Platinum-catalyzed hydrogen evolution reaction for sensitive electrochemical immunoassay of tetracycline residues

•A sensitive electrochemical immunoassay is developed for detection of tetracycline residues.•Platinum-catalyzed hydrogen evolution reaction is used for signal amplification.•Graphene-enriched platinum nanoparticles is used for the labeling of biomolecules.

A new signal amplification strategy for sensitive electrochemical determination of tetracycline (TC) was developed by using platinum-catalyzed hydrogen evolution reaction (HER) on an anti-TC antibody-modified immunosensor. To construct such a HER, platinum nanoparticles were initially deposited to graphene nanosheets, and the as-synthesized platinum/graphene nanosheets (PtGN) were then used for the labeling of tetracycline-bovine serum albumin conjugates (TC–BSA). With a competitive immunoassay format, the resulting immunosensor was immersed into a platinum developer solution containing 1.0 mM PtCl42-, 0.1 M formate (reductant) and 0.5% Tween 80 (pH 6.5) to promote the platinum growth. The amplified electrochemical signal mainly derived from the platinum-catalyzed HER in an acidic medium containing 10 mM HCl and 1.0 M KCl. Two labeling methods and assay protocols including Pt-labeled TC–BSA and PtGN-labeled TC–BSA with or without the platinum enhancement were investigated for determination of target TC, respectively, and improved analytical features were obtained with graphene nanosheets and platinum growth mechanism. With PtGN-labeled TC–BSA, the effects of incubation time for antigen–antibody reaction and deposition time of platinum on the currents of the immunosensors were also studied. The strong attachment of TC–BSA to the PtGN resulted in a good repeatability and intermediate precision down to 9.8%. The dynamic concentration range spanned from 0.05 ng/mL to 100 ng/mL tetracycline with a low detection limit of 6 pg/mL at the 3sblank level. In addition, the methodology was further validated with tetracycline spiked samples including honey, milk and peanut, and the recoveries were 86–118%.