Immunoassays

Abstract

Immunoassays are biochemical tests that utilize antibodies as reagents to detect the presence and/or concentration of ANALYTES. This chapter focuses on immunoassays; however the principles apply also to other ligand binding assays that do not utilize antibodies but instead bind the ANALYTE with ligands, receptors, binding proteins, or other macromolecules. The basic principle of the immunoassay is antibody-antigen interaction, which typically is of high AFFINITY and specificity. This feature allows the detection and quantification of low-abundant ANALYTES. ANALYTES measured by immunoassays can be small molecule drugs, hormones, glycans/saccharides, lipids, peptides, proteins, and even larger structures like viruses and bacteria. Immunoassays measure ANALYTES not only in pure systems (e.g., buffer, cell medium) but also in complex MATRICES including cell lysate, serum, plasma, urine, synovial fluid, bronchoalveolar lavage, sputum, and amniotic fluid. The result can be available in a few minutes (e.g., pregnancy tests); however, it is more typical that a few hours pass between sample preparation and result.