Development of impedimetric and optical calcium biosensor by using modified gold electrode with porcine S100A12 protein

We describe the development of a label free method to analyze the interactions between Ca2+ and the porcine S100A12 protein immobilized on polyvinyl butyral (PVB). The modified gold electrodes were characterized using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and surface plasmon resonance (SPR) techniques. SEM analyses of PVB and PVB-S100A12 showed a heterogeneous distribution of PVB spherules on gold surface. EIS and CV measurements have shown that redox probe reactions on the modified gold electrodes were partially blocked due the adsorption of PVB-S100A12, and confirm the existence of a positive response of the immobilized S100A12 to the presence of calcium ions. The biosensor exhibited a wide linear response to Ca2+ concentrations ranging from 12.5 to 200 mM. The PVB-S100A12 seems to be bound to the gold electrode surface by physical adsorption; we observed an increase of 1184.32 m° in the SPR angle after the adsorption of the protein on the PVB surface (in an indication that 9.84 ng of S100A12 are adsorbed per mm2 of the Au-PVB electrode), followed by a further increase of 581.66 m° after attachment of the Ca2+ ions. In addition, no SPR response is obtained for non-specific ions. These studies might be useful as a platform for the design of new reusable and sensitive biosensing devices that could find use in the clinical applications.