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

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 3s _blank level. In addition, the methodology was further validated with tetracycline spiked samples including honey, milk and peanut, and the recoveries were 86-118%.