Surface Nanostructure Effects on Dopamine Adsorption and Electrochemistry on Glassy Carbon ElectrodesClick to copy article linkArticle link copied!
- Dalia L. SwinyaDalia L. SwinyaDepartment of Chemistry, University of Warwick, Coventry CV4 7AL, United KingdomMore by Dalia L. Swinya
- Daniel Martín-Yerga*Daniel Martín-Yerga*Email: [email protected]Department of Chemistry, University of Warwick, Coventry CV4 7AL, United KingdomMore by Daniel Martín-Yerga
- Marc WalkerMarc WalkerDepartment of Physics, University of Warwick, Coventry CV4 7AL, United KingdomMore by Marc Walker
- Patrick R. Unwin*Patrick R. Unwin*Email: [email protected]Department of Chemistry, University of Warwick, Coventry CV4 7AL, United KingdomMore by Patrick R. Unwin
Abstract
Dopamine (DA) adsorption and electron-transfer kinetics are strongly sensitive to the structure and composition of carbon electrodes. Activation of carbon surfaces is a popular method to improve DA detection, but the role of carbon structural features on DA behavior remains uncertain. Herein, we use scanning electrochemical cell microscopy (SECCM) for local anodization of glassy carbon (GC) electrodes in acid media followed by electrochemical imaging of DA adsorption and electrochemistry covering both unmodified and anodized GC regions of the same electrode. Electrochemical measurements of adsorbed DA involve the delivery of DA from the SECCM meniscus (30 μM) for 1 s periods followed by voltammetric analysis at a reasonable sweep rate (47 V s–1). This general approach reduces effects from interelectrode variability and allows for considerable numbers of measurements and statistical analysis of electrochemical data sets. Localized electrode activity is correlated to surface structure and chemistry by a range of characterization techniques. Anodization enhances DA electron-transfer kinetics and provides more sites for adsorption (higher specific surface area). A consequence is that adsorption takes longer to approach completion on the anodized surface. In fact, normalizing DA surface coverage by the electrochemical surface area (ECSA) reveals that adsorption is less extensive on anodized surfaces compared to as-prepared GC on the same time scale. Thus, ECSA, which has often been overlooked when calculating DA surface coverage on carbon electrodes, even where different activation methods would be expected to result in different surface roughness and nanostructure, is an important consideration. Lower graphitic and higher oxygen content on anodized GC also suggest that oxygen-containing functional groups do not necessarily enhance DA adsorption and may have the opposite effect. This work further demonstrates SECCM as a powerful technique for revealing surface structure–function relationships and correlations at heterogeneous electrodes.
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You are free to share(copy and redistribute) this article in any medium or format and to adapt(remix, transform, and build upon) the material for any purpose, even commercially within the parameters below:
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License Summary*
You are free to share(copy and redistribute) this article in any medium or format and to adapt(remix, transform, and build upon) the material for any purpose, even commercially within the parameters below:
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Attribution (BY): Credit must be given to the creator.
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Introduction
Methods
Materials and Chemicals
Local Electrochemical Measurements
Surface Characterization
Results and Discussion
Characterization of Locally Anodized Glassy Carbon
Dopamine Adsorption and Oxidation on Locally Anodized Glassy Carbon
Effect of Anodization on Electron-Transfer Kinetics
Effect of the Electrochemical Surface Area on the Apparent Dopamine Adsorption
Effect of Anodization Time on Dopamine Adsorption and Reactivity
Conclusions
Supporting Information
The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.jpcc.2c02801.
Additional electrochemical data and XPS and EDS spectra (PDF)
Spatially resolved electrochemical (i–E) movie (110 pixels over a 55 × 50 μm scan area, hopping distance = 5 μm) obtained with the SECCM protocol (first voltammetric cycle), visualizing the activity of DA oxidation on a GC surface locally anodized for 60 s. The pipet probe contained 30 μM DA in PBS, and the scan rate was 47 V s–1 (MP4)
Spatially resolved electrochemical (i–E) movie (110 pixels over a 55 × 50 μm scan area, hopping distance = 5 μm) obtained with the SECCM protocol (fifth voltammetric cycle), visualizing the activity of DA oxidation on a GC surface locally anodized for 60 s. The pipet probe contained 30 μM DA in PBS, and the scan rate was 47 V s–1 (MP4)
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Acknowledgments
D.L.S. acknowledges the Libyan Ministry of Higher Education and Scientific Research for funding. D.M.-Y. and P.R.U. acknowledge funding from the EPSRC UK Faraday Institution (EP/S003053/1) through the Characterisation project (FIRG013). We thank Dr. Ben Breeze for helping with Raman measurements and Xiangdong Xu for SEM imaging and the use of the Spectroscopy and Electron Microscopy Research Technology Platforms at the University of Warwick.
References
This article references 70 other publications.
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- 11Patel, A. N.; Tan, S.; Miller, T. S.; Macpherson, J. V.; Unwin, P. R. Comparison and Reappraisal of Carbon Electrodes for the Voltammetric Detection of Dopamine. Anal. Chem. 2013, 85, 11755– 11764, DOI: 10.1021/ac401969qGoogle Scholar11https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhslyms7zF&md5=95ab8dfec178dca70c369b20bc68f6edComparison and Reappraisal of Carbon Electrodes for the Voltammetric Detection of DopaminePatel, Anisha N.; Tan, Sze-yin; Miller, Thomas S.; Macpherson, Julie V.; Unwin, Patrick R.Analytical Chemistry (Washington, DC, United States) (2013), 85 (24), 11755-11764CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)The electrooxidn. of dopamine (DA) was studied on the unmodified surfaces of five different classes of C electrodes: glassy C (GC), O-terminated polycryst. B-doped diamond (pBDD), edge plane pyrolytic graphite (EPPG), basal plane pyrolytic graphite (BPPG), and the basal surface of highly oriented pyrolytic graphite (HOPG), encompassing five distinct grades with step edge d. and coverage varying by >2 orders of magnitude. Surfaces were prepd. carefully and characterized by a range of techniques, including at. force microscopy (AFM), field emission SEM (FE-SEM), and Raman spectroscopy. Although pBDD is the least susceptible to surface fouling (even at relatively high DA concns.), the reaction showed sluggish kinetics on this electrode. In contrast, DA electrooxidn. at pristine basal plane HOPG at concns. ≤100 μM in 0.15 M PBS, pH 7.2, showed fast kinetics and only minor susceptibility toward surface fouling from DA byproducts, although the extent of HOPG surface contamination by oxidn. products increased substantially at higher concns. (with the response similar on all grades, irresp. of step edge coverage). EPPG also showed a fast response, with little indication of passivation with repeated voltammetric cycling but a relatively high background signal due to the high capacitance of this graphite surface termination. Of all five C electrode types, freshly cleaved basal plane HOPG showed the clearest signal (distinct from the background) at low concns. of DA (<10 μM) as a consequence of the low capacitance. Studies of the electrochem. oxidn. of DA in the presence of the common interferents ascorbic acid (AA) and serotonin (5-HT), of relevance to neurochem. anal., showed that the signals for DA were still clearly and easily resolved at basal plane HOPG surfaces. In the presence of AA, repetitive voltammetry caused products of AA electrooxidn. to adsorb onto the HOPG surface, forming a permselective film that allowed the electrochem. oxidn. of DA to proceed unimpeded, while greatly inhibiting the electrochem. response of AA itself. The studies presented provide conclusive evidence that the pristine surface of basal plane HOPG is highly active for the detection of DA, irresp. of the step edge d. and method of cleavage, and adds to a growing body of evidence that the basal plane of HOPG is a much more active electrode for many classes of electrode reactions than previously believed.
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- 13McCreery, R. L. Advanced Carbon Electrode Materials for Molecular Electrochemistry. Chem. Rev. 2008, 108, 2646– 2687, DOI: 10.1021/cr068076mGoogle Scholar13https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXnt1Wjsb8%253D&md5=7f0e9958035ae161b937dd0508b959bfAdvanced Carbon Electrode Materials for Molecular ElectrochemistryMcCreery, Richard L.Chemical Reviews (Washington, DC, United States) (2008), 108 (7), 2646-2687CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)A review. The properties of C are described and how these properties relate electrochem. properties, including electrode kinetics, adsorption and electrocatalysis. Fabrication and novel aspects are described for carbon materials, including, boron-doped diamond, carbon nanotubes, vapor deposited carbon films and various composite electrodes. Carbon electrode material for org. and biol. redox reactions are cited.
- 14Venton, B. J.; Cao, Q. Fundamentals of Fast-Scan Cyclic Voltammetry for Dopamine Detection. Analyst 2020, 145, 1158– 1168, DOI: 10.1039/C9AN01586HGoogle Scholar14https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXisVyqsrnP&md5=7c87cc2797c92a70ad60a638f9b74056Fundamentals of fast-scan cyclic voltammetry for dopamine detectionVenton, B. Jill; Cao, QunAnalyst (Cambridge, United Kingdom) (2020), 145 (4), 1158-1168CODEN: ANALAO; ISSN:0003-2654. (Royal Society of Chemistry)A review. Fast-scan cyclic voltammetry (FSCV) was used with carbon-fiber microelectrodes for the real-time detection of neurotransmitters on the subsecond time scale. With FSCV, the potential is ramped up from a holding potential to a switching potential and back, usually at a 400 V s-1 scan rate and a frequency of 10 Hz. The plot of current vs. applied potential, the cyclic voltammogram (CV), has a very different shape for FSCV than for traditional cyclic voltammetry collected at scan rates which are 1000-fold slower. Here, the authors explore the theory of FSCV, with a focus on dopamine detection. First, the authors examine the shape of the CVs. Background currents, which are 100-fold higher than faradaic currents, are subtracted out. Peak sepn. is primarily due to slow electron transfer kinetics, while the sym. peak shape is due to exhaustive electrolysis of all the adsorbed neurotransmitters. Second, the authors explain the origins of the dopamine waveform, and the factors that limit the holding potential (oxygen redn.), switching potential (water oxidn.), scan rate (electrode instability), and repetition rate (adsorption). Third, data anal., from data visualization with color plots, to the automated algorithms like principal components regression that distinguish dopamine from pH changes are discussed. Finally, newer applications are discussed, including optimization of waveforms for analyte selectivity, carbon nanomaterial electrodes that trap dopamine, and basal level measurements that facilitate neurotransmitter measurements on a longer time scale. FSCV theory is complex, but understanding it enables better development of new techniques to monitor neurotransmitters in vivo.
- 15Thiagarajan, S.; Tsai, T.-H.; Chen, S.-M. Easy Modification of Glassy Carbon Electrode for Simultaneous Determination of Ascorbic Acid, Dopamine and Uric Acid. Biosens. Bioelectron. 2009, 24, 2712– 2715, DOI: 10.1016/j.bios.2008.12.010Google Scholar15https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXjvVyltbw%253D&md5=8eccb096c0a20732f3b9f64843ea2908Easy modification of glassy carbon electrode for simultaneous determination of ascorbic acid, dopamine and uric acidThiagarajan, Soundappan; Tsai, Tsung-Hsuan; Chen, Shen-MingBiosensors & Bioelectronics (2009), 24 (8), 2712-2715CODEN: BBIOE4; ISSN:0956-5663. (Elsevier B.V.)A glassy carbon electrode (GCE) was modified by electrochem. oxidn. in mild acidic media (0.1 mol L-1 H2SO4) and could be applied for individual and simultaneous detn. of ascorbic acid (AA), dopamine (DA), and uric acid (UA). Oxidized GCE shows a single redox couple (E0' = -2.5 mV) which is based on the formation functional groups during the electrochem. pretreatment process. The proposed GCE successfully decreases the over potentials for the oxidn. process of these species (AA, DA, and UA) compared with bare GCE. The oxidized GCE has its own simplicity, stability, high sensitivity, and possesses the potential for simultaneous detn. of AA, DA, and UA.
- 16Sansuk, S.; Bitziou, E.; Joseph, M. B.; Covington, J. A.; Boutelle, M. G.; Unwin, P. R.; Macpherson, J. V. Ultrasensitive Detection of Dopamine Using a Carbon Nanotube Network Microfluidic Flow Electrode. Anal. Chem. 2013, 85, 163– 169, DOI: 10.1021/ac3023586Google Scholar16https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhsleqtLnM&md5=422de4efd3fc1d0c4f2e829514223ec6Ultrasensitive Detection of Dopamine Using a Carbon Nanotube Network Microfluidic Flow ElectrodeSansuk, Siriwat; Bitziou, Eleni; Joseph, Maxim B.; Covington, James A.; Boutelle, Martyn G.; Unwin, Patrick R.; MacPherson, Julie V.Analytical Chemistry (Washington, DC, United States) (2013), 85 (1), 163-169CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)The electrochem. measurement of dopamine (DA), in phosphate buffer soln. (pH 7.4), with a limit of detection (LOD) of ∼5 pM in 50 μL (∼ 250 attomol) is achieved using a band electrode comprised of a sparse network of pristine single-walled carbon nanotubes (SWNTs), which covers <1% of the insulating substrate. The SWNT electrodes are deployed as amperometric (anodic) detectors in microfluidic cells, produced by microstereolithog., designed specifically for flow injection anal. (FIA). The flow cells, have a channel (duct) geometry, with cell height of 25 μm, and are shown to be hydrodynamically well-defined, with laminar Poiseuille flow. In the arrangement where soln. continuously flows over the electrode but the electrode is only exposed to the analyte for short periods of time, the SWNT electrodes do not foul and can be used repeatedly for many months. The LOD for dopamine (DA), reported herein, is significantly lower than previous reports using FIA-electrochem. detection. Furthermore, the SWNT electrodes can be used as grown, i.e., they do not require chem. modification or cleanup. The extremely low background signals of the SWNT electrodes, as a consequence of the sparse surface coverage and the low intrinsic capacitance of the SWNTs, means that no signal processing is required to measure the low currents for DA oxidn. at trace levels. DA detection in artificial cerebral fluid is also possible with a LOD of ∼50 pM in 50 μL (∼2.5 fmol).
- 17Schmidt, A. C.; Wang, X.; Zhu, Y.; Sombers, L. A. Carbon Nanotube Yarn Electrodes for Enhanced Detection of Neurotransmitter Dynamics in Live Brain Tissue. ACS Nano 2013, 7, 7864– 7873, DOI: 10.1021/nn402857uGoogle Scholar17https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXht1Ghs7bK&md5=cb67d35dec757652c58cf51917a943ecCarbon Nanotube Yarn Electrodes for Enhanced Detection of Neurotransmitter Dynamics in Live Brain TissueSchmidt, Andreas C.; Wang, Xin; Zhu, Yuntian; Sombers, Leslie A.ACS Nano (2013), 7 (9), 7864-7873CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)This work demonstrates the potential of nanoscale carbon electrode materials for improved detection of electroactive neurotransmitter dynamics in the brain. Individual multiwalled carbon nanotubes were synthesized via chem. vapor deposition, spun into yarns, and used in the fabrication of disk microelectrodes that were subsequently characterized using scanning electron and at. force microscopies. The carbon nanotube yarn electrodes were coupled with fast-scan cyclic voltammetry and used to discriminately detect rapid neurotransmitter fluctuations in acute brain slices. The results demonstrate that the distinct structural and electronic properties of the nanotubes result in improved selectivity, sensitivity, and spatial resoln., as well as faster apparent electron transfer kinetics when compared to the conventional carbon-fiber microelectrodes typically used in vivo.
- 18Martín-Yerga, D.; Costa Rama, E.; Costa García, A. Electrochemical Study and Determination of Electroactive Species with Screen-Printed Electrodes. J. Chem. Educ. 2016, 93, 1270– 1276, DOI: 10.1021/acs.jchemed.5b00755Google Scholar18https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xls1Orsrk%253D&md5=78555a5d619c04c4219161e0c68abfedElectrochemical Study and Determination of Electroactive Species with Screen-Printed ElectrodesMartin-Yerga, Daniel; Costa Rama, Estefania; Costa Garcia, AgustinJournal of Chemical Education (2016), 93 (7), 1270-1276CODEN: JCEDA8; ISSN:0021-9584. (American Chemical Society and Division of Chemical Education, Inc.)A lab appropriate to introduce voltammetric techniques and basic electrochem. parameters is described in this work. It is suitable to study theor. concepts of electrochem. in an applied way for anal. undergraduate courses. Two electroactive species, hexaammineruthenium and dopamine, are used as simple redox systems. Screen-printed electrodes are used in order to allow the students to focus on the electrochem. and avoid tedious instrumentation prepn. The anal. detn. of the species studied with sensitive techniques such as differential-pulse or square-wave voltammetry is also performed.
- 19Suzuki, A.; Ivandini, T. A.; Yoshimi, K.; Fujishima, A.; Oyama, G.; Nakazato, T.; Hattori, N.; Kitazawa, S.; Einaga, Y. Fabrication, Characterization, and Application of Boron-Doped Diamond Microelectrodes for in Vivo Dopamine Detection. Anal. Chem. 2007, 79, 8608– 8615, DOI: 10.1021/ac071519hGoogle Scholar19https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXhtFalurnM&md5=e9fb365269a0b600e7df8d8fad6cf81fFabrication, characterization, and application of boron-doped diamond microelectrodes for in vivo dopamine detectionSuzuki, Akane; Ivandini, Tribidasari A.; Yoshimi, Kenji; Fujishima, Akira; Oyama, Genko; Nakazato, Taizo; Hattori, Nobutaka; Kitazawa, Shigeru; Einaga, YasuakiAnalytical Chemistry (Washington, DC, United States) (2007), 79 (22), 8608-8615CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Highly boron-doped diamond (BDD) was deposited on chem. etched micrometer-sized tungsten wires using microwave plasma assisted chem. vapor deposition (MPCVD), and these were used to fabricate BDD microelectrodes. BDD microelectrodes with very small diam. (about 5 μm) and 250 μm in length could be made successfully. In addn. to the unique properties of BDD electrodes, such as a very low background current, high stability, and selective oxidn. of dopamine (DA) in the presence of ascorbic acid (AA), other superior properties of the microelectrodes, including a const. current response, an increase in the mass transport, and the ability for use in high resistance media were also shown. An application study was conducted for in vivo detection of DA in mouse brain, where the BDD microelectrode was inserted into the corpus striatum of the mouse brain. A clear signal current response following medial forebrain bundle (MFB) stimulation could be obtained with high sensitivity. Excellent stability was achieved, indicating that the BDD microelectrodes are very promising for future in vivo electroanal.
- 20Sánchez Calvo, A.; Botas, C.; Martín-Yerga, D.; Álvarez, P.; Menéndez, R.; Costa-García, A. Comparative Study of Screen-Printed Electrodes Modified with Graphene Oxides Reduced by a Constant Current. J. Electrochem. Soc. 2015, 162, B282, DOI: 10.1149/2.1021510jesGoogle ScholarThere is no corresponding record for this reference.
- 21Yang, C.; Wang, Y.; Jacobs, C. B.; Ivanov, I. N.; Venton, B. J. O2 Plasma Etching and Antistatic Gun Surface Modifications for CNT Yarn Microelectrode Improve Sensitivity and Antifouling Properties. Anal. Chem. 2017, 89, 5605– 5611, DOI: 10.1021/acs.analchem.7b00785Google Scholar21https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXmt12kt7s%253D&md5=b92895213511294e2046e9e6fbd0d7c9O2 Plasma Etching and Antistatic Gun Surface Modifications for CNT Yarn Microelectrode Improve Sensitivity and Antifouling PropertiesYang, Cheng; Wang, Ying; Jacobs, Christopher B.; Ivanov, Ilia N.; Venton, B. JillAnalytical Chemistry (Washington, DC, United States) (2017), 89 (10), 5605-5611CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Carbon nanotube (CNT) based microelectrodes exhibit rapid and selective detection of neurotransmitters. While different fabrication strategies and geometries of CNT microelectrodes have been characterized, relatively little research has investigated ways to selectively enhance their electrochem. properties. In this work, the authors introduce two simple, reproducible, low-cost, and efficient surface modification methods for carbon nanotube yarn microelectrodes (CNTYMEs): O2 plasma etching and antistatic gun treatment. O2 plasma etching was performed by a microwave plasma system with oxygen gas flow and the optimized time for treatment was 1 min. The antistatic gun treatment flows ions by the electrode surface; two triggers of the antistatic gun was the optimized no. on the CNTYME surface. Current for dopamine at CNTYMEs increased 3-fold after O2 plasma etching and 4-fold after antistatic gun treatment. When the two treatments were combined, the current increased 12-fold, showing the two effects are due to independent mechanisms that tune the surface properties. O2 plasma etching increased the sensitivity due to increased surface oxygen content but did not affect surface roughness while the antistatic gun treatment increased surface roughness but not oxygen content. The effect of tissue fouling on CNT yarns was studied for the first time, and the relatively hydrophilic surface after O2 plasma etching provided better resistance to fouling than unmodified or antistatic gun treated CNTYMEs. Overall, O2 plasma etching and antistatic gun treatment improve the sensitivity of CNTYMEs by different mechanisms, providing the possibility to tune the CNTYME surface and enhance sensitivity.
- 22Jacobs, C. B.; Vickrey, T. L.; Venton, B. J. Functional Groups Modulate the Sensitivity and Electron Transfer Kinetics of Neurochemicals at Carbon Nanotube Modified Microelectrodes. Analyst 2011, 136, 3557– 3565, DOI: 10.1039/c0an00854kGoogle Scholar22https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXpvFCqsbY%253D&md5=212086d8c0800ed68d848f193f80678dFunctional groups modulate the sensitivity and electron transfer kinetics of neurochemicals at carbon nanotube modified microelectrodesJacobs, Christopher B.; Vickrey, Trisha L.; Venton, B. JillAnalyst (Cambridge, United Kingdom) (2011), 136 (17), 3557-3565CODEN: ANALAO; ISSN:0003-2654. (Royal Society of Chemistry)The surface properties of carbon-based electrodes are critically important for the detection of biomols. and can modulate electrostatic interactions, adsorption and electrocatalysis. Carbon nanotube (CNT) modified electrodes have previously been shown to have increased oxidative sensitivity and reduced overpotential for catecholamine neurotransmitters, but the effect of surface functionalities on these properties has not been characterized. In this study, we modified carbon-fiber microelectrodes (CFMEs) with three differently functionalized single-wall carbon nanotubes and measured their response to serotonin, dopamine, and ascorbic acid using fast-scan cyclic voltammetry. Both carboxylic acid functionalized and amide functionalized CNTs increased the oxidative current of CFMEs by approx. 2-6 fold for the cationic neurotransmitters serotonin and dopamine, but octadecylamine functionalized CNTs resulted in no significant signal change. Similarly, electron transfer was faster for both amide and carboxylic acid functionalized CNT modified electrodes but slower for octadecylamine CNT modified electrodes. Oxidn. of ascorbic acid was only increased with carboxylic acid functionalized CNTs although all CNT-modified electrodes showed a trend towards increased reversibility for ascorbic acid. Carboxylic acid-CNT modified disk electrodes were then tested for detection of serotonin in the ventral nerve cord of a Drosophila melanogaster larva, and the increase in sensitivity was maintained in biol. tissue. The functional groups of CNTs therefore modulate the electrochem. properties, and the increase in sensitivity from CNT modification facilitates measurements in biol. samples.
- 23Bath, B. D.; Michael, D. J.; Trafton, B. J.; Joseph, J. D.; Runnels, P. L.; Wightman, R. M. Subsecond Adsorption and Desorption of Dopamine at Carbon-Fiber Microelectrodes. Anal. Chem. 2000, 72, 5994– 6002, DOI: 10.1021/ac000849yGoogle Scholar23https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXotVyis7s%253D&md5=6e2c2e1202ae88e8ec4bfbcd274dc976Subsecond adsorption and desorption of dopamine at carbon-fiber microelectrodesBath, Bradley D.; Michael, Darren J.; Trafton, B. Jill; Joseph, Joshua D.; Runnels, Petrise L.; Wightman, R. MarkAnalytical Chemistry (2000), 72 (24), 5994-6002CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)High-repetition fast-scan cyclic voltammetry and chronoamperometry were used to quantify and characterize the kinetics of dopamine and dopamine-o-quinone adsorption and desorption at carbon-fiber microelectrodes. A flow injection anal. system was used for the precise introduction and removal of a bolus of electroactive substance on a sub-second time scale to the disk-shaped surface of a microelectrode that was fabricated from a single carbon fiber (Thornel type T650 or P55). Pretreatment of the electrode surfaces consisted of soaking them in purified iso-Pr alc. for a min. of 10 min, which resulted in S/N increasing by 200-400% for dopamine above that for those that were soaked in reagent grade solvent. Because of adsorption, high scan rates (2000 V/s) are shown to exhibit equiv. S/N ratios as compared to slower, more traditional scan rates. In addn., the steady-state response to a concn. bolus is shown to occur more rapidly when cyclic voltammetric scans are repeated at short intervals (4 ms). The new methodologies allow for more accurate detns. of the kinetics of neurotransmitter release events (10-500 ms) in biol. systems. Brain slice and in vivo expts. using T650 cylinder microelectrodes show that voltammetrically measured uptake kinetics in the caudate are faster using 2000 V/s and 240 Hz measurements, as compared to 300 V/s and 10 Hz.
- 24Heien, M. L. A. V.; Phillips, P. E. M.; Stuber, G. D.; Seipel, A. T.; Wightman, R. M. Overoxidation of Carbon-Fiber Microelectrodes Enhances Dopamine Adsorption and Increases Sensitivity. Analyst 2003, 128, 1413– 1419, DOI: 10.1039/b307024gGoogle Scholar24https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXpsFymsLY%253D&md5=6eaf749094e6cd0faf2d8d169b2220f8Overoxidation of carbon-fiber microelectrodes enhances dopamine adsorption and increases sensitivityHeien, Michael L. A. V.; Phillips, Paul E. M.; Stuber, Garret D.; Seipel, Andrew T.; Wightman, R. MarkAnalyst (Cambridge, United Kingdom) (2003), 128 (12), 1413-1419CODEN: ANALAO; ISSN:0003-2654. (Royal Society of Chemistry)The voltammetric responses of carbon-fiber microelectrodes with a 1.0 V and a 1.4 V anodic limit were compared in this study. Fast-scan cyclic voltammetry was used to characterize the response to dopamine and several other neurochems. An increase in the adsorption properties of the carbon fiber leads to an increase in sensitivity of 9-fold in vivo. However the temporal response of the sensor is slower with the more pos. anodic limit. Increased electron transfer kinetics also causes a decrease in the relative sensitivity for dopamine vs. other neurochems., and a change in their cyclic voltammograms. Stimulated release in the caudate-putamen was pharmacol. characterized in vivo using Ro-04-1284 and pargyline, and was consistent with that expected for dopamine.
