Magnesium-doped ZnO nanorod electrolyte–insulator–semiconductor (EIS) sensor for detecting calcium ions

Electrolyte-Membrane-Insulator-Semiconductor (EMIS) sensors based on ZnO undoped and doped with a different molar ratio of Mg/Zn are demonstrated to detect calcium ions. The samples grown on the silicon substrates by the hydrothermal method were characterized to explore the impact of Mg content on the structural and compositional characteristics and sensing performance by X-ray diffraction analysis, field emission scanning electron microscopy, and X-ray photoelectron spectroscopy. The results indicated that the EIMS based on ZnO nanorods doped with 3% Mg had a high Ca2+ ion sensitivity (69 mV/decade) and linearity (99.8%). In addition, the samples have good stability with a low drift rate of 0.398 mV/h and possess great selectivity over other interference ions such as Na+, K+, Mg2+, and Ni2+ due to the employment of an ionophore membrane.