Scintillation Proximity Assay SPA

In 1979, the first SPA was described by Hart and Greenwald [15, 17]. It was an immunoassay using two polymer beads coated with antigens, one labeled with a fluorophore and the other with tritium ( H). In the following years, Amersham Biosdences Inc. further optimized this radioisotopic assay technology [18, 19]. 

SPA beads are prepared from inorganic materials such as yttrium silicate (YSi) 

Energy absorbed by buffer medium no light generation 

Different SPA formats can be set up with these generic beads, which can be grouped into two main classes based on the assay principle (see Table 1). 

(ii) Signal decrease. In this format, the radiolabeled substrate is linked via biotin to streptavidin-coated SPA beads. The substrate is designed such that the action of hydrolytic enzymes such as nucleases, proteases, esterases, and phospho- 

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Radioactive assays have fallen out of favor over the last decade, and few HTS assays are run using radioactive tracers. Safety, cost, and the need to dispose of large amounts of waste, along with the availability of nonradioactive formats have hastened their decrease. However, scintillation proximity assays (SPA) are still run in some HTS laboratories. 

HTS screening is often based on miniaturized cell assays that enable chemical libraries to be screened for molecules that present different biological activities and sometimes-different biological targets using fluorescence, scintillation proximity assays (SPA) and luminescence as detection techniques. 

Scintillation proximity assay (SPA) is a variety, or part, of RIA. This method is based on the measurement of the scintillation of radioactive molecules. On the basis of the power of the scintillation, it is possible to determine the amount of radioactivity. Then, it is possible to count the alkaloid content. This method was used recently in the biosynthesis of communesin alkaloids . ... 

The key to these assays is to find a suitable method by which the bound labeled ligand can be measured, separate from the unbound fraction. Three separate methods have been used to measure hERG binding filtration through glass fiber filters [36, 37], scintillation proximity assay (SPA) technology [38] and fluorescence... 

Method C. Most researchers have carried out CETP assay using a Scintillation Proximity Assay (SPA) kit [79]. The reaction mixtures containing a test sample, [3H]CE-HDL, and biotin-LDL, are thoroughly mixed. The reaction is initiated by the addition of CETP. After a 4-hr incubation at 37°C, the reaction is terminated by the addition of streptavidin SPA beads, and allowed to stand for 1 hr at room temperature. Finally, the transfer of [3H]CE from [3H]CE-HDL to LDL is measured by scintillation counter. 

The availability of a new version of isotopically labeled ATP, [33P]ATP, provided benefits of safety and longer half-life. The lowered energy was also better suited for scintillation proximity assays (SPAs). The SPA was a major step forward because it eliminated the need for wash steps by capturing the [33P]-labeled peptide on a functionalized scintillating crystal, usually via a biotin-streptavidin interaction. 

Fig. 5 Schematic representation of Scintillation Proximity Assay (SPA). The SPA bead absorbs the radiation energy of a radioisotope labeled ligand bound to the target molecule and generates a light signal. The energy released from an unbound radioligand is dissipated before reaching the bead.

In scintillation proximity assays (SPA),a plastic bead containing a fluor and coated with a lectin binds the carbohydrate extracellular... 

Methods based on radiolabels continue to hold an important place in routine analysis and in research related to clinical testing. The main techniques included in this group are radioimmunoassy (RIA), immunoradiometric assay (IRMA), and scintillation proximity assay (SPA). Many researchers in this field use short-lived radioisotopes and chelating agents in antibody labeling.139 The most popular types of immunoassay are methods that use enzymatic labels the enzyme-linked immunosorbent assay (ELISA), the enzyme-monitored immunotest (EMIT), the competitive binding enzyme immunoassay (EIA), and the immunoenzymometric assay (IEMA). 

Enzyme inhibitory UV, colorimetric, radiolabeled, scintillation proximity assay (SPA)... 

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