × 10-6 to 0.1 mol kg-1 with a low detection limit of 2.8 × 10-7 mol kg-1, high selectivity, and little pH influence. The as-prepd. electrode was used for the detection of the [C6mim]+ in distd. water, tap water, and river water with a good recovery. It was also successfully applied in the detn. of mean activity coeffs. of [C6mim]Br in fructose + water systems based on the potentiometric method at 298.15 K.
- 94Sacramento, A. S.; Moreira, F. T. C.; Guerreiro, J. L.; Tavares, A. P.; Sales, M. G. F. Novel biomimetic composite material for potentiometric screening of acetylcholine, a neurotransmitter in Alzheimer’s disease. Mater. Sci. Eng., C 2017, 79, 541– 549, DOI: 10.1016/j.msec.2017.05.098Google Scholar94https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtVWqs7nE&md5=88231945d853885d37a6adee40d1a322Novel biomimetic composite material for potentiometric screening of acetylcholine, a neurotransmitter in Alzheimer's diseaseSacramento, Ana S.; Moreira, Felismina T. C.; Guerreiro, Joana L.; Tavares, Ana P.; Sales, M. Goreti F.Materials Science & Engineering, C: Materials for Biological Applications (2017), 79 (), 541-549CODEN: MSCEEE; ISSN:0928-4931. (Elsevier B.V.)This work describes a novel approach to produce an antibody-like biomimetic material. It includes prepg. composite imprinted material never presented before, with highly conductive support nanostructures and assembling a high cond. polymeric layer at low temp. Overall, such highly conductive material may enhance the final features of elec.-based devices. Acetylcholine (ACh) was selected as target analyte, a neurotransmitter of importance in Alzheimer's disease. Potentiometric transduction was preferred, allowing quick responses and future adaptation to point-of-care requirements. The biomimetic material was obtained by bulk polymn., where ACh was placed in a composite matrix of multiwalled carbon nanotubes (MWCNTs) and aniline (ANI). Subsequent polymn., initiated by radical species, yielded a polymeric structure of polyaniline (PANI) acting as phys. support of the composite. A non-imprinted material (NIM) having only PANI/MWCNT (without ACh) has been prepd. for comparison of the biomimetic-imprinted material (BIM). RAMAN and Fourier Transform IR spectroscopy (FTIR), Transmission Electron microscopy (TEM), and Scanning Electron microscope (SEM) anal. characterized the structures of the materials. The ability of this biomaterial to rebind ACh was confirmed by including it as electroactive compd. in a PVC/plasticizer mixt. The membranes with imprinted material and anionic additive presented the best anal. characteristics, with a sensitivity of 83.86 mV decade- 1 and limit of detection (LOD) of 3.45 × 10- 5 mol/L in HEPES buffer pH 4.0. Good selectivity was obsd. against creatinine, creatine, glucose, cysteine and urea. The electrodes were also applied on synthetic serum samples and seemed a reliable tool for screening ACh in synthetic serum samples. The overall performance showed fast response, reusability, simplicity and low price.
- 95Alizadeh, T.; Nayeri, S.; Mirzaee, S. A high performance potentiometric sensor for lactic acid determination based on molecularly imprinted polymer/MWCNTs/PVC nanocomposite film covered carbon rod electrode. Talanta 2019, 192, 103– 111, DOI: 10.1016/j.talanta.2018.08.027Google Scholar95https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhslKqur7M&md5=1f4e37ae411af1fd594b16f6f283d577A high performance potentiometric sensor for lactic acid determination based on molecularly imprinted polymer/MWCNTs/PVC nanocomposite film covered carbon rod electrodeAlizadeh, Taher; Nayeri, Sahar; Mirzaee, SaharTalanta (2019), 192 (), 103-111CODEN: TLNTA2; ISSN:0039-9140. (Elsevier B.V.)A novel nano-sized imprinted polymer/multi-walled carbon nanotube (MWCNTs)-based potentiometric sensor is introduced for lactic acid (LA) sensing in dairy products. The imprinted polymer was synthesized using allyl amine (AA) and ethylene glycol dimethacrylate as functional monomer and cross-linker, resp. It was demonstrated that the amide linkage was created between LA and AA during copolymn. reaction which was finally hydrolyzed when removing template from the synthesized MIP. It was also shown that the MIP cavities, compatible with LA anion, were created during polymn. reaction which influenced the potentiometric response behavior of the MIP-based electrode. This novel potentiometric sensor is a carbon rod electrode, coated with a membrane consisting of the MIP nanoparticles (2.5%), MWCNTs (2%), dibutylphthalate (DBP) (65%), poly-vinyl chloride (PVC) (28.5%) and tetra Ph phosphonium bromide (TPPB) (2%). The active ion sensed by the electrode is the LA anion formed at elevated pH condition. The sensor exhibited Nernstian slope of 30.3 ± 0.4 mVdecade-1 in the working concn. range of 1.0 × 10-1to 1.0 × 10-6 mol L-1 with detection limit of 7.3 × 10-7 mol L-1. The sensor displayed a stable potential response in the pH range of 5-8 and fast response time of less than 60 s. It exhibited also high selectivity over the interfering species. The proposed sensor was successfully applied for the detn. of LA in real samples (milk and yoghurt).
- 96Li, P. J.; Liang, R. N.; Yang, X. F.; Qin, W. Imprinted nanobead-based disposable screen-printed potentiometric sensor for highly sensitive detection of 2-naphthoic acid. Mater. Lett. 2018, 225, 138– 141, DOI: 10.1016/j.matlet.2018.04.119Google Scholar96https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXptVGitrk%253D&md5=d3066013cc97bc2af776968e59ff5788Imprinted nanobead-based disposable screen-printed potentiometric sensor for highly sensitive detection of 2-naphthoic acidLi, Pengjuan; Liang, Rongning; Yang, Xiaofeng; Qin, WeiMaterials Letters (2018), 225 (), 138-141CODEN: MLETDJ; ISSN:0167-577X. (Elsevier B.V.)Currently, potentiometric sensors based on various molecularly imprinted polymer (MIP) receptors were successfully fabricated for detection of org. species. However, almost all of the previously developed potentiometric sensors based on MIPs are in traditional liq.-contact mode in which lower detection limits were restricted by zero-current transmembrane ion fluxes. Herein, a screen-printed potentiometric sensor for detn. of 2-naphthoic acid was developed. It is based on the MIP nanobeads as the selective receptor and the electrochem. reduced graphene oxide film as the solid contact. Compared with the classical potentiometric sensor, the proposed sensor based on nonequil. sensing mechanism exhibits remarkably improved detection sensitivity for 2-naphthoic acid with a low detection limit of 6.9 × 10-11 M.
- 97Kupis-Rozmyslowicz, J.; Wagner, M.; Bobacka, J.; Lewenstam, A.; Migdalski, J. Biomimetic membranes based on molecularly imprinted conducting polymers as a sensing element for determination of taurine. Electrochim. Acta 2016, 188, 537– 544, DOI: 10.1016/j.electacta.2015.12.007Google Scholar97https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXitVeitLjN&md5=c0abd93d189eab4109b2ef56200c9199Biomimetic membranes based on molecularly imprinted conducting polymers as a sensing element for determination of taurineKupis-Rozmyslowicz, Justyna; Wagner, Michal; Bobacka, Johan; Lewenstam, Andrzej; Migdalski, JanElectrochimica Acta (2016), 188 (), 537-544CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Ltd.)Molecularly Imprinted Conducting Polymer based films (MICP films) devoted for the taurine detn. is described. MICP films were electrodeposited from an aq. soln. contg. 3,4-ethylenedioxythiophene, acetic acid thiophene, FMN, and taurine. The presence of taurine inside freshly deposited MICP films as well as absence of taurine in the outer layer of the MICP film after extn. process was confirmed by the XPS spectra. After taurine extn., MICP films can be used as a potentiometric sensor giving close to Nernstian response towards taurine equal to 53.8 ± 2.6 mV/p[taurine] in the concn. range 10-2 to 10-4 mol dm-3.
- 98Wang, T. T.; Liang, R. N.; Yin, T. J.; Yao, R. Q.; Qin, W. An all-solid-state imprinted polymer-based potentiometric sensor for determination of bisphenol S. RSC Adv. 2016, 6, 73308– 73312, DOI: 10.1039/C6RA14461FGoogle Scholar98https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xht1Cktr7N&md5=824784006b8778a13cc02ab3967cad9bAn all-solid-state imprinted polymer-based potentiometric sensor for determination of bisphenol SWang, Tiantian; Liang, Rongning; Yin, Tanji; Yao, Ruiqing; Qin, WeiRSC Advances (2016), 6 (77), 73308-73312CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)An all-solid-state polymeric membrane potentiometric sensor for detn. of bisphenol S has been developed by using the imprinted polymer as the receptor and a nanoporous gold film as the solid contact. The sensor has a linear concn. range of 0.1 to 2 μM with a detection limit of 0.04 μM.
- 99Zhang, H.; Yao, R. Q.; Wang, N.; Liang, R. N.; Qin, W. Soluble Molecularly Imprinted Polymer-Based Potentiometric Sensor for Determination of Bisphenol AF. Anal. Chem. 2018, 90, 657– 662, DOI: 10.1021/acs.analchem.7b03432Google Scholar99https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhvFGjt7fN&md5=df84e26c4b51508e4b2fa47a5b7ee48cSoluble Molecularly Imprinted Polymer-Based Potentiometric Sensor for Determination of Bisphenol AFZhang, Huan; Yao, Ruiqing; Wang, Ning; Liang, Rongning; Qin, WeiAnalytical Chemistry (Washington, DC, United States) (2018), 90 (1), 657-662CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Molecularly imprinted polymer (MIP)-based polymeric membrane potentiometric sensors have been successfully developed for detn. of org. compds. in their ionic and neutral forms. However, most of the MIP receptors in potentiometric sensors developed so far are insol. and cannot be well dissolved in the polymeric membranes. The heterogeneous mol. recognitions between the analytes and MIPs in the membranes are inefficient due to the less available binding sites of the MIPs. Herein the authors describe a novel polymeric membrane potentiometric sensor using a sol. MIP (s-MIP) as a receptor. The s-MIP is synthesized by the swelling of the traditional MIP at a high temp. The obtained MIP can be dissolved in the plasticized polymeric membrane for homogeneous binding of the imprinted polymer to the target mols. By using neutral bisphenol AF as a model, the proposed method exhibits an improved sensitivity compared to the conventional MIP-based sensor with a lower detection limit of 60 nM. Moreover, the present sensor exhibits an excellent selectivity over other phenols. The authors believe that s-MIPs can provide an appealing substitute for the traditional insol. MIP receptors in the development of polymeric membrane-based electrochem. and optical sensors.
- 100Pankratova, N.; Cuartero, M.; Jowett, L. A.; Howe, E. N. W.; Gale, P. A.; Bakker, E.; Crespo, G. A. Fluorinated tripodal receptors for potentiometric chloride detection in biological fluids. Biosens. Bioelectron. 2018, 99, 70– 76, DOI: 10.1016/j.bios.2017.07.001Google Scholar100https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXht1Gis7%252FP&md5=8f3602cb36c92d2741aa895474fd02f5Fluorinated tripodal receptors for potentiometric chloride detection in biological fluidsPankratova, Nadezda; Cuartero, Maria; Jowett, Laura A.; Howe, Ethan N. W.; Gale, Philip A.; Bakker, Eric; Crespo, Gaston A.Biosensors & Bioelectronics (2018), 99 (), 70-76CODEN: BBIOE4; ISSN:0956-5663. (Elsevier B.V.)Fluorinated tripodal compds. were recently reported to be efficient transmembrane transporters for a series of inorg. anions. In particular, this class of receptors has been shown to be suitable for the effective complexation of chloride, nitrate, bicarbonate and sulfate anions via hydrogen bonding. The potentiometric properties of urea and thiourea-based fluorinated tripodal receptors are explored here for the first time, in light of the need for reliable sensors for chloride monitoring in undiluted biol. fluids. The ion selective electrode (ISE) membranes with tren-based tris-urea bis(CF3) tripodal compd. (ionophore I) were found to exhibit the best selectivity for chloride over major lipophilic anions such as salicylate (logKpotCl-/Sal- = + 1.0) and thiocyanate (logKpotCl-/SCN- = + 0.1). Ionophore I-based ISEs were successfully applied for chloride detn. in undiluted human serum as well as artificial serum sample, the slope of the linear calibration at the relevant background of interfering ions being close to Nernstian (49.8±1.7 mV). The results of potentiometric measurements were confirmed by argentometric titrn. Moreover, the ionophore I-based ISE membrane was shown to exhibit a very good long-term stability of potentiometric performance over the period of 10 wk. NMR (NMR) titrns., potentiometric sandwich membrane expts. and d. functional theory (DFT) computational studies were performed to det. the binding consts. and suggest 1:1 complexation stoichiometry for the ionophore I with chloride as well as salicylate.
- 101Yagi, Y.; Masaki, S.; Iwata, T.; Nakane, D.; Yasui, T.; Yuchi, A. Triphosphate Ion-Selective Electrode Based on Zr-Porphyrin Complex. Anal. Chem. 2017, 89, 3937– 3942, DOI: 10.1021/acs.analchem.6b03754Google Scholar101https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXjvVWhsLs%253D&md5=859587f3f9267986bf6cb1abdd5809a2Triphosphate Ion-Selective Electrode Based on Zr-Porphyrin ComplexYagi, Yuma; Masaki, Shuhei; Iwata, Tetsuki; Nakane, Daisuke; Yasui, Takashi; Yuchi, AkioAnalytical Chemistry (Washington, DC, United States) (2017), 89 (7), 3937-3942CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Ion-selective electrode using Zr(IV) complex with octaethylporphin (H2oep) as a carrier showed high selectivity to triphosphate (TP, H5tp) against other hydrophilic anions including diphosphate and phosphate. The electroactive species was identified to be [Zr4(oep)4(Htp)2] (TP/Zr ratio of 0.5) of the unique structure; triphosphates are recognized by one Zr atom through three O atoms on three different P atoms and by another Zr atom through two O atoms on two terminal P atoms and are also involved in complementary intermol. H bonding to be surrounded by four porphyrin complexes. In contrast, Zr(IV) in the other complex with tetraphenylporphin has the higher Lewis acidity, due to the electron-withdrawing property of Ph rings and, at the higher TP concn., forms a species having a TP/Zr ratio of unity, which ppts. to lose the electroactivity. The electrode was successfully applied to monitor hydrolysis of TP that provides diphosphate and phosphate.
- 102Zahran, E. M.; Fatila, E. M.; Chen, C. H.; Flood, A. H.; Bachas, L. G. Cyanostar: C-H Hydrogen Bonding Neutral Carrier Scaffold for Anion-Selective Sensors. Anal. Chem. 2018, 90, 1925– 1933, DOI: 10.1021/acs.analchem.7b04008Google Scholar102https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXht1ynu7o%253D&md5=924990a1505ef5b0eb03cbb15febdca6Cyanostar: C-H Hydrogen Bonding Neutral Carrier Scaffold for Anion-Selective SensorsZahran, Elsayed M.; Fatila, Elisabeth M.; Chen, Chun-Hsing; Flood, Amar H.; Bachas, Leonidas G.Analytical Chemistry (Washington, DC, United States) (2018), 90 (3), 1925-1933CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Cyanostar, a pentagonal macrocyclic compd. with an electropos. cavity, binds anions with CH-based hydrogen bonding. The large size of the cyanostar's cavity along with its planarity favor formation of 2:1 sandwich complexes with larger anions, like perchlorate, ClO4-, relative to the smaller chloride. Also cyanostar is selective for ClO4- over the bulky salicylate anions by using NMR titrn. studies to measure affinity. The performance of this novel macrocycle as an anion ionophore in membrane ion sensors was evaluated. The cyanostar-based electrodes demonstrated a Nernstian response toward perchlorate with selectivity patterns distinctly different from the normal Hofmeister series. Different membrane compns. were explored to identify the optimum concns. of the ionophore, plasticizer, and lipophilic additive that give rise to the best perchlorate selectivity. Changing the concn. of the lipophilic additive tridodecylmethylammonium chloride was found to impact the selectivity pattern and the anal. dynamic range of the electrodes. The high selectivity of the cyanostar sensors and their detection limit could enable the detn. of ClO4- in contaminated environmental samples. This novel class of macrocycle provides a suitable scaffold for designing various anion-selective ionophores by altering the size of the central cavity and its functionalization.
- 103Shehab, O. R.; Mansour, A. M. Potentiometric Sensing of Aspirin Metabolite in Human Plasma and Pharmaceutical Preparations Using Co(III)-complex Based Electrodes: Experimental and Quantum Chemical Calculations. Electroanalysis 2016, 28, 1100– 1111, DOI: 10.1002/elan.201501059Google Scholar103https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XjslansA%253D%253D&md5=d4b0d0aa646da42ffdd419077d96c4daPotentiometric Sensing of Aspirin Metabolite in Human Plasma and Pharmaceutical Preparations Using Co(III)-complex Based Electrodes: Experimental and Quantum Chemical CalculationsShehab, Ola R.; Mansour, Ahmed M.Electroanalysis (2016), 28 (5), 1100-1111CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)Three novel poly vinyl chloride PVC A, carbon paste CP B, and coated glassy carbon-MWCNT CGC C salicylate sal- sensors based on new synthesized [CoL2ClCl3H2O]-H2O complex L2Cl=1H-benzimidazol-2-ylmethyl-N-2-chloro-phenyl- amine, o-nitrophenyloctyl ether as a mediator and tridodecy lmethylammonium chloride as a cationic additive were successfully used for detn. of sal- in human plasma and pharmaceutical formulations. The sal--sensors exhibited enhanced sensitivity with slope of -63.5, -60.5 and -58.9 mV/decade and detection limit of 1.0 × 10-5, 4.0 × 10-7, and 1.0 × 10-6 mol L-1 for A-C sensors resp. Quantum chem. calcns. were carried out by HF and DFT/B3LYP methods to explore and investigate the interaction between the receptor and the different anions. The intermol. H-bond created between the uncoordinated C=O of salicylate group and the secondary amino group in the complex is the key factor of the selectivity of the proposed sensor. A linear relation is established between the natural charge on the Co center and the value of the binding energy, where the decrease in pos. charge is assocd. by an increase in the anion binding energy.
- 104Abdel-Haleem, F. M.; Badr, I. H. A.; Rizk, M. S. Electroanalysis 2016, 28, 2922– 2929, DOI: 10.1002/elan.201600335Google Scholar104https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhtFert7vL&md5=1d6011e137c3429cf0d36bbb84b8087bPotentiometric Anion Selectivity and Analytical Applications of Polymer Membrane Electrodes Based on Novel Mn(III)- and Mn(IV)-Salophen ComplexesAbdel-Haleem, Fatehy M.; Badr, Ibrahim H. A.; Rizk, Mahmoud S.Electroanalysis (2016), 28 (12), 2922-2929CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)New Mn(III)-L and Mn(IV)-L complexes were prepd. from the highly lipophilic salophen ligand (L): phenol 2,2'-[(4,5-dimethyl-1,2-phenylene)bis[(E)-nitrilomethylidyne]]bis[4,6-bis(1,1-dimethylethyl)]. The prepd. complexes were fully characterized and used for the construction of thiocyanate membrane electrodes. Optimized membrane electrodes contained 33.0 mg PVC, 66.0 mg o-nitrophenyloctylether, 50 or 5 (mole %) tetrakis(trifluoromethyl)phenyl borate and 1 mg Mn(III)-L (sensor 2) or Mn-(IV)-L (sensor 12), resp. Such electrodes exhibited linear responses toward thiocynate in a concn. range of 10-1-10-5 M and detection limits of 8.3×10-6, 8.9×10-6 M for sensor 2 and 12, resp. Optimized membrane electrodes exhibited high selectivity toward thiocayante compared to more lipophilic anions. The obsd. thiocyanate selectivity of the optimized membranes was confirmed by formation const. calcns. for Mn(III)-L and Mn(IV)-L with SCN-, β=1014.1 and 1012.5, which was measured potentiometrically using the sandwich membrane method. Furthermore, computational study using DFT calcns. was performed to at DFT/B3LYP level of theory to confirm the obsd. selectivity data. The response times were 3 and 0.5 min for low and high concns. The lifetimes of the optimized electrodes were ∼4-6 wk. The anal. utility of the optimized membrane electrodes was demonstrated by the anal. of thiocyanate level in different saliva samples.
- 105Lenik, J.; Nieszporek, J. Construction of a glassy carbon ibuprofen electrode modified with multi-walled carbon nanotubes and cyclodextrins. Sens. Actuators, B 2018, 255, 2282– 2289, DOI: 10.1016/j.snb.2017.09.034Google Scholar105https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsFCqtbjF&md5=4a13f376ae467b1b83da6c327ce44435Construction of a glassy carbon ibuprofen electrode modified with multi-walled carbon nanotubes and cyclodextrinsLenik, Joanna; Nieszporek, JolantaSensors and Actuators, B: Chemical (2018), 255 (Part_2), 2282-2289CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)The prepn. of glassy carbon (GC) ibuprofen (2-(4- isobutylphenyl)propionic acid) membrane sensors was examd. in the study described below. The optimal membrane was based on functionalized β-cyclodextrins: heptakis (2,3,6-tri-O-benzoyl)-β-cyclodextrin (GC/MWCNT-HBβCD). The following basic anal. parameters of the drug electrode were detd.: sensitivity, measuring range, detection limit, reversibility, and selectivity coeffs. for some org. and inorg. anions. The electrode exhibited good Nernstian slope of 59.9 mV/decade, measuring range of 3.2 × 10-5-10-2, pH range of 5-9, and very good response time of 5 s. The advantages of the GC electrode with the use of multi-walled carbon nanotubes, i.e. high cond. (bulk resistance 5,76 × 102 Ω) was confirmed by the impedance spectroscopy method whereas high selectivity and the stable potential are the parameters detd. in the potentiometric measurements.
- 106Lisak, G.; Tamaki, T.; Ogawa, T. Dualism of Sensitivity and Selectivity of Porphyrin Dimers in Electroanalysis. Anal. Chem. 2017, 89, 3943– 3951, DOI: 10.1021/acs.analchem.6b04179Google Scholar106https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXjvVWjt70%253D&md5=3e827b9eaae88e1b96fc47ca77c0a8eaDualism of Sensitivity and Selectivity of Porphyrin Dimers in ElectroanalysisLisak, Grzegorz; Tamaki, Takashi; Ogawa, TakujiAnalytical Chemistry (Washington, DC, United States) (2017), 89 (7), 3943-3951CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)This work uncovers the application of porphyrin dimers for the use in electroanal., such as potentiometric detn. of ions. It also puts in question a current perception of an occurrence of the super-Nernstian response, as a result of the possible dimerization of single porphyrins within an ion-selective membrane. To study that, four various porphyrin dimers were used as ionophores, namely freebase-freebase, Zn-Zn, Zn-freebase and freebase-Zn. Since the Zn-freebase and freebase-Zn porphyrin dimers carried both anion- and cation-sensitive porphyrin units, their application in ISEs was used in both anion- and cation-sensitive sensors. In respect to the lipophilic salt added, both porphyrins dimers were found anion- and cation-sensitive. This allowed using a single mol. as novel type of versatile ionophore (anion- and cation-selective), simply by varying the membrane compn. All anion-sensitive sensors were perchlorate-sensitive, while the cation-selective sensors were silver-sensitive. The selectivity of the sensors depended primarily on the porphyrin dimers in the ion-selective membrane. Furthermore, the selectivity of cation-sensitive dimer based sensors was found significantly superior to the ones measured for the single porphyrin unit based sensors (precursors of the porphyrin dimers). Thus, the dimerization of single porphyrins may actually be a factor to increase or modulate porphyrin selectivity. Moreover, in the case of cation-sensitive sensors, the selectivity vastly depended on the order of porphyrin units in the dimer. This opens a new approach of regulating and adjusting sensitivity and selectivity of the sensor through the application of complex porphyrin systems with more than one porphyrin units with mix sensitive porphyrins.
- 107Juarez-Gomez, J.; Ramirez-Silva, M. T.; Romero-Romo, M.; Rodriguez-Sevilla, E.; Perez-Garcia, F.; Palomar-Pardave, M. Ion-Selective Electrodes for Mercury Determination at Low Concentrations: Construction, Optimization and Application. J. Electrochem. Soc. 2016, 163, B90– B96, DOI: 10.1149/2.0621603jesGoogle ScholarThere is no corresponding record for this reference.
- 108Said, N. R.; Rezayi, M.; Narimani, L.; Al-Mohammed, N. N.; Manan, N. S. A.; Alias, Y. A New N-Heterocyclic Carbene Ionophore in Plasticizer-free Polypyrrole Membrane for Determining Ag+ in Tap Water. Electrochim. Acta 2016, 197, 10– 22, DOI: 10.1016/j.electacta.2016.02.173Google Scholar108https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xkt1Wqs70%253D&md5=8ec9d54946011fb34bfa76f4f3322415A New N-Heterocyclic Carbene Ionophore in Plasticizer-free Polypyrrole Membrane for Determining Ag+ in Tap WaterSaid, Nur Rahimah; Rezayi, Majid; Narimani, Leila; Al-Mohammed, Nassir N.; Manan, Ninie Suhana Abdul; Alias, YatimahElectrochimica Acta (2016), 197 (), 10-22CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Ltd.)A bis[1-benzyl-benzimidazoliumethyl]-4-methylbenzenesufonamide bromide ligand (NHCL) as a new type of ionophore was successfully synthesized for the 1st time and used for the fabrication of Ag+ ion selective electrode as a new type of ionophore, based on the self-plasticizing method. The ionophore was characterized using CHN elemental anal., FTIR, 1H NMR, 13C NMR, UV-visible spectroscopic techniques and x-ray single crystal diffraction. The interection between NHCL and Ag+ cation was studied spectrophotometerically and the stoichiometry of the complex (1:2) NHCL:Ag+ in DMSO solvent was detd. The potentiometric response of the electrode toward Ag+ cation was linear from 2.5 × 10-6 to 1.0 × 10-1 M with detection limit of 2.00 × 10-6 M and a Nernstian slope of 58.48 ± 0.75 mV decade-1. The sensor exhibited a response time of ∼20 s at room temp. and working pH range between 3.5-9.0. The electrode showed a good selectivity towards Ag+ cations in comparison with other soft and hard metals, while most of these metal ions did not show significant interference (KpotAg+,M). The proposed electrode also applied in the direct detn. of Ag+ cations in tap H2O and std. samples with sensible accuracy and precision.
- 109Omran, O. A.; Elgendy, F. A.; Nafady, A. Fabrication and Applications of Potentiometric Sensors Based on p-tert-butylthiacalix 4 arene Comprising Two Triazole Rings Ionophore for Silver Ion Detection. Int. J. Electrochem. Sci. 2016, 11, 4729– 4742, DOI: 10.20964/2016.06.35Google Scholar109https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xhs1Omsr3K&md5=2a66f6a87ae534f8ac414c8ad676576bFabrication and applications of potentiometric sensors based on p-tert-butylthiacalix[4]arene comprising two triazole rings ionophore for silver ion detectionOmran, Omran A.; Elgendy, Fadl A.; Nafady, AymanInternational Journal of Electrochemical Science (2016), 11 (6), 4729-4742CODEN: IJESIV; ISSN:1452-3981. (Electrochemical Science Group)This work describes the fabrication and applications of potentiometric silver-selective sensors, based on the use of a newly synthesized p-tert-butylthiacalix[4]arene comprising two triazole rings, as a novel neutral ionophore in plasticized poly(vinyl chloride) (PVC) membranes. The effect of lipophilic anionic additives on the voltammetric responses of the sensors was investigated in details. The constructed sensors exhibited a Nernstian behavior with 53 ± 0.9 mV per decade change in Ag+ activity over the range from 7.0 × 10-6 to 8.0 × 10-3, with a repetitive detection limit of 0.421μg mL-1. Moreover, the effect of lipophilic salts, plasticizers and various interfering ions were probed. Importantly, validation of the method is achieved in terms of good performance characteristics, including good selectivity for Ag+ over alkali, alk. earth and transition metal ions (e.g. Na+, K+, Pb2+, Mg2+, Co2+ Ni2+, and Cu2+) together with long life span. Other important characteristics such as low detection limit, acceptable accuracy and precision, long term stability, reproducibility were also demonstrated. On the application side, the sensors were utilized for facile potentiometric measurements of iodide ions (I-) over the concn. range of 0.749 to 856μg mL-1 and also employed for probing sequential titrn. of some importantly relevant anions (e.g. Cl-, Br-, I-, SCN- and N-3). Significantly, sequential binding of these anions with Ag+ cations produces sharp stepwise titrn. curves with consecutive end point breaks at the equiv. points.
- 110Kawakami, T. M.; Obita, M.; Tsujinaka, T.; Higashikado, A.; Moriuchi, T. Ionophoric Properties of 14 Tetraazaannulene Derivatives and Substituent Effect on the Cation-selectivity. Electroanalysis 2017, 29, 1712– 1720, DOI: 10.1002/elan.201700011Google Scholar110https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXlvVGgu7o%253D&md5=b2288e6ae0ac26879012a8d276aeada6Ionophoric Properties of [14]Tetraazaannulene Derivatives and Substituent Effect on the Cation-selectivityKawakami, T. M.; Obita, M.; Tsujinaka, T.; Higashikado, A.; Moriuchi, T.Electroanalysis (2017), 29 (7), 1712-1720CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)[14]Tetraazaannulene derivs. 1-4 (I-IV) with various substituents were synthesized as ion recognition compds. All solvent polymeric membrane electrodes incorporating [14]tetraazaannulene derivs. I-IV showed rapid response for the Cu2+ ion and exhibited excellent selectivity over other mono- and divalent cations such as Ag+ and Ni2+ ions. The solvent polymeric membrane electrode based on [14]tetraazaannulene deriv. I has a linear response to the Cu2+ ion from 5.01 × 10-7-2.63 × 10-4 M with a slope of 29.56 mV per decade. DFT calcns. showed that the selectivities for the Cu2+ ion of the ISEs based on [14]tetraazaannulene derivs. I-IV depended on both their topol. and electrostatic properties caused by the introduced substituents.
- 111Kumar, S.; Mittal, S. K.; Kaur, N.; Kaur, R. Improved performance of Schiff based ionophore modified with MWCNT for Fe(II) sensing by potentiometry and voltammetry supported with DFT studies. RSC Adv. 2017, 7, 16474– 16483, DOI: 10.1039/C7RA00393EGoogle Scholar111https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXksVCrsbo%253D&md5=8bf1bd35b1ae629c2f78a7838d2e9e79Improved performance of Schiff based ionophore modified with MWCNT for Fe(II) sensing by potentiometry and voltammetry supported with DFT studiesKumar, Sanjeev; Mittal, Susheel K.; Kaur, Navneet; Kaur, RavneetRSC Advances (2017), 7 (27), 16474-16483CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)A novel potentiometric and voltammetric sensor for creating a cationic response for Fe(II) is introduced. These methods were applied to produce an Fe(II) selective sensor based on (E)-3-((2-aminoethylimino)methyl)-4H-chromen-4-one (IFE). The influence of variables including the amt. of ionophore, plasticizers, anion excluder and multiwalled carbon nanotubes (MWCNTs) on the performance of the potentiometric sensor were investigated. The sensor for Fe(II) improvised the dynamic linear range (1 × 10-7 to 1 × 10-1 mol L-1) with a slope of 27 mV per decade and a detection limit of 2.5 × 10-8 mol L-1. Selectivity of the ion selective electrode improved after modification with MWCNTs. The redn. and oxidn. properties of IFE were studied by voltammetric measurements. Differential pulse voltammetry was applied to the optimized electrode and a linear dynamic range from (9.9 × 10-7 to 2.9 × 10-5 mol L-1) with a detection limit of 6.13 × 10-8 mol L-1 was obtained. The compn. and morphol. of the modified ion selective electrode were characterized with SEM. The modified electrodes have good selectivity for Fe(II) ions over a no. of metal ions. It was successfully applied for direct detn. of Fe(II) ions in different real life samples. Theor. calcns. also supported the complexation behavior of Fe(II) with IFE.
- 112Rezayi, M.; Gholami, M.; Said, N. R.; Alias, Y. A novel polymeric membrane sensor for determining titanium (III) in real samples: Experimental, molecular and regression modeling. Sens. Actuators, B 2016, 224, 805– 813, DOI: 10.1016/j.snb.2015.10.089Google Scholar112https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhvVKrsL7J&md5=5fc539cc0e8bcfa78fd6bb336d0190b3A novel polymeric membrane sensor for determining titanium (III) in real samples: Experimental, molecular and regression modelingRezayi, Majid; Gholami, Mehrdad; Rahimah Said, Nur; Alias, YatimahSensors and Actuators, B: Chemical (2016), 224 (), 805-813CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)The construction of a potentiometric titanium(III)-selective electrode based on methylcalix[4]resorcinarene (CMCR) incorporated into a poly(vinyl chloride) (PVC) matrix is reported. The polymeric membrane incorporates 8.0 mg CMCR as an electroactive sensing material, 59.0 mg dioctylphthalate (DOP) as a plasticizer, 3.0 mg sodium tetra-Ph borate (NaTPB) as an anionic additive and 30 mg PVC as a neutral matrix exhibiting a Nernstain potential response of 30.38 ± 0.15 mV per decade in the concn. range from 1 × 10-6 to 1 × 10-2 M with a detection limit of 8.9 × 10-7 M and fast response time of 15 s. The proposed sensor was successfully applied to det. titanium cations in real samples and the obtained results were compared to those of spectroscopy methods such as AAS and ICP instruments. The structure of CMCR ligand and its complexation with some common cations were investigated using quantum mech. DFT calcns. where the titanium (III) cation showed prominent affinity for the CMCR carrier. The regression model was applied to obtain the membrane compn. model of Ti(III)-ISE affecting the potential response of the polymeric sensor. The results show that the regression model can be used as a practical method for obtaining the Nernstian slope of the proposed sensor in this study.
- 113Zahran, E. M.; Paeng, K. J.; Badr, I. H. A.; Hume, D.; Lynn, B. C.; Johnson, R. D.; Bachas, L. G. Correlating the potentiometric selectivity of cyclosporin-based electrodes with binding patterns obtained from electrospray ionization-mass spectrometry. Analyst 2017, 142, 3241– 3249, DOI: 10.1039/C6AN01252CGoogle Scholar113https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtlSrsbfK&md5=ccdec0e860c49726cce47b4a4e67b46fCorrelating the potentiometric selectivity of cyclosporin-based electrodes with binding patterns obtained from electrospray ionization-mass spectrometryZahran, Elsayed M.; Paeng, Ki-Jung; Badr, Ibrahim H. A.; Hume, David; Lynn, Bert C.; Daniel Johnson, R.; Bachas, Leonidas G.Analyst (Cambridge, United Kingdom) (2017), 142 (17), 3241-3249CODEN: ANALAO; ISSN:0003-2654. (Royal Society of Chemistry)Electrospray ionization mass spectrometry ESI-MS is a powerful technique for the characterization of macromols. and their noncovalent binding with guest ions. The authors herein evaluate the feasibility of using ESI-MS as a screening tool for predicting potentiometric selectivities of ionophores. Ion-selective electrodes based on the cyclic peptide, cyclosporin A, were developed, and their potentiometric selectivity pattern was evaluated. Optimized electrodes demonstrated near-Nernstian slopes with micromolar detection limits toward calcium. ESI-MS and ESI-MS/MS were employed to det. the relative assocn. strengths of cyclosporin A with various cations. The obsd. MS intensities of ion-ionophore complexes correlate favorably with the potentiometric selectivity pattern that was demonstrated by cyclosporin-based electrodes. This correlation holds true for other established ionophores, such as valinomycin and benzo-18-crown-6. Taken together, these expts. demonstrate that mass spectrometry could be used to predict the selectivity patterns of new ionophores for potentiometric and optical ion sensors. Further, this approach could be useful in screening mixts. or libraries of newly-synthesized compds. to identify selective ionophores.
- 114Guinovart, T.; Hernandez-Alonso, D.; Adriaenssens, L.; Blondeau, P.; Martinez-Belmonte, M.; Rius, F. X.; Andrade, F. J.; Ballester, P. Recognition and Sensing of Creatinine. Angew. Chem., Int. Ed. 2016, 55, 2435– 2440, DOI: 10.1002/anie.201510136Google Scholar114https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XmslGhsA%253D%253D&md5=6660d0e43c2e1e32802343bc12ff152dRecognition and Sensing of CreatinineGuinovart, Tomas; Hernandez-Alonso, Daniel; Adriaenssens, Louis; Blondeau, Pascal; Martinez-Belmonte, Marta; Rius, F. Xavier; Andrade, Francisco J.; Ballester, PabloAngewandte Chemie, International Edition (2016), 55 (7), 2435-2440CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)Current methods for creatinine quantification suffer from significant drawbacks when aiming to combine accuracy, simplicity, and affordability. Here, an unprecedented synthetic receptor, an aryl-substituted calix[4]pyrrole with a monophosphonate bridge, is reported that displays remarkable affinity for creatinine and the creatininium cation. The receptor works by including the guest in its deep and polar arom. cavity and establishing directional interactions in three dimensions. When incorporated into a suitable polymeric membrane, this mol. acts as an ionophore. A highly sensitive and selective potentiometric sensor suitable for the detn. of creatinine levels in biol. fluids, such as urine or plasma, in an accurate, fast, simple, and cost-effective way has thus been developed.
- 115Guinovart, T.; Hernandez-Alonso, D.; Adriaenssens, L.; Blondeau, P.; Rius, F. X.; Ballester, P.; Andrade, F. J. Characterization of a new ionophore-based ion-selective electrode for the potentiometric determination of creatinine in urine. Biosens. Bioelectron. 2017, 87, 587– 592, DOI: 10.1016/j.bios.2016.08.025Google Scholar115https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhsFSlt7nF&md5=0083915b99552cbaf23c55b80a74e116Characterization of a new ionophore-based ion-selective electrode for the potentiometric determination of creatinine in urineGuinovart, Tomas; Hernandez-Alonso, Daniel; Adriaenssens, Louis; Blondeau, Pascal; Rius, F. Xavier; Ballester, Pablo; Andrade, Francisco J.Biosensors & Bioelectronics (2017), 87 (), 587-592CODEN: BBIOE4; ISSN:0956-5663. (Elsevier B.V.)The optimization, anal. characterization and validation of a novel ion-selective electrode for the highly sensitive and selective detn. of creatinine in urine is presented. A newly synthesized calix[4]pyrrole-based mol. is used as an ionophore for the enhanced recognition of creatininium cations. The calcn. of the complex formation consts. in the polymeric membrane with creatininium, potassium and sodium confirms the strong selective interactions between the ionophore and the target. The optimization of the potentiometric sensor presented here yields an outstanding anal. performance, with a linear range that spans from 1μM to 10 mM and limit of detection of 10-6.2 M. The calcn. of the selectivity coeffs. against most commonly found interferences also show significant improvements when compared to other sensors already reported. The performance of this novel sensor is tested by measuring creatinine in real urine samples (N=50) and comparing the values against the std. colorimetric approach (Jaffe's reaction). The results show that this sensor allows the fast and accurate detn. of creatinine in real samples with minimal sample manipulation.
- 116Khaled, E.; Khalil, M. M.; el Aziz, G. M. A. Calixarene/carbon nanotubes based screen printed sensors for potentiometric determination of gentamicin sulphate in pharmaceutical preparations and spiked surface water samples. Sens. Actuators, B 2017, 244, 876– 884, DOI: 10.1016/j.snb.2017.01.033Google Scholar116https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtFOmsbw%253D&md5=ac2b35ec414d628c2f4972f2b51ee51eCalixarene/carbon nanotubes based screen printed sensors for potentiometric determination of gentamicin sulphate in pharmaceutical preparations and spiked surface water samplesKhaled, Elmorsy; Khalil, M. M.; Abed el Aziz, G. M.Sensors and Actuators, B: Chemical (2017), 244 (), 876-884CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)Sensitive disposable sensors have been introduced for potentiometric detn. of gentamicin sulfate (GNS) based on multi-walled carbon nanotubes-polyvinyl chloride (MWNTs-PVC) composite in presence of calixarene as a mol. recognition element. The proposed sensors showed remarkable selectivity and sensitivity in the GNS concn. range from 10-7 to 10-2 mol L-1 with Nernstian slope 30.5 ± 0.4 mV decade-1 and detection limit of 7.5 × 10-8 mol L-1. Modification with carbon nanotubes improved the sensors performance was through promotion of the electron-transfer processes and enhancing the stability of potential reading, response time, and shelf lifetime of sensors. The proposed method has been applied for the potentiometric assay of GNS in different dosage forms and spiked surface water samples with av. recoveries agreeable with the reported official method.
- 117Bliem, C.; Fruhmann, P.; Stoica, A. I.; Kleber, C. Development and Optimization of an Ion-selective Electrode for Serotonin Detection. Electroanalysis 2017, 29, 1635– 1642, DOI: 10.1002/elan.201600782Google Scholar117https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXlsV2htLw%253D&md5=fb25c2c6431bece736393c25b4be552eDevelopment and Optimization of an Ion-selective Electrode for Serotonin DetectionBliem, Christina; Fruhmann, Philipp; Stoica, Anca-Iulia; Kleber, ChristophElectroanalysis (2017), 29 (6), 1635-1642CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)The authors' studies are focused on the development of novel potentiometric sensors for the quantification of the neurotransmitter serotonin. Therefore, ion-selective electrodes based on plasticized PVC membranes are applied. The electroactive part of the membrane consists of an ion pair complex formed between the protonated analyte and a carborane anion [Co(1,2-C2B9H11)2]-. The anal. performance of the electrode was studied regarding sensitivity, concn. range, limit of detection and potential stability. The ion-selective electrodes were optimized with respect to the material of the transducing element, as well as the membrane thickness and its compn. Stable, all solid state ISEs could be developed, using the non-polar plasticizer NPOE and a graphite rod with high surface area as transducing element. The authors thus achieved a near Nernstian response over three decades of concn. (2.25·10-5-1.00·10-2 M) and a limit of detection in the μ-molar range for the optimized electrodes. The electrodes could successfully be miniaturized using carbon based screen printed electrodes.
- 118Hu, J. B.; Stein, A.; Bühlmann, P. A Disposable Planar Paper-Based Potentiometric Ion-Sensing Platform. Angew. Chem., Int. Ed. 2016, 55, 7544– 7547, DOI: 10.1002/anie.201603017Google Scholar118https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XotFOjsb8%253D&md5=fb55fa74ec04449887a57125222470c7A Disposable Planar Paper-Based Potentiometric Ion-Sensing PlatformHu, Jinbo; Stein, Andreas; Buehlmann, PhilippeAngewandte Chemie, International Edition (2016), 55 (26), 7544-7547CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)Ion-selective electrodes (ISEs) are widely used tools for fast and accurate ion sensing. Herein their design is simplified by embedding a potentiometric cell into paper, complete with an ISE, a ref. electrode, and a paper-based microfluidic sample zone that offer the full function of a conventional ISE setup. The disposable planar paper-based ion-sensing platform is suitable for low-cost point-of-care and in-field testing applications. The design is sym. and each interfacial potential within the cell is well defined and reproducible, so that the response of the device can be theor. predicted. For a demonstration of clin. applications, paper-based Cl- and K+ sensors are fabricated with highly reproducible and linear responses towards different concns. of analyte ions in aq. and biol. samples. The single-use devices can be fabricated by a scalable method, do not need any pretreatment prior to use, and only require a sample vol. of 20 μL.
- 119Ding, J. W.; Li, B. W.; Chen, L. X.; Qin, W. A Three-Dimensional Origami Paper-Based Device for Potentiometric Biosensing. Angew. Chem., Int. Ed. 2016, 55, 13033– 13037, DOI: 10.1002/anie.201606268Google Scholar119https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhsFams7zE&md5=cde9c02cf5119cba1d2bcbc5f8a67cf8A Three-Dimensional Origami Paper-Based Device for Potentiometric BiosensingDing, Jiawang; Li, Bowei; Chen, Lingxin; Qin, WeiAngewandte Chemie, International Edition (2016), 55 (42), 13033-13037CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)Current paper-based potentiometric ion-sensing platforms are planar devices used for clin. relevant ions. These devices, however, have not been designed for the potentiometric biosensing of proteins or small mol. analytes. A three-dimensional origami paper-based device, in which a solid-contact ion-selective electrode is integrated with an all-solid-state ref. electrode, is described for the first time. The device is made by impregnation of paper with appropriate bioreceptors and reporting reagents on different zones. By folding and unfolding the paper structures, versatile potentiometric bioassays can be performed. A USB-controlled miniaturized electrochem. detector can be used for simple and in situ measurements. Using butyrylcholinesterase as a model enzyme, the device has been successfully applied to the detection of enzyme activities and organophosphate pesticides involved in the enzymic system as inhibitors. The proposed 3D origami paper device allows the potentiometric biosensing of proteins and small mols. in a simple, portable, and cost-effective way.
- 120Fayose, T.; Mendecki, L.; Ullah, S.; Radu, A. Single strip solid contact ion selective electrodes on a pencil-drawn electrode substrate. Anal. Methods 2017, 9, 1213– 1220, DOI: 10.1039/C6AY02860HGoogle Scholar120https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXkvFGqsg%253D%253D&md5=015009457c80c2c9e46495645bbfa2c6Single strip solid contact ion selective electrodes on a pencil-drawn electrode substrateFayose, T.; Mendecki, L.; Ullah, S.; Radu, A.Analytical Methods (2017), 9 (7), 1213-1220CODEN: AMNEGX; ISSN:1759-9679. (Royal Society of Chemistry)A simple and low-cost approach for the prepn. of ion-selective electrodes (ISEs) is proposed as a favorable alternative to traditional paper-based electrodes. This involved the application of graphite from a simple household pencil via mech. abrasion onto a modified acetate sheet. The resulting electrodes exhibited excellent sensing properties towards all tested ions, including a wide dynamic response range, fast response time and satisfactory long-term stability. The same methodol. was used to produce stable and functional ref. electrodes. These electrodes were then combined with other graphite-based ISEs to yield single strip solid-contact electrodes for simultaneous detection of cations and anions in aq. solns. The described approach, which is analogous to simply drawing on paper, opens new avenues for the development of sensing devices using very cheap and easily accessible components.
- 121Sjöberg, P.; Maattanen, A.; Vanamo, U.; Novell, M.; Ihalainen, P.; Andrade, F. J.; Bobacka, J.; Peltonen, J. Paper-based potentiometric ion sensors constructed on ink-jet printed gold electrodes. Sens. Actuators, B 2016, 224, 325– 332, DOI: 10.1016/j.snb.2015.10.051Google Scholar121https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhslGisLjJ&md5=dbf1a614c1de765c811c906254e1cce4Paper-based potentiometric ion sensors constructed on ink-jet printed gold electrodesSjoberg, Pia; Maattanen, Anni; Vanamo, Ulriika; Novell, Marta; Ihalainen, Petri; Andrade, Francisco J.; Bobacka, Johan; Peltonen, JoukoSensors and Actuators, B: Chemical (2016), 224 (), 325-332CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)Printed electrodes on a recyclable low-cost coated paper were used as a platform for constructing potentiometric ion sensors consisting of an ion-selective electrode (ISE) and a ref. electrode (RE). The ref. and working electrodes were printed by using a stable suspension of gold nanoparticles (AuNP) as the ink. Sintering turned the printed electrodes conductive. A poly(3,4-ethylenedioxythiophene) (PEDOT) layer, with poly(styrene sulfonate) (PSS) ions as counterions was deposited on the gold electrodes by electropolymn., drop-casting or ink-jet printing. The ref. electrode was prepd. by further coating the PEDOT(PSS) layer with a poly(vinyl chloride) (PVC) membrane contg. a lipophilic salt, tetrabutylammonium tetrabutylborate (TBA-TBB), thus resulting in a solid-contact ref. electrode (SCRE). The working electrode was modified by coating the PEDOT(PSS) layer with a K+-selective membrane, to obtain a solid-contact K+-ISE. The electrochem. characteristics of the resulting electrode systems were studied by amperometric, potentiometric and electrochem. impedance spectroscopic (EIS) measurements. The potentiometric response toward K+ ions was addnl. studied. The surface structure of the PEDOT(PSS) layers deposited by the different methods was studied with at. force microscopic (AFM) measurements. It was shown that a well-functioning planar electrode platform with good electrochem. characteristics could be prepd. by ink-jet printing in a repeatable manner. The planar electrode platform presented here offers a user-friendly and ecol. alternative to perform chem. anal. from small sample vols.
- 122Armas, S. M.; Manhan, A. J.; Younce, O.; Calvo-Marzal, P.; Chumbimuni-Torres, K. Y. Ready-to-use single-strip paper based sensor for multiplex ion detection. Sens. Actuators, B 2018, 255, 1781– 1787, DOI: 10.1016/j.snb.2017.08.194Google Scholar122https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsVOhs7rL&md5=09afd8324c508423a6a92eddaf933ff8Ready-to-use single-strip paper based sensor for multiplex ion detectionArmas, Stephanie M.; Manhan, Andrew J.; Younce, Olivia; Calvo-Marzal, Percy; Chumbimuni-Torres, Karin Y.Sensors and Actuators, B: Chemical (2018), 255 (Part_2), 1781-1787CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)Ion-selective electrodes (ISEs) are an efficient and versatile tool for ion detection. However, portability and applicability for field applications are often limited by the need of a conditioning step, and high cost of the needed bulky ref. electrode. Herein, the traditional conditioning protocol of ISEs has been eliminated and a paper-based solid-contact ISE (PBSC-ISE) has been integrated with a paper-based solid-contact ref. electrode (PBSC-RE) in a single strip format for on-site anal. The PBSC-RE is based on the copolymer Me methacrylate-co-decyl methacrylate (MMA-DMA) (support matrix), combined with ionic liqs. (ILs) to create and maintain a stable potential that is un-affected by a change in ionic activity. This single-strip ready-to-use sensor yields a Nernstian response towards Na+, K+, and I- ions with submicromolar limits of detection, and is able to be used for multiplex anal.
- 123Parrilla, M.; Canovas, R.; Andrade, F. J. Enhanced Potentiometric Detection of Hydrogen Peroxide Using a Platinum Electrode Coated with Nafion. Electroanalysis 2017, 29, 223– 230, DOI: 10.1002/elan.201600403Google Scholar123https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhsVChtb%252FK&md5=eedf00f03fbb36904c4e782296c51676Enhanced Potentiometric Detection of Hydrogen Peroxide Using a Platinum Electrode Coated with NafionParrilla, Marc; Canovas, Rocio; Andrade, Francisco J.Electroanalysis (2017), 29 (1), 223-230CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)The potentiometric response to hydrogen peroxide of a platinum electrode coated with a layer of Nafion is presented. The Nafion membrane acts as an effective permselective barrier, thus significantly reducing the response to some redox active species, such as ascorbate. Even more interesting, these coated electrodes show a significantly enhanced sensitivity to hydrogen peroxide (H2O2) when the measurements were performed in solns. of high ionic strength. The influence of pH, ionic strength and supporting electrolyte on this enhancement are presented. Under optimized conditions these coated electrodes show a linear dependence with the logarithm of the concn. of H2O2, with sensitivities of -125.1 ± 5.9 mV decade-1 (several times higher than the bare electrodes) and a linear range that spans from 10-5 M to 10-3 M of H2O2. Preliminary studies suggest that the coupling between the redox potential on the Pt electrode and the Donnan potential of the membrane plays a role on this enhancement. Considering this improved sensitivity, selectivity, stability and linear ranges, this system shows promise as a future platform to build enzyme-based potentiometric biosensors.
- 124Canovas, R.; Parrilla, M.; Blondeau, P.; Andrade, F. J. A novel wireless paper-based potentiometric platform for monitoring glucose in blood. Lab Chip 2017, 17, 2500– 2507, DOI: 10.1039/C7LC00339KGoogle Scholar124https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXpvFyjtr8%253D&md5=010b78d249d3b04343810ec70bc639d7A novel wireless paper-based potentiometric platform for monitoring glucose in bloodCanovas, Rocio; Parrilla, Marc; Blondeau, Pascal; Andrade, Francisco J.Lab on a Chip (2017), 17 (14), 2500-2507CODEN: LCAHAM; ISSN:1473-0189. (Royal Society of Chemistry)A novel low-cost, compact and sensitive paper-based platform for the accurate monitoring of glucose in biol. fluids is presented. Paper-based working and ref. electrodes are combined to build a whole potentiometric cell, which also fits a sampling module for simple and fast detn. of glucose in a single drop of blood. The working electrode is built using a platinized filter paper coated with a Nafion membrane that entraps the enzyme glucose oxidase; the ref. electrode is made by casting a polyvinylbutyral-based membrane onto a conductive paper. The system works by detecting the hydrogen peroxide generated as a result of the enzymic reaction. Selectivity is achieved due to the permselective behavior of Nafion, while a significant enhancement of the sensitivity is reached by exploiting the Donnan-coupled formal potential. Under optimum conditions, a sensitivity of -95.9 ± 4.8 mV per decade in the 0.3-3 mM range is obtained. Validation of the measurements has been performed against std. methods in human serum and blood. Final integration with a wireless reader allows for truly in situ measurements with a less than 2 min procedure including a two-point calibration, washing and measurement. This low-cost anal. device opens up new prospects for rapid diagnostic results in non-lab. settings.
- 125Guadarrama-Fernandez, L.; Novell, M.; Blondeau, P.; Andrade, F. J. A disposable, simple, fast and low-cost paper-based biosensor and its application to the determination of glucose in commercial orange juices. Food Chem. 2018, 265, 64– 69, DOI: 10.1016/j.foodchem.2018.05.082Google Scholar125https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXpslynuro%253D&md5=a291e815dd24aa3244588fdac06d701cA disposable, simple, fast and low-cost paper-based biosensor and its application to the determination of glucose in commercial orange juicesGuadarrama-Fernandez, Leonor; Novell, Marta; Blondeau, Pascal; Andrade, Francisco J.Food Chemistry (2018), 265 (), 64-69CODEN: FOCHDJ; ISSN:0308-8146. (Elsevier Ltd.)A new biosensor for monitoring glucose levels in beverages is presented. The measurements are performed using potentiometric detection. Working electrodes are made using platinized paper as support and a biocompatible polymeric membrane made of a mixt. of polyvinyl alc. and chitosan contg. glucose oxidase as the recognition layer. The system is based on the detection of the hydrogen peroxide generated by an enzymic reaction performed in a highly sensitive, selective and simple way. The biosensors display suitable anal. performance (sensitivity -119.6 ± 6.4 mV/dec in the 0.03-1.0 mM range with a limit of detection of 0.02 mM). Detn. of glucose in com. orange juices is presented. These results were validated against conventional std. methods, showing good accuracy and fast anal. response. The methodol. presented herein does not require complex samples treatment, offering an alternative to conventional methods, particularly for detns. performed with minimal expertise and without a lab. infrastructure.
- 126Ruecha, N.; Chailapakul, O.; Suzuki, K.; Citterio, D. Fully Inkjet-Printed Paper-Based Potentiometric Ion-Sensing Devices. Anal. Chem. 2017, 89, 10608– 10616, DOI: 10.1021/acs.analchem.7b03177Google Scholar126https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtl2lsb%252FP&md5=4e2561055b025bd1c18573ce72a4c5a0Fully Inkjet-Printed Paper-Based Potentiometric Ion-Sensing DevicesRuecha, Nipapan; Chailapakul, Orawon; Suzuki, Koji; Citterio, DanielAnalytical Chemistry (Washington, DC, United States) (2017), 89 (19), 10608-10616CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)A fully inkjet-printed disposable and low cost paper-based device for potentiometric Na+- or K+-ion sensing has been developed. A printed ionophore-based all-solid-state ion selective electrode on a graphene/poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (G/PEDOT:PSS) nanocomposite solid contact and a printed all-solid state ref. electrode consisting of a pseudosilver/silver chloride electrode coated by a lipophilic salt-incorporating poly(vinyl chloride) membrane overprinted with potassium chloride have been combined on a microfluidically patterned paper substrate. Devices are built on std. filter paper using off-the-shelf materials. Ion sensing has been achieved within 180 s by simple addn. of 20 μL of sample soln. without electrode preconditioning. The limits of detection were 32 and 101 μM for Na+ and K+, resp. The individual single-use sensing devices showed near Nernstian response of 62.5 ± 2.1 mV/decade (Na+) and 62.9 ± 1.1 mV/decade (K+) with excellent std. potential (E0) reproducibilities of 455.7 ± 5.1 mV (Na+) and 433.9 ± 2.8 mV (K+). The current work demonstrates the promising possibility of obtaining low-cost and disposable paper-based potentiometric sensing devices potentially manufacturable at large scales with industrial inkjet printing technol.
- 127Nery, E. W.; Kubota, L. T. Integrated, paper-based potentiometric electronic tongue for the analysis of beer and wine. Anal. Chim. Acta 2016, 918, 60– 68, DOI: 10.1016/j.aca.2016.03.004Google Scholar127https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XkvVertr8%253D&md5=2946d80323c8778ee97becbbb1a57922Integrated, paper-based potentiometric electronic tongue for the analysis of beer and wineNery, Emilia Witkowska; Kubota, Lauro T.Analytica Chimica Acta (2016), 918 (), 60-68CODEN: ACACAM; ISSN:0003-2670. (Elsevier B.V.)The following manuscript details the stages of construction of a novel paper-based electronic tongue with an integrated Ag/AgCl ref., which can operate using a minimal amt. of sample (40 μL). First, we optimized the fabrication procedure of silver electrodes, testing a set of different methodologies (electroless plating, use of silver nanoparticles and com. silver paints). Later a novel, integrated electronic tongue system was assembled with the use of readily available materials such as paper, wax, lamination sheets, bleach etc. New system was thoroughly characterized and the ion-selective potentiometric sensors presented performance close to theor. An electronic tongue, composed of electrodes sensitive to sodium, calcium, ammonia and a cross-sensitive, anion-selective electrode was used to analyze 34 beer samples (12 types, 19 brands). This system was able to discriminate beers from different brands, and types, indicate presence of stabilizers and antioxidants, dyes or even unmalted cereals and carbohydrates added to the fermn. wort. Samples could be classified by type of fermn. (low, high) and system was able to predict pH and in part also alc. content of tested beers. In the next step sample vol. was minimalized by the use of paper sample pads and measurement in flow conditions. In order to test the impact of this advancement a four electrode system, with cross-sensitive (anion-selective, cation-selective, Ca2+/Mg2+, K+/Na+) electrodes was applied for the anal. of 11 types of wine (4 types of grapes, red/white, 3 countries). Proposed matrix was able to group wines produced from different varieties of grapes (Chardonnay, Americanas, Malbec, Merlot) using only 40 μL of sample. Apart from that, storage stability studies were performed using a multimeter, therefore showing that not only fabrication but also detection can be accomplished by means of off-the-shelf components. This manuscript not only describes new paper-based, potentiometric sensors but also according to our knowledge is the first description of an electrochem. paper-based electronic tongue with integrated ref.
- 128Ding, J. W.; He, N.; Lisak, G.; Qin, W.; Bobacka, J. Paper-based microfluidic sampling and separation of analytes for potentiometric ion sensing. Sens. Actuators, B 2017, 243, 346– 352, DOI: 10.1016/j.snb.2016.11.128Google Scholar128https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XitVaqtbfP&md5=b7a2d516f1b32342fb23cc68c58e85ebPaper-based microfluidic sampling and separation of analytes for potentiometric ion sensingDing, Jiawang; He, Ning; Lisak, Grzegorz; Qin, Wei; Bobacka, JohanSensors and Actuators, B: Chemical (2017), 243 (), 346-352CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)This work demonstrates a paper-based microfluidic sampling and sepn. platform that allows potentiometric sensing of chloride ions in presence of strongly interfering salicylate ions using a solid-contact ion-selective electrode as a detector. The device was composed of two pieces of paper with different shapes and pore sizes. A "T" shaped filter paper with a pore size of 12-25μm was used as the detection zone. A filter paper with a pore size of 2.0μm was modified with a complexing agent (Fe3+) and served as the sepn. zone. The two pieces of the paper were joined together just like a jigsaw. A solid-contact Cl- -selective electrode and a ref. electrode were gently pressed onto the detection zone to create a direct contact between the electrodes and the soln. absorbed in the paper. Utilizing the possibility to form stable complexes between Fe3+ and salicylate, the proposed platform enables the sepn. of salicylate and detection of chloride. This system offers a convenient platform for both sampling and sepn. of ions, in which sample pretreatment procedures can be simplified or avoided.
