inTrOducTiOn Enzyme immunoassay (EIA) and enzyme-linked immunosorbent assay (ELISA) are both widely used as diagnostic tools in medicine and as quality control measures in various industries; they are also used as analytical tools in biomedical research for the detection and quantification of specific antigens or antibodies in a given sample. These two procedures share similar basic principles and are derived from the radioimmunoassay (RIA). RIA was first described by Berson and Yalow (Yalow and Berson, 1960), for which Yalow was awarded the Nobel Prize in 1977, to measure endogenous plasma insulin. RIA was then developed into a novel technique to detect and measure biological molecules present in very small quantities, paving the way for the analysis and detection of countless other biological molecules, including hormones, peptides, and proteins. Because of the safety concern regarding its use of radioactivity, RIA assays were modified by replacing the radioisotope with an enzyme, thus creating the modern-day EIA and ELISA.