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1

Time-resolved fluorescence correlation spectroscopy  

Microsoft Academic Search

A new method of performing fluorescence correlation spectroscopy (FCS) measurements for mixtures of several fluorescent molecular species is introduced. It uses time-resolved fluorescence detection for separating the different FCS- contributions from the different species. This allows simultaneous and independent monitoring of the diffusion of several molecular species in one sample, or performing multi-label cross-correlation measurements. In this way, the proposed

Martin B; Michael Wahl; Rainer Erdmann

2002-01-01

2

Time-resolved fluorescence correlation spectroscopy  

Microsoft Academic Search

A new method of performing fluorescence correlation spectroscopy (FCS) measurements for mixtures of several fluorescent molecular species is introduced. It uses time-resolved fluorescence detection for separating the different FCS-contributions from the different species. This allows simultaneous and independent monitoring of the diffusion of several molecular species in one sample, or performing multi-label cross-correlation measurements. In this way, the proposed method

Martin Böhmer; Michael Wahl; Hans-Jürgen Rahn; Rainer Erdmann; Jörg Enderlein

2002-01-01

3

Emerging biomedical applications of time-resolved fluorescence spectroscopy  

NASA Astrophysics Data System (ADS)

Time-resolved fluorescence spectroscopy is presently regarded as a research tool in biochemistry, biophysics, and chemical physics. Advances in laser technology, the development of long-wavelength probes, and the use of lifetime-based methods are resulting in the rapid migration of time-resolved fluorescence to the clinical chemistry lab, to the patient's bedside, to flow cytometers, to the doctor's office, and even to home health care. Additionally, time-resolved imaging is now a reality in fluorescence microscopy, and will provide chemical imaging of a variety of intracellular analytes and/or cellular phenomena. In this overview paper we attempt to describe some of the opportunities available using chemical sensing based on fluorescence lifetimes, and to predict those applications of lifetime-based sensing which are most likely in the near future.

Lakowicz, Joseph R.; Szmacinski, Henryk; Koen, Peter A.

1994-07-01

4

Time-Resolved Single Vibronic Level Fluorescence Spectroscopy: Glyoxal.  

National Technical Information Service (NTIS)

Fluorescence originating from a single vibronic level of glyoxal 5 superscript 1 has been simultaneously resolved with respect to wavelength and time. The resultant time-resolved single vibronic level (TRSVL) spectra provide data concerning excited-state ...

E. Photos G. H. Atkinson

1975-01-01

5

Time-resolved Hyperspectral Fluorescence Spectroscopy using Frequency Modulated Excitation  

SciTech Connect

An intensity-modulated excitation light source is used together with a micro channel plate intensified CCD (ICCD) detector gated at a slightly different frequency to generate a beat frequency from a fluorescent sample. The addition of a spectrograph produces a hyperspectral time-resolved data product where the resulting beat frequency is detected with a low frame rate camera. Measuring the beat frequency of the spectrum as a function of time allows separation of the excited fluorescence from ambient constant light sources. The excitation and detector repetition rates are varied over a range of discrete frequencies, and the phase shift of the beat wave maps out the emission decay rate(s).

,; Neill, M

2012-07-01

6

Diagnosis of Vulnerable Atherosclerotic Plaques by Time-Resolved Fluorescence Spectroscopy and Ultrasound Imaging  

Microsoft Academic Search

In this study, time-resolved laser-induced fluorescence spectroscopy (TR-LIFS) and ultrasonography were applied to detect vulnerable (high-risk) atherosclerotic plaque. A total of 813 TR-LIFS measurements were taken from carotid plaques of 65 patients, and subsequently analyzed using the Laguerre deconvolution technique. The investigated spots were classified by histopathology as thin, fibrotic, calcified, low-inflamed, inflamed and necrotic lesions. Spectral and time-resolved parameters

J. A. Jo; Q. Fang; T. Papaioannou; J. H. Qiao; M. C. Fishbein; B. Beseth; A. H. Dorafshar; T. Reil; D. Baker; J. Freischlag; K. K. Shung; L. Sun; L. Marcu

2006-01-01

7

Excitation emission and time-resolved fluorescence spectroscopy of selected varnishes used in historical musical instruments.  

PubMed

The analysis of various varnishes from different origins, which are commonly found on historical musical instruments was carried out for the first time with both fluorescence excitation emission spectroscopy and laser-induced time-resolved fluorescence spectroscopy. Samples studied include varnishes prepared using shellac, and selected diterpenoid and triterpenoid resins from plants, and mixtures of these materials. Fluorescence excitation emission spectra have been collected from films of naturally aged varnishes. In parallel, time-resolved fluorescence spectroscopy of varnishes provides means for discriminating between short- (less than 2.0 ns) and long-lived (greater than 7.5 ns) fluorescence emissions in each of these complex materials. Results suggest that complementary use of the two non destructive techniques allows a better understanding of the main fluorophores responsible for the emission in shellac, and further provides means for distinguishing the main classes of other varnishes based on differences in fluorescence lifetime behaviour. Spectrofluorimetric data and time resolved spectra presented here may form the basis for the interpretation of results from future in situ fluorescence examination and time resolved fluorescence imaging of varnished musical instruments. PMID:19782228

Nevin, Austin; Echard, Jean-Philippe; Thoury, Mathieu; Comelli, Daniela; Valentini, Gianluca; Cubeddu, Rinaldo

2009-07-04

8

Detection of experimental brain tumors using time-resolved laser-induced fluorescence spectroscopy  

NASA Astrophysics Data System (ADS)

Time-Resolved Laser-Induced Fluorescence Spectroscopy (TR-LIFS) has the potential to provide a non- invasive characterization and detection of tumors. We utilized TR-LIFS to detect gliomas in-vivo in the rat C6 glioma model. Time-resolved emission spectra of both normal brain and tumor were analyzed to determine if unique fluorescence signatures could be used to distinguish the two. Fluorescence parameters derived from both spectral and time domain were used for tissue characterization. Our results show that in the rat C6 glioma model, TR-LIFS can be used to differentiate brain tumors from normal tissue (gray and white mater) based upon time- resolved fluorescence signatures seen in brain tumors.

Thompson, Reid C.; Black, Keith L.; Kateb, Babak; Marcu, Laura

2002-05-01

9

Tubulin equilibrium unfolding followed by time-resolved fluorescence and fluorescence correlation spectroscopy  

PubMed Central

The pathway for the in vitro equilibrium unfolding of the tubulin heterodimer by guanidinium chloride (GdmCl) has been studied using several spectroscopic techniques, specifically circular dichroism (CD), two-photon Fluorescence Correlation Spectroscopy (FCS), and time-resolved fluorescence, including lifetime and dynamic polarization. The results show that tubulin unfolding is characterized by distinct processes that occur in different GdmCl concentration ranges. From 0 to 0.5 M GdmCl, a slight alteration of the tubulin heterodimer occurs, as evidenced by a small, but reproducible increase in the rotational correlation time of the protein and a sharp decrease in the secondary structure monitored by CD. In the range 0.5–1.5 M GdmCl, significant decreases in the steady-state anisotropy and average lifetime of the intrinsic tryptophan fluorescence occur, as well as a decrease in the rotational correlation time, from 48 to 26 nsec. In the same GdmCl range, the number of protein molecules (labeled with Alexa 488), as determined by two-photon FCS measurements, increases by a factor of two, indicating dissociation of the tubulin dimer into monomers. From 1.5 to 4 M GdmCl, these monomers unfold, as evidenced by the continual decrease in the tryptophan steady-state anisotropy, average lifetime, and rotational correlation time, concomitant with secondary structural changes. These results help to elucidate the unfolding pathway of the tubulin heterodimer and demonstrate the value of FCS measurements in studies on oligomeric protein systems.

Sanchez, Susana A.; Brunet, Juan E.; Jameson, David M.; Lagos, Rosalba; Monasterio, Octavio

2004-01-01

10

Arterial fluorescent components involved in atherosclerotic plaque instability: differentiation by time-resolved fluorescence spectroscopy  

NASA Astrophysics Data System (ADS)

As part of our ongoing research on spectroscopic differentiation between unstable and stable atherosclerotic lesions, we report data on time-resolved fluorescence of components of arterial intima matrix (different types of cholesterols, lipoproteins, and collagens). Certain compositional features of atherosclerotic plaque have been associated with plaque instability and rupture. We have characterized and compared the time-resolved spectra of structural proteins (Types I and III collagens, and elastin), lipoproteins (LDL, VLDL), and cholesterols (free cholesterol, and cholesteryl oleate and linoleate) induced with nitrogen laser excitation pulses (337 nm, 3 ns) and detected (360-510 nm range, 5 nm interval) with an MCP-PMT connected to a fast digitizer (2 Gsamples/s). Spectral intensities and time-dependent parameters (lifetime (tau) f; decay constants (tau) 1 (fast-term), (tau) 2 (slow-term), A1 (fast-term amplitude contribution)) derived from the time-resolved spectra were used for samples characterization and comparison. We observed that time- resolved data distinguish collagens from cholesterols and from lipoproteins, and additionally, distinguish different types of cholesterols, different types of lipoproteins and different types of collagen from each other. For instance, the collagen lifetime (390 nm: Type I 5.2 ns, Type III 2.95 ns) was significantly longer than that of cholesterols (free 1.5 ns, linoleate 0.9 ns, oleate 1.0 ns) and that of lipoproteins (LDL 0.95 ns, VLDL 0.85 ns).

Marcu, Laura; Grundfest, Warren S.; Maarek, Jean-Michel I.

2001-05-01

11

Uptake of trivalent actinides (curium(III)) by hardened cement paste: a time-resolved laser fluorescence spectroscopy study  

Microsoft Academic Search

The curium(III) interaction with cement was investigated using time-resolved laser fluorescence spectroscopy at trace concentrations. Four different Cm(III) species were identified: a nonfluorescing species which corresponds to curium hydroxide real colloids, which were characterized in detail by laser-induced breakdown detection (LIBD), a fluorescing Cm(III)\\/portlandite sorption species, and two fluorescing Cm(III)\\/calcium silicate hydrate (CSH) species. From the fluorescence emission lifetimes it

Thorsten Stumpf; Clemens Walther; Erich Wieland; Thomas Fanghänel

2004-01-01

12

Intraoperative delineation of primary brain tumors using time-resolved fluorescence spectroscopy  

NASA Astrophysics Data System (ADS)

The goal of this study is to determine the potential of time-resolved laser-induced fluorescence spectroscopy (TR-LIFS) as an adjunctive tool for delineation of brain tumor from surrounding normal tissue in order to assist the neurosurgeon in near-complete tumor excision. A time-domain TR-LIFS prototype apparatus (gated photomultiplier detection, fast digitizer) was used for recording tissue autofluorescence in normal cortex (NC), normal white matter (NWM), and various grades of gliomas intraoperatively. Tissue fluorescence was induced with a pulsed nitrogen laser (337 nm, 700 ps), and the intensity decay profiles were recorded in the 360- to 550-nm spectral range (10-nm interval). Histopathological analysis (hematoxylin & eosin) of the biopsy samples taken from the site of TR-LIFS measurements was used for validation of spectroscopic results. Preliminary results on 17 patients demonstrate that normal cortex (N=16) and normal white matter (N=3) show two peaks of fluorescence emission at 390 nm (lifetime=1.8+/-0.3 ns) and 460 nm (lifetime=0.8+/-0.1 ns). The 390-nm emission peak is absent in low-grade glioma (N=5; lifetime=1.1 ns) and reduced in high-grade glioma (N=9; lifetime=1.7+/-0.4 ns). The emission characteristics at 460 nm in all tissues correlated with the nicotinamide adenine dinucleotide fluorescence (peak: 440 to 460 nm lifetime: 0.8 to 1.0 ns). These findings demonstrate the potential of using TR-LIFS as a tool for enhanced delineation of brain tumors during surgery. In addition, this study evaluates similarities and differences between TR-LIFS signatures of brain tumors obtained in vivo and those previously reported in ex vivo brain tumor specimens.

Butte, Pramod V.; Fang, Qiyin; Jo, Javier A.; Yong, William H.; Pikul, Brian K.; Black, Keith L.; Marcu, Laura

2010-03-01

13

Fluorescence imaging of petroleum accelerants by time-resolved spectroscopy with a pulsed Nd-YAG laser  

Microsoft Academic Search

In this paper, fluorescence of petroleum accelerants such as kerosene, motor gasoline and diesel fuel were measured by the nanosecond time-resolved spectroscopy with a pulsed Nd-YAG laser. The excitation wavelengths are 266nm (fourth harmonic generation) and 355nm (third harmonic generation). Fluorescence was detected by a cooled CCD camera with an image intensifier. From these measurements, fluorescence lifetime was determined. We

Naoki Saitoh; Shigeki Takeuchi

2006-01-01

14

Complexation of curium(III) with hydroxamic acids investigated by time-resolved laser-induced fluorescence spectroscopy  

Microsoft Academic Search

The unknown complex formation of Cm(III) with two hydroxamic acids, salicylhydroxamic (SHA) and benzohydroxamic acid (BHA) was studied by time-resolved laser-induced fluorescence spectroscopy (TRLFS). Hydroxamate containing chelating substances have the potential to enhance the solubility and mobility of metals and radionuclides by forming complexes. We explored the fluorescence properties, lifetimes and individual fluorescence emission spectra of the formed Cm(III) hydroxamate

M. Glorius; H. Moll; G. Bernhard

2008-01-01

15

Adsorption of Uranyl on Gibbsite: A Time-Resolved Laser-Induced Fluorescence Spectroscopy Study  

SciTech Connect

Uranyl adsorbed on gibbsite at pH 4.0-8.0 and ionic strengths (ISs) 0.001-0.4 M (NaClO4) in the absence of carbonate was studied using time-resolved laser-induced fluorescence spectroscopy (TRLIFS) under cryogenic conditions. TRLIFS data showed the presence of several distinct emission components. Their contributions were determined using the evolving factor analysis approach. Four components denoted as species A, B, C, and D were discerned. Each of them was characterized by a characteristic response to pH and IS changes and also by a unique combination of the values of the fundamental transition energy E0,0, vibronic spacing E, and half-width of the vibronic lines W. Species A and B were major contributors to the overall emission. They were mainly affected by the pH and predominated below and above pH 5.0, respectively. In contrast with that, the contribution of species C was noticeable only at IS = 0.001 M, while it was suppressed or absent at high IS values. It was concluded that species A and B are likely to correspond to inner-sphere surface aluminol complexes AlO-(UO2)+ and AlO-(UO2)OH, while species C was hypothesized to correspond to electrostatically bound uranyl complexes (predominantly [UO2(OH)3]-).

Chang, Hyun-shik; Korshin, Gregory V.; Wang, Zheming; Zachara, John M.

2006-02-15

16

Conformational Analysis of DNA Repair Intermediates by Time-Resolved Fluorescence Spectroscopy  

NASA Astrophysics Data System (ADS)

DNA repair enzymes are essential for maintaining the integrity of the DNA sequence. Unfortunately, very little is known about how these enzymes recognize damaged regions along the helix. Structural analysis of cellular repair enzymes bound to DNA reveals that these enzymes are able to recognize DNA in a variety of conformations. However, the prevalence of these deformations in the absence of enzymes remains unclear, as small populations of DNA conformations are often difficult to detect by NMR and X-ray crystallography. Here, we used time-resolved fluorescence spectroscopy to examine the conformational dynamics of linear, nicked, gapped, and bulged DNA in the absence of protein enzymes. This analysis reveals that damaged DNA is polymorphic in nature and able to adopt multiple individual conformations. We show that DNA repair intermediates that contain a one-nucleotide gap and bulge have a significant propensity to adopt conformations in which the orphan base resides outside the DNA helix, while DNA structures damaged by a nick or two-nucleotide gap favor intrahelical conformations. Because changes in DNA conformation appear to guide the recognition of DNA repair enzymes, we suggest that the current approach could be used to study the mechanism of DNA repair.

Lin, Su; Horning, David P.; Szostak, Jack W.; Chaput, John C.

2009-08-01

17

Time resolved fluorescence spectroscopy of quercetin and morin complexes with Al3+.  

PubMed

The association process of Al3+ with quercetin and morin in methanol was studied by electronic absorption and emission spectroscopies. The number of species in solution with different absorption spectra were determined by the method of Rank analysis of the absorbance matrix, and the stoichiometries of the complexes were evaluated using the Job method. The number of fluorescent species in solution were calculated from the Rank analysis method of the time resolved emission spectra (TRES), and compared with a global analysis of the decay surface using a proper multi-exponential decay model. The association of Al3+ with morin gives rise to two complexes with 1:1 and 2:1 (morin: Al3+) stoichiometries, but in both species the association of the cation involves the carbonyl and 3-hydroxyl groups of the pyrone ring. The fluorescence decay surface of this system is biexponential and the lifetimes of the 1:1 and 2:1 complexes are 4.3 and 2.0 ns, respectively. The association of Al3+ with quercetin forms preferentially two complexes with 1:1 and 1:2 (quercetin: Al3+) stoichiometries where the first cation binds to the site of the pyrone ring but the second one is bound to the cathecol group of the molecule. However, the multichelation character of the quercetin ligand allows larger aggregates to be formed, thereby the species Al2Q3 is also detected in methanol. The lifetime of the 1:1 complex is about 2.7 ns, while for 1:2 and 3:2 complexes the lifetimes measured are 3.5 and 1.8 ns, respectively. PMID:11808653

Gutierrez, Amanda C; Gehlen, Marcelo H

2002-01-01

18

Time resolved fluorescence spectroscopy of quercetin and morin complexes with Al 3+  

NASA Astrophysics Data System (ADS)

The association process of Al 3+ with quercetin and morin in methanol was studied by electronic absorption and emission spectroscopies. The number of species in solution with different absorption spectra were determined by the method of Rank analysis of the absorbance matrix, and the stoichiometries of the complexes were evaluated using the Job method. The number of fluorescent species in solution were calculated from the Rank analysis method of the time resolved emission spectra (TRES), and compared with a global analysis of the decay surface using a proper multi-exponential decay model. The association of Al 3+ with morin gives rise to two complexes with 1:1 and 2:1 (morin: Al 3+) stoichiometries, but in both species the association of the cation involves the carbonyl and 3-hydroxyl groups of the pyrone ring. The fluorescence decay surface of this system is biexponential and the lifetimes of the 1:1 and 2:1 complexes are 4.3 and 2.0 ns, respectively. The association of Al 3+ with quercetin forms preferentially two complexes with 1:1 and 1:2 (quercetin: Al 3+) stoichiometries where the first cation binds to the site of the pyrone ring but the second one is bound to the cathecol group of the molecule. However, the multichelation character of the quercetin ligand allows larger aggregates to be formed, thereby the species Al 2Q 3 is also detected in methanol. The lifetime of the 1:1 complex is about 2.7 ns, while for 1:2 and 3:2 complexes the lifetimes measured are 3.5 and 1.8 ns, respectively.

Gutierrez, Amanda C.; Gehlen, Marcelo H.

2002-01-01

19

Time-resolved hyperspectral fluorescence spectroscopy using frequency-modulated excitation  

NASA Astrophysics Data System (ADS)

An intensity-modulated excitation light source is used together with a micro-channel plate intensified CCD detector gated at a slightly different frequency to generate a beat frequency from a fluorescent sample. The addition of a spectrograph produces a hyperspectral time-resolved data product where the resulting beat frequency is detected with a low frame rate camera. Measuring the beat frequency of the spectrum as a function of time allows separation of the excited fluorescence from ambient constant light sources. The excitation and detector repetition rates are varied over a range of discrete frequencies, and the phase shift of the beat wave maps out the emission decay rate(s).

DiBenedetto, John; Capelle, Gene A.; O'Neill, Mary

2012-07-01

20

Time-resolved and steady-state fluorescence spectroscopy from bacteria subjected to bactericidal agents  

NASA Astrophysics Data System (ADS)

The time-resolved and steady-state changes in fluorescence were investigated from one spore-forming (Bacillus subtilis) and four non-spore forming (Escherichia coli, Staphylococcus aureus, Enterococcus faecalis, and Pseudomonas aeruginosa) bacteria subjected to different bactericidal agents. The bactericidal agents were sodium hypochlorite (bleach) hydrogen peroxide, formaldehyde, and UV light exposure. Application of sodium hypochlorite resulted in an almost total lose of fluorescence signal and large decrease in the optical density of the bacterial suspension. Addition of hydrogen peroxide resulted in a 35% decrease in emission intensity fom the Sa and an 85-95% decrease for the other bacteria. Ultraviolet light exposure resulted in a 5-35% decrease in the emission intensity of the tryptophan band. The addition of formaldehyde to the bacteria did not result in significant changes in the steady-state emission intensity, but did shift the tryptophan emission peak position to shorter wavelengths by 3 to 5 nm. Time-resolved fluorescence measurements showed that the fluorescence lifetime of tryptophan in the bacteria could not be described by a single exponential decay, and was similar to that of tryptophan in neutral aqueous solution. Upon addition of formaldehyde to the Gram positive bacteria (Bs and Sa) the strength of the short lifetime component increased dramatically, while for the Gram negative bacteria, a smaller increase was observed. These fluorescence changes reflect the different mechanisms of the bactericidal agents and may provide a useful tool to monitor the effectiveness of disinfectants.

Katz, Alvin; Alimova, Alexandra; Siddique, Masood; Savage, Howard E.; Shah, Mahendra; Rosen, Richard; Alfano, Robert

21

Fluorescent DNA base analogs: preparation, incorporation into oligonucleotides, and time-resolved fluorescence spectroscopy  

NASA Astrophysics Data System (ADS)

The synthesis of fluorescent DNA base analogs that can replace the natural bases adenine, thymine and cytosine and their incorporation into synthetic oligodeoxynucleotides is described. The effect on the stability of such modified nucleotides like 2-aminopurine and some pteridine derivatives, is studied by thermal melting studies and comparison with the corresponding unaltered oligonucleotides. The fluorescence spectroscopic properties and several applications of these new fluorescent DNA probes are described in greater detail. Structural information on the conformation of special oligonucleotides like hairpins, junctions and bulged duplexes can be obtained from fluorescence lifetime and fluorescence depolarization data. For example the fluorescence lifetime pattern of 2-aminopurine is a sensitive indicator of DNA base pairing. As examples the structure of the oligonucleotide-linker junction in a synthetically linked oligonucleotide hairpin and the base-pairing of the first 'deoxyribozyme' are discussed. A third application uses doubly, i.e., donor and acceptor, labeled oligonucleotides to measure distances by fluorescence resonance energy transfer.

Hochstrasser, Remo A.

1996-04-01

22

Structural incorporation of Cm(III) in trioctahedral smectite hectorite: A time-resolved laser fluorescence spectroscopy (TRLFS) study  

NASA Astrophysics Data System (ADS)

Structural incorporation of the actinide curium in the octahedral layer of the trioctahedral Mg-rich smectite hectorite was studied using time-resolved laser fluorescence spectroscopy. Organo-hectorite nanoparticles were synthesized at 90 °C in the presence of Cm(III). Within 120 h, hectorite particles were formed. Time-resolved laser fluorescence spectroscopy was used to identify Cm(III) species during various synthesis steps and to characterize the structural incorporation mechanism. The formation of a Cm-containing Mg hydroxide precursor and the reaction with aqueous silica in a pH range of 9-10 to form TOT layers were identified to be key steps for trivalent actinide incorporation in hectorite via coprecipitation.

Brandt, Heike; Bosbach, Dirk; Panak, Petra J.; Fanghänel, Thomas

2007-01-01

23

Time-resolved fluorescence spectroscopy and photolysis of the photoreceptor blepharismin.  

PubMed

Blepharismin is the photoreceptor for the photophobic response in the ciliate Blepharisma japonicum (Scevoli, P., Bisi, F., Colombetti, G., Ghetti, F., Lenci, F., and Passarelli, V. (1987) J. Photochem. Photobiol.: B. Biol. 1, 75-84; Lenci, F., Ghetti, F., Gioffre, D., Heelis, P.F., Thomas, B., Phillips, G.O., and Song, P.-S. (1989) J. Photochem. Photobiol.: B. Biol. 3, 449-453). Blepharismin was solubilized from the red cells with 2% n-octylglucopyranoside. A crude pigment-protein preparation was then successively subjected to Bio-Gel A1.5 filtration, FPLC/hydroxyapatite and FPLC/DEAE ion-exchange chromatography. At least two spectrally distinct forms of blepharismin, with the respective absorbance maxima at 597 +/- 1 and 601 +/- 1 nm, were resolved. The steady state fluorescence emission maxima were at 602.5 and 617.5 nm, respectively. The fluorescence decay curves for these pigments were non-exponential. The major component possesses relatively short fluorescence lifetime (200-500 ps) for the former, according to a global analysis. This analysis suggests that the excited state of the shorter wavelength-absorbing form of blepharismin undergoes primary photoprocess faster than that of the free parental chromophore hypericin. Photolysis of blepharismin in solution yielded a irreversible product, accompanied by a 10-12 nm bathochromic shift of the absorbance maximum. However, the mechanistic nature of the time-resolved fluorescence and the photochemistry of blepharismin remains to be elucidated. PMID:8329440

Yamazaki, T; Yamazaki, I; Nishimura, Y; Dai, R; Song, P S

1993-07-26

24

Fluorescence Instrument Response Standards in Two-Photon Time-Resolved Spectroscopy  

PubMed Central

We studied the fluorescence properties of several potential picosecond lifetime standards suitable for two-photon excitation from a Ti : sapphire femtosecond laser. The fluorescence emission of the selected fluorophores (rose bengal, pyridine 1, and LDS 798) covered the visible to near-infrared wavelength range from 550 to 850 nm. We suggest that these compounds can be used to measure the appropriate instrument response functions needed for accurate deconvolution of fluorescence lifetime data. Lifetime measurements with multiphoton excitation that use scatterers as a reference may fail to properly resolve fluorescence intensity decays. This is because of the different sensitivities of photodetectors in different spectral regions. Also, detectors often lose sensitivity in the near-infrared region. We demonstrate that the proposed references allow a proper reconvolution of measured lifetimes. We believe that picosecond lifetime standards for two-photon excitation will find broad applications in multiphoton spectroscopy and in fluorescence lifetime imaging microscopy (FLIM).

LUCHOWSKI, RAFAL; SZABELSKI, MARIUSZ; SARKAR, PABAK; APICELLA, ELISA; MIDDE, KRISHNA; RAUT, SANGRAM; BOREJDO, JULIAN; GRYCZYNSKI, ZYGMUNT; GRYCZYNSKI, IGNACY

2011-01-01

25

Time resolved fluorescence spectroscopy of quercetin and morin complexes with Al 3+  

Microsoft Academic Search

The association process of Al3+ with quercetin and morin in methanol was studied by electronic absorption and emission spectroscopies. The number of species in solution with different absorption spectra were determined by the method of Rank analysis of the absorbance matrix, and the stoichiometries of the complexes were evaluated using the Job method. The number of fluorescent species in solution

Amanda C. Gutierrez; Marcelo H. Gehlen

2002-01-01

26

Studies of Time-Resolved Fluorescence Spectroscopy and Resolved Absorption Spectra of Nucleic Acid Components.  

NASA Astrophysics Data System (ADS)

There is considerable uncertainty about dynamic aspects of the photophysics of the adenylyl chromophore, stemming from the discordant values reported for the room temperature fluorescence lifetimes (tau_1 = 5 ps, tau_2 = 330 ps for 9MeAde; tau_1 = 290 ps, tau_2 = 4.17 ns for ATP). Spectra reported in conjunction with these lifetimes create difficulties in assignment of emission. To clarify this situation I have investigated the fluorescence decay times and time -resolved emission spectra of adenylyl compounds under a variety of conditions (concentration, pH, solvent) using sub-ns laser excitation at 265 nm together with gated fast sampling (100 ps) detection and signal averaging. Multi -component decays and spectra are observed in aqueous solution. Major slow components (tau = 4.4 +/- 0.2 ns) with emission maxima at 380 nm are found for all components at pH 1.1 and for ATP at pH 4.4. At pH 7 a fast component (<100 ps) predominates. There is no marked evidence for a concentration dependence, the oscillator strengths are 10^ {-3}-10^{-5} and transitions must be classified as weakly forbidden. Single component emission is observed in acetonitrile and ethanol. The UV absorption spectra of biomolecules d(CG) and polyd(GC)cdotpolyd(GC) exhibit the different hypochromic effects due to different interactions between guanosine(G) and cytidine(C) in stacked form. The present work has been carried out to explain this quantitatively. To approach this problem the absorption spectra of G and C have been resolved into gaussian components using the PeakFit program. The absorption spectra (220-310 nm) of d(CG) and polyd(GC)cdotpolyd(GC) have been fitted with gaussian components of G and C (in the order of increasing energy, G1 and G2, and C1, C2 and C3, respectively), and the contribution to both spectra from individual gaussians is estimated in terms of oscillator strengths. The fitting results suggest that the small hypochromism in absorption spectrum of d(CG) may be attributed to the interactions between G1 and C1; the large hypochromism in absorption spectrum of polyd(GC)cdotpolyd(GC) probably originates from the interactions between G1, C1, C2 and C3. The present work has also resolved a series of absorption spectra of cytidyl chromophore in different pH aqueous solution and various solvents. Time-resolved emission spectra of GMP, dCMP and m^5 -dCMP in different pH aqueous solutions have been determined. The results show that pH affects the lifetimes and spectral characteristics of GMP significantly, but does not affect dCMP and m^5-dCMP.

Fu, Yingxian

1993-01-01

27

Solvation dynamics of coumarin 153 embedded in AOT + phenol organogels studied by time-resolved fluorescence spectroscopy  

NASA Astrophysics Data System (ADS)

We investigate solvation dynamics of organogel utilizing ps-ns fluorescence spectroscopy. The organogel studied in this Letter comprises bis(2-ethylhexyl) sulfosuccinate (AOT) and p-chlorophenol in the m-xylene solvent, that produce an organogel architecture with self-assembly. Within the organogel, an emitting probe, coumarin 153 (C153), is embedded. We then obtain dynamic response functions of solvation derived from the time-resolved fluorescence spectra of C153. We propose that total energy of the C153-organogel system relaxes with a relaxation time of 3.9 ns, whereas the entire rearrangement of the organogel structure around C153 is achieved with that of 6.1 ns, respectively.

Nishiyama, Katsura; Takata, Kei; Watanabe, Keiichi; Shigematsu, Hirotake

2012-03-01

28

Development of a dual-modal tissue diagnostic system combining time-resolved fluorescence spectroscopy and ultrasonic backscatter microscopy  

PubMed Central

We report a tissue diagnostic system which combines two complementary techniques of time-resolved laser-induced fluorescence spectroscopy (TR-LIFS) and ultrasonic backscatter microscopy (UBM). TR-LIFS evaluates the biochemical composition of tissue, while UBM provides tissue microanatomy and enables localization of the region of diagnostic interest. The TR-LIFS component consists of an optical fiber-based time-domain apparatus including a spectrometer, gated multichannel plate photomultiplier, and fast digitizer. It records the fluorescence with high sensitivity (nM concentration range) and time resolution as low as 300 ps. The UBM system consists of a transducer, pulser, receiving circuit, and positioning stage. The transducer used here is 45 MHz, unfocused, with axial and lateral resolutions 38 and 200 ?m. Validation of the hybrid system and ultrasonic and spectroscopic data coregistration were conducted both in vitro (tissue phantom) and ex vivo (atherosclerotic tissue specimens of human aorta). Standard histopathological analysis of tissue samples was used to validate the UBM-TRLIFS data. Current results have demonstrated that spatially correlated UBM and TR-LIFS data provide complementary characterization of both morphology (necrotic core and calcium deposits) and biochemistry (collagen, elastin, and lipid features) of the atherosclerotic plaques at the same location. Thus, a combination of fluorescence spectroscopy with ultrasound imaging would allow for better identification of features associated with tissue pathologies. Current design and performance of the hybrid system suggests potential applications in clinical diagnosis of atherosclerotic plaque.