- 25Li, Y.; Ross, A. E. Plasma-Treated Carbon-Fiber Microelectrodes for Improved Purine Detection with Fast-Scan Cyclic Voltammetry. Analyst 2020, 145, 805– 815, DOI: 10.1039/C9AN01636HGoogle Scholar25https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXit1Kqsb%252FM&md5=f4408cb75c5f280272acfec43d7dd2a8Plasma-treated carbon-fiber microelectrodes for improved purine detection with fast-scan cyclic voltammetryLi, Yuxin; Ross, Ashley E.Analyst (Cambridge, United Kingdom) (2020), 145 (3), 805-815CODEN: ANALAO; ISSN:0003-2654. (Royal Society of Chemistry)Here, the authors developed N2 and O2 plasma-treated carbon-fiber microelectrodes (CFME) for improved purine detection with fast-scan cyclic voltammetry (FSCV). Plasma treatment affects the topol. and functionality of carbon which impacts the electrode-analyte interaction. CFME's are less sensitive to purines compared to catecholamines. Knowledge of how the electrode surface drives purine-electrode interaction would provide insight into methods to improve purine detection. Here, plasma-treated CFME's with N2 and O2 plasma was used to study the extent to which the surface functionality and topol. affects purine detection and to improve purine sensing with FSCV. On av., O2 plasma increased the oxidative current for adenosine and ATP by 6.0 ± 1.2-fold and 6.4 ± 1.6-fold, and guanosine and GTP by 2.8 ± 0.47-fold and 5.8 ± 1.4-fold, resp. (n = 9). The O2 plasma increased the surface roughness and oxygen functionality. N2 plasma increased the oxidative current for adenosine and ATP by 1.5 ± 0.15-fold and 1.9 ± 0.23-fold, and guanosine and GTP by 1.4 ± 0.20-fold and 1.5 ± 0.20-fold, resp. (n = 11). N2 plasma increased the nitrogen functionality with minimal increases in roughness. Both plasma treatments impacted purines more than dopamine. Langmuir isotherms revealed that both plasma gases impact the theor. surface coverage and adsorption strength of purines at the electrode. Overall, purine detection is improved at surfaces with increased surface roughness, and oxygen and amine functionality. Plasma-treated CFMEs could be used in the future to study the analyte-electrode interaction of other neurochems.
- 26Fagan, D. T.; Hu, I. F.; Kuwana, T. Vacuum Heat-Treatment for Activation of Glassy Carbon Electrodes. Anal. Chem. 1985, 57, 2759– 2763, DOI: 10.1021/ac00291a006Google Scholar26https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2MXlvVGlu7c%253D&md5=528592970c8a368e7379b20e16f4a9b8Vacuum heat-treatment for activation of glassy carbon electrodesFagan, Dan T.; Hu, Ing Feng; Kuwana, TheodoreAnalytical Chemistry (1985), 57 (14), 2759-63CODEN: ANCHAM; ISSN:0003-2700.Heat treatment of glassy C (gc) at 725° under high vacuum (<2 × 10-6 torr was shown to produce an active electrode for the redox reaction of ferri-/ferrocyanide and the oxidn. of ascorbic acid. Electrons treated by this method exhibit a dramatic redn. in the background charging current as indicated gy chronocoulometry. Differential pulse voltammetry indicates that O surface functional groups are removed by vacuum heat treatment (VHT) and XPS shows a factor of 6 redn. in the O content of the surface. The main reasons for activation are believed to be due to an increase in the active site d. as a consequence of the removal of surface contaminants and the exposure of fresh C.
- 27Poon, M.; McCreery, R. L. In Situ Laser Activation of Glassy Carbon Electrodes. Anal. Chem. 1986, 58, 2745– 2750, DOI: 10.1021/ac00126a036Google Scholar27https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL28XlvVSgsro%253D&md5=ac191ef7f9b8cdc0fc9c36db6be19deaIn situ laser activation of glassy carbon electrodesPoon, Melanie; McCreery, Richard L.Analytical Chemistry (1986), 58 (13), 2745-50CODEN: ANCHAM; ISSN:0003-2700.Laser pulses of short duration (10 ns) and high intensity (20 MW/cm2) canincrease the rate of heterogeneous electron transfer at a glassy C electrode by 1-3 orders of magnitude. The laser pulse may be delivered in situ, directly in the soln. of interest, repeatedly if desired. The heterogeneous electron transfer rate const., k°, for the ferri-ferrocyanide redox system increases from 0.004 to 0.20 cm s-1 with laser activation, resulting in the highest k° yet obsd. for this system on glassy C. Laser activation results in minor morphol. changes to the surface, as obsd. by SEM, mainly removal of an apparent layer of C microparticles. The technique holds promise as a means to repeatedly activate glassy C electrodes in situ, thus circumventing the need for renewal or reactivation by polishing or other ex situ treatments.
- 28Rice, R. J.; Pontikos, N. M.; McCreery, R. L. Quantitative Correlations of Heterogeneous Electron-Transfer Kinetics with Surface Properties of Glassy Carbon Electrodes. J. Am. Chem. Soc. 1990, 112, 4617– 4622, DOI: 10.1021/ja00168a001Google Scholar28https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3cXisVajtbo%253D&md5=49aae9fd2f0978fa800df00927c192f9Quantitative correlations of heterogeneous electron-transfer kinetics with surface properties of glassy carbon electrodesRice, Ronald J.; Pontikos, Nicholas M.; McCreery, Richard L.Journal of the American Chemical Society (1990), 112 (12), 4617-22CODEN: JACSAT; ISSN:0002-7863.Raman spectra, capacitance (C°), phenanthrenequinone (PQ) adsorption, and heterogeneous electron-transfer rates for ferri/ferrocyanide, dopamine, and ascorbic acid were monitored after fracturing, polishing, and laser activating glassy C electrodes (GC-30). Alterations in the Raman spectrum indicate changes in C microstructure, while PQ adsorption and C° provide measures of microscopic surface area. Polishing caused minor changes in C disorder and microscopic surface area, but the polished surface had poor electron-transfer kinetics. Laser activation increased k° for Fe(CN)63-/4- by at least a factor of 200 but increased PQ adsorption and C° by less than 50% and had negligible effects on the Raman spectrum. A k° of above 0.5 cm s-1 was obsd. for Fe(CN)63-/4- for the first time. A clean, fractured GC surface exhibited a k° of 0.5 cm s-1 and was very active toward ascorbic acid and dopamine oxidn. The results are consistent with a surface-cleaning mechanism for laser activation, accompanied by little or no observable surface restructuring or roughening. The results on GC are in contrast to those on laser activation of highly oriented pyrolytic graphite, where the mechanism involved formation of active sites. The conclusions reached here permit evaluation of the main variables affecting electron-transfer rate for Fe(CN)63-/4-, ascorbic acid, and dopamine on GC. The active sites for electron transfer are on graphite edges inherent in the GC structure, and the principal function of the laser is exposure of these sites by removal of chemi- and physisorbed impurities.
- 29DeClements, R.; Swain, G. M.; Dallas, T.; Holtz, M. W.; Herrick, R. D.; Stickney, J. L. Electrochemical and Surface Structural Characterization of Hydrogen Plasma Treated Glassy Carbon Electrodes. Langmuir 1996, 12, 6578– 6586, DOI: 10.1021/la960380vGoogle Scholar29https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28XntFyjtbs%253D&md5=87c248730d11366b19444ee26c81b74bElectrochemical and surface structural characterization of hydrogen plasma-treated glassy carbon electrodesDeClements, Roger; Swain, Greg M.; Dallas, Tim; Holtz, Mark W.; Herrick, Robert D., II; Stickney, John L.Langmuir (1996), 12 (26), 6578-6586CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)Electrochem. and structural characterization of glassy carbon (GC) electrodes exposed to the plasma conditions necessary to nucleate and grow diamond were performed for the first time. The electrodes are referred to as diamond-coated (DGC) if the surface was exposed to a CH4/H2 plasma and as hydrogenated (HGC) if the surface was exposed to only an H2 plasma. Continuous diamond films were formed on the surfaces exposed to both plasma conditions, but due to poor adhesion, the films were easily lifted, exposing a modified GC surface. The results demonstrate that these modified surfaces exhibit lower voltammetric background currents and higher faradaic currents for Fe(CN)64-/3- than does freshly polished GC. The enhanced signal-to-background (S/B) ratios lead to lower limits of detection for this redox analyte. The electrodes exhibited near-Nernstian behavior (ΔEp ∼70-85 mV) for this redox analyte without any conventional surface pretreatment, and the response remained stable for long periods of time up to several weeks. The nucleation and growth mechanism of diamond on GC first involves hydrogenation of the unsatd. edge plane sites on the surface, producing an sp3 bonded "diamond-like" phase. These surfaces are relatively O2-free, as H is chemisorbed at the edge plane sites, replacing the O functional groups. Formation of this surface phase is followed by subsequent nucleation and growth of a diamond film. Voltammetric data for Fe(CN)64-/3-, Ru(NH3)62+/3+, Fe2+/3+, and ascorbic acid at these surfaces are presented as are structural characterization data by SEM, at. force microscopy, Raman spectroscopy, and Auger electron spectroscopy.
- 30Kamau, G. N.; Willis, W. S.; Rusling, J. F. Electrochemical and Electron Spectroscopic Studies of Highly Polished Glassy Carbon Electrodes. Anal. Chem. 1985, 57, 545– 551, DOI: 10.1021/ac50001a049Google Scholar30https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2MXlt1yrsg%253D%253D&md5=e9d13604ba17d0234fdb51da9e2e66fbElectrochemical and electron spectroscopic studies of highly-polished glassy carbon electrodesKamau, Geoffrey N.; Willis, William S.; Rusling, James F.Analytical Chemistry (1985), 57 (2), 545-51CODEN: ANCHAM; ISSN:0003-2700.Prepn. of glassy C electrodes by high-speed polishing with successively smaller particles size SiC, diamond paste, and γ-Al2O3, and ultrasonic cleaning, yielded reproducible activation for anodic oxidns. of ferrocyanide, ferrocene, ascorbate, hydroquinones, and catharanthine. Electron spectroscopy showed that the highly polished electrodes had a higher O content in the outer 20-30 nm than in the bulk material or in unactivated electrodes. A major portion of the O is probably assocd. with phenolic-like groups. For simple electron transfers, creation of a favorable charge d. at the electrode is an important factor in the activation, but other nonspecific interactions may also be involved. For proton-coupled reactions, such as those of ascorbate and dopamine, specific interactions of reactants with catalytic groups created on the surface may play a significant role in electrode activation. Response of the electrodes degraded with time.
- 31Allred, C. D.; McCreery, R. L. Adsorption of Catechols on Fractured Glassy Carbon Electrode Surfaces. Anal. Chem. 1992, 64, 444– 448, DOI: 10.1021/ac00028a020Google Scholar31https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK38XptlOntg%253D%253D&md5=62a34aab0b1076fc6d50c06241e0b781Adsorption of catechols on fractured glassy carbon electrode surfacesAllred, Christie D.; McCreery, Richard L.Analytical Chemistry (1992), 64 (4), 444-8CODEN: ANCHAM; ISSN:0003-2700.Glassy carbon surfaces exposed by fracturing a glassy carbon rod in the electrolyte soln. exhibit fast electron transfer kinetics compared to conventionally polished surfaces, implying that glassy carbon is inherently active toward electron transfer before any intentional surface modification. The adsorption of dopamine and related compds. was examd. on fractured glassy carbon surfaces and compared to polished or electrochem. pretreated (ECP) surfaces. While the catechols and ascorbic acid had the anticipated fast electron transfer on fractured glassy carbon, their adsorption behavior differed substantially from that reported for polished, ECP, or vapor-deposited carbon. Dopamine, 4-methylcatechol (4-MC), and dihydroxyphenylacetic acid (DOPAC) adsorbed to similar degrees on fractured glassy carbon, with no apparent discrimination on the basis of adsorbate charge. If the surface was partially oxidized, however, cationic dopamine was preferentially adsorbed over anionic DOPAC or neutral 4-MC. The results support an adsorption mechanism on fractured glassy carbon which is not charge specific and probably involves the catechol ring rather than the side chain. The implications of this finding to the anal. utility of carbon electrodes are discussed.
- 32Behan, J. A.; Grajkowski, F.; Jayasundara, D. R.; Vilella-Arribas, L.; García-Melchor, M.; Colavita, P. E. Influence of Carbon Nanostructure and Oxygen Moieties on Dopamine Adsorption and Charge Transfer Kinetics at Glassy Carbon Surfaces. Electrochim. Acta 2019, 304, 221– 230, DOI: 10.1016/j.electacta.2019.02.103Google Scholar32https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXksVahtrc%253D&md5=5052b20b8588a122a887415114eb306dInfluence of carbon nanostructure and oxygen moieties on dopamine adsorption and charge transfer kinetics at glassy carbon surfacesBehan, James A.; Grajkowski, Filip; Jayasundara, Dilushan R.; Vilella-Arribas, Laia; Garcia-Melchor, Max; Colavita, Paula E.Electrochimica Acta (2019), 304 (), 221-230CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Ltd.)Abnormal levels of the neurotransmitter dopamine were linked to a variety of neurochem. disorders including depression and Parkinson's disease. Dopamine concns. are often quantified electrochem. using biosensors prepd. from C electrode materials such as C paste or glassy C. The charge transfer kinetics of dopamine is highly sensitive to C surface termination, including the presence of certain O functional groups and adsorption sites. However, the nature of the binding sites and the effects of surface oxidn. on the voltammetry of dopamine are both poorly understood. The electrochem. response of dopamine at glassy C model surfaces was studied to understand the effects of altering both the C nanostructure and O surface chem. on dopamine charge transfer kinetics and adsorption. Glassy C electrodes with low O content and a high degree of surface graphitization were prepd. via thermal annealing at 900°, while highly oxidized glassy C electrodes were obtained through electrochem. anodization at 1.8 V vs. Ag/AgCl. The C surface structure and compn. in each case was studied via XPS. Voltammetry in solns. of dopamine at acidic pH confirmed that both annealing and anodization treatments result in C surfaces with rapid charge transfer kinetics. However, dopamine adsorption occurs only at the low-O, highly-graphitized C surface. D. functional theory studies on graphene model surfaces reveal that this behavior is due to noncovalent interactions between the π-system of dopamine and the basal sites in the annealed surface. Simulations also show that the introduction of O moieties disrupt these interactions and inhibit dopamine adsorption, in agreement with expts. The results clarify the role of O moieties and basal plane sites in facilitating both the adsorption of and charge transfer to DA at C electrodes.
- 33Engstrom, R. C.; Strasser, V. A. Characterization of Electrochemically Pretreated Glassy Carbon Electrodes. Anal. Chem. 1984, 56, 136– 141, DOI: 10.1021/ac00266a005Google Scholar33https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2cXktFGlsQ%253D%253D&md5=fc782d7153bcd08cf5805cae3f167da3Characterization of electrochemically pretreated glassy carbon electrodesEngstrom, Royce C.; Strasser, Vernon A.Analytical Chemistry (1984), 56 (2), 136-41CODEN: ANCHAM; ISSN:0003-2700.Electrochem. pretreatment of glassy C electrodes was done by applying 1.75 V vs. SCE for 5 min followed by -1.0 V for 1 min. The effects of pretreatment on the functional, phys., and chem. characteristics of the electrodes were studied. The pretreated electrodes showed enhanced electrochem. activity, higher background currents, increased wettability, and no change in electrochem. surface area or topog. as detd. by SEM. XPS showed that pretreatment produces a surface more highly oxygenated than that of a freshly polished electrode. Electrochem. pretreatment cleans the surface of contaminants introduced in the polishing step of electrode prepn. and changes the chem. nature of the glassy C surface itself. The chem. changes influence the reaction of ascorbic acid but do not influence reaction of the ferricyanide-ferrocyanide system.
- 34Kiema, G. K.; Aktay, M.; McDermott, M. T. Preparation of Reproducible Glassy Carbon Electrodes by Removal of Polishing Impurities. J. Electroanal. Chem. 2003, 540, 7– 15, DOI: 10.1016/S0022-0728(02)01264-0Google Scholar34https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXis1SqtA%253D%253D&md5=e44d31370a8702924f31ac658ba83497Preparation of reproducible glassy carbon electrodes by removal of polishing impuritiesKiema, Gregory K.; Aktay, Mirwais; McDermott, Mark T.Journal of Electroanalytical Chemistry (2003), 540 (), 7-15CODEN: JECHES ISSN:. (Elsevier Science B.V.)This paper describes a simple and rapid electrochem. oxidative procedure that removes polishing contaminants from glassy carbon (GC) surfaces. The method involves oxidn. of polished GC electrodes in basic media for short periods of time (∼10 s). Tapping mode scanning force microscopy (TM SFM), XPS and nanoindentation surface characterization techniques were utilized to track the removal of the polishing layer. Several electrochem. characterizations of the modified GC surface were carried out to assess changes in electrode reactivity following removal of the microparticle polishing layer. Electrochem. measurements obtained on the anodized GC electrodes show a more reproducible surface relative to polished GC.
- 35Kiema, G. K.; Ssenyange, S.; McDermott, M. T. Microfabrication of Glassy Carbon by Electrochemical Etching. J. Electrochem. Soc. 2004, 151, C142– C148, DOI: 10.1149/1.1639165Google Scholar35https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXkvV2jsA%253D%253D&md5=f8e0562713148cb26f4915263e63c800Microfabrication of Glassy Carbon by Electrochemical EtchingKiema, Gregory K.; Ssenyange, Solomon; McDermott, Mark T.Journal of the Electrochemical Society (2004), 151 (2), C142-C148CODEN: JESOAN; ISSN:0013-4651. (Electrochemical Society)Due to the broad impact of microfabrication technol. on chem. and biol., new methods to pattern and etch a variety of materials are being explored in a no. of labs. The authors have developed a method for the etching of glassy C (GC) that opens pathways for the creation of new electrode patterns and devices. The method involves std. pattern transfer to a photoresist layer and anodization of the exposed GC substrate in basic electrolyte. The electrode reaction results in a breakup of the C lattice and likely involves the intercalation of hydroxide anions. The depth of etching can be controlled with potential, time or charge. The etching process is isotropic due to the nano-scale graphitic microcrystallite size of GC. The authors demonstrate the fabrication of microchannel structures directly into GC and the prepn. of arrays of submicrometer sized C electrodes via the etching of patterned C films.
- 36Sullivan, M. G.; Schnyder, B.; Bärtsch, M.; Alliata, D.; Barbero, C.; Imhof, R.; Kötz, R. Electrochemically Modified Glassy Carbon for Capacitor Electrodes Characterization of Thick Anodic Layers by Cyclic Voltammetry, Differential Electrochemical Mass Spectrometry, Spectroscopic Ellipsometry, X-Ray Photoelectron Spectroscopy, FTIR, and AFM. J. Electrochem. Soc. 2000, 147, 2636– 2643, DOI: 10.1149/1.1393582Google Scholar36https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXltVCrtrg%253D&md5=76401e861af82efb81369b96316b9d6cElectrochemically modified glassy carbon for capacitor electrodes. Characterization of thick anodic layers by cyclic voltammetry, differential electrochemical mass spectrometry, spectroscopic ellipsometry, X-ray photoelectron spectroscopy, FTIR, and AFMSullivan, M. G.; Schnyder, B.; Bartsch, M.; Alliata, D.; Barbero, C.; Imhof, R.; Kotz, R.Journal of the Electrochemical Society (2000), 147 (7), 2636-2643CODEN: JESOAN; ISSN:0013-4651. (Electrochemical Society)Glassy carbon (GC) electrodes were activated by electrochem. const. potential anodization to generate high-surface area, high-capacitance electrodes. After anodic oxidn. in sulfuric acid the electrodes exhibited increased capacitance. After subsequent electrochem. redn. of the activated layer, a further significant increase in capacitance was obsd. Growth, structure, and surface properties of the activated electrodes were monitored by cyclic voltammetry, differential electrochem. mass spectrometry, spectroscopic ellipsometry, XPS, and at. force microscopy (AFM). Two different types of glassy carbon obtained by pyrolysis at 1000° and at 2200° were compared. Differential electrochem. mass spectrometry reveals that CO2 is the main reaction product during oxidn., while CO2 and H2 are detected during redn. The values of surface layer capacitance and thickness detd. by spectroscopic ellipsometry increase as linear functions of oxidn. time. The resulting volumetric capacitance was at least 100 F/cm3. After oxidn., the presence of functional surface groups was demonstrated by XPS. The relative contributions of the different surface functionalities depend on the pyrolysis temp. of the GC. Redn. lowered the concn. of oxygen-contg. functional surface groups. The XPS results were qual. confirmed by FTIR measurements carried out at the same samples. AFM measurements on glassy carbon showed that the film growth both into and out of the substrate, resulted in a raised surface after activation. A qual. model for film growth is presented.
- 37Alliata, D. In Situ Atomic Force Microscopy of Electrochemically Activated Glassy Carbon. Electrochem. Solid-State Lett. 1999, 2, 33– 35, DOI: 10.1149/1.1390725Google Scholar37https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXhslw%253D&md5=a2454a0cbda9bcbbed2d65aa147b18d8In situ atomic force microscopy of electrochemically activated glassy carbonAlliata, D.; Haring, P.; Haas, O.; Kotz, R.; Siegenthaler, H.Electrochemical and Solid-State Letters (1999), 2 (1), 33-35CODEN: ESLEF6; ISSN:1099-0062. (Electrochemical Society)Glassy carbon (GC) electrodes were activated by anodic oxidn. at a potential of 1.95 V std. calomel electrode in 1 M H2SO4. The activated electrodes were investigated by in situ contact at. force microscopy. In order to monitor differences between activated and nonactivated areas, part of the electrode surface was covered by a polymeric varnish during electrochem. activation. The edge between activated and nonactivated regions was analyzed after removal of the varnish. The surface of the activated region was significantly higher than that of the nonactivated region, indicating significant swelling of the GC during anodic oxidn. After drying, the activated film collapsed. Swelling of the activated layer was a linear function of activation time and depended on the state of the electrode. In the oxidized state the film thickness was larger than in the reduced state.
- 38Sullivan, M. G.; Kötz, R.; Haas, O. Thick Active Layers of Electrochemically Modified Glassy Carbon. Electrochemical Impedance Studies. J. Electrochem. Soc. 2000, 147, 308, DOI: 10.1149/1.1393192Google Scholar38https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXmvFCjsw%253D%253D&md5=be0de0f6186c78fded4f49845a2c6384Thick active layers of electrochemically modified glassy carbon electrochemical impedance studiesSullivan, Melani G.; Kotz, Rudiger; Haas, OttoJournal of the Electrochemical Society (2000), 147 (1), 308-317CODEN: JESOAN; ISSN:0013-4651. (Electrochemical Society)Glassy carbon electrodes were electrochem. modified by an anodization/cathodization procedure in aq. H2SO4. Depending on the anodization time, the active-layer thickness could be controlled from less than a micrometer to nearly 100 μm. Electrochem. impedance measurements indicated that the capacitance per unit vol. of the active layer was similar to various other porous carbons and sufficient for application as an electrochem. capacitor material. The small-signal a.c. capacitance is 80-460 F/cm3 (single-electrode capacitance), depending on potential, for the higher-pyrolysis-temp. carbon, and 25-420 F/cm3 for the lower-pyrolysis-temp. carbon. The resistance of the active layer depended even more strongly on the pyrolysis temp. of the glassy carbon. The active layer on the carbon pyrolyzed at a temp. of 2200° had a resistance which was ∼1000 times lower than that of a corresponding layer grown on glassy carbon pyrolyzed at 1000°.
- 39Cabaniss, G. E.; Diamantis, A. A.; Murphy, W. R., Jr.; Linton, R. W.; Meyer, T. J. Electrocatalysis of Proton-Coupled Electron-Transfer Reactions at Glassy Carbon Electrodes. J. Am. Chem. Soc. 1985, 107, 1845– 1853, DOI: 10.1021/ja00293a007Google Scholar39https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2MXhtl2ltrs%253D&md5=f70528beb693153bacae10021cc10117Electrocatalysis of proton-coupled electron-transfer reactions at glassy carbon electrodesCabaniss, George E.; Diamantis, A. A.; Murphy, W. Rorer, Jr.; Linton, R. W.; Meyer, T. J.Journal of the American Chemical Society (1985), 107 (7), 1845-53CODEN: JACSAT; ISSN:0002-7863.The activation of glassy C electrodes toward electron-transfer pathways involving proton-coupled electron transfer was investigated. Oxidative activation of glassy C electrodes leads to the catalysis of heterogeneous charge transfer for couples involving catechol (1,2-dihydroxybenzene), (bpy)2(H2O)Ru(OH)2+ (bpy = 2,2'-bipyridine), and (NH3)5Ru(OH)2+ where there are changes in proton content upon oxidn. XPS was used to det. the changes induced at the electrode surface by the activation procedure. Comparison of the spectral and electrochem. results with earlier studies on related homogeneous proton-coupled electron-transfer reactions suggests that, although a no. of effects may be operative, an important basis for electrode activation may be the appearance of phenolic-like groups on the glassy C surface and their subsequent involvement in proton-coupled electron transfer.
- 40DuVall, S. H.; McCreery, R. L. Control of Catechol and Hydroquinone Electron-Transfer Kinetics on Native and Modified Glassy Carbon Electrodes. Anal. Chem. 1999, 71, 4594– 4602, DOI: 10.1021/ac990399dGoogle Scholar40https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXlslCit7o%253D&md5=b2023cb5d42610292ec440954b296d1bControl of Catechol and Hydroquinone Electron-Transfer Kinetics on Native and Modified Glassy Carbon ElectrodesDuVall, Stacy Hunt; McCreery, Richard L.Analytical Chemistry (1999), 71 (20), 4594-4602CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)The electrochem. oxidn. of dopamine, 4-methylcatechol, dihydroxyphenylacetic acid, dihydroxyphenyl ethylene glycol, and hydroquinone was examd. on several native and modified glassy carbon (GC) surfaces. Treatment of polished GC with pyridine yielded small ΔEp values for cyclic voltammetry of all systems studied, implying fast electron-transfer kinetics. Changes in surface oxide coverage had little effect on kinetics, nor did the charge of the catechol species or the soln. pH. Small ΔEp values correlated with catechol adsorption, and surface pretreatments that decreased adsorption also increased ΔEp. Electron transfer from catechols was profoundly inhibited by a monolayer of nitrophenyl or (trifluoromethyl)phenyl (TFMP) groups on the GC surface, so that voltammetric waves were not obsd. The ΔEp increased monotonically with surface coverage of TFMP groups. The results indicate that catechol adsorption to GC is required for fast electron transfer for the redox systems studied. Unlike Ru(NH3)63+/2+, chlorpromazine, Me viologen, and several others, electron tunneling through monolayer films was not obsd. for the catechols. The results are not consistent with an electron-transfer mechanism involving proton transfer or electrostatic interactions between the catechols and surface sites on the GC surface. The vital role of adsorption in the electron-transfer process is currently under study but appears to involve changes in the inner-sphere reorganization energy.
