A sensitive electrochemical immunosensor for alpha-fetoprotein based on covalently incorporating a bio-recognition element onto a graphene modified electrode via diazonium chemistry

Abstract

Detection and accurate quantification of biomarkers are key aspects of early stage cancer diagnosis. An electrochemical sandwich immunosensor for sensitive detection of cancer biomarkers was developed by using graphene as the sensing platform and diazonium chemistry as the immobilization method. The glassy carbon electrode was first modified with graphene and the resulting graphene modified electrode offered an excellent platform for high performance biosensing applications. The immunosensor was fabricated by covalently coupling the capture antibody onto the surface of the graphene modified electrode, which was first electrochemically grafted with an aminophenyl group by reduction of the in situ generated aminophenyl diazonium cation generated from p-phenylenediamine, using glutaraldehyde as the cross-linker. A sandwich immunoassay for alpha-fetoprotein (AFP), a biomarker of liver cancer that was used as a model, was developed using the horseradish peroxidase-conjugated anti-AFP antibody as the electrochemical probe. The electrochemical immunosensor exhibited high sensitivity and specificity for the detection of AFP. A linear relationship between electrochemical signals and the concentrations of AFP was obtained in the range from 0.1 ng mL−1 to 2 ng mL−1. The detection limit of AFP was 0.03 ng mL−1 (S/N = 3). This work demonstrates that the employment of graphene as a novel sensing platform and diazonium chemistry as an immobilization method is a promising approach to a stable and sensitive determination of biomolecules and will be promising in the point-of-care diagnostics application of clinical screening of cancer biomarkers.