Biology · Biotechnology and Its Applications · NEET
ELISA means Enzyme Linked Immuno-Sorbent Assay. Break the words: 'Immuno' = it uses antibodies, 'Sorbent' = molecules are stuck (adsorbed) to a plate, and 'Enzyme Linked' = an enzyme is attached that produces a colour/signal so you can see the result. It is one of the molecular diagnostic techniques used for early detection of a disease.
ELISA is based on the principle of antigen-antibody interaction. An antigen binds only to its own specific antibody, like a lock and key. So if the pathogen's antigen and your antibody meet, they bind, an enzyme-linked marker gives a signal, and the test comes out positive. This specificity is why NEET repeats the one-line answer: 'ELISA is based on antigen-antibody interaction.'
It can do both. An infection can be detected by the presence of antigens (proteins, glycoproteins, etc.) of the pathogen, OR by detecting the antibodies that the body has synthesised against that pathogen. NCERT gives both options, so do not tick only one in a statement question.
No. Both are used for early diagnosis, but they detect different things. PCR amplifies and detects nucleic acid (DNA/RNA) of the pathogen even at very low amounts. ELISA detects protein antigens or antibodies. NCERT lists recombinant DNA technology, PCR and ELISA together as the techniques that serve the purpose of early diagnosis.
HIV can hide in the body for years before symptoms appear. ELISA can pick up the viral antigens or the antibodies against HIV in blood, so infection is found before the disease is visible. That is why NCERT calls ELISA 'a widely used diagnostic test for AIDS.'
The DNA probe method (hybridisation + autoradiography) detects the gene/nucleic acid using a radioactive single-stranded probe that pairs with complementary DNA. ELISA detects proteins — the antigen or antibody — using an enzyme-linked colour signal, not radioactivity. Both give early detection but target different molecules.
For effective treatment of the disease, early diagnosis and understanding its pathophysiology is very important. Which of the following molecular diagnostic techniques is very useful for early detection?
Match List-I with List-II. List-I: (A) Gene therapy (B) RNA interference (C) ELISA (D) Gel Electrophoresis List-II: (I) Separation of DNA fragments (II) Diagnostic test for AIDS (III) Cellular defence (IV) Allows correction of a gene defect
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Enzyme Linked Immuno-Sorbent Assay.
On the principle of antigen-antibody interaction — the antigen binds specifically to its matching antibody.
AIDS. ELISA is a widely used diagnostic test to detect HIV infection.
Yes. Along with PCR and recombinant DNA technology, ELISA is used for early diagnosis, detecting antigens or antibodies at low levels before disease symptoms show.
The enzyme is linked to a marker and produces a visible signal (usually a colour change) when antigen-antibody binding occurs, confirming a positive result.