- 41Yi, Y.; Weinberg, G.; Prenzel, M.; Greiner, M.; Heumann, S.; Becker, S.; Schlögl, R. Electrochemical Corrosion of a Glassy Carbon Electrode. Catal. Today 2017, 295, 32– 40, DOI: 10.1016/j.cattod.2017.07.013Google Scholar41https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtF2ktLjN&md5=6ccdcedfafaf8534ee426bcb534e10c7Electrochemical corrosion of a glassy carbon electrodeYi, Youngmi; Weinberg, Gisela; Prenzel, Marina; Greiner, Mark; Heumann, Saskia; Becker, Sylvia; Schloegl, RobertCatalysis Today (2017), 295 (), 32-40CODEN: CATTEA; ISSN:0920-5861. (Elsevier B.V.)Glassy C is widely used in electrochem. due to its properties of high temp. resistance, hardness, low d. and low elec. resistance. The present study focuses on the chem. resistance under electrochem. oxidative conditions, which occur under O-involving reactions like O redn. reaction (ORR) and O evolution reaction (OER). The electrochem. performance of glassy C studied in alk., neutral and acidic media reveal the same chem. processes during the OER but showing different degrdn. mechanism. The electrochem. signature of the corrosion in different media could be directly assocd. with the formation of O functional groups detd. by spectroscopic methods like Raman, IR and XPS. The morphol. change of the C surface caused by C oxidn. was studied by microscopy. A rough surface was obtained in the acidic case, whereas dents were seen in alk. media. It is assumed that the glassy C electrode in acidic media degrades by forming surface oxides by acid catalyzed process leading to ring opening in the graphitic structure and therefore oxidn. in the bulk. In alk. media OH radicals preferentially react with alkyl site chains, leading to oxidn. of the edges of C layers until they become hydrophilic and dissolve.
- 42Patel, A. N.; McKelvey, K.; Unwin, P. R. Nanoscale Electrochemical Patterning Reveals the Active Sites for Catechol Oxidation at Graphite Surfaces. J. Am. Chem. Soc. 2012, 134, 20246– 20249, DOI: 10.1021/ja3095894Google Scholar42https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhslOlsbbJ&md5=47806e196bb4b5b0348aad244cc6086cNanoscale Electrochemical Patterning Reveals the Active Sites for Catechol Oxidation at Graphite SurfacesPatel, Anisha N.; McKelvey, Kim; Unwin, Patrick R.Journal of the American Chemical Society (2012), 134 (50), 20246-20249CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Graphite-based electrodes (graphite, graphene, and nanotubes) were used widely in electrochem., and there is a long-standing view that graphite step edges are needed to catalyze many reactions, with the basal surface considered to be inert. This model was tested directly for the 1st time using scanning electrochem. cell microscopy reactive patterning and is incorrect. For the electrooxidn. of dopamine as a model process, the reaction rate was measured at high spatial resoln. across a surface of highly oriented pyrolytic graphite. Oxidn. products left behind in a pattern defined by the scanned electrochem. cell served as surface-site markers, allowing the electrochem. activity to be correlated directly with the graphite structure on the nanoscale. This process produced tens of thousands of electrochem. measurements at different locations across the basal surface, unambiguously revealing it to be highly electrochem. active, with step edges providing no enhanced activity. This new model of graphite electrodes has significant implications for the design of C-based biosensors, and the results are addnl. important for understanding electrochem. processes on related sp2-hybridized materials such as pristine graphene and nanotubes.
- 43Martín-Yerga, D.; Costa-García, A.; Unwin, P. R. Correlative Voltammetric Microscopy: Structure–Activity Relationships in the Microscopic Electrochemical Behavior of Screen Printed Carbon Electrodes. ACS Sens. 2019, 4, 2173– 2180, DOI: 10.1021/acssensors.9b01021Google Scholar43https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhsVGhsLjL&md5=61024414d3770735e09dca65f1c95959Correlative Voltammetric Microscopy: Structure-Activity Relationships in the Microscopic Electrochemical Behavior of Screen Printed Carbon ElectrodesMartin-Yerga, Daniel; Costa-Garcia, Agustin; Unwin, Patrick R.ACS Sensors (2019), 4 (8), 2173-2180CODEN: ASCEFJ; ISSN:2379-3694. (American Chemical Society)Screen-printed carbon electrodes (SPCEs) are widely used for electrochem. sensors. However, little is known about their electrochem. behavior at the microscopic level. In this work, we use voltammetric scanning electrochem. cell microscopy (SECCM), with dual-channel probes, to det. the microscopic factors governing the electrochem. response of SPCEs. SECCM cyclic voltammetry (CV) measurements are performed directly in hundreds of different locations of SPCEs, with high spatial resoln., using a submicrometer sized probe. Further, the localized electrode activity is spatially correlated to colocated surface structure information from SEM and micro-Raman spectroscopy. This approach is applied to two model electrochem. processes: hexaammineruthenium(III/II) ([Ru(NH3)6]3+/2+), a well-known outer-sphere redox couple, and dopamine (DA), which undergoes a more complex electron-proton coupled electro-oxidn., with complications from adsorption of both DA and side-products. The electrochem. redn. of [Ru(NH3)6]3+ proceeds fairly uniformly across the surface of SPCEs on the submicrometer scale. In contrast, DA electro-oxidn. shows a strong dependence on the microstructure of the SPCE. By studying this process at different concns. of DA, the relative contributions of (i) intrinsic electrode kinetics and (ii) adsorption of DA are elucidated in detail, as a function of local electrode character and surface structure. These studies provide major new insights on the electrochem. activity of SPCEs and further position voltammetric SECCM as a powerful technique for the electrochem. imaging of complex, heterogeneous, and topog. rough electrode surfaces.
- 44Chen, B.; Perry, D.; Teahan, J.; McPherson, I. J.; Edmondson, J.; Kang, M.; Valavanis, D.; Frenguelli, B. G.; Unwin, P. R. Artificial Synapse: Spatiotemporal Heterogeneities in Dopamine Electrochemistry at a Carbon Fiber Ultramicroelectrode. ACS Meas. Sci. Au 2021, 1, 6– 10, DOI: 10.1021/acsmeasuresciau.1c00006Google Scholar44https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXhsVelt7rF&md5=7b4a92ace8a28fa00c48074fa70c6082Artificial Synapse: Spatiotemporal Heterogeneities in Dopamine Electrochemistry at a Carbon Fiber UltramicroelectrodeChen, Baoping; Perry, David; Teahan, James; McPherson, Ian J.; Edmondson, James; Kang, Minkyung; Valavanis, Dimitrios; Frenguelli, Bruno G.; Unwin, Patrick R.ACS Measurement Science Au (2021), 1 (1), 6-10CODEN: AMACHV; ISSN:2694-250X. (American Chemical Society)An artificial synapse is developed that mimics ultramicroelectrode (UME) amperometric detection of single cell exocytosis. It comprises the nanopipette of a scanning ion conductance microscope (SICM), which delivers rapid pulses of neurotransmitter (dopamine) locally and on demand at >1000 defined locations of a carbon fiber (CF) UME in each expt. Anal. of the resulting UME current-space-time data reveals spatiotemporal heterogeneous electrode activity on the nanoscale and submillisecond time scale for dopamine electrooxidn. at typical UME detection potentials. Through complementary surface charge mapping and finite element method (FEM) simulations, these previously unseen variations in electrochem. activity are related to heterogeneities in the surface chem. of the CF UME.
- 45Chen, B.; Perry, D.; Page, A.; Kang, M.; Unwin, P. R. Scanning Ion Conductance Microscopy: Quantitative Nanopipette Delivery–Substrate Electrode Collection Measurements and Mapping. Anal. Chem. 2019, 91, 2516– 2524, DOI: 10.1021/acs.analchem.8b05449Google Scholar45https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXjtlKmuw%253D%253D&md5=74d798d40c1f8984c07dfb7ad9b2d996Scanning Ion Conductance Microscopy: Quantitative Nanopipette Delivery-Substrate Electrode Collection Measurements and MappingChen, Baoping; Perry, David; Page, Ashley; Kang, Minkyung; Unwin, Patrick R.Analytical Chemistry (Washington, DC, United States) (2019), 91 (3), 2516-2524CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Scanning ion conductance microscopy (SICM) is becoming a powerful multifunctional tool for probing and analyzing surfaces and interfaces. This work outlines methodol. for the quant. controlled delivery of ionic redox-active mols. from a nanopipette to a substrate electrode, with a high degree of spatial and temporal precision. Through control of the SICM bias applied between a quasi-ref. counter electrode (QRCE) in the SICM nanopipette probe and a similar electrode in bulk soln., it is shown that ionic redox species can be held inside the nanopipette, and then pulse-delivered to a defined region of a substrate positioned beneath the nanopipette. A self-referencing hopping mode imaging protocol is implemented, where reagent is released in bulk soln. (ref. measurement) and near the substrate surface at each pixel in an image, with the tip and substrate currents measured throughout. Anal. of the tip and substrate current data provides an improved understanding of mass transport and nanoscale delivery in SICM and a new means of synchronously mapping electrode reactivity, surface topog., and charge. Expts. on Ru(NH3)63+ redn. to Ru(NH3)62+ and dopamine oxidn. in aq. soln. at a carbon fiber ultramicroelectrode (UME), used as the substrate, illustrate these aspects. Finite element method (FEM) modeling provides quant. understanding of mol. delivery in SICM. The approach outlined constitutes a new methodol. for electrode mapping and provides improved insights on the use of SICM for controlled delivery to interfaces generally.
- 46Patten, H. V.; Lai, S. C. S.; Macpherson, J. V.; Unwin, P. R. Active Sites for Outer-Sphere, Inner-Sphere, and Complex Multistage Electrochemical Reactions at Polycrystalline Boron-Doped Diamond Electrodes (PBDD) Revealed with Scanning Electrochemical Cell Microscopy (SECCM). Anal. Chem. 2012, 84, 5427– 5432, DOI: 10.1021/ac3010555Google Scholar46https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38Xnt1Wrs7k%253D&md5=79e267ef80b8067dc49df1f175b2e129Active Sites for Outer-Sphere, Inner-Sphere, and Complex Multistage Electrochemical Reactions at Polycrystalline Boron-Doped Diamond Electrodes (pBDD) Revealed with Scanning Electrochemical Cell Microscopy (SECCM)Patten, Hollie V.; Lai, Stanley C. S.; Macpherson, Julie V.; Unwin, Patrick R.Analytical Chemistry (Washington, DC, United States) (2012), 84 (12), 5427-5432CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)The local rate of heterogeneous electron transfer (HET) at polycryst. B-doped diamond (pBDD) electrodes was visualized at high spatial resoln. for various aq. electrochem. reactions, using scanning electrochem. cell microscopy (SECCM), which is a technique that uses a mobile pipet-based electrochem. cell as an imaging probe. As exemplar systems, three important classes of electrode reactions were studied: outer-sphere (1-electron oxidn. of ferrocenylmethyltrimethylammonium (FcTMA+)), inner-sphere (1-electron oxidn. of Fe2+), and complex processes with coupled electron transfer and chem. reactions (oxidn. of serotonin). In all cases, the pattern of reactivity is similar: the entire pBDD surface is electroactive, but there are variations in activity between different crystal facets which correlate directly with differences in the local dopant level, as visualized qual. by field-emission SEM (FE-SEM). No evidence was found for enhanced activity at grain boundaries for any of the reactions. The case of serotonin oxidn. is particularly interesting, as this process is known to lead to deterioration of the electrodes, because of blocking by reaction products, and therefore cannot be studied with conventional scanning electrochem. probe microscopy (SEPM) techniques. Yet, the authors found this system nonproblematic to study, because the meniscus of the scanning pipet is only in contact with the surface studied for a brief time and any blocking product is left behind as the pipet moves to a new location. Thus, SECCM opens up the possibility of studying and visualizing much more complex heterogeneous electrode reactions than possible presently with other SEPM techniques.
- 47Patel, A. N.; Tan, S.; Unwin, P. R. Epinephrine Electro-Oxidation Highlights Fast Electrochemistry at the Graphite Basal Surface. Chem. Commun. 2013, 49, 8776, DOI: 10.1039/c3cc45022hGoogle Scholar47https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhsVSls7fK&md5=aa40afb4adc23e16f3ad45f8167e962bEpinephrine electro-oxidation highlights fast electrochemistry at the graphite basal surfacePatel, Anisha N.; Tan, Sze-yin; Unwin, Patrick R.Chemical Communications (Cambridge, United Kingdom) (2013), 49 (78), 8776-8778CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)Macroscale and nanoscale measurements of epinephrine electrooxidn. at graphite electrodes, with different step edge densities, demonstrate unequivocally that the reaction occurs readily at the basal surface, and that step edges are not required for mol. electrocatalysis, in contrast to the current literature model.
- 48Ebejer, N.; Güell, A. G.; Lai, S. C. S.; McKelvey, K.; Snowden, M. E.; Unwin, P. R. Scanning Electrochemical Cell Microscopy: A Versatile Technique for Nanoscale Electrochemistry and Functional Imaging. Annu. Rev. Anal. Chem. 2013, 6, 329– 351, DOI: 10.1146/annurev-anchem-062012-092650Google Scholar48https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhsVCnsr3E&md5=260a4579441b78641eb0f2668aa8f98cScanning electrochemical cell microscopy: a versatile technique for nanoscale electrochemistry and functional imagingEbejer, Neil; Guell, Aleix G.; Lai, Stanley C. S.; McKelvey, Kim; Snowden, Michael E.; Unwin, Patrick R.Annual Review of Analytical Chemistry (2013), 6 (), 329-351CODEN: ARACFU; ISSN:1936-1327. (Annual Reviews)A review. Scanning electrochem. cell microscopy (SECCM) is a new pipet-based imaging technique purposely designed to allow simultaneous electrochem., conductance, and topog. visualization of surfaces and interfaces. SECCM uses a tiny meniscus or droplet, at the end of a double-barreled (theta) pipet, for high-resoln. functional imaging and nanoscale electrochem. measurements. Here, this technique is introduced and an overview of its principles, instrumentation, and theory is provided. The power of SECCM in resolving complex structure-activity problems is discussed and considerable new information on electrode processes is provided by referring to key example systems, including graphene, graphite, carbon nanotubes, nanoparticles, and conducting diamond. The many longstanding questions that SECCM was able to answer during its short existence demonstrate its potential to become a major technique in electrochem. and interfacial science.
- 49Wahab, O. J.; Kang, M.; Unwin, P. R. Scanning Electrochemical Cell Microscopy: A Natural Technique for Single Entity Electrochemistry. Curr. Opin. Electrochem. 2020, 22, 120– 128, DOI: 10.1016/j.coelec.2020.04.018Google Scholar49https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXitFymtLvP&md5=75aa33e918a588a55ce4d95244d3f9abScanning electrochemical cell microscopy and A natural technique for single entity electrochemistryWahab, Oluwasegun J.; Kang, Minkyung; Unwin, Patrick R.Current Opinion in Electrochemistry (2020), 22 (), 120-128CODEN: COEUCY; ISSN:2451-9111. (Elsevier B.V.)A review Scanning electrochem. cell microscopy (SECCM) is a robust and versatile scanning electrochem. probe microscopy technique that allows direct correlation of structure-activity at the nanoscale. SECCM uses a mobile droplet cell to investigate and visualize electrochem. activity at interfaces with high spatiotemporal resoln., while also providing topog. information. This article highlights diverse contemporary challenges in the field of single entity electrochem. tackled by the increasing uptake of SECCM globally. Various applications of SECCM in single entity electrochem. are featured herein, including electrocatalysis, electrodeposition, corrosion science and materials science, with electrode materials spanning particles, polymers, two-dimensional materials and complex polycryst. substrates. The use of SECCM for patterning structures is also highlighted.
- 50Bentley, C. L.; Kang, M.; Unwin, P. R. Scanning Electrochemical Cell Microscopy: New Perspectives on Electrode Processes in Action. Curr. Opin. Electrochem. 2017, 6, 23– 30, DOI: 10.1016/j.coelec.2017.06.011Google Scholar50https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhtVGgsbzK&md5=ae05c709a59c54d24576efde38f6c131Scanning electrochemical cell microscopy: New perspectives on electrode processes in actionBentley, Cameron L.; Kang, Minkyung; Unwin, Patrick R.Current Opinion in Electrochemistry (2017), 6 (1), 23-30CODEN: COEUCY; ISSN:2451-9111. (Elsevier B.V.)Scanning electrochem. probe microscopy (SEPM) methods allow interfacial fluxes to be visualized at high spatial resoln. and are consequently invaluable for understanding physicochem. processes at electrode/soln. interfaces. This article highlights recent progress in scanning electrochem. cell microscopy (SECCM), a scanning-droplet-based method that is able to visualize electrode activity free from topog. artifacts and, further, offers considerable versatility in terms of the range of interfaces and environments that can be studied. Advances in the speed and sensitivity of SECCM are highlighted, with applications as diverse as the creation of movies of electrochem. (electrocatalytic) processes in action to tracking the motion and activity of nanoparticles near electrode surfaces.
- 51Engstrom, R. C. Electrochemical Pretreatment of Glassy Carbon Electrodes. Anal. Chem. 1982, 54, 2310– 2314, DOI: 10.1021/ac00250a038Google Scholar51https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL38XlsFaqs7Y%253D&md5=4c3c805940601b442c982837d6bf4944Electrochemical pretreatment of glassy carbon electrodesEngstrom, Royce C.Analytical Chemistry (1982), 54 (13), 2310-14CODEN: ANCHAM; ISSN:0003-2700.The effects of preanodization and precathodization on the electrochem. oxidn. of hydroquinone [123-31-9], ferrocyanide [13408-63-4], and hydrazine [302-01-2] were studied at glassy C electrodes. Pretreatment was characterized with respect to the sequence of voltages applied to the electrode, the amplitude of the applied voltage, and the duration of pretreatment. For all 3 electroactive species, preanodization at <1.5 V vs. SCE was required to activate a freshly polished electrode. Ferrocyanide and hydrazine also required precathodization to remove an inhibitory layer formed during preanodization. In all cases, pretreatment resulted in a substantial improvement in the half-wave potential of the voltammetric wave and in the reproducibility of the wave. The results are interpreted in terms of 3 distinct electrode surface conditions.
- 52Kiema, G. K.; Fitzpatrick, G.; McDermott, M. T. Probing Morphological and Compositional Variations of Anodized Carbon Electrodes with Tapping-Mode Scanning Force Microscopy. Anal. Chem. 1999, 71, 4306– 4312, DOI: 10.1021/ac9904056Google Scholar52https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXlsFSku7s%253D&md5=cb626ed1dd297e5c1f1f89e2f9f89601Probing Morphological and Compositional Variations of Anodized Carbon Electrodes with Tapping-Mode Scanning Force MicroscopyKiema, Gregory K.; Fitzpatrick, Glen; McDermott, Mark T.Analytical Chemistry (1999), 71 (19), 4306-4312CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)This paper demonstrates the 1st application of tapping-mode scanning force microscopy (TM SFM) in the compositional mapping of modified glassy carbon (GC) electrodes. Using TM SFM, the authors were able to track both compositional and topog. changes of polished GC induced by electrochem. pretreatment (ECP). Photoresist-based microfabrication techniques were employed to produce surfaces consisting of segregated modified and unmodified regions for direct comparison in the same image. ECP of GC via anodization in basic solns. for short times (∼10 s) initially removes the ubiquitous layer of polishing debris via an etching process. Longer anodization in basic electrolyte results in significant etching of the GC surface. ECP in acidic solns. yields little topog. change compared to basic electrolytes. Electrochem. results obtained for three redox systems studied on both modified and unmodified GC electrodes correlate with the TM SFM images collected.
- 53Virtanen, P.; Gommers, R.; Oliphant, T. E.; Haberland, M.; Reddy, T.; Cournapeau, D.; Burovski, E.; Peterson, P.; Weckesser, W.; Bright, J. SciPy 1.0: Fundamental Algorithms for Scientific Computing in Python. Nat. Methods 2020, 17, 261– 272, DOI: 10.1038/s41592-019-0686-2Google Scholar53https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXislCjuro%253D&md5=f007632188adeb57a43469157898e0a8SciPy 1.0: fundamental algorithms for scientific computing in PythonVirtanen, Pauli; Gommers, Ralf; Oliphant, Travis E.; Haberland, Matt; Reddy, Tyler; Cournapeau, David; Burovski, Evgeni; Peterson, Pearu; Weckesser, Warren; Bright, Jonathan; van der Walt, Stefan J.; Brett, Matthew; Wilson, Joshua; Millman, K. Jarrod; Mayorov, Nikolay; Nelson, Andrew R. J.; Jones, Eric; Kern, Robert; Larson, Eric; Carey, C. J.; Polat, Ilhan; Feng, Yu; Moore, Eric W.; Vander Plas, Jake; Laxalde, Denis; Perktold, Josef; Cimrman, Robert; Henriksen, Ian; Quintero, E. A.; Harris, Charles R.; Archibald, Anne M.; Ribeiro, Antonio H.; Pedregosa, Fabian; van Mulbregt, PaulNature Methods (2020), 17 (3), 261-272CODEN: NMAEA3; ISSN:1548-7091. (Nature Research)Abstr.: SciPy is an open-source scientific computing library for the Python programming language. Since its initial release in 2001, SciPy has become a de facto std. for leveraging scientific algorithms in Python, with over 600 unique code contributors, thousands of dependent packages, over 100,000 dependent repositories and millions of downloads per yr. In this work, we provide an overview of the capabilities and development practices of SciPy 1.0 and highlight some recent tech. developments.
- 54Ferrari, A. C.; Robertson, J. Interpretation of Raman Spectra of Disordered and Amorphous Carbon. Phys. Rev. B 2000, 61, 14095– 14107, DOI: 10.1103/PhysRevB.61.14095Google Scholar54https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXjs1Smu7c%253D&md5=e451e6f21e1f6cf375931e6a23e836bbInterpretation of Raman spectra of disordered and amorphous carbonFerrari, A. C.; Robertson, J.Physical Review B: Condensed Matter and Materials Physics (2000), 61 (20), 14095-14107CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)The model and theor. understanding of the Raman spectra in disordered and amorphous C are given. The nature of the G and D vibration modes in graphite is analyzed in terms of the resonant excitation of π states and the long-range polarizability of π bonding. Visible Raman data on disordered, amorphous, and diamondlike C are classified in a 3-stage model to show the factors that control the position, intensity, and widths of the G and D peaks. The visible Raman spectra depend formally on the configuration of the sp2 sites in sp2-bonded clusters. In cases where the sp2 clustering is controlled by the sp3 fraction, such as in as-deposited tetrahedral amorphous C (ta-C) or hydrogenated amorphous C (a-C:H) films, the visible Raman parameters can be used to derive the sp3 fraction.
- 55Sze, S. Raman Spectroscopic Characterization of Carbonaceous Aerosols. Atmos. Environ. 2001, 35, 561– 568, DOI: 10.1016/S1352-2310(00)00325-3Google Scholar55https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXovF2js7o%253D&md5=97d2ecfe1ad053c87ee108fff816d0fdRaman spectroscopic characterization of carbonaceous aerosolsSze, S.-K.; Siddique, N.; Sloan, J. J.; Escribano, R.Atmospheric Environment (2000), 35 (3), 561-568CODEN: AENVEQ; ISSN:1352-2310. (Elsevier Science Ltd.)Raman spectroscopy was used to characterize a variety of C-contg. particulate matter, including samples collected from ambient urban atmospheres. Based on the Raman spectra of known, com. particles, a simple empirical model was derived that reflects their micro-chem. and micro-physics. This model gives information on crystal size and morphol. of the graphitic component, which correlates with known characteristics of the com. samples. Similar information was derived about the graphitic component of ambient particles, suggesting this method might be used to systematically characterize ambient particles in the future.
- 56Sadezky, A.; Muckenhuber, H.; Grothe, H.; Niessner, R.; Pöschl, U. Raman Microspectroscopy of Soot and Related Carbonaceous Materials: Spectral Analysis and Structural Information. Carbon 2005, 43, 1731– 1742Google Scholar56https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXltFGrtLc%253D&md5=045e6d9ee2eb3d84bd001fca25bc7f62Raman microspectroscopy of soot and related carbonaceous materials. Spectral analysis and structural informationSadezky, A.; Muckenhuber, H.; Grothe, H.; Niessner, R.; Poeschl, U.Carbon (2005), 43 (8), 1731-1742CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)Exptl. conditions and math. fitting procedures for the collection and anal. of Raman spectra of soot and related carbonaceous materials were investigated and optimized with a Raman microscope system operated at 3 different laser excitation wavelengths (514, 633, and 780 nm). Several band combinations for spectral anal. were tested, and a combination of 4 Lorentzian-shaped bands (G, D1, D2, D4) at about 1580, 1350, 1620, and 1200 cm-1, resp., with a Gaussian-shaped band (D3) at ∼1500 cm-1 was best suited for the 1st-order spectra. The 2nd-order spectra were best fitted with Lorentzian-shaped bands at about 2450, 2700, 2900, and 3100 cm-1. Spectral parameters (band positions, full widths at half max., and intensity ratios) are reported for several types of industrial C black (Degussa Printex, Cabot Monarch), diesel soot (particulate matter from modern heavy duty vehicle and passenger car engine exhaust, NIST SRM1650), spark-discharge soot (Palas GfG100), and graphite. Several parameters, in particular the width of the D1 band at ∼1350 cm-1, provide structural information and allow to discriminate the sample materials, but the characterization and distinction of different types of soot is limited by the exptl. reproducibility of the spectra and the statistical uncertainties of curve fitting. The results are discussed and compared with x-ray diffraction measurements and earlier Raman spectroscopic studies of comparable materials, where different measurement and fitting procedures was applied.
- 57Mitchell, E. C.; Dunaway, L. E.; McCarty, G. S.; Sombers, L. A. Spectroelectrochemical Characterization of the Dynamic Carbon-Fiber Surface in Response to Electrochemical Conditioning. Langmuir 2017, 33, 7838– 7846, DOI: 10.1021/acs.langmuir.7b01443Google Scholar57https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtFyqsbbM&md5=3d588d53a33f0ecf06fa9c10a9b34c01Spectroelectrochemical Characterization of the Dynamic Carbon-Fiber Surface in Response to Electrochemical ConditioningMitchell, Edwin C.; Dunaway, Lars E.; McCarty, Gregory S.; Sombers, Leslie A.Langmuir (2017), 33 (32), 7838-7846CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)The effects of electrochem. preconditioning of P-55 pitch-based C-fiber microelectrodes were quant. examd. Microstructural characterization of the electrode surface was done using Raman spectroscopy and SEM. Electrochem. performance was evaluated using cyclic voltammetry. Application of pos. potentials provides beneficial structural modifications to the electrode surface. Electrodes that were preconditioned using a static potential of +1.0 V exhibited enhanced sensitivity and electron transfer properties when compared to electrodes conditioned for the same amt. of time with dynamic (triangular) waveforms reaching +1.0 V. Conditioning elicited microstructural changes to the electrode surface that were dependent on the amt. of time spent at potentials ⪆1.0 V. Importantly, the data demonstrate that the C-fiber microstructure is dynamic. It is able to quickly and continuously undergo rapid structural reorganization as potential is applied, repeatedly alternating between a relatively ordered state and one that exhibits greater disorder in response to applied electrochem. potentials that span the range commonly used in voltammetric expts.
