ELISA (Enzyme-Linked Immunosorbent Assay) is the workhorse of serodiagnosis. In a sandwich (capture) ELISA used to detect an antigen, arrange the layers correctly from solid phase to detection:

• A Solid phase → Patient sample (antigen) → Enzyme-labelled anti-antigen antibody → Substrate
• B Solid phase → Capture antibody → Patient antigen → Enzyme-labelled detection antibody (against different antigen epitope) → Substrate ✓
• C Solid phase → Antigen → Patient antibody → Enzyme-labelled anti-human IgG → Substrate
• D Solid phase → Enzyme-labelled antigen → Patient antibody → Substrate

Explanation

The sandwich (capture) ELISA for antigen detection uses: (1) a capture antibody coated on the solid phase (plate); (2) patient sample containing the antigen is added — antigen binds capture antibody; (3) a second enzyme-labelled detection antibody (directed against a different, non-competing epitope on the same antigen) is added, forming the 'sandwich'; (4) enzyme substrate is added, producing a colorimetric signal proportional to antigen quantity. Option C describes the indirect ELISA for antibody detection (e.g., anti-HCV, anti-HIV antibody tests). Sandwich ELISA is used for HBsAg, NS1 antigen detection, HBeAg, etc.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.