Development of ultrasensitive enzyme immunoassay reviewed with emphasis on factors which limit the sensitivity.

Development of ultrasensitive enzyme immunoassays for antigens, haptens and antibodies is reviewed with emphasis on factors which limit the sensitivity. One of the most important conditions for ultrasensitive immunoassays is the use of non-competitive solid phase assay systems rather than competitive ones. Although non-competitive immunoassays are available for antigens and antibodies, there are only competitive immunoassays for hapten molecules which can not be bound simultaneously by two different antibodies. In order to overcome this difficulty, methods have been developed to derivatize haptens with amino groups so that the derivatized haptens may be measured by two-site assays. The other condition for ultrasensitive immunoassays is to minimize the non-specific binding of labelled reactants. This has been achieved by developing methods to transfer the complex of analytes and labelled reactants from solid phase to solid phase without dissociation. Thus, the sensitivity for antigens, haptens and antibodies has been markedly improved. However, the sensitivity for the detection of label enzymes remains to be improved.