Fluorescence intensity decay

The "add-to-memory" signal averaging method currently available to us distorts fluorescence intensity versus time plots when the fluorescence intensity is a non-linear function of incident laser energy and the laser energy varies from shot to shot. For this reason we have not attempted detailed kinetic modelling of the observed fluorescence intensity decay curves recorded at high 532 nm laser fluence. 

At present, two main streams of techniques exist for the measurement of fluorescence lifetimes, time domain based methods, and frequency domain methods. In the frequency domain, the fluorescence lifetime is derived from the phase shift and demodulation of the fluorescent light with respect to the phase and the modulation depth of a modulated excitation source. Measurements in the time domain are generally performed by recording the fluorescence intensity decay after exciting the specimen with a short excitation pulse. 

In this paper, to determine the steady state SCP across the transition layer, we analyze the fluorescence intensity decay of dye molecules covalently bound to the polymer chains. The decay is due to the permeation of... 

Poly(methyl methacrylate) [PMMA] is an excellent polymer for studying photoresist dissolution because of its minimal swelling characteristic. For this work, PMMA molecules were labelled with phenanthrene (Phe) dye since its fluorescence is quenched by MEK. In addition, this dye has the advantage of forming few excimers (23-241 which results in self-quenching. Thus, the reduction in fluorescence intensity of PMMA-Phe is virtually solely due to MEK quenching. Consequently, the permeation of MEK into a PMMA film can be monitored from fluorescence intensity decay. 

A typical time profile of the excited PMMA-Phe fluorescence intensity decay is shown in Figure 2. The MEK permeation commences at 24 sec. The SPR increases during the plasticization period until it becomes constant, the onset of the steady state. It is characterized by a linear relationship between the amount of solvent absorbed and time. It was determined from a linear regression analysis that the PMMA-Phe fluorescence intensity starts to deviate from linearity at 197 sec. This indicates a decrease in the SPR and/or the unquenched PMMA-Phe. The decrease in SPR is unexpected at this film thickness since the SPR in thicker PMMA-Phe films show no anomaly at 1 /tm. A more plausible explanation is the reduction in available PMMA-Phe, which is expected when the front end of the SCP reaches the substrate. 

Donor and acceptors can be covalently linked using a chemical spacer. Assume that we have the same D-A pair Eosin-Phenol Red. In this case we will have a mixture of two linked donor-acceptor species (Eosin-Phenol Red protonated and Eosin-Phenol Red unprotonated) characterized by the same distance distribution and different critical distances (ftoi = 28.3 A and Rm = 52.5 A) for FRET. A distribution of D- to -A distances will be present because the linker is typically flexible. The fractional intensity of the first species at time t = 0 is gi and that of the second species is (1 - 1). The fractional intensity at time t = 0 is equal to fractional concentration of each form, which can be in case of pH indicator (Phenol Red) calculated using Eq. (10.31). The donor fluorescence intensity decay of the mixture is described by the equation... 

The fluorescence decay parameters of tyrosine and several tyrosine analogues at neutral pH are listed in Table 1.2. Tyrosine zwitterion and analogues with an ionized a-carboxyl group exhibit monoexponential decay kinetics. Conversion of the a-carboxyl group to the corresponding amide results in a fluorescence intensity decay that requires at least a double exponential to fit the data. While not shown in Table 1.2, protonation of the carboxyl group also results in complex decay kinetics.(38)... 

There are several biologically important peptides which contain tyrosine but not tryptophan. These include small molecules with molecular weights of about 1000 or less. Molecules such as oxytocin, vasopressin, and tyrocidine A are cyclic, while others such as angiotensin II and enkephalin are linear. Schiller 19) has reviewed the literature up through 1984 on fluorescence of these and several other peptides. One major finding that has been reported recently is that the anisotropy and fluorescence intensity decays of many peptides are complex. This is especially evident in some of the tyrosine-containing peptides, and we expect that there will be considerable effort made over the next few years toward understanding the physical basis for these complex kinetics. 

Fluorescence intensity decay curves for H, TPP Figure 4A shows... 

