A precise pH microsensor using RF-sputtering IrO2 and Ta2O5 films on Pt-electrode

In this study, an easily implemented surface modification scheme is reported employing Ta2O5 membrane which covers IrO2 electrode in response to H+ and eliminating redox species interference. Evidence shows that H+ can pass through Ta2O5 films and react with IrO2/Pt electrodes due to proton–electron double injection. A Ta2O5 membrane, an ionic conductor with an insulating property, blocks the transport of electrons generated from oxygen perturbation in the solution. The conduction of both electrons and protons preserve the current continuity across the interface. Owing to proton–electron double injection, IrO2 will be reduced to Ir(OH)3 during pH detection. The [IrO2]/[Ir(OH)3] will remain constant and therefore the Nernstian electrode potential performs stably as a function of pH (−59.447 to −59.504 mV/pH, 2 < pH <13). In addition, the proposed pH microsensor displayed high ion selectivity with respect to K+, Na+, and Li+, with log KH,M values (∼−12.4) and has a working lifetime over one week.