Electrochemical immunoassay based on catalytic conversion of substrate by labeled metal ion and polarographic detection of the product generated.

In a new electrochemical immunoassay based on the conversion of a substrate catalyzed by a labeled metal ion and the polarographic detection of the product generated, metal copper ion was used to label model antigen human serum albumin through the bifunctional chelating agent diethylenetriaminepentaacetic acid. After heterogeneous competitive immunoreaction, the labeled copper ion was released or activated by acidification and chemically catalyzed the conversion of the substrate o-phenylenediamine to the electroactive product 2,3-diaminophenazine (DAP). The DAP was quantified using linear-potential scan polarography. The sensitivity of the proposed assay was 100 times higher than that of the previous methods based on direct detection of the metal ion labels. This immunoassay can be used to detect any protein of interest.