What is Enzyme-Linked Immunosorbent Assay (ELISA)?
Historical Background
Key Points
12 points- 1.
ELISA relies on the principle of antigen-antibody interaction. An antigen is a substance that triggers an immune response, while an antibody is a protein produced by the body to neutralize the antigen. ELISA uses these interactions to detect and quantify the presence of specific antigens or antibodies in a sample.
- 2.
There are several types of ELISA, including direct, indirect, sandwich, and competitive ELISA. Each type has its own advantages and disadvantages, and the choice of which type to use depends on the specific application and the characteristics of the target substance.
- 3.
In a direct ELISA, an antigen is immobilized on a surface, and an enzyme-labeled antibody is added. The antibody binds directly to the antigen, and the enzyme activity is measured to determine the amount of antigen present. This is simpler but less sensitive.
- 4.
Recent Real-World Examples
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Source Topic
Supreme Court examines mandatory NAT testing for safer blood transfusions
Polity & GovernanceUPSC Relevance
Frequently Asked Questions
61. What's the most common MCQ trap regarding ELISA types (direct, indirect, sandwich, competitive)?
The most common trap is confusing the order of antibody binding and enzyme labeling. Students often incorrectly assume that in indirect ELISA, the primary antibody is enzyme-labeled. The correct order is: antigen immobilized, unlabeled primary antibody, then enzyme-labeled secondary antibody. Examiners test this by presenting options with incorrect labeling sequences.
Exam Tip
Remember 'Indirect' means *another* antibody is used for detection, hence the secondary antibody is labeled, not the primary.
2. ELISA is used to detect both antigens and antibodies. How does the *sample preparation* differ when testing for each?
When testing for an antigen, the sample is prepared to *isolate and present the antigen* in a purified or semi-purified form. This might involve cell lysis, protein extraction, or chromatography. When testing for antibodies, the sample (usually serum or plasma) is often used *directly* or with minimal dilution, assuming the antibodies are already present in the liquid fraction. The key difference is whether you're trying to extract the target or just make it accessible.