pH-sensitive solid-state electrode based on electrodeposited nanoporous platinum

The nanoporous platinum oxide ([H.sub.1]-ePtO) as a hydrogen ion-selective sensing material is reported. Bare nanoporous platinum oxides exhibit near-Nernstian behavior (e.g., -55 mV/pH in PBS), ignorable hysteresis, a short response time, and high precision, which are remarkably better than those of flat platinum oxides. The electrode potential of a nanoporous platinum oxide responds exclusively to hydrogen ion, which implies its usefulness as a solid-state pH sensor. In the present study, the performance of nanoporous platinum oxide was investigated and compared with that of Ir[O.sub.x] in terms of selectivity and the influences of ionic strength, temperature, complexing ligands, and surfactants. HrePtO functions well as a pH-sensing solid-state material, and it is viewed as a promising alternative to Ir[O.sub.x]. Interference by redox couples was successfully suppressed by covering the [H.sub.1]-ePtO surface with a protective layer, e.g., an electropolymerized polyphenol thin film. Since the nanoporous platinum oxide with such a protective layer is particularly suitable for miniaturization and micropatterning, our findings suggest its usefulness in applications such as solid-state pH sensors embedded in chip-based microanalysis systems.