- 129Farzbod, A.; Moon, H. Integration of reconfigurable potentiometric electrochemical sensors into a digital microfluidic platform. Biosens. Bioelectron. 2018, 106, 37– 42, DOI: 10.1016/j.bios.2018.01.048Google Scholar129https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXitV2ktbo%253D&md5=004c40164a66a48f9ae89d6ccde35ec4Integration of reconfigurable potentiometric electrochemical sensors into a digital microfluidic platformFarzbod, Ali; Moon, HyejinBiosensors & Bioelectronics (2018), 106 (), 37-42CODEN: BBIOE4; ISSN:0956-5663. (Elsevier B.V.)This paper presents the demonstration of on-chip fabrication of a potassium-selective sensor array enabled by electrowetting on dielec. digital microfluidics for the first time. This demonstration proves the concept that electrochem. sensors can be seamlessly integrated with sample prepn. units in a digital microfluidic platform. More significantly, the successful on-chip fabrication of a sensor array indicates that sensors become reconfigurable and have longer lifetime in a digital microfluidic platform. The on-chip fabrication of ion-selective electrodes includes electroplating Ag followed by forming AgCl layer by chem. oxidn. and depositing a thin layer of desired polymer-based ion selective membrane on one of the sensor electrodes. In this study, potassium ionophores work as potassium ion channels and make the membrane selective to potassium ions. This selectiveness results in the voltage difference across the membrane layer, which is correlated with potassium ion concn. The calibration curve of the fabricated potassium-selective electrode demonstrates the slope of 58mV/dec for potassium concn. in KCl sample solns. and shows good agreement with the ideal Nernstian response. The proposed sensor platform is an outstanding candidate for a portable home-use for continuous monitoring of ions thanks to its advantages such as easy automation of sample prepn. and detection processes, elongated sensor lifetime, minimal membrane and sample consumption, and user-definable/reconfigurable sensor array.
- 130Gosselin, D.; Gougis, M.; Baque, M.; Navarro, F. P.; Belgacem, M. N.; Chaussy, D.; Bourdat, A.-G.; Mailley, P.; Berthier, J. Anal. Chem. 2017, 89, 10124– 10128, DOI: 10.1021/acs.analchem.7b02394Google Scholar130https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsVKmurzN&md5=82a3104e867d7bb279283887c6aea325Screen-Printed Polyaniline-Based Electrodes for the Real-Time Monitoring of Loop-Mediated Isothermal Amplification ReactionsGosselin, David; Gougis, Maxime; Baque, Melissa; Navarro, Fabrice P.; Belgacem, Mohamed N.; Chaussy, Didier; Bourdat, Anne-Gaelle; Mailley, Pascal; Berthier, JeanAnalytical Chemistry (Washington, DC, United States) (2017), 89 (19), 10124-10128CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Nucleic acid amplification testing is a very powerful method to perform efficient and early diagnostics. However, the integration of a DNA amplification reaction with its assocd. detection in a low-cost, portable, and autonomous device remains challenging. Addressing this challenge, the use of screen-printed electrochem. sensor is reported. To achieve the detection of the DNA amplification reaction, a real-time monitoring of the hydronium ions concn., a byproduct of this reaction, is performed. Such measurements are done by potentiometry using polyaniline (PAni)-based working electrodes and silver/silver chloride ref. electrodes. The developed potentiometric sensor is shown to enable the real-time monitoring of a loop-mediated isothermal amplification (LAMP) reaction with an initial no. of DNA strands as low as 10 copies. In addn., the performance of this PAni-based sensor is compared to fluorescence measurements, and it is shown that similar results are obtained for both methods.
- 131Wang, S. Q.; Wu, Y. J.; Gu, Y.; Li, T.; Luo, H.; Li, L. H.; Bai, Y. Y.; Li, L. L.; Liu, L.; Cao, Y. D.; Ding, H. Y.; Zhang, T. Wearable Sweatband Sensor Platform Based on Gold Nanodendrite Array as Efficient Solid Contact of Ion-Selective Electrode. Anal. Chem. 2017, 89, 10224– 10231, DOI: 10.1021/acs.analchem.7b01560Google Scholar131https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsVWmsr3O&md5=c2dd63e8ce8ecb156540659eb1f97a05Wearable Sweatband Sensor Platform Based on Gold Nanodendrite Array as Efficient Solid Contact of Ion-Selective ElectrodeWang, Shuqi; Wu, Yongjin; Gu, Yang; Li, Tie; Luo, Hui; Li, Lian-Hui; Bai, Yuanyuan; Li, Lili; Liu, Lin; Cao, Yudong; Ding, Haiyan; Zhang, TingAnalytical Chemistry (Washington, DC, United States) (2017), 89 (19), 10224-10231CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)As chem. sensors are in great need for portable and wearable anal. applications, effort is highly desired to develop all-solid-state ion-selective electrode (ISE) and ref. electrode (RE) platform that can match simplicity and stability. Here we proposed a wearable sensor platform with a new type of all-solid-state ISE based on a gold nanodendrites (AuNDs) array electrode as the solid contact and a polyvinyl acetate/inorg. salt (PVA/KCl) membrane coated all-solid-state RE. A simple and controllable method was developed to fabricate the AuNDs on a microwell array patterned chip by one-step electrodeposition without addnl. process. For the first time, the AuNDs electrodes with different real surface area and double layer capacitance were developed as solid contact of the Na+-ISE to investigate the relationship between the performance of the ISE and the value of surface area. The as-prepd. AuNDs-ISE with larger surface area (∼7.23 cm2) exhibited an enhanced potential stability in comparison with the smaller surface area of AuNDs-ISE (∼1.85 cm2) and the bare Au ISE. Important as the ISE, the PVA/KCl membrane coated Ag/AgCl RE exhibited a very stable potential even after 3 mo' storage. Finally, a wearable "Sweatband" sensor platform was developed for efficient sweat collection and real-time anal. of sweat sodium during an indoor exercise. This all-solid-state ISE and RE integrated sensor platform provided a very simple and reliable way to construct diverse portable and wearable devices for healthcare, sports, clin. diagnosis and environmental anal. applications.
- 132Parrilla, M.; Ferre, J.; Guinovart, T.; Andrade, F. J. Wearable Potentiometric Sensors Based on Commercial Carbon Fibres for Monitoring Sodium in Sweat. Electroanalysis 2016, 28, 1267– 1275, DOI: 10.1002/elan.201600070Google Scholar132https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XmtVKitrY%253D&md5=b208edea4cbfdf01f5f392fa7f742a09Wearable Potentiometric Sensors Based on Commercial Carbon Fibres for Monitoring Sodium in SweatParrilla, Marc; Ferre, Jordi; Guinovart, Tomas; Andrade, Francisco J.Electroanalysis (2016), 28 (6), 1267-1275CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)The use of com. carbon fibers (CCF) to build wearable potentiometric sensors for the real-time monitoring of sodium levels in sweat during exercise is presented. CCF are an attractive substrate for building wearable electrochem. sensors because of their good elec. cond., chem. inertness, flexibility and mech. resilience. In the first part of this work, the anal. performance of these novel potentiometric ion-selective electrodes made with CCFs is presented. Then, through the incorporation of a solid-contact ref. electrode, the development of a complete miniaturized potentiometric cell with a Nernstian response (59.2±0.6 mV/log [Na+], N=4) is obtained. Finally, the cell is integrated into a wearable patch and attached onto the skin of an athlete. The anal. characterization of the wearable patch shows a near-Nernstian response (55.9±0.8 mV/log [Na+], N=3) for sodium levels from 10-3 M to 10-1 M in artificial sweat, well within the physiol. range of interest. The device shows low noise levels and very good stability (-0.4±0.3 mV · h-1). To improve the usability of the sensor in real scenarios, a calibration-free approach is also explored. This platform opens new and attractive avenues for the generation of meaningful personalized physiol. information that could be applied - among many other fields - in sports, nutrition and healthcare.
- 133Matzeu, G.; O’Quigley, C.; McNamara, E.; Zuliani, C.; Fay, C.; Glennon, T.; Diamond, D. An integrated sensing and wireless communications platform for sensing sodium in sweat. Anal. Methods 2016, 8, 64– 71, DOI: 10.1039/C5AY02254AGoogle Scholar133https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhslKltbvI&md5=02299a3c317c690e63d5218719a5a4a0An integrated sensing and wireless communications platform for sensing sodium in sweatMatzeu, G.; O'Quigley, C.; McNamara, E.; Zuliani, C.; Fay, C.; Glennon, T.; Diamond, D.Analytical Methods (2016), 8 (1), 64-71CODEN: AMNEGX; ISSN:1759-9679. (Royal Society of Chemistry)The ability to non-invasively monitor sodium levels in sweat is of significant importance. Sodium is one of the preferred markers to diagnose and track the progression of cystic fibrosis, and knowledge of sodium levels could potentially enable personalized hydration strategies to be implemented for athletes or people working under severe environmental conditions. Herein we present a novel approach for the realization of disposable potentiometric strips that allow for real-time monitoring of sodium in sweat. Our platform consists of a Solid-Contact Ion-Selective Electrode (SC-ISE) for Na+ detection and of a liq.-junction-free Ref. Electrode (RE), combined together on a dual screen-printed substrate. Different poly-3,4-ethylenedioxythiophene (PEDOT) based films were tested as solid-contact, showing a significant impact on sensor characteristics such as sensitivity (i.e. differing from sub-Nernstian to Nernstian), dynamic range (i.e. 10-5 to 10-2.5 or 10-5 to 10-1aNa+), and esp. within-batch reproducibility. The SC-ISE/RE combination was integrated into a microfluidic chip that was tested and optimized via on-bench trials. The Potentiometric Microfluidic Chip (PotMicroChip) was then connected to a wireless electronic platform to realize a wearable device whose performance was assessed during real-time stationary cycling sessions.
- 134Glennon, T.; O’Quigley, C.; McCaul, M.; Matzeu, G.; Beirne, S.; Wallace, G. G.; Stroiescu, F.; O’Mahoney, N.; White, P.; Diamond, D. ″SWEATCH’: A Wearable Platform for Harvesting and Analysing Sweat Sodium Content. Electroanalysis 2016, 28, 1283– 1289, DOI: 10.1002/elan.201600106Google Scholar134https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XmvFaktrY%253D&md5=656bb51bdf0fe5ec9e8ffcccea8c9e72'SWEATCH': A Wearable Platform for Harvesting and Analysing Sweat Sodium ContentGlennon, Tom; O'Quigley, Conor; McCaul, Margaret; Matzeu, Giusy; Beirne, Stephen; Wallace, Gordon G.; Stroiescu, Florin; O'Mahoney, Niamh; White, Paddy; Diamond, DermotElectroanalysis (2016), 28 (6), 1283-1289CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)A platform for harvesting and analyzing the sodium content of sweat in real time is presented. One is a 'watch' format in which the sampling and fluidic system, electrodes, circuitry and battery are arranged vertically, while in the other 'pod' format, the electronics and battery components, and the fluidics electrodes are arranged horizontally. The platforms are designed to be securely attached to the skin using a velcro strap. Sweat enters into the device through a sampling orifice and passes over solid-state sodium-selective and ref. electrodes and into a storage area contg. a high capacity adsorbent material. The liq. movement is entirely driven by capillary action, and the flow rate through the device can be mediated through variation of the width of a fluidic channel linking the electrodes to the sample storage area. Changing the width dimension through 750, 500 and 250 μm produces flow rates of 38.20, 21.48 and 6.61 μL/min, resp. Variation of the sweat uptake rate and the storage vol. capacity enables the duration of usage to be varied according to the needs of the user. The devices can be easily disassembled to replace the electrodes and the high capacity adsorbent material. The storage sweat is available for subsequent measurement of the total vol. of sweat harvested and the av. concn. of sodium over the period of use. Signals generated by the electrodes are passed to a custom designed electronics board with high input impedance to accurately capture the voltage. The real-time data is transmitted wirelessly using incorporated Bluetooth circuitry to a remote basestation (laptop, mobile phone, tablet) for data visualization and storage in std. formats. Results obtained during trials over a period of ca. 30 min controlled exercise are consistent with previously published data, showing a gradual relatively slow increase of the sodium concn. in the sweat during this period.
- 135Roy, S.; David-Pur, M.; Hanein, Y. Carbon Nanotube-Based Ion Selective Sensors for Wearable Applications. ACS Appl. Mater. Interfaces 2017, 9, 35169– 35177, DOI: 10.1021/acsami.7b07346Google Scholar135https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsFWhu73O&md5=775c010f2119fac7042ad407de1319aeCarbon Nanotube-Based Ion Selective Sensors for Wearable ApplicationsRoy, Soumyendu; David-Pur, Moshe; Hanein, YaelACS Applied Materials & Interfaces (2017), 9 (40), 35169-35177CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)Wearable electronics offer new opportunities in a wide range of applications, esp. sweat anal. using skin sensors. A fundamental challenge in these applications is the formation of sensitive and stable electrodes. In this article we report the development of a wearable sensor based on carbon nanotube (CNT) electrode arrays for sweat sensing. Solid-state ion selective electrodes (ISEs), sensitive to Na+ ions, were prepd. by drop coating plasticized poly(vinyl chloride) (PVC) doped with ionophore and ion exchanger on CNT electrodes. The ion selective membrane (ISM) filled the intertubular spaces of the highly porous CNT film and formed an attachment that was stronger than that achieved with flat Au, Pt, or carbon electrodes. Concn. of the ISM soln. used influenced the attachment to the CNT film, the ISM surface morphol., and the overall performance of the sensor. Sensitivity of 56 ± 3 mV/decade to Na+ ions was achieved. Optimized solid-state ref. electrodes (REs), suitable for wearable applications, were prepd. by coating CNT electrodes with colloidal dispersion of Ag/AgCl, agarose hydrogel with 0.5 M NaCl, and a passivation layer of PVC doped with NaCl. The CNT-based REs had low sensitivity (-1.7 ± 1.2 mV/decade) toward the NaCl soln. and high repeatability and were superior to bare Ag/AgCl, metals, carbon, and CNT films, reported previously as REs. CNT-based ISEs were calibrated against CNT-based REs, and the short-term stability of the system was tested. We demonstrate that CNT-based devices implemented on a flexible support are a very attractive platform for future wearable technol. devices.
- 136Parrilla, M.; Canovas, R.; Jeerapan, I.; Andrade, F. J.; Wang, J. A Textile-Based Stretchable Multi-Ion Potentiometric Sensor. Adv. Healthcare Mater. 2016, 5, 996– 1001, DOI: 10.1002/adhm.201600092Google Scholar136https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XjvVyku7s%253D&md5=03e2a02c3c32dd0fd4da4ce09e00624bA Textile-Based Stretchable Multi-Ion Potentiometric SensorParrilla, Marc; Canovas, Rocio; Jeerapan, Itthipon; Andrade, Francisco J.; Wang, JosephAdvanced Healthcare Materials (2016), 5 (9), 996-1001CODEN: AHMDBJ; ISSN:2192-2640. (Wiley-VCH Verlag GmbH & Co. KGaA)This article reports a highly stretchable and printable textile-based potentiometric sensor array for simultaneous multi-ion sweat anal. using variety of fabric materials towards diverse healthcare and fitness applications. Textile-based potentiometric sensors was fabricated by combining polyurethane-based ion- selective membranes and inks with a serpentine sensor pattern and stretch-enduring printed electrodes. Combining stretchable components like polyurethane, Ecoflex, and stretch-enduring inks, along with a serpentine design, this printed textile sensor array can withstand high tensile stress and mech. deformation and can thus act as an efficient wearable biomedical sensor.
- 137Choi, D.-H.; Kim, J. S.; Cutting, G. R.; Searson, P. C. Anal. Chem. 2016, 88, 12241– 12247, DOI: 10.1021/acs.analchem.6b03391Google Scholar137https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhvVGqtr7F&md5=7f8490e716d0380dff93142c675dcfeeWearable Potentiometric Chloride Sweat Sensor: The Critical Role of the Salt BridgeChoi, Dong-Hoon; Kim, Jin Seob; Cutting, Garry R.; Searson, Peter C.Analytical Chemistry (Washington, DC, United States) (2016), 88 (24), 12241-12247CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)The components of sweat provide an array of potential biomarkers for health and disease. Sweat chloride is of interest as a biomarker for cystic fibrosis, electrolyte metab. disorders, electrolyte balance, and electrolyte loss during exercise. Developing wearable sensors for biomarkers in sweat is a major technol. challenge. Potentiometric sensors provide a relatively simple technol. for on-body sweat chloride measurement; however, equilibration between ref. and test solns. has limited the time over which accurate measurements can be made. Here, the authors report on a wearable potentiometric chloride sweat sensor. The authors performed parametric studies to show how the salt bridge geometry dets. equilibration between the ref. and test solns. The authors show that a sweat chloride sensor can be designed to provide accurate measurements over extended times. The authors then performed on-body tests on healthy subjects while exercising to establish the feasibility of using this technol. as a wearable device.
- 138Zoerner, A.; Oertel, S.; Jank, M. P. M.; Frey, L.; Langenstein, B.; Bertsch, T. Human Sweat Analysis Using a Portable Device Based on a Screen-printed Electrolyte Sensor. Electroanalysis 2018, 30, 665– 671, DOI: 10.1002/elan.201700672Google Scholar138https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhvFyjsrbM&md5=ee00482c05536765957ede8ae3084ba9Human Sweat Analysis Using a Portable Device Based on a Screen-Printed Electrolyte SensorZoerner, Alicia; Oertel, Susanne; Jank, Michael P. M.; Frey, Lothar; Langenstein, Bernd; Bertsch, ThomasElectroanalysis (2018), 30 (4), 665-671CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)Anal. of ammonium in human sweat during phys. strain using a portable sensor device and enzymic measurements are compared. The portable device is based on a screen-printed electrolyte sensor connected with an evaluation board for data acquisition and transfer. During performance tests with artificial sweat, the sensor shows a low detection limit of 0.3 mM. Thus, the typical concn. range of ammonium in sweat lies within the working range of the sensor. The authors also demonstrate the necessity of the comparison measurement for verification of the correct performance of screen-printed sensors and show how other components of human sweat influence the measured potential. Regarding the change in ammonium concn. during different levels of work out intensity, the authors point out a different behavior of what is expected physiol. With this the importance of consideration of several parameters during sweating, like the sweat rate and other ingredients in human sweat, was demonstrated for correct detn. of the ammonium concn.
- 139Hoekstra, R.; Blondeau, P.; Andrade, F. J. IonSens: A Wearable Potentiometric Sensor Patch for Monitoring Total Ion Content in Sweat. Electroanalysis 2018, 30, 1536– 1544, DOI: 10.1002/elan.201800128Google Scholar139https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhtVShurnI&md5=025f15ccc164a86e56591454bd055c3bIonSens: a Wearable Potentiometric Sensor Patch for Monitoring Total Ion Content in SweatHoekstra, Rafael; Blondeau, Pascal; Andrade, Francisco J.Electroanalysis (2018), 30 (7), 1536-1544CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)A sensor for monitoring total ion activity is described, and its performance as a wearable device for monitoring the total ion levels of sweat is evaluated. The sensor works by tracking changes in the Donnan potential generated across a Nafion membrane. This cation-exchange polymer was cast on a paper coated with carbon-ink, making the platform elegantly simple. Anal. parameters during calibration in aq. soln. include a sensitivity of 56.3±1.0 mV/dec.a(Na+) and a std. deviation between std. electrode potentials of 5.3 mV (N=5) for first time use. By integrating a paper-based pseudo-ref. electrode, a miniature disposable electrochem. cell (the "IonSens" device) was created and demonstrated as a wearable sensor. Potentiometric measurements estg. the total ion activities were validated against cond. measurements. Recoveries of eleven raw sweat samples were detd. to be 95.2±6.6 % (n=3). The perspiration cond. profile of an athlete during exercise was monitored in real-time and visualized on a mobile phone application connected via Bluetooth. The excellent reproducibility of the electrode without any conditioning is noteworthy and lends itself to applications including - but not limited to - the monitoring of total ion activity in sweat.
- 140Uria, N.; Abramova, N.; Bratov, A.; Muñoz-Pascual, F.-X.; Baldrich, E. Talanta 2016, 147, 364– 369, DOI: 10.1016/j.talanta.2015.10.011Google Scholar140https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhs1Gku7bO&md5=b5c2178e67cbfd67df4651d6ade3a9baMiniaturized metal oxide pH sensors for bacteria detectionUria, Naroa; Abramova, Natalia; Bratov, Andrey; Munoz-Pascual, Francesc-Xavier; Baldrich, EvaTalanta (2016), 147 (), 364-369CODEN: TLNTA2; ISSN:0039-9140. (Elsevier B.V.)It is well known that the metabolic activity of some microorganisms results in changes of pH of the culture medium, a phenomenon that can be used for detection and quantification of bacteria. However, conventional glass electrodes that are commonly used for pH measurements are bulky, fragile and expensive, which hinders their application in miniaturized systems and encouraged to the search for alternatives. In this work, two types of metal oxide pH sensors have been tested to detect the metabolic activity of the bacterium Escherichia coli (E. coli). These pH sensors were produced on silicon chips with platinum metal contacts, onto which thin layers of IrOx or Ta2O5 were incorporated by two different methods (electrodeposition and e-beam sputtering, resp.). In order to facilitate measurement in small sample vols., an Ag/AgCl pseudo-ref. was also screen-printed in the chip and was assayed in parallel to an external Ag/AgCl ref. electrode. As it is shown, the developed sensors generated results indistinguishable from those provided by a conventional glass pH-electrode but could be operated in significantly smaller sample vols. After optimization of the detection conditions, the metal oxide sensors are successfully applied for detection of increasing concns. of viable E. coli, with detection of less than 103 cfu mL-1 in undiluted culture medium in just 5 h.
- 141Salazar, P.; Garcia-Garcia, F. J.; Yubero, F.; Gil-Rostra, J.; González-Elipe, A. R. Electrochim. Acta 2016, 193, 24– 31, DOI: 10.1016/j.electacta.2016.02.040Google Scholar141https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xis1ejsbc%253D&md5=2305eee103eac008f8fb65656f34af44Characterization and application of a new pH sensor based on magnetron sputtered porous WO3 thin films deposited at oblique anglesSalazar, Pedro; Garcia-Garcia, Francisco J.; Yubero, Francisco; Gil-Rostra, Jorge; Gonzalez-Elipe, Agustin R.Electrochimica Acta (2016), 193 (), 24-31CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Ltd.)The authors report about an outstanding solid-state pH sensor based on amorphous nanocolumnar porous thin film electrodes. Transparent WO3 thin films were deposited by reactive magnetron sputtering in an oblique angle configuration to enhance their porosity onto In Sn oxide (ITO) and screen printed electrodes (SPE). The potentiometric pH response of the nanoporous WO3-modified ITO electrode revealed a quasi-Nernstian behavior, i.e. a linear working range from pH 1 to 12 with a slope of ∼-57.7 mV/pH. pH detection with this electrode was quite reproducible, displayed excellent anti-interference properties and a high stable response that remained unaltered over at least 3 mo. Finally, a pH sensor was developed using nanoporous WO3-modified screen printed electrode (SPE) using a polypyrrole-modified Ag/AgCl electrode as internal ref. electrode. This full solid state pH sensor presented a Nernstian behavior with a slope of ∼-59 mV/pH and offered important anal. and operation advantages for decentralized pH measurements in different applications.
- 142Manjakkal, L.; Zaraska, K.; Cvejin, K.; Kulawik, J.; Szwagierczak, D. Talanta 2016, 147, 233– 240, DOI: 10.1016/j.talanta.2015.09.069Google Scholar142https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhs1elsr%252FK&md5=dce15ae291b95a3d4003f757472973b9Potentiometric RuO2-Ta2O5 pH sensors fabricated using thick film and LTCC technologiesManjakkal, Libu; Zaraska, Krzysztof; Cvejin, Katarina; Kulawik, Jan; Szwagierczak, DorotaTalanta (2016), 147 (), 233-240CODEN: TLNTA2; ISSN:0039-9140. (Elsevier B.V.)The paper reports on the prepn., properties and application of potentiometric pH sensors with thick film RuO2-Ta2O5 sensing electrode and Ag/AgCl/KCl ref. electrode screen printed on an alumina substrate. Also, it presents fabrication procedure and characterization of a new miniaturized pH sensor on LTCC (low temp. co-fired ceramics) substrate, destined for wireless monitoring. The crystal structure, phase and elemental compn., and microstructure of the films were studied by x-ray diffractometry, Raman spectroscopy, SEM and energy dispersive spectroscopy. Potentiometric characterization was performed in a wide pH range of 2-12 for different storage conditions and pH loops. The advantages of the proposed thick film pH sensors are: (a) low cost and easy fabrication, (b) excellent sensitivity close to the Nernstian response (56 mV/pH) in the wide pH range, (c) fast response, (d) long lifetime, (e) good reproducibility, (f) low hysteresis and drift effects, and (g) low cross-sensitivity towards Li+, Na+ and K+ as interfering ions. The applicability of the sensors for pH measurement of river, tap and distd. water, and some drinks was also tested.
- 143Lonsdale, W.; Maurya, D. K.; Wajrak, M.; Alameh, K. Effect of ordered mesoporous carbon contact layer on the sensing performance of sputtered RuO2 thin film pH sensor. Talanta 2017, 164, 52– 56, DOI: 10.1016/j.talanta.2016.11.020Google Scholar143https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhvFaisbrP&md5=617058021d59baf2e76f03ef7a429518Effect of ordered mesoporous carbon contact layer on the sensing performance of sputtered RuO2 thin film pH sensorLonsdale, W.; Maurya, D. K.; Wajrak, M.; Alameh, K.Talanta (2017), 164 (), 52-56CODEN: TLNTA2; ISSN:0039-9140. (Elsevier B.V.)The effect of contact layer on the pH sensing performance of a sputtered RuO2 thin film pH sensor was studied. The response of pH sensors employing RuO2 thin film electrodes on screen-printed Pt, carbon and ordered mesoporous carbon (OMC) contact layers are measured over a pH range from 4 to 10. Working electrodes with OMC contact layer have Nernstian pH sensitivity (-58.4 mV/pH), low short-term drift rate (5.0 mV/h), low hysteresis values (1.13 mV) and fast reaction times (30 s), after only 1 h of conditioning. A pH sensor constructed with OMC carbon contact layer displays improved sensing performance compared to Pt and carbon-based counterparts, making this electrode more attractive for applications requiring highly-accurate pH sensing with reduced conditioning time.
- 144Lonsdale, W.; Wajrak, M.; Alameh, K. Sens. Actuators, B 2017, 252, 251– 256, DOI: 10.1016/j.snb.2017.05.171Google Scholar144https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXpvFygsr4%253D&md5=6677b50a34a9b95bfc92f8818441715bEffect of conditioning protocol, redox species and material thickness on the pH sensitivity and hysteresis of sputtered RuO2 electrodesLonsdale, W.; Wajrak, M.; Alameh, K.Sensors and Actuators, B: Chemical (2017), 252 (), 251-256CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)In this paper, the effects of conditioning-pH, RuO2 material thickness and oxidizing/reducing agents on the E0 value and hysteresis of RuO2 pH-sensitive working electrodes is investigated. Exptl. results show that, in order to obtain a pH sensor that Exhibits 0.01 units of precision, it is necessary to use an electrode with at least 500 nm thickness of RuO2; while thinner RuO2 electrodes (> 50 nm) can be used to achieve a precision of 0.05 pH units. In addn., investigation of the redox interference and pH sensing performance of RuO2 electrodes at high/low pH suggests that hysteresis and redox interference are due to shifts in the E0 value due to a change in the electrodes compn., i.e. the ratio of RuIII to RuIV present in the electrode material.
- 145Jovic, M.; Hidalgo-Acosta, J. C.; Lesch, A.; Bassetto, V. C.; Smirnov, E.; Cortes-Salazar, F.; Girault, H. H. Large-scale layer-by-layer inkjet printing of flexible iridium-oxide based pH sensors. J. Electroanal. Chem. 2018, 819, 384– 390, DOI: 10.1016/j.jelechem.2017.11.032Google Scholar145https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhvVajsbvJ&md5=c99bb832887e485fb287506abaa13e78Large-scale layer-by-layer inkjet printing of flexible iridium-oxide based pH sensorsJovic, Milica; Hidalgo-Acosta, Jonnathan C.; Lesch, Andreas; Costa Bassetto, Victor; Smirnov, Evgeny; Cortes-Salazar, Fernando; Girault, Hubert H.Journal of Electroanalytical Chemistry (2018), 819 (), 384-390CODEN: JECHES; ISSN:1873-2569. (Elsevier B.V.)Metal oxide based pH sensors were used in various applications, esp. when the conventional glass electrode is unsuitable due to its fragility or when the applications require disposable sensors, e.g. for biomedical, clin. or food process monitoring. Generally, such pH sensors are produced by thermal oxidn. or electrochem. deposition, neither suited for mass prodn. nor miniaturization. Herein, the authors report on the fabrication of reliable and sensitive pH sensors based on the nano-assembly of Ir oxide (IrOx) nanoparticles and polydiallyldimethylammonium (PDDA) polymer layers. Such potentiometric sensors were very reproducibly fabricated on a large-scale via a layer-by-layer inkjet printing (LbL IJP) methodol. The obtained results indicated the ability of the LbL IJP technique to easily manipulate the NP coverage by the no. of printed bilayers, leading to a swift sensor optimization. Open-circuit potentials were recorded to evaluate the pH sensitivity, response time, and reproducibility of the pH electrodes, which exhibit a rapid, linear and near-Nernstian pH response of ∼59 mV/pH. Also, an relative std. deviation of 0.6% for five different electrodes from the same printing batch showed the excellent reproducibility of the IJP process with a correlation coeff. of 0.99 for all measurements. The insights gained in this study could be the basis for a new approach of developing scalable, patterned and flexible pH sensors with improved performance and a wide range of applications.
- 146Pol, R.; Moya, A.; Gabriel, G.; Gabriel, D.; Céspedes, F.; Baeza, M. Inkjet-Printed Sulfide-Selective Electrode. Anal. Chem. 2017, 89, 12231– 12236, DOI: 10.1021/acs.analchem.7b03041Google Scholar446https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsleiurjF&md5=7f04a5fa49584375eb93775debe7a490Inkjet-Printed Sulfide-Selective ElectrodePol, Roberto; Moya, Ana; Gabriel, Gemma; Gabriel, David; Cespedes, Francisco; Baeza, MireiaAnalytical Chemistry (Washington, DC, United States) (2017), 89 (22), 12231-12236CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Inkjet printing technol. has emerged as an alternative manufg. method for low-cost prodn. of electrodes. Despite significant progress, there is still a lack in the prodn. of ion-selective electrodes. Herein, the two-step fabrication of the first inkjet-printed sulfide-selective electrode (IPSSE) is described. The two-step fabrication consists of printing a silver electrode followed by an electrochem. deposition of sulfide to produce a second kind electrode (Ag/Ag2S). The performance of this novel device was tested using potentiometric measurements. Nernstian response (-29.4 ± 0.3 mV·decade-1) was obtained within concns. of 0.03-50 mM with a response time of ∼3 s. Furthermore, river/sea-spiked environmental samples and samples from a bioreactor for sulfate redn. to sulfide were measured and compared against a com. sensor giving no significant differences. The IPSSE described in this work showed good reproducibility and durability during daily measurements over 15 days without any special storage conditions. Considering all the current challenges in inkjet-printed ion-selective electrodes, this different fabrication approach opens a new perspective for mass prodn. of all-solid state ion-selective electrodes.
- 147Toczylowska-Maminska, R.; Kloch, M.; Zawistowska-Deniziak, A.; Bala, A. Design and characterization of novel all-solid-state potentiometric sensor array dedicated to physiological measurements. Talanta 2016, 159, 7– 13, DOI: 10.1016/j.talanta.2016.06.001Google Scholar146https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XpslWktrg%253D&md5=b5829dadc7f6d376fb5248eb19db4a99Design and characterization of novel all-solid-state potentiometric sensor array dedicated to physiological measurementsToczylowska-Maminska, Renata; Kloch, Monika; Zawistowska-Deniziak, Anna; Bala, AgnieszkaTalanta (2016), 159 (), 7-13CODEN: TLNTA2; ISSN:0039-9140. (Elsevier B.V.)A novel construction of all-solid-state potentiometric sensor array designed for physiol. measurements has been presented. The planar construction and elimination of liq. phase creates broad opportunities for the modifications in the sensing part of the sensor. The designed construction is based on all-solid-state ion-selective electrodes integrated with the ionic-liq. based ref. electrode. Work parameters of the sensor arrays were characterized. It has been shown that presented sensor design indicates high sensitivity (55.2±1 mV/dec, 56.3±2 mV/dec, 58.4±1 mV/dec and 53.5±1 mV/pH for sodium-, potassium-, chloride- and pH-selective electrodes, resp. in 10-5-10-1.5 M range of primary ions), low response time (t95 did not exceed 10 s), high potential stability (potential drift in 28-h measurement was ca. ±2 mV) and potential repeatability ca. ±1 mV. The system was successfully applied to the simultaneous detn. of K+, Cl-, Na+ and pH in the model physiol. soln. and for the ion flux studies in human colon epithelium Caco-2 cell line as well.
- 148Zajac, M.; Lewenstam, A.; Dolowy, K. Multi-electrode system for measurement of transmembrane ion-fluxes through living epithelial cells. Bioelectrochemistry 2017, 117, 65– 73, DOI: 10.1016/j.bioelechem.2017.06.007Google Scholar147https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtVWqsb7M&md5=d68d3984a946d8d966ed2af248879c79Multi-electrode system for measurement of transmembrane ion-fluxes through living epithelial cellsZajac, Miroslaw; Lewenstam, Andrzej; Dolowy, KrzysztofBioelectrochemistry (2017), 117 (), 65-73CODEN: BIOEFK; ISSN:1567-5394. (Elsevier B.V.)Cystic Fibrosis (CF) is the most common fatal human genetic disease. It is caused by the defect in a single anion channel protein which affects ion and water transport across the epithelial tissue. A flat multi-electrode platform of diam. 12 mm, allowing for measurement of four ions: sodium, potassium, hydrogen and chloride by exchangeable/replaceable ion-selective electrodes is described. The measurement is possible owing to the architecture of the platform which accommodates all the electrodes and inlets/outlets. The platform fits to the cup and operates in a small vol. of the soln. bathing the living epithelial cell layer (membrane) deposited on a porous support of the cup, which allows for effective monitoring of ion concn. changes. By applying two multi-electrode platforms, it is possible to measure the ion transmembrane fluxes. The inlet and outlet tubes in the platforms allow for on-fly change of the calibrants, ion-concn. changes and ion channel blockers. Using different ion-concn. gradients and blockers of ion-transporting mols. we show for the first time that sodium ions flow from the basolateral to apical face of the cell monolayer via a paracellular route and return also via a transcellular one, while chloride anions are transported back and forth exclusively via a transcellular route.
- 149Church, J.; Armas, S. M.; Patel, P. K.; Chumbimuni-Torres, K.; Lee, W. H. Development and Characterization of Needle-type Ion-selective Microsensors for insitu Determination of Foliar Uptake of Zn2+ in Citrus Plants. Electroanalysis 2018, 30, 626– 632, DOI: 10.1002/elan.201700697Google Scholar148https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhvFegs7zE&md5=8be302cabf606d370a117bcf3f7b196aDevelopment and Characterization of Needle-Type Ion-Selective Microsensors for in situ Determination of Foliar Uptake of Zn2+ in Citrus PlantsChurch, Jared; Armas, Stephanie M.; Patel, Parth K.; Chumbimuni-Torres, Karin; Lee, Woo HyoungElectroanalysis (2018), 30 (4), 626-632CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)For over a decade, the incidence of Huanglongbing (HLB) has grown at an alarming rate, affecting citrus crops worldwide. Current methods of nutrient therapy have little to no effect in alleviating symptoms of HLB, and scarce research has been put forth towards non-destructive tools for monitoring zinc transport in citrus plants. Here, we have developed and characterized a solid contact micro-ion-selective electrode (SC-μ-ISE) for the detn. of zinc transport in sour orange seedlings using a non-invasive microelectrode ion flux estn. (MIFE) technique. The SC-μ-ISE displayed a 26.05±0.13 mV decade-1 Nernstian response and a LOD of (3.96±2.09)×10-7 M. Results showed a significant Zn2+ uptake in the leaves and roots of sour orange seedlings when bulk concns. were higher than 5.99 mM. Above this concn., a linear relationship between flux and bulk Zn2+ concn. was obsd. This relationship suggests passive diffusion may be a key mechanism for Zn transport into plants. Overall, this study is the first to use a Zn2+ SC-μ-ISE for the detn. of ion transport processes in plants. This novel tool can be used to further knowledge the effect of nutrient therapy and disease progression on HLB infected citrus plants.
- 150Ma, X. M.; Armas, S. M.; Soliman, M.; Lytle, D. A.; Chumbimuni-Torres, K.; Tetard, L.; Lee, W. H. In Situ Monitoring of Pb2+ Leaching from the Galvanic Joint Surface in a Prepared Chlorinated Drinking Water. Environ. Sci. Technol. 2018, 52, 2126– 2133, DOI: 10.1021/acs.est.7b05526Google Scholar149https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhvVWit7g%253D&md5=4ca9002f8f343bf8085c5927a979ce0aIn Situ Monitoring of Pb2+ Leaching from the Galvanic Joint Surface in a Prepared Chlorinated Drinking WaterMa, Xiangmeng; Armas, Stephanie M.; Soliman, Mikhael; Lytle, Darren A.; Chumbimuni-Torres, Karin; Tetard, Laurene; Lee, Woo HyoungEnvironmental Science & Technology (2018), 52 (4), 2126-2133CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)A novel method using a micro-ion-selective electrode (micro-ISE) technique was developed for in situ lead monitoring at the water-metal interface of a brass-leaded solder galvanic joint in a prepd. chlorinated drinking water environment. The developed lead micro-ISE (100 μm tip diam.) showed excellent performance toward sol. lead (Pb2+) with sensitivity of 22.2 ± 0.5 mV decade-1 and limit of detection (LOD) of 1.22 × 10-6 M (0.25 mg L-1). The response time was less than 10 s with a working pH range of 2.0-7.0. Using the lead micro-ISE, lead concn. microprofiles were measured from the bulk to the metal surface (within 50 μm) over time. Combined with two-dimensional (2D) pH mapping, this work clearly demonstrated that Pb2+ ions build-up across the lead anode surface was substantial, nonuniform, and dependent on local surface pH. A large pH gradient (ΔpH = 6.0) developed across the brass and leaded-tin solder joint coupon. Local pH decreases were obsd. above the leaded solder to a pH as low as 4.0, indicating it was anodic relative to the brass. The low pH above the leaded solder supported elevated lead levels where even small local pH differences of 0.6 units (ΔpH = 0.6) resulted in about four times higher surface lead concns. (42.9 vs 11.6 mg L-1) and 5 times higher fluxes (18.5 × 10-6 vs 3.5 × 10-6 mg cm-2 s-1). Continuous surface lead leaching monitoring was also conducted for 16 h.
- 151Hao, J.; Xiao, T. F.; Wu, F.; Yu, P.; Mao, L. Q. High Antifouling Property of Ion-Selective Membrane: toward In Vivo Monitoring of pH Change in Live Brain of Rats with Membrane-Coated Carbon Fiber Electrodes. Anal. Chem. 2016, 88, 11238– 11243, DOI: 10.1021/acs.analchem.6b03854Google Scholar150https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xhs1yltLfM&md5=9f363ec126336bb1e2c674828fb39fd9High Antifouling Property of Ion-Selective Membrane: toward In Vivo Monitoring of pH Change in Live Brain of Rats with Membrane-Coated Carbon Fiber ElectrodesHao, Jie; Xiao, Tongfang; Wu, Fei; Yu, Ping; Mao, LanqunAnalytical Chemistry (Washington, DC, United States) (2016), 88 (22), 11238-11243CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)In vivo monitoring of pH in live brain remains very essential to understanding acid-base chem. in various physiol. processes. This study demonstrates a potentiometric method for in vivo monitoring of pH in the central nervous system with carbon fiber-based proton-selective electrodes (CF-H+ISEs) with high antifouling property. The CF-H+ISEs are prepd. by formation of a H+-selective membrane (H+ISM) with polyvinyl chloride polymeric matrixes contg. plasticizer bis(2-ethylhexyl)sebacate, H+ ionophore tridodecylamine, and ion exchanger potassium tetrakis(4-chlorophenyl)borate onto carbon fiber electrodes (CFEs). Both in vitro and in vivo studies demonstrate that the H+ISM exhibits strong antifouling property against proteins, which enables the CF-H+ISEs to well maintain the sensitivity and reversibility for pH sensing after in vivo measurements. Moreover, the CF-H+ISEs exhibit a good response to pH changes within a narrow physiol. pH range from 6.0 to 8.0 in quick response time with high reversibility and selectivity against species endogenously existing in the central nervous system. The applicability of the CF-H+ISEs is illustrated by real-time monitoring of pH changes during acid-base disturbances, in which the brain acidosis is induced by CO2 inhalation and brain alkalosis is induced by bicarbonate injections. The results demonstrate that brain pH value rapidly decreases in the amygdaloid nucleus by ∼0.14±0.01 (n = 5) when the rats breath in pure CO2 gas, while increases in the cortex by ∼0.77±0.12 (n = 3) following i.p. injection of 5 mmol/kg NaHCO3. This study demonstrates a new potentiometric method for in vivo measurement of pH change in the live brain of rats with high reliability.
- 152Moon, J.; Ha, Y.; Kim, M.; Sim, J.; Lee, Y.; Suh, M. Dual Electrochemical Microsensor for Real-Time Simultaneous Monitoring of Nitric Oxide and Potassium Ion Changes in a Rat Brain during Spontaneous Neocortical Epileptic Seizure. Anal. Chem. 2016, 88, 8942– 8948, DOI: 10.1021/acs.analchem.6b02396Google Scholar151https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhtlKnu7vJ&md5=7615215ff8de0b6f7c4e28f4f6131599Dual Electrochemical Microsensor for Real-Time Simultaneous Monitoring of Nitric Oxide and Potassium Ion Changes in a Rat Brain during Spontaneous Neocortical Epileptic SeizureMoon, Jungmi; Ha, Yejin; Kim, Misun; Sim, Jeongeun; Lee, Youngmi; Suh, MinahAnalytical Chemistry (Washington, DC, United States) (2016), 88 (18), 8942-8948CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)The authors developed a dual amperometric/potentiometric microsensor for sensing nitric oxide (NO) and potassium ion (K+). The dual NO/K+ sensor was prepd. based on a dual recessed electrode possessing Pt (diam., 50 μm) and Ag (diam., 76.2 μm) microdisks. The Pt disk surface (WE1) was modified with electroplatinization and the following coating with fluorinated xerogel; and the Ag disk surface (WE2) was oxidized to AgCl on which K+ ion selective membrane was loaded subsequent to the silanization. WE1 and WE2 of a dual microsensor were used for amperometric sensing of NO (106 ± 28 pA μM-1, n = 10, at +0.85 V applied vs. Ag/AgCl) and for potentiometric sensing of K+ (51.6 ± 1.9 mV pK-1, n = 10), resp., with high sensitivity. In addn., the sensor showed good selectivity over common biol. interferents, sufficiently fast response time and relevant stability (within 6 h in-vivo expt.). The sensor had a small dimension (end plane diam., 428 ± 97 μm, n = 20) and needle-like sharp geometry which allowed the sensor to be inserted in biol. tissues. Taking advantage of this insertability, the sensor was applied for the simultaneous monitoring of NO and K+ changes in living rat brain cortex at a depth of 1.19 ± 0.039 mm and near the spontaneous epileptic seizure focus. The seizures were induced with 4-aminopyridine injection onto the rat brain cortex. NO and K+ levels were dynamically changed in clear correlation with the electrophysiol. recording of seizures. The dual NO/K+ sensor's measurements well reflect membrane potential changes of neurons and assocd. cellular components of neurovascular coupling. The newly developed NO/K+ dual microsensor showed the feasibility of real-time fast monitoring of dynamic changes of closely linked NO and K+in vivo.
- 153Filotas, D.; Fernandez-Perez, B. M.; Izquierdo, J.; Nagy, L.; Nagy, G.; Souto, R. M. Novel dual microelectrode probe for the simultaneous visualization of local Zn2+ and pH distributions in galvanic corrosion processes. Corros. Sci. 2017, 114, 37– 44, DOI: 10.1016/j.corsci.2016.10.014Google Scholar152https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhslegsLjE&md5=ee11217492ca99fb781bd8ef2c055a76Novel dual microelectrode probe for the simultaneous visualization of local Zn2+ and pH distributions in galvanic corrosion processesFilotas, D.; Fernandez-Perez, B. M.; Izquierdo, J.; Nagy, L.; Nagy, G.; Souto, R. M.Corrosion Science (2017), 114 (), 37-44CODEN: CRRSAA; ISSN:0010-938X. (Elsevier Ltd.)Novel dual potentiometric microsensor probe has been developed for the simultaneous detection of Zn2+ concn. and pH distributions in the Scanning Electrochem. Microscopy investigation of corroding galvanized steel. The individual sensors show nearly theor. behavior over a wide concn. range. The applicability of this probe is first demonstrated on a Fe-Zn galvanic couple, as it shows excellent performance in these simultaneous model expts. In addn., linear scans recorded over a cut edge of coated galvanized steel evidence the complementary information gathered on the electrochem. behavior of the corroding sample, and adumbrates promising and feasible applications of multi-barrel microelectrodes in corrosion research.
- 154Ummadi, J. G.; Downs, C. J.; Joshi, V. S.; Ferracane, J. L.; Koley, D. Carbon-Based Solid-State Calcium Ion-Selective Microelectrode and Scanning Electrochemical Microscopy: A Quantitative Study of pH-Dependent Release of Calcium Ions from Bioactive Glass. Anal. Chem. 2016, 88, 3218– 3226, DOI: 10.1021/acs.analchem.5b04614Google Scholar153https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XitlCjsLg%253D&md5=7aa0d86fcc717648e1f1cafebb98f31cCarbon-Based Solid-State Calcium Ion-Selective Microelectrode and Scanning Electrochemical Microscopy: A Quantitative Study of pH-Dependent Release of Calcium Ions from Bioactive GlassUmmadi, Jyothir Ganesh; Downs, Corey J.; Joshi, Vrushali S.; Ferracane, Jack L.; Koley, DipankarAnalytical Chemistry (Washington, DC, United States) (2016), 88 (6), 3218-3226CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Solid-state ion-selective electrodes are used as scanning electrochem. microscope (SECM) probes because of their inherent fast response time and ease of miniaturization. In this study, we report the development of a solid-state, low-poly(vinyl chloride), carbon-based calcium ion-selective microelectrode (Ca2+-ISME), 25 μm in diam., capable of performing an amperometric approach curve and serving as a potentiometric sensor. The Ca2+-ISME has a broad linear response range of 5 μM to 200 mM with a near Nernstian slope of 28 mV/log[aCa2+]. The calcd. detection limit for Ca2+-ISME is 1 μM. The selectivity coeffs. of this Ca2+-ISME are log KCa2+,A = -5.88, -5.54, and -6.31 for Mg2+, Na+, and K+, resp. We used this new type of Ca2+-ISME as an SECM probe to quant. map the chem. microenvironment produced by a model substrate, bioactive glass (BAG). In acidic conditions (pH 4.5), BAG was found to increase the calcium ion concn. from 0.7 mM ([Ca2+] in artificial saliva) to 1.4 mM at 20 μm above the surface. In addn., a solid-state dual SECM pH probe was used to correlate the release of calcium ions with the change in local pH. Three-dimensional pH and calcium ion distribution mapping were also obtained by using these solid-state probes. The quant. mapping of pH and Ca2+ above the BAG elucidates the effectiveness of BAG in neutralizing and releasing calcium ions in acidic conditions.
- 155Zhu, Z.; Liu, X. Y.; Ye, Z. N.; Zhang, J. Q.; Cao, F. H.; Zhang, J. X. A fabrication of iridium oxide film pH micro-sensor on Pt-ultramicroelectrode and its application on in-situ pH distribution of 316L stainless steel corrosion at open circuit potential. Sens. Actuators, B 2018, 255, 1974– 1982, DOI: 10.1016/j.snb.2017.08.219Google Scholar154https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsVOhs7vO&md5=558bc34fabd2aa6faae8951d098ee130A fabrication of iridium oxide film pH micro-sensor on Pt ultramicroelectrode and its application on in-situ pH distribution of 316L stainless steel corrosion at open circuit potentialZhu, Zejie; Liu, Xiaoyan; Ye, Zhenni; Zhang, Jianqing; Cao, Fahe; Zhang, JunxiSensors and Actuators, B: Chemical (2018), 255 (Part_2), 1974-1982CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)An all solid-state pH micro-sensor has been developed using anodic electrodeposition of an iridium oxide (IrOx) film onto a 10μm platinum ultramicroelectrode. The electrochem. growth of the IrOx film was accomplished by 100 potential sweeps at 50 mV/s, at different potential ranges of electrochem. deposition, followed by heat treatment at 100°C for 2 h. The pH micro-sensor shows quick response to the pH variation, excellent sensitivity, stability and long lifetime in a wide pH range between 1.0 and 13.0. The slope of potential-pH response curve is found to dependent on the Ir(III)/Ir(IV) ratio of in the film, detd. by XPS anal., which is a consequence of scanning potential range during the anodic electrodeposition. The sensor has been employed to explore the localized pH distribution during the corrosion of 316L stainless steel in NaCl soln. at open circuit potential and results show that localized anodic and cathodic sites on the 316L stainless steel can be accurately monitored and the pH difference between the cathodic and anodic zones increases from 0.22 to 1.27 with the prolonging of the immersion time.
- 156Zhu, Z. J.; Ye, Z. N.; Zhang, Q. H.; Zhang, J. Q.; Cao, F. H. Novel dual Pt-Pt/IrOx ultramicroelectrode for pH imaging using SECM in both potentiometric and amperometric modes. Electrochem. Commun. 2018, 88, 47– 51, DOI: 10.1016/j.elecom.2018.01.018Google Scholar155https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXitVeqsbo%253D&md5=26e8f6a8d0f5259e64afa142acaa15b3Novel dual Pt-Pt/IrOx ultramicroelectrode for pH imaging using SECM in both potentiometric and amperometric modesZhu, Zejie; Ye, Zhenni; Zhang, Qinhao; Zhang, Jianqing; Cao, FaheElectrochemistry Communications (2018), 88 (), 47-51CODEN: ECCMF9; ISSN:1388-2481. (Elsevier B.V.)Potentiometric Scanning Electrochem.Microscopy (SECM) allows the pH distribution at electrode/electrolyte interfaces to be mapped at the micrometer and submicrometer scale using ion-selective ultramicroelectrodes (UMEs) as scanning probes. However, this technique lacks precise control of the tip-to-substrate distance. Herein we propose a novel dual Pt-Pt/IrOx UME for local in situ pH visualization of 316L stainless steel (316L-SS) corrosion processes with precise tip-substrate distance control using both amperometric and potentiometric SECM modes. Simulations based on COMSOL and exptl. approach curves obtained with this dual UME configuration are used to precisely establish the tip-substrate distance. Higher pH values were obsd. for smaller tip-substrate sepns.when this probe configuration is used with bulk electrolyte of the same pH. Furthermore, during the corrosion process local anodic and cathodic zones were obsd. to form, disappear and regenerate at a vertical tip-substrate distance of 12μm as a result of the localized corrosion and repassivation of 316L-SS.
- 157Freeman, C. J.; Farghaly, A. A.; Choudhary, H.; Chavis, A. E.; Brady, K. T.; Reiner, J. E.; Collinson, M. M. Anal. Chem. 2016, 88, 3768– 3774, DOI: 10.1021/acs.analchem.5b04668Google Scholar156https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XksV2gsLs%253D&md5=a3b9f594a79d74dd1e49d129f3bd7199Microdroplet-Based Potentiometric Redox Measurements on Gold Nanoporous ElectrodesFreeman, Christopher J.; Farghaly, Ahmed A.; Choudhary, Hajira; Chavis, Amy E.; Brady, Kyle T.; Reiner, Joseph E.; Collinson, Maryanne M.Analytical Chemistry (Washington, DC, United States) (2016), 88 (7), 3768-3774CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Potentiometric redox measurements were made in subnanoliter droplets of solns. using an optically transparent nanoporous Au electrode strategically mounted on the stage of an inverted microscope. Nanoporous Au was prepd. via dealloying Au leaf with concd. HNO3 and was chemisorbed to a std. microscope coverslip with (3-mercaptopropyl)trimethoxysilane. The Au surface was further modified with 1-hexanethiol to optimize hydrophobicity of the surface to allow for redox measurements to be made in nanoscopic vols. Time traces of the open-circuit potential (OCP) were used to construct Nernst plots to evaluate the applicability of the droplet-based potentiometric redox measurement system. Two poised 1-electron transfer systems (K ferricyanide/ferrocyanide and ferrous/ferric ammonium sulfate) yielded Nernstian slopes of -58.5 and -60.3 mV, resp., with regression coeffs. >0.99. The y-intercepts of the two agreed well to the formal potential of the two std. oxidn.-redn. potential (ORP) calibrants, ZoBell's and Light's soln. The benzoquinone and hydroquinone redox couple was examd. as a representative two-electron redox system; a Nernst slope of -30.8 mV was obtained. Addnl., two unpoised systems (K ferricyanide and ascorbic acid) were studied to evaluate the system under conditions where only one form of the redox couple is present in appreciable concns. Again, slopes near the Nernstian values of -59 and -29 mV, resp., were obtained. All expts. were carried out using soln. vols. between 280 and 1400 pL with injection vols. between 8 and 100 pL. The miniscule vols. allowed for extremely rapid mixing (<305 ms) as well. The small vols. and rapid mixing along with the high accuracy and sensitivity of these measurements lend support to the use of this approach in applications where time is a factor and only small vols. are available for testing.
- 158Asadnia, M.; Myers, M.; Umana-Membreno, G. A.; Sanders, T. M.; Mishra, U. K.; Nener, B. D.; Baker, M. V.; Parish, G. Ca2+ detection utilising AlGaN/GaN transistors with ion-selective polymer membranes. Anal. Chim. Acta 2017, 987, 105– 110, DOI: 10.1016/j.aca.2017.07.066Google Scholar157https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtlegsr3E&md5=abd443c9e987cc36149a1f9f5af5d30dCa2+ detection utilising AlGaN/GaN transistors with ion-selective polymer membranesAsadnia, Mohsen; Myers, Matthew; Umana-Membreno, Gilberto A.; Sanders, Tarun M.; Mishra, Umesh K.; Nener, Brett D.; Baker, Murray V.; Parish, GiacintaAnalytica Chimica Acta (2017), 987 (), 105-110CODEN: ACACAM; ISSN:0003-2670. (Elsevier B.V.)The authors demonstrate highly selective and sensitive potentiometric ion sensors for calcium ion detection, operated without the use of a ref. electrode. The sensors consist of AlGaN/GaN heterostructure-based transistor devices with chem. functionalization of the gate area using poly(vinylchloride)-based (PVC) membranes having high selectivity towards calcium ions, Ca2+. The sensors exhibited stable and rapid responses when introduced to various concns. of Ca2+. In both 0.01 M KCl and 0.01 M NaCl ionic strength buffer solns., the sensors exhibited near Nernstian responses with detection limits of <10-7 M, and a linear response range between 10-7-10-2 M. Also, detection limits of <10-6 M were achieved for the sensors in both 0.01 M MgCl2 and 0.01 M LiCl buffer solns. AlGaN/GaN-based devices for Ca2+ detection demonstrate excellent selectivity and response range for a wide variety of applications. This work represents an important step towards multi-ion sensing using arrays of ion-selective field effect transistor (ISFET) devices.
- 159Kaisti, M.; Boeva, Z.; Koskinen, J.; Nieminen, S.; Bobacka, J.; Levon, K. Hand-Held Transistor Based Electrical and Multiplexed Chemical Sensing System. ACS Sens. 2016, 1, 1423– 1431, DOI: 10.1021/acssensors.6b00520Google Scholar158https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhvFCgsrbF&md5=ede6b01e922bc18d560cc8074abec6deHand-Held Transistor Based Electrical and Multiplexed Chemical Sensing SystemKaisti, Matti; Boeva, Zhanna; Koskinen, Juho; Nieminen, Sami; Bobacka, Johan; Levon, KalleACS Sensors (2016), 1 (12), 1423-1431CODEN: ASCEFJ; ISSN:2379-3694. (American Chemical Society)The authors describe a hand-held sensing system using a transistor based multiplexed platform and a detector that couples the electrochem. information wirelessly to a smartphone. The custom disposable platform exploits the ion-sensitive FET (ISFET) technol. Via simple surface modifications the design allows a broad range of analytes to be tested with low-cost. The authors compared their read-out device to a com. potentiometer using K+ as an example species analyte. The developed sensing system has slightly better limit of detection and notably is less susceptible to external noise which is commonly obsd. with potentiometers. The designed platform is fabricated using std. electronic processes with gold surface and the authors used com. discrete transistors as the transducing element. It can be mass produced with high yield and low-cost. To circumvent the drift that typically occurs with modified solid state electrodes the authors incorporated a transducing layer between the elec. conductor (gold pad) and the ionically conducting ion-selective-membrane. The polyaniline doped with dinonylnaphthalene sulfonic acid (PANI-DNNSA) was used as a transducing layer for the first time. The PANI-DNNSA layer significantly reduces the drift of the electrodes compared to a configuration without the transducing layer. The system is easy to use with a transistor based detection that can be modified for a vast variety of existing potentiometric tests.
- 160Briggs, E. M.; Sandoval, S.; Erten, A.; Takeshita, Y.; Kummel, A. C.; Martz, T. R. Solid State Sensor for Simultaneous Measurement of Total Alkalinity and pH of Seawater. ACS Sens. 2017, 2, 1302– 1309, DOI: 10.1021/acssensors.7b00305Google Scholar159https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtlSkurzJ&md5=081f3653269ab54d74b6946f4a8cef30Solid State Sensor for Simultaneous Measurement of Total Alkalinity and pH of SeawaterBriggs, Ellen M.; Sandoval, Sergio; Erten, Ahmet; Takeshita, Yuichiro; Kummel, Andrew C.; Martz, Todd R.ACS Sensors (2017), 2 (9), 1302-1309CODEN: ASCEFJ; ISSN:2379-3694. (American Chemical Society)A novel design is demonstrated for a solid state, reagent-less sensor capable of rapid and simultaneous measurement of pH and Total Alky. (AT) using ion sensitive field effect transistor (ISFET) technol. to provide a simplified means of characterization of the aq. carbon dioxide system through measurement of two "master variables": pH and AT. ISFET-based pH sensors that achieve 0.001 precision are widely used in various oceanog. applications. A modified ISFET is demonstrated to perform a nanoliter-scale acid-base titrn. of AT in under 40 s. This method of measuring AT, a Coulometric Diffusion Titrn., involves electrolytic generation of titrant, H+, through the electrolysis of water on the surface of the chip via a microfabricated electrode eliminating the requirement of external reagents. Characterization has been performed in seawater as well as titrating individual components (i.e., OH-, HCO3-, CO32-, B(OH)4-, PO43-) of seawater AT. The seawater measurements are consistent with the design in reaching the benchmark goal of 0.5% precision in AT over the range of seawater AT of ∼2200-2500 μmol kg-1 which demonstrates great potential for autonomous sensing.
- 161Andrianova, M. S.; Gubanova, O. V.; Komarova, N. V.; Kuznetsov, E. V.; Kuznetsov, A. E. Electroanalysis 2016, 28, 1311– 1321, DOI: 10.1002/elan.201500411Google Scholar160https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhtFOns70%253D&md5=a7f20b4850f3bc0aa8d6d7d65a75d9bdDevelopment of a Biosensor Based on Phosphotriesterase and n-Channel ISFET for Detection of PesticidesAndrianova, M. S.; Gubanova, O. V.; Komarova, N. V.; Kuznetsov, E. V.; Kuznetsov, A. E.Electroanalysis (2016), 28 (6), 1311-1321CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)A biosensor for the direct detn. of organophosphorus pesticides (OPs) is described. It utilizes an ion-selective field-effect transistor and phosphotriesterase enzyme (PTE), which provides cleavage of OPs. The sensitivity of the biosensor was increased after PTE immobilization on the surface of the transistor. Packaging of the integrated circuit and creation of a microfluidic system for analyte delivery stabilized the signal. This system was able to detect 0.1 μM paraoxon and 0.5 μM parathion and methyl parathion and was stable for at least 1 mo (PBS, 1°), and could thus provide the basis for a portable device for analyzing OPs in water.
- 162Melzer, K.; Bhatt, V. D.; Jaworska, E.; Mittermeier, R.; Maksymiuk, K.; Michalska, A.; Lugli, P. Enzyme assays using sensor arrays based on ion-selective carbon nanotube field-effect transistors. Biosens. Bioelectron. 2016, 84, 7– 14, DOI: 10.1016/j.bios.2016.04.077Google Scholar161https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XntFCrtrs%253D&md5=1cb68e06a914b8b58f910d9a30af8e60Enzyme assays using sensor arrays based on ion-selective carbon nanotube field-effect transistorsMelzer, K.; Bhatt, V. Deep; Jaworska, E.; Mittermeier, R.; Maksymiuk, K.; Michalska, A.; Lugli, P.Biosensors & Bioelectronics (2016), 84 (), 7-14CODEN: BBIOE4; ISSN:0956-5663. (Elsevier B.V.)In the fields of clin. diagnostics and point-of-care diagnosis as well as food and environmental monitoring there is a high demand for reliable high-throughput, rapid and highly sensitive assays for a simultaneous detection of several analytes in complex and low-vol. samples. Sensor platforms based on soln.-processable electrolyte-gated carbon nanotube field-effect transistors (CNT-FETs) are a simple and cost-effective alternative for conventional assays. The authors demonstrate a selective as well as direct detection of the products of an enzyme-substrate interaction, here the for metabolic processes important urea-urease system, with sensors based on spray-coated CNT-FETs. The selective and direct detection is achieved by immobilizing the enzyme urease via certain surface functionalization techniques on the sensor surface and further modifying the active interfaces with polymeric ion-selective membranes as well as pH-sensitive layers. Thereby, the authors can avoid the generally applied approach for a field-effect based detection of enzyme reactions via detecting changes in the pH value due to an on-going enzymic reaction and directly detect selectively the products of the enzymic conversion. Thus, the authors can realize a buffering-capacity independent monitoring of changes in the substrate concn.
