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, 1D 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 (ΔpH = 0.43), which demonstrates a practical application for pH monitoring in ocean environments.
Choi S.-J., Savagatrup S., Kim Y., Lang J. H. & Swager T. M., in press. Precision pH sensor based on WO3 nanofiber-polymer composites and differential amplification. American Chemical Society: Sensors. Article (subscription required).
