Quenched Fluorescence

The design of a beacon is in general a 25-30 base synthetic oligonucleotide (ssDNA) equipped with a primary amine at its 3 end, and a sulfide at its 5 end, enabling to covalently link the fluorophore as well as the duster (or an organic quencher). The hairpin-loop structure is achieved by complementary sequences of the 3 and 5 end. 

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In addition to the processes that can compete with fluorescence within the molecule itself, external actions can rob the molecule of excitation energy. Such an action or process is referred to as quenching. Quenching of fluorescence can occur because the dye system is too warm, which is a very common phenomenon. Solvents, particularly those that contain heavy atoms such as bromine or groups that ate detrimental to fluorescence in a dye molecule, eg, the nitro group, ate often capable of quenching fluorescence as ate nonfluorescent dye molecules. 

Several other biosensors have been developed usiag this oxygen-quenched fluorescence approach. Target species iaclude ethanol [64-17-5] hydrogen peroxide [7722-84-17, H2O2, lactate, and xanthine [69-89-6] C H4N402, usiag alcohol oxidase, catalase [9001-05-2] lactate oxidase, and xanthine oxidase, respectively. An additional technique for biocatalytic biosensors iavolves the firefly chemiluminescent reaction (17) ... 

Fast concentration and sample injection are considered with the use of a theory of vibrational relaxation. A possibility to reduce a detection limit for trinitrotoluene to 10 g/cnf in less than 1 min is shown. Such a detection limit can by obtained using selective ionization combined with ion drift spectrometry. The time of detection in this case is 1- 3 s. A detection technique based on fluorescent reinforcing polymers, when the target molecules strongly quench fluorescence, holds much promise for developing fast detectors. 

Absorption and emission spectra of six 2-substituted imidazo[4,5-/]quinolines (R = H, Me, CH2Ph, Ph, 2-Py, R = H CH2Ph, R = Ph) were studied in various solvents. These studies revealed a solvent-independent, substituent-dependent character of the title compounds. They also exhibited bathochromic shifts in acidic and basic solutions. The phenyl group in the 2-position is in complete conjugation with the imidazoquinoline moiety. The fluorescence spectra of the compounds exhibited a solvent dependency, and, on changing to polar solvents, bathochromic shifts occur. Anomalous bathochromic shifts in water, acidic solution, and a new emission band in methanol are attributed to the protonated imidazoquinoline in the excited state. Basic solutions quench fluorescence (87IJC187). 

Nitroxides have the property of quenching fluorescence. Thus radical trapping with nitroxides containing fluorophores (e.g. 114) can be monitored by observing the appearance of fluorescence.511015 The method is highly sensitive and has been applied to quantitatively determine radical yields in PLP experiments (Section... 

The high-spin/low-spin interconverison in a Ni11 complex of the cyclam derivative (639) bearing a luminescent naphthalene substituent has been used as a fluorescent molecular thermometer.161 The Ni11 tends to quench fluorescence of the proximate naphthalene subunit, but the two spin states exert a different influence on the emission properties. Emission is temperature dependent, since the high spin —> low spin conversion is endothermic, i.e., a temperature increase favors formation of the low-spin form. 

The quantum yield for the formation of the cycloaddition product has been found to be temperature dependent, increasing by a factor of approximately three as the temperature is lowered from 65 ( = 0.24) to 5°C ( = 0.69). Photolysis of mixtures of the olefin and f/my-stilbene in the presence of sensitizers yielded no cycloaddition product (42) but rather only m-stilbene. This suggests that the cycloadduct is produced via a singlet reaction. This conclusion is supported by the fact that tetramethylethylene quenches fluorescence from the /rans-stilbene singlet. A plot of l/ (42) vs. 1/[TME] (TME = tetramethylethylene) is linear. The slope of this plot yields rate constants for cycloadduct formation which show a negative temperature dependence. To account for this fact, a reversibly formed exciplex leading to (42) was proposed in the following mechanism<82) ... 

Exploration of collective effects in multiple transfers that appear when the donor and acceptor are the same molecules and display the so-called homotransfer. In this case, the presence of only one molecular quencher can quench fluorescence of the whole ensemble of emitters coupled by homotransfer [32]. The other possibility of using homo-FRET is the detection of intermolecular interactions by the decrease of anisotropy [33]. 

Table 1. Common materials used in quenched-fluorescence oxygen sensing (Ru(dpp)3(C104)2 tris(diphenylphenantroline) ruthenium(II) perchlorate PtOEPK platinum(II)-octaethyl-porphine-ketone PtPFPP platinum(II)-tetrakis(pentafluorophenyl)porphine PS.poly(styrene), PSu poly(sulfone) PSB poly(styrene-butadiene) block co-polymer PVC polyvinylchloride) APET amorphous poly(ethyleneterephthalate) PE poly(ethylene).

Using the same PAbs an optical biosensor system has been developed for 2,4,6-TCP [224]. The principle is the detection of laser-induced fluorescence (LIF) in single microdroplets by a homogeneous quenching fluorescence immunoassay (QFIA). The competitive immunoassay occurs in microdroplets (d=58.4 mm) produced by a piezoelectric generator system. A continuous Ar ion laser (488 nm) excites the fluorescent tracer and its fluorescence is detected by a spectrometer attached to a cooled, charge-coupled device (CCD) camera... 

The quantum yield of flavin fluorescence in proteins is very low in many cases, and the lifetimes are on the order of picoseconds. This is a result of the high electrophilicity of oxidized flavins, and their ability to quench fluorescence following electron transfer from the electron-rich groups of... 

Fluorescence quenching has proven to be a powerful means to determine location of tryptophans. Small organic molecules, such as acetone, acrylamide, and amino acids, have been used to quench fluorescence of tryptophans which are exposed to the solvent.(50 51) These molecules apparently quench by close interaction and so provide a tool to determine the surface accessibility7 of tryptophan in a protein. 

In actual experiments in biophysics, the interface may not be a simple interface between two media, but rather a stratified multilayer system. One example is the case of a biological membrane or lipid bilayer interposed between glass and aqueous media. Another example is a thin metal film coating, which quenches fluorescence within the first 10 nm of the surface... 

IQ (iron quench) Pierce Biotechnology, Inc. Iron compound binds fluorophore-labeled peptides after phosphorylation and quenches fluorescence intensity... 

Heavy atoms in solution quench fluorescence by colliding with excited molecules so that their energy is dissipated, e.g. chloride or bromide ions in solution cause collisional quenching. 

Finally, the question of whether the oxygen present in air-saturated PS and PMMA hosts can quench fluorescence is considered. In a study of naphthalene in a PS host, Nowakowska et al. 36) have shown that the increase in kM for air-saturated films rela-... 

Biacetyl as sensitizer phosphorescence quenched fluorescence not affected, release of NH S No apparent degradation of biacetyl ... 

This apparent contradiction may be related to UV absorbance contributed by mineral forms. The gel permeation technique used in this laboratory has been observed to concentrate mineral components. For example, nitrate in this fraction has been found to exceed 1 g/L. Furthermore, some mineral forms such as ferrous iron have been observed to absorb at 260 nm. Chelates have been found to quench fluorescence. Thus, the concentrations of all minerals and their contributions to UV absorbance or fluorescence quenching should be carefully examined. High concentrations of metallic ions also may play a catalytic role during pyrolysis and further contribute to the absence of pyrolysis products (27). 

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