Amplified inhibition of the electrochemical signal of graphene–thionine nanocomposites using silica nanoprobes for ultrasensitive electrochemical immunoassays

Abstract

An ultrasensitive immunoassay method was developed based on the amplified inhibition of the electrochemical signal of graphene–thionine nanocomposites. The graphene–thionine nanocomposite was prepared by one-step reduction of graphene oxide in thionine solution and used to modify a glassy carbon electrode. The immunosensor was prepared by stepwise assembly of gold nanoparticles (Au NPs) and a capture antibody at this nanocomposite modified electrode. The thionine on the immunosensor surface exhibited a good electrochemical signal which was further promoted by the presence of Au NPs. After a sandwich immunoreaction, the current response of the immunosensor decreased due to the formation of a dielectric antibody–antigen immunocomplex on its surface. This current decrease could be further amplified by the captured antibody conjugated silica nanosphere with low electric conductivity. Based on this amplified signal inhibition mechanism, a novel detection strategy for the ultrasensitive electrochemical immunoassay was developed. Using human IgG as a model protein, a wide linear range in four orders of magnitude and a low detection limit down to 7 pg mL⁻¹ were achieved. In addition, the immunosensor has low cost, satisfactory reproducibility and stability, and acceptable reliability, thus providing promising potential for clinical applications.