IonSens: A Wearable Potentiometric Sensor Patch for Monitoring Total Ion Content in Sweat

A sensor for monitoring total ion activity is described, and its performance as a wearable device for monitoring the total ion levels of sweat is evaluated. The sensor works by tracking changes in the Donnan potential generated across a Nafion (R) membrane. This cation-exchange polymer was cast on a paper coated with carbon-ink, making the platform elegantly simple. Analytical parameters during calibration in aqueous solution include a sensitivity of 56.3 +/- 1.0mV/dec.a((Na+)) and a standard deviation between standard electrode potentials of 5.3mV (N=5) for first time use. By integrating a paper-based pseudo-reference electrode, a miniature disposable electrochemical cell (the IonSens device) was created and demonstrated as a wearable sensor. Potentiometric measurements estimating the total ion activities were validated against conductivity measurements. Recoveries of eleven raw sweat samples were determined to be 95.2 +/- 6.6% (n=3). The perspiration conductivity profile of an athlete during exercise was monitored in real-time and visualized on a mobile phone application connected via Bluetooth (R). The excellent reproducibility of the electrode without any conditioning is noteworthy and lends itself to applications including - but not limited to - the monitoring of total ion activity in sweat.