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

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.