A Review of Enzyme Linked Immunoabsorbent Assay (ELISA) and Chemiluminescence Immunoassay (CLIA) Technologies

Immunoassays are powerful analytical tools widely employed to detect and quantify analytes, primarily proteins, in biological fluids such as serum, urine, saliva, and sweat. Among the most common types are enzyme-linked immunosorbent assay (ELISA) and chemiluminescence- operational efficiency. ELISA, first introduced in the 1970s, has become a cornerstone in diagnostics and research due to its cost-effectiveness, ease of use, and adaptability to a wide range of targets. However, ELISA systems are often limited by their detection sensitivity for low-abundance analytes. To address this, more advanced immunoassay systems such as chemiluminescent immunoassay (CLIA) and electrochemiluminescence immunoassay (ECLIA) have emerged, offering enhanced detection capabilities. This paper outlines the evolution of immunoassay platforms, comparing traditional ELISA techniques with modern commercial systems including Fluorescent Polarization Immunoassay (FPIA), Enzyme Multiplied Immunoassay Technique (EMIT), Cloned Enzyme Donor Immunoassay (CEDIA), and Luminescent Oxygen Channeling Immunoassay (LOCI). Furthermore, it delves into the underlying mechanisms of CLIA, highlighting biologically derived chemiluminescent agents, such as firefly luciferase and aequorin, as well as non-biological agents like acridinium esters. Novel approaches including magnetic bead-based CLIA, flow injection systems, and capillary electrophoresis-based assays are also discussed for their contributions to improving automation, sensitivity, and speed. Special attention is given to the ADVIA Centaur XP system, a fully automated CLIA platform, for its clinical utility and scalable laboratory applications. This review consolidates the current landscape of immunoassay technologies and emphasizes their growing relevance in clinical diagnostics, pharmaceutical monitoring, and bioanalytical research.