Fluorescence fluorophores

The method is dependent upon the production of an intensely fluorescent fluorophor which provides the basis for a rapid and sensitive assay of methyl isocyanate after collection on the adsorbent. Monomethyl amine, which is the only known interference, can be eliminated by absorption in aqueous solution of cupric chloride. 

It is possible that surface enhancement effects, similar to the observations made earlier in metal-fluorophore systems [11, 83-85] may occur. Metal surfaces are known to have effects on fluorophores such as increasing or decreasing rates of radiative decay or resonance energy transfer. A similar effect may take place in ZnO nanomaterial platforms. However, decay lengths of fluorescence enhancement observed in the semiconducting ZnO NRs are not commensurate with the length scale seen on metals such as Au or Ag. For effective metal enhanced fluorescence, fluorophores should be placed approximately between 5-20 nm away from the metal surface. However, fluorescence enhancement effect on ZnO NRs is observed even when fluorophores are located well beyond 20 nm away from the NR surface. At the same time, no quenching effec en when they are placed directly onto ZnO NR surfaces. In addition, there overlap between the absorption and emission... 

It is known that fluorescing fluorophores behave like radiating dipoles. The intensity of light radiated from a... 

Sensor 14 [53] equips a fluorescent fluorophore-spacer-receptor system with a pyridine receptor for H" " which becomes more reducible by protOTiation. So 14 galvanizes fluorescence-quenching PET from the pyrazoUne fluorophore to the pyridine receptor (Mily when H" " arrives. 

Fluorescence quenching is due to non-radiative loss of energy from the excited state as a consequence of either collision with a quencher ion (or molecule) in solution or by formation of a non-fluorescent or poorly fluorescent fluorophore-quencher complex. In both cases the quenching process follows the Stem-Volmer equation ... 

Bhawalkar J D, Swiatkiewicz J, Pan S J, Samarabandu J K, Liou W S, He G S, Berezney R, Cheng P C and Prasad P N 1996 Three-dimensional laser scanning two-photon fluorescence confocal microscopy of polymer materials using a new, efficient upconverting fluorophore Scanning 18 562-6... 

Carlsson Kand Liljeborg A 1997 Confocal fluorescence microscopy using spectral and lifetime information to simultaneously record four fluorophores with high channel separation J. Microsc. 185 37-46... 

Tokunaga M, Kitamura K, Saito K, Iwane A H and Yanagida T 1997 Single molecule imaging of fluorophores and enzymatic reactions achieved by objective-type total internal reflection fluorescence microscopy Biochem. Biophys. Res. Commun. 235 47-53... 

In time-resolved fluorescence, rare earths are frequently used as fluorescent labels. The fluorophores have large Stokes shifts, ie, shifts of the emitted light to a higher wavelength relative to the absorption wavelength, and comparatively long decay times, approximately 0.5 ms. This simplifies the optical... 

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... 

Jablonski (48-49) developed a theory in 1935 in which he presented the now standard Jablonski diagram" of singlet and triplet state energy levels that is used to explain excitation and emission processes in luminescence. He also related the fluorescence lifetimes of the perpendicular and parallel polarization components of emission to the fluorophore emission lifetime and rate of rotation. In the same year, Szymanowski (50) measured apparent lifetimes for the perpendicular and parallel polarization components of fluorescein in viscous solutions with a phase fluorometer. It was shown later by Spencer and Weber (51) that phase shift methods do not give correct values for polarized lifetimes because the theory does not include the dependence on modulation frequency. 

Applications of the oxalate-hydrogen peroxide chemiluminescence-based and fluorescence-based assays with NDA/CN derivatives to the analysis of amino acids and peptides are included. The sensitivity of the chemiluminescence and fluorescence methods is compared for several analytes. In general, peroxyoxalate chemiluminescence-based methods are 10 to 100 times more sensitive than their fluorescence-based counterparts. The chief limitation of chemiluminescence is that chemical excitation of the fluorophore apparently depends on its structure and oxidation potential. 

Though we and others (27-29) have demonstrated the utility and the improved sensitivity of the peroxyoxalate chemiluminescence method for analyte detection in RP-HPLC separations for appropriate substrates, a substantial area for Improvement and refinement of the technique remains. We have shown that the reactions of hydrogen peroxide and oxalate esters yield a very complex array of reactive intermediates, some of which activate the fluorophor to its fluorescent state. The mechanism for the ester reaction as well as the process for conversion of the chemical potential energy into electronic (excited state) energy remain to be detailed. Finally, the refinement of the technique for routine application of this sensitive method, including the optimization of the effi-ciencies for each of the contributing factors, is currently a major effort in the Center for Bioanalytical Research. 

The data were collected using fluorescence measurements, which allow both identification and quantitation of the fluorophore in solvent extraction. Important experimental considerations such as solvent choice, temperature, and concentrations of the modifier and the analytes are discussed. The utility of this method as a means of simplifying complex PAH mixtures is also evaluated. In addition, the coupling of cyclodextrin-modified solvent extraction with luminescence measurements for qualitative evaluation of components in mixtures will be discussed briefly. 

Fluorescence lifetime measurements can increase the analytical specificity when analyzing mixtures (1-4) and can indicate changes in chemical binding of the fluorophores under various environmental conditions (5). 

This chapter presents new information about the physical properties of humic acid fractions from the Okefenokee Swamp, Georgia. Specialized techniques of fluorescence depolarization spectroscopy and phase-shift fluorometry allow the nondestructive determination of molar volume and shape in aqueous solutions. The techniques also provide sufficient data to make a reliable estimate of the number of different fluorophores in the molecule their respective excitation and emission spectra, and their phase-resolved emission spectra. These measurements are possible even in instances where two fluorophores have nearly identical emission specta. The general theoretical background of each method is presented first, followed by the specific results of our measurements. Parts of the theoretical treatment of depolarization and phase-shift fluorometry given here are more fully expanded upon in (5,9-ll). Recent work and reviews of these techniques are given by Warner and McGown (72). 

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