Graphene oxide as nanogold carrier for ultrasensitive electrochemical immunoassay of Shewanella oneidensis with silver enhancement strategy

•A sensitive immunosensor developed upon Ab/AuNPs/BSA/GO conjugate.•BSA-modified graphene oxide carries lots of gold nanoparticles and antibody.•Signal amplification achieved through efficient GO-carrier and gold-silver staining.•The method exhibited detection limit of 12 cfu/mL and feasibility in real sample.

The genus Shewanella is ubiquitous in environment and has been extensively studied for their applications in bioremediation. A novel immunoassay for ultrasensitive detection of Shewanella oneidensis was presented based on graphene oxide (GO) as nanogold carrier with silver enhancement strategy. The enhanced sensitivity was achieved by employing conjugate-featuring gold nanoparticles (AuNPs) and antibodies (Ab) assembled on bovine serum albumin (BSA)-modified GO (Ab/AuNPs/BSA/GO). After a sandwich-type antigen–antibody reaction, Ab/AuNPs/BSA/GO conjugate binding on the target analyte produced an enhanced immune-recognition response by the reduction of silver ion in the present of hydroquinone. The deposited silver metal was dissolved with nitric acid and subsequently quantified by anodic stripping voltammetry. The high AuNPs loading capacity of GO and the obvious signal amplification by gold-catalyzed silver deposition offer an excellent detection method with a wide range of linear relationship between 7.0×101 and 7.0×107 cfu/mL. Furthermore, the immunoassay developed in this work exhibited high sensitivity, acceptable stability and reproducibility. This simple and sensitive assay method has promising application in various fields for rapid detection of bacteria, protein and DNA.