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Revision as of 08:25, 1 May 2005

For the artificial intelligence program, see ELIZA

The Enzyme-Linked Immunosorbent Assay (ELISA or EIA for short) is a method usually employed in biochemistry to detect if a certain substance is present in a sample. It utilizes antibodies specific to the substance; these antibodies are linked to an enzyme which causes a chromogenic substrate to produce a signal.

The steps of the general ELISA test are:

  1. Apply the sample to some sticky substrate, usually a plate with wells.
  2. Apply the enzyme-linked antibodies and let them bind to the substance.
  3. Wash the plate, so that unbound antibodies are removed.
  4. Apply a chemical which is converted by the enzyme into a fluorescent signal.
  5. View the result: if it fluoresces, then the sample contained the substance.

The enzyme acts as an amplifier: even if only few enzyme-linked antibodies are present, the enzyme molecules will produce many fluorescent signal molecules.

A variant of this technique is used in medicine to detect if a person's blood contains antibodies against a certain antigen (which would indicate past or present infection). The initial screening test for HIV infection is such an ELISA test. The steps are as follows:

  1. Prepare a plate to which the antigen is bound
  2. Apply the human serum to be tested
  3. Wash the plate, so that unbound antibodies are removed.
  4. Apply the enzyme-linked antibodies which specifically bind to the human antibodies.
  5. Wash the plate, so that unbound enzyme-linked antibodies are removed.
  6. Apply a chemical which is converted by the enzyme into a fluorescent signal.
  7. View the result: if it fluoresces, then the serum sample contained antibodies against the antigen.

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