ELISA involves several steps. First, the antigen is attached to a solid surface, usually a microplate. Then, a specific antibody is added to bind with the antigen. A secondary antibody, which is linked to an enzyme, is introduced to bind to the first antibody. Finally, a substrate is added that reacts with the enzyme to produce a measurable color change. The intensity of the color change correlates with the concentration of the substance being measured.
