Chromogenic redox assay for beta-lactamases yielding water-insoluble products. II. Heterogeneous sandwich assay for hCG.
A very sensitive and rapid heterogeneous sandwich enzyme immunoassay for human chorionic gonadotropin (hCG) is described. The assay is based on the application of the novel chromogenic redox substrate system for beta-lactamase which is used as label. The chromogen system consists of a thioacetylcephalosporin beta-lactamase substrate, which upon turnover by the enzyme label releases the thiolate with the concomitant reduction of the tetrazolium salt to a colored formazan. The concentration of the formazan is directly related to the amount of the hormone in the sample and is read spectrophotometrically. The enzyme-antibody conjugates, produced through use of heterobifunctional maleimide crosslinker, maintain 90% of the enzyme activity after 30 days at 25 degrees C. Concentrations of the hormone as low as 5 mIU/ml, equivalent to 25 fmol/ml, are detectable in 3 h.
Bieniarz
C
C
Department of Immunochemistry, Abbott Laboratories, North Chicago, Illinois 60064.
Cornwell
M J
MJ
Young
D F
DF
D000906:Antibodies; D006063:Chorionic Gonadotropin / Q000032:analysis*; D002863:Chromogenic Compounds; D003102:Colloids; D003124:Colorimetry / Q000379:methods; D003432:Cross-Linking Reagents; D006801:Humans; D007124:Immunoenzyme Techniques; D008832:Microchemistry / Q000379:methods; D010084:Oxidation-Reduction; D013997:Time Factors; D001618:beta-Lactamases / Q000032:analysis* / Q000378:metabolism
D000906:Antibodies; D006063:Chorionic Gonadotropin; D002863:Chromogenic Compounds; D003102:Colloids; D003432:Cross-Linking Reagents; D001618:beta-Lactamases