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ArticleJune 3, 2019

Wearable Potentiometric Ion Patch for On-Body Electrolyte Monitoring in Sweat: Toward a Validation Strategy to Ensure Physiological Relevance
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Marc Parrilla
Marc Parrilla
Department of Chemistry, School of Engineering Science in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, Teknikringen 30, SE-100 44 Stockholm, Sweden
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Inmaculada Ortiz-Gómez
Inmaculada Ortiz-Gómez
Department of Chemistry, School of Engineering Science in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, Teknikringen 30, SE-100 44 Stockholm, Sweden
Department of Analytical Chemistry, Campus Fuentenueva, Faculty of Sciences, University of Granada, 18071 Granada, Spain
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Rocío Cánovas
Rocío Cánovas
Department of Chemistry, School of Engineering Science in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, Teknikringen 30, SE-100 44 Stockholm, Sweden
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Alfonso Salinas-Castillo
Alfonso Salinas-Castillo
Department of Analytical Chemistry, Campus Fuentenueva, Faculty of Sciences, University of Granada, 18071 Granada, Spain
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María Cuartero
María Cuartero
Department of Chemistry, School of Engineering Science in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, Teknikringen 30, SE-100 44 Stockholm, Sweden
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http://orcid.org/0000-0002-3858-8466
Gastón A. Crespo*
Gastón A. Crespo
Department of Chemistry, School of Engineering Science in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, Teknikringen 30, SE-100 44 Stockholm, Sweden
*E-mail: [email protected]
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http://orcid.org/0000-0002-1221-3906

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Analytical Chemistry

Cite this: Anal. Chem. 2019, 91, 13, 8644–8651

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https://doi.org/10.1021/acs.analchem.9b02126

Published June 3, 2019

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Abstract

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Herein, the reproducibility and a double validation of on-body measurements provided by new wearable potentiometric ion sensors (WPISs) is presented. Sweat collected during sport practice was first analyzed using the developed device, the pH-meter, and ion chromatography (IC) prior to on-body measurements (off-site validation). Subsequently, the accuracy of on-body measurements accomplished by the WPISs was evaluated by comparison with pH-meter readings and IC after collecting sweat (every 10–12.5 min) during sport practice. The developed device contains sensors for pH, Cl^–, K⁺, and Na⁺ that are embedded in a flexible sampling cell for sweat analysis. The electrode array was fabricated employing MWCNTs (as an ion-to-electron transducer) and stretchable materials that have been exhaustively characterized in terms of analytical performance, presenting Nernstian slopes within the expected physiological range of each ion analyte (Cl^–, 10–100 mM; K⁺, 10–10 mM; and Na⁺, 10–100 mM and pH, 4.5–7.5), drift suitable for midterm exercise practice (0.3 ± 0.2 mV h^–1), fast response time, adequate selectivity for sweat measurements, and excellent reversibility. Besides that, the designed sampling cell avoids any sweat contamination and evaporation issues while supplying a passive sweat flow encompassing specifically the individual’s perspiration. The interpretation of ion concentration profiles may permit the identification of personal dynamic patterns in sweat composition while practicing sport.

Subjects

The ability to monitor chemical events in a continuous and periodic manner has become of general interest in many fields, especially in environmental sensing and healthcare. (1) Analytical devices that can be on-bodily worn without disturbing the individual’s status are key players as interfaces between vital chemical events and the digitalization of related observations. (2) Today, these gadgets are actively proposed in the literature in the form of wristbands, textiles and skin patches, among others, (3) giving rise to new opportunities for the digitalization of unique data that was inaccessible before this recent paradigm shift.

The growth experienced in the field of wearable chemical sensors over the past decade is undoubtedly connected to increasing market expectations. (5) Thus, market outlooks predict that the immediate revenue from electronic skin patches will reach $10bn by 2023 and $15bn by 2028. (6) However, these numbers are primarily based on the unquestionable success of physical sensors (i.e., temperature, pressure, and movement) over chemical ones. (6) Considering that the information provided by these two kind of sensors is different while complementary, it is absolutely necessary a breakthrough in wearable chemical sensors by demonstrating reliable operability in real scenarios.

Electrochemical sensors are the most convenient platform to develop wearable chemical sensors as inferred from the large number of scientific contributions. (7) These sensors allow for the monitoring of critical biomarkers, such as biomolecules (e.g., glucose, lactate, and drugs), through amperometric readout and ions (K⁺ and Na⁺) using potentiometry. (8) Indeed, the well-established all-solid-state technology offers a broad range of advantages in terms of technical specifications, such as simplicity, miniaturization, and low consumption of resources and power, that are essential toward a potential commercialization.

Regarding the value of the chemical information monitored by electrochemical devices, so-called wearable potentiometric ion sensors (WPISs) may particularly enable unique observations related to applied human physiology and health care by measuring ion levels in sweat (and other biological fluids). (9) From a medical perspective, WPISs are striving to supply data suitable for diagnosis of cystic fibrosis and other diseases that involve electrolyte imbalance disorders. (10,11) These devices are also useful from a fitness perspective, permitting the monitoring of certain indicators of the dehydration status of the individual (through sodium and chloride concentrations), (12) muscle activity (potassium), (13) exercise intensity (ammonium), (14) acid–base equilibria (pH), (15) or muscle strength (magnesium). (16)

Recently, certain reviews in the field of WPISs have reported the key requirements for the development of WPISs toward a successful on-body application. (9) These include (i) fast response time to obtain real-time electrolyte dynamics; (ii) reversibility of the electrode response to detect any fluctuations of the ion analyte as a result of physiological events; (iii) resiliency and stability of the electrode response during the wearability; (17) (iv) appropriate calibration protocol to minimize any possible error in the calculation of the electrolyte concentration (number of points, comparison between pre- and postcalibration, concentration versus activity, possibility of calibration-free sensor, influence of the sweat rate, etc.); (18) (v) the noninvasive nature of the device and sampling strategy; (vi) the provision of a sampling approach (i.e., sampling cell) that allows for obtaining a constant sweat flow without the influence of any evaporation or contamination issue; (19−22) and (vii) proper validation of on-body measurements. Hence, the inappropriate fulfillment of any of the mentioned requirements may lead to important errors in the calculation of the concentration of the tested ions, therefore ending in a mistaken decision-making process by the physician (medical purpose) or coach (fitness perspective) (Figure 1).

Figure 1. Illustration of the research question in this article. Is the on-body data provided by WPISs reliable? What is the proper validation protocol to evaluate reliability of the real-time observations?.

Concerning the validation of on-body measurements, the collection of enough sample volume suitable for later analysis utilizing a standard technique (i.e., ion chromatography (IC) and others) justifies the validation of on-body measurements only at longer sampling times (1 h of monitoring). This has resulted in a lack of validation criteria of the reported data despite the developed devices being promising. (23,24)

We propose herein a new protocol to validate on-body measurements provided by any WPISs. Indeed, we have developed a novel design for pH, Cl^–, K⁺, and Na⁺ detection in sweat and use it as proof-of-concept. It is worth mentioning, that the developed wearable device incorporates a sampling cell for constant sweat flow specifically tailored for an individual’s perspiration while avoiding any evaporation and contamination issues. In the final part of the work, validated on-body data demonstrate the potential of the WPISs in supplying reproducible (n = 3) and reliable data during the monitoring of physical activity of different subjects in a total of 9 on-body tests (T1–T9). To the best of our knowledge, this is the first time that such deep validation of on-body measurements provided by WPISs as well as its reproducibility is reported.

Experimental Section

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Fabrication of the Electrode Array

Figure 2a illustrates the procedure for the fabrication of the electrode array on a flexible polyurethane (PU) substrate. The electrodes consisted of five circular patterns prepared with stretchable carbon ink (CI-2051, Engineered Conductive Materials, Inc.) that were in turn connected to a serpentine track made of stretchable silver ink (CI-1036, Engineered Conductive Materials, Inc.). The electrodic path was fabricated on the PU substrate with the screen-printing technique (SPR-45 Automated SMT Stencil Printer, DDM Novastar, Inc., USA). Subsequently, the electrodes were modified first with a layer of multiwalled carbon nanotubes (MWCNTs) and thereafter with the selective membrane on top (see Table S1 for the compositions). For more details, the reader should refer to the Supporting Information.

Figure 2. (a) Electrodes before and after functionalization. (b) Images of the electrode array, the sampling cell, and entire wearable device. (c) Sweat flow in the sampling cell once it is attached to the skin. (d) WPISs attached to the skin. ISM = ion-selective membrane.

First, the analytical performances of the selective electrodes were characterized against a commercial Ag/AgCl reference electrode (6.0726.100, Metrohm Nordic, Sweden) when they were immersed in a beaker. The electrodes displayed a Nernstian slope as well as limits of detection (LODs) and linear ranges of responses (LRRs) suitable to detect the selected ions in sweat (Table S1). Interestingly, the expected physiological range for the tested ions during sport monitoring were for chloride 10–100 mM, potassium 3–10 mM, sodium 20–100 mM, and pH 4–7.5. (9) Between-electrode reproducibility (n = 3), response repeatability, medium-term drift, and selectivity were also adequate (Figures S1 and S2 and Tables S2 and S3). Indeed, other sensors already reported in the literature using conventional materials featured similar values (Table S3).

The reference electrode was prepared by modifying the method proposed by Bühlman et al. (25) in order to provide stretchability and durability by avoiding the use of a plasticizer (see the Supporting Information). Figure S3 displays the characterization of the analytical performances of this new reference electrode in terms of membrane composition (Table S4), interferences, medium-term stability, and the influence of light on the electrode response. The optimal condition obtained was the use of a PU without a plasticizer, which exhibits higher stability that is likely explained by the decrease of the leaching of the membrane components. (26)

Implementation of the Electrodes into the Sampling Cell for On-Body Measurements

The electrode array was then coupled to the sampling cell (Figure 2b). A circular collection zone allowed for the eccrine glands to collect sweat, which passively flows through the sensing channel up to the outlet of the sampling cell (Figure 2c) (see the Supporting Information for specific details). For example, as the total volume is 8.8 μL, the collected sweat will begin to flow through the sensing channel after 4.8 min of an individual sweating at a rate of 1 μL cm^–2 min^–1, which is a typical rate for a midintensity sport in several parts of the body. (27,28) All the zones and channels of the sampling cell have rounded shapes to enhance the homogenization of the sample. (29) The sampling cell is attached to the electrode array by adhesive transfer tape, thereby avoiding any possible leaking of sweat and allowing for an adequate pressure from the eccrine glands (14) (Figure 2d). Finally, the device (electrode array + sampling cell) is attached to the skin for on-body measurements through adhesive transfer tape.

Results and Discussion

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In Vitro Performance of the WPISs

The analytical performances of the electrode array incorporating all-solid-state sensors for Cl^–, K⁺, Na⁺, and pH, together with the reference electrode, were evaluated in water and artificial sweat before and after the implementation of the sampling cell. Figure S4 depicts the observed individual calibration graphs as well as the carry-over response, which is important for confirming the reversibility of the electrode response. The obtained calibration parameters (Tables S5 and S6) were similar to those displayed using the commercial reference electrode, pointing out the correct functioning of the reference electrode. Thus, the electrodes displayed a reproducible Nernstian slope (−63.0 ± 2.4 mV for Cl^–, 56.8 ± 2.5 mV for K⁺, 54.2 ± 1.3 mV for Na⁺, and 50.1 ± 0.5 mV for H⁺) within the same LRRs (1–100 mM, Cl^–; 0.1–100 mM, Na⁺; 0.1–100 mM, K⁺; and 4–7.5, pH), which include the physiological ranges expected for these ions in sweat. In addition, the electrodes showed robust response (reversibility) even under different types of mechanical stress. This latter is crucial as any change caused by the sensors’ portability during on-body measurements while practicing any sport activity may lead to important errors in the quantification of the analyte concentration. In this sense, the development of advanced materials with the ability to provide resiliency to the electrode response while maintaining the rest of the analytical performances is being actively explored by many authors. (30,31) In the present work, the entire WPIS device (electrodes + sampling cell) has been engineered with elastomeric materials that confer elasticity while maintaining the analytical characteristics of the potentiometric sensors.

Figure S5 portrays the calibration curves of the developed electrode array under linear stretching (up to 50% elongation) and during the bending effort (up to 80°). Importantly, these resiliency tests largely emulate the mechanical strain that the electrodes may experience during on-body measurements. Although, in some of the cases, it was found that the applied deformation modified the analytical behavior up to 30% (Table S7), this is unlikely to be experienced during on-body tests.

Off-Site Evaluation of the WPISs Performance

The strategy applied for sweat-sampling coupled to the WPISs is one of the major concerns when dealing with the accuracy of on-body sweat analysis. Accordingly, potentiometric sensors must be embedded in a gadget that offers (i) effective sweat renewal encompassed through the individual’s perspiration during sport practice in order to allow for the real-time monitoring of the ion analytes; (ii) no risk of sweat evaporation that leads to biased results towing to the analyte enrichment in the fluid; (iii) no risk of sample contamination; and (iv) compatibility with different sweating rates. (4,9) Regarding this latter requirement, elite athletes usually have high sweat rates (0.7–5.9 μL cm^–2 min^–1) (28) that may require a larger capacity of the sampling cell in order to negate excessive pressure from the eccrine sweat glands. This may lead to modifications of physiological sweating behavior in the skin zone (e.g., hydromeiosis events), therefore masking the on-body observations. (24,32) In contrast, WPISs for medical diagnostics should involve microfluidic cells with tiny sampling in order to be coupled to lower sweat rates provoked by iontophoresis approaches (198–354 nL cm^–2 min^–1). (11,33)

The design of the sampling cell (Figure 2b,c) was here conceived to fulfill all the aforementioned necessities. First, the microfluidic cell was 3D-printed with the PU substrate to confer conformability to the gadget for further attachment to the human body. The dimensions of the cell were engineered to provide a constant and passive flow of sweat through the sensing channel while the individual is sweating during sport practice. Hence, it is necessary that the sweat fills in first the collecting zone (volume of 8.8 μL), and then the sensing channel (volume of 12.6 μL) will be able to begin the potentiometric measurements.

The total time needed slightly depends on the sweating rate of the individual. For example, considering active perspiration of the back during midintensity physical activity, a sweating rate close to 1 μL cm^–2 min^–1 will occur. (24,27) This sweat flow would involve 4.8 min to fill the collection zone and 7 min more to completely fill the sensing zone. After ca. 12 min, a continuous sweat renewal takes place in a passive manner while the subject is sweating (see Figure 2c). This was experimentally confirmed by flowing artificial sweat at 4 μL min^–1 by means of a peristaltic pump. This flow rate mimics the sweating rate of 2 μL cm^–2 min^–1 considering an area of 2 cm², achieved under extreme conditions during on-body tests. (27)

The sampling cell was additionally designed to isolate the collected sweat from the environment, hence avoiding any evaporation or contamination of sweat during on-body tests. Moreover, the entire device was fixed onto a subject’s skin by means of adhesive transfer tape (3 M 9471LE), which is commonly used for the attachment of wearable sensors to the body. (19,21)

The analytical performance of the WPISs were also evaluated under flow conditions by means of a peristaltic pump. Figure 3a displays the potential response of three pH electrodes when the sample pH was increased by almost one pH unit to assess the response time of the device. A time of 5 min is necessary for the electrodes to sense this change in pH at a flow rate of 4 μL min^–1. Indeed, each electrode starts to respond 30 s after the other according to its order along the sensing channel.

Figure 3. (a) Response of three pH electrodes for a pH change from 5.6 to 4.7. Flow rate = 4 μL min^–1. Dotted lines indicate the response time. (b) Response of three pH electrodes in a solution of pH 5.6 at 4, 8, and 16 μL min^–1. (c) pH calibrations at 4, 8, and 16 μL min^–1. (d) WPISs under torsion deformation. Response of a K⁺ electrode after applying different torsion deformations. (e) Calibrations using WPISs for Cl^–, Na⁺, K⁺, and pH before and after the incorporation of the sampling cell and after on-body measurements. All the calibration curves were accomplished in artificial sweat.

