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

Abstract

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.

Why ammonium detection is particularly challenging but insightful with ionophore-based potentiometric sensors – an overview of the progress in the last 20 years

“…In particular, in the case of NH 4 + , four H-bonds are formed between the cation and four ether oxygens of nonactin ( Fig. 1b), as demonstrated by 13 C NMR, IR, and crystallography studies. 28,29 This is the primary difference between NH 4 + and K + binding with nonactin, thereby yielding a slightly higher preference toward NH 4 + as compared to that toward K + , regardless of the plausibility of the described H-bonds in the complex medium/ environment.…”

“…[1][2][3][4][5] Major examples that evidence the success of ISEs are the membrane-based design of a sensor and have been applied for ion determination mainly in water quality assessment, 1,6,7 clinical analyses, [8][9][10][11] and monitoring of sport practices. 2,[12][13][14] Looking back at the development history of ISEs, the integration of ion-selective membranes (ISMs) as the sensing element has undoubtedly been a disruptive event in this field. 15 Today, the technology involving ISM fabrication is well entrenched and the criteria for selecting components/ materials as well as the necessary features have been known for decades.…”

Solid-Contact Ion-Selective Electrodes: Response Mechanisms, Transducer Materials and Wearable Sensors

“…In addition, evaluation of the redox or EDL-capacitance of the SC materials should provide the specific capacitance for comparison. For the wearable sensors, a standard measure protocol should be also presented as soon as possible including calibration and data validity [83]. (2) In addition to the WE of SC-ISEs, the RE should be given more attention.…”

“…The real-time on-body monitoring results showed 90% accuracy compared with results verified by ex-situ analysis. Crespo et al fabricated a four-channel wearable SC-ISEs by using MWCNT as the ion-to-electron transducer [83] ( Figure 9E). In this work, importantly, the authors proposed a protocol for the on-body sweat analysis to assure the data validation.…”

“…It should be noted that the importance of calibration of SC-ISEs to assure the accuracy of real-time analysis. Reprinted with permission from [83], Copyright (2019) American Chemical Society.…”