Improvement of estradiol enzymoimmunoassay, using a monoclonal antibody and an avidin/biotin amplification system

A microtitre plate enzyme immunoassay for estradiol, using a purified monoclonal antibody covalently bound to peroxidase and a small amount of immobilized immunogen, was optimized. Decreasing the antibody concentration to 2×10−10M (Kd/5) gave optimum estradiol detectability. The enzymatic signal was, however, very low in this assay. A 14-fold enhancement could be obtained using an avidin-biotin system in which several biotin molecules are conjugated with the antibody, providing multiple sites for binding by an avidin-enzyme complex. Further reagent concentration optimization gave an assay in which a range of 2 to 140 pg estradiol/well could be assayed simply and reproducibly.