ELISA is based on the principle of

Antigen - Antibody interaction

The correct answer is Option (3) → Antigen - Antibody interaction

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.

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.

Antibodies are specialized blood proteins produced as a response to specific antigens, and ELISA serves as a valuable tool to assess the presence of these antibodies, particularly in the context of infectious diseases.