Enzymimmunoassays

Enzymimmunoassays, commonly referred to as enzyme immunoassays (ELISAs), are immunoassay formats that use an enzyme attached to an antibody or antigen as a detectable label. The enzyme catalyzes a reaction with a substrate to produce a measurable signal, typically a color change, fluorescence, or chemiluminescence, which is proportional to the concentration of the target substance in the sample.

Common formats include the sandwich ELISA, in which a capture antibody binds the analyte and a labeled detection antibody reports its presence, and the competitive ELISA, in which labeled and unlabeled analytes compete for binding. Indirect ELISA uses a coating antigen and a labeled secondary antibody for signal generation. Many enzyme immunoassays employ a solid phase such as a microplate to facilitate washing and separation.

Procedure generally involves adding a sample to a solid phase with a bound capture molecule, allowing binding through incubation, washing away unbound material, and adding an enzyme-labeled detection reagent. After a second wash, substrate is added and the enzymatic reaction yields a signal that is measured by spectrophotometry, fluorometry, or chemiluminescence, enabling quantification of the analyte.

Applications of enzymimmunoassays are widespread, especially in clinical diagnostics to quantify hormones, drugs, tumor markers, infectious disease antigens or antibodies; in food safety testing; and in environmental monitoring. They are valued for their potential high throughput and relatively low cost per test, with results available within hours.

Advantages include high sensitivity and specificity and a broad dynamic range. Limitations involve potential cross-reactivity or interference, dependence on well-characterized antibodies, and the need for appropriate equipment and reagents. The method has evolved into automated and multiplex formats, expanding its clinical and research utility.