Biotechnological Applications In Medicine

ELISA, which stands for Enzyme Linked Immunosorbent Assay, is based on the highly specific binding between an antigen and its corresponding antibody, as described in NCERT Class 12, Chapter 11 (Biotechnology and its Applications). When a pathogen infects the body, it either presents antigens or stimulates the production of antibodies, and ELISA detects either of these to confirm infection. A colour-producing enzyme linked to the antibody generates a measurable signal, allowing the presence and amount of the target to be estimated. The option naming only enzyme and substrate is incomplete, because although an enzyme reaction produces the visible signal, the diagnostic specificity comes from the antigen-antibody recognition, not the enzyme alone. DNA and RNA interactions form the basis of nucleic acid hybridisation and PCR, not ELISA. Hormone and receptor binding governs cell signalling and is unrelated to immunoassays. A consistency check confirms the answer: the word immunosorbent points directly to an immune-based recognition, which is the antigen-antibody interaction.