Metal oxide sensors for long term pH monitoring

The determination of pH, a measure of concentration of hydrogen ions in a solution, is an important task in analytical chemistry since various biological and chemical reaction mechanisms are pH dependent. While the conventional glass type electrodes are widely used for their high accuracy; they are not amenable to miniaturization, and suffer from sluggish response [1], [2], [3]. Various solid-state metal oxide pH sensing electrodes, chiefly iridium oxide and ruthenium oxide (RuOx), have been investigated as an alternate. RuOx exhibits several unique advantages over other metal oxides such as thermal stability, excellent corrosion resistance, low hysteresis, low cost and high sensitivity [4]. In this work, we developed and investigated the long-term performance of the RuOx films on platinum electrode. The sensors exhibited near-Nernstian response at 55 mV/pH and long-term stability of over 4 weeks