- 163Cuartero, M.; Bakker, E. Environmental water analysis with membrane electrodes. Curr. Opin. Electrochem. 2017, 3, 97– 105, DOI: 10.1016/j.coelec.2017.06.010Google Scholar162https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhtVGgsLbL&md5=01988be9764f84e8daae0ad4590c8719Environmental water analysis with membrane electrodesCuartero, Maria; Bakker, EricCurrent Opinion in Electrochemistry (2017), 3 (1), 97-105CODEN: COEUCY; ISSN:2451-9111. (Elsevier B.V.)A review. The monitoring of key parameters and analytes (including ions) in aquatic systems is crucial to our understanding of biogeochem. processes and their possible correlation with anthropogenic activities. The use of centralised anal. methodologies is most established for this purpose, but the risk of sample alteration during sampling and transport and the limited data acquisition frequency are promoting a paradigm shift towards in situ approaches. These focus on performing the measurement shipboard, from on site platforms or through submersible probes. This latter option is the most attractive for environmental scientists since it provides real-time profiles with high spatial and temporal resoln., even allowing the study of aquatic processes that evolve at the minute time scale. Potentiometric ion-selective electrodes, esp. based on polymeric membranes, have therefore been widely used to detect important ions in marine and fresh water systems. Importantly, their inherent characteristics make them particularly suitable for implementation into submersible probes. This crit. review highlights some recent examples related to the application of membrane electrodes for water anal. with particular attention to the efforts towards in situ detection. Sensor technol. is sometimes overlooked in environmental anal. and this review aims to bring electrochemists, analysts and environmentalists together to better appreciate the strengths of membrane electrodes targeted to this aim.
- 164Pankratova, N.; Afshar, M. G.; Yuan, D. J.; Crespo, G. A.; Bakker, E. Local Acidification of Membrane Surfaces for Potentiometric Sensing of Anions in Environmental Samples. ACS Sens. 2016, 1, 48– 54, DOI: 10.1021/acssensors.5b00015Google Scholar163https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhs1altLjM&md5=5bfacbf341a3510bc21dd67c64b8c411Local Acidification of Membrane Surfaces for Potentiometric Sensing of Anions in Environmental SamplesPankratova, Nadezda; Ghahraman Afshar, Majid; Yuan, Dajing; Crespo, Gaston A.; Bakker, EricACS Sensors (2016), 1 (1), 48-54CODEN: ASCEFJ; ISSN:2379-3694. (American Chemical Society)The work dramatically improves the lower detection limit of anion selective membranes at environmental pH by using local acidification to suppress hydroxide interference at the membrane surface. Three sep. localized acidification strategies are explored to achieve this, with ionophore-based membrane electrodes selective for nitrite and dihydrogen phosphate as guiding examples. In a 1st approach, a concd. acetic acid soln. (∼1 M) is placed in the inner filling soln. of the PVC-based membrane electrode, forcing a significant acid gradient across the membrane. A 2nd strategy achieves the same type of passive acidification by using an external proton source (fast diffusive doped polypropylene membrane) placed in front of a potentiometric solid contact anion selective electrode where the thin layer gap allows one to observe spontaneous acidification at the opposing detection electrode. The 3rd approach shares the same configuration, but protons are here released by electrochem. control from the selective proton source into the thin layer sample. All three protocols improve the limit of detection by >2 orders of magnitude at environmental pH. Nitrite and dihydrogen phosphate detns. in artificial and natural samples are demonstrated.
- 165Pankratova, N.; Cuartero, M.; Cherubini, T.; Crespo, G. A.; Bakker, E. In-Line Acidification for Potentiometric Sensing of Nitrite in Natural Waters. Anal. Chem. 2017, 89, 571– 575, DOI: 10.1021/acs.analchem.6b03946Google Scholar164https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XitVGnsbrN&md5=73adab866b9bfa567d75886a380336e9In-Line Acidification for Potentiometric Sensing of Nitrite in Natural WatersPankratova, Nadezda; Cuartero, Maria; Cherubini, Thomas; Crespo, Gaston A.; Bakker, EricAnalytical Chemistry (Washington, DC, United States) (2017), 89 (1), 571-575CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)We report on a novel approach for in-line sample acidification that results in a significant improvement of the limit of detection of potentiometric anion-selective electrodes aiming at detg. nutrients in natural waters. The working principle of the developed acidification module relies on the cation-exchange process between the sample and an ion-exchange Donnan exclusion membrane in its protonated form. The resulting in-line acidification of natural waters with millimolar NaCl level (freshwater, drinking water, aquarium water as well as dechlorinated seawater) decreases the pH down to ∼5. Using the acidification module the limit of detection of nitrite-selective electrodes significantly improves by ≥2 orders of magnitude with respect to that obsd. at environmental pH. The originality of the proposed flow cell lies in the possibility to adjust the pH of the sample by modifying its exposure time with the membrane by varying the volumetric flow rate. Facile coupling with a detection technique of choice, miniaturized configuration and simple implementation for long-term monitoring with submersible probes for environmental anal. are possible anal. configurations. This approach was applied to the potentiometric detection of nitrite in aquarium and dechlorinated seawater.
- 166Cuartero, M.; Crespo, G.; Cherubini, T.; Pankratova, N.; Confalonieri, F.; Massa, F.; Tercier-Waeber, M. L.; Abdou, M.; Schafer, J.; Bakker, E. In Situ Detection of Macronutrients and Chloride in Seawater by Submersible Electrochemical Sensors. Anal. Chem. 2018, 90, 4702– 4710, DOI: 10.1021/acs.analchem.7b05299Google Scholar165https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXktFWjsbw%253D&md5=96e30b2d08887c5184362d6144c9943fIn Situ Detection of Macronutrients and Chloride in Seawater by Submersible Electrochemical SensorsCuartero, Maria; Crespo, Gaston; Cherubini, Thomas; Pankratova, Nadezda; Confalonieri, Fabio; Massa, Francesco; Tercier-Waeber, Mary-Lou; Abdou, Melina; Schafer, Jorg; Bakker, EricAnalytical Chemistry (Washington, DC, United States) (2018), 90 (7), 4702-4710CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)A new submersible probe for the in situ detection of nitrate, nitrite, and chloride in seawater is presented. Inline coupling of a desalination unit, an acidification unit, and a sensing flow cell contg. all-solid-state membrane electrodes allows for the potentiometric detection of nitrate and nitrite after removal of the key interfering ions in seawater, chloride and hydroxide. Thus, the electrodes exhibited attractive anal. performances for the potentiometric detection of nitrate and nitrite in desalinated and acidified seawater: fast response time (t95 < 12 s), excellent stability (long-term drifts of <0.5 mV h-1), good reproducibility (calibration parameter deviation of <3%), and satisfactory accuracy (uncertainties <8%Diff compared to ref. technique). The desalination cell, which can be repetitively used for about 30 times, may addnl. be used as an exhaustive, and therefore calibration-free, electrochem. sensor for chloride and indirect salinity detection. The detection of these two parameters together with nitrate and nitrite may be useful for the correlation of relative changes in macronutrient levels with salinity cycles, which is of special interest in recessed coastal water bodies. The system is capable of autonomous operation during deployment, with routines for repetitive measurements (every 2 h), data storage and management, and computer visualization of the data in real time. In situ temporal profiles obsd. in the Arcachon Bay (France) showed valuable environmental information concerning tide-dependent cycles of nitrate and chloride levels in the lagoon, which are here obsd. for the first time using direct in situ measurements. The submersible probe based on membrane electrodes presented herein may facilitate the study of biogeochem. processes occurring in marine ecosystems by the direct monitoring of nitrate and nitrite levels, which are key chem. targets in coastal waters.
- 167Cuartero, M.; Pankratova, N.; Cherubini, T.; Crespo, G. A.; Massa, F.; Confalonieri, F.; Bakker, E. In Situ Detection of Species Relevant to the Carbon Cycle in Seawater with Submersible Potentiometric Probes. Environ. Sci. Technol. Lett. 2017, 4, 410– 415, DOI: 10.1021/acs.estlett.7b00388Google Scholar166https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsFOgt7nK&md5=d3ad81428f6ae008250633b1dc076aa6In Situ Detection of Species Relevant to the Carbon Cycle in Seawater with Submersible Potentiometric ProbesCuartero, Maria; Pankratova, Nadezda; Cherubini, Thomas; Crespo, Gaston A.; Massa, Francesco; Confalonieri, Fabio; Bakker, EricEnvironmental Science & Technology Letters (2017), 4 (10), 410-415CODEN: ESTLCU; ISSN:2328-8930. (American Chemical Society)We report on the development of a submersible probe for the simultaneous potentiometric detection of carbonate, calcium, and pH in seawater. All-solid-state electrodes incorporating nanomaterials provide an adequate response time (<10 s), stability (drifts of <0.9 mV h-1), reproducibility (calibration parameter deviation of <0.7%), and accuracy (deviation of <8% compared to ref. techniques) for real-time monitoring of seawater using a flow system. The functioning of the deployable prototype was checked in an outdoor mesocosm and via long-term monitoring in Genoa Harbor. The electrodes worked properly for 3 wk, and the system demonstrated the capability to autonomously operate with routines for repetitive measurements, data storage, and management. In situ profiles obsd. in Genoa Harbor and Arcachon Bay were validated using on site and ex situ techniques. The validation of in situ-detected carbonate is a challenge because both re-equilibration of the sample with atm. CO2 and the use of apparent thermodn. consts. for speciation calcns. lead to some differences (<20% deviation). The submersible probe is a promising tool for obtaining rapid and trustworthy information about chem. levels in marine systems. Moreover, the fluidic approach allows for the integration of other ion sensors that may require sample pretreatment.
- 168Athavale, R.; Dinkel, C.; Wehrli, B.; Bakker, E.; Crespo, G. A.; Brand, A. Robust Solid-Contact Ion Selective Electrodes for High-Resolution In Situ Measurements in Fresh Water Systems. Environ. Sci. Technol. Lett. 2017, 4, 286– 291, DOI: 10.1021/acs.estlett.7b00130Google Scholar167https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXnsVWrtrY%253D&md5=a34360ca85238b58dfa03196a110ed01Robust Solid-Contact Ion Selective Electrodes for High-Resolution In Situ Measurements in Fresh Water SystemsAthavale, Rohini; Dinkel, Christian; Wehrli, Bernhard; Bakker, Eric; Crespo, Gaston A.; Brand, AndreasEnvironmental Science & Technology Letters (2017), 4 (7), 286-291CODEN: ESTLCU; ISSN:2328-8930. (American Chemical Society)Biogeochem. processes are often confined to very narrow zones in aquatic systems. Therefore, highly resolved in situ measurements are required to study these processes. Potentiometric solid-contact ion selective electrodes (SC-ISEs) are promising tools for such measurements. SC-ISEs show good performance in analyses under controlled exptl. conditions. Very few sensor designs, however, can sustain the challenges of natural water matrixes and external environmental conditions during in situ applications. We fabricated ammonium and pH selective SC-ISEs with functionalized multiwalled carbon nanotubes (f-MWCNT) as a solid contact. Their functionality was tested in the lab. and applied in situ for vertical profiling in a eutrophic lake. Sensors were insensitive to strong redox changes, high sulfide concns., and bright daylight conditions during the application in the lake. In addn., sensors are easily fabricated and exhibit short response times (<10 s). The proposed design of SC-ISEs based on f-MWCNTs is quite suitable for high-resoln. in situ profiling of ionic species in fresh water lakes.
- 169Ding, L.; Ding, J. W.; Ding, B. J.; Qin, W. Solid-contact Potentiometric Sensor for the Determination of Total Ammonia Nitrogen in Seawater. Int. J. Electrochem. Sci. 2017, 12, 3296– 3308, DOI: 10.20964/2017.04.01Google Scholar168https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtV2jt7%252FL&md5=c5e5d881879e0df1bae248637e69a702Solid-contact potentiometric sensor for the determination of total ammonia nitrogen in seawaterDing, Lan; Ding, Jiawang; Ding, Baojun; Qin, WeiInternational Journal of Electrochemical Science (2017), 12 (4), 3296-3308CODEN: IJESIV; ISSN:1452-3981. (Electrochemical Science Group)A solid-contact potentiometric sensor for in situ detection of total ammonia nitrogen (TAN, free ammonia plus the ammonium ion) in seawater is described. In the compact system, an all-solid-state polymeric membrane ammonium-seletive electrode is integrated with a polyvinyl alc. hydrogel buffer film of pH 7.0 and a gas-permeable membrane. The gaseous NH3 in seawater diffuses through the gas-permeable membrane and is converted to NH4+ in the hydrogel buffer, which can be potentiometrically sensed by the solid-contact ammonium-sensitive membrane electrode. The electrode configuration facilitates the alteration of NH3 to NH4+ in the hydrogel buffer film and improves the sensitivity for the detection of TAN by the buffer trap effect. The gas-permeable membrane effectively eliminates the ion interferences from the seawater sample matrixes. The proposed sensor shows a stable potentiometric response in the concn. range of 10-6 - 10-4 M with a detection limit of 6.4 × 10-7 M, and has been successfully applied to the detection of TAN in seawater.
- 170Chango, G.; Palacio, E.; Cerdà, V. Talanta 2018, 186, 554– 560, DOI: 10.1016/j.talanta.2018.04.087Google Scholar169https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXpsVOgs7Y%253D&md5=c21fe1c813f7a9f28443075810b416d9Potentiometric chip-based multipumping flow system for the simultaneous determination of fluoride, chloride, pH, and redox potential in water samplesChango, Gabriela; Palacio, Edwin; Cerda, VictorTalanta (2018), 186 (), 554-560CODEN: TLNTA2; ISSN:0039-9140. (Elsevier B.V.)A simple potentiometric chip-based multipumping flow system (MPFS) has been developed for the simultaneous detn. of fluoride, chloride, pH, and redox potential in water samples. The proposed system was developed by using a poly(Me methacrylate) chip microfluidic-conductor using the advantages of flow techniques with potentiometric detection. For this purpose, an automatic system has been designed and built by optimizing the variables involved in the process, such as: pH, ionic strength, stirring and sample vol. This system was applied successfully to water samples getting a versatile system with an anal. frequency of 12 samples per h. Good correlation between chloride and fluoride concn. measured with ISE and ionic chromatog. technique suggests satisfactory reliability of the system.
- 171Shen, J.; Gagliardi, S.; McCoustra, M. R. S.; Arrighi, V. Effect of humic substances aggregation on the determination of fluoride in water using an ion selective electrode. Chemosphere 2016, 159, 66– 71, DOI: 10.1016/j.chemosphere.2016.05.069Google Scholar170https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XpvFaktLY%253D&md5=f1b1381475e4fe47dd6b635bd4dd0172Effect of humic substances aggregation on the determination of fluoride in water using an ion selective electrodeShen, Junjie; Gagliardi, Simona; McCoustra, Martin R. S.; Arrighi, ValeriaChemosphere (2016), 159 (), 66-71CODEN: CMSHAF; ISSN:0045-6535. (Elsevier Ltd.)The control of drinking water quality is crit. in preventing fluorosis. In this study humic substances (HS) are considered as representative of natural org. matter (NOM) in water. We show that when HS aggregate the response of fluoride ion selective electrodes (ISE) may be perturbed. Dynamic light scattering (DLS) results of both synthetic solns. and natural water sample suggest that low pH and high ionic strength induce HS aggregation. In the presence of HS aggregates, fluoride concn. measured by ISE has a redn. up to 19%. A new "open cage" concept has been developed to explain this reversible phenomenon. The interference of HS aggregation on fluoride measurement can be effectively removed by centrifugation pretreatment.
- 172Machado, A.; Mesquita, R. B. R.; Oliveira, S.; Bordalo, A. A. Talanta 2017, 167, 688– 694, DOI: 10.1016/j.talanta.2017.03.017Google Scholar171https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXktVCrs7c%253D&md5=7b72f447e598daf2cb2fbf5374e4a174Development of a robust, fast screening method for the potentiometric determination of iodide in urine and salt samplesMachado, Ana; Mesquita, Raquel B. R.; Oliveira, Sara; Bordalo, Adriano A.Talanta (2017), 167 (), 688-694CODEN: TLNTA2; ISSN:0039-9140. (Elsevier B.V.)In this work, a potentiometric flow injection method is described for the fast bi-parametric detn. of iodide and iodate in urine and salt samples. The developed methodol. aimed for iodine speciation with a potentially portable system (running on batteries). The iodate redn. to iodide was effectively attained in line within the same manifold. The iodide detn. was accomplished in the dynamic range of 2.50×10-6-1.00×10-3 M and the total iodine dynamic range, resulted from iodide plus iodate, was 3.50×10-6-2.00×10-3 M. The calcd. limits of detection were 1.39×10-6 M and 1.77×10-6 M for iodide and iodate, resp. A detn. rate of 21 h-1 for the bi-parametric iodide and iodate detn. was obtained for sample injection. The urine samples (RSD <5.8% for iodide and RSD <7.0% for iodate) results were in agreement with those obtained by the classic Sandell-Kolthoff reaction colorimetric ref. procedure (RD <7.0%) and std. samples from Centers for Disease Control and Prevention, Atlanta, USA (CDC) international inter-lab. EQUIP program. The developed flow method was also successfully applied to the iodide and iodate detn. in salt samples (RSD <3.1% for iodate and iodide), with comparable results to conventional procedures. No significant interferences were obsd. interference percentage <9% for both detns.
- 173Atherton, J.; King, W. E.; Guzinski, M.; Jasinski, A.; Pendley, B.; Lindner, E. A method to monitor urinary carbon dioxide in patients with septic shock. Sens. Actuators, B 2016, 236, 77– 84, DOI: 10.1016/j.snb.2016.05.076Google Scholar172https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xps1agt7s%253D&md5=1b61032bf913e26397af04b05d7331e6A method to monitor urinary carbon dioxide in patients with septic shockAtherton, James; William E., King, III; Guzinski, Marcin; Jasinski, Artur; Pendley, Bradford; Lindner, ErnoSensors and Actuators, B: Chemical (2016), 236 (), 77-84CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)Severe sepsis and septic shock are life-threatening conditions with mortality rates exceeding 31% (Levy et al., 2012) [1]. Septicemia was the most expensive US hospital condition in 2011 (Torio and Andrews, 2006) [2]. Urinary carbon dioxide may provide rapid, clin. useful information about a patient's status, empowering physicians to intervene earlier and improve septic shock mortality. The objective of this paper is to validate a protocol with a Severinghaus-type CO2 probe for the measurement of urinary CO2 of septic shock patients. This protocol includes (i) sampling urine from a Foley catheter in an intensive care unit setting, (ii) storing samples until anal. at a sep. facility, (iii) calibration of the Severinghaus-type CO2 sensor, and (iv) measuring urinary CO2 levels. We discuss the prepn. and stability of std. solns., storage of urine samples, and the performance characteristics of the Severinghaus type CO2 sensor in relation to mock urine samples, urine quality control stds., and urine samples from healthy volunteers as well as patients in severe sepsis or septic shock. We report the influence of the sample pH, temp., and ionic strength on the precision and accuracy of the measurements of urinary CO2 levels and show that the protocol developed for the quant. assessment of urinary CO2 levels is adequate for the anal. of urine samples collected from a Foley catheter.
- 174Zajda, J.; Crist, N. R.; Malinowska, E.; Meyerhoff, M. E. Asymmetric Anion-selective Membrane Electrode for Determining Nitric Oxide Release Rates from Ppolymeric Films/Electrochemical Devices. Electroanalysis 2016, 28, 277– 281, DOI: 10.1002/elan.201500395Google Scholar173https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXht1Gls7zJ&md5=a0b4376491ceefaa1bbbd3e451c5cd7aAsymmetric anion-selective membrane electrode for determining nitric oxide release rates from polymeric films/electrochemical devices.Zajda, Joanna; Crist, Natalie R.; Malinowska, Elzbieta; Meyerhoff, Mark E.Electroanalysis (2016), 28 (2), 277-281CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)A novel potentiometric method for the detn. of nitric oxide (NO) is presented. The assessment of NO levels is based on the rapid reaction of NO with oxyHb, during which nitrate is formed and then detected potentiometrically using a polymeric membrane anion-selective electrode. The compn. of the anion-selective membrane is optimized to eliminate the response to high levels of oxyHb reagent used to react with NO to form NO3-. The practical utility of the method is demonstrated by detg. the NO release rates from NO donor-doped polymeric films, as well as from a new electrochem. NO generation system within the range of 10 to 55 × 10-10 mol · min-1. The values measured with the new assay system are shown to correlate well with a chemiluminescence ref. method after accounting for the trapping efficiency of NO by the oxyHb soln.
- 175Cuartero, M.; Perez, S.; Garcia, M. S.; Garcia-Canovas, F.; Ortuño, J. A. Comparative enzymatic studies using ion-selective electrodes. The case of cholinesterases. Talanta 2018, 180, 316– 322, DOI: 10.1016/j.talanta.2017.12.029Google Scholar174https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXit1Kgsg%253D%253D&md5=b3282fe489ff0be734c5b24d02797bb2Comparative enzymatic studies using ion-selective electrodes. The case of cholinesterasesCuartero, Maria; Perez, Soraya; Garcia, Maria S.; Garcia-Canovas, Francisco; Ortuno, Joaquin A.Talanta (2018), 180 (), 316-322CODEN: TLNTA2; ISSN:0039-9140. (Elsevier B.V.)The application of traditional ion-selective electrodes for comparative enzymic anal. was demonstrated for the first time in this study. A kinetic-potentiometric method based on the monitoring of the concn. of the ionic substrate involved in the enzymic reaction catalyzed by different cholinesterases is used for this purpose. A comparative study was performed comprising both enzymic assays using different ionic substrates and the corresponding inhibited reactions in presence of neostigmine (a synthetic anticholinesterase). The developed approach is used to obtain valuable comparative results through calcn. of kinetic parameters, such as Michaelis and inhibition consts. Interesting results were obtained for acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) enzymes, which were selected as proof-of-concept: (i) the binding affinity that these enzymes have for their natural substrates showed to be higher (acetylcholine and butyrylcholine resp.) than for their corresponding thiol derivs. (acetylthiocholine and butyrylthiocholine), which are traditionally used in spectrophotometric enzymic assays; (ii) as expected, the max. hydrolysis rate found in the assays of each enzyme was independent of the substrate used; and (iii) acetylcholinesterase enzyme inhibition due to neostigmine was found to be higher (higher inhibition const.). Advantageously, the use of ion-selective electrodes permits to perform cholinesterases' enzymic assays using their natural substrates and under physiol. conditions, unlike the traditional spectrophotometric methods used in routine enzymic assays. Importantly, while well-known enzymes are use throughout this work, this approach can be extended to other types of enzymic assays as a tangible alternative to traditional spectrophotometric methods.
- 176Urbanowicz, M.; Jasinski, A.; Jasinska, M.; Drucis, K.; Ekman, M.; Szarmach, A.; Suchodolski, R.; Pomecko, R.; Bochenska, M. Simultaneous Determination of Na+, K+, Ca2+, Mg2+ and Cl- in Unstimulated and Stimulated Human Saliva Using All Solid State Multisensor Platform. Electroanalysis 2017, 29, 2232– 2238, DOI: 10.1002/elan.201700149Google Scholar175https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtVyqsLnN&md5=a62a2bef2613125ddc3fc89e3181cf65Simultaneous Determination of Na+, K+, Ca2+, Mg2+ and Cl- in Unstimulated and Stimulated Human Saliva Using All Solid State Multisensor PlatformUrbanowicz, Marcin; Jasinski, Artur; Jasinska, Malgorzata; Drucis, Kamil; Ekman, Marcin; Szarmach, Arkadiusz; Suchodolski, Rafal; Pomecko, Radoslaw; Bochenska, MariaElectroanalysis (2017), 29 (10), 2232-2238CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)Human saliva is one of the body fluids which collection method is relatively simple and non-invasive. The article is dedicated to assess concn. (activity) of Na+, K+, Ca2+, Mg2+ and Cl- in fresh, unstimulated or stimulated human saliva samples using single solid contact ion-selective electrodes with conventional ref. electrode and self-made multisensor platform (MP) equipped with ion-selective membranes for Na+, K+, Ca2+, Mg2+ and Cl- and ref. electrode made in solid state technol., based on dispersed KCl in the polymer. Both kind of electrodes, single ISE and miniaturized electrodes in multisensor platform (ISE-MP) were made of glassy carbon. The electrode surfaces have been modified by conductive polymer (PEDOT) layer deposition; with the exception of Cl- electrode, in which conducting polymer was not applied. Potentiometric measurements were used to compare the changes of the ionic compn. in various samples of saliva.
- 177Goda, T.; Yamada, E.; Katayama, Y.; Tabata, M.; Matsumoto, A.; Miyahara, Y. Potentiometric responses of ion-selective microelectrode with bovine serum albumin adsorption. Biosens. Bioelectron. 2016, 77, 208– 214, DOI: 10.1016/j.bios.2015.09.023Google Scholar176https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhsFGgsLfI&md5=683f64dcfb9bafd7d947fd8425aa6d95Potentiometric responses of ion-selective microelectrode with bovine serum albumin adsorptionGoda, Tatsuro; Yamada, Eriko; Katayama, Yurika; Tabata, Miyuki; Matsumoto, Akira; Miyahara, YujiBiosensors & Bioelectronics (2016), 77 (), 208-214CODEN: BBIOE4; ISSN:0956-5663. (Elsevier B.V.)There is a growing demand for an in situ measurement of local pH and ion concns. in biol. milieu to monitor ongoing process of bioreaction and bioresponse in real time. An ion-selective microelectrode can meet the requirements. However, the contact of the electrode with biol. fluids induces biofouling by protein adsorption to result in a noise signal. Therefore, we investigated the relationship between the amt. of nonspecific protein adsorption and the elec. signals in potentiometry by using ion-selective microelectrodes, namely silver/silver chloride (Ag/AgCl), iridium/iridium oxides (Ir/IrOx), and platinum/iridium oxides (Pt/IrOx). The microelectrodes reduced a potential change following the adsorption of bovine serum albumin (BSA) by comparison with the original metal microelectrodes without oxide layers. Suppression in the noise signal was attributed to the increased capacitance at the electrode/soln. interface due to the formation of granulated metal oxide layer rather than a decrease in the amt. of protein adsorbed. Ion sensitivity was maintained for Ir/IrOx against proton, but it was not for Ag/AgCl against chloride ion (Cl-), because of the interference of the equil. reaction by adsorbed BSA mols. on the electrode surface at<10-2 M [Cl-] in the soln. The results open up the application of the Ir/IrOx microelectrode for measuring local pH in realistic dirty samples with a limited influence of electrode pollution by protein adsorption.
- 178Lisak, G.; Arnebrant, T.; Lewenstam, A.; Bobacka, J.; Ruzgas, T. In Situ Potentiometry and Ellipsometry: A Promising Tool to Study Biofouling of Potentiometric Sensors. Anal. Chem. 2016, 88, 3009– 3014, DOI: 10.1021/acs.analchem.5b04364Google Scholar177https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XitlCjs74%253D&md5=2e8e4cb092ad14f58db314f232941177In Situ Potentiometry and Ellipsometry: A Promising Tool to Study Biofouling of Potentiometric SensorsLisak, Grzegorz; Arnebrant, Thomas; Lewenstam, Andrzej; Bobacka, Johan; Ruzgas, TautgirdasAnalytical Chemistry (Washington, DC, United States) (2016), 88 (6), 3009-3014CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)In situ potentiometry and null ellipsometry were combined and used as a tool to follow the kinetics of biofouling of ion-selective electrodes (ISEs). The study was performed using custom-made solid-contact K+-ISEs consisting of a gold surface with immobilized 6-(ferrocenyl)hexanethiol as ion-to-electron transducer that was coated with a potassium-selective plasticized polymer membrane. The electrode potential and the ellipsometric signal (corresponding to the amt. of adsorbed protein) were recorded simultaneously during adsorption of bovine serum albumin (BSA) at the surface of the K+-ISEs. This in situ method may become useful in developing sensors with minimized biofouling.
- 179Ferguson, S. A.; Meyerhoff, M. E. Advances in electrochemical and optical polyion sensing: A review. Sens. Actuators, B 2018, 272, 643– 654, DOI: 10.1016/j.snb.2018.06.127Google Scholar178https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhtlCmsrzI&md5=ebb8c1b8efdd22f27e6819535a117b00Advances in electrochemical and optical polyion sensing: A reviewFerguson, Stephen A.; Meyerhoff, Mark E.Sensors and Actuators, B: Chemical (2018), 272 (), 643-654CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)A review. Electrochem. and optical sensing of polyions were first introduced in the early to mid 1990s via the development and study of the first heparin-sensitive potentiometric and optical polyion sensors. Since then, the no. of reports relating to electrochem. and optical polyion sensing technologies have grown substantially. Both biol. and industrially relevant polyions can be detected using these methods. This paper provides an overview of key accomplishments with respect to polyion sensor-based technologies over the past 25+ years. A summary of the basic designs and sensing principles of single-use/fully reversible polymeric membrane-type potentiometric polyion sensors, voltammetric polyion-sensitive electrodes, and single-use polyion-sensitive optodes is provided. The expansion of polyion sensing to more industrial and cosmetic polyions (i.e., polyquaterniums) is also discussed. Lastly, potential new directions/applications are provided for electrochem. and optical polyion sensors based on all-solid-contact designs (for electrochem.) and paper-based sensing devices (both electrochem. and optical).
- 180Ferguson, S. A.; Wang, X. W.; Meyerhoff, M. E. Detecting levels of polyquaternium-10 (PQ-10) via potentiometric titration with dextran sulphate and monitoring the equivalence point with a polymeric membrane-based polyion sensor. Anal. Methods 2016, 8, 5806– 5811, DOI: 10.1039/C6AY01748GGoogle Scholar179https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhtFSitL3K&md5=5f7ff03eddc373d68f65b0d04e2cfdc0Detecting levels of polyquaternium-10 (PQ-10) via potentiometric titration with dextran sulphate and monitoring the equivalence point with a polymeric membrane-based polyion sensorFerguson, Stephen A.; Wang, Xuewei; Meyerhoff, Mark E.Analytical Methods (2016), 8 (29), 5806-5811CODEN: AMNEGX; ISSN:1759-9679. (Royal Society of Chemistry)Polymeric quaternary ammonium salts (polyquaterniums) have found increasing use in industrial and cosmetic applications in recent years. More specifically, polyquaternium-10 (PQ-10) is routinely used in cosmetic applications as a conditioner in personal care product formulations. Herein, we demonstrate the use of potentiometric polyion-sensitive polymeric membrane-based electrodes to quantify PQ-10 levels. Mixts. contg. both PQ-10 and sodium lauryl sulfate (SLS) are used as model samples to illustrate this new method. SLS is often present in cosmetic samples that contain PQ-10 (e.g., shampoos, etc.) and this surfactant species interferes with the polyion sensor detection chem. However, it is shown here that SLS can be readily sepd. from the PQ-10/SLS mixt. by use of an anion-exchange resin and that the PQ-10 can then be titrated with dextran sulfate (DS). This titrn. is monitored by potentiometric polyanion sensors to provide equivalence points that are directly proportional to PQ-10 concns.
- 181Ferguson, S. A.; Meyerhoff, M. E. Characterization and Quantification of Polyquaterniums via Single Use Polymer Membrane-Based Polyion-Sensitive Electrodes. ACS Sens. 2017, 2, 268– 273, DOI: 10.1021/acssensors.6b00787Google Scholar180https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXmslSlsQ%253D%253D&md5=45428d3c4356daf6602f7656bcf7ccb2Characterization and Quantification of Polyquaterniums via Single-Use Polymer Membrane-Based Polyion-Sensitive ElectrodesFerguson, Stephen A.; Meyerhoff, Mark E.ACS Sensors (2017), 2 (2), 268-273CODEN: ASCEFJ; ISSN:2379-3694. (American Chemical Society)Two facile, robust, and universal methods by which various polymeric quaternary ammonium salts (polyquaterniums (PQs)) can be quantified and characterized using simple potentiometric polymeric membrane polyion-sensitive electrodes as detectors are described. The two methods are (a) direct detection with polycation sensitive membrane electrodes based on the sodium salt of dinonylnaphthalenesulfonate (NaDNNS), and (b) indirect detection using polyanion sensors based on tridodecylmethylammonium chloride (TDMAC) and dextran sulfate (DS) as a titrant to complex the various polyquaternary species (four different PQs: PQ-2, PQ-6, PQ-10, and poly(2-methacryloxyethyltrimethylammonium) chloride (PMETAC)). Direct detection yields information regarding the charge d. of the polycationic species. For the titrn. method, a series of polyanion sensors doped with TDMAC are used to follow a potentiometric titrn. of a PQ species using a syringe pump to deliver the titrant. This indirect detection method is more reliable and yields limits of detection in the ppm range for the four PQs examd. The titrn. method is further explored for detecting excess levels of PQ-6, a common flocculating agent for municipal water supply systems, within the purified water emitted by the Ann Arbor, MI, drinking water treatment plant.
- 182Ferguson, S. A.; Meyerhoff, M. E. Manual and Flow-Injection Detection/Quantification of Polyquaterniums via Fully Reversible Polyion-Sensitive Polymeric Membrane-Based Ion-Selective Electrodes. ACS Sens. 2017, 2, 1505– 1511, DOI: 10.1021/acssensors.7b00527Google Scholar181https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsVagu7vF&md5=540a1f226237c9cf80d5d6708f1b3e0cManual and Flow-Injection Detection/Quantification of Polyquaterniums via Fully Reversible Polyion-Sensitive Polymeric Membrane-Based Ion-Selective ElectrodesFerguson, Stephen A.; Meyerhoff, Mark E.ACS Sensors (2017), 2 (10), 1505-1511CODEN: ASCEFJ; ISSN:2379-3694. (American Chemical Society)The detection of four different polyquaterniums (PQs) using a fully reversible potentiometric polyion sensor in three different detection modes is described. The polyion sensing "pulstrodes" serve as the detector for direct dose-response expts., beaker titrns., and in a flow-injection anal. (FIA) system. Direct polycation response toward PQ-2, PQ-6, PQ-10, and poly(2-methacryloxyethyltrimethylammonium) chloride (PMETAC) yields characteristic information about each PQ species (e.g., relative charge densities, etc.) via syringe pump addn. of each PQ species to a background electrolyte soln. Quant. titrns. were performed using a syringe pump to deliver heparin as the polyanion titrant to quantify all four PQs at μg/mL levels. Both the direct and indirect methods incorporate the use of a three-electrode system including counter, double junction ref., and working electrodes. The working electrode possesses a plasticized poly(vinyl chloride) (PVC) membrane contg. the neutral lipophilic salt of dinonylnaphthalenesulfonate (DNNS-) tridodecylmethylammonium (TDMA+). Further, the titrn. method is useful to quantify PQ-6 levels in recreational swimming pool water collected in Ann Arbor, MI. Finally, a FIA system equipped with a pulstrode detector was used to demonstrate the ability to potentially quantify PQ levels via a more streamlined and semiautomated testing platform.
- 183Cahill, K.; Suttmiller, R.; Oehrle, M.; Sabelhaus, A.; Gemene, K. L. Pulsed Chronopotentiometric Detection of Thrombin Activity Using Reversible Polyion Selective Electrodes. Electroanalysis 2017, 29, 448– 455, DOI: 10.1002/elan.201600401Google Scholar182https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhtlOrt73N&md5=d08683baf1df369dc794a8a55b2833f6Pulsed Chronopotentiometric Detection of Thrombin Activity Using Reversible Polyion Selective ElectrodesCahill, Kaitlin; Suttmiller, Rebecca; Oehrle, Melissa; Sabelhaus, Andrew; Gemene, Kebede L.Electroanalysis (2017), 29 (2), 448-455CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)A simple and rapid electrochem. method for the detection of thrombin activity is presented here for the first time using a synthetic polypeptide substrate and a pulsed chronopotentiometry transduction protocol with polyion selective electrodes. A cathodic current applied across a polyion selective membrane electrode causes the extn. of the polypeptides from the sample into the membrane and the membrane potential, which is a function of the concn. of these polypeptides in the sample, was measured at the same time. Since the polyion extn. is a diffusion-controlled mass transfer process, depletion of the polypeptides at the membrane-sample interface at a characteristic transition time occurs. The square root of the transition time is directly proportional to the concn. of the polypeptide substrate according to the Sand equation. Upon addn. of thrombin, the polypeptide substrate undergoes proteolysis and yields smaller peptide fragments that exhibit smaller measured emf responses since they are less preferred by the membrane, and the transition times become shorter. The rate of change of the square root of the transition time is directly proportional to the change in the polypeptide concn., which in turn relates to the polypeptide hydrolysis time, and can be used for monitoring enzyme activity. Indeed, the square root of transition time is linear with the proteolysis time with R2 = 0.98. The activity of thrombin is 3.6 μg substrate per μg thrombin per Min.
- 184Zhao, G. T.; Ding, J. W.; Yu, H.; Yin, T. J.; Qin, W. Potentiometric Aptasensing of Vibrio alginolyticus Based on DNA Nanostructure-Modified Magnetic Beads. Sensors 2016, 16, 2052, DOI: 10.3390/s16122052Google Scholar183https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXps12kuw%253D%253D&md5=76d48c207f83915f3037063093926e6fPotentiometric aptasensing of Vibrio alginolyticus based on DNA nanostructure-modified magnetic beadsZhao, Guangtao; Ding, Jiawang; Yu, Han; Yin, Tanji; Qin, WeiSensors (2016), 16 (12), 2052/1-2052/9CODEN: SENSC9; ISSN:1424-8220. (MDPI AG)A potentiometric aptasensing assay that couples the DNA nanostructure-modified magnetic beads with a solid-contact polycation-sensitive membrane electrode for the detection of Vibrio alginolyticus is herein described. The DNA nanostructure-modified magnetic beads are used for amplification of the potential response and elimination of the interfering effect from a complex sample matrix. The solid-contact polycation-sensitive membrane electrode using protamine as an indicator is employed to chronopotentiometrically detect the change in the charge or DNA concn. on the magnetic beads, which is induced by the interaction between Vibrio alginolyticus and the aptamer on the DNA nanostructures. The present potentiometric aptasensing method shows a linear range of 10-100 CFU mL-1 with a detection limit of 10 CFU mL-1, and a good specificity for the detection of Vibrio alginolyticus. This proposed strategy can be used for the detection of other microorganisms by changing the aptamers in the DNA nanostructures.
- 185Mikysek, T.; Stoces, M.; Vytras, K. Two Novelties in Ion-pair Formation-based Potentiometric Titrations of Anionic Surfactants. Electroanalysis 2016, 28, 2688– 2691, DOI: 10.1002/elan.201600231Google Scholar184https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhtlOnsrbJ&md5=720064ba9e662297482ab11314b953bbTwo Novelties in Ion-pair Formation-based Potentiometric Titrations of Anionic SurfactantsMikysek, Tomas; Stoces, Matej; Vytras, KarelElectroanalysis (2016), 28 (11), 2688-2691CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)Two novel approaches in ion-pair formation-based potentiometric titrns. of anionic surfactants are presented. First, a new type of the low ohmic coated-wire ion-selective electrode is introduced; the polymeric membrane contg. a plasticizer mixed with carbon powder. Second, didecyldimethylammonium chloride as the cationic titrant is for the first time proposed and applied, providing the titrn. curves with the highest potential jump.
- 186Galovic, O.; Samardzic, M.; Hajdukovic, M.; Sak-Bosnar, M. A new graphene-based surfactant sensor for the determination of anionic surfactants in real samples. Sens. Actuators, B 2016, 236, 257– 267, DOI: 10.1016/j.snb.2016.05.166Google Scholar185https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XpslamsLs%253D&md5=3798cfc42210526bbfb46f9a78aff297A new graphene-based surfactant sensor for the determination of anionic surfactants in real samplesGalovic, Olivera; Samardzic, Mirela; Hajdukovic, Mateja; Sak-Bosnar, MilanSensors and Actuators, B: Chemical (2016), 236 (), 257-267CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)A new high-sensitivity potentiometric all-solid-state sensor for the detn. of anionic surfactants is constructed based on the dimethyldioctadecylammonium-tetraphenylborate (DDA-TPB) ion pair as a sensing material and graphene. Graphene nanoparticles are used for immobilization of the sensing material in the membrane, preventing the leaching of electroactive material from the membrane, thus reducing its elec. resistance and signal noise. The sensor exhibits a Nernstian response for dodecylbenzenesulfonate (DBS) and a sub-Nernstian response for dodecyl sulfate (DS) in the concn. range of 2.5 × 10-7-4.5 × 10-3 M. The detection limits for DS and DBS are 1.5 × 10-7 and 2.5 × 10-7 M, resp. The sensor demonstrates a stable potentiometric response with a signal drift of -1.2 mV/h and exhibits excellent selectivity performance for DS over almost all of the org. and inorg. anions commonly used in com. products. The main application of the sensor is in the detection of the endpoint in potentiometric titrns. of anionic surfactants. The magnitudes of inflexion at the equivalence point range from 174 to 270 mV. The sensor shows satisfactory anal. performance within a pH range of 2-7. The two-component mixts. contg. sodium decanesulfonate (C10) and sodium dodecanesulfonate (C12) are also successfully differentially titrated.
- 187Khaled, E.; Hassan, H. N. A.; Abdelaziz, M. A.; El-Attar, R. O. Novel Enzymatic Potentiometric Approaches for Surfactant Analysis. Electroanalysis 2017, 29, 716– 721, DOI: 10.1002/elan.201600565Google Scholar186https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xhs1Cksr%252FF&md5=0a775258acb45a5ea8e5a93ba40fa82bNovel Enzymatic Potentiometric Approaches for Surfactant AnalysisKhaled, Elmorsy; Hassan, Hassan N. A.; Abdelaziz, Mona A.; El-Attar, Rehab O.Electroanalysis (2017), 29 (3), 716-721CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)The present study described a novel application of simple potentiometric enzymic method for anal. of surfactants based on their inhibitory effect on acetylcholinesterase enzyme (AChE). The enzymic activity was measured through monitoring hydrolysis of acetylcholine (ACh) with a disposable acetylcholine potentiometric sensor. Comprehensive investigations were carried out including the effect of incubation time, cholinesterase enzyme and the working calibration ranges. Based on inhibition of AChE, different cationic, anionic and nonionic surfactants were detd. in the concn. range from 0 to 40 μg mL-1 with detection limits reaching 0.07 μg mL-1 depending on the nature of surfactants. The degree of AChE inhibition caused by different tested surfactants were as follows: cetylpyridinium chloride (CPC)>benzyldimethylhexadecyl ammonium chloride (BDHAC)>Hyamine (Hy)>cetyltrimethylammonium bromide (CTAB)>Triton X-100 (TX-100)>sodium dodecyl sulfate (SDS). The proposed method was applied for detn. of surfactants in pharmaceutical formulation, detergents products and environmental samples with acceptable sensitivity and reproducibility.
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, 88-103. https://doi.org/10.1007/s42242-023-00262-2
- Meixue Lai, Lijie Zhong, Siyi Liu, Yitian Tang, Tingting Han, Huali Deng, Yu Bao, Yingming Ma, Wei Wang, Li Niu, Shiyu Gan. Carbon fiber-based multichannel solid-contact potentiometric ion sensors for real-time sweat electrolyte monitoring. Analytica Chimica Acta 2024, 1287 , 342046. https://doi.org/10.1016/j.aca.2023.342046
Analytical Chemistry
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Abstract
Figure 1
Figure 1. Lindner’s test for the presence of a water layer between an H+-selective membrane and the transducer layer. (12) If a water layer is present, an increasing CO2 sample concentration results in diffusive transport through the membrane and into the water layer. This will result in a pH change at the backside of the membrane and a significant negative potential drift.
Figure 2
Figure 2. Simplified ion-selective electrode selectivity theory for ions of different charge. The two traces show the calculated fraction of primary ion remaining in the membrane phase after ion exchange as a function of sample composition, calculated according to the self-consistent equilibrium model and by a simpler, averaged Nikolsky-Eisenman equation. Top: monovalent primary and divalent interfering ion. Bottom: divalent primary and monovalent interfering ion. (52) To average, the second Nikolsky-Eisenman equation is written to treat the interfering ion as the primary one as vice versa. This averaged Nikolsky-Eisenman equation provides results that are in excellent agreement with the values predicted by the most rigorous model for the entire range of ion exchange.
Figure 3
Figure 3. Coulometric readout principle for solid-contact ISEs with a capacitive layer as a transducer material between electrode surface and ion-selective membrane. (58) The electrochemical cell is held at a constant potential. Any potential change at the sample–membrane interface that is driven by a change in primary ion sample activity is compensated by an opposite potential change at the transducing layer. As shown on the right, this results in a transient current response until a new equilibrium state is reached. A linear relationship between accumulated charge and the logarithmic primary ion activity change is observed and serves as the analytical signal.
Figure 4
Figure 4. Ion transfer at the membrane–solution interface resulting from the oxidation/reduction of a redox probe in the transducing layer as an analytical tool for ion sensing. (68−77) On the right, two response regimes are identified depending on the analyte concentration range. At low sample concentrations, the peak current linearly depends on concentration (diffusion limitation) while at high concentration the peak position exhibits a Nernstian shift with analyte activity change.
Figure 5
Figure 5. Potential change of a potentiometric sensing probe can be visualized by the color change of redox indicator using a closed bipolar electrode configuration. (80) If a constant potential is applied across the bipolar electrode, the potentiometric signal change at the sample side results in an opposite potential change at the detection side, which imposes a new concentration ratio of the redox indicator that results in a visible color change. A colorimetric calibration curve of the bipolar electrode is shown on the right. Reproduced from Jansod, S.; Cuartero, M.; Cherubini, T.; Bakker, E. Anal. Chem., 2018, 90, 6376–6379 (ref (80)). Copyright 2018 American Chemical Society.
Figure 6
Figure 6. Representation of permselectivity properties of solid-state modified gold nanopores. (86,87) The gold surface may be modified with thiol terminated compounds that contain ion-exchanger groups. As a result, ions of the same charge sign are rejected and those of opposite charge are being readily transported. Further chemical functionalization endows the sensing probe with desired chemical selectivity.
Figure 7
Figure 7. Three-dimensional origami paper-based device for potentiometric biosensing of organophosphate pesticides. (119) Left: The device consists of one test pad with electrodes and three folding pads, each for the deposition of sample, enzyme, and substrate reagents, respectively. The folding sequence is identified as Steps I, II, and III. Right: The EMF difference observed between samples with and without analyte resulting from the ability of organophosphate pesticides to inhibit the activity of the enzyme is used to calculate analyte concentration.
Figure 8
Figure 8. Wearable potentiometric sensors for the real-time monitoring of electrolyte level in sweat have become an important direction of research.
Figure 9
Figure 9. Submersible probes containing ion-selective sensing probes are deployed in marine environments for the in situ potentiometric monitoring of macronutrients (166) and species relevant to the carbon cycle. (167) The probes were integrated in a titanium cage containing pumps, electronics, sensors, and an additional multiparameter CTD module for simultaneous conductivity, temperature, and depth measurements.
References
This article references 187 other publications.
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- 2Hu, J. B.; Stein, A.; Bühlmann, P. Rational design of all-solid-state ion-selective electrodes and reference electrodes. TrAC, Trends Anal. Chem. 2016, 76, 102– 114, DOI: 10.1016/j.trac.2015.11.0042https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXitVSqu7fK&md5=e1d8f838c3c01cfa4c121ae10edd283cRational design of all-solid-state ion-selective electrodes and reference electrodesHu, Jinbo; Stein, Andreas; Buhlmann, PhilippeTrAC, Trends in Analytical Chemistry (2016), 76 (), 102-114CODEN: TTAEDJ; ISSN:0165-9936. (Elsevier B. V.)A review. Potentiometric sensing, which requires the use of ion-selective electrodes (ISEs) and ref. electrodes, is used to det. electrochem. the concn. of target ions in a variety of chem. environments. In view of the need for more affordable and portable anal. devices with small sample vols., all-solid-state ISEs and ref. electrodes, in which a solid contact is used as ion-to-electron transducer, are highly desirable. This review describes how all-solid-state ISEs and ref. electrodes function and presents important aspects that should be considered when designing such sensors for specific applications. Approaches to improving reproducibility, the stability of the emf response, lowering detection limits, and novel sensor designs are discussed along with specific examples from the recent literature. Emphasis is placed on the ion-to-electron transduction mechanism and the development of new solid contact materials, with a particular view to miniaturized ion-sensing devices with low cost and calibration-free sensing.
- 3Sophocleous, M.; Atkinson, J. K. A review of screen-printed silver/silver chloride (Ag/AgCl) reference electrodes potentially suitable for environmental potentiometric sensors. Sens. Actuators, A 2017, 267, 106– 120, DOI: 10.1016/j.sna.2017.10.0133https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhs1GqtbrE&md5=1ca943d88e6ed33070ba96f1b65397dbA review of screen-printed silver/silver chloride (Ag/AgCl) reference electrodes potentially suitable for environmental potentiometric sensorsSophocleous, Marios; Atkinson, John K.Sensors and Actuators, A: Physical (2017), 267 (), 106-120CODEN: SAAPEB; ISSN:0924-4247. (Elsevier B.V.)A review. The screen-printed (SP), ref. electrode (RE) has been shown to be a crucial element of potentiometric sensors but it is also the stumbling block for reliable and accurate SP sensors. The easiest, most common and most environmentally friendly, type of RE is the Silver/Silver Chloride (Ag/AgCl) RE. Unfortunately, until now the only reliable RE of this kind is the conventional, liq. or gel-filled type. However, for most environmental and soil applications the use of the conventional RE is not an option, which raises the demand for a robust, rugged and low-cost version to replace the conventional RE. This paper presents a review of the various attempts to produce reliable, SP, Ag/AgCl REs, and explain why almost all of them never reach the commercialisation stage. The paper provides an overview of the main challenges that need to be overcome, details of the electrode's construction, an anal. comparison of their performance in terms of chloride susceptibility, cross-sensitivity and lifetime, and their suitability in different applications depending on their performance characteristics.
- 4Chopade, S. A.; Anderson, E. L.; Schmidt, P. W.; Lodge, T. P.; Hillmyer, M. A.; Bühlmann, P. Self-Supporting, Hydrophobic, Ionic Liquid-Based Reference Electrodes Prepared by Polymerization-Induced Microphase Separation. ACS Sens. 2017, 2, 1498– 1504, DOI: 10.1021/acssensors.7b005124https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsFCjsrbL&md5=00d264a16f9c6854295a93e3b580eedaSelf-Supporting, Hydrophobic, Ionic Liquid-Based Reference Electrodes Prepared by Polymerization-Induced Microphase SeparationChopade, Sujay A.; Anderson, Evan L.; Schmidt, Peter W.; Lodge, Timothy P.; Hillmyer, Marc A.; Buhlmann, PhilippeACS Sensors (2017), 2 (10), 1498-1504CODEN: ASCEFJ; ISSN:2379-3694. (American Chemical Society)Interfaces of ionic liqs. and aq. solns. exhibit stable elec. potentials over a wide range of aq. electrolyte concns. This makes ionic liqs. suitable as bridge materials that sep. in electroanal. measurements the ref. electrode from samples with low and/or unknown ionic strengths. However, methods for the prepn. of ionic liq.-based ref. electrodes were not explored widely. The authors have designed a convenient and reliable synthesis of ionic liq.-based ref. electrodes by polymn.-induced microphase sepn. This technique allows for a facile, single-pot synthesis of ready-to-use ref. electrodes that incorporate ion conducting nanochannels filled with either 1-octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide or 1-dodecyl-3-methylimidazolium bis(trifluoromethyl sulfonyl)imide as ionic liq., supported by a mech. robust cross-linked polystyrene phase. This synthesis procedure allows for the straightforward design of various ref. electrode geometries. These ref. electrodes exhibit a low resistance as well as good ref. potential stability and reproducibility when immersed into aq. solns. varying from deionized, purified H2O to 100 mM KCl, while requiring no correction for liq. junction potentials.
- 5Lewenstam, A.; Blaz, T.; Migdalski, J. Anal. Chem. 2017, 89, 1068– 1072, DOI: 10.1021/acs.analchem.6b027625https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XitVKqtb%252FE&md5=d3be840a0968d0c29a15d5eb4a89fe60All-Solid-State Reference Electrode with Heterogeneous MembraneLewenstam, Andrzej; Blaz, Teresa; Migdalski, JanAnalytical Chemistry (Washington, DC, United States) (2017), 89 (2), 1068-1072CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Novel ref. electrodes with a solid contact coated by a heterogeneous polymer membrane are described. The electrodes were obtained using Ag nanoparticles, AgBr, KBr suspended in THF soln. of PVC and DOS and deposited on Ag substrate, or another substrate covered with Ag, by drop casting. After a short period of soaking in a KBr soln., stable and reproducible formal potentials of -157 ± 2 mV (vs. Ag/AgCl/3 M KCl) were obsd., and the solid-contact ref. electrodes were ready to use. The described ref. electrodes are relatively insensitive to the changes in the sample matrix, the concns. of ions, the pH and the redox potential. These electrodes can also be fabricated in miniaturized form, and thus used to produce miniaturized multielectrode probes.
- 6Zhao, Z. G.; Tu, H. G.; Kim, E. G. R.; Sloane, B. F.; Xu, Y. A flexible Ag/AgCl micro reference electrode based on a parylene tube structure. Sens. Actuators, B 2017, 247, 92– 97, DOI: 10.1016/j.snb.2017.02.1356https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXksVChtrs%253D&md5=bc9f5b8a7e1508ae456f15d66864e25aA flexible Ag/AgCl micro reference electrode based on a parylene tube structureZhao, Zhiguo; Tu, Hongen; Kim, Eric G. R.; Sloane, Bonnie F.; Xu, YongSensors and Actuators, B: Chemical (2017), 247 (), 92-97CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)In the effort of developing micro-electrochem. sensors, the miniaturization of ref. electrodes has been a challenging task. In this paper, a flexible micro ref. electrode with an internal electrolyte reservoir is reported. This new device is based on a unique microfabricated parylene tube structure, which is filled with Cl- rich electrolyte, into which a 50μm diam. silver (Ag) wire covered with a 7.4μm thick silver chloride (AgCl) layer is inserted. The distal end of the tube is filled with potassium chloride (KCl) satd. agarose gel. The Ag wire, thick AgCl layer, and internal electrolyte reservoir lead to a long operation time and a stable ref. voltage. The drift over a 10-h period has been found to be less than 2 mV. The total operation time of the device has exceeded 100 h. Furthermore, the compatibility with microfabrication allows the integration of other components, leading to truly miniaturized electrochem. sensors or sensing systems. To prove this, we demonstrated a pH sensor by combining the ref. electrode and an iridium oxide electrode monolithically integrated on the surface of the parylene tube.
- 7Li, Q. F.; Tang, W.; Su, Y. Z.; Huang, Y. K.; Peng, S.; Zhuo, B. G.; Qiu, S.; Ding, L.; Li, Y. Z.; Guo, X. J. Stable Thin-Film Reference Electrode on Plastic Substrate for All-Solid-State Ion-Sensitive Field-Effect Transistor Sensing System. IEEE Electron Device Lett. 2017, 38, 1469– 1472, DOI: 10.1109/LED.2017.27323527https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXitV2jurvF&md5=a3c3ba0ab8731e5f8648a43ad16ff7c2Stable thin-film reference electrode on plastic substrate for all-solid-state ion-sensitive field-effect transistor sensing systemLi, Qiaofeng; Tang, Wei; Su, Yuezeng; Huang, Yukun; Peng, Sai; Zhuo, Bengang; Qiu, Shi; Ding, Li; Li, Yuanzhe; Guo, XiaojunIEEE Electron Device Letters (2017), 38 (10), 1469-1472CODEN: EDLEDZ; ISSN:1558-0563. (Institute of Electrical and Electronics Engineers)Solid-state thin-film ref. electrodes (REs) were fabricated on plastic substrate based on a titanium/gold/silver/silver chloride (Ti/Au/Ag/AgCl) multi-layer metal structure for ion-sensitive field-effect transistor (ISFET)-based sensing systems. A porous structure polyvinyl butyral membrane was formed on top to maintain a const. concn. of chloride as well as acting as a bridge between the electrolyte inside the membrane and the test soln. Excellent measurement stability was achieved with the fabricated RE, with a small drift rate of the open circuit potential less than 1.7 mV per h. An all-solid-state ISFET sensing system was thus able to be built using the RE for pH measurement, showing excellent reproducibility. The system was finally applied for measuring different beverages, and the measurement results agreed well with those obtained with a com. pH meter.
- 8Mechaour, S. S.; Derardja, A.; Oulmi, K.; Deen, M. J. Effect of the Wire Diameter on the Stability of Micro-Scale Ag/AgCl Reference Electrode. J. Electrochem. Soc. 2017, 164, E560– E564, DOI: 10.1149/2.1211714jes8https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXkslWrtQ%253D%253D&md5=0c0e084190c116852df3c43ec98f765bEffect of the Wire Diameter on the Stability of Micro-Scale Ag/AgCl Reference ElectrodeMechaour, S. Seghir; Derardja, A.; Oulmi, K.; Deen, M. J.Journal of the Electrochemical Society (2017), 164 (14), E560-E564CODEN: JESOAN; ISSN:0013-4651. (Electrochemical Society)Ag chloride that is commonly used as a ref. electrode in many chem. sensors is stable when its dimensions are relatively large. However, its use in sensors, esp. in nanosensors, requires that its size be reduced significantly. The authors report that the stability of very small Ag chloride electrodes could be obtained if a specific potential is applied. The AgCl wires produced by electrodeposition were studied by the chronoamperometry technique. SEM was used to study the properties of the surface of the fabricated wires surface obtained. The stability depends on the Ag chloride surface morphol. Indeed, the Ag/AgCl wire provided a more stable potential when its surface morphol. is like nanosheets. It seems that this surface morphol. obtained for Ag/AgCl wire with a micrometric diam. is a promising element that could be used to measure a variety of biol. parameters such as membrane potential, intracellular free ion concns. and cell-to-cell communication.
- 9Mousavi, M. P. S.; Saba, S. A.; Anderson, E. L.; Hillmyer, M. A.; Bühlmann, P. Avoiding Errors in Electrochemical Measurements: Effect of Frit Material on the Performance of Reference Electrodes with Porous Frit Junctions. Anal. Chem. 2016, 88, 8706– 8713, DOI: 10.1021/acs.analchem.6b020259https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xht1CltrfN&md5=8347f1c3872feb03091a7efacf53c4abAvoiding Errors in Electrochemical Measurements: Effect of Frit Material on the Performance of Reference Electrodes with Porous Frit JunctionsMousavi, Maral P. S.; Saba, Stacey A.; Anderson, Evan L.; Hillmyer, Marc A.; Buhlmann, PhilippeAnalytical Chemistry (Washington, DC, United States) (2016), 88 (17), 8706-8713CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)In many com. available and inhouse-prepd. ref. electrodes, nanoporous glass frits (often of the brand named Vycor) contain the electrolyte soln. that forms a salt bridge between the sample and the ref. soln. Recently, in samples with low ionic strength, the half-cell potentials of ref. electrodes comprising nanoporous Vycor frits are affected by the sample and can shift in response to the sample compn. by >50 mV (which can cause up to 900% error in potentiometric measurements). The large potential variations result from electrostatic screening of ion transfer through the frit due to the neg. charged surfaces of the glass nanopores. Since the com. prodn. of porous Vycor glass was recently discontinued, new materials were used lately as porous frits in com. available ref. electrodes, frits made of Teflon, polyethylene, or one of two porous glasses sold under the brand names CoralPor and Electro-porous KT. The authors studied the effect of the frit characteristics on the performance of ref. electrodes, and show that the unwanted changes in the ref. potential are not unique to electrodes with Vycor frits. Increasing the pore size in the glass frits from the <10 nm into the 1 μm range or switching to polymeric frits with pores in the 1 to 10 μm range nearly eliminates the potential variations caused by electrostatic screening of ion transport through the frit pores. Unfortunately, bigger frit pores result in larger flow rates of the ref. soln. through the pores, which can result in the contamination of test solns.
