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

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.