Preparation of a Highly Conductive Seed Layer for Calcium Sensor Fabrication with Enhanced Sensing Performance

The seed layer plays a crucial role in achieving high electrical conductivity and ensuring higher performance of devices. In this study, we report fabrication of a solution-gated field-effect transistor (FET) sensor based on zinc oxide nanorods (ZnO NRs) modified iron oxide nanoparticles (α-Fe 2 O 3 NPs) grown on a highly conductive sandwich-like seed layer (ZnO seed layer/Ag nanowires/ZnO seed layer). The sandwich-like seed layer and ZnO NRs modification with α-Fe 2 O 3 NPs provide excellent conductivity and prevent possible ZnO NRs surface damage from low pH enzyme immobilization, respectively. The highly conductive solution-gated FET sensor employed the calmodulin (CaM) immobilization on the surface of α-Fe 2 O 3 -ZnO NRs for selective detection of calcium ions (Ca 2+ ). The solution-gated FET sensor exhibited a substantial change in conductance upon introduction of different concentrations of Ca 2+ and showed high sensitivity (416.8 μA cm -2 mM -1 ) and wide linear range (0.01-3.0 mM). In addition, the total Ca 2+ concentration in water and serum samples was also measured. Compared to the analytically obtained data, our sensor was found to measure Ca 2+ in the water and serum samples accurately, suggesting a potential alternative for Ca 2+ determination in water and serum samples, specifically used for drinking/irrigation and clinical analysis.