ELISA refers to the biochemical technique--enzyme-linked immunoabsorbent assay--which is also known as enzyme immunoassay. It utilizes an antibody to detect the presence and amount of a particular antigen. It may also be done in reverse where an antigen is used to detect the presence of an antibody. An antigen is any molecular substance that is recognized by antibodies. Antibodies are large globular proteins produced by B cells of the immune system, which can also be made in the laboratory. One of the most widely used ELISAs is the pregnancy test, which detects the amount of human chorionic gonadotropin in the urine and the result is displayed as a color change on a test strip.
Process
For the ELISA procedure, a blood sample or other type of sample is collected, diluted and then placed onto a surface, such as a microwell plate, which is coated with an antibody. The plate incubates for a small amount of time and then is rinsed. At this point the amount of antigen in the sample is now bound to the antibody on the surface of the plate. A second antibody that detects the first antibody is added to the plate and incubated. This antibody is attached to an enzyme. The enzyme typically converts a substance to a colored product that can be detected by a spectrophotometer, an instrument that measures the amount of light that passes through a sample. The amount of color produced is proportional to the amount of antigen in the sample.
Advantages
The primary advantages of the ELISA are that it is highly specific and it replaces immunoassays that required the use of radioactivity. A review article published in “The Journal of Gerontology: Biological Sciences” reports that ELISAs are highly quantitative and reproducible.
Disadvantages
Although relatively inexpensive in comparison to other methods of antigen detection, the ELISA procedure requires a laboratory and expensive equipment. As reported in “The Journal of Gerontology: Biological Sciences,” other weaknesses of ELISAs are that they are capable of detecting only one antigen at a time and their results are dependent on the skills of the technician and the quality of the ELISA kit.
Applications
The ELISA procedure has a broad range of applications from disease diagnosis to testing for toxic substances. The ELISA is used to diagnose many diseases, including infectious diseases, autoimmune disease, certain cancers and Alzheimer’s. The ELISA facilitates drug discovery by identifying drug targets, evaluating disease progression and regression and by analyzing toxicity. A review article in “Analytical and Bioanalytical Chemistry” notes that the ELISA is useful for the detection of potentially hazardous allergens in food.
New Technology
The ELISA was first developed in the 1970s and new technology has improved the traditional ELISA. The new technology is called multiplexing and allows for the detection of multiple antigens in one sample. Additionally, instead of using colorimetric detection newer ELISAs employ electrochemiluminescence detection, which detects light emitted from electrochemical reactions and is more sensitive. The review article in “The Journal of Gerontology: Biological Sciences” reported the advantages of the new generation of ELISA-based multiplex arrays include: detection of multiple antigens, requirement of less sample, greater efficiency, less costly, and they can compare the concentrations of multiple antigens in samples and have a greater dynamic range. The disadvantage of the new technology is the initial investment that is required.
