Fluorescence quenching sensors

Chen YG, Zhao D, He ZK, Ai XP (2007) Fluorescence quenching of water-soluble conjugated polymer by metal cations and its application in sensor. Spectrochim Acta A Mol Biomol Spectrosc 66 448 -52... 

Because squaraines are sensitive toward nucleophilic attack resulting in decoloration and fluorescence quenching, they can be used as specific chemodosimeters for t/i/oZ-containing compounds. Squaraines 4 have been successfully applied as sensors for low-molecular-weight aminothiols like cysteine in a complex multicomponent mixture (e.g., human plasma) [91]. 

L. Chen, D.W. McBranch, H.-L. Wang, R. Helgeson, F. Wudl, and D.G. Whitten, Highly sensitive biological and chemical sensors based on reversible fluorescence quenching in a conjugated polymer, Proc. Natl. Acad. Sci. USA, 96 12287-12292, 1999. 

There is a linear relationship between tq/t and the concentration of the quencher. In these sensors, the static fluorescence quenching has no effect on the lifetimes. 

Yet the majority of cation sensors are mediator-based sensing. One type of optical sensor is based on the fluorescence quenching of fluor-ophore Rhodamine 6G by transition metals such as Co(II), Cr(III),... 

A.K. McEvoy, C.M. McDonagh and B.D. MacCraith, Dissolved oxygen sensor based on fluorescence quenching of oxygen-sensitive ruthenium complexes immobilized in sol-gel-derived porous silica coatings, Analyst, 121(6) (1996) 785-788. 

The silver clusters can be applied as fluorescent probes to retrieve information about the chemical environment. There are reported three classes of sensors based on silver clusters. First, we discuss silver cluster sensors of which the fluorescence quenches in the presence of the analyte. Second, we discuss a sensor in which fluorescent clusters are formed only in presence of the analyte. Finally, we discuss the shift in the absorption and fluorescence bands of silver clusters while sensing the chemical environment. 

CEF Chelation or Complexation Enhancement of Fluorescence CEQ Chelation or Complexation Enhancement of Quenching Fig. 10.1. Main classes of fluorescent molecular sensors of ions or molecules. 

Most fluorescent PET molecular sensors, including pH indicators of this type, consist of a fluorophore linked to an amine moiety via a methylene spacer. Photo-induced electron transfer (see Chapter 4, Section 4.3), which takes place from amino groups to aromatic hydrocarbons, causes fluorescence quenching of the latter. When the amino group is protonated (or strongly interacts with a cation), electron transfer is hindered and a very large enhancement of fluorescence is observed. 

Many fluorescent molecular sensors for halide ions (except F ) are based on collisional quenching of a dye. In particular, the determination of chloride anions in living cells is done according to this principle. Examples of halide ion sensors are given in Figure 10.29. 

Appropriate combinations of boronic acid and fluorophores lead to a remarkable class of fluorescent sensors of saccharides (Shinkai et ah, 1997, 2000, 2001). The concept of PET (photoinduced electron transfer) sensors (see Section 10.2.2.5 and Figure 10.7) has been introduced successfully as follows a boronic acid moiety is combined intramolecularly with an aminomethylfluorophore consequently, PET from the amine to the fluorophore causes fluorescence quenching of the latter. In the presence of a bound saccharide, the interaction between boronic acid and amine is intensified, which inhibits the PET process (Figure 10.42). S-l is an outstanding example of a selective sensor for glucose based on this concept (see Box 10.4). 

This type of probe, often called fluorescent photoinduced electron transfer (PET) sensors, has been extensively studied (for reviews, see Refs. 22 and 23). Figure 2.2 illustrates how a cation can control the photoinduced charge transfer in a fluoroiono-phore in which the cation receptor is an electron donor (e.g., amino group) and the fluorophore (e.g., anthracene) plays the role of an acceptor. On excitation of the fluorophore, an electron of the highest occupied molecular orbital (HOMO) is promoted to the lowest unoccupied molecular orbital (LUMO), which enables photoinduced electron transfer from the HOMO of the donor (belonging to the free cation receptor) to that of the fluorophore, causing fluorescence quenching of the latter. On... 

Sensors based on the fluorescence quenching ofrhodamine 6G in resins by iodide ions(43) and in Nafion polymer by metal ions in solution 44,45) have been demonstrated. However, complex fluorescence decay mechanisms often hinder interpretation in lifetime-based sensing and much progress is still to be made in this area before the true potential of lifetime-based sensing becomes a reality. For example, rhodamine 6G in... 

W. A. Wyatt, F. V. Bright and G. M. Hieftje, Characterization and comparison of three fiber-optic sensors for iodide determination based on dynamic fluorescence quenching ofrhodamine 6G, Anal. Chem. 59, 2272-2276 (1987). 

There are several luminescence flow-through sensors based on both fluorescence quenching phenomena and biolimiinescent reactions. 

A sensor for halides, Ch, Br and I , using fluorescence quenching of either acridinium or quinidinium-based fluorescent reagents covalently bound to a glass support via carbodiimide has been described. Other examples are sensors for Na, K+ and Ca. ... 

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