Competitive ELISA

In competitive ELISA, unlabeled antibody is incubated in the presence of its antigen. Then these bound antibody/antigen complexes are then added to an antigen coated well. After washing, unbound antibodies are removed. The more analytes in the sample, the less antibodies will be able to bind to antigens in the well. The signal is then detected using labeled secondary antibodies and the decrease in signal is compared to a control. The major advantage of a competitive ELISA is the ability to use crude or impure samples and still selectively bind any antigen that may be present.

Indirect ELISA

The indirect ELISA is used primarily to determine the strength and/or amount of antibody response in a sample. In the assay, the antigen of interested is immobilized by direct adsorption to the assay plate. Detection of the antigen can then be performed by using a matched set of primary antibody and conjugated secondary antibodies.

Sandwich ELISA

The Sandwich ELISA measures the amount of analyte between capture antibody and detection antibody. The analyte needs to have two different epitope sites available for antibody binding.