ELISA, a technique used for early diagnosis of infection, is based on the principle of:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → antigen-antibody interaction
ELISA stands for Enzyme Linked Immuno-sorbent Assay. It is one of the techniques of molecular diagnosis, along with recombinant DNA technology and PCR, that help find an infection early. Each technique works on its own principle.
Option (1) antigen-antibody interaction — Correct. When a pathogen infects the body, its antigens (proteins, glycoproteins) appear, and the body makes antibodies against them. ELISA detects the infection by finding either these antigens or these antibodies, so it rests on antigen-antibody interaction.
Option (2) amplification of nucleic acid — Incorrect. Amplification of nucleic acid is the principle of PCR (polymerase chain reaction). PCR copies the DNA or RNA of a pathogen many times, so even a very low concentration can be detected.
Option (3) hybridisation of a radioactive probe with complementary DNA — Incorrect. A single-stranded DNA or RNA tagged with a radioactive molecule (a probe) that hybridises to its complementary DNA, followed by autoradiography, is used to detect mutated genes. ELISA uses no such probe.
Option (4) separation of DNA fragments according to their size — Incorrect. Separating DNA fragments by size is done by gel electrophoresis, where smaller fragments move farther through the agarose gel. It is a step in recombinant DNA technology, not the principle of ELISA.
NCERT Extract:
Molecular Diagnosis – “… Recombinant DNA technology, Polymerase Chain Reaction (PCR) and Enzyme Linked Immuno-sorbent Assay (ELISA) are some of the techniques that serve the purpose of early diagnosis. … A single stranded DNA or RNA, tagged with a radioactive molecule (probe) is allowed to hybridise to its complementary DNA in a clone of cells followed by detection using autoradiography. … ELISA is based on the principle of antigen-antibody interaction. Infection by pathogen can be detected by the presence of antigens (proteins, glycoproteins, etc.) or by detecting the antibodies synthesised against the pathogen.”