Sun, Yang; Park, Jesung; Stephens, Douglas N.; Jo, Javier A.; Sun, Lei; Cannata, Jonathan M.; Saroufeem, Ramez M. G.; Shung, K. Kirk; Marcu, Laura

2009-01-01

29

Time-resolved spectroscopy of the blue fluorescence of spinach leaves  

Microsoft Academic Search

When excited by ultraviolet radiation, leaves of a great number of species of higher plants exhibit emission of blue fluorescence, comparable in intensity to the red emission of chlorophyll. The fluorescence decay of the blue emission of spinach leaves recorded by single photon counting techniques is decomposed into exponential components and it is shown that at least three different components

Yves Goulas; Ismael Moya; Guido Schmuck

1990-01-01

30

Coherent photon interference elimination and spectral correction in femtosecond time-resolved fluorescence non-collinear optical parametric amplification spectroscopy  

NASA Astrophysics Data System (ADS)

We report an improved setup of femtosecond time-resolved fluorescence non-collinear optical parametric amplification spectroscopy (FNOPAS) with a 210 fs temporal response. The system employs a Cassegrain objective to collect and focus fluorescence photons, which eliminates the interference from the coherent photons in the fluorescence amplification by temporal separation of the coherent photons and the fluorescence photons. The gain factor of the Cassegrain objective-assisted FNOPAS is characterized as 1.24 × 105 for Rhodamine 6G. Spectral corrections have been performed on the transient fluorescence spectra of Rhodamine 6G and Rhodamine 640 in ethanol by using an intrinsic calibration curve derived from the spectrum of superfluorescence, which is generated from the amplification of the vacuum quantum noise. The validity of spectral correction is illustrated by comparisons of spectral shape and peak wavelength between the corrected transient fluorescence spectra of these two dyes acquired by FNOPAS and their corresponding standard reference spectra collected by the commercial streak camera. The transient fluorescence spectra of the Rhodamine 6G were acquired in an optimized phase match condition, which gives a deviation in the peak wavelength between the retrieved spectrum and the reference spectrum of 1.0 nm, while those of Rhodamine 640 were collected in a non-optimized phase match condition, leading to a deviation in a range of 1.0-3.0 nm. Our results indicate that the improved FNOPAS can be a reliable tool in the measurement of transient fluorescence spectrum for its high temporal resolution and faithfully corrected spectrum.

Dang, Wei; Mao, Pengcheng; Weng, Yuxiang

2013-07-01

31

Steady state and time resolved effects of guanidine hydrochloride on the structure of Humicola lanuginosa lipase revealed by fluorescence spectroscopy.  

PubMed Central

Effects of guanidine hydrochloride (GdnHCl) on the structure and dynamics of wild-type Humicola lanuginosa lipase (HLL) and its two mutants were studied. The latter were S146A (with the active site Ser replaced by Ala) and the single Trp mutant W89m, with substitutions W117F, W221H, and W260H. Steady-state, stopped-flow, and time-resolved laser-induced fluorescence spectroscopy were carried out as a function of [GdnHCl]. The maximum emission wavelength and fluorescence lifetimes revealed the microenvironment of the tryptophan(s) in these lipases to become more polar upon increasing [GdnHCl]. However, significant extent of tertiary structure in GdnHCl is suggested by the observation that both wild-type HLL and W89m remain catalytically active at rather high GdnHCl concentrations of >6 and 4.0 M, respectively. Changes in steady-state emission anisotropy, as well as variation in rotational correlation times and residual anisotropy values, demonstrate that upon increasing [GdnHCl] the structure of the lipases became more loose, with increasing amplitude of structural fluctuations. Finally, intermediate states in the course of exposure of the proteins to GdnHCl were revealed by stopped-flow fluorescence measurements.

Zhu, K.; Jutila, A.; Kinnunen, P. K.

2000-01-01

32

Time-resolved laser fluorescence spectroscopy study on the interaction of curium(III) with Desulfovibrio äspöensis DSM 10631T.  

PubMed

The influence of microorganisms on migration processes of actinides has to be taken into account for the risk assessment of potential high-level nuclear waste disposal sites. Therefore it is necessary to characterize the actinide-bacteria species formed and to elucidate the reaction mechanisms involved. This work is focused on the sulfate-reducing bacterial (SRB) strain Desulfovibrio äspöensis (D. äspöensis) DSM 10631T which frequently occurs in the deep granitic rock aquifers at the Aspö Hard Rock Laboratory (Aspö HRL), Sweden. We chose Cm(III) due to its high fluorescence spectroscopic sensitivity as a model system for exploring the interactions of trivalent actinides with D. äspöensis in the trace concentration range of 3 x 10(-7) mol/L. A time-resolved laser fluorescence spectroscopy (TRLFS) study has been carried out in the pH range from 3.00 to 7.55 in 0.154 mol/L NaCl. We interpret the pH dependence of the emission spectra with a biosorption forming an inner-sphere surface complex of Cm(III) onto the D. äspöensis cell envelope. This Cm(III)-D. äspöensis-surface complex is characterized by its emission spectrum (peak maximum at 600.1 nm) and its fluorescence lifetime (162 +/- 5 micros). No evidence was found for incorporation of Cm(III) into the bacterial cells under the chosen experimental conditions. PMID:15046347

Moll, H; Stumpf, Th; Merroun, M; Rossberg, A; Selenska-Pobell, S; Bernhard, G

2004-03-01

33

Highly Time Resolved Measurements of OH during POPCORN Using Laser-Induced Fluorescence Spectroscopy  

Microsoft Academic Search

Tropospheric hydroxyl radical (OH) concentrations were measured by laser-induced fluorescence (LIF) during the POPCORN field campaign in August 1994 at a rural site in the North East of Germany. Ambient air spectra were recorded by tuning the laser wavelength over a spectral region covering the Q11(3), Q21(3), and P11(1) rotational transitions of the (0-0) band in the A-X system of

F. Holland; U. Aschmutat; M. Heßling; A. Hofzumahaus; D. H. Ehhalt

1998-01-01

34

Studies of Time-Resolved Fluorescence Spectroscopy and Resolved Absorption Spectra of Nucleic Acid Components  

Microsoft Academic Search

There is considerable uncertainty about dynamic aspects of the photophysics of the adenylyl chromophore, stemming from the discordant values reported for the room temperature fluorescence lifetimes (tau_1 = 5 ps, tau_2 = 330 ps for 9MeAde; tau_1 = 290 ps, tau_2 = 4.17 ns for ATP). Spectra reported in conjunction with these lifetimes create difficulties in assignment of emission. To

Yingxian Fu

1993-01-01

35

Nondestructive Evaluation of Tissue Engineered Articular Cartilage Using Time-Resolved Fluorescence Spectroscopy and Ultrasound Backscatter Microscopy  

PubMed Central

The goal of this study is to evaluate the ability of a bimodal technique integrating time-resolved fluorescence spectroscopy (TRFS) and ultrasound backscatter microscopy (UBM) for nondestructive detection of changes in the biochemical, structural, and mechanical properties of self-assembled engineered articular cartilage constructs. The cartilage constructs were treated with three chemical agents (collagenase, chondroitinase-ABC, and ribose) to induce changes in biochemical content (collagen and glycosaminoglycan [GAG]) of matured constructs (4 weeks); and to subsequently alter the mechanical properties of the construct. The biochemical changes were evaluated using TRFS. The microstructure and the thickness of the engineered cartilage samples were characterized by UBM. The optical and ultrasound results were validated against those acquired via conventional techniques including collagen and GAG quantification and measurement of construct stiffness. Current results demonstrated that a set of optical parameters (e.g., average fluorescence lifetime and decay constants) showed significant correlation (p<0.05) with biochemical and mechanical data. The high-resolution ultrasound images provided complementary cross-section information of the cartilage samples morphology. Therefore, the technique was capable of nondestructively evaluating the composition of extracellular matrix and the microstructure of engineered tissue, demonstrating great potential as an alternative to traditional destructive assays.

Responte, Donald; Xie, Hongtao; Liu, Jing; Fatakdawala, Hussain; Hu, Jerry; Athanasiou, Kyriacos A.

2012-01-01

36

Conformational dynamics of bovine Cu, Zn superoxide dismutase revealed by time-resolved fluorescence spectroscopy of the single tyrosine residue.  

PubMed Central

The structural dynamics of bovine erythrocyte Cu, Zn superoxide dismutase (BSOD) was studied by time-resolved fluorescence spectroscopy. BSOD is a homodimer containing a single tyrosine residue (and no tryptophan) per subunit. Frequency-domain fluorometry revealed a heterogeneous fluorescence decay that could be described with a Lorentzian distribution of lifetimes. The lifetime distribution parameters (center and width) were markedly dependent on temperature. The distribution center (average lifetime) displayed Arrhenius behavior with an Ea of 4.2 kcal/mol, in contrast with an Ea of 7.4 kcal/mol for the single-exponential decay of L-tyrosine. This indicated that thermal quenching of tyrosine emission was not solely responsible for the effect of temperature on the lifetimes of BSOD. The distribution width was broad (1 ns at 8 degrees C) and decreased significantly at higher temperatures. Furthermore, the width of the lifetime distribution increased in parallel to increasing viscosity of the medium. The combined effects of temperature and viscosity on the fluorescence decay suggest the existence of multiple conformational substrates in BSOD that interconvert during the excited-state lifetime. Denaturation of BSOD by guanidine hydrochloride produced an increase in the lifetime distribution width, indicating a larger number of conformations probed by the tyrosine residue in the denatured state. The rotational mobility of the tyrosine in BSOD was also investigated. Analysis of fluorescence anisotropy decay data enabled resolution of two rotational correlation times. One correlation time corresponded to a fast (picosecond) rotation that contributed 62% of the anisotropy decay and likely reported local mobility of the tyrosine ring. The longer correlation time was 50% of the expected value for rotation of the whole (dimeric) BSOD molecule and appeared to reflect segmental motions in the protein in addition to overall tumbling. Comparison between rotational correlation times and fluorescence lifetimes of BSOD indicates that the heterogeneity in lifetimes does not arise from mobility of the tyrosine per se, but rather from dynamics of the protein matrix surrounding this residue which affect its fluorescence decay.

Ferreira, S T; Stella, L; Gratton, E

1994-01-01

37

Fully automated deconvolution method for on-line analysis of time-resolved fluorescence spectroscopy data based on an iterative Laguerre expansion technique  

Microsoft Academic Search

Time-resolved fluorescence spectroscopy (TRFS) is a powerful analytical tool for quantifying the biochemical composition of organic and inorganic materials. The potential of TRFS for tissue diagnosis has been recently demonstrated. To facilitate the translation of TRFS to the clinical arena, algorithms for online TRFS data analysis are essential. A fast model-free TRFS deconvolution algorithm based on the Laguerre expansion method

Aditi S. Dabir; Chintan A. Trivedi; Yeontack Ryu; Paritosh Pande; Javier A. Jo

2009-01-01

38

Comparison of beetroot extracts originating from several sites using time-resolved laser-induced fluorescence spectroscopy  

NASA Astrophysics Data System (ADS)

Beetroot (Beta vulgaris) juice contains a large number of fluorophores which can fluoresce. There is a growing interest in beetroot extracts analysis. In contrast, there is only limited information about beetroot obtained without sample preparation and/or extraction of components from the sample. In this work, we continue our previous study (Rabasovi? et al 2009 Acta Phys. Pol. A 116 570-2), analyzing and comparing beetroot extracts from several sites, using the time-resolved laser-induced fluorescence technique to measure the fluorescence of samples at different excitation wavelengths (340-470?nm) and for different sample dilutions.

Rabasovi?, M. S.; Ševi?, D.; Terzi?, M.; Marinkovi?, B. P.

2012-05-01

39

Time-resolved fluorescence anisotropy imaging.  

PubMed

Fluorescence can be characterized by its intensity, position, wavelength, lifetime, and polarization. The more of these features are acquired in a single measurement, the more can be learned about the sample, i.e., the microenvironment of the fluorescence probe. Polarization-resolved fluorescence lifetime imaging-time-resolved fluorescence anisotropy imaging, TR-FAIM-allows mapping of viscosity or binding or of homo-FRET which can indicate dimerization or generally oligomerization. PMID:24108641

Suhling, Klaus; Levitt, James; Chung, Pei-Hua

2014-01-01

40

Conformational dynamics of di-(perylene bisimide acrylate) and its footprints in steady-state, time-resolved, and fluorescence-correlation spectroscopy.  

PubMed

Employing steady-state spectroscopy, time-resolved fluorescence spectroscopy, and fluorescence (cross-) correlation spectroscopy we investigated di-(perylene bisimide acrylate) and compared the results with those from monomeric perylene bisimide acrylate. For the dimeric structure two emitting species were found. By comparison with the spectroscopic results from monomeric perylene bisimide one species was assigned to perylene moieties in an isolated, unstacked conformation, whereas the other species is attributed to aggregated ?-stacked perylene moieties. The transition dynamics between these conformations was uncovered by fluorescence (cross) correlation spectroscopy. A consistent description of the various correlation curves is derived for a dynamic model that considers an additional non-fluorescent dark state that is associated exclusively with the aggregated species. PMID:22538934

Spreitler, Florian; Sommer, Michael; Thelakkat, Mukundan; Köhler, Jürgen

2012-04-27

41

Effect of ouabain on metabolic oxidative state in living cardiomyocytes evaluated by time-resolved spectroscopy of endogenous NAD(P)H fluorescence.  

PubMed

Time-resolved spectrometry of endogenous nicotinamide dinucleotide phosphate [NAD(P)H] fluorescence is a useful method to evaluate metabolic oxidative state in living cells. Ouabain is a well-known pharmaceutical drug used in the treatment of cardiovascular disease, the effects of which on myocardial metabolism were recently demonstrated. Mechanisms implicated in these actions are still poorly understood. We investigate the effect of ouabain on the metabolic oxidative state of living cardiac cells identified by time-resolved fluorescence spectroscopy of mitochondrial NAD(P)H. Spectral unmixing is used to resolve individual NAD(P)H fluorescence components. Ouabain decreased the integral intensity of NAD(P)H fluorescence, leading to a reduced component amplitudes ratio corresponding to a change in metabolic state. We also noted that lactate/pyruvate, affecting the cytosolic NADH gradient, increased the effect of ouabain on the component amplitudes ratio. Cell oxidation levels, evaluated as the percentage of oxidized NAD(P)H, decreased exponentially with rising concentrations of the cardiac glycoside. Ouabain also stimulated the mitochondrial NADH production. Our study sheds a new light on the role that ouabain plays in the regulation of metabolic state, and presents perspective on a noninvasive, pharmaceutical approach for testing the effect of drugs on the mitochondrial metabolism by means of time-resolved fluorescence spectroscopy in living cells. PMID:23223981

Chorvatova, Alzbeta; Elzwiei, Fathia; Mateasik, Anton; Chorvat, Dusan

2012-10-01

42

Photosystem II does not possess a simple excitation energy funnel: time-resolved fluorescence spectroscopy meets theory.  

PubMed

The experimentally obtained time-resolved fluorescence spectra of photosystem II (PS II) core complexes, purified from a thermophilic cyanobacterium Thermosynechococcus vulcanus, at 5-180 K are compared with simulations. Dynamic localization effects of excitons are treated implicitly by introducing exciton domains of strongly coupled pigments. Exciton relaxations within a domain and exciton transfers between domains are treated on the basis of Redfield theory and generalized Förster theory, respectively. The excitonic couplings between the pigments are calculated by a quantum chemical/electrostatic method (Poisson-TrEsp). Starting with previously published values, a refined set of site energies of the pigments is obtained through optimization cycles of the fits of stationary optical spectra of PS II. Satisfactorily agreement between the experimental and simulated spectra is obtained for the absorption spectrum including its temperature dependence and the linear dichroism spectrum of PS II core complexes (PS II-CC). Furthermore, the refined site energies well reproduce the temperature dependence of the time-resolved fluorescence spectrum of PS II-CC, which is characterized by the emergence of a 695 nm fluorescence peak upon cooling down to 77 K and the decrease of its relative intensity upon further cooling below 77 K. The blue shift of the fluorescence band upon cooling below 77 K is explained by the existence of two red-shifted chlorophyll pools emitting at around 685 and 695 nm. The former pool is assigned to Chl45 or Chl43 in CP43 (Chl numbering according to the nomenclature of Loll et al. Nature2005, 438, 1040) while the latter is assigned to Chl29 in CP47. The 695 nm emitting chlorophyll is suggested to attract excitations from the peripheral light-harvesting complexes and might also be involved in photoprotection. PMID:23537277

Shibata, Yutaka; Nishi, Shunsuke; Kawakami, Keisuke; Shen, Jian-Ren; Renger, Thomas

2013-04-24

43

Mass spectra and time-resolved fluorescence spectroscopy of the reaction product of glycine with 1,2-indanedione in methanol.  

PubMed

The reaction products of 1,2-indanedione (a new fluorescent fingerprint reagent) with glycine in methanol, at room temperature have been studied using excitation and emission and time-resolved fluorescence spectroscopy. Gas chromatography-mass spectroscopy (GC/MS) has also been used to determine which compounds are formed. Reaction products were identified using GC/MS as 2-carboxymethyliminoindanone (MW=203 g) and 1,2-di(carboxymethylimino)indane (MW=260 g). Identified compounds show room temperature fluorescence lifetimes of tau(1)=7.69 ns and tau(2)=1.27 ns. It is not clear yet which compound is having fluorescence lifetime of 7.69 ns and which one is showing 1.27 ns. PMID:15978348

Alaoui, I Mekkaoui; Menzel, E R; Farag, M; Cheng, K H; Murdock, R H

2005-09-10

44

Time-resolved multiple probe spectroscopy  

SciTech Connect

Time-resolved multiple probe spectroscopy combines optical, electronic, and data acquisition capabilities to enable measurement of picosecond to millisecond time-resolved spectra within a single experiment, using a single activation pulse. This technology enables a wide range of dynamic processes to be studied on a single laser and sample system. The technique includes a 1 kHz pump, 10 kHz probe flash photolysis-like mode of acquisition (pump-probe-probe-probe, etc.), increasing the amount of information from each experiment. We demonstrate the capability of the instrument by measuring the photolysis of tungsten hexacarbonyl (W(CO){sub 6}) monitored by IR absorption spectroscopy, following picosecond vibrational cooling of product formation through to slower bimolecular diffusion reactions on the microsecond time scale.

Greetham, G. M.; Sole, D.; Clark, I. P.; Parker, A. W.; Pollard, M. R.; Towrie, M. [Central Laser Facility, Science and Technology Facilities Council, Research Complex at Harwell, Rutherford Appleton Laboratory, Harwell, Oxfordshire, OX11 0QX (United Kingdom)

2012-10-15

45

Time-resolved fluorescence decay measurements for flowing particles  

DOEpatents

Time-resolved fluorescence decay measurements for flowing particles. An apparatus and method for the measurement and analysis of fluorescence for individual cells and particles in flow are described, wherein the rapid measurement capabilities of flow cytometry and the robust measurement and analysis procedures of time-domain fluorescence lifetime spectroscopy are combined. A pulse-modulated cw laser is employed for excitation of the particles. The characteristics and the repetition rate of the excitation pulses can be readily adjusted to accommodate for fluorescence decays having a wide range of lifetimes.

Deka, Chiranjit (Miami, FL); Steinkamp, John A. (Los Alamos, NM)

1999-01-01

46

Time-resolved fluorescence decay measurements for flowing particles  

DOEpatents

Time-resolved fluorescence decay measurements are disclosed for flowing particles. An apparatus and method for the measurement and analysis of fluorescence for individual cells and particles in flow are described, wherein the rapid measurement capabilities of flow cytometry and the robust measurement and analysis procedures of time-domain fluorescence lifetime spectroscopy are combined. A pulse-modulated CW laser is employed for excitation of the particles. The characteristics and the repetition rate of the excitation pulses can be readily adjusted to accommodate for fluorescence decays having a wide range of lifetimes. 12 figs.

Deka, C.; Steinkamp, J.A.

1999-06-01

47

Global analysis of time-resolved fluorescence data.  

PubMed

In this chapter, we describe the global analysis approach for processing time-resolved fluorescence spectroscopy data of molecules in the condensed phase. Combining simultaneous analysis of data measured under different experimental conditions (spatial coordinates, temperature, concentration, emission wavelength, excitation intensity, etc.) with the fitting strategy, enabling parameter linkage and thus decreasing the total amount of estimated variables, makes global analysis more robust and more consistent compared to a sequential fit of single experimental data. We consider the main stages of the global analysis approach and provide some details that are important for its practical implementation. The application of the global approach to the analysis of time-resolved fluorescence anisotropy is demonstrated on experimental data of (enhanced) green fluorescent protein in aqueous solution. PMID:24108629

Digris, Anatoli V; Novikov, Eugene G; Skakun, Victor V; Apanasovich, Vladimir V

2014-01-01

48

Uptake of Cm(III) and Eu(III) by calcium silicate hydrates: a solution chemistry and time-resolved laser fluorescence spectroscopy study.  

PubMed

The interaction of the two chemical homologues [Cm(III) and Eu(III)] with calcium silicate hydrates (CSH phases) at pH 13.3 has been investigated in batch-type sorption studies using Eu(III) and complemented with time-resolved laser fluorescence spectroscopy (TRLFS) using Cm(III). The sorption data for Eu(III) reveal fast sorption kinetics and a strong uptake by CSH phases with distribution ratios of (6 +/- 3) x 10(5) L kg(-1). Three different Cm(III) species have been identified: A nonfluorescing species, which was identified as a curium hydroxide (surface) precipitate, and two fluorescing Cm(III)/CSH-sorbed species. The fluorescing sorbed species have characteristic emission spectra with main peak maxima at 618.9 and 620.9 nm and fluorescence emission lifetimes of 289 +/- 11 and 1482 +/- 200 micros, respectively. From the fluorescence lifetimes, it was calculated that the two fluorescing Cm(III) species have one or two and no water molecules left in their first coordination sphere, suggesting that these species are incorporated into the CSH structure. A structural model for Cm(III) and Eu(III) incorporation into CSH phases is proposed based on the substitution for Ca at two different types of sites in the CSH structure. PMID:12953867

Tits, Jan; Stumpf, Thorsten; Rabung, Thomas; Wieland, Erich; Fanghänel, Thomas

2003-08-15

49

Time-resolved laser-induced fluorescence spectroscopy of Nd3+ in molten LiCl-KCl eutectic  

NASA Astrophysics Data System (ADS)

The characteristics of the laser-induced fluorescence of Nd3+ in LiCl-KCl eutectic in the wavelength region of 360-900 nm were investigated for information concerning the chemical speciation of Nd-chloride complexes. When pumped at either 355 or 532 nm, Nd3+ in molten salt emits visible and near-IR fluorescence. The fluorescence peaks at 750 nm (4F7/2 + 4S3/2 ? 4I9/2) and 810 nm (4F5/2 + 2H9/2 ? 4I9/2) were particularly prominent at temperatures above the melting point. The fluorescence decay of these transition lines showed a bi-exponential behaviour of the fluorescence lifetime. These results provide evidence that two different chemical species of Nd3+ coexist in this system.

Jung, E. C.; Bae, S.-E.; Park, Y. J.; Song, K.

2011-11-01

50

Surface speciation of Eu3+ adsorbed on kaolinite by time-resolved laser fluorescence spectroscopy (TRLFS) and parallel factor analysis (PARAFAC).  

PubMed

Time-resolved laser fluorescence spectroscopy (TRLFS) is an effective speciation technique for fluorescent metal ions and can be further extended by the parallel factor analysis (PARAFAC). The adsorption of Eu(3+) on kaolinite as well as gibbsite as a reference mineral was investigated by TRLFS together with batch adsorption measurements. The PAFAFAC modeling provided the fluorescence spectra, decay lifetimes, and relative intensity profiles of three Eu(3+) surface complexes with kaolinite; an outer-sphere (factor A) complex and two inner-sphere (factors B and C) complexes. Their intensity profiles qualitatively explained the measured adsorption of Eu(3+). Based on the TRLFS results in varied H(2)O/D(2)O media, it was shown that the outer-sphere complex exhibited more rapid fluorescence decay than Eu(3+) aquo ion, because of the energy transfer to the surface. Factor B was an inner-sphere complex, which became dominant at relatively high pH, high salt concentration and low Eu(3+) concentration. Its spectrum and lifetime were similar to those of Eu(3+) adsorbed on gibbsite, suggesting its occurrence on the edge face of the gibbsite layer of kaolinite. From the comparison with the spectra and lifetimes of crystalline or aqueous Eu(OH)(3), factor C was considered as a poly-nuclear surface complex of Eu(3+) formed at relatively high Eu(3+) concentration. PMID:22377490

Ishida, Keisuke; Saito, Takumi; Aoyagi, Noboru; Kimura, Takaumi; Nagaishi, Ryuji; Nagasaki, Shinya; Tanaka, Satoru

2012-02-08

51

Modification of energy-transfer processes in the cyanobacterium, Arthrospira platensis, to adapt to light conditions, probed by time-resolved fluorescence spectroscopy.  

PubMed

In cyanobacteria, the interactions among pigment-protein complexes are modified in response to changes in light conditions. In the present study, we analyzed excitation energy transfer from the phycobilisome and photosystem II to photosystem I in the cyanobacterium Arthrospira (Spirulina) platensis. The cells were grown under lights with different spectral profiles and under different light intensities, and the energy-transfer characteristics were evaluated using steady-state absorption, steady-state fluorescence, and picosecond time-resolved fluorescence spectroscopy techniques. The fluorescence rise and decay curves were analyzed by global analysis to obtain fluorescence decay-associated spectra. The direct energy transfer from the phycobilisome to photosystem I and energy transfer from photosystem II to photosystem I were modified depending on the light quality, light quantity, and cultivation period. However, the total amount of energy transferred to photosystem I remained constant under the different growth conditions. We discuss the differences in energy-transfer processes under different cultivation and light conditions. PMID:23605291

Akimoto, Seiji; Yokono, Makio; Aikawa, Shimpei; Kondo, Akihiko

2013-04-21

52

In vivo validation of a bimodal technique combining time-resolved fluorescence spectroscopy and ultrasonic backscatter microscopy for diagnosis of oral carcinoma  

NASA Astrophysics Data System (ADS)

Tissue diagnostic features generated by a bimodal technique integrating scanning time-resolved fluorescence spectroscopy (TRFS) and ultrasonic backscatter microscopy (UBM) are investigated in an in vivo hamster oral carcinoma model. Tissue fluorescence is excited by a pulsed nitrogen laser and spectrally and temporally resolved using a set of filters/dichroic mirrors and a fast digitizer, respectively. A 41-MHz focused transducer (37-?m axial, 65-?m lateral resolution) is used for UBM scanning. Representative lesions of the different stages of carcinogenesis show that fluorescence characteristics complement ultrasonic features, and both correlate with histological findings. These results demonstrate that TRFS-UBM provide a wealth of co-registered, complementary data concerning tissue composition and structure as it relates to disease status. The direct co-registration of the TRFS data (sensitive to surface molecular changes) with the UBM data (sensitive to cross-sectional structural changes and depth of tumor invasion) is expected to play an important role in pre-operative diagnosis and intra-operative determination of tumor margins.

Sun, Yang; Xie, Hongtao; Liu, Jing; Lam, Matthew; Chaudhari, Abhijit J.; Zhou, Feifei; Bec, Julien; Yankelevich, Diego R.; Dobbie, Allison; Tinling, Steven L.; Gandour-Edwards, Regina F.; Monsky, Wayne L.; Gregory Farwell, D.; Marcu, Laura

2012-11-01

53

Microviscosity of supercooled water confined within aminopropyl-modified mesoporous silica as studied by time-resolved fluorescence spectroscopy.  

PubMed

The fluorescence dynamics of rhodamine B (RhB) immobilized on the pore surface of aminopropyl (AP)-modified mesoporous silica (diameter of the silica framework, 3.1 nm) was examined at temperatures between 293 and 193 K to study the microviscosity of supercooled water confined inside the pores. The mesoporous silica specimen with a dense AP layer (2.1 molecules nm(-2)) was prepared, and RhB isothiocyanate was covalently bound to part of the surface AP groups. The fluorescence lifetime of the surface RhB increased with decreasing temperature from 293 to 223 K, indicating that freezing of the confined water did not occur in this temperature range. The microviscosity of the supercooled confined water was evaluated from an analysis of the lifetime data based on a frequency-dependent friction model. PMID:23149606

Yamaguchi, Akira; Namekawa, Manato; Itoh, Tetsuji; Teramae, Norio

2012-01-01

54

Long-lived primary radical pair state detected by time-resolved fluorescence and absorption spectroscopy in an isolated Photosystem two core  

Microsoft Academic Search

A Photosystem two (PS II) core preparation containing the chlorophyll a binding proteins CP 47, CP 43, D1 and D2, and the non-chlorophyll binding cytochrome-b559 and 33 kDA polypeptides, has been isolated from PS II-enriched membranes of peas using the non-ionic detergent heptylthioglucopyranoside and elevated ionic strengths. The primary radical pair state, P680+Pheo-, was studied by time-resolved absorption and fluorescence

J. Las Rivas; B. Crystall; P. J. Booth; J. R. Durrant; S. Özer; G. Porter; D. R. Klug; J. Barber

1992-01-01

55

A homogeneous time-resolved fluorescence detection of telomerase activity  

Microsoft Academic Search

The homogeneous time-resolved fluorescence (HTRF®) technology is an assay developed to study the interaction between biomolecules. This detection system is based on a fluorescence resonance energy transfer (FRET) between a Tris-bipyridine europium cryptate used as a long-lived fluorescent donor and a chemically modified allophycocyanine as acceptor. This technology is characterized by both a spectral selectivity and a temporal selectivity (due

Manuel Gabourdes; Valérie Bourgine; Gérard Mathis; Hervé Bazin; Béatrice Alpha-Bazin

2004-01-01

56

Time resolved spectroscopy using synchrotron infrared pulses  

SciTech Connect

Electron synchrotron storage rings, such as the VUV ring at the National Synchrotron Light Source (NSLS), produce short pulses of infrared (IR) radiation suitable for investigating the time-dependent phenomena in a variety of interesting experimental systems. In contrast to other pulses sources of IR, the synchrotron produces a continuum spectral output over the entire IR (and beyond), though at power levels typically below those obtained from laser systems. The infrared synchrotron radiation (IRSR) source is therefore well-suited as a probe using standard FTIR spectroscopic techniques. Here the authors describe the pump-probe spectroscopy facility being established at the NSLS and demonstrate the technique by measuring the photocarrier decay in a semiconductor.

Carr, G.L. [Brookhaven National Lab., Upton, NY (United States). National Synchrotron Light Source; Lobo, R.P.S.M. [Brookhaven National Lab., Upton, NY (United States). National Synchrotron Light Source]|[Univ. of Florida, Gainesville, FL (United States). Physics Dept.; Hirschmugl, C.J. [Lawrence Berkeley National Lab., CA (United States). Advanced Light Source; LaVeigne, J.; Reitze, D.H.; Tanner, D.B. [Univ. of Florida, Gainesville, FL (United States). Physics Dept.

1997-09-01

57

Amine-functionalized lanthanide-doped zirconia nanoparticles: optical spectroscopy, time-resolved fluorescence resonance energy transfer biodetection, and targeted imaging.  

PubMed

Ultrasmall inorganic oxide nanoparticles doped with trivalent lanthanide ions (Ln(3+)), a new and huge family of luminescent bioprobes, remain nearly untouched. Currently it is a challenge to synthesize biocompatible ultrasmall oxide bioprobes. Herein, we report a new inorganic oxide bioprobe based on sub-5 nm amine-functionalized tetragonal ZrO(2)-Ln(3+) nanoparticles synthesized via a facile solvothermal method and ligand exchange. By utilizing the long-lived luminescence of Ln(3+), we demonstrate its application as a sensitive time-resolved fluorescence resonance energy transfer (FRET) bioprobe to detect avidin with a record-low detection limit of 3.0 nM. The oxide nanoparticles also exhibit specific recognition of cancer cells overexpressed with urokinase plasminogen activator receptor (uPAR, an important marker of tumor biology and metastasis) and thus may have great potentials in targeted bioimaging. PMID:22913455

Liu, Yongsheng; Zhou, Shanyong; Tu, Datao; Chen, Zhuo; Huang, Mingdong; Zhu, Haomiao; Ma, En; Chen, Xueyuan

2012-08-30

58

Europium speciation by time-resolved laser-induced fluorescence  

Microsoft Academic Search

Time-resolved laser-induced fluorescence has been used to investigate Eu complexes formed with a few main ligands encountered in natural waters: hydroxide, carbonate and humic substances. By varying pH and concentrations of ligands at fixed europium concentration and ionic strength, it was possible, together with free europium Eu3+, to identify spectrally and temporally carbonate complexes, namely Eu(CO3)+, Eu(CO3)2? and Eu(CO3)33? and

Gabriel Plancque; Valérie Moulin; Pierre Toulhoat; Christophe Moulin

2003-01-01

59

A 0.18-um CMOS Array Sensor for Integrated Time-Resolved Fluorescence Detection  

PubMed Central

This paper describes the design of an active, integrated CMOS sensor array for fluorescence applications which enables time-gated, time-resolved fluorescence spectroscopy. The 64-by-64 array is sensitive to photon densities as low as 8.8 × 106 photons/cm2 with 64-point averaging and, through a differential pixel design, has a measured impulse response of better than 800 ps. Applications include both active microarrays and high-frame-rate imagers for fluorescence lifetime imaging microscopy.

Huang, Ta-chien D.; Sorgenfrei, Sebastian; Gong, Ping; Levicky, Rastislav; Shepard, Kenneth L.

