ELISA, or enzyme-linked immunosorbent assay, is a plate-based immunological test that detects and measures specific proteins such as antibodies, antigens or hormones using enzyme-linked antibodies and a color change readout.
Explanation
In an ELISA, either an antigen or an antibody is immobilized on a solid surface, commonly the wells of a polystyrene microplate. A sample containing the target analyte is added so that the target binds to the immobilized component. After unbound material is washed away, a secondary antibody linked to an enzyme is introduced. This conjugated antibody binds to the target complex. When a chromogenic substrate is added, the enzyme catalyses a reaction that produces a measurable color change proportional to the amount of target present. Various ELISA formats exist. In a direct ELISA the detecting antibody is enzyme-linked and binds directly to the immobilized antigen. Indirect ELISA uses an unlabeled primary antibody and an enzyme-linked secondary antibody, which amplifies the signal. Sandwich ELISA captures the analyte between two antibodies and is often used for larger antigens. Competitive ELISA measures the decrease in signal as unlabeled antigen competes with labeled antigen for binding sites. ELISAs are widely used in diagnostic laboratories, vaccine development, food industry quality control and research because they are sensitive, quantitative and adaptable to high-throughput screening.
Applications and Clinical Significance
ELISA techniques are used to diagnose infections such as HIV, hepatitis B and SARS-CoV-2 by detecting antibodies or viral antigens in patient sera. Hormone assays for human chorionic gonadotropin in pregnancy tests and for thyroid hormones use ELISA. In food safety, ELISA kits detect allergens such as peanut or gluten proteins in processed foods. Research laboratories use ELISAs to measure cytokines, growth factors and other biomarkers in cell culture supernatants or blood samples. Because the assay is modular and can be automated, it is a standard tool in serology and immunology laboratories.
ELISA combines specificity from antibody-antigen interactions with the sensitivity of enzyme amplification. This synergy makes it a reliable technique for quantifying proteins and monitoring disease exposure or immune responses.
Related Terms: Immunoassay, Antibody, Antigen, Western blot, Immunofluorescence