The influence of the flow rate on electrode response was assessed, as sporadic changes in the sweating rate of the individual are expected during the workout. Moreover, the perspiration rate may substantially change with the region of the body. (28) This behavior was studied by measuring the potential of a solution at pH 5.6 while successively increasing and decreasing (4, 8, and 16 μL cm^–2 min^–1) the flow rate of the pump (Figure 3b). These flow rates were chosen to mimic high sweat rates that may exist in the body during sport practice, e.g., forehead sweat rate of 5.9 ± 3.0 μL cm^–2 min^–1, (28) which means a flow rate of 16.0 μL min^–1 according to the area of the collection zone of the sampling cell developed herein. A negligible change was determined for the potentiometric response under these conditions, manifesting such that the WPISs could be used in any part of the body at any intensity of physical activity. No influence was found for the entire calibration graph (pH 7.5–4.7), maintaining even the response reversibility (Figure 3c). Therefore, the same calibration graph may be suitable for the calculation of pH in sweat despite any change on the perspiration rate.

In this sense, the average of the six calibration graphs presented in Figure 3c obtained at different flow rates and with a carry-over evaluation leads to a slope and intercept of 51.7 ± 0.6 mV pH^–1 and 201.5 ± 4.4 mV, respectively. Considering the standard deviations for the calibration parameters, the maximum error expected in the pH calculation is 1–3% considering this curve as one that is universal. This level of error is generally considered acceptable in measurements involving the screening of the physiological status of an individual. (5) Notably, the errors in slope and E⁰ for the pH sensor were calculated under drastic changes of pH and flow rates. That is, the pH sensor will show uncertainty of 3% at much. But this level of uncertainty will be even lower for on-body measurements, as the sensors were calibrated before and after its portability, see below.

A similar behavior was observed for the Cl^–, K⁺, and Na⁺ electrodes, and therefore, no influence of the perspiration rate on the response of the entire electrode array was detected (as an example, the response of three K⁺ electrodes are shown in Figure S6). Indeed, even though any influence in the diffusion process of the ion analyte when its activity is changed in the bulk solution (such as solution stirring and flow rate) may affect the response of the potentiometric sensors, (34) this is here unnoticeable based on the very low flow rates.

Figure 3d presents a resiliency test of K⁺ sensors implemented with the sampling cell (i.e., WPISs only containing K⁺ sensors) based on applying different torsion strains to the device. The calibration graph did not change under these conditions (slope of 53.7 ± 1.4 mV with an intercept of 67.0 ± 4.9). Besides that, and to confirm that any corporal movement during on-body portability does not affect the electrode response, the electrode array was calibrated for every ion analyte before and after on-body measurements. No changes were observed in the calibration graphs (Figure 3e). Furthermore, the calibration graphs are the same as those obtained in the beaker before the implementation of the sampling cell, which were determined without stirring by immersing the electrodes in separate solutions (Figure 3e). As a result, either of these three calibration graphs (i.e., in the beaker, or in the WPISs before and after the test) can be used to calculate on-body electrolyte concentration.

Validation of the WPISs

As mentioned in the Introduction section, yet, there is not an established protocol for the validation of WPISs, and only some recent papers attempted to perform a few additional measurements to establish its accuracy. (35,36)

Current methods for sweat analysis performed in physiology laboratories related to sport performance consist of collecting sweat during the workout using either the regional absorbent patch method (REG) or whole-body washdown technique (WBW), (13,28) with the subsequent use of different analytical techniques, such as IC, (28) ion-selective electrodes (ISE), (37) or inductively coupled plasma-mass spectrometry (ICP-MS), (36) to analyze electrolyte concentration. In principle, it is worthy to base the validation of the WPISs in these approaches. In this sense, we propose a double validation of the WPISs operating first out of the body by pumping the sweat toward the WPIS (off-body validation) and then during on-body measurements, comparing the results with IC and a pH meter.

The protocol employed to convert the profiles of the potentiometric signal observed with the WPISs into ion analyte concentrations is seen in Figure S7. Briefly, raw data (dynamic recording of the electrode potential) is converted into ion activity using the precalibration. Subsequently, the ion concentration is calculated from the activity coefficient, which is determined by the ionic strength of artificial sweat (see the Supporting Information). Importantly, while the direct use of ion concentration in the calibration graph shortens the practical calculations, it is not formally correct and may induce additional errors, as demonstrated in the following.

First, human sweat was collected at different times following the REG method from the back of a subject, as described in the Supporting Information, and the samples were analyzed by the WPISs operating by means of a peristaltic pump (i.e., off-site the body), IC, and the pH meter. Briefly, REG consists of attaching a cotton pad (oval-shaped pads of 85 × 70 mm and circular-shaped pads of 58 mm diameter) on the skin with hydrofilm tape, and after a certain length of time, the pad is detached from the skin, demounted from the tape, and finally centrifuged (5.000 rpm) to extract the sweat. The back of individuals participating in this study was chosen as the local region to fix the WPISs during all the on-body tests to maximize the collected volume (27,28) (10–80 μL, 100–700 μL, and 1–3 mL after 5, 10, and 60 min of sweating, respectively). These ranges may slightly vary between subjects, but still, this volume is enough for analysis with the pH meter or IC after dilution (1:100).

Figure S8 displays the correlation plots for all the tested ions using the off-body validation. As a general trend, samples collected over a short time (5–10 min) exhibited over concentrated values, i.e., concentrations outside of the physiological ranges of K⁺, Na⁺, and Cl^– (delimited with colored squares). However, samples collected over longer times (60 min) were within physiological ranges (see below). In addition, whatever the collection time was, excellent correlations were observed between WPISs and gold standard techniques (Figure S8, Pearson correlation coefficient of 0.97 for Cl^–, 0.89 for K⁺, 0.91 for Na⁺, and 0.94 for pH). This indicates that the overestimation issue is related to how the sample is collected in/from the pad, as the same samples were analyzed with different techniques obtaining similar values.

The second part of the validation comprised the comparison of on-body measurements with the gold standard techniques (IC and pH meter) along an 1-h workout. The WPISs and absorbent pads (3 pads of 85 × 70 mm and/or 58 mm diameter dimensions) were attached to the low and medium back of the subjects to collect enough sample volume during sport practice using a professional bike kept in a static trainer (Figure S9). Importantly, every ion was individually measured through a wearable device comprising three twin electrodes and two reference electrodes (one acting as a reference and the other a regular working electrode). This allowed for evaluating the reproducibility of the developed sensors for the first time, as far as we know, during on-body measurements.

Figure 4a depicts the on-body concentration profiles for Cl^–, K⁺, Na⁺, and pH obtained with independent devices for each ion during an 1-h workout. The reproducibility among the three replicates was additionally evaluated, exhibiting relative standard deviations of 12.5 ± 3.2% for Cl^–, 11.3 ± 6.1% for Na⁺, 11.5 ± 2.1 for K⁺n and 0.9 ± 0.4% for pH (see the dynamic profile of the RSD in Figure S10), which are really appropriate values considering possible variability implied in any kind of in situ measurements. Furthermore, as in the case of the previous off-site validation of the WPISs, the values yielded by IC every 5 or 10 min were always higher than those measured on the body (i.e., Cl^– > 100 mM, K⁺ > 8 mM, and Na⁺ > 100 mM) and rendered of nonphysiological meaning unless the subject experienced unhealthy conditions (see Table S8). Thus, we confirmed the incompatibility of the application of the REG method for short collection times of 5–10 min, as they gave rise to values very different between the IC and the WPISs (ca. 60–300% of difference), and because the values measured with IC were totally outside the ranges expected in healthy volunteers.

Figure 4. (a) Concentration profiles observed with the WPISs during 60 min of a cycling workout. The WPISs contained three twin electrodes for each ion. (b) Validation of K⁺ on-body measurements. Every ion was measured in a different on-body test (with n = 3). A total number of 5 tests were accomplished, labeled as T1–T5.

Therefore, we modified the REG method (m-REG) to minimize evaporation issues of the sample during its collection and manipulation, which may be the cause for an over concentration of the ion analytes (Figure S9). Briefly, (i) the period of sweat collection was increased to 10–12.5 min; (ii) the absorbent pad was squeezed by means of a syringe immediately after removal from the body rather than the traditional centrifugation process; and (iii) sample dilution (1:100) was then quickly accomplished, and the sample was immediately stored in the fridge (4 °C). This method permitted gathering from 100 to 500 μL of sweat depending on the perspiration rate.

Figure 4b portrays the on-body profile (n = 3) for K⁺ concentrations with the analysis of the samples obtained from the IC and WPISs additionally operating out of the body (in a flow mode with the peristaltic pump) after sweat sampling employing the new m-REG method (every 12.5 min), and one pad collecting sweat during the entire exercise. Now, all the measurements analyzed with the IC fit within the physiological range of ions and agreed with the on-body profiles. Indeed, this agreement was also observed with the WPISs coupled to the peristaltic pump (Pearson correlation of 0.99, Figure S11a). In addition, the sweat at the outlet of the sampling cell was collected during the on-body test and analyzed in the IC for comparative purposes (DROP). The results were also in line with the on-body profile, K⁺ concentration of 7.1 mM at 18 min, 4.0mM at 30 min, 5.0 mM at 36 min, 4.1 mM at 38 min, 4.3 mM at 46 min, 4.1 mM at 50 min, and 4.6 mM at 60 min, which correspond to the differences of 17.9, 6, 13.8, 3.7, 1.4, and 18.8%, respectively, calculated from the WPISs and collected drop. An analogous experiment was accomplished for on-body Na⁺ detection providing the same conclusions (Figure S11b, on-body test T6).

Conveniently, the assessment of the calibration graph in artificial sweat permits the use of coefficient activities for the formal construction of the potentiometric calibration graph used for the final calculation of the concentrations (see Figure S7). Otherwise, either the application of a calibration graph based on concentration rather than activity or the comparison of activity with the concentrations found with other gold standard techniques (i.e., IC) introduced greater error in the observed values (see Table S9 for a comparison between different tests).

Table 1 shows the calculated concentrations during the validation of on-body measurements by comparison with IC and the pH-meter. In addition, the same samples were measured by WPISs operating out of the body (Table S10). Whether the data from the gold standard techniques are considered as the true concentrations in sweat, these differences serve as accuracy in terms of error of the developed WPISs. The error across all the tests was below 16% with an average of 7.9 ± 4.7%, which is acceptable with respect to a reliable decision-making process based on real-time measurements assessed in real scenarios. A proper agreement with the WPISs operating out of the body was also observed (Table S10).

Table 1. Sweat Analysis during On-Body Tests

	period (min)	WPISs (mM or pH)^a,^b	IC (mM) or pH meter	IC-WPISs difference (%)
K⁺	10–22.5	6.3 ± 1.4	5.9	7.4
	22.5–35	4.9 ± 0.5	4.2	15.3
	35–47.5	4.5 ± 0.4	4.3	5.9
	47.5–60	4.0 ± 0.4	4.2	5.3
	10–60	4.7 ± 0.9	4.7	1.4
	10–60	4.7 ± 0.9	4.6	2.2
Na⁺	10–22.5	79.9 ± 10.1	84.8	5.8
	22.5–35	79.7 ± 5.9	83.7	4.9
	35–47.5	77.8 ± 6.1	89.5	13.1
	47.5–60	72.4 ± 6.6	83.5	13.3
	10–60	76.9 ± 7.4	84.9	9.4
	10–60	76.9 ± 7.4	85.1	9.6
Cl^–	20–30	46.0 ± 3.9	54.6	15.8
	30–40	52.7 ± 1.7	56.2	6.1
	40–50	56.7 ± 2.9	61.9	8.4
	50–60	59.1 ± 1.9	51.6	14.6
pH	20–30	8.0 ± 0.1	7.5	7.3
	30–40	7.9 ± 0.1	7.6	4.3
	40–50	7.7 ± 0.1	7.7	0.5
	50–60	7.5 ± 0.1	7.3	3.0

^{^a}

The corresponding experiments are shown in Figure 4b (K⁺, T5), Figure S11b (Na⁺, T6), Figure 5b (Cl^–, subject 1, T8), and Figure 4a (pH, T4).

^{^b}

Average corresponding to the entire collection time.

Finally, the WPISs were evaluated under different conditions, (i) Na⁺ profile of one subject under high physical activity (constant workload at level 7–8 out of 10 exercise intensity) and without any water intake during the practice (on-body test T7), and (ii) Cl^– and pH profiles of 2 different individuals subjected to the same activity conditions but under hydration conditions (22 °C, 1 h cycling, medium intensity, on-body tests T8 and T9). In the case of the exercise practice without any water intake (Figure 5a), after 45 min of cycling, there was a gradual increase in Na⁺ concentration that may suggest a dehydration status of the subject, as previously reported. (8,12) However, this information may be carefully interpreted as the observed increase in Na⁺ may be a consequence of the local increase of skin temperature, change in the exercise intensity or other factors. Therefore, further on-body tests (i.e., massive validation) are needed to confirm this finding and others from a physiological point of view.

Figure 5. (a) Electrolyte dynamics observed during on-body tests. (a) Na⁺ concentration of an individual subjected to 1-h cycling at high intensity (on-body test T7). (b) Cl^– and pH monitoring in two different individuals subjected to the same physical activity (22 °C, relative humidity 70%, 1-h cycling, high intensity). The dots indicate the concentrations of sweat analyzed by IC after sweat collection by m-REG. On-body tests T8 and T9.

Regarding the second experiment (Figure 5b), subject 1 had more acidic pH levels, with Cl^– concentrations within the common healthy range (10–100 mM), while subject 2 showed more basic pH levels and lower Cl^– concentrations. These differences may be associated with the diet, the fitness condition of each subject, and hydration status. However, the interpretation of these results is far beyond the scope of this work. Overall, these observations encourage the further testing of WPISs in athletes at known physiological conditions to assess the differences in electrolyte dynamics.

Conclusions

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We have demonstrated, for the first time, the reproducibility and reliability of on-body measurements accomplished by new WPISs for pH, Cl^–, K⁺, and Na⁺ analysis in sweat. The validation of these measurements has been advantageously assessed through a two-step protocol, considering, first, the off-site performance of the WPISs and then on-body operation. All measurements were compared with the results from gold standard techniques, such as IC and a pH meter. The incorporation of an innovative sampling cell additionally permitted the realization of on-body measurements in real time through the provision of a continuous and passive sweat flow encompassing the subjects’ perspiration. Overall, it is here demonstrated, the potential of the developed WPISs for providing reliable physiological and personal data of body status during sports activity. It is expected, that the advances presented in this article will contribute to the appropriate validation of future wearable chemical sensors that will constitute the next generation of digital health solutions for personalized hydration and recovery strategies in sport performance and wellbeing.

Supporting Information

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The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.analchem.9b02126.

Experimental section, analytical parameters and membrane compositions, and data treatment and validation (PDF)

ac9b02126_si_001.pdf (2.54 MB)

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Author Information

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Corresponding Author
- Gastón A. Crespo - Department of Chemistry, School of Engineering Science in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, Teknikringen 30, SE-100 44 Stockholm, Sweden; http://orcid.org/0000-0002-1221-3906; Email: [email protected]
Authors
- Marc Parrilla - Department of Chemistry, School of Engineering Science in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, Teknikringen 30, SE-100 44 Stockholm, Sweden
- Inmaculada Ortiz-Gómez - Department of Chemistry, School of Engineering Science in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, Teknikringen 30, SE-100 44 Stockholm, Sweden; Department of Analytical Chemistry, Campus Fuentenueva, Faculty of Sciences, University of Granada, 18071 Granada, Spain
- Rocío Cánovas - Department of Chemistry, School of Engineering Science in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, Teknikringen 30, SE-100 44 Stockholm, Sweden
- Alfonso Salinas-Castillo - Department of Analytical Chemistry, Campus Fuentenueva, Faculty of Sciences, University of Granada, 18071 Granada, Spain
- María Cuartero - Department of Chemistry, School of Engineering Science in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, Teknikringen 30, SE-100 44 Stockholm, Sweden; http://orcid.org/0000-0002-3858-8466
Notes
The authors declare no competing financial interest.

Acknowledgments

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The authors acknowledge the financial support of the KTH Royal Institute of Technology (K-2017-0371), Swedish Research Council (VR-2017-4887), Swedish Foundation for Strategic Research (GMT14-0071), WPCRN (K-2017-0804 and K-2017-0809), and Metrohm Nordic AB. M.C. is grateful for the financial support of the European Union (H2020-MSCA-IF-2017, Grant 792824). R.C. thanks the Alfonso Martin Escudero Foundation. I.O.G acknowledges the Spanish Research Council (CTQ2016-78754-C2-1-R). Alexander Wiorek and Kequan Xu are acknowledged for the help with the on-body tests.

References

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This article references 37 other publications.

