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

Seed layer plays a crucial role to achieve high electrical conductivity and ensure higher performance of the 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-Fe2O3 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-Fe2O3 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-Fe2O3-ZnO NRs for selective detection of calcium ions (Ca2+). The solution-gated FET sensor exhibited a substantial change in conductance upon introduction of different concentrations of Ca2+ and showed high sensitivity (416.8 µA cm-2 mM-1) and wide linear range (0.01-3.0 mM). As well, the total Ca2+ concentration in water and serum samples were also measured. Compared to the analytically obtained data, our sensor was found to measure Ca2+ in the water and serum samples accurately, suggesting a potential alternative for Ca2+ determination in water and serum samples, specifically used for drinking/irrigation and clinical analysis.