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# Apply the enzyme-linked antibody and let it bind to the substance. # Apply the enzyme-linked antibody and let it bind to the substance.
# Wash the plate, so that unbound antibody is removed. # Wash the plate, so that unbound antibody is removed.
# Apply a chemical which is coverted by the enzyme into a fluorescent signal. # Apply a chemical which is converted by the enzyme into a fluorescent signal.
# View the result: if it fluoresces, then the sample contained the substance. # View the result: if it fluoresces, then the sample contained the substance.


Line 17: Line 17:
# Apply an enzyme-linked antibody which specifically binds to human antibody. # Apply an enzyme-linked antibody which specifically binds to human antibody.
# Wash the plate, so that the unbound enzyme-linked antibody is removed. # Wash the plate, so that the unbound enzyme-linked antibody is removed.
# Apply a chemical which is coverted by the enzyme into a fluorescent signal. # Apply a chemical which is converted by the enzyme into a fluorescent signal.
# View the result: if it fluoresces, then the serum sample contained antibody against the antigen. # View the result: if it fluoresces, then the serum sample contained antibody against the antigen.


Revision as of 03:50, 1 December 2002

The Enzyme Linked Immuno-Sorbent Assay or ELISA is a method commonly employed in biochemistry to detect if a certain substance is present in a sample. It employs antibody specific to the substance; these antibody are linked to an enzyme which produces a signal.

The steps of the general ELISA test are as follows:

  1. Apply the sample to some sticky substrate, usually a plate with wells.
  2. Apply the enzyme-linked antibody and let it bind to the substance.
  3. Wash the plate, so that unbound antibody is 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 antibody are present, the enzyme molecules will produce many fluorescent signal molecules.

A variant of this techniqe is used in medicine to detect if a person's blood contains antibody against a certain antigen (which would indicate 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 antibody is removed.
  4. Apply an enzyme-linked antibody which specifically binds to human antibody.
  5. Wash the plate, so that the unbound enzyme-linked antibody is 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 antibody against the antigen.

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