2010-01-01

60

Ultrafast time resolved vibrational spectroscopy in liquid systems  

SciTech Connect

The ultrafast dynamics of small molecules in the liquid phase can successfully be studied tracing the relaxation pathways of vibrational excess energy. Two complementing experimental techniques, picosecond IR double resonance spectroscopy and time resolved incoherent Anti-Stokes Raman spectroscopy, are very powerful tools for such studies. The capabilities of investigations combining these methods are discussed on the example of new experimental data on liquid dichloromethane (CH{sub 2}Cl{sub 2}). {copyright} {ital 1996 American Institute of Physics.}

Seifert, G.; Hofmann, M.; Weidlich, K.; Graener, H. [Physics Institute, University of Bayreuth, D-95440 Bayreuth (Germany)

1996-04-01

61

Application of time resolved area normalized emission spectroscopy to multicomponent systems  

NASA Astrophysics Data System (ADS)

Time resolved emission spectroscopy (TRES) provides information on the excited state kinetics and heterogeneity of emissive species in a system. Time resolved area normalized emission spectroscopy (TRANES), an extension to TRES, is a novel, model-free method for the analysis of intrinsic or extrinsic fluorescence probes in complex chemical and biophysical systems [Koti, Krishna, and Periasamy, J. Phys. Chem. A 105, 1767 (2001)]. Observation of a single isoemissive point in TRANES analysis of fluorescence is an unambiguous indication of the presence of two emissive species in the system. The presence of multiple isoemissive points in TRANES spectra is confirmed using simulation and experimental data of multicomponent systems.

Koti, A. S. R.; Periasamy, N.

2001-10-01

62

Time resolved spectroscopy of GRB030501 using INTEGRAL  

Microsoft Academic Search

The Gamma-ray instruments on-board INTEGRAL offer a unique opportunity to perform time resolved analysis on GRBs. The imager IBIS allows accurate positioning of GRBs and broad band spectral analysis, while SPI provides high resolution spectroscopy. GRB 030501 was discovered by the INTEGRAL Burst Alert System in the ISGRI field of view. Although the burst was fairly weak (fluence F20–200keV?3.5×10?6 erg

V. Beckmann; J. Borkowski; T. J.-L. Courvoisier; D. Götz; P. Favre; R. Hudec; S. Mereghetti; S. E. Shaw; A. von Kienlin; C. Wigger

2004-01-01

63

Time resolved spectroscopy of GRB 030501 using INTEGRAL  

Microsoft Academic Search

The gamma-ray instruments on-board INTEGRAL offer an unique opportunity to perform time resolved analysis on GRBs. The imager IBIS allows accurate positioning of GRBs and broad band spectral analysis, while SPI provides high resolution spectroscopy. GRB 030501 was discovered by the INTEGRAL Burst Alert System in the ISGRI field of view. Although the burst was fairly weak (fluence F20-200 keV

V. Beckmann; J. Borkowski; T. J.-L. Courvoisier; D. Götz; R. Hudec; F. Hroch; N. Lund; S. Mereghetti; S. E. Shaw; A. von Kienlin; C. Wigger

2003-01-01

64

Time-resolved fluorescence anisotropies in mixed surfactant solutions  

SciTech Connect

Time-resolved fluorescence anisotropy decays of solutions of Triton X-114 (TX-114) with various amounts of sodium dodecyl sulfate (SDS) were measured using the emission both from the surfactant itself and from added perylene. In the former case, the monomer and aggregate species of the surfactant were spectroscopically isolated and were shown to have significantly different rotational correlation times. The rotational diffusion of perylene in micellar TX-114 with small amounts of added SDS appeared to have a component with a very short correlation time. The anisotropy decay curves showed the existence of limiting anisotropies (r{sub {infinity}}), indicating hindered probe rotation in the micellar environment. At higher SDS concentrations, the fast-decaying component slowed down and the limiting anisotropy decreased substantially, suggesting some migration of the probe to the interior of the micelle.

McCarroll, M.E.; Joly, A.G.; Wang, Z.; Friedrich, D.M.; Wandruszka, R. von

1999-10-01

65

Time-Resolved Laser-Induced Fluorescence of Asbestos in Visible Region  

NASA Astrophysics Data System (ADS)

Nanosecond time-resolved laser-induced fluorescence spectroscopy was performed on five types of asbestos (chrysotile, crocidolite, amosite, tremolite, and anthophyllite) using an ultraviolet laser pulse of 266 nm. Most of the fluorescence spectra had a broad wavelength band of 350-700 nm and a maximum at approximately 450 nm in the visible region. The spectra also varied in shape over time. Although all the spectra were similar in shape, a significant difference in the relative ratio of fluorescence intensity between the two different wavelength regions was identified. The lifetime and total fluorescence intensity were also investigated and differences were observed for the different types of asbestos. The observed fluorescence decay curves of the different types of asbestos were almost biexponential in form. The total fluorescence intensity for anthophyllite was the largest among the five types of asbestos. Several methods potentially useful for identifying asbestos from other materials on the basis of their fluorescence characteristics are discussed.

Ohzu, Akira; Esaka, Fumitaka; Yasuda, Kenichiro

2009-04-01

66

Time-resolved fluorescence spectroscopy investigation of the effect of 4-hydroxynonenal on endogenous NAD(P)H in living cardiac myocytes.  

PubMed

Lipid peroxidation is a major biochemical consequence of the oxidative deterioration of polyunsaturated lipids in cell membranes and causes damage to membrane integrity and loss of protein function. 4-hydroxy-2-nonenal (HNE), one of the most reactive products of n-6 polyunsaturated fatty acid peroxidation of membrane phospholipids, has been shown to be capable of affecting both nicotinamide adenine dinucleotide (phosphate) reduced [NAD(P)H] as well as NADH production. However, the understanding of its effects in living cardiac cells is still lacking. Our goal was to therefore investigate HNE effects on NAD(P)H noninvasively in living cardiomyocytes. Spectrally resolved lifetime detection of endogenous fluorescence, an innovative noninvasive technique, was employed. Individual fluorescence components were resolved by spectral linear unmixing approach. Gathered results revealed that HNE reduced the amplitude of both resolved NAD(P)H components in a concentration-dependent manner. In addition, HNE increased flavoprotein fluorescence and responsiveness of the NAD(P)H component ratio to glutathione reductase (GR) inhibitor. HNE also increased the percentage of oxidized nucleotides and decreased maximal NADH production. Presented data indicate that HNE provoked an important cell oxidation by acting on NAD(P)H regulating systems in cardiomyocytes. Understanding the precise role of oxidative processes and their products in living cells is crucial for finding new noninvasive tools for biomedical diagnostics of pathophysiological states. PMID:23804217

Chorvatova, Alzbeta; Aneba, Swida; Mateasik, Anton; Chorvat, Dusan; Comte, Blandine

2013-06-01

67

Time-resolved fluorescence spectroscopy of two-photon laser-excited 8p, 9p, 5f, and 6f levels in neutral xenon  

SciTech Connect

Laser-induced fluorescence of two-photon excited 8p, 9p, J=0,2 and 5f, 6f, J=2 levels in neutral xenon has been investigated in the pressure regime between 4 and 120 Pa. Radiative lifetimes and collisional deactivation rates have been deduced especially for the 5f[3/2]{sub 2}, 5f[5/2]{sub 2}, and 8p[1/2]{sub 0} levels using the Stern-Volmer approach. The spontaneous lifetimes for 5f[3/2]{sub 2}, 5f[5/2]{sub 2}, and 8p[1/2]{sub 0} levels are 94, 78, and 207 ns, respectively. These lifetimes have been calculated also by applying extended multiconfiguration Dirac-Fock wave functions and are found in agreement with experiment within 10-25%.

Eichhorn, Christoph; Loehle, Stefan; Knapp, Andreas [Institut fuer Raumfahrtsysteme, Universitaet Stuttgart, Pfaffenwaldring 31, D-70569 Stuttgart (Germany); Fritzsche, Stephan [Gesellschaft fuer Schwerionenforschung (GSI), D-64291 Darmstadt (Germany); Department of Physical Sciences, University of Oulu, P.O. Box 3000, Oulu Fin-90014 (Finland); Auweter-Kurtz, Monika [Universitaet Hamburg, Edmund-Siemers Allee 1, D-20196 Hamburg (Germany)

2009-08-15

68

Radiationless processes in KCl:Eu2+ (time-resolved and photoacoustic spectroscopy)  

Microsoft Academic Search

Several zero-phonon lines are observed in the fluorescence spectrum at low temperatures and annealing experiments show that these are associated with aggregation of Eu2+-K+ vacancy pairs. Time-resolved spectroscopy measurements show that energy transfer takes place from ions in non-aggregated sites to those in aggregated centres. The time dependence is consistent with resonant electric dipole-dipole interaction with no back-transfer taking place.

L. D. Merkle; R. C. Powell; T. M. Wilson

1978-01-01

69

High harmonic spectroscopy and time-resolved holography with photoelectrons  

NASA Astrophysics Data System (ADS)

I will describe recent applications of high harmonic generation for tracking attosecond dynamics of electrons and holes in molecules, and our hopes to use photo-electron spectra for the same purpose. Interaction of intense infrared laser light with atoms and molecules leads to rich dynamics which presents unique combination of quantum and classical physics, ripe with unusual opportunities for imaging dynamics of electrons and nuclei at the time-scale from about 100 attoseconds to a few femtoseconds. As the infrared laser field strips an electron from an atom or a molecule, the electron starts to oscillate in the laser field. Energy E of these oscillations scales linearly with laser intensity I and quadratically with wavelength ? and can easily exceed 100 eV for typical experimental conditions. Re-encounter of the electron with the parent ion during such oscillations leads to several effects, including (i) high harmonic generation, which results from recombination of the returning electron with hole left in the ion, and (ii) electron parent-ion diffraction and electron holography, which results from electron-parent ion scattering. These processes encode spatial and temporal information about the parent ion. Spatial resolution can be better than an angstrom, courtesy of the electron de-Broglie wavelength. Temporal resolution can exceed 100 attoseconds, thanks to the dependence of the returning electron energy on the instant of its return: this energy changes from almost zero to the maximum value in less than half of the laser cycle T (T=2.6 fsec for ?=800 nm). I will first introduce the basic ideas underlying time-resolved electron holography and show recent proof-of-principle experimental results. The bulk of this talk will focus on high harmonic spectroscopy. The properties of high harmonic radiation - amplitude, phase, and polarization - encode detailed information about attosecond to few-femtosecond motion of electrons and light nuclei in the molecule. Experimental challenge is to completely characterize the emitted radiation, measuring not only light intensity but also phase and polarization. Theoretical challenge is to interpret the experimental data, taking into account highly nonlinear, non-perturbative nature of laser-induced dynamics. I will illustrate the potential of the technique by showing several examples of successful joint experimental and theoretical efforts, which gave us sometimes unexpected insight into core rearrangement during strong-field ionization. I will also show results of using high harmonic generation to time-resolve electron tunnelling from atoms and molecules.

Ivanov, Misha

2012-06-01

70

Noninvasive Multimodal Evaluation of Bioengineered Cartilage Constructs Combining Time-Resolved Fluorescence and Ultrasound Imaging  

PubMed Central

A multimodal diagnostic system that integrates time-resolved fluorescence spectroscopy, fluorescence lifetime imaging microscopy, and ultrasound backscatter microscopy is evaluated here as a potential tool for assessing changes in engineered tissue composition and microstructure nondestructively and noninvasively. The development of techniques capable of monitoring the quality of engineered tissue, determined by extracellular matrix (ECM) content, before implantation would alleviate the need for destructive assays over multiple time points and advance the widespread development and clinical application of engineered tissues. Using a prototype system combining time-resolved fluorescence spectroscopy, FLIM, and UBM, we measured changes in ECM content occurring during chondrogenic differentiation of equine adipose stem cells on 3D biodegradable matrices. The optical and ultrasound results were validated against those acquired via conventional techniques, including collagen II immunohistochemistry, picrosirius red staining, and measurement of construct stiffness. Current results confirm the ability of this multimodal approach to follow the progression of tissue maturation along the chondrogenic lineage by monitoring ECM production (namely, collagen type II) and by detecting resulting changes in mechanical properties of tissue constructs. Although this study was directed toward monitoring chondrogenic tissue maturation, these data demonstrate the feasibility of this approach for multiple applications toward engineering other tissues, including bone and vascular grafts.

Fite, Brett Z.; Decaris, Martin; Sun, Yinghua; Sun, Yang; Lam, Adrian; Ho, Clark K.L.

2011-01-01

71

Steady state and time-resolved fluorescence spectroscopic characterization of normal and cancerous urine  

NASA Astrophysics Data System (ADS)

Urine is one of the diagnostically important bio fluids, as it has many metabolites and some of them are native fluorophores. There may be a variation in the distribution and the physiochemical properties of the fluorophores during any metabolic change and pathologic conditions. Native fluorescence spectroscopy has been considered as a promising tool to characterize the fluorophores present in the urine. In this study, we aimed at characterizing the urine of both normal and patients with confirmed cancer using steady state and time-resolved fluorescence spectroscopy at 280 nm and 350 nm excitation. It is observed that the metabolites indoxyl sulphate and neopterin and its derivatives are responsible for altered spectral signatures at 280 nm, and 350 nm excitation. The overall spectral data were subjected to Principal Component Analysis and the resultant components were used as input in the linear discriminant analysis. As a total, 84% and 81.8% of samples were correctly classified at 280 nm and 350 nm respectively.

Rajasekaran, Ramu; Aruna, Prakasa Rao; Balu David, Munusamy; Koteeswaran, Dornadula; Muthuvelu, Kulandaivel; Rai, R.; Ganesan, Singaravelu

72

Time-resolved X-ray spectroscopy of ultrashort plasmas  

Microsoft Academic Search

Summary form only given. Results obtained at INRS by using the C850X streak camera are discussed. The experiments were carried out using the INRS Table Top Terawatt 500-fs laser (1.053 ?m) at an intensity of 1016 to 1017 W\\/cm2. Time-resolved spectra have been obtained for non-beam irradiation at 1 ?m and 0.53 ?m. The cold K? emission is time-resolved, giving

C. Y. Cote; J. C. Kieffer; M. Chaker; Y. Beaudoin; Z. Jiang; A. Mens; R. Verrecchia; R. Sauneuf; C. Schirmann

1993-01-01

73

Looking inside catalyst extrudates with time-resolved surface-enhanced Raman spectroscopy (TR-SERS).  

PubMed

Raman spectroscopy is one of the major characterization methods employed over the last few decades as a nondestructive technique for the study of heterogeneous catalysts and related catalytic reactions. However, the promise of practical applicability on millimeter-sized catalyst bodies, such as extrudates, has not been fulfilled completely. Large fluorescence signals and the highly scattering nature of the extrudates often hamper its practical usage. Different approaches to overcome this problem were examined, including the use of time-resolved Raman spectroscopy (TRRS), spatially offset Raman spectroscopy (SORS), surface-enhanced Raman spectroscopy (SERS), and combinations of these techniques. This paper demonstrates that especially TRRS can provide chemical information at depth within catalyst bodies, overcoming fluorescence background signals and allowing for visualization of analytes at different depths. It also examines the application of time-resolved SERS within catalyst bodies to gain insight into localized activity. With these options a wider applicability of Raman spectroscopy for industrial catalysis research becomes within reach. PMID:23031701

Harvey, Clare E; Iping Petterson, Ingeborg E; Weckhuysen, Bert M; Gooijer, Cees; Ariese, Freek; Mank, Arjan J G

2012-10-01

74

Planetary Surface Exploration Using Time-Resolved Laser Spectroscopy on Rovers and Landers  

NASA Astrophysics Data System (ADS)

Planetary surface exploration using laser spectroscopy has become increasingly relevant as these techniques become a reality on Mars surface missions. The ChemCam instrument onboard the Curiosity rover is currently using laser induced breakdown spectroscopy (LIBS) on a mast-mounted platform to measure elemental composition of target rocks. The RLS Raman Spectrometer is included on the payload for the ExoMars mission to be launched in 2018 and will identify minerals and organics on the Martian surface. We present a next-generation instrument that builds on these widely used techniques to provide a means for performing both Raman spectroscopy and LIBS in conjunction with microscopic imaging. Microscopic Raman spectroscopy with a laser spot size smaller than the grains of interest can provide surface mapping of mineralogy while preserving morphology. A very small laser spot size (~ 1 µm) is often necessary to identify minor phases that are often of greater interest than the matrix phases. In addition to the difficulties that can be posed by fine-grained material, fluorescence interference from the very same material is often problematic. This is particularly true for many of the minerals of interest that form in environments of aqueous alteration and can be highly fluorescent. We use time-resolved laser spectroscopy to eliminate fluorescence interference that can often make it difficult or impossible to obtain Raman spectra. As an added benefit, we have found that with small changes in operating parameters we can include microscopic LIBS using the same hardware. This new technique relies on sub-ns, high rep-rate lasers with relatively low pulse energy and compact solid state detectors with sub-ns time resolution. The detector technology that makes this instrument possible is a newly developed Single-Photon Avalanche Diode (SPAD) sensor array based on Complementary Metal-Oxide Semiconductor (CMOS) technology. The use of this solid state time-resolved detector offers a significant reduction in size, weight, power, and overall complexity - making time resolved detection feasible for planetary applications. We will discuss significant advances leading to the feasibility of a compact time-resolved spectrometer. We will present results on planetary analog minerals to demonstrate the instrument performance including fluorescence rejection and combined Raman-LIBS capability.

Blacksberg, Jordana; Alerstam, Erik; Maruyama, Yuki; Charbon, Edoardo; Rossman, George

2013-04-01

75

Simulations of time-resolved fluorescence in multilayered biological tissues: applications to clinical data modeling  

Microsoft Academic Search

We present a computational code capable of simulating time-resolved fluorescence emission from multi-layered biological tissues, and apply this code to model tissue fluorescence emission data acquired in vivo during clinical endoscopy. The code for multi-layered media is based on a Monte Carlo model we developed previously to simulate time-resolved fluorescence propagation in a semi-infinite turbid medium. Here, the code is

Mary-Ann Mycek; Karthik Vishwanath; Brian W. Pogue; Kevin T. Schomacker; Norman S. Nishioka

2003-01-01

76

EXAFS and time-resolved laser fluorescence spectroscopy (TRLFS) investigations of the structure of Cm(III)/Eu(III) complexed with di(chlorophenyl)dithiophosphinic acid and different synergistic agents.  

PubMed

The complexes of trivalent actinide curium (Cm(III)) with di(chlorophenyl)dithiophosphinic acid ((ClPh)2PSSH) and three different neutral complexing agents as synergists in tert-butylbenzene are studied by EXAFS and time-resolved laser fluorescence spectroscopy (TRLFS). The results are compared with those from the corresponding europium (Eu(III)) complexes. The aim of these investigations is to understand the chemical interactions responsible for the high selectivity of the synergistic systems of (ClPh)2PSSH and neutral complexing agents tri-n-octylphosphine oxide, tributylphosphate and tris(2-ethylhexyl)phosphate for trivalent actinide cations in liquid-liquid extraction. In our structural chemistry study, we find that the inner coordination sphere of extracted Cm(III) and Eu(III) complexes are different. In all complexes the (ClPh)2PSSH is bound to the metal cation in a bidentate fashion and the oxygen donor of the neutral complexing agent used as synergist is directly coordinated to the metal cation. Comparison of the Cm(III) and Eu(III) complexes shows that Cm(III) preferentially binds to the sulfur of (ClPh)2PSSH, whereas Eu(III) is preferentially bound to oxygen. A good selectivity in liquid-liquid extraction is correlated with a high ratio of the sulfur coordination number to oxygen coordination number. This leads to the conclusion that the observed differences in the coordination structure between Cm(III) and Eu(III) complexes play an important role in the selectivity of these extraction systems. PMID:15782265

Weigl, Michael; Denecke, Melissa A; Panak, Petra J; Geist, Andreas; Gompper, Klaus

2005-03-01

77

Time-resolved optical spectroscopy measurements of shocked liquid deuterium  

NASA Astrophysics Data System (ADS)

Time-resolved optical spectroscopy has been used to measure the shock pressure steadiness, emissivity, and temperature of liquid deuterium shocked to 22-90 GPa. The shock was produced using magnetically accelerated flyer plate impact, and spectra were acquired with a suite of four fiber-optic-coupled spectrometers with streak camera detectors. The shock pressure changes by an average of -1.2% over the 10-30 ns cell transit time, determined from the relative changes in the shock front self-emission with time. The shock front reflectivity was measured from 5140Å and 5320Å laser light reflected from the D2 shock. The emissivity inferred from the reflectivity measurements was in reasonably good agreement with quantum molecular dynamics simulation predictions. The spectral radiance wavelength dependence was found to agree well (average normalized ?2=1.6 ) with a Planckian multiplied by the emissivity. The shock front temperature was determined from the emissivity and the wavelength-dependent shock self-emission. Thirty-seven temperature measurements spanning the 22-90 GPa range were accumulated. The large number of temperature measurements enables a comparison of the scatter in the data with expectations for a Gaussian distribution. This facilitates determination of uncertainties that incorporate both apparatus contributions and otherwise unquantified systematic effects that cause self-emission variations from one experiment to another. Agreement between temperatures determined from the absolute spectral radiance and from the relative shape of the spectrum further substantiates the absence of systematic biases. The weighted mean temperature uncertainties were as low as ±3-4% , enabling the discrimination between competing models for the D2 equation of state (EOS). The temperature results agree well with models that predict a maximum compression of ˜4.4 . Softer models that predict approximately sixfold compression are inconsistent with the data to a very high statistical confidence level. Previous analysis [D. Saumon and T. Guillot, Astrophys. J. 609, 1170 (2004)] of Jupiter’s internal structure has shown that the core mass is restricted to be less than approximately three times the mass of the Earth, if EOS models consistent with these temperature measurements are employed.

Bailey, J. E.; Knudson, M. D.; Carlson, A. L.; Dunham, G. S.; Desjarlais, M. P.; Hanson, D. L.; Asay, J. R.

2008-10-01

78

Time-resolved ultrafast electron (e,2e) momentum spectroscopy  

NASA Astrophysics Data System (ADS)

The (e,2e) process is analyzed for the case of an ultrafast electron pulse incident upon a target prepared in a time-varying, coherent superposition of states. Conditions under which time-resolved target momentum densities can be obtained from experimental measurements are discussed. Results for coherent electronic motions in both the H atom and the H2+ molecule are used to illustrate the capability of an ultrafast electron pulse to image time-dependent target electron dynamics.

Shao, Hua-Chieh; Starace, Anthony F.

2013-05-01

79

Polar plot representation of time-resolved fluorescence.  

PubMed

Measuring changes in a molecule's fluorescence emission is a common technique to study complex biological systems such as cells and tissues. Although the steady-state fluorescence intensity is frequently used, measuring the average amount of time that a molecule spends in the excited state (the fluorescence lifetime) reveals more detailed information about its local environment. The lifetime is measured in the time domain by detecting directly the decay of fluorescence following excitation by short pulse of light. The lifetime can also be measured in the frequency domain by recording the phase and amplitude of oscillation in the emitted fluorescence of the sample in response to repetitively modulated excitation light. In either the time or frequency domain, the analysis of data to extract lifetimes can be computationally intensive. For example, a variety of iterative fitting algorithms already exist to determine lifetimes from samples that contain multiple fluorescing species. However, recently a method of analysis referred to as the polar plot (or phasor plot) is a graphical tool that projects the time-dependent features of the sample's fluorescence in either the time or frequency domain into the Cartesian plane to characterize the sample's lifetime. The coordinate transformations of the polar plot require only the raw data, and hence, there are no uncertainties from extensive corrections or time-consuming fitting in this analysis. In this chapter, the history and mathematical background of the polar plot will be presented along with examples that highlight how it can be used in both cuvette-based and imaging applications. PMID:24108625

Eichorst, John Paul; Wen Teng, Kai; Clegg, Robert M

2014-01-01

80

Time-resolved fluorescence microscopy for probing mitochondrial metabolites  

NASA Astrophysics Data System (ADS)

A novel set-up for time-gated (nanosecond) detection of fluorescence spectra and images of microscopic samples was recently developed. The apparatus was now used to measure the fluorescence of mitochondrial coenzymes (NADH, flavins) and a marker molecule (rhodamine 123) in endothelial cells from calf aorta. In these cultivated cells the electron transport chain was inhibited at various sites of the inner mitochondrial membrane. It could be shown that the fluorescence intensity of the free coenzyme NADH depended on the site of inhibition. In addition, an increased energy transfer from mitochondrial coenzymes (NADH, flavins) to rhodamine 123 molecules was observed, if the inhibition occurred in complex I (NADH- coenzyme Q reductase) or complex III (coenzyme QH2-cytochrome c reductase) of the respiratory chain. The diagnostic potential of these findings are discussed.

Gschwend, M. H.; Strauss, Wolfgang S.; Schneckenburger, Herbert; Steiner, Rudolf W.

1996-01-01

81

The analysis of time-resolved optical waveguide absorption spectroscopy based on positive matrix factorization.  

PubMed

Time-resolved optical waveguide absorption spectroscopy (OWAS) makes use of an evanescent field to detect the polarized absorption spectra of sub-monomolecular adlayers. This technique is suitable for the investigation of kinetics at the solid/liquid interface of dyes, pigments, fluorescent molecules, quantum dots, metallic nanoparticles, and proteins with chromophores. In this work, we demonstrate the application of positive matrix factorization (PMF) to analyze time-resolved OWAS for the first time. Meanwhile, PCA is researched to compare with PMF. The absorption/desorption kinetics of Rhodamine 6G (R6G) onto a hydrophilic glass surface and the dynamic process of Meisenheimer complex between Cysteine and TNT are selected as samples to verify experimental system and analytical methods. The results are shown that time-resolved OWAS can well record the absorption/desorption of R6G onto a hydrophilic glass surface and the dynamic formation process of Meisenheimer complexes. The feature of OWAS extracted by PMF is dynamic and consistent with the results analyzed by the traditional function of time/wavelength-absorbance. Moreover, PMF prevents the negative factors from occurring, avoids contradicting physical reality, and makes factors more easily interpretable. Therefore, we believe that PMF will provide a valuable analysis route to allow processing of increasingly large and complex data sets. PMID:23673009

Liu, Ping; Li, Zhu; Li, Bo; Shi, Guolong; Li, Minqiang; Yu, Daoyang; Liu, Jinhuai

2013-04-03

82

Time resolved laser induced fluorescence measurements: Considerations when using Nd:YAG based system  

NASA Astrophysics Data System (ADS)

Time-resolved laser-induced fluorescence (TR-LIF) and the laser induced breakdown spectroscopy (LIBS) have been shown to be methods which are fast and sensitive to provide information about the constituents in analyzed samples. TR-LIF and LIBS have similar hardware requirements. In this paper, we analyze some characteristics of TR-LIF/LIBS system implemented in our laboratory, considering the fact that the excitation part of the system is based on Nd:YAG laser and Optical Parametric Oscillator (OPO). The laser is more than powerful enough (365 mJ at 1064 nm, variable OPO output >5 mJ) for LIBS, but somehow slow (the length of fundamental laser harmonic output pulse is about 5 ns) for fluorescence measurements in our present area of interest, namely plants and food products. Fortunately, the pulse length of tunable OPO output (320-475 nm) is less then 1 ns, so by means of a correct deconvolution procedure it is possible to measure the fluorescence lifetimes in the range as small as a few nanoseconds. The fluorescence detection part of our system is based on picosecond streak camera. Using the fluorescent dyes (Rhodamine B and Fluorescein) ethanol solutions we verified the analyzing capabilities of our TR-LIF system.

Rabasovic, Maja S.; Sevic, Dragutin; Terzic, Mira; Marinkovic, Bratislav P.

2012-05-01

83

Time-resolved fluorescence measurements of actin-phalloidin interactions  

NASA Astrophysics Data System (ADS)

Compounds that interact with the cytoskeleton affect mobility and division, making them useful for treatment of certain types of cancer. Actin binding drugs such as the phallotoxins (small, bicyclic peptides) bind to and stabilize actin polymers (F-actin) without binding to actin monomers (G-actin). It has been shown that the intensity of fluorescently labeled phallotoxins such as fluorescein- phalloidin and rhodamine-phalloidin increases upon bind F- actin. We used LJL BioSystems' new FLAReTM technology to measure excited state lifetime changes of fluorescein- phalloidin and rhodamine-phalloidin upon binding to F- actin.

Helms, Michael K.; French, Todd E.

2000-03-01

84

Time-resolved Fourier spectroscopy for activated optical materials  

NASA Astrophysics Data System (ADS)

A low-cost add-on to commercial Fourier-transform spectrometers that have a continuously scanning Michelson interferometer has been developed for high-resolution, broadband, time-resolved spectros- copy. A number of innovations have been implemented to enable near-IR, visible, and UV photoluminescence studies. These include error correction and normalization of interferogram points to correct for laser intensity variations and missed shots, reduction of mirror-speed variations with recognition and avoidance of the timing mistakes they cause, and simple white-light-interferogram advancement optics that leave high-frequency modulation efficiency for the signal of interest unchanged in dynamically aligned systems. Application to energy-transfer phenomena in solid-state-laser media is described. laser crystals.

Weidner, H.; Peale, R. E.

1996-06-01

85

Analytical applications of time-resolved infrared absorption spectroscopy  

Microsoft Academic Search

Infrared absorption spectroscopy is a well established method for the study of molecular species. The power and utility of infrared spectroscopy cannot be contested. However, until recently it suffered from two major limitations. Dispersive infrared spectrometers suffered from relatively poor sensitivity. With the introduction of Fourier transform techniques to spectroscopy in general, and IR specifically, the sensitivity limitation has been

Schwab

1992-01-01

86

Optical Biopsy of Benign and Malignant Tissue by Time Resolved Spectroscopy.  

PubMed

Pathological condition of malignant tissue could be analyzed by spectral domain or time domain spectroscopy, the two being the complementary to each other in optical biopsy (OB) of cancer. This paper reports results of time resolved emission spectroscopy (TRS) of 24 excised tissue samples of breast and prostate (normal control = 12; benign = 4; malignant = 8), employing a 390 nm, 100 fs, Ti-Sapphire laser pulses.The fluorescence decay times were measured using streak camera and the resultant data were fitted for single and bi-exponential decays with reliability of 97%. Our results show the distinct difference between normal, benign and malignant tissues mostly due to the emission spectra of Nicotinamide Adenine Dinucleotide (NADH), Flavin Mononucleotide (FAD) and also due to the heterogeneity of micro environments associated with the diseased tissues. In this short report, fit is also shown that TRS of breast tissues are similar to those of prostate tissues. PMID:23745786

Masilamani, V; Das, B B; Secor, J; Alsalhi, M; Devanesan, S; Prasad, S; Rabah, D; Alfano, R R

2013-06-01

87

Time-resolved fluorescence spectroscopic study of flavin fluorescence in purified enzymes of bioluminescent bacteria  

NASA Astrophysics Data System (ADS)

Time-resolved fluorescence intensity and anisotropy decay measurements have been used to study the environment and rotational mobility of endogenous flavin in two purified enzymes of bioluminescent bacteria, Luciferase from Photobacterium leiognathi and NAD(P)H:FMN-oxidoreductase from Vibrio fischeri. We compared the time-resolved fluorescence parameters, intensity decay lifetimes, rotational correlation times, and their fractional contribution, of the endogeneous flavin fluorescence in each of the two enzymes in the presence or absence of quinones of different structures and redox potentials. The endogeneous flavin exhibited multi-exponential decay characteristics as compared to a single decay lifetime of around 5 ns for free flavin, suggesting a complex and heterogeneous environment of flavin bound to the enzyme. In addition, a significant increase in the rotational correlation time and a certain degree of ordering of the molecule were observed for endogenous flavin when compared to a single and fast rotational correlation time of 150 ps of free flavin. Quinone significantly altered both the lifetime and rotational characteristics of endogenous flavin suggesting specific interactions of quinones to the endogeneous flavin in the bacterial enzyme.

Vetrova, Elena; Kudryasheva, N.; Cheng, K.