- 10Guzinski, M.; Jarvis, J. M.; Perez, F.; Pendley, B. D.; Lindner, E.; De Marco, R.; Crespo, G. A.; Acres, R. G.; Walker, R.; Bishop, J. PEDOT(PSS) as Solid Contact for Ion-Selective Electrodes: The Influence of the PEDOT(PSS) Film Thickness on the Equilibration Times. Anal. Chem. 2017, 89, 3508– 3516, DOI: 10.1021/acs.analchem.6b0462510https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXis1yiu7k%253D&md5=fcf88a16e72e65fba548b22f0336afedPEDOT(PSS) as Solid Contact for Ion-Selective Electrodes: The Influence of the PEDOT(PSS) Film Thickness on the Equilibration TimesGuzinski, Marcin; Jarvis, Jennifer M.; Perez, Felio; Pendley, Bradford D.; Lindner, Erno; De Marco, Roland; Crespo, Gaston A.; Acres, Robert G.; Walker, Raymart; Bishop, JosiahAnalytical Chemistry (Washington, DC, United States) (2017), 89 (6), 3508-3516CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)To understand the rate detg. processes during the equilibration of poly(3,4-ethylenedioxythiophene):polystyrenesulfonate-based (PEDOT(PSS)-based) solid contact (SC) ion-selective electrodes (ISEs), the surfaces of Pt, Au, and GC electrodes were coated with 0.1, 1.0, 2.0, and 4.0 μm thick galvanostatically deposited PEDOT(PSS) films. Next, potential vs. time transients were recorded with these electrodes, with and without an addnl. K ion-selective membrane (ISM) coating, following their 1st contact with 0.1M KCl solns. The transients were significantly different when the multilayered sensor structures were assembled on Au or GC compared to Pt. The differences in the rate of equilibration were interpreted as a consequence of differences in the hydrophilicity of PEDOT(PSS) in contact with the substrate electrode surfaces based on XPS and synchrotron radiation-XPS (SR-XPS) anal. of 10-100 nm thick PEDOT(PSS) films. The influence of the layer thickness of the electrochem. deposited PEDOT(PSS)-films on the hydrophilicity of these films was documented by contact angle measurements over PEDOT(PSS)-coated Au, GC, and Pt electrode surfaces. It is possible to minimize the equilibration (conditioning) time of SC ISEs with aq. solns. before usage by optimizing the thickness of the SC layer with a controlled ISM thickness. PEDOT(PSS)-coated Au and GC electrodes exhibit a significant neg. potential drift during their equilibration in an aq. soln. By coating the PEDOT(PSS) surface with an ISM, the neg. potential drift is compensated by a pos. potential drift related to the hydration of the ISM and activity changes at the PEDOT(PSS)|ISM interface. The potential drifts related to activity changes in the ISM were detd. by a novel adaptation of the sandwich membrane method.
- 11Jarvis, J. M.; Guzinski, M.; Perez, F.; Pendley, B. D.; Lindner, E. Differences in Electrochemically Deposited PEDOT(PSS) Films on Au and Pt Substrate Electrodes: A Quartz Crystal Microbalance Study. Electroanalysis 2018, 30, 710– 715, DOI: 10.1002/elan.20170069911https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhs1KktQ%253D%253D&md5=348cc448fda55d1e3a88c33217373aa2Differences in Electrochemically Deposited PEDOT(PSS) Films on Au and Pt Substrate Electrodes: a Quartz Crystal Microbalance StudyJarvis, Jennifer M.; Guzinski, Marcin; Perez, Felio; Pendley, Bradford D.; Lindner, ErnoElectroanalysis (2018), 30 (4), 710-715CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)Studying the responses of K ion-selective electrodes with poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate), PEDOT(PSS), as solid contact (SC) revealed significant differences in the equilibration times and std. potentials of the electrodes fabricated on Au or Pt as substrate electrodes. To trace the source of these differences, PEDOT(PSS) films were deposited under the same conditions onto Au and Pt electrodes on the surface of 10 MHz quartz crystals. During the galvanostatic polymn., the frequency decrease of the quartz crystal was monitored by an electrochem. quartz crystal microbalance (EQCM). In the initial 15 s of the electrochem. deposition, the rate of PEDOT(PSS) polymer growth was significantly faster on Au compared to Pt although the c.d. used for the deposition was the same. Consequently, the total frequency change after a given electrolysis time was always larger on Au compared to Pt, indicating a larger deposited mass or PEDOT(PSS) layer thickness. The differences in the thicknesses of the PEDOT(PSS) films on Au and Pt could be quant. confirmed by XPS etching studies. SEM anal. of PEDOT(PSS) films on Au and Pt also showed characteristic differences.
- 12Guzinski, M.; Jarvis, J. M.; D’Orazio, P.; Izadyar, A.; Pendley, B. D.; Lindner, E. Solid-Contact pH Sensor without CO2 Interference with a Superhydrophobic PEDOT-C-14 as Solid Contact: The Ultimate ″Water Layer″ Test. Anal. Chem. 2017, 89, 8468– 8475, DOI: 10.1021/acs.analchem.7b0200912https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtFChsLrP&md5=b8d022e3431810bd9fa7cab8dcf6d539Solid-Contact pH Sensor without CO2 Interference with a Superhydrophobic PEDOT-C14 as Solid Contact: The Ultimate "Water Layer" TestGuzinski, Marcin; Jarvis, Jennifer M.; DOrazio, Paul; Izadyar, Anahita; Pendley, Bradford D.; Lindner, ErnoAnalytical Chemistry (Washington, DC, United States) (2017), 89 (16), 8468-8475CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)The aim of this study was to find a conducting polymer-based solid contact (SC) for ion-selective electrodes (ISEs) that could become the ultimate, generally applicable SC, which in combination with all kinds of ion-selective membranes (ISMs) would match the performance characteristics of conventional ISEs. The authors present data collected with electrodes using PEDOT-C14, a highly hydrophobic deriv. of poly(3,4-ethylenedioxythiophene) (PEDOT), as SC and compare its performance characteristics with PEDOT-based SC ISEs. PEDOT-C14 has not been used in SC ISEs previously. The PEDOT-C14-based solid contact (SC) ion-selective electrodes (ISEs) (H+, K+, and Na+) have outstanding performance characteristics (theor. response slope, short equilibration time, excellent potential stability, etc.). Most importantly, PEDOT-C14-based SC pH sensors have no CO2 interference, an essential pH sensors property when aimed for whole-blood anal. The superhydrophobic properties (water contact angle: 136 ± 5°) of the PEDOT-C14 SC prevent the detachment of the ion-selective membrane (ISM) from its SC and the accumulation of an aq. film between the ISM and the SC. The accumulation of an aq. film between the ISM and its SC has a detrimental effect on the sensor performance. Although there is a test for the presence of an undesirable water layer, if the conditions for this test are not selected properly, it does not provide an unambiguous answer. However, recording the potential drifts of SC electrodes with pH-sensitive membranes in samples with different CO2 levels can effectively prove the presence or absence of a water layer in a short time period.
- 13Plawinska, Z.; Michalska, A.; Maksymiuk, K. Optimization of capacitance of conducting polymer solid contact in ion-selective electrodes. Electrochim. Acta 2016, 187, 397– 405, DOI: 10.1016/j.electacta.2015.11.05013https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhvFWit7zJ&md5=37f06a65ddc8ae40bfb7bf223f9ec8e3Optimization of capacitance of conducting polymer solid contact in ion-selective electrodesPlawinska, Zaneta; Michalska, Agata; Maksymiuk, KrzysztofElectrochimica Acta (2016), 187 (), 397-405CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Ltd.)All-solid-state ion-selective electrodes with conducting polymer solid contact represent good anal. parameters, comparable with those of classical sensors with internal filling soln. One of parameters characterizing quality of the solid contact, related to ion-to-electron transduction, is the elec. capacitance. However, in many cases this capacitance is lower than for the solid contact only, in the absence of ion-selective membrane. This effect can be disadvantageous, particularly for sensors working under polarization conditions, in galvanostatic mode. The capacitance redn. effect was studied on example of model systems of anion- and cation-selective electrodes with poly(3,4-ethylenedioxythiophene) solid contact with anion- or cation-exchange properties. Basing on results obtained for these membranes and contacts as well as some model calcns., the reasons of reduced capacitance were ascribed to low amt. of ions transferrable across the solid contact/membrane interface. This effect can result from low concn. of mobile ions in the conducting polymer contact or concn. polarization effects. Procedures or pretreatment methods probably minimize the effect of capacitance decrease.
- 14Szucs, J.; Lindfors, T.; Bobacka, J.; Gyurcsanyi, R. E. Ion-selective Electrodes with 3D Nanostructured Conducting Polymer Solid Contact. Electroanalysis 2016, 28, 778– 786, DOI: 10.1002/elan.20150046514https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhslOnsbzM&md5=df2a9d820958401f052e6a690a854c69Ion-selective Electrodes with 3D Nanostructured Conducting Polymer Solid ContactSzucs, Julia; Lindfors, Tom; Bobacka, Johan; Gyurcsanyi, Robert E.Electroanalysis (2016), 28 (4), 778-786CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)Until now both ion-to-electron transducers as well as large surface area nanostructured conducting materials were successfully used as solid contacts for polymer-based ion-selective electrodes. We were interested to explore the combination of these two approaches by fabricating ordered elec. conducting polymer (ECP) nanostructures using 3D nanosphere lithog. and electrosynthesis to provide a high surface area and capacitive interface for solid contact ion-selective electrodes (SC-ISEs). For these studies we used poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT(PSS)) films with 750 nm diam. interconnected pores as the intermediate layer between a glassy carbon electrode and a Ag+ -selective polymeric membrane. We also investigated the feasibility of loading the voids created in the polymer film with a lipophilic redox mediator (1,1'-dimethylferrocene) to provide the resp. ISEs with well-defined/controllable E0 values. These expectations were fulfilled as the std. deviation of E0 values were reduced with almost an order of magnitude for 3D nanostructured SC-ISEs filled with the redox mediator as compared to their redox mediator-free analogs. The detrimental effect of the redox mediator extn. into the plasticized PVC-based ion-selective membrane (ISM) was efficiently suppressed by replacing the PVC-based ISMs with a low diffusivity silicone rubber matrix.
- 15He, N.; Papp, S.; Lindfors, T.; Höfler, L.; Latonen, R. M.; Gyurcsanyi, R. E. Pre-Polarized Hydrophobic Conducting Polymer Solid-Contact Ion Selective Electrodes with Improved Potential Reproducibility. Anal. Chem. 2017, 89, 2598– 2605, DOI: 10.1021/acs.analchem.6b0488515https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsFGitb0%253D&md5=22e50a2763833c564c25fbf246b66935Pre-Polarized Hydrophobic Conducting Polymer Solid-Contact Ion-Selective Electrodes with Improved Potential ReproducibilityHe, Ning; Papp, Soma; Lindfors, Tom; Hofler, Lajos; Latonen, Rose-Marie; Gyurcsanyi, Robert E.Analytical Chemistry (Washington, DC, United States) (2017), 89 (4), 2598-2605CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Elec. conducting polymers (ECPs) are one of the most popular types of materials to interface ion-selective membranes (ISMs) with electron-conducting substrates to construct solid-contact ion-selective electrodes (SCISEs). For optimal ion-to-electron transduction and potential stability, the p-doped ECPs with low oxidn. potentials such as PPy need to be generally in their conducting form along with providing a sufficiently hydrophobic interface to counteract the aq. layer formation. The 1st criterion requires that the ECPs are in their oxidized state, but the high charge d. of this state is detrimental for the prevention of the aq. layer formation. The authors offer here a soln. to this paradox by implementing a highly hydrophobic perfluorinated anion (perfluorooctanesulfonate, PFOS-) as doping ion by which the oxidized form of the ECP becomes hydrophobic. The proof of concept is shown by using polypyrrole (PPy) films doped with PFOS- (PPy-PFOS) as the solid contact in K+-selective SCISEs (K+-SCISE). Prior to applying the plasticized poly(vinyl chloride) ISM, the oxidn. state of the electrodeposited PPy-PFOS was adjusted by polarization to the known open-circuit potential of the solid contact in 0.1M KCl. The prepolarization results in a hydrophobic PPy-PFOS film with a H2O contact angle of 97 ± 5°, which effectively prevents the aq. layer formation under the ISM. Under optimal conditions the K+-SCISEs had a very low std. deviation of E0 of only 501.0 ± 0.7 mV that is the best E0 reproducibility reported for ECP-based SCISEs.
- 16Jaworska, E.; Michalska, A.; Maksymiuk, K. Polypyrrole Nanospheres - Electrochemical Properties and Application as a Solid Contact in Ion-selective Electrodes. Electroanalysis 2017, 29, 123– 130, DOI: 10.1002/elan.20160055416https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhslCnsbbF&md5=12331ab6e61cebeaa54d50ad07fece18Polypyrrole Nanospheres - Electrochemical Properties and Application as a Solid Contact in Ion-selective ElectrodesJaworska, Ewa; Michalska, Agata; Maksymiuk, KrzysztofElectroanalysis (2017), 29 (1), 123-130CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)Polypyrrole nanospheres of uniform size, close to 40 nm, of highly active and unblocked surface were obtained. The novel synthetic approach applied used poly(Bu acrylate) microspheres to deliver the monomer (pyrrole) to the oxidant (iron(III) nitrate) aq. soln. Small portions of dispersion of these nanoparticles were coated on glassy carbon electrodes, yielding stable films suitable for electrochem. studies. Electrochem. expts.: Cyclic voltammetry and electrochem. impedance spectroscopy revealed high transport rate of ions inside the polymer and high charge transfer reactions rate, manifested in highly capacitive characteristics of such layers. These properties are different from those of classical electrochem. obtained polypyrrole. Due to their capacitive properties, polypyrrole nanospheres layers were applied as a solid contact in ion-selective electrodes, on example of a potassium-selective potentiometric sensor. Although the capacitance of the conducting polymer was much lower than in the absence of the ion-selective membrane, it was sufficiently high to obtain sensors with stable potentiometric signals.
- 17Jaworska, E.; Kisiel, A.; Michalska, A.; Maksymiuk, K. Electrochemical Properties of Polypyrrole Nanoparticles - The Role of Doping Ions and Synthesis Medium. Electroanalysis 2018, 30, 716– 726, DOI: 10.1002/elan.20170068517https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhs1KktA%253D%253D&md5=87ee32a283d6037ee69115ad33055526Electrochemical Properties of Polypyrrole Nanoparticles - The Role of Doping Ions and Synthesis MediumJaworska, Ewa; Kisiel, Anna; Michalska, Agata; Maksymiuk, KrzysztofElectroanalysis (2018), 30 (4), 716-726CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)Electrochem. properties of polypyrrole nanoparticles coated on glassy C electrodes were studied. The nanoparticles were obtained in a chem. polymn. step using a novel templateless procedure - oxidn. of pyrrole released either from poly(Bu acrylate) microspheres or from micelles of crosslinked alternating polymer (poly(maleic anhydride-alt-1-octadecene)). Voltammetric measurements confirmed high ion transport rate inside the polymer and minor influence of the kind of doping ion and electrolyte ions present in the soln. However, electrochem. impedance spectroscopy measurements revealed a significant difference in the properties of polypyrrole nanoparticles, depending on the synthesis conditions. In case of polypyrrole synthesized in the presence of poly(Bu acrylate) microspheres EIS spectra were almost independent of kind of electrolyte ions and doping anion, pointing to exposed bulk capacitive properties. However, polypyrrole nanoparticles obtained in the presence of alternating polymer micelles represent a typical const. phase element behavior with impedance significantly dependent on the kind of oxidizing (doping) anion. Due to their capacitive properties polypyrrole nanoparticles obtained in the presence of poly(Bu acrylate) microspheres were applied as solid contacts in ion-selective electrodes.
- 18Jaworska, E.; Gniadek, M.; Maksymiuk, K.; Michalska, A. Polypyrrole Nanoparticles Based Disposable Potentiometric Sensors. Electroanalysis 2017, 29, 2766– 2772, DOI: 10.1002/elan.20170044118https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsFOisLjN&md5=b2c28580f95984b11b46942028138e04Polypyrrole Nanoparticles Based Disposable Potentiometric SensorsJaworska, Ewa; Gniadek, Marianna; Maksymiuk, Krzysztof; Michalska, AgataElectroanalysis (2017), 29 (12), 2766-2772CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)In this work polypyrrole nanoparticles of high electrochem. activity were used to prep. disposable, potentiometric sensors with a paper support. The paper support modified with polypyrrole nanoparticles served as elec. lead and ion-to-electron transducer and it was covered by a typical poly(vinyl chloride) based ion-selective membrane. The properties of this arrangement were tested on example of potassium-selective electrodes. The sensors prepd. benefited from the properties of conducting polymer nanostructures: high elec. cond. and electroactivity as well as absence of suspension stabilizing agent. The obtained electrodes were characterized with anal. parameters well comparable with those of classical ion-selective electrodes.
- 19Yu, K.; He, N.; Kumar, N.; Wang, N. X.; Bobacka, J.; Ivaska, A. Electrosynthesized polypyrrole/zeolite composites as solid contact in potassium ion-selective electrode. Electrochim. Acta 2017, 228, 66– 75, DOI: 10.1016/j.electacta.2017.01.00919https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtVKrsLY%253D&md5=ff6cf8f65f9a798c8a9505183a0fe4e7Electrosynthesized polypyrrole/zeolite composites as solid contact in potassium ion-selective electrodeYu, Kai; He, Ning; Kumar, Narendra; Wang, Nian Xing; Bobacka, Johan; Ivaska, AriElectrochimica Acta (2017), 228 (), 66-75CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Ltd.)Polypyrrole/zeolite composites were studied as solid contact material in potassium ion-selective electrodes (K+-ISEs). Proton-exchanged Zeolite Socony Mobil-5 (H-ZSM-5) with SiO2/Al2O3 ratios of 23, 80 and 280 were electrochem. synthesized with polypyrrole (PPy). The anionic groups on the zeolite framework functioned as the counterions for PPy during the reaction. H-ZSM-5 particles were obsd. on the surface as well as inside the composite films. PPy/H-ZSM-5 composites gave a similar cyclic voltammogram as PPy doped with chloride, PPy(Cl-). The hydrophobicity of the composites decreased in the order PPy/H-ZSM-5-23 > PPy/H-ZSM-5-80 > PPy/H-ZSM-5-280. The redox capacitance of the composite was better used than that of PPy(Cl-) after they were coated with a plasticized PVC membrane. PPy/H-ZSM-5 composite-based K+-ISEs exhibited similar potential stability as the PPy(Cl-)-based K+-ISE. However, when compared with the PPy(Cl-)-based K+-ISE, the detection limit of PPy/H-ZSM-5 composite-based K+-ISEs was enhanced after a long-term conditioning.
- 20Jarvis, J. M.; Guzinski, M.; Pendley, B. D.; Lindner, E. Poly(3-octylthiophene) as solid contact for ion-selective electrodes: contradictions and possibilities. J. Solid State Electrochem. 2016, 20, 3033– 3041, DOI: 10.1007/s10008-016-3340-220https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xht1yqt7nE&md5=76caeae349b41310c5da8c7f5909fc00Poly(3-octylthiophene) as solid contact for ion-selective electrodes: contradictions and possibilitiesJarvis, Jennifer M.; Guzinski, Marcin; Pendley, Bradford D.; Lindner, ErnoJournal of Solid State Electrochemistry (2016), 20 (11), 3033-3041CODEN: JSSEFS; ISSN:1432-8488. (Springer)The hydrophobic conductive polymer, poly(3-octylthiophene) (POT), is considered as uniquely suited to be used as an ion-to-electron transducer in solid contact (SC) ion-selective electrodes (ISEs).the reports on the performance characteristics of POT-based SC ISEs are quite conflicting. the potential sources of the contradicting results on the ambiguous drift and poor potential reproducibility of POT-based ISEs are compiled, and different approaches to minimize the drift and the differences in the std. potentials of POT-based SC ISEs are shown. To set the potential of the POT film, it has been loaded with a 7,7,8,8-tetracyanoquinodimethane (TCNQ/TCNQ·-) redox couple. It is hypothesized that once the POT film has a stable, highly reproducible redox potential, it will provide similarly stable and reproducible interfacial potentials between the POT film and the electron-conducting substrate and result in SC ISEs with excellent reproducibility and potential stability. the potentials of Au, GC, and Pt electrodes with drop-cast POT film coatings were recorded in KCl solns. as a function of time.Some of the POT films were loaded with TCNQ and coated with a K+-selective membrane. The improvement in the potential stabilities and sensor-to-sensor reproducibility as a consequence of the incorporation of TCNQ in the POT film and the potentiostatic control of the TCNQ/TCNQ·-ratio is reported.
- 21Zdrachek, E.; Bakker, E. Electrochemically Switchable Polymeric Membrane Ion-Selective Electrodes. Anal. Chem. 2018, 90, 7591– 7599, DOI: 10.1021/acs.analchem.8b0128221https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhtVWntL7I&md5=96edae264dcac3ae4a4b446b71d85433Electrochemically Switchable Polymeric Membrane Ion-Selective ElectrodesZdrachek, Elena; Bakker, EricAnalytical Chemistry (Washington, DC, United States) (2018), 90 (12), 7591-7599CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)We present here for the first time a solid contact ion-selective electrode suitable for the simultaneous sensing of cations (tetrabutylammonium) and anions (hexafluorophosphate), achieved by electrochem. switching. The membrane is based on a thin plasticized polyurethane membrane deposited on poly(3-octylthiophene) (POT) and contains a cation exchanger and lipophilic electrolyte (ETH 500). The cation exchanger is initially in excess; the ion-selective electrode exhibits an initial potentiometric response to cations. During an oxidative current pulse, POT is converted into POT+, which results in the expulsion of cations from the membrane followed by the extn. of anions from the sample soln. to fulfill the electroneutrality condition. This creates a defined excess of lipophilic cation in the membrane, resulting in a potentiometric anion response. A reductive current pulse restores the original cation response by triggering the conversion of POT+ back into POT, which is accompanied by the expulsion of anions from the membrane and the extn. of cations from the sample soln. Various current pulse magnitudes and durations are explored, and the best results in terms of response slope values and signal stability were obsd. with an oxidn. current pulse of 140 μA cm-2 applied for 8 s and a redn. current pulse of -71 μA cm-2 applied for 8 s.
- 22Jaworska, E.; Mazur, M.; Maksymiuk, K.; Michalska, A. Fate of Poly(3-octylthiophene) Transducer in Solid Contact Ion-Selective Electrodes. Anal. Chem. 2018, 90, 2625– 2630, DOI: 10.1021/acs.analchem.7b0423322https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXnvVGgsw%253D%253D&md5=d2d76871224b3f5edb3c64d7c05b4acdFate of Poly(3-octylthiophene) Transducer in Solid Contact Ion-Selective ElectrodesJaworska, Ewa; Mazur, Maciej; Maksymiuk, Krzysztof; Michalska, AgataAnalytical Chemistry (Washington, DC, United States) (2018), 90 (4), 2625-2630CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)An exptl. approach allowing visualization and quantification of underestimated spontaneous process of partition of conducting polymer transducer material to the ion-selective membrane phase is proposed. The approach proposed is based on optical properties of the transducer material applied, using polythiophene as a model system. It is shown that this process occurs not only during sensor prepn. step but also during pretreatment of the sensor before use. As shown, this uncontrolled partition of the transducer to the receptor leads to conducting polymer contents in the membrane phase reaching 0.5 % wt./wt.; this process is accompanied by a partial spontaneous change of the oxidn. state of polythiophene. The conducting polymer present in the membrane participates to some extent in the overall response of the sensor, which can be obsd. as a change in the polythiophene optical emission spectra. Fluorescence microscopic images obtained clearly show that the conducting polymer is distributed throughout the membrane thickness, being present also at the membrane / soln. interface. The exptl. results presented were obtained for K+-selective sensors using poly(3-octylthiophene) as a model transducer, however, the proposed approach is also applicable for other systems.
- 23Liu, C. C.; Jiang, X. H.; Zhao, Y. Y.; Jiang, W. W.; Zhang, Z. M.; Yu, L. M. A solid-contact Pb2+- selective electrode based on electrospun polyaniline microfibers film as ion-to-electron transducer. Electrochim. Acta 2017, 231, 53– 60, DOI: 10.1016/j.electacta.2017.01.16223https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXivVKmtrw%253D&md5=d47f164b0d06e38bcf5d32ea60800510A solid-contact Pb2+- selective electrode based on electrospun polyaniline microfibers film as ion-to-electron transducerLiu, Chenchen; Jiang, Xiaohui; Zhao, Yunyan; Jiang, Wenwen; Zhang, Zhiming; Yu, LiangminElectrochimica Acta (2017), 231 (), 53-60CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Ltd.)Electrospun polyaniline (PANI) microfibers are applied as ion-to-electron transducer in solid contact Pb2+-ion-selective electrode (GC/s-PANI/Pb2+-ISE). The corresponding electrode shows a Nernstian slope of 28.4 mV/decade, and a detection limit of 6.3 × 10-10 M can be acquired within a range of 10-9-10-3M Pb(NO3)2, with a response time shorter than 10s. The GC/s-PANI/Pb2+-ISE performs higher capacitance and lower impedance than the drop-coating GC/d-PANI/Pb2+-ISE measured by CV and EIS, demonstrating faster ion-to-electron transportation. Addnl., in the H2O layer test, interfacial H2O film is eliminated in the GC/s-PANI/Pb2+-ISE. The developed electrode is applied to the detn. of lead in real tap H2O, and the corresponding results are in compliance with those detd. by at. absorption spectrometry (AAS) method. This study targeted at PANI microfibers demonstrates a novel strategy of boosting potential stability and decreasing detection limit for solid contact ion-selective electrodes.
- 24Abramova, N.; Moral-Vico, J.; Soley, J.; Ocana, C.; Bratov, A. Solid contact ion sensor with conducting polymer layer copolymerized with the ion-selective membrane for determination of calcium in blood serum. Anal. Chim. Acta 2016, 943, 50– 57, DOI: 10.1016/j.aca.2016.09.01724https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhsFKmtrbJ&md5=7b6653163c4ad7ad60631cb74496fdafSolid contact ion sensor with conducting polymer layer copolymerized with the ion-selective membrane for determination of calcium in blood serumAbramova, Natalia; Moral-Vico, Javier; Soley, Jordi; Ocana, Cristina; Bratov, AndreyAnalytica Chimica Acta (2016), 943 (), 50-57CODEN: ACACAM; ISSN:0003-2670. (Elsevier B.V.)A new solid contact ion selective electrode with intermediate conducting polymer (CP) layer formed by electropolymn. on a gold electrode of a bifunctional monomer, n-phenyl-ethylenediamine-methacrylamide (NPEDMA), which contains a methacrylamide group attached to aniline, is presented. The conducting polymer was studied by means of optical spectroscopy, cyclic voltammetry and potentiometric measurements. Ca2+-ion-selective membrane based on acrylated urethane polymer was shown to co-polymerize with the CP forming highly adhesive boundary that prevents formation of water layers between the CP and membrane, thus enhancing the stability and life-time of the sensor. The designed ion-selective electrode was successfully used for detn. of total calcium ion concn. in blood serum samples.
- 25Boeva, Z. A.; Lindfors, T. Few-layer graphene and polyaniline composite as ion-to-electron transducer in silicone rubber solid-contact ion-selective electrodes. Sens. Actuators, B 2016, 224, 624– 631, DOI: 10.1016/j.snb.2015.10.05425https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhvVSlurbJ&md5=b002bed47df0ad36308ba56e8ae2ea41Few-layer graphene and polyaniline composite as ion-to-electron transducer in silicone rubber solid-contact ion-selective electrodesBoeva, Zhanna A.; Lindfors, TomSensors and Actuators, B: Chemical (2016), 224 (), 624-631CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)We have used for the first time a composite consisting of few-layer exfoliated graphene and elec. conducting polyaniline (PANI) as the ion-to-electron transducer (solid-contact) in Ca2+-selective solid-contact electrodes (CaSCISEs). The drop cast transducer deposited from the graphene-PANI dispersion in N-methylpyrrolidone makes use of the synergistic effect of these two materials. It maintains the ion-to-electron transduction which is characteristic for the elec. conducting polymers (ECP), but in addn., graphene improves the reproducibility of the std. potential of the SCISEs compared to the neat PANI based electrodes and increases the hydrophobicity of the transducer (ca. 30° higher water contact angle) which counteracts the water layer formation. Our results reveal that the incorporation of few-layer graphene in the transducer layer improved also the initial potential stability and the response characteristics of the CaSCISEs due to the electrocatalytic effect of the graphene-ECP composite, which facilitates the electron transfer at the transducer/substrate interface. We obtained a potential reproducibility of only ±4 mV (n = 3) for the CaSCISEs having graphene-PANI as the solid-contact. The CaSCISEs in this study had a detection limit of 5 × 10-8 M Ca2+, which was obtained without any sophisticated pre-treatment protocols.
- 26He, N.; Gyurcsanyi, R. E.; Lindfors, T. Electropolymerized hydrophobic polyazulene as solid-contacts in potassium-selective electrodes. Analyst 2016, 141, 2990– 2997, DOI: 10.1039/C5AN02664D26https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xkt1Wrsb8%253D&md5=1a356a1c115bf510deb31f7eab217cd8Electropolymerized hydrophobic polyazulene as solid-contacts in potassium-selective electrodesHe, Ning; Gyurcsanyi, Robert E.; Lindfors, TomAnalyst (Cambridge, United Kingdom) (2016), 141 (10), 2990-2997CODEN: ANALAO; ISSN:0003-2654. (Royal Society of Chemistry)Electropolymd. hydrophobic polyazulene (PAz) based solid-state potassium ion-selective electrodes (SC-ISEs) have been characterized in terms of their suitability for clin. application. Polarization of the PAz solid contact before applying the plasticized poly(vinyl chloride) based K+-selective membrane was implemented as a convenient approach to address the general problem of the irreproducible std. potential (E0) of SC-ISEs. Using this method, the E0 reproducibility among different electrodes was, in the worst case, ±7.9 mV (n = 4). The effectiveness of the redox buffer-free approach presented here in stabilizing E0 is strengthened by the absence of light, oxygen and carbon dioxide sensitivity of the PAz SC-ISEs. No evidence was found for the formation of an aq. layer for the PAz-based SC-ISEs. Thus the hydrophobic carbon structure of PAz having a water contact angle of 98 ± 11°, which is slightly higher than that for graphene, can apparently efficiently counteract the aq. layer formation. In terms of the specific application, the PAz solid contact ISEs were found to show a remarkably good potential stability at their first contact with an aq. sample. We also confirmed that the PAz-based SC-ISEs can be used for the accurate detn. of the K+ concn. in serum solns. Overall, the PAz solid contact shows significant advantages as compared to the state-of-the-art of elec. conducting polymer based SC-ISEs.
- 27Cuartero, M.; Bishop, J.; Walker, R.; Acres, R. G.; Bakker, E.; De Marco, R.; Crespo, G. A. Evidence of double layer/capacitive charging in carbon nanomaterial-based solid contact polymeric ion-selective electrodes. Chem. Commun. 2016, 52, 9703– 9706, DOI: 10.1039/C6CC04876E27https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhtFSitLbE&md5=6d69f20c07c48f538c1a802da1a20c06Evidence of double layer/capacitive charging in carbon nanomaterial-based solid contact polymeric ion-selective electrodesCuartero, Maria; Bishop, Josiah; Walker, Raymart; Acres, Robert G.; Bakker, Eric; De Marco, Roland; Crespo, Gaston A.Chemical Communications (Cambridge, United Kingdom) (2016), 52 (62), 9703-9706CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)This paper presents the first direct spectroscopic evidence for double layer or capacitive charging of carbon nanomaterial-based solid contacts in all-solid-state polymeric ion-selective electrodes (ISEs). Here, we used synchrotron radiation-XPS (SR-XPS) and SR valence band (VB) spectroscopy in the elucidation of the charging mechanism of the SCs.
- 28Jaworska, E.; Maksymiuk, K.; Michalska, A. Optimizing Carbon Nanotubes Dispersing Agents from the Point of View of Ion-selective Membrane Based Sensors Performance - Introducing Carboxymethylcellulose as Dispersing Agent for Carbon Nanotubes Based Solid Contacts. Electroanalysis 2016, 28, 947– 953, DOI: 10.1002/elan.20150060928https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhvFemsb%252FM&md5=0ce7e436e291b433fd6163939ffc948cOptimizing carbon nanotubes dispersing agents from the point of view of ion-selective membrane based sensors performance-introducing carboxymethylcellulose as dispersing agent for carbon nanotubes based solid contactsJaworska, Ewa; Maksymiuk, Krzysztof; Michalska, AgataElectroanalysis (2016), 28 (5), 947-953CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)The influence of dispersing agent used to prep. carbon nanotubes solid-contact on the performance of all-solid state ion-selective electrodes was evaluated. Excess of surfactant dispersing agent is leading to deterioration of sensor performance, however, removal of dispersing agent - a typically applied approach - is resulting in substantial change of transducer layer phys. properties, which can influence sensor performance. As remedy the authors propose application of a polymeric dispersing agent - CM-cellulose. Thus obtained ion-selective electrodes were characterized by high potential readings stability both within day and between days.
- 29Lv, E. G.; Ding, J. W.; Qin, W. Potentiometric aptasensing of small molecules based on surface charge change. Sens. Actuators, B 2018, 259, 463– 466, DOI: 10.1016/j.snb.2017.12.06729https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXitVWlsbzN&md5=777c768d56d027a4def722951b50a41aPotentiometric aptasensing of small molecules based on surface charge changeLv, Enguang; Ding, Jiawang; Qin, WeiSensors and Actuators, B: Chemical (2018), 259 (), 463-466CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)Solid-state potentiometric sensors based on surface charge change are well-established tools for measuring ions and biol. species. However, their use for detection of small mols. with high sensitivity and good selectivity is still elusive. In this work, a novel potentiometric aptasensing platform for small mols. is presented, using bisphenol A (BPA) as a model. The proposed sensor can be prepd. by layer-by-layer assembling of carboxylated multiwall carbon nanotubes, poly(diallyldimethylammonium chloride) (polycation), and aptamer (polyanion) on the electrode surface. The presence of BPA induces the conformational change and detachment of the aptamer at the surface of the modified electrode, which leads to a variation of the surface charge (neg. to pos.) and therefore a potential change. The introduction of polyions can cause substantial charge change on the electrode surface, thus improving the sensitivity of the sensor. The morphol. and electron-transfer properties of the electrode have been characterized. Under optimum conditions, the present sensor shows a stable response to BPA in the concn. range from 3.2 × 10-8 to 1.0 × 10-6 M with a detection limit of 1.0 × 10-8 M. The proposed methodol. can be used for sensitive potentiometric sensing of other small mols. involved in aptamer/target binding events.
- 30Yin, T. J.; Li, J. H.; Qin, W. An All-solid-state Polymeric Membrane Ca2+-selective Electrode Based on Hydrophobic Alkyl-chain-functionalized Graphene Oxide. Electroanalysis 2017, 29, 821– 827, DOI: 10.1002/elan.20160038330https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xhslygu7vL&md5=81725aa3a2a0ccef36108b1e03a30052An All-solid-state Polymeric Membrane Ca2+-selective Electrode Based on Hydrophobic Alkyl-chain-functionalized Graphene OxideYin, Tanji; Li, Jinghui; Qin, WeiElectroanalysis (2017), 29 (3), 821-827CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)An all-solid-state polymeric membrane Ca2+-selective electrode based on hydrophobic octadecylamine-functionalized graphene oxide has been developed. The hydrophobic composite in the ion-selective membrane not only acts as a transduction element to improve the potential stability for the all-solid-state Ca2+-selective electrode, but also is used to immobilize Ca2+ ionophore with lipophilic side chains through hydrophobic interactions. The developed all-solid-state Ca2+-selective electrode shows a stable potential response in the linear range of 3.0×10-7-1.0×10-3 M with a slope of 24.7±0.3 mV/dec, and the detection limit is (1.6±0.2 )×10-7 M (n=3). Addnl., due to the hydrophobicity and elec. cond. of the composite, the proposed all-solid-state ion-selective electrode exhibits an improved stability with the absence of water layer between the ion-selective membrane and the underlying glassy carbon electrode. This work provides a simple, efficient and low-cost methodol. for developing stable and robust all-solid-state ion-selective electrode with ionophore immobilization.
- 31Paczosa-Bator, B.; Piech, R.; Wardak, C.; Cabaj, L. Application of graphene supporting platinum nanoparticles layer in electrochemical sensors with potentiometric and voltammetric detection. Ionics 2018, 24, 2455– 2464, DOI: 10.1007/s11581-017-2356-731https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhvVKltbbO&md5=94397cb97b7a5f3fd5d2dfb8f916c0ecApplication of graphene supporting platinum nanoparticles layer in electrochemical sensors with potentiometric and voltammetric detectionPaczosa-Bator, Beata; Piech, Robert; Wardak, Cecylia; Cabaj, LeszekIonics (2018), 24 (8), 2455-2464CODEN: IONIFA; ISSN:0947-7047. (Springer)The present work reports a possibility of using a layer made of graphene supporting platinum nanoparticles (PtNPs-GR) in electrochem. sensors as active and intermediate layer. New sensors with greatly improved both potentiometric and voltammetric signals were prepd. by using a simple and effective drop casting method and characterized by a cyclic voltammetry and a electrochem. impedance spectroscopy. The performance of the new potentiometric sensor was evaluated by the use an ion-selective membrane with well-known valinomycin ion carrier. Potassium electrodes had a Nernstian slope (59.10 mV/pK), high stability and reproducibility of the std. potential values, and a very small drift potential. Under optimized operating conditions, the voltammetric sensor with PtNPs-GR responded to paracetamol concn. in the range from 20 nM to 2.2 μM with the detection limit of 8 nM.
- 32Li, J. H.; Yin, T. J.; Qin, W. An effective solid contact for an all-solid-state polymeric membrane Cd2+-selective electrode: Three-dimensional porous graphene-mesoporous platinum nanoparticle composite. Sens. Actuators, B 2017, 239, 438– 446, DOI: 10.1016/j.snb.2016.08.00832https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhtlehurrL&md5=57f1602b9a8c864f8bfbc9034b438146An effective solid contact for an all-solid-state polymeric membrane Cd2+-selective electrode: Three-dimensional porous graphene-mesoporous platinum nanoparticle compositeLi, Jinghui; Yin, Tanji; Qin, WeiSensors and Actuators, B: Chemical (2017), 239 (), 438-446CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)The three-dimensional porous graphene-mesoporous platinum nanoparticle (3D PGR-MPN) composite is used as solid contact for developing an all-solid-state polymeric membrane Cd2+ ion-selective electrode (Cd2+-ISE). The 3D PGR with MPNs as crosslinking sites can be synthesized by a facile hydrothermal co-assembly method. The obtained 3D PGR-MPN composite is promising for acting as solid contact due to its unique characteristics such as high interfacial area, superior double layer capacitance, excellent cond. and high hydrophobicity. The ISE exhibits a stable Nernstian response in the range of 10-8-10-4 M and the detection limit is 10-8.8 M. The 3D PGR-MPN-based Cd2+-ISE shows good potential response and no water layer exists between the polymeric membrane and the 3D PGR-MPN layer. Addnl., the proposed Cd2+-ISE is robust to O2, CO2 and light interferences. This work provides a versatile method for prepg. an effective solid contact to develop a stable and reliable all-solid-state ISE.
- 33Xu, J. A.; Jia, F.; Li, F. H.; An, Q. B.; Gan, S. Y.; Zhang, Q. X.; Ivaska, A.; Niu, L. Simple and Efficient Synthesis of Gold Nanoclusters and Their Performance as Solid Contact of Ion Selective Electrode. Electrochim. Acta 2016, 222, 1007– 1012, DOI: 10.1016/j.electacta.2016.11.06933https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhvFegur%252FJ&md5=a5ad4edf36dea7efcac74a295282c06dSimple and Efficient Synthesis of Gold Nanoclusters and Their Performance as Solid Contact of Ion Selective ElectrodeXu, Jianan; Jia, Fei; Li, Fenghua; An, Qingbo; Gan, Shiyu; Zhang, Qixian; Ivaska, Ari; Niu, LiElectrochimica Acta (2016), 222 (), 1007-1012CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Ltd.)Gold nanoclusters are ideal materials as solid transducer in all-solid-state ion-selective electrodes (ISEs) due to their high hydrophobicity, excellent ion-to-electron transduction, high specific capacitance and outstanding chem. stability. In this paper, monolayer-protected gold nanoclusters (MPCs) were synthesized by a simple one-phase method requiring a relatively short reaction time with high yield (60%). Transmittance electronic microscopy (TEM) and at.-force microscopy (AFM) were used to characterize the morphol. of MPCs. The compn. of MPCs was studied by UV-vis spectrometry, Matrix-assisted laser desorption ionization (MALDI) mass spectrometry, X-ray diffraction (XRD) measurement and XPS measurements. The performance of MPCs based ISEs was thoroughly characterized by electrochem. impedance, emf. and chronopotentiometry measurement. Comparison with the performance of ISE with other signal transducing materials such as conductive polymer, carbon nanotube, graphene and fullerene, the MPCs based ISEs have higher potential st ability and reproducibility, lower detection limit, longer operating life (one year) and higher anti-interference ability.
- 34An, Q. B.; Jiao, L. S.; Jia, F.; Ye, J. J.; Li, F. H.; Gan, S. Y.; Zhang, Q. X.; Ivaska, A.; Niu, L. Robust single-piece all-solid-state potassium-selective electrode with monolayer-protected Au clusters. J. Electroanal. Chem. 2016, 781, 272– 277, DOI: 10.1016/j.jelechem.2016.10.05334https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhslGqtrbN&md5=14d5565790cbae23c01d68396ae8538eRobust single-piece all-solid-state potassium-selective electrode with monolayer-protected Au clustersAn, Qingbo; Jiao, Liansheng; Jia, Fei; Ye, Junjin; Li, Fenghua; Gan, Shiyu; Zhang, Qixian; Ivaska, Ari; Niu, LiJournal of Electroanalytical Chemistry (2016), 781 (), 272-277CODEN: JECHES; ISSN:1873-2569. (Elsevier B.V.)High stability of the signal and simplicity in fabrication of the device are the two important requirements in development of potentiometric sensors. A robust single-piece all-solid-state potassium-selective electrode (K-SPE) was developed by incorporating monolayer-protected Au clusters (MPCs) as advanced ion-to-electron transducers into a conventional ion-selective membrane (ISM). The extraordinary properties of MPCs such as high soly., profound hydrophobicity and large capacitance make them quite suitable to be used in fabrication of single-piece electrodes (SPEs) with advanced performance. The developed KSPEs contg. small amt. of MPCs in the membrane showed a significant increase in the potential stability (12.9 μV/h), lower detection limit (10-6.1 M) and prolonged life time (high performance still after 3 wk). The multi-valence MPCs in the membrane facilitated the ion-to-electron transduction and fast establishment of the potential equil. resulting in fast response time in potential measurements. The inserted MPCs did not cause any interference either in the potential formation process or in the selectivity of the ion-selective membrane.
- 35Yin, T. J.; Jiang, X. J.; Qin, W. A magnetic field-directed self-assembly solid contact for construction of an all-solid-state polymeric membrane Ca2+- selective electrode. Anal. Chim. Acta 2017, 989, 15– 20, DOI: 10.1016/j.aca.2017.08.01535https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtl2rsLvE&md5=1d56c31935f4f95a946da9d97160d462A magnetic field-directed self-assembly solid contact for construction of an all-solid-state polymeric membrane Ca2+-selective electrodeYin, Tanji; Jiang, Xiaojing; Qin, WeiAnalytica Chimica Acta (2017), 989 (), 15-20CODEN: ACACAM; ISSN:0003-2670. (Elsevier B.V.)A magnetic field-directed self-assembly solid contact has been proposed for developing an all-solid-state polymeric membrane Ca2+-selective electrode. The solid contact was prepd. by phys. adsorbing magnetic graphene powder on a magnetic gold electrode under the direction of the magnetic field. The proposed method for prepg. solid contact avoids using the aq. solns. and is simple, fast and general as compared to the multilayer drop-casting and electrodeposition methods. The all-solid-state Ca2+-selective electrode based on magnetic graphene as solid contact shows a stable potential response in the linear range of 1.0 × 10-6-1.0 × 10-3 M with a slope of 28.2 mV/decade, and the detection limit is ∼4.0 × 10-7 M. Addnl., the magnetic graphene-based electrode shows a comparable potential stability performance to other graphene-based all-solid-state ion-selective electrodes, such as a reduced undesirable water layer and being insensitive to the interferences of O2, CO2 and light. This work provides a favorable way to prep. solid contact for use in the field of all-solid-state ion-selective electrodes.
- 36He, Q.; Das, S. R.; Garland, N. T.; Jing, D. P.; Hondred, J. A.; Cargill, A. A.; Ding, S. W.; Karunakaran, C.; Claussen, J. C. Enabling Inkjet Printed Graphene for Ion Selective Electrodes with Postprint Thermal Annealing. ACS Appl. Mater. Interfaces 2017, 9, 12719– 12727, DOI: 10.1021/acsami.7b0009236https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXivVOisLw%253D&md5=bda54e91f82a089ecd7e32f355bce1e9Enabling Inkjet Printed Graphene for Ion Selective Electrodes with Postprint Thermal AnnealingHe, Qing; Das, Suprem R.; Garland, Nathaniel T.; Jing, Dapeng; Hondred, John A.; Cargill, Allison A.; Ding, Shaowei; Karunakaran, Chandran; Claussen, Jonathan C.ACS Applied Materials & Interfaces (2017), 9 (14), 12719-12727CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)Inkjet printed graphene (IPG) has recently shown tremendous promise in reducing the cost and complexity of graphene circuit fabrication. Herein we demonstrate, for the first time, the fabrication of an ion selective electrode (ISE) with IPG. A thermal annealing process in a nitrogen ambient environment converts the IPG into a highly conductive electrode (sheet resistance changes from 52.8 ± 7.4 MΩ/for unannealed graphene to 172.7 ± 33.3Ω/for graphene annealed at 950°C). Raman spectroscopy and field emission SEM (FESEM) anal. reveals that the printed graphene flakes begin to smooth at an annealing temp. of 500 °C and then become more porous and more elec. conductive when annealed at temps. of 650 °C and above. The resultant thermally annealed, IPG electrodes are converted into potassium ISEs via functionalization with a polyvinyl chloride (PVC) membrane and valinomycin ionophore. The developed potassium ISE displays a wide linear sensing range (0.01mM to 100 mM), a low detection limit (7 μM), minimal drift (8.6 10-6 V/s), and a negligible interference during electrochem. potassium sensing against the backdrop of interfering ions [i.e., sodium (Na), magnesium (Mg), and calcium (Ca)] and artificial eccrine perspiration. Thus, the IPG ISE shows potential for potassium detection in a wide variety of human fluids including plasma, serum, and sweat.
- 37Weber, A. W.; O’Neil, G. D.; Kounaves, S. P. Solid Contact Ion-Selective Electrodes for in Situ Measurements at High Pressure. Anal. Chem. 2017, 89, 4803– 4807, DOI: 10.1021/acs.analchem.7b0036637https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXlvVGqsr0%253D&md5=6be68464dacd04c826d7e48c1f09f81cSolid Contact Ion-Selective Electrodes for in Situ Measurements at High PressureWeber, Andrew W.; O'Neil, Glen D.; Kounaves, Samuel P.Analytical Chemistry (Washington, DC, United States) (2017), 89 (9), 4803-4807CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Solid contact polymeric ion-selective electrodes (SC-ISEs) have been fabricated using microporous carbon (μPC) as the ion-to-electron transducer, loaded with a liq. membrane cocktail contg. both ionophore and additive dissolved in plasticizer. These SC-ISEs were characterized and are suitable for anal. in aq. environments at pressures of 100 bar. Potassium ISEs, prepd. in this manner, showed excellent performance at both atm. and elevated pressures, as evaluated by their response slopes and potential stability. These novel SC-ISEs are capable of measuring K+ at pressures under which traditional liq.-filled ISEs fail. Furthermore, the effect of pressure on the response of these sensors had little or no effect on potential, sensitivity, or limit of detection. High pressure sensor calibrations were performed in std. solns. as well as simulated seawater samples to demonstrate their usefulness as sensors in a deep-sea environment. These novel SC-ISE sensors show promise of providing the ability to make in situ real-time measurements of ion-fluxes near deep-ocean geothermal vents.
- 38Piek, M.; Piech, R.; Paczosa-Bator, B. All-solid-state nitrate selective electrode with graphene/tetrathiafulvalene nanocomposite as high redox and double layer capacitance solid contact. Electrochim. Acta 2016, 210, 407– 414, DOI: 10.1016/j.electacta.2016.05.17038https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XpsVygsrc%253D&md5=9c3e4d35dffbc51575b2aababf9b5f9eAll-solid-state nitrate selective electrode with graphene/tetrathiafulvalene nanocomposite as high redox and double layer capacitance solid contactPiek, Magdalena; Piech, Robert; Paczosa-Bator, BeataElectrochimica Acta (2016), 210 (), 407-414CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Ltd.)Electrodes with graphene-tetrathiafulvalene nanocomposite intermediate layer between a glassy C disk electrode and an ionophore-doped solvent polymeric membrane were made as a new type of all-solid-state ion-selective electrodes. The proposed interlayers prepd. in a quite simple drop casting method exhibited a high redox and double layer capacitance resulting from the use of both, tetrathiafulvalene (TTF/TTF+) as redox-reaction based transducer and graphene (GR) as C material with a large surface area forming high elec. double layer at the ion-selective membrane and the solid contact interface. The influence of the used solid-contact compn. on metrol. parameters of studied electrodes was characterized by electrochem. measurements. The graphene-TTF/TTF+ solid contact layer capacitance detd. applying a current 5 nA was 1.18 mF and potential drift was only 4.26 μV s-1. The GR-TTF/TTF+-modified electrodes exhibited a good Nernstian response with a slope of -59.14 mV/dec at 10-6-10-1 M nitrate ions.
- 39Piek, M.; Piech, R.; Paczosa-Bator, B. The Complex Crystal of NaTCNQ-TCNQ Supported on Different Carbon Materials as Ion-to-Electron Transducer in All-Solid-State Sodium-Selective Electrode. J. Electrochem. Soc. 2016, 163, B573– B579, DOI: 10.1149/2.0341613jes39https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXpslentLk%253D&md5=0114dce2f6774666e7d38026adce8172The complex crystal of NaTCNQ-TCNQ supported on different carbon materials as ion-to-electron transducer in all-solid-state sodium-selective electrodePiek, Magdalena; Piech, Robert; Paczosa-Bator, BeataJournal of the Electrochemical Society (2016), 163 (13), B573-B579CODEN: JESOAN; ISSN:0013-4651. (Electrochemical Society)This work demonstrates the application of conductive org. crystals (7,7,8,8-tetracyanoquinodimethane (TCNQ) and its Na salt (NaTCNQ)) supported on C nanomaterials (CNMs) as solid contact layer in all-solid-state ion-selective electrodes (ASS-ISEs). As ion-to-electron transducer between the ionically conducting membrane and the electronically conducting glassy C new layers based on a high capacity of charge transfer and a redox TCNQ/TCNQ- reaction are proposed. Developed CNM-NaTCNQ- TCNQ-contacted sensors provided a near to Nernstian response to Na and excellent elec. parameters. The highest electrode capacitance was 2.15 mF, as the potential drift (and electrodes resistance) are significantly reduced due to the presence in solid contact combination of materials having ionic or electron cond. Also, the introduction of NaTCNQ in Na-selective electrodes improves their selectivity toward to interfering cations. C nanomaterials type used in the interlayer affects, in the different way, the anal. and elec. parameters of proposed ASS-ISEs. The possibility of improving the electrodes sensitivity, linear range and detection limit, by changing the NaTCQ:TCNQ ratio, is also presented.
- 40Piek, M.; Piech, R.; Paczosa-Bator, B. TTF-TCNQ Solid Contact Layer in All-Solid-State Ion-Selective Electrodes for Potassium or Nitrate Determination. J. Electrochem. Soc. 2018, 165, B60– B65, DOI: 10.1149/2.0161803jes40https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXjtlKjs7k%253D&md5=2f7c68e318020ea5ed8fc5b2d96c8b50TTF-TCNQ Solid Contact Layer in All-Solid-State Ion-Selective Electrodes for Potassium or Nitrate DeterminationPiek, Magdalena; Piech, Robert; Paczosa-Bator, BeataJournal of the Electrochemical Society (2018), 165 (2), B60-B65CODEN: JESOAN; ISSN:0013-4651. (Electrochemical Society)Nowadays, org. donor-acceptor mols. have attracted a lot of scientific attention because of their unique properties and potential applications in various fields. Although tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) is well known charge transfer salt for a long time, the first application of this material as ion-to-electron transducer in ion-selective electrodes is presented. As a proof of concept, potassium-selective and nitrate-selective solid-state electrodes were constructed. Moreover, TTF-TCNQ intermediate layers were fabricated using two org. solvents. Developed potassium sensors displayed a good Nernstian response with a slope of 58.52 mV/decade (10-6-10-1 M K+), whereas the nitrate-selective electrodes showed a sensitivity of -58.47 mV/decade (10-5-10-1 M NO-3). Reproducible std. potentials and low detection limits were obsd. Potential stability of studied electrodes was evaluated using current-reversal chronopotentiometry. The capacitance of TTF-TCNQ-contacted electrodes is 255 μF and 629 μF for K+ and NO-3 sensors. The results of measurements conducted reveal that TTF-TCNQ has an appropriate effect on potentiometric sensors performance.
- 41Jaworska, E.; Naitana, M. L.; Stelmach, E.; Pomarico, G.; Wojciechowski, M.; Bulska, E.; Maksymiuk, K.; Paolesse, R.; Michalska, A. Introducing Cobalt(II) Porphyrin/Cobalt(III) Corrole Containing Transducers for Improved Potential Reproducibility and Performance of All-Solid-State Ion-Selective Electrodes. Anal. Chem. 2017, 89, 7107– 7114, DOI: 10.1021/acs.analchem.7b0102741https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXpvVSltbk%253D&md5=524ffa437fc229842608dd57287baca9Introducing Cobalt(II) Porphyrin/Cobalt(III) Corrole Containing Transducers for Improved Potential Reproducibility and Performance of All-Solid-State Ion-Selective ElectrodesJaworska, Ewa; Naitana, Mario L.; Stelmach, Emilia; Pomarico, Giuseppe; Wojciechowski, Marcin; Bulska, Ewa; Maksymiuk, Krzysztof; Paolesse, Roberto; Michalska, AgataAnalytical Chemistry (Washington, DC, United States) (2017), 89 (13), 7107-7114CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)A novel solid contact type for all-solid-state ion-selective electrodes is introduced, yielding high stability and reproducibility of potential readings between sensors as well as improved anal. performance. The transducer phase herein proposed takes advantage of the presence of porphyrinoids contg. the same metal ion at different oxidn. states. In contrast to the traditional approach, the compds. of choice are not a redox pair; although they have different oxidn. states, they cannot be electrochem. driven one to another. The compds. of choice were cobalt(II) porphyrin and cobalt(III) corrole, both characterized by a high stability of the coordinated metal ions in their resp. redox states and elec. neutrality, as well as relatively high lipophilicity. The porphyrinoids were used together with carbon nanotubes to yield transducer layers for ion-selective electrodes. As a result, the authors obtained a high stability of potential readings of the resulting ion-selective electrodes together with good reproducibility between different sensor batches. Moreover, advantageously the presence of porphyrinoids in the transducer phase results in improvement of the anal. performance of the sensors: linear response range and selectivity due to interactions with membrane components, resulting in tailoring of ion fluxes through the membrane phase. Thus, carbon nanotubes with the cobalt(II) porphyrin/cobalt(III) corrole system are promising alternatives for existing transducer systems for potentiometric sensors.
- 42Ishige, Y.; Klink, S.; Schuhmann, W. Intercalation Compounds as Inner Reference Electrodes for Reproducible and Robust Solid-Contact Ion-Selective Electrodes. Angew. Chem., Int. Ed. 2016, 55, 4831– 4835, DOI: 10.1002/anie.20160011142https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XktFGktbg%253D&md5=0c3309e479f473f8a6c748f58f4861d1Intercalation Compounds as Inner Reference Electrodes for Reproducible and Robust Solid-Contact Ion-Selective ElectrodesIshige, Yu; Klink, Stefan; Schuhmann, WolfgangAngewandte Chemie, International Edition (2016), 55 (15), 4831-4835CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)With billions of assays performed every year, ion-selective electrodes (ISEs) provide a simple and fast technique for clin. anal. of blood electrolytes. The development of cheap, miniaturized solid-contact (SC-)ISEs for integrated systems, however, remains a difficult balancing act between size, robustness, and reproducibility, because the defined interface potentials between the ion-selective membrane and the inner ref. electrode (iRE) are often compromised. Target cation-sensitive intercalation compds., such as partially charged Li Fe phosphate (LFP), can be applied as iREs of the quasi-first kind for ISEs. The sym. response of the interface potentials towards target cations ultimately results in ISEs with high robustness towards the inner filling (∼5 mV dec-1 conc.) as well as robust and miniaturized SC-ISEs. They have a predictable and stable potential derived from the LiFePO4/FePO4 redox couple (97.0 ± 1.5 mV after 42 days).
- 43Komaba, S.; Akatsuka, T.; Ohura, K.; Suzuki, C.; Yabuuchi, N.; Kanazawa, S.; Tsuchiya, K.; Hasegawa, T. All-solid-state ion-selective electrodes with redox-active lithium, sodium, and potassium insertion materials as the inner solid-contact layer. Analyst 2017, 142, 3857– 3866, DOI: 10.1039/C7AN01068K43https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsVejtbfK&md5=1ce57189145e07d57885747f68c71cbeAll-solid-state ion-selective electrodes with redox-active lithium, sodium, and potassium insertion materials as the inner solid-contact layerKomaba, Shinichi; Akatsuka, Tatsuya; Ohura, Kohei; Suzuki, Chihiro; Yabuuchi, Naoaki; Kanazawa, Shintaro; Tsuchiya, Kazuhiko; Hasegawa, TakuAnalyst (Cambridge, United Kingdom) (2017), 142 (20), 3857-3866CODEN: ANALAO; ISSN:0003-2654. (Royal Society of Chemistry)All-solid-state ion-selective electrodes as potentiometric ion sensors for Li, Na, and K were demonstrated by installing a composite layer contg. a powder of alkali insertion materials, LixFePO4, Na0.33MnO2, and KxMnO2·nH2O, resp., as an inner solid-contact layer between the electrode substrate and plasticized poly(vinyl chloride) (PVC)-based ion-sensitive membrane contg. the corresponding ionophores for Li+, Na+, and K+ ions. These double-layer ion-selective electrodes, consisting of the composite and PVC layers prepd. by a simple drop cast method, exhibit a quick potential response (<5 s) to each alkali-metal ion with sufficient Nernstian slopes of calibration curves, ∼59 mV per decade. The installation of the insertion materials as the inner solid-contact layers is highly efficient for the stabilization of membrane potential, resulting in a prompt response to the alkali ion activity in the analyte, compared to those of the electrodes without the alkali insertion materials. From a.c. impedance measurements for the electrodes, the inner layer of the installed alkali insertion materials drastically reduces the impedance of the membrane/electrode interface, leading to an improvement in their ion-sensing performance.
- 44Klink, S.; Ishige, Y.; Schuhmann, W. Prussian Blue Analogues: A Versatile Framework for Solid-Contact Ion-Selective Electrodes with Tunable Potentials. ChemElectroChem 2017, 4, 490– 494, DOI: 10.1002/celc.20170009144https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXitlClsbw%253D&md5=2f313bf2b5bc81572fae2397aa58d5daPrussian Blue Analogues: A Versatile Framework for Solid-Contact Ion-Selective Electrodes with Tunable PotentialsKlink, Stefan; Ishige, Yu; Schuhmann, WolfgangChemElectroChem (2017), 4 (3), 490-494CODEN: CHEMRA; ISSN:2196-0216. (Wiley-VCH Verlag GmbH & Co. KGaA)The development of solid-contact ion-selective electrodes (SC-ISEs) (e.g. for point-of-care sensors) requires simple inner ref. electrodes (iREs) with predictable and reproducible potentials. Intercalation compds. fulfill these requirements, as they respond to target ions present in the ion-selective membrane. Their applicability, however, is limited by the availability of intercalation frameworks capable to intercalate the target ion of interest. We report that Prussian Blue analogs (PBAs) can serve as versatile iREs for a range of target ions of clin. interest, such as Na+, K+, or Ca2+. Combining target-ion intercalated PBAs with ion-selective membranes results in a family of all-solid SC-ISEs, which are capable as ISEs with an inner filling, yet cheap and suitable for mass-prodn. The SC-ISEs' std. potential is predictable and can be tuned by altering the PBAs' redox-active transition metal or by changing its state of charge.
- 45Zeng, X. Z.; Qin, W. A solid-contact potassium-selective electrode with MoO2 microspheres as ion-to-electron transducer. Anal. Chim. Acta 2017, 982, 72– 77, DOI: 10.1016/j.aca.2017.05.03245https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtVGnsbrL&md5=f42660f9463012fbc1c63f77171e80b3A solid-contact potassium-selective electrode with MoO2 microspheres as ion-to-electron transducerZeng, Xianzhong; Qin, WeiAnalytica Chimica Acta (2017), 982 (), 72-77CODEN: ACACAM; ISSN:0003-2670. (Elsevier B.V.)A solid-contact ion-selective electrode (SC-ISE) for potassium with MoO2 microspheres as ion-to-electron transducer is described. MoO2 microsphers can be synthesized via the redn. of MoO3 nanobelts in an isopropanol solvent with a mild process, and the obtained MoO2 microspheres were characterized by x-ray diffraction and field-emission SEM. With the application of MoO2 microspheres, the newly fabricated SC-ISE for K+ exhibits a stable and rapid potential response. A near Nernstian slope of 55 mV/decade to potassium activities in the range of 10-5 - 10-3 M is found and the detection limit is 10-5.5 M. Impedance spectra and chronopotentiometry results show that a smaller resistance together with a larger double layer capacitance is guaranteed due to the introduction of the intermediate layer of MoO2 microspheres. Addnl., light, O2 and CO2 do not induce significant influences to the present SC-ISE, and a reduced water layer between the ion selective membrane and the underlying conductor is formed. Thus, MoO2 microspheres, as metallic analogs, can be used as a good candidate for the new type of transducing layer in SC-ISEs.