- 58Yumitori, S. Correlation of C1s Chemical State Intensities with the O1s Intensity in the XPS Analysis of Anodically Oxidized Glass-like Carbon Samples. J. Mater. Sci. 2000, 35, 139– 146, DOI: 10.1023/A:1004761103919Google Scholar58https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXhtV2js7Y%253D&md5=7da67f90ee41dab4f35c1d5b0bb7030eCorrelation of C1s chemical state intensities with the O1s intensity in the XPS analysis of anodically oxidized glass-like carbon samplesYumitori, ShujiJournal of Materials Science (2000), 35 (1), 139-146CODEN: JMTSAS; ISSN:0022-2461. (Kluwer Academic Publishers)An XPS study of anodic oxidized glass-like carbon (GC) was conducted in order to investigate the inconsistency between O1s/C1s and oxygen concn. (Ocal.) calcd. from the curve fitting results of the C1s spectrum. Consideration of the asym. peak shape of the C1s spectrum is normally done in order to obtain precise curve fitting results. However, it was found that the 2nd-carbon peak should also be taken into consideration in the curve fitting process in addn. to the effect of asym. peak shape of carbon to obtain a consistent value of O1s/C1s. The 2nd graphitic peak is normally located +0.7-+0.8 eV away from the original C1s spectrum. The ratio of the 2nd graphitic peak area in the C1s spectrum increased as the elec. charge increased. However, the peak shapes of C1s spectra of anodic oxidized GC after heat treatment at 1500°C in argon atm. were almost the same as the C1s of untreated GC. Although the origin of the 2nd graphitic peak is not well understood, it may be related to the amt. of oxygen on the GC surface.
- 59Gengenbach, T. R.; Major, G. H.; Linford, M. R.; Easton, C. D. Practical Guides for X-Ray Photoelectron Spectroscopy (XPS): Interpreting the Carbon 1s Spectrum. J. Vac. Sci. Technol., A 2021, 39, 013204 DOI: 10.1116/6.0000682Google Scholar59https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXosVaqsg%253D%253D&md5=5a0800ea1909f4d480a1e9ea4ea7c88fPractical guides for x-ray photoelectron spectroscopy (XPS): Interpreting the carbon 1s spectrumGengenbach, Thomas R.; Major, George H.; Linford, Matthew R.; Easton, Christopher D.Journal of Vacuum Science & Technology, A: Vacuum, Surfaces, and Films (2021), 39 (1), 013204CODEN: JVTAD6; ISSN:0734-2101. (American Institute of Physics)The carbon 1s photoelectron spectrum is the most widely fit and analyzed narrow scan in the XPS literature. It is, therefore, critically important to adopt well-established protocols based on best practices for its anal., since results of these efforts affect research outcomes in a wide range of different application areas across materials science. Unfortunately, much XPS peak fitting in the scientific literature is inaccurate. In this guide, we describe and explain the most common problems assocd. with C 1s narrow scan anal. in the XPS literature. We then provide an overview of rules, principles, and considerations that, taken together, should guide the approach to the anal. of C 1s spectra. We propose that following this approach should result in (1) the avoidance of common problems and (2) the extn. of reliable, reproducible, and meaningful information from exptl. data. (c) 2021 American Institute of Physics.
- 60Momotenko, D.; Byers, J. C.; McKelvey, K.; Kang, M.; Unwin, P. R. High-Speed Electrochemical Imaging. ACS Nano 2015, 9, 8942– 8952, DOI: 10.1021/acsnano.5b02792Google Scholar60https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhtlWmurrP&md5=92612b126dbfeb0d7c08e8656d2326cdHigh-Speed Electrochemical ImagingMomotenko, Dmitry; Byers, Joshua C.; McKelvey, Kim; Kang, Minkyung; Unwin, Patrick R.ACS Nano (2015), 9 (9), 8942-8952CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)The design, development, and application of high-speed scanning electrochem. probe microscopy is reported. The approach allows the acquisition of high-resoln. images (typically 1000 pixels μm-2) at rates approaching 4 s per frame, while collecting up to 8000 image pixels per s, ∼1000 times faster than typical imaging speeds used. The focus is on scanning electrochem. cell microscopy (SECCM), but the principles and practicalities are applicable to many electrochem. imaging methods. The versatility of the high-speed scan concept is demonstrated at a variety of substrates, including imaging the electroactivity of a patterned self-assembled monolayer on gold, visualization of chem. reactions occurring at single wall carbon nanotubes, and probing nanoscale electrocatalysts for water splitting. These studies provide movies of spatial variations of electrochem. fluxes as a function of potential and a platform for the further development of high speed scanning with other electrochem. imaging techniques.
- 61Snowden, M. E.; Güell, A. G.; Lai, S. C. S.; McKelvey, K.; Ebejer, N.; O’Connell, M. A.; Colburn, A. W.; Unwin, P. R. Scanning Electrochemical Cell Microscopy: Theory and Experiment for Quantitative High Resolution Spatially-Resolved Voltammetry and Simultaneous Ion-Conductance Measurements. Anal. Chem. 2012, 84, 2483– 2491, DOI: 10.1021/ac203195hGoogle Scholar61https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhsVWjsL8%253D&md5=8863b846ef531cfd3b8272638ebc1126Scanning Electrochemical Cell Microscopy: Theory and Experiment for Quantitative High Resolution Spatially-Resolved Voltammetry and Simultaneous Ion-Conductance MeasurementsSnowden, Michael E.; Guell, Aleix G.; Lai, Stanley C. S.; McKelvey, Kim; Ebejer, Neil; O'Connell, Michael A.; Colburn, Alexander W.; Unwin, Patrick R.Analytical Chemistry (Washington, DC, United States) (2012), 84 (5), 2483-2491CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Scanning electrochem. cell microscopy (SECCM) is a high resoln. electrochem. scanning probe technique that employs a dual-barrel theta pipet probe contg. electrolyte soln. and quasi-ref. counter electrodes (QRCE) in each barrel. A thin layer of electrolyte protruding from the tip of the pipet ensures that a gentle meniscus contact is made with a substrate surface, which defines the active surface area of an electrochem. cell. The substrate can be an elec. conductor, semiconductor, or insulator. The main focus here is on the general case where the substrate is a working electrode, and both ion-conductance measurements between the QRCEs in the two barrels and voltammetric/amperometric measurements at the substrate can be made simultaneously. In usual practice, a small perpendicular oscillation of the probe with respect to the substrate is employed, so that an alternating conductance current (a.c.) develops, due to the change in the dimensions of the electrolyte contact (and hence resistance), as well as the direct conductance current (d.c.). The d.c. current can be predicted for a fixed probe by solving the Nernst-Planck equation and the a.c. response can also be derived from this response. Both responses agree well with expt. The pipet geometry plays an important role in controlling the d.c. conductance current and this is easily measured by microscopy. A key feature of SECCM is that mass transport to the substrate surface is by diffusion and, for charged analytes, ion migration which can be controlled and varied quantifiably via the bias between the two QRCEs. For a working electrode substrate this means that charged redox-active analytes can be transported to the electrode/soln. interface in a well-defined and controllable manner and that relatively fast heterogeneous electron transfer kinetics can be studied. The factors controlling the voltammetric response are detd. by both simulation and expt. Expts. demonstrate the realization of simultaneous quant. voltammetric and ion conductance measurements and also identify a general rule of thumb that the surface contacted by electrolyte is of the order of the pipet probe dimensions.
- 62Ebejer, N.; Schnippering, M.; Colburn, A. W.; Edwards, M. A.; Unwin, P. R. Localized High Resolution Electrochemistry and Multifunctional Imaging: Scanning Electrochemical Cell Microscopy. Anal. Chem. 2010, 82, 9141– 9145, DOI: 10.1021/ac102191uGoogle Scholar62https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXht12ju73O&md5=a669d8c8c6ae7ee63b48cb7fe61ce0a9Localized High Resolution Electrochemistry and Multifunctional Imaging: Scanning Electrochemical Cell MicroscopyEbejer, Neil; Schnippering, Mathias; Colburn, Alexander W.; Edwards, Martin A.; Unwin, Patrick R.Analytical Chemistry (Washington, DC, United States) (2010), 82 (22), 9141-9145CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)We describe highly localized electrochem. measurements and imaging using a simple, mobile theta pipet cell. Each channel (diam. <500 nm) of a tapered theta pipet is filled with electrolyte soln. and a Ag/AgCl electrode, between which a bias is applied, resulting in a conductance current across a thin meniscus of soln. at the end of the pipet, which is typically deployed in air or a controlled gaseous environment. When the position of the pipet normal to a surface of interest is oscillated, an oscillating component in the conductance current is generated when the meniscus at the end of the probe comes into contact with the surface and undergoes periodic (reversible) deformation, so as to modulate the soln. resistance. This oscillating current component can be used to maintain gentle contact of the soln. from the pipet cell with the surface and as a set point for high resoln. topog. imaging with the pipet. Simultaneously, the mean conductance current that flows between the pipet channels can be measured and is sensitive to the local nature of the interface, informing one, for example, on wettability and ion flow into or out of the surface investigated. Furthermore, conductor or semiconductor surfaces can be connected as a working electrode, with one of the electrodes in the pipet serving as a quasi-ref. electrode. This pipet cell then constitutes part of a dynamic electrochem. cell, with which direct voltammetric-amperometric imaging can be carried out simultaneously with conductance and topog. imaging. This provides multifunctional electrochem. maps of surfaces and interfaces at high spatial resoln. The prospects for the use of this new methodol. widely are highlighted through exemplar studies and a brief discussion of future applications.
- 63Bentley, C. L.; Kang, M.; Unwin, P. R. Scanning Electrochemical Cell Microscopy (SECCM) in Aprotic Solvents: Practical Considerations and Applications. Anal. Chem. 2020, 92, 11673– 11680, DOI: 10.1021/acs.analchem.0c01540Google Scholar63https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXhtFelur7J&md5=ef16375722f42c43595d8aec1de4fc50Scanning Electrochemical Cell Microscopy (SECCM) in Aprotic Solvents: Practical Considerations and ApplicationsBentley, Cameron L.; Kang, Minkyung; Unwin, Patrick R.Analytical Chemistry (Washington, DC, United States) (2020), 92 (17), 11673-11680CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Many applications in modern electrochem., notably electrosynthesis and energy storage/conversion take advantage of the "tunable" physicochem. properties (e.g., proton availability and/or electrochem. stability) of nonaq. (e.g., aprotic) electrolyte media. This work develops general guidelines pertaining to the use of scanning electrochem. cell microscopy (SECCM) in aprotic solvent electrolyte media to address contemporary structure-electrochem. activity problems. Using the simple outer-sphere Fc0/+ process (Fc = ferrocene) as a model system, high b.p. (low vapor pressure) solvents give rise to highly robust and reproducible electrochem., whereas volatile (low b.p.) solvents need to be mixed with suitable low m.p. supporting electrolytes (e.g., ionic liqs.) or high b.p. solvents to avoid complications assocd. with salt pptn./crystn. on the scanning (minutes to hours) time scale. When applied to perform microfabrication-specifically the electrosynthesis of the conductive polymer, polypyrrole-the optimized SECCM set up produces highly reproducible arrays of synthesized (electrodeposited) material on a commensurate scale to the employed pipet probe. Applying SECCM to map electrocatalytic activity-specifically the electro-oxidn. of iodide at polycryst. platinum-reveals unique (i.e., structure-dependent) patterns of surface activity, with grains of specific crystallog. orientation, grain boundaries and areas of high local surface misorientation identified as potential electrocatalytic "hot spots". The work herein further cements SECCM as a premier technique for structure-function-activity studies in (electro)materials science and will open up exciting new possibilities through the use of aprotic solvents for rational anal./design in electrosynthesis, microfabrication, electrochem. energy storage/conversion, and beyond.
- 64Dekanski, A.; Stevanović, J.; Stevanović, R.; Nikolić, B. Ž.; Jovanović, V. M. Glassy Carbon Electrodes I. Characterization and Electrochemical Activation. Carbon 2001, 39, 1195– 1205, DOI: 10.1016/S0008-6223(00)00228-1Google Scholar64https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXjtlSkurc%253D&md5=95b55c281b848052583a1a098c5d5a0fGlassy carbon electrodes. I. Characterization and electrochemical activationDekanski, A.; Stevanovic, J.; Stevanovic, R.; Nikolic, B. Z.; Jovanovic, V. M.Carbon (2001), 39 (8), 1195-1205CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Science Ltd.)Electrochem. properties of glassy carbon electrodes of two types were examd., one thermally treated at 1000°C (sample K) and another thermally treated at 2500° (sample G). Mech. polished or electrochem. polarized electrodes were characterized in NaOH, HClO4 and H2SO4 solns. by cyclic voltammetry (cv) at different sweep rates in the potential range between the hydrogen and oxygen evolution. The activity of the electrodes depended on the properties of the glassy carbon examd., as detd. by both the temp. of thermal treatment and the mech. or electrochem. pretreatment of the sample. It was noticed that both types of electrodes, when polished exhibited an increase in the double layer charge upon increasing the pH value of the soln. The cv charges, for both types of samples, increase upon anodic polarization. The higher the potential of oxidn., the more pronounced is the increase in charge, particularly in acidic soln. The increase in charge amts. from below 1 mC cm-2 for polished glassy carbon up to few hundreds of mC cm-2 for surfaces anodically polarized in acidic soln. Anal. of the dependence of voltammetric charge, as well as morphol. changes of the electrode surface, on the time of oxidn. suggests the existence of three stages in the electrochem. activation process. The first one occurs only once at the beginning of the activation, while the other two repeat themselves, reflecting a periodical activation and deactivation process. These stages were discussed and ascribed to a surface layer oxidn., graphite oxide layer growth and mech. destruction of the surface. Independent surface anal. by AES, XPS and STM confirms the results obtained by electrochem. methods.
- 65Soriaga, M. P.; Hubbard, A. T. Determination of the Orientation of Adsorbed Molecules at Solid-Liquid Interfaces by Thin-Layer Electrochemistry: Aromatic Compounds at Platinum Electrodes. J. Am. Chem. Soc. 1982, 104, 2735– 2742, DOI: 10.1021/ja00374a008Google Scholar65https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL38XhvV2ms7Y%253D&md5=1d02c1a22255875ba82772cfebc7bc43Determination of the orientation of adsorbed molecules at solid-liquid interfaces by thin-layer electrochemistry: aromatic compounds at platinum electrodesSoriaga, Manuel P.; Hubbard, Arthur T.Journal of the American Chemical Society (1982), 104 (10), 2735-42CODEN: JACSAT; ISSN:0002-7863.Accurate measurements of the limiting coverages of adsorbed mols. on smooth Pt electrodes are reported. Comparison of measurements with values calcd. for various possible mol. orientations indicates the predominant orientations of the adsorbed mols. Exptl. data were obtained by linear potential scan voltammetry and potential-step chronocoulometry using thin-layer electrodes. Calcns. were based upon covalent and van der Waals radii as tabulated by Pauling and were tested against the results of classical adsorption expts. Representing a wide range of structures and chem. properties, 40 of the following type of compds. were studied: simple diphenols and quinones; alkyl-substituted diphenols and quinones; dihydroxybenzaldehydes; halogenated diphenols and quinones; polyhydroxybenzenes and quinones; hexaoxocyclohexane; N-heteroaroms.; diphenols having surface-active side chains; polycyclic diphenols and quinones. The most probable orientation was detd. for each adsorbed compd.
- 66Chen, L.; Tanner, E. E. L.; Lin, C.; Compton, R. G. Impact Electrochemistry Reveals That Graphene Nanoplatelets Catalyse the Oxidation of Dopamine via Adsorption. Chem. Sci. 2018, 9, 152– 159, DOI: 10.1039/C7SC03672HGoogle Scholar66https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhslemt7bI&md5=ea404bed5d5b9447a30e1a31c5f4e3d3Impact electrochemistry reveals that graphene nanoplatelets catalyse the oxidation of dopamine via adsorptionChen, Lifu; Tanner, Eden E. L.; Lin, Chuhong; Compton, Richard G.Chemical Science (2018), 9 (1), 152-159CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)Graphene nanoplatelets are shown to electrocatalyze the oxidn. of dopamine. Single entity measurements ('nano-impacts') coupled with microdisc voltammetry and UV-visible spectroscopy reveal that adsorption of dopamine and its oxidised product on the graphene nanoplatelets is the key factor causing the obsd. catalysis. Genetic implications are drawn both for the study of catalysts in general and for graphene nanoplatelets in particular.
- 67Soriaga, M. P.; Hubbard, A. T. Determination of the Orientation of Aromatic Molecules Adsorbed on Platinum Electrodes. The Effect of Solute Concentration. J. Am. Chem. Soc. 1982, 104, 3937– 3945, DOI: 10.1021/ja00378a026Google Scholar67https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL38XktlSiu7o%253D&md5=98ef00c29ef0463ac52e1376f98c268dDetermination of the orientation of aromatic molecules adsorbed on platinum electrodes. The effect of solute concentrationSoriaga, Manuel P.; Hubbard, Arthur T.Journal of the American Chemical Society (1982), 104 (14), 3937-45CODEN: JACSAT; ISSN:0002-7863.Accurate measurements of the amts. of arom. mols. adsorbed on smooth polycryst. Pt electrodes in aq. solns. are reported as a function of concn. The measurements were made by electrochem. methods using thin-layer cells. A plot of adsorbed amt. vs. concn. shows that most of the subject compds. display multiple plateaus sepd. by abrupt transitions to higher densities at higher concns. Comparison of plateau values with model calcns., based upon covalent and van der Waals radii tabulated by Pauling, reveals that a series of definite orientations are adopted as the adsorbate concn. is increased; each individual orientation was stable over an appreciable range of concn. Twenty-six compds., representing a variety of structures and chem. properties, were studied: simple diphenols; alkyldiphenols; polyhydroxybenzenes; halogenated diphenols; N-heteroaroms.; diphenols having surface-active side chains; polycyclic phenols and quinones; and hydroquinone mercaptans.
- 68Bard, A. J.; Faulkner, L. R. Electrochemical Methods: Fundamentals and Applications, 2nd ed.; Wiley, 2001.Google ScholarThere is no corresponding record for this reference.
- 69DuVall, S. H.; McCreery, R. L. Self-Catalysis by Catechols and Quinones during Heterogeneous Electron Transfer at Carbon Electrodes. J. Am. Chem. Soc. 2000, 122, 6759– 6764, DOI: 10.1021/ja000227uGoogle Scholar69https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXksVejsLs%253D&md5=18f9b55d102c8efa1a03322bf5a65af0Self-catalysis by Catechols and Quinones during Heterogeneous Electron Transfer at Carbon ElectrodesDuVall, Stacy H.; McCreery, Richard L.Journal of the American Chemical Society (2000), 122 (28), 6759-6764CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Heterogeneous electron transfer kinetics for several catechols were examd. on glassy carbon (GC) electrodes in aq. soln. Electrode prepns. yielded GC surfaces with low levels of oxides or adsorbed impurities, which exhibited strong adsorption of dopamine (DA) and related catechols. Conversely, modification of GC with an org. monolayer suppressed DA adsorption and in many cases prevented electron transfer. By relating catechol adsorption to obsd. electron transfer, an adsorbed layer of catechol acts as an electrocatalyst for soln.-phase redox components. Physisorbed or chemisorbed monolayers of several quinones, including duroquinone, anthraquinone, and dopamine itself, are catalytic toward dopamine oxidn. and redn., but nitrophenyl, trifluoromethylphenyl, and methylene blue monolayers severely inhibit electron transfer. The magnitude of inhibition was affected by electrostatic attraction or repulsion between the surface and the redox system, but the major factor controlling electron-transfer kinetics is not electrostatic in origin. The most plausible mechanism is self-catalysis by an adsorbed quinone, which remained adsorbed during electron transfer to a redox couple in soln. The results are inconsistent with a redox mediation mechanism involving a redox cross-reaction between adsorbed and soln. quinone couples. An interaction between the adsorbed and soln. quinone species during electron transfer appears to catalyze one or more of the steps in the scheme of squares mechanism for hydroquinone/quinone redox systems. The results explain a variety of observations about catechol and hydroquinone electrochem., as well as provide more fundamental insights into quinone electron-transfer mechanisms.
- 70Syeed, A. J.; Li, Y.; Ostertag, B. J.; Brown, J. W.; Ross, A. E. Nanostructured Carbon-Fiber Surfaces for Improved Neurochemical Detection. Faraday Discuss. 2022, 233, 336– 353, DOI: 10.1039/D1FD00049GGoogle ScholarThere is no corresponding record for this reference.https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=&md5=9874b665cc7a056b8e2f928dd3112440
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This article references 70 other publications.
- 1Baur, J. E.; Kristensen, E. W.; May, L. J.; Wiedemann, D. J.; Wightman, R. M. Fast-Scan Voltammetry of Biogenic Amines. Anal. Chem. 1988, 60, 1268– 1272, DOI: 10.1021/ac00164a0061https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL1cXktVegs7s%253D&md5=bd5eecd3cba2ae2916121587dbb149d3Fast-scan voltammetry of biogenic aminesBaur, John E.; Kristensen, Eric W.; May, Leslie J.; Wiedemann, Donna J.; Wightman, R. MarkAnalytical Chemistry (1988), 60 (13), 1268-72CODEN: ANCHAM; ISSN:0003-2700.The use of fast-scan cyclic voltammetry was explored as an anal. technique for the detection of biogenic amines. Cyclic voltammograms were recorded at a scan rate of 200 V s-1 at C-fiber electrodes with and without coating of a perfluorinated ion-exchange material. Voltammograms were recorded in a flow-injection app., and background subtraction was used to remove the residual current. Voltammograms for the oxidn. of 4-methylcatechol at uncoated electrodes had the peak amplitude expected for the previously published oxidn. mechanism for catechols at intermediate pH. In contrast, voltammograms for dopamine, dihydroxybenzylamine, and norepinephrine showed much larger peak currents. Semiintegration of these voltammograms gives a peak-shaped curve indicative of adsorption. At coated electrodes, the voltammograms for anionic species are greatly attenuated, whereas for the biogenic amines the peak currents are larger than at uncoated electrodes. Fast-scan voltammetry is particularly advantageous for the detn. of 5-hydroxytryptamine. The short electrolysis time prevents the oxidn. products from forming an insulating film on the electrode. Although adsorption of these compds. occurs in their reduced form, this feature is advantageous since it increases the signal-to-noise ratio. Submicromolar detection limits can be achieved because of the preconcn. on the electrode surface.
- 2Heien, M. L. A. V.; Khan, A. S.; Ariansen, J. L.; Cheer, J. F.; Phillips, P. E. M.; Wassum, K. M.; Wightman, R. M. Real-Time Measurement of Dopamine Fluctuations after Cocaine in the Brain of Behaving Rats. Proc. Natl. Acad. Sci. U. S. A. 2005, 102, 10023– 10028, DOI: 10.1073/pnas.05046571022https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXmvVeltLc%253D&md5=2bdc42f6641711d1a5f1a282c7ee82b1Real-time measurement of dopamine fluctuations after cocaine in the brain of behaving ratsHeien, Michael L. A. V.; Khan, Amina S.; Ariansen, Jennifer L.; Cheer, Joseph F.; Phillips, Paul E. M.; Wassum, Kate M.; Wightman, R. MarkProceedings of the National Academy of Sciences of the United States of America (2005), 102 (29), 10023-10028CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)Dopamine neurotransmission has been implicated in the modulation of many cognitive processes. Both rapid (phasic) and slower (tonic) changes in its extracellular concn. contribute to its complex actions. Fast in vivo electrochem. techniques can measure extracellular dopamine on a rapid time scale but without the selectivity afforded with slower techniques that use chem. sepns. Cyclic voltammetry improves chem. resoln. over other electrochem. methods, and it can resolve dopamine changes in the brains of behaving rodents over short epochs (<10 s). With this method, however, selective detection of slower dopamine changes is still elusive. Here we demonstrate that principal component regression of cyclic voltammetry data enables quantification of changes in dopamine and extracellular pH. Using this method, we show that cocaine modifies dopamine release in two ways: dopamine concn. transients increase in frequency and magnitude, whereas a gradual increase in steady-state dopamine concn. occurs over 90 s.
- 3Garris, P. A.; Wightman, R. M. In Vivo Voltammetric Measurement of Evoked Extracellular Dopamine in the Rat Basolateral Amygdaloid Nucleus. J. Physiol. 1994, 478, 239– 249, DOI: 10.1113/jphysiol.1994.sp0202463https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2cXlsV2mtrY%253D&md5=2f1c389d7482609ab93baf35dd2e68eaIn vivo voltammetric measurement of evoked extracellular dopamine in the rat basolateral amygdaloid nucleusGarris, Paul A.; Wightman, R. MarkJournal of Physiology (Cambridge, United Kingdom) (1994), 478 (2), 239-49CODEN: JPHYA7; ISSN:0022-3751.The in vivo measurement of evoked extracellular dopamine was established in the basolateral amygdaloid nucleus (BAN) using fast-scan cyclic voltammetry at carbon-fiber microelectrodes. The identification of evoked extracellular dopamine in the BAN was based on anatomical, electrochem. and pharmacol. criteria. Electrochem. and pharmacol. evidence indicated that the species was a catecholamine. Mesencephalic sites eliciting overflow and amygdaloid sites supporting overflow correlated well with the mesoamygdaloid dopamine innervation. Marked differences in the dynamics and magnitude of evoked dopamine overflow were obsd. in the BAN, caudate-putamen and amygdalo-striatal transition area. The results underscore the importance of making spatially resolved measurements of extracellular dopamine in the amygdala. Mesoamygdaloid dopamine neurons have similar release characteristics as mesostriatal dopamine neurons but share with mesoprefrontal cortical dopamine neurons the ability to use a greater percentage of intraneuronal dopamine stores for release.
