Fluorescence dynamic spectroscopies

Fluorescence intensity detected with a confocal microscope for the small area of diluted solution temporally fluctuates in sync with (i) motions of solute molecules going in/out of the confocal volume, (ii) intersystem crossing in the solute, and (hi) quenching by molecular interactions. The degree of fluctuation is also dependent on the number of dye molecules in the confocal area (concentration) with an increase in the concentration of the dye, the degree of fluctuation decreases. The autocorrelation function (ACF) of the time profile of the fluorescence fluctuation provides quantitative information on the dynamics of molecules. This method of measurement is well known as fluorescence correlation spectroscopy (FCS) [8, 9]. 

Hosokawa, C., Yoshikawa, H. and Masuhara, H. (2004) Optical assembling dynamics of individual polymer nanospheres investigated by singleparticle fluorescence detection. Phys. Rev. E, 70, 061410-1-061410-7 (2005) Cluster formation of nanoparticles in an optical trap studied by fluorescence correlation spectroscopy. Phys. Rev. E, 72, 021408-1-021408-7. 

Underwood, D. E., Kippeny, T. and Rosenthal, S. J. (2001) Ultrafast carrier dynamics in CdSe nanocrystals determined by femtosecond fluorescence upconversion spectroscopy. /. Phys. Chem. B, 105,436-443. 

Fluorescence correlation spectroscopy (FCS) measures rates of diffusion, chemical reaction, and other dynamic processes of fluorescent molecules. These rates are deduced from measurements of fluorescence fluctuations that arise as molecules with specific fluorescence properties enter or leave an open sample volume by diffusion, by undergoing a chemical reaction, or by other transport or reaction processes. Studies of unfolded proteins benefit from the fact that FCS can provide information about rates of protein conformational change both by a direct readout from conformation-dependent fluorescence changes and by changes in diffusion coefficient. 

Haupts U, Maiti S, Schwille P, Webb WW (1998) Dynamics of fluorescence fluctuations in green fluorescent protein observed by fluorescence correlation spectroscopy. Proc Natl Acad Sci USA 95 13573-13578... 

Schwille P, Kummer S, Heikal AA, Moemer WE, Webb WW (2000) Fluorescence correlation spectroscopy reveals fast optical excitation-driven intramolecular dynamics of yellow fluorescent proteins. Proc Natl Acad Sci USA 97 151-156... 

This technique does not require the equilibrium of the chemical system to be perturbed to measure the host-guest binding dynamics. Fluorescence correlation spectroscopy is based on the measurement of changes in the fluorescence intensity of individual molecules, which lead to intensity fluctuations.58 63 For this reason, the measurements are made by detecting the emission from a small sample volume (femtoliters to microliters) containing a small number of fluorophores. 

Fluorescence correlation spectroscopy can be used to measure the binding dynamics of host-guest complexes when the fluorescence quantum yields for the free and bound hosts are different. Analysis of fluorescence correlation spectra depends on the profile for the excitation pulse, which impacts the shape of the emission profile and mechanistic assumptions are made with respect to the diffusion of the various species in solution.58 For each chemical system different assumptions are made. 

The dynamics of intercalation of small molecules with DNA, groove binding and binding to specific sites, such as base pair mismatches have been studied by stopped-flow,23,80 108 temperature jump experiments,26,27,94 109 120 surface plasmon resonance,121 129 NMR,86,130 135 flash photolysis,136 138 and fluorescence correlation spectroscopy.64 The application of the various techniques to study the binding dynamics of small molecules will be analyzed for specific examples of each type of binding. 

Studies on the dynamics of complexation for guests with cyclodextrins have been carried out using ultrasonic relaxation,40 151 168 temperature jump experiments,57 169 183 stopped-flow,170,178,184 197 flash photolysis,57 198 202 NMR,203 205 fluorescence correlation spectroscopy,65 phosphorescence measurements,56,206 and fluorescence methods.45,207 In contrast to the studies with DNA described above, there are only a few examples in which different techniques were employed to study the binding dynamics of the same guest with CDs. This probably reflects that the choice of technique was based on the properties of the guests. The examples below are grouped either by a type of guest or under the description of a technique. 

Supramolecular dynamics, techniques for fluorescence correlation spectroscopy, 178-181... 