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Wearable sensors allow continuous monitoring of metabolites for diabetes, sports medicine, exercise science, and physiol. research. These sensors can continuously detect target analytes in skin interstitial fluid (ISF), tears, saliva, and sweat. In this review, we will summarize developments on wearable devices and their potential applications in research, clin. practice, and recreational and sporting activities. Sampling skin ISF can require insertion of a needle into the skin, whereas sweat, tears, and saliva can be sampled by devices worn outside the body. The most widely sampled metabolite from a wearable device is glucose in skin ISF for monitoring diabetes patients. Continuous ISF glucose monitoring allows estn. of the glucose concn. in blood without the pain, inconvenience, and blood waste of fingerstick capillary blood glucose testing. This tool is currently used by diabetes patients to provide information for dosing insulin and detg. a diet and exercise plan. Similar technologies for measuring concns. of other analytes in skin ISF could be used to monitor athletes, emergency responders, warfighters, and others in states of extreme physiol. stress. Sweat is a potentially useful substrate for sampling analytes for metabolic monitoring during exercise. Lactate, sodium, potassium, and hydrogen ions can be measured in sweat. Tools for converting the concns. of these analytes sampled from sweat, tears, and saliva into blood concns. are being developed. As an understanding of the relationships between the concns. of analytes in blood and easily sampled body fluid increases, then the benefits of new wearable devices for metabolic monitoring will also increase.
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A review. Wearable potentiometric sensors have received considerable attention owing to their great potential in a wide range of physiol. and clin. applications, particularly involving ion detection in sweat. Despite the significant progress in the manner that potentiometric sensors are integrated in wearable devices, in terms of materials and fabrication approaches, there is yet plenty of room for improvement in the strategy adopted for the sample collection. Essentially, this involves a fluidic sampling cell for continuous sweat anal. during sport performance or sweat accumulation via iontophoresis induction for one-spot measurements in medical settings. Even though the majority of the reported papers from the last five years describe on-body tests of wearable potentiometric sensors while the individual is practicing a phys. activity, the medical utilization of these devices has been demonstrated on very few occasions and only in the context of cystic fibrosis diagnosis. In this sense, it may be important to explore the implementation of wearable potentiometric sensors into the anal. of other biofluids, such as saliva, tears and urine, as herein discussed. While the fabrication and uses of wearable potentiometric sensors vary widely, there are many common issues related to the anal. characterization of such devices that must be consciously addressed, esp. in terms of sensor calibration and the validation of on-body measurements. After the assessment of key wearable potentiometric sensors reported over the last five years, with particular attention paid to those for medical applications, the present review offers tentative guidance regarding the characterization of anal. performance as well as anal. and clin. validations, thereby aiming at generating debate in the scientific community to allow for the establishment of well-conceived protocols.
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Aim: To det. whether acute exercise-heat-induced dehydration affects sweat compn., eight males cycled for 2 h at 39.5±1.6% VO2peak on two sep. occasions in a hot-humid environment (38.0±0.0°, 60.0±0.1% relative humidity). Methods: During exercise, subjects ingested either no fluid (dehydration) or a 20 mmol·L-1 sodium chloride soln. (euhydration). The vol. of soln., calcd. from whole-body sweat loss and detd. in a familiarization trial, was ingested at 0 min and every 15 min thereafter. Venous blood was collected at 0, 60 and 120 min of exercise and sweat was aspirated from a patch located on the dominant forearm at 120 min. Results: Following the 2-h cycling exercise, sweat [Na+] and [Cl-] was greater (P < 0.05) in the dehydration trial (Na+ 91.1±6.8 mmol·L-1; Cl- 73.3±3.5 mmol·L-1) compared with the euhydration trial (Na+ 81.1±5.9 mmol·L-1; Cl- 68.5±3.3 mmol·L-1). In addn., dehydration invoked a greater serum [Na+] (142.2±0.7 mmol·L-1; P < 0.05), [Cl-] (105.8±0.6 mmol·L-1; P < 0.05) and [K+] (5.27±0.2 mmol·L-1; P < 0.05) over the euhydration values for [Na+], [Cl-] and [K+], resp. (138.9±0.6, 102.9±0.5 and 4.88±0.1 mmol·L-1). Plasma aldosterone was also significantly higher during exercise in the dehydration trial compared with the euhydration trial (53.8±3.8 vs. 40.0±4.3 ng·dL-1; P < 0.05). Conclusions: Acute exercise-heat stress without fluid replacement resulted in a greater sweat [Na+] and [Cl-] which was potentially related to greater extracellular fluid [Na+], plasma aldosterone or sympathetic nervous activity.
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Journal of Applied Physiology (2009), 107 (3), 887-895CODEN: JAPHEV; ISSN:8750-7587. (American Physiological Society)
This study compared simultaneous whole body washdown (WBW) and regional skin surface (REG) sweat collections to generate regression equations to predict WBW sweat Na+ concn. ([Na+]) and K+ concn. ([K+]) from single- and five-site REG sweat patch collections. Athletes (10 men, 10 women) cycled in a plastic chamber for 90 min in the heat. Before exercise, the subject and bike were washed with deionized water. After the onset of sweating, sterile patches were attached to the forearm, back, chest, forehead, and thigh and removed on satn. After exercise, the subject and bike were washed with ammonium sulfate soln. to collect all sweat electrolyte loss and det. the vol. of un-evapd. sweat. All individual patch sites and five-site REG (weighted for local sweat rate and body surface area) were significantly (P = 0.000) correlated with WBW sweat [Na+]. The equation for predicting WBW sweat [Na+] from five-site REG was y = 0.68x + 0.44 [r = 0.97, intraclass correlation coeff. (ICC) = 0.70] and did not differ between sexes. There were sex differences in the regression results between five-site REG and WBW sweat [K+] (men: y = 0.74x + 0.30, r = 0.89, ICC = 0.73; women: y = 0.04x + 3.18, r = 0.03, ICC = 0.00). Five-site REG sweat [Na+] and [K+] significantly overestimated that of WBW sweat (59 ± 27 vs. 41 ± 19 meq/l, P = 0.000 and 4.4 ± 0.7 vs. 3.6 ± 0.7 meq/l, P = 0.000, resp.). For both sexes, the best sites for predicting WBW sweat [Na+] and [K+] were the thigh (1 ± 8 meq/l < WBW, P = 1.000, y = 0.75x + 11.37, r = 0.96, ICC = 0.93) and chest (0.2 ± 0.3 meq/l > WBW, P = 1.000, y = 0.76x + 0.55, r = 0.89, ICC = 0.87), resp. In conclusion, regression equations can be used to accurately and reliably predict WBW sweat [Na+] and [K+] from REG sweat collections when study conditions and techniques are similar to that of the present protocol.
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Biomicrofluidics (2015), 9 (3), 031301/1-031301/19CODEN: BIOMGB; ISSN:1932-1058. (American Institute of Physics)
Non-invasive and accurate access of biomarkers remains a holy grail of the biomedical community. Human eccrine sweat is a surprisingly biomarker-rich fluid which is gaining increasing attention. This is esp. true in applications of continuous bio-monitoring where other biofluids prove more challenging, if not impossible. However, much confusion on the topic exists as the microfluidics of the eccrine sweat gland has never been comprehensively presented and models of biomarker partitioning into sweat are either underdeveloped and/or highly scattered across literature. Reported here are microfluidic models for eccrine sweat generation and flow which are coupled with review of blood-to-sweat biomarker partition pathways, therefore providing insights such as how biomarker concn. changes with sweat flow rate. Addnl., it is shown that both flow rate and biomarker diffusion det. the effective sampling rate of biomarkers at the skin surface (chronol. resoln.). The discussion covers a broad class of biomarkers including ions (Na+, Cl-, K+, NH4+), small mols. (ethanol, cortisol, urea, and lactate), and even peptides or small proteins (neuropeptides and cytokines). The models are not meant to be exhaustive for all biomarkers, yet collectively serve as a foundational guide for further development of sweat-based diagnostics and for those beginning exploration of new biomarker opportunities in sweat. (c) 2015 American Institute of Physics.
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Ali Saba M; Yosipovitch Gil
Acta dermato-venereologica (2013), 93 (3), 261-7 ISSN:.
The "acid mantle" is a topic not only of historical interest, but also of clinical significance and has recently been linked to vital stratum corneum function. Despite compelling basic science evidence placing skin pH as a key factor in barrier homeostasis, stratum corneum integrity, and antimicrobial defense, application of the acid mantle concept in clinical care is lacking. We review recent basic science investigations into skin pH, discuss skin disorders characterized by aberrant pH, and finally discuss practical application for preservation of the acid mantle. Recognizing factors that alter skin pH and selecting products that preserve the acid mantle is of prime importance in treating dermatologic patients.
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Bohl, C. H.; Volpe, S. L. Magnesium and Exercise. Crit. Rev. Food Sci. Nutr. 2002, 42, 533– 563, DOI: 10.1080/20024091054247
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Magnesium and exercise
Bohl, Caroline H.; Volpe, Stella L.
Critical Reviews in Food Science and Nutrition (2002), 42 (6), 533-563CODEN: CRFND6; ISSN:1040-8398. (CRC Press LLC)
A review. Magnesium is an essential element that regulates membrane stability and neuromuscular, cardiovascular, immune, and hormonal functions. Mg is a crit. cofactor in many metabolic reactions. The Dietary Ref. Intake for magnesium in adult humans is 310-420 mg/day, but the actual intake is often suboptimal. Mg deficiency may lead to changes in gastrointestinal, cardiovascular, and neuromuscular functions. Phys. exercise may deplete Mg, which, together with marginal dietary Mg intake, may impair energy metab. efficiency and the capacity for phys. work. Mg nutritional assessment is a challenge because of the absence of accurate and convenient assessment methods. Recently, Mg has been touted as an agent for increasing athletic performance. Data from various studies on the relationship of Mg and exercise are discussed.
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Parrilla, M.; Cánovas, R.; Jeerapan, I.; Andrade, F. J.; Wang, J. A Textile-Based Stretchable Multi-Ion Potentiometric Sensor. Adv. Healthcare Mater. 2016, 5, 996– 1001, DOI: 10.1002/adhm.201600092
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A Textile-Based Stretchable Multi-Ion Potentiometric Sensor
Parrilla, Marc; Canovas, Rocio; Jeerapan, Itthipon; Andrade, Francisco J.; Wang, Joseph
Advanced Healthcare Materials (2016), 5 (9), 996-1001CODEN: AHMDBJ; ISSN:2192-2640. (Wiley-VCH Verlag GmbH & Co. KGaA)
This article reports a highly stretchable and printable textile-based potentiometric sensor array for simultaneous multi-ion sweat anal. using variety of fabric materials towards diverse healthcare and fitness applications. Textile-based potentiometric sensors was fabricated by combining polyurethane-based ion- selective membranes and inks with a serpentine sensor pattern and stretch-enduring printed electrodes. Combining stretchable components like polyurethane, Ecoflex, and stretch-enduring inks, along with a serpentine design, this printed textile sensor array can withstand high tensile stress and mech. deformation and can thus act as an efficient wearable biomedical sensor.
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Parrilla, M.; Ferré, J.; Guinovart, T.; Andrade, F. J. Wearable Potentiometric Sensors Based on Commercial Carbon Fibres for Monitoring Sodium in Sweat. Electroanalysis 2016, 28, 1267– 1275, DOI: 10.1002/elan.201600070
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Wearable Potentiometric Sensors Based on Commercial Carbon Fibres for Monitoring Sodium in Sweat
Parrilla, Marc; Ferre, Jordi; Guinovart, Tomas; Andrade, Francisco J.
Electroanalysis (2016), 28 (6), 1267-1275CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)
The use of com. carbon fibers (CCF) to build wearable potentiometric sensors for the real-time monitoring of sodium levels in sweat during exercise is presented. CCF are an attractive substrate for building wearable electrochem. sensors because of their good elec. cond., chem. inertness, flexibility and mech. resilience. In the first part of this work, the anal. performance of these novel potentiometric ion-selective electrodes made with CCFs is presented. Then, through the incorporation of a solid-contact ref. electrode, the development of a complete miniaturized potentiometric cell with a Nernstian response (59.2±0.6 mV/log [Na+], N=4) is obtained. Finally, the cell is integrated into a wearable patch and attached onto the skin of an athlete. The anal. characterization of the wearable patch shows a near-Nernstian response (55.9±0.8 mV/log [Na+], N=3) for sodium levels from 10-3 M to 10-1 M in artificial sweat, well within the physiol. range of interest. The device shows low noise levels and very good stability (-0.4±0.3 mV · h-1). To improve the usability of the sensor in real scenarios, a calibration-free approach is also explored. This platform opens new and attractive avenues for the generation of meaningful personalized physiol. information that could be applied - among many other fields - in sports, nutrition and healthcare.
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Alizadeh, A.; Burns, A.; Lenigk, R.; Gettings, R.; Ashe, J.; Porter, A.; McCaul, M.; Barrett, R.; Diamond, D.; White, P.; Skeath, P.; Tomczak, M. A Wearable Patch for Continuous Monitoring of Sweat Electrolytes during Exertion. Lab Chip 2018, 18, 2632– 2641, DOI: 10.1039/C8LC00510A
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A wearable patch for continuous monitoring of sweat electrolytes during exertion
Alizadeh, Azar; Burns, Andrew; Lenigk, Ralf; Gettings, Rachel; Ashe, Jeffrey; Porter, Adam; McCaul, Margaret; Barrett, Ruairi; Diamond, Dermot; White, Paddy; Skeath, Perry; Tomczak, Melanie
Lab on a Chip (2018), 18 (17), 2632-2641CODEN: LCAHAM; ISSN:1473-0189. (Royal Society of Chemistry)
Implementation of wearable sweat sensors for continuous measurement of fluid based biomarkers (including electrolytes, metabolites and proteins) is an attractive alternative to common, yet intrusive and invasive, practices such as urine or blood anal. Recent years have witnessed several key demonstrations of sweat based electrochem. sensing in wearable formats, however, there are still significant challenges and opportunities in this space for clin. acceptance, and thus mass implementation of these devices. For instance, there are inherent challenges in establishing direct correlations between sweat-based and gold-std. plasma-based biomarker concns. for clin. decision-making. In addn., the wearable sweat monitoring devices themselves may exacerbate these challenges, as they can significantly alter sweat physiol. (example, sweat rate and compn.). Reported here is the demonstration of a fully integrated, wireless, wearable and flexible sweat sensing device for non-obtrusive and continuous monitoring of electrolytes during moderate to intense exertion as a metric for hydration status. The focus of this work is twofold: 1- design of a conformable fluidics systems to suit conditions of operation for sweat collection (to minimize sensor lag) with rapid removal of sweat from the sensing site (to minimize effects on sweat physiol.). 2- integration of Na+ and K+ ion-selective electrodes (ISEs) with flexible microfluidics and low noise small footprint electronics components to enable wireless, wearable sweat monitoring. While this device is specific to electrolyte anal. during intense perspiration, the lessons in microfluidics and overall system design are likely applicable across a broad range of analytes.
