Graphene/quantum dot bionanoconjugates as signal amplifiers in stripping voltammetric detection of EpCAM biomarkers

A sensitive electrochemical immunosensor for the detection of epithelial cell adhesion molecule (EpCAM) antigen, a common marker for tumors of epithelial origin, employing bionanoconjugates as signal-transduction labels has been developed. The bionanoconjugates were fabricated by carboxylation of the two-dimensional graphene oxide nanosheets (GRs) and immobilizing streptavidin and amine-functionalized CdSe quantum dots (QDs) on carboxylated GRs via carbodiimide coupling chemistry, followed by the immunoreaction with the biotinylated secondary antibodies. Since carboxylated GRs have a higher density of active sites, it allows a large number of CdSe QDs to be immobilized onto the surface of the bionanoconjugates, and hence, enhance the sensitivity of the immunosensor. The method enabled detection limits of 100 fg/mL and 1 pg/mL (based on the S/N = 3) in PBS buffer and serum samples, respectively, using anodic stripping voltammetric readout. The immunosensor showed a good selectivity, reproducibility, and long-storage stability, and may become a promising technique for the early detection of tumor biomarker in clinical/biological samples.

► A simple signal amplification route has been developed for sensitive electrochemical detection of EpCAM antigens.
► A ‘bionanoconjugate’ comprised of graphene oxide nanosheets decorated with CdSe QDs and specific antibodies used as an electrochemical signal amplifier.
► High density of active sites on the carboxylated graphene oxide nanosheets allows higher number of immobilized CdSe QDs and antibodies onto it.
► The use of bionanoconjugate allows a single EpCAM antibody-antigen binding event gives rise to a “burst” of cadmium ions.