2006-10-01

88

Simulation modelling of a micro-system for time-resolved fluorescence measurements  

Microsoft Academic Search

This paper presents the simulation modelling of a typical experimental setup for time-resolved fluorescence measurement. The developed model takes into account the setup geometry, characteristics of light source, detector and fluorescent sample as well as the adopted measurement technique. A qualitative verification of the model has been reported before. In this paper, we present a quantitative analysis and verification of

Marina Repich; David Stoppa; Bruce R. Rae; Robert K. Henderson; Gian-Franco Dalla Betta

2010-01-01

89

Evidence of fluorescent carbon nanoparticles produced in premixed flames by time-resolved fluorescence polarization anisotropy  

SciTech Connect

In this work we report on the analysis of combustion-generated nano-organic carbon (NOC) particles by means of time-resolved fluorescence polarization anisotropy (TRFPA). NOC samples were collected in water from nonsooting regions of ethylene/air laminar flames. The size of collected particles was determined with subnanometer accuracy by exploiting femtosecond laser pulses as an excitation source. Moreover, the TRFPA measurements were realized by selecting narrow-wavelength bands within the fluorescence spectrum. With this procedure, the ensemble-averaged size of particles emitting in the selected fluorescence band was determined, to provide additional information on composition and spectroscopic properties of the investigated particles. In particular, the NOC samples consisted of two groups of particles, preferentially emitting in two distinct wavelength bands: smaller particles, with diameter d=1-1.5nm, mostly fluorescing in the UV ({lambda}{proportional_to}300-470nm), and larger particles, d>2nm, fluorescing in the visible ({lambda}{proportional_to}490-580nm). The results of this work strongly support the attribution of UV/visible fluorescence generally detected in flames to nanoparticles. They also evidence that nanoparticles undergo a chemical transformation during the growth process, which produces a red shift in the fluorescence spectrum. (author)

Bruno, A.; de Lisio, C. [Centro di Ricerca e Sviluppo ''Coherentia,'' C.N.R.-I.N.F.M., Unita di Ricerca di Napoli, and Dipartimento di Scienze Fisiche, Universita di Napoli ''Federico II,'' Complesso di Monte S. Angelo, Via Cintia, 80126, Napoli (Italy); Minutolo, P. [Istituto di Ricerche sulla Combustione, CNR, P.le Tecchio, 80, 80126, Napoli (Italy); D'Alessio, A. [Dipartimento di Ingegneria Chimica, Universita di Napoli ''Federico II,'' P.le Tecchio, 80, 80126, Napoli (Italy)

2007-11-15

90

The application of time-resolved luminescence spectroscopy to a remote uranyl sensor  

SciTech Connect

Time resolved luminescence spectroscopy is an effective method for the determination of a wide range of uranyl concentrations in aqueous samples. We have applied this technique to the development of a remote sensing device using fiber optic cables coupled with a micro flow cell in order to probe for uranyl in aqueous samples. This sensor incorporates a Nafion membrane through which UO{sub 2}{sup 2+} can diffuse in to a reaction/analysis chamber which holds phosphoric acid, a reagent which enhances the uranyl luminescence intensity and lifetime. With this device, anionic and fluorescing organic interferences could be eliminated, allowing for the determination of uranyl over a concentration range of 10{sup 4} to 10{sup {minus}9}M. 17 refs., 5 figs.

Varineau, P.T.; Duesing, R.; Wangen, L.E.

1991-01-01

91

Time-resolved terahertz spectroscopy of semiconductor quantum dots  

Microsoft Academic Search

Spectroscopy in the far-infrared part of the electromagnetic spectrum based on the time-domain measurements of transient terahertz pulses has become a standard experimental technique. In the first part of this thesis we present results regarding applications of this technique to the problem of near-field, sub-wavelength imaging and the effect of finite-size beams in optical pump\\/terahertz probe experiments. The second part

Georgi Dakovski

2008-01-01

92

Time-resolved atomic inner-shell spectroscopy  

Microsoft Academic Search

The characteristic time constants of the relaxation dynamics of core-excited atoms have hitherto been inferred from the linewidths of electronic transitions measured by continuous-wave extreme ultraviolet or X-ray spectroscopy. Here we demonstrate that a laser-based sampling system, consisting of a few-femtosecond visible light pulse and a synchronized sub-femtosecond soft X-ray pulse, allows us to trace these dynamics directly in the

M. Drescher; M. Hentschel; R. Kienberger; M. Uiberacker; V. Yakovlev; A. Scrinzi; Th. Westerwalbesloh; U. Kleineberg; U. Heinzmann; F. Krausz

2002-01-01

93

Time-resolved and steady-state FRET spectroscopy on commercial biocompatible quantum dots  

NASA Astrophysics Data System (ADS)

Semiconductor nanocrystals (quantum dots - QDs) possess unique photophysical properties that make them highly interesting for many biochemical applications. Besides their common use as fluorophores in conventional spectroscopy and microscopy, QDs are well-suited for studying Förster resonance energy transfer (FRET). Size-dependent broadband absorption and narrow emission bands offer several advantages for the use of QDs both as FRET donors and acceptors. QD-based FRET pairs can be efficiently used as biological and chemical sensors for highly sensitive multiplexed detection. In this contribution we present the use of several commercially available QDs (Qdot® Nanocrystals - Invitrogen) as FRET donors in combination with commercial organic dyes as FRET acceptors. In order to investigate the FRET process within our donor-acceptor pairs, we used biotinylated QDs and streptavidin-labeled dyes. The well-known biotinstreptavidin molecular recognition enables effective FRET from QDs to dye molecules and provides defined distances between donor and acceptor. Steady-state and time-resolved fluorescence measurements were performed in order to investigate QD-to-dye FRET. Despite a thick polymer shell around the QDs, our results demonstrate the potential of these QDs as efficient donors both for steady-state and time-resolved FRET applications in nano-biotechnology.

Wegner, D.; Geißler, D.; Stufler, S.; Löhmannsröben, H.-G.; Hildebrandt, N.

2011-02-01

94

Time-resolved laser-induced fluorescence study on dyes used in DNA sequencing  

SciTech Connect

Research on the time-resolved fluorescence of fluorescein isothiocyanate, NBD, tetramethylrhodamine isothiocyanate, and Texas Red - the dyes used for fluorescence-based DNA sequencing - is described. Mean fluorescence lifetiems in both aqueous buffer solution and 5.3%T, 4.8%C polyacrylamide gel were determined as a function of excitation wave-lengths at 337, 470, and 550 nm and were found to be 3.5, 1.1, 2.5, and 4.3 ns; the detection limits are 10, 200, 200 and 200 amol for FITC, NBD, TEMR, and T. Red, respectively. Comparisons of fluorescence parameters between the conjugated dyes and the free dyes are also reported. Results on the optimization of the excitation source wavelengths to improve sensitivity and reduce background scattering in polyacrylamide gel are also reported. Time-resolved fluorescence was successfully applied to resolve spectral overlapping of emissions in both solution and in polyacrylamide gel. 12 refs., 6 figs., 1 tab.

Chang, Kaisyang; Force, R.K. (Univ. of Rhode Island, Kingston (United States))

1993-01-01

95

Time-resolved photoelectron spectroscopy using synchrotron radiation time structure.  

PubMed

Synchrotron radiation time structure is becoming a common tool for studying dynamic properties of materials. The main limitation is often the wide time domain the user would like to access with pump-probe experiments. In order to perform photoelectron spectroscopy experiments over time scales from milliseconds to picoseconds it is mandatory to measure the time at which each measured photoelectron was created. For this reason the usual CCD camera-based two-dimensional detection of electron energy analyzers has been replaced by a new delay-line detector adapted to the time structure of the SOLEIL synchrotron radiation source. The new two-dimensional delay-line detector has a time resolution of 5?ns and was installed on a Scienta SES 2002 electron energy analyzer. The first application has been to characterize the time of flight of the photoemitted electrons as a function of their kinetic energy and the selected pass energy. By repeating the experiment as a function of the available pass energy and of the kinetic energy, a complete characterization of the analyzer behaviour in the time domain has been obtained. Even for kinetic energies as low as 10?eV at 2?eV pass energy, the time spread of the detected electrons is lower than 140?ns. These results and the time structure of the SOLEIL filling modes assure the possibility of performing pump-probe photoelectron spectroscopy experiments with the time resolution given by the SOLEIL pulse width, the best performance of the beamline and of the experimental station. PMID:21335912

Bergeard, N; Silly, M G; Krizmancic, D; Chauvet, C; Guzzo, M; Ricaud, J P; Izquierdo, M; Stebel, L; Pittana, P; Sergo, R; Cautero, G; Dufour, G; Rochet, F; Sirotti, F

2011-02-05

96

Ultrafast time-resolved spectroscopy of the light-harvesting complex 2 (LH2) from the photosynthetic bacterium Thermochromatium tepidum.  

PubMed

The light-harvesting complex 2 from the thermophilic purple bacterium Thermochromatium tepidum was purified and studied by steady-state absorption and fluorescence, sub-nanosecond-time-resolved fluorescence and femtosecond time-resolved transient absorption spectroscopy. The measurements were performed at room temperature and at 10 K. The combination of both ultrafast and steady-state optical spectroscopy methods at ambient and cryogenic temperatures allowed the detailed study of carotenoid (Car)-to-bacteriochlorophyll (BChl) as well BChl-to-BChl excitation energy transfer in the complex. The studies show that the dominant Cars rhodopin (N=11) and spirilloxanthin (N=13) do not play a significant role as supportive energy donors for BChl a. This is related with their photophysical properties regulated by long ?-electron conjugation. On the other hand, such properties favor some of the Cars, particularly spirilloxanthin (N=13) to play the role of the direct quencher of the excited singlet state of BChl. PMID:21984346

Niedzwiedzki, Dariusz M; Fuciman, Marcel; Kobayashi, Masayuki; Frank, Harry A; Blankenship, Robert E

2011-10-08

97

TIME-RESOLVED FLUORESCENCE DETECTION OF TOXINS AND PATHOGENIC BACTERIA IN FOODS  

Technology Transfer Automated Retrieval System (TEKTRAN)

Immunomagnetic beads specific to Shiga-Like Toxin 1 (SLT-I) and Shiga-Like Toxin 2 (SLT-II) were applied to capture and concentrate the toxins in solution. The captured toxins were further labeled by Europium (Eu) -tagged anti-toxin antibody prior to detection by a time-resolved fluorescence (TRF) ...

98

Time-resolved fluorescence of the single tryptophan of Bacillus stearothermophilus phosphofructokinase.  

PubMed Central

The fluorescence of the single tryptophan in Bacillus stearothermophilus phosphofructokinase was characterized by steady-state and time-resolved techniques. The enzyme is a tetramer of identical subunits, which undergo a concerted allosteric transition. Time-resolved emission spectral data were fitted to discrete and distributed lifetime models. The fluorescence decay is a double exponential with lifetimes of 1.6 and 4.4 ns and relative amplitudes of 40 and 60%. The emission spectra of both components are identical with maxima at 327 nm. The quantum yield is 0.31 +/- 0.01. The shorter lifetime is independent of temperature; the longer lifetime has weak temperature dependence with activation energy of 1 kcal/mol. The fluorescence intensity and decay are the same in H2O and D2O solutions, indicating that the indole ring is not accessible to bulk aqueous solution. The fluorescence is not quenched significantly by iodide, but it is quenched by acrylamide with bimolecular rate constant of 5 x 10(8) M-1 s-1. Static and dynamic light scattering measurements show that the enzyme is a tetramer in solution with hydrodynamic radius of 40 A. Steady-state and time-resolved fluorescence anisotropies indicate that the tryptophan is immobile. The allosteric transition has little effect on the fluorescence properties. The fluorescence results are related to the x-ray structure.

Kim, S J; Chowdhury, F N; Stryjewski, W; Younathan, E S; Russo, P S; Barkley, M D

1993-01-01

99

Femtosecond time-resolved photoelectron spectroscopy of phenol  

NASA Astrophysics Data System (ADS)

Resonance-Enhanced Multi-Photon Ionization Photoelectron Spectroscopy has been used to study the ultrafast dynamics of phenol in a molecular beam. A wide variety of pathways to photoionization are available to the molecule as it absorbs laser photons. Ultraviolet laser pulses excite phenol to either the S1 or S2 state. The excited state molecules can be directly ionized by subsequent absorption of a second photon. Franck-Condon factors govern the vibrational intensities seen in the ions based on the vibrational levels accessed in the excited states. Propensity rules dictate the intensities of energetically available ion states based on configuration interaction in the excited states. Pump-probe experiments have determined the lifetime of the S2 state to be shorter than 350 femtoseconds. Our experiments show that high-lying excited states of phenol can be generated when an additional photon is absorbed from the initially prepared excited state. For some of the experiments, the energy of the highly excited valence state lies above the ionization potential, and thus the state is referred to as a superexcited state. These states have very short lifetimes as evidenced by pump-probe experiments. The spectra show the dynamics of energy flow from the superexcited states into a set of Rydberg states. The Rydberg states can be accessed by excitation through either S1 or S2. In addition, we report the use of a Genetic Algorithm to solve a multi-dimensional problem of optimizing the ion detection efficiency and resolution of our mass spectrometer. The two-photon ionization of phenol was the molecular system employed for this optimization, which improved the ion detection efficiency by a factor of 10 and the resolution by a factor of 11 over previous settings.

Schick, Carolyn Patricia

100

Fast dynamics in protein folding: Time-resolved fluorescence and absorbance studies of polypeptide reconfigurations  

NASA Astrophysics Data System (ADS)

We are at an era where we are beginning to understand the physical aspects of protein folding. The energy landscape theory of protein folding explains why protein-folding reactions are so rapid compared to random search. The high friction limit of Kramers theory for diffusion-driven reactions best describes protein folding kinetics. However, key biophysical questions remain, particularly in folding dynamics at fast time scales. Why do some protein molecules fold so fast? What physical parameters control the folding rates near the speed limit? We contributed to understanding protein folding at fast time scales by developing and improving techniques to probe submillisecond kinetics and by studying the fastest-folding protein systems: tryptophan cage and the compact late-stage intermediate of ferrocytochrome c. We studied fast dynamics in protein folding by time-resolved fluorescence and absorbance measurements. We fabricated and characterized a submillisecond laminar-flow mixing device that allows UV-excitation and observation of kinetic fluorescence changes in peptides with picomolar sample consumption. Together with equilibrium circular dichroism and fluorescence measurements, we used temperature-jump data to characterize the two-state folding of the designed miniprotein tryptophan cage. We have applied laser flash photolysis to the heme-CO bond and used nanosecond-resolved transient absorption spectroscopy to look at the fast M ? N folding transitions in ferrocytochrome c. We are currently developing experiments based on triplet-triplet energy transfer to do time-resolved optical absorption measurements on reconfigurations of tryptophan-containing proteins and peptides. The miniprotein tryptophan cage folds in 4 microseconds and sets the conditions for fast folding: a two-state reaction, a weak folding activation energy barrier, a nearly optimized free energy landscape, and pre-organized structures in the unfolded state. In ferrocytochrome c, the folding time from a compact configuration is 12 microseconds in water. Analysis of the solvent viscosity-dependence of the folding time using a model based on Kramers rate theory allowed us to identify two limiting time scales in protein folding: the time scale for solvent-coupled reorganizations and the time scale controlled by the internal friction within the protein molecule.

Pabit, Sersita Suzette A.

101

Computational modeling of device-tissue interface geometries for time-resolved fluorescence in layered tissue  

Microsoft Academic Search

Temporal measurements of fluorescence emitted from biological tissue provide information on biochemistry and morphology which may be useful in identifying neoplasia onset. Depth-selective detection of time-resolved fluorescence may enable enhanced discrimination of signals originating from individual tissue layers and thus improve device efficacy. In this study, we investigate how illumination-collection design parameters influence a device's ability to measure fluorophore lifetime

T. Joshua Pfefer; Anant Agrawal; Rebekah A. Drezek

2006-01-01

102

TIME-RESOLVED INFRARED SPECTROSCOPY IN THE U121R BEAMLINE AT THE NSLS  

SciTech Connect

A facility for performing time-resolved infrared spectroscopy has been developed at the NSLS, primarily at beamline U12IR. The pulsed IR light from the synchrotron is used to perform pump-probe spectroscopy. The authors present here a description of the facility and results for the relaxation of photoexcitations in both a semiconductor and superconductor.

CARR,G.L.; LAVEIGNE,J.D.; LOBO,R.P.S.M.; REITZE,D.H.; TANNER,D.B.

1999-07-19

103

Fluorescence lifetime heterogeneity in aggregates of LHCII revealed by time-resolved microscopy.  

PubMed Central

Two-photon excitation, time-resolved fluorescence microscopy was used to investigate the fluorescence quenching mechanisms in aggregates of light-harvesting chlorophyll a/b pigment protein complexes of photosystem II from green plants (LHCII). Time-gated microscopy images show the presence of large heterogeneity in fluorescence lifetimes not only for different LHCII aggregates, but also within a single aggregate. Thus, the fluorescence decay traces obtained from macroscopic measurements reflect an average over a large distribution of local fluorescence kinetics. This opens the possibility to resolve spatially different structural/functional units in chloroplasts and other heterogeneous photosynthetic systems in vivo, and gives the opportunity to investigate individually the excited states dynamics of each unit. We show that the lifetime distribution is sensitive to the concentration of quenchers contained in the system. Triplets, which are generated at high pulse repetition rates of excitation (>1 MHz), preferentially quench domains with initially shorter fluorescence lifetimes. This proves our previous prediction from singlet-singlet annihilation investigations (Barzda, V., V. Gulbinas, R. Kananavicius, V. Cervinskas, H. van Amerongen, R. van Grondelle, and L. Valkunas. 2001. Biophys. J. 80:2409-2421) that shorter fluorescence lifetimes originate from larger domains in LHCII aggregates. We found that singlet-singlet annihilation has a strong effect in time-resolved fluorescence microscopy of connective systems and has to be taken into consideration. Despite that, clear differences in fluorescence decays can be detected that can also qualitatively be understood.

Barzda, V; de Grauw, C J; Vroom, J; Kleima, F J; van Grondelle, R; van Amerongen, H; Gerritsen, H C

2001-01-01

104

Multicolor Photometry and Time-resolved Spectroscopy of Two sdBV Stars  

NASA Astrophysics Data System (ADS)

Observational mode constraints have mostly been lacking for short period pulsating sdB stars, yet such identifications are vital to constrain models. Time-resolved spectroscopy and multicolor photometry have been employed with mixed results for short-period pulsating sdB stars. Time-resolved spectroscopy has successfully measured radial velocity, temperature, and gravity variations in six pulsators, yet interpreting results is far from straightforward. Multicolor photometry requires extremely high precision to discern between low-degree modes, yet has been used effectively to eliminate high-degree modes. Combining radial velocity (RV) and multicolor measurements has also been shown as an effective means of constraining mode identifications. We present preliminary results for Feige 48 and EC 01541-1409 using both time-resolved spectroscopy and multicolor photometry and an initial examination of their pulsation modes using the atmospheric codes BRUCE and KYLIE.

Reed, M. D.; O'Toole, S. J.; Telting, J. H.; Østensen, R. H.; Heber, U.; Barlow, B. N.; Reichart, D. E.; Nysewander, M. C.; LaCluyze, A. P.; Ivarsen, K. M.; Haislip, J. B.; Bean, J.

2012-03-01

105

Multiplexed analysis using time-resolved near-IR fluorescence for the detection of genomic material  

NASA Astrophysics Data System (ADS)

While fluorescence continues to be an important tool in genomics, new challenges are being encountered due to increased efforts toward miniaturization reducing detection volumes and the need for screening multiple targets simultaneously. We have initiated work on developing time- resolved near-IR fluorescence as an additional tool for the multiplexed analyses of DNA, either for sequencing or mutation detection. We have fabricated simple and compact time-resolved fluorescence microscopes for reading fluorescence from electrophoresis or DNA microarrays. These microscopes consist of solid-state diode lasers and diode detectors and due to their compact size, the optical components and laser head can be mounted on high-speed micro-translational stages to read fluorescence from either multi-channel capillary electrophoresis instruments or micro fabricated DNA sorting devices. The detector is configured in a time-correlated single photon counting format to allow acquisition of fluorescence lifetimes on-the-fly during data acquisition in the limit of low counting statistics. In multiplexed analyses, lifetime discrimination serves as a method for dye-reporter identification using only a single readout channel. Also, coupled to multi-color systems, lifetime identification can significantly increase the number of probes monitored in a single instrument. In this work, near-IR fluorescence, including dye-labels and hardware, will be discussed as well as the implementation of near-IR fluorescence in DNA sequencing using slab gel electrophoresis and DNA microarrays.

Stryjewski, Wieslaw J.; Soper, Steven A.; Lassiter, Suzzane; Davis, Lloyd M.

2002-06-01

106

Status And New Applications Of Time-Resolved X-Ray Absorption Spectroscopy  

SciTech Connect

Time-resolved X-ray absorption spectroscopy is a valuable tool for detailed investigations of fast chemical reactions, thin film deposition phenomena, solid state reactions, phase transformations etc. We will report on latest experimental developments which employ a new monochromator design consisting of a cam driven tilt table for rapid angular oscillations and a fixed-exit channel cut crystal. Using cryogenic cooling, the silicon crystal can cope with the full heat load from third generation undulator sources such as the APS, SPring-8 or the ESRF. Depending on photon flux and sample quality, repetition rates of about 100 Hz can be realized for the XANES range, while the acquisition of full EXAFS spectra with a scan range of typically 1 keV are feasible at a repetition rate of 10 Hz. An excellent data quality can be obtained. Since a fast sequential energy scanning technique is used, the detection of fluorescence radiation or surface sensitive techniques can be applied, and a reference sample can be monitored simultaneously with each measurement to detect even minor edge shifts reliably. Furthermore, XANES microtomography in transmisson and fluorescence becomes feasible using the fast scanning monochromator in combination with refractive X-ray lenses for beam focusing.

Frahm, R.; Griesebock, B.; Richwin, M.; Luetzenkirchen-Hecht, D. [Institut fuer Materialwissenschaften und Fachbereich Physik, Bergische Universitaet Wuppertal, Gaussstr. 20, 42097 Wuppertal (Germany)

2004-05-12

107

Steady-state and time-resolved fluorescence investigations of pyrene excimer formation in supercritical CO{sub 2}  

SciTech Connect

Detailed studies on the formation of pyrene excimer in supercritical CO{sub 2} are reported. The photophysics of pyrene are investigated as a function of temperature and fluid density. Over the broad density range studied, there is no evidence for ground-state (solute-solute) interaction. Comparison is made between excimer formation in supercritical CO{sub 2} and ground-state dimerization of pyrene in {gamma}-cyclodextrin ({gamma}-CD). Time-resolved fluorescence spectroscopy is used to recover the individual rate terms that describe the total emission process. The recovered density-dependent bimolecular rates for pyrene excimer formation in supercritical CO{sub 2} follow a simple diffusion-controlled model. This result parallels reports on pyrene excimer formation in normal liquid solvents. Finally, the relative decrease in pyrene excimer formation, with increased fluid density, is easily explained from time-resolved experiments. 73 refs., 15 figs., 3 tabs.

Zagrobelny, J.; Betts, T.A.; Bright, F.V. [State Univ. of New York, Buffalo, NY (United States)

1992-06-17

108

Subcellular localization-dependent changes in EGFP fluorescence lifetime measured by time-resolved flow cytometry.  

PubMed

Intracellular protein transport and localization to subcellular regions are processes necessary for normal protein function. Fluorescent proteins can be fused to proteins of interest to track movement and determine localization within a cell. Currently, fluorescence microscopy combined with image processing is most often used to study protein movement and subcellular localization. In this contribution we evaluate a high-throughput time-resolved flow cytometry approach to correlate intracellular localization of human LC3 protein with the fluorescence lifetime of enhanced green fluorescent protein (EGFP). Subcellular LC3 localization to autophagosomes is a marker of the cellular process called autophagy. In breast cancer cells expressing native EGFP and EGFP-LC3 fusion proteins, we measured the fluorescence intensity and lifetime of (i) diffuse EGFP (ii) punctate EGFP-LC3 and (iii) diffuse EGFP-?LC3 after amino acid starvation to induce autophagy-dependent LC3 localization. We verify EGFP-LC3 localization with low-throughput confocal microscopy and compare to fluorescence intensity measured by standard flow cytometry. Our results demonstrate that time-resolved flow cytometry can be correlated to subcellular localization of EGFP fusion proteins by measuring changes in fluorescence lifetime. PMID:24010001

Gohar, Ali Vaziri; Cao, Ruofan; Jenkins, Patrick; Li, Wenyan; Houston, Jessica P; Houston, Kevin D

2013-07-19

109

Subcellular localization-dependent changes in EGFP fluorescence lifetime measured by time-resolved flow cytometry  

PubMed Central

Intracellular protein transport and localization to subcellular regions are processes necessary for normal protein function. Fluorescent proteins can be fused to proteins of interest to track movement and determine localization within a cell. Currently, fluorescence microscopy combined with image processing is most often used to study protein movement and subcellular localization. In this contribution we evaluate a high-throughput time-resolved flow cytometry approach to correlate intracellular localization of human LC3 protein with the fluorescence lifetime of enhanced green fluorescent protein (EGFP). Subcellular LC3 localization to autophagosomes is a marker of the cellular process called autophagy. In breast cancer cells expressing native EGFP and EGFP-LC3 fusion proteins, we measured the fluorescence intensity and lifetime of (i) diffuse EGFP (ii) punctate EGFP-LC3 and (iii) diffuse EGFP-?LC3 after amino acid starvation to induce autophagy-dependent LC3 localization. We verify EGFP-LC3 localization with low-throughput confocal microscopy and compare to fluorescence intensity measured by standard flow cytometry. Our results demonstrate that time-resolved flow cytometry can be correlated to subcellular localization of EGFP fusion proteins by measuring changes in fluorescence lifetime.

Gohar, Ali Vaziri; Cao, Ruofan; Jenkins, Patrick; Li, Wenyan; Houston, Jessica P.; Houston, Kevin D.

2013-01-01

110

Europium complexes investigations in natural waters by time-resolved laser-induced fluorescence  

Microsoft Academic Search

Time-resolved laser-induced fluorescence (TRLIF) has been used to investigate Eu complexes formed with inorganic and organic ligands encountered in natural waters as well as Eu complexes formed during the interaction of simulated nuclear waste glass with claywater. By comparing spectral and temporal data obtained by TRLIF on various europium solutions containing humic acids (HA) and carbonates (CO3), it has been

Christophe Moulin; Jiang Wei; Pierre Van Iseghem; Ivan Laszak; Gabriel Plancque; Valérie Moulin

1999-01-01

111

A simulation-based study of reconstruction in Time-resolved Fluorescence Diffuse Optical Tomography in Cylindrical geometry  

Microsoft Academic Search

The present paper is devoted to fluorescence diffuse optical tomography by using time resolved signals for the reconstruction of the 3D biodistribution of fluorescent probes embedded in biological tissues. The focus is made on the reconstruction of a methodology for an efficient exploitation of the time resolved data. The study is restricted to the examination of the three first moments

Nicolas Ducros; Anabela Da Silva; Jean-Marc Dinten; F. Peyrin

2007-01-01

112

BHHST: An improved lanthanide chelate for time-resolved fluorescence applications  

NASA Astrophysics Data System (ADS)

The detection of the waterborne pathogens Giardia lamblia and Cryptosporidium parvum in environmental water bodies requires concentration of large volumes of water due to the low dose required for infection. The highly concentrated (10,000-fold) water sample is often rich in strongly autofluorescent algae, organic debris and mineral particles that can obscure immunofluorescently labeled (oo)cysts during analysis. Time-resolved fluorescence techniques exploit the long fluorescence lifetimes of lanthanide chelates (ms) to differentiate target fluorescence from background autofluorescence (ns). Relatively simple instrumentation can be used to enhance the signal-to-noise ratio (S/N) of labelled target. Time-resolved fluorescence techniques exploit the large difference in lifetime by briefly exciting fluorescence from the sample using a pulsed excitation source. Capture of the resulting fluorescence emission is delayed until the more rapidly decaying autofluorescence has faded beyond detection, whereon the much stronger and slower fading emission from labelled target is collected. BHHCT is a tetradentate beta-diketone chelate that is activated to bind with protein (antibody) as the chlorosulfonate. The high activity of this residue makes conjugations difficult to control and can lead to the formation of unstable immunoconjugates. To overcome these limitations a 5-atom hydrophylic molecular tether was attached to BHHCT via the chlorosulfonate and the BHHCT derivative was then activated to bind to proteins as the succinimide. The new compound (BHHST) could be prepared in high purity and was far more stable than the chlorosulfonate on storage. A high activity immunocojugate was prepared against Cryptosporidium that yielded an 8-fold increase in SNR using a lab-built time-resolved fluorescence microscope.

Connally, Russell; Jin, Dayong; Piper, James

2005-04-01

113

Spectra-resolved technique of a sensitive time-resolved fluorescence immunoassay instrument  

NASA Astrophysics Data System (ADS)

The lanthanide trivalence ion and its chelates are used for marking substance in time-resolved fluorescence immunoassay (TRFIA), marking the protein, hormone, antibody, nucleic acid probe or biologica alive cell, to measure the concentration of the analysis substance inside the reaction system with time-resolved fluorometry after the reaction system occurred, and attain the quantitative analysis's purpose. TRFIA has been become a kind of new and more sensitive measure method after radioisotope marking, enzymatic marking, chemiluminescence, electrochemiluminescence, it primarily is decided by the special physics and chemistry characteristic of lanthanide trivalence ion and its chelates. In this paper, the result of spectroscopic evaluation of europium trivalence ion and its chelate, and the principle of spectra-resolved technology and a sensitive time-resolved fluorescence immunoassay instrument made by ourselves are reported. In the set, a high frequency Xenon pulsed-light was adopted as exciting light, and two special filters was utilized according to spectra-resolved technique. Thus the influence of scattering light and short-lifetime fluorescence was removed. And the sensitivity is 10-12mol/L (when Eu3+ was used for marking substance), examination repeat is CV <= 5%, examination linearity is from 10-8mol/L to 10-12mol/L, correlation coefficient r >= 95% (p < 0.01).

Guo, Zhouyi; Tian, Zhen; Jia, Yali

2004-07-01

114

Time-resolved X-ray absorption spectroscopy using an energy dispersive optics: Strengths and limitations  

Microsoft Academic Search

X-ray Absorption Spectroscopy has undergone a great theoretical and experimental development in the last years. This technique has proved to be a powerful tool in elucidating huge number of questions in materials science. Great interest exists in time-resolved experiments achieved with extreme energy resolution and energy scale stability taking full advantage of the strong correlation between the stereochemical environment of

Alouin Fontaine; Elisabeth Dartyge; Jean Itie; Alain Jucha; Alain Polian; Helio Tolentino; Gerard Tourillon

115

Time-resolved optical spectroscopy of the chest: is it possible to probe the lung?  

NASA Astrophysics Data System (ADS)

Monte Carlo simulations and preliminary time-resolved spectroscopy measurements were performed to investigate the feasibility of the in vivo optical diagnostics of lung conditions and diseases. Absorption and reduced scattering properties of the chest, arising from in vivo spectral measurements on volunteers are presented.

Quarto, G.; Farina, A.; Pifferi, A.; Taroni, P.; Miniati, M.

2013-06-01

116

Accurate time-resolved laser spectroscopy on sodium and bismuth atoms  

Microsoft Academic Search

It is demonstrated that time resolved laser spectroscopy can give atomic lifetime data with an accuracy of better than 0.5%. This is achieved by a single-photon counting delayed coincidence technique, using a mode-locked dye laser for the excitation. Natural radiative lifetimes are measured for the sodium and bismuth atoms.

J. Carlsson

1988-01-01

117

Homogeneous time-resolved fluoroimmunoassay of bensulfuron-methyl by using terbium fluorescence energy transfer  

Microsoft Academic Search

A sensitive homogenous time-resolved fluoroimmunoassay (TR-FIA) method for bensulfuron-methyl (BSM) based on fluorescence resonance energy transfer (FRET) from a Tb3+ fluorescent chelate with N,N,N?,N?-[2,6-bis(3?-aminomethyl-1?-pyrazoly)-4-phenylpyridine] tetrakis(acetic acid) (BPTA–Tb3+) to organic dye, Cy3 or Cy3.5 has been developed. New method combined the use of BPTA–Tb3+ labeled streptavidin, Cy3 or Cy3.5 labeled anti-BSM monoclonal antibody and biotinylated BSM–BSA conjugate (BSA is bovine serum

Guilan Wang; Jingli Yuan; Kazuko Matsumoto; Zhide Hu

2001-01-01

118

Time-resolved photoluminescence spectroscopy of individual Te impurity centers in ZnSe  

NASA Astrophysics Data System (ADS)

Tellurium impurity centers in ZnSe were individually probed with time-resolved photoluminescence (PL) spectroscopy. Resolution-limited peaks with an ultralow spatial density originate in the recombination of excitons deeply bound to isolated nearest-neighbor isoelectronic Te pairs (Te2) . This interpretation is supported by ab initio calculations. The peaks reveal antibunched photon emission and a doublet structure polarized along [110] and [1¯10] . The temperature dependence of the time-resolved PL decay exposes the dark excitonic states which indirectly affect the radiative recombination of single fine-structure split excitons.

Muller, A.; Bianucci, P.; Piermarocchi, C.; Fornari, M.; Robin, I. C.; André, R.; Shih, C. K.

2006-02-01

119

Two-photon absorption and time-resolved stimulated emission depletion spectroscopy of a new fluorenyl derivative.  

