Electrochemical investigation on calcium ion sensing and steady-state diffusion analysis using zinc oxide modified glassy carbon electrode

The concentration of calcium ions in human blood serum typically falls within a narrow range of 2 and 2.5 mmol/L. However, hyperthyroidism, resulting from an overactive parathyroid gland, can lead to an elevation of calcium ion concentration beyond 2.5 mmol/L, necessitating the development of a highly sensitive and selective electrochemical sensor for calcium ion detection. To address this issue, a highly sensitive and selective electrochemical sensor based on zinc oxide nanoparticles-chitosan composite modified glassy carbon electrode (GC/ZnO-Chitosan) was fabricated for the detection of calcium ions. Cyclic voltammetric analysis revealed that the fabricated electrode possesses excellent electrocatalytic activity for calcium ion oxidation and reduction. The fabricated electrode showed high sensitivity (449.887 µA mM−1) towards calcium ions over the wide detection range of 2.14–3.5 mM with a low detection limit of 2.26 µM, and a low quantification limit of 7.45 µM. Moreover, the fabricated electrode showed fast response time (<25 s) due to the synergistic effect of enhanced adsorption of calcium ions (Γ=2.17×10-7 mol cm−2), efficient electron shuttling capacity of ZnO nanoparticles between GCE (ks=6.01 s−1) and the adsorbed calcium ions, and enhanced diffusion of calcium ions (DCa2+=1.2788×10-6cm2s-1) within the ZnO-Chitosan composite film. Genocchi polynomial approximation method was employed for the establishment of a precise mathematical relationship between the steady-state concentration of calcium ions and the distance from the electrode's surface. This newly developed GC/ZnO-Chitosan electrode presents a significant improvement over previously developed electrodes for calcium ions, as it enables the precise analysis of calcium ion diffusion profiles at steady-state.