As is the case for the previously described MALDI-TOF technique, ELISA techniques also had their roots in the immunology and biotechnology fields. Again this is a complicated technique, requiring the generation of specific antibodies to an organism. A second antibody linked to an enzyme is also prepared, and is specific to the primary antibody. This enzyme has the ability to convert a colorless substrate to a colored one. The organism (antigen) is isolated and fixed to a substrate and the primary antibody applied. If it is a "match" it will adhere to the organism. If the antibody were not a match, by washing the substrate, it would be removed.
The secondary antibody is then applied and if the organism has been matched it will attach to the primary antibody. The substrate is washed again and the indicator applied. The enzyme on the secondary antibody cleaves the indicator to produce a visible colored compound. Clearly, if there is no match at any stage, the colour does not develop. A large number of specific antibodies need to be available, therefore this technique is often used after an initial screening has narrowed the choices. Once again this would not be a technique suitable for routine use.
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