PubMed

The synthesis, comprehensive linear photophysical characterization, two-photon absorption (2PA), steady-state and time-resolved stimulated emission depletion properties of a new fluorene derivative, (E)-1-(2-(di-p-tolylamino)-9,9-diethyl-9H-fluoren-7-yl)-3-(thiophen-2-yl)prop-2-en-1-one (1), are reported. The primary linear spectral properties, including excitation anisotropy, fluorescence lifetimes, and photostability, were investigated in a number of aprotic solvents at room temperature. The degenerate 2PA spectra of 1 were obtained with open-aperture Z-scan and two-photon induced fluorescence methods, using a 1 kHz femtosecond laser system, and maximum 2PA cross-sections of ?400-600 GM were obtained. The nature of the electronic absorption processes in 1 was investigated by DFT-based quantum chemical methods implemented in the Gaussian 09 program. The one- and two-photon stimulated emission spectra of 1 were measured over a broad spectral range using a femtosecond pump-probe-based fluorescence quenching technique, while a new methodology for time-resolved fluorescence emission spectroscopy is proposed. An effective application of 1 in fluorescence bioimaging was demonstrated by means of one- and two-photon fluorescence microscopy images of HCT 116 cells containing dye encapsulated micelles. PMID:22887914

Belfield, Kevin D; Bondar, Mykhailo V; Morales, Alma R; Yue, Xiling; Luchita, Gheorghe; Przhonska, Olga V; Kachkovsky, Olexy D

2012-08-07

120

Time-resolved spectroscopy of endogenous NAD(P)H in Gluconobacter oxydans  

NASA Astrophysics Data System (ADS)

The genus Gluconobacter is frequently used for biotechnological and/or nanotechnological applications. We studied endogenous fluorescence of nicotinamide adenine dinucleotide (phosphate) (NAD(P)H), indicator of the oxidative metabolic state in mammalian cells, in Gluconobacter oxydans (G. oxydans). Time-resolved measurements (excitation by 375nm pulsed diode laser) were employed to record the bacterial fluorescence intensity, as well as its modifications by metabolic modulation. Results were gathered on fresh bacteria, on de-frozen ones, as well as on bacteria encapsulated in alginate beads. NAD(P)H fluorescence increased linearly with the concentration of bacteria. Freezing, which has little effect on the viability of bacteria or the concentration-dependent fluorescence rise, affected the temperature-dependence of NAD(P)H fluorescence. Sodium cyanide (10 mM) provoked significant rise in the NAD(P)H fluorescence, while dinitrophenol (200 ?M) induced its decrease, confirming the bacterial NAD(P)H fluorescence sensitivity to modulators of electron transport chain. Gathered results demonstrate that endogenous NAD(P)H fluorescence can be successfully recorded in the bacterial strain G. oxydans using time-resolved measurements.

Horilova, J.; Kromkova, K.; Bucko, M.; Illesova, A.; Vikartovska, A.; Stefuca, V.; Mateasik, A.; Chorvat, D.; Chorvatova, A.

2013-02-01

121

Evidence for a Novel Mechanism of Time-Resolved Flavin Fluorescence Depolarization in Glutathione Reductase  

PubMed Central

Time-resolved flavin fluorescence anisotropy studies on glutathione reductase (GR) have revealed a remarkable new phenomenon: wild-type GR displays a rapid process of fluorescence depolarization, that is absent in mutant enzymes lacking a nearby tyrosine residue that blocks the NADPH-binding cleft. Fluorescence lifetime data, however, have shown a more rigid active-site structure for wild-type GR than for the tyrosine mutants. These results suggest that the rapid depolarization in wild-type GR originates from an interaction with the flavin-shielding tyrosine, and not from restricted reorientational motion of the flavin. A novel mechanism of fluorescence depolarization is proposed that involves a transient charge-transfer complex between the tyrosine and the light-excited flavin, with a concomitant change in the direction of the emission dipole moment of the flavin. This interaction is likely to result from side-chain relaxation of the tyrosine in the minor fraction of enzyme molecules in which this residue is in an unsuitable position for immediate fluorescence quenching at the moment of excitation. Support for this mechanism is provided by binding studies with NADP+ and 2?P-5?ADP-ribose that can intercalate between the flavin and tyrosine and/or block the latter. Fluorescence depolarization analyses as a function of temperature and viscosity confirm the dynamic nature of the process. A comparison with fluorescence depolarization effects in a related flavoenzyme indicates that this mechanism of flavin fluorescence depolarization is more generally applicable.

van den Berg, Petra A. W.; van Hoek, Arie; Visser, Antonie J. W. G.

2004-01-01

122

Cucurbiturils: molecular nanocapsules for time-resolved fluorescence-based assays.  

PubMed

A new fluorescent host-guest system based on the inclusion of the fluorophore 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) into the cavity of the molecular container compound cucurbit[7]uril (CB7) has been designed which possesses an exceedingly long-lived emission (690 ns in aerated water). The large binding constant of (4 +/- 1) x 10(5) M(-1) along with the resistance of the CB7.DBO complex toward external fluorescence quenchers allow the use of CB7 as an enhancer in time-resolved fluorescence-based assays, e.g., to screen enzyme activity or inhibition by using DBO-labeled peptides as substrates. The response of CB7.DBO to different environmental conditions and possible quenchers are described. PMID:15382642

Marquez, Cesar; Huang, Fang; Nau, Werner M

2004-03-01

123

Fluorescence time-resolved imaging system embedded in an ultrasound prostate probe  

PubMed Central

Ultrasound imaging (US) of the prostate has a low specificity to distinguish tumors from the surrounding tissues. This limitation leads to systematic biopsies. Fluorescent diffuse optical imaging may represent an innovative approach to guide biopsies to tumors marked with high specificity contrast agents and therefore enable an early detection of prostate cancer. This article describes a time-resolved optical system embedded in a transrectal US probe, as well as the fluorescence reconstruction method and its performance. Optical measurements were performed using a pulsed laser, optical fibers and a time-resolved detection system. A novel fast reconstruction method was derived and used to locate a 45 µL ICG fluorescent inclusion at a concentration of 10 µM, in a liquid prostate phantom. Very high location accuracy (0.15 cm) was achieved after reconstruction, for different positions of the inclusion, in the three directions of space. The repeatability, tested with ten sequential measurements, was of the same order of magnitude. Influence of the input parameters (optical properties and lifetime) is presented. These results confirm the feasibility of using optical imaging for prostate guided biopsies.

Laidevant, Aurelie; Herve, Lionel; Debourdeau, Mathieu; Boutet, Jerome; Grenier, Nicolas; Dinten, Jean-Marc

2011-01-01

124

Time resolved fluorescence polarization anisotropy of carbonaceous particles produced in combustion systems  

NASA Astrophysics Data System (ADS)

The size of nanometric carbonaceous particles produced in various combustion systems is determined by means of time resolved fluorescence polarization anisotropy (TRFPA). We also compare the performances of two different experimental implementations of thetechnique, which are complementary in terms of cost, simplicity and resolution. Both methods are first employed on standard molecules to demonstrate the reliability of the results. A study of the sizes of nanometric particles collected at the exhaust of diesel and gasoline vehicle engine, as well as from controlled laminar flames is presented. The high sensitivity (0.04 nm) achieved with the use of a streak camera as detector makes the TRFPA technique particularly suitable for characterizing nanometric particles.

Bruno, Annalisa; de Lisio, Corrado; Minutolo, Patrizia

2005-07-01

125

Simultaneous reference and differential waveform acquisition in time-resolved terahertz spectroscopy.  

PubMed

We present a new method for data acquisition in time-resolved terahertz spectroscopy experiments. Our approach is based on simultaneous collection of reference and differential THz scans. Both the optical THz generation beam and the pump beam are modulated at two different frequencies that are not harmonic with respect to each other. Our method allows not only twice as fast data acquisition but also minimization of noise connected to slowly varying laser power fluctuations and timing instabilities. Our use of the nonlinear crystal N-benzyl-2-methyl-4-nitroaniline (BNA) enables time-resolved THz spectroscopy to beyond 5 THz, thereby highlighting that the presented method is especially valuable at higher frequencies where phase errors in the data acquisition become increasingly important. PMID:19997441

Iwaszczuk, Krzysztof; Cooke, David G; Fujiwara, Masazumi; Hashimoto, Hideki; Jepsen, Peter Uhd

2009-11-23

126

Time-resolved Terahertz spectroscopy using a Ti:Sapphire laser oscillator  

NASA Astrophysics Data System (ADS)

In time-resolved terahertz spectroscopy, electromagnetic radiation in the frequency range 0.3 - 3 THz (corresponding to wavelengths of 0.1 - 1.0 mm) is used to probe the dynamic properties of charge carriers within materials. When a sample material is excited using an ultrafast optical laser pulse, the terahertz probe that passes through the sample a time later reveals the subsequent behavior of the charge carriers in the sample. Real-time mapping of the dynamics can then be achieved through a pump-probe delay experiment. To date, most time-resolved terahertz spectroscopy has relied on high-power laser systems in order both to excite the sample as well as to generate the probing terahertz radiation. Here, we investigate the feasibility of adapting this technology to a relatively less expensive Ti:sapphire laser oscillator. We present preliminary data and discuss challenges going forward.

Kharel, Pradosh; Waquar, Wassam; Gagnon, Etienne

2013-03-01

127

Photothermal properties of gold nanocages studied by time-resolved spectroscopy  

Microsoft Academic Search

Gold nanocages of different sizes synthesized via galvanic replacement reaction have been studied by ultrafast time-resolved spectroscopy. The vibrational phonon modes were excited and the periods of these modes increase with the size of the gold nanocages. For a specific size of nanocage, experiments with different excitation powers of the pump laser were performed (from 2 muJ to 20 muJ),

Min Hu; Jingyi Chen; Younan Xia; Xingde Li; Hristina Petrova; Gregory Hartland; Manuel Marquez

2006-01-01

128

Time-Resolved Kerr Rotation Spectroscopy of Spin Dynamics in a Quantum Hall System  

SciTech Connect

A Time-resolved Kerr rotation spectroscopy under selective excitation by narrow spectrum pump beam is applied to high-mobility two dimensional (2D) electrons. The large non-oscillating Kerr signal is ascribed to the formation of Skyrmions by photoexcited carrier, and is confirmed by the selective excitation in TRKR measurement. The collapse of the spin coherence (dip of T{sub 2}*) near nu = 1 may be related by the formation of Skyrmions and anti-Skyrmiosn pair under photoexcitation.

Fukuoka, D.; Tanaka, N.; Oto, K.; Muro, K. [Graduate School of Science, Chiba University, Chiba-shi, Chiba 263-8522 (Japan); Hirayama, Y. [Graduate School of Science, Tohoku University, Sendai-shi, Miyagi 980-8577 (Japan); ERATO Nuclear Spin Electronics Project, Miyagi 980-8578 (Japan); Kumada, N.; Yamaguchi, H. [NTT Basic Research Laboratories, NTT Corporation, Atsugi-shi, Kanagawa 243-0198 (Japan)

2010-01-04

129

Time-resolved polarization imaging by pump-probe (stimulated emission) fluorescence microscopy.  

PubMed Central

We report the application of pump-probe fluorescence microscopy in time-resolved polarization imaging. We derived the equations governing the pump-probe stimulated emission process and characterized the pump and probe laser power levels for signal saturation. Our emphasis is to use this novel methodology to image polarization properties of fluorophores across entire cells. As a feasibility study, we imaged a 15-microm orange latex sphere and found that there is depolarization that is possibly due to energy transfer among fluorescent molecules inside the sphere. We also imaged a mouse fibroblast labeled with CellTracker Orange CMTMR (5-(and-6)-(((4-chloromethyl)benzoyl)amino)tetramethyl-rhodamine). We observed that Orange CMTMR complexed with gluthathione rotates fast, indicating the relatively low fluid-phase viscosity of the cytoplasmic microenvironment as seen by Orange CMTMR. The measured rotational correlation time ranged from approximately 30 to approximately 150 ps. This work demonstrates the effectiveness of stimulated emission measurements in acquiring high-resolution, time-resolved polarization information across the entire cell.

Buehler, C; Dong, C Y; So, P T; French, T; Gratton, E

2000-01-01

130

Application of time-resolved fluorescence for direct and continuous probing of release from polymeric delivery vehicles.  

PubMed

Though accurately evaluating the kinetics of release is critical for validating newly designed therapeutic carriers for in vivo applications, few methods yet exist for release measurement in real time and without the need for any sample preparation. Many of the current approaches (e.g. chromatographic methods, absorption spectroscopy, or NMR spectroscopy) rely on isolation of the released material from the loaded vehicles, which require additional sample purification and can lead to loss of accuracy when probing fast kinetics of release. In this study we describe the use of time-resolved fluorescence for in situ monitoring of small molecule release kinetics from biodegradable polymeric drug delivery systems. This method relies on the observation that fluorescent reporters being released from polymeric drug delivery systems possess distinct excited-state lifetime components, reflecting their different environments in the particle suspensions, i.e., confined in the polymer matrices or free in the aqueous environment. These distinct lifetimes enable real-time quantitative mapping of the relative concentrations of dye in each population to obtain precise and accurate temporal information on the release profile of particular carrier/payload combinations. We found that fluorescence lifetime better distinguishes subtle differences in release profiles (e.g. differences associated with dye loading) than conventional steady-state fluorescence measurements, which represent the averaged dye behavior over the entire scan. Given the method's applicability to both hydrophobic and hydrophilic cargo, it could be employed to model the release of any drug-carrier combination. PMID:23792808

Viger, Mathieu L; Sheng, Wangzhong; McFearin, Cathryn L; Berezin, Mikhail Y; Almutairi, Adah

2013-06-20

131

Investigation of RNA Hairpin Loop Folding with Time-Resolved Infrared Spectroscopy  

NASA Astrophysics Data System (ADS)

Ribonucleic acids (RNAs) are a group of functional biopolymers central to the molecular underpinnings of life. To complete the many processes they mediate, RNAs must fold into precise three-dimensional structures. Hairpin loops are the most ubiquitous and basic structural elements present in all folded RNAs, and are the foundation upon which all complex tertiary structures are built. A hairpin loop forms when a single stranded RNA molecule folds back on itself creating a helical stem of paired bases capped by a loop. This work investigates the formation of UNCG hairpin loops with the sequence 5'-GC(UNCG)GC-3' (N = A, U, G, or C) using both equilibrium infrared (IR) and time-resolved IR spectroscopy. Equilibrium IR melting data were used to determine thermodynamic parameters. Melting temperatures ranged from 50 to 60°C, and enthalpies of unfolding were on the order of 100 kJ/mol. In the time-resolved work, temperature jumps of up to 20°C at 2.5°C increments were obtained with transient relaxation kinetics spanning nanoseconds to hundreds of microseconds. The relaxation kinetics for all of the oligomers studied were fit to first or second order exponentials. Multiple vibrational transitions were probed on each oligomer for fully folded and partially denatured structures. In the time-resolved limit, in contrast to equilibrium melting, RNA does not fold according to two-state behavior. These results are some of the first to show that RNA hairpins fold according to a rugged energy landscape, which contradicts their relatively simple nature. In addition, this work has proven that time-resolved IR spectroscopy is a powerful and novel tool for investigating the earliest events of RNA folding, the formation of the hairpin loop.

Stancik, Aaron Lee

132

A Vertically Integrated CMOS Microsystem for Time-Resolved Fluorescence Analysis.  

PubMed

We describe a two-chip micro-scale time-resolved fluorescence analyzer integrating excitation, detection, and filtering. A new 8×8 array of drivers realized in standard low-voltage 0.35-?m complementary metal-oxide semiconductor is bump-bonded to AlInGaN blue micro-pixellated light-emitting diodes (micro-LEDs). The array is capable of producing sample excitation pulses with a width of 777 ps (FWHM), enabling short lifetime fluorophores to be investigated. The fluorescence emission is detected by a second, vertically-opposed 16 × 4 array of single-photon avalanche diodes (SPADs) fabricated in 0.35-?m high-voltage CMOS technology with in-pixel time-gated photon counting circuitry. Captured chip data are transferred to a PC for further processing, including histogramming, lifetime extraction, calibration and background/noise compensation. This constitutes the smallest reported solid-state microsystem for fluorescence decay analysis, replacing lasers, photomultiplier tubes, bulk optics, and discrete electronics. The system is demonstrated with measurements of fluorescent colloidal quantum dot and Rhodamine samples. PMID:23853381

Rae, Bruce R; Jingbin Yang; McKendry, Jonathan; Zheng Gong; Renshaw, David; Girkin, John M; Erdan Gu; Dawson, Martin D; Henderson, R K

2010-12-01

133

Full time-resolved scheme data in time-domain fluorescence diffuse optical tomography  

NASA Astrophysics Data System (ADS)

In this study, time-domain fluorescence diffuse optical tomography (FDOT) in biological tissue is investigated by solving the inverse problem using a convolution and deconvolution of the zero-lifetime emission light intensity and the exponential function for a finite lifetime, respectively. We firstly formulate the fundamental equations in time-domain assuming that the fluorescence lifetime is equal to zero, and then the solution including the lifetime is obtained by convolving the emission light intensity and the lifetime function. The model is a 2-D 10 mm-radius circle with the optical properties simulating biological tissue for the near infrared light, and contains some regions with fluorophores. Temporal and spatial profiles of excitation and emission light intensities are calculated and discussed for several models. The inverse problem of fluorescence diffuse optical tomography is solved using simulated measurement emission intensities for reconstructing fluorophore concentration. A time-domain measurement system uses ultra-short pulsed laser for excitation and measures the temporal and spatial distributions of fluorescence emitting from the tissue surface. To improve image quality, we propose implementation of a FDOT algorithm using full time-resolved (TR) data.

Marjono, Andhi; Yano, Akira; Okawa, Shinpei; Gao, Feng; Yamada, Yukio

2007-03-01

134

Design and validation of a homogeneous time-resolved fluorescence-based leptin receptor binding assay.  

PubMed

The pleiotropic cytokine hormone leptin, by activating its receptor OB-R, plays a major role in many biological processes, including energy homeostasis, immune function, and cell survival and proliferation. Abnormal leptin action is associated with obesity, autoimmune diseases, and cancer. The pharmacological characterization of OB-R and the development of synthetic OB-R ligands are still in their infancy because currently available binding assays are not compatible with ligand saturation binding experiments and high-throughput screening (HTS) approaches. We have developed here a novel homogeneous time-resolved fluorescence-based binding assay that overcomes these limitations. In this assay, fluorescently labeled leptin or leptin antagonist binds to the SNAP-tagged OB-R covalently labeled with terbium cryptate (Tb). Successful binding is monitored by measuring the energy transfer between the Tb energy donor and the fluorescently labeled leptin energy acceptor. Ligand binding saturation experiments revealed high-affinity dissociation constants in the subnanomolar range with an excellent signal-to-noise ratio. The assay performed in a 384-well format shows high specificity and reproducibility, making it perfectly compatible with HTS applications to identify new OB-R agonists or antagonists. In addition, fluorescently labeled leptin and SNAP-tagged OB-R will be valuable tools for monitoring leptin and OB-R trafficking in cells and tissues. PMID:23333588

Vauthier, Virginie; Derviaux, Carine; Douayry, Najim; Roux, Thomas; Trinquet, Eric; Jockers, Ralf; Dam, Julie

2013-01-17

135

Comparison of the rate constants for energy transfer in the light-harvesting protein, C-phycocyanin, calculated from Foerster`s theory and experimentally measured by time-resolved fluorescence spectroscopy  

SciTech Connect

We have measured and assigned rate constants for energy transfer between chromophores in the light-harvesting protein C-phycocyanin (PC), in the monomeric and trimeric aggregation states, isolated from Synechococcus sp. PCC 7002. In order to compare the measured rate constants with those predicted by Fdrster`s theory of inductive resonance in the weak coupling limit, we have experimentally resolved several properties of the three chromophore types ({beta}{sub 155} {alpha}{sub 84}, {beta}{sub 84}) found in PC monomers, including absorption and fluorescence spectra, extinction coefficients, fluorescence quantum yields, and fluorescence lifetimes. The cpcB/C155S mutant, whose PC is missing the {beta}{sub 155} chromophore, was, useful in effecting the resolution of the chromophore properties and in assigning the experimentally observed rate constants for energy transfer to specific pathways.

Debreczeny, M.P.

1994-05-01

136

Binding and relaxation behavior of Coumarin-153 in lecithin-taurocholate mixed micelles: A time resolved fluorescence spectroscopic study  

NASA Astrophysics Data System (ADS)

The microenvironment of the bile salt-lecithin mixed aggregates has been investigated using steady state and picosecond time resolved fluorescence spectroscopy. The steady state spectra show that the polarity of the bile salt is higher compared to lecithin vesicles or the mixed aggregates. We have observed slow solvent relaxation in bile salt micelles and lecithin vesicles. The solvation time is gradually slowed down due to gradual addition of the bile salt in lecithin vesicles. Addition of bile salt leads to the tighter head group packing in lecithin. Thus, mobility of the water molecules becomes slower and consequently the solvation time is also retarded. We have observed bimodal slow rotational relaxation time in all these systems.

Chakrabarty, Debdeep; Chakraborty, Anjan; Seth, Debabrata; Hazra, Partha; Sarkar, Nilmoni

2005-09-01

137

A CMOS Time-Resolved Fluorescence Lifetime Analysis Micro-System  

PubMed Central

We describe a CMOS-based micro-system for time-resolved fluorescence lifetime analysis. It comprises a 16 × 4 array of single-photon avalanche diodes (SPADs) fabricated in 0.35 ?m high-voltage CMOS technology with in-pixel time-gated photon counting circuitry and a second device incorporating an 8 × 8 AlInGaN blue micro-pixellated light-emitting diode (micro-LED) array bump-bonded to an equivalent array of LED drivers realized in a standard low-voltage 0.35 ?m CMOS technology, capable of producing excitation pulses with a width of 777 ps (FWHM). This system replaces instrumentation based on lasers, photomultiplier tubes, bulk optics and discrete electronics with a PC-based micro-system. Demonstrator lifetime measurements of colloidal quantum dot and Rhodamine samples are presented.

Rae, Bruce R.; Muir, Keith R.; Gong, Zheng; McKendry, Jonathan; Girkin, John M.; Gu, Erdan; Renshaw, David; Dawson, Martin D.; Henderson, Robert K.

2009-01-01

138

Estimation of crude oil grade using time-resolved fluorescence spectra.  

PubMed

Time-resolved fluorescence (TRF) spectra of six crude oils from the eastern province of Saudi Arabia were excited using a pulsed laser radiation at 250 nm and measured at specific time gates (TG) within the leading and trailing edges of the laser temporal pulse. The spectra showed the presence of a shoulder near 380 nm that systematically decreased in intensity from high-grade to low-grade crudes, and also from earlier to later TGs. The intensities of these shoulders are shown to be useful in estimating the grades of crude oils, particularly when the TRF spectra are measured at TGs within the leading edge of the laser temporal pulse. Contour diagrams depicting the shapes of the TRF spectra as function of TG (within the leading and trailing edges) are also presented to serve as true fingerprints of the crudes. PMID:18968578

Hegazi, E; Hamdan, A

2002-04-01

139

A CMOS Time-Resolved Fluorescence Lifetime Analysis Micro-System.  

PubMed

We describe a CMOS-based micro-system for time-resolved fluorescence lifetime analysis. It comprises a 16 × 4 array of single-photon avalanche diodes (SPADs) fabricated in 0.35 ?m high-voltage CMOS technology with in-pixel time-gated photon counting circuitry and a second device incorporating an 8 × 8 AlInGaN blue micro-pixellated light-emitting diode (micro-LED) array bump-bonded to an equivalent array of LED drivers realized in a standard low-voltage 0.35 ?m CMOS technology, capable of producing excitation pulses with a width of 777 ps (FWHM). This system replaces instrumentation based on lasers, photomultiplier tubes, bulk optics and discrete electronics with a PC-based micro-system. Demonstrator lifetime measurements of colloidal quantum dot and Rhodamine samples are presented. PMID:22291564

Rae, Bruce R; Muir, Keith R; Gong, Zheng; McKendry, Jonathan; Girkin, John M; Gu, Erdan; Renshaw, David; Dawson, Martin D; Henderson, Robert K

2009-11-18

140

Time resolved spectroscopy of the multiperiodic pulsating subdwarf B star PG 1605+072  

NASA Astrophysics Data System (ADS)

We present results for the 2m spectroscopic part of the MultiSite Spectroscopic Telescope campaign, which took place in May/June 2002. In order to perform an asteroseismological analysis on the multiperiodic pulsating subdwarf B star PG 1605+072 we used over 150 hours of time resolved spectroscopy to search for and analyse line profile variations by using phase binning. This pilot analysis using the BRUCE and KYLIE programs and assuming strong rotation and low inclination favours models with ?=1 or ?=2 with m?0. %

Tillich, A.; Heber, U.; O'Toole, S. J.

2007-06-01

141

Time Resolved Spectroscopy of the Multi-Periodic Pulsating Subdwarf B Star PG1605+072  

NASA Astrophysics Data System (ADS)

We present results for the 2m spectroscopic part of the MultiSite Spectroscopic Telescope (MSST) campaign, which took place in May/June 2002. In order to perform an asteroseismological analysis on the multi-periodic pulsating subdwarf B star PG 1605+072 we used over 150 hours of time resolved spectroscopy in order to search for and analyse line profile variations by using phase binning. We succeeded in finding variations in effective temperature and gravity for four modes. A pilot analysis using the BRUCE and KYLIE programs and assuming strong rotation and low inclination favours models with l=1 or l=2 with m?0.

Tillich, A.; Heber, U.; O'Toole, S. J.

2007-09-01

142

Application of time-resolved resonance Raman spectroscopy to intramolecular electron transfer  

SciTech Connect

Time-resolved resonance Raman spectroscopy has been applied for the first time to the study of intramolecular electron transfer in a chromophore-quencher complex, based on a metal-to-ligand charge-transfer (MLCT) excited state. These measurements allow for (1) the identification of redox sites that are reached following excitation and (2) the inferring of structural information in short-lived intermediates. This technique is a more sensitive probe than transient absorption as shown by its application to the redox-separated complex shown below involving a pyridinium acceptor and a phenothiazine donor.

Schoonover, J.R.; Strouse, G.F.; Chen, P.; Bates, D.; Meyer, T.J. (Univ. of North Carolina, Chapel Hill (United States))

1993-06-09

143

Time-resolved spectroscopy of plasma resonances in highly excited silicon and germanium  

SciTech Connect

The dynamics of the electron-hole plasma in silicon and germanium samples irradiated by 20 ps. 532 nm laser pulses has been investigated in the near infrared by the time-resolved picosecond optical spectroscopy. The experimental reflectivities and transmission are compared with the predictions of the thermal model for degenerate carrier distributions through the Drude formalism. Above a certain fluence, a significant deviation between measured and calculated values indicates a strong increase of the recombination rate as soon as the plasma resonances become comparable with the band gaps. These new plasmon-aided recombination channels are particularly pronounced in germanium. 15 refs., 8 figs.

Huang, C.Y.; Malvezzi, A.M.; Bloembergen, N.; Kurz, H.

1985-01-01

144

Nonlinear Raman Techniques in Femtosecond Time Resolved Spectroscopy for the Analysis and Control of Molecular Dynamics  

SciTech Connect

The use of four-wave mixing techniques in femtosecond time-resolved spectroscopy has considerable advantages. Due to the many degrees of freedom offered e.g. by coherent anti-Stokes Raman scattering (CARS), the dynamics even of complex systems can be analyzed in detail. Using pulse shaping techniques in combination with a self-learning loop approach, molecular mode excitation can be controlled very efficiently in a multi-photon excitation process. Results obtained from the optimal control of CARS on {beta}-carotene are discussed.

Materny, Arnulf; Konradi, Jakow; Namboodiri, Vinu; Namboodiri, Mahesh; Scaria, Abraham [Jacobs University Bremen, School of Science and Engineering Campus Ring 1, 28759 Bremen (Germany)

2008-11-14

145

Comparison of organic phantom recipes and characterization by time-resolved diffuse optical spectroscopy  

NASA Astrophysics Data System (ADS)

Three recipes for tissue constituent-equivalent phantoms of water and lipids are presented. Nature phantoms are made using no emulsifying agent, but just a professional disperser, instead Agar and Triton phantoms are made using agar or Triton X-100, respectively, as agents to emulsify water and lipids. Different water-to-lipid ratios ranging from 30 to 70 percent by mass are proposed and tested. Optical characterization by time-resolved spectroscopy was performed in terms of optical properties, homogeneity, reproducibility and composition retrieval.

Quarto, G.; Pifferi, A.; Bargigia, I.; Farina, A.; Cubeddu, R.; Taroni, P.

2013-06-01

146

Time-resolved photoelectron spectroscopy of coupled electron-nuclear motion  

SciTech Connect

We investigate pump-probe electron detachment spectroscopy in a model system which is ideally suited to study coupled electronic and nuclear wave-packet dynamics. Time-resolved photoelectron spectra are calculated within the adiabatic approximation and a discretization of the detachment continuum. These spectra are compared to those which derive from a non-Born-Oppenheimer description and a numerically exact treatment of the detachment process. In this way it is possible to identify the influence of non-adiabatic effects on the spectra in a systematic way and also to test commonly applied approximations.

Falge, Mirjam; Engel, Volker [Institut fuer Physikalische und Theoretische Chemie and Roentgen Research Center for Complex Material Systems, Universitaet Wuerzburg, Am Hubland, 97074 Wuerzburg (Germany); Graefe, Stefanie [Institute for Theoretical Physics, Vienna University of Technology, Wiedner Hauptstr. 8-10, A-1040 Vienna (Austria)

2011-05-14

147

A CAMAC system controlled by an IBM AT computer for time-resolved spectroscopy  

SciTech Connect

An IBM AT computer interfaced to a small CAMAC system offers considerable power without the complexity and expense of a large general-purpose system. Our system for time-resolved spectroscopy features menu-driven FORTRAN-based software; high-resolution and high-speed (8K channels, 5-..mu..s fixed dead time) ADCs; segmentable histogram memories (24-bit counts) with large memory space for many histogram segments; independently variable separate histogram dwell times; remote control via a CAMAC serial highway; and ground isolation between the data acquisition equipment and control computer by means of fiber optics.

Lindquist, L.O.; Moss, C.E.

1987-01-01

148

Absorption spectroscopy of powdered materials using time-resolved diffuse optical methods.  

PubMed

In this paper a novel method, based on time-resolved diffuse optical spectroscopy, is proposed to measure the absorption of small amounts of nanostructured powder materials independent of scattering. Experimental validation, in the visible and near-infrared spectral range, has been carried out on India Inkparticles. The effectiveness of the technique to measure scattering-free absorption is demonstrated on carbon nanotubes. The comparison between the absorption spectra acquired by the proposed method and conventional measurements performed with a commercial spectrophotometer is discussed. PMID:23142900

D'Andrea, Cosimo; Obraztsova, Ekaterina A; Farina, Andrea; Taroni, Paola; Lanzani, Guglielmo; Pifferi, Antonio

2012-11-10

149

Photolytic interruptions of the bacteriorhodopsin photocycle examined by time-resolved resonance Raman spectroscopy  

SciTech Connect

An investigation of the photolytic conditions used to initiate and spectroscopically monitor the bacteriorhodopsin (BR) photocycle utilizing time-resolved resonance Raman (TR3) spectroscopy has revealed and characterized two photoinduced reactions that interrupt the thermal pathway. One reaction involves the photolytic interconversion of M-412 and M', and the other involves the direct photolytic conversion of the BR-570/K-590 photostationary mixture either to M-412 and M' or to M-like intermediates within 10 ns. The photolytic threshold conditions describing both reactions have been quantitatively measured and are discussed in terms of experimental parameters.

Grieger, I.; Atkinson, G.H.

1985-09-24

150

Applications of Phasors to In Vitro Time-Resolved Fluorescence Measurements  

PubMed Central

The phasor method of treating fluorescence lifetime data provides a facile and convenient approach to characterize lifetime heterogeneity and to detect the presence of excited state reactions, such as solvent relaxation and Förster Resonance Energy Transfer. The method utilizes a plot of M sin(?) versus M cos(?), where M is the modulation ratio and ? is the phase angle taken from frequency domain fluorometry. A principle advantage of the phasor method is that it provides a model-less approach to time-resolved data, amenable to visual inspection. Although the phasor approach has been recently applied to Fluorescence Lifetime Imaging Microscopy it has not been extensively utilized for cuvette studies. In the present study we explore the applications of the method to in vitro samples. The phasors of binary and ternary mixtures of fluorescent dyes demonstrates the utility of the method for investigating complex mixtures. Data from excited state reactions, such as dipolar relaxation in membrane and protein systems and also energy transfer from the tryptophan residue to the chromophore in EGFP, are also presented.

Stefl, Martin; James, Nicholas G.; Ross, Justin A.; Jameson, David M.

2010-01-01

151

Detection of membrane packing defects by time-resolved fluorescence depolarization.  

