Protein conjugated carboxylated gold@reduced graphene oxide for aflatoxin B₁ detection

A sensitive, reproducible, stable and label-free immunosensor has been prepared via simultaneous reduction of graphene oxide and gold(III) salt using an eco-friendly and non-toxic reducing agent sodium citrate resulting in uniformly distributed gold nanoparticles on reduced graphene oxide (rGO) sheets. The in situ grown gold@carboxylated reduced graphene oxide (Au@rGO) surface has been used for bioconjugation with monoclonal antibodies of aflatoxin B₁ using EDC-NHS chemistry. The in situ growth of AuNPs (gold nanoparticles) onto the rGO sheet results in improved electrocatalytic activity and loading of the antibodies due to the enhanced surface area. The monodispersion of the Au nanoparticles on the rGO sheets yields heterogeneous electron transfer (2.85 × 10^-4 cm s^-1) resulting in improved biosensor efficacy compared to that based on the rGO electrode. This immunosensor is sensitive to detect as low as 0.1 ng mL^-1 concentration of aflatoxin compared to the reported ELISA (enzyme-linked immunosorbent assay) standard method. The Au@rGO based immunosensor exhibits high sensitivity (182.4 μA (ng mL^-1)^-1 cm^-2) in a wide linear detection range of 0.1-12 ng mL^-1. Results of the studies related to this immunosensor reveal that the Au@rGO nanocomposite is a suitable platform for the development of a compact biosensing device for food toxin monitoring.