Practice question

Sandwich configuration captures antigen between two antibodies recognizing different regions. Capture antibody immobilized on plate holds antigen, while detection antibody binds elsewhere to generate signal. For simultaneous binding without steric hindrance, antigen must display at least two distinct epitopes spatially separated. A molecule possessing only single epitope cannot be bridged by two antibodies at once, causing assay failure. Larger proteins and multimeric antigens naturally provide multiple determinants, enabling high specificity and sensitivity, whereas haptens require competitive formats because they lack dual binding sites.