- 46Zeng, X. Z.; Yu, S. Y.; Yuan, Q.; Qin, W. Solid-contact K+-selective electrode based on three-dimensional molybdenum sulfide nanoflowers as ion-to-electron transducer. Sens. Actuators, B 2016, 234, 80– 83, DOI: 10.1016/j.snb.2016.04.15346https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XntFymtL4%253D&md5=43235ed5ded9161f1424ec62e990cfbaSolid-contact K+-selective electrode based on three-dimensional molybdenum sulfide nanoflowers as ion-to-electron transducerZeng, Xianzhong; Yu, Shunyang; Yuan, Qun; Qin, WeiSensors and Actuators, B: Chemical (2016), 234 (), 80-83CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)Three-dimensional (3D) molybdenum sulfide (MoS2) nanoflowers have been synthesized via a novel hydrothermal method and applied as ion-to-electron transducer for solid-contact ion-selective electrodes (SC-ISEs). The morphol. and elemental compn. of the prepd. nanomaterials have been characterized. The performance of the developed K+-SC-ISE has been demonstrated by detg. K+ in soln. with a polymeric membrane contg. valinomycin as the ionophore. A Nernstian slope of 55.8 mV/decade with a detection limit of 10-5.5 M can be obtained. Using the 3D flowerlike MoS2 as solid contact, the fabricated K+-SC-ISE exhibits a smaller impedance and more stable potential response than the coated-wire electrode. In addn., the novel SC-ISE behaves well in the water layer test and shows good resistance to interferences from light, O2 and CO2. It is believed that the 3D MoS2 nanoflowers can be a good alternative as solid contact in SC-ISEs.
- 47Egorov, V. V.; Novakovskii, A. D.; Zdrachek, E. A. Modeling of the effect of diffusion processes on the response of ion-selective electrodes by the finite difference technique: Comparison of theory with experiment and critical evaluation. J. Anal. Chem. 2017, 72, 793– 802, DOI: 10.1134/S106193481707004847https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtFaqsLvP&md5=7f3eb3b035a723103b70eea1ca34946aModeling of the effect of diffusion processes on the response of ion-selective electrodes by the finite difference technique: Comparison of theory with experiment and critical evaluationEgorov, V. V.; Novakovskii, A. D.; Zdrachek, E. A.Journal of Analytical Chemistry (2017), 72 (7), 793-802CODEN: JACTE2; ISSN:1061-9348. (Pleiades Publishing, Ltd.)Exptl. data are compared with the results of calcns. by the finite difference technique within the dynamic diffusion model of the interphase potential on an example of a picrate-selective electrode in real scenarios corresponding to the conditions of the detn. of selectivity coeffs. by the methods recommended by IUPAC. In the majority of the considered cases, the calcd. values of the potential and selectivity coeffs. and also the dynamics of potential change at particular steps well agree with the exptl. data. The model has principal restrictions, leading the failure of calcns., when the concn. of potential-detg. ions in the near-electrode layer of the soln. performed is low according to the algorithm of measurements, whereas the instant increase in its concn. in the surface membrane layer due to the replacement of the sample soln. induces a flux of these ions from the surface deep into of the membrane.
- 48Egorov, V. V.; Novakovskii, A. D.; Zdrachek, E. A. A Simple Dynamic Diffusion Model of the Response of Highly Selective Electrodes: The Effect of Simulation Parameters and Boundary Conditions on the Results of Calculations. Russ. J. Electrochem. 2018, 54, 381– 390, DOI: 10.1134/S102319351804003148https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXotF2nt70%253D&md5=efd97478de852d068c082bb4850d52e5A Simple Dynamic Diffusion Model of the Response of Highly Selective Electrodes: The Effect of Simulation Parameters and Boundary Conditions on the Results of CalculationsEgorov, V. V.; Novakovskii, A. D.; Zdrachek, E. A.Russian Journal of Electrochemistry (2018), 54 (4), 381-390CODEN: RJELE3; ISSN:1023-1935. (Pleiades Publishing, Ltd.)For a tetrabutylammonium-selective electrode with a ion-exchange membrane, in the real-work scenario corresponding to the detn. of selectivity coeffs. by the IUPAC-recommended method of sep. solns., it is shown that of the results of calcns. obtained within the framework of the dynamic diffusion model based on the use of the finite-difference technique substantially depend on of the chosen boundary conditions and the values of arbitrarily set simulation parameters. The key parameter that dets. the quality of simulation results is the thickness of the elementary layer in the membrane phase, esp. for low diffusion coeffs. It is found that the use of thin elementary layers in membranes and thick elementary layers in the aq. phase makes it possible to combine the high quality with the high calcn. rate. In simulating the long-term expts., account should be taken of the accumulation of the potential-detg. ion in the aq. soln. vol. as a result of its displacement by a foreign ion from the membrane. A good correspondence between calcn. data and exptl. results is demonstrated.
- 49Egorov, V. V.; Novakovskii, A. D.; Zdrachek, E. A. An Interface Equilibria-Triggered Time-Dependent Diffusion Model of the Boundary Potential and Its Application for the Numerical Simulation of the Ion-Selective Electrode Response in Real Systems. Anal. Chem. 2018, 90, 1309– 1316, DOI: 10.1021/acs.analchem.7b0413449https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhvFGjtr3L&md5=7a477189564d3cde5f4859d1f5fafad7An Interface Equilibria-Triggered Time-Dependent Diffusion Model of the Boundary Potential and Its Application for the Numerical Simulation of the Ion-Selective Electrode Response in Real SystemsEgorov, Vladimir V.; Novakovskii, Andrei D.; Zdrachek, Elena A.Analytical Chemistry (Washington, DC, United States) (2018), 90 (2), 1309-1316CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)A simple dynamic model of the phase boundary potential of ion-selective electrodes is presented. The model is based on the calcns. of the concn. profiles of the components in membrane and sample soln. phases by finite difference method. The fundamental idea behind the discussed model is that the concn. gradients in membrane and sample soln. phases det. only the diffusion of the components inside corresponding phases, but not the transfer across the interface. The transfer of the components across the interface at any instant of time is detd. by the corresponding local interphase equil. According to the presented model, each new calcn. cycle begins with the correction of the components concns. in the near-boundary (1st) layers of the membrane and soln., based on the consts. of the interphase equil. and the concns. established at a given time as a result of diffusion. The cor. concns. of the components in the boundary layers every time give a start to a new cycle of the diffusion processes calcns. inside each phase from the 1st layer to the 2nd one etc. In contrast to the known Morf's model, the above-mentioned layers do not comprise an imaginary part and they are entirely localized in the corresponding phases, and this allows performing the equil. concns. calcns. taking into account material balance for each component. The model remains operational for any realistic scenarios of the electrode functioning. The efficiency and predictive ability of the proposed model are confirmed by comparing the results of calcns. with the exptl. data on the dynamics of the potential change of a picrate-selective electrode in nitrate solns. when detg. the selectivity coeffs. using the methods recommended by IUPAC.
- 50Yuan, D. J.; Bakker, E. Overcoming Pitfalls in Boundary Elements Calculations with Computer Simulations of Ion Selective Membrane Electrodes. Anal. Chem. 2017, 89, 7828– 7831, DOI: 10.1021/acs.analchem.7b0177750https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtFGnsLfK&md5=b2ec2a0682aae7c9a86a457683739734Overcoming Pitfalls in Boundary Elements Calculations with Computer Simulations of Ion Selective Membrane ElectrodesYuan, Dajing; Bakker, EricAnalytical Chemistry (Washington, DC, United States) (2017), 89 (15), 7828-7831CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Finite difference anal. of ion-selective membranes is a valuable tool for understanding a range of time dependent phenomena such as response times, long and medium term potential drifts, detn. of selectivity, and (re)conditioning kinetics. It is here shown that an established approach based on the diffusion layer model applied to an ion-exchange membrane fails to use mass transport to account for concn. changes at the membrane side of the phase boundary. Instead, such concns. are imposed by the ion-exchange equil. condition, without taking into account the source of these ions. The limitation is illustrated with a super-Nernstian potential jump, where a membrane initially void of analyte ion is exposed to incremental concns. of analyte in the sample. To overcome this limitation, the two boundary elements, one at either side of the sample-membrane interface, are treated here as a combined entity and its total concn. change is dictated by diffusional fluxes into and out of the interface. For each time step, the concn. distribution between the two boundary elements is then computed by ion-exchange theory. The resulting finite difference simulation is much more robust than the earlier model and gives a good correlation to expts.
- 51Sanders, T. M.; Myers, M.; Asadnia, M.; Umana-Membreno, G. A.; Baker, M.; Fowkes, N.; Parish, G.; Nener, B. Description of ionophore-doped membranes with a blocked interface. Sens. Actuators, B 2017, 250, 499– 508, DOI: 10.1016/j.snb.2017.04.14351https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXns1aiu7c%253D&md5=358f2c76b9118a0bc7290d55f4e02c7cDescription of ionophore-doped membranes with a blocked interfaceSanders, Tarun M.; Myers, Matthew; Asadnia, Mohsen; Umana-Membreno, Gilberto A.; Baker, Murray; Fowkes, Neville; Parish, Giacinta; Nener, BrettSensors and Actuators, B: Chemical (2017), 250 (), 499-508CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)Ion sensors with blocked interfaces, such as coated-wire electrodes (CWEs) and ion-selective field effect transistors (ISFETs), are increasingly being used as alternatives to traditional ion-selective electrodes (ISEs). This work provides insights into the behavior of ionophore-doped membranes in soln., where one side completely blocks ion transfer, using the Nernst-Planck-Poisson (NPP) model, including reaction terms. Extensive investigations were conducted, demonstrating that the NPP model provides reasonable predictions, as well as insight into the interplay between interfacial kinetics, complexation, diffusion and elec. processes. Model validation is achieved through its application to and anal of exptl results obtained for AlGaN/GaN ISFETs with ionophore-doped membranes.
- 52Zdrachek, E.; Bakker, E. Describing Ion Exchange at Membrane Electrodes for Ions of Different Charge. Electroanalysis 2018, 30, 633– 640, DOI: 10.1002/elan.20170070052https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhvFegs73M&md5=d89d42b84212f7ddab34ef28ce2a9b27Describing Ion Exchange at Membrane Electrodes for Ions of Different ChargeZdrachek, Elena; Bakker, EricElectroanalysis (2018), 30 (4), 633-640CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)It is well-documented in the literature that the Nikolsky-Eisenman equation cannot accurately describe the equil. of ion exchange at membrane electrodes for ions of different charge. Despite this, unfortunately, it is still widely used owing to the complexity of the more rigorous formalism developed by Bakker et al. in 1994. Here, different available approaches are presented in a unified manner and compared. This includes two different approxns. that are equally appropriate for cases of low level of interference where the extent of ion-exchange is comparatively small, one of which is introduced here for the 1st time. The comparison also considers the permutated form of the Nikolsky-Eisenman equation, where the primary ion is treated as the interfering ion and vice versa. As the permutated form gives a deviation from the thermodn. model that is opposite that of the regular Nikolsky-Eisenman equation, the two can be combined to give a semi-empirical equation that is surprisingly close to the thermodn. model and that comprises a single equation for any charge combination. The different choices presented here may be helpful to solve more complex theor. problems, as for example in the modeling of the time dependence of the electrode response by numerical simulation where the interfacial step condition is a unique and difficult feature of the calcn.
- 53Zdrachek, E.; Bakker, E. Time-Dependent Determination of Unbiased Selectivity Coefficients of Ion-Selective Electrodes for Multivalent Ions. Anal. Chem. 2017, 89, 13441– 13448, DOI: 10.1021/acs.analchem.7b0372653https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhvVSjurnK&md5=4c25593b04c680159bc5295704c4197aTime-Dependent Determination of Unbiased Selectivity Coefficients of Ion-Selective Electrodes for Multivalent IonsZdrachek, Elena; Bakker, EricAnalytical Chemistry (Washington, DC, United States) (2017), 89 (24), 13441-13448CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)A method for the detn. of unbiased low selectivity coeffs. for two of the most prevalent cases of multivalent ions (zi = 2, zj = 1 and zi = 1, zj = 2) was theor. and exptl. substantiated. The method is based on eliminating the primary ion concn. near the membrane by extrapolating the linearized time dependencies of selectivity coeffs. detd. by the sep. solns. method KPotij(SSM) as a function of t-1/3 or t-1/6, depending on the charge combination of the two ions, to infinite time. The applicability of the method is demonstrated for ionophore-based Mg2+-, Ca2+-, and Na+-selective electrodes. The high level of primary ion impurities in the salts of interfering ions can significantly limit the efficiency of the technique, as demonstrated with salts of different purity levels.
- 54Jasielec, J. J.; Mousavi, Z.; Granholm, K.; Sokalski, T.; Lewenstam, A. Anal. Chem. 2018, 90, 9644– 9649, DOI: 10.1021/acs.analchem.8b0265954https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhtFyqur7P&md5=3eec1fc653c580c308745aada89d0d99Sensitivity and Selectivity of Ion-Selective Electrodes Interpreted Using the Nernst-Planck-Poisson ModelJasielec, Jerzy J.; Mousavi, Zekra; Granholm, Kim; Sokalski, Tomasz; Lewenstam, AndrzejAnalytical Chemistry (Washington, DC, United States) (2018), 90 (15), 9644-9649CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)The Nernst-Planck-Poisson model is used for modeling the sensitivity and selectivity of ion-selective electrodes (ISEs) with plastic membranes. Two pivotal parameters characterizing ISE response are in focus: sensitivity and selectivity. An interpretation of sensitivity, which considers the concurrent influence of anions and cations on the ISE slope, is presented. The interpretation of selectivity shows the validity and limits of approaches hitherto taken to measure the true (unbiased) selectivity coeff. The validity of more idealized interpretations by the diffusion-layer model is conceived.
- 55Ivanova, A. D.; Koltashova, E. S.; Solovyeva, E. V.; Peshkova, M. A.; Mikhelson, K. N. Impact of the Electrolyte Co-Extraction to the Response of the Ionophore-based Ion-Selective Electrodes. Electrochim. Acta 2016, 213, 439– 446, DOI: 10.1016/j.electacta.2016.07.14255https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xht1OrsrbJ&md5=baccf0ad1039de78ed2d3dab6bb37a2dImpact of the Electrolyte Co-Extraction to the Response of the Ionophore-based Ion-Selective ElectrodesIvanova, Anastasiya D.; Koltashova, Evgeniya S.; Solovyeva, Elena V.; Peshkova, Maria A.; Mikhelson, Konstantin N.Electrochimica Acta (2016), 213 (), 439-446CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Ltd.)The impact of the aq. electrolyte coextn. to the potentiometric response of ionophore-based ion-selective electrodes (ISEs) was studied theor. and exptl. A simple theor. model is developed to describe quant. how coextn. of electrolytes influences the lower and the upper detection limits of ISEs. The theory is successfully verified with valinomycin-based K+-ISE as a model system, using potentiometric, chronopotentiometric, impedance and UV-visible measurements. A special (sym.) setup of the galvanic cell is proposed which clearly demonstrates how coextn. from the internal soln. dets. the lower detection limit of ISEs. The values of the partition coeffs. of K salts used in the study are consistent with the resp. Gibbs energies of anion transfer from H2O to org. phase. The model also gives a hint why the slope of real ISEs is typically slightly sub-Nernstian.
- 56Kondratyeva, Y. O.; Solovyeva, E. V.; Khripoun, G. A.; Mikhelson, K. N. Non-constancy of the bulk resistance of ionophore-based ion-selective electrode: A result of electrolyte co-extraction or of something else?. Electrochim. Acta 2018, 259, 458– 465, DOI: 10.1016/j.electacta.2017.10.17656https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhslOisLnE&md5=f8186ad6cf0a2e5075ed57b89b10bb7eNon-constancy of the bulk resistance of ionophore-based ion-selective electrode: A result of electrolyte co-extraction or of something else?Kondratyeva, Yevgeniya O.; Solovyeva, Elena V.; Khripoun, Galina A.; Mikhelson, Konstantin N.Electrochimica Acta (2018), 259 (), 458-465CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Ltd.)The bulk resistance of ionophore-based ion-selective electrodes (ISEs) was studied by chronopotentiometry and electrochem. impedance using Ca2+-ISEs with PVC membranes contg. ETH 1001 as a model system. The membrane bulk resistance is roughly the same within the range of CaCl2 concns. from 0.3 to 10-3 M, and increases significantly when the concn. is decreased to 10-4 and 10-5 M, although the potentiometric response of the ISEs is Nernstian in all these solns. This increase of the resistance when 10-3 M CaCl2 is further deleted is larger than the decrease of the resistance when CaCl2 is replaced with Ca(SCN)2 and Ca(ClO4)2. Probably the non-constancy of the ISE bulk resistance is not caused by coextn. of CaCl2 and therefore is not in conflict with the Nernstian behavior of the IESs potentials. The effect is tentatively ascribed to the regularities of H2O uptake by ISE membranes.
- 57Rich, M.; Mendecki, L.; Mensah, S. T.; Blanco-Martinez, E.; Armas, S.; Calvo-Marzal, P.; Radu, A.; Chumbimuni-Torres, K. Y. Circumventing Traditional Conditioning Protocols in Polymer Membrane-Based Ion-Selective Electrodes. Anal. Chem. 2016, 88, 8404– 8408, DOI: 10.1021/acs.analchem.6b0154257https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xhtleiu77E&md5=17ab64fbc68666f6c9ea9816c6fcf308Circumventing Traditional Conditioning Protocols in Polymer Membrane-Based Ion-Selective ElectrodesRich, Michelle; Mendecki, Lukasz; Mensah, Samantha T.; Blanco-Martinez, Enrique; Armas, Stephanie; Calvo-Marzal, Percy; Radu, Aleksandar; Chumbimuni-Torres, Karin Y.Analytical Chemistry (Washington, DC, United States) (2016), 88 (17), 8404-8408CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Prepn. of ion-selective electrodes (ISEs) often requires long and complicated conditioning protocols limiting their application as tools for in-field measurements. Herein, the authors eliminated the need for electrode conditioning by loading the membrane cocktail directly with primary ion soln. This proof of concept expt. was performed with iodide, silver, and sodium selective electrodes. The proposed methodol. significantly shortened the prepn. time of ISEs, yielding functional electrodes with submicromolar detection limits. Also, it is anticipated that this approach may form the basis for the development of miniaturized all-solid-state ion-selective electrodes for in situ measurements.
- 58Vanamo, U.; Hupa, E.; Yrjana, V.; Bobacka, J. New Signal Readout Principle for Solid-Contact Ion-Selective Electrodes. Anal. Chem. 2016, 88, 4369– 4374, DOI: 10.1021/acs.analchem.5b0480058https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XkvVOqt7c%253D&md5=5be5a1912490c7cf909b05514f5d45ceNew Signal Readout Principle for Solid-Contact Ion-Selective ElectrodesVanamo, Ulriika; Hupa, Elisa; Yrjana, Ville; Bobacka, JohanAnalytical Chemistry (Washington, DC, United States) (2016), 88 (8), 4369-4374CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)A novel approach to signal transduction concerning solid-contact ion-selective electrodes (SC-ISE) with a conducting polymer (CP) as the solid contact was studied. The method presented here is based on const. potential coulometry, where the potential of the SC-ISE vs. the ref. electrode is kept const. using a potentiostat. The change in the potential at the interface between the ion-selective membrane (ISM) and the sample soln., due to the change in the activity of the primary ion, is compensated with a corresponding but opposite change in the potential of the CP solid contact. This enforced change in the potential of the solid contact results in a transient reducing/oxidizing current flow through the SC-ISE. By measuring and integrating the current needed to transfer the CP to a new state of equil., the total cumulated charge that is linearly proportional to the change of the logarithm of the primary ion activity was obtained. Different thicknesses of poly(3,4-ethylenedioxythiophene) (PEDOT) doped with poly(styrenesulfonate) (PSS) were used as solid contact. Also, coated wire electrodes (CWEs) were included in the study to show the general validity of the new approach. The ISM employed was selective for K+ ions, and the selectivity of the membrane under implementation of the presented transduction mechanism was confirmed by measurements performed with a const. background concn. of Na+ ions. A unique feature of this signal readout principle is that it allows amplification of the anal. signal by increasing the capacitance (film thickness) of the solid contact of the SC-ISE.
- 59Han, T. T.; Vanamo, U.; Bobacka, J. Influence of Electrode Geometry on the Response of Solid-Contact Ion-Selective Electrodes when Utilizing a New Coulometric Signal Readout Method. ChemElectroChem 2016, 3, 2071– 2077, DOI: 10.1002/celc.20160057559https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhvVygt7rP&md5=dd43d9822aad047bd840372854f6b1d9Influence of Electrode Geometry on the Response of Solid-Contact Ion-Selective Electrodes when Utilizing a New Coulometric Signal Readout MethodHan, Tingting; Vanamo, Ulriika; Bobacka, JohanChemElectroChem (2016), 3 (12), 2071-2077CODEN: CHEMRA; ISSN:2196-0216. (Wiley-VCH Verlag GmbH & Co. KGaA)This article describes the influence of electrode geometry on the response of solid-contact ion-selective electrodes (SC-ISE) with a conducting polymer (CP) as solid contact, when using a recently reported signal readout method based on const. potential coulometry. Poly(3,4-ethylenedioxythiophene) (PEDOT) doped with poly(styrenesulfonate) (PSS) was electropolymd. on glassy carbon disk electrodes with areas ranging from 0.031 cm2 to 0.79 cm2. The polymn. charge was kept const. (1 mC) for all electrodes, meaning that the redox capacitance of PEDOT was const. for all electrodes while the PEDOT thickness decreased with increasing electrode area. The thickness of the K+-selective membrane covering the CP was kept const., so that the total resistance of the K+-selective membrane decreased with increasing electrode area. When utilizing the coulometric signal readout method, the response time of the SC-ISEs was significantly shortened by increasing the electrode area.
- 60Jarolimova, Z.; Han, T. T.; Mattinen, U.; Bobacka, J.; Bakker, E. Capacitive Model for Coulometric Readout of Ion-Selective Electrodes. Anal. Chem. 2018, 90, 8700– 8707, DOI: 10.1021/acs.analchem.8b0214560https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhtFeqs7rI&md5=5c62bad2d285e911da9c66a34829266eCapacitive Model for Coulometric Readout of Ion-Selective ElectrodesJarolimova, Zdenka; Han, Tingting; Mattinen, Ulriika; Bobacka, Johan; Bakker, EricAnalytical Chemistry (Washington, DC, United States) (2018), 90 (14), 8700-8707CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)We present here a capacitive model for the coulometric signal transduction readout of solid-contact ion-selective membrane electrodes (SC-ISE) with a conducting polymer (CP) as an intermediate layer for the detection of anions. The capacitive model correlates well with exptl. data obtained for chloride-selective SC-ISEs utilizing poly(3,4-ethylenedioxythiophene) (PEDOT) doped with chloride as the ion-to-electron transducer. Addnl., Prussian blue is used as a simple sodium capacitor to further demonstrate the role of the transduction layer. The influence of different thicknesses of PEDOT as a conducting polymer transducer, different thicknesses of the overlaying ion-selective membranes deposited by drop casting and spin coating, and different compns. of the chloride-selective membrane are explored. The responses are evaluated in terms of current-time, charge-time, and charge-chloride activity relationships. The utility of the sensor with coulometric readout is illustrated by the monitoring of very small concn. changes in soln.
- 61Nagy, X.; Höfler, L. Lowering Detection Limits Toward Target Ions Using Quasi-Symmetric Polymeric Ion-Selective Membranes Combined with Amperometric Measurements. Anal. Chem. 2016, 88, 9850– 9855, DOI: 10.1021/acs.analchem.6b0304361https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhsFWqtrbF&md5=b0fcee2bfc5a767ea3745686904d256cLowering Detection Limits Toward Target Ions Using Quasi-Symmetric Polymeric Ion-Selective Membranes Combined with Amperometric MeasurementsNagy, Xenia; Hofler, LajosAnalytical Chemistry (Washington, DC, United States) (2016), 88 (19), 9850-9855CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)An amperometric method is reported that compensates for the interference from marginally discriminated interfering ions when using traditional polymeric ion-selective membrane (ISM) electrodes. The concept involves using two ISMs in a three-compartment electrochem. cell configuration. The two ISMs are identical in compn. except for the addn. of an ionophore to one of the membranes. Initially, all three compartments contain the same concn. of interfering ion and the membrane does not contain primary ions. Ref. electrodes are placed into each of the two outer compartments. At this point, there is no p.d. between the two ref. electrodes. The authors show exptl. and theor. that, when the concn. of an interfering species is increased in the sample compartment, the phase-boundary potentials of both sample soln.|ISMs change similarly. However, when the primary ion is added to the sample, an asymmetry will emerge, and the membrane with the ionophore will exhibit a larger phase-boundary potential change. At low concns., the difference in membrane potentials can be too small for reliable potentiometric detection. Current, which can be routinely measured on pA levels, can be used instead to detect the small primary ion concn. changes with a significant lowering of detection limits. The theory of this method is described by Nernst-Planck-Poisson finite element simulations, and both amperometric and potentiometric exptl. verification is demonstrated using ammonium ISM. Amperometric measurements enable 200 nM ammonium to be detected in the presence of 0.1 mM of K, detection capability that is not possible via conventional potentiometry.
- 62Yu, N. N.; Ding, J. W.; Wang, W. W.; Wang, X. D.; Qin, W. Pulsed galvanostatic control of a solid-contact ion-selective electrode for potentiometric biosensing of microcystin-LR. Sens. Actuators, B 2016, 230, 785– 790, DOI: 10.1016/j.snb.2016.02.12162https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xjslyqtb0%253D&md5=dbdd05c0e778b7924a77e93124eda02cPulsed galvanostatic control of a solid-contact ion-selective electrode for potentiometric biosensing of microcystin-LRYu, Nana; Ding, Jiawang; Wang, Wenwei; Wang, Xuedong; Qin, WeiSensors and Actuators, B: Chemical (2016), 230 (), 785-790CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)We report here on the development of a chronopotentiometric assay for microcystin-LR based on enzymic inhibition. The inhibition of protein phosphatase by microcystin-LR can be sensed potentiometrically by using 4-nitrophenyl phosphate as an enzyme substrate. A solid-contact ion-selective electrode (ISE) with poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) as a transduction layer has been designed for potentiometric biosensing using the pulsed galvanastatic technique. By applying an anodic current, the enzymic generated p-nitrophenol can be extd. into the polymeric membrane with tetradodecylammonium tetrakis(4-chlorophenyl)- borate to produce the chronopotentiometric signal. Meanwhile, a controlled voltage was applied to refresh the membrane for multiple consecutive measurements. The proposed potentiometric assay showed a linear response for microcystin-LR in the range 1-100 μg/L with a detection limit of 0.5 μg/L (3s). We believe that the proposed method can be employed for sensitive, rapid and reliable detn. of analytes involved in enzyme inhibition.
- 63Ding, J.; Yu, N.; Wang, X.; Qin, W. Anal. Chem. 2018, 90, 1734– 1739, DOI: 10.1021/acs.analchem.7b0352263https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhtVarurs%253D&md5=02be456215669b3c18a8914ee3ad0477Sequential and Selective Detection of Two Molecules with a Single Solid-Contact Chronopotentiometric Ion-Selective ElectrodeDing, Jiawang; Yu, Nana; Wang, Xuedong; Qin, WeiAnalytical Chemistry (Washington, DC, United States) (2018), 90 (3), 1734-1739CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)A polymeric membrane ion-selective electrode (ISE) is typically designed for the detn. of one specific ion using a conventional method. In this work, we demonstrate a simple, versatile, and sensitive platform for simultaneous detection of two mols. with a single ISE. Under a series of periodic galvanostatic polarization, a solid-contact ISE without ion exchanger properties under zero-current conditions has been successfully used for simultaneous detection of two opposite charged ions with high sensitivity, good selectivity, and fast reversibility. By integration of biorecognition elements with the potentiometric measurement, highly sensitive and selective detection of a broad range of different mol. targets can be predicted. As a proof of concept, a potentiometric genosensor based on magnetic beads-enzyme sandwich assay has been designed for sensitive and selective detection of pathogenic bacteria Escherichia coli O157:H7 and Staphylococcus aureus. Under optimal conditions, two bacteria nucleic acid sequences can be detected simultaneously with high sensitivity and good selectivity by using a single solid-contact potentiometric ISE. The detection limits of Escherichia coli O157:H7 DNA and Staphylococcus aureus DNA are 120 and 54 fM (3σ), resp. Because of its simplicity, this potentiometric technique based on ISE can be an attractive tool or detector to perform two analyte measurements.
- 64Liang, R. N.; Ding, J. W.; Gao, S. S.; Qin, W. Mussel-Inspired Surface-Imprinted Sensors for Potentiometric Label-Free Detection of Biological Species. Angew. Chem., Int. Ed. 2017, 56, 6833– 6837, DOI: 10.1002/anie.20170189264https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXntlyls7k%253D&md5=b6dd46b0b4038bd6336a690d9f8016d8Mussel-Inspired Surface-Imprinted Sensors for Potentiometric Label-Free Detection of Biological SpeciesLiang, Rongning; Ding, Jiawang; Gao, Shengshuai; Qin, WeiAngewandte Chemie, International Edition (2017), 56 (24), 6833-6837CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)Using sensors to quantify clin. relevant biol. species has emerged as a fascinating research field due to their potential to revolutionize clin. diagnosis and therapeutic monitoring. Taking advantage of the wide utility in clin. anal. and low cost of potentiometric ion sensors, the authors demonstrate a method to use such ion sensors to quantify bioanalytes without chem. labels. This is achieved by combination of chronopotentiometry with a mussel-inspired surface imprinting technique. The biomimetic sensing method is based on a blocking mechanism by which the recognition reaction between the surface imprinted polymer and a bioanalyte can block the current-induced ion transfer of an indicator ion, thus causing a potential change. The present method offers high sensitivity and excellent selectivity for detection of biol. analytes. As models, trypsin and yeast cells can be measured at levels down to 0.03 U mL-1 and 50 CFU mL-1, resp.
- 65Afshar, M. G.; Crespo, G. A.; Bakker, E. Flow Chronopotentiometry with Ion-Selective Membranes for Cation, Anion, and Polyion Detection. Anal. Chem. 2016, 88, 3945– 3952, DOI: 10.1021/acs.analchem.6b00141There is no corresponding record for this reference.
- 66Jansod, S.; Afshar, M. G.; Crespo, G. A.; Bakker, E. Phenytoin speciation with potentiometric and chronopotentiometric ion-selective membrane electrodes. Biosens. Bioelectron. 2016, 79, 114– 120, DOI: 10.1016/j.bios.2015.12.01166https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXitVems7nK&md5=6aaf5af33b2daf1ed4c6a725c159a955Phenytoin speciation with potentiometric and chronopotentiometric ion-selective membrane electrodesJansod, Sutida; Afshar, Majid Ghahraman; Crespo, Gaston A.; Bakker, EricBiosensors & Bioelectronics (2016), 79 (), 114-120CODEN: BBIOE4; ISSN:0956-5663. (Elsevier B.V.)We report on an electrochem. protocol based on perm-selective membranes to provide valuable information about the speciation of ionizable drugs, with phenytoin as a model example. Membranes contg. varying amts. of tetradodecylammonium chloride (TDDA) were read out at zero current (potentiometry) and with applied current techniques (chronopotentiometry). Potentiometry allows one to assess the ionized form of phenytoin (pKa∼8.2) that corresponds to a neg. monocharged ion. A careful optimization of the membrane components resulted in a lower limit of detection (∼1.6 μM) than previous reports. Once the pH (from 9 to 10) or the concn. of albumin is varied in the sample (from 0 to 30 g L-1), the potentiometric signal changes abruptly as a result of reducing/increasing the ionized concn. of phenytoin. Therefore, potentiometry as a single technique is by itself not sufficient to obtain information about the concn. and speciation of the drug in the system. For this reason, a tandem configuration with chronopotentiometry as addnl. readout principle was used to det. the total and ionized concn. of phenytoin. In samples contg. excess albumin the rate-limiting step for the chronopotentiometry readout appears to be the diffusion of ionized phenytoin preceded by comparatively rapid deprotonation and decomplexation reactions. This protocol was applied to measure phenytoin in pharmaceutical tables (100 mg per tablet). This tandem approach can likely be extended to more ionizable drugs and may eventually be utilized in view of pharmacol. monitoring of drugs during the delivery process.
- 67Jansod, S.; Afshar, M. G.; Crespo, G. A.; Bakker, E. Alkalinization of Thin Layer Samples with a Selective Proton Sink Membrane Electrode for Detecting Carbonate by Carbonate-Selective Electrodes. Anal. Chem. 2016, 88, 3444– 3448, DOI: 10.1021/acs.analchem.6b0034667https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XktFaqu7Y%253D&md5=0fccaeb9bcd3fbb548a9f9db36bf0f66Alkalinization of Thin Layer Samples with a Selective Proton Sink Membrane Electrode for Detecting Carbonate by Carbonate-Selective ElectrodesJansod, Sutida; Ghahraman Afshar, Majid; Crespo, Gaston A.; Bakker, EricAnalytical Chemistry (Washington, DC, United States) (2016), 88 (7), 3444-3448CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Potentiometry is known to be sensitive to so-called free ion activity and is a potentially valuable tool in environmental speciation anal. Here, the direct detection of free and total carbonate is demonstrated by alkalinization of a thin layer sample (∼100 μm), which is electrochem. triggered at a pH responsive membrane placed opposite a carbonate-selective membrane electrode. The concept may serve as a promising future methodol. for in situ environmental sensing applications where traditional sampling and pretreatment steps are no longer required. The possibility of increasing the pH of the sample was demonstrated 1st with a proton selective membrane (pH readout at zero current) placed opposite the thin layer gap. An optimal applied potential (600 mV) for 300 s resulted in a pH increase of 4 units in an artificial sample, with a relative std. deviation (RSD) of ∼2%. The pH probe was subsequently replaced by a solid contact carbonate selective electrode for the detn. of carbonate species (4.17μM) in a sample of 1mM NaHCO3. Increasing the pH to 12.1 by the electrochem. controlled proton sink allowed one to convert bicarbonate to the detectable carbonate species. Initial bicarbonate concn. (∼1 mM) was obtained as the difference between the converted bicarbonate and the initial carbonate concn. An initial application of this concept was illustrated by the speciation anal. of an unfiltered sample from the Arve River (12.3±0.2μM and 22.5±0.3mM carbonate and bicarbonate, resp.). The values were confirmed by volumetric titrn.
- 68Cuartero, M.; Crespo, G. A.; Bakker, E. Ionophore-Based Voltammetric Ion Activity Sensing with Thin Layer Membranes. Anal. Chem. 2016, 88, 1654– 1660, DOI: 10.1021/acs.analchem.5b0361168https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXitV2ntr%252FO&md5=fc1a1919bd579e1e69a5fc6e773d616bIonophore-Based Voltammetric Ion Activity Sensing with Thin Layer MembranesCuartero, Maria; Crespo, Gaston A.; Bakker, EricAnalytical Chemistry (Washington, DC, United States) (2016), 88 (3), 1654-1660CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)As shown in recent work, thin layer ion-selective multi-ionophore membranes can be interrogated by cyclic voltammetry to detect the ion activity of multiple species simultaneously and selectively. Addnl. fundamental evidence is put forward on ion discrimination with thin multi-ionophore-based membranes with thicknesses of 200 ± 25 nm and backside contacted with poly-3-octylthiophene (POT). An anodic potential scan partially oxidizes the POT film (to POT+), thereby initiating the release of hydrophilic cations from the membrane phase to the sample soln. at a characteristic potential. Varying concn. of added cation-exhanger demonstrates that it limits the ion transfer charge and not the deposited POT film. Voltammograms with multiple peaks are obsd. with each assocd. with the transfer of one type of ion (lithium, potassium, and sodium). Exptl. conditions (thickness and compn. of the membrane and concn. of the sample) are chosen that allow one to describe the system by a thermodn. rather than kinetic model. As a consequence, apparent stability consts. for sodium, potassium, and lithium (assuming 1:1 stoichiometry) with their resp. ionophores are calcd. and agree well with the values obtained by the potentiometric sandwich membrane technique. As an anal. application, a membrane contg. three ionophores was used to det. lithium, sodium, and potassium in artificial samples at the same location and within a single voltammetric scan. Lithium and potassium were also detd. in undiluted human plasma in the therapeutic concn. range.
- 69Cuartero, M.; Crespo, G. A.; Bakker, E. Polyurethane Ionophore-Based Thin Layer Membranes for Voltammetric Ion Activity Sensing. Anal. Chem. 2016, 88, 5649– 5654, DOI: 10.1021/acs.analchem.6b0108569https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XnvFKiurc%253D&md5=4e4ec5ef3b915fe9cb6035a2fd1d96ddPolyurethane Ionophore-Based Thin Layer Membranes for Voltammetric Ion Activity SensingCuartero, Maria; Crespo, Gaston A.; Bakker, EricAnalytical Chemistry (Washington, DC, United States) (2016), 88 (11), 5649-5654CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)We report on a plasticized polyurethane ionophore-based thin film material (of hundreds of nanometer thickness) for simultaneous voltammetric multianalyte ion activity detection triggered by the oxidn./redn. of an underlying poly(3-octylthiophene) film. This material provides excellent mech., phys., and chem. robustness compared to other polymers. Polyurethane films did not exhibit leaching of lipophilic additives after rinsing with a direct water jet and exhibited resistance to detachment from the underlying electrode surface, resulting in a voltammetric current response with less than <1.5% RSD variation (n = 50). In contrast, plasticized poly(vinyl chloride), polystyrene, and poly(acrylate) ionophore-based membranes of the same thickness and compn. exhibited a significant deterioration of the signal after identical treatment. While previously reported works emphasized fundamental advancement of multi-ion detection with multi-ionophore-based thin films, polyurethane thin membranes allow one to achieve real world measurements without sacrificing anal. performance. Indeed, polyurethane membranes are demonstrated to be useful for the simultaneous detn. of potassium and lithium in undiluted human serum and blood with attractive precision.
- 70Cuartero, M.; Acres, R. G.; De Marco, R.; Bakker, E.; Crespo, G. A. Electrochemical Ion Transfer with Thin Films of Poly(3-octylthiophene). Anal. Chem. 2016, 88, 6939– 6946, DOI: 10.1021/acs.analchem.6b0180070https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XpsVOgt7g%253D&md5=2bc6e8fcd24419f4c53a6cfdd16c9d40Electrochemical ion transfer with thin films of poly(3-octylthiophene)Cuartero, Maria; Acres, Robert G.; De Marco, Roland; Bakker, Eric; Crespo, Gaston A.Analytical Chemistry (Washington, DC, United States) (2016), 88 (13), 6939-6946CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)We report on the limiting conditions for ion-transfer voltammetry between an ion-exchanger doped and plasticized poly(vinyl chloride) (PVC) membrane and an electrolyte soln. that was triggered via the oxidn. of a poly(3-octylthiophene) (POT) solid-contact (SC), which was unexpectedly related to the thickness of the POT SC. An electropolymd. 60 nm thick film of POT coated with a plasticized PVC membrane exhibited a significant sodium transfer voltammetric signal whereas a thicker film (180 nm) did not display a measurable level of ion transfer due to a lack of oxidn. of thick POT beneath the membrane film. In contrast, this peculiar phenomenon was not obsd. when the POT film was in direct contact with an org. solvent-based electrolyte. This evidence is indicative of three key points: (i) the coated membrane imposes a degree of rigidity to the system, which restricts the swelling of the POT film and its concomitant p-doping; (ii) this phenomenon is exacerbated with thicker POT films due to an initial morphol. (rougher comprising a network of large POT nanoparticles), which gives rise to a diminished surface area and electrochem. reactivity in the POT SC; (iii) the rate of sodium transfer is higher with a thin POT film due to a smoother surface morphol. made up of a network of smaller POT nanoparticles with an increased surface area and electrochem. reactivity. A variety of techniques including cyclic voltammetry (CV), electrochem. impedance spectroscopy (EIS), ellipsometry, SEM (SEM), at. force microscopy (AFM), and synchrotron radiation-XPS (SR-XPS) were used to elucidate the mechanism of the POT thickness/POT surface roughness dependency on the electrochem. reactivity of the PVC/POT SC system.
- 71Yuan, D. J.; Cuartero, M.; Crespo, G. A.; Bakker, E. Voltammetric Thin-Layer lonophore-Based Films: Part 1. Experimental Evidence and Numerical Simulations. Anal. Chem. 2017, 89, 586– 594, DOI: 10.1021/acs.analchem.6b0335471https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhvFKns7rO&md5=736b18423f8b6620d591990a719be73eVoltammetric Thin-Layer Ionophore-Based Films: Part 1. Experimental Evidence and Numerical SimulationsYuan, Dajing; Cuartero, Maria; Crespo, Gaston A.; Bakker, EricAnalytical Chemistry (Washington, DC, United States) (2017), 89 (1), 586-594CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Voltammetric thin layer (∼200 nm) ionophore-based polymeric films of defined ion-exchange capacity have recently emerged as a promising approach to acquire multi-ion information about the sample, in analogy to performing multiple potentiometric measurements with individual membranes. They behave under two different regimes that are dependent on the ion concn. A thin layer control (no mass transport limitation of the polymer film or soln.) is identified for ion concns. of >10 μM, in which case the peak potential serves as the readout signal, in analogy to a potentiometric sensor. However, ion transfer at lower concns. is chiefly controlled by diffusional mass transport from the soln. to the sensing film, resulting in an increase of peak current with ion concn. This concn. range is suitable for electrochem. ion transfer stripping anal. Here, the transition between the two mentioned scenarios is explored exptl., using a highly Ag-selective membrane as a proof-of-concept under different conditions (variation of ion concn. in the sample from 0.1 μM to 1 mM, scan rate from 25 mV s-1 to 200 mV s-1, and angular frequency from 100 rpm to 6400 rpm). Apart from exptl. evidence, a numerical simulation is developed that considers an idealized conducting polymer behavior and permits one to predict exptl. behavior under diffusion or thin-layer control.
- 72Yuan, D. J.; Cuartero, M.; Crespo, G. A.; Bakker, E. Voltammetric Thin-Layer Ionophore-Based Films: Part 2. Semi-Empirical Treatment. Anal. Chem. 2017, 89, 595– 602, DOI: 10.1021/acs.analchem.6b0335572https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhvFKnsL3K&md5=eddb144ef4d5a7c00c788e60fed56779Voltammetric Thin-Layer Ionophore-Based Films: Part 2. Semi-Empirical TreatmentYuan, Dajing; Cuartero, Maria; Crespo, Gaston A.; Bakker, EricAnalytical Chemistry (Washington, DC, United States) (2017), 89 (1), 595-602CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)This work reports on a semiempirical treatment that allows one to rationalize and predict exptl. conditions for thin-layer ionophore-based films with cation-exchange capacity read out with cyclic voltammetry. The transition between diffusional mass transport and thin-layer regime is described with a parameter (α), which depends on membrane compn., diffusion coeff., scan rate, and electrode rotating speed. Once the thin-layer regime is fulfilled (α = 1), the membrane behaves in some analogy to a potentiometric sensor with a second discrimination variable (the applied potential) that allows one to operate such electrodes in a multianalyte detection mode owing to the variable applied ion-transfer potentials. The limit of detection of this regime is defined with a second parameter (β = 2) and is chosen in analogy to the definition of the detection limit for potentiometric sensors provided by the IUPAC. The anal. equations were validated through the simulation of the resp. cyclic voltammograms under the same exptl. conditions. While simulations of high complexity and better accuracy satisfactorily reproduced the exptl. voltammograms during the forward and backward potential sweeps (companion paper 1), the semiempirical treatment here, while less accurate, is of low complexity and allows one to quite easily predict relevant exptl. conditions for this emergent methodol.
- 73Greenawalt, P. J.; Amemiya, S. Voltammetric Mechanism of Multiion Detection with Thin lonophore-Based Polymeric Membrane. Anal. Chem. 2016, 88, 5827– 5834, DOI: 10.1021/acs.analchem.6b0039773https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XmsFOmsL4%253D&md5=a2463c6f31911d9a94238f34517098a6Voltammetric Mechanism of Multiion Detection with Thin Ionophore-Based Polymeric MembraneGreenawalt, Peter J.; Amemiya, ShigeruAnalytical Chemistry (Washington, DC, United States) (2016), 88 (11), 5827-5834CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)The capability to detect multianalyte ions in their mixed soln. is an important advantage of voltammetry with an ionophore-based polymeric membrane against the potentiometric and optical counterparts. This advanced capability is highly attractive for the anal. of physiol. ions at millimolar concns. in biol. and biomedical samples. Herein, we report on the comprehensive response mechanisms based on the voltammetric exchange and transfer of millimolar multiions at a thin polymeric membrane, where an ionophore is exhaustively depleted upon the transfer of the most favorable primary ion, IzI. With a new voltammetric ion-exchange mechanism, the primary ion is exchanged with the secondary favorable ion, JzJ, at more extreme potentials to transfer a net charge of |zJ|/nJ - |zI|/nI for each ionophore mol., which forms 1:nI and 1:nJ complexes with the resp. ions. Alternatively, an ion-transfer mechanism utilizes the second ionophore that independently transfers the secondary ion without ion exchange. Exptl., a membrane is doped with a Na+- or Li+-selective ionophore to detect not only the primary ion, but also the secondary alk. earth ion, based on the ion-exchange mechanism, where both ions form 1:1 complexes with the ionophores to transfer a net charge of +1. Interestingly, the resultant peak potentials of the secondary divalent ion vary with its sample activity to yield an apparently super-Nernstian slope as predicted theor. By contrast, the voltammetric exchange of calcium ion (nI = 3) with lithium ion (nJ = 1) by a Ca2+-selective ionophore is thermodynamically unfavorable, thereby requiring a Li+-selective ionophore for the ion-transfer mechanism.
- 74Amemiya, S. Voltammetric Ion Selectivity of Thin Ionophore-Based Polymeric Membranes: Kinetic Effect of Ion Hydrophilicity. Anal. Chem. 2016, 88, 8893– 8901, DOI: 10.1021/acs.analchem.6b0255174https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xhtlehs7zP&md5=dc86043c1594ca1609000e4876ce3d31Voltammetric Ion Selectivity of Thin Ionophore-Based Polymeric Membranes: Kinetic Effect of Ion HydrophilicityAmemiya, ShigeruAnalytical Chemistry (Washington, DC, United States) (2016), 88 (17), 8893-8901CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)The high ion selectivity of potentiometric and optical sensors based on ionophore-based polymeric membranes is thermodynamically limited. Here, the authors report that the voltammetric selectivity of thin ionophore-based polymeric membranes can be kinetically improved by several orders of magnitude in comparison with their thermodn. selectivity. The kinetic improvement of voltammetric selectivity is evaluated quant. by newly introducing a voltammetric selectivity coeff. in addn. to a thermodn. selectivity coeff. Exptl., both voltammetric and thermodn. selectivity coeffs. are detd. from cyclic voltammograms of excess amts. of analyte and interfering ions with respect to the amt. of a Na+- or Li+-selective ionophore in thin polymeric membranes. The authors reveal the slower ionophore-facilitated transfer of a smaller alk. earth metal cation with higher hydrophilicity across the membrane/water interface, thereby kinetically improving voltammetric Na+ selectivity against calcium, strontium, and barium ions by 3, 2, and 1 order of magnitude, resp., in sep. solns. Remarkably, voltammetric Na+ and Li+ selectivity against calcium and magnesium ions in mixed solns. is improved by 4 and >7 orders of magnitude, resp., owing to both thermodn. and kinetic effects in comparison with thermodn. selectivity in sep. solns. Advantageously, the simultaneous detection of sodium and calcium ions is enabled voltammetrically in contrast to the potentiometric and optical counterparts. Mechanistically, the authors propose a new hypothetical model that the slower transfer of a more hydrophilic ion is controlled by its partial dehydration during the formation of the adduct with a water finger prior to complexation with an ionophore at the membrane/water interface.
- 75Jansod, S.; Wang, L.; Cuartero, M.; Bakker, E. Electrochemical ion transfer mediated by a lipophilic Os(II)/Os(III) dinonyl bipyridyl probe incorporated in thin film membranes. Chem. Commun. 2017, 53, 10757– 10760, DOI: 10.1039/C7CC05908F75https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsVKgsb3E&md5=41b2c890ee1a8ce2232d4e2852dd1967Electrochemical ion transfer mediated by a lipophilic Os(II)/Os(III) dinonyl bipyridyl probe incorporated in thin film membranesJansod, Sutida; Wang, Lu; Cuartero, Maria; Bakker, EricChemical Communications (Cambridge, United Kingdom) (2017), 53 (78), 10757-10760CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)A new lipophilic dinonyl bipyridyl Os(II)/Os(III) complex successfully mediates ion transfer processes across voltammetric thin membranes. An added lipophilic cation-exchanger may impose voltammetric anion or cation transfer waves of Gaussian shape that are reversible and repeatable. The peak potential is found to shift with the ion concn. in agreement with the Nernst equation. The addn. of tridodecylmethylammonium nitrate to the polymeric film dramatically reduces the peak sepn. from 240 mV to 65 mV, and the peak width to a near-theor. value of 85 mV, which agrees with a surface confined process. Probably the cationic additive serves as a phase transfer catalyst.
- 76Jarolimova, Z.; Bosson, J.; Labrador, G. M.; Lacour, J.; Bakker, E. Ion Transfer Voltammetry at Thin Films Based on Functionalized Cationic [6]Helicenes. Electroanalysis 2018, 30, 650– 657, DOI: 10.1002/elan.20170066976https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhvFegs7zL&md5=9127c91365f959af7605e6ed9250223cIon Transfer Voltammetry at Thin Films Based on Functionalized Cationic [6]HelicenesJarolimova, Zdenka; Bosson, Johann; Labrador, Geraldine M.; Lacour, Jerome; Bakker, EricElectroanalysis (2018), 30 (4), 650-657CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)The authors describe a new family of mol. ion-to-electron redox probes based on cationic diaza, azaoxa, and dioxa [6]helicenes and their derivs. Their unique structure combines, in a single framework, two privileged families of mols. - helicenes and triaryl Me carbenium moieties. These cationic [6]helicenes exhibit reversible and reproducible oxidn./redn. behavior and facilitate the ion transfer into thin layer sensing films composed of bis(2-ethylhexyl)sebacate (DOS), polyurethane (PU), sodium tetrakis 3.5-bis(trifluoromethyl)phenyl borate, sodium ionophore X and diaza+(C8)2Br2 for cation transfer. Cyclic voltammetry was used to interrogate the thin films. The cationic response can be tuned by adjusting the membrane loading. Addn. of lipophilic cation exchanger into the membrane film results in transfer waves of Gaussian shape for cations. A peak sepn. of 60 mV and peak width of 110 mV are near the theor. values for a surface confined process. While Nernstian shifts of the peak potentials with analyte concn. was obtained for membranes based on cationic [6]helicenes and doped with sodium-selective ionophore X, this ionophore was found to promote a gradual loss of redox active species from the ionophore-based membranes into the sample soln.
- 77Jarolimova, Z.; Bosson, J.; Labrador, G. M.; Lacour, J.; Bakker, E. Ion Transfer Voltammetry in Polyurethane Thin Films Based on Functionalised Cationic [6]Helicenes for Carbonate Detection. Electroanalysis 2018, 30, 1378– 1385, DOI: 10.1002/elan.20180008077https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXkt1Gmtb4%253D&md5=53534d8adb8288c2394c2d591454ccccIon Transfer Voltammetry in Polyurethane Thin Films Based on Functionalised Cationic [6]Helicenes for Carbonate DetectionJarolimova, Zdenka; Bosson, Johann; Labrador, Geraldine M.; Lacour, Jerome; Bakker, EricElectroanalysis (2018), 30 (7), 1378-1385CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)We explore here mol. ion-to-electron redox probes based on cationic diaza, azaoxa, and dioxa [6]helicenes and their derivs. as ion-to-electron transducers for the electrochem. detection of anions. These cationic [6]helicenes exhibit reversible and reproducible oxidn./redn. behavior and facilitate the anion transfer of Gaussian shape into polymeric thin layer sensing films. Films composed of bis(2-ethylhexyl) sebacate (DOS), polyurethane (PU), tetrakis(4-chlorophenyl)borate tetradodecylammonium salt (ETH 500) and [6]helicenes were interrogated by cyclic voltammetry. Even though the peak sepn. of 90 mV is larger than ideal, the obsd. peak width at half max. of 130 mV and the linear relationship between current and scan rate are near theor. values, confirming a surface confined process. A Nernstian shift of the peaks with increasing carbonate concn. is obtained in the presence of carbonate ionophore VII incorporated into the thin sensing film. The concn. of carbonate was detd. in an unfiltered sample of the Arve river (flowing from Chamonix to Geneva) and compared to a ref. method (automatic titrator with potentiometric detection). The results suggested that cationic diaza [6]helicene functionalized with two bromine atoms is an attractive mol. ion-to-electron transducer for anion-selective electrodes.
- 78Cuartero, M.; Acres, R. G.; Bradley, J.; Jarolimova, Z.; Wang, L.; Bakker, E.; Crespo, G. A.; De Marco, R. Electrochemical Mechanism of Ferrocene-Based Redox Molecules in Thin Film Membrane Electrodes. Electrochim. Acta 2017, 238, 357– 367, DOI: 10.1016/j.electacta.2017.04.04778https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXmtVyqs7g%253D&md5=9080ee64d0549e572b4b1523c6380813Electrochemical Mechanism of Ferrocene-Based Redox Molecules in Thin Film Membrane ElectrodesCuartero, Maria; Acres, Robert G.; Bradley, John; Jarolimova, Zdenka; Wang, Lu; Bakker, Eric; Crespo, Gaston A.; De Marco, RolandElectrochimica Acta (2017), 238 (), 357-367CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Ltd.)Cyclic voltammetry (CV) in chloride-based aq. electrolytes of ferrocene mol. doped thin membranes (∼200 nm in thickness) on glassy carbon (GC) substrate electrodes, both plasticized poly(vinyl chloride) (PVC) and unplasticized poly(Me methacrylate)/poly(decyl methacrylate) (PMMA-PDMA) membranes, has shown that the electrochem. oxidn. behavior is irreversible due most likely to degrdn. of ferrocene at the buried interface (GC|membrane). Furthermore, CV of the ferrocene mols. at GC electrodes in org. solvents employing chloride-based and chloride-free org. electrolytes has demonstrated that the chloride anion is inextricably linked to this irreversible ferrocene oxidn. electrochem. Accordingly, we have explored the electrochem. oxidn. mechanism of ferrocene-based redox mols. in thin film plasticized and unplasticized polymeric membrane electrodes by coupling synchrotron radiation-XPS (SR-XPS) and near edge X-ray absorption fine structure (NEXAFS) with argon ion sputtering to depth profile the electrochem. oxidized thin membrane systems. With the PVC depth profiling studies, it was not possible to precisely study the influence of chloride on the ferrocene reactivity due to the high at. ratio of chloride in the PVC membrane; however, the depth profiling results obtained with a chlorine-free polymer (PMMA-PDMA) provided irrefutable evidence for the formation of a chloride-based iron product at the GC|PMMA-PDMA interface. Finally, we have identified conditions that prevent the irreversible conversion of ferrocene by utilizing a high loading of redox active reagent and/or an ionic liq. (IL) membrane plasticizer with high ionicity that suppresses the mass transfer of chloride.
- 79Cuartero, M.; Acres, R. G.; Jarolimova, Z.; Bakker, E.; Crespo, G. A.; De Marco, R. Electron Hopping between Fe 3d States in Ethynylferrocene-doped Poly(Methyl Methacrylate)-poly(Decyl Methacrylate) Copolymer Membranes. Electroanalysis 2018, 30, 596– 601, DOI: 10.1002/elan.20170051079https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhs1CitLbM&md5=d2fb8c79d2538d25cd72eb2c8d62608eElectron Hopping Between Fe 3 d States in Ethynylferrocene-doped Poly(Methyl Methacrylate)-poly(Decyl Methacrylate) Copolymer MembranesCuartero, Maria; Acres, Robert G.; Jarolimova, Zdenka; Bakker, Eric; Crespo, Gaston A.; De Marco, RolandElectroanalysis (2018), 30 (4), 596-601CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)Synchrotron radiation-valence band spectroscopy (SR-VBS) was used in a study of redox mol. valence states implicated in the electron hopping mechanism of ethynylferrocene in unplasticized poly(Me methacrylate)-poly(decyl methacrylate) [PMMA-PDMA] membranes. At high concns. of ethynylferrocene, there are observable Fe 3d valence states that are likely linked to electron hopping between ferrocene moieties of neighboring redox mols. Also, electrochem. induced stratification of ethynylferrocene in an oxidized PMMA-PDMA membrane produces a gradient of Fe 3d states toward the buried interface at the glassy C/PMMA-PDMA membrane enabling electron hopping and electrochem. reactivity of dissolved ethynylferrocene across this buried film.
- 80Jansod, S.; Cuartero, M.; Cherubini, T.; Bakker, E. Colorimetric Readout for Potentiometric Sensors with Closed Bipolar Electrodes. Anal. Chem. 2018, 90, 6376– 6379, DOI: 10.1021/acs.analchem.8b0158580https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXpvVejtLs%253D&md5=9b8baf19fade2f0723427e4fb7e385b7Colorimetric Readout for Potentiometric Sensors with Closed Bipolar ElectrodesJansod, Sutida; Cuartero, Maria; Cherubini, Thomas; Bakker, EricAnalytical Chemistry (Washington, DC, United States) (2018), 90 (11), 6376-6379CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)We present here a general strategy to translate potential change at a potentiometric probe into a tunable color readout. It is achieved with a closed bipolar electrode where the ion-selective component is confined to one end of the electrode while color is generated at the opposite pole, allowing one to phys. sep. the detection compartment from the sample. An elec. potential is imposed across the bipolar electrode by soln. contact such that the potentiometric signal change at the sample side modulates the potential at the detection side. This triggers the turnover of a redox indicator in the thin detection layer until a new equil. state is established. The approach is demonstrated in sep. expts. with a chloride responsive Ag/AgCl element and a liq. membrane based calcium-selective membrane electrode, using the redox indicator ferroin in the detection compartment. The principle can be readily extended to other ion detection materials and optical readout principles.
- 81Ding, J. W.; Lv, E. G.; Zhu, L. Y.; Qin, W. Optical Ion Sensing Platform Based on Potential-Modulated Release of Enzyme. Anal. Chem. 2017, 89, 3235– 3239, DOI: 10.1021/acs.analchem.7b0007281https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXjs1KmtbY%253D&md5=90a4323d4025182b07b06fc3e1a8c35aOptical Ion Sensing Platform Based on Potential-Modulated Release of EnzymeDing, Jiawang; Lv, Enguang; Zhu, Liyan; Qin, WeiAnalytical Chemistry (Washington, DC, United States) (2017), 89 (6), 3235-3239CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)The authors report here on an optical ion sensing platform, in which a polymeric membrane ion-selective electrode (ISE) serves as not only a potentiometric transducer for ion activities in the sample soln. but also a ref. electrode for the potential-modulated release of enzyme from an iron-alginate-horseradish peroxidase (HRP) thin film modified working electrode. The ISE and working electrode are phys. sepd. by a salt bridge. The dissoln. of the HRP-embedded thin film can be triggered by the redn. of Fe3+, which is modulated by the potential response of the ISE to the target ion in the sample. The released enzyme induces the oxidn. of its substrate mediated by H2O2 to produce a visual color change. With this setup, an optical ion sensing platform for both cations (e.g., NH4+) and anions (e.g., Cl-) can be obtained. The proposed platform provides a general and versatile visual-sensing strategy for ions and allows optical ion sensing in colored and turbid solns.
- 82Lugert-Thom, E. C.; Gladysz, J. A.; Rabai, J.; Bühlmann, P. Cleaning of pH Selective Electrodes with Ionophore-doped Fluorous Membranes in NaOH Solution at 90 degrees C. Electroanalysis 2018, 30, 611– 618, DOI: 10.1002/elan.20170022882https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXht1Sgs7nF&md5=ca1389c542434b8c0dcffab94c41dbf0Cleaning of pH Selective Electrodes with Ionophore-Doped Fluorous Membranes in NaOH Solution at 90 °CLugert-Thom, Elizabeth C.; Gladysz, John A.; Rabai, Jozsef; Buehlmann, PhilippeElectroanalysis (2018), 30 (4), 611-618CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)This work demonstrates the remarkable stability of fluorous ion-selective electrode (ISE) membranes by exposing them to cleaning-in-place treatments (CIP) as they were used in many industrial processes. The sensing membranes consisted of Teflon AF2400 plasticized with a linear perfluoropolyether and doped with ionic sites and a H+ ionophore (i.e., tris[3-(perfluorooctyl)propyl]amine, 1, or tris[3-(perfluorooctyl)pentyl]amine, 2). To mimic a typical CIP treatment, the electrodes were repeatedly exposed for 30 min to a 3.0% NaOH soln. at 90° (pH 12.7). ISE membranes doped with the less strongly H+ binding ionophore 1 started to show reduced potentiometric response slopes and increased resistances after one exposure for 30 min to hot 3.0% NaOH soln. No decompn. of the ionic sites and ionophore 1 at 90° was evident by 1H NMR spectroscopy, suggesting that the performance of membranes doped with 1 was compromised primarily by leaching of the neg. charged ionic sites along with H+ into the hot caustic soln. In contrast, even after ten exposures to hot 3.0% NaOH for a cumulative 5 h at 90°, the fluorous sensing membranes doped with the more strongly H+ binding ionophore 2 still showed the ability to respond with a theor. (Nernstian) slope up to pH 12. Addn. of the fluorophilic electrolyte salt methyltris[3-(perfluorooctyl)propyl]ammonium tetrakis[3,5-bis(perfluorohexyl)phenyl]borate reduced the membrane resistance by an order of magnitude.