PubMed Central

Packing defects in lipid bilayer play a significant role in the biological activities of cell membranes. Time-resolved fluorescence depolarization has been used to detect and characterize the onset of packing defects in binary mixtures of dilinoleoylphosphatidylethanolamine/1-palmitoyl-2- oleoylphosphatidylcholine (PE/PC). These PE/PC mixtures exhibit mesoscopic packing defect state (D), as well as one-dimensional lambellar liquid crystalline (L alpha) and two-dimensional inverted hexagonal (HII) ordered phases. Based on previous electron microscopic investigations, this D state is characterized by the presence of interlamellar attachments and precursors of HII phase between the lipid layers. Using a rotational diffusion model for rod-shaped fluorophore in a curved matrix, rotational dynamics parameters, second rank order parameter, localized wobbling diffusion, and curvature-dependent rotational diffusion constants of dipyenylhexatriene (DPH)-labeled PC (DPH-PC) in the host PE/PC matrix were recovered from the measured fluorescence depolarization decays of DPH fluorescence. At approximately 60% PE, abrupt increases in these rotational dynamics parameters were observed, reflecting the onset of packing defects in the host PE/PC matrix. We have demonstrated that rotational dynamics parameters are very sensitive in detecting the onset of curvature-associating packing defects in lipid membranes. In addition, the presence of the D state can be characterized by the enhanced wobbling diffusional motion and order packing of lipid molecules, and by the presence of localized curvatures in the lipid layers.

Chen, S Y; Cheng, K H

1996-01-01

152

Detection of membrane packing defects by time-resolved fluorescence depolarization.  

PubMed

Packing defects in lipid bilayer play a significant role in the biological activities of cell membranes. Time-resolved fluorescence depolarization has been used to detect and characterize the onset of packing defects in binary mixtures of dilinoleoylphosphatidylethanolamine/1-palmitoyl-2- oleoylphosphatidylcholine (PE/PC). These PE/PC mixtures exhibit mesoscopic packing defect state (D), as well as one-dimensional lambellar liquid crystalline (L alpha) and two-dimensional inverted hexagonal (HII) ordered phases. Based on previous electron microscopic investigations, this D state is characterized by the presence of interlamellar attachments and precursors of HII phase between the lipid layers. Using a rotational diffusion model for rod-shaped fluorophore in a curved matrix, rotational dynamics parameters, second rank order parameter, localized wobbling diffusion, and curvature-dependent rotational diffusion constants of dipyenylhexatriene (DPH)-labeled PC (DPH-PC) in the host PE/PC matrix were recovered from the measured fluorescence depolarization decays of DPH fluorescence. At approximately 60% PE, abrupt increases in these rotational dynamics parameters were observed, reflecting the onset of packing defects in the host PE/PC matrix. We have demonstrated that rotational dynamics parameters are very sensitive in detecting the onset of curvature-associating packing defects in lipid membranes. In addition, the presence of the D state can be characterized by the enhanced wobbling diffusional motion and order packing of lipid molecules, and by the presence of localized curvatures in the lipid layers. PMID:8842226

Chen, S Y; Cheng, K H

1996-08-01

153

A multi-analytical investigation of semi-conductor pigments with time-resolved spectroscopy and imaging  

NASA Astrophysics Data System (ADS)

We present the non-invasive study of historical and modern Zn- and Cd-based pigments with time-resolved fluorescence spectroscopy, fluorescence multispectral imaging and fluorescence lifetime imaging (FLIM). Zinc oxide and Zinc sulphide are semiconductors which have been used as white pigments in paintings, and the luminescence of these pigments from trapped states is strongly dependent on the presence of impurities and crystal defects. Cadmium sulphoselenide pigments vary in hue from yellow to deep red based on their composition, and are another class of semiconductor pigments which emit both in the visible and the near infrared. The Fluorescence lifetime of historical and modern pigments has been measured using both an Optical Multichannel Analyser (OMA) coupled with a Nd:YAG nslaser, and a streak camera coupled with a ps-laser for spectrally-resolved fluorescence lifetime measurements. For Znbased pigments we have also employed Fluorescence Lifetime Imaging (FLIM) for the measurement of luminescence. A case study of FLIM applied to the analysis of the painting by Vincent Van Gogh on paper - "Les Bretonnes et le pardon de Pont-Aven" (1888) is presented. Through the integration of complementary, portable and non-invasive spectroscopic techniques, new insights into the optical properties of Zn- and Cd-based pigments have been gained which will inform future analysis of late 19th] and early 20th C. paintings.

Nevin, A.; Cesaratto, A.; D'Andrea, C.; Valentini, Gianluca; Comelli, D.

2013-05-01

154

A versatile and reconfigurable setup for all-terahertz time-resolved pump-probe spectroscopy  

NASA Astrophysics Data System (ADS)

A versatile optical setup for all-terahertz (THz) time resolved pump-probe spectroscopy was designed and tested. By utilizing a dual THz pulse generator emitter module, independent and synchronized THz radiation pump and probe pulses were produced, thus eliminating the need for THz beam splitters and the limitations associated with their implementation. The current THz setup allows for precise control of the electric fields splitting ratio between the THz radiation pump and probe pulses, as well as in-phase, out-of-phase, and polarization dependent pump-probe spectroscopy. Since the present THz pump-probe setup does not require specialized THz radiation optical components, such as phase shifters, polarization rotators, or wide bandwidth beam splitters, it can be easily implemented with minimal alterations to a conventional THz time domain spectroscopy system. The present setup is valuable for studying the time dynamics of THz coherent phenomena in solid-state, chemical, and biological systems.

Elezzabi, A. Y.; Maraghechi, P.

2012-05-01

155

Uranium and nitrate remote sensing in the nuclear fuel cycle by time-resolved laser-induced fluorescence  

Microsoft Academic Search

Time-Resolved Laser-Induced Fluorescence has been used for uranium and nitrate remote sensing in the nuclear fuel cycle. Advantages of this technique are aside sensitivity and selectivity, its ability to perform remote measurements via fiber optics and optode. Uranium is usually determined by the standard addition method but by applying a fluorescence model taking into account complexation and absorption phenomena, it

Christophe Moulin; Laurent Couston; Pierre Decambox; Patrick Mauchien; Dominique Pouyat

1994-01-01

156

Clinical evaluation of time-resolved spectroscopy by measuring cerebral hemodynamics during cardiopulmonary bypass surgery.  

PubMed

We developed a three-wavelength time-resolved spectroscopy (TRS) system, which allows quantitative measurement of hemodynamics within relatively large living tissue. We clinically evaluated this TRS system by monitoring cerebral circulation during cardiopulmonary bypass surgery. Oxyhemoglobin, deoxyhemoglobin, total hemoglobin and oxygen saturation (SO(2)) were determined by TRS on the left forehead attached with an optode spacing of 4 cm. We also simultaneously monitored jugular venous oxygen saturation (SjvO(2)) and arterial blood hematocrit (Hct) using conventional methods. The validity and usefulness of the TRS system were assessed by comparing parameters obtained with the TRS and conventional methods. Although the changes in SO(2) were lower than those in SjvO(2), SO(2) obtained by TRS paralleled the fluctuations in SjvO(2), and a good correlation between these values was observed. The only exceptions occurred during the perfusion period. Moreover, there was a good correlation between tHb and Hct values (r(2)=0.63). We concluded that time-resolved spectroscopy reflected the conditions of cerebral hemodynamics of patients during surgical operations. PMID:18163815

Ohmae, Etsuko; Oda, Motoki; Suzuki, Toshihiko; Yamashita, Yutaka; Kakihana, Yasuyuki; Matsunaga, Akira; Kanmura, Yuichi; Tamura, Mamoru

157

Tryptophan dynamics of the FK506 binding protein: time-resolved fluorescence and simulations.  

PubMed Central

The FK506-binding protein (FKBP12) is important in the immunosuppressant action of FK506 and rapamycin. We have investigated Trp side chain dynamics in FKBP12, with and without a bound immunosuppressant, by measuring the Trp time-resolved fluorescence anisotropy decay r(t). The r(t) for W59 in aqueous uncomplexed FKBP12 at 20 degrees C is well described by a single exponential with a recovered initial anisotropy, r(eff)o, of 0.192 and an overall rotational correlation time for the protein, phi p, of 4.7 ns; r(eff)o = 0.214 and phi p = 4.2 ns for the FKBP12/FK506 complex. Using an expression for the order parameter squared, namely S2 = r(eff)o/rTo, where rTo is the vitrified steady-state excitation anisotropy, we recovered an S2 of 0.75 for W59 fluorescence in uncomplexed FKBP12 and S2 approximately equal to 1 in the FKBP12/FK506 complex. Results obtained for the FKBP12/rapamycin complex are similar to those found for the FKBP12/FK506 complex. Minimum perturbation mapping simulations were performed on the free and complexed forms of FKBP12 and the results were generally in agreement with the experimental data. Images FIGURE 5 FIGURE 6

Silva, N D; Prendergast, F G

1996-01-01

158

Correlative Time-Resolved Fluorescence Microscopy To Assess Antibiotic Diffusion-Reaction in Biofilms  

PubMed Central

The failure of antibiotics to inactivate in vivo pathogens organized in biofilms has been shown to trigger chronic infections. In addition to mechanisms involving specific genetic or physiological cell properties, antibiotic sorption and/or reaction with biofilm components may lessen the antibiotic bioavailability and consequently decrease their efficiency. To assess locally and accurately the antibiotic diffusion-reaction, we used for the first time a set of advanced fluorescence microscopic tools (fluorescence recovery after photobleaching, fluorescence correlation spectroscopy, and fluorescence lifetime imaging) that offer a spatiotemporal resolution not available with the commonly used time-lapse confocal imaging method. This set of techniques was used to characterize the dynamics of fluorescently labeled vancomycin in biofilms formed by two Staphylococcus aureus human isolates. We demonstrate that, at therapeutic concentrations of vancomycin, the biofilm matrix was not an obstacle to the diffusion-reaction of the antibiotic that can reach all cells through the biostructure.

Daddi Oubekka, S.; Briandet, R.; Fontaine-Aupart, M.-P.

2012-01-01

159

Unfolding of acrylodan-labeled human serum albumin probed by steady-state and time-resolved fluorescence methods.  

PubMed Central

Steady-state and time-resolved fluorescence spectroscopy was used to follow the local and global changes in structure and dynamics during chemical and thermal denaturation of unlabeled human serum albumin (HSA) and HSA with an acrylodan moiety bound to Cys34. Acrylodan fluorescence was monitored to obtain information about unfolding processes in domain I, and the emission of the Trp residue at position 214 was used to examine domain II. In addition, Trp-to-acrylodan resonance energy transfer was examined to probe interdomain spatial relationships during unfolding. Increasing the temperature to less than 50 degrees C or adding less than 1.0 M GdHCl resulted in an initial, reversible separation of domains I and II. Denaturation by heating to 70 degrees C or by adding 2.0 M GdHCl resulted in irreversible unfolding of domain II. Further denaturation of HSA by either method resulted in irreversible unfolding of domain I. These results clearly demonstrate that HSA unfolds by a pathway involving at least three distinct steps. The low detection limits and high information content of dual probe fluorescence should allow this technique to be used to study the unfolding behavior of entrapped or immobilized HSA.

Flora, K; Brennan, J D; Baker, G A; Doody, M A; Bright, F V

1998-01-01

160

Picosecond time-resolved fluorescence study of all-trans retinal. The existence of two fluorescent singlet excited states  

NASA Astrophysics Data System (ADS)

Picosecond time-resolved fluorescence spectra of all-trans retinal in hexane have been measured with 8 ps time-resolution with use of a highly sensitive streak camera. The observed fluorescence consists of a fast (tau less than 1 ps, lambda(sub max) approximately = 470 nm) and a slow (tau = 33-34 ps, lambda(sub max) approximately = 540 nm) component. The lifetime of the slow component agrees well with the reported rise time of the triplet-triplet absorption. It is concluded that the photoexcitation first produces the optically allowed S(sub 2) state and it relaxes to the optically forbidden S(sub 1) state within 1 ps. The fast and slow fluorescence components are assigned to the S(sub 2) and S(sub 1) states, respectively.

Tahara, Tahei; Hamaguchi, Hiro-O.

1995-03-01

161

Nanosecond time-resolved circular polarization of fluorescence: study of NADH bound to horse liver alcohol dehydrogenase.  

PubMed Central

Circularly polarized luminescence (CPL) spectroscopy provides information on the excited-state chirality of a lumiphore analogous but complementary to information regarding the ground-state chirality derived from circular dichroism. The sensitivity of CPL spectra to molecular conformation makes this technique uniquely suited for the study of biomolecular structure, as extensively demonstrated in earlier studies. Unfortunately, the CPL spectra of many biomolecules often contain significantly overlapping contributions from emitting species either because multiple lumiphores are present (e.g., tryptophan residues in a protein) or because multiple conformations of the biomolecule simultaneously exist, each with a unique CPL spectrum. Increased resolution between individual contributions to the CPL may be achieved by time-resolving this signal, thus taking advantage of the fact that, as a rule, each of the emitting species also has a characteristic decay time associated with its electronically excited state. In addition, the time resolution provides information regarding dynamics associated with the different chiral states of the system. The present study describes an instrument for the determination of time-resolved CPL (TR-CPL) with subnanosecond resolution and its application to several chiral systems. The technique was first demonstrated on a model system with a strong time-dependent CPL signal. Subsequently, the circularly polarized component in the fluorescence of reduced nicotinamide adenine dinucleotide (NADH) bound to liver alcohol dehydrogenase was time-resolved. The CPL of NADH in the binary enzyme-coenzyme complex is time-dependent, reflecting structural differences around the reduced nicotinamide possibly due to a dynamic restructuring. In contrast, the CPL of the coenzyme in the ternary complex formed with enzyme and the substrate analog isobutyramide is essentially time-independent, likely reflecting a more rigid binding domain. Since the linear polarization of the fluorescence of the two complexes did not show any local flexibility of the NADH chromophore, the excited-state conformational rearrangement of the binary complex indicates a subtle change in its interactions with group(s) in direct contact with it.

Schauerte, J A; Schlyer, B D; Steel, D G; Gafni, A

1995-01-01

162

CMOS driven micro-pixel LEDs integrated with single photon avalanche diodes for time resolved fluorescence measurements  

NASA Astrophysics Data System (ADS)

We describe a single chip approach to time resolved fluorescence measurements based on time correlated single photon counting. Using a single complementary metal oxide silicon (CMOS) chip, bump bonded to a 4 × 16 array of AlInGaN UV micro-pixellated light-emitting diodes, a prototype integrated microsystem has been built that demonstrates fluorescence excitation and detection on a nanosecond time scale. Demonstrator on-chip measurements of lifetimes of fluorescence colloidal quantum dot samples are presented.

Rae, B. R.; Griffin, C.; McKendry, J.; Girkin, J. M.; Zhang, H. X.; Gu, E.; Renshaw, D.; Charbon, E.; Dawson, M. D.; Henderson, R. K.

2008-05-01

163

Time-resolved emission spectroscopy for the combustion analysis of series production engines  

NASA Astrophysics Data System (ADS)

This paper presents a device that detects light emerging from the combustion inside a series production automotive engine. Simultaneous time and wavelength resolution is achieved by this system and it can be applied in a simple manner to either diesel or spark ignition (SI) engines without any geometrical modification or the combustion chamber. An optical probe is inserted into spark plug or glow plug. A fiber is connected to the probe and leads the light to a spectrograph, which provides spectral analysis in the UV and visible wavelength ranges. An intensified streak camera with time resolution in the microsecond range completes the detection unit. This measuring system enables time-resolved emission spectroscopy applied to the light emitted during the combustion in a series production engine. Time-resolved emission spectra are presented from both a diesel and an SI engine. The time behavior of the internal temperature in a diesel engine combustion chamber and its dependence on engine speed and load are measured with this setup using a multiple two-color method. In an SI engine, the time behavior of the emissions of specific molecules or radicals is detected. Thus, differences in the combustion process are demonstrated to be caused by operation with different fuels.

Block, Bernd; Moeser, Petra; Hentschel, Werner

1997-04-01

164

Dynamic time-resolved diffuse spectroscopy based on supercontinuum light pulses  

NASA Astrophysics Data System (ADS)

We present a detailed characterization of a system for fast time-resolved spectroscopy of turbid media based on supercontinuum generation in a photonic crystal fiber. The light source provides subpicosecond pulses in the 550-1000-nm spectral range, at 85 MHz, at an average power of up to 50 mW. Wavelength-resolved detection is accomplished by means of a spectrometer coupled to a 16-channel, multianode photomultiplier tube, giving a resolution of 4.5-35 nm/channel, depending on the grating. Time-dispersion curves are acquired with time-correlated single-photon counting, and absorption and reduced scattering coefficients are determined by fitting the data to the diffusion equation. We characterized the system by measuring the time-resolved diffuse reflectance of epoxy phantoms and by assessing the performance in terms of accuracy, linearity, noise sensitivity, stability, and reproducibility. The results were similar to those from previous systems, whereas the full-spectrum (610-810 nm) acquisition time was as short as 1 s owing to the parallel acquisition. We also present the first in vivo real-time dynamic spectral measurements showing tissue oxygenation changes in the arm of a human subject.

Swartling, Johannes; Bassi, Andrea; D/Andrea, Cosimo; Pifferi, Antonio; Torricelli, Alessandro; Cubeddu, Rinaldo

2005-08-01

165

Time-resolved photoemission spectroscopy on a metal/ferroelectric heterostructure  

NASA Astrophysics Data System (ADS)

In thin-film ferroelectric (FE) capacitors the chemical and electronic structure of the electrode/FE interface can play a crucial role in determining the kinetics of polarization switching. We investigate the electronic structure of a Pt/BaTiO3/SrTiO3:Nb capacitor using time-resolved photoemission spectroscopy. The chemical, electronic, and depth sensitivity of core-level photoemission are used to probe the transient response of different parts of the upper electrode/ferroelectric interface to voltage-pulse-induced polarization reversal. The linear response of the electronic structure agrees quantitatively with a simple RC circuit model. The nonlinear response due to the polarization switch is demonstrated by the time-resolved response of the characteristic core levels of the electrode and the ferroelectric. Adjustment of the RC circuit model allows an estimation of the Pt/BaTiO3 (BTO) interface capacitance. The experiment shows that the interface capacitance is at least 100 times higher than the bulk capacitance of the BTO film, in qualitative agreement with theoretical predictions from the literature.

Rault, J. E.; Agnus, G.; Maroutian, T.; Pillard, V.; Lecoeur, Ph.; Niu, G.; Vilquin, B.; Silly, M. G.; Bendounan, A.; Sirotti, F.; Barrett, N.

2013-10-01

166

Investigation of Prolactin Receptor Activation and Blockade Using Time-Resolved Fluorescence Resonance Energy Transfer  

PubMed Central

The prolactin receptor (PRLR) is emerging as a therapeutic target in oncology. Knowledge-based drug design led to the development of a pure PRLR antagonist (Del1-9-G129R-hPRL) that was recently shown to prevent PRL-induced mouse prostate tumorogenesis. In humans, the first gain-of-function mutation of the PRLR (PRLRI146L) was recently identified in breast tumor patients. At the molecular level, the actual mechanism of action of these two novel players in the PRL system remains elusive. In this study, we addressed whether constitutive PRLR activation (PRLRI146L) or PRLR blockade (antagonist) involved alteration of receptor oligomerization and/or of inter-chain distances compared to unstimulated and PRL-stimulated PRLR. Using a combination of various biochemical and spectroscopic approaches (co-IP, blue native electrophoresis, BRET1), we demonstrated that preformed PRLR homodimers are altered neither by PRL- or I146L-induced receptor triggering, nor by antagonist-mediated blockade. These findings were confirmed using a novel time-resolved fluorescence resonance energy transfer (TR-FRET) technology that allows monitoring distance changes between cell surface tagged receptors. This technology revealed that PRLR blockade or activation did not involve detectable distance changes between extracellular domains of receptor chains within the dimer. This study merges with our previous structural investigations suggesting that the mechanism of PRLR activation solely involves intermolecular contact adaptations leading to subtle intramolecular rearrangements.

Tallet, Estelle; Fernandez, Isabelle; Zhang, Chi; Salsac, Marion; Gregor, Nathalie; Ayoub, Mohammed Akli; Pin, Jean Philippe; Trinquet, Eric; Goffin, Vincent

2011-01-01

167

Monte Carlo modeling of time-resolved fluorescence for depth-selective interrogation of layered tissue.  

PubMed

Computational approaches for simulation of light-tissue interactions have provided extensive insight into biophotonic procedures for diagnosis and therapy. However, few studies have addressed simulation of time-resolved fluorescence (TRF) in tissue and none have combined Monte Carlo simulations with standard TRF processing algorithms to elucidate approaches for cancer detection in layered biological tissue. In this study, we investigate how illumination-collection parameters (e.g., collection angle and source-detector separation) influence the ability to measure fluorophore lifetime and tissue layer thickness. Decay curves are simulated with a Monte Carlo TRF light propagation model. Multi-exponential iterative deconvolution is used to determine lifetimes and fractional signal contributions. The ability to detect changes in mucosal thickness is optimized by probes that selectively interrogate regions superficial to the mucosal-submucosal boundary. Optimal accuracy in simultaneous determination of lifetimes in both layers is achieved when each layer contributes 40-60% of the signal. These results indicate that depth-selective approaches to TRF have the potential to enhance disease detection in layered biological tissue and that modeling can play an important role in probe design optimization. PMID:21111507

Pfefer, T Joshua; Wang, Quanzeng; Drezek, Rebekah A

2010-11-26

168

Picosecond Time-Resolved Fluorescence from Detergent-Free Photosystem I Particles  

PubMed Central

Picosecond time-resolved fluorescence measurements have been taken on a detergent-free P700-enriched complex at room temperature isolated from the blue-green alga Phormidium luridum with a chlorophyll a to reaction center ratio of 100. Emission at greater than 665 nm is characterized by two exponential-decay components. A fast component, which dominates the initial decay with an average lifetime of 16 ps and 87% amplitude, is attributed to excitations in the core antenna chlorophyll-proteins, which are rapidly trapped by the primary electron donor, P700. A second component, with an average lifetime of 106 ps and 13% amplitude, is attributed to the peripheral antenna proteins. For 532-nm, 30-ps pulse excitation the results are virtually independent of fluence in the range of 2 × 1012 to 4 × 1016 photons/cm2 and the oxidation state of P700. Addition of sodium dodecyl sulfate to 0.1% causes the second component's lifetime to increase by an average of a factor of 2.5. Only minor changes are observed in the first component's lifetime and the relative amplitudes of the two components. Two fractions isolated from the detergent-treated samples have also been examined. Our results indicate that excitation energy transfer within photosystem I is very efficient and that the excitation kinetics of the antennae may be limited by the trapping rate of P700 or strongly affected by the heterogeneity of the antennae.

Wittmershaus, Bruce P.; Berns, Donald S.; Huang, Cinnia

1987-01-01

169

Microscopic dynamics of the glass transition investigated by time-resolved fluorescence measurements of doped chromophores  

NASA Astrophysics Data System (ADS)

The microscopic dynamics of several monomeric and polymeric glass-forming materials has been investigated by time-resolved fluorescence measurements of doped malachite green molecules in a wide temperature region. For monomers, 1-propanol, propylene glycol, and glycerol, and a polymer without side chains, poly- butadiene, the temperature dependence of nonradiative decay time of doped malachite green molecules behaves in a similar way through the glass-transition region. Besides a kink around the calorimetric glass-transition temperature Tg, another crossover at a critical temperature Tc about 30-50 K above Tg has been clearly observed. This experimental finding is in agreement with the prediction of the mode-coupling theory that a dynamical transition exists well above Tg. On the other hand, for the complex polymers with side chains, poly(vinyl acetate), poly(methyl acrylate), and poly(ethyl methacrylate), the crossover at Tg is less pronounced than those for the monomers and the polymer without side chains. Moreover, although we could not distinguish any singularities above Tg for these complex polymers, we observed another kink below Tg, which may be attributed to the side-chain motions.

Ye, Jing Yong; Hattori, Toshiaki; Nakatsuka, Hiroki; Maruyama, Yoshihiro; Ishikawa, Mitsuru

1997-09-01

170

Kinetics of photon upconversion in ionic liquids: time-resolved analysis of delayed fluorescence.  

PubMed

Photon upconversion (UC) based on triplet-triplet annihilation (TTA) is an emerging wavelength shifting technology, which is applicable to sunlight. Previously we found that the quantum efficiency of TTA-UC (?UC) carried out in ionic liquids (ILs) is dependent on the type of IL employed. In this article we investigate the kinetics of the triplet emitter molecules (perylene) that implement TTA to determine the origin of the IL dependence of ?UC. We measure the time-resolved delayed UC fluorescence intensities from samples made with five imidazolium-based ILs, and their intensity decay curves are analyzed with an analytical model. Consequently, several important aspects regarding both the first-order and second-order decays are elucidated. It is revealed that the IL dependence of ?UC primarily originates from the IL dependence of the branching ratio toward TTA upon an encounter of two triplet emitter molecules. Additionally, a strong correlation between the viscosity of the ILs and the branching ratios toward TTA is found. This finding is supported by temperature-dependent measurements, from which ?UC is found to be significantly affected by the viscosity of the IL. The results of this study should provide a clue for further improving ?UC. PMID:23534480

Murakami, Yoichi; Kikuchi, Hitomi; Kawai, Akio

2013-04-12

171

Fluorescence Spectroscopy  

NSDL National Science Digital Library

This resource, part of the Spectroscopy Lab Suite, simulates optical transitions in a Fluorescent light. In this illustration, the transitions between bands in the phosphor coating of the light are shown. The phosphor is excited by discharge in a mercury gas. The energy levels and transitions in the phosphor material can be changed.

Zollman, Dean

2010-05-21

172

Time-resolved Fourier transform intracavity spectroscopy with a Cr2+:ZnSe laser  

PubMed Central

Intracavity laser absorption spectroscopy (ICLAS) with an evacuated Cr2+: ZnSe laser is performed with a high-resolution time-resolved Fourier transform interferometer with a minimum detectable absorption coefficient equal to 4 10?9 cm?1 Hz?½ in the 2.5?m region. This represents the extreme limit presently reached in the infrared by ICLAS with Doppler limited resolution. The broad gain band of the crystal allows a spectral coverage at most equal to 125 nm, wide enough to see entire vibration bands. Weak CO2 bands observed up to now only in the Venus atmosphere are recorded for the first time in a laboratory. H2O detection limit down to 0.9 ppbv is also demonstrated.

Picque, Nathalie; Gueye, Fatou; Guelachvili, Guy; Sorokin, Evgeni; Sorokina, Irina T.

2010-01-01

173

Label-Free Toxin Detection by Means of Time-Resolved Electrochemical Impedance Spectroscopy  

PubMed Central

The real-time detection of trace concentrations of biological toxins requires significant improvement of the detection methods from those reported in the literature. To develop a highly sensitive and selective detection device it is necessary to determine the optimal measuring conditions for the electrochemical sensor in three domains: time, frequency and polarization potential. In this work we utilized a time-resolved electrochemical impedance spectroscopy for the detection of trace concentrations of Staphylococcus enterotoxin B (SEB). An anti-SEB antibody has been attached to the nano-porous aluminum surface using 3-aminopropyltriethoxysilane/glutaraldehyde coupling system. This immobilization method allows fabrication of a highly reproducible and stable sensing device. Using developed immobilization procedure and optimized detection regime, it is possible to determine the presence of SEB at the levels as low as 10 pg/mL in 15 minutes.

Chai, Changhoon; Takhistov, Paul

2010-01-01

174

Time-resolved fluorescence anisotropy of fluorescent-labeled lysophospholipid and taurodeoxycholate aggregates.  

PubMed Central

Previous work from this laboratory demonstrated that the environment-sensitive lysolipid N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)- monomyristoylphosphatidylethanolamine (N-NBD-MPE), at concentrations below its critical micelle concentration (CMCN-NBD-MPE = 4 microM), reached maximum fluorescence yield upon the addition of taurodeoxycholate (TDC) at concentrations well below its CMC (CMCTDC = 2.5 mM). These data indicated the formation of micellar aggregates of the two amphiphiles at concentrations below both of their CMCs. In the present study, fluorescence lifetime and differential polarization measurements were made to determine the size of these aggregates. In the absence of TDC and at 0.5 mM TDC a single lifetime (tau) and rotational correlation time (phi) were measured for N-NBD-MPE at the submicellar concentration of 2 microM, indicating a lack of interaction between the two molecules at this concentration. Above 0.5 mM TDC, two discrete lifetimes were resolved. Based on these lifetimes, two distinct rotational correlation times were established through polarization measurements. The shorter phi(0.19-0.73 ns) was ascribed to local probe motions, whereas the longer phi was in a time range expected for global rotation of aggregates the size of simple bile salt micelles (3-6.5 ns). From the longer phi, molecular volume and hydrodynamic radii were calculated, ranging from approximately 15 A at 1 mM to approximately 18 A at 5 mM TDC. These data support the conclusion that monomeric lysolipids in solution seed the aggregation of numerous TDC molecules (aggregation number = 16 at 1 mM TDC) to form a TDC micelle with a lysolipid core at concentrations below which they both self-aggregate.

DeLong, L J; Nichols, J W

1996-01-01

175

Application of time-resolved in-situ X-ray absorption spectroscopy in solid-state chemistry  

Microsoft Academic Search

Time-resolved X-ray absorption spectroscopy (TR-XAS) possesses excellent capabilities to reveal quantitative phase composition and average valence together with the evolution of the local structure of a system under dynamic reaction conditions. The work discussed here focused on time-resolved in-situ XAS investigations aiming, first, at understanding structural evolution under dynamic conditions and, second, at revealing properties of the system studied not

T. Ressler

2003-01-01

176

Time-resolved detection of fluorescent light during inflow of ICG to the brain—a methodological study  

NASA Astrophysics Data System (ADS)

It was reported that time-resolved reflectance measurements carried out during inflow and washout of an optical contrast agent may provide information on the blood supply to the brain cortex of human adults. It was also shown that a measurement of fluorescence excited in the dye circulating in the brain is feasible. Unfortunately, patterns of time-resolved fluorescence signals observed during in vivo measurements are difficult to interpret. The aim of this study was to analyze the influence of several factors on the fluorescence signals measured during in vivo experiments. A laboratory instrument for recording the distributions of arrival of fluorescence photons was constructed and optimized for measurements on humans. Monte Carlo simulations and laboratory measurements on liquid phantoms as well as in vivo measurements on healthy volunteers were carried out. An influence of source-detector separation, position of the source-detector pair on the head, as well as a dose of the injected indocyanine green (ICG) on the fluorescence signals were studied in detail. It was shown that even for a small dose of ICG (0.025 mg kg-1) the time-resolved signals can be successfully detected on the surface of the head. Strong influence of the studied factors on the fluorescence signals was observed. It was also noted that the changes in moments of distributions of arrival times of fluorescence photons depend on the anatomical structure of the tissues located between the source and the detector.

Milej, Daniel; Gerega, Anna; ?o?ek, Norbert; Weigl, Wojciech; Kacprzak, Micha?; Sawosz, Piotr; M?czewska, Joanna; Fronczewska, Katarzyna; Mayzner-Zawadzka, Ewa; Królicki, Leszek; Maniewski, Roman; Liebert, Adam

2012-10-01

177

Time-resolved studies of the C-A transition in avalanche discharges; Fluorescence and gain-loss studies  

SciTech Connect

Time-resolved XeF {ital C}-{ital A} fluorescence and gain-loss studies are conducted in an avalanche discharge using arc-type UV preionization in a variety of devices that deliver peak powers from 1 to 13 MW/cm{sup 3} in time intervals from 10 to 30 ns. The results coupled with extensive fluorescence measurements give indications about the possibility of developing a successful XeF {ital C}-{ital A} transition avalanche discharge laser.

