Electrochemical immunosensor for casein based on gold nanoparticles and poly(l-Arginine)/multi-walled carbon nanotubes composite film functionalized interface

In this paper, a novel electrochemical immunosensor for the determination of casein based on gold nanoparticles and poly(l-Arginine)/multi-walled carbon nanotubes (P-l-Arg/MWCNTs) composite film was proposed. The P-l-Arg/MWCNTs composite film was used to modify glassy carbon electrode (GCE) to fabricate P-l-Arg/MWCNTs/GCE through electropolymerization of l-Arginine on MWCNTs/GCE. Gold nanoparticles were adsorbed on the modified electrode to immobilize the casein antibody and to construct the immunosensor. The stepwise assembly process of the immunosensor was characterized by cyclic voltammetry and differential pulse voltammetry. Results demonstrated that the peak currents of [Fe(CN)6]3−/4− redox pair decreased due to the formation of antibody–antigen complex on the modified electrode. The optimization of the adsorption time of gold nanoparticles, the pH of supporting electrolyte and the incubation time were investigated in details. Under optimal conditions, the peak currents obtained by DPV decreased linearly with the increasing casein concentrations in the range from 1 × 10−7 to 1 × 10−5 g mL−1 with a linear coefficiency of 0.993. This electrochemical immunoassay has a low detection limit of 5 × 10−8 g mL−1 and was successfully applied to the determination of casein in cheese samples.