Super-Nernstian sensitivity in microfabricated electrochemical pH sensor based on CeTi_xO_y film for biofluid monitoring

In this paper, we proposed a microfabricated electrolyte–insulator–semiconductor (EIS) sensor based on CeTi_xO_y sensing membrane for pH detection in biofluid. Structural and morphological behaviors of the sensing films at different fabrication temperatures were investigated by X-ray diffraction, atomic force microscopy, high-resolution transmission electron microscopy, electron energy loss spectroscopy, and X-ray photoelectron spectroscopy. The EIS sensor fabricated with the CeTi_xO_y sensing membrane annealed at 800 °C exhibited a super-Nernstian pH sensitivity of 89.81 mV/pH (in the range pH ∼ 2 to 12) with a smaller hysteresis voltage of 1 mV and a lower drift rate of 0.34 mV/h at standard buffer solution of pH = 7. This result is attributed to the ion exchanges in the surface layer of electrode membrane containing OH⁻ groups and redox transition between two oxidation states of Ce(III) oxide and Ce(IV) oxide.