Sze, R.C. (Los Alamos National Lab., Los Alamos, NM (US)); Sakai, T. (Rice Univ., Houston, TX (US)); Vannini, M. (Inst. di Elletronica Quantistica, Florence (IT)); Sentis, M.L. (Inst. de Mecanique des Fluides, Marseille (FR))

1991-01-01

178

Monitoring Absorption Changes in a Layered Diffusive Medium by White-Light Time-Resolved Reflectance Spectroscopy  

Microsoft Academic Search

Diffuse spectroscopy of turbid media has assumed a crucial role in the characterization of biological tissues. In particular, broadband time-resolved optical spectroscopy allows the direct determination in a single measurement of both the optical parameters of the tissue and the concentration of its main constituents. Moreover, the possibility of performing parallel wavelength measurements allows the recording of data in real

Arianna Giusto; Cosimo D'Andrea; Lorenzo Spinelli; Davide Contini; Alessandro Torricelli; Fabrizio Martelli; Giovanni Zaccanti; Rinaldo Cubeddu

2010-01-01

179

Cyclohexene Photo-oxidation over Vanadia Catalyst Analyzed by Time Resolved ATR-FT-IR Spectroscopy  

SciTech Connect

Vanadia was incorporated in the 3-dimensional mesoporous material TUD-1 with a loading of 2percent w/w vanadia. The performance in the selective photo-oxidation of liquid cyclohexene was investigated using ATR-FT-IR spectroscopy. Under continuous illumination at 458 nm a significant amount of product, i.e. cyclohexenone, was identified. This demonstrates for the first time that hydroxylated vanadia centers in mesoporous materials can be activated by visible light to induce oxidation reactions. Using the rapid scan method, a strong perturbation of the vanadyl environment could be observed in the selective oxidation process induced by a 458 nm laser pulse of 480 ms duration. This is proposed to be caused by interaction of the catalytic centre with a cyclohexenyl hydroperoxide intermediate. The restoration of the vanadyl environment could be kinetically correlated to the rate of formation of cyclohexenone, and is explained by molecular rearrangement and dissociation of the peroxide to ketone and water. The ketone diffuses away from the active center and ATR infrared probing zone, resulting in a decreasing ketone signal on the tens of seconds time scale after initiation of the photoreaction. This study demonstrates the high potential of time resolved ATR FT-IR spectroscopy for mechanistic studies of liquid phase reactions by monitoring not only intermediates and products, but by correlating the temporal behavior of these species to molecular changes of the vanadyl catalytic site.

Frei, Heinz; Mul, Guido; Wasylenko, Walter; Hamdy, M. Sameh; Frei, Heinz

2008-06-04

180

Ultrafast time-resolved broadband fluorescence studies of the benzene-tetracyanoethylene complex: solvation, vibrational relaxation, and charge recombination dynamics.  

PubMed

The charge-transfer (CT) state relaxation dynamics of the benzene-tetracyanoethylene (BZ-TCNE) complex was studied with broadband ultrafast time-resolved fluorescence spectroscopy implemented by optical Kerr gating in three solvents of different polarities. The CT state of the BZ-TCNE complex is reached via femtosecond laser excitation, and the subsequent temporal evolutions of the fluorescence spectra were measured. Analyses of various time-dependent spectral properties revealed rapid relaxations along solvent and vibrational coordinates in competition with charge recombination (CR). By comparing the results in solvents of different polarities, we partially separated solvation and vibrational relaxation dynamics and explored the solvent-dependent CR dynamics. Time-dependent dynamic fluorescence Stokes shift (TDFSS) measurements unveiled the solvation and vibrational relaxation contributions to the observed spectral relaxation. The biphasic and slow time scales of the vibrational contributions identified in TDFSS suggested nonstatistical and hindered intramolecular vibrational-energy redistribution that can be attributed to the unique structural properties of EDA complexes. The slowest spectral relaxation of 10-15 ps identified in TDFSS was ascribed to relaxation of the BZ(+)-TCNE(-) intermolecular vibrations, which is equivalent to a structural relaxation from the initial Franck-Condon configuration to the equilibrium CT-state structure. The time scales of vibrational relaxation indicate that a fraction of the CT-state population undergoes CR reactions before complete vibrational/structural equilibrium is achieved. In carbon tetrachloride, a nonexponential temporal profile was observed and attributed to vibrational nonequilibrium CR. In dichloromethane, polar solvation greatly accelerates CR reactions, and a slower reaction-field-induced structural relaxation gives rise to a pronounced biexponential decay. The equilibrium CR time constants of the BZ-TCNE CT state are 29 ps, 150 ps, and 68 ps in dichloromethane, carbon tetrachloride, and cyclohexane, respectively. PMID:23865400

Chiu, Chih-Chung; Hung, Chih-Chang; Chen, Chien-Lin; Cheng, Po-Yuan

2013-08-07

181

Time-Resolved Spectroscopy and Near Infrared Imaging for Prostate Cancer Detection: Receptor-targeted and Native Biomarker  

NASA Astrophysics Data System (ADS)

Optical spectroscopy and imaging using near-infrared (NIR) light provides powerful tools for non-invasive detection of cancer in tissue. Optical techniques are capable of quantitative reconstructions maps of tissue absorption and scattering properties, thus can map in vivo the differences in the content of certain marker chromophores and/or fluorophores in normal and cancerous tissues (for example: water, tryptophan, collagen and NADH contents). Potential clinical applications of optical spectroscopy and imaging include functional tumor detection and photothermal therapeutics. Optical spectroscopy and imaging apply contrasts from intrinsic tissue chromophores such as water, collagen and NADH, and extrinsic optical contrast agents such as Indocyanine Green (ICG) to distinguish disease tissue from the normal one. Fluorescence spectroscopy and imaging also gives high sensitivity and specificity for biomedical diagnosis. Recent developments on specific-targeting fluorophores such as small receptor-targeted dye-peptide conjugate contrast agent offer high contrast between normal and cancerous tissues hence provide promising future for early tumour detection. This thesis focus on a study to distinguish the cancerous prostate tissue from the normal prostate tissues with enhancement of specific receptor-targeted prostate cancer contrast agents using optical spectroscopy and imaging techniques. The scattering and absorption coefficients, and anisotropy factor of cancerous and normal prostate tissues were investigated first as the basis for the biomedical diagnostic and optical imaging. Understanding the receptors over-expressed prostate cancer cells and molecular target mechanism of ligand, two small ICG-derivative dye-peptides, namely Cypate-Bombesin Peptide Analogue Conjugate (Cybesin) and Cypate-Octreotate Peptide Conjugate (Cytate), were applied to study their clinical potential for human prostate cancer detection. In this work, the steady-state and time-resolved fluorescence spectroscopy of Cybesin (Cytate) in solution, and in cancerous and normal prostate tissues were studied. It was found that more Cybesin (Cytate) was uptaken in the cancerous prostate tissue than those in the normal tissue. The preferential uptake of Cybesin (Cytate) in cancerous tissue was used to image and distinguish cancerous areas from the normal tissue. To investigate rotational dynamics and fluorescence polarization anisotropy of the contrast agents in prostate tissues, an analytical model was used to extract the rotational times and polarization anisotropies, which were observed for higher values of Cybesin (Cytate)-stained cancerous prostate tissue in comparison with the normal tissue. These reflect changes of microstructures of cancerous and normal tissues and their different binding affinity with contrast agents. The results indicate that the use of optical spectroscopy and imaging combined with receptor-targeted contrast agents is a valuable tool to study microenvironmental changes of tissue, and detect prostate cancer in early stage.

Pu, Yang

182

Probing Kinetic Mechanisms of Protein Function and Folding with Time-Resolved Natural and Magnetic Chiroptical Spectroscopies  

PubMed Central

Recent and ongoing developments in time-resolved spectroscopy have made it possible to monitor circular dichroism, magnetic circular dichroism, optical rotatory dispersion, and magnetic optical rotatory dispersion with nanosecond time resolution. These techniques have been applied to determine structural changes associated with the function of several proteins as well as to determine the nature of early events in protein folding. These studies have required new approaches in triggering protein reactions as well as the development of time-resolved techniques for polarization spectroscopies with sufficient time resolution and sensitivity to probe protein structural changes.

Kliger, David S.; Chen, Eefei; Goldbeck, Robert A.

2012-01-01

183

Lanthanide labeling of a potent protease activated receptor-2 agonist for time-resolved fluorescence analysis  

PubMed Central

Protease activated receptor-2 (PAR2) is one of four G-protein coupled receptors (GPCRs) that can be activated by exogenous or endogenous proteases, which cleave the extracellular amino-terminus to expose a tethered ligand and subsequent G-protein signaling. Alternatively, PAR2 can be activated by peptide or peptidomimetic ligands derived from the sequence of the natural tethered ligand. Screening of novel ligands that directly bind to PAR2 to agonize or antagonize the receptor has been hindered by the lack of a sensitive, high-throughput, affinity binding assay. In this report we describe the synthesis and use of a modified PAR2 peptidomimetic agonist, 2-furoyl-LIGRLO-(diethylenetriaminepentaacetic acid)-NH2 (2-f-LIGRLO-dtpa), designed for lanthanide-based time resolved fluorescence screening. We first demonstrate that 2-f-LIGRLO-dtpa is a potent and specific PAR2 agonist across a full spectrum of in vitro assays. We then show that 2-f-LIGRLO-dtpa can be utilized in an affinity binding assay to evaluate the ligand-receptor interactions between known high potency peptidomimetic agonists (2-furoyl-LIGRLO-NH2, 2-f-LIGRLO; 2-aminothiazol-4-yl-LIGRL-NH2, 2-at-LIGRL and; 6-aminonicotinyl-LIGRL-NH2, 6-an-LIGRL) and PAR2. A separate N-terminal peptidomimetic modification (3-indoleacetyl-LIGRL-NH2, 3-ia-LIGRL) that does not activate PAR2 signaling was used as a negative control. All three peptidomimetic agonists demonstrated sigmoidal competitive binding curves, with the more potent agonists (2-f-LIGRLO and 2-at-LIGRL) displaying increased competition. In contrast, the control peptide (3-ia-LIGRL) displayed limited competition for PAR2 binding. In summary, we have developed a Europium-containing PAR2 agonist that can be used in a highly sensitive affinity binding assay to screen novel PAR2 ligands in a high-throughput format. This ligand can serve as a critical tool in the screening and development of PAR2 ligands.

Hoffman, Justin; Flynn, Andrea N.; Tillu, Dipti V.; Zhang, Zhenyu; Patek, Renata; Price, Theodore J.; Vagner, Josef; Boitano, Scott

2012-01-01

184

Time-resolved energy transfer spectroscopy for measuring mitochondrial metabolism in living cells  

NASA Astrophysics Data System (ADS)

Energy transfer from NADH to the mitochondrial marker rhodamine 123 (R123) was used to probe mitochondrial malfunction of cultivated endothelial cells incubated with various inhibitors of specific enzyme complexes of the respiratory chain. Pronounced differences of 'energy transfer efficacy' of incubated cells as compared to controls were deduced from the ratio of fluorescence intensity and intracellular amount of the acceptor. A combination of cw and time-gated (nanosecond) fluorescence spectroscopy appeared to be an appropriate tool for probing mitochondrial malfunction in various kinds of diseases.

Schneckenburger, Herbert; Gschwend, Michael H.; Strauss, Wolfgang S.; Sailer, Reinhard; Bauer, Manfred; Steiner, Rudolf W.

1997-12-01

185

Time-resolved fluorescence studies of a transmembrane peptide sequence of the dopamine D2 receptor  

NASA Astrophysics Data System (ADS)

Highly hydrophobic peptides in small unilamellar vesicles can be used to model membrane-embedded proteins such as the dopamine D2 receptor. The transmembrane domains of the dopamine D2 receptor are known to contain residues corresponding to the binding sites for natural receptor ligands. We have developed a model system consisting of a peptide whose sequence was taken from the transmembrane region of the dopamine D2 receptor and incorporated it into phospholipid bilayers. This polypeptide sequence, NH2-D-V-L-Y-S-A-F-T-W-L-G-Y-V-N-S-A-V-N-P-I-I-Y-T- T-F-N-V-CO2H, contains a single tryptophan residue, whose fluorescence properties provides an intrinsic probe of the microenvironment of the peptide within the bilayer. Purification of this highly hydrophobic peptide required the development of a novel alcohol-based reversed-phase HPLC solvent system. The vesicles were produces by cosonication of the peptide with dimyristoylphosphatidylcholine lipid and were characterized by electron microscopy and fluorescence spectroscopy. Time- correlated single photon counting was sued to measure the fluorescence anisotropy of the system as a function of temperature across the lipid phase transition range and as a function of the peptide/lipid ratio.

Williams, Valerie L.; Courtney, Scott H.; Schuster, David I.; Murphy, Randall B.

1994-08-01

186

Initial Process of Proton Transfer in Salicylideneaniline Studied by Time-Resolved Photoelectron Spectroscopy  

NASA Astrophysics Data System (ADS)

Excited state intramolecular proton transfer (ESIPT) in salicylideneaniline (SA) molecules expanded in a supersonic gas jet has been investigated by femtosecond time-resolved photoelectron spectroscopy. Although ESIPT in SA was predicted to take place in a planar structure, the fattening process of a molecule from a twisted Franck-Condon state has never been resolved. Here, we identified the twisting motion of the anilino ring during the fattening process in the decay dynamics of the photoelectron yield, taking account of the energy surface of the S1(?, ? ?) state of the enol form and the potential surface of ESIPT calculated by a time-dependent density functional theory (TDDFT). The twisting motion was found to be slower in the bromide and methylated SAs, while that in the nitrated SA did not change significantly. These substitution effects are explained by the modification of the potential barriers by the substituents, also predicted by the TDDFT calculation, and support the assignment of the decay dynamics to the twisting motion of the anilino ring prior ESIPT.

Sekikawa, T.; Schalk, O.; Wu, G.; Boguslavskiy, A. E.; Stolow, A.

187

Time-resolved spectroscopy of nonequilibrium ionization in laser-produced plasmas  

NASA Astrophysics Data System (ADS)

The highly transient ionization characteristic of laser-produced plasmas at high energy densities has been investigated experimentally, using x ray spectroscopy with time resolution of less than 20 ps. Spectroscopic diagnostics of plasma density and temperature were used, including line ratios, line profile broadening and continuum emission, to characterize the plasma conditions without relying immediately on ionization modeling. The experimentally measured plasma parameters were used as independent variables, driving an ionization code, as a test of ionization modelling, divorced from hydrodynamic calculations. Several state-of-the-art streak spectrographs, each recording a fiducial of the laser peak along with the time-resolved spectrum, characterized the laser heating of thin signature layers of different atomic numbers imbedded in plastic targets. Spherical targets were illuminated uniformly with the OMEGA 351 nm laser system, to approximate a one-dimensional homogeneous plasma. A novel design of crystal spectrograph, with a conically curved crystal, was developed. Coupled with a streak camera, it provided high resolution and a collection efficiency roughly 20 to 50 times that of planar crystal spectrographs, affording improved spectra for quantitative reduction and greater sensitivity for the diagnosis of weak emitters.

Marjoribanks, Robin Stewart

1990-03-01

188

Optical analysis of cirrhotic liver by near infrared time resolved spectroscopy  

NASA Astrophysics Data System (ADS)

The severity of liver cirrhosis was related with the optical properties of liver tissue. Various grades of liver cirrhosis were produced in rats by intraperitoneal injection of thioacetamide (TAA) for different periods: 4 weeks, 8 weeks, 12 weeks, and 16 weeks. Optical properties of the liver, absorption, coefficient ((mu) a) and scattering coefficient (microsecond(s) '), were measured by near-infrared time- resolved spectroscopy. Histological examination confirmed cirrhotic changes in the liver, which were more severe in rats with TAA administration for longer periods. The (mu) a increased in 4- and 8-week rats, and then decreased in 12- and 16-week rats. The (mu) a of blood-free liver decreased as liver cirrhosis progressed. The hemoglobin content in the liver calculated from the (mu) a values increased in 4- and 8-week rats and decreased in 12- and 16-week rats. The microsecond(s) ' decreased in the cirrhotic liver, probably reflecting the decrease in the mitochondria content. It was shown that (mu) a and microsecond(s) ' determination is useful to assess the severity of liver cirrhosis.

Nishio, Toshihiro; Kitai, Toshiyuki; Miwa, Mitsuharu; Takahashi, Rei; Yamaoka, Yoshio

1999-10-01

189

High-resolution Time-resolved Extreme Ultraviolet Spectroscopy on NSTX  

NASA Astrophysics Data System (ADS)

We report on high-resolution, time-resolved spectroscopy in the extreme ultraviolet spectral region (10-200 å) on the NSTX tokamak. This work utilizes two flat-field spectrometers on loan from LLNL's electron beam ion trap facility. XEUS, installed in 2004, has a 2400 line/mm flat-field grating with field of view of ˜50 åthat can be positioned to survey 5 - 135 åwith an instrumental resolution of ˜0.1 åand ?/??˜100 at 10åto ˜1000 at 100 å. LoWEUS, installed in 2008, utilizes a 1200 line/mm grating with field of view of ˜180,s typically positioned to survey 60-280 åwith an instrumental resolution of ˜0.3 åand ?/??˜300 at 100åto ˜600 at 200å. New cameras have achieved a time resolution of 12-13 ms for both instruments. We can now examine time dependence and evolution of both intrinsic and extrinsic impurities on NSTX in the EUV band. Of particular interest is monitoring the entry of molybdenum into the plasma after installation of Mo tiles for the 2011 run. [4pt] Work supported by DOE General Plasma Science program. Part of this work performed under the auspices of DOE by LLNL under contract DE-AC52-07NA27344 and PPPL under contract DE-AC02-09CH11466.

Lepson, J. K.; Beiersdorfer, P.; Clementson, J.; Bitter, M.; Hill, K.; Kaita, R.; Roquemore, L.; Skinner, C. H.; Zimmer, G.

2011-11-01

190

Velocity distribution function of sputtered Cu atoms obtained by time resolved optical absorption spectroscopy  

NASA Astrophysics Data System (ADS)

A new method based on time resolved optical absorption spectroscopy is proposed to determine the velocity distribution function of sputtered Cu atoms in a magnetron plasma discharge. The method consists of applying a short pulse of 1.5 ?s and of recording time variations in copper atom density in off pulse at different positions (1, 2, and 3 cm) from target surface under 3-30 mTorr. The time evolution of the density is then converted into velocity distribution. We estimate that only sputtered atoms with radial velocity component lower than 0.5 km/s are detected. The average velocity of Cu atoms is evaluated as the first order moment of the velocity distribution functions. The velocity distribution functions become the more dispersive the farther from target surface. The average velocities vary in the range of 2.5-3 km/s at the vicinity of target surface whereas at 3 cm a decrease from 2.5 to 1.2 km/s is observed at 30 mTorr.

Kang, Namjun; Oh, Soo-Ghee; Gaboriau, Freddy; Ricard, André

2010-01-01

191

Infrared and X-ray simultaneous spectroscopy: a novel conceptual beamline design for time resolved experiments.  

PubMed

Many physical/chemical processes such as metal-insulator transitions or self-assembly phenomena involve correlated changes of electronic and atomic structure in a wide time range from microseconds to minutes. To investigate these dynamic processes we not only need a highly brilliant photon source in order to achieve high spatial and time resolution but new experimental methods have to be implemented. Here we present a new optical layout for performing simultaneous or concurrent infrared and X-ray measurements. This approach may indeed return unique information for example the interplay between structural changes and chemical processes occurring in the investigated sample. A beamline combining two X-ray and IR beams may really take advantage of the unique synchrotron radiation properties: the high brilliance and the broad spectrum. In this contribution we will describe the conceptual layout and the expected performance of a complex system designed to collect IR and X-ray radiation from the same bending magnet on a third-generation synchrotron radiation ring. If realized, this beamline will enable time-resolved spectroscopy experiments offering new scientific opportunities at the frontiers of science. PMID:20461504

Marcelli, Augusto; Xu, Wei; Hampai, Dariush; Malfatti, Luca; Innocenzi, Plinio; Schade, Ulrich; Wu, Ziyu

2010-05-12

192

Time-resolved resonance Raman spectroscopy of p-aminophenol radical cation in aqueous solution  

SciTech Connect

Examination of the intermediates associated with the 410-450-nm absorption in the pulse radiolytic oxidation of aqueous p-aminophenol by time-resolved resonance Raman spectroscopy shows that below pH 2 the transient species responsible is the p-aminophenol radical cation. Strongly resonance enhanced in the Raman spectrum of the radical cation are the {nu}{sub 8a} phenyl ring stretching vibration at 1,631 cm{sup {minus}1} and the {nu}{sub 9a} CH bending vibration at 1,178 cm{sup {minus}1}. The phenyl modes {nu}{sub 7a} and {nu}{sub 13}, which involve significant contributions from the CN and CO stretching motions, are observed prominently at 1516 and 1406 cm{sup {minus}1}. In basic solutions this absorption spectrum, which is shifted slightly to the red, is ascribed to the p-aminophenoxyl radical. In the neutral radical the CN and CO stretching motions are strongly coupled, and only one intense band representing the in-phase vibration is observed at 1,434 cm{sup {minus}1}.

Sun, Q.; Tripathi, G.N.R.; Schuler, R.H. (Univ. of Notre Dame, IN (USA))

1990-08-09

193

Photothermal properties of gold nanocages studied by time-resolved spectroscopy  

NASA Astrophysics Data System (ADS)

Gold nanocages of different sizes synthesized via galvanic replacement reaction have been studied by ultrafast time-resolved spectroscopy. The vibrational phonon modes were excited and the periods of these modes increase with the size of the gold nanocages. For a specific size of nanocage, experiments with different excitation powers of the pump laser were performed (from 2 ?J to 20 ?J), we found that the period of the vibrational mode increased with the laser intensity. This was compared to experiments on spherical gold nanoparticles, which allow us to roughly estimate the temperature of the nanocages when the electrons and the phonons reach the equilibrium. The temperature of the nanocages can increase up to 1000 K, near the melting point of the bulk metal, while the particles maintain their integrity. This makes the nanocages potentially useful for photothermal therapy applications. The heat dissipation rate for the nanocages was also studied in these experiments, and was found to have the similar trend as spherical nanoparticles, i.e., larger particles stay hot for longer times than smaller particles.

Hu, Min; Chen, Jingyi; Xia, Younan; Li, Xingde; Petrova, Hristina; Hartland, Gregory; Marquez, Manuel

2006-03-01

194

Ultrafast protein dynamics of hemoglobin as studied by picosecond time-resolved resonance Raman spectroscopy  

NASA Astrophysics Data System (ADS)

Time-resolved resonance Raman spectroscopy on human adult hemoglobin (HbA) following ligand photolysis revealed that the frequency of the iron-histidine stretching [?(Fe-His)] mode exhibited a 2-cm-1 downshift with a time constant of about 300 ps, suggesting a structural change in the heme pocket following the ligand photolysis. Low-frequency heme modes suggested that the primary metastable form of HbA has a more disordered orientation of propionates and a less strained environment than the deoxy form. The latter fact is consistent with the experimental observation that the ?(Fe-His) frequency of the metastable form is higher than the deoxy form. The present study shows that HbA adopts a metastable structure within the instrument response time and remains little changed in the subnanosecond to nanosecond time regime. Characteristics of the primary protein response of HbA based on the comparison of the results of HbA with those of the isolated chains and myoglobin are discussed.

Mizutani, Yasuhisa; Nagai, Masako

2012-03-01

195

Nanosecond time-resolved infrared spectroscopy distinguishes two K species in the bacteriorhodopsin photocycle.  

PubMed Central

The photochemical reaction process of bacteriorhodopsin in the nanosecond time range (-120-860 ns) was measured in the 1400-900 cm-1 region with an improved time resolved dispersive-type infrared spectrometer. The system is equipped with a newly developed detection unit whose instrumental response to a 5-ns laser pulse has a full width of the half-maximum of 60 ns. It provides highly accurate data that enabled us to extract a kinetic process one order of magnitude faster than the instrumental response. The spectral changes in the 1400-900 cm-1 region were analyzed by singular value decomposition and resolved into three components. These components were separated by fitting with 10- and 1000-ns exponential functions and a step function, which were convoluted with the instrumental response function. The components with decay time constants of 10 and 1000 ns are named K and KL, respectively, on the basis of previous visible spectroscopy. The spectral shapes of K and KL are distinguishable by their hydrogen-out-of-plane (HOOP) modes, at 958 and 984 cm-1, respectively. The former corresponds to the K intermediate recorded at 77 K and the latter to a K-like photoproduct at 135 K. On the basis of published data, these bands are assigned to the 15-HOOP mode, indicating that the K and KL differ in a twist around the C14-C15 bond.

Sasaki, J; Yuzawa, T; Kandori, H; Maeda, A; Hamaguchi, H

1995-01-01

196

Electron transfer in hydrogenated nanocrystalline silicon observed by time-resolved terahertz spectroscopy  

NASA Astrophysics Data System (ADS)

We report on the ultrafast carrier dynamics in hydrogenated nanocrystalline silicon (nc-Si:H) using time-resolved terahertz spectroscopy. Photoexcitation at 407 nm primarily produces charge carriers in the a-Si phase, but they undergo a rapid electron transfer to the c-Si phase prior to complete thermalization into the band-tail states of a-Si. We studied the carrier dynamics on a range of nc-Si:H samples with varying crystalline volume fractions (Xc) and mapped out the carrier dynamics with sub-ps resolution. Our measurements are consistent with a model in which electrons are first trapped at interface states at the a-Si-c-Si boundary prior to being thermally emitted into the c-Si phase. Wavelength and temperature dependent measurements are consistent with our model. The phenomena observed here have implications toward solar cell structures that utilize an amorphous material as an absorber layer, previously thought to have a mobility value too low to attain effective charge transport in a device.

Bergren, Matthew R.; Simonds, Brian J.; Yan, Baojie; Yue, Guozhen; Ahrenkiel, Richard; Furtak, Thomas E.; Collins, Reuben T.; Taylor, P. Craig; Beard, Matthew C.

2013-02-01

197

Noninvasive detection of concealed explosives: depth profiling through opaque plastics by time-resolved Raman spectroscopy.  

PubMed

The detection of explosives concealed behind opaque, diffusely scattering materials is a challenge that requires noninvasive analytical techniques for identification without having to manipulate the package. In this context, this study focuses on the application of time-resolved Raman spectroscopy (TRRS) with a picosecond pulsed laser and an intensified charge-coupled device (ICCD) detector for the noninvasive identification of explosive materials through several millimeters of opaque polymers or plastic packaging materials. By means of a short (250 ps) gate which can be delayed several hundred picoseconds after the laser pulse, the ICCD detector allows for the temporal discrimination between photons from the surface of a sample and those from deeper layers. TRRS was applied for the detection of the two main isomers of dinitrotoluene, 2,4-dinitrotoluene, and 2,6-dinitrotoluene as well as for various other components of explosive mixtures, including akardite II, diphenylamine, and ethyl centralite. Spectra were obtained through different diffuse scattering white polymer materials: polytetrafluoroethylene (PTFE), polyoxymethylene (POM), and polyethylene (PE). Common packaging materials of various thicknesses were also selected, including polystyrene (PS) and polyvinyl chloride (PVC). With the demonstration of the ability to detect concealed, explosives-related compounds through an opaque first layer, this study may have important applications in the security and forensic fields. PMID:21967622

Petterson, Ingeborg E Iping; López-López, María; García-Ruiz, Carmen; Gooijer, Cees; Buijs, Joost B; Ariese, Freek

2011-10-17

198

Multiwavelength time-resolved detection of fluorescence during the inflow of indocyanine green into the adult's brain  

NASA Astrophysics Data System (ADS)

Optical technique based on diffuse reflectance measurement combined with indocyanine green (ICG) bolus tracking is extensively tested as a method for clinical assessment of brain perfusion in adults at the bedside. Methodology of multiwavelength and time-resolved detection of fluorescence light excited in the ICG is presented and advantages of measurements at multiple wavelengths are discussed. Measurements were carried out: 1. on a physical homogeneous phantom to study the concentration dependence of the fluorescence signal, 2. on the phantom to simulate the dynamic inflow of ICG at different depths, and 3. in vivo on surface of the human head. Pattern of inflow and washout of ICG in the head of healthy volunteers after intravenous injection of the dye was observed for the first time with time-resolved instrumentation at multiple emission wavelengths. The multiwavelength detection of fluorescence signal confirms that at longer emission wavelengths, probability of reabsorption of the fluorescence light by the dye itself is reduced. Considering different light penetration depths at different wavelengths, and the pronounced reabsorption at longer wavelengths, the time-resolved multiwavelength technique may be useful in signal decomposition, leading to evaluation of extra- and intracerebral components of the measured signals.

Gerega, Anna; Milej, Daniel; Weigl, Wojciech; Botwicz, Marcin; Zolek, Norbert; Kacprzak, Michal; Wierzejski, Wojciech; Toczylowska, Beata; Mayzner-Zawadzka, Ewa; Maniewski, Roman; Liebert, Adam

2012-08-01

199

Time-Resolved Fluorescence Emission Measurements of Photosystem I Particles of Various Cyanobacteria: A Unified Compartmental Model  

Microsoft Academic Search

Photosystem I (PS-I) contains a small fraction of chlorophylls (Chls) that absorb at wavelengths longer than the primary electron donor P700. The total number of these long wavelength Chls and their spectral distribution are strongly species dependent. In this contribution we present room temperature time-resolved fluorescence data of five PS-I core complexes that contain different amounts of these long wavelength

Bas Gobets; Ivo H. M. van Stokkum; Matthias Rögner; Jochen Kruip; Eberhard Schlodder; Navassard V. Karapetyan; Jan P. Dekker; Rienk van Grondelle

2001-01-01

200

Cooper pair breaking and superconducting state recovery dynamics in MgB2 probed by time-resolved THz spectroscopy  

Microsoft Academic Search

We measured the Cooper pair breaking and condensate recovery dynamics in MgB2 by means of time-resolved optical pump-terahertz probe spectroscopy. The observed photoexcitation intensity dependence of Cooper-pair breaking is attributed to the presence of two superconducting gaps in MgB2.

J. Demsar; R. D. Averitt; A. J. Taylor; W.-N. Kang; H. J. Kim; E.-M. Choi; S.-I. Lee

2003-01-01

201

Design of the Optical System for a New Time-Resolved X-ray Absorption Spectroscopy Apparatus.  

National Technical Information Service (NTIS)

Calculations of total reflection mirror optics and analyzing crystal polychromator optics are done to design a new time-resolved soft X-ray absorption spectroscopy apparatus. This apparatus utilizes pulsed soft X-rays of pseudo-continuum energy which are ...

A. Miyashita O. Yoda

1988-01-01

202

Development of a time-resolved fluorometric method for observing hybridization in living cells using fluorescence resonance energy transfer.  

PubMed Central

We previously showed that a specific kind of mRNA (c-fos) was detected in a living cell under a microscope by introducing two fluorescently labeled oligodeoxynucleotides, each labeled with donor or acceptor, into the cytoplasm, making them hybridize to adjacent locations on c-fos mRNA, and taking images of fluorescence resonance energy transfer (FRET) (A. Tsuji, H. Koshimoto, Y. Sato, M. Hirano. Y. Sei-Iida, S. Kondo, and K. Ishibashi, 2000, Biophys. J. 78:3260-3274). On the formed hybrid, the distance between donor and acceptor becomes close and FRET occurs. To observe small numbers of mRNA in living cells using this method, it is required that FRET fluorescence of hybrid must be distinguished from fluorescence of excess amounts of non-hybridizing probes and from cell autofluorescence. To meet these requirements, we developed a time-resolved method using acceptor fluorescence decays. When a combination of a donor having longer fluorescence lifetime and an acceptor having shorter lifetime is used, the measured fluorescence decays of acceptors under FRET becomes slower than the acceptor fluorescence decay with direct excitation. A combination of Bodipy493/503 and Cy5 was selected as donor and acceptor. When the formed hybrid had a configuration where the target RNA has no single-strand part between the two fluorophores, the acceptor fluorescence of hybrid had a sufficiently longer delay to detect fluorescence of hybrid in the presence of excess amounts of non-hybridizing probes. Spatial separation of 10-12 bases between two fluorophores on the hybrid is also required. The decay is also much slower than cell autofluorescence, and smaller numbers of hybrid were detected with less interference of cell autofluorescence in the cytoplasm of living cells under a time-resolved fluorescence microscope with a time-gated function equipped camera. The present method will be useful when observing induced expressions of mRNA in living cells.

Tsuji, A; Sato, Y; Hirano, M; Suga, T; Koshimoto, H; Taguchi, T; Ohsuka, S

2001-01-01

203

Time-Resolved Spectroscopy of Nonequilibrium Ionization in Laser-Produced Plasmas.  

NASA Astrophysics Data System (ADS)

The highly transient ionization characteristic of laser-produced plasmas at high energy densities has been investigated experimentally, using x-ray spectroscopy with time resolution of less than 20 ps. Spectroscopic diagnostics of plasma density and temperature were used, including line ratios, line profile broadening and continuum emission, to characterize the plasma conditions without relying immediately on ionization modelling. The experimentally measured plasma parameters were used as independent variables, driving an ionization code, as a test of ionization modelling, divorced from hydrodynamic calculations. Several state-of-the-art streak spectrographs, each recording a fiducial of the laser peak along with the time-resolved spectrum, characterized the laser heating of thin signature layers of different atomic numbers imbedded in plastic targets. Spherical targets were illuminated uniformly with the OMEGA 351 nm laser system ( tau ~ 1 ns, I ~ 5 times 10 ^{14} Wcm^{ -2}), to approximate a one-dimensional homogeneous plasma. A novel design of crystal spectrograph, with a conically curved crystal, was developed. Coupled with a streak camera, it provided high resolution ( lambda/Deltalambda > 1000) and a collection efficiency roughly 20-50 times that of planar crystal spectrographs, affording improved spectra for quantitative reduction and greater sensitivity for the diagnosis of weak emitters. A novel temperature diagnostic was developed, using special targets with a known proportion of elements: analogous emission lines from isoelectronic charge-states were used to provide a temperature-sensitive diagnostic ratio. Experimental results were compared to hydrocode and ionization code simulations, with poor agreement. The conclusions question the appropriateness of describing electron velocity distributions by a temperature parameter during the time of laser illumination and emphasize the importance of characterizing the distribution more generally.