- 4Adams, R. N. Probing Brain Chemistry with Electroanalytical Techniques. Anal. Chem. 1976, 48, 1126A– 1138A, DOI: 10.1021/ac50008a0014https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE28XlvVymsr4%253D&md5=e31be3ff1e797e8c5b16e830d76333e9Probing brain chemistry with electroanalytical techniquesAdams, Ralph N.Analytical Chemistry (1976), 48 (14), 1126A-1138ACODEN: ANCHAM; ISSN:0003-2700.A review with 33 refs. describing the use of such electroanal. techniques as voltammetry, chronoamperometry, various pulsing methods, etc. in neurochem. and neurophysiol. research.
- 5Wightman, R. M.; May, L. J.; Michael, A. C. Detection of Dopamine Dynamics in the Brain. Anal. Chem. 1988, 60, 769A– 779A, DOI: 10.1021/ac00164a0015https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL1cXksVymsLg%253D&md5=ad9372ae0e12b8209e32bd46a2d8ac7bDetection of dopamine dynamics in the brainWightman, R. Mark; May, Leslie J.; Michael, Adrian C.Analytical Chemistry (1988), 60 (13), 769A-770A, 772A, 774A-776A, 778A-779ACODEN: ANCHAM; ISSN:0003-2700.A review, with 36 refs., on the detn. of dopamine dynamics in the brain with emphasis on in vitro electrochem. and voltammetry.
- 6Ferapontova, E. E. Electrochemical Analysis of Dopamine: Perspectives of Specific In Vivo Detection. Electrochim. Acta 2017, 245, 664– 671, DOI: 10.1016/j.electacta.2017.05.1836https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXht1WhtLjE&md5=50c5f57894d5228d89c3d0abb884c729Electrochemical Analysis of Dopamine: Perspectives of Specific In Vivo DetectionFerapontova, Elena E.Electrochimica Acta (2017), 245 (), 664-671CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Ltd.)A review. Direct electrochem. anal. of in vivo levels of dopamine, whose metabolic transformation in the brain can be correlated with a no. of neurodegenerative disorders such as Parkinson's and Alzheimer's diseases as well as psychosis and drug addiction, allows studying their mechanisms and the ways they can be treated. However, direct electrochem. anal. of dopamine can often be masked by electrochem. responses from structurally related neurotransmitters, dopamine precursors and products of its metabolic transformation, whose redox potentials overlap with those of dopamine. In this mini-review, the state-of-the-art in the field and recent trends in specific electroanal. of dopamine in the presence of structurally related neurotransmitters are reviewed and critically discussed.
- 7Lin, Q.; Li, Q.; Batchelor-McAuley, C.; Compton, R. G. Two-Electron, Two-Proton Oxidation of Catechol: Kinetics and Apparent Catalysis. J. Phys. Chem. C 2015, 119, 1489– 1495, DOI: 10.1021/jp511414b7https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXitFehsLzK&md5=3122ebe4789aaa27174f1f83a48a04f9Two-Electron, Two-Proton Oxidation of Catechol: Kinetics and Apparent CatalysisLin, Qianqi; Li, Qian; Batchelor-McAuley, Christopher; Compton, Richard G.Journal of Physical Chemistry C (2015), 119 (3), 1489-1495CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)The study of proton-coupled electron transfer reactions is of great current interest. In this work, the catechol redox process was studied voltammetrically in the pH range from 1.0 to 14.0 using a glassy carbon electrode. Anal. of the peak potentials and currents together with Tafel anal. allowed the inference of the likely transition states and electrode reaction mechanism. Modification of the glassy carbon electrode surface with sparse coverages of alumina particles was shown to lead to strong apparent catalysis of the catechol redox process at low pH. A possible mechanism for this is proposed.
- 8Hawley, M. D.; Tatawawadi, S. V.; Piekarski, S.; Adams, R. N. Electrochemical Studies of the Oxidation Pathways of Catecholamines. J. Am. Chem. Soc. 1967, 89, 447– 450, DOI: 10.1021/ja00978a0518https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaF2sXksF2lsw%253D%253D&md5=4bf675e95e57d0f53c7519ee9ad79ffcElectrochemical studies of the oxidation pathways of catechol aminesHawley, M. Dale; Tatwawadi, Shankar V.; Piekarski, S.; Adams, Ralph NormanJournal of the American Chemical Society (1967), 89 (2), 447-50CODEN: JACSAT; ISSN:0002-7863.Modern, fast-sweep electrochem. techniques have been applied to the study of the oxidn. pathways of catechol amines in vitro. These techniques allow pos. identifications of the transient intermediates, i.e., the open-chain o-quinones, and precise detns. of the rate of intramol. cyclization to the substituted indole and its subsequent oxidn. to the aminochrome. Significant differences in the rates of cyclization of adrenaline and noradrenaline are consistent with recent findings on the reactions of these catechol amines. 20 references.
- 9Lin, C.; Chen, L.; Tanner, E. E. L.; Compton, R. G. Electroanalytical Study of Dopamine Oxidation on Carbon Electrodes: From the Macro- to the Micro-Scale. Phys. Chem. Chem. Phys. 2018, 20, 148– 157, DOI: 10.1039/C7CP07450F9https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhvFSmsL3P&md5=ceb8cc0fbda4e0f6b86df4993dc372beElectroanalytical study of dopamine oxidation on carbon electrodes: from the macro- to the micro-scaleLin, Chuhong; Chen, Lifu; Tanner, Eden E. L.; Compton, Richard G.Physical Chemistry Chemical Physics (2018), 20 (1), 148-157CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)The oxidn. of dopamine in strongly acidic (pH = 0) soln. was studied using microdisk, microcylinder and macro-electrodes together with a range of voltage scan rates. Kinetic and mechanistic anal. over the full range of mass transport conditions show a behavior consistent with an ECE process with a fast chem. step and in which the 2nd electron transfer is thermodynamically more favorable than the 1st step. Accordingly the reaction effectively behaves as an EE process.
- 10Li, Y.; Liu, M.; Xiang, C.; Xie, Q.; Yao, S. Electrochemical Quartz Crystal Microbalance Study on Growth and Property of the Polymer Deposit at Gold Electrodes during Oxidation of Dopamine in Aqueous Solutions. Thin Solid Films 2006, 497, 270– 278, DOI: 10.1016/j.tsf.2005.10.04810https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XjvVSktw%253D%253D&md5=cbda5744e511adf6ebad78fb774699e0Electrochemical quartz crystal microbalance study on growth and property of the polymer deposit at gold electrodes during oxidation of dopamine in aqueous solutionsLi, Yunlong; Liu, Meiling; Xiang, Canhui; Xie, Qingji; Yao, ShouzhuoThin Solid Films (2006), 497 (1-2), 270-278CODEN: THSFAP; ISSN:0040-6090. (Elsevier B.V.)Polymer growth at Au electrodes during cyclic voltammetric oxidn. of dopamine (DA) in aq. solns. was studied as functions of DA concn., soln. pH and potential-sweep rate using electrochem. quartz crystal microbalance technique. When the DA concn. was 2 × 10- 4 M or above and the soln. pH was 3.86 or above, the intramol. cyclization of the 1st-step oxidn. product of DA occurred significantly and further isomerization and oxidn. of the cyclization product led to polymer growth at an Au electrode. An ECECEE mechanism for DA oxidn. and subsequent polymn. of the oxidn. product (5,6-indolequinone) at favorable pH is suggested. The poly(indole)-like polymn. pathway was acceptably supported by comparative minigrid-electrode expts. via FTIR characterization of poly(indole) and the polymer from DA oxidn. The quasi 1st-order rate const. of the intramol. cyclization was estd. at several pH values by cyclic voltammetry. Also the intramol. cyclization and subsequent polymer deposition at the electrode can be notably inhibited by using various high-concn. supporting electrolytes, with inhibition sequences as ClO4- > NO3- > SO42- > gluconate > F- > citrate > AcO- for anions and NH4+ > Na+ > Li+ > K+ > Cs+ > Rb+ for cations. An Au electrode modified with the polymer from DA oxidn. exhibited attractive cationic permselectivity, namely, effectively blocking the electrochem. reactions of anionic ferrocyanide and ascorbic acid (AA) while well retaining the electrochem. activities of hexaammineruthenium (III) and DA as cationic species. A 500-Hz polymer film could effectively block the redox current of AA up to 2.0 mM. The semi-deriv. voltammetric peak height for DA oxidn. was linear with DA concn. up to 1.3 × 10- 5 M, with sensitivities of 0.0766 and 0.119 μA s- 1/2/μM, as well as lower detection limits of 4 × 10- 7 and 2 × 10- 7 M (S / N = 3) in a phosphate buffer soln. without AA and with 1.0 mM coexisting AA, resp.
- 11Patel, A. N.; Tan, S.; Miller, T. S.; Macpherson, J. V.; Unwin, P. R. Comparison and Reappraisal of Carbon Electrodes for the Voltammetric Detection of Dopamine. Anal. Chem. 2013, 85, 11755– 11764, DOI: 10.1021/ac401969q11https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhslyms7zF&md5=95ab8dfec178dca70c369b20bc68f6edComparison and Reappraisal of Carbon Electrodes for the Voltammetric Detection of DopaminePatel, Anisha N.; Tan, Sze-yin; Miller, Thomas S.; Macpherson, Julie V.; Unwin, Patrick R.Analytical Chemistry (Washington, DC, United States) (2013), 85 (24), 11755-11764CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)The electrooxidn. of dopamine (DA) was studied on the unmodified surfaces of five different classes of C electrodes: glassy C (GC), O-terminated polycryst. B-doped diamond (pBDD), edge plane pyrolytic graphite (EPPG), basal plane pyrolytic graphite (BPPG), and the basal surface of highly oriented pyrolytic graphite (HOPG), encompassing five distinct grades with step edge d. and coverage varying by >2 orders of magnitude. Surfaces were prepd. carefully and characterized by a range of techniques, including at. force microscopy (AFM), field emission SEM (FE-SEM), and Raman spectroscopy. Although pBDD is the least susceptible to surface fouling (even at relatively high DA concns.), the reaction showed sluggish kinetics on this electrode. In contrast, DA electrooxidn. at pristine basal plane HOPG at concns. ≤100 μM in 0.15 M PBS, pH 7.2, showed fast kinetics and only minor susceptibility toward surface fouling from DA byproducts, although the extent of HOPG surface contamination by oxidn. products increased substantially at higher concns. (with the response similar on all grades, irresp. of step edge coverage). EPPG also showed a fast response, with little indication of passivation with repeated voltammetric cycling but a relatively high background signal due to the high capacitance of this graphite surface termination. Of all five C electrode types, freshly cleaved basal plane HOPG showed the clearest signal (distinct from the background) at low concns. of DA (<10 μM) as a consequence of the low capacitance. Studies of the electrochem. oxidn. of DA in the presence of the common interferents ascorbic acid (AA) and serotonin (5-HT), of relevance to neurochem. anal., showed that the signals for DA were still clearly and easily resolved at basal plane HOPG surfaces. In the presence of AA, repetitive voltammetry caused products of AA electrooxidn. to adsorb onto the HOPG surface, forming a permselective film that allowed the electrochem. oxidn. of DA to proceed unimpeded, while greatly inhibiting the electrochem. response of AA itself. The studies presented provide conclusive evidence that the pristine surface of basal plane HOPG is highly active for the detection of DA, irresp. of the step edge d. and method of cleavage, and adds to a growing body of evidence that the basal plane of HOPG is a much more active electrode for many classes of electrode reactions than previously believed.
- 12Peltola, E.; Sainio, S.; Holt, K. B.; Palomäki, T.; Koskinen, J.; Laurila, T. Electrochemical Fouling of Dopamine and Recovery of Carbon Electrodes. Anal. Chem. 2018, 90, 1408– 1416, DOI: 10.1021/acs.analchem.7b0479312https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhvFGjtrjE&md5=41dc88ce2a110d7f61d43eaea339c0e0Electrochemical Fouling of Dopamine and Recovery of Carbon ElectrodesPeltola, Emilia; Sainio, Sami; Holt, Katherine B.; Palomaki, Tommi; Koskinen, Jari; Laurila, TomiAnalytical Chemistry (Washington, DC, United States) (2018), 90 (2), 1408-1416CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)A significant problem with implantable sensors is electrode fouling, which has been proposed as the main reason for biosensor failures in vivo. Electrochem. fouling is typical for dopamine (DA) as its oxidn. products are very reactive and the resulting polydopamine has a robust adhesion capability to virtually all types of surfaces. The degree of DA fouling of different carbon electrodes with different terminations was detd. using cyclic voltammetry (CV) and scanning electrochem. microscopy (SECM) approach curves and imaging. The rate of electron transfer kinetics at the fouled electrode surface was detd. from SECM approach curves, allowing a comparison of insulating film thickness for the different terminations. SECM imaging allowed the detn. of different morphologies, such as continuous layers or islands, of insulating material. Heterogeneous modification of carbon electrodes with carboxyl-amine functionalities offers protection against formation of an insulating polydopamine layer, while retaining the ability to detect DA. The benefits of the heterogeneous termination are proposed to be due to the electrostatic repulsion between amino-functionalities and DA. Furthermore, the cond. of the surfaces as well as the response toward DA was recovered close to the original performance level after cleaning the surfaces for 10-20 cycles in H2SO4 on all materials but pyrolytic carbon (PyC). The recovery capacity of the PyC electrode was lower, possibly due to stronger adsorption of DA on the surface.
- 13McCreery, R. L. Advanced Carbon Electrode Materials for Molecular Electrochemistry. Chem. Rev. 2008, 108, 2646– 2687, DOI: 10.1021/cr068076m13https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXnt1Wjsb8%253D&md5=7f0e9958035ae161b937dd0508b959bfAdvanced Carbon Electrode Materials for Molecular ElectrochemistryMcCreery, Richard L.Chemical Reviews (Washington, DC, United States) (2008), 108 (7), 2646-2687CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)A review. The properties of C are described and how these properties relate electrochem. properties, including electrode kinetics, adsorption and electrocatalysis. Fabrication and novel aspects are described for carbon materials, including, boron-doped diamond, carbon nanotubes, vapor deposited carbon films and various composite electrodes. Carbon electrode material for org. and biol. redox reactions are cited.
- 14Venton, B. J.; Cao, Q. Fundamentals of Fast-Scan Cyclic Voltammetry for Dopamine Detection. Analyst 2020, 145, 1158– 1168, DOI: 10.1039/C9AN01586H14https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXisVyqsrnP&md5=7c87cc2797c92a70ad60a638f9b74056Fundamentals of fast-scan cyclic voltammetry for dopamine detectionVenton, B. Jill; Cao, QunAnalyst (Cambridge, United Kingdom) (2020), 145 (4), 1158-1168CODEN: ANALAO; ISSN:0003-2654. (Royal Society of Chemistry)A review. Fast-scan cyclic voltammetry (FSCV) was used with carbon-fiber microelectrodes for the real-time detection of neurotransmitters on the subsecond time scale. With FSCV, the potential is ramped up from a holding potential to a switching potential and back, usually at a 400 V s-1 scan rate and a frequency of 10 Hz. The plot of current vs. applied potential, the cyclic voltammogram (CV), has a very different shape for FSCV than for traditional cyclic voltammetry collected at scan rates which are 1000-fold slower. Here, the authors explore the theory of FSCV, with a focus on dopamine detection. First, the authors examine the shape of the CVs. Background currents, which are 100-fold higher than faradaic currents, are subtracted out. Peak sepn. is primarily due to slow electron transfer kinetics, while the sym. peak shape is due to exhaustive electrolysis of all the adsorbed neurotransmitters. Second, the authors explain the origins of the dopamine waveform, and the factors that limit the holding potential (oxygen redn.), switching potential (water oxidn.), scan rate (electrode instability), and repetition rate (adsorption). Third, data anal., from data visualization with color plots, to the automated algorithms like principal components regression that distinguish dopamine from pH changes are discussed. Finally, newer applications are discussed, including optimization of waveforms for analyte selectivity, carbon nanomaterial electrodes that trap dopamine, and basal level measurements that facilitate neurotransmitter measurements on a longer time scale. FSCV theory is complex, but understanding it enables better development of new techniques to monitor neurotransmitters in vivo.
- 15Thiagarajan, S.; Tsai, T.-H.; Chen, S.-M. Easy Modification of Glassy Carbon Electrode for Simultaneous Determination of Ascorbic Acid, Dopamine and Uric Acid. Biosens. Bioelectron. 2009, 24, 2712– 2715, DOI: 10.1016/j.bios.2008.12.01015https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXjvVyltbw%253D&md5=8eccb096c0a20732f3b9f64843ea2908Easy modification of glassy carbon electrode for simultaneous determination of ascorbic acid, dopamine and uric acidThiagarajan, Soundappan; Tsai, Tsung-Hsuan; Chen, Shen-MingBiosensors & Bioelectronics (2009), 24 (8), 2712-2715CODEN: BBIOE4; ISSN:0956-5663. (Elsevier B.V.)A glassy carbon electrode (GCE) was modified by electrochem. oxidn. in mild acidic media (0.1 mol L-1 H2SO4) and could be applied for individual and simultaneous detn. of ascorbic acid (AA), dopamine (DA), and uric acid (UA). Oxidized GCE shows a single redox couple (E0' = -2.5 mV) which is based on the formation functional groups during the electrochem. pretreatment process. The proposed GCE successfully decreases the over potentials for the oxidn. process of these species (AA, DA, and UA) compared with bare GCE. The oxidized GCE has its own simplicity, stability, high sensitivity, and possesses the potential for simultaneous detn. of AA, DA, and UA.
- 16Sansuk, S.; Bitziou, E.; Joseph, M. B.; Covington, J. A.; Boutelle, M. G.; Unwin, P. R.; Macpherson, J. V. Ultrasensitive Detection of Dopamine Using a Carbon Nanotube Network Microfluidic Flow Electrode. Anal. Chem. 2013, 85, 163– 169, DOI: 10.1021/ac302358616https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhsleqtLnM&md5=422de4efd3fc1d0c4f2e829514223ec6Ultrasensitive Detection of Dopamine Using a Carbon Nanotube Network Microfluidic Flow ElectrodeSansuk, Siriwat; Bitziou, Eleni; Joseph, Maxim B.; Covington, James A.; Boutelle, Martyn G.; Unwin, Patrick R.; MacPherson, Julie V.Analytical Chemistry (Washington, DC, United States) (2013), 85 (1), 163-169CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)The electrochem. measurement of dopamine (DA), in phosphate buffer soln. (pH 7.4), with a limit of detection (LOD) of ∼5 pM in 50 μL (∼ 250 attomol) is achieved using a band electrode comprised of a sparse network of pristine single-walled carbon nanotubes (SWNTs), which covers <1% of the insulating substrate. The SWNT electrodes are deployed as amperometric (anodic) detectors in microfluidic cells, produced by microstereolithog., designed specifically for flow injection anal. (FIA). The flow cells, have a channel (duct) geometry, with cell height of 25 μm, and are shown to be hydrodynamically well-defined, with laminar Poiseuille flow. In the arrangement where soln. continuously flows over the electrode but the electrode is only exposed to the analyte for short periods of time, the SWNT electrodes do not foul and can be used repeatedly for many months. The LOD for dopamine (DA), reported herein, is significantly lower than previous reports using FIA-electrochem. detection. Furthermore, the SWNT electrodes can be used as grown, i.e., they do not require chem. modification or cleanup. The extremely low background signals of the SWNT electrodes, as a consequence of the sparse surface coverage and the low intrinsic capacitance of the SWNTs, means that no signal processing is required to measure the low currents for DA oxidn. at trace levels. DA detection in artificial cerebral fluid is also possible with a LOD of ∼50 pM in 50 μL (∼2.5 fmol).
- 17Schmidt, A. C.; Wang, X.; Zhu, Y.; Sombers, L. A. Carbon Nanotube Yarn Electrodes for Enhanced Detection of Neurotransmitter Dynamics in Live Brain Tissue. ACS Nano 2013, 7, 7864– 7873, DOI: 10.1021/nn402857u17https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXht1Ghs7bK&md5=cb67d35dec757652c58cf51917a943ecCarbon Nanotube Yarn Electrodes for Enhanced Detection of Neurotransmitter Dynamics in Live Brain TissueSchmidt, Andreas C.; Wang, Xin; Zhu, Yuntian; Sombers, Leslie A.ACS Nano (2013), 7 (9), 7864-7873CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)This work demonstrates the potential of nanoscale carbon electrode materials for improved detection of electroactive neurotransmitter dynamics in the brain. Individual multiwalled carbon nanotubes were synthesized via chem. vapor deposition, spun into yarns, and used in the fabrication of disk microelectrodes that were subsequently characterized using scanning electron and at. force microscopies. The carbon nanotube yarn electrodes were coupled with fast-scan cyclic voltammetry and used to discriminately detect rapid neurotransmitter fluctuations in acute brain slices. The results demonstrate that the distinct structural and electronic properties of the nanotubes result in improved selectivity, sensitivity, and spatial resoln., as well as faster apparent electron transfer kinetics when compared to the conventional carbon-fiber microelectrodes typically used in vivo.
- 18Martín-Yerga, D.; Costa Rama, E.; Costa García, A. Electrochemical Study and Determination of Electroactive Species with Screen-Printed Electrodes. J. Chem. Educ. 2016, 93, 1270– 1276, DOI: 10.1021/acs.jchemed.5b0075518https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xls1Orsrk%253D&md5=78555a5d619c04c4219161e0c68abfedElectrochemical Study and Determination of Electroactive Species with Screen-Printed ElectrodesMartin-Yerga, Daniel; Costa Rama, Estefania; Costa Garcia, AgustinJournal of Chemical Education (2016), 93 (7), 1270-1276CODEN: JCEDA8; ISSN:0021-9584. (American Chemical Society and Division of Chemical Education, Inc.)A lab appropriate to introduce voltammetric techniques and basic electrochem. parameters is described in this work. It is suitable to study theor. concepts of electrochem. in an applied way for anal. undergraduate courses. Two electroactive species, hexaammineruthenium and dopamine, are used as simple redox systems. Screen-printed electrodes are used in order to allow the students to focus on the electrochem. and avoid tedious instrumentation prepn. The anal. detn. of the species studied with sensitive techniques such as differential-pulse or square-wave voltammetry is also performed.
- 19Suzuki, A.; Ivandini, T. A.; Yoshimi, K.; Fujishima, A.; Oyama, G.; Nakazato, T.; Hattori, N.; Kitazawa, S.; Einaga, Y. Fabrication, Characterization, and Application of Boron-Doped Diamond Microelectrodes for in Vivo Dopamine Detection. Anal. Chem. 2007, 79, 8608– 8615, DOI: 10.1021/ac071519h19https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXhtFalurnM&md5=e9fb365269a0b600e7df8d8fad6cf81fFabrication, characterization, and application of boron-doped diamond microelectrodes for in vivo dopamine detectionSuzuki, Akane; Ivandini, Tribidasari A.; Yoshimi, Kenji; Fujishima, Akira; Oyama, Genko; Nakazato, Taizo; Hattori, Nobutaka; Kitazawa, Shigeru; Einaga, YasuakiAnalytical Chemistry (Washington, DC, United States) (2007), 79 (22), 8608-8615CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Highly boron-doped diamond (BDD) was deposited on chem. etched micrometer-sized tungsten wires using microwave plasma assisted chem. vapor deposition (MPCVD), and these were used to fabricate BDD microelectrodes. BDD microelectrodes with very small diam. (about 5 μm) and 250 μm in length could be made successfully. In addn. to the unique properties of BDD electrodes, such as a very low background current, high stability, and selective oxidn. of dopamine (DA) in the presence of ascorbic acid (AA), other superior properties of the microelectrodes, including a const. current response, an increase in the mass transport, and the ability for use in high resistance media were also shown. An application study was conducted for in vivo detection of DA in mouse brain, where the BDD microelectrode was inserted into the corpus striatum of the mouse brain. A clear signal current response following medial forebrain bundle (MFB) stimulation could be obtained with high sensitivity. Excellent stability was achieved, indicating that the BDD microelectrodes are very promising for future in vivo electroanal.
- 20Sánchez Calvo, A.; Botas, C.; Martín-Yerga, D.; Álvarez, P.; Menéndez, R.; Costa-García, A. Comparative Study of Screen-Printed Electrodes Modified with Graphene Oxides Reduced by a Constant Current. J. Electrochem. Soc. 2015, 162, B282, DOI: 10.1149/2.1021510jesThere is no corresponding record for this reference.
- 21Yang, C.; Wang, Y.; Jacobs, C. B.; Ivanov, I. N.; Venton, B. J. O2 Plasma Etching and Antistatic Gun Surface Modifications for CNT Yarn Microelectrode Improve Sensitivity and Antifouling Properties. Anal. Chem. 2017, 89, 5605– 5611, DOI: 10.1021/acs.analchem.7b0078521https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXmt12kt7s%253D&md5=b92895213511294e2046e9e6fbd0d7c9O2 Plasma Etching and Antistatic Gun Surface Modifications for CNT Yarn Microelectrode Improve Sensitivity and Antifouling PropertiesYang, Cheng; Wang, Ying; Jacobs, Christopher B.; Ivanov, Ilia N.; Venton, B. JillAnalytical Chemistry (Washington, DC, United States) (2017), 89 (10), 5605-5611CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Carbon nanotube (CNT) based microelectrodes exhibit rapid and selective detection of neurotransmitters. While different fabrication strategies and geometries of CNT microelectrodes have been characterized, relatively little research has investigated ways to selectively enhance their electrochem. properties. In this work, the authors introduce two simple, reproducible, low-cost, and efficient surface modification methods for carbon nanotube yarn microelectrodes (CNTYMEs): O2 plasma etching and antistatic gun treatment. O2 plasma etching was performed by a microwave plasma system with oxygen gas flow and the optimized time for treatment was 1 min. The antistatic gun treatment flows ions by the electrode surface; two triggers of the antistatic gun was the optimized no. on the CNTYME surface. Current for dopamine at CNTYMEs increased 3-fold after O2 plasma etching and 4-fold after antistatic gun treatment. When the two treatments were combined, the current increased 12-fold, showing the two effects are due to independent mechanisms that tune the surface properties. O2 plasma etching increased the sensitivity due to increased surface oxygen content but did not affect surface roughness while the antistatic gun treatment increased surface roughness but not oxygen content. The effect of tissue fouling on CNT yarns was studied for the first time, and the relatively hydrophilic surface after O2 plasma etching provided better resistance to fouling than unmodified or antistatic gun treated CNTYMEs. Overall, O2 plasma etching and antistatic gun treatment improve the sensitivity of CNTYMEs by different mechanisms, providing the possibility to tune the CNTYME surface and enhance sensitivity.
