Precision pH Sensor Based on WO3 Nanofiber-Polymer Composites and Differential Amplification

Abstract

We report a new type of potentiometric pH sensor with sensitivity exceeding the theoretical Nernstian behavior (-59.1 mV/pH). For the pH-sensitive electrode, ID tungsten oxide (WO3) nanofibers (NFs) were prepared to obtain large surface area and high porosity. These NFs were then stabilized in a reactive porous chloromethylated triptycene poly(ether sulfone) (Cl-TPES) binder, to facilitate proton diffusion into the polymer membrane. The measurements were performed with a differential amplifier using matched MOSFETs and providing a 10-fold amplified signal over a simple potentiometric determination. A high pH sensitivity of -377.5 mV/pH and a linearity of 0.9847 were achieved over the pH range of 6.90-8.94. Improved signal-to-noise ratios with large EMF signal changes of 175 mV were obtained in artificial seawater ranging pH 8.07-7.64 (Delta pH = 0.43), which demonstrates a practical application for pH monitoring in ocean environments.