Homogeneous enzyme immunoassay
Homogeneous enzyme immunoassay (Forensic Science)
Immunoassays combine biochemistry with the specific binding tendency of antibody to antigen to produce a measurable signal. Immunoassays may be heterogeneous or homogeneous. Heterogeneous immunoassay requires the additional step of separating bound and unbound components, whereas homogeneous immunoassay returns a measurement without separating the antigen and antibody. Enzyme assays use an enzyme-bound antibody to detect the antigen. The enzyme then signals with a color reaction when exposed to the substrate. Because the homogeneous assay is quicker and easier, it is often the test preferred by forensic scientists in cases involving drugs of abuse.
In response to an antigen, which is any substance the body considers as foreign, specific antibodies bind in lock-and-key fashion, forming a complex that awaits destruction by other components of the immune system. Immunoassays take advantage of this binding specificity. The analyte (that is, the substance being analyzed) may be either antibody or antigen. Analytes may be hormones (such as testosterone or cortisol), markers of cardiovascular damage (such as creatinine or myoglobin), hepatitis strains (such as hepatitis B), tumor markers (such as certain proteins), congenital infectious agents (such as rubella), or metabolics (such as folate or vitamin B12). Examples of drugs of abuse that are amenable to homogeneous immunoassay are opiates, amphetamines, barbiturates, benzodiazepines, and cocaine...
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Further Reading (Forensic Science)
Jenkins, Amanda J., and Bruce A. Goldberger, eds. On-Site Drug Testing. Totowa, N.J.: Humana Press, 2002.
Mieczkowski, Tom, ed. Drug Testing Technology: Assessment of Field Applications. Boca Raton, Fla.: CRC Press, 1999.
Smith, Frederick P., ed. Handbook of Forensic Drug Analysis. Burlington, Mass.: Elsevier Academic Press, 2005.
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