ELISA-type assays

The screening assay is, in general, a binding assay, mostly an ELISA-type assay, or a radio-immune-precipitation method. Standard ELISA-type immunoassays are not always considered appropriate, however, for measuring binding... 

Early descriptions of SPR technology for bioanalytical applications were based on simple physical adsorption of proteins to an active metal surface [1]. However, it was soon realized that a more sophisticated approach was needed in order to meet the challenges demanded by the range of potential applications involved. Commonly used metal substrates such as gold and silver show a high tendency for spontaneous adsorption of proteins and other molecules. This passive binding to the metal substrate results in a loss of the bioactivity. Similarly, studies on antibody binding activities in ELISA-type assays after their adsorption to plastic surfaces have shown levels as low as 2-10% of the adsorbed amount [2]. 

Application of assay format is attractive because it allows a mass-screening of the samples for rapid and inexpensive monitoring of the important classes of herbicides. Three assay systems based on specific properties of D1 protein have been tested, such as ELISA-type assay, DELFIA fluoro-mettic assay and assay based on the liposomes incorporated D1 protein. 

Like antibodies, aptamers are characterized by very impressive, unsurpassed affinity, and selectivity properties. Such remarkable feature has determined immense potentialities in the diagnostic field and various analytical systems have been developed, notably in the field of biosensors, ELISA-type assays, flow cytometry, or separation techniques [6, 7]. Specifically, aptamers constitute, with antibodies, the most popular affinity reagent employed for the development of bioaffinity-based LC and CE methodologies. However, the aptamers present many advantages over antibodies. Aptamers can be regenerated within minutes via a denaturation-renaturation... 

A number of assays for the hydrolase-type of Hyals were developed in the last decade that facilitated their characterization. These include microtiter-based ELISA-like assays, in which a highly specific HA-binding protein substitutes for the antibody component [186]. Biotinylated HA bound to microtiter plates is subjected to Hyal activity, and the remaining HA quantified by an avidin-enzyme color reaction [107]. HA substrate gel zymography procedures were also formulated that facilitated additional studies of these enzymes [187]. 

Laboratory confirmation is vital to effective treatment of HSV, especially in individuals in whom a clinical diagnosis cannot be obtained. There are several methods by which a definitive diagnosis may be acquired, and these include virologic typing, serologic diagnosis, rapid point-of-care antigen detection, enzyme-linked immunosorbent assay (ELISA), immunoblot, and DNA polymerase chain reaction.27... 

Additionally it has been our experience that mass spectrometry as a routine detection/identification technique for bacteria is not well received by microbiologists and clinicians who prefer less expensive, less complicated approaches to bacterial typing and identification, such as methods based on polymerase chain reaction (PCR) and enzyme-linked immunosorbent assays (ELISA). For that reason we have adapted our MS approach to serve as a means of biomarker discovery that feeds candidate proteins or leads into development as PCR targets or other immunoassay techniques. 

Many variations on the assay exist, but the ELISA, shown schematically below, is currently highly favored because of its simplicity once established in a laboratory sensitivity, detecting about one adduct per 107 bases and ability to screen many samples because of easy automations. The current prerequisite for the assay is that DNA can be modified to sufficiently high levels with the ultimate carcinogen to make it suitably antigenic. These types of antigens have been used to raise polyclonal antibodies in rabbits (41) and monoclonal antibodies from mice (42). 

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). 

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