An enzymatic amplification cycle for high sensitive immunoassay

An amplification cycle consisting of oligosaccharide dehydrogenase (ODH) and laccase is found to be highly sensitive to several catecholamines and p-aminophenol. An immunoassay is constructed by combining this amplification cycle with a suitable enzyme label, of which p-aminophenol is the product of the enzymatic reaction. Alkaline phosphatase and beta-galactosidase were tested as labels for immunoglobulin G from goat (gtIgG) and human thyroid stimulating hormone (hTSH) immunoassay. The combination of enzymatic amplification cycles with a sandwich type immunoassay yields high sensitivity measurement of hTSH. The assay was found to have two linear ranges: the first one is between 0.2 and 20 ng/ml, the second one from 0.0005 to 0.5 ng/ml, depending on assay procedure. Both together cover well the diagnostically relevant range of 0.1-100 mU/l (0.017-17 ng/ml); the detection limit is at 0.3 pg/ml (1.8 mu U/l).