ELISA utilizes enzyme-labeledantigensandantibodiesto detect biological molecules. Antigens are immobilized in 96-well microtiter plates. A specific capture antibody (primary antibody) is added to the wells and binds to the antigen. Anenzyme-coupled detection antibody(secondary antibody) is then added and binds to the primary antibody. Chromogenic substrates for the enzyme are added, yielding a visible color change, thus indicating the presence of the antigen. The color intensity can be measured quantitatively and/or qualitatively to identify the amount of antigen present.