- 83Carey, J. L.; Hirao, A.; Sugiyama, K.; Buhlmann, P. Semifluorinated Polymers as Ion-selective Electrode Membrane Matrixes. Electroanalysis 2017, 29, 739– 747, DOI: 10.1002/elan.20160058683https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xhsl2ht7nJ&md5=2d29037de8190f5b0699fde5d6e81c16Semifluorinated Polymers as Ion-selective Electrode Membrane MatrixesCarey, Jesse L. III; Hirao, Akira; Sugiyama, Kenji; Buehlmann, PhilippeElectroanalysis (2017), 29 (3), 739-747CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)Most com. available fluorous polymers are ill suited for the fabrication of ion-selective electrode (ISE) membranes. Therefore, we synthesized semifluorinated polymers for this purpose. Ionophore-free ion-exchanger electrodes made with these polymers show a selectivity range (≈14 orders of magnitude) that is nearly as wide as found previously for liq. fluorous ion-exchanger electrodes. These polymers were also used to construct ISE membranes doped with fluorophilic silver ionophores. While the resulting ISEs were somewhat less selective than their fluorous counterparts, the semifluorinated polymers offer the advantage that they can be doped both with fluorophilic ionophores and traditional lipophilic ionophores, such as the silver ionophore Cu(II)-I (o-xylylenebis[N,N-diisobutyldithiocarbamate]). We also cross-linked these polymers, producing very durable membranes that retained broad selectivity ranges. K+ ISEs made with the cross-linked semifluorinated polymer and the ionophore valinomycin showed selectivities similar to those of PVC membrane ISEs but with a superior thermal stability, the majority of the electrodes still giving a theor. (Nernstian) response after exposure to a boiling aq. soln. for 10 h.
- 84Ogawara, S.; Carey, J. L.; Zou, X. U.; Bühlmann, P. Donnan Failure of Ion-Selective Electrodes with Hydrophilic High-Capacity Ion-Exchanger Membranes. ACS Sens. 2016, 1, 95– 101, DOI: 10.1021/acssensors.5b0012884https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhvVarsbvF&md5=53db0365ffd9ae1601bb66871bda34c2Donnan Failure of Ion-Selective Electrodes with Hydrophilic High-Capacity Ion-Exchanger MembranesOgawara, Shogo; Carey, Jesse L.; Zou, Xu U.; Buhlmann, PhilippeACS Sensors (2016), 1 (1), 95-101CODEN: ASCEFJ; ISSN:2379-3694. (American Chemical Society)Hydrophilic ion-exchanger membranes with a high ion-exchange capacity not only find numerous applications in ion sepns., but also have interesting properties when used as sensing membranes of ion-selective electrodes (ISEs). As pointed out in the literature, the hydrophilic nature of these membranes may reduce biofouling of ISE sensing membranes as caused by elec. neutral, hydrophobic interferents. This work shows that hydrophilic high-capacity ion-exchanger membranes are more resistant to Donnan failure (i.e., the limitation of the upper detection limit by co-ion transfer into the sensing membrane) than both hydrophobic ionophore-doped and hydrophobic ionophore-free ion-exchanger membranes. Nernstian responses of hydrophilic anion-exchanger membranes were found for anions as large as 2.0 nm, in spite of the cross-linked nature of the anion exchanger that was used. This shows that the high resistance of hydrophilic anion-exchangers to Donnan failure caused by cations such as tetrabutylammonium is not the result of size exclusion. For typical ions, the hydrophilicity of the anion exchanger does not play a decisive factor either. Instead, the excellent resistance to Donnan failure exhibited by hydrophilic ion exchange membranes is primarily caused by the high activity of exchangeable ions in the ion exchanger phase, which disfavors partitioning of ions of opposite charge (along with target ions) from samples into these sensing membranes. The absence of Donnan failure caused by hydrophobic co-ions may be of substantial benefit for measurements in biol. samples.
- 85Kisiel, A.; Michalska, A.; Maksymiuk, K. Bilayer membranes for ion-selective electrodes. J. Electroanal. Chem. 2016, 766, 128– 134, DOI: 10.1016/j.jelechem.2016.01.04085https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XisFyhsL4%253D&md5=52fafbcde3f336270f0e53f412e39d2fBilayer membranes for ion-selective electrodesKisiel, Anna; Michalska, Agata; Maksymiuk, KrzysztofJournal of Electroanalytical Chemistry (2016), 766 (), 128-134CODEN: JECHES; ISSN:1873-2569. (Elsevier B.V.)In most cases described so far a potentiometric ion-selective membrane is made of one polymer (or one copolymer) used with ion-exchanger, ionophore and with a plasticizer of choice. A concept of potentiometric bilayer membranes is introduced and their benefits from both theor. and practical point of view are presented. They are related to response mechanism interpretation and to detection limit lowering of ion-selective electrodes. The novel structurized bilayer potentiometric membranes represent a sequence of polyacrylate polymers with ion-exchangers (the same or different), the polymers applied were either poly(hexyl acrylate) or poly(lauryl acrylate) characterized by different ionic mobilities. Tailoring of the polymer material for the component layers, kind of ion-exchanger and the layer thickness can result in significantly improved anal. performance represented by wide linear response range and low detection limit, as shown in example of K-selective electrode. This effect was achieved due to controlled compensation of spontaneous ion fluxes in bilayer system. The exptl. data were supplemented by digital simulation results explaining the role of the thickness of the internal layer on the ion fluxes and thus on the detection limit.
- 86Makra, I.; Brajnovits, A.; Jagerszki, G.; Furjes, P.; Gyurcsanyi, R. E. Potentiometric sensing of nucleic acids using chemically modified nanopores. Nanoscale 2017, 9, 739– 747, DOI: 10.1039/C6NR05886H86https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhvFKjt7vP&md5=c5dda159f0e4c79dfec35f82e7d21732Potentiometric sensing of nucleic acids using chemically modified nanoporesMakra, Istvan; Brajnovits, Alexandra; Jagerszki, Gyula; Furjes, Peter; Gyurcsanyi, Robert E.Nanoscale (2017), 9 (2), 739-747CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)Unlike the overwhelming majority of nanopore sensors that are based on the measurement of a transpore ionic current, here we introduce a potentiometric sensing scheme and demonstrate its application for the selective detection of nucleic acids. The sensing concept uses the charge inversion that occurs in the sensing zone of a nanopore upon binding of neg. charged microRNA strands to pos. charged peptide-nucleic acid (PNA) modified nanopores. The initial anionic permselectivity of PNA-modified nanopores is thus gradually changed to cationic permselectivity, which can be detected simply by measuring the nanoporous membrane potential. A quant. theor. treatment of the potentiometric microRNA response is provided based on the Nernst-Planck/Poisson model for the nanopore system assuming first order kinetics for the nucleic acid hybridization. An excellent correlation between the theor. and exptl. results was obsd., which revealed that the binding process is focused at the nanopore entrance with contributions from both in pore and out of pore sections of the nanoporous membrane. The theor. treatment is able to give clear guidelines for further optimization of potentiometric nanopore-based nucleic acid sensors by predicting the effect of the most important exptl. parameters on the potential response.
- 87Papp, S.; Jagerszki, G.; Gyurcsanyi, R. E. Ion-Selective Electrodes Based on Hydrophilic Ionophore-Modified Nanopores. Angew. Chem., Int. Ed. 2018, 57, 4752– 4755, DOI: 10.1002/anie.20180095487https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXkt1Gqu7c%253D&md5=a7ea53acc9cdceca82fdd22362083472Ion-Selective Electrodes Based on Hydrophilic Ionophore-Modified NanoporesPapp, Soma; Jagerszki, Gyula; Gyurcsanyi, Robert E.Angewandte Chemie, International Edition (2018), 57 (17), 4752-4755CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)We report the synthesis and anal. application of the first Cu2+-selective synthetic ion channel based on peptide-modified gold nanopores. A Cu2+-binding peptide motif (Gly-Gly-His) along with two addnl. functional thiol derivs. inferring cation-permselectivity and hydrophobicity was self-assembled on the surface of gold nanoporous membranes comprising of about 5 nm diam. pores. These membranes were used to construct ion-selective electrodes (ISEs) with extraordinary Cu2+ selectivities, approaching six orders of magnitude over certain ions. Since all constituents are immobilized to a supporting nanoporous membrane, their leaching, that is a ubiquitous problem of conventional ionophore-based ISEs was effectively suppressed.
- 88Mendecki, L.; Callan, N.; Ahern, M.; Schazmann, B.; Radu, A. Influence of Ionic Liquids on the Selectivity of Ion Exchange-Based Polymer Membrane Sensing Layers. Sensors 2016, 16, 1106, DOI: 10.3390/s1607110688https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsVOnsrbJ&md5=7e2d3544da0f75504899fee78b84cd2dInfluence of ionic liquids on the selectivity of ion exchange-based polymer membrane sensing layersMendecki, Lukasz; Callan, Nicole; Ahern, Meghan; Schazmann, Benjamin; Radu, AleksandarSensors (2016), 16 (7), 1106/1-1106/11CODEN: SENSC9; ISSN:1424-8220. (MDPI AG)The applicability of ion exchange membranes is mainly defined by their permselectivity towards specific ions. For instance, the needed selectivity can be sought by modifying some of the components required for the prepn. of such membranes. In this study, a new class of materials-trihexyl(tetradecyl)phosphonium based ionic liqs. (ILs) were used to modify the properties of ion exchange membranes. We detd. selectivity coeffs. for iodide as model ion utilizing six phosphonium-based ILs and compared the selectivity with two classical plasticizers. The dielec. properties of membranes plasticized with ionic liqs. and their response characteristics towards ten different anions were investigated using potentiometric and impedance measurements. In this large set of data, deviations of obtained selectivity coeffs. from the well-established Hofmeister series were obsd. on many occasions thus indicating a multitude of applications for these ion-exchanging systems.
- 89Schazmann, B.; Demey, S.; Ali, Z. W.; Plissart, M. S.; Brennan, E.; Radu, A. Robust, Bridge-less Ion-selective Electrodes with Significantly Reduced Need for Pre- and Post-application Handling. Electroanalysis 2018, 30, 740– 747, DOI: 10.1002/elan.20170071689https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXit1WnsbY%253D&md5=81516de86b416c50eceb92b470b9095fRobust, Bridge-Less Ion-Selective Electrodes with Significantly Reduced Need for Pre- and Post-Application HandlingSchazmann, B.; Demey, S.; Ali, Z. Waqar; Plissart, M.-S.; Brennan, E.; Radu, A.Electroanalysis (2018), 30 (4), 740-747CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)We are demonstrating robust, single-layer ion-selective electrode (ISE) utilizing simple Ag/AgCl electrode as solid support without the need for intermediate polymer layer. We have created and chem. linked a family of imidazolium ionic liqs. (ILs) with poly (vinyl chloride) (PVC) using click chem., resulting in hybrid materials with tunable characteristics. The resultant material inherently contains chloride ion thus offering the ability to stabilize interfacial potential. This allowed us to construct very simple, single-layer membranes with significantly reduced need for conditioning as an added bonus compared to traditional sensors. Chem. immobilization of ISE membrane components also led to extended lifetime as the potential for material loss is reduced and detection limits are lowered. In our characterization we focused on perchlorate as a model ion. It's levels of around 10-7 M could be repeatedly quantified over a 100 day period despite const. exposure of ISEs to aq. soln. over this time. Most importantly, the electrodes exhibited stable and reproducible signal with significantly simplified pre- and post-operation handling protocols. This offers potential for in situ applications as well as to advanced fabrication techniques and miniaturization. Simplicity of construction and operation, and low cost of the solid substrate allows for disposable ISE formats.
- 90Rzhevskaia, A. V.; Shvedene, N. V.; Pletnev, I. V. Anion-selective electrodes based on solidified 1,3-dihexadecylimidazolium ionic liquids with halide and pseudohalide anions. J. Electroanal. Chem. 2016, 783, 274– 279, DOI: 10.1016/j.jelechem.2016.11.00990https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhvVGgtb3O&md5=439aa5be157e2bca3eaf5a4cacb97e8dAnion-selective electrodes based on solidified 1,3-dihexadecylimidazolium ionic liquids with halide and pseudohalide anionsRzhevskaia, A. V.; Shvedene, N. V.; Pletnev, I. V.Journal of Electroanalytical Chemistry (2016), 783 (), 274-279CODEN: JECHES; ISSN:1873-2569. (Elsevier B.V.)In this study screen-printed solid-state electrodes using low-melting ionic liqs. with cation of 1,3-dihexadecylimidazolium and such anions as chloride, iodide, and thiocyanate were developed. Potentiometric response and electrochem. characteristics of ion-selective electrodes in KCl, KI, and KSCN solns. were studied. All sensors exhibited sensitivity toward the corresponding anions, the slopes close to Nernstian ones, low detection limits (3.0 • 10-6 M for SCN-), and high selectivity in the presence of the extraneous anions. Operation time of the sensors was not less than one year. The applicability of the developed electrodes for the potentiometric detn. of iodide in pharmaceuticals and thiocyanate in human saliva was demonstrated.
- 91Mendecki, L.; Chen, X. R.; Callan, N.; Thompson, D. F.; Schazmann, B.; Granados-Focil, S.; Radu, A. Simple, Robust, and Plasticizer-Free Iodide-Selective Sensor Based on Copolymerized Triazole-Based Ionic Liquid. Anal. Chem. 2016, 88, 4311– 4317, DOI: 10.1021/acs.analchem.5b0446191https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XjvFyrsbw%253D&md5=53ae8f2644b3a8a7fa5afa9d72af21aaSimple, Robust, and Plasticizer-Free Iodide-Selective Sensor Based on Copolymerized Triazole-Based Ionic LiquidMendecki, Lukasz; Chen, Xiaorui; Callan, Nicole; Thompson, David F.; Schazmann, Benjamin; Granados-Focil, Sergio; Radu, AleksandarAnalytical Chemistry (Washington, DC, United States) (2016), 88 (8), 4311-4317CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Novel solid-contact iodide-selective electrodes based on covalently attached 1,2,3 triazole ionic liq. (IL) were prepd. and investigated in this study. Triazole-based IL moieties were synthesized using click chem. and were further copolymd. with lauryl methacrylate via a simple one-step free radical polymn. to produce a "self-plasticized" copolymer. The mech. properties of the copolymer are suitable for the fabrication of plasticizer-free ion-selective membrane electrodes. We demonstrate that covalently attached IL moieties provide adequate functionality to the ion-selective membrane, thus achieving a very simple, one-component sensing membrane. We also demonstrate that the presence of iodide as the counterion in the triazole moiety has direct influence on the membrane's functionality. Potentiometric expts. revealed that each electrode displays high selectivity toward iodide anions over a no. of inorg. anions. Moreover, the inherent presence of the iodide in the membrane reduces the need for conditioning. The nonconditioned electrodes show strikingly similar response characteristics compared to the conditioned ones. The electrodes exhibited a near Nernstian behavior with a slope of -56.1 mV per decade across a large concn. range with lower detection limits found at approx. 6.3 × 10-8 M or 8 ppb. These all-solid-state sensors were utilized for the selective potentiometric detn. of iodide ions in artificial urine samples in the nanomolar concn. range.
- 92Abdel-Ghany, M. F.; Hussein, L. A.; El Azab, N. F. Novel potentiometric sensors for the determination of the dinotefuran insecticide residue levels in cucumber and soil samples. Talanta 2017, 164, 518– 528, DOI: 10.1016/j.talanta.2016.12.01992https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XitV2ls7zO&md5=3d2434d6dfe05d1a6d7e8ea89b8ed02fNovel potentiometric sensors for the determination of the dinotefuran insecticide residue levels in cucumber and soil samplesAbdel-Ghany, Maha F.; Hussein, Lobna A.; El Azab, Noha F.Talanta (2017), 164 (), 518-528CODEN: TLNTA2; ISSN:0039-9140. (Elsevier B.V.)Five new potentiometric membrane sensors for the detn. of the dinotefuran levels in cucumber and soil samples have been developed. Four of these sensors were based on a newly designed molecularly imprinted polymer (MIP) material consisting of acrylamide or methacrylic acid as a functional monomer in a plasticized PVC (polyvinyl chloride) membrane before and after elution of the template. A fifth sensor, a carboxylated PVC-based sensor plasticized with dioctyl phthalate, was also prepd. and tested. Sensor 1 (acrylamide washed) and sensor 3 (methacrylic acid washed) exhibited significantly enhanced responses towards dinotefuran over the concn. range of 10-7-10-2 mol L-1. The limit of detection (LOD) for both sensors was 0.35 μg L-1. The response was near-Nernstian, with av. slopes of 66.3 and 50.8 mV/decade for sensors 1 and 3 resp. Sensors 2 (acrylamide non-washed), 4 (methacrylic acid non-washed) and 5 (carboxylated-PVC) exhibited non-Nernstian responses over the concn. range of 10-7-10-3 mol L-1, with LODs of 10.07, 6.90, and 4.30 μg L-1, resp., as well as av. slopes of 39.1, 27.2 and 33 mV/decade, resp. The application of the proposed sensors to the detn. of the dinotefuran levels in spiked soil and cucumber samples was demonstrated. The av. recoveries from the cucumber samples were from 7.93% to 106.43%, with a std. deviation of less than 13.73%, and recoveries from soil samples were from 97.46% to 108.71%, with a std. deviation of less than 10.66%. The sensors were applied successfully to the detn. of the dinotefuran residue, its rate of disappearance and its half-life in cucumbers in soil in which a safety pre-harvest interval for dinotefuran was suggested.
- 93Zhuo, K. L.; Ma, X. L.; Chen, Y. J.; Wang, C. Y.; Li, A. Q.; Yan, C. L. Molecularly imprinted polymer based potentiometric sensor for the determination of 1-hexyl-3-methylimidazolium cation in aqueous solution. Ionics 2016, 22, 1947– 1955, DOI: 10.1007/s11581-016-1708-z93https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xmt1Smur8%253D&md5=ce88df34395b37653db0d1ff9606d18aMolecularly imprinted polymer based potentiometric sensor for the determination of 1-hexyl-3-methylimidazolium cation in aqueous solutionZhuo, Kelei; Ma, Xueli; Chen, Yujuan; Wang, Congyue; Li, Aoqi; Yan, ChanglingIonics (2016), 22 (10), 1947-1955CODEN: IONIFA; ISSN:0947-7047. (Springer)The mol. imprinting technique is powerful to prep. functional materials with mol. recognition properties. In this work, a potentiometric sensor was fabricated by dispersing molecularly imprinted polymers (MIPs) into plasticized PVC matrix and used for the detn. of 1-hexyl-3-methylimidazolium cation ([C6mim]+) in aq. soln. The MIPs were synthesized by pptn. polymn. using 1-hexyl-3-methylimidazolium chloride ([C6mim]Cl) as the template mol., methacrylic acid (MAA) and ethylene glycol dimethacrylate (EGDMA) as the functional monomers, and EGDMA also as the crosslinking agent. The as-prepd. electrode exhibited a Nernstian response (58.87 ± 0.3 mV per decade) to [C6mim]+ in a concn. range from 1.0 × 10-6 to 0.1 mol kg-1 with a low detection limit of 2.8 × 10-7 mol kg-1, high selectivity, and little pH influence. The as-prepd. electrode was used for the detection of the [C6mim]+ in distd. water, tap water, and river water with a good recovery. It was also successfully applied in the detn. of mean activity coeffs. of [C6mim]Br in fructose + water systems based on the potentiometric method at 298.15 K.
- 94Sacramento, A. S.; Moreira, F. T. C.; Guerreiro, J. L.; Tavares, A. P.; Sales, M. G. F. Novel biomimetic composite material for potentiometric screening of acetylcholine, a neurotransmitter in Alzheimer’s disease. Mater. Sci. Eng., C 2017, 79, 541– 549, DOI: 10.1016/j.msec.2017.05.09894https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtVWqs7nE&md5=88231945d853885d37a6adee40d1a322Novel biomimetic composite material for potentiometric screening of acetylcholine, a neurotransmitter in Alzheimer's diseaseSacramento, Ana S.; Moreira, Felismina T. C.; Guerreiro, Joana L.; Tavares, Ana P.; Sales, M. Goreti F.Materials Science & Engineering, C: Materials for Biological Applications (2017), 79 (), 541-549CODEN: MSCEEE; ISSN:0928-4931. (Elsevier B.V.)This work describes a novel approach to produce an antibody-like biomimetic material. It includes prepg. composite imprinted material never presented before, with highly conductive support nanostructures and assembling a high cond. polymeric layer at low temp. Overall, such highly conductive material may enhance the final features of elec.-based devices. Acetylcholine (ACh) was selected as target analyte, a neurotransmitter of importance in Alzheimer's disease. Potentiometric transduction was preferred, allowing quick responses and future adaptation to point-of-care requirements. The biomimetic material was obtained by bulk polymn., where ACh was placed in a composite matrix of multiwalled carbon nanotubes (MWCNTs) and aniline (ANI). Subsequent polymn., initiated by radical species, yielded a polymeric structure of polyaniline (PANI) acting as phys. support of the composite. A non-imprinted material (NIM) having only PANI/MWCNT (without ACh) has been prepd. for comparison of the biomimetic-imprinted material (BIM). RAMAN and Fourier Transform IR spectroscopy (FTIR), Transmission Electron microscopy (TEM), and Scanning Electron microscope (SEM) anal. characterized the structures of the materials. The ability of this biomaterial to rebind ACh was confirmed by including it as electroactive compd. in a PVC/plasticizer mixt. The membranes with imprinted material and anionic additive presented the best anal. characteristics, with a sensitivity of 83.86 mV decade- 1 and limit of detection (LOD) of 3.45 × 10- 5 mol/L in HEPES buffer pH 4.0. Good selectivity was obsd. against creatinine, creatine, glucose, cysteine and urea. The electrodes were also applied on synthetic serum samples and seemed a reliable tool for screening ACh in synthetic serum samples. The overall performance showed fast response, reusability, simplicity and low price.
- 95Alizadeh, T.; Nayeri, S.; Mirzaee, S. A high performance potentiometric sensor for lactic acid determination based on molecularly imprinted polymer/MWCNTs/PVC nanocomposite film covered carbon rod electrode. Talanta 2019, 192, 103– 111, DOI: 10.1016/j.talanta.2018.08.02795https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhslKqur7M&md5=1f4e37ae411af1fd594b16f6f283d577A high performance potentiometric sensor for lactic acid determination based on molecularly imprinted polymer/MWCNTs/PVC nanocomposite film covered carbon rod electrodeAlizadeh, Taher; Nayeri, Sahar; Mirzaee, SaharTalanta (2019), 192 (), 103-111CODEN: TLNTA2; ISSN:0039-9140. (Elsevier B.V.)A novel nano-sized imprinted polymer/multi-walled carbon nanotube (MWCNTs)-based potentiometric sensor is introduced for lactic acid (LA) sensing in dairy products. The imprinted polymer was synthesized using allyl amine (AA) and ethylene glycol dimethacrylate as functional monomer and cross-linker, resp. It was demonstrated that the amide linkage was created between LA and AA during copolymn. reaction which was finally hydrolyzed when removing template from the synthesized MIP. It was also shown that the MIP cavities, compatible with LA anion, were created during polymn. reaction which influenced the potentiometric response behavior of the MIP-based electrode. This novel potentiometric sensor is a carbon rod electrode, coated with a membrane consisting of the MIP nanoparticles (2.5%), MWCNTs (2%), dibutylphthalate (DBP) (65%), poly-vinyl chloride (PVC) (28.5%) and tetra Ph phosphonium bromide (TPPB) (2%). The active ion sensed by the electrode is the LA anion formed at elevated pH condition. The sensor exhibited Nernstian slope of 30.3 ± 0.4 mVdecade-1 in the working concn. range of 1.0 × 10-1to 1.0 × 10-6 mol L-1 with detection limit of 7.3 × 10-7 mol L-1. The sensor displayed a stable potential response in the pH range of 5-8 and fast response time of less than 60 s. It exhibited also high selectivity over the interfering species. The proposed sensor was successfully applied for the detn. of LA in real samples (milk and yoghurt).
- 96Li, P. J.; Liang, R. N.; Yang, X. F.; Qin, W. Imprinted nanobead-based disposable screen-printed potentiometric sensor for highly sensitive detection of 2-naphthoic acid. Mater. Lett. 2018, 225, 138– 141, DOI: 10.1016/j.matlet.2018.04.11996https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXptVGitrk%253D&md5=d3066013cc97bc2af776968e59ff5788Imprinted nanobead-based disposable screen-printed potentiometric sensor for highly sensitive detection of 2-naphthoic acidLi, Pengjuan; Liang, Rongning; Yang, Xiaofeng; Qin, WeiMaterials Letters (2018), 225 (), 138-141CODEN: MLETDJ; ISSN:0167-577X. (Elsevier B.V.)Currently, potentiometric sensors based on various molecularly imprinted polymer (MIP) receptors were successfully fabricated for detection of org. species. However, almost all of the previously developed potentiometric sensors based on MIPs are in traditional liq.-contact mode in which lower detection limits were restricted by zero-current transmembrane ion fluxes. Herein, a screen-printed potentiometric sensor for detn. of 2-naphthoic acid was developed. It is based on the MIP nanobeads as the selective receptor and the electrochem. reduced graphene oxide film as the solid contact. Compared with the classical potentiometric sensor, the proposed sensor based on nonequil. sensing mechanism exhibits remarkably improved detection sensitivity for 2-naphthoic acid with a low detection limit of 6.9 × 10-11 M.
- 97Kupis-Rozmyslowicz, J.; Wagner, M.; Bobacka, J.; Lewenstam, A.; Migdalski, J. Biomimetic membranes based on molecularly imprinted conducting polymers as a sensing element for determination of taurine. Electrochim. Acta 2016, 188, 537– 544, DOI: 10.1016/j.electacta.2015.12.00797https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXitVeitLjN&md5=c0abd93d189eab4109b2ef56200c9199Biomimetic membranes based on molecularly imprinted conducting polymers as a sensing element for determination of taurineKupis-Rozmyslowicz, Justyna; Wagner, Michal; Bobacka, Johan; Lewenstam, Andrzej; Migdalski, JanElectrochimica Acta (2016), 188 (), 537-544CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Ltd.)Molecularly Imprinted Conducting Polymer based films (MICP films) devoted for the taurine detn. is described. MICP films were electrodeposited from an aq. soln. contg. 3,4-ethylenedioxythiophene, acetic acid thiophene, FMN, and taurine. The presence of taurine inside freshly deposited MICP films as well as absence of taurine in the outer layer of the MICP film after extn. process was confirmed by the XPS spectra. After taurine extn., MICP films can be used as a potentiometric sensor giving close to Nernstian response towards taurine equal to 53.8 ± 2.6 mV/p[taurine] in the concn. range 10-2 to 10-4 mol dm-3.
- 98Wang, T. T.; Liang, R. N.; Yin, T. J.; Yao, R. Q.; Qin, W. An all-solid-state imprinted polymer-based potentiometric sensor for determination of bisphenol S. RSC Adv. 2016, 6, 73308– 73312, DOI: 10.1039/C6RA14461F98https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xht1Cktr7N&md5=824784006b8778a13cc02ab3967cad9bAn all-solid-state imprinted polymer-based potentiometric sensor for determination of bisphenol SWang, Tiantian; Liang, Rongning; Yin, Tanji; Yao, Ruiqing; Qin, WeiRSC Advances (2016), 6 (77), 73308-73312CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)An all-solid-state polymeric membrane potentiometric sensor for detn. of bisphenol S has been developed by using the imprinted polymer as the receptor and a nanoporous gold film as the solid contact. The sensor has a linear concn. range of 0.1 to 2 μM with a detection limit of 0.04 μM.
- 99Zhang, H.; Yao, R. Q.; Wang, N.; Liang, R. N.; Qin, W. Soluble Molecularly Imprinted Polymer-Based Potentiometric Sensor for Determination of Bisphenol AF. Anal. Chem. 2018, 90, 657– 662, DOI: 10.1021/acs.analchem.7b0343299https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhvFGjt7fN&md5=df84e26c4b51508e4b2fa47a5b7ee48cSoluble Molecularly Imprinted Polymer-Based Potentiometric Sensor for Determination of Bisphenol AFZhang, Huan; Yao, Ruiqing; Wang, Ning; Liang, Rongning; Qin, WeiAnalytical Chemistry (Washington, DC, United States) (2018), 90 (1), 657-662CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Molecularly imprinted polymer (MIP)-based polymeric membrane potentiometric sensors have been successfully developed for detn. of org. compds. in their ionic and neutral forms. However, most of the MIP receptors in potentiometric sensors developed so far are insol. and cannot be well dissolved in the polymeric membranes. The heterogeneous mol. recognitions between the analytes and MIPs in the membranes are inefficient due to the less available binding sites of the MIPs. Herein the authors describe a novel polymeric membrane potentiometric sensor using a sol. MIP (s-MIP) as a receptor. The s-MIP is synthesized by the swelling of the traditional MIP at a high temp. The obtained MIP can be dissolved in the plasticized polymeric membrane for homogeneous binding of the imprinted polymer to the target mols. By using neutral bisphenol AF as a model, the proposed method exhibits an improved sensitivity compared to the conventional MIP-based sensor with a lower detection limit of 60 nM. Moreover, the present sensor exhibits an excellent selectivity over other phenols. The authors believe that s-MIPs can provide an appealing substitute for the traditional insol. MIP receptors in the development of polymeric membrane-based electrochem. and optical sensors.
- 100Pankratova, N.; Cuartero, M.; Jowett, L. A.; Howe, E. N. W.; Gale, P. A.; Bakker, E.; Crespo, G. A. Fluorinated tripodal receptors for potentiometric chloride detection in biological fluids. Biosens. Bioelectron. 2018, 99, 70– 76, DOI: 10.1016/j.bios.2017.07.001100https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXht1Gis7%252FP&md5=8f3602cb36c92d2741aa895474fd02f5Fluorinated tripodal receptors for potentiometric chloride detection in biological fluidsPankratova, Nadezda; Cuartero, Maria; Jowett, Laura A.; Howe, Ethan N. W.; Gale, Philip A.; Bakker, Eric; Crespo, Gaston A.Biosensors & Bioelectronics (2018), 99 (), 70-76CODEN: BBIOE4; ISSN:0956-5663. (Elsevier B.V.)Fluorinated tripodal compds. were recently reported to be efficient transmembrane transporters for a series of inorg. anions. In particular, this class of receptors has been shown to be suitable for the effective complexation of chloride, nitrate, bicarbonate and sulfate anions via hydrogen bonding. The potentiometric properties of urea and thiourea-based fluorinated tripodal receptors are explored here for the first time, in light of the need for reliable sensors for chloride monitoring in undiluted biol. fluids. The ion selective electrode (ISE) membranes with tren-based tris-urea bis(CF3) tripodal compd. (ionophore I) were found to exhibit the best selectivity for chloride over major lipophilic anions such as salicylate (logKpotCl-/Sal- = + 1.0) and thiocyanate (logKpotCl-/SCN- = + 0.1). Ionophore I-based ISEs were successfully applied for chloride detn. in undiluted human serum as well as artificial serum sample, the slope of the linear calibration at the relevant background of interfering ions being close to Nernstian (49.8±1.7 mV). The results of potentiometric measurements were confirmed by argentometric titrn. Moreover, the ionophore I-based ISE membrane was shown to exhibit a very good long-term stability of potentiometric performance over the period of 10 wk. NMR (NMR) titrns., potentiometric sandwich membrane expts. and d. functional theory (DFT) computational studies were performed to det. the binding consts. and suggest 1:1 complexation stoichiometry for the ionophore I with chloride as well as salicylate.
- 101Yagi, Y.; Masaki, S.; Iwata, T.; Nakane, D.; Yasui, T.; Yuchi, A. Triphosphate Ion-Selective Electrode Based on Zr-Porphyrin Complex. Anal. Chem. 2017, 89, 3937– 3942, DOI: 10.1021/acs.analchem.6b03754101https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXjvVWhsLs%253D&md5=859587f3f9267986bf6cb1abdd5809a2Triphosphate Ion-Selective Electrode Based on Zr-Porphyrin ComplexYagi, Yuma; Masaki, Shuhei; Iwata, Tetsuki; Nakane, Daisuke; Yasui, Takashi; Yuchi, AkioAnalytical Chemistry (Washington, DC, United States) (2017), 89 (7), 3937-3942CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Ion-selective electrode using Zr(IV) complex with octaethylporphin (H2oep) as a carrier showed high selectivity to triphosphate (TP, H5tp) against other hydrophilic anions including diphosphate and phosphate. The electroactive species was identified to be [Zr4(oep)4(Htp)2] (TP/Zr ratio of 0.5) of the unique structure; triphosphates are recognized by one Zr atom through three O atoms on three different P atoms and by another Zr atom through two O atoms on two terminal P atoms and are also involved in complementary intermol. H bonding to be surrounded by four porphyrin complexes. In contrast, Zr(IV) in the other complex with tetraphenylporphin has the higher Lewis acidity, due to the electron-withdrawing property of Ph rings and, at the higher TP concn., forms a species having a TP/Zr ratio of unity, which ppts. to lose the electroactivity. The electrode was successfully applied to monitor hydrolysis of TP that provides diphosphate and phosphate.
- 102Zahran, E. M.; Fatila, E. M.; Chen, C. H.; Flood, A. H.; Bachas, L. G. Cyanostar: C-H Hydrogen Bonding Neutral Carrier Scaffold for Anion-Selective Sensors. Anal. Chem. 2018, 90, 1925– 1933, DOI: 10.1021/acs.analchem.7b04008102https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXht1ynu7o%253D&md5=924990a1505ef5b0eb03cbb15febdca6Cyanostar: C-H Hydrogen Bonding Neutral Carrier Scaffold for Anion-Selective SensorsZahran, Elsayed M.; Fatila, Elisabeth M.; Chen, Chun-Hsing; Flood, Amar H.; Bachas, Leonidas G.Analytical Chemistry (Washington, DC, United States) (2018), 90 (3), 1925-1933CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Cyanostar, a pentagonal macrocyclic compd. with an electropos. cavity, binds anions with CH-based hydrogen bonding. The large size of the cyanostar's cavity along with its planarity favor formation of 2:1 sandwich complexes with larger anions, like perchlorate, ClO4-, relative to the smaller chloride. Also cyanostar is selective for ClO4- over the bulky salicylate anions by using NMR titrn. studies to measure affinity. The performance of this novel macrocycle as an anion ionophore in membrane ion sensors was evaluated. The cyanostar-based electrodes demonstrated a Nernstian response toward perchlorate with selectivity patterns distinctly different from the normal Hofmeister series. Different membrane compns. were explored to identify the optimum concns. of the ionophore, plasticizer, and lipophilic additive that give rise to the best perchlorate selectivity. Changing the concn. of the lipophilic additive tridodecylmethylammonium chloride was found to impact the selectivity pattern and the anal. dynamic range of the electrodes. The high selectivity of the cyanostar sensors and their detection limit could enable the detn. of ClO4- in contaminated environmental samples. This novel class of macrocycle provides a suitable scaffold for designing various anion-selective ionophores by altering the size of the central cavity and its functionalization.
- 103Shehab, O. R.; Mansour, A. M. Potentiometric Sensing of Aspirin Metabolite in Human Plasma and Pharmaceutical Preparations Using Co(III)-complex Based Electrodes: Experimental and Quantum Chemical Calculations. Electroanalysis 2016, 28, 1100– 1111, DOI: 10.1002/elan.201501059103https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XjslansA%253D%253D&md5=d4b0d0aa646da42ffdd419077d96c4daPotentiometric Sensing of Aspirin Metabolite in Human Plasma and Pharmaceutical Preparations Using Co(III)-complex Based Electrodes: Experimental and Quantum Chemical CalculationsShehab, Ola R.; Mansour, Ahmed M.Electroanalysis (2016), 28 (5), 1100-1111CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)Three novel poly vinyl chloride PVC A, carbon paste CP B, and coated glassy carbon-MWCNT CGC C salicylate sal- sensors based on new synthesized [CoL2ClCl3H2O]-H2O complex L2Cl=1H-benzimidazol-2-ylmethyl-N-2-chloro-phenyl- amine, o-nitrophenyloctyl ether as a mediator and tridodecy lmethylammonium chloride as a cationic additive were successfully used for detn. of sal- in human plasma and pharmaceutical formulations. The sal--sensors exhibited enhanced sensitivity with slope of -63.5, -60.5 and -58.9 mV/decade and detection limit of 1.0 × 10-5, 4.0 × 10-7, and 1.0 × 10-6 mol L-1 for A-C sensors resp. Quantum chem. calcns. were carried out by HF and DFT/B3LYP methods to explore and investigate the interaction between the receptor and the different anions. The intermol. H-bond created between the uncoordinated C=O of salicylate group and the secondary amino group in the complex is the key factor of the selectivity of the proposed sensor. A linear relation is established between the natural charge on the Co center and the value of the binding energy, where the decrease in pos. charge is assocd. by an increase in the anion binding energy.
- 104Abdel-Haleem, F. M.; Badr, I. H. A.; Rizk, M. S. Electroanalysis 2016, 28, 2922– 2929, DOI: 10.1002/elan.201600335104https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhtFert7vL&md5=1d6011e137c3429cf0d36bbb84b8087bPotentiometric Anion Selectivity and Analytical Applications of Polymer Membrane Electrodes Based on Novel Mn(III)- and Mn(IV)-Salophen ComplexesAbdel-Haleem, Fatehy M.; Badr, Ibrahim H. A.; Rizk, Mahmoud S.Electroanalysis (2016), 28 (12), 2922-2929CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)New Mn(III)-L and Mn(IV)-L complexes were prepd. from the highly lipophilic salophen ligand (L): phenol 2,2'-[(4,5-dimethyl-1,2-phenylene)bis[(E)-nitrilomethylidyne]]bis[4,6-bis(1,1-dimethylethyl)]. The prepd. complexes were fully characterized and used for the construction of thiocyanate membrane electrodes. Optimized membrane electrodes contained 33.0 mg PVC, 66.0 mg o-nitrophenyloctylether, 50 or 5 (mole %) tetrakis(trifluoromethyl)phenyl borate and 1 mg Mn(III)-L (sensor 2) or Mn-(IV)-L (sensor 12), resp. Such electrodes exhibited linear responses toward thiocynate in a concn. range of 10-1-10-5 M and detection limits of 8.3×10-6, 8.9×10-6 M for sensor 2 and 12, resp. Optimized membrane electrodes exhibited high selectivity toward thiocayante compared to more lipophilic anions. The obsd. thiocyanate selectivity of the optimized membranes was confirmed by formation const. calcns. for Mn(III)-L and Mn(IV)-L with SCN-, β=1014.1 and 1012.5, which was measured potentiometrically using the sandwich membrane method. Furthermore, computational study using DFT calcns. was performed to at DFT/B3LYP level of theory to confirm the obsd. selectivity data. The response times were 3 and 0.5 min for low and high concns. The lifetimes of the optimized electrodes were ∼4-6 wk. The anal. utility of the optimized membrane electrodes was demonstrated by the anal. of thiocyanate level in different saliva samples.
- 105Lenik, J.; Nieszporek, J. Construction of a glassy carbon ibuprofen electrode modified with multi-walled carbon nanotubes and cyclodextrins. Sens. Actuators, B 2018, 255, 2282– 2289, DOI: 10.1016/j.snb.2017.09.034105https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsFCqtbjF&md5=4a13f376ae467b1b83da6c327ce44435Construction of a glassy carbon ibuprofen electrode modified with multi-walled carbon nanotubes and cyclodextrinsLenik, Joanna; Nieszporek, JolantaSensors and Actuators, B: Chemical (2018), 255 (Part_2), 2282-2289CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)The prepn. of glassy carbon (GC) ibuprofen (2-(4- isobutylphenyl)propionic acid) membrane sensors was examd. in the study described below. The optimal membrane was based on functionalized β-cyclodextrins: heptakis (2,3,6-tri-O-benzoyl)-β-cyclodextrin (GC/MWCNT-HBβCD). The following basic anal. parameters of the drug electrode were detd.: sensitivity, measuring range, detection limit, reversibility, and selectivity coeffs. for some org. and inorg. anions. The electrode exhibited good Nernstian slope of 59.9 mV/decade, measuring range of 3.2 × 10-5-10-2, pH range of 5-9, and very good response time of 5 s. The advantages of the GC electrode with the use of multi-walled carbon nanotubes, i.e. high cond. (bulk resistance 5,76 × 102 Ω) was confirmed by the impedance spectroscopy method whereas high selectivity and the stable potential are the parameters detd. in the potentiometric measurements.
- 106Lisak, G.; Tamaki, T.; Ogawa, T. Dualism of Sensitivity and Selectivity of Porphyrin Dimers in Electroanalysis. Anal. Chem. 2017, 89, 3943– 3951, DOI: 10.1021/acs.analchem.6b04179106https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXjvVWjt70%253D&md5=3e827b9eaae88e1b96fc47ca77c0a8eaDualism of Sensitivity and Selectivity of Porphyrin Dimers in ElectroanalysisLisak, Grzegorz; Tamaki, Takashi; Ogawa, TakujiAnalytical Chemistry (Washington, DC, United States) (2017), 89 (7), 3943-3951CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)This work uncovers the application of porphyrin dimers for the use in electroanal., such as potentiometric detn. of ions. It also puts in question a current perception of an occurrence of the super-Nernstian response, as a result of the possible dimerization of single porphyrins within an ion-selective membrane. To study that, four various porphyrin dimers were used as ionophores, namely freebase-freebase, Zn-Zn, Zn-freebase and freebase-Zn. Since the Zn-freebase and freebase-Zn porphyrin dimers carried both anion- and cation-sensitive porphyrin units, their application in ISEs was used in both anion- and cation-sensitive sensors. In respect to the lipophilic salt added, both porphyrins dimers were found anion- and cation-sensitive. This allowed using a single mol. as novel type of versatile ionophore (anion- and cation-selective), simply by varying the membrane compn. All anion-sensitive sensors were perchlorate-sensitive, while the cation-selective sensors were silver-sensitive. The selectivity of the sensors depended primarily on the porphyrin dimers in the ion-selective membrane. Furthermore, the selectivity of cation-sensitive dimer based sensors was found significantly superior to the ones measured for the single porphyrin unit based sensors (precursors of the porphyrin dimers). Thus, the dimerization of single porphyrins may actually be a factor to increase or modulate porphyrin selectivity. Moreover, in the case of cation-sensitive sensors, the selectivity vastly depended on the order of porphyrin units in the dimer. This opens a new approach of regulating and adjusting sensitivity and selectivity of the sensor through the application of complex porphyrin systems with more than one porphyrin units with mix sensitive porphyrins.
- 107Juarez-Gomez, J.; Ramirez-Silva, M. T.; Romero-Romo, M.; Rodriguez-Sevilla, E.; Perez-Garcia, F.; Palomar-Pardave, M. Ion-Selective Electrodes for Mercury Determination at Low Concentrations: Construction, Optimization and Application. J. Electrochem. Soc. 2016, 163, B90– B96, DOI: 10.1149/2.0621603jesThere is no corresponding record for this reference.
- 108Said, N. R.; Rezayi, M.; Narimani, L.; Al-Mohammed, N. N.; Manan, N. S. A.; Alias, Y. A New N-Heterocyclic Carbene Ionophore in Plasticizer-free Polypyrrole Membrane for Determining Ag+ in Tap Water. Electrochim. Acta 2016, 197, 10– 22, DOI: 10.1016/j.electacta.2016.02.173108https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xkt1Wqs70%253D&md5=8ec9d54946011fb34bfa76f4f3322415A New N-Heterocyclic Carbene Ionophore in Plasticizer-free Polypyrrole Membrane for Determining Ag+ in Tap WaterSaid, Nur Rahimah; Rezayi, Majid; Narimani, Leila; Al-Mohammed, Nassir N.; Manan, Ninie Suhana Abdul; Alias, YatimahElectrochimica Acta (2016), 197 (), 10-22CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Ltd.)A bis[1-benzyl-benzimidazoliumethyl]-4-methylbenzenesufonamide bromide ligand (NHCL) as a new type of ionophore was successfully synthesized for the 1st time and used for the fabrication of Ag+ ion selective electrode as a new type of ionophore, based on the self-plasticizing method. The ionophore was characterized using CHN elemental anal., FTIR, 1H NMR, 13C NMR, UV-visible spectroscopic techniques and x-ray single crystal diffraction. The interection between NHCL and Ag+ cation was studied spectrophotometerically and the stoichiometry of the complex (1:2) NHCL:Ag+ in DMSO solvent was detd. The potentiometric response of the electrode toward Ag+ cation was linear from 2.5 × 10-6 to 1.0 × 10-1 M with detection limit of 2.00 × 10-6 M and a Nernstian slope of 58.48 ± 0.75 mV decade-1. The sensor exhibited a response time of ∼20 s at room temp. and working pH range between 3.5-9.0. The electrode showed a good selectivity towards Ag+ cations in comparison with other soft and hard metals, while most of these metal ions did not show significant interference (KpotAg+,M). The proposed electrode also applied in the direct detn. of Ag+ cations in tap H2O and std. samples with sensible accuracy and precision.
- 109Omran, O. A.; Elgendy, F. A.; Nafady, A. Fabrication and Applications of Potentiometric Sensors Based on p-tert-butylthiacalix 4 arene Comprising Two Triazole Rings Ionophore for Silver Ion Detection. Int. J. Electrochem. Sci. 2016, 11, 4729– 4742, DOI: 10.20964/2016.06.35109https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xhs1Omsr3K&md5=2a66f6a87ae534f8ac414c8ad676576bFabrication and applications of potentiometric sensors based on p-tert-butylthiacalix[4]arene comprising two triazole rings ionophore for silver ion detectionOmran, Omran A.; Elgendy, Fadl A.; Nafady, AymanInternational Journal of Electrochemical Science (2016), 11 (6), 4729-4742CODEN: IJESIV; ISSN:1452-3981. (Electrochemical Science Group)This work describes the fabrication and applications of potentiometric silver-selective sensors, based on the use of a newly synthesized p-tert-butylthiacalix[4]arene comprising two triazole rings, as a novel neutral ionophore in plasticized poly(vinyl chloride) (PVC) membranes. The effect of lipophilic anionic additives on the voltammetric responses of the sensors was investigated in details. The constructed sensors exhibited a Nernstian behavior with 53 ± 0.9 mV per decade change in Ag+ activity over the range from 7.0 × 10-6 to 8.0 × 10-3, with a repetitive detection limit of 0.421μg mL-1. Moreover, the effect of lipophilic salts, plasticizers and various interfering ions were probed. Importantly, validation of the method is achieved in terms of good performance characteristics, including good selectivity for Ag+ over alkali, alk. earth and transition metal ions (e.g. Na+, K+, Pb2+, Mg2+, Co2+ Ni2+, and Cu2+) together with long life span. Other important characteristics such as low detection limit, acceptable accuracy and precision, long term stability, reproducibility were also demonstrated. On the application side, the sensors were utilized for facile potentiometric measurements of iodide ions (I-) over the concn. range of 0.749 to 856μg mL-1 and also employed for probing sequential titrn. of some importantly relevant anions (e.g. Cl-, Br-, I-, SCN- and N-3). Significantly, sequential binding of these anions with Ag+ cations produces sharp stepwise titrn. curves with consecutive end point breaks at the equiv. points.
- 110Kawakami, T. M.; Obita, M.; Tsujinaka, T.; Higashikado, A.; Moriuchi, T. Ionophoric Properties of 14 Tetraazaannulene Derivatives and Substituent Effect on the Cation-selectivity. Electroanalysis 2017, 29, 1712– 1720, DOI: 10.1002/elan.201700011110https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXlvVGgu7o%253D&md5=b2288e6ae0ac26879012a8d276aeada6Ionophoric Properties of [14]Tetraazaannulene Derivatives and Substituent Effect on the Cation-selectivityKawakami, T. M.; Obita, M.; Tsujinaka, T.; Higashikado, A.; Moriuchi, T.Electroanalysis (2017), 29 (7), 1712-1720CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)[14]Tetraazaannulene derivs. 1-4 (I-IV) with various substituents were synthesized as ion recognition compds. All solvent polymeric membrane electrodes incorporating [14]tetraazaannulene derivs. I-IV showed rapid response for the Cu2+ ion and exhibited excellent selectivity over other mono- and divalent cations such as Ag+ and Ni2+ ions. The solvent polymeric membrane electrode based on [14]tetraazaannulene deriv. I has a linear response to the Cu2+ ion from 5.01 × 10-7-2.63 × 10-4 M with a slope of 29.56 mV per decade. DFT calcns. showed that the selectivities for the Cu2+ ion of the ISEs based on [14]tetraazaannulene derivs. I-IV depended on both their topol. and electrostatic properties caused by the introduced substituents.
- 111Kumar, S.; Mittal, S. K.; Kaur, N.; Kaur, R. Improved performance of Schiff based ionophore modified with MWCNT for Fe(II) sensing by potentiometry and voltammetry supported with DFT studies. RSC Adv. 2017, 7, 16474– 16483, DOI: 10.1039/C7RA00393E111https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXksVCrsbo%253D&md5=8bf1bd35b1ae629c2f78a7838d2e9e79Improved performance of Schiff based ionophore modified with MWCNT for Fe(II) sensing by potentiometry and voltammetry supported with DFT studiesKumar, Sanjeev; Mittal, Susheel K.; Kaur, Navneet; Kaur, RavneetRSC Advances (2017), 7 (27), 16474-16483CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)A novel potentiometric and voltammetric sensor for creating a cationic response for Fe(II) is introduced. These methods were applied to produce an Fe(II) selective sensor based on (E)-3-((2-aminoethylimino)methyl)-4H-chromen-4-one (IFE). The influence of variables including the amt. of ionophore, plasticizers, anion excluder and multiwalled carbon nanotubes (MWCNTs) on the performance of the potentiometric sensor were investigated. The sensor for Fe(II) improvised the dynamic linear range (1 × 10-7 to 1 × 10-1 mol L-1) with a slope of 27 mV per decade and a detection limit of 2.5 × 10-8 mol L-1. Selectivity of the ion selective electrode improved after modification with MWCNTs. The redn. and oxidn. properties of IFE were studied by voltammetric measurements. Differential pulse voltammetry was applied to the optimized electrode and a linear dynamic range from (9.9 × 10-7 to 2.9 × 10-5 mol L-1) with a detection limit of 6.13 × 10-8 mol L-1 was obtained. The compn. and morphol. of the modified ion selective electrode were characterized with SEM. The modified electrodes have good selectivity for Fe(II) ions over a no. of metal ions. It was successfully applied for direct detn. of Fe(II) ions in different real life samples. Theor. calcns. also supported the complexation behavior of Fe(II) with IFE.
- 112Rezayi, M.; Gholami, M.; Said, N. R.; Alias, Y. A novel polymeric membrane sensor for determining titanium (III) in real samples: Experimental, molecular and regression modeling. Sens. Actuators, B 2016, 224, 805– 813, DOI: 10.1016/j.snb.2015.10.089112https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhvVKrsL7J&md5=5fc539cc0e8bcfa78fd6bb336d0190b3A novel polymeric membrane sensor for determining titanium (III) in real samples: Experimental, molecular and regression modelingRezayi, Majid; Gholami, Mehrdad; Rahimah Said, Nur; Alias, YatimahSensors and Actuators, B: Chemical (2016), 224 (), 805-813CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)The construction of a potentiometric titanium(III)-selective electrode based on methylcalix[4]resorcinarene (CMCR) incorporated into a poly(vinyl chloride) (PVC) matrix is reported. The polymeric membrane incorporates 8.0 mg CMCR as an electroactive sensing material, 59.0 mg dioctylphthalate (DOP) as a plasticizer, 3.0 mg sodium tetra-Ph borate (NaTPB) as an anionic additive and 30 mg PVC as a neutral matrix exhibiting a Nernstain potential response of 30.38 ± 0.15 mV per decade in the concn. range from 1 × 10-6 to 1 × 10-2 M with a detection limit of 8.9 × 10-7 M and fast response time of 15 s. The proposed sensor was successfully applied to det. titanium cations in real samples and the obtained results were compared to those of spectroscopy methods such as AAS and ICP instruments. The structure of CMCR ligand and its complexation with some common cations were investigated using quantum mech. DFT calcns. where the titanium (III) cation showed prominent affinity for the CMCR carrier. The regression model was applied to obtain the membrane compn. model of Ti(III)-ISE affecting the potential response of the polymeric sensor. The results show that the regression model can be used as a practical method for obtaining the Nernstian slope of the proposed sensor in this study.
- 113Zahran, E. M.; Paeng, K. J.; Badr, I. H. A.; Hume, D.; Lynn, B. C.; Johnson, R. D.; Bachas, L. G. Correlating the potentiometric selectivity of cyclosporin-based electrodes with binding patterns obtained from electrospray ionization-mass spectrometry. Analyst 2017, 142, 3241– 3249, DOI: 10.1039/C6AN01252C113https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtlSrsbfK&md5=ccdec0e860c49726cce47b4a4e67b46fCorrelating the potentiometric selectivity of cyclosporin-based electrodes with binding patterns obtained from electrospray ionization-mass spectrometryZahran, Elsayed M.; Paeng, Ki-Jung; Badr, Ibrahim H. A.; Hume, David; Lynn, Bert C.; Daniel Johnson, R.; Bachas, Leonidas G.Analyst (Cambridge, United Kingdom) (2017), 142 (17), 3241-3249CODEN: ANALAO; ISSN:0003-2654. (Royal Society of Chemistry)Electrospray ionization mass spectrometry ESI-MS is a powerful technique for the characterization of macromols. and their noncovalent binding with guest ions. The authors herein evaluate the feasibility of using ESI-MS as a screening tool for predicting potentiometric selectivities of ionophores. Ion-selective electrodes based on the cyclic peptide, cyclosporin A, were developed, and their potentiometric selectivity pattern was evaluated. Optimized electrodes demonstrated near-Nernstian slopes with micromolar detection limits toward calcium. ESI-MS and ESI-MS/MS were employed to det. the relative assocn. strengths of cyclosporin A with various cations. The obsd. MS intensities of ion-ionophore complexes correlate favorably with the potentiometric selectivity pattern that was demonstrated by cyclosporin-based electrodes. This correlation holds true for other established ionophores, such as valinomycin and benzo-18-crown-6. Taken together, these expts. demonstrate that mass spectrometry could be used to predict the selectivity patterns of new ionophores for potentiometric and optical ion sensors. Further, this approach could be useful in screening mixts. or libraries of newly-synthesized compds. to identify selective ionophores.
- 114Guinovart, T.; Hernandez-Alonso, D.; Adriaenssens, L.; Blondeau, P.; Martinez-Belmonte, M.; Rius, F. X.; Andrade, F. J.; Ballester, P. Recognition and Sensing of Creatinine. Angew. Chem., Int. Ed. 2016, 55, 2435– 2440, DOI: 10.1002/anie.201510136114https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XmslGhsA%253D%253D&md5=6660d0e43c2e1e32802343bc12ff152dRecognition and Sensing of CreatinineGuinovart, Tomas; Hernandez-Alonso, Daniel; Adriaenssens, Louis; Blondeau, Pascal; Martinez-Belmonte, Marta; Rius, F. Xavier; Andrade, Francisco J.; Ballester, PabloAngewandte Chemie, International Edition (2016), 55 (7), 2435-2440CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)Current methods for creatinine quantification suffer from significant drawbacks when aiming to combine accuracy, simplicity, and affordability. Here, an unprecedented synthetic receptor, an aryl-substituted calix[4]pyrrole with a monophosphonate bridge, is reported that displays remarkable affinity for creatinine and the creatininium cation. The receptor works by including the guest in its deep and polar arom. cavity and establishing directional interactions in three dimensions. When incorporated into a suitable polymeric membrane, this mol. acts as an ionophore. A highly sensitive and selective potentiometric sensor suitable for the detn. of creatinine levels in biol. fluids, such as urine or plasma, in an accurate, fast, simple, and cost-effective way has thus been developed.
- 115Guinovart, T.; Hernandez-Alonso, D.; Adriaenssens, L.; Blondeau, P.; Rius, F. X.; Ballester, P.; Andrade, F. J. Characterization of a new ionophore-based ion-selective electrode for the potentiometric determination of creatinine in urine. Biosens. Bioelectron. 2017, 87, 587– 592, DOI: 10.1016/j.bios.2016.08.025115https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhsFSlt7nF&md5=0083915b99552cbaf23c55b80a74e116Characterization of a new ionophore-based ion-selective electrode for the potentiometric determination of creatinine in urineGuinovart, Tomas; Hernandez-Alonso, Daniel; Adriaenssens, Louis; Blondeau, Pascal; Rius, F. Xavier; Ballester, Pablo; Andrade, Francisco J.Biosensors & Bioelectronics (2017), 87 (), 587-592CODEN: BBIOE4; ISSN:0956-5663. (Elsevier B.V.)The optimization, anal. characterization and validation of a novel ion-selective electrode for the highly sensitive and selective detn. of creatinine in urine is presented. A newly synthesized calix[4]pyrrole-based mol. is used as an ionophore for the enhanced recognition of creatininium cations. The calcn. of the complex formation consts. in the polymeric membrane with creatininium, potassium and sodium confirms the strong selective interactions between the ionophore and the target. The optimization of the potentiometric sensor presented here yields an outstanding anal. performance, with a linear range that spans from 1μM to 10 mM and limit of detection of 10-6.2 M. The calcn. of the selectivity coeffs. against most commonly found interferences also show significant improvements when compared to other sensors already reported. The performance of this novel sensor is tested by measuring creatinine in real urine samples (N=50) and comparing the values against the std. colorimetric approach (Jaffe's reaction). The results show that this sensor allows the fast and accurate detn. of creatinine in real samples with minimal sample manipulation.
- 116Khaled, E.; Khalil, M. M.; el Aziz, G. M. A. Calixarene/carbon nanotubes based screen printed sensors for potentiometric determination of gentamicin sulphate in pharmaceutical preparations and spiked surface water samples. Sens. Actuators, B 2017, 244, 876– 884, DOI: 10.1016/j.snb.2017.01.033116https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtFOmsbw%253D&md5=ac2b35ec414d628c2f4972f2b51ee51eCalixarene/carbon nanotubes based screen printed sensors for potentiometric determination of gentamicin sulphate in pharmaceutical preparations and spiked surface water samplesKhaled, Elmorsy; Khalil, M. M.; Abed el Aziz, G. M.Sensors and Actuators, B: Chemical (2017), 244 (), 876-884CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)Sensitive disposable sensors have been introduced for potentiometric detn. of gentamicin sulfate (GNS) based on multi-walled carbon nanotubes-polyvinyl chloride (MWNTs-PVC) composite in presence of calixarene as a mol. recognition element. The proposed sensors showed remarkable selectivity and sensitivity in the GNS concn. range from 10-7 to 10-2 mol L-1 with Nernstian slope 30.5 ± 0.4 mV decade-1 and detection limit of 7.5 × 10-8 mol L-1. Modification with carbon nanotubes improved the sensors performance was through promotion of the electron-transfer processes and enhancing the stability of potential reading, response time, and shelf lifetime of sensors. The proposed method has been applied for the potentiometric assay of GNS in different dosage forms and spiked surface water samples with av. recoveries agreeable with the reported official method.
- 117Bliem, C.; Fruhmann, P.; Stoica, A. I.; Kleber, C. Development and Optimization of an Ion-selective Electrode for Serotonin Detection. Electroanalysis 2017, 29, 1635– 1642, DOI: 10.1002/elan.201600782117https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXlsV2htLw%253D&md5=fb25c2c6431bece736393c25b4be552eDevelopment and Optimization of an Ion-selective Electrode for Serotonin DetectionBliem, Christina; Fruhmann, Philipp; Stoica, Anca-Iulia; Kleber, ChristophElectroanalysis (2017), 29 (6), 1635-1642CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)The authors' studies are focused on the development of novel potentiometric sensors for the quantification of the neurotransmitter serotonin. Therefore, ion-selective electrodes based on plasticized PVC membranes are applied. The electroactive part of the membrane consists of an ion pair complex formed between the protonated analyte and a carborane anion [Co(1,2-C2B9H11)2]-. The anal. performance of the electrode was studied regarding sensitivity, concn. range, limit of detection and potential stability. The ion-selective electrodes were optimized with respect to the material of the transducing element, as well as the membrane thickness and its compn. Stable, all solid state ISEs could be developed, using the non-polar plasticizer NPOE and a graphite rod with high surface area as transducing element. The authors thus achieved a near Nernstian response over three decades of concn. (2.25·10-5-1.00·10-2 M) and a limit of detection in the μ-molar range for the optimized electrodes. The electrodes could successfully be miniaturized using carbon based screen printed electrodes.