Time-Resolved Fluorescence. To improve our understanding of the photophysics of the PRODAN-CF3H system we performed a series of time-resolved fluorescence experiments at pr = 1.25 as a function of temperature. Traditionally, one describes the time-resolved fluorescence intensity decay (I(t)) by a sum of (n) discrete exponentials of the form (43,46) ... 

Recent reports from many groups, including our own, have shown (47-55) that systems originally described by discrete decay processes (Eqn. 2) are more accurately described using continuous distributions of decay times. In these situations, the fluorescence intensity decay can be written in integral form as ... 

The above described model sequences have been studied both as oligomers [7,8,11-13,19] and as polymers [9,11,20]. An increase in the size of the helix is known to reinforce its stability, as revealed by their melting curves [18] and attested by X-ray diffraction measurements in solution [21]. Therefore, in this chapter we focus on the polymeric duplexes poly(dGdC).poly(dGdC) [= 1000 base-pairs], poly(dAdT).poly(dAdT) [= 200-400 base-pairs] and poly(dA).poly(dT) [= 2000 base-pairs] studied by us. First we discuss the absorption spectra, which reflect the properties of Franck-Condon states, in connection with theoretical studies. Then we turn to fluorescence properties fluorescence intensity decays (hereafter called simply fluorescence decays ), fluorescence anisotropy decays and time-resolved fluorescence spectra. We... 

The cytochrome b2 core from the yeast Hansenula anomala has a molecular mass of 14 kDa, and its sequence shows the presence of two tryptophan residues. Their fluorescence intensity decay can be adequately described by a sum of three exponentials. Lifetimes obtained from the fitting are equal to 0.054,0.529, and 2.042 ns, with fractional intensities equal to 0.922, 0.068, and 0.010. The mean fluorescence lifetime, r0, is 0.0473 ns. 

I. Chung and M. G. Bawendi, Relationship between single quantum-dot intermittency and fluorescence intensity decays from collections of dots. Phys. Rev. B, 70 165304 (2004). 

The principles of time-resolved fluorometry are illustrated in Fig. 7.4. The d-pulse response of a fluorescent sample (i.e. the fluorescence intensity decay in response to an infinitely short light pulse mathematically represented by the Dirac function <5(t) delta excitation) is, in the simplest case, a single exponential whose time constant is the excited-state lifetime, but more frequently it is a sum of discrete exponentials, or a more complicated function sometimes, the system is characterized by a distribution of decay times. For any excitation function E(t), the response R(t) of the sample is the convolution product of this function by the <5-pulse response ... 

The second method for measuring FRET involves time-resolved fluorescence measurements. This method provides a way of obtaining average lifetimes without a precise knowledge of donor concentrations. The technique enables the quantitative determination of donor-acceptor separation distances, and is based on the measurements of the donor lifetime in the presence and absence of the acceptor. Measuring fluorescence intensity decay as a function of time elucidates the emission dynamics of... 

In the time-resolved Stokes shift experiment, the fluorescence intensity decays were monitored at multiple wavelengths. At the blue edge of the steady-state emission spectrum, at short times there was an additional fast decay overlaid on the fluorescence decay at the red edge of the steady-state spectrum, there was an additional rise at short times (Fig. 4.38). The difference in the decays at the two wavelengths was caused by a dynamic Stokes shift, induced by DNA motion. From the data taken at 10 wavelengths, the emission spectra could be reconstructed to show a red shift in time (Fig. 4.39), and from this information the response function of the DNA was evaluated (Fig. 4.40). It was estimated that 80% of the Stokes shift was happening faster than the time resolution of the experimental setup (100 ps), and the two components that were observable had time constants of 300 ps and 13 ns [232]. 

Analysis of the fluorescence intensity decay data as a sum of 150 exponentials was performed by the Maximum Entropy Method (MEM) (Livesey and Brochon, 1987), using the commercially available library of subroutines MEMSYS 5 (MEDC Ltd, UK) as a library of subroutines. 

The fluorescence intensity decay is obtained by summing the parallel and perpendicular components ... 

The fluorescence intensity decay of 029 SSB can be analyzed with three exponential decays 0.4, 1.5 and 3.8 ns. We can in no way assign the fluorescence lifetimes to any particular tyrosine residues. 

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