Enzyme-linked immunosorbent assay (ELISA) is a widely used technique for detecting concentration of proteins, using enzyme tagged antibodies with which react with dyes to produce a colorimetric or fluorescent signal. Sandwich ELISA takes this one step further, by pre-coating plastic wells with a known concentration of a "capture" antibody which reacts specifically to the antigen under test. A secondary antibody is then applied, tagged with an enzyme.