- 118Hu, J. B.; Stein, A.; Bühlmann, P. A Disposable Planar Paper-Based Potentiometric Ion-Sensing Platform. Angew. Chem., Int. Ed. 2016, 55, 7544– 7547, DOI: 10.1002/anie.201603017118https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XotFOjsb8%253D&md5=fb55fa74ec04449887a57125222470c7A Disposable Planar Paper-Based Potentiometric Ion-Sensing PlatformHu, Jinbo; Stein, Andreas; Buehlmann, PhilippeAngewandte Chemie, International Edition (2016), 55 (26), 7544-7547CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)Ion-selective electrodes (ISEs) are widely used tools for fast and accurate ion sensing. Herein their design is simplified by embedding a potentiometric cell into paper, complete with an ISE, a ref. electrode, and a paper-based microfluidic sample zone that offer the full function of a conventional ISE setup. The disposable planar paper-based ion-sensing platform is suitable for low-cost point-of-care and in-field testing applications. The design is sym. and each interfacial potential within the cell is well defined and reproducible, so that the response of the device can be theor. predicted. For a demonstration of clin. applications, paper-based Cl- and K+ sensors are fabricated with highly reproducible and linear responses towards different concns. of analyte ions in aq. and biol. samples. The single-use devices can be fabricated by a scalable method, do not need any pretreatment prior to use, and only require a sample vol. of 20 μL.
- 119Ding, J. W.; Li, B. W.; Chen, L. X.; Qin, W. A Three-Dimensional Origami Paper-Based Device for Potentiometric Biosensing. Angew. Chem., Int. Ed. 2016, 55, 13033– 13037, DOI: 10.1002/anie.201606268119https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhsFams7zE&md5=cde9c02cf5119cba1d2bcbc5f8a67cf8A Three-Dimensional Origami Paper-Based Device for Potentiometric BiosensingDing, Jiawang; Li, Bowei; Chen, Lingxin; Qin, WeiAngewandte Chemie, International Edition (2016), 55 (42), 13033-13037CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)Current paper-based potentiometric ion-sensing platforms are planar devices used for clin. relevant ions. These devices, however, have not been designed for the potentiometric biosensing of proteins or small mol. analytes. A three-dimensional origami paper-based device, in which a solid-contact ion-selective electrode is integrated with an all-solid-state ref. electrode, is described for the first time. The device is made by impregnation of paper with appropriate bioreceptors and reporting reagents on different zones. By folding and unfolding the paper structures, versatile potentiometric bioassays can be performed. A USB-controlled miniaturized electrochem. detector can be used for simple and in situ measurements. Using butyrylcholinesterase as a model enzyme, the device has been successfully applied to the detection of enzyme activities and organophosphate pesticides involved in the enzymic system as inhibitors. The proposed 3D origami paper device allows the potentiometric biosensing of proteins and small mols. in a simple, portable, and cost-effective way.
- 120Fayose, T.; Mendecki, L.; Ullah, S.; Radu, A. Single strip solid contact ion selective electrodes on a pencil-drawn electrode substrate. Anal. Methods 2017, 9, 1213– 1220, DOI: 10.1039/C6AY02860H120https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXkvFGqsg%253D%253D&md5=015009457c80c2c9e46495645bbfa2c6Single strip solid contact ion selective electrodes on a pencil-drawn electrode substrateFayose, T.; Mendecki, L.; Ullah, S.; Radu, A.Analytical Methods (2017), 9 (7), 1213-1220CODEN: AMNEGX; ISSN:1759-9679. (Royal Society of Chemistry)A simple and low-cost approach for the prepn. of ion-selective electrodes (ISEs) is proposed as a favorable alternative to traditional paper-based electrodes. This involved the application of graphite from a simple household pencil via mech. abrasion onto a modified acetate sheet. The resulting electrodes exhibited excellent sensing properties towards all tested ions, including a wide dynamic response range, fast response time and satisfactory long-term stability. The same methodol. was used to produce stable and functional ref. electrodes. These electrodes were then combined with other graphite-based ISEs to yield single strip solid-contact electrodes for simultaneous detection of cations and anions in aq. solns. The described approach, which is analogous to simply drawing on paper, opens new avenues for the development of sensing devices using very cheap and easily accessible components.
- 121Sjöberg, P.; Maattanen, A.; Vanamo, U.; Novell, M.; Ihalainen, P.; Andrade, F. J.; Bobacka, J.; Peltonen, J. Paper-based potentiometric ion sensors constructed on ink-jet printed gold electrodes. Sens. Actuators, B 2016, 224, 325– 332, DOI: 10.1016/j.snb.2015.10.051121https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhslGisLjJ&md5=dbf1a614c1de765c811c906254e1cce4Paper-based potentiometric ion sensors constructed on ink-jet printed gold electrodesSjoberg, Pia; Maattanen, Anni; Vanamo, Ulriika; Novell, Marta; Ihalainen, Petri; Andrade, Francisco J.; Bobacka, Johan; Peltonen, JoukoSensors and Actuators, B: Chemical (2016), 224 (), 325-332CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)Printed electrodes on a recyclable low-cost coated paper were used as a platform for constructing potentiometric ion sensors consisting of an ion-selective electrode (ISE) and a ref. electrode (RE). The ref. and working electrodes were printed by using a stable suspension of gold nanoparticles (AuNP) as the ink. Sintering turned the printed electrodes conductive. A poly(3,4-ethylenedioxythiophene) (PEDOT) layer, with poly(styrene sulfonate) (PSS) ions as counterions was deposited on the gold electrodes by electropolymn., drop-casting or ink-jet printing. The ref. electrode was prepd. by further coating the PEDOT(PSS) layer with a poly(vinyl chloride) (PVC) membrane contg. a lipophilic salt, tetrabutylammonium tetrabutylborate (TBA-TBB), thus resulting in a solid-contact ref. electrode (SCRE). The working electrode was modified by coating the PEDOT(PSS) layer with a K+-selective membrane, to obtain a solid-contact K+-ISE. The electrochem. characteristics of the resulting electrode systems were studied by amperometric, potentiometric and electrochem. impedance spectroscopic (EIS) measurements. The potentiometric response toward K+ ions was addnl. studied. The surface structure of the PEDOT(PSS) layers deposited by the different methods was studied with at. force microscopic (AFM) measurements. It was shown that a well-functioning planar electrode platform with good electrochem. characteristics could be prepd. by ink-jet printing in a repeatable manner. The planar electrode platform presented here offers a user-friendly and ecol. alternative to perform chem. anal. from small sample vols.
- 122Armas, S. M.; Manhan, A. J.; Younce, O.; Calvo-Marzal, P.; Chumbimuni-Torres, K. Y. Ready-to-use single-strip paper based sensor for multiplex ion detection. Sens. Actuators, B 2018, 255, 1781– 1787, DOI: 10.1016/j.snb.2017.08.194122https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsVOhs7rL&md5=09afd8324c508423a6a92eddaf933ff8Ready-to-use single-strip paper based sensor for multiplex ion detectionArmas, Stephanie M.; Manhan, Andrew J.; Younce, Olivia; Calvo-Marzal, Percy; Chumbimuni-Torres, Karin Y.Sensors and Actuators, B: Chemical (2018), 255 (Part_2), 1781-1787CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)Ion-selective electrodes (ISEs) are an efficient and versatile tool for ion detection. However, portability and applicability for field applications are often limited by the need of a conditioning step, and high cost of the needed bulky ref. electrode. Herein, the traditional conditioning protocol of ISEs has been eliminated and a paper-based solid-contact ISE (PBSC-ISE) has been integrated with a paper-based solid-contact ref. electrode (PBSC-RE) in a single strip format for on-site anal. The PBSC-RE is based on the copolymer Me methacrylate-co-decyl methacrylate (MMA-DMA) (support matrix), combined with ionic liqs. (ILs) to create and maintain a stable potential that is un-affected by a change in ionic activity. This single-strip ready-to-use sensor yields a Nernstian response towards Na+, K+, and I- ions with submicromolar limits of detection, and is able to be used for multiplex anal.
- 123Parrilla, M.; Canovas, R.; Andrade, F. J. Enhanced Potentiometric Detection of Hydrogen Peroxide Using a Platinum Electrode Coated with Nafion. Electroanalysis 2017, 29, 223– 230, DOI: 10.1002/elan.201600403123https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhsVChtb%252FK&md5=eedf00f03fbb36904c4e782296c51676Enhanced Potentiometric Detection of Hydrogen Peroxide Using a Platinum Electrode Coated with NafionParrilla, Marc; Canovas, Rocio; Andrade, Francisco J.Electroanalysis (2017), 29 (1), 223-230CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)The potentiometric response to hydrogen peroxide of a platinum electrode coated with a layer of Nafion is presented. The Nafion membrane acts as an effective permselective barrier, thus significantly reducing the response to some redox active species, such as ascorbate. Even more interesting, these coated electrodes show a significantly enhanced sensitivity to hydrogen peroxide (H2O2) when the measurements were performed in solns. of high ionic strength. The influence of pH, ionic strength and supporting electrolyte on this enhancement are presented. Under optimized conditions these coated electrodes show a linear dependence with the logarithm of the concn. of H2O2, with sensitivities of -125.1 ± 5.9 mV decade-1 (several times higher than the bare electrodes) and a linear range that spans from 10-5 M to 10-3 M of H2O2. Preliminary studies suggest that the coupling between the redox potential on the Pt electrode and the Donnan potential of the membrane plays a role on this enhancement. Considering this improved sensitivity, selectivity, stability and linear ranges, this system shows promise as a future platform to build enzyme-based potentiometric biosensors.
- 124Canovas, R.; Parrilla, M.; Blondeau, P.; Andrade, F. J. A novel wireless paper-based potentiometric platform for monitoring glucose in blood. Lab Chip 2017, 17, 2500– 2507, DOI: 10.1039/C7LC00339K124https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXpvFyjtr8%253D&md5=010b78d249d3b04343810ec70bc639d7A novel wireless paper-based potentiometric platform for monitoring glucose in bloodCanovas, Rocio; Parrilla, Marc; Blondeau, Pascal; Andrade, Francisco J.Lab on a Chip (2017), 17 (14), 2500-2507CODEN: LCAHAM; ISSN:1473-0189. (Royal Society of Chemistry)A novel low-cost, compact and sensitive paper-based platform for the accurate monitoring of glucose in biol. fluids is presented. Paper-based working and ref. electrodes are combined to build a whole potentiometric cell, which also fits a sampling module for simple and fast detn. of glucose in a single drop of blood. The working electrode is built using a platinized filter paper coated with a Nafion membrane that entraps the enzyme glucose oxidase; the ref. electrode is made by casting a polyvinylbutyral-based membrane onto a conductive paper. The system works by detecting the hydrogen peroxide generated as a result of the enzymic reaction. Selectivity is achieved due to the permselective behavior of Nafion, while a significant enhancement of the sensitivity is reached by exploiting the Donnan-coupled formal potential. Under optimum conditions, a sensitivity of -95.9 ± 4.8 mV per decade in the 0.3-3 mM range is obtained. Validation of the measurements has been performed against std. methods in human serum and blood. Final integration with a wireless reader allows for truly in situ measurements with a less than 2 min procedure including a two-point calibration, washing and measurement. This low-cost anal. device opens up new prospects for rapid diagnostic results in non-lab. settings.
- 125Guadarrama-Fernandez, L.; Novell, M.; Blondeau, P.; Andrade, F. J. A disposable, simple, fast and low-cost paper-based biosensor and its application to the determination of glucose in commercial orange juices. Food Chem. 2018, 265, 64– 69, DOI: 10.1016/j.foodchem.2018.05.082125https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXpslynuro%253D&md5=a291e815dd24aa3244588fdac06d701cA disposable, simple, fast and low-cost paper-based biosensor and its application to the determination of glucose in commercial orange juicesGuadarrama-Fernandez, Leonor; Novell, Marta; Blondeau, Pascal; Andrade, Francisco J.Food Chemistry (2018), 265 (), 64-69CODEN: FOCHDJ; ISSN:0308-8146. (Elsevier Ltd.)A new biosensor for monitoring glucose levels in beverages is presented. The measurements are performed using potentiometric detection. Working electrodes are made using platinized paper as support and a biocompatible polymeric membrane made of a mixt. of polyvinyl alc. and chitosan contg. glucose oxidase as the recognition layer. The system is based on the detection of the hydrogen peroxide generated by an enzymic reaction performed in a highly sensitive, selective and simple way. The biosensors display suitable anal. performance (sensitivity -119.6 ± 6.4 mV/dec in the 0.03-1.0 mM range with a limit of detection of 0.02 mM). Detn. of glucose in com. orange juices is presented. These results were validated against conventional std. methods, showing good accuracy and fast anal. response. The methodol. presented herein does not require complex samples treatment, offering an alternative to conventional methods, particularly for detns. performed with minimal expertise and without a lab. infrastructure.
- 126Ruecha, N.; Chailapakul, O.; Suzuki, K.; Citterio, D. Fully Inkjet-Printed Paper-Based Potentiometric Ion-Sensing Devices. Anal. Chem. 2017, 89, 10608– 10616, DOI: 10.1021/acs.analchem.7b03177126https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtl2lsb%252FP&md5=4e2561055b025bd1c18573ce72a4c5a0Fully Inkjet-Printed Paper-Based Potentiometric Ion-Sensing DevicesRuecha, Nipapan; Chailapakul, Orawon; Suzuki, Koji; Citterio, DanielAnalytical Chemistry (Washington, DC, United States) (2017), 89 (19), 10608-10616CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)A fully inkjet-printed disposable and low cost paper-based device for potentiometric Na+- or K+-ion sensing has been developed. A printed ionophore-based all-solid-state ion selective electrode on a graphene/poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (G/PEDOT:PSS) nanocomposite solid contact and a printed all-solid state ref. electrode consisting of a pseudosilver/silver chloride electrode coated by a lipophilic salt-incorporating poly(vinyl chloride) membrane overprinted with potassium chloride have been combined on a microfluidically patterned paper substrate. Devices are built on std. filter paper using off-the-shelf materials. Ion sensing has been achieved within 180 s by simple addn. of 20 μL of sample soln. without electrode preconditioning. The limits of detection were 32 and 101 μM for Na+ and K+, resp. The individual single-use sensing devices showed near Nernstian response of 62.5 ± 2.1 mV/decade (Na+) and 62.9 ± 1.1 mV/decade (K+) with excellent std. potential (E0) reproducibilities of 455.7 ± 5.1 mV (Na+) and 433.9 ± 2.8 mV (K+). The current work demonstrates the promising possibility of obtaining low-cost and disposable paper-based potentiometric sensing devices potentially manufacturable at large scales with industrial inkjet printing technol.
- 127Nery, E. W.; Kubota, L. T. Integrated, paper-based potentiometric electronic tongue for the analysis of beer and wine. Anal. Chim. Acta 2016, 918, 60– 68, DOI: 10.1016/j.aca.2016.03.004127https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XkvVertr8%253D&md5=2946d80323c8778ee97becbbb1a57922Integrated, paper-based potentiometric electronic tongue for the analysis of beer and wineNery, Emilia Witkowska; Kubota, Lauro T.Analytica Chimica Acta (2016), 918 (), 60-68CODEN: ACACAM; ISSN:0003-2670. (Elsevier B.V.)The following manuscript details the stages of construction of a novel paper-based electronic tongue with an integrated Ag/AgCl ref., which can operate using a minimal amt. of sample (40 μL). First, we optimized the fabrication procedure of silver electrodes, testing a set of different methodologies (electroless plating, use of silver nanoparticles and com. silver paints). Later a novel, integrated electronic tongue system was assembled with the use of readily available materials such as paper, wax, lamination sheets, bleach etc. New system was thoroughly characterized and the ion-selective potentiometric sensors presented performance close to theor. An electronic tongue, composed of electrodes sensitive to sodium, calcium, ammonia and a cross-sensitive, anion-selective electrode was used to analyze 34 beer samples (12 types, 19 brands). This system was able to discriminate beers from different brands, and types, indicate presence of stabilizers and antioxidants, dyes or even unmalted cereals and carbohydrates added to the fermn. wort. Samples could be classified by type of fermn. (low, high) and system was able to predict pH and in part also alc. content of tested beers. In the next step sample vol. was minimalized by the use of paper sample pads and measurement in flow conditions. In order to test the impact of this advancement a four electrode system, with cross-sensitive (anion-selective, cation-selective, Ca2+/Mg2+, K+/Na+) electrodes was applied for the anal. of 11 types of wine (4 types of grapes, red/white, 3 countries). Proposed matrix was able to group wines produced from different varieties of grapes (Chardonnay, Americanas, Malbec, Merlot) using only 40 μL of sample. Apart from that, storage stability studies were performed using a multimeter, therefore showing that not only fabrication but also detection can be accomplished by means of off-the-shelf components. This manuscript not only describes new paper-based, potentiometric sensors but also according to our knowledge is the first description of an electrochem. paper-based electronic tongue with integrated ref.
- 128Ding, J. W.; He, N.; Lisak, G.; Qin, W.; Bobacka, J. Paper-based microfluidic sampling and separation of analytes for potentiometric ion sensing. Sens. Actuators, B 2017, 243, 346– 352, DOI: 10.1016/j.snb.2016.11.128128https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XitVaqtbfP&md5=b7a2d516f1b32342fb23cc68c58e85ebPaper-based microfluidic sampling and separation of analytes for potentiometric ion sensingDing, Jiawang; He, Ning; Lisak, Grzegorz; Qin, Wei; Bobacka, JohanSensors and Actuators, B: Chemical (2017), 243 (), 346-352CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)This work demonstrates a paper-based microfluidic sampling and sepn. platform that allows potentiometric sensing of chloride ions in presence of strongly interfering salicylate ions using a solid-contact ion-selective electrode as a detector. The device was composed of two pieces of paper with different shapes and pore sizes. A "T" shaped filter paper with a pore size of 12-25μm was used as the detection zone. A filter paper with a pore size of 2.0μm was modified with a complexing agent (Fe3+) and served as the sepn. zone. The two pieces of the paper were joined together just like a jigsaw. A solid-contact Cl- -selective electrode and a ref. electrode were gently pressed onto the detection zone to create a direct contact between the electrodes and the soln. absorbed in the paper. Utilizing the possibility to form stable complexes between Fe3+ and salicylate, the proposed platform enables the sepn. of salicylate and detection of chloride. This system offers a convenient platform for both sampling and sepn. of ions, in which sample pretreatment procedures can be simplified or avoided.
- 129Farzbod, A.; Moon, H. Integration of reconfigurable potentiometric electrochemical sensors into a digital microfluidic platform. Biosens. Bioelectron. 2018, 106, 37– 42, DOI: 10.1016/j.bios.2018.01.048129https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXitV2ktbo%253D&md5=004c40164a66a48f9ae89d6ccde35ec4Integration of reconfigurable potentiometric electrochemical sensors into a digital microfluidic platformFarzbod, Ali; Moon, HyejinBiosensors & Bioelectronics (2018), 106 (), 37-42CODEN: BBIOE4; ISSN:0956-5663. (Elsevier B.V.)This paper presents the demonstration of on-chip fabrication of a potassium-selective sensor array enabled by electrowetting on dielec. digital microfluidics for the first time. This demonstration proves the concept that electrochem. sensors can be seamlessly integrated with sample prepn. units in a digital microfluidic platform. More significantly, the successful on-chip fabrication of a sensor array indicates that sensors become reconfigurable and have longer lifetime in a digital microfluidic platform. The on-chip fabrication of ion-selective electrodes includes electroplating Ag followed by forming AgCl layer by chem. oxidn. and depositing a thin layer of desired polymer-based ion selective membrane on one of the sensor electrodes. In this study, potassium ionophores work as potassium ion channels and make the membrane selective to potassium ions. This selectiveness results in the voltage difference across the membrane layer, which is correlated with potassium ion concn. The calibration curve of the fabricated potassium-selective electrode demonstrates the slope of 58mV/dec for potassium concn. in KCl sample solns. and shows good agreement with the ideal Nernstian response. The proposed sensor platform is an outstanding candidate for a portable home-use for continuous monitoring of ions thanks to its advantages such as easy automation of sample prepn. and detection processes, elongated sensor lifetime, minimal membrane and sample consumption, and user-definable/reconfigurable sensor array.
- 130Gosselin, D.; Gougis, M.; Baque, M.; Navarro, F. P.; Belgacem, M. N.; Chaussy, D.; Bourdat, A.-G.; Mailley, P.; Berthier, J. Anal. Chem. 2017, 89, 10124– 10128, DOI: 10.1021/acs.analchem.7b02394130https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsVKmurzN&md5=82a3104e867d7bb279283887c6aea325Screen-Printed Polyaniline-Based Electrodes for the Real-Time Monitoring of Loop-Mediated Isothermal Amplification ReactionsGosselin, David; Gougis, Maxime; Baque, Melissa; Navarro, Fabrice P.; Belgacem, Mohamed N.; Chaussy, Didier; Bourdat, Anne-Gaelle; Mailley, Pascal; Berthier, JeanAnalytical Chemistry (Washington, DC, United States) (2017), 89 (19), 10124-10128CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Nucleic acid amplification testing is a very powerful method to perform efficient and early diagnostics. However, the integration of a DNA amplification reaction with its assocd. detection in a low-cost, portable, and autonomous device remains challenging. Addressing this challenge, the use of screen-printed electrochem. sensor is reported. To achieve the detection of the DNA amplification reaction, a real-time monitoring of the hydronium ions concn., a byproduct of this reaction, is performed. Such measurements are done by potentiometry using polyaniline (PAni)-based working electrodes and silver/silver chloride ref. electrodes. The developed potentiometric sensor is shown to enable the real-time monitoring of a loop-mediated isothermal amplification (LAMP) reaction with an initial no. of DNA strands as low as 10 copies. In addn., the performance of this PAni-based sensor is compared to fluorescence measurements, and it is shown that similar results are obtained for both methods.
- 131Wang, S. Q.; Wu, Y. J.; Gu, Y.; Li, T.; Luo, H.; Li, L. H.; Bai, Y. Y.; Li, L. L.; Liu, L.; Cao, Y. D.; Ding, H. Y.; Zhang, T. Wearable Sweatband Sensor Platform Based on Gold Nanodendrite Array as Efficient Solid Contact of Ion-Selective Electrode. Anal. Chem. 2017, 89, 10224– 10231, DOI: 10.1021/acs.analchem.7b01560131https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsVWmsr3O&md5=c2dd63e8ce8ecb156540659eb1f97a05Wearable Sweatband Sensor Platform Based on Gold Nanodendrite Array as Efficient Solid Contact of Ion-Selective ElectrodeWang, Shuqi; Wu, Yongjin; Gu, Yang; Li, Tie; Luo, Hui; Li, Lian-Hui; Bai, Yuanyuan; Li, Lili; Liu, Lin; Cao, Yudong; Ding, Haiyan; Zhang, TingAnalytical Chemistry (Washington, DC, United States) (2017), 89 (19), 10224-10231CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)As chem. sensors are in great need for portable and wearable anal. applications, effort is highly desired to develop all-solid-state ion-selective electrode (ISE) and ref. electrode (RE) platform that can match simplicity and stability. Here we proposed a wearable sensor platform with a new type of all-solid-state ISE based on a gold nanodendrites (AuNDs) array electrode as the solid contact and a polyvinyl acetate/inorg. salt (PVA/KCl) membrane coated all-solid-state RE. A simple and controllable method was developed to fabricate the AuNDs on a microwell array patterned chip by one-step electrodeposition without addnl. process. For the first time, the AuNDs electrodes with different real surface area and double layer capacitance were developed as solid contact of the Na+-ISE to investigate the relationship between the performance of the ISE and the value of surface area. The as-prepd. AuNDs-ISE with larger surface area (∼7.23 cm2) exhibited an enhanced potential stability in comparison with the smaller surface area of AuNDs-ISE (∼1.85 cm2) and the bare Au ISE. Important as the ISE, the PVA/KCl membrane coated Ag/AgCl RE exhibited a very stable potential even after 3 mo' storage. Finally, a wearable "Sweatband" sensor platform was developed for efficient sweat collection and real-time anal. of sweat sodium during an indoor exercise. This all-solid-state ISE and RE integrated sensor platform provided a very simple and reliable way to construct diverse portable and wearable devices for healthcare, sports, clin. diagnosis and environmental anal. applications.
- 132Parrilla, M.; Ferre, J.; Guinovart, T.; Andrade, F. J. Wearable Potentiometric Sensors Based on Commercial Carbon Fibres for Monitoring Sodium in Sweat. Electroanalysis 2016, 28, 1267– 1275, DOI: 10.1002/elan.201600070132https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XmtVKitrY%253D&md5=b208edea4cbfdf01f5f392fa7f742a09Wearable Potentiometric Sensors Based on Commercial Carbon Fibres for Monitoring Sodium in SweatParrilla, Marc; Ferre, Jordi; Guinovart, Tomas; Andrade, Francisco J.Electroanalysis (2016), 28 (6), 1267-1275CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)The use of com. carbon fibers (CCF) to build wearable potentiometric sensors for the real-time monitoring of sodium levels in sweat during exercise is presented. CCF are an attractive substrate for building wearable electrochem. sensors because of their good elec. cond., chem. inertness, flexibility and mech. resilience. In the first part of this work, the anal. performance of these novel potentiometric ion-selective electrodes made with CCFs is presented. Then, through the incorporation of a solid-contact ref. electrode, the development of a complete miniaturized potentiometric cell with a Nernstian response (59.2±0.6 mV/log [Na+], N=4) is obtained. Finally, the cell is integrated into a wearable patch and attached onto the skin of an athlete. The anal. characterization of the wearable patch shows a near-Nernstian response (55.9±0.8 mV/log [Na+], N=3) for sodium levels from 10-3 M to 10-1 M in artificial sweat, well within the physiol. range of interest. The device shows low noise levels and very good stability (-0.4±0.3 mV · h-1). To improve the usability of the sensor in real scenarios, a calibration-free approach is also explored. This platform opens new and attractive avenues for the generation of meaningful personalized physiol. information that could be applied - among many other fields - in sports, nutrition and healthcare.
- 133Matzeu, G.; O’Quigley, C.; McNamara, E.; Zuliani, C.; Fay, C.; Glennon, T.; Diamond, D. An integrated sensing and wireless communications platform for sensing sodium in sweat. Anal. Methods 2016, 8, 64– 71, DOI: 10.1039/C5AY02254A133https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhslKltbvI&md5=02299a3c317c690e63d5218719a5a4a0An integrated sensing and wireless communications platform for sensing sodium in sweatMatzeu, G.; O'Quigley, C.; McNamara, E.; Zuliani, C.; Fay, C.; Glennon, T.; Diamond, D.Analytical Methods (2016), 8 (1), 64-71CODEN: AMNEGX; ISSN:1759-9679. (Royal Society of Chemistry)The ability to non-invasively monitor sodium levels in sweat is of significant importance. Sodium is one of the preferred markers to diagnose and track the progression of cystic fibrosis, and knowledge of sodium levels could potentially enable personalized hydration strategies to be implemented for athletes or people working under severe environmental conditions. Herein we present a novel approach for the realization of disposable potentiometric strips that allow for real-time monitoring of sodium in sweat. Our platform consists of a Solid-Contact Ion-Selective Electrode (SC-ISE) for Na+ detection and of a liq.-junction-free Ref. Electrode (RE), combined together on a dual screen-printed substrate. Different poly-3,4-ethylenedioxythiophene (PEDOT) based films were tested as solid-contact, showing a significant impact on sensor characteristics such as sensitivity (i.e. differing from sub-Nernstian to Nernstian), dynamic range (i.e. 10-5 to 10-2.5 or 10-5 to 10-1aNa+), and esp. within-batch reproducibility. The SC-ISE/RE combination was integrated into a microfluidic chip that was tested and optimized via on-bench trials. The Potentiometric Microfluidic Chip (PotMicroChip) was then connected to a wireless electronic platform to realize a wearable device whose performance was assessed during real-time stationary cycling sessions.
- 134Glennon, T.; O’Quigley, C.; McCaul, M.; Matzeu, G.; Beirne, S.; Wallace, G. G.; Stroiescu, F.; O’Mahoney, N.; White, P.; Diamond, D. ″SWEATCH’: A Wearable Platform for Harvesting and Analysing Sweat Sodium Content. Electroanalysis 2016, 28, 1283– 1289, DOI: 10.1002/elan.201600106134https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XmvFaktrY%253D&md5=656bb51bdf0fe5ec9e8ffcccea8c9e72'SWEATCH': A Wearable Platform for Harvesting and Analysing Sweat Sodium ContentGlennon, Tom; O'Quigley, Conor; McCaul, Margaret; Matzeu, Giusy; Beirne, Stephen; Wallace, Gordon G.; Stroiescu, Florin; O'Mahoney, Niamh; White, Paddy; Diamond, DermotElectroanalysis (2016), 28 (6), 1283-1289CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)A platform for harvesting and analyzing the sodium content of sweat in real time is presented. One is a 'watch' format in which the sampling and fluidic system, electrodes, circuitry and battery are arranged vertically, while in the other 'pod' format, the electronics and battery components, and the fluidics electrodes are arranged horizontally. The platforms are designed to be securely attached to the skin using a velcro strap. Sweat enters into the device through a sampling orifice and passes over solid-state sodium-selective and ref. electrodes and into a storage area contg. a high capacity adsorbent material. The liq. movement is entirely driven by capillary action, and the flow rate through the device can be mediated through variation of the width of a fluidic channel linking the electrodes to the sample storage area. Changing the width dimension through 750, 500 and 250 μm produces flow rates of 38.20, 21.48 and 6.61 μL/min, resp. Variation of the sweat uptake rate and the storage vol. capacity enables the duration of usage to be varied according to the needs of the user. The devices can be easily disassembled to replace the electrodes and the high capacity adsorbent material. The storage sweat is available for subsequent measurement of the total vol. of sweat harvested and the av. concn. of sodium over the period of use. Signals generated by the electrodes are passed to a custom designed electronics board with high input impedance to accurately capture the voltage. The real-time data is transmitted wirelessly using incorporated Bluetooth circuitry to a remote basestation (laptop, mobile phone, tablet) for data visualization and storage in std. formats. Results obtained during trials over a period of ca. 30 min controlled exercise are consistent with previously published data, showing a gradual relatively slow increase of the sodium concn. in the sweat during this period.
- 135Roy, S.; David-Pur, M.; Hanein, Y. Carbon Nanotube-Based Ion Selective Sensors for Wearable Applications. ACS Appl. Mater. Interfaces 2017, 9, 35169– 35177, DOI: 10.1021/acsami.7b07346135https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsFWhu73O&md5=775c010f2119fac7042ad407de1319aeCarbon Nanotube-Based Ion Selective Sensors for Wearable ApplicationsRoy, Soumyendu; David-Pur, Moshe; Hanein, YaelACS Applied Materials & Interfaces (2017), 9 (40), 35169-35177CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)Wearable electronics offer new opportunities in a wide range of applications, esp. sweat anal. using skin sensors. A fundamental challenge in these applications is the formation of sensitive and stable electrodes. In this article we report the development of a wearable sensor based on carbon nanotube (CNT) electrode arrays for sweat sensing. Solid-state ion selective electrodes (ISEs), sensitive to Na+ ions, were prepd. by drop coating plasticized poly(vinyl chloride) (PVC) doped with ionophore and ion exchanger on CNT electrodes. The ion selective membrane (ISM) filled the intertubular spaces of the highly porous CNT film and formed an attachment that was stronger than that achieved with flat Au, Pt, or carbon electrodes. Concn. of the ISM soln. used influenced the attachment to the CNT film, the ISM surface morphol., and the overall performance of the sensor. Sensitivity of 56 ± 3 mV/decade to Na+ ions was achieved. Optimized solid-state ref. electrodes (REs), suitable for wearable applications, were prepd. by coating CNT electrodes with colloidal dispersion of Ag/AgCl, agarose hydrogel with 0.5 M NaCl, and a passivation layer of PVC doped with NaCl. The CNT-based REs had low sensitivity (-1.7 ± 1.2 mV/decade) toward the NaCl soln. and high repeatability and were superior to bare Ag/AgCl, metals, carbon, and CNT films, reported previously as REs. CNT-based ISEs were calibrated against CNT-based REs, and the short-term stability of the system was tested. We demonstrate that CNT-based devices implemented on a flexible support are a very attractive platform for future wearable technol. devices.
- 136Parrilla, M.; Canovas, R.; Jeerapan, I.; Andrade, F. J.; Wang, J. A Textile-Based Stretchable Multi-Ion Potentiometric Sensor. Adv. Healthcare Mater. 2016, 5, 996– 1001, DOI: 10.1002/adhm.201600092136https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XjvVyku7s%253D&md5=03e2a02c3c32dd0fd4da4ce09e00624bA Textile-Based Stretchable Multi-Ion Potentiometric SensorParrilla, Marc; Canovas, Rocio; Jeerapan, Itthipon; Andrade, Francisco J.; Wang, JosephAdvanced Healthcare Materials (2016), 5 (9), 996-1001CODEN: AHMDBJ; ISSN:2192-2640. (Wiley-VCH Verlag GmbH & Co. KGaA)This article reports a highly stretchable and printable textile-based potentiometric sensor array for simultaneous multi-ion sweat anal. using variety of fabric materials towards diverse healthcare and fitness applications. Textile-based potentiometric sensors was fabricated by combining polyurethane-based ion- selective membranes and inks with a serpentine sensor pattern and stretch-enduring printed electrodes. Combining stretchable components like polyurethane, Ecoflex, and stretch-enduring inks, along with a serpentine design, this printed textile sensor array can withstand high tensile stress and mech. deformation and can thus act as an efficient wearable biomedical sensor.
- 137Choi, D.-H.; Kim, J. S.; Cutting, G. R.; Searson, P. C. Anal. Chem. 2016, 88, 12241– 12247, DOI: 10.1021/acs.analchem.6b03391137https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhvVGqtr7F&md5=7f8490e716d0380dff93142c675dcfeeWearable Potentiometric Chloride Sweat Sensor: The Critical Role of the Salt BridgeChoi, Dong-Hoon; Kim, Jin Seob; Cutting, Garry R.; Searson, Peter C.Analytical Chemistry (Washington, DC, United States) (2016), 88 (24), 12241-12247CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)The components of sweat provide an array of potential biomarkers for health and disease. Sweat chloride is of interest as a biomarker for cystic fibrosis, electrolyte metab. disorders, electrolyte balance, and electrolyte loss during exercise. Developing wearable sensors for biomarkers in sweat is a major technol. challenge. Potentiometric sensors provide a relatively simple technol. for on-body sweat chloride measurement; however, equilibration between ref. and test solns. has limited the time over which accurate measurements can be made. Here, the authors report on a wearable potentiometric chloride sweat sensor. The authors performed parametric studies to show how the salt bridge geometry dets. equilibration between the ref. and test solns. The authors show that a sweat chloride sensor can be designed to provide accurate measurements over extended times. The authors then performed on-body tests on healthy subjects while exercising to establish the feasibility of using this technol. as a wearable device.
- 138Zoerner, A.; Oertel, S.; Jank, M. P. M.; Frey, L.; Langenstein, B.; Bertsch, T. Human Sweat Analysis Using a Portable Device Based on a Screen-printed Electrolyte Sensor. Electroanalysis 2018, 30, 665– 671, DOI: 10.1002/elan.201700672138https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhvFyjsrbM&md5=ee00482c05536765957ede8ae3084ba9Human Sweat Analysis Using a Portable Device Based on a Screen-Printed Electrolyte SensorZoerner, Alicia; Oertel, Susanne; Jank, Michael P. M.; Frey, Lothar; Langenstein, Bernd; Bertsch, ThomasElectroanalysis (2018), 30 (4), 665-671CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)Anal. of ammonium in human sweat during phys. strain using a portable sensor device and enzymic measurements are compared. The portable device is based on a screen-printed electrolyte sensor connected with an evaluation board for data acquisition and transfer. During performance tests with artificial sweat, the sensor shows a low detection limit of 0.3 mM. Thus, the typical concn. range of ammonium in sweat lies within the working range of the sensor. The authors also demonstrate the necessity of the comparison measurement for verification of the correct performance of screen-printed sensors and show how other components of human sweat influence the measured potential. Regarding the change in ammonium concn. during different levels of work out intensity, the authors point out a different behavior of what is expected physiol. With this the importance of consideration of several parameters during sweating, like the sweat rate and other ingredients in human sweat, was demonstrated for correct detn. of the ammonium concn.
- 139Hoekstra, R.; Blondeau, P.; Andrade, F. J. IonSens: A Wearable Potentiometric Sensor Patch for Monitoring Total Ion Content in Sweat. Electroanalysis 2018, 30, 1536– 1544, DOI: 10.1002/elan.201800128139https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhtVShurnI&md5=025f15ccc164a86e56591454bd055c3bIonSens: a Wearable Potentiometric Sensor Patch for Monitoring Total Ion Content in SweatHoekstra, Rafael; Blondeau, Pascal; Andrade, Francisco J.Electroanalysis (2018), 30 (7), 1536-1544CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)A sensor for monitoring total ion activity is described, and its performance as a wearable device for monitoring the total ion levels of sweat is evaluated. The sensor works by tracking changes in the Donnan potential generated across a Nafion membrane. This cation-exchange polymer was cast on a paper coated with carbon-ink, making the platform elegantly simple. Anal. parameters during calibration in aq. soln. include a sensitivity of 56.3±1.0 mV/dec.a(Na+) and a std. deviation between std. electrode potentials of 5.3 mV (N=5) for first time use. By integrating a paper-based pseudo-ref. electrode, a miniature disposable electrochem. cell (the "IonSens" device) was created and demonstrated as a wearable sensor. Potentiometric measurements estg. the total ion activities were validated against cond. measurements. Recoveries of eleven raw sweat samples were detd. to be 95.2±6.6 % (n=3). The perspiration cond. profile of an athlete during exercise was monitored in real-time and visualized on a mobile phone application connected via Bluetooth. The excellent reproducibility of the electrode without any conditioning is noteworthy and lends itself to applications including - but not limited to - the monitoring of total ion activity in sweat.
- 140Uria, N.; Abramova, N.; Bratov, A.; Muñoz-Pascual, F.-X.; Baldrich, E. Talanta 2016, 147, 364– 369, DOI: 10.1016/j.talanta.2015.10.011140https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhs1Gku7bO&md5=b5c2178e67cbfd67df4651d6ade3a9baMiniaturized metal oxide pH sensors for bacteria detectionUria, Naroa; Abramova, Natalia; Bratov, Andrey; Munoz-Pascual, Francesc-Xavier; Baldrich, EvaTalanta (2016), 147 (), 364-369CODEN: TLNTA2; ISSN:0039-9140. (Elsevier B.V.)It is well known that the metabolic activity of some microorganisms results in changes of pH of the culture medium, a phenomenon that can be used for detection and quantification of bacteria. However, conventional glass electrodes that are commonly used for pH measurements are bulky, fragile and expensive, which hinders their application in miniaturized systems and encouraged to the search for alternatives. In this work, two types of metal oxide pH sensors have been tested to detect the metabolic activity of the bacterium Escherichia coli (E. coli). These pH sensors were produced on silicon chips with platinum metal contacts, onto which thin layers of IrOx or Ta2O5 were incorporated by two different methods (electrodeposition and e-beam sputtering, resp.). In order to facilitate measurement in small sample vols., an Ag/AgCl pseudo-ref. was also screen-printed in the chip and was assayed in parallel to an external Ag/AgCl ref. electrode. As it is shown, the developed sensors generated results indistinguishable from those provided by a conventional glass pH-electrode but could be operated in significantly smaller sample vols. After optimization of the detection conditions, the metal oxide sensors are successfully applied for detection of increasing concns. of viable E. coli, with detection of less than 103 cfu mL-1 in undiluted culture medium in just 5 h.
- 141Salazar, P.; Garcia-Garcia, F. J.; Yubero, F.; Gil-Rostra, J.; González-Elipe, A. R. Electrochim. Acta 2016, 193, 24– 31, DOI: 10.1016/j.electacta.2016.02.040141https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xis1ejsbc%253D&md5=2305eee103eac008f8fb65656f34af44Characterization and application of a new pH sensor based on magnetron sputtered porous WO3 thin films deposited at oblique anglesSalazar, Pedro; Garcia-Garcia, Francisco J.; Yubero, Francisco; Gil-Rostra, Jorge; Gonzalez-Elipe, Agustin R.Electrochimica Acta (2016), 193 (), 24-31CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Ltd.)The authors report about an outstanding solid-state pH sensor based on amorphous nanocolumnar porous thin film electrodes. Transparent WO3 thin films were deposited by reactive magnetron sputtering in an oblique angle configuration to enhance their porosity onto In Sn oxide (ITO) and screen printed electrodes (SPE). The potentiometric pH response of the nanoporous WO3-modified ITO electrode revealed a quasi-Nernstian behavior, i.e. a linear working range from pH 1 to 12 with a slope of ∼-57.7 mV/pH. pH detection with this electrode was quite reproducible, displayed excellent anti-interference properties and a high stable response that remained unaltered over at least 3 mo. Finally, a pH sensor was developed using nanoporous WO3-modified screen printed electrode (SPE) using a polypyrrole-modified Ag/AgCl electrode as internal ref. electrode. This full solid state pH sensor presented a Nernstian behavior with a slope of ∼-59 mV/pH and offered important anal. and operation advantages for decentralized pH measurements in different applications.
- 142Manjakkal, L.; Zaraska, K.; Cvejin, K.; Kulawik, J.; Szwagierczak, D. Talanta 2016, 147, 233– 240, DOI: 10.1016/j.talanta.2015.09.069142https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhs1elsr%252FK&md5=dce15ae291b95a3d4003f757472973b9Potentiometric RuO2-Ta2O5 pH sensors fabricated using thick film and LTCC technologiesManjakkal, Libu; Zaraska, Krzysztof; Cvejin, Katarina; Kulawik, Jan; Szwagierczak, DorotaTalanta (2016), 147 (), 233-240CODEN: TLNTA2; ISSN:0039-9140. (Elsevier B.V.)The paper reports on the prepn., properties and application of potentiometric pH sensors with thick film RuO2-Ta2O5 sensing electrode and Ag/AgCl/KCl ref. electrode screen printed on an alumina substrate. Also, it presents fabrication procedure and characterization of a new miniaturized pH sensor on LTCC (low temp. co-fired ceramics) substrate, destined for wireless monitoring. The crystal structure, phase and elemental compn., and microstructure of the films were studied by x-ray diffractometry, Raman spectroscopy, SEM and energy dispersive spectroscopy. Potentiometric characterization was performed in a wide pH range of 2-12 for different storage conditions and pH loops. The advantages of the proposed thick film pH sensors are: (a) low cost and easy fabrication, (b) excellent sensitivity close to the Nernstian response (56 mV/pH) in the wide pH range, (c) fast response, (d) long lifetime, (e) good reproducibility, (f) low hysteresis and drift effects, and (g) low cross-sensitivity towards Li+, Na+ and K+ as interfering ions. The applicability of the sensors for pH measurement of river, tap and distd. water, and some drinks was also tested.
- 143Lonsdale, W.; Maurya, D. K.; Wajrak, M.; Alameh, K. Effect of ordered mesoporous carbon contact layer on the sensing performance of sputtered RuO2 thin film pH sensor. Talanta 2017, 164, 52– 56, DOI: 10.1016/j.talanta.2016.11.020143https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhvFaisbrP&md5=617058021d59baf2e76f03ef7a429518Effect of ordered mesoporous carbon contact layer on the sensing performance of sputtered RuO2 thin film pH sensorLonsdale, W.; Maurya, D. K.; Wajrak, M.; Alameh, K.Talanta (2017), 164 (), 52-56CODEN: TLNTA2; ISSN:0039-9140. (Elsevier B.V.)The effect of contact layer on the pH sensing performance of a sputtered RuO2 thin film pH sensor was studied. The response of pH sensors employing RuO2 thin film electrodes on screen-printed Pt, carbon and ordered mesoporous carbon (OMC) contact layers are measured over a pH range from 4 to 10. Working electrodes with OMC contact layer have Nernstian pH sensitivity (-58.4 mV/pH), low short-term drift rate (5.0 mV/h), low hysteresis values (1.13 mV) and fast reaction times (30 s), after only 1 h of conditioning. A pH sensor constructed with OMC carbon contact layer displays improved sensing performance compared to Pt and carbon-based counterparts, making this electrode more attractive for applications requiring highly-accurate pH sensing with reduced conditioning time.
- 144Lonsdale, W.; Wajrak, M.; Alameh, K. Sens. Actuators, B 2017, 252, 251– 256, DOI: 10.1016/j.snb.2017.05.171144https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXpvFygsr4%253D&md5=6677b50a34a9b95bfc92f8818441715bEffect of conditioning protocol, redox species and material thickness on the pH sensitivity and hysteresis of sputtered RuO2 electrodesLonsdale, W.; Wajrak, M.; Alameh, K.Sensors and Actuators, B: Chemical (2017), 252 (), 251-256CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)In this paper, the effects of conditioning-pH, RuO2 material thickness and oxidizing/reducing agents on the E0 value and hysteresis of RuO2 pH-sensitive working electrodes is investigated. Exptl. results show that, in order to obtain a pH sensor that Exhibits 0.01 units of precision, it is necessary to use an electrode with at least 500 nm thickness of RuO2; while thinner RuO2 electrodes (> 50 nm) can be used to achieve a precision of 0.05 pH units. In addn., investigation of the redox interference and pH sensing performance of RuO2 electrodes at high/low pH suggests that hysteresis and redox interference are due to shifts in the E0 value due to a change in the electrodes compn., i.e. the ratio of RuIII to RuIV present in the electrode material.
- 145Jovic, M.; Hidalgo-Acosta, J. C.; Lesch, A.; Bassetto, V. C.; Smirnov, E.; Cortes-Salazar, F.; Girault, H. H. Large-scale layer-by-layer inkjet printing of flexible iridium-oxide based pH sensors. J. Electroanal. Chem. 2018, 819, 384– 390, DOI: 10.1016/j.jelechem.2017.11.032145https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhvVajsbvJ&md5=c99bb832887e485fb287506abaa13e78Large-scale layer-by-layer inkjet printing of flexible iridium-oxide based pH sensorsJovic, Milica; Hidalgo-Acosta, Jonnathan C.; Lesch, Andreas; Costa Bassetto, Victor; Smirnov, Evgeny; Cortes-Salazar, Fernando; Girault, Hubert H.Journal of Electroanalytical Chemistry (2018), 819 (), 384-390CODEN: JECHES; ISSN:1873-2569. (Elsevier B.V.)Metal oxide based pH sensors were used in various applications, esp. when the conventional glass electrode is unsuitable due to its fragility or when the applications require disposable sensors, e.g. for biomedical, clin. or food process monitoring. Generally, such pH sensors are produced by thermal oxidn. or electrochem. deposition, neither suited for mass prodn. nor miniaturization. Herein, the authors report on the fabrication of reliable and sensitive pH sensors based on the nano-assembly of Ir oxide (IrOx) nanoparticles and polydiallyldimethylammonium (PDDA) polymer layers. Such potentiometric sensors were very reproducibly fabricated on a large-scale via a layer-by-layer inkjet printing (LbL IJP) methodol. The obtained results indicated the ability of the LbL IJP technique to easily manipulate the NP coverage by the no. of printed bilayers, leading to a swift sensor optimization. Open-circuit potentials were recorded to evaluate the pH sensitivity, response time, and reproducibility of the pH electrodes, which exhibit a rapid, linear and near-Nernstian pH response of ∼59 mV/pH. Also, an relative std. deviation of 0.6% for five different electrodes from the same printing batch showed the excellent reproducibility of the IJP process with a correlation coeff. of 0.99 for all measurements. The insights gained in this study could be the basis for a new approach of developing scalable, patterned and flexible pH sensors with improved performance and a wide range of applications.
- 146Pol, R.; Moya, A.; Gabriel, G.; Gabriel, D.; Céspedes, F.; Baeza, M. Inkjet-Printed Sulfide-Selective Electrode. Anal. Chem. 2017, 89, 12231– 12236, DOI: 10.1021/acs.analchem.7b03041446https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsleiurjF&md5=7f04a5fa49584375eb93775debe7a490Inkjet-Printed Sulfide-Selective ElectrodePol, Roberto; Moya, Ana; Gabriel, Gemma; Gabriel, David; Cespedes, Francisco; Baeza, MireiaAnalytical Chemistry (Washington, DC, United States) (2017), 89 (22), 12231-12236CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Inkjet printing technol. has emerged as an alternative manufg. method for low-cost prodn. of electrodes. Despite significant progress, there is still a lack in the prodn. of ion-selective electrodes. Herein, the two-step fabrication of the first inkjet-printed sulfide-selective electrode (IPSSE) is described. The two-step fabrication consists of printing a silver electrode followed by an electrochem. deposition of sulfide to produce a second kind electrode (Ag/Ag2S). The performance of this novel device was tested using potentiometric measurements. Nernstian response (-29.4 ± 0.3 mV·decade-1) was obtained within concns. of 0.03-50 mM with a response time of ∼3 s. Furthermore, river/sea-spiked environmental samples and samples from a bioreactor for sulfate redn. to sulfide were measured and compared against a com. sensor giving no significant differences. The IPSSE described in this work showed good reproducibility and durability during daily measurements over 15 days without any special storage conditions. Considering all the current challenges in inkjet-printed ion-selective electrodes, this different fabrication approach opens a new perspective for mass prodn. of all-solid state ion-selective electrodes.
- 147Toczylowska-Maminska, R.; Kloch, M.; Zawistowska-Deniziak, A.; Bala, A. Design and characterization of novel all-solid-state potentiometric sensor array dedicated to physiological measurements. Talanta 2016, 159, 7– 13, DOI: 10.1016/j.talanta.2016.06.001146https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XpslWktrg%253D&md5=b5829dadc7f6d376fb5248eb19db4a99Design and characterization of novel all-solid-state potentiometric sensor array dedicated to physiological measurementsToczylowska-Maminska, Renata; Kloch, Monika; Zawistowska-Deniziak, Anna; Bala, AgnieszkaTalanta (2016), 159 (), 7-13CODEN: TLNTA2; ISSN:0039-9140. (Elsevier B.V.)A novel construction of all-solid-state potentiometric sensor array designed for physiol. measurements has been presented. The planar construction and elimination of liq. phase creates broad opportunities for the modifications in the sensing part of the sensor. The designed construction is based on all-solid-state ion-selective electrodes integrated with the ionic-liq. based ref. electrode. Work parameters of the sensor arrays were characterized. It has been shown that presented sensor design indicates high sensitivity (55.2±1 mV/dec, 56.3±2 mV/dec, 58.4±1 mV/dec and 53.5±1 mV/pH for sodium-, potassium-, chloride- and pH-selective electrodes, resp. in 10-5-10-1.5 M range of primary ions), low response time (t95 did not exceed 10 s), high potential stability (potential drift in 28-h measurement was ca. ±2 mV) and potential repeatability ca. ±1 mV. The system was successfully applied to the simultaneous detn. of K+, Cl-, Na+ and pH in the model physiol. soln. and for the ion flux studies in human colon epithelium Caco-2 cell line as well.
- 148Zajac, M.; Lewenstam, A.; Dolowy, K. Multi-electrode system for measurement of transmembrane ion-fluxes through living epithelial cells. Bioelectrochemistry 2017, 117, 65– 73, DOI: 10.1016/j.bioelechem.2017.06.007147https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtVWqsb7M&md5=d68d3984a946d8d966ed2af248879c79Multi-electrode system for measurement of transmembrane ion-fluxes through living epithelial cellsZajac, Miroslaw; Lewenstam, Andrzej; Dolowy, KrzysztofBioelectrochemistry (2017), 117 (), 65-73CODEN: BIOEFK; ISSN:1567-5394. (Elsevier B.V.)Cystic Fibrosis (CF) is the most common fatal human genetic disease. It is caused by the defect in a single anion channel protein which affects ion and water transport across the epithelial tissue. A flat multi-electrode platform of diam. 12 mm, allowing for measurement of four ions: sodium, potassium, hydrogen and chloride by exchangeable/replaceable ion-selective electrodes is described. The measurement is possible owing to the architecture of the platform which accommodates all the electrodes and inlets/outlets. The platform fits to the cup and operates in a small vol. of the soln. bathing the living epithelial cell layer (membrane) deposited on a porous support of the cup, which allows for effective monitoring of ion concn. changes. By applying two multi-electrode platforms, it is possible to measure the ion transmembrane fluxes. The inlet and outlet tubes in the platforms allow for on-fly change of the calibrants, ion-concn. changes and ion channel blockers. Using different ion-concn. gradients and blockers of ion-transporting mols. we show for the first time that sodium ions flow from the basolateral to apical face of the cell monolayer via a paracellular route and return also via a transcellular one, while chloride anions are transported back and forth exclusively via a transcellular route.
- 149Church, J.; Armas, S. M.; Patel, P. K.; Chumbimuni-Torres, K.; Lee, W. H. Development and Characterization of Needle-type Ion-selective Microsensors for insitu Determination of Foliar Uptake of Zn2+ in Citrus Plants. Electroanalysis 2018, 30, 626– 632, DOI: 10.1002/elan.201700697148https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhvFegs7zE&md5=8be302cabf606d370a117bcf3f7b196aDevelopment and Characterization of Needle-Type Ion-Selective Microsensors for in situ Determination of Foliar Uptake of Zn2+ in Citrus PlantsChurch, Jared; Armas, Stephanie M.; Patel, Parth K.; Chumbimuni-Torres, Karin; Lee, Woo HyoungElectroanalysis (2018), 30 (4), 626-632CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)For over a decade, the incidence of Huanglongbing (HLB) has grown at an alarming rate, affecting citrus crops worldwide. Current methods of nutrient therapy have little to no effect in alleviating symptoms of HLB, and scarce research has been put forth towards non-destructive tools for monitoring zinc transport in citrus plants. Here, we have developed and characterized a solid contact micro-ion-selective electrode (SC-μ-ISE) for the detn. of zinc transport in sour orange seedlings using a non-invasive microelectrode ion flux estn. (MIFE) technique. The SC-μ-ISE displayed a 26.05±0.13 mV decade-1 Nernstian response and a LOD of (3.96±2.09)×10-7 M. Results showed a significant Zn2+ uptake in the leaves and roots of sour orange seedlings when bulk concns. were higher than 5.99 mM. Above this concn., a linear relationship between flux and bulk Zn2+ concn. was obsd. This relationship suggests passive diffusion may be a key mechanism for Zn transport into plants. Overall, this study is the first to use a Zn2+ SC-μ-ISE for the detn. of ion transport processes in plants. This novel tool can be used to further knowledge the effect of nutrient therapy and disease progression on HLB infected citrus plants.
- 150Ma, X. M.; Armas, S. M.; Soliman, M.; Lytle, D. A.; Chumbimuni-Torres, K.; Tetard, L.; Lee, W. H. In Situ Monitoring of Pb2+ Leaching from the Galvanic Joint Surface in a Prepared Chlorinated Drinking Water. Environ. Sci. Technol. 2018, 52, 2126– 2133, DOI: 10.1021/acs.est.7b05526149https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhvVWit7g%253D&md5=4ca9002f8f343bf8085c5927a979ce0aIn Situ Monitoring of Pb2+ Leaching from the Galvanic Joint Surface in a Prepared Chlorinated Drinking WaterMa, Xiangmeng; Armas, Stephanie M.; Soliman, Mikhael; Lytle, Darren A.; Chumbimuni-Torres, Karin; Tetard, Laurene; Lee, Woo HyoungEnvironmental Science & Technology (2018), 52 (4), 2126-2133CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)A novel method using a micro-ion-selective electrode (micro-ISE) technique was developed for in situ lead monitoring at the water-metal interface of a brass-leaded solder galvanic joint in a prepd. chlorinated drinking water environment. The developed lead micro-ISE (100 μm tip diam.) showed excellent performance toward sol. lead (Pb2+) with sensitivity of 22.2 ± 0.5 mV decade-1 and limit of detection (LOD) of 1.22 × 10-6 M (0.25 mg L-1). The response time was less than 10 s with a working pH range of 2.0-7.0. Using the lead micro-ISE, lead concn. microprofiles were measured from the bulk to the metal surface (within 50 μm) over time. Combined with two-dimensional (2D) pH mapping, this work clearly demonstrated that Pb2+ ions build-up across the lead anode surface was substantial, nonuniform, and dependent on local surface pH. A large pH gradient (ΔpH = 6.0) developed across the brass and leaded-tin solder joint coupon. Local pH decreases were obsd. above the leaded solder to a pH as low as 4.0, indicating it was anodic relative to the brass. The low pH above the leaded solder supported elevated lead levels where even small local pH differences of 0.6 units (ΔpH = 0.6) resulted in about four times higher surface lead concns. (42.9 vs 11.6 mg L-1) and 5 times higher fluxes (18.5 × 10-6 vs 3.5 × 10-6 mg cm-2 s-1). Continuous surface lead leaching monitoring was also conducted for 16 h.
- 151Hao, J.; Xiao, T. F.; Wu, F.; Yu, P.; Mao, L. Q. High Antifouling Property of Ion-Selective Membrane: toward In Vivo Monitoring of pH Change in Live Brain of Rats with Membrane-Coated Carbon Fiber Electrodes. Anal. Chem. 2016, 88, 11238– 11243, DOI: 10.1021/acs.analchem.6b03854150https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xhs1yltLfM&md5=9f363ec126336bb1e2c674828fb39fd9High Antifouling Property of Ion-Selective Membrane: toward In Vivo Monitoring of pH Change in Live Brain of Rats with Membrane-Coated Carbon Fiber ElectrodesHao, Jie; Xiao, Tongfang; Wu, Fei; Yu, Ping; Mao, LanqunAnalytical Chemistry (Washington, DC, United States) (2016), 88 (22), 11238-11243CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)In vivo monitoring of pH in live brain remains very essential to understanding acid-base chem. in various physiol. processes. This study demonstrates a potentiometric method for in vivo monitoring of pH in the central nervous system with carbon fiber-based proton-selective electrodes (CF-H+ISEs) with high antifouling property. The CF-H+ISEs are prepd. by formation of a H+-selective membrane (H+ISM) with polyvinyl chloride polymeric matrixes contg. plasticizer bis(2-ethylhexyl)sebacate, H+ ionophore tridodecylamine, and ion exchanger potassium tetrakis(4-chlorophenyl)borate onto carbon fiber electrodes (CFEs). Both in vitro and in vivo studies demonstrate that the H+ISM exhibits strong antifouling property against proteins, which enables the CF-H+ISEs to well maintain the sensitivity and reversibility for pH sensing after in vivo measurements. Moreover, the CF-H+ISEs exhibit a good response to pH changes within a narrow physiol. pH range from 6.0 to 8.0 in quick response time with high reversibility and selectivity against species endogenously existing in the central nervous system. The applicability of the CF-H+ISEs is illustrated by real-time monitoring of pH changes during acid-base disturbances, in which the brain acidosis is induced by CO2 inhalation and brain alkalosis is induced by bicarbonate injections. The results demonstrate that brain pH value rapidly decreases in the amygdaloid nucleus by ∼0.14±0.01 (n = 5) when the rats breath in pure CO2 gas, while increases in the cortex by ∼0.77±0.12 (n = 3) following i.p. injection of 5 mmol/kg NaHCO3. This study demonstrates a new potentiometric method for in vivo measurement of pH change in the live brain of rats with high reliability.
- 152Moon, J.; Ha, Y.; Kim, M.; Sim, J.; Lee, Y.; Suh, M. Dual Electrochemical Microsensor for Real-Time Simultaneous Monitoring of Nitric Oxide and Potassium Ion Changes in a Rat Brain during Spontaneous Neocortical Epileptic Seizure. Anal. Chem. 2016, 88, 8942– 8948, DOI: 10.1021/acs.analchem.6b02396151https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhtlKnu7vJ&md5=7615215ff8de0b6f7c4e28f4f6131599Dual Electrochemical Microsensor for Real-Time Simultaneous Monitoring of Nitric Oxide and Potassium Ion Changes in a Rat Brain during Spontaneous Neocortical Epileptic SeizureMoon, Jungmi; Ha, Yejin; Kim, Misun; Sim, Jeongeun; Lee, Youngmi; Suh, MinahAnalytical Chemistry (Washington, DC, United States) (2016), 88 (18), 8942-8948CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)The authors developed a dual amperometric/potentiometric microsensor for sensing nitric oxide (NO) and potassium ion (K+). The dual NO/K+ sensor was prepd. based on a dual recessed electrode possessing Pt (diam., 50 μm) and Ag (diam., 76.2 μm) microdisks. The Pt disk surface (WE1) was modified with electroplatinization and the following coating with fluorinated xerogel; and the Ag disk surface (WE2) was oxidized to AgCl on which K+ ion selective membrane was loaded subsequent to the silanization. WE1 and WE2 of a dual microsensor were used for amperometric sensing of NO (106 ± 28 pA μM-1, n = 10, at +0.85 V applied vs. Ag/AgCl) and for potentiometric sensing of K+ (51.6 ± 1.9 mV pK-1, n = 10), resp., with high sensitivity. In addn., the sensor showed good selectivity over common biol. interferents, sufficiently fast response time and relevant stability (within 6 h in-vivo expt.). The sensor had a small dimension (end plane diam., 428 ± 97 μm, n = 20) and needle-like sharp geometry which allowed the sensor to be inserted in biol. tissues. Taking advantage of this insertability, the sensor was applied for the simultaneous monitoring of NO and K+ changes in living rat brain cortex at a depth of 1.19 ± 0.039 mm and near the spontaneous epileptic seizure focus. The seizures were induced with 4-aminopyridine injection onto the rat brain cortex. NO and K+ levels were dynamically changed in clear correlation with the electrophysiol. recording of seizures. The dual NO/K+ sensor's measurements well reflect membrane potential changes of neurons and assocd. cellular components of neurovascular coupling. The newly developed NO/K+ dual microsensor showed the feasibility of real-time fast monitoring of dynamic changes of closely linked NO and K+in vivo.