- 22Jacobs, C. B.; Vickrey, T. L.; Venton, B. J. Functional Groups Modulate the Sensitivity and Electron Transfer Kinetics of Neurochemicals at Carbon Nanotube Modified Microelectrodes. Analyst 2011, 136, 3557– 3565, DOI: 10.1039/c0an00854k22https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXpvFCqsbY%253D&md5=212086d8c0800ed68d848f193f80678dFunctional groups modulate the sensitivity and electron transfer kinetics of neurochemicals at carbon nanotube modified microelectrodesJacobs, Christopher B.; Vickrey, Trisha L.; Venton, B. JillAnalyst (Cambridge, United Kingdom) (2011), 136 (17), 3557-3565CODEN: ANALAO; ISSN:0003-2654. (Royal Society of Chemistry)The surface properties of carbon-based electrodes are critically important for the detection of biomols. and can modulate electrostatic interactions, adsorption and electrocatalysis. Carbon nanotube (CNT) modified electrodes have previously been shown to have increased oxidative sensitivity and reduced overpotential for catecholamine neurotransmitters, but the effect of surface functionalities on these properties has not been characterized. In this study, we modified carbon-fiber microelectrodes (CFMEs) with three differently functionalized single-wall carbon nanotubes and measured their response to serotonin, dopamine, and ascorbic acid using fast-scan cyclic voltammetry. Both carboxylic acid functionalized and amide functionalized CNTs increased the oxidative current of CFMEs by approx. 2-6 fold for the cationic neurotransmitters serotonin and dopamine, but octadecylamine functionalized CNTs resulted in no significant signal change. Similarly, electron transfer was faster for both amide and carboxylic acid functionalized CNT modified electrodes but slower for octadecylamine CNT modified electrodes. Oxidn. of ascorbic acid was only increased with carboxylic acid functionalized CNTs although all CNT-modified electrodes showed a trend towards increased reversibility for ascorbic acid. Carboxylic acid-CNT modified disk electrodes were then tested for detection of serotonin in the ventral nerve cord of a Drosophila melanogaster larva, and the increase in sensitivity was maintained in biol. tissue. The functional groups of CNTs therefore modulate the electrochem. properties, and the increase in sensitivity from CNT modification facilitates measurements in biol. samples.
- 23Bath, B. D.; Michael, D. J.; Trafton, B. J.; Joseph, J. D.; Runnels, P. L.; Wightman, R. M. Subsecond Adsorption and Desorption of Dopamine at Carbon-Fiber Microelectrodes. Anal. Chem. 2000, 72, 5994– 6002, DOI: 10.1021/ac000849y23https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXotVyis7s%253D&md5=6e2c2e1202ae88e8ec4bfbcd274dc976Subsecond adsorption and desorption of dopamine at carbon-fiber microelectrodesBath, Bradley D.; Michael, Darren J.; Trafton, B. Jill; Joseph, Joshua D.; Runnels, Petrise L.; Wightman, R. MarkAnalytical Chemistry (2000), 72 (24), 5994-6002CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)High-repetition fast-scan cyclic voltammetry and chronoamperometry were used to quantify and characterize the kinetics of dopamine and dopamine-o-quinone adsorption and desorption at carbon-fiber microelectrodes. A flow injection anal. system was used for the precise introduction and removal of a bolus of electroactive substance on a sub-second time scale to the disk-shaped surface of a microelectrode that was fabricated from a single carbon fiber (Thornel type T650 or P55). Pretreatment of the electrode surfaces consisted of soaking them in purified iso-Pr alc. for a min. of 10 min, which resulted in S/N increasing by 200-400% for dopamine above that for those that were soaked in reagent grade solvent. Because of adsorption, high scan rates (2000 V/s) are shown to exhibit equiv. S/N ratios as compared to slower, more traditional scan rates. In addn., the steady-state response to a concn. bolus is shown to occur more rapidly when cyclic voltammetric scans are repeated at short intervals (4 ms). The new methodologies allow for more accurate detns. of the kinetics of neurotransmitter release events (10-500 ms) in biol. systems. Brain slice and in vivo expts. using T650 cylinder microelectrodes show that voltammetrically measured uptake kinetics in the caudate are faster using 2000 V/s and 240 Hz measurements, as compared to 300 V/s and 10 Hz.
- 24Heien, M. L. A. V.; Phillips, P. E. M.; Stuber, G. D.; Seipel, A. T.; Wightman, R. M. Overoxidation of Carbon-Fiber Microelectrodes Enhances Dopamine Adsorption and Increases Sensitivity. Analyst 2003, 128, 1413– 1419, DOI: 10.1039/b307024g24https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXpsFymsLY%253D&md5=6eaf749094e6cd0faf2d8d169b2220f8Overoxidation of carbon-fiber microelectrodes enhances dopamine adsorption and increases sensitivityHeien, Michael L. A. V.; Phillips, Paul E. M.; Stuber, Garret D.; Seipel, Andrew T.; Wightman, R. MarkAnalyst (Cambridge, United Kingdom) (2003), 128 (12), 1413-1419CODEN: ANALAO; ISSN:0003-2654. (Royal Society of Chemistry)The voltammetric responses of carbon-fiber microelectrodes with a 1.0 V and a 1.4 V anodic limit were compared in this study. Fast-scan cyclic voltammetry was used to characterize the response to dopamine and several other neurochems. An increase in the adsorption properties of the carbon fiber leads to an increase in sensitivity of 9-fold in vivo. However the temporal response of the sensor is slower with the more pos. anodic limit. Increased electron transfer kinetics also causes a decrease in the relative sensitivity for dopamine vs. other neurochems., and a change in their cyclic voltammograms. Stimulated release in the caudate-putamen was pharmacol. characterized in vivo using Ro-04-1284 and pargyline, and was consistent with that expected for dopamine.
- 25Li, Y.; Ross, A. E. Plasma-Treated Carbon-Fiber Microelectrodes for Improved Purine Detection with Fast-Scan Cyclic Voltammetry. Analyst 2020, 145, 805– 815, DOI: 10.1039/C9AN01636H25https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXit1Kqsb%252FM&md5=f4408cb75c5f280272acfec43d7dd2a8Plasma-treated carbon-fiber microelectrodes for improved purine detection with fast-scan cyclic voltammetryLi, Yuxin; Ross, Ashley E.Analyst (Cambridge, United Kingdom) (2020), 145 (3), 805-815CODEN: ANALAO; ISSN:0003-2654. (Royal Society of Chemistry)Here, the authors developed N2 and O2 plasma-treated carbon-fiber microelectrodes (CFME) for improved purine detection with fast-scan cyclic voltammetry (FSCV). Plasma treatment affects the topol. and functionality of carbon which impacts the electrode-analyte interaction. CFME's are less sensitive to purines compared to catecholamines. Knowledge of how the electrode surface drives purine-electrode interaction would provide insight into methods to improve purine detection. Here, plasma-treated CFME's with N2 and O2 plasma was used to study the extent to which the surface functionality and topol. affects purine detection and to improve purine sensing with FSCV. On av., O2 plasma increased the oxidative current for adenosine and ATP by 6.0 ± 1.2-fold and 6.4 ± 1.6-fold, and guanosine and GTP by 2.8 ± 0.47-fold and 5.8 ± 1.4-fold, resp. (n = 9). The O2 plasma increased the surface roughness and oxygen functionality. N2 plasma increased the oxidative current for adenosine and ATP by 1.5 ± 0.15-fold and 1.9 ± 0.23-fold, and guanosine and GTP by 1.4 ± 0.20-fold and 1.5 ± 0.20-fold, resp. (n = 11). N2 plasma increased the nitrogen functionality with minimal increases in roughness. Both plasma treatments impacted purines more than dopamine. Langmuir isotherms revealed that both plasma gases impact the theor. surface coverage and adsorption strength of purines at the electrode. Overall, purine detection is improved at surfaces with increased surface roughness, and oxygen and amine functionality. Plasma-treated CFMEs could be used in the future to study the analyte-electrode interaction of other neurochems.
- 26Fagan, D. T.; Hu, I. F.; Kuwana, T. Vacuum Heat-Treatment for Activation of Glassy Carbon Electrodes. Anal. Chem. 1985, 57, 2759– 2763, DOI: 10.1021/ac00291a00626https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2MXlvVGlu7c%253D&md5=528592970c8a368e7379b20e16f4a9b8Vacuum heat-treatment for activation of glassy carbon electrodesFagan, Dan T.; Hu, Ing Feng; Kuwana, TheodoreAnalytical Chemistry (1985), 57 (14), 2759-63CODEN: ANCHAM; ISSN:0003-2700.Heat treatment of glassy C (gc) at 725° under high vacuum (<2 × 10-6 torr was shown to produce an active electrode for the redox reaction of ferri-/ferrocyanide and the oxidn. of ascorbic acid. Electrons treated by this method exhibit a dramatic redn. in the background charging current as indicated gy chronocoulometry. Differential pulse voltammetry indicates that O surface functional groups are removed by vacuum heat treatment (VHT) and XPS shows a factor of 6 redn. in the O content of the surface. The main reasons for activation are believed to be due to an increase in the active site d. as a consequence of the removal of surface contaminants and the exposure of fresh C.
- 27Poon, M.; McCreery, R. L. In Situ Laser Activation of Glassy Carbon Electrodes. Anal. Chem. 1986, 58, 2745– 2750, DOI: 10.1021/ac00126a03627https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL28XlvVSgsro%253D&md5=ac191ef7f9b8cdc0fc9c36db6be19deaIn situ laser activation of glassy carbon electrodesPoon, Melanie; McCreery, Richard L.Analytical Chemistry (1986), 58 (13), 2745-50CODEN: ANCHAM; ISSN:0003-2700.Laser pulses of short duration (10 ns) and high intensity (20 MW/cm2) canincrease the rate of heterogeneous electron transfer at a glassy C electrode by 1-3 orders of magnitude. The laser pulse may be delivered in situ, directly in the soln. of interest, repeatedly if desired. The heterogeneous electron transfer rate const., k°, for the ferri-ferrocyanide redox system increases from 0.004 to 0.20 cm s-1 with laser activation, resulting in the highest k° yet obsd. for this system on glassy C. Laser activation results in minor morphol. changes to the surface, as obsd. by SEM, mainly removal of an apparent layer of C microparticles. The technique holds promise as a means to repeatedly activate glassy C electrodes in situ, thus circumventing the need for renewal or reactivation by polishing or other ex situ treatments.
- 28Rice, R. J.; Pontikos, N. M.; McCreery, R. L. Quantitative Correlations of Heterogeneous Electron-Transfer Kinetics with Surface Properties of Glassy Carbon Electrodes. J. Am. Chem. Soc. 1990, 112, 4617– 4622, DOI: 10.1021/ja00168a00128https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3cXisVajtbo%253D&md5=49aae9fd2f0978fa800df00927c192f9Quantitative correlations of heterogeneous electron-transfer kinetics with surface properties of glassy carbon electrodesRice, Ronald J.; Pontikos, Nicholas M.; McCreery, Richard L.Journal of the American Chemical Society (1990), 112 (12), 4617-22CODEN: JACSAT; ISSN:0002-7863.Raman spectra, capacitance (C°), phenanthrenequinone (PQ) adsorption, and heterogeneous electron-transfer rates for ferri/ferrocyanide, dopamine, and ascorbic acid were monitored after fracturing, polishing, and laser activating glassy C electrodes (GC-30). Alterations in the Raman spectrum indicate changes in C microstructure, while PQ adsorption and C° provide measures of microscopic surface area. Polishing caused minor changes in C disorder and microscopic surface area, but the polished surface had poor electron-transfer kinetics. Laser activation increased k° for Fe(CN)63-/4- by at least a factor of 200 but increased PQ adsorption and C° by less than 50% and had negligible effects on the Raman spectrum. A k° of above 0.5 cm s-1 was obsd. for Fe(CN)63-/4- for the first time. A clean, fractured GC surface exhibited a k° of 0.5 cm s-1 and was very active toward ascorbic acid and dopamine oxidn. The results are consistent with a surface-cleaning mechanism for laser activation, accompanied by little or no observable surface restructuring or roughening. The results on GC are in contrast to those on laser activation of highly oriented pyrolytic graphite, where the mechanism involved formation of active sites. The conclusions reached here permit evaluation of the main variables affecting electron-transfer rate for Fe(CN)63-/4-, ascorbic acid, and dopamine on GC. The active sites for electron transfer are on graphite edges inherent in the GC structure, and the principal function of the laser is exposure of these sites by removal of chemi- and physisorbed impurities.
- 29DeClements, R.; Swain, G. M.; Dallas, T.; Holtz, M. W.; Herrick, R. D.; Stickney, J. L. Electrochemical and Surface Structural Characterization of Hydrogen Plasma Treated Glassy Carbon Electrodes. Langmuir 1996, 12, 6578– 6586, DOI: 10.1021/la960380v29https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28XntFyjtbs%253D&md5=87c248730d11366b19444ee26c81b74bElectrochemical and surface structural characterization of hydrogen plasma-treated glassy carbon electrodesDeClements, Roger; Swain, Greg M.; Dallas, Tim; Holtz, Mark W.; Herrick, Robert D., II; Stickney, John L.Langmuir (1996), 12 (26), 6578-6586CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)Electrochem. and structural characterization of glassy carbon (GC) electrodes exposed to the plasma conditions necessary to nucleate and grow diamond were performed for the first time. The electrodes are referred to as diamond-coated (DGC) if the surface was exposed to a CH4/H2 plasma and as hydrogenated (HGC) if the surface was exposed to only an H2 plasma. Continuous diamond films were formed on the surfaces exposed to both plasma conditions, but due to poor adhesion, the films were easily lifted, exposing a modified GC surface. The results demonstrate that these modified surfaces exhibit lower voltammetric background currents and higher faradaic currents for Fe(CN)64-/3- than does freshly polished GC. The enhanced signal-to-background (S/B) ratios lead to lower limits of detection for this redox analyte. The electrodes exhibited near-Nernstian behavior (ΔEp ∼70-85 mV) for this redox analyte without any conventional surface pretreatment, and the response remained stable for long periods of time up to several weeks. The nucleation and growth mechanism of diamond on GC first involves hydrogenation of the unsatd. edge plane sites on the surface, producing an sp3 bonded "diamond-like" phase. These surfaces are relatively O2-free, as H is chemisorbed at the edge plane sites, replacing the O functional groups. Formation of this surface phase is followed by subsequent nucleation and growth of a diamond film. Voltammetric data for Fe(CN)64-/3-, Ru(NH3)62+/3+, Fe2+/3+, and ascorbic acid at these surfaces are presented as are structural characterization data by SEM, at. force microscopy, Raman spectroscopy, and Auger electron spectroscopy.
- 30Kamau, G. N.; Willis, W. S.; Rusling, J. F. Electrochemical and Electron Spectroscopic Studies of Highly Polished Glassy Carbon Electrodes. Anal. Chem. 1985, 57, 545– 551, DOI: 10.1021/ac50001a04930https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2MXlt1yrsg%253D%253D&md5=e9d13604ba17d0234fdb51da9e2e66fbElectrochemical and electron spectroscopic studies of highly-polished glassy carbon electrodesKamau, Geoffrey N.; Willis, William S.; Rusling, James F.Analytical Chemistry (1985), 57 (2), 545-51CODEN: ANCHAM; ISSN:0003-2700.Prepn. of glassy C electrodes by high-speed polishing with successively smaller particles size SiC, diamond paste, and γ-Al2O3, and ultrasonic cleaning, yielded reproducible activation for anodic oxidns. of ferrocyanide, ferrocene, ascorbate, hydroquinones, and catharanthine. Electron spectroscopy showed that the highly polished electrodes had a higher O content in the outer 20-30 nm than in the bulk material or in unactivated electrodes. A major portion of the O is probably assocd. with phenolic-like groups. For simple electron transfers, creation of a favorable charge d. at the electrode is an important factor in the activation, but other nonspecific interactions may also be involved. For proton-coupled reactions, such as those of ascorbate and dopamine, specific interactions of reactants with catalytic groups created on the surface may play a significant role in electrode activation. Response of the electrodes degraded with time.
- 31Allred, C. D.; McCreery, R. L. Adsorption of Catechols on Fractured Glassy Carbon Electrode Surfaces. Anal. Chem. 1992, 64, 444– 448, DOI: 10.1021/ac00028a02031https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK38XptlOntg%253D%253D&md5=62a34aab0b1076fc6d50c06241e0b781Adsorption of catechols on fractured glassy carbon electrode surfacesAllred, Christie D.; McCreery, Richard L.Analytical Chemistry (1992), 64 (4), 444-8CODEN: ANCHAM; ISSN:0003-2700.Glassy carbon surfaces exposed by fracturing a glassy carbon rod in the electrolyte soln. exhibit fast electron transfer kinetics compared to conventionally polished surfaces, implying that glassy carbon is inherently active toward electron transfer before any intentional surface modification. The adsorption of dopamine and related compds. was examd. on fractured glassy carbon surfaces and compared to polished or electrochem. pretreated (ECP) surfaces. While the catechols and ascorbic acid had the anticipated fast electron transfer on fractured glassy carbon, their adsorption behavior differed substantially from that reported for polished, ECP, or vapor-deposited carbon. Dopamine, 4-methylcatechol (4-MC), and dihydroxyphenylacetic acid (DOPAC) adsorbed to similar degrees on fractured glassy carbon, with no apparent discrimination on the basis of adsorbate charge. If the surface was partially oxidized, however, cationic dopamine was preferentially adsorbed over anionic DOPAC or neutral 4-MC. The results support an adsorption mechanism on fractured glassy carbon which is not charge specific and probably involves the catechol ring rather than the side chain. The implications of this finding to the anal. utility of carbon electrodes are discussed.
- 32Behan, J. A.; Grajkowski, F.; Jayasundara, D. R.; Vilella-Arribas, L.; García-Melchor, M.; Colavita, P. E. Influence of Carbon Nanostructure and Oxygen Moieties on Dopamine Adsorption and Charge Transfer Kinetics at Glassy Carbon Surfaces. Electrochim. Acta 2019, 304, 221– 230, DOI: 10.1016/j.electacta.2019.02.10332https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXksVahtrc%253D&md5=5052b20b8588a122a887415114eb306dInfluence of carbon nanostructure and oxygen moieties on dopamine adsorption and charge transfer kinetics at glassy carbon surfacesBehan, James A.; Grajkowski, Filip; Jayasundara, Dilushan R.; Vilella-Arribas, Laia; Garcia-Melchor, Max; Colavita, Paula E.Electrochimica Acta (2019), 304 (), 221-230CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Ltd.)Abnormal levels of the neurotransmitter dopamine were linked to a variety of neurochem. disorders including depression and Parkinson's disease. Dopamine concns. are often quantified electrochem. using biosensors prepd. from C electrode materials such as C paste or glassy C. The charge transfer kinetics of dopamine is highly sensitive to C surface termination, including the presence of certain O functional groups and adsorption sites. However, the nature of the binding sites and the effects of surface oxidn. on the voltammetry of dopamine are both poorly understood. The electrochem. response of dopamine at glassy C model surfaces was studied to understand the effects of altering both the C nanostructure and O surface chem. on dopamine charge transfer kinetics and adsorption. Glassy C electrodes with low O content and a high degree of surface graphitization were prepd. via thermal annealing at 900°, while highly oxidized glassy C electrodes were obtained through electrochem. anodization at 1.8 V vs. Ag/AgCl. The C surface structure and compn. in each case was studied via XPS. Voltammetry in solns. of dopamine at acidic pH confirmed that both annealing and anodization treatments result in C surfaces with rapid charge transfer kinetics. However, dopamine adsorption occurs only at the low-O, highly-graphitized C surface. D. functional theory studies on graphene model surfaces reveal that this behavior is due to noncovalent interactions between the π-system of dopamine and the basal sites in the annealed surface. Simulations also show that the introduction of O moieties disrupt these interactions and inhibit dopamine adsorption, in agreement with expts. The results clarify the role of O moieties and basal plane sites in facilitating both the adsorption of and charge transfer to DA at C electrodes.
- 33Engstrom, R. C.; Strasser, V. A. Characterization of Electrochemically Pretreated Glassy Carbon Electrodes. Anal. Chem. 1984, 56, 136– 141, DOI: 10.1021/ac00266a00533https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2cXktFGlsQ%253D%253D&md5=fc782d7153bcd08cf5805cae3f167da3Characterization of electrochemically pretreated glassy carbon electrodesEngstrom, Royce C.; Strasser, Vernon A.Analytical Chemistry (1984), 56 (2), 136-41CODEN: ANCHAM; ISSN:0003-2700.Electrochem. pretreatment of glassy C electrodes was done by applying 1.75 V vs. SCE for 5 min followed by -1.0 V for 1 min. The effects of pretreatment on the functional, phys., and chem. characteristics of the electrodes were studied. The pretreated electrodes showed enhanced electrochem. activity, higher background currents, increased wettability, and no change in electrochem. surface area or topog. as detd. by SEM. XPS showed that pretreatment produces a surface more highly oxygenated than that of a freshly polished electrode. Electrochem. pretreatment cleans the surface of contaminants introduced in the polishing step of electrode prepn. and changes the chem. nature of the glassy C surface itself. The chem. changes influence the reaction of ascorbic acid but do not influence reaction of the ferricyanide-ferrocyanide system.
- 34Kiema, G. K.; Aktay, M.; McDermott, M. T. Preparation of Reproducible Glassy Carbon Electrodes by Removal of Polishing Impurities. J. Electroanal. Chem. 2003, 540, 7– 15, DOI: 10.1016/S0022-0728(02)01264-034https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXis1SqtA%253D%253D&md5=e44d31370a8702924f31ac658ba83497Preparation of reproducible glassy carbon electrodes by removal of polishing impuritiesKiema, Gregory K.; Aktay, Mirwais; McDermott, Mark T.Journal of Electroanalytical Chemistry (2003), 540 (), 7-15CODEN: JECHES ISSN:. (Elsevier Science B.V.)This paper describes a simple and rapid electrochem. oxidative procedure that removes polishing contaminants from glassy carbon (GC) surfaces. The method involves oxidn. of polished GC electrodes in basic media for short periods of time (∼10 s). Tapping mode scanning force microscopy (TM SFM), XPS and nanoindentation surface characterization techniques were utilized to track the removal of the polishing layer. Several electrochem. characterizations of the modified GC surface were carried out to assess changes in electrode reactivity following removal of the microparticle polishing layer. Electrochem. measurements obtained on the anodized GC electrodes show a more reproducible surface relative to polished GC.
- 35Kiema, G. K.; Ssenyange, S.; McDermott, M. T. Microfabrication of Glassy Carbon by Electrochemical Etching. J. Electrochem. Soc. 2004, 151, C142– C148, DOI: 10.1149/1.163916535https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXkvV2jsA%253D%253D&md5=f8e0562713148cb26f4915263e63c800Microfabrication of Glassy Carbon by Electrochemical EtchingKiema, Gregory K.; Ssenyange, Solomon; McDermott, Mark T.Journal of the Electrochemical Society (2004), 151 (2), C142-C148CODEN: JESOAN; ISSN:0013-4651. (Electrochemical Society)Due to the broad impact of microfabrication technol. on chem. and biol., new methods to pattern and etch a variety of materials are being explored in a no. of labs. The authors have developed a method for the etching of glassy C (GC) that opens pathways for the creation of new electrode patterns and devices. The method involves std. pattern transfer to a photoresist layer and anodization of the exposed GC substrate in basic electrolyte. The electrode reaction results in a breakup of the C lattice and likely involves the intercalation of hydroxide anions. The depth of etching can be controlled with potential, time or charge. The etching process is isotropic due to the nano-scale graphitic microcrystallite size of GC. The authors demonstrate the fabrication of microchannel structures directly into GC and the prepn. of arrays of submicrometer sized C electrodes via the etching of patterned C films.
- 36Sullivan, M. G.; Schnyder, B.; Bärtsch, M.; Alliata, D.; Barbero, C.; Imhof, R.; Kötz, R. Electrochemically Modified Glassy Carbon for Capacitor Electrodes Characterization of Thick Anodic Layers by Cyclic Voltammetry, Differential Electrochemical Mass Spectrometry, Spectroscopic Ellipsometry, X-Ray Photoelectron Spectroscopy, FTIR, and AFM. J. Electrochem. Soc. 2000, 147, 2636– 2643, DOI: 10.1149/1.139358236https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXltVCrtrg%253D&md5=76401e861af82efb81369b96316b9d6cElectrochemically modified glassy carbon for capacitor electrodes. Characterization of thick anodic layers by cyclic voltammetry, differential electrochemical mass spectrometry, spectroscopic ellipsometry, X-ray photoelectron spectroscopy, FTIR, and AFMSullivan, M. G.; Schnyder, B.; Bartsch, M.; Alliata, D.; Barbero, C.; Imhof, R.; Kotz, R.Journal of the Electrochemical Society (2000), 147 (7), 2636-2643CODEN: JESOAN; ISSN:0013-4651. (Electrochemical Society)Glassy carbon (GC) electrodes were activated by electrochem. const. potential anodization to generate high-surface area, high-capacitance electrodes. After anodic oxidn. in sulfuric acid the electrodes exhibited increased capacitance. After subsequent electrochem. redn. of the activated layer, a further significant increase in capacitance was obsd. Growth, structure, and surface properties of the activated electrodes were monitored by cyclic voltammetry, differential electrochem. mass spectrometry, spectroscopic ellipsometry, XPS, and at. force microscopy (AFM). Two different types of glassy carbon obtained by pyrolysis at 1000° and at 2200° were compared. Differential electrochem. mass spectrometry reveals that CO2 is the main reaction product during oxidn., while CO2 and H2 are detected during redn. The values of surface layer capacitance and thickness detd. by spectroscopic ellipsometry increase as linear functions of oxidn. time. The resulting volumetric capacitance was at least 100 F/cm3. After oxidn., the presence of functional surface groups was demonstrated by XPS. The relative contributions of the different surface functionalities depend on the pyrolysis temp. of the GC. Redn. lowered the concn. of oxygen-contg. functional surface groups. The XPS results were qual. confirmed by FTIR measurements carried out at the same samples. AFM measurements on glassy carbon showed that the film growth both into and out of the substrate, resulted in a raised surface after activation. A qual. model for film growth is presented.
- 37Alliata, D. In Situ Atomic Force Microscopy of Electrochemically Activated Glassy Carbon. Electrochem. Solid-State Lett. 1999, 2, 33– 35, DOI: 10.1149/1.139072537https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXhslw%253D&md5=a2454a0cbda9bcbbed2d65aa147b18d8In situ atomic force microscopy of electrochemically activated glassy carbonAlliata, D.; Haring, P.; Haas, O.; Kotz, R.; Siegenthaler, H.Electrochemical and Solid-State Letters (1999), 2 (1), 33-35CODEN: ESLEF6; ISSN:1099-0062. (Electrochemical Society)Glassy carbon (GC) electrodes were activated by anodic oxidn. at a potential of 1.95 V std. calomel electrode in 1 M H2SO4. The activated electrodes were investigated by in situ contact at. force microscopy. In order to monitor differences between activated and nonactivated areas, part of the electrode surface was covered by a polymeric varnish during electrochem. activation. The edge between activated and nonactivated regions was analyzed after removal of the varnish. The surface of the activated region was significantly higher than that of the nonactivated region, indicating significant swelling of the GC during anodic oxidn. After drying, the activated film collapsed. Swelling of the activated layer was a linear function of activation time and depended on the state of the electrode. In the oxidized state the film thickness was larger than in the reduced state.
