Which ELISA type detects antigens between capture and detection antibodies?
Sandwich ELISA provides high specificity for antigen quantification. Capture antibody specific to target is immobilized on plate, blocking reduces nonspecific binding. Antigen present in sample binds capture antibody and is retained. A second detection antibody recognizing different epitope on same antigen is added, sandwiched between two antibodies. Enzyme conjugated secondary antibody then generates colorimetric signal proportional to antigen. Direct ELISA coats antigen directly, indirect detects antibodies using labeled secondary, competitive relies on competition. Sandwich format is preferred for proteins like cytokines.
Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.