- 153Filotas, D.; Fernandez-Perez, B. M.; Izquierdo, J.; Nagy, L.; Nagy, G.; Souto, R. M. Novel dual microelectrode probe for the simultaneous visualization of local Zn2+ and pH distributions in galvanic corrosion processes. Corros. Sci. 2017, 114, 37– 44, DOI: 10.1016/j.corsci.2016.10.014152https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhslegsLjE&md5=ee11217492ca99fb781bd8ef2c055a76Novel dual microelectrode probe for the simultaneous visualization of local Zn2+ and pH distributions in galvanic corrosion processesFilotas, D.; Fernandez-Perez, B. M.; Izquierdo, J.; Nagy, L.; Nagy, G.; Souto, R. M.Corrosion Science (2017), 114 (), 37-44CODEN: CRRSAA; ISSN:0010-938X. (Elsevier Ltd.)Novel dual potentiometric microsensor probe has been developed for the simultaneous detection of Zn2+ concn. and pH distributions in the Scanning Electrochem. Microscopy investigation of corroding galvanized steel. The individual sensors show nearly theor. behavior over a wide concn. range. The applicability of this probe is first demonstrated on a Fe-Zn galvanic couple, as it shows excellent performance in these simultaneous model expts. In addn., linear scans recorded over a cut edge of coated galvanized steel evidence the complementary information gathered on the electrochem. behavior of the corroding sample, and adumbrates promising and feasible applications of multi-barrel microelectrodes in corrosion research.
- 154Ummadi, J. G.; Downs, C. J.; Joshi, V. S.; Ferracane, J. L.; Koley, D. Carbon-Based Solid-State Calcium Ion-Selective Microelectrode and Scanning Electrochemical Microscopy: A Quantitative Study of pH-Dependent Release of Calcium Ions from Bioactive Glass. Anal. Chem. 2016, 88, 3218– 3226, DOI: 10.1021/acs.analchem.5b04614153https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XitlCjsLg%253D&md5=7aa0d86fcc717648e1f1cafebb98f31cCarbon-Based Solid-State Calcium Ion-Selective Microelectrode and Scanning Electrochemical Microscopy: A Quantitative Study of pH-Dependent Release of Calcium Ions from Bioactive GlassUmmadi, Jyothir Ganesh; Downs, Corey J.; Joshi, Vrushali S.; Ferracane, Jack L.; Koley, DipankarAnalytical Chemistry (Washington, DC, United States) (2016), 88 (6), 3218-3226CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Solid-state ion-selective electrodes are used as scanning electrochem. microscope (SECM) probes because of their inherent fast response time and ease of miniaturization. In this study, we report the development of a solid-state, low-poly(vinyl chloride), carbon-based calcium ion-selective microelectrode (Ca2+-ISME), 25 μm in diam., capable of performing an amperometric approach curve and serving as a potentiometric sensor. The Ca2+-ISME has a broad linear response range of 5 μM to 200 mM with a near Nernstian slope of 28 mV/log[aCa2+]. The calcd. detection limit for Ca2+-ISME is 1 μM. The selectivity coeffs. of this Ca2+-ISME are log KCa2+,A = -5.88, -5.54, and -6.31 for Mg2+, Na+, and K+, resp. We used this new type of Ca2+-ISME as an SECM probe to quant. map the chem. microenvironment produced by a model substrate, bioactive glass (BAG). In acidic conditions (pH 4.5), BAG was found to increase the calcium ion concn. from 0.7 mM ([Ca2+] in artificial saliva) to 1.4 mM at 20 μm above the surface. In addn., a solid-state dual SECM pH probe was used to correlate the release of calcium ions with the change in local pH. Three-dimensional pH and calcium ion distribution mapping were also obtained by using these solid-state probes. The quant. mapping of pH and Ca2+ above the BAG elucidates the effectiveness of BAG in neutralizing and releasing calcium ions in acidic conditions.
- 155Zhu, Z.; Liu, X. Y.; Ye, Z. N.; Zhang, J. Q.; Cao, F. H.; Zhang, J. X. A fabrication of iridium oxide film pH micro-sensor on Pt-ultramicroelectrode and its application on in-situ pH distribution of 316L stainless steel corrosion at open circuit potential. Sens. Actuators, B 2018, 255, 1974– 1982, DOI: 10.1016/j.snb.2017.08.219154https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsVOhs7vO&md5=558bc34fabd2aa6faae8951d098ee130A fabrication of iridium oxide film pH micro-sensor on Pt ultramicroelectrode and its application on in-situ pH distribution of 316L stainless steel corrosion at open circuit potentialZhu, Zejie; Liu, Xiaoyan; Ye, Zhenni; Zhang, Jianqing; Cao, Fahe; Zhang, JunxiSensors and Actuators, B: Chemical (2018), 255 (Part_2), 1974-1982CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)An all solid-state pH micro-sensor has been developed using anodic electrodeposition of an iridium oxide (IrOx) film onto a 10μm platinum ultramicroelectrode. The electrochem. growth of the IrOx film was accomplished by 100 potential sweeps at 50 mV/s, at different potential ranges of electrochem. deposition, followed by heat treatment at 100°C for 2 h. The pH micro-sensor shows quick response to the pH variation, excellent sensitivity, stability and long lifetime in a wide pH range between 1.0 and 13.0. The slope of potential-pH response curve is found to dependent on the Ir(III)/Ir(IV) ratio of in the film, detd. by XPS anal., which is a consequence of scanning potential range during the anodic electrodeposition. The sensor has been employed to explore the localized pH distribution during the corrosion of 316L stainless steel in NaCl soln. at open circuit potential and results show that localized anodic and cathodic sites on the 316L stainless steel can be accurately monitored and the pH difference between the cathodic and anodic zones increases from 0.22 to 1.27 with the prolonging of the immersion time.
- 156Zhu, Z. J.; Ye, Z. N.; Zhang, Q. H.; Zhang, J. Q.; Cao, F. H. Novel dual Pt-Pt/IrOx ultramicroelectrode for pH imaging using SECM in both potentiometric and amperometric modes. Electrochem. Commun. 2018, 88, 47– 51, DOI: 10.1016/j.elecom.2018.01.018155https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXitVeqsbo%253D&md5=26e8f6a8d0f5259e64afa142acaa15b3Novel dual Pt-Pt/IrOx ultramicroelectrode for pH imaging using SECM in both potentiometric and amperometric modesZhu, Zejie; Ye, Zhenni; Zhang, Qinhao; Zhang, Jianqing; Cao, FaheElectrochemistry Communications (2018), 88 (), 47-51CODEN: ECCMF9; ISSN:1388-2481. (Elsevier B.V.)Potentiometric Scanning Electrochem.Microscopy (SECM) allows the pH distribution at electrode/electrolyte interfaces to be mapped at the micrometer and submicrometer scale using ion-selective ultramicroelectrodes (UMEs) as scanning probes. However, this technique lacks precise control of the tip-to-substrate distance. Herein we propose a novel dual Pt-Pt/IrOx UME for local in situ pH visualization of 316L stainless steel (316L-SS) corrosion processes with precise tip-substrate distance control using both amperometric and potentiometric SECM modes. Simulations based on COMSOL and exptl. approach curves obtained with this dual UME configuration are used to precisely establish the tip-substrate distance. Higher pH values were obsd. for smaller tip-substrate sepns.when this probe configuration is used with bulk electrolyte of the same pH. Furthermore, during the corrosion process local anodic and cathodic zones were obsd. to form, disappear and regenerate at a vertical tip-substrate distance of 12μm as a result of the localized corrosion and repassivation of 316L-SS.
- 157Freeman, C. J.; Farghaly, A. A.; Choudhary, H.; Chavis, A. E.; Brady, K. T.; Reiner, J. E.; Collinson, M. M. Anal. Chem. 2016, 88, 3768– 3774, DOI: 10.1021/acs.analchem.5b04668156https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XksV2gsLs%253D&md5=a3b9f594a79d74dd1e49d129f3bd7199Microdroplet-Based Potentiometric Redox Measurements on Gold Nanoporous ElectrodesFreeman, Christopher J.; Farghaly, Ahmed A.; Choudhary, Hajira; Chavis, Amy E.; Brady, Kyle T.; Reiner, Joseph E.; Collinson, Maryanne M.Analytical Chemistry (Washington, DC, United States) (2016), 88 (7), 3768-3774CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Potentiometric redox measurements were made in subnanoliter droplets of solns. using an optically transparent nanoporous Au electrode strategically mounted on the stage of an inverted microscope. Nanoporous Au was prepd. via dealloying Au leaf with concd. HNO3 and was chemisorbed to a std. microscope coverslip with (3-mercaptopropyl)trimethoxysilane. The Au surface was further modified with 1-hexanethiol to optimize hydrophobicity of the surface to allow for redox measurements to be made in nanoscopic vols. Time traces of the open-circuit potential (OCP) were used to construct Nernst plots to evaluate the applicability of the droplet-based potentiometric redox measurement system. Two poised 1-electron transfer systems (K ferricyanide/ferrocyanide and ferrous/ferric ammonium sulfate) yielded Nernstian slopes of -58.5 and -60.3 mV, resp., with regression coeffs. >0.99. The y-intercepts of the two agreed well to the formal potential of the two std. oxidn.-redn. potential (ORP) calibrants, ZoBell's and Light's soln. The benzoquinone and hydroquinone redox couple was examd. as a representative two-electron redox system; a Nernst slope of -30.8 mV was obtained. Addnl., two unpoised systems (K ferricyanide and ascorbic acid) were studied to evaluate the system under conditions where only one form of the redox couple is present in appreciable concns. Again, slopes near the Nernstian values of -59 and -29 mV, resp., were obtained. All expts. were carried out using soln. vols. between 280 and 1400 pL with injection vols. between 8 and 100 pL. The miniscule vols. allowed for extremely rapid mixing (<305 ms) as well. The small vols. and rapid mixing along with the high accuracy and sensitivity of these measurements lend support to the use of this approach in applications where time is a factor and only small vols. are available for testing.
- 158Asadnia, M.; Myers, M.; Umana-Membreno, G. A.; Sanders, T. M.; Mishra, U. K.; Nener, B. D.; Baker, M. V.; Parish, G. Ca2+ detection utilising AlGaN/GaN transistors with ion-selective polymer membranes. Anal. Chim. Acta 2017, 987, 105– 110, DOI: 10.1016/j.aca.2017.07.066157https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtlegsr3E&md5=abd443c9e987cc36149a1f9f5af5d30dCa2+ detection utilising AlGaN/GaN transistors with ion-selective polymer membranesAsadnia, Mohsen; Myers, Matthew; Umana-Membreno, Gilberto A.; Sanders, Tarun M.; Mishra, Umesh K.; Nener, Brett D.; Baker, Murray V.; Parish, GiacintaAnalytica Chimica Acta (2017), 987 (), 105-110CODEN: ACACAM; ISSN:0003-2670. (Elsevier B.V.)The authors demonstrate highly selective and sensitive potentiometric ion sensors for calcium ion detection, operated without the use of a ref. electrode. The sensors consist of AlGaN/GaN heterostructure-based transistor devices with chem. functionalization of the gate area using poly(vinylchloride)-based (PVC) membranes having high selectivity towards calcium ions, Ca2+. The sensors exhibited stable and rapid responses when introduced to various concns. of Ca2+. In both 0.01 M KCl and 0.01 M NaCl ionic strength buffer solns., the sensors exhibited near Nernstian responses with detection limits of <10-7 M, and a linear response range between 10-7-10-2 M. Also, detection limits of <10-6 M were achieved for the sensors in both 0.01 M MgCl2 and 0.01 M LiCl buffer solns. AlGaN/GaN-based devices for Ca2+ detection demonstrate excellent selectivity and response range for a wide variety of applications. This work represents an important step towards multi-ion sensing using arrays of ion-selective field effect transistor (ISFET) devices.
- 159Kaisti, M.; Boeva, Z.; Koskinen, J.; Nieminen, S.; Bobacka, J.; Levon, K. Hand-Held Transistor Based Electrical and Multiplexed Chemical Sensing System. ACS Sens. 2016, 1, 1423– 1431, DOI: 10.1021/acssensors.6b00520158https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhvFCgsrbF&md5=ede6b01e922bc18d560cc8074abec6deHand-Held Transistor Based Electrical and Multiplexed Chemical Sensing SystemKaisti, Matti; Boeva, Zhanna; Koskinen, Juho; Nieminen, Sami; Bobacka, Johan; Levon, KalleACS Sensors (2016), 1 (12), 1423-1431CODEN: ASCEFJ; ISSN:2379-3694. (American Chemical Society)The authors describe a hand-held sensing system using a transistor based multiplexed platform and a detector that couples the electrochem. information wirelessly to a smartphone. The custom disposable platform exploits the ion-sensitive FET (ISFET) technol. Via simple surface modifications the design allows a broad range of analytes to be tested with low-cost. The authors compared their read-out device to a com. potentiometer using K+ as an example species analyte. The developed sensing system has slightly better limit of detection and notably is less susceptible to external noise which is commonly obsd. with potentiometers. The designed platform is fabricated using std. electronic processes with gold surface and the authors used com. discrete transistors as the transducing element. It can be mass produced with high yield and low-cost. To circumvent the drift that typically occurs with modified solid state electrodes the authors incorporated a transducing layer between the elec. conductor (gold pad) and the ionically conducting ion-selective-membrane. The polyaniline doped with dinonylnaphthalene sulfonic acid (PANI-DNNSA) was used as a transducing layer for the first time. The PANI-DNNSA layer significantly reduces the drift of the electrodes compared to a configuration without the transducing layer. The system is easy to use with a transistor based detection that can be modified for a vast variety of existing potentiometric tests.
- 160Briggs, E. M.; Sandoval, S.; Erten, A.; Takeshita, Y.; Kummel, A. C.; Martz, T. R. Solid State Sensor for Simultaneous Measurement of Total Alkalinity and pH of Seawater. ACS Sens. 2017, 2, 1302– 1309, DOI: 10.1021/acssensors.7b00305159https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtlSkurzJ&md5=081f3653269ab54d74b6946f4a8cef30Solid State Sensor for Simultaneous Measurement of Total Alkalinity and pH of SeawaterBriggs, Ellen M.; Sandoval, Sergio; Erten, Ahmet; Takeshita, Yuichiro; Kummel, Andrew C.; Martz, Todd R.ACS Sensors (2017), 2 (9), 1302-1309CODEN: ASCEFJ; ISSN:2379-3694. (American Chemical Society)A novel design is demonstrated for a solid state, reagent-less sensor capable of rapid and simultaneous measurement of pH and Total Alky. (AT) using ion sensitive field effect transistor (ISFET) technol. to provide a simplified means of characterization of the aq. carbon dioxide system through measurement of two "master variables": pH and AT. ISFET-based pH sensors that achieve 0.001 precision are widely used in various oceanog. applications. A modified ISFET is demonstrated to perform a nanoliter-scale acid-base titrn. of AT in under 40 s. This method of measuring AT, a Coulometric Diffusion Titrn., involves electrolytic generation of titrant, H+, through the electrolysis of water on the surface of the chip via a microfabricated electrode eliminating the requirement of external reagents. Characterization has been performed in seawater as well as titrating individual components (i.e., OH-, HCO3-, CO32-, B(OH)4-, PO43-) of seawater AT. The seawater measurements are consistent with the design in reaching the benchmark goal of 0.5% precision in AT over the range of seawater AT of ∼2200-2500 μmol kg-1 which demonstrates great potential for autonomous sensing.
- 161Andrianova, M. S.; Gubanova, O. V.; Komarova, N. V.; Kuznetsov, E. V.; Kuznetsov, A. E. Electroanalysis 2016, 28, 1311– 1321, DOI: 10.1002/elan.201500411160https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhtFOns70%253D&md5=a7f20b4850f3bc0aa8d6d7d65a75d9bdDevelopment of a Biosensor Based on Phosphotriesterase and n-Channel ISFET for Detection of PesticidesAndrianova, M. S.; Gubanova, O. V.; Komarova, N. V.; Kuznetsov, E. V.; Kuznetsov, A. E.Electroanalysis (2016), 28 (6), 1311-1321CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)A biosensor for the direct detn. of organophosphorus pesticides (OPs) is described. It utilizes an ion-selective field-effect transistor and phosphotriesterase enzyme (PTE), which provides cleavage of OPs. The sensitivity of the biosensor was increased after PTE immobilization on the surface of the transistor. Packaging of the integrated circuit and creation of a microfluidic system for analyte delivery stabilized the signal. This system was able to detect 0.1 μM paraoxon and 0.5 μM parathion and methyl parathion and was stable for at least 1 mo (PBS, 1°), and could thus provide the basis for a portable device for analyzing OPs in water.
- 162Melzer, K.; Bhatt, V. D.; Jaworska, E.; Mittermeier, R.; Maksymiuk, K.; Michalska, A.; Lugli, P. Enzyme assays using sensor arrays based on ion-selective carbon nanotube field-effect transistors. Biosens. Bioelectron. 2016, 84, 7– 14, DOI: 10.1016/j.bios.2016.04.077161https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XntFCrtrs%253D&md5=1cb68e06a914b8b58f910d9a30af8e60Enzyme assays using sensor arrays based on ion-selective carbon nanotube field-effect transistorsMelzer, K.; Bhatt, V. Deep; Jaworska, E.; Mittermeier, R.; Maksymiuk, K.; Michalska, A.; Lugli, P.Biosensors & Bioelectronics (2016), 84 (), 7-14CODEN: BBIOE4; ISSN:0956-5663. (Elsevier B.V.)In the fields of clin. diagnostics and point-of-care diagnosis as well as food and environmental monitoring there is a high demand for reliable high-throughput, rapid and highly sensitive assays for a simultaneous detection of several analytes in complex and low-vol. samples. Sensor platforms based on soln.-processable electrolyte-gated carbon nanotube field-effect transistors (CNT-FETs) are a simple and cost-effective alternative for conventional assays. The authors demonstrate a selective as well as direct detection of the products of an enzyme-substrate interaction, here the for metabolic processes important urea-urease system, with sensors based on spray-coated CNT-FETs. The selective and direct detection is achieved by immobilizing the enzyme urease via certain surface functionalization techniques on the sensor surface and further modifying the active interfaces with polymeric ion-selective membranes as well as pH-sensitive layers. Thereby, the authors can avoid the generally applied approach for a field-effect based detection of enzyme reactions via detecting changes in the pH value due to an on-going enzymic reaction and directly detect selectively the products of the enzymic conversion. Thus, the authors can realize a buffering-capacity independent monitoring of changes in the substrate concn.
- 163Cuartero, M.; Bakker, E. Environmental water analysis with membrane electrodes. Curr. Opin. Electrochem. 2017, 3, 97– 105, DOI: 10.1016/j.coelec.2017.06.010162https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhtVGgsLbL&md5=01988be9764f84e8daae0ad4590c8719Environmental water analysis with membrane electrodesCuartero, Maria; Bakker, EricCurrent Opinion in Electrochemistry (2017), 3 (1), 97-105CODEN: COEUCY; ISSN:2451-9111. (Elsevier B.V.)A review. The monitoring of key parameters and analytes (including ions) in aquatic systems is crucial to our understanding of biogeochem. processes and their possible correlation with anthropogenic activities. The use of centralised anal. methodologies is most established for this purpose, but the risk of sample alteration during sampling and transport and the limited data acquisition frequency are promoting a paradigm shift towards in situ approaches. These focus on performing the measurement shipboard, from on site platforms or through submersible probes. This latter option is the most attractive for environmental scientists since it provides real-time profiles with high spatial and temporal resoln., even allowing the study of aquatic processes that evolve at the minute time scale. Potentiometric ion-selective electrodes, esp. based on polymeric membranes, have therefore been widely used to detect important ions in marine and fresh water systems. Importantly, their inherent characteristics make them particularly suitable for implementation into submersible probes. This crit. review highlights some recent examples related to the application of membrane electrodes for water anal. with particular attention to the efforts towards in situ detection. Sensor technol. is sometimes overlooked in environmental anal. and this review aims to bring electrochemists, analysts and environmentalists together to better appreciate the strengths of membrane electrodes targeted to this aim.
- 164Pankratova, N.; Afshar, M. G.; Yuan, D. J.; Crespo, G. A.; Bakker, E. Local Acidification of Membrane Surfaces for Potentiometric Sensing of Anions in Environmental Samples. ACS Sens. 2016, 1, 48– 54, DOI: 10.1021/acssensors.5b00015163https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhs1altLjM&md5=5bfacbf341a3510bc21dd67c64b8c411Local Acidification of Membrane Surfaces for Potentiometric Sensing of Anions in Environmental SamplesPankratova, Nadezda; Ghahraman Afshar, Majid; Yuan, Dajing; Crespo, Gaston A.; Bakker, EricACS Sensors (2016), 1 (1), 48-54CODEN: ASCEFJ; ISSN:2379-3694. (American Chemical Society)The work dramatically improves the lower detection limit of anion selective membranes at environmental pH by using local acidification to suppress hydroxide interference at the membrane surface. Three sep. localized acidification strategies are explored to achieve this, with ionophore-based membrane electrodes selective for nitrite and dihydrogen phosphate as guiding examples. In a 1st approach, a concd. acetic acid soln. (∼1 M) is placed in the inner filling soln. of the PVC-based membrane electrode, forcing a significant acid gradient across the membrane. A 2nd strategy achieves the same type of passive acidification by using an external proton source (fast diffusive doped polypropylene membrane) placed in front of a potentiometric solid contact anion selective electrode where the thin layer gap allows one to observe spontaneous acidification at the opposing detection electrode. The 3rd approach shares the same configuration, but protons are here released by electrochem. control from the selective proton source into the thin layer sample. All three protocols improve the limit of detection by >2 orders of magnitude at environmental pH. Nitrite and dihydrogen phosphate detns. in artificial and natural samples are demonstrated.
- 165Pankratova, N.; Cuartero, M.; Cherubini, T.; Crespo, G. A.; Bakker, E. In-Line Acidification for Potentiometric Sensing of Nitrite in Natural Waters. Anal. Chem. 2017, 89, 571– 575, DOI: 10.1021/acs.analchem.6b03946164https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XitVGnsbrN&md5=73adab866b9bfa567d75886a380336e9In-Line Acidification for Potentiometric Sensing of Nitrite in Natural WatersPankratova, Nadezda; Cuartero, Maria; Cherubini, Thomas; Crespo, Gaston A.; Bakker, EricAnalytical Chemistry (Washington, DC, United States) (2017), 89 (1), 571-575CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)We report on a novel approach for in-line sample acidification that results in a significant improvement of the limit of detection of potentiometric anion-selective electrodes aiming at detg. nutrients in natural waters. The working principle of the developed acidification module relies on the cation-exchange process between the sample and an ion-exchange Donnan exclusion membrane in its protonated form. The resulting in-line acidification of natural waters with millimolar NaCl level (freshwater, drinking water, aquarium water as well as dechlorinated seawater) decreases the pH down to ∼5. Using the acidification module the limit of detection of nitrite-selective electrodes significantly improves by ≥2 orders of magnitude with respect to that obsd. at environmental pH. The originality of the proposed flow cell lies in the possibility to adjust the pH of the sample by modifying its exposure time with the membrane by varying the volumetric flow rate. Facile coupling with a detection technique of choice, miniaturized configuration and simple implementation for long-term monitoring with submersible probes for environmental anal. are possible anal. configurations. This approach was applied to the potentiometric detection of nitrite in aquarium and dechlorinated seawater.
- 166Cuartero, M.; Crespo, G.; Cherubini, T.; Pankratova, N.; Confalonieri, F.; Massa, F.; Tercier-Waeber, M. L.; Abdou, M.; Schafer, J.; Bakker, E. In Situ Detection of Macronutrients and Chloride in Seawater by Submersible Electrochemical Sensors. Anal. Chem. 2018, 90, 4702– 4710, DOI: 10.1021/acs.analchem.7b05299165https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXktFWjsbw%253D&md5=96e30b2d08887c5184362d6144c9943fIn Situ Detection of Macronutrients and Chloride in Seawater by Submersible Electrochemical SensorsCuartero, Maria; Crespo, Gaston; Cherubini, Thomas; Pankratova, Nadezda; Confalonieri, Fabio; Massa, Francesco; Tercier-Waeber, Mary-Lou; Abdou, Melina; Schafer, Jorg; Bakker, EricAnalytical Chemistry (Washington, DC, United States) (2018), 90 (7), 4702-4710CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)A new submersible probe for the in situ detection of nitrate, nitrite, and chloride in seawater is presented. Inline coupling of a desalination unit, an acidification unit, and a sensing flow cell contg. all-solid-state membrane electrodes allows for the potentiometric detection of nitrate and nitrite after removal of the key interfering ions in seawater, chloride and hydroxide. Thus, the electrodes exhibited attractive anal. performances for the potentiometric detection of nitrate and nitrite in desalinated and acidified seawater: fast response time (t95 < 12 s), excellent stability (long-term drifts of <0.5 mV h-1), good reproducibility (calibration parameter deviation of <3%), and satisfactory accuracy (uncertainties <8%Diff compared to ref. technique). The desalination cell, which can be repetitively used for about 30 times, may addnl. be used as an exhaustive, and therefore calibration-free, electrochem. sensor for chloride and indirect salinity detection. The detection of these two parameters together with nitrate and nitrite may be useful for the correlation of relative changes in macronutrient levels with salinity cycles, which is of special interest in recessed coastal water bodies. The system is capable of autonomous operation during deployment, with routines for repetitive measurements (every 2 h), data storage and management, and computer visualization of the data in real time. In situ temporal profiles obsd. in the Arcachon Bay (France) showed valuable environmental information concerning tide-dependent cycles of nitrate and chloride levels in the lagoon, which are here obsd. for the first time using direct in situ measurements. The submersible probe based on membrane electrodes presented herein may facilitate the study of biogeochem. processes occurring in marine ecosystems by the direct monitoring of nitrate and nitrite levels, which are key chem. targets in coastal waters.
- 167Cuartero, M.; Pankratova, N.; Cherubini, T.; Crespo, G. A.; Massa, F.; Confalonieri, F.; Bakker, E. In Situ Detection of Species Relevant to the Carbon Cycle in Seawater with Submersible Potentiometric Probes. Environ. Sci. Technol. Lett. 2017, 4, 410– 415, DOI: 10.1021/acs.estlett.7b00388166https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsFOgt7nK&md5=d3ad81428f6ae008250633b1dc076aa6In Situ Detection of Species Relevant to the Carbon Cycle in Seawater with Submersible Potentiometric ProbesCuartero, Maria; Pankratova, Nadezda; Cherubini, Thomas; Crespo, Gaston A.; Massa, Francesco; Confalonieri, Fabio; Bakker, EricEnvironmental Science & Technology Letters (2017), 4 (10), 410-415CODEN: ESTLCU; ISSN:2328-8930. (American Chemical Society)We report on the development of a submersible probe for the simultaneous potentiometric detection of carbonate, calcium, and pH in seawater. All-solid-state electrodes incorporating nanomaterials provide an adequate response time (<10 s), stability (drifts of <0.9 mV h-1), reproducibility (calibration parameter deviation of <0.7%), and accuracy (deviation of <8% compared to ref. techniques) for real-time monitoring of seawater using a flow system. The functioning of the deployable prototype was checked in an outdoor mesocosm and via long-term monitoring in Genoa Harbor. The electrodes worked properly for 3 wk, and the system demonstrated the capability to autonomously operate with routines for repetitive measurements, data storage, and management. In situ profiles obsd. in Genoa Harbor and Arcachon Bay were validated using on site and ex situ techniques. The validation of in situ-detected carbonate is a challenge because both re-equilibration of the sample with atm. CO2 and the use of apparent thermodn. consts. for speciation calcns. lead to some differences (<20% deviation). The submersible probe is a promising tool for obtaining rapid and trustworthy information about chem. levels in marine systems. Moreover, the fluidic approach allows for the integration of other ion sensors that may require sample pretreatment.
- 168Athavale, R.; Dinkel, C.; Wehrli, B.; Bakker, E.; Crespo, G. A.; Brand, A. Robust Solid-Contact Ion Selective Electrodes for High-Resolution In Situ Measurements in Fresh Water Systems. Environ. Sci. Technol. Lett. 2017, 4, 286– 291, DOI: 10.1021/acs.estlett.7b00130167https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXnsVWrtrY%253D&md5=a34360ca85238b58dfa03196a110ed01Robust Solid-Contact Ion Selective Electrodes for High-Resolution In Situ Measurements in Fresh Water SystemsAthavale, Rohini; Dinkel, Christian; Wehrli, Bernhard; Bakker, Eric; Crespo, Gaston A.; Brand, AndreasEnvironmental Science & Technology Letters (2017), 4 (7), 286-291CODEN: ESTLCU; ISSN:2328-8930. (American Chemical Society)Biogeochem. processes are often confined to very narrow zones in aquatic systems. Therefore, highly resolved in situ measurements are required to study these processes. Potentiometric solid-contact ion selective electrodes (SC-ISEs) are promising tools for such measurements. SC-ISEs show good performance in analyses under controlled exptl. conditions. Very few sensor designs, however, can sustain the challenges of natural water matrixes and external environmental conditions during in situ applications. We fabricated ammonium and pH selective SC-ISEs with functionalized multiwalled carbon nanotubes (f-MWCNT) as a solid contact. Their functionality was tested in the lab. and applied in situ for vertical profiling in a eutrophic lake. Sensors were insensitive to strong redox changes, high sulfide concns., and bright daylight conditions during the application in the lake. In addn., sensors are easily fabricated and exhibit short response times (<10 s). The proposed design of SC-ISEs based on f-MWCNTs is quite suitable for high-resoln. in situ profiling of ionic species in fresh water lakes.
- 169Ding, L.; Ding, J. W.; Ding, B. J.; Qin, W. Solid-contact Potentiometric Sensor for the Determination of Total Ammonia Nitrogen in Seawater. Int. J. Electrochem. Sci. 2017, 12, 3296– 3308, DOI: 10.20964/2017.04.01168https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtV2jt7%252FL&md5=c5e5d881879e0df1bae248637e69a702Solid-contact potentiometric sensor for the determination of total ammonia nitrogen in seawaterDing, Lan; Ding, Jiawang; Ding, Baojun; Qin, WeiInternational Journal of Electrochemical Science (2017), 12 (4), 3296-3308CODEN: IJESIV; ISSN:1452-3981. (Electrochemical Science Group)A solid-contact potentiometric sensor for in situ detection of total ammonia nitrogen (TAN, free ammonia plus the ammonium ion) in seawater is described. In the compact system, an all-solid-state polymeric membrane ammonium-seletive electrode is integrated with a polyvinyl alc. hydrogel buffer film of pH 7.0 and a gas-permeable membrane. The gaseous NH3 in seawater diffuses through the gas-permeable membrane and is converted to NH4+ in the hydrogel buffer, which can be potentiometrically sensed by the solid-contact ammonium-sensitive membrane electrode. The electrode configuration facilitates the alteration of NH3 to NH4+ in the hydrogel buffer film and improves the sensitivity for the detection of TAN by the buffer trap effect. The gas-permeable membrane effectively eliminates the ion interferences from the seawater sample matrixes. The proposed sensor shows a stable potentiometric response in the concn. range of 10-6 - 10-4 M with a detection limit of 6.4 × 10-7 M, and has been successfully applied to the detection of TAN in seawater.
- 170Chango, G.; Palacio, E.; Cerdà, V. Talanta 2018, 186, 554– 560, DOI: 10.1016/j.talanta.2018.04.087169https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXpsVOgs7Y%253D&md5=c21fe1c813f7a9f28443075810b416d9Potentiometric chip-based multipumping flow system for the simultaneous determination of fluoride, chloride, pH, and redox potential in water samplesChango, Gabriela; Palacio, Edwin; Cerda, VictorTalanta (2018), 186 (), 554-560CODEN: TLNTA2; ISSN:0039-9140. (Elsevier B.V.)A simple potentiometric chip-based multipumping flow system (MPFS) has been developed for the simultaneous detn. of fluoride, chloride, pH, and redox potential in water samples. The proposed system was developed by using a poly(Me methacrylate) chip microfluidic-conductor using the advantages of flow techniques with potentiometric detection. For this purpose, an automatic system has been designed and built by optimizing the variables involved in the process, such as: pH, ionic strength, stirring and sample vol. This system was applied successfully to water samples getting a versatile system with an anal. frequency of 12 samples per h. Good correlation between chloride and fluoride concn. measured with ISE and ionic chromatog. technique suggests satisfactory reliability of the system.
- 171Shen, J.; Gagliardi, S.; McCoustra, M. R. S.; Arrighi, V. Effect of humic substances aggregation on the determination of fluoride in water using an ion selective electrode. Chemosphere 2016, 159, 66– 71, DOI: 10.1016/j.chemosphere.2016.05.069170https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XpvFaktLY%253D&md5=f1b1381475e4fe47dd6b635bd4dd0172Effect of humic substances aggregation on the determination of fluoride in water using an ion selective electrodeShen, Junjie; Gagliardi, Simona; McCoustra, Martin R. S.; Arrighi, ValeriaChemosphere (2016), 159 (), 66-71CODEN: CMSHAF; ISSN:0045-6535. (Elsevier Ltd.)The control of drinking water quality is crit. in preventing fluorosis. In this study humic substances (HS) are considered as representative of natural org. matter (NOM) in water. We show that when HS aggregate the response of fluoride ion selective electrodes (ISE) may be perturbed. Dynamic light scattering (DLS) results of both synthetic solns. and natural water sample suggest that low pH and high ionic strength induce HS aggregation. In the presence of HS aggregates, fluoride concn. measured by ISE has a redn. up to 19%. A new "open cage" concept has been developed to explain this reversible phenomenon. The interference of HS aggregation on fluoride measurement can be effectively removed by centrifugation pretreatment.
- 172Machado, A.; Mesquita, R. B. R.; Oliveira, S.; Bordalo, A. A. Talanta 2017, 167, 688– 694, DOI: 10.1016/j.talanta.2017.03.017171https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXktVCrs7c%253D&md5=7b72f447e598daf2cb2fbf5374e4a174Development of a robust, fast screening method for the potentiometric determination of iodide in urine and salt samplesMachado, Ana; Mesquita, Raquel B. R.; Oliveira, Sara; Bordalo, Adriano A.Talanta (2017), 167 (), 688-694CODEN: TLNTA2; ISSN:0039-9140. (Elsevier B.V.)In this work, a potentiometric flow injection method is described for the fast bi-parametric detn. of iodide and iodate in urine and salt samples. The developed methodol. aimed for iodine speciation with a potentially portable system (running on batteries). The iodate redn. to iodide was effectively attained in line within the same manifold. The iodide detn. was accomplished in the dynamic range of 2.50×10-6-1.00×10-3 M and the total iodine dynamic range, resulted from iodide plus iodate, was 3.50×10-6-2.00×10-3 M. The calcd. limits of detection were 1.39×10-6 M and 1.77×10-6 M for iodide and iodate, resp. A detn. rate of 21 h-1 for the bi-parametric iodide and iodate detn. was obtained for sample injection. The urine samples (RSD <5.8% for iodide and RSD <7.0% for iodate) results were in agreement with those obtained by the classic Sandell-Kolthoff reaction colorimetric ref. procedure (RD <7.0%) and std. samples from Centers for Disease Control and Prevention, Atlanta, USA (CDC) international inter-lab. EQUIP program. The developed flow method was also successfully applied to the iodide and iodate detn. in salt samples (RSD <3.1% for iodate and iodide), with comparable results to conventional procedures. No significant interferences were obsd. interference percentage <9% for both detns.
- 173Atherton, J.; King, W. E.; Guzinski, M.; Jasinski, A.; Pendley, B.; Lindner, E. A method to monitor urinary carbon dioxide in patients with septic shock. Sens. Actuators, B 2016, 236, 77– 84, DOI: 10.1016/j.snb.2016.05.076172https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xps1agt7s%253D&md5=1b61032bf913e26397af04b05d7331e6A method to monitor urinary carbon dioxide in patients with septic shockAtherton, James; William E., King, III; Guzinski, Marcin; Jasinski, Artur; Pendley, Bradford; Lindner, ErnoSensors and Actuators, B: Chemical (2016), 236 (), 77-84CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)Severe sepsis and septic shock are life-threatening conditions with mortality rates exceeding 31% (Levy et al., 2012) [1]. Septicemia was the most expensive US hospital condition in 2011 (Torio and Andrews, 2006) [2]. Urinary carbon dioxide may provide rapid, clin. useful information about a patient's status, empowering physicians to intervene earlier and improve septic shock mortality. The objective of this paper is to validate a protocol with a Severinghaus-type CO2 probe for the measurement of urinary CO2 of septic shock patients. This protocol includes (i) sampling urine from a Foley catheter in an intensive care unit setting, (ii) storing samples until anal. at a sep. facility, (iii) calibration of the Severinghaus-type CO2 sensor, and (iv) measuring urinary CO2 levels. We discuss the prepn. and stability of std. solns., storage of urine samples, and the performance characteristics of the Severinghaus type CO2 sensor in relation to mock urine samples, urine quality control stds., and urine samples from healthy volunteers as well as patients in severe sepsis or septic shock. We report the influence of the sample pH, temp., and ionic strength on the precision and accuracy of the measurements of urinary CO2 levels and show that the protocol developed for the quant. assessment of urinary CO2 levels is adequate for the anal. of urine samples collected from a Foley catheter.
- 174Zajda, J.; Crist, N. R.; Malinowska, E.; Meyerhoff, M. E. Asymmetric Anion-selective Membrane Electrode for Determining Nitric Oxide Release Rates from Ppolymeric Films/Electrochemical Devices. Electroanalysis 2016, 28, 277– 281, DOI: 10.1002/elan.201500395173https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXht1Gls7zJ&md5=a0b4376491ceefaa1bbbd3e451c5cd7aAsymmetric anion-selective membrane electrode for determining nitric oxide release rates from polymeric films/electrochemical devices.Zajda, Joanna; Crist, Natalie R.; Malinowska, Elzbieta; Meyerhoff, Mark E.Electroanalysis (2016), 28 (2), 277-281CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)A novel potentiometric method for the detn. of nitric oxide (NO) is presented. The assessment of NO levels is based on the rapid reaction of NO with oxyHb, during which nitrate is formed and then detected potentiometrically using a polymeric membrane anion-selective electrode. The compn. of the anion-selective membrane is optimized to eliminate the response to high levels of oxyHb reagent used to react with NO to form NO3-. The practical utility of the method is demonstrated by detg. the NO release rates from NO donor-doped polymeric films, as well as from a new electrochem. NO generation system within the range of 10 to 55 × 10-10 mol · min-1. The values measured with the new assay system are shown to correlate well with a chemiluminescence ref. method after accounting for the trapping efficiency of NO by the oxyHb soln.
- 175Cuartero, M.; Perez, S.; Garcia, M. S.; Garcia-Canovas, F.; Ortuño, J. A. Comparative enzymatic studies using ion-selective electrodes. The case of cholinesterases. Talanta 2018, 180, 316– 322, DOI: 10.1016/j.talanta.2017.12.029174https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXit1Kgsg%253D%253D&md5=b3282fe489ff0be734c5b24d02797bb2Comparative enzymatic studies using ion-selective electrodes. The case of cholinesterasesCuartero, Maria; Perez, Soraya; Garcia, Maria S.; Garcia-Canovas, Francisco; Ortuno, Joaquin A.Talanta (2018), 180 (), 316-322CODEN: TLNTA2; ISSN:0039-9140. (Elsevier B.V.)The application of traditional ion-selective electrodes for comparative enzymic anal. was demonstrated for the first time in this study. A kinetic-potentiometric method based on the monitoring of the concn. of the ionic substrate involved in the enzymic reaction catalyzed by different cholinesterases is used for this purpose. A comparative study was performed comprising both enzymic assays using different ionic substrates and the corresponding inhibited reactions in presence of neostigmine (a synthetic anticholinesterase). The developed approach is used to obtain valuable comparative results through calcn. of kinetic parameters, such as Michaelis and inhibition consts. Interesting results were obtained for acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) enzymes, which were selected as proof-of-concept: (i) the binding affinity that these enzymes have for their natural substrates showed to be higher (acetylcholine and butyrylcholine resp.) than for their corresponding thiol derivs. (acetylthiocholine and butyrylthiocholine), which are traditionally used in spectrophotometric enzymic assays; (ii) as expected, the max. hydrolysis rate found in the assays of each enzyme was independent of the substrate used; and (iii) acetylcholinesterase enzyme inhibition due to neostigmine was found to be higher (higher inhibition const.). Advantageously, the use of ion-selective electrodes permits to perform cholinesterases' enzymic assays using their natural substrates and under physiol. conditions, unlike the traditional spectrophotometric methods used in routine enzymic assays. Importantly, while well-known enzymes are use throughout this work, this approach can be extended to other types of enzymic assays as a tangible alternative to traditional spectrophotometric methods.
- 176Urbanowicz, M.; Jasinski, A.; Jasinska, M.; Drucis, K.; Ekman, M.; Szarmach, A.; Suchodolski, R.; Pomecko, R.; Bochenska, M. Simultaneous Determination of Na+, K+, Ca2+, Mg2+ and Cl- in Unstimulated and Stimulated Human Saliva Using All Solid State Multisensor Platform. Electroanalysis 2017, 29, 2232– 2238, DOI: 10.1002/elan.201700149175https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtVyqsLnN&md5=a62a2bef2613125ddc3fc89e3181cf65Simultaneous Determination of Na+, K+, Ca2+, Mg2+ and Cl- in Unstimulated and Stimulated Human Saliva Using All Solid State Multisensor PlatformUrbanowicz, Marcin; Jasinski, Artur; Jasinska, Malgorzata; Drucis, Kamil; Ekman, Marcin; Szarmach, Arkadiusz; Suchodolski, Rafal; Pomecko, Radoslaw; Bochenska, MariaElectroanalysis (2017), 29 (10), 2232-2238CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)Human saliva is one of the body fluids which collection method is relatively simple and non-invasive. The article is dedicated to assess concn. (activity) of Na+, K+, Ca2+, Mg2+ and Cl- in fresh, unstimulated or stimulated human saliva samples using single solid contact ion-selective electrodes with conventional ref. electrode and self-made multisensor platform (MP) equipped with ion-selective membranes for Na+, K+, Ca2+, Mg2+ and Cl- and ref. electrode made in solid state technol., based on dispersed KCl in the polymer. Both kind of electrodes, single ISE and miniaturized electrodes in multisensor platform (ISE-MP) were made of glassy carbon. The electrode surfaces have been modified by conductive polymer (PEDOT) layer deposition; with the exception of Cl- electrode, in which conducting polymer was not applied. Potentiometric measurements were used to compare the changes of the ionic compn. in various samples of saliva.
- 177Goda, T.; Yamada, E.; Katayama, Y.; Tabata, M.; Matsumoto, A.; Miyahara, Y. Potentiometric responses of ion-selective microelectrode with bovine serum albumin adsorption. Biosens. Bioelectron. 2016, 77, 208– 214, DOI: 10.1016/j.bios.2015.09.023176https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhsFGgsLfI&md5=683f64dcfb9bafd7d947fd8425aa6d95Potentiometric responses of ion-selective microelectrode with bovine serum albumin adsorptionGoda, Tatsuro; Yamada, Eriko; Katayama, Yurika; Tabata, Miyuki; Matsumoto, Akira; Miyahara, YujiBiosensors & Bioelectronics (2016), 77 (), 208-214CODEN: BBIOE4; ISSN:0956-5663. (Elsevier B.V.)There is a growing demand for an in situ measurement of local pH and ion concns. in biol. milieu to monitor ongoing process of bioreaction and bioresponse in real time. An ion-selective microelectrode can meet the requirements. However, the contact of the electrode with biol. fluids induces biofouling by protein adsorption to result in a noise signal. Therefore, we investigated the relationship between the amt. of nonspecific protein adsorption and the elec. signals in potentiometry by using ion-selective microelectrodes, namely silver/silver chloride (Ag/AgCl), iridium/iridium oxides (Ir/IrOx), and platinum/iridium oxides (Pt/IrOx). The microelectrodes reduced a potential change following the adsorption of bovine serum albumin (BSA) by comparison with the original metal microelectrodes without oxide layers. Suppression in the noise signal was attributed to the increased capacitance at the electrode/soln. interface due to the formation of granulated metal oxide layer rather than a decrease in the amt. of protein adsorbed. Ion sensitivity was maintained for Ir/IrOx against proton, but it was not for Ag/AgCl against chloride ion (Cl-), because of the interference of the equil. reaction by adsorbed BSA mols. on the electrode surface at<10-2 M [Cl-] in the soln. The results open up the application of the Ir/IrOx microelectrode for measuring local pH in realistic dirty samples with a limited influence of electrode pollution by protein adsorption.
- 178Lisak, G.; Arnebrant, T.; Lewenstam, A.; Bobacka, J.; Ruzgas, T. In Situ Potentiometry and Ellipsometry: A Promising Tool to Study Biofouling of Potentiometric Sensors. Anal. Chem. 2016, 88, 3009– 3014, DOI: 10.1021/acs.analchem.5b04364177https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XitlCjs74%253D&md5=2e8e4cb092ad14f58db314f232941177In Situ Potentiometry and Ellipsometry: A Promising Tool to Study Biofouling of Potentiometric SensorsLisak, Grzegorz; Arnebrant, Thomas; Lewenstam, Andrzej; Bobacka, Johan; Ruzgas, TautgirdasAnalytical Chemistry (Washington, DC, United States) (2016), 88 (6), 3009-3014CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)In situ potentiometry and null ellipsometry were combined and used as a tool to follow the kinetics of biofouling of ion-selective electrodes (ISEs). The study was performed using custom-made solid-contact K+-ISEs consisting of a gold surface with immobilized 6-(ferrocenyl)hexanethiol as ion-to-electron transducer that was coated with a potassium-selective plasticized polymer membrane. The electrode potential and the ellipsometric signal (corresponding to the amt. of adsorbed protein) were recorded simultaneously during adsorption of bovine serum albumin (BSA) at the surface of the K+-ISEs. This in situ method may become useful in developing sensors with minimized biofouling.
- 179Ferguson, S. A.; Meyerhoff, M. E. Advances in electrochemical and optical polyion sensing: A review. Sens. Actuators, B 2018, 272, 643– 654, DOI: 10.1016/j.snb.2018.06.127178https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhtlCmsrzI&md5=ebb8c1b8efdd22f27e6819535a117b00Advances in electrochemical and optical polyion sensing: A reviewFerguson, Stephen A.; Meyerhoff, Mark E.Sensors and Actuators, B: Chemical (2018), 272 (), 643-654CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)A review. Electrochem. and optical sensing of polyions were first introduced in the early to mid 1990s via the development and study of the first heparin-sensitive potentiometric and optical polyion sensors. Since then, the no. of reports relating to electrochem. and optical polyion sensing technologies have grown substantially. Both biol. and industrially relevant polyions can be detected using these methods. This paper provides an overview of key accomplishments with respect to polyion sensor-based technologies over the past 25+ years. A summary of the basic designs and sensing principles of single-use/fully reversible polymeric membrane-type potentiometric polyion sensors, voltammetric polyion-sensitive electrodes, and single-use polyion-sensitive optodes is provided. The expansion of polyion sensing to more industrial and cosmetic polyions (i.e., polyquaterniums) is also discussed. Lastly, potential new directions/applications are provided for electrochem. and optical polyion sensors based on all-solid-contact designs (for electrochem.) and paper-based sensing devices (both electrochem. and optical).
- 180Ferguson, S. A.; Wang, X. W.; Meyerhoff, M. E. Detecting levels of polyquaternium-10 (PQ-10) via potentiometric titration with dextran sulphate and monitoring the equivalence point with a polymeric membrane-based polyion sensor. Anal. Methods 2016, 8, 5806– 5811, DOI: 10.1039/C6AY01748G179https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhtFSitL3K&md5=5f7ff03eddc373d68f65b0d04e2cfdc0Detecting levels of polyquaternium-10 (PQ-10) via potentiometric titration with dextran sulphate and monitoring the equivalence point with a polymeric membrane-based polyion sensorFerguson, Stephen A.; Wang, Xuewei; Meyerhoff, Mark E.Analytical Methods (2016), 8 (29), 5806-5811CODEN: AMNEGX; ISSN:1759-9679. (Royal Society of Chemistry)Polymeric quaternary ammonium salts (polyquaterniums) have found increasing use in industrial and cosmetic applications in recent years. More specifically, polyquaternium-10 (PQ-10) is routinely used in cosmetic applications as a conditioner in personal care product formulations. Herein, we demonstrate the use of potentiometric polyion-sensitive polymeric membrane-based electrodes to quantify PQ-10 levels. Mixts. contg. both PQ-10 and sodium lauryl sulfate (SLS) are used as model samples to illustrate this new method. SLS is often present in cosmetic samples that contain PQ-10 (e.g., shampoos, etc.) and this surfactant species interferes with the polyion sensor detection chem. However, it is shown here that SLS can be readily sepd. from the PQ-10/SLS mixt. by use of an anion-exchange resin and that the PQ-10 can then be titrated with dextran sulfate (DS). This titrn. is monitored by potentiometric polyanion sensors to provide equivalence points that are directly proportional to PQ-10 concns.
- 181Ferguson, S. A.; Meyerhoff, M. E. Characterization and Quantification of Polyquaterniums via Single Use Polymer Membrane-Based Polyion-Sensitive Electrodes. ACS Sens. 2017, 2, 268– 273, DOI: 10.1021/acssensors.6b00787180https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXmslSlsQ%253D%253D&md5=45428d3c4356daf6602f7656bcf7ccb2Characterization and Quantification of Polyquaterniums via Single-Use Polymer Membrane-Based Polyion-Sensitive ElectrodesFerguson, Stephen A.; Meyerhoff, Mark E.ACS Sensors (2017), 2 (2), 268-273CODEN: ASCEFJ; ISSN:2379-3694. (American Chemical Society)Two facile, robust, and universal methods by which various polymeric quaternary ammonium salts (polyquaterniums (PQs)) can be quantified and characterized using simple potentiometric polymeric membrane polyion-sensitive electrodes as detectors are described. The two methods are (a) direct detection with polycation sensitive membrane electrodes based on the sodium salt of dinonylnaphthalenesulfonate (NaDNNS), and (b) indirect detection using polyanion sensors based on tridodecylmethylammonium chloride (TDMAC) and dextran sulfate (DS) as a titrant to complex the various polyquaternary species (four different PQs: PQ-2, PQ-6, PQ-10, and poly(2-methacryloxyethyltrimethylammonium) chloride (PMETAC)). Direct detection yields information regarding the charge d. of the polycationic species. For the titrn. method, a series of polyanion sensors doped with TDMAC are used to follow a potentiometric titrn. of a PQ species using a syringe pump to deliver the titrant. This indirect detection method is more reliable and yields limits of detection in the ppm range for the four PQs examd. The titrn. method is further explored for detecting excess levels of PQ-6, a common flocculating agent for municipal water supply systems, within the purified water emitted by the Ann Arbor, MI, drinking water treatment plant.
- 182Ferguson, S. A.; Meyerhoff, M. E. Manual and Flow-Injection Detection/Quantification of Polyquaterniums via Fully Reversible Polyion-Sensitive Polymeric Membrane-Based Ion-Selective Electrodes. ACS Sens. 2017, 2, 1505– 1511, DOI: 10.1021/acssensors.7b00527181https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsVagu7vF&md5=540a1f226237c9cf80d5d6708f1b3e0cManual and Flow-Injection Detection/Quantification of Polyquaterniums via Fully Reversible Polyion-Sensitive Polymeric Membrane-Based Ion-Selective ElectrodesFerguson, Stephen A.; Meyerhoff, Mark E.ACS Sensors (2017), 2 (10), 1505-1511CODEN: ASCEFJ; ISSN:2379-3694. (American Chemical Society)The detection of four different polyquaterniums (PQs) using a fully reversible potentiometric polyion sensor in three different detection modes is described. The polyion sensing "pulstrodes" serve as the detector for direct dose-response expts., beaker titrns., and in a flow-injection anal. (FIA) system. Direct polycation response toward PQ-2, PQ-6, PQ-10, and poly(2-methacryloxyethyltrimethylammonium) chloride (PMETAC) yields characteristic information about each PQ species (e.g., relative charge densities, etc.) via syringe pump addn. of each PQ species to a background electrolyte soln. Quant. titrns. were performed using a syringe pump to deliver heparin as the polyanion titrant to quantify all four PQs at μg/mL levels. Both the direct and indirect methods incorporate the use of a three-electrode system including counter, double junction ref., and working electrodes. The working electrode possesses a plasticized poly(vinyl chloride) (PVC) membrane contg. the neutral lipophilic salt of dinonylnaphthalenesulfonate (DNNS-) tridodecylmethylammonium (TDMA+). Further, the titrn. method is useful to quantify PQ-6 levels in recreational swimming pool water collected in Ann Arbor, MI. Finally, a FIA system equipped with a pulstrode detector was used to demonstrate the ability to potentially quantify PQ levels via a more streamlined and semiautomated testing platform.
- 183Cahill, K.; Suttmiller, R.; Oehrle, M.; Sabelhaus, A.; Gemene, K. L. Pulsed Chronopotentiometric Detection of Thrombin Activity Using Reversible Polyion Selective Electrodes. Electroanalysis 2017, 29, 448– 455, DOI: 10.1002/elan.201600401182https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhtlOrt73N&md5=d08683baf1df369dc794a8a55b2833f6Pulsed Chronopotentiometric Detection of Thrombin Activity Using Reversible Polyion Selective ElectrodesCahill, Kaitlin; Suttmiller, Rebecca; Oehrle, Melissa; Sabelhaus, Andrew; Gemene, Kebede L.Electroanalysis (2017), 29 (2), 448-455CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)A simple and rapid electrochem. method for the detection of thrombin activity is presented here for the first time using a synthetic polypeptide substrate and a pulsed chronopotentiometry transduction protocol with polyion selective electrodes. A cathodic current applied across a polyion selective membrane electrode causes the extn. of the polypeptides from the sample into the membrane and the membrane potential, which is a function of the concn. of these polypeptides in the sample, was measured at the same time. Since the polyion extn. is a diffusion-controlled mass transfer process, depletion of the polypeptides at the membrane-sample interface at a characteristic transition time occurs. The square root of the transition time is directly proportional to the concn. of the polypeptide substrate according to the Sand equation. Upon addn. of thrombin, the polypeptide substrate undergoes proteolysis and yields smaller peptide fragments that exhibit smaller measured emf responses since they are less preferred by the membrane, and the transition times become shorter. The rate of change of the square root of the transition time is directly proportional to the change in the polypeptide concn., which in turn relates to the polypeptide hydrolysis time, and can be used for monitoring enzyme activity. Indeed, the square root of transition time is linear with the proteolysis time with R2 = 0.98. The activity of thrombin is 3.6 μg substrate per μg thrombin per Min.
- 184Zhao, G. T.; Ding, J. W.; Yu, H.; Yin, T. J.; Qin, W. Potentiometric Aptasensing of Vibrio alginolyticus Based on DNA Nanostructure-Modified Magnetic Beads. Sensors 2016, 16, 2052, DOI: 10.3390/s16122052183https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXps12kuw%253D%253D&md5=76d48c207f83915f3037063093926e6fPotentiometric aptasensing of Vibrio alginolyticus based on DNA nanostructure-modified magnetic beadsZhao, Guangtao; Ding, Jiawang; Yu, Han; Yin, Tanji; Qin, WeiSensors (2016), 16 (12), 2052/1-2052/9CODEN: SENSC9; ISSN:1424-8220. (MDPI AG)A potentiometric aptasensing assay that couples the DNA nanostructure-modified magnetic beads with a solid-contact polycation-sensitive membrane electrode for the detection of Vibrio alginolyticus is herein described. The DNA nanostructure-modified magnetic beads are used for amplification of the potential response and elimination of the interfering effect from a complex sample matrix. The solid-contact polycation-sensitive membrane electrode using protamine as an indicator is employed to chronopotentiometrically detect the change in the charge or DNA concn. on the magnetic beads, which is induced by the interaction between Vibrio alginolyticus and the aptamer on the DNA nanostructures. The present potentiometric aptasensing method shows a linear range of 10-100 CFU mL-1 with a detection limit of 10 CFU mL-1, and a good specificity for the detection of Vibrio alginolyticus. This proposed strategy can be used for the detection of other microorganisms by changing the aptamers in the DNA nanostructures.
- 185Mikysek, T.; Stoces, M.; Vytras, K. Two Novelties in Ion-pair Formation-based Potentiometric Titrations of Anionic Surfactants. Electroanalysis 2016, 28, 2688– 2691, DOI: 10.1002/elan.201600231184https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhtlOnsrbJ&md5=720064ba9e662297482ab11314b953bbTwo Novelties in Ion-pair Formation-based Potentiometric Titrations of Anionic SurfactantsMikysek, Tomas; Stoces, Matej; Vytras, KarelElectroanalysis (2016), 28 (11), 2688-2691CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)Two novel approaches in ion-pair formation-based potentiometric titrns. of anionic surfactants are presented. First, a new type of the low ohmic coated-wire ion-selective electrode is introduced; the polymeric membrane contg. a plasticizer mixed with carbon powder. Second, didecyldimethylammonium chloride as the cationic titrant is for the first time proposed and applied, providing the titrn. curves with the highest potential jump.
- 186Galovic, O.; Samardzic, M.; Hajdukovic, M.; Sak-Bosnar, M. A new graphene-based surfactant sensor for the determination of anionic surfactants in real samples. Sens. Actuators, B 2016, 236, 257– 267, DOI: 10.1016/j.snb.2016.05.166185https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XpslamsLs%253D&md5=3798cfc42210526bbfb46f9a78aff297A new graphene-based surfactant sensor for the determination of anionic surfactants in real samplesGalovic, Olivera; Samardzic, Mirela; Hajdukovic, Mateja; Sak-Bosnar, MilanSensors and Actuators, B: Chemical (2016), 236 (), 257-267CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)A new high-sensitivity potentiometric all-solid-state sensor for the detn. of anionic surfactants is constructed based on the dimethyldioctadecylammonium-tetraphenylborate (DDA-TPB) ion pair as a sensing material and graphene. Graphene nanoparticles are used for immobilization of the sensing material in the membrane, preventing the leaching of electroactive material from the membrane, thus reducing its elec. resistance and signal noise. The sensor exhibits a Nernstian response for dodecylbenzenesulfonate (DBS) and a sub-Nernstian response for dodecyl sulfate (DS) in the concn. range of 2.5 × 10-7-4.5 × 10-3 M. The detection limits for DS and DBS are 1.5 × 10-7 and 2.5 × 10-7 M, resp. The sensor demonstrates a stable potentiometric response with a signal drift of -1.2 mV/h and exhibits excellent selectivity performance for DS over almost all of the org. and inorg. anions commonly used in com. products. The main application of the sensor is in the detection of the endpoint in potentiometric titrns. of anionic surfactants. The magnitudes of inflexion at the equivalence point range from 174 to 270 mV. The sensor shows satisfactory anal. performance within a pH range of 2-7. The two-component mixts. contg. sodium decanesulfonate (C10) and sodium dodecanesulfonate (C12) are also successfully differentially titrated.
- 187Khaled, E.; Hassan, H. N. A.; Abdelaziz, M. A.; El-Attar, R. O. Novel Enzymatic Potentiometric Approaches for Surfactant Analysis. Electroanalysis 2017, 29, 716– 721, DOI: 10.1002/elan.201600565186https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xhs1Cksr%252FF&md5=0a775258acb45a5ea8e5a93ba40fa82bNovel Enzymatic Potentiometric Approaches for Surfactant AnalysisKhaled, Elmorsy; Hassan, Hassan N. A.; Abdelaziz, Mona A.; El-Attar, Rehab O.Electroanalysis (2017), 29 (3), 716-721CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)The present study described a novel application of simple potentiometric enzymic method for anal. of surfactants based on their inhibitory effect on acetylcholinesterase enzyme (AChE). The enzymic activity was measured through monitoring hydrolysis of acetylcholine (ACh) with a disposable acetylcholine potentiometric sensor. Comprehensive investigations were carried out including the effect of incubation time, cholinesterase enzyme and the working calibration ranges. Based on inhibition of AChE, different cationic, anionic and nonionic surfactants were detd. in the concn. range from 0 to 40 μg mL-1 with detection limits reaching 0.07 μg mL-1 depending on the nature of surfactants. The degree of AChE inhibition caused by different tested surfactants were as follows: cetylpyridinium chloride (CPC)>benzyldimethylhexadecyl ammonium chloride (BDHAC)>Hyamine (Hy)>cetyltrimethylammonium bromide (CTAB)>Triton X-100 (TX-100)>sodium dodecyl sulfate (SDS). The proposed method was applied for detn. of surfactants in pharmaceutical formulation, detergents products and environmental samples with acceptable sensitivity and reproducibility.
