Enzyme-linked immunosorbent assays (ELISA) are laboratory techniques used to detect and quantify proteins, antibodies, or hormones in a sample. This method relies on the specific binding between an antigen and an antibody, allowing researchers to measure the presence of target substances in various biological samples, such as blood or tissue. In an ELISA, a sample is added to a plate coated with a specific antibody. If the target substance is present, it binds to the antibody. An enzyme-linked secondary antibody is then added, which binds to the target. A substrate is introduced, producing a measurable color change that indicates the amount of the target substance, making ELISA a valuable tool in diagnostics and research.