The indirect ELISA involves several steps. First, an antigen is coated on a microplate. The sample, which may contain the antibody of interest, is then added. If the antibody is present, it binds to the antigen. A secondary antibody, which is enzyme-linked and specific to the primary antibody, is added. This secondary antibody binds to the primary antibody. Finally, a substrate is added, and the enzyme catalyzes a reaction that produces a measurable color change. The intensity of the color is proportional to the amount of antibody in the sample.
