What does ELISA primarily measure?

• A. A qualitative test for cell viability using dye uptake.
• B. A genetic assay for sequencing proteins.
• C. A concentration assay used to determine the presence and concentration of a specific protein using antibody-antigen.
• D. A hydration test for solution osmolarity.

Answer: (C)

ELISA measures the amount of a specific protein in a sample by using antibodies that recognize that protein, making it a concentration assay. The test works by capturing the target protein on a solid surface with a specific antibody, then adding a secondary antibody linked to an enzyme. When a substrate is added, the enzyme produces a color change or other signal that increases with the amount of protein present, allowing quantitative or qualitative determination of concentration. This is different from dye-based viability tests, genetic sequencing methods, or osmolarity measurements, which assess cell health, nucleic acids, or solution properties rather than a specific protein’s amount.