Fluorescent probes for small molecules

The design of fluorescence-based detection systems for small molecules is influenced immediately by the fact that the vast majority of these target analytes are nonfluorescent. Therefore, sensors are required that probe the analyte and incorporate fluorophores which respond sensitively to the probe-analyte interaction. As stated above, in type I sensors these fluorophores are coupled to the sensor unit of the reporter. A vast array of fluorescent molecules is known. Here we give a brief overview of these fluorophores by family—small molecules, proteins, and the new fluorescent nanomaterials—and comment on how they may be incorporated into sensors for small molecules. The description of the sensor units is usually unique to the analyte of interest and is detailed in Section 6.3. 

Recent progress in fluorescent probes for Zn /Cd based on small organic molecules 12CJO1803. 

Overall, the implementation of lanthanide probes in chemical sensor technology is still in its initial stage. Up to now they have not found their way into commercialized sensor systems. Particularly, with respect to p02 and pH sensors, it cannot be foreseen that LLCs may displace established fluorescent indicators. Sensors for small molecules such as hydrogen peroxide, phosphate, or ATP can be useful in enzymatic assays in which the conversion of the substrate has to be monitored. In this case, the selectivity is provided by the enzyme involved. A concrete example is presented by means of a glucose sensor based on immobilized glucose oxidase and... 

Murata, A. Sato, S. Kawazoe, Y Uesugi, M. Small-molecule fluorescent probes for specific RNA targets. Chent Commun. 2011,47,4712-4714. 

Bertoncini, C. W. Celej, M. S. Small molecule fluorescent probes for the detection of amyloid self-assembly in vitro and in vivo. Curr. Protein Pept. Sci. 2011,12, 206-220. 

The formation of a microphase structure can be sensitively detected by using hydrophobic fluorescent probes. Hydrophobic microdomains tend to solubilize hydrophobic small molecules present together in aqueous solution. For example, diphenylhexatriene (DHT) is hydrophobically bound to the St aggregates in ASt-x in aqueous solution and, as a result, the fluorescence intensity is greatly enhanced. Figure 9 shows the fluorescence intensity of DHT in the presence of ASt-x relative to the intensity in its absence (I/I0) as a function of the ASt-x concentration [29],... 

It is possible, however, that the electrochromic response of some styrylpyridi-nium probes, for example, RH421 (see Fig. 2), is enhanced by a reorientation of the dye molecule as a whole within the membrane. There is a steep gradient in polarity on going from the aqueous environment across the lipid headgroup region and into the hydrocarbon interior of a lipid membrane. Therefore, any small reorientation of a probe within the membrane is likely to lead to a change in its local polarity and hence a solvatochromic shift of its fluorescence excitation spectrum. Such a... 

When compared to fluorescent proteins, fluorophores and quenchers of fluorescence (short quenchers) are small molecules with sizes varying from 1 to 10 A. They are the main building blocks for constructing small molecule FRET probes. As molecular entities, they might influence the performance of the probe to a great extent. Their fluorescent properties will determine the sensitivity and dynamic range of the sensor. The success of the probe for a specific application will depend on the selection of the right fluorophores... 

Proteases are one of the largest families of enzymes and are involved in a multitude of vital processes. Due to their biological relevance and diversity, multiple fluorescent reporters monitoring their activity have been designed and successfully applied in vitro and in vivo [112-114]. Standard small molecule FRET probes for proteases consist of an amino acid sequence flanked by a FRET pair, consisting of two fluorophores or one fluorophore and a quencher molecule. Upon cleavage of the peptide sequence, the emission of the donor fluorophore is dequenched and the intensity increases whereas the emission of the acceptor decreases and vanishes more or less completely in those cases where the acceptor is fluorescent (see Fig. 6.11). 

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