A novel sensitive electrochemical immunoassay method was proposed base on gold nanoparticle mediated biocatalytic deposition of platinum followed by stripping voltammetric determination. The feasibility of the approach was investigated using a “sandwich” immunoassay format with human immunoglobulin G (HIgG) as the analyte. HIgG was firstly captured by primary goat anti-HIgG polyclonal antibody (HIgG Ab) immobilized on polystyrene microwells. Gold nanopartcile-labeled alkaline phosphatase (ALP)-HIgG Ab was then bound to the microwells through sandwiched HIgG. The surface-bound alkaline phosphate catalyzed the generation of ascorbic acid, which, in turn, reduced platinum ions into its metal form in the presence of gold nanoparticles. The depositedmetal was released in aqua regia (three parts HCl, one part HNO3), and reduced on glassy-carbon electrode, which generated a significant cathodic current due to the platinum-catalyzed hydrogen evolution. The cathodic current was observed to show linear correlation to logarithmic HIgG concentration over the range from 0.1ng/ml to 100ng/ml with a detection limit as low as 22 pg/ml. The high performance of the method is attributed to the sensitive determination of platinum and the catalytic precipitation-based amplification mediated by gold nanopartcile-labeled ALP-HIgG Ab.

Key words: biocatalytic deposition, gold Nanopartice, electrochemical immunoassay, catalytic hydrogen electrochemical determination