Electrochemical impedance characterization of antibody–antigen interaction with signal amplification based on polypyrrole–streptavidin

Streptavidin, as a dopant, has been incorporated into a polypyrrole film to bind biotinylated antibody onto the electrode surface. With four biotin binding sites, the incorporation of streptavdin, as confirmed by FTIR and impedance spectroscopy, provided a new method to amplify the response signal from antibody–antigen interaction. Biotinylated anti-goat IgG, as a probe, and goat IgG, as a target, were employed to evaluate the characteristics of the biosensor. With the amplification strategy, the detection sensitivity of the electrochemical impedance spectroscopy was significantly improved. A linear relationship between the charge transfer resistance change (ΔRt) and the concentration of goat IgG ranging from 10 pg/ml to100 ng/ml was obtained.