Preparation of TiO₂ nanowire arrays through hydrothermal growth method and their pH sensing characteristics

The use of a TiO₂ nanowire (NW) hydrothermally grown on an fluorine-doped tin oxide (FTO) substrate as a separated sensing electrode of an extended-gate field-effect-transistor (SE-EGFET) pH sensor is demonstrated. Sensing responses to the prepared samples in a wide pH range (2-12) are presented and compared with responses of a film-type TiO₂ electrode. The pH sensors with the NW-type and film-type electrodes show a sensitivity of 62 and 50mV/pH, respectively, and a comparably good linearity in the pH range of 2-12. The superiority of the NW-type TiO2 electrode (24% improvement in sensitivity compared with that of the film-type electrode) is attributed mainly to the higher surface-to-volume (SV) ratio and higher conductivity of the hydrogen thermal growth (HTG) nanowires.