Enzyme-linked immunosorbent assay antigen-antibody complexes

Antibodies can be combined with enzymes and color reagents or radioactive antigens to produce quantitative testing for drugs. The ELISA or Enzyme-Linked ImmunoSorbant Assay uses antibodies generated against the Ag to be tested for covalently linked to an enzyme which can catalyze a color change reaction such as the NADH to NAD conversion (Xmax at 340 nm). When the Ag-Ab complex is formed the enzyme is activated and the color can be detected. 

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). 

Figure 19-13 illustrates the principle of an enzyme-linked immunosorbent assay, abbreviated ELISA in biochemical literature. Antibody 1, which is specific for the analyte of interest (the antigen), is bound to a polymeric support. In steps 1 and 2, analyte is incubated with the polymer-bound antibody to form a complex. The fraction of antibody sites that bind analyte is proportional to the concentration of analyte in the unknown. The surface is then... 

At their most elaborate, epitope mapping techniques can provide detailed information on the amino acid residues in a protein antigen, which are in direct contact with the antibody binding site. X-ray crystallography of antibody-antigen complexes can identify contact residues directly and unequivocally, though not surprisingly in view of the effort required, this method is not in routine use. At the other extreme, demonstration by competition enzyme-linked immunosorbent assay (ELISA) methods that two antibodies bind to different sites on... 

Friguet, B., Chaffotte, A. F., Djavadi-Ohamance, L, and Goldberg, M. E (1985) Measurements of the true affinity constant in solution of antigen-antibody complexes by enzyme-linked immunosorbent-assay. J Immunol Methods 77,305-319... 

This chapter presents an approach to perform enzyme linked immunosorbent assays (ELISA) in a microfluidic format with electrochemical detection. This field of analytical chemistry has shown a strong activity in recent years, and many reports have presented the use of capillary-sized reactors for running immunoassays either in homogeneous format (where the antigen-antibody complex and the labelled revelation reagents are separated prior to detection, as for instance by capillary electrophoresis [1-3]) or in heterogeneous format (where the antibody is immobilised on the inner surface of the microsensor device [4] or on microbeads [5,6]). 

The heterogeneous enzyme immunoassays, which include the enzyme-linked immunosorbent assay (ELISA), are based on the same principles as are used in radioimmunoassays (RIA). In short, after incubation of antigen and antibodies, the antigen-antibody complexes formed are separated from free antigen and antibody by one of a number of different techniques, and the activity in one or both of the fractions is determined. 

All immunoassays are based on the principle detection method employed. Commonly used meth-of competitive displacement of a labeled drug ods include fluorescence polarization, enzyme im-from an antigen-antibody complex by unlabeled munoassay, cloned enzyme donor immunoassay, drug in the sample. The fundamental difference enzyme-linked immunosorbent assay, and radioin the currently available immunoassays is the immunoassay. 

ELISA Enzyme-linked immunosorbent assay. A sensitive biotechnology analytical technique in which an enzyme is complexed to an antigen or antibody. The analyte is bound and complexed, and then removed for quantification via color development or other instrumental analysis techniques (i.e., fluorescence). ELISA is used as a rapid and accurate technique to quantify most mycotoxins. 

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