Polarographic immunoassay coupled with catalytic amplification of labeled copper ions
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A new approach of polarographic immunoassay based on the catalytic amplification of the labeled metal ions and the polarographic detection of the catalytic product was developed. In this approach, the copper ions used as the catalyst for substrate conversion instead of natural enzyme were labeled to model antigen diphtheria toxoid (DT) through the bifunctional chelating reagent diethylenetriamine pentaacetic acid (DTPA). After heterogeneous competitive immunoreaction, the oxidation of substrate o-phenylenediamine (OPD) was catalyzed by the labeled copper ions to generate an electroactive product 2. 3-diaminophenazine (DAP); subsequently, the product DAP was detected with linear-sweep polarography. The proposed assay can determine the concentration in the range of 10–1000 ng/mL of DT, two orders of magnitude more sensitive than those based on the direct detection of the metal ion labels. The proposed immunoassay can be applied to detecting various proteins of interest.
Keywordsdiphtheria toxoid (DT) copper catalytic amplification immunoassay linear-sweep polarography
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