 Performing an ELISA involves at least one antibody with specificity for a particular antigen.The sample with an unknown amount of antigen is immobilized on a solid support (usually a polystyrene microtiter plate) either non-specifically (via adsorption to the surface) or specifically (via capture by another antibody specific to the same antigen, in a "sandwich" ELISA).After the antigen is immobilized, the detection antibody is added, forming a complex with the antigen.