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Nyein, H. Y. Y.; Tai, L.; Ngo, Q. P.; Chao, M.; Zhang, G. B.; Gao, W.; Bariya, M.; Bullock, J.; Kim, H.; Fahad, H. M.; Javey, A. A Wearable Microfluidic Sensing Patch for Dynamic Sweat Secretion Analysis. ACS Sensors 2018, 3, 944– 952, DOI: 10.1021/acssensors.7b00961
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A Wearable Microfluidic Sensing Patch for Dynamic Sweat Secretion Analysis
Nyein, Hnin Yin Yin; Tai, Li-Chia; Ngo, Quynh Phuong; Chao, Minghan; Zhang, George B.; Gao, Wei; Bariya, Mallika; Bullock, James; Kim, Hyungjin; Fahad, Hossain M.; Javey, Ali
ACS Sensors (2018), 3 (5), 944-952CODEN: ASCEFJ; ISSN:2379-3694. (American Chemical Society)
Wearable sweat sensing is a rapidly rising research area driven by its promising potential in health, fitness, and diagnostic applications. Despite the growth in the field, major challenges in relation to sweat metrics remain to be addressed. These challenges include sweat rate monitoring for its complex relation with sweat compns. and sweat sampling for sweat dynamics studies. The authors present a flexible microfluidic sweat sensing patch that enhances real-time electrochem. sensing and sweat rate anal. via sweat sampling. The device contains a spiral-patterned microfluidic component that is embedded with ion-selective sensors and an elec. impedance-based sweat rate sensor on a flexible plastic substrate. The patch is enabled to autonomously perform sweat anal. by interfacing the sensing component with a printed circuit board that is capable of on-site signal conditioning, anal., and transmission. Progressive sweat flow in the microfluidic device, governed by the pressure induced by the secreted sweat, enhances sweat sampling and electrochem. detection via a defined sweat collection chamber and a directed sweat route. The characteristic of the sweat rate sensor is validated through a theor. simulation, and the precision and accuracy of the flow rate is verified with a com. syringe pump and a Macroduct sweat collector. On-body simultaneous monitoring of ion (H+, Na+, K+, Cl-) concn. and sweat rate is also demonstrated for sensor functionality. This sweat sensing patch provides an integrated platform for a comprehensive sweat secretion anal. and facilitates physiol. and clin. studies by closely monitoring interrelated sweat parameters.
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Sempionatto, J. R.; Martin, A.; García-Carmona, L.; Barfidokht, A.; Kurniawan, J. F.; Moreto, J. R.; Tang, G.; Shin, A.; Liu, X.; Escarpa, A.; Wang, J. Skin-Worn Soft Microfluidic Potentiometric Detection System. Electroanalysis 2019, 31, 239– 245, DOI: 10.1002/elan.201800414
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Skin-Worn Soft Microfluidic Potentiometric Detection System
Sempionatto, Juliane R.; Martin, Aida; Garcia-Carmona, Laura; Barfidokht, Abbas; Kurniawan, Jonas F.; Moreto, Jose R.; Tang, Guangda; Shin, Andrew; Liu, Xiaofeng; Escarpa, Alberto; Wang, Joseph
Electroanalysis (2019), 31 (2), 239-245CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)
A flexible skin-mounted microfluidic potentiometric device for simultaneous electrochem. monitoring of sodium and potassium in sweat is presented. The wearable device allows efficient natural sweat pumping to the potentiometric detection chamber, contg. solid-contact ion-selective Na+ and K+ electrodes, during exercise activity. The fabricated microchip electrolyte-sensing device displays good anal. performance and addresses sweat mixing and carry-over issues of early epidermal potentiometric sensors. Such soft skin-worn microchip platform integrates potentiometric measurement, microfluidic technologies with flexible electronics for real-time wireless data transmission to mobile devices. The new fully integrated microfluidic electrolyte-detection device paves the way for practical fitness and health monitoring applications.
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Anastasova, S.; Crewther, B.; Bembnowicz, P.; Curto, V.; Ip, H. M.; Rosa, B.; Yang, G. Z. A Wearable Multisensing Patch for Continuous Sweat Monitoring. Biosens. Bioelectron. 2017, 94, 730, DOI: 10.1016/j.bios.2017.03.018
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Corrigendum to "A wearable multisensing patch for continuous sweat monitoring" [Biosens. Bioelectron. (2016)] [Erratum to document cited in CA170:328723]
Anastasova, S.; Crewther, B.; Bembnowicz, P.; Curto, V.; Ip, H. M.; Rosa, B.; Yang, G.-Z.
Biosensors & Bioelectronics (2017), 94 (), 730CODEN: BBIOE4; ISSN:0956-5663. (Elsevier B.V.)
There is no expanded citation for this reference.
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Dziedzic, C. E.; Ross, M. L.; Slater, G. J.; Burke, L. M. Variability of Measurements of Sweat Sodium Using the Regional Absorbent-Patch Method. Int. J. Sport Physiol. Perform. 2014, 9, 832– 838, DOI: 10.1123/ijspp.2013-0480
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There is no corresponding record for this reference.
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Baker, L. B. Sweating Rate and Sweat Sodium Concentration in Athletes: A Review of Methodology and Intra/Interindividual Variability. Sports Med. 2017, 47, 111– 128, DOI: 10.1007/s40279-017-0691-5
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Sweating Rate and Sweat Sodium Concentration in Athletes: A Review of Methodology and Intra/Interindividual Variability
Baker Lindsay B
Sports medicine (Auckland, N.Z.) (2017), 47 (Suppl 1), 111-128 ISSN:.
Athletes lose water and electrolytes as a consequence of thermoregulatory sweating during exercise and it is well known that the rate and composition of sweat loss can vary considerably within and among individuals. Many scientists and practitioners conduct sweat tests to determine sweat water and electrolyte losses of athletes during practice and competition. The information gleaned from sweat testing is often used to guide personalized fluid and electrolyte replacement recommendations for athletes; however, unstandardized methodological practices and challenging field conditions can produce inconsistent/inaccurate results. The primary objective of this paper is to provide a review of the literature regarding the effect of laboratory and field sweat-testing methodological variations on sweating rate (SR) and sweat composition (primarily sodium concentration [Na(+)]). The simplest and most accurate method to assess whole-body SR is via changes in body mass during exercise; however, potential confounding factors to consider are non-sweat sources of mass change and trapped sweat in clothing. In addition, variability in sweat [Na(+)] can result from differences in the type of collection system used (whole body or localized), the timing/duration of sweat collection, skin cleaning procedure, sample storage/handling, and analytical technique. Another aim of this paper is to briefly review factors that may impact intra/interindividual variability in SR and sweat [Na(+)] during exercise, including exercise intensity, environmental conditions, heat acclimation, aerobic capacity, body size/composition, wearing of protective equipment, sex, maturation, aging, diet, and/or hydration status. In summary, sweat testing can be a useful tool to estimate athletes' SR and sweat Na(+) loss to help guide fluid/electrolyte replacement strategies, provided that data are collected, analyzed, and interpreted appropriately.
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Hu, J.; Ho, K. T.; Zou, X. U.; Smyrl, W. H.; Stein, A.; Buhlmann, P. All-Solid-State Reference Electrodes Based on Colloid-Imprinted Mesoporous Carbon and Their Application in Disposable Paper-Based Potentiometric Sensing Devices. Anal. Chem. 2015, 87, 2981– 2987, DOI: 10.1021/ac504556s
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All-Solid-State Reference Electrodes Based on Colloid-Imprinted Mesoporous Carbon and Their Application in Disposable Paper-based Potentiometric Sensing Devices
Hu, Jinbo; Ho, Kieu T.; Zou, Xu U.; Smyrl, William H.; Stein, Andreas; Buhlmann, Philippe
Analytical Chemistry (Washington, DC, United States) (2015), 87 (5), 2981-2987CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
Ref. electrodes are used in almost every electroanal. measurement. Here, all-solid-state ref. electrodes are described that employ colloid-imprinted mesoporous (CIM) carbon as solid contact and a poly(vinyl chloride) ref. membrane to contact the sample. Such a ref. membrane is doped with a moderately hydrophilic ionic liq. and a hydrophobic redox couple, leading to well-defined const. potentials at the interfaces of this membrane to the sample and to the solid contact, resp. Due to the intrinsic properties of CIM carbon, ref. electrodes with a CIM carbon solid contact exhibit excellent resistance to common interfering agents such as light and O2, with outstanding potential stability in continuous potentiometric measurements. The potential drift of CIM carbon-based ref. electrodes without redox couple is ≥1.7 μV/h over 110 h, making them the most stable all-solid-state ref. electrodes reported so far. To demonstrate the compatibility of CIM carbon-based ref. electrodes with miniaturized potentiometric systems, these ref. electrodes were integrated into paper-based potentiometric sensing devices, successfully replacing the conventional ref. electrode with its ref. electrolyte soln. As a proof of concept, disposable paper-based Cl- sensing devices that contain stencil-printed Ag/AgCl-based Cl- selective electrodes and CIM carbon-based ref. electrodes were constructed. These sensing devices are inexpensive, easy to use, and offer highly reproducible Cl- measurements with sample vols. ≥10 μL.
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Cuartero, M.; Crespo, G. A.; Bakker, E. Polyurethane Ionophore-Based Thin Layer Membranes for Voltammetric Ion Activity Sensing. Anal. Chem. 2016, 88, 5649– 5654, DOI: 10.1021/acs.analchem.6b01085
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Polyurethane Ionophore-Based Thin Layer Membranes for Voltammetric Ion Activity Sensing
Cuartero, Maria; Crespo, Gaston A.; Bakker, Eric
Analytical Chemistry (Washington, DC, United States) (2016), 88 (11), 5649-5654CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
We report on a plasticized polyurethane ionophore-based thin film material (of hundreds of nanometer thickness) for simultaneous voltammetric multianalyte ion activity detection triggered by the oxidn./redn. of an underlying poly(3-octylthiophene) film. This material provides excellent mech., phys., and chem. robustness compared to other polymers. Polyurethane films did not exhibit leaching of lipophilic additives after rinsing with a direct water jet and exhibited resistance to detachment from the underlying electrode surface, resulting in a voltammetric current response with less than <1.5% RSD variation (n = 50). In contrast, plasticized poly(vinyl chloride), polystyrene, and poly(acrylate) ionophore-based membranes of the same thickness and compn. exhibited a significant deterioration of the signal after identical treatment. While previously reported works emphasized fundamental advancement of multi-ion detection with multi-ionophore-based thin films, polyurethane thin membranes allow one to achieve real world measurements without sacrificing anal. performance. Indeed, polyurethane membranes are demonstrated to be useful for the simultaneous detn. of potassium and lithium in undiluted human serum and blood with attractive precision.
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Smith, C. J.; Havenith, G. Body Mapping of Sweating Patterns in Male Athletes in Mild Exercise-Induced Hyperthermia. Eur. J. Appl. Physiol. 2011, 111, 1391– 1404, DOI: 10.1007/s00421-010-1744-8
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Body mapping of sweating patterns in male athletes in mild exercise-induced hyperthermia
Smith Caroline J; Havenith George
European journal of applied physiology (2011), 111 (7), 1391-404 ISSN:.
Regional variation in sweating over the body is widely recognised. However, most studies only measured a limited number of regions, with the use of differing thermal states across studies making a good meta-analysis to obtain a whole body map problematic. A study was therefore conducted to investigate regional sweat rates (RSR) and distributions over the whole body in male athletes. A modified absorbent technique was used to collect sweat at two exercise intensities [55% (I1) and 75% (I2) VO2(max)] in moderately warm conditions (25°C, 50% rh, 2 m s(-1) air velocity). At I1 and I2, highest sweat rates were observed on the central (upper and mid) and lower back, with values as high as 1,197, 1,148, and 856 g m(-2) h(-1), respectively, at I2. Lowest values were observed on the fingers, thumbs, and palms, with values of 144, 254, and 119 g m(-2) h(-1), respectively at I2. Sweat mapping of the head demonstrated high sweat rates on the forehead (1,710 g m(-2) h(-1) at I2) compared with low values on the chin (302 g m(-2) h(-1) at I2) and cheeks (279 g m(-2) h(-1) at I2). Sweat rate increased significantly in all regions from the low to high exercise intensity, with exception of the feet and ankles. No significant correlation was present between RSR and regional skin temperature (T (sk)), nor did RSR correspond to known patterns of regional sweat gland density. The present study has provided detailed regional sweat data over the whole body and has demonstrated large intra- and inter-segmental variation and the presence of consistent patterns of regional high versus low sweat rate areas in Caucasians male athletes. This data may have important applications for clothing design, thermophysiological modelling and thermal manikin design.
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Baker, L. B.; Ungaro, C. T.; Sopeña, B. C.; Nuccio, R. P.; Reimel, A. J.; Carter, J. M.; Stofan, J. R.; Barnes, K. A. Body Map of Regional vs. Whole Body Sweating Rate and Sweat Electrolyte Concentrations in Men and Women during Moderate Exercise-Heat Stress. J. Appl. Physiol. 2018, 124, 1304– 1318, DOI: 10.1152/japplphysiol.00867.2017
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Body map of regional vs. whole body sweating rate and sweat electrolyte concentrations in men and women during moderate exercise-heat stress
Baker, Lindsay B.; Ungaro, Corey T.; Sopena, Bridget C.; Nuccio, Ryan P.; Reimel, Adam J.; Carter, James M.; Stofan, John R.; Barnes, Kelly A.
Journal of Applied Physiology (2018), 124 (5), 1304-1318CODEN: JAPHEV; ISSN:1522-1601. (American Physiological Society)
