Labeled immunochemical assays formats

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). 

The previously discussed methods rely on evaluating the immune complex formation as an index of antigen antibody reaction. As demonstrated previously in equation (1), the overall reaction occurs in sequential phases, and only the final phase is the formation of the immune complex. However, the initial binding of the antibody and antigen has also been demonstrated to be very useful analytically and has been used with labeled antigens and antibodies to develop many sensitive and specific immunochemical assays. The reaction describing this initial binding and the kinetic constant for the overall reaction are shown in equations (4a) and (4b), respectively ... 

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. 

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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