- 38Sullivan, M. G.; Kötz, R.; Haas, O. Thick Active Layers of Electrochemically Modified Glassy Carbon. Electrochemical Impedance Studies. J. Electrochem. Soc. 2000, 147, 308, DOI: 10.1149/1.139319238https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXmvFCjsw%253D%253D&md5=be0de0f6186c78fded4f49845a2c6384Thick active layers of electrochemically modified glassy carbon electrochemical impedance studiesSullivan, Melani G.; Kotz, Rudiger; Haas, OttoJournal of the Electrochemical Society (2000), 147 (1), 308-317CODEN: JESOAN; ISSN:0013-4651. (Electrochemical Society)Glassy carbon electrodes were electrochem. modified by an anodization/cathodization procedure in aq. H2SO4. Depending on the anodization time, the active-layer thickness could be controlled from less than a micrometer to nearly 100 μm. Electrochem. impedance measurements indicated that the capacitance per unit vol. of the active layer was similar to various other porous carbons and sufficient for application as an electrochem. capacitor material. The small-signal a.c. capacitance is 80-460 F/cm3 (single-electrode capacitance), depending on potential, for the higher-pyrolysis-temp. carbon, and 25-420 F/cm3 for the lower-pyrolysis-temp. carbon. The resistance of the active layer depended even more strongly on the pyrolysis temp. of the glassy carbon. The active layer on the carbon pyrolyzed at a temp. of 2200° had a resistance which was ∼1000 times lower than that of a corresponding layer grown on glassy carbon pyrolyzed at 1000°.
- 39Cabaniss, G. E.; Diamantis, A. A.; Murphy, W. R., Jr.; Linton, R. W.; Meyer, T. J. Electrocatalysis of Proton-Coupled Electron-Transfer Reactions at Glassy Carbon Electrodes. J. Am. Chem. Soc. 1985, 107, 1845– 1853, DOI: 10.1021/ja00293a00739https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2MXhtl2ltrs%253D&md5=f70528beb693153bacae10021cc10117Electrocatalysis of proton-coupled electron-transfer reactions at glassy carbon electrodesCabaniss, George E.; Diamantis, A. A.; Murphy, W. Rorer, Jr.; Linton, R. W.; Meyer, T. J.Journal of the American Chemical Society (1985), 107 (7), 1845-53CODEN: JACSAT; ISSN:0002-7863.The activation of glassy C electrodes toward electron-transfer pathways involving proton-coupled electron transfer was investigated. Oxidative activation of glassy C electrodes leads to the catalysis of heterogeneous charge transfer for couples involving catechol (1,2-dihydroxybenzene), (bpy)2(H2O)Ru(OH)2+ (bpy = 2,2'-bipyridine), and (NH3)5Ru(OH)2+ where there are changes in proton content upon oxidn. XPS was used to det. the changes induced at the electrode surface by the activation procedure. Comparison of the spectral and electrochem. results with earlier studies on related homogeneous proton-coupled electron-transfer reactions suggests that, although a no. of effects may be operative, an important basis for electrode activation may be the appearance of phenolic-like groups on the glassy C surface and their subsequent involvement in proton-coupled electron transfer.
- 40DuVall, S. H.; McCreery, R. L. Control of Catechol and Hydroquinone Electron-Transfer Kinetics on Native and Modified Glassy Carbon Electrodes. Anal. Chem. 1999, 71, 4594– 4602, DOI: 10.1021/ac990399d40https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXlslCit7o%253D&md5=b2023cb5d42610292ec440954b296d1bControl of Catechol and Hydroquinone Electron-Transfer Kinetics on Native and Modified Glassy Carbon ElectrodesDuVall, Stacy Hunt; McCreery, Richard L.Analytical Chemistry (1999), 71 (20), 4594-4602CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)The electrochem. oxidn. of dopamine, 4-methylcatechol, dihydroxyphenylacetic acid, dihydroxyphenyl ethylene glycol, and hydroquinone was examd. on several native and modified glassy carbon (GC) surfaces. Treatment of polished GC with pyridine yielded small ΔEp values for cyclic voltammetry of all systems studied, implying fast electron-transfer kinetics. Changes in surface oxide coverage had little effect on kinetics, nor did the charge of the catechol species or the soln. pH. Small ΔEp values correlated with catechol adsorption, and surface pretreatments that decreased adsorption also increased ΔEp. Electron transfer from catechols was profoundly inhibited by a monolayer of nitrophenyl or (trifluoromethyl)phenyl (TFMP) groups on the GC surface, so that voltammetric waves were not obsd. The ΔEp increased monotonically with surface coverage of TFMP groups. The results indicate that catechol adsorption to GC is required for fast electron transfer for the redox systems studied. Unlike Ru(NH3)63+/2+, chlorpromazine, Me viologen, and several others, electron tunneling through monolayer films was not obsd. for the catechols. The results are not consistent with an electron-transfer mechanism involving proton transfer or electrostatic interactions between the catechols and surface sites on the GC surface. The vital role of adsorption in the electron-transfer process is currently under study but appears to involve changes in the inner-sphere reorganization energy.
- 41Yi, Y.; Weinberg, G.; Prenzel, M.; Greiner, M.; Heumann, S.; Becker, S.; Schlögl, R. Electrochemical Corrosion of a Glassy Carbon Electrode. Catal. Today 2017, 295, 32– 40, DOI: 10.1016/j.cattod.2017.07.01341https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtF2ktLjN&md5=6ccdcedfafaf8534ee426bcb534e10c7Electrochemical corrosion of a glassy carbon electrodeYi, Youngmi; Weinberg, Gisela; Prenzel, Marina; Greiner, Mark; Heumann, Saskia; Becker, Sylvia; Schloegl, RobertCatalysis Today (2017), 295 (), 32-40CODEN: CATTEA; ISSN:0920-5861. (Elsevier B.V.)Glassy C is widely used in electrochem. due to its properties of high temp. resistance, hardness, low d. and low elec. resistance. The present study focuses on the chem. resistance under electrochem. oxidative conditions, which occur under O-involving reactions like O redn. reaction (ORR) and O evolution reaction (OER). The electrochem. performance of glassy C studied in alk., neutral and acidic media reveal the same chem. processes during the OER but showing different degrdn. mechanism. The electrochem. signature of the corrosion in different media could be directly assocd. with the formation of O functional groups detd. by spectroscopic methods like Raman, IR and XPS. The morphol. change of the C surface caused by C oxidn. was studied by microscopy. A rough surface was obtained in the acidic case, whereas dents were seen in alk. media. It is assumed that the glassy C electrode in acidic media degrades by forming surface oxides by acid catalyzed process leading to ring opening in the graphitic structure and therefore oxidn. in the bulk. In alk. media OH radicals preferentially react with alkyl site chains, leading to oxidn. of the edges of C layers until they become hydrophilic and dissolve.
- 42Patel, A. N.; McKelvey, K.; Unwin, P. R. Nanoscale Electrochemical Patterning Reveals the Active Sites for Catechol Oxidation at Graphite Surfaces. J. Am. Chem. Soc. 2012, 134, 20246– 20249, DOI: 10.1021/ja309589442https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhslOlsbbJ&md5=47806e196bb4b5b0348aad244cc6086cNanoscale Electrochemical Patterning Reveals the Active Sites for Catechol Oxidation at Graphite SurfacesPatel, Anisha N.; McKelvey, Kim; Unwin, Patrick R.Journal of the American Chemical Society (2012), 134 (50), 20246-20249CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Graphite-based electrodes (graphite, graphene, and nanotubes) were used widely in electrochem., and there is a long-standing view that graphite step edges are needed to catalyze many reactions, with the basal surface considered to be inert. This model was tested directly for the 1st time using scanning electrochem. cell microscopy reactive patterning and is incorrect. For the electrooxidn. of dopamine as a model process, the reaction rate was measured at high spatial resoln. across a surface of highly oriented pyrolytic graphite. Oxidn. products left behind in a pattern defined by the scanned electrochem. cell served as surface-site markers, allowing the electrochem. activity to be correlated directly with the graphite structure on the nanoscale. This process produced tens of thousands of electrochem. measurements at different locations across the basal surface, unambiguously revealing it to be highly electrochem. active, with step edges providing no enhanced activity. This new model of graphite electrodes has significant implications for the design of C-based biosensors, and the results are addnl. important for understanding electrochem. processes on related sp2-hybridized materials such as pristine graphene and nanotubes.
- 43Martín-Yerga, D.; Costa-García, A.; Unwin, P. R. Correlative Voltammetric Microscopy: Structure–Activity Relationships in the Microscopic Electrochemical Behavior of Screen Printed Carbon Electrodes. ACS Sens. 2019, 4, 2173– 2180, DOI: 10.1021/acssensors.9b0102143https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhsVGhsLjL&md5=61024414d3770735e09dca65f1c95959Correlative Voltammetric Microscopy: Structure-Activity Relationships in the Microscopic Electrochemical Behavior of Screen Printed Carbon ElectrodesMartin-Yerga, Daniel; Costa-Garcia, Agustin; Unwin, Patrick R.ACS Sensors (2019), 4 (8), 2173-2180CODEN: ASCEFJ; ISSN:2379-3694. (American Chemical Society)Screen-printed carbon electrodes (SPCEs) are widely used for electrochem. sensors. However, little is known about their electrochem. behavior at the microscopic level. In this work, we use voltammetric scanning electrochem. cell microscopy (SECCM), with dual-channel probes, to det. the microscopic factors governing the electrochem. response of SPCEs. SECCM cyclic voltammetry (CV) measurements are performed directly in hundreds of different locations of SPCEs, with high spatial resoln., using a submicrometer sized probe. Further, the localized electrode activity is spatially correlated to colocated surface structure information from SEM and micro-Raman spectroscopy. This approach is applied to two model electrochem. processes: hexaammineruthenium(III/II) ([Ru(NH3)6]3+/2+), a well-known outer-sphere redox couple, and dopamine (DA), which undergoes a more complex electron-proton coupled electro-oxidn., with complications from adsorption of both DA and side-products. The electrochem. redn. of [Ru(NH3)6]3+ proceeds fairly uniformly across the surface of SPCEs on the submicrometer scale. In contrast, DA electro-oxidn. shows a strong dependence on the microstructure of the SPCE. By studying this process at different concns. of DA, the relative contributions of (i) intrinsic electrode kinetics and (ii) adsorption of DA are elucidated in detail, as a function of local electrode character and surface structure. These studies provide major new insights on the electrochem. activity of SPCEs and further position voltammetric SECCM as a powerful technique for the electrochem. imaging of complex, heterogeneous, and topog. rough electrode surfaces.
- 44Chen, B.; Perry, D.; Teahan, J.; McPherson, I. J.; Edmondson, J.; Kang, M.; Valavanis, D.; Frenguelli, B. G.; Unwin, P. R. Artificial Synapse: Spatiotemporal Heterogeneities in Dopamine Electrochemistry at a Carbon Fiber Ultramicroelectrode. ACS Meas. Sci. Au 2021, 1, 6– 10, DOI: 10.1021/acsmeasuresciau.1c0000644https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXhsVelt7rF&md5=7b4a92ace8a28fa00c48074fa70c6082Artificial Synapse: Spatiotemporal Heterogeneities in Dopamine Electrochemistry at a Carbon Fiber UltramicroelectrodeChen, Baoping; Perry, David; Teahan, James; McPherson, Ian J.; Edmondson, James; Kang, Minkyung; Valavanis, Dimitrios; Frenguelli, Bruno G.; Unwin, Patrick R.ACS Measurement Science Au (2021), 1 (1), 6-10CODEN: AMACHV; ISSN:2694-250X. (American Chemical Society)An artificial synapse is developed that mimics ultramicroelectrode (UME) amperometric detection of single cell exocytosis. It comprises the nanopipette of a scanning ion conductance microscope (SICM), which delivers rapid pulses of neurotransmitter (dopamine) locally and on demand at >1000 defined locations of a carbon fiber (CF) UME in each expt. Anal. of the resulting UME current-space-time data reveals spatiotemporal heterogeneous electrode activity on the nanoscale and submillisecond time scale for dopamine electrooxidn. at typical UME detection potentials. Through complementary surface charge mapping and finite element method (FEM) simulations, these previously unseen variations in electrochem. activity are related to heterogeneities in the surface chem. of the CF UME.
- 45Chen, B.; Perry, D.; Page, A.; Kang, M.; Unwin, P. R. Scanning Ion Conductance Microscopy: Quantitative Nanopipette Delivery–Substrate Electrode Collection Measurements and Mapping. Anal. Chem. 2019, 91, 2516– 2524, DOI: 10.1021/acs.analchem.8b0544945https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXjtlKmuw%253D%253D&md5=74d798d40c1f8984c07dfb7ad9b2d996Scanning Ion Conductance Microscopy: Quantitative Nanopipette Delivery-Substrate Electrode Collection Measurements and MappingChen, Baoping; Perry, David; Page, Ashley; Kang, Minkyung; Unwin, Patrick R.Analytical Chemistry (Washington, DC, United States) (2019), 91 (3), 2516-2524CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Scanning ion conductance microscopy (SICM) is becoming a powerful multifunctional tool for probing and analyzing surfaces and interfaces. This work outlines methodol. for the quant. controlled delivery of ionic redox-active mols. from a nanopipette to a substrate electrode, with a high degree of spatial and temporal precision. Through control of the SICM bias applied between a quasi-ref. counter electrode (QRCE) in the SICM nanopipette probe and a similar electrode in bulk soln., it is shown that ionic redox species can be held inside the nanopipette, and then pulse-delivered to a defined region of a substrate positioned beneath the nanopipette. A self-referencing hopping mode imaging protocol is implemented, where reagent is released in bulk soln. (ref. measurement) and near the substrate surface at each pixel in an image, with the tip and substrate currents measured throughout. Anal. of the tip and substrate current data provides an improved understanding of mass transport and nanoscale delivery in SICM and a new means of synchronously mapping electrode reactivity, surface topog., and charge. Expts. on Ru(NH3)63+ redn. to Ru(NH3)62+ and dopamine oxidn. in aq. soln. at a carbon fiber ultramicroelectrode (UME), used as the substrate, illustrate these aspects. Finite element method (FEM) modeling provides quant. understanding of mol. delivery in SICM. The approach outlined constitutes a new methodol. for electrode mapping and provides improved insights on the use of SICM for controlled delivery to interfaces generally.
- 46Patten, H. V.; Lai, S. C. S.; Macpherson, J. V.; Unwin, P. R. Active Sites for Outer-Sphere, Inner-Sphere, and Complex Multistage Electrochemical Reactions at Polycrystalline Boron-Doped Diamond Electrodes (PBDD) Revealed with Scanning Electrochemical Cell Microscopy (SECCM). Anal. Chem. 2012, 84, 5427– 5432, DOI: 10.1021/ac301055546https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38Xnt1Wrs7k%253D&md5=79e267ef80b8067dc49df1f175b2e129Active Sites for Outer-Sphere, Inner-Sphere, and Complex Multistage Electrochemical Reactions at Polycrystalline Boron-Doped Diamond Electrodes (pBDD) Revealed with Scanning Electrochemical Cell Microscopy (SECCM)Patten, Hollie V.; Lai, Stanley C. S.; Macpherson, Julie V.; Unwin, Patrick R.Analytical Chemistry (Washington, DC, United States) (2012), 84 (12), 5427-5432CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)The local rate of heterogeneous electron transfer (HET) at polycryst. B-doped diamond (pBDD) electrodes was visualized at high spatial resoln. for various aq. electrochem. reactions, using scanning electrochem. cell microscopy (SECCM), which is a technique that uses a mobile pipet-based electrochem. cell as an imaging probe. As exemplar systems, three important classes of electrode reactions were studied: outer-sphere (1-electron oxidn. of ferrocenylmethyltrimethylammonium (FcTMA+)), inner-sphere (1-electron oxidn. of Fe2+), and complex processes with coupled electron transfer and chem. reactions (oxidn. of serotonin). In all cases, the pattern of reactivity is similar: the entire pBDD surface is electroactive, but there are variations in activity between different crystal facets which correlate directly with differences in the local dopant level, as visualized qual. by field-emission SEM (FE-SEM). No evidence was found for enhanced activity at grain boundaries for any of the reactions. The case of serotonin oxidn. is particularly interesting, as this process is known to lead to deterioration of the electrodes, because of blocking by reaction products, and therefore cannot be studied with conventional scanning electrochem. probe microscopy (SEPM) techniques. Yet, the authors found this system nonproblematic to study, because the meniscus of the scanning pipet is only in contact with the surface studied for a brief time and any blocking product is left behind as the pipet moves to a new location. Thus, SECCM opens up the possibility of studying and visualizing much more complex heterogeneous electrode reactions than possible presently with other SEPM techniques.
- 47Patel, A. N.; Tan, S.; Unwin, P. R. Epinephrine Electro-Oxidation Highlights Fast Electrochemistry at the Graphite Basal Surface. Chem. Commun. 2013, 49, 8776, DOI: 10.1039/c3cc45022h47https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhsVSls7fK&md5=aa40afb4adc23e16f3ad45f8167e962bEpinephrine electro-oxidation highlights fast electrochemistry at the graphite basal surfacePatel, Anisha N.; Tan, Sze-yin; Unwin, Patrick R.Chemical Communications (Cambridge, United Kingdom) (2013), 49 (78), 8776-8778CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)Macroscale and nanoscale measurements of epinephrine electrooxidn. at graphite electrodes, with different step edge densities, demonstrate unequivocally that the reaction occurs readily at the basal surface, and that step edges are not required for mol. electrocatalysis, in contrast to the current literature model.
- 48Ebejer, N.; Güell, A. G.; Lai, S. C. S.; McKelvey, K.; Snowden, M. E.; Unwin, P. R. Scanning Electrochemical Cell Microscopy: A Versatile Technique for Nanoscale Electrochemistry and Functional Imaging. Annu. Rev. Anal. Chem. 2013, 6, 329– 351, DOI: 10.1146/annurev-anchem-062012-09265048https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhsVCnsr3E&md5=260a4579441b78641eb0f2668aa8f98cScanning electrochemical cell microscopy: a versatile technique for nanoscale electrochemistry and functional imagingEbejer, Neil; Guell, Aleix G.; Lai, Stanley C. S.; McKelvey, Kim; Snowden, Michael E.; Unwin, Patrick R.Annual Review of Analytical Chemistry (2013), 6 (), 329-351CODEN: ARACFU; ISSN:1936-1327. (Annual Reviews)A review. Scanning electrochem. cell microscopy (SECCM) is a new pipet-based imaging technique purposely designed to allow simultaneous electrochem., conductance, and topog. visualization of surfaces and interfaces. SECCM uses a tiny meniscus or droplet, at the end of a double-barreled (theta) pipet, for high-resoln. functional imaging and nanoscale electrochem. measurements. Here, this technique is introduced and an overview of its principles, instrumentation, and theory is provided. The power of SECCM in resolving complex structure-activity problems is discussed and considerable new information on electrode processes is provided by referring to key example systems, including graphene, graphite, carbon nanotubes, nanoparticles, and conducting diamond. The many longstanding questions that SECCM was able to answer during its short existence demonstrate its potential to become a major technique in electrochem. and interfacial science.
- 49Wahab, O. J.; Kang, M.; Unwin, P. R. Scanning Electrochemical Cell Microscopy: A Natural Technique for Single Entity Electrochemistry. Curr. Opin. Electrochem. 2020, 22, 120– 128, DOI: 10.1016/j.coelec.2020.04.01849https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXitFymtLvP&md5=75aa33e918a588a55ce4d95244d3f9abScanning electrochemical cell microscopy and A natural technique for single entity electrochemistryWahab, Oluwasegun J.; Kang, Minkyung; Unwin, Patrick R.Current Opinion in Electrochemistry (2020), 22 (), 120-128CODEN: COEUCY; ISSN:2451-9111. (Elsevier B.V.)A review Scanning electrochem. cell microscopy (SECCM) is a robust and versatile scanning electrochem. probe microscopy technique that allows direct correlation of structure-activity at the nanoscale. SECCM uses a mobile droplet cell to investigate and visualize electrochem. activity at interfaces with high spatiotemporal resoln., while also providing topog. information. This article highlights diverse contemporary challenges in the field of single entity electrochem. tackled by the increasing uptake of SECCM globally. Various applications of SECCM in single entity electrochem. are featured herein, including electrocatalysis, electrodeposition, corrosion science and materials science, with electrode materials spanning particles, polymers, two-dimensional materials and complex polycryst. substrates. The use of SECCM for patterning structures is also highlighted.
- 50Bentley, C. L.; Kang, M.; Unwin, P. R. Scanning Electrochemical Cell Microscopy: New Perspectives on Electrode Processes in Action. Curr. Opin. Electrochem. 2017, 6, 23– 30, DOI: 10.1016/j.coelec.2017.06.01150https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhtVGgsbzK&md5=ae05c709a59c54d24576efde38f6c131Scanning electrochemical cell microscopy: New perspectives on electrode processes in actionBentley, Cameron L.; Kang, Minkyung; Unwin, Patrick R.Current Opinion in Electrochemistry (2017), 6 (1), 23-30CODEN: COEUCY; ISSN:2451-9111. (Elsevier B.V.)Scanning electrochem. probe microscopy (SEPM) methods allow interfacial fluxes to be visualized at high spatial resoln. and are consequently invaluable for understanding physicochem. processes at electrode/soln. interfaces. This article highlights recent progress in scanning electrochem. cell microscopy (SECCM), a scanning-droplet-based method that is able to visualize electrode activity free from topog. artifacts and, further, offers considerable versatility in terms of the range of interfaces and environments that can be studied. Advances in the speed and sensitivity of SECCM are highlighted, with applications as diverse as the creation of movies of electrochem. (electrocatalytic) processes in action to tracking the motion and activity of nanoparticles near electrode surfaces.
- 51Engstrom, R. C. Electrochemical Pretreatment of Glassy Carbon Electrodes. Anal. Chem. 1982, 54, 2310– 2314, DOI: 10.1021/ac00250a03851https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL38XlsFaqs7Y%253D&md5=4c3c805940601b442c982837d6bf4944Electrochemical pretreatment of glassy carbon electrodesEngstrom, Royce C.Analytical Chemistry (1982), 54 (13), 2310-14CODEN: ANCHAM; ISSN:0003-2700.The effects of preanodization and precathodization on the electrochem. oxidn. of hydroquinone [123-31-9], ferrocyanide [13408-63-4], and hydrazine [302-01-2] were studied at glassy C electrodes. Pretreatment was characterized with respect to the sequence of voltages applied to the electrode, the amplitude of the applied voltage, and the duration of pretreatment. For all 3 electroactive species, preanodization at <1.5 V vs. SCE was required to activate a freshly polished electrode. Ferrocyanide and hydrazine also required precathodization to remove an inhibitory layer formed during preanodization. In all cases, pretreatment resulted in a substantial improvement in the half-wave potential of the voltammetric wave and in the reproducibility of the wave. The results are interpreted in terms of 3 distinct electrode surface conditions.
- 52Kiema, G. K.; Fitzpatrick, G.; McDermott, M. T. Probing Morphological and Compositional Variations of Anodized Carbon Electrodes with Tapping-Mode Scanning Force Microscopy. Anal. Chem. 1999, 71, 4306– 4312, DOI: 10.1021/ac990405652https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXlsFSku7s%253D&md5=cb626ed1dd297e5c1f1f89e2f9f89601Probing Morphological and Compositional Variations of Anodized Carbon Electrodes with Tapping-Mode Scanning Force MicroscopyKiema, Gregory K.; Fitzpatrick, Glen; McDermott, Mark T.Analytical Chemistry (1999), 71 (19), 4306-4312CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)This paper demonstrates the 1st application of tapping-mode scanning force microscopy (TM SFM) in the compositional mapping of modified glassy carbon (GC) electrodes. Using TM SFM, the authors were able to track both compositional and topog. changes of polished GC induced by electrochem. pretreatment (ECP). Photoresist-based microfabrication techniques were employed to produce surfaces consisting of segregated modified and unmodified regions for direct comparison in the same image. ECP of GC via anodization in basic solns. for short times (∼10 s) initially removes the ubiquitous layer of polishing debris via an etching process. Longer anodization in basic electrolyte results in significant etching of the GC surface. ECP in acidic solns. yields little topog. change compared to basic electrolytes. Electrochem. results obtained for three redox systems studied on both modified and unmodified GC electrodes correlate with the TM SFM images collected.
- 53Virtanen, P.; Gommers, R.; Oliphant, T. E.; Haberland, M.; Reddy, T.; Cournapeau, D.; Burovski, E.; Peterson, P.; Weckesser, W.; Bright, J. SciPy 1.0: Fundamental Algorithms for Scientific Computing in Python. Nat. Methods 2020, 17, 261– 272, DOI: 10.1038/s41592-019-0686-253https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXislCjuro%253D&md5=f007632188adeb57a43469157898e0a8SciPy 1.0: fundamental algorithms for scientific computing in PythonVirtanen, Pauli; Gommers, Ralf; Oliphant, Travis E.; Haberland, Matt; Reddy, Tyler; Cournapeau, David; Burovski, Evgeni; Peterson, Pearu; Weckesser, Warren; Bright, Jonathan; van der Walt, Stefan J.; Brett, Matthew; Wilson, Joshua; Millman, K. Jarrod; Mayorov, Nikolay; Nelson, Andrew R. J.; Jones, Eric; Kern, Robert; Larson, Eric; Carey, C. J.; Polat, Ilhan; Feng, Yu; Moore, Eric W.; Vander Plas, Jake; Laxalde, Denis; Perktold, Josef; Cimrman, Robert; Henriksen, Ian; Quintero, E. A.; Harris, Charles R.; Archibald, Anne M.; Ribeiro, Antonio H.; Pedregosa, Fabian; van Mulbregt, PaulNature Methods (2020), 17 (3), 261-272CODEN: NMAEA3; ISSN:1548-7091. (Nature Research)Abstr.: SciPy is an open-source scientific computing library for the Python programming language. Since its initial release in 2001, SciPy has become a de facto std. for leveraging scientific algorithms in Python, with over 600 unique code contributors, thousands of dependent packages, over 100,000 dependent repositories and millions of downloads per yr. In this work, we provide an overview of the capabilities and development practices of SciPy 1.0 and highlight some recent tech. developments.
