Enzyme immunoassay using a crossed-beam thermal lens technique

An enzyme immunoassay based on the use of crossed-beam thermal lens detecti on is described. In this assay, poly-N-isopropylacrylamide, a water-soluble , thermally precipitating synthetic polymer, was used as a carrier to minim ize non-specific binding. The enzyme substrate of the horseradish peroxidas e that was employed was 3,3',5,5'-tetramethylbenzidine. The color developme nt of the enzyme-substrate reaction was stopped by SDS and Na2SO3 to achiev e a stable blue solution. The background reduction and stabilization made i t possible to use a crossed-beam thermal lens technique as the measurement method. This method was demonstrated to be applicable by determination of h epatitis B surface antigen in human serum. A detection limit of 0.15 ng/ml was obtained. This was more sensitive than that of the commercially availab le ELISA method. (C) 2000 Elsevier Science B.V. All rights reserved.