Which of following involves theory of antigen-antibody interaction?

ELISA

The correct answer is Option (2)- ELISA

ELISA (Enzyme-Linked Immunosorbent Assay)

True: ELISA is a widely used technique that involves antigen-antibody interactions to detect and quantify the presence of specific antigens or antibodies in a sample. Infection by pathogen can be detected by the presence of antigens (proteins, glycoproteins, etc.) or by detecting the antibodies synthesized against the pathogen.

PCR (Polymerase Chain Reaction)

False: PCR is a technique used to amplify specific DNA sequences. It does not involve antigen-antibody interactions. Instead, it relies on the denaturation, annealing, and extension of DNA using specific primers and a DNA polymerase enzyme.

Gene Therapy

False: Gene therapy involves introducing, removing, or altering genetic material within a person's cells to treat or cure disease. It does not involve antigen-antibody interactions.

Gel Electrophoresis

False: Gel electrophoresis is a technique used to separate DNA, RNA, or proteins based on their size and charge by applying an electric field to a gel matrix. It does not involve antigen-antibody interactions. The separation occurs due to the migration of molecules through the gel under the influence of an electric current.

In summary, ELISA is the technique that involves the theory of antigen-antibody interaction.