Patent ID: 7642064

Claim:
A method of detecting and quantifying an analyte of interest from a biological sample in an enzyme immunoassay (EIA), comprising the steps of: (a) contacting said biological sample with a primary antibody immobilized on a solid support, such that a primary antibody-analyte complex will form when analyte is present in the biological sample; (b) contacting said complex formed in step (a) with a secondary antibody conjugated to a label enzyme selected from the group consisting of alkaline phosphatase, acid phosphatase, alpha- and beta-galactosidases, and esterases, such that a primary antibody-analyte-secondary antibody complex will form when analyte is present in the biological sample; (c) contacting said primary antibody-analyte-secondary antibody complex formed in step (b) with a redox inactive reductive species in the presence of metal ion, wherein said redox inactive reductive species is a substrate for said label enzyme, and wherein said label enzyme converts said redox inactive reductive species to a redox active reductive species that reduces said metal ion such that a metal precipitate will form on the solid support following reduction of said metal ion; (d) enhancing said metal precipitate; and (e) detecting and quantifying the analyte in the biological sample by quantifying the metal precipitate formed on the solid support.