Dark quenchers

In many microfluidic applications, a fluorescent acceptor is preferable to a dark quencher (i.e., a nonfluorescent acceptor). The potential... 

Cook, R. M. Lyttle, M. Dick, D. Synthesis and methods for dark quencher probes for donor-acceptor energy transfer. PCT Int. Appl. WO 2001086001, 2001 Chem. Abstr. 2001,135, 368945. 

Le Reste, L. Hohlbein, J. Gryte, K. Kapanidis, A. N. Characterization of dark quencher chromophores as nonfluorescent acceptors for single-molecule FRET. Biophys. J. 2012,102, 2658-2668. 

The recombination of trapped electrons and holes produces the fluorescence. Adsorbed oxygen scavenges electrons producing O2" which also is adsorbed. OJ is a much better quencher than Oj. Its accumulation under illumination therefore leads to the decrease in fluorescence intensity. During the dark period disappears. During the illumination in the presence of oxygen, the colloid undergoes photoanodic dissolution (see Sect. 3.2). The ZnS particles become smaller in this way, and this finally leads to an increase in fluorescence yield as already described for CdS. 

Fig. 5. Illustration of the 5 -nucleotidase (TaqMan) assay for allele discrimination. (A) The allele discrimination assay employs two unlabeled PCR primers and two doubly fluorescent labeled PCR probes for visuaUzation of a mutant allele. The target sequence is initially denatured and amplified in the presence of each of the primers and probes. Increasing polymerization in the presence of a thermostable polymerase which contains a 5 proofreading function allows cleavage of one fluorescent indicator from an appropriate probe during the cycling reaction. (B) Probes are designed with a fluorescent reporter and a quencher moiety. AmpUfication reactions are spiked with additional fluorescent quenchers in order to render the reaction initially dark to the photomultipUer mbe or diode. The probes are designed...

Both stereoisomers were formed, implying a loss of stereochemical integrity during the formation of the second carbon-carbon bond. When the reaction was conducted on ZnO, surface-related processes affected both the rate and stereochemistry. The effect of various quenchers could be explained as competitive adsorption at active sites, with or without interference with electron transfer. A reaction scheme involving formation of dimer, both in the adsorbed state and in solution, was proposed, the former route being the more important On CdS, the reaction could sometimes be induced in the dark as well because of the presence of acceptor-iike surface states. Neither particle size, surface area, nor crystal structure appeared to significantly influence the dimerization observations parallel to those found in the CdS photoinduced dimerization of N-vinylcarbazole... 

Absolute emission quantum yields ity-are not easily measured in the solid state. However, to a good approximation CPs can be placed in two distinct classes. Some CPs are practically nonfluorescent (yields <10-4) for instance, trans-PA or PDAs in the solid state. Others have r f yields greater than 1% and sometimes much more for instance, about 35% for MEH-PPV [152]. The yields may be limited in the solid state by quenchers for excitons or dark recombination centers for carriers, so they might be improved in better quality materials. 

The existence of Qa was initially inferred from chlorophyll-a fluorescence measurements. In 1963 when Duysens and Sweers found that the fluorescence yield of dark-adapted chloroplasts increases with time of illumination. These workers explained the phenomenon by suggesting that when the PS-II electron acceptor is present in the oxidized state, it can quench fluorescence, whereas it does not quench fluorescence once it is reduced, i.e., in its reduced state it inhibits the normal utilization of absorbed light energy to promote electron transport. Therefore, the electron acceptor was called Q, taken from the expression quencher of fluorescence. When it was subsequently established that the stable primary electron acceptor is a quinone molecule, the symbol Q became even more appropriate. 

Metal acetylacetonates and thio-organic complexes show a strong interaction during processing as they yield dark colored samples. These materials are not acceptable as UV stabilizers. Hindered amine light stabilizers (HALS)s are commonly used polymer photostabilizers. HALSs are ineffective in imparting photostability to the polymer. Successful photostabilization of PPS can be achieved by using UV absorbers rather than quencher-type additives. 

NATA and DHE, respectively. These values imply that quench concentrations near 03M are required to quench one-half of the fluorophores by a static p x)ces8. Such a weak association suggests that the fluorophores and quenchers do not actually form a ground-state complex. Instead, it seems that the apparent static con nent is due to the quencher being adjacent to the fluorophore at the moment of excitation. These closely spaced fluorophore-quencher pairs are immedi ely quenched and thus appear to be dark com dcxes. 

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