What is the basic principle underlying ELISA assays?

• A. It relies on nucleic acid hybridization to detect proteins
• B. It measures cell viability by dye uptake
• C. It uses antibody-antigen binding with an enzyme readout
• D. It sequences proteins by mass spectrometry

Answer: (C)

ELISA works because it relies on the specific binding between an antibody and its target antigen, with an enzyme attached to that binding event providing the detectable signal. In a typical ELISA, the target molecule is captured on a solid surface, an antibody binds specifically to it, and a second antibody that carries an enzyme binds to the first antibody. When a suitable substrate is added, the enzyme catalyzes a reaction that produces a color, light, or fluorescence. The signal magnitude reflects how much target is present, allowing either quantitative or qualitative assessment.

This approach is distinct from other methods: nucleic acid hybridization detects DNA or RNA rather than proteins; dye uptake assays measure cell viability rather than specific antibody–antigen interactions; and mass spectrometry analyzes protein identity or sequence rather than providing a reporter signal from an enzyme linked to binding.