Q.What is ELISA?

Conventional diagnostic methods (microscopy, serum and urine analysis) are indirect and often only catch a disease once the pathogen load is already high. Molecular diagnostics instead detect the pathogen or its markers directly at very low concentrations. ELISA (Enzyme Linked Immunosorbent Assay, Engvall and Perlmann, 1971) detects specific antigens or antibodies by immobilising a sample antigen on a plate, adding a specific antibody, then an enzyme-linked anti-antibody, and finally a substrate that yields a colour proportional to the amount of antigen present; it is the standard HIV test and comes in direct, indirect, sandwich and competitive forms. PCR (Polymerase Chain Reaction, Kary Mullis, 1983) amplifies a target DNA sequence into billions of copies through repeated cycles of denaturation (heat splits double-stranded DNA), annealing (primers bind the single strands) and extension (heat-stable Taq polymerase copies each primed strand) — because Taq polymerase survives the repeated heating, one reaction mix can …