This study detd. the relations between regional (REG) and whole body (WB) sweating rate (RSR and WBSR, resp.) as well as REG and WB sweat Na+ concn. ([Na+]) during exercise. Twenty-six recreational athletes (17 men, 9 women) cycled for 90 min while WB sweat [Na+] was measured using the washdown technique. RSR and REG sweat [Na+] were measured from nine regions using absorbent patches. RSR and REG sweat [Na+] from all regions were significantly (P < 0.05) correlated with WBSR (r = 0.58- 0.83) and WB sweat [Na+] (r = 0.74-0.88), resp. However, the slope and y-intercept of the regression lines for most models were significantly different than 1 and 0, resp. The coeffs. of detn. (r2) were 0.44-0.69 for RSR predicting WBSR [best predictors: dorsal forearm (r2 = 0.62) and triceps (r2 = 0.69)] and 0.55- 0.77 for REG predicting WB sweat [Na+] [best predictors: ventral forearm (r2 = 0.73) and thigh (r2= 0.77)]. There was a significant (P <0.05) effect of day-to-day variability on the regression model predicting WBSR from RSR at most regions but no effect on predictions of WB sweat [Na+] from REG. Results suggest that REG cannot be used as a direct surrogate for WB sweating responses. Nonetheless, the use of regression equations to predict WB sweat [Na+] from REG can provide an estn. of WB sweat [Na+] with an acceptable level of accuracy, esp. using the forearm or thigh. However, the best practice for measuring WBSR remains conventional WB mass balance calcns. since prediction of WBSR from RSR using absorbent patches does not meet the accuracy or reliability required to inform fluid intake recommendations. NEW & NOTEWORTHY This study developed a body map of regional sweating rate and regional (REG) sweat electrolyte concns. and detd. the effect of within-subject (bilateral and day-to-day) and between-subject (sex) factors on the relations between REG and the whole body (WB). Regression equations can be used to predict WB sweat Na+ concn. from REG, esp. using the forearm or thigh. However, prediction of WB sweating rate from REG sweating rate using absorbent patches does not reach the accuracy or reliability required to inform fluid intake recommendations. This study developed a body map of regional sweating rate and regional (REG) sweat electrolyte concns. and detd. the effect of within-subject (bilateral and day-to-day) and between-subject (sex) factors on the relations between REG and the whole body (WB). Regression equations can be used to predict WB sweat [Na+] concn. from REG, esp. using the forearm or thigh. However, prediction of WB sweating rate from REG sweating rate using absorbent patches does not reach the accuracy or reliability required to inform fluid intake recommendations.
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Dixit, C. K.; Kadimisetty, K.; Rusling, J. 3D-Printed Miniaturized Fluidic Tools in Chemistry and Biology. TrAC, Trends Anal. Chem. 2018, 106, 37– 52, DOI: 10.1016/j.trac.2018.06.013
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3D-printed miniaturized fluidic tools in chemistry and biology
Dixit, C. K.; Kadimisetty, K.; Rusling, J.
TrAC, Trends in Analytical Chemistry (2018), 106 (), 37-52CODEN: TTAEDJ; ISSN:0165-9936. (Elsevier B.V.)
3D printing (3DP), an additive manufg. (AM) approach allowing for rapid prototyping and decentralized fabrication on-demand, has become a common method for creating parts or whole devices. The wide scope of the AM extends from organized sectors of construction, ornament, medical, and R&D industries to individual explorers attributed to the low cost, high quality printers along with revolutionary tools and polymers. While progress is being made but big manufg. challenges are still there. Considering the quickly shifting narrative towards miniaturized anal. systems (MAS) we focus on the development/rapid prototyping and manufg. of MAS with 3DP, and application dependent challenges in engineering designs and choice of the polymeric materials and provide an exhaustive background to the applications of 3DP in biol. and chem. This will allow readers to perceive the most important features of AM in creating (i) various individual and modular components, and (ii) complete integrated tools.
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Kim, J.; Kumar, R.; Bandodkar, A. J.; Wang, J. Advanced Materials for Printed Wearable Electrochemical Devices: A Review. Adv. Electron. Mater. 2017, 3, 1600260, DOI: 10.1002/aelm.201600260
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Cánovas, R.; Parrilla, M.; Mercier, P.; Andrade, F. J.; Wang, J. Balloon-Embedded Sensors Withstanding Extreme Multiaxial Stretching and Global Bending Mechanical Stress: Towards Environmental and Security Monitoring. Adv. Mater. Technol. 2016, 1, 1600061, DOI: 10.1002/admt.201600061
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Sato, K.; Kang, W. H.; Saga, K.; Sato, K. T. Biology of Sweat Glands and Their Disorders. I. Normal Sweat Gland Function. J. Am. Acad. Dermatol. 1989, 20, 537– 563, DOI: 10.1016/S0190-9622(89)70063-3
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Biology of sweat glands and their disorders. I. Normal sweat gland function
Sato K; Kang W H; Saga K; Sato K T
Journal of the American Academy of Dermatology (1989), 20 (4), 537-63 ISSN:0190-9622.
The basic mechanisms of sweat gland function and an updated review of some relatively common disorders of sweat secretion, are presented. Although sweat secretion and ductal absorption are basically biophysical and biologic cellular processes, a detailed description of the basic biophysical principles of membrane transport has been avoided to make the discussion more readable. The cited references will, however, help those readers primarily interested in the basic details of sweat gland function. Part I of this article includes a discussion of morphologic characteristics, central and peripheral nervous control of sweat secretion, neurotransmitters, intracellular mediators and stimulus secretion coupling, Na-K-Cl cotransport model for the ionic mechanism of sweat secretion, ingredients of sweat, ductal function, the pathogenesis of abnormal sweat gland function in cystic fibrosis, and the discovery of the apoeccrine sweat gland. Part II, to be published in the May issue of the Journal, reviews reports of all those major disorders of hyperhidrosis and hypohidrosis that have appeared in the literature during the past 10 years. It is hoped that this review will serve as a resource for clinicians who encounter puzzling disorders of sweating in their patients, as well as for investigators who wish to obtain a quick update on sweat gland function.
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Emaminejad, S.; Gao, W.; Wu, E.; Davies, Z. A.; Yin Yin Nyein, H.; Challa, S.; Ryan, S. P.; Fahad, H. M.; Chen, K.; Shahpar, Z.; Talebi, S.; Milla, C.; Javey, A.; Davis, R. W. Autonomous Sweat Extraction and Analysis Applied to Cystic Fibrosis and Glucose Monitoring Using a Fully Integrated Wearable Platform. Proc. Natl. Acad. Sci. U. S. A. 2017, 114, 4625, DOI: 10.1073/pnas.1701740114
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Autonomous sweat extraction and analysis applied to cystic fibrosis and glucose monitoring using a fully integrated wearable platform
Emaminejad, Sam; Gao, Wei; Wu, Eric; Davies, Zoe A.; Nyein, Hnin Yin Yin; Challa, Samyuktha; Ryan, Sean P.; Fahad, Hossain M.; Chen, Kevin; Shahpar, Ziba; Talebi, Salmonn; Milla, Carlos; Javey, Ali; Davis, Ronald W.
Proceedings of the National Academy of Sciences of the United States of America (2017), 114 (18), 4625-4630CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)
Perspiration-based wearable biosensors facilitate continuous monitoring of individuals' health states with real-time and mol.-level insight. The inherent inaccessibility of sweat in sedentary individuals in large vol. (≥10 μL) for on-demand and in situ anal. has limited our ability to capitalize on this noninvasive and rich source of information. A wearable and miniaturized iontophoresis interface is an excellent soln. to overcome this barrier. The iontophoresis process involves delivery of stimulating agonists to the sweat glands with the aid of an elec. current. The challenge remains in devising an iontophoresis interface that can ext. sufficient amt. of sweat for robust sensing, without electrode corrosion and burning/causing discomfort in subjects. Here, we overcame this challenge through realizing an electrochem. enhanced iontophoresis interface, integrated in a wearable sweat anal. platform. This interface can be programmed to induce sweat with various secretion profiles for real-time anal., a capability which can be exploited to advance our knowledge of the sweat gland physiol. and the secretion process. To demonstrate the clin. value of our platform, human subject studies were performed in the context of the cystic fibrosis diagnosis and preliminary investigation of the blood/sweat glucose correlation. With our platform, we detected the elevated sweat electrolyte content of cystic fibrosis patients compared with that of healthy control subjects. Furthermore, our results indicate that oral glucose consumption in the fasting state is followed by increased glucose levels in both sweat and blood. Our soln. opens the possibility for a broad range of noninvasive diagnostic and general population health monitoring applications.
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Tóth, K.; Fucskó, J.; Lindner, E.; Fehér, Z.; Pungor, E. Potentiometric Detection in Flow Analysis. Anal. Chim. Acta 1986, 179, 359– 370, DOI: 10.1016/S0003-2670(00)84480-3
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Potentiometric detection in flow analysis
Toth, K.; Fucsko, J.; Lindner, E.; Feher, Z.; Pungor, E.
Analytica Chimica Acta (1986), 179 (), 359-70CODEN: ACACAM; ISSN:0003-2670.
Special aspects of ion-selective electrodes relevant to applications in flow-through systems are discussed. The predominant role of the dynamic response characteristics of the sensors, esp. in flow-injection anal., is emphasized. Indirectly, these characteristics can affect the linear response range, the detection limit, and the selectivity properties of the sensors. As examples, flow-injection methods are described for the detn. of F- in rain-water samples and of K+ activity in blood serum.
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Cazalé, A.; Sant, W.; Ginot, F.; Launay, J.-C.; Savourey, G.; Revol-Cavalier, F.; Lagarde, J. M.; Heinry, D.; Launay, J.; Temple-Boyer, P. Physiological Stress Monitoring Using Sodium Ion Potentiometric Microsensors for Sweat Analysis. Sens. Actuators, B 2016, 225, 1– 9, DOI: 10.1016/j.snb.2015.10.114
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Physiological stress monitoring using sodium ion potentiometric microsensors for sweat analysis
Cazale, A.; Sant, W.; Ginot, F.; Launay, J.-C.; Savourey, G.; Revol-Cavalier, F.; Lagarde, J. M.; Heinry, D.; Launay, J.; Temple-Boyer, P.
Sensors and Actuators, B: Chemical (2016), 225 (), 1-9CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)
In the frame of sweat anal., two technologies, based on either ISE or ISFET devices, were developed for the implementation of pNa potentiometric microsensors. Both of them demonstrated good sodium ion Na+ detection properties with a global sensitivity of around 110 mV/pNa in NaCl-based solns. due to the use of an integrated "Ag/AgCl ink" pseudo-ref. electrode. Then, in order to deal with in vivo anal. of sweat natremia, a physiol. sweatband prototype was developed, consisting of pNa-ISE and pNa-ISFET electronic detection modules as well as a textile-based sweat pump. Finally, sweating process was studied during series of expts. on twenty-five healthy consenting subjects. The sodium ion concn. [Na+] was successfully monitored in sweat during various heat exposures, demonstrating a global increase with exercise trial duration. Furthermore, a strong correlation was found between the sweat [Na+] concn. and the subject's internal temp. θ, allowing monitoring the subject's heat stress state. All in all, the relevance of the Na+ ion anal. was demonstrated for the physiol. stress monitoring and pNa potentiometric microsensors were shown to be very promising for the development of smart sweatbands.
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Nyein, H. Y. Y.; Gao, W.; Shahpar, Z.; Emaminejad, S.; Challa, S.; Chen, K.; Fahad, H. M.; Tai, L.-C.; Ota, H.; Davis, R. W.; Javey, A. A Wearable Electrochemical Platform for Noninvasive Simultaneous Monitoring of Ca 2+ and PH. ACS Nano 2016, 10, 7216– 7224, DOI: 10.1021/acsnano.6b04005
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A Wearable Electrochemical Platform for Noninvasive Simultaneous Monitoring of Ca2+ and pH
Nyein, Hnin Yin Yin; Gao, Wei; Shahpar, Ziba; Emaminejad, Sam; Challa, Samyuktha; Chen, Kevin; Fahad, Hossain M.; Tai, Li-Chia; Ota, Hiroki; Davis, Ronald W.; Javey, Ali
ACS Nano (2016), 10 (7), 7216-7224CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
Homeostasis of ionized calcium in biofluids is crit. for human biol. functions and organ systems. Measurement of ionized calcium for clin. applications is not easily accessible due to its strict procedures and dependence on pH. pH balance in body fluids greatly affects metabolic reactions and biol. transport systems. Here, the authors demonstrate a wearable electrochem. device for continuous monitoring of ionized calcium and pH of body fluids using a disposable and flexible array of Ca2+ and pH sensors that interfaces with a flexible printed circuit board. This platform enables real-time quant. anal. of these sensing elements in body fluids such as sweat, urine, and tears. Accuracy of Ca2+ concn. and pH measured by the wearable sensors is validated through inductively coupled plasma-mass spectrometry technique and a com. pH meter, resp. The authors' results show that the wearable sensors have high repeatability and selectivity to the target ions. Real-time on-body assessment of sweat is also performed, and the authors' results indicate that calcium concn. increases with decreasing pH. This platform can be used in noninvasive continuous anal. of ionized calcium and pH in body fluids for disease diagnosis such as primary hyperparathyroidism and kidney stones.
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Baker, L. B.; Ungaro, C. T.; Barnes, K. A.; Nuccio, R. P.; Reimel, A. J.; Stofan, J. R. Validity and Reliability of a Field Technique for Sweat Na+and K+analysis during Exercise in a Hot-Humid Environment. Physiol. Rep. 2014, 2, e12007, DOI: 10.14814/phy2.12007
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Validity and reliability of a field technique for sweat Na+ and K+ analysis during exercise in a hot-humid environment
Baker, Lindsay B.; Ungaro, Corey T.; Barnes, Kelly A.; Nuccio, Ryan P.; Reimel, Adam J.; Stofan, John R.
Physiological Reports (2014), 2 (5), e12007/1-e12007/11CODEN: PRHEJ2; ISSN:2051-817X. (Wiley-Blackwell)
This study compared a field vs. ref. lab. technique for extg. (syringe vs. centrifuge) and analyzing sweat [Na+] and [K+] (compact Horiba B-722 and B-731, HORIBA vs. ion chromatog., HPLC) collected with regional absorbent patches during exercise in a hot-humid environment. Sweat samples were collected from seven anatomical sites on 30 athletes during 1-h cycling in a heat chamber (33°C, 67% rh). Ten minutes into exercise, skin was cleaned/dried and two sweat patches were applied per anatomical site. After removal, one patch per site was centrifuged and sweat was analyzed with HORIBA in the heat chamber (CENTRIFUGE HORIBA) vs. HPLC (CENTRIFUGE HPLC). Sweat from the second patch per site was extd. using a 5-mL syringe and analyzed with HORIBA in the heat chamber (SYRINGE HORIBA) vs. HPLC (SYRINGE HPLC). CENTRIFUGE HORIBA, SYRINGE HPLC, and SYRINGE HORIBA were highly related to CENTRIFUGE HPLC ([Na+]: ICC = 0.96, 0.94, and 0.93, resp.; [K+]: ICC = 0.87, 0.92, and 0.84, resp.), while mean differences from CENTRIFUGE HPLC were small but usually significant ([Na+]: 4.7 ± 7.9 mEql/L, -2.5 ± 9.3 mEq/L, 4.0 ± 10.9 mEq/L (all P < 0.001), resp.; [K+]: 0.44 ± 0.52 mEq/L (P < 0.001), 0.01 ± 0.49 mEq/L (P = 0.77), 0.50 ± 0.48 mEq/L (P < 0.001), resp.). On the basis of typical error of the measurement results, sweat [Na+] and [K+] obtained with SYRINGE HORIBA falls within ±15.4 mEq/L and ±0.68 mEq/L, resp., of CENTRIFUGE HPLC 95% of the time. The field (SYRINGE HORIBA) method of extg. and analyzing sweat from regional absorbent patches may be useful in obtaining sweat [Na+] when rapid ests. in a hot-humid field setting are needed.
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Analytical Chemistry

