Fluorescence profile

Anthracene has also been used as an acceptor (Fig. 10). In solution, 26 emits a single fluorescence band that is somewhat structured in nonpolar solvents and becomes broad and structureless with increasing polarity [58]. The strongly hindered molecule 27 also exhibits a similar behavior, but its absorption spectrum is better structured [59]. The rate of formation of a charge transfer state is higher for 27 than for 26. Based on this observation, it appears that the twist around the anthryl-phenyl C-C bond plays a significant role in the fluorescence profile of the probes [60]. Acridines, such as 28, behave similarly to anthracene except that acridine is a better electron acceptor [61]. 

Figure 1. Representative anthracene fluorescence profile during the photosensitization of diaryliodonium salts in pure propanol at 30°C.

Comparison of the Experimental and Simulation Results. The preceding discussion has shown that both the experimental anthracene fluorescence profiles and the simulated anthracene concentration profiles decrease in a manner which closely follows an exponential decay. Therefore, the most convenient way to compare the simulation results to the experimental data is to define an effective overall photosensitization rate constant, kx or k2, as described above. Adoption of this lumped-parameter effective kinetic constant allows us to conveniently and efficiently compare the experimental data to the simulation results by contrasting the rate constant obtained from the steady-state fluorescence decay with the value obtained from the simulated decrease in the anthracene concentration. 

Fig. 3. Fluorescence profiles of 2, 7 -dichlorofluorescin-loaded cells assayed in whole blood. (A) Compares the fluorescence histograms of unstimulated, control cells (shaded curve) with granulocytes exposed to opsonized S. aureus (open curve). (B) illustrates the two-color analysis profde of the granulocytes that were exposed to Texas Red-labeled S. aureus. Red fluorescence is the result of particle association with each granulocyte, whereas green fluorescence is the result of the oxidation of 2, 7 -dichlorofluorescin to 2, 7 -dichlorofluorescein (DCF). The red and green fluorescence analyses were performed with log-scale detection amplification for each fluorochrome.

The wavelength of a laser line, however, is determined by two factors the fluorescence profile of the corresponding transition in the laser medium and the eigenfrequencies of the laser resonator modes. At normal multimode operation of a laser, where many axial and transverse modes participate in laser oscillation, these eigenfrequencies cover the whole spontaneous line profile nearly uniformly. 

Spectrofluorometry underpins all luminescent techniques for characterizing the target analyte and the associated sample matrix. LIF occurs from the vacuum UV through the NIR range, but is most common between 250 nm and 800 nm. A typical fluorescent profile contains an absorption spectrum and an emission spectrum as depicted in Figure 11.3. Spectrofluorometric excitation profiling at emission maxima and syn-chronons scanning are common methods to characterize a fluorophore. 

Until recently, previous studies for continuous monitoring of hepatic function with ICG utilized the absorption mode. However, new studies demonstrate that the highly sensitive fluorescence technique can equally be used [148-150]. In addition to high sensitivity, in-depth analysis of the emission, excitation and polarization properties of fluorescence spectroscopy furnishes additional functional information about the dye molecule. In this system, the fluorescence profile emanating from the clearance of injected biocompatible dye is monitored with a small photodetector. Fig. 8 shows the in vivo fluorescence detection apparatus developed for continuous monitoring of organ functions [147,148]. 

The analysis of the temporal fluorescence profiles in Figs. 2.17a and 2.17b shows that the kinetic scheme used is a fairly good description at least for the case shown The ratio of the preexponential factors for rise and decay parts of the A fluorescence is 0.96, thus very close to the theoretical value of 1.0 predicted by Eq. (2.29), and the decay time of the B fluorescence is similar to the rise time of the A fluorescence. 

Fig. 6.17. The two-color fluorescence profile of peripheral blood mononuclear cells stained simultaneously with six different monoclonal antibodies to delineate five different populations of cells. From Floran et al. (1986).

Figure 8. StB3 2,u — X3%, fluorescence profiles above the burner surface in a...

Fluorescence profiles for SH in a rich H2/O2/N2 flame containing varying amounts of H2S are shown in Figure 12. The similarity with the profiles for S2 in Figure 8 suggests that S2 and SH are chemically coupled. 

Fluorescence profiles for SO in a rich flame with added H2S are presented in Figure 15. The corresponding profiles for S02 are shown in Figure 16. Similarity of the SO and S02 profiles suggest that they are chemically coupled. 

Figure 12. SH A2X — X2U fluorescence profiles above the burner surface for Hg-Ot-Nt (4 1 6) flames with added HtS (a),l. 0% (b), 0.5% (c), 0.25%. Laser excitation at 323.76 nm with detection at 328.0 nm.

Reaction (7) couples S2 and SH, as was noted from their fluorescence profiles. Similarly, reaction (12) links SO to S02. Reactions (13) and (14) connect oxidized and reduced species, SO with S2 and SH. The model relates all sulfur bearing species in the flames. The non-equilibrium concentrations of H and OH radicals generated in the flame front by the fast radical chain branching reactions... 

The time resolution of the electronics in a single photon counting system can be better than 50 ps. A problem arises because of the inherent dispersion in electron transit times in the photomultiplier used to detect fluorescence, which are typically 0.1—0.5 ns. Although this does not preclude measurements of sub-nanosecond lifetimes, the lifetimes must be deconvoluted from the decay profile by mathematical methods [50, 51]. The effects of the laser pulsewidth and the instrument resolution combine to give an overall system response, L(f). This can be determined experimentally by observing the profile of scattered light from the excitation source. If the true fluorescence profile is given by F(f) then the... 

Fig. 15. Limiting effects of 6-bits resolution in the Biomation 6500 transient recorder. The upper trace shows the fluorescence profile following a single laser pulse. The middle trace shows the average of 1000 laser shots and the last trace shows the logarithm of this decay profile. Note the distortion of the decay curve at long times (see text).

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