A flexible pH sensor based on the iridium oxide sensing film

• Published in: Sensors and actuators. A. Physical. Vol. 169; no. 1; pp. 1 - 11
• Main Authors: Huang, Wen-Ding, Cao, Hung, Deb, Sanchali, Chiao, Mu, Chiao, J.C.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 10.09.2011
• Subjects: Deformable sensors; Detection; Electric potential; electrochemistry; Electrodes; Iridium; Iridium oxide; Miniature pH sensor array; oxidation; Oxides; Polyimide flexible substrate; Sensors; silver chloride; Sol gel process; Miniature pH sensor array; Iridium oxide; Deformable sensors; Sol–gel process; Polyimide flexible substrate
• ISSN: 0924-4247; 1873-3069
• DOI: 10.1016/j.sna.2011.05.016

We have developed a novel flexible pH sensor based on a polymeric substrate by low-cost sol–gel fabrication process of iridium oxide (IrO x ) sensing film. A pair of miniature IrO x /AgCl electrodes on a flexible substrate generated electrical potentials in solutions by electrochemical mechanisms responding to their pH levels. Our flexible IrO x 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 IrO x 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.