Enzyme-linked immunosorbent assay antigen-antibody interactions

Liposome conjugates may be used in various immunoassay procedures. The lipid vesicle can provide a multivalent surface to accommodate numerous antigen-antibody interactions and thus increase the sensitivity of an assay. At the same time, it can function as a vessel to carry encapsulated detection components needed for the assay system. This type of enzyme-linked immunosorbent assay (ELISA) is called a liposome immunosorbent assay or LISA. One method of using liposomes in an immunoassay is to modify the surface so that it can interact to form biotin-avidin or biotin-streptavidin complexes. The avidin-biotin interaction can be used to increase detectability or sensitivity in immunoassay tests (Chapter 23) (Savage et al., 1992). 

Enzyme-linked immunosorbent assay (ELISA) is a new method in alkaloid studies. The application of ELISA to alkaloid study is based on antibody incubations. It differs from classical precipitation-based methods in that specific antigen-antibody interactions are recognized by assaying an enzyme label conjugated to one reactant, usually an antibody. Because of the sensitivity with which enzyme... 

The most predominant application of antibodies has been in the area of diagnostic assays, known as immunoassays, which exploits the specific interaction between the antibody and antigen. The world immunoassay market for clinical and food diagnostics, environmental analysis and other applications exceeded 1.2 billion in 1990. ELISA (Enzyme-Linked Immunosorbant Assay) represents 60% of that market (2). Annual growth rates have been projected at 10-15%. The food diagnostics is projected to grow to 500 million by the year 2000 (3). 

On the basis of an enzyme thermistor, Mattiasson et al. (1977) developed one of the first immunosensors. Immobilized antibodies against albumin are placed in a column and set into an ET. After injection of an albumin-sample and a known amount of enzyme-labeled albumin, both are separated from the sample matrix by antibody-antigen-interaction. After injection of a substrate, the change in heat is a measure of analyte concentration. The less heat produced means that more albumin has been bound. An elution step regenerates the ELISA. Due to its thermal detection principle, the procedure is called TELISA (thermometric enzyme-linked immunosorbent assay). Figure 3 shows the principle of the TELISA procedure in its sandwich configuration. 

Immunoassay techniques are based on the antigen-antibody interaction. These techniques involve a competitive reaction between antigen molecules of the target molecules and labeled antigen molecules for a limited number of antibodies. Enzyme-linked immunosorbent assays (ELISA) in which antibodies are immobilized on a solid phase are the most popular for pesticide detection. As pesticides are small molecules, in order to synthesize antibodies, pesticide derivatives (haptens) must be synthesized and coupled to carrier proteins. ... 

When the concentration of the analyte in the biological solution is too lowfor detection using spectrophotometry, more sensitive methods such as immunoassays are used for the measurement. Immunoassays utilize antibodies developed against the analyte of interest. Since the antigen and the antibody have a very specific interaction and has very high affinity toward each other, the resulting detection system also has a very high sensitivity. A specific example, the enzyme linked immunosorbent assay (ELISA), will be described here. 

Immunological methods make use of antibodies as analytical tool for detecting a plethora of clinical, environmental, and food-relevant analytes. The special features that had made immunoassay widely increased in the last decades are the highly sensitivity and specificity of the antibody-antigen interaction. Although enzyme-linked immunosorbent assay (ELISA), currently performed in microtiter plates is the most common technique, a variety of assay types can be performed depending of the analytes or samples. 

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