page_title: ELISA
section_title: Applications
hierarchical_section_title: ELISA / Applications
caption_attribution_description: „Anti human IgG“ Double Antibody Sandwich ELISA
context_page_description: The enzyme-linked immunosorbent assay is a commonly used analytical biochemistry assay, first described by Engvall and Perlmann in 1971. The assay uses a solid-phase type of enzyme immunoassay to detect the presence of a ligand in a liquid sample using antibodies directed against the protein to be measured. ELISA has been used as a diagnostic tool in medicine, plant pathology, and biotechnology, as well as a quality control check in various industries.
  In the most simple form of an ELISA, antigens from the sample to be tested are attached to a surface. Then, a matching antibody is applied over the surface so it can bind the antigen. This antibody is linked to an enzyme and then any unbound antibodies are removed. In the final step, a substance containing the enzyme's substrate is added. If there was binding the subsequent reaction produces a detectable signal, most commonly a color change.
  Performing an ELISA involves at least one antibody with specificity for a particular antigen. The sample with an unknown amount of antigen is immobilized on a solid support either non-specifically or specifically.
context_section_description: Because the ELISA can be performed to evaluate either the presence of antigen or the presence of antibody in a sample, it is a useful tool for determining serum antibody concentrations (such as with the HIV test or West Nile virus). It has also found applications in the food industry in detecting potential food allergens, such as milk, peanuts, walnuts, almonds, and eggs and as serological blood test for coeliac disease. ELISA can also be used in toxicology as a rapid presumptive screen for certain classes of drugs.
  The ELISA was the first screening test widely used for HIV because of its high sensitivity. In an ELISA, a person's serum is diluted 400 times and applied to a plate to which HIV antigens are attached. If antibodies to HIV are present in the serum, they may bind to these HIV antigens. The plate is then washed to remove all other components of the serum. A specially prepared "secondary antibody"—an antibody that binds to other antibodies—is then applied to the plate, followed by another wash. This secondary antibody is chemically linked in advance to an enzyme.
  Thus, the plate will contain enzyme in proportion to the amount of secondary antibody bound to the plate. A substrate for the enzyme is applied, and catalysis by the enzyme leads to a change in color or fluorescence. ELISA results are reported as a number; the most controversial aspect of this test is determining the "cut-off" point between a positive and a negative result.
  A cut-off point may be determined by comparing it with a known standard. If an ELISA test is used for drug screening at workplace, a cut-off concentration, 50 ng/ml, for example, is established, and a sample containing the standard concentration of analyte will be prepared. Unknowns that generate a stronger signal than the known sample are "positive." Those that generate weaker signal are "negative".
  Dr Dennis E Bidwell and Alister Voller created the ELISA test to detect various kind of diseases, such as dengue, malaria, Chagas disease, Johne's disease, and others. ELISA tests also are used as in in vitro diagnostics in medical laboratories. The other uses of ELISA include:
  detection of Mycobacterium antibodies in tuberculosis
  detection of rotavirus in feces
  detection of hepatitis B markers in serum
  detection of hepatitis C markers in serum
  detection of enterotoxin of E. coli in feces
  detection of HIV antibodies in blood samples
  detection of SARS-CoV-2 antibodies in blood samples
caption: Human anti-IgG, double antibody sandwich ELISA
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