Immunological technique to detect a biological substance.
The sandwich ELISA is started by attaching a first antibody protein X to a plastic plate (1). Each well is then incubated with each sample having to be determined (2). A second anti-X antibody binds to this protein X (3). This antibody is then be detected by an antibody (4) coupled with an enzyme in which the hydrolysis of the substrate causes a color change (5). Thus a dark color reflects a larger concentration of X.