Enzyme assay radioactive technologies

Considerable effort was expended in the development of alternative technologies that did not require the use and measurement of radioactivity. A number of nonisotopic assays for T4 were subsequently developed commercially for use on fuUy automated immunoassay systems or for use with existing chemistry analyzers. According to a 2002 College of American Pathologists Ligand Assay Survey, more than 95% of laboratories now use a nonisotopic T4 method. A variety of different labels were used to construct these nonisotopic assays. Enzymes such as horseradish peroxidase, alkaline phosphatase, and [3-D-galactosidase were the most... 

Enzyme-linked immimosorbent assays (ELISAs) are sensitive enough to detect relevant concentrations of small molecules and proteins. Their detection limits are inadequate for direct analysis of DNA in most cases. Eor this reason, it was not until the development of PCR that nucleic acid analysis became routine. Prior to PCR, the large quantities of nucleic acid required for hybridization precluded routine use and mandated the use of radioactive probes. After PCR, the abundance of amplified sequences allowed many methods of detection. In this environment, it was natural that immunochemical technologies first developed for immunoassay would be applied to analysis of amplified DNA. 

The first quantitative immunoassays were based on the use of radioactive reporter molecules, mainly and " C. These radioimmunoassays (RIAs) have gradually been replaced by nomadioactive reporter molecules or labels, e.g., enzymes, fluorescent, and luminescent molecules and combinations of these. The nonradio-active labels facilitated development of automated immunoassays, and they also contributed to the design of assays with substantially reduced detection limits. However, nomadioactive assay have an advantage only in immunometric sandwich assays in inhibition assays, the use on nonradioactive labels has not provided any improvement in assay sensitivity as compared to RIA [1]. The development in immunoassay technology has been reviewed by Ekins [2]. 

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