Term: immunoassay https://doi.org/10.1351/goldbook.I02979 Definition: A ligand-binding assay that uses a specific antigen or antibody, capable of binding to the analyte, to identify and quantify substances. The antibody can be linked to a radiosotope (radioimmunoassay, RIA), or to an enzyme which catalyses an easily monitored reaction (enzyme-linked immunosorbent assay, ELISA), or to a highly fluorescent compound by which the location of an antigen can be visualized (immunofluorescene). Related Terms: 1) assay (http://doi.org/10.1351/goldbook.A00470). 2) antibody (http://doi.org/10.1351/goldbook.A00384). 3) radioimmunoassay (http://doi.org/10.1351/goldbook.R05105). 4) antigen (http://doi.org/10.1351/goldbook.A00394). 5) enzyme (http://doi.org/10.1351/goldbook.E02159). Source: PAC, 1992, 64, 143. 'Glossary for chemists of terms used in biotechnology (IUPAC Recommendations 1992)' on page 157 (https://doi.org/10.1351/pac199264010143) Citation: 'immunoassay' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.I02979 License: The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) for individual terms. Disclaimer: The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using.