High performance GdTi_xO_y electrolyte-insulator-semiconductor pH sensor and biosensor

In this paper, we report an electrolyte-insulator-semiconductor (EIS) device incorporating Gd₂O₃ and GdTi_xO_y sensing films deposited on Si substrates through reactive radio frequency sputtering for biomedical engineering applications. We employed X-ray diffraction, X-ray photoelectron spectroscopy, and atomic force microscopy to investigate the structural and morphological features of these films with annealing at various temperatures. Compared with Gd₂O₃ sensing membrane, the EIS device featuring GdTi_xO_y sensing membrane annealed at 900 °C exhibited a higher sensitivity (64.13 mV/pH in the solutions from pH 2 to 12), a smaller hysteresis voltage (1 mV in the pH loop 7→4→7→10→7), and a lower drift rate (0.4 mV/h in the pH 7 buffer solution). This outstanding pH sensitivity may be attributed to the high surface roughness of sensing film. Finally, we successfully demonstrated the use of EIS with glucose oxidase-immobilized alginate film for the detection of glucose in serum. The concentration of serum glucose measured by a GdTi_xO_y EIS biosensor is comparable to that determined by commercial assay kit. The GdTi_xO_y glucose biosensor can detect glucose with reasonable sensitivity (8.37 mV/mM) in solutions containing glucose at concentrations in the range 0.5-6 mM; this sensitivity is adequate for general clinical examination of blood glucose.