Immunoassay, DNA Analysis, and Other Ligand Binding Assay Techniques: From Electropherograms to Multiplexed, Ultrasensitive Microarrays on a Chip

Abstract

Ligand or assays have made a major impact on biomedical research and clinical diagnosis since their development in the late 1950s. Immunoassay techniques (relying on specific antibodies to bind the target analyte) represent the best-known example, but analogous DNA and RNA analysis methods (using oligonucleotides to recognize defined polynucleotide sequences) are rapidly gaining in importance and are likely to exert profound effects on human society. The evolution of these methods may be divided into three phases: (i) the initial development and widespread use of sensitive competitive assays relying on radioisotopically labeled analyte to monitor the binding reaction; (ii) the introduction in the 1980s of ultrasensitive, noncompetitive, labeled antibody methods relying on high-specific-activity nonisotopic labels, leading to the emergence of the automatic analyzers that now dominate the field, and (iii) the present development of microarraymethods based on antibody or oligonucleotide microspots (each recognizing an individual analyte) arrayed on a solid support and relying on observation (typically by confocal microscopy) of fluorescent signals emitted from each spot. Miniaturized microarray methods permitting ultrasensitive measurement of hundreds of different analytes in a minute sample are likely to revolutionize medicine and related fields within the next decade.