Cite this: Anal. Chem. 2019, 91, 13, 8644–8651

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https://doi.org/10.1021/acs.analchem.9b02126

Published June 3, 2019

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Abstract
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Figure 1
Figure 1. Illustration of the research question in this article. Is the on-body data provided by WPISs reliable? What is the proper validation protocol to evaluate reliability of the real-time observations?.
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Figure 2
Figure 2. (a) Electrodes before and after functionalization. (b) Images of the electrode array, the sampling cell, and entire wearable device. (c) Sweat flow in the sampling cell once it is attached to the skin. (d) WPISs attached to the skin. ISM = ion-selective membrane.
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Figure 3
Figure 3. (a) Response of three pH electrodes for a pH change from 5.6 to 4.7. Flow rate = 4 μL min^–1. Dotted lines indicate the response time. (b) Response of three pH electrodes in a solution of pH 5.6 at 4, 8, and 16 μL min^–1. (c) pH calibrations at 4, 8, and 16 μL min^–1. (d) WPISs under torsion deformation. Response of a K⁺ electrode after applying different torsion deformations. (e) Calibrations using WPISs for Cl^–, Na⁺, K⁺, and pH before and after the incorporation of the sampling cell and after on-body measurements. All the calibration curves were accomplished in artificial sweat.
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Figure 4
Figure 4. (a) Concentration profiles observed with the WPISs during 60 min of a cycling workout. The WPISs contained three twin electrodes for each ion. (b) Validation of K⁺ on-body measurements. Every ion was measured in a different on-body test (with n = 3). A total number of 5 tests were accomplished, labeled as T1–T5.
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Figure 5
Figure 5. (a) Electrolyte dynamics observed during on-body tests. (a) Na⁺ concentration of an individual subjected to 1-h cycling at high intensity (on-body test T7). (b) Cl^– and pH monitoring in two different individuals subjected to the same physical activity (22 °C, relative humidity 70%, 1-h cycling, high intensity). The dots indicate the concentrations of sweat analyzed by IC after sweat collection by m-REG. On-body tests T8 and T9.
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References
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  Gao, Wei; Emaminejad, Sam; Nyein, Hnin Yin Yin; Challa, Samyuktha; Chen, Kevin; Peck, Austin; Fahad, Hossain M.; Ota, Hiroki; Shiraki, Hiroshi; Kiriya, Daisuke; Lien, Der-Hsien; Brooks, George A.; Davis, Ronald W.; Javey, Ali
  Nature (London, United Kingdom) (2016), 529 (7587), 509-514CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
  Wearable sensor technologies are essential to the realization of personalized medicine through continuously monitoring an individual's state of health. Sampling human sweat, which is rich in physiol. information, could enable non-invasive monitoring. Previously reported sweat-based and other non-invasive biosensors either can only monitor a single analyte at a time or lack on-site signal processing circuitry and sensor calibration mechanisms for accurate anal. of the physiol. state. Given the complexity of sweat secretion, simultaneous and multiplexed screening of target biomarkers is crit. and requires full system integration to ensure the accuracy of measurements. Here we present a mech. flexible and fully integrated (i.e., no external anal. is needed) sensor array for multiplexed in situ perspiration anal., which simultaneously and selectively measures sweat metabolites (such as glucose and lactate) and electrolytes (such as sodium and potassium ions), as well as the skin temp. (to calibrate the response of the sensors). Our work bridges the technol. gap between signal transduction, conditioning (amplification and filtering), processing and wireless transmission in wearable biosensors by merging plastic-based sensors that interface with the skin with silicon integrated circuits consolidated on a flexible circuit board for complex signal processing. This application could not have been realized using either of these technologies alone owing to their resp. inherent limitations. The wearable system is used to measure the detailed sweat profile of human subjects engaged in prolonged indoor and outdoor phys. activities, and to make a real-time assessment of the physiol. state of the subjects. This platform enables a wide range of personalized diagnostic and physiol. monitoring applications.
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9. 9
  Parrilla, M.; Cuartero, M.; Crespo, G. A. Wearable Potentiometric Ion Sensors. TrAC, Trends Anal. Chem. 2019, 110, 303– 320, DOI: 10.1016/j.trac.2018.11.024
  9
  Wearable potentiometric ion sensors
  Parrilla, Marc; Cuartero, Maria; Crespo, Gaston A.
  TrAC, Trends in Analytical Chemistry (2019), 110 (), 303-320CODEN: TTAEDJ; ISSN:0165-9936. (Elsevier B.V.)
  Wearable potentiometric ion sensors (WPISs) have become an exciting anal. platform that combines chem., material and electronic efforts to supply physiol. information during certain human activities. The real possibility of wearing an anal. device with diverse configurations-sweatband, patches, garments-without disturbing the welfare of the carrier has enabled potentiometric ion sensors both as health quality and sport performance controllers. Recent studies show a large involvement of WPISs in the following of crit. biomarkers (timely or continuously), such as sodium, potassium, calcium, magnesium, ammonium and chloride, which are present at relatively high concns. in sweat (∼mM levels). Certainly, the non-invasive nature of WPISs and other significant features, e.g., simplicity and cost-effectiveness, have broadened new horizons in relation to applied anal. chem. This has been pointed out in the literature over the last decade with the predominance of two anal. outcomes: (i) the improvement of sport performance as a result of continuous detection of ions in sweat (health status of the individual) while decreasing physiol. complications (injuries, muscle cramps, fatigue and dehydration) during practice; and (ii) advancements in clin. diagnostics and preventive medicine as a consequence of the monitoring of the health status of patients suffering from any kind of disorder. Beyond the undeniable importance of the integration of WPISs to satisfy current societal needs, the following crucial questions about misleading and missing anal. features need to be answered: To what extent is WPIS technol. a reliable anal. tool for the quantification of ions. Is cross-validation the current bottleneck toward further progress. Which are the fundamental steps involving the ion-selective electrode side that would benefit WPIS outcomes. Why is sweat the main (and almost the only) biol. fluid to be monitored by WPISs. What is the best sampling strategy to be incorporated into WPIS devices for on-body monitoring of sweat. Which precision limits should be considered to assure a reliable decision-making process. Accordingly, this review focuses on the progression of WPISs from an anal. perspective-merely our vision of the field-within the period between 2010 and 2018. An updated search using specific keywords (wearable, ion, potentiometry, sensor) provided 43 contributions, which are herein highlighted, with a sustainable acceleration over the last three years. Thus, this review describes the current state of WPIS technol., the construction of wearable all-solid-state potentiometric sensors, crit. requirements of potentiometric sensors to be fulfilled in a wearable configuration and key features regarding the ideal implementation of WPISs as reliable messengers of physiol. information in real scenarios.
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10. 10
  Choi, D. H.; Thaxton, A.; Jeong, I.; Kim, K.; Sosnay, P. R.; Cutting, G. R.; Searson, P. C. Sweat Test for Cystic Fibrosis: Wearable Sweat Sensor vs. Standard Laboratory Test. J. Cyst. Fibros. 2018, 17, e35– e38, DOI: 10.1016/j.jcf.2018.03.005
  There is no corresponding record for this reference.
11. 11
  Cuartero, M.; Parrilla, M.; Crespo, G. A. Wearable Potentiometric Sensors for Medical Applications. Sensors. 2019, 19, 363– 387, DOI: 10.3390/s19020363
  11
  Wearable potentiometric sensors for medical applications
  Cuartero, Maria; Parrilla, Marc; Crespo, Gaston A.
  Sensors (2019), 19 (2), 363/1-363/24CODEN: SENSC9; ISSN:1424-8220. (MDPI AG)
  A review. Wearable potentiometric sensors have received considerable attention owing to their great potential in a wide range of physiol. and clin. applications, particularly involving ion detection in sweat. Despite the significant progress in the manner that potentiometric sensors are integrated in wearable devices, in terms of materials and fabrication approaches, there is yet plenty of room for improvement in the strategy adopted for the sample collection. Essentially, this involves a fluidic sampling cell for continuous sweat anal. during sport performance or sweat accumulation via iontophoresis induction for one-spot measurements in medical settings. Even though the majority of the reported papers from the last five years describe on-body tests of wearable potentiometric sensors while the individual is practicing a phys. activity, the medical utilization of these devices has been demonstrated on very few occasions and only in the context of cystic fibrosis diagnosis. In this sense, it may be important to explore the implementation of wearable potentiometric sensors into the anal. of other biofluids, such as saliva, tears and urine, as herein discussed. While the fabrication and uses of wearable potentiometric sensors vary widely, there are many common issues related to the anal. characterization of such devices that must be consciously addressed, esp. in terms of sensor calibration and the validation of on-body measurements. After the assessment of key wearable potentiometric sensors reported over the last five years, with particular attention paid to those for medical applications, the present review offers tentative guidance regarding the characterization of anal. performance as well as anal. and clin. validations, thereby aiming at generating debate in the scientific community to allow for the establishment of well-conceived protocols.
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12. 12
  Morgan, R. M.; Patterson, M. J.; Nimmo, M. a. Acute Effects of Dehydration on Sweat Composition in Men during Prolonged Exercise in the Heat. Acta Physiol. Scand. 2004, 182, 37– 43, DOI: 10.1111/j.1365-201X.2004.01305.x
  12
  Acute effects of dehydration on sweat composition in men during prolonged exercise in the heat
  Morgan, R. M.; Patterson, M. J.; Nimmo, M. A.
  Acta Physiologica Scandinavica (2004), 182 (1), 37-43CODEN: APSCAX; ISSN:0001-6772. (Blackwell Publishing Ltd.)
  Aim: To det. whether acute exercise-heat-induced dehydration affects sweat compn., eight males cycled for 2 h at 39.5±1.6% VO2peak on two sep. occasions in a hot-humid environment (38.0±0.0°, 60.0±0.1% relative humidity). Methods: During exercise, subjects ingested either no fluid (dehydration) or a 20 mmol·L-1 sodium chloride soln. (euhydration). The vol. of soln., calcd. from whole-body sweat loss and detd. in a familiarization trial, was ingested at 0 min and every 15 min thereafter. Venous blood was collected at 0, 60 and 120 min of exercise and sweat was aspirated from a patch located on the dominant forearm at 120 min. Results: Following the 2-h cycling exercise, sweat [Na+] and [Cl-] was greater (P < 0.05) in the dehydration trial (Na+ 91.1±6.8 mmol·L-1; Cl- 73.3±3.5 mmol·L-1) compared with the euhydration trial (Na+ 81.1±5.9 mmol·L-1; Cl- 68.5±3.3 mmol·L-1). In addn., dehydration invoked a greater serum [Na+] (142.2±0.7 mmol·L-1; P < 0.05), [Cl-] (105.8±0.6 mmol·L-1; P < 0.05) and [K+] (5.27±0.2 mmol·L-1; P < 0.05) over the euhydration values for [Na+], [Cl-] and [K+], resp. (138.9±0.6, 102.9±0.5 and 4.88±0.1 mmol·L-1). Plasma aldosterone was also significantly higher during exercise in the dehydration trial compared with the euhydration trial (53.8±3.8 vs. 40.0±4.3 ng·dL-1; P < 0.05). Conclusions: Acute exercise-heat stress without fluid replacement resulted in a greater sweat [Na+] and [Cl-] which was potentially related to greater extracellular fluid [Na+], plasma aldosterone or sympathetic nervous activity.
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13. 13
  Baker, L. B.; Stofan, J. R.; Hamilton, A. A.; Horswill, C. A. Comparison of Regional Patch Collection vs. Whole Body Washdown for Measuring Sweat Sodium and Potassium Loss during Exercise. J. Appl. Physiol. 2009, 107, 887– 895, DOI: 10.1152/japplphysiol.00197.2009
  13
  Comparison of regional patch collection vs. whole body washdown for measuring sweat sodium and potassium loss during exercise
  Baker, Lindsay B.; Stofan, John R.; Hamilton, Adam A.; Horswill, Craig A.
  Journal of Applied Physiology (2009), 107 (3), 887-895CODEN: JAPHEV; ISSN:8750-7587. (American Physiological Society)
  This study compared simultaneous whole body washdown (WBW) and regional skin surface (REG) sweat collections to generate regression equations to predict WBW sweat Na+ concn. ([Na+]) and K+ concn. ([K+]) from single- and five-site REG sweat patch collections. Athletes (10 men, 10 women) cycled in a plastic chamber for 90 min in the heat. Before exercise, the subject and bike were washed with deionized water. After the onset of sweating, sterile patches were attached to the forearm, back, chest, forehead, and thigh and removed on satn. After exercise, the subject and bike were washed with ammonium sulfate soln. to collect all sweat electrolyte loss and det. the vol. of un-evapd. sweat. All individual patch sites and five-site REG (weighted for local sweat rate and body surface area) were significantly (P = 0.000) correlated with WBW sweat [Na+]. The equation for predicting WBW sweat [Na+] from five-site REG was y = 0.68x + 0.44 [r = 0.97, intraclass correlation coeff. (ICC) = 0.70] and did not differ between sexes. There were sex differences in the regression results between five-site REG and WBW sweat [K+] (men: y = 0.74x + 0.30, r = 0.89, ICC = 0.73; women: y = 0.04x + 3.18, r = 0.03, ICC = 0.00). Five-site REG sweat [Na+] and [K+] significantly overestimated that of WBW sweat (59 ± 27 vs. 41 ± 19 meq/l, P = 0.000 and 4.4 ± 0.7 vs. 3.6 ± 0.7 meq/l, P = 0.000, resp.). For both sexes, the best sites for predicting WBW sweat [Na+] and [K+] were the thigh (1 ± 8 meq/l < WBW, P = 1.000, y = 0.75x + 11.37, r = 0.96, ICC = 0.93) and chest (0.2 ± 0.3 meq/l > WBW, P = 1.000, y = 0.76x + 0.55, r = 0.89, ICC = 0.87), resp. In conclusion, regression equations can be used to accurately and reliably predict WBW sweat [Na+] and [K+] from REG sweat collections when study conditions and techniques are similar to that of the present protocol.
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14. 14
  Sonner, Z.; Wilder, E.; Heikenfeld, J.; Kasting, G.; Beyette, F.; Swaile, D.; Sherman, F.; Joyce, J.; Hagen, J.; Kelley-Loughnane, N.; Naik, R. The Microfluidics of the Eccrine Sweat Gland, Including Biomarker Partitioning, Transport, and Biosensing Implications. Biomicrofluidics 2015, 9, 031301, DOI: 10.1063/1.4921039
  14
  The microfluidics of the eccrine sweat gland, including biomarker partitioning, transport, and biosensing implications
  Sonner, Z.; Wilder, E.; Heikenfeld, J.; Kasting, G.; Beyette, F.; Swaile, D.; Sherman, F.; Joyce, J.; Hagen, J.; Kelley-Loughnane, N.; Naik, R.
  Biomicrofluidics (2015), 9 (3), 031301/1-031301/19CODEN: BIOMGB; ISSN:1932-1058. (American Institute of Physics)
  Non-invasive and accurate access of biomarkers remains a holy grail of the biomedical community. Human eccrine sweat is a surprisingly biomarker-rich fluid which is gaining increasing attention. This is esp. true in applications of continuous bio-monitoring where other biofluids prove more challenging, if not impossible. However, much confusion on the topic exists as the microfluidics of the eccrine sweat gland has never been comprehensively presented and models of biomarker partitioning into sweat are either underdeveloped and/or highly scattered across literature. Reported here are microfluidic models for eccrine sweat generation and flow which are coupled with review of blood-to-sweat biomarker partition pathways, therefore providing insights such as how biomarker concn. changes with sweat flow rate. Addnl., it is shown that both flow rate and biomarker diffusion det. the effective sampling rate of biomarkers at the skin surface (chronol. resoln.). The discussion covers a broad class of biomarkers including ions (Na+, Cl-, K+, NH4+), small mols. (ethanol, cortisol, urea, and lactate), and even peptides or small proteins (neuropeptides and cytokines). The models are not meant to be exhaustive for all biomarkers, yet collectively serve as a foundational guide for further development of sweat-based diagnostics and for those beginning exploration of new biomarker opportunities in sweat. (c) 2015 American Institute of Physics.
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15. 15
  Ali, S. M.; Yosipovitch, G. Skin PH: From Basic Science to Basic Skin Care. Acta Derm. Venereol. 2013, 93, 261– 267, DOI: 10.2340/00015555-1531
  15
  Skin pH: from basic science to basic skin care
  Ali Saba M; Yosipovitch Gil
  Acta dermato-venereologica (2013), 93 (3), 261-7 ISSN:.
  The "acid mantle" is a topic not only of historical interest, but also of clinical significance and has recently been linked to vital stratum corneum function. Despite compelling basic science evidence placing skin pH as a key factor in barrier homeostasis, stratum corneum integrity, and antimicrobial defense, application of the acid mantle concept in clinical care is lacking. We review recent basic science investigations into skin pH, discuss skin disorders characterized by aberrant pH, and finally discuss practical application for preservation of the acid mantle. Recognizing factors that alter skin pH and selecting products that preserve the acid mantle is of prime importance in treating dermatologic patients.
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16. 16
  Bohl, C. H.; Volpe, S. L. Magnesium and Exercise. Crit. Rev. Food Sci. Nutr. 2002, 42, 533– 563, DOI: 10.1080/20024091054247
  16
  Magnesium and exercise
  Bohl, Caroline H.; Volpe, Stella L.
  Critical Reviews in Food Science and Nutrition (2002), 42 (6), 533-563CODEN: CRFND6; ISSN:1040-8398. (CRC Press LLC)
