Practice question

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.