ZnO-Based Chemiresistive Ion Sensors for Identifying Alkali Metal and Alkaline Earth Metal Ions in Solutions

Metal-oxide-semiconductor-based chemiresistive ion sensors are promising for daily health monitoring applications. This study demonstrates zinc oxide (ZnO)-based chemiresistive sensors for detecting and identifying ions in solutions. Sensors based on nanoporous ZnO, both without and with NiO particles, exhibited distinct ion sensing performances for potassium, sodium, and calcium ions in solutions at 30 °C. These performances depend on the ion species and concentrations and the presence of NiO particles. Under dc bias, the percentage response changes to 100 ppm calcium ions were +518 and −193% for the ZnO and ZnO/NiO sensors, respectively. Under ac bias, the ZnO sensor showed the smallest response change (−26.1%) to 100 ppm potassium ions, whereas the ZnO/NiO sensor exhibited its most significant response change (−49.6%) to 100 ppm calcium ions. Principal component analysis, using these sensing parameters, demonstrated the possibility of differentiating and identifying each ion species.