  A review. Magnesium is an essential element that regulates membrane stability and neuromuscular, cardiovascular, immune, and hormonal functions. Mg is a crit. cofactor in many metabolic reactions. The Dietary Ref. Intake for magnesium in adult humans is 310-420 mg/day, but the actual intake is often suboptimal. Mg deficiency may lead to changes in gastrointestinal, cardiovascular, and neuromuscular functions. Phys. exercise may deplete Mg, which, together with marginal dietary Mg intake, may impair energy metab. efficiency and the capacity for phys. work. Mg nutritional assessment is a challenge because of the absence of accurate and convenient assessment methods. Recently, Mg has been touted as an agent for increasing athletic performance. Data from various studies on the relationship of Mg and exercise are discussed.
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17. 17
  Parrilla, M.; Cánovas, R.; Jeerapan, I.; Andrade, F. J.; Wang, J. A Textile-Based Stretchable Multi-Ion Potentiometric Sensor. Adv. Healthcare Mater. 2016, 5, 996– 1001, DOI: 10.1002/adhm.201600092
  17
  A Textile-Based Stretchable Multi-Ion Potentiometric Sensor
  Parrilla, Marc; Canovas, Rocio; Jeerapan, Itthipon; Andrade, Francisco J.; Wang, Joseph
  Advanced Healthcare Materials (2016), 5 (9), 996-1001CODEN: AHMDBJ; ISSN:2192-2640. (Wiley-VCH Verlag GmbH & Co. KGaA)
  This article reports a highly stretchable and printable textile-based potentiometric sensor array for simultaneous multi-ion sweat anal. using variety of fabric materials towards diverse healthcare and fitness applications. Textile-based potentiometric sensors was fabricated by combining polyurethane-based ion- selective membranes and inks with a serpentine sensor pattern and stretch-enduring printed electrodes. Combining stretchable components like polyurethane, Ecoflex, and stretch-enduring inks, along with a serpentine design, this printed textile sensor array can withstand high tensile stress and mech. deformation and can thus act as an efficient wearable biomedical sensor.
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18. 18
  Parrilla, M.; Ferré, J.; Guinovart, T.; Andrade, F. J. Wearable Potentiometric Sensors Based on Commercial Carbon Fibres for Monitoring Sodium in Sweat. Electroanalysis 2016, 28, 1267– 1275, DOI: 10.1002/elan.201600070
  18
  Wearable Potentiometric Sensors Based on Commercial Carbon Fibres for Monitoring Sodium in Sweat
  Parrilla, Marc; Ferre, Jordi; Guinovart, Tomas; Andrade, Francisco J.
  Electroanalysis (2016), 28 (6), 1267-1275CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)
  The use of com. carbon fibers (CCF) to build wearable potentiometric sensors for the real-time monitoring of sodium levels in sweat during exercise is presented. CCF are an attractive substrate for building wearable electrochem. sensors because of their good elec. cond., chem. inertness, flexibility and mech. resilience. In the first part of this work, the anal. performance of these novel potentiometric ion-selective electrodes made with CCFs is presented. Then, through the incorporation of a solid-contact ref. electrode, the development of a complete miniaturized potentiometric cell with a Nernstian response (59.2±0.6 mV/log [Na+], N=4) is obtained. Finally, the cell is integrated into a wearable patch and attached onto the skin of an athlete. The anal. characterization of the wearable patch shows a near-Nernstian response (55.9±0.8 mV/log [Na+], N=3) for sodium levels from 10-3 M to 10-1 M in artificial sweat, well within the physiol. range of interest. The device shows low noise levels and very good stability (-0.4±0.3 mV · h-1). To improve the usability of the sensor in real scenarios, a calibration-free approach is also explored. This platform opens new and attractive avenues for the generation of meaningful personalized physiol. information that could be applied - among many other fields - in sports, nutrition and healthcare.
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19. 19
  Alizadeh, A.; Burns, A.; Lenigk, R.; Gettings, R.; Ashe, J.; Porter, A.; McCaul, M.; Barrett, R.; Diamond, D.; White, P.; Skeath, P.; Tomczak, M. A Wearable Patch for Continuous Monitoring of Sweat Electrolytes during Exertion. Lab Chip 2018, 18, 2632– 2641, DOI: 10.1039/C8LC00510A
  19
  A wearable patch for continuous monitoring of sweat electrolytes during exertion
  Alizadeh, Azar; Burns, Andrew; Lenigk, Ralf; Gettings, Rachel; Ashe, Jeffrey; Porter, Adam; McCaul, Margaret; Barrett, Ruairi; Diamond, Dermot; White, Paddy; Skeath, Perry; Tomczak, Melanie
  Lab on a Chip (2018), 18 (17), 2632-2641CODEN: LCAHAM; ISSN:1473-0189. (Royal Society of Chemistry)
  Implementation of wearable sweat sensors for continuous measurement of fluid based biomarkers (including electrolytes, metabolites and proteins) is an attractive alternative to common, yet intrusive and invasive, practices such as urine or blood anal. Recent years have witnessed several key demonstrations of sweat based electrochem. sensing in wearable formats, however, there are still significant challenges and opportunities in this space for clin. acceptance, and thus mass implementation of these devices. For instance, there are inherent challenges in establishing direct correlations between sweat-based and gold-std. plasma-based biomarker concns. for clin. decision-making. In addn., the wearable sweat monitoring devices themselves may exacerbate these challenges, as they can significantly alter sweat physiol. (example, sweat rate and compn.). Reported here is the demonstration of a fully integrated, wireless, wearable and flexible sweat sensing device for non-obtrusive and continuous monitoring of electrolytes during moderate to intense exertion as a metric for hydration status. The focus of this work is twofold: 1- design of a conformable fluidics systems to suit conditions of operation for sweat collection (to minimize sensor lag) with rapid removal of sweat from the sensing site (to minimize effects on sweat physiol.). 2- integration of Na+ and K+ ion-selective electrodes (ISEs) with flexible microfluidics and low noise small footprint electronics components to enable wireless, wearable sweat monitoring. While this device is specific to electrolyte anal. during intense perspiration, the lessons in microfluidics and overall system design are likely applicable across a broad range of analytes.
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20. 20
  Nyein, H. Y. Y.; Tai, L.; Ngo, Q. P.; Chao, M.; Zhang, G. B.; Gao, W.; Bariya, M.; Bullock, J.; Kim, H.; Fahad, H. M.; Javey, A. A Wearable Microfluidic Sensing Patch for Dynamic Sweat Secretion Analysis. ACS Sensors 2018, 3, 944– 952, DOI: 10.1021/acssensors.7b00961
  20
  A Wearable Microfluidic Sensing Patch for Dynamic Sweat Secretion Analysis
  Nyein, Hnin Yin Yin; Tai, Li-Chia; Ngo, Quynh Phuong; Chao, Minghan; Zhang, George B.; Gao, Wei; Bariya, Mallika; Bullock, James; Kim, Hyungjin; Fahad, Hossain M.; Javey, Ali
  ACS Sensors (2018), 3 (5), 944-952CODEN: ASCEFJ; ISSN:2379-3694. (American Chemical Society)
  Wearable sweat sensing is a rapidly rising research area driven by its promising potential in health, fitness, and diagnostic applications. Despite the growth in the field, major challenges in relation to sweat metrics remain to be addressed. These challenges include sweat rate monitoring for its complex relation with sweat compns. and sweat sampling for sweat dynamics studies. The authors present a flexible microfluidic sweat sensing patch that enhances real-time electrochem. sensing and sweat rate anal. via sweat sampling. The device contains a spiral-patterned microfluidic component that is embedded with ion-selective sensors and an elec. impedance-based sweat rate sensor on a flexible plastic substrate. The patch is enabled to autonomously perform sweat anal. by interfacing the sensing component with a printed circuit board that is capable of on-site signal conditioning, anal., and transmission. Progressive sweat flow in the microfluidic device, governed by the pressure induced by the secreted sweat, enhances sweat sampling and electrochem. detection via a defined sweat collection chamber and a directed sweat route. The characteristic of the sweat rate sensor is validated through a theor. simulation, and the precision and accuracy of the flow rate is verified with a com. syringe pump and a Macroduct sweat collector. On-body simultaneous monitoring of ion (H+, Na+, K+, Cl-) concn. and sweat rate is also demonstrated for sensor functionality. This sweat sensing patch provides an integrated platform for a comprehensive sweat secretion anal. and facilitates physiol. and clin. studies by closely monitoring interrelated sweat parameters.
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21. 21
  Sempionatto, J. R.; Martin, A.; García-Carmona, L.; Barfidokht, A.; Kurniawan, J. F.; Moreto, J. R.; Tang, G.; Shin, A.; Liu, X.; Escarpa, A.; Wang, J. Skin-Worn Soft Microfluidic Potentiometric Detection System. Electroanalysis 2019, 31, 239– 245, DOI: 10.1002/elan.201800414
  21
  Skin-Worn Soft Microfluidic Potentiometric Detection System
  Sempionatto, Juliane R.; Martin, Aida; Garcia-Carmona, Laura; Barfidokht, Abbas; Kurniawan, Jonas F.; Moreto, Jose R.; Tang, Guangda; Shin, Andrew; Liu, Xiaofeng; Escarpa, Alberto; Wang, Joseph
  Electroanalysis (2019), 31 (2), 239-245CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)
  A flexible skin-mounted microfluidic potentiometric device for simultaneous electrochem. monitoring of sodium and potassium in sweat is presented. The wearable device allows efficient natural sweat pumping to the potentiometric detection chamber, contg. solid-contact ion-selective Na+ and K+ electrodes, during exercise activity. The fabricated microchip electrolyte-sensing device displays good anal. performance and addresses sweat mixing and carry-over issues of early epidermal potentiometric sensors. Such soft skin-worn microchip platform integrates potentiometric measurement, microfluidic technologies with flexible electronics for real-time wireless data transmission to mobile devices. The new fully integrated microfluidic electrolyte-detection device paves the way for practical fitness and health monitoring applications.
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22. 22
  Anastasova, S.; Crewther, B.; Bembnowicz, P.; Curto, V.; Ip, H. M.; Rosa, B.; Yang, G. Z. A Wearable Multisensing Patch for Continuous Sweat Monitoring. Biosens. Bioelectron. 2017, 94, 730, DOI: 10.1016/j.bios.2017.03.018
  22
  Corrigendum to "A wearable multisensing patch for continuous sweat monitoring" [Biosens. Bioelectron. (2016)] [Erratum to document cited in CA170:328723]
  Anastasova, S.; Crewther, B.; Bembnowicz, P.; Curto, V.; Ip, H. M.; Rosa, B.; Yang, G.-Z.
  Biosensors & Bioelectronics (2017), 94 (), 730CODEN: BBIOE4; ISSN:0956-5663. (Elsevier B.V.)
  There is no expanded citation for this reference.
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23. 23
  Dziedzic, C. E.; Ross, M. L.; Slater, G. J.; Burke, L. M. Variability of Measurements of Sweat Sodium Using the Regional Absorbent-Patch Method. Int. J. Sport Physiol. Perform. 2014, 9, 832– 838, DOI: 10.1123/ijspp.2013-0480
  There is no corresponding record for this reference.
24. 24
  Baker, L. B. Sweating Rate and Sweat Sodium Concentration in Athletes: A Review of Methodology and Intra/Interindividual Variability. Sports Med. 2017, 47, 111– 128, DOI: 10.1007/s40279-017-0691-5
  24
  Sweating Rate and Sweat Sodium Concentration in Athletes: A Review of Methodology and Intra/Interindividual Variability
  Baker Lindsay B
  Sports medicine (Auckland, N.Z.) (2017), 47 (Suppl 1), 111-128 ISSN:.
  Athletes lose water and electrolytes as a consequence of thermoregulatory sweating during exercise and it is well known that the rate and composition of sweat loss can vary considerably within and among individuals. Many scientists and practitioners conduct sweat tests to determine sweat water and electrolyte losses of athletes during practice and competition. The information gleaned from sweat testing is often used to guide personalized fluid and electrolyte replacement recommendations for athletes; however, unstandardized methodological practices and challenging field conditions can produce inconsistent/inaccurate results. The primary objective of this paper is to provide a review of the literature regarding the effect of laboratory and field sweat-testing methodological variations on sweating rate (SR) and sweat composition (primarily sodium concentration [Na(+)]). The simplest and most accurate method to assess whole-body SR is via changes in body mass during exercise; however, potential confounding factors to consider are non-sweat sources of mass change and trapped sweat in clothing. In addition, variability in sweat [Na(+)] can result from differences in the type of collection system used (whole body or localized), the timing/duration of sweat collection, skin cleaning procedure, sample storage/handling, and analytical technique. Another aim of this paper is to briefly review factors that may impact intra/interindividual variability in SR and sweat [Na(+)] during exercise, including exercise intensity, environmental conditions, heat acclimation, aerobic capacity, body size/composition, wearing of protective equipment, sex, maturation, aging, diet, and/or hydration status. In summary, sweat testing can be a useful tool to estimate athletes' SR and sweat Na(+) loss to help guide fluid/electrolyte replacement strategies, provided that data are collected, analyzed, and interpreted appropriately.
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25. 25
  Hu, J.; Ho, K. T.; Zou, X. U.; Smyrl, W. H.; Stein, A.; Buhlmann, P. All-Solid-State Reference Electrodes Based on Colloid-Imprinted Mesoporous Carbon and Their Application in Disposable Paper-Based Potentiometric Sensing Devices. Anal. Chem. 2015, 87, 2981– 2987, DOI: 10.1021/ac504556s
  25
  All-Solid-State Reference Electrodes Based on Colloid-Imprinted Mesoporous Carbon and Their Application in Disposable Paper-based Potentiometric Sensing Devices
  Hu, Jinbo; Ho, Kieu T.; Zou, Xu U.; Smyrl, William H.; Stein, Andreas; Buhlmann, Philippe
  Analytical Chemistry (Washington, DC, United States) (2015), 87 (5), 2981-2987CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
  Ref. electrodes are used in almost every electroanal. measurement. Here, all-solid-state ref. electrodes are described that employ colloid-imprinted mesoporous (CIM) carbon as solid contact and a poly(vinyl chloride) ref. membrane to contact the sample. Such a ref. membrane is doped with a moderately hydrophilic ionic liq. and a hydrophobic redox couple, leading to well-defined const. potentials at the interfaces of this membrane to the sample and to the solid contact, resp. Due to the intrinsic properties of CIM carbon, ref. electrodes with a CIM carbon solid contact exhibit excellent resistance to common interfering agents such as light and O2, with outstanding potential stability in continuous potentiometric measurements. The potential drift of CIM carbon-based ref. electrodes without redox couple is ≥1.7 μV/h over 110 h, making them the most stable all-solid-state ref. electrodes reported so far. To demonstrate the compatibility of CIM carbon-based ref. electrodes with miniaturized potentiometric systems, these ref. electrodes were integrated into paper-based potentiometric sensing devices, successfully replacing the conventional ref. electrode with its ref. electrolyte soln. As a proof of concept, disposable paper-based Cl- sensing devices that contain stencil-printed Ag/AgCl-based Cl- selective electrodes and CIM carbon-based ref. electrodes were constructed. These sensing devices are inexpensive, easy to use, and offer highly reproducible Cl- measurements with sample vols. ≥10 μL.
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26. 26
  Cuartero, M.; Crespo, G. A.; Bakker, E. Polyurethane Ionophore-Based Thin Layer Membranes for Voltammetric Ion Activity Sensing. Anal. Chem. 2016, 88, 5649– 5654, DOI: 10.1021/acs.analchem.6b01085
  26
  Polyurethane Ionophore-Based Thin Layer Membranes for Voltammetric Ion Activity Sensing
  Cuartero, Maria; Crespo, Gaston A.; Bakker, Eric
  Analytical Chemistry (Washington, DC, United States) (2016), 88 (11), 5649-5654CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
  We report on a plasticized polyurethane ionophore-based thin film material (of hundreds of nanometer thickness) for simultaneous voltammetric multianalyte ion activity detection triggered by the oxidn./redn. of an underlying poly(3-octylthiophene) film. This material provides excellent mech., phys., and chem. robustness compared to other polymers. Polyurethane films did not exhibit leaching of lipophilic additives after rinsing with a direct water jet and exhibited resistance to detachment from the underlying electrode surface, resulting in a voltammetric current response with less than <1.5% RSD variation (n = 50). In contrast, plasticized poly(vinyl chloride), polystyrene, and poly(acrylate) ionophore-based membranes of the same thickness and compn. exhibited a significant deterioration of the signal after identical treatment. While previously reported works emphasized fundamental advancement of multi-ion detection with multi-ionophore-based thin films, polyurethane thin membranes allow one to achieve real world measurements without sacrificing anal. performance. Indeed, polyurethane membranes are demonstrated to be useful for the simultaneous detn. of potassium and lithium in undiluted human serum and blood with attractive precision.
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27. 27
  Smith, C. J.; Havenith, G. Body Mapping of Sweating Patterns in Male Athletes in Mild Exercise-Induced Hyperthermia. Eur. J. Appl. Physiol. 2011, 111, 1391– 1404, DOI: 10.1007/s00421-010-1744-8
  27
  Body mapping of sweating patterns in male athletes in mild exercise-induced hyperthermia
  Smith Caroline J; Havenith George
  European journal of applied physiology (2011), 111 (7), 1391-404 ISSN:.
  Regional variation in sweating over the body is widely recognised. However, most studies only measured a limited number of regions, with the use of differing thermal states across studies making a good meta-analysis to obtain a whole body map problematic. A study was therefore conducted to investigate regional sweat rates (RSR) and distributions over the whole body in male athletes. A modified absorbent technique was used to collect sweat at two exercise intensities [55% (I1) and 75% (I2) VO2(max)] in moderately warm conditions (25°C, 50% rh, 2 m s(-1) air velocity). At I1 and I2, highest sweat rates were observed on the central (upper and mid) and lower back, with values as high as 1,197, 1,148, and 856 g m(-2) h(-1), respectively, at I2. Lowest values were observed on the fingers, thumbs, and palms, with values of 144, 254, and 119 g m(-2) h(-1), respectively at I2. Sweat mapping of the head demonstrated high sweat rates on the forehead (1,710 g m(-2) h(-1) at I2) compared with low values on the chin (302 g m(-2) h(-1) at I2) and cheeks (279 g m(-2) h(-1) at I2). Sweat rate increased significantly in all regions from the low to high exercise intensity, with exception of the feet and ankles. No significant correlation was present between RSR and regional skin temperature (T (sk)), nor did RSR correspond to known patterns of regional sweat gland density. The present study has provided detailed regional sweat data over the whole body and has demonstrated large intra- and inter-segmental variation and the presence of consistent patterns of regional high versus low sweat rate areas in Caucasians male athletes. This data may have important applications for clothing design, thermophysiological modelling and thermal manikin design.
