Labeled immunochemical assays enzyme immunoassay

The immunochemical interaction between the antigen and antibody is very specific. By labeling either the antigen or antibody, the method s sensitivity is increased. The most frequently used labels to increase sensitivity are radionuclides (see Radioisotopes) where the assay process is called radioimmunoassay (RIA), or enzymes where the assay is named enzyme immunoassay (EIA) (see Enzyme applications). 

In the decade following the pioneering developments of Yalow and Berson, all immunoassays used a radioactive label in a competitive assay format. Since the introduction of enzyme immunochemical assays in the 1970s, a vast array of sophisticated immunochemical assays have evolved and have been very widely applied. Specific examples of several of these assays follow others are briefly described in Box 9-4. 

Immunoassays, electrochemical — A quantitative or qualitative assay based on the highly selective antibody-antigen binding and electrochemical detection. Poten-tiometric, capacitive, and voltammetric methods are used to detect the immunoreaction, either directly without a label or indirectly with a label compound. The majority of electrochemical immunoassays are based on -> voltammetry (-> amperometry) and detection of redox-active or enzyme labels of one of the immunochemical reaction partners. The assay formats are competitive and noncompetitive (see also -> ELISA). 

Only limited development of new methodologies has taken place for immunochemical analysis of nucleic acids. Most published methods rely on modifications to classical DNA probe hybridization or immunoassay methods, with considerable blending of the two. For example, some methods employ immobilized oligonucleotide probes to capture the analyte DNA followed by immunoenzymatic detection. Other methods use immunocapture followed by detection with an enzyme-labeled DNA probe. Distinctly new methodologies mostly impact on assay formats (e.g., DNA microarrays and in situ hybridization) and detection reagents (e.g., chemiluminescent enzyme substrates). 

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