- 54Ferrari, A. C.; Robertson, J. Interpretation of Raman Spectra of Disordered and Amorphous Carbon. Phys. Rev. B 2000, 61, 14095– 14107, DOI: 10.1103/PhysRevB.61.1409554https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXjs1Smu7c%253D&md5=e451e6f21e1f6cf375931e6a23e836bbInterpretation of Raman spectra of disordered and amorphous carbonFerrari, A. C.; Robertson, J.Physical Review B: Condensed Matter and Materials Physics (2000), 61 (20), 14095-14107CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)The model and theor. understanding of the Raman spectra in disordered and amorphous C are given. The nature of the G and D vibration modes in graphite is analyzed in terms of the resonant excitation of π states and the long-range polarizability of π bonding. Visible Raman data on disordered, amorphous, and diamondlike C are classified in a 3-stage model to show the factors that control the position, intensity, and widths of the G and D peaks. The visible Raman spectra depend formally on the configuration of the sp2 sites in sp2-bonded clusters. In cases where the sp2 clustering is controlled by the sp3 fraction, such as in as-deposited tetrahedral amorphous C (ta-C) or hydrogenated amorphous C (a-C:H) films, the visible Raman parameters can be used to derive the sp3 fraction.
- 55Sze, S. Raman Spectroscopic Characterization of Carbonaceous Aerosols. Atmos. Environ. 2001, 35, 561– 568, DOI: 10.1016/S1352-2310(00)00325-355https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXovF2js7o%253D&md5=97d2ecfe1ad053c87ee108fff816d0fdRaman spectroscopic characterization of carbonaceous aerosolsSze, S.-K.; Siddique, N.; Sloan, J. J.; Escribano, R.Atmospheric Environment (2000), 35 (3), 561-568CODEN: AENVEQ; ISSN:1352-2310. (Elsevier Science Ltd.)Raman spectroscopy was used to characterize a variety of C-contg. particulate matter, including samples collected from ambient urban atmospheres. Based on the Raman spectra of known, com. particles, a simple empirical model was derived that reflects their micro-chem. and micro-physics. This model gives information on crystal size and morphol. of the graphitic component, which correlates with known characteristics of the com. samples. Similar information was derived about the graphitic component of ambient particles, suggesting this method might be used to systematically characterize ambient particles in the future.
- 56Sadezky, A.; Muckenhuber, H.; Grothe, H.; Niessner, R.; Pöschl, U. Raman Microspectroscopy of Soot and Related Carbonaceous Materials: Spectral Analysis and Structural Information. Carbon 2005, 43, 1731– 174256https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXltFGrtLc%253D&md5=045e6d9ee2eb3d84bd001fca25bc7f62Raman microspectroscopy of soot and related carbonaceous materials. Spectral analysis and structural informationSadezky, A.; Muckenhuber, H.; Grothe, H.; Niessner, R.; Poeschl, U.Carbon (2005), 43 (8), 1731-1742CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)Exptl. conditions and math. fitting procedures for the collection and anal. of Raman spectra of soot and related carbonaceous materials were investigated and optimized with a Raman microscope system operated at 3 different laser excitation wavelengths (514, 633, and 780 nm). Several band combinations for spectral anal. were tested, and a combination of 4 Lorentzian-shaped bands (G, D1, D2, D4) at about 1580, 1350, 1620, and 1200 cm-1, resp., with a Gaussian-shaped band (D3) at ∼1500 cm-1 was best suited for the 1st-order spectra. The 2nd-order spectra were best fitted with Lorentzian-shaped bands at about 2450, 2700, 2900, and 3100 cm-1. Spectral parameters (band positions, full widths at half max., and intensity ratios) are reported for several types of industrial C black (Degussa Printex, Cabot Monarch), diesel soot (particulate matter from modern heavy duty vehicle and passenger car engine exhaust, NIST SRM1650), spark-discharge soot (Palas GfG100), and graphite. Several parameters, in particular the width of the D1 band at ∼1350 cm-1, provide structural information and allow to discriminate the sample materials, but the characterization and distinction of different types of soot is limited by the exptl. reproducibility of the spectra and the statistical uncertainties of curve fitting. The results are discussed and compared with x-ray diffraction measurements and earlier Raman spectroscopic studies of comparable materials, where different measurement and fitting procedures was applied.
- 57Mitchell, E. C.; Dunaway, L. E.; McCarty, G. S.; Sombers, L. A. Spectroelectrochemical Characterization of the Dynamic Carbon-Fiber Surface in Response to Electrochemical Conditioning. Langmuir 2017, 33, 7838– 7846, DOI: 10.1021/acs.langmuir.7b0144357https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtFyqsbbM&md5=3d588d53a33f0ecf06fa9c10a9b34c01Spectroelectrochemical Characterization of the Dynamic Carbon-Fiber Surface in Response to Electrochemical ConditioningMitchell, Edwin C.; Dunaway, Lars E.; McCarty, Gregory S.; Sombers, Leslie A.Langmuir (2017), 33 (32), 7838-7846CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)The effects of electrochem. preconditioning of P-55 pitch-based C-fiber microelectrodes were quant. examd. Microstructural characterization of the electrode surface was done using Raman spectroscopy and SEM. Electrochem. performance was evaluated using cyclic voltammetry. Application of pos. potentials provides beneficial structural modifications to the electrode surface. Electrodes that were preconditioned using a static potential of +1.0 V exhibited enhanced sensitivity and electron transfer properties when compared to electrodes conditioned for the same amt. of time with dynamic (triangular) waveforms reaching +1.0 V. Conditioning elicited microstructural changes to the electrode surface that were dependent on the amt. of time spent at potentials ⪆1.0 V. Importantly, the data demonstrate that the C-fiber microstructure is dynamic. It is able to quickly and continuously undergo rapid structural reorganization as potential is applied, repeatedly alternating between a relatively ordered state and one that exhibits greater disorder in response to applied electrochem. potentials that span the range commonly used in voltammetric expts.
- 58Yumitori, S. Correlation of C1s Chemical State Intensities with the O1s Intensity in the XPS Analysis of Anodically Oxidized Glass-like Carbon Samples. J. Mater. Sci. 2000, 35, 139– 146, DOI: 10.1023/A:100476110391958https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXhtV2js7Y%253D&md5=7da67f90ee41dab4f35c1d5b0bb7030eCorrelation of C1s chemical state intensities with the O1s intensity in the XPS analysis of anodically oxidized glass-like carbon samplesYumitori, ShujiJournal of Materials Science (2000), 35 (1), 139-146CODEN: JMTSAS; ISSN:0022-2461. (Kluwer Academic Publishers)An XPS study of anodic oxidized glass-like carbon (GC) was conducted in order to investigate the inconsistency between O1s/C1s and oxygen concn. (Ocal.) calcd. from the curve fitting results of the C1s spectrum. Consideration of the asym. peak shape of the C1s spectrum is normally done in order to obtain precise curve fitting results. However, it was found that the 2nd-carbon peak should also be taken into consideration in the curve fitting process in addn. to the effect of asym. peak shape of carbon to obtain a consistent value of O1s/C1s. The 2nd graphitic peak is normally located +0.7-+0.8 eV away from the original C1s spectrum. The ratio of the 2nd graphitic peak area in the C1s spectrum increased as the elec. charge increased. However, the peak shapes of C1s spectra of anodic oxidized GC after heat treatment at 1500°C in argon atm. were almost the same as the C1s of untreated GC. Although the origin of the 2nd graphitic peak is not well understood, it may be related to the amt. of oxygen on the GC surface.
- 59Gengenbach, T. R.; Major, G. H.; Linford, M. R.; Easton, C. D. Practical Guides for X-Ray Photoelectron Spectroscopy (XPS): Interpreting the Carbon 1s Spectrum. J. Vac. Sci. Technol., A 2021, 39, 013204 DOI: 10.1116/6.000068259https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXosVaqsg%253D%253D&md5=5a0800ea1909f4d480a1e9ea4ea7c88fPractical guides for x-ray photoelectron spectroscopy (XPS): Interpreting the carbon 1s spectrumGengenbach, Thomas R.; Major, George H.; Linford, Matthew R.; Easton, Christopher D.Journal of Vacuum Science & Technology, A: Vacuum, Surfaces, and Films (2021), 39 (1), 013204CODEN: JVTAD6; ISSN:0734-2101. (American Institute of Physics)The carbon 1s photoelectron spectrum is the most widely fit and analyzed narrow scan in the XPS literature. It is, therefore, critically important to adopt well-established protocols based on best practices for its anal., since results of these efforts affect research outcomes in a wide range of different application areas across materials science. Unfortunately, much XPS peak fitting in the scientific literature is inaccurate. In this guide, we describe and explain the most common problems assocd. with C 1s narrow scan anal. in the XPS literature. We then provide an overview of rules, principles, and considerations that, taken together, should guide the approach to the anal. of C 1s spectra. We propose that following this approach should result in (1) the avoidance of common problems and (2) the extn. of reliable, reproducible, and meaningful information from exptl. data. (c) 2021 American Institute of Physics.
- 60Momotenko, D.; Byers, J. C.; McKelvey, K.; Kang, M.; Unwin, P. R. High-Speed Electrochemical Imaging. ACS Nano 2015, 9, 8942– 8952, DOI: 10.1021/acsnano.5b0279260https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhtlWmurrP&md5=92612b126dbfeb0d7c08e8656d2326cdHigh-Speed Electrochemical ImagingMomotenko, Dmitry; Byers, Joshua C.; McKelvey, Kim; Kang, Minkyung; Unwin, Patrick R.ACS Nano (2015), 9 (9), 8942-8952CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)The design, development, and application of high-speed scanning electrochem. probe microscopy is reported. The approach allows the acquisition of high-resoln. images (typically 1000 pixels μm-2) at rates approaching 4 s per frame, while collecting up to 8000 image pixels per s, ∼1000 times faster than typical imaging speeds used. The focus is on scanning electrochem. cell microscopy (SECCM), but the principles and practicalities are applicable to many electrochem. imaging methods. The versatility of the high-speed scan concept is demonstrated at a variety of substrates, including imaging the electroactivity of a patterned self-assembled monolayer on gold, visualization of chem. reactions occurring at single wall carbon nanotubes, and probing nanoscale electrocatalysts for water splitting. These studies provide movies of spatial variations of electrochem. fluxes as a function of potential and a platform for the further development of high speed scanning with other electrochem. imaging techniques.
- 61Snowden, M. E.; Güell, A. G.; Lai, S. C. S.; McKelvey, K.; Ebejer, N.; O’Connell, M. A.; Colburn, A. W.; Unwin, P. R. Scanning Electrochemical Cell Microscopy: Theory and Experiment for Quantitative High Resolution Spatially-Resolved Voltammetry and Simultaneous Ion-Conductance Measurements. Anal. Chem. 2012, 84, 2483– 2491, DOI: 10.1021/ac203195h61https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhsVWjsL8%253D&md5=8863b846ef531cfd3b8272638ebc1126Scanning Electrochemical Cell Microscopy: Theory and Experiment for Quantitative High Resolution Spatially-Resolved Voltammetry and Simultaneous Ion-Conductance MeasurementsSnowden, Michael E.; Guell, Aleix G.; Lai, Stanley C. S.; McKelvey, Kim; Ebejer, Neil; O'Connell, Michael A.; Colburn, Alexander W.; Unwin, Patrick R.Analytical Chemistry (Washington, DC, United States) (2012), 84 (5), 2483-2491CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Scanning electrochem. cell microscopy (SECCM) is a high resoln. electrochem. scanning probe technique that employs a dual-barrel theta pipet probe contg. electrolyte soln. and quasi-ref. counter electrodes (QRCE) in each barrel. A thin layer of electrolyte protruding from the tip of the pipet ensures that a gentle meniscus contact is made with a substrate surface, which defines the active surface area of an electrochem. cell. The substrate can be an elec. conductor, semiconductor, or insulator. The main focus here is on the general case where the substrate is a working electrode, and both ion-conductance measurements between the QRCEs in the two barrels and voltammetric/amperometric measurements at the substrate can be made simultaneously. In usual practice, a small perpendicular oscillation of the probe with respect to the substrate is employed, so that an alternating conductance current (a.c.) develops, due to the change in the dimensions of the electrolyte contact (and hence resistance), as well as the direct conductance current (d.c.). The d.c. current can be predicted for a fixed probe by solving the Nernst-Planck equation and the a.c. response can also be derived from this response. Both responses agree well with expt. The pipet geometry plays an important role in controlling the d.c. conductance current and this is easily measured by microscopy. A key feature of SECCM is that mass transport to the substrate surface is by diffusion and, for charged analytes, ion migration which can be controlled and varied quantifiably via the bias between the two QRCEs. For a working electrode substrate this means that charged redox-active analytes can be transported to the electrode/soln. interface in a well-defined and controllable manner and that relatively fast heterogeneous electron transfer kinetics can be studied. The factors controlling the voltammetric response are detd. by both simulation and expt. Expts. demonstrate the realization of simultaneous quant. voltammetric and ion conductance measurements and also identify a general rule of thumb that the surface contacted by electrolyte is of the order of the pipet probe dimensions.
- 62Ebejer, N.; Schnippering, M.; Colburn, A. W.; Edwards, M. A.; Unwin, P. R. Localized High Resolution Electrochemistry and Multifunctional Imaging: Scanning Electrochemical Cell Microscopy. Anal. Chem. 2010, 82, 9141– 9145, DOI: 10.1021/ac102191u62https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXht12ju73O&md5=a669d8c8c6ae7ee63b48cb7fe61ce0a9Localized High Resolution Electrochemistry and Multifunctional Imaging: Scanning Electrochemical Cell MicroscopyEbejer, Neil; Schnippering, Mathias; Colburn, Alexander W.; Edwards, Martin A.; Unwin, Patrick R.Analytical Chemistry (Washington, DC, United States) (2010), 82 (22), 9141-9145CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)We describe highly localized electrochem. measurements and imaging using a simple, mobile theta pipet cell. Each channel (diam. <500 nm) of a tapered theta pipet is filled with electrolyte soln. and a Ag/AgCl electrode, between which a bias is applied, resulting in a conductance current across a thin meniscus of soln. at the end of the pipet, which is typically deployed in air or a controlled gaseous environment. When the position of the pipet normal to a surface of interest is oscillated, an oscillating component in the conductance current is generated when the meniscus at the end of the probe comes into contact with the surface and undergoes periodic (reversible) deformation, so as to modulate the soln. resistance. This oscillating current component can be used to maintain gentle contact of the soln. from the pipet cell with the surface and as a set point for high resoln. topog. imaging with the pipet. Simultaneously, the mean conductance current that flows between the pipet channels can be measured and is sensitive to the local nature of the interface, informing one, for example, on wettability and ion flow into or out of the surface investigated. Furthermore, conductor or semiconductor surfaces can be connected as a working electrode, with one of the electrodes in the pipet serving as a quasi-ref. electrode. This pipet cell then constitutes part of a dynamic electrochem. cell, with which direct voltammetric-amperometric imaging can be carried out simultaneously with conductance and topog. imaging. This provides multifunctional electrochem. maps of surfaces and interfaces at high spatial resoln. The prospects for the use of this new methodol. widely are highlighted through exemplar studies and a brief discussion of future applications.
- 63Bentley, C. L.; Kang, M.; Unwin, P. R. Scanning Electrochemical Cell Microscopy (SECCM) in Aprotic Solvents: Practical Considerations and Applications. Anal. Chem. 2020, 92, 11673– 11680, DOI: 10.1021/acs.analchem.0c0154063https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXhtFelur7J&md5=ef16375722f42c43595d8aec1de4fc50Scanning Electrochemical Cell Microscopy (SECCM) in Aprotic Solvents: Practical Considerations and ApplicationsBentley, Cameron L.; Kang, Minkyung; Unwin, Patrick R.Analytical Chemistry (Washington, DC, United States) (2020), 92 (17), 11673-11680CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Many applications in modern electrochem., notably electrosynthesis and energy storage/conversion take advantage of the "tunable" physicochem. properties (e.g., proton availability and/or electrochem. stability) of nonaq. (e.g., aprotic) electrolyte media. This work develops general guidelines pertaining to the use of scanning electrochem. cell microscopy (SECCM) in aprotic solvent electrolyte media to address contemporary structure-electrochem. activity problems. Using the simple outer-sphere Fc0/+ process (Fc = ferrocene) as a model system, high b.p. (low vapor pressure) solvents give rise to highly robust and reproducible electrochem., whereas volatile (low b.p.) solvents need to be mixed with suitable low m.p. supporting electrolytes (e.g., ionic liqs.) or high b.p. solvents to avoid complications assocd. with salt pptn./crystn. on the scanning (minutes to hours) time scale. When applied to perform microfabrication-specifically the electrosynthesis of the conductive polymer, polypyrrole-the optimized SECCM set up produces highly reproducible arrays of synthesized (electrodeposited) material on a commensurate scale to the employed pipet probe. Applying SECCM to map electrocatalytic activity-specifically the electro-oxidn. of iodide at polycryst. platinum-reveals unique (i.e., structure-dependent) patterns of surface activity, with grains of specific crystallog. orientation, grain boundaries and areas of high local surface misorientation identified as potential electrocatalytic "hot spots". The work herein further cements SECCM as a premier technique for structure-function-activity studies in (electro)materials science and will open up exciting new possibilities through the use of aprotic solvents for rational anal./design in electrosynthesis, microfabrication, electrochem. energy storage/conversion, and beyond.
- 64Dekanski, A.; Stevanović, J.; Stevanović, R.; Nikolić, B. Ž.; Jovanović, V. M. Glassy Carbon Electrodes I. Characterization and Electrochemical Activation. Carbon 2001, 39, 1195– 1205, DOI: 10.1016/S0008-6223(00)00228-164https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXjtlSkurc%253D&md5=95b55c281b848052583a1a098c5d5a0fGlassy carbon electrodes. I. Characterization and electrochemical activationDekanski, A.; Stevanovic, J.; Stevanovic, R.; Nikolic, B. Z.; Jovanovic, V. M.Carbon (2001), 39 (8), 1195-1205CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Science Ltd.)Electrochem. properties of glassy carbon electrodes of two types were examd., one thermally treated at 1000°C (sample K) and another thermally treated at 2500° (sample G). Mech. polished or electrochem. polarized electrodes were characterized in NaOH, HClO4 and H2SO4 solns. by cyclic voltammetry (cv) at different sweep rates in the potential range between the hydrogen and oxygen evolution. The activity of the electrodes depended on the properties of the glassy carbon examd., as detd. by both the temp. of thermal treatment and the mech. or electrochem. pretreatment of the sample. It was noticed that both types of electrodes, when polished exhibited an increase in the double layer charge upon increasing the pH value of the soln. The cv charges, for both types of samples, increase upon anodic polarization. The higher the potential of oxidn., the more pronounced is the increase in charge, particularly in acidic soln. The increase in charge amts. from below 1 mC cm-2 for polished glassy carbon up to few hundreds of mC cm-2 for surfaces anodically polarized in acidic soln. Anal. of the dependence of voltammetric charge, as well as morphol. changes of the electrode surface, on the time of oxidn. suggests the existence of three stages in the electrochem. activation process. The first one occurs only once at the beginning of the activation, while the other two repeat themselves, reflecting a periodical activation and deactivation process. These stages were discussed and ascribed to a surface layer oxidn., graphite oxide layer growth and mech. destruction of the surface. Independent surface anal. by AES, XPS and STM confirms the results obtained by electrochem. methods.
- 65Soriaga, M. P.; Hubbard, A. T. Determination of the Orientation of Adsorbed Molecules at Solid-Liquid Interfaces by Thin-Layer Electrochemistry: Aromatic Compounds at Platinum Electrodes. J. Am. Chem. Soc. 1982, 104, 2735– 2742, DOI: 10.1021/ja00374a00865https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL38XhvV2ms7Y%253D&md5=1d02c1a22255875ba82772cfebc7bc43Determination of the orientation of adsorbed molecules at solid-liquid interfaces by thin-layer electrochemistry: aromatic compounds at platinum electrodesSoriaga, Manuel P.; Hubbard, Arthur T.Journal of the American Chemical Society (1982), 104 (10), 2735-42CODEN: JACSAT; ISSN:0002-7863.Accurate measurements of the limiting coverages of adsorbed mols. on smooth Pt electrodes are reported. Comparison of measurements with values calcd. for various possible mol. orientations indicates the predominant orientations of the adsorbed mols. Exptl. data were obtained by linear potential scan voltammetry and potential-step chronocoulometry using thin-layer electrodes. Calcns. were based upon covalent and van der Waals radii as tabulated by Pauling and were tested against the results of classical adsorption expts. Representing a wide range of structures and chem. properties, 40 of the following type of compds. were studied: simple diphenols and quinones; alkyl-substituted diphenols and quinones; dihydroxybenzaldehydes; halogenated diphenols and quinones; polyhydroxybenzenes and quinones; hexaoxocyclohexane; N-heteroaroms.; diphenols having surface-active side chains; polycyclic diphenols and quinones. The most probable orientation was detd. for each adsorbed compd.
- 66Chen, L.; Tanner, E. E. L.; Lin, C.; Compton, R. G. Impact Electrochemistry Reveals That Graphene Nanoplatelets Catalyse the Oxidation of Dopamine via Adsorption. Chem. Sci. 2018, 9, 152– 159, DOI: 10.1039/C7SC03672H66https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhslemt7bI&md5=ea404bed5d5b9447a30e1a31c5f4e3d3Impact electrochemistry reveals that graphene nanoplatelets catalyse the oxidation of dopamine via adsorptionChen, Lifu; Tanner, Eden E. L.; Lin, Chuhong; Compton, Richard G.Chemical Science (2018), 9 (1), 152-159CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)Graphene nanoplatelets are shown to electrocatalyze the oxidn. of dopamine. Single entity measurements ('nano-impacts') coupled with microdisc voltammetry and UV-visible spectroscopy reveal that adsorption of dopamine and its oxidised product on the graphene nanoplatelets is the key factor causing the obsd. catalysis. Genetic implications are drawn both for the study of catalysts in general and for graphene nanoplatelets in particular.
- 67Soriaga, M. P.; Hubbard, A. T. Determination of the Orientation of Aromatic Molecules Adsorbed on Platinum Electrodes. The Effect of Solute Concentration. J. Am. Chem. Soc. 1982, 104, 3937– 3945, DOI: 10.1021/ja00378a02667https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL38XktlSiu7o%253D&md5=98ef00c29ef0463ac52e1376f98c268dDetermination of the orientation of aromatic molecules adsorbed on platinum electrodes. The effect of solute concentrationSoriaga, Manuel P.; Hubbard, Arthur T.Journal of the American Chemical Society (1982), 104 (14), 3937-45CODEN: JACSAT; ISSN:0002-7863.Accurate measurements of the amts. of arom. mols. adsorbed on smooth polycryst. Pt electrodes in aq. solns. are reported as a function of concn. The measurements were made by electrochem. methods using thin-layer cells. A plot of adsorbed amt. vs. concn. shows that most of the subject compds. display multiple plateaus sepd. by abrupt transitions to higher densities at higher concns. Comparison of plateau values with model calcns., based upon covalent and van der Waals radii tabulated by Pauling, reveals that a series of definite orientations are adopted as the adsorbate concn. is increased; each individual orientation was stable over an appreciable range of concn. Twenty-six compds., representing a variety of structures and chem. properties, were studied: simple diphenols; alkyldiphenols; polyhydroxybenzenes; halogenated diphenols; N-heteroaroms.; diphenols having surface-active side chains; polycyclic phenols and quinones; and hydroquinone mercaptans.
- 68Bard, A. J.; Faulkner, L. R. Electrochemical Methods: Fundamentals and Applications, 2nd ed.; Wiley, 2001.There is no corresponding record for this reference.
- 69DuVall, S. H.; McCreery, R. L. Self-Catalysis by Catechols and Quinones during Heterogeneous Electron Transfer at Carbon Electrodes. J. Am. Chem. Soc. 2000, 122, 6759– 6764, DOI: 10.1021/ja000227u69https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXksVejsLs%253D&md5=18f9b55d102c8efa1a03322bf5a65af0Self-catalysis by Catechols and Quinones during Heterogeneous Electron Transfer at Carbon ElectrodesDuVall, Stacy H.; McCreery, Richard L.Journal of the American Chemical Society (2000), 122 (28), 6759-6764CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Heterogeneous electron transfer kinetics for several catechols were examd. on glassy carbon (GC) electrodes in aq. soln. Electrode prepns. yielded GC surfaces with low levels of oxides or adsorbed impurities, which exhibited strong adsorption of dopamine (DA) and related catechols. Conversely, modification of GC with an org. monolayer suppressed DA adsorption and in many cases prevented electron transfer. By relating catechol adsorption to obsd. electron transfer, an adsorbed layer of catechol acts as an electrocatalyst for soln.-phase redox components. Physisorbed or chemisorbed monolayers of several quinones, including duroquinone, anthraquinone, and dopamine itself, are catalytic toward dopamine oxidn. and redn., but nitrophenyl, trifluoromethylphenyl, and methylene blue monolayers severely inhibit electron transfer. The magnitude of inhibition was affected by electrostatic attraction or repulsion between the surface and the redox system, but the major factor controlling electron-transfer kinetics is not electrostatic in origin. The most plausible mechanism is self-catalysis by an adsorbed quinone, which remained adsorbed during electron transfer to a redox couple in soln. The results are inconsistent with a redox mediation mechanism involving a redox cross-reaction between adsorbed and soln. quinone couples. An interaction between the adsorbed and soln. quinone species during electron transfer appears to catalyze one or more of the steps in the scheme of squares mechanism for hydroquinone/quinone redox systems. The results explain a variety of observations about catechol and hydroquinone electrochem., as well as provide more fundamental insights into quinone electron-transfer mechanisms.
- 70Syeed, A. J.; Li, Y.; Ostertag, B. J.; Brown, J. W.; Ross, A. E. Nanostructured Carbon-Fiber Surfaces for Improved Neurochemical Detection. Faraday Discuss. 2022, 233, 336– 353, DOI: 10.1039/D1FD00049GThere is no corresponding record for this reference.https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=&md5=9874b665cc7a056b8e2f928dd3112440
Supporting Information
Supporting Information
The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.jpcc.2c02801.
Additional electrochemical data and XPS and EDS spectra (PDF)
Spatially resolved electrochemical (i–E) movie (110 pixels over a 55 × 50 μm scan area, hopping distance = 5 μm) obtained with the SECCM protocol (first voltammetric cycle), visualizing the activity of DA oxidation on a GC surface locally anodized for 60 s. The pipet probe contained 30 μM DA in PBS, and the scan rate was 47 V s–1 (MP4)
Spatially resolved electrochemical (i–E) movie (110 pixels over a 55 × 50 μm scan area, hopping distance = 5 μm) obtained with the SECCM protocol (fifth voltammetric cycle), visualizing the activity of DA oxidation on a GC surface locally anodized for 60 s. The pipet probe contained 30 μM DA in PBS, and the scan rate was 47 V s–1 (MP4)
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