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28. 28
  Baker, L. B.; Ungaro, C. T.; Sopeña, B. C.; Nuccio, R. P.; Reimel, A. J.; Carter, J. M.; Stofan, J. R.; Barnes, K. A. Body Map of Regional vs. Whole Body Sweating Rate and Sweat Electrolyte Concentrations in Men and Women during Moderate Exercise-Heat Stress. J. Appl. Physiol. 2018, 124, 1304– 1318, DOI: 10.1152/japplphysiol.00867.2017
  28
  Body map of regional vs. whole body sweating rate and sweat electrolyte concentrations in men and women during moderate exercise-heat stress
  Baker, Lindsay B.; Ungaro, Corey T.; Sopena, Bridget C.; Nuccio, Ryan P.; Reimel, Adam J.; Carter, James M.; Stofan, John R.; Barnes, Kelly A.
  Journal of Applied Physiology (2018), 124 (5), 1304-1318CODEN: JAPHEV; ISSN:1522-1601. (American Physiological Society)
  This study detd. the relations between regional (REG) and whole body (WB) sweating rate (RSR and WBSR, resp.) as well as REG and WB sweat Na+ concn. ([Na+]) during exercise. Twenty-six recreational athletes (17 men, 9 women) cycled for 90 min while WB sweat [Na+] was measured using the washdown technique. RSR and REG sweat [Na+] were measured from nine regions using absorbent patches. RSR and REG sweat [Na+] from all regions were significantly (P < 0.05) correlated with WBSR (r = 0.58- 0.83) and WB sweat [Na+] (r = 0.74-0.88), resp. However, the slope and y-intercept of the regression lines for most models were significantly different than 1 and 0, resp. The coeffs. of detn. (r2) were 0.44-0.69 for RSR predicting WBSR [best predictors: dorsal forearm (r2 = 0.62) and triceps (r2 = 0.69)] and 0.55- 0.77 for REG predicting WB sweat [Na+] [best predictors: ventral forearm (r2 = 0.73) and thigh (r2= 0.77)]. There was a significant (P <0.05) effect of day-to-day variability on the regression model predicting WBSR from RSR at most regions but no effect on predictions of WB sweat [Na+] from REG. Results suggest that REG cannot be used as a direct surrogate for WB sweating responses. Nonetheless, the use of regression equations to predict WB sweat [Na+] from REG can provide an estn. of WB sweat [Na+] with an acceptable level of accuracy, esp. using the forearm or thigh. However, the best practice for measuring WBSR remains conventional WB mass balance calcns. since prediction of WBSR from RSR using absorbent patches does not meet the accuracy or reliability required to inform fluid intake recommendations. NEW & NOTEWORTHY This study developed a body map of regional sweating rate and regional (REG) sweat electrolyte concns. and detd. the effect of within-subject (bilateral and day-to-day) and between-subject (sex) factors on the relations between REG and the whole body (WB). Regression equations can be used to predict WB sweat Na+ concn. from REG, esp. using the forearm or thigh. However, prediction of WB sweating rate from REG sweating rate using absorbent patches does not reach the accuracy or reliability required to inform fluid intake recommendations. This study developed a body map of regional sweating rate and regional (REG) sweat electrolyte concns. and detd. the effect of within-subject (bilateral and day-to-day) and between-subject (sex) factors on the relations between REG and the whole body (WB). Regression equations can be used to predict WB sweat [Na+] concn. from REG, esp. using the forearm or thigh. However, prediction of WB sweating rate from REG sweating rate using absorbent patches does not reach the accuracy or reliability required to inform fluid intake recommendations.
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29. 29
  Dixit, C. K.; Kadimisetty, K.; Rusling, J. 3D-Printed Miniaturized Fluidic Tools in Chemistry and Biology. TrAC, Trends Anal. Chem. 2018, 106, 37– 52, DOI: 10.1016/j.trac.2018.06.013
  29
  3D-printed miniaturized fluidic tools in chemistry and biology
  Dixit, C. K.; Kadimisetty, K.; Rusling, J.
  TrAC, Trends in Analytical Chemistry (2018), 106 (), 37-52CODEN: TTAEDJ; ISSN:0165-9936. (Elsevier B.V.)
  3D printing (3DP), an additive manufg. (AM) approach allowing for rapid prototyping and decentralized fabrication on-demand, has become a common method for creating parts or whole devices. The wide scope of the AM extends from organized sectors of construction, ornament, medical, and R&D industries to individual explorers attributed to the low cost, high quality printers along with revolutionary tools and polymers. While progress is being made but big manufg. challenges are still there. Considering the quickly shifting narrative towards miniaturized anal. systems (MAS) we focus on the development/rapid prototyping and manufg. of MAS with 3DP, and application dependent challenges in engineering designs and choice of the polymeric materials and provide an exhaustive background to the applications of 3DP in biol. and chem. This will allow readers to perceive the most important features of AM in creating (i) various individual and modular components, and (ii) complete integrated tools.
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30. 30
  Kim, J.; Kumar, R.; Bandodkar, A. J.; Wang, J. Advanced Materials for Printed Wearable Electrochemical Devices: A Review. Adv. Electron. Mater. 2017, 3, 1600260, DOI: 10.1002/aelm.201600260
  There is no corresponding record for this reference.
31. 31
  Cánovas, R.; Parrilla, M.; Mercier, P.; Andrade, F. J.; Wang, J. Balloon-Embedded Sensors Withstanding Extreme Multiaxial Stretching and Global Bending Mechanical Stress: Towards Environmental and Security Monitoring. Adv. Mater. Technol. 2016, 1, 1600061, DOI: 10.1002/admt.201600061
  There is no corresponding record for this reference.
32. 32
  Sato, K.; Kang, W. H.; Saga, K.; Sato, K. T. Biology of Sweat Glands and Their Disorders. I. Normal Sweat Gland Function. J. Am. Acad. Dermatol. 1989, 20, 537– 563, DOI: 10.1016/S0190-9622(89)70063-3
  32
  Biology of sweat glands and their disorders. I. Normal sweat gland function
  Sato K; Kang W H; Saga K; Sato K T
  Journal of the American Academy of Dermatology (1989), 20 (4), 537-63 ISSN:0190-9622.
  The basic mechanisms of sweat gland function and an updated review of some relatively common disorders of sweat secretion, are presented. Although sweat secretion and ductal absorption are basically biophysical and biologic cellular processes, a detailed description of the basic biophysical principles of membrane transport has been avoided to make the discussion more readable. The cited references will, however, help those readers primarily interested in the basic details of sweat gland function. Part I of this article includes a discussion of morphologic characteristics, central and peripheral nervous control of sweat secretion, neurotransmitters, intracellular mediators and stimulus secretion coupling, Na-K-Cl cotransport model for the ionic mechanism of sweat secretion, ingredients of sweat, ductal function, the pathogenesis of abnormal sweat gland function in cystic fibrosis, and the discovery of the apoeccrine sweat gland. Part II, to be published in the May issue of the Journal, reviews reports of all those major disorders of hyperhidrosis and hypohidrosis that have appeared in the literature during the past 10 years. It is hoped that this review will serve as a resource for clinicians who encounter puzzling disorders of sweating in their patients, as well as for investigators who wish to obtain a quick update on sweat gland function.
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33. 33
  Emaminejad, S.; Gao, W.; Wu, E.; Davies, Z. A.; Yin Yin Nyein, H.; Challa, S.; Ryan, S. P.; Fahad, H. M.; Chen, K.; Shahpar, Z.; Talebi, S.; Milla, C.; Javey, A.; Davis, R. W. Autonomous Sweat Extraction and Analysis Applied to Cystic Fibrosis and Glucose Monitoring Using a Fully Integrated Wearable Platform. Proc. Natl. Acad. Sci. U. S. A. 2017, 114, 4625, DOI: 10.1073/pnas.1701740114
  33
  Autonomous sweat extraction and analysis applied to cystic fibrosis and glucose monitoring using a fully integrated wearable platform
  Emaminejad, Sam; Gao, Wei; Wu, Eric; Davies, Zoe A.; Nyein, Hnin Yin Yin; Challa, Samyuktha; Ryan, Sean P.; Fahad, Hossain M.; Chen, Kevin; Shahpar, Ziba; Talebi, Salmonn; Milla, Carlos; Javey, Ali; Davis, Ronald W.
  Proceedings of the National Academy of Sciences of the United States of America (2017), 114 (18), 4625-4630CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)
  Perspiration-based wearable biosensors facilitate continuous monitoring of individuals' health states with real-time and mol.-level insight. The inherent inaccessibility of sweat in sedentary individuals in large vol. (≥10 μL) for on-demand and in situ anal. has limited our ability to capitalize on this noninvasive and rich source of information. A wearable and miniaturized iontophoresis interface is an excellent soln. to overcome this barrier. The iontophoresis process involves delivery of stimulating agonists to the sweat glands with the aid of an elec. current. The challenge remains in devising an iontophoresis interface that can ext. sufficient amt. of sweat for robust sensing, without electrode corrosion and burning/causing discomfort in subjects. Here, we overcame this challenge through realizing an electrochem. enhanced iontophoresis interface, integrated in a wearable sweat anal. platform. This interface can be programmed to induce sweat with various secretion profiles for real-time anal., a capability which can be exploited to advance our knowledge of the sweat gland physiol. and the secretion process. To demonstrate the clin. value of our platform, human subject studies were performed in the context of the cystic fibrosis diagnosis and preliminary investigation of the blood/sweat glucose correlation. With our platform, we detected the elevated sweat electrolyte content of cystic fibrosis patients compared with that of healthy control subjects. Furthermore, our results indicate that oral glucose consumption in the fasting state is followed by increased glucose levels in both sweat and blood. Our soln. opens the possibility for a broad range of noninvasive diagnostic and general population health monitoring applications.
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34. 34
  Tóth, K.; Fucskó, J.; Lindner, E.; Fehér, Z.; Pungor, E. Potentiometric Detection in Flow Analysis. Anal. Chim. Acta 1986, 179, 359– 370, DOI: 10.1016/S0003-2670(00)84480-3
  34
  Potentiometric detection in flow analysis
  Toth, K.; Fucsko, J.; Lindner, E.; Feher, Z.; Pungor, E.
  Analytica Chimica Acta (1986), 179 (), 359-70CODEN: ACACAM; ISSN:0003-2670.
  Special aspects of ion-selective electrodes relevant to applications in flow-through systems are discussed. The predominant role of the dynamic response characteristics of the sensors, esp. in flow-injection anal., is emphasized. Indirectly, these characteristics can affect the linear response range, the detection limit, and the selectivity properties of the sensors. As examples, flow-injection methods are described for the detn. of F- in rain-water samples and of K+ activity in blood serum.
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35. 35
  Cazalé, A.; Sant, W.; Ginot, F.; Launay, J.-C.; Savourey, G.; Revol-Cavalier, F.; Lagarde, J. M.; Heinry, D.; Launay, J.; Temple-Boyer, P. Physiological Stress Monitoring Using Sodium Ion Potentiometric Microsensors for Sweat Analysis. Sens. Actuators, B 2016, 225, 1– 9, DOI: 10.1016/j.snb.2015.10.114
  35
  Physiological stress monitoring using sodium ion potentiometric microsensors for sweat analysis
  Cazale, A.; Sant, W.; Ginot, F.; Launay, J.-C.; Savourey, G.; Revol-Cavalier, F.; Lagarde, J. M.; Heinry, D.; Launay, J.; Temple-Boyer, P.
  Sensors and Actuators, B: Chemical (2016), 225 (), 1-9CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)
  In the frame of sweat anal., two technologies, based on either ISE or ISFET devices, were developed for the implementation of pNa potentiometric microsensors. Both of them demonstrated good sodium ion Na+ detection properties with a global sensitivity of around 110 mV/pNa in NaCl-based solns. due to the use of an integrated "Ag/AgCl ink" pseudo-ref. electrode. Then, in order to deal with in vivo anal. of sweat natremia, a physiol. sweatband prototype was developed, consisting of pNa-ISE and pNa-ISFET electronic detection modules as well as a textile-based sweat pump. Finally, sweating process was studied during series of expts. on twenty-five healthy consenting subjects. The sodium ion concn. [Na+] was successfully monitored in sweat during various heat exposures, demonstrating a global increase with exercise trial duration. Furthermore, a strong correlation was found between the sweat [Na+] concn. and the subject's internal temp. θ, allowing monitoring the subject's heat stress state. All in all, the relevance of the Na+ ion anal. was demonstrated for the physiol. stress monitoring and pNa potentiometric microsensors were shown to be very promising for the development of smart sweatbands.
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36. 36
  Nyein, H. Y. Y.; Gao, W.; Shahpar, Z.; Emaminejad, S.; Challa, S.; Chen, K.; Fahad, H. M.; Tai, L.-C.; Ota, H.; Davis, R. W.; Javey, A. A Wearable Electrochemical Platform for Noninvasive Simultaneous Monitoring of Ca 2+ and PH. ACS Nano 2016, 10, 7216– 7224, DOI: 10.1021/acsnano.6b04005
  36
  A Wearable Electrochemical Platform for Noninvasive Simultaneous Monitoring of Ca2+ and pH
  Nyein, Hnin Yin Yin; Gao, Wei; Shahpar, Ziba; Emaminejad, Sam; Challa, Samyuktha; Chen, Kevin; Fahad, Hossain M.; Tai, Li-Chia; Ota, Hiroki; Davis, Ronald W.; Javey, Ali
  ACS Nano (2016), 10 (7), 7216-7224CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
  Homeostasis of ionized calcium in biofluids is crit. for human biol. functions and organ systems. Measurement of ionized calcium for clin. applications is not easily accessible due to its strict procedures and dependence on pH. pH balance in body fluids greatly affects metabolic reactions and biol. transport systems. Here, the authors demonstrate a wearable electrochem. device for continuous monitoring of ionized calcium and pH of body fluids using a disposable and flexible array of Ca2+ and pH sensors that interfaces with a flexible printed circuit board. This platform enables real-time quant. anal. of these sensing elements in body fluids such as sweat, urine, and tears. Accuracy of Ca2+ concn. and pH measured by the wearable sensors is validated through inductively coupled plasma-mass spectrometry technique and a com. pH meter, resp. The authors' results show that the wearable sensors have high repeatability and selectivity to the target ions. Real-time on-body assessment of sweat is also performed, and the authors' results indicate that calcium concn. increases with decreasing pH. This platform can be used in noninvasive continuous anal. of ionized calcium and pH in body fluids for disease diagnosis such as primary hyperparathyroidism and kidney stones.
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37. 37
  Baker, L. B.; Ungaro, C. T.; Barnes, K. A.; Nuccio, R. P.; Reimel, A. J.; Stofan, J. R. Validity and Reliability of a Field Technique for Sweat Na+and K+analysis during Exercise in a Hot-Humid Environment. Physiol. Rep. 2014, 2, e12007, DOI: 10.14814/phy2.12007
  37
  Validity and reliability of a field technique for sweat Na+ and K+ analysis during exercise in a hot-humid environment
  Baker, Lindsay B.; Ungaro, Corey T.; Barnes, Kelly A.; Nuccio, Ryan P.; Reimel, Adam J.; Stofan, John R.
  Physiological Reports (2014), 2 (5), e12007/1-e12007/11CODEN: PRHEJ2; ISSN:2051-817X. (Wiley-Blackwell)
  This study compared a field vs. ref. lab. technique for extg. (syringe vs. centrifuge) and analyzing sweat [Na+] and [K+] (compact Horiba B-722 and B-731, HORIBA vs. ion chromatog., HPLC) collected with regional absorbent patches during exercise in a hot-humid environment. Sweat samples were collected from seven anatomical sites on 30 athletes during 1-h cycling in a heat chamber (33°C, 67% rh). Ten minutes into exercise, skin was cleaned/dried and two sweat patches were applied per anatomical site. After removal, one patch per site was centrifuged and sweat was analyzed with HORIBA in the heat chamber (CENTRIFUGE HORIBA) vs. HPLC (CENTRIFUGE HPLC). Sweat from the second patch per site was extd. using a 5-mL syringe and analyzed with HORIBA in the heat chamber (SYRINGE HORIBA) vs. HPLC (SYRINGE HPLC). CENTRIFUGE HORIBA, SYRINGE HPLC, and SYRINGE HORIBA were highly related to CENTRIFUGE HPLC ([Na+]: ICC = 0.96, 0.94, and 0.93, resp.; [K+]: ICC = 0.87, 0.92, and 0.84, resp.), while mean differences from CENTRIFUGE HPLC were small but usually significant ([Na+]: 4.7 ± 7.9 mEql/L, -2.5 ± 9.3 mEq/L, 4.0 ± 10.9 mEq/L (all P < 0.001), resp.; [K+]: 0.44 ± 0.52 mEq/L (P < 0.001), 0.01 ± 0.49 mEq/L (P = 0.77), 0.50 ± 0.48 mEq/L (P < 0.001), resp.). On the basis of typical error of the measurement results, sweat [Na+] and [K+] obtained with SYRINGE HORIBA falls within ±15.4 mEq/L and ±0.68 mEq/L, resp., of CENTRIFUGE HPLC 95% of the time. The field (SYRINGE HORIBA) method of extg. and analyzing sweat from regional absorbent patches may be useful in obtaining sweat [Na+] when rapid ests. in a hot-humid field setting are needed.
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Supporting Information
Supporting Information
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- Experimental section, analytical parameters and membrane compositions, and data treatment and validation (PDF)
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Wearable Potentiometric Ion Patch for On-Body Electrolyte Monitoring in Sweat: Toward a Validation Strategy to Ensure Physiological RelevanceClick to copy article linkArticle link copied!

Analytical Chemistry

Abstract

Figure 1

Experimental Section

Fabrication of the Electrode Array

Figure 2

Implementation of the Electrodes into the Sampling Cell for On-Body Measurements

Results and Discussion

In Vitro Performance of the WPISs

Off-Site Evaluation of the WPISs Performance

Figure 3

Validation of the WPISs

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Analytical Chemistry

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Wearable Potentiometric Ion Patch for On-Body Electrolyte Monitoring in Sweat: Toward a Validation Strategy to Ensure Physiological Relevance
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