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 x 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 similar to 0.4-0.8 pH from a commercial glass pH electrode, while limit-of-quantification (LOQ) was measured to be similar to 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 degrees, 30 degrees at 55 mm radius, 45 degrees at 37 mm, and 90 degrees 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.