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ELISA (Enzyme-linked Immunosorbent Assay)

Enzyme-linked Immunosorbent Assay (ELISA) was developed in 1970 and rapidly became accepted as a standard routine assay technology. The assay format is sometimes referred to as EIA (Enzyme Immuno Assay).

The assay format combine the specificity of antibodies with the sensitivity of simple enzyme assays, by using antibodies or antigens coupled to an easily-assayed enzyme. ELISAs can provide a useful measurement of antigen or antibody concentration. There are two main variations on this method: The ELISA can be used to detect the presence of antigens that are recognized by an antibody or it can be used to test for antibodies that recognize an antigen.

An ELISA is a five-step procedure:

  1. Coat the microtiter plate wells with antigen
  2. Block all unbound sites to prevent false positive results
  3. Add antibody to the wells
  4. Add anti- IgG conjugated to an enzyme
  5. Reaction of a substrate with the enzyme to produce a colored product, thus indicating a positive reaction. The color development is related to bound ligand and is measured spectrophotometrically.

There are many different types of ELISAs. Currently the most important ones are:

  • Competitive methods
  • Sandwich methods
  • Antibody capture methods