What is the ELISA technique?

ELISA is the acronym for the enzyme-linked immunosorbent assay (enzyme-linked immunosorbent assay). This is a laboratory technique that was designed by Swedish and Dutch scientists in 1971, which allows the detection of small particles called antigens, which are usually fragments of proteins. The identification is specific, that is, it makes small segments of proteins stand out and can not be confused with others.

In order to identify the antigens, molecules with two components are used: an antibody (which binds to the antigen in a specific way) and an enzyme (which activates and signals the binding to the antigen). Prior to the discovery of the ELISA, radioactive molecules were used instead of enzymes, which meant an unnecessary added risk in the laboratory and a higher cost.

Thanks to this technique, scientific studies have been carried out in fields such as biology, biochemistry and medicine. In the hospital it is mainly used to identify aggressive germs that are found in the blood, urine, sputum, et cetera. The technique was soon generalized with the use of simple and very cheap equipment that are still used today in many diagnostic centers around the world.

The different types of ELISA are:

  • Direct ELISA: is the most basic form of performing the technique. It consists of collecting a sample to be studied and placed in a well (a small container) in front of an equal sample but contaminated with the germ to be studied, and another sample in which it is known that there is no germ. The antibody is applied with the enzyme in the three wells and the sample is compared with the other two.
  • Indirect ELISA: it is performed similarly to the direct ELISA, but in this case an antibody is added without enzyme and then one with enzyme. In this way, the signal emitted by the enzyme is much more powerful and the test is more sensitive.
  • Sandwich ELISA: in this case in the wells first an antibody is added and then the sample, so that the antigens are already retained in the bottom of the well. The antibody is then added with the enzyme. It is the most effective way of performing the test.
  • ELISPOT: this is an ELISA type that allows quantitative detection of the antigen, even identifying the specific number of cells where it is found.