Marjoribanks, Robin Stewart

204

Time-resolved NMR spectroscopy: ligand-induced refolding of riboswitches.  

PubMed

A detailed understanding of cellular mechanisms requires knowledge of structure and dynamics of the involved biomacromolecules at atomic resolution. NMR spectroscopy uniquely allows determination of static and dynamic processes at atomic level, including structured states often represented by a single state as well as by unstructured conformational ensembles. While a high-resolution description of structured states may also be obtained by other techniques, the characterization of structural transitions occurring during biomolecular folding is only feasible exploiting NMR spectroscopic methods. The NMR methodical strategy includes the fast initiation of a folding reaction in situ and the possibility to detect the induced process with sufficient time resolution on the respective NMR time scale. In the case of ligand-induced structural transitions of RNA, the initiation of the folding reaction can be achieved by laser-triggered deprotection of a photolabile caged ligand whose release induces folding of a riboswitch RNA. The strategy discussed here is general and can also be transferred to other biological processes, where at least one key reagent or substrate, e.g., ions, ligands, pH, or one specific conformational state, can be photochemically caged. The rates of reversible and irreversible reactions or structural transitions that can be covered by real-time NMR methods range from milliseconds up to hours.In this chapter, we discuss the application of a time-resolved NMR strategy to resolve the ligand-induced folding of the guanine-sensing riboswitch aptamer domain of the B. subtilis xpt-pbuX operon. PMID:19381559

Buck, Janina; Fürtig, Boris; Noeske, Jonas; Wöhnert, Jens; Schwalbe, Harald

2009-01-01

205

Steady-state and time-resolved fluorescence of tetramethylrhodamine attached to DNA: correlation with DNA sequences.  

PubMed

Time-resolved fluorescence as well as steady-state absorption and fluorescence were detected in order to study the interactions between tetramethylrhodamine (TAMRA) and DNA when TAMRA was covalently labeled on single- and double-stranded oligonucleotides. Fluorescence intensity quenching and lifetime changes were characterized and correlated with different DNA sequences. The results demonstrated that the photoinduced electron transfer interaction between guanosine residues and TAMRA introduced a short lifetime fluorescence component when guanosine residues were at the TAMRA-attached terminal of the DNA sequences. The discrepancy of two-state and three-state models in previous studies was due to the DNA sequence selection and sensitivity of techniques used to detect the short lifetime component. The results will help the design of fluorescence-based experiments related to a dye labeled probe. Copyright © 2012 John Wiley & Sons, Ltd. PMID:23109120

Chen, Tingting; Fu, Leixiaomeng; Zu, Lily

2012-10-28

206

Ultrafast Time-Resolved Spectroscopy of Photoinduced Electron Transfer in Novel Photovoltaic Devices  

NASA Astrophysics Data System (ADS)

We present work toward an understanding of the fundamental photophysics of photoinduced electon transfer between 9-anthracenecarboxylic acid (9-AC) and TiO2 nanoparticles in order to apply the techniques to a novel photovoltaic device. The active layers of a proposed device consist of a broad-spectrum, metallo-organic absorberootnotetextM.H.Chisholm, et al., Inorg.Chem.47, 3415 (2008). covalently bound through a carboxylic acid to a nano-porous TiO2 structure. To study the electron transfer, a model compound, 9-AC, is covalently bound to TiO2 nanoparticles. Ultrafast electron transfer from the excited 9-AC to the TiO2 is observed within 50 fs using ultrafast broadband spectroscopy. Further evidence of this transfer is shown from quenching of the fluorescence of the 9-AC with increasing concentrations of TiO2 with no effects on the lifetime of the fluorescence.

Mier, L. M.; Carter, A. R.; Gustafson, T. L.; Epstein, A. J.

2009-03-01

207

Time-resolved flavin adenine dinucleotide fluorescence study of the interaction between immobilized glucose oxidase and glucose.  

PubMed

Time-resolved fluorescence experiments have shown that flavin adenine dinucleotide (FAD) fluorescence emission of sol-gel immobilized glucose oxidase (GOD) exhibits a three-exponential decaying behaviour characterized by long- (about 2.0-3.0 ns), intermediate- (about 300 ps) and short- (less than 10 ps) lifetime, each one being characteristic of a peculiar conformational state of the FAD structure. In the present work time-resolved fluorescence is used to monitor FAD signals in the time interval immediately following the addition of glucose at various concentrations in order to detect the conformational changes occurring during the interaction between sol-gel immobilized GOD and glucose. The analysis of time-dependent fluorescence emission signal has shown that the FAD conformational state changes during the process from a configuration with a prevalence of the state characterized by the long lifetime to a configuration with increased contribution from the process with the intermediate lifetime. The time needed to complete this configuration change decreases with the concentration of added glucose. The results here reported indicate that time-resoled fluorescence can be extremely useful for a better understanding of solid phase biocatalysis that is particularly important in light of their clinical and biotechnological applications. PMID:23576005

Esposito, Rosario; Delfino, Ines; Lepore, Maria

2013-04-11

208

Multispectral fluorescence lifetime imaging of feces-contaminated apples by time-resolved laser-induced fluorescence imaging system with tunable excitation wavelengths  

NASA Astrophysics Data System (ADS)

We recently developed a time-resolved multispectral laser-induced fluorescence (LIF) imaging system capable of tunable wavelengths in the visible region for sample excitation and nanosecond-scale characterizations of fluorescence responses (lifetime imaging). Time-dependent fluorescence decay characteristics and fluorescence lifetime imaging of apples artificially contaminated with a range of diluted cow feces were investigated at 670 and 685 nm emission bands obtained by 418, 530, and 630 nm excitations. The results demonstrated that a 670 nm emission with a 418 nm excitation provided the greatest difference in time-dependent fluorescence responses between the apples and feces-treated spots. The versatilities of the time-resolved LIF imaging system, including fluorescence lifetime imaging of a relatively large biological object in a multispectral excitation-emission wavelength domain, were demonstrated.

Kim, Moon S.; Cho, Byoung-Kwan; Lefcourt, Alan M.; Chen, Yud-Ren; Kang, Sukwon

2008-04-01

209

Ns-scale time-resolved laser induced fluorescence imaging for detection of fecal contamination on apples  

NASA Astrophysics Data System (ADS)

Our laboratory has been utilizing fluorescence techniques as a potential means for detection of quality and wholesomeness of food products. A system with a short pulse light source such as a laser coupled with a gated detector can be used to harvest fluorescence in ambient light conditions from biological samples with relatively low fluorescence yields. We present a versatile multispectral laser-induced fluorescence (LIF) imaging system capable of ns-scale time resolved fluorescence. The system is equipped with a tunable pulse laser system that emits in the visible range from 410 nm to 690 nm. Ns-scale, time-dependent multispectral fluorescence emissions of apples contaminated with a range of diluted cow feces were acquired. Four spectral bands, F670, F680, F685 and F730, centered near the emission peak wavelengths of the major constituents responsible for the red fluorescence emissions from apples artificially contaminated with cow feces were examined to determine a suitable single red fluorescence band and optimal ns-gate window for detection of fecal contamination on apples. The results based on the ns decay curves showed that 670 nm with 10 nm full width at half maximum (FWHM) at a gate-delay of 4 ns from the laser excitation peak provided the greatest differences in time-dependent fluorescence responses between feces contaminated spots and apples surfaces.

Kim, Moon S.; Lefcourt, Alan M.; Chen, Yud-Ren

2004-11-01

210

An investigation of coordinatively unsaturated metal carbonyls using time-resolved infrared spectroscopy  

Microsoft Academic Search

This dissertation details the work done implementing a state of the art (100 ns temporal response with sub wavenumber frequency resolution) time resolved infrared (TRIR) spectrophotometer to study the reactive chemical species produced by pulsed laser photolysis which are proposed to be related to the key intermediates generated in thermal reactions. Photolysis (308 nm XeCl Excimer laser) of ambient temperature

Ryba

1992-01-01

211

Electronic continua in time-resolved photoelectron spectroscopy. II. Corresponding ionization correlations  

Microsoft Academic Search

We investigate further the role of ion electronic continua in time-resolved photoelectron spectroscopic measurements of ultrafast nonadiabatic coupling. In the preceding paper [Blanchet, Zgierski, and Stolow, J. Chem. Phys. 114, 1194 (2000)], the limiting case of complementary ionization correlations permitted a disentangling of electronic from vibrational dynamics. Here we examine the other limiting case in which the nonadiabatically coupled sates

M. Schmitt; S. Lochbrunner; J. P. Shaffer; J. J. Larsen; M. Z. Zgierski; Albert Stolow

2001-01-01

212

Dynamic structural science: recent developments in time-resolved spectroscopy and X-ray crystallography.  

PubMed

To understand the mechanism of biological processes, time-resolved methodologies are required to investigate how functionality is linked to changes in molecular structure. A number of spectroscopic techniques are available that probe local structural rearrangements with high temporal resolution. However, for macromolecules, these techniques do not yield an overall high-resolution description of the structure. Time-resolved X-ray crystallographic methods exist, but, due to both instrument availability and stringent sample requirements, they have not been widely applied to macromolecular systems, especially for time resolutions below 1 s. Recently, there has been a resurgent interest in time-resolved structural science, fuelled by the recognition that both chemical and life scientists face many of the same challenges. In the present article, we review the current state-of-the-art in dynamic structural science, highlighting applications to enzymes. We also look to the future and discuss current method developments with the potential to widen access to time-resolved studies across discipline boundaries. PMID:24059517

Trincao, Jose; Hamilton, Michelle L; Christensen, Jeppe; Pearson, Arwen R

2013-10-01

213

Two-Dimensional Subpicosecond Time-Resolved Fluorescence Anisotropy: Optical Kerr-Gating with a Dynamic Polarization Excitation.  

NASA Astrophysics Data System (ADS)

With an advent of ultrafast lasers, a number of applications are widely adopted to probe photophysical and photochemical properties of a molecule that occurs in an ultrafast (femtosecond to picosecond) time scale. Intramolecular charge transfer (ICT) or proton transfer in photoexcited electron donor-acceptor (EDA) molecules, for instance, has been a topic of very extensive time-resolved studies for several decades. Time-evolution of an anisotropic property can track dipole orientations or conformational changes in their photoexcited molecular systems, which is of extreme importance to examine its structure and excited-state dynamics rather than probing an isotropic "population change".With this respect, we recently developed a subpicosecond time-resolved 2-D fluorescence anisotropy (TRFA) in which method implements a dynamic alternation of laser polarizations to excite a sample using a photoelastic modulator (PEM). In the combination of an ultrafast optical shutter (Kerr-gating) and a spectrograph that is coupled with a CCD, two signal phases so-obtained dynamically, I_{?}( t, ?) and I_{?}( t, ?), provide a 2-D mapped information on both a wide range for spectra and time-resolved kinetics of photoexcited molecules of interest. From the definition of an anisotropy 2-D TRFA, r (t, ?), is given instantly and even more reliably at a single measurement. In this paper we will present benchmark tests of some target samples to establish performance of TRFA.

Fujiwara, Takashige; Romano, Natalie C.; Modarelli, David A.; Lim, Edward C.

2013-06-01

214

Studies on the aggregation-induced emission of silole film and crystal by time-resolved fluorescence technique  

NASA Astrophysics Data System (ADS)

In this Letter, the photoluminescence of 1,1,2,3,4,5-hexaphenylsilole (HPS) and poly 1,1-[(1,2,3,4,5-pentaphenylsiloly)oxy]-1-phenyl-1-undecyne (PS9PA) was studied in detail by time-resolved fluorescence technique to investigate possible mechanisms of their unique aggregation-induced emissions. Enhanced emissions and long lifetimes of HPS and PS9PA films were detected in PMMA matrix compared to those of their solutions. Furthermore, strong fluorescence with nanosecond lifetimes was also obtained in the single crystal of HPS. These results show that intramolecular vibrational and torsional motions can act as efficient nonradiative pathways for the excited states to decay in the solutions and that suppression of these motions by restricting intramolecular vibrations in the solid state leads to enhanced fluorescence.

Ren, Yan; Dong, Yongqiang; Lam, Jacky W. Y.; Tang, Ben Zhong; Wong, Kam Sing

2005-02-01

215

Time resolved FRET strategy with fluorescent ligands to analyze receptor interactions in native tissues: application to GPCR oligomerization.  

PubMed

G protein-coupled receptors (GPCRs) play a key role in the regulation of physiological functions. Deregulation of their activities often results in pathological disorders and therefore these receptors constitute major targets for drug development. The emergence of new concepts such as GPCR oligomerization has modified our understanding of these proteins, and identifying the role of receptor complexes is probably a major challenge for the next decade. Various experimental strategies have been developed to study GPCR oligomers and energy transfer experiments between partners within a complex constitute one of the most convenient approaches. These experimental strategies usually require receptor fusion to tags or fluorescent or luminescent proteins and therefore cannot be easily applied to native tissues. We developed a new experimental approach based on the labeling of receptors with high affinity fluorescent ligands compatible with time-resolved energy transfer measurements. Because of the very high signal-to-noise ratio of the time-resolved fluorescent energy transfer (TR-FRET) signals, this approach constitutes a breakthrough since it allows the direct identification of wild-type GPCR oligomers in native tissues. PMID:21607869

Cottet, Martin; Albizu, Laura; Comps-Agrar, Laetitia; Trinquet, Eric; Pin, Jean-Philippe; Mouillac, Bernard; Durroux, Thierry

2011-01-01

216

A homogeneous europium cryptate-based assay for the diagnosis of mutations by time-resolved fluorescence resonance energy transfer  

PubMed Central

Oligonucleotide ligation assay (OLA) is considered to be a very useful methodology for the detection and characterization of mutations, particularly for clinical purposes. The fluorescence resonance energy transfer between a fluorescent donor and a suitable fluorophore as acceptor has been applied in the past to several scientific fields. This technique is well adapted to nucleic acid analysis such as DNA sequencing, DNA hybridization and polymerase chain reaction. We describe here a homogeneous format based on the use of a rare earth cryptate label as donor: tris-bipyridine-Eu3+. The long-lived fluorescence of this label makes it possible to reach a high sensitivity by using a time-resolved detection mode. A non-radiative energy transfer technology, known as time-resolved amplification of cryptate emission (TRACE®) characterized by a temporal and spectral selectivity has been developed. The TRACE® detection of characterized single nucleotide polymorphism using the OLA for allelic discrimination is proposed. We demonstrate the potentialities of this OLA–TRACE® methodology through the analysis of K-ras oncogene point mutations.

Lopez-Crapez, E.; Bazin, H.; Andre, E.; Noletti, J.; Grenier, J.; Mathis, G.

2001-01-01

217

Detection of Metastable Chlorine Ions in Time-Modulated Plasma by Time Resolved Laser-Induced Fluorescence  

NASA Astrophysics Data System (ADS)

Metastable chlorine ions (Cl+*) were detected in time-modulated inductively coupled plasma bya time-resolved laser-induced fluorescence technique.By varying the rf power, gas pressure and modulationfrequency, the Cl+* density was measured in detail.In the discharge-on period, the Cl+* density increasedas the rf power increased.In the discharge-off period, the rf power decreased within 1 µs,however, the Cl+* density decreased more slowly and persisted for a while.The decay constant was evaluated to be around 10 µs by fitting the decay curve under our experimental conditions.In addition, the diffusion coefficient of Cl+* was also estimated.

Kumagai, Shinya; Sasaki, Minoru; Koyanagi, Mitsumasa; Hane, Kazuhiro

1999-12-01

218

Time-resolved x-ray absorption spectroscopy apparatus using laser plasma as an x-ray source  

Microsoft Academic Search

A time-resolved x-ray absorption spectroscopy apparatus on a laboratory scale is being prepared which utilizes a laser plasma as an x-ray source. One of the major aims imposed on this apparatus is to observe x-ray absorption or reflection spectra of various materials in an energy region from 100 eV up to 3 keV. For this purpose, two sets of optical

Osamu Yoda; Atsumi Miyashita; Kouichi Murakami; Sadao Aoki; Naohiro Yamaguchi

1991-01-01

219

Time-resolved evanescent wave absorption spectroscopy for real-time monitoring of heme protein adsorption to glass  

Microsoft Academic Search

Evanescent wave has been recognized as a highly sensitive optical probe for surface monitoring. By use of slab optical waveguides, time-resolved evanescent wave absorption spectroscopy was developed for the investigation of the interfacial behavior of biomolecules with a chromophore. In this study, 30-?m thick glass sheets served as freestanding multimode waveguides that were combined with a simple fiber-coupling method to

Zhi-Mei Qi; Shanhong Xia; Naoki Matsuda

2008-01-01

220

Picosecond Dynamics of G-Protein Coupled Receptor Activation in Rhodopsin from Time-Resolved UV Resonance Raman Spectroscopy †  

Microsoft Academic Search

The protein response to retinal chromophore isomerization in the visual pigment rhodopsin is studied using picosecond time-resolved UV resonance Raman spectroscopy. High signal-to-noise Raman spectra are obtained using a 1 kHz Ti:Sapphire laser apparatus that provides <3 ps visible (466 nm) pump and UV (233 nm) probe pulses. When there is no time delay between the pump and probe events,

Judy E. Kim; Duohai Pan; Richard A. Mathies

2003-01-01

221

Time-resolved laser optogalvanic spectroscopy of iodine in a radio frequency discharge  

Microsoft Academic Search

Pulsed laser optogalvanic (LOG) spectra of iodine vapor in a \\/similar to\\/32 MHz rf discharge were excited at 14 900--17 100 cm⁻¹. Two distinct, time-resolved components were observed: a fast component, synchronous with the laser pulse, width \\/similar to\\/1 ..mu..s, followed by a slow component, width \\/similar to\\/100 ..mu..s, delayed relative to the laser pulse. The fast component exhibits atomic

D. Kumar; P. L. Clancy; S. P. McGlynn

1989-01-01

222

Detection of ClSO with time-resolved Fouriertransform infrared absorption spectroscopy  

Microsoft Academic Search

ClSO was produced as an intermediate upon irradiating a flowing mixture of Cl2SO and Ar with a KrF excimer laser at 248 nm. A step-scan Fourier-transform infrared spectrometer coupled with a small multipass absorption cell was employed to detect time-resolved absorption spectrum of ClSO. A transient spectrum in the region 1120-1200 cm-1, which diminished on prolonged reaction, is assigned to

Li-Kang Chu; Yuan-Pern Lee; Eric Y. Jiang

2004-01-01

223

Time-resolved two-dimensional plasma spectroscopy using coherence-imaging techniques  

Microsoft Academic Search

We describe methods for time-resolved imaging of the complex coherence of a spectral scene at one or more optical delays using electro-optically modulated polarization interferometers. By encoding the coherence information at harmonics of the electro-optic modulation frequency, it can be possible to obtain unambiguous spatio-temporal information about important physical parameters that govern the spectral content of the scene. We discuss

J. Howard; C. Michael; F. Glass; A. Danielsson

2003-01-01

224

Spin and beat phenomena in time-resolved Hubble Space Telescope UV spectroscopy of PQ GEM  

Microsoft Academic Search

Results of the first low-resolution (6 Angstroms), time-resolved Hubble Space Telescope (HST) Faint Object Spectrograph (FOS) observation of the prototypical strong-field intermediate polar system, PQ Gem, are presented. The lambdalambda1150-2600 continuum light curve is dominated by the 13.9-min rotational signature of the white dwarf at all UV wavelengths covered, with a broadly constant fractional modulation depth. The rotational profile contains

D. Stavroyiannopoulos; S. R. Rosen; M. G. Watson; K. O. Mason; S. B. Howell

1997-01-01

225

Steady-state and time-resolved spectroscopy of porous silicon  

Microsoft Academic Search

We present experimental data on steady-state properties, time-resolved properties and on polarization characteristics of porous silicon photoluminescence and models for the decay processes of the red-orange band. The manifold manifestation of inhomogeneous broadening of this band in emission, excitation, polarization, kinetics and degradation supports the model in which porous silicon is treated as a network of crystallites connected via an

S. V. Gaponenko; E. P. Petrov; U. Woggon; O. Wind; C. Klingshirn; Y. H. Xie; I. N. Germanenko; A. P. Stupak

1996-01-01

226

Time-resolved spectroscopy in ZnWO4 and ZnWO4 : Fe  

NASA Astrophysics Data System (ADS)

Time-resolved luminescence and absorption of ZnWO4 and ZnWO4:Fe have been studied. The fast decaying luminescence at similar to 1.7 eV is attributed to either Fe2+ or a Fe3+ related center. The two observed stages in luminescence decay kinetics under ionising radiation are suggested to be due to two types of self-trapped excitons.

Grigorjeva, L.; Pankratov, V.; Millers, D.; Chernov, S.; Nagirnyi, V.; Kotlov, A.; Watterich, A.

2003-01-01

227

Quantifying the cerebral metabolic rate of oxygen by combining diffuse correlation spectroscopy and time-resolved near-infrared spectroscopy.  

PubMed

Preterm infants are highly susceptible to ischemic brain injury; consequently, continuous bedside monitoring to detect ischemia before irreversible damage occurs would improve patient outcome. In addition to monitoring cerebral blood flow (CBF), assessing the cerebral metabolic rate of oxygen (CMRO2) would be beneficial considering that metabolic thresholds can be used to evaluate tissue viability. The purpose of this study was to demonstrate that changes in absolute CMRO2 could be measured by combining diffuse correlation spectroscopy (DCS) with time-resolved near-infrared spectroscopy (TR-NIRS). Absolute CBF was determined using bolus-tracking TR-NIRS to calibrate the DCS measurements. Cerebral venous blood oxygenation (SvO2) was determined by multiwavelength TR-NIRS measurements, the accuracy of which was assessed by directly measuring the oxygenation of sagittal sinus blood. In eight newborn piglets, CMRO2 was manipulated by varying the anesthetics and by injecting sodium cyanide. No significant differences were found between the two sets of SvO2 measurements obtained by TR-NIRS or sagittal sinus blood samples and the corresponding CMRO2 measurements. Bland-Altman analysis showed a mean CMRO2 difference of 0.0268 ± 0.8340 mLO2/100 g/min between the two techniques over a range from 0.3 to 4 mL O2/100 g/min. PMID:23389684

Verdecchia, Kyle; Diop, Mamadou; Lee, Ting-Yim; St Lawrence, Keith

2013-02-01

228

Quantifying the cerebral metabolic rate of oxygen by combining diffuse correlation spectroscopy and time-resolved near-infrared spectroscopy  

NASA Astrophysics Data System (ADS)

Preterm infants are highly susceptible to ischemic brain injury; consequently, continuous bedside monitoring to detect ischemia before irreversible damage occurs would improve patient outcome. In addition to monitoring cerebral blood flow (CBF), assessing the cerebral metabolic rate of oxygen (CMRO2) would be beneficial considering that metabolic thresholds can be used to evaluate tissue viability. The purpose of this study was to demonstrate that changes in absolute CMRO2 could be measured by combining diffuse correlation spectroscopy (DCS) with time-resolved near-infrared spectroscopy (TR-NIRS). Absolute CBF was determined using bolus-tracking TR-NIRS to calibrate the DCS measurements. Cerebral venous blood oxygenation (SvO2) was determined by multiwavelength TR-NIRS measurements, the accuracy of which was assessed by directly measuring the oxygenation of sagittal sinus blood. In eight newborn piglets, CMRO2 was manipulated by varying the anesthetics and by injecting sodium cyanide. No significant differences were found between the two sets of SvO2 measurements obtained by TR-NIRS or sagittal sinus blood samples and the corresponding CMRO2 measurements. Bland-Altman analysis showed a mean CMRO2 difference of 0.0268±0.8340 mL O2/100 g/min between the two techniques over a range from 0.3 to 4 mL O2/100 g/min.

Verdecchia, Kyle; Diop, Mamadou; Lee, Ting-Yim; St. Lawrence, Keith

2013-02-01

229

Time-resolved fluorescence studies of surface recombination in CdSe electrodes. Technical progress.  

National Technical Information Service (NTIS)

The long range goal of our investigations is to understand the dynamics of heterogeneous electron transfer reactions. The primary method we use to monitor the carrier dynamics is the fluorescence of the bandgap emission. This all optical approach circumve...

1991-01-01

230

Active illumination for wide-field time-resolved fluorescence imaging  

NASA Astrophysics Data System (ADS)

The large dynamic range of fluorescence emission collected is one of the major challenges in wide-field fluorescence lifetime imaging. To overcome this challenge, we developed an active illumination strategy to acquire optimal fluorescence signals over the sample imaged even in the presence of large fluorophore concentration distributions. We validated the stability of our approach in a multi-well plate setting with fluorophore concentrations ranging <2 orders of magnitude. We report the ability of our method to retrieve accurately the lifetime over this concentration range based on optimized wide-field data. Our results demonstrate that active wide-field illumination can improve the signal-to-noise ratio and weak-signal sensitivity for enhanced accuracy of fluorescence decay curve fitting and lifetime estimation at high acquisition speed.

Zhao, Lingling; Abe, Ken; Barroso, Margarida; Intes, Xavier

2013-06-01

231

Cucurbiturils: molecular nanocapsules for time-resolved fluorescence-based assays  

Microsoft Academic Search

A new fluorescent host-guest system based on the inclusion of the fluorophore 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) into the cavity of the molecular container compound cucurbit[7]uril (CB7) has been designed which possesses an exceedingly long-lived emission (690 ns in aerated water). The large binding constant of (4±1)×105 M-1 along with the resistance of the CB7·DBO complex toward external fluorescence quenchers allow the use

Cesar Marquez; Fang Huang; Werner M. Nau

2004-01-01

232

Novel flashlamp-based time-resolved fluorescence microscope reduces autofluorescence for 30-fold contrast enhancement in environmental samples  

NASA Astrophysics Data System (ADS)

The abundance of naturally fluorescing components (autofluorophors) encountered in environmentally sourced samples can greatly hinder the detection and identification of fluorescently labeled target using fluorescence microscopy. Time-resolved fluorescence microscopy (TRFM) is a technique that reduces the effects of autofluorescence through precisely controlled time delays. Lanthanide chelates have fluorescence lifetimes many orders of magnitude greater than typical autofluorophors, and persist in their luminescence long after autofluorescence has ceased. An intense short pulse of (UV) light is used to excite fluorescence in the sample and after a short delay period the longer persisting fluorescence from the chelate is captured with an image-intensified CCD camera. The choice of pulsed excitation source for TRFM has a large impact on the price and performance of the instrument. A flashlamp with a short pulse duration was selected for our instrument because of the high spectral energy in the UV region and short pulse length. However, flash output decays with an approximate lifetime of 18?s and the TRFM requires a long-lived chelate to ensure probe fluorescence is still visible after decay of the flash plasma. We synthesized a recently reported fluorescent chelate (BHHCT) and conjugated it to a monoclonal antibody directed against the water-borne parasite Giardia lamblia. Fluorescence lifetime of the construct was determined to be 339?s +/- 14?s and provided a 45-fold enhancement of labeled Giardia over background using a gate delay of 100?s. Despite the sub-optimal decay characteristics of the light pulse, flashlamps have many advantages compared to optical chopper wheels and modulated lasers. Their low cost, lack of vibration, ease of interface and small footprint are important factors to consider in TRFM design.

Connally, Russell; Veal, Duncan; Piper, James A.

2003-07-01

233

Single-label kinase and phosphatase assays for tyrosine phosphorylation using nanosecond time-resolved fluorescence detection.  

PubMed

The collision-induced fluorescence quenching of a 2,3-diazabicyclo[2.2.2]oct-2-ene-labeled asparagine (Dbo) by hydrogen atom abstraction from the tyrosine residue in peptide substrates was introduced as a single-labeling strategy to assay the activity of tyrosine kinases and phosphatases. The assays were tested for 12 different combinations of Dbo-labeled substrates and with the enzymes p60c-Src Src kinase, EGFR kinase, YOP protein tyrosine phosphatase, as well as acid and alkaline phosphatases, thereby demonstrating a broad application potential. The steady-state fluorescence changed by a factor of up to 7 in the course of the enzymatic reaction, which allowed for a sufficient sensitivity of continuous monitoring in steady-state experiments. The fluorescence lifetimes (and intensities) were found to be rather constant for the phosphotyrosine peptides (ca. 300 ns in aerated water), while those of the unphosphorylated peptides were as short as 40 ns (at pH 7) and 7 ns (at pH 13) as a result of intramolecular quenching. Owing to the exceptionally long fluorescence lifetime of Dbo, the assays were alternatively performed by using nanosecond time-resolved fluorescence (Nano-TRF) detection, which leads to an improved discrimination of background fluorescence and an increased sensitivity. The potential for inhibitor screening was demonstrated through the inhibition of acid and alkaline phosphatases by molybdate. PMID:18044894

Sahoo, Harekrushna; Hennig, Andreas; Florea, Mara; Roth, Doris; Enderle, Thilo; Nau, Werner M

2007-11-29

234

Monitoring on-chip Pictet-Spengler reactions by integrated analytical separation and label-free time-resolved fluorescence.  

PubMed

High-throughput screening for optimal reaction conditions and the search for efficient catalysts is of eminent importance in the development of chemical processes and for expanding the spectrum of synthetic methodologies in chemistry. In this context we report a novel approach for a microfluidic chemical laboratory integrating organic synthesis, separation and time-resolved fluorescence detection on a single microchip. The feasibility of our integrated laboratory is demonstrated by monitoring the formation of tetrahydroisoquinoline derivatives by Pictet-Spengler condensation. After on-chip reaction the products and residual starting material were separated enantioselectively on the same chip. On-chip deep UV laser-induced fluorescence detection with time-correlated single photon counting was applied for compound assignment. The system was utilized to screen reaction conditions and various substrates for Pictet-Spengler reactions on-chip. Finally, the microlab was successfully applied to investigate enantioselective reactions using BINOL-based phosphoric acids as organocatalysts. PMID:22179940

Ohla, Stefan; Beyreiss, Reinhild; Fritzsche, Stefanie; Glaser, Petra; Nagl, Stefan; Stockhausen, Kai; Schneider, Christoph; Belder, Detlev

2011-12-16

235

Time-resolved fluorescence resonance energy transfer as a versatile tool in the development of homogeneous cellular kinase assays.  

PubMed

Homogeneous cellular assays can streamline product detection in the drug discovery process. One commercially available assay employing time-resolved fluorescence resonance energy transfer (TR-FRET) that detects phosphorylated products was used to evaluate inhibitors of the receptor tyrosine kinase AXL in a cell line expressing an AXL-green fluorescent protein fusion protein. This TR-FRET assay was modified to evaluate the phosphorylation state of the AXL family member MER in a cell line expressing MER with a V5 tag by adding a fluorescein-labeled anti-V5 antibody. This homogeneous cellular assay was further modified to evaluate the nonreceptor tyrosine kinase focal adhesion kinase (FAK) in cell lines that expressed an untagged kinase by the inclusion of a commercially available anti-FAK antibody conjugated with an acceptor dye. The methods described here can be further adapted for TR-FRET detection of other cellular kinase activities. PMID:22428805

Saville, Lisa; Spais, Chrysanthe; Mason, Jennifer L; Albom, Mark S; Murthy, Seetha; Meyer, Sheryl L; Ator, Mark A; Angeles, Thelma S; Husten, Jean

2012-03-19

236

Time-resolved and temperature-dependent fluorescence spectra of anthracene and pyrene in crystalline and liquid states  

SciTech Connect

Excimer states of anthracene have been found not only in the cyrstalline phase at high temperatures but also in the liquid phase by observing stationary and time-resolved fluorescence spectra. Fluorescence decay times in the liquid phase are very short, 0.2-0.3 ns, without any emission wavelength dependence even at the excimer band. On the other hand, there seems to appear a separate component around the excimer band of pyrene liquid, of which the origin is tentatively assigned to a monomer emission band. The change of profiles in Raman spectra of anthracene at the transition from crystal to liquid has been observed and discussed in relation to the disordered and/or ordered structures.

Horiguchi, R.; Iwasaki, N.; Maruyama, Y.

1987-09-10

237

Dynamic structural changes in microbial membranes in response to high hydrostatic pressure analyzed using time-resolved fluorescence anisotropy measurement.  

PubMed

High hydrostatic pressure has a profound physiological impact on lipid membranes, primarily resulting in tighter packing and restriction of acyl-chain motion. To fulfill membrane protein functions in high-pressure environments, deep-sea organisms possess specialized cell membranes. Although the effects of high