Batch Fabrication of Microminiaturized pH Sensor Integrated With IrO x Film and Solid State Ag/AgCl Electrode for Tap Water Quality Online Detection

Abstract

Considering the indispensable of pH for tap water, a pH sensor with the characteristics of an implantable, long-term stable, and long lifetime is urgently needed for on-line and in situ pH monitoring in tap water, but this is always a challenging issue. In this article, a competitive integrated electrochemical pH sensor is developed and batch manufactured via micro-electro-mechanical system (MEMS). A dense and ultrasensitive IrOx electrode is obtained for almost 1.5 times Nernst response (−82.88 mV/pH), after preparation process optimization. A Si-Si3N4-KCl agar gel-polydimethylsiloxane (PDMS) multilayer structured Ag/AgCl electrode is designed and proven to be a long lifetime (>40 days) and be stable. By integrating with the IrOx film and solid-state Ag/AgCl electrode on a mini chip and verifying the effectiveness of the as-fabricated sensor by pH detection, the miniature pH sensor demonstrates wide detection range (1.8–12), stirring sensitivity, desirable linearity ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}^{2}=0.999$ </tex-math></inline-formula> ), ideal repeatability and good resistance to other interference substances. Particularly, by employing the mass-production technique, favorable response consistency (relative standard deviation (RSD) < 2%) is witnessed, offering the opportunity to mass-produce the proposed sensor in the future. What’s more, the sensor still kept 91.7% sensitivity when compared to the sensitivity obtained at its initial state, after continuously operating for 32 days. Undoubtedly, the sensitive, durable, miniaturized, and mass-produced pH sensor proposed in this article is a competitive device to implant into the water pipeline for pH in situ online monitoring.