Enhanced pH Sensing Capability by Platinum Adsorption Onto Titanium Dioxide Nanorods

Titanium dioxide (TiO2) and Pt/TiO2 nanorods are fabricated on fluorine-doped tin oxide (FTO) glass substrates using hydrothermal methods and sputter coating. These materials serve as the sensing films for pH sensors that operate based on an extended-gate field-effect transistor (EGFET). The sensors measure the potential difference between the sensing film and an Ag/AgCl reference electrode across various pH buffer solutions. The {I}_{\text {DS}} - {V}_{\text {G}} curves indicate that the reference voltage ( {V}_{\text {ref}} ) increases with pH. The voltage sensitivity and linearity, determined through linear fitting with the I_{\text {DS}} fixed at 1 mA, are 28.5 mV/pH and 0.947 for TiO2 nanorods, respectively. These values increase to 50 mV/pH and 0.991 with the addition of Pt on TiO2. Current sensitivity, a crucial metric for sensor quality, is evaluated in the saturation region ( {I}_{\text {DS}} - {V}_{\text {DS}} curves) at a fixed saturation voltage of 3 V. As pH increases, {I}_{\text {DS}} decreases, with current sensitivity for TiO2 nanorods at 38.3~\mu A/pH and linearity at 0.921. This sensitivity enhances to 63.8~\mu A/pH with the linearity of 0.988 when Pt is added to TiO2. Hysteresis and stability tests demonstrate that Pt/TiO2 nanorods maintain a broad sensing range (pH 3-11) and exhibit superior stability. The increased sensitivity of the EGFET with Pt/TiO2 coating compared to TiO2 can be attributed to higher surface site density, improved ion detection, enhanced conductivity, better carrier transport, and greater surface roughness, all of which enhance reactivity and boost voltage and current sensitivities. Consequently, Pt/TiO2 nanorods are exceptionally suitable for biomedical applications and pH sensing.