The enzyme-linked immunosorbant assay, which is commonly abbreviated to ELISA, is a technique that promotes the binding of the target antigen or antibody to a substrate, followed by the binding of an enzyme-linked molecule to the bound antigen or antibody. The presence of the antigen or antibody is revealed by color development in a reaction that is catalyzed by the enzyme which is bound to the antigen or antibody.

Typically, an ELISA is performed using a plastic plate which contains an 8 x 12 arrangement of 96 wells. Each well permits a sample to be tested against a whole battery of antigens.

There are several different variations on the ELISA theme. In the so-called direct ELISA, the antigen that is fixed to the surface of the test surface is the target for the binding of a complimentary antibody to which has been linked an enzyme...