Zinc Magnesium Oxide-Based Nanorods for High-Precision pH Sensing

We developed a zinc magnesium oxide-based nanosensor platform for pH sensing. pH is a parameter strongly influential in various chemical, biological, and biomedical applications. Oxide-based semiconductors are preferred as pH sensing materials because of their robustness, size modulation, high sensitivity, cost effectiveness, reversibility of the sensing process, and long lifetime. Vertical nanorods of zinc magnesium oxide were fabricated for the nanosensor platform. Their high crystalline quality was confirmed through various structural characterization techniques such as high-resolution X-ray diffraction and scanning and transmission electron microscopy. Absorption spectroscopy revealed a bandgap of 3.56 eV corresponding to 12% magnesium. pH dependent photoluminescence (PL) measurements showed a shift in the visible range spectrum with decrease in PL intensity. The developed sensor showed high sensitivity of 44.4 ± 3.8 mV/pH, close to the theoretical value, in the 2.4-10 pH range. AC- and DC-based current measurements were performed to study the sensing mechanism. Conductance-based pH measurement, a unique and precise technique, yielded a high sensitivity of 4.59 mS/pH. The proposed nanosensors, which are low cost and easy to fabricate and use, exhibited rapid response, long-term stability, high sensitivity (in both potentiometric as well as conductance-based measurements), and high repeatability.