Flexible Iridium Oxide Based pH Sensor Integrated With Inductively Coupled Wireless Transmission System for Wearable Applications

This work presents a pH sensor platform combining the high performance of iridium oxide (IrOx) fabricated by cyclic voltammetry with inductively-coupled wireless (ICW) transmission. Data included presents flexible potentiometric pH sensors having IrOx as the sensing electrode and a cured Ag/AgCl paste as the pseudo-reference electrode; further investigations concerning performance tailoring via fabrication processes are shown. The fabricated sensors show the best performance with a probe surface area of 1 × 1 mm ² , electrodeposited for 100 cyclic voltammetry (CV) sweeps, at 100 mV/s. The sensitivity of the fabricated sensor is typically in the range of 65-75 mV/pH, as tested using either pH 4-9 (six points) or 2-10 (five points) buffers. The sensors exhibiting those sensitivities in buffer solutions yielded a response from “artificial sweat” solutions differing by ~0.4-0.8 pH from a commercial glass pH electrode, while limit-of-quantification (LOQ) was measured to be ~0.04-0.08 pH. The sensing electrode shows a response time of less than 2 seconds and minimal hysteresis effects. Cationic interferences from up to 1M Na+ resulted in +3-8 mV/pH changes in sensitivity, depending on solution pH and probe, with minimal effects to LOQ. The performance under different bending conditions (0°, 30° at 55 mm radius, 45° at 37 mm, and 90° at 20 mm) of the flexible sensor probe show negligible variation. Finally, the presented sensors were integrated with an inductively coupled wireless (ICW) communication system for a demonstration of online monitoring. This sensor platform can easily be miniaturized due to a low count of necessary components and absence of onboard energy storage.