Competitive ELISA

The most complex ELISA. This is common when the antigen is small and has only one epitope. In competitive ELISA, labeled purified antigen is used. First, the capture antibody is coated to the plate. Then, unlabeled antigen from the sample and labeled antigen compete for binding to the capture antibody.

If there is a high concentration of antigen in the sample, there will be a significant reduction in signal from the labeled purified antigen. Conversely, if there is little antigen in the sample, there will be minimal reduction in the signal compared to assay wells with labeled antigen alone.