Chemiluminescent labelled streptavidin (STAV) as a universal marker in steroid and peptide immunoassays

The tetrameric structure of streptavidin and its exceptionally strong affinity to biotin (Ka = 10(15)M 1) can be exploited to achieve an amplification of the signal in immunoassays. In the approach described here streptavidin (STAV) labelled with aminobutylethyl-isoluminol (ABEI) served as a universal marker in immunoassays for both haptens and big antigens. The advantageous features of streptavidin can be applied to any immunoassay using biotinylated antibodies as the primary probe. In two-site immunometric assays for larger antigens the liquid phase 'tracer' antibody is biotinylated. In hapten assays the solid phase antigen technique (Wood et al., 1982) is employed, in which sample-antigen and solid phase-antigen compete for a biotinylated antibody. In this paper we demonstrate the use of STAV-ABEI as a universal chemiluminescent label in steroid assays and in an immunometric assay using human growth hormone (hGH) as an example.