Quenching and enhancement

Quenching and enhancement FIA Homogeneous assays, possible background serum (urine) interference (36), (37) 

Fluorescence polarization (polarization FIA) Homogeneous assays, rapid and precise specialized equipment sensitivity often low (38) 

Energy transfer Homgeneous assay, two labelling procedures is a disadvantage (23) 

Fluorescence protection Homogeneous assays, two antibodies required (39), (40) 

Fluorescence lifetime (time-resolved FIA) Serum background overcome (41) 

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Samples for studies of CDx effects on fluorescence enhancement in organic solution were prepared using pyrene, because pyrene possesses a long lifetime and is very susceptible to quenching and enhancement in solution (23). An aliquot of pyrene stock solution in cyclohexane was placed under a nitrogen purge to evaporate the cyclohexane. Samples were redissolved in a 1 A mixture of Isopropyl ether and 1-butanol, which was saturated with aqueous CDx solution. Pyrene samples were also prepared in which the organic solvent was not saturated with CDx solution. The mixed solvent was used in order to minimize the effects of ether evaporation and thus allow more accurate quantitation. Fluorescence measurements were made on diluted samples of these solutions. The solvent used to make up the... 

J. Tauc, Time-Resolved Spectroscopy of Electronic Relaxation Processes P.E. Vanier, IR-Induced Quenching and Enhancement of Photoconductivity and Photoluminescence... 

Recently, there has been a flurry of experimental work investigating the phenomenon of MEF with a range of metal nanoparticle shapes and sizes. In this Section, we provide a brief overview of some recent experiments that have shown quenching and enhancement effects, and demonstrate a correlation between observed effects on fluorescence and the morphology of the nanoparticles employed. 

There are essentially two models that describe the interaction between an excited fluorophore and the SPR of the metal to account for quenching and enhancement of the fluorescence. They both depend on coupling of the fluorophore excited state to the SPR and this is dependent of the spectral overlap of the emission of the fluorophore and the SPR, and the distance between the fluorophore and the metal nanoparticle surface. 

The presence of at least two fluorophores, and possibly a third, associated with metal ion binding in fulvic acid strongly suggests the need for multiple binding site models. Existing linear and nonlinear models will be reviewed for both fluorescence quenching and enhancement. A new modified 1 1 Stem - Volmer model will be introduced as well as two site and multiple site models. Application of the models to Cu binding by fulvic acid and certain well defined model systems are discussed. 

Fig. 4.20 650 X 650 pm2 fluorescence microscopy image of the TM4 fluorescent monolayer on glass in which Cu2+ and Ca2+ (Cu (C104)2 and Ca (C104)2, 10 3 M, acetonitrile) were printed with PDMS stamps with an array of 10 pm dots. This image clearly shows that the fluorescence of the glass slide was quenched and enhanced where the Cu2+ and the Ca2+ ions, respectively, were printed, i.e. the dotted pattern 87. Copyright Wiley-VCH Verlag GmbH Co. KGaA. Reproduced with permission...

Effects of cationic and anionic QDs PL quenching and enhancement by oppositely charged polyelectrolytes are also presented in Fig. 1, where the PL spectra of anionic and cationic QDs are normalized and superposed. PL intensity of cationic QDs decreases rapidly by one order of magnitude (Fig. lb) in the presence of anionic PSS. Moreover, the emission from these complexes became undetectable in the solution and on slides at the next days. The relative intensities of anionic QDs in presence of cationic PAA (Fig. lc) increase up to 4 times, and its photostability is enhanced too. The fluorescent images of anionic QDs on cationic PAA (Fig. Id) are bright and stable for months. 

Shan Y, Xu JJ, Chen UY (2009) Distance-dependent quenching and enhancing of electrochemiluminescence from a CdS Mn nanocrystal film by Au nanoparticles for highly sensitive detection of DNA. Chem Commun 905-907... 

Hsu H-Y, Chiang H-C, Hu J-Y et al (2013) Field-induced fluorescence quenching and enhancement of porphyrin sensitizers on Ti02 films and in PMMA films. J Phys Chem C 117(47) 24761-24766... 

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