title: Enzyme amplification for immunoassays. Detection limit of one hundredth of an attomole.
abstract: A method is described for increasing the response of enzyme immunoassays employing alkaline phosphatase as the label initiating 2 sequential catalytic reactions. First, NADP is dephosphorylated to produce NAD, which catalytically activates a specific redox-cycle involving the enzymes alcohol dehydrogenase and diaphorase. During each turn of the cycle 1 molecule of a tetrazolium salt is reduced to an intensely coloured formazan. The method is capable of detecting as little as 0.01 amol alkaline phosphatase, and when applied to an immunoassay for TSH a sensitivity (zero + 2.5 standard deviations) of 0.0013 mIU/l was obtained.
mesh_terms: D000469:Alkaline Phosphatase / Q000032:analysis; D003124:Colorimetry; D004305:Dose-Response Relationship, Drug; D007124:Immunoenzyme Techniques; D008722:Methods; D008832:Microchemistry; D009249:NADP / Q000378:metabolism; D010084:Oxidation-Reduction; D012044:Regression Analysis; D013778:Tetrazolium Salts / Q000378:metabolism; D013972:Thyrotropin / Q000032:analysis
chemical_list: D013778:Tetrazolium Salts; D009249:NADP; D013972:Thyrotropin; D000469:Alkaline Phosphatase