Optical techniques antigen-antibody reactions

Immobilization techniques have been applied in the preparation of immobilized CL reagents, with specific advantages such as reusability, improved stability, and increased efficiency. These strategies have been applied in the development of CL sensors, which today constitute the most important tools in analytical chemistry because of the high sensitivity offered. Optical fibers have been used to transfer light in order to improve the quality of detection, and new types of flow-through cells have been introduced in the construction of CL sensors. Also, selectivity has been considerably improved by the utilization of enzymatic or antigen-antibody reactions. 

These two optical techniques are particularly applicable to methods measuring the precipitate formation in antigen antibody reactions (see Chapter 9). Turbidimetry is used in several chemistry immunoassay systems for therapeutic drug monitoring and specific protein assays. Details of turbidimetry and nephelometry are discussed in Chapter 3. 

Ellipsometry is a reflectance technique that depends on the optical constants and thickness of surface layer. For colorless layers, a polarized light beam will change its plane of polarization upon reflection by the surface film. The thickness can sometimes be determined when optical constants are known or approximated by constants of the bulk material. Antibody-antigen surface reaction can be detected this way. 

A fiber-optic flow-injection analysis in which a fluorescent reporter molecule is utilized to monitor a competition reaction between a labelled and an unlabelled antigen molecule for an immobilized antibody has been reported [100]. It is based on the evanescent wave technique. 

Since antibody-antigen binding does not produce a detectable signal by itself, several techniques involve a tag such as an enzyme, radioisotope, or fluoroph-ore to monitor the reaction with a variety of optical and electrochemical detectors. One group of detectors generally uses fluorescence and chemiluminescence while another employs amperometry and potentiometry. Electrochemical immunoassays are emergent alternatives to existing immunochemical... 

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