Indicator displacement assays IDAs

Indicator displacement assays (IDAs) - or, in the specific case of fluorescent indicators, F-IDAs - are based on the next alternative concept described here. A receptor with an affinity for a given analyte is loaded with an indicator, usually a fluorescent or colored dye, whose spectral properties undergo a change upon complexation with the receptor. Treatment of this indicator-receptor complex with the analyte results in the displacement of the indicator from the receptor and a restoration of the indicator s original spectral properties, indirectly reporting analyte coordination (Fig. 27). For effective detection, two main requirements have to be fulfilled (1) the receptor/indicator interaction must be reversible and weaker than the interaction of the receptor with the designated analyte and (2) the indicator must show significantly different optical properties when bound to the receptor and when freely dissolved in solution. 

The binding of citrate by 4.28 has been investigated by the indicator displacement assay (IDA) method (cf. EDTA titrations, Section 3.1.3). Binding of an organic dye indicator with comparable structure to citrate competes with the substrate for the same binding site. The binding of the indicator... 

Scheme 5 Basic concept of an indicator displacement assay (IDA) the optical properties of an indicator (color, fluorescence) change upon replacement hy an analyte...

Artificial receptors can be converted into sensors by covalent attachment of a signaling unit such as a fluorescent dye. An interesting alternative are soindicator displacement assays (IDAs) [9]. These assays are based on receptors that are bound to dyes (or fluorescent ligands) via noncovalent interactions. Upon addition of an analyte, the dyes are displaced, which results in a change of their optical properties. These changes can be used to identify and/or quantify the analyte. 

Competitive binding assays are well established in bio-analysis. Over the past decade, substantial efforts have been made to use competition experiments in other research areas, especially supramolecular chemistry. Instead of covering all types of competition experiments, this chapter focuses on a unique competition assay, the so-called indicator displacement assay (IDA), which has become a standard strategy for molecular recognition and sensing. ... 

A competitive assay (indicator displacement assay, IDA) was reported by Anslyn using the Zn(II) complex 49 shown in Figure 21. This 2,2 6,2"-terpyridine complex forms a chemosensing ensemble with pyrocatechol violet because of the ability of the dye to chelate the Zn(II) cation. On addition of a series of unprotected amino acids to a solution of the chemosensing ensemble, the release of the dye was visually verified and spectroscopically measured (1 1... 

Indicator displacement assays (IDAs) These are a complementary approach to... 

Fig. 27 (a) Representative scheme for a displacement assay protocol in which first a fluorescent indicator is coordinated to a host. As a consequence, its optical properties are altered Second upon analyte addition, the higher affinity of the analyte for the host leads to dissociation of the complex and displacement of the indicator. The original optical properties of the fluorophore are restored, signaling indirectly the presence of the analyte (b) Some examples of receptors and fluorescent indicators reported in the literature for F-IDAs... 

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