The reader is referred to other reviews for detailed discussions of the electronic states and luminescence of nucleic acids and their constituents/0 fluorescence correlation spectroscopy/2) spectroscopy of dye/DNA complexes/0 and ethidium fluorescence assays/4,0 A brief review of early work on DNA dynamics as well as a review of tRNA kinetics and dynamics have also appeared. The diverse and voluminous literature on the use of fluorescence techniques to assay the binding of proteins and antitumor drugs to nucleic acids and on the use of fluorescent DNA/dye complexes in cytometry and cytochemistry lies entirely outside the scope of this chapter. 

The host-guest p-cyclodextrin-C522 complex formation was determined based on fluorescence blue shift as a function of the increasing p-cyclodextrin concentration from 10 6 to 10 2 M. Similar result was observed for coumarin C6 [4] and this blue shift was considered along with anisotropy results as a proof of the host-guest formation. Time-resolved fluorescence spectroscopy was utilized to differentiate between fluorescence dynamics of... 

The time and wavelength resolved fluorescence dynamics of bianthryl has been investigated by several groups [30, 82, 132, 133, 115, 116]. In addition, this molecule has been studied by picosecond absorption spectroscopy [115], electric field induced fluorescence anisotropy measurements [117] and optically induced dielectric absorption (microwave) measurements [118, 119]. The results are generally in accord with the theoretical model presented in Sections III.A and III.B. One of the challenges of studying the photodynamics of BA is that the LE and CT interconversion is so rapid (i.e., on the time scale of solvation) that it is necessary to employ ultraviolet subpicosecond and even femtosecond fluorescence spectroscopy which has only recently become available [30, 82, 132, 133]. 

Dynamic processes at thermodynamic equilibrium that occur within a time range from sub-microseconds to seconds can be probed without the imposition of a transient disturbance by optical intensity fluctuation spectroscopy. As such, dynamic light scattering (DLS) [155] measures the fluctuation of quasielastic scattering intensity and fluorescence correlation spectroscopy (FCS) [156-158] measures concentration fluctuations of specific fluorescent molecules... 

Clamme JP, Krishnamoorthy G, Mely Y (2003) Intracellular dynamics of the gene delivery vehicle polyethylenimine during transfection investigation by two-photon fluorescence correlation spectroscopy. Biochim Biophys Acta 1617 52-61... 

FIGURE 4.1 Assays commonly used in GPCR research. SPA = scintillation proximity assay FP = fluorescence polarization TR-FRET = time-resolved fluorescence resonance energy transfer FCS = fluorescence correlation spectroscopy SeAP = secreted alkaline phosphate TF = transcription factor EFC = enzyme fragment complementation DMR = dynamic mass redistribution CDS = cellular dielectric spectroscopy. 

It is well known that both nanometre and nanosecond-picosecond resolutions at an interface can be achieved by total internal reflection (TIR) fluorescence spectroscopy. Unlike steady-state fluorescence spectroscopy, fluorescence dynamics is highly sensitive to microscopic environments, so that time-resolved TIR fluorometry at water/oil interfaces is worth exploring to obtain a clearer picture of the interfacial phenomena [1]. One of the interesting targets to be studied is the characteristics of dynamic motions of a molecule adsorbed on a water/oil interface. Dynamic molecular motions at a liquid/liquid interface are considered to be influenced by subtle changes in the chemical/physical properties of the interface, particularly in a nanosecond-picosecond time regime. Therefore, time-resolved spectroscopy is expected to be useful to study the nature of a water/oil interface. 

In order to obtain a clearer picture on the interfacial polarity, we conducted picosecond TIR fluorescence spectroscopy by using sulforhodamine B (SRB) as a polarity probe molecule [5]. On the basis of fluorescence dynamic measurements of SRB adsorbed on a water/oil interface, we studied a relationship between thickness/roughness and the polarity at the interface. 

Thompson NL, Steele BL. Total internal reflection with fluorescence correlation spectroscopy. Nat. Protoc. 2007 2 878-890. Sund SE, Axelrod D. Actin dynamics at the living cell submembrane imaged by total internal reflection fluorescence photobleach-ing. Biophys. J. 2000 79 1655-1669. 

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