A flexible pH sensor based on the iridium oxide sensing film

We have developed a novel flexible pH sensor based on a polymeric substrate by low-cost sol–gel fabrication process of iridium oxide (IrOx) sensing film. A pair of miniature IrOx/AgCl electrodes on a flexible substrate generated electrical potentials in solutions by electrochemical mechanisms responding to their pH levels. Our flexible IrOx pH sensors exhibited promising sensing performance with a near-Nernstian response in sensitivity repeatedly and reversibly between −51.1 mV/pH and −51.7 mV/pH in the pH range between 1.5 and 12 at 25 °C. The fabrication processes including sol–gel deposition, thermal oxidation, and AgCl electro-plating on polymeric substrates were reported. The performance and characterization of the flexible pH sensors in sensitivity, response time, stability, reversibility, repeatability and selectivity were also discussed. Our IrOx pH electrodes on a deformable substrate demonstrated their sensing capability while they were conformed to a curved surface inside a limited space with distinct responding potentials at various pH levels similar to the traditional glass-rod pH electrodes.