ELISA Tests

• ELISA tests (enzyme-linked immunosorbent assays) are used to detect the presence of a particular substance (e.g. an antigen) in a sample of liquid using monoclonal antibodies.

  For example, testing for the presence of a virus in a sample of blood plasma.
• First, a monoclonal antibody is produced that binds specifically to an antigen found on the virus. An enzyme is then attached to this antibody to form an enzyme-antibody complex.
• 𝗦𝗧𝗘𝗣 𝟭:

  The liquid that is thought to contain the suspected antigen is placed into one of the wells in a plastic plate.
• 𝗦𝗧𝗘𝗣 𝟮:

  The liquid samples are left for a short while to give the antigen time to adhere to the plastic (it is immobilised). The Mab-enzyme complex is added and binds to any present antigens. The plate is washed to clear away any unbound Mab-enzyme complexes.
• 𝗦𝗧𝗘𝗣 𝟯:

  The substrate of the enzyme is added and the liquid changes colour in the presence of a Mab-enzyme complex, which would only be present if it was bound to an antigen. The colour change indicates the presence of the suspected antigen.
• In the plastic well plate, further samples of the same liquid can be added to the other wells, or different liquids may be put into each other. For example, a sample that is known to contain antigens may be used as a control, or a sample that is known to not contain antigens.