- ELISA is a Non isotopic immunoassay in which a stable enzyme is used as a label instead of a radioactive compound and the principle is similar to that of radioimmunoassay(RIA).
- Principle and Procedure:-
- Specific antigen is coated in the wells of a microwell plate.
- A sample containing antibodies is added to the wells and incubated.
- If the antibodies bind to the antigen, they form a complex that stays in the wells.
- The wells are washed to remove unbound antibodies.
- A second antibody that is linked to an enzyme is added to the wells and incubated.
- If the second antibody binds to the first antibody, it forms a sandwich complex that stays in the wells.
- The wells are washed to remove unbound enzyme-linked antibodies.
- A substrate that reacts with the enzyme is added to the wells and incubated.
- If the enzyme reacts with the substrate, it produces a color change that indicates the presence and amount of antibodies in the sample.
- Applications:-
- Used to detect/measure antigens/antibodies present in very small quantities.
- Estimation of hormones in serum.
- Estimation of tumor markers like PSA, AFP, HCG, etc in serum.
- Estimation of infectious disease antibodies against bacterial toxins, viruses, etc.
- Autoantibodies like anti-DNA, ANA(Antinuclear antibody), etc.