In the first step of this Free B-HCG ELISA Assay Kit, the serum sample and the Conjugate are added to the microplate coated with Streptavidin. The Conjugate contains two monoclonal antibodies direct against different epitopes of free b-HCG: one is biotinylated, the other one is bound to the horseradish peroxidase (HRP); these antibodies compete for the native free b-HCG in the sample, thus at the end of first step a sandwich between the antibodies and the free b-HCG is formed; this complex binds to the microplate wells through the specific interaction between biotine and streptavidin. Sample Types: serum. Range: 2 -50 mIU/mL. Sensitivity: 0.09 mIU/mL. Time: 1.5 hours ? Eagle Biosciences Free Beta-HCG ELISA Assay Kit is an immunoenzymatic colorimetric method for quantitative determination of Free B-HCG (Free b-subunit Human Chorionic Gonadotropin) concentration in human serum. Eagle Biosciences Free B-HCG ELISA Assay Kit is intended for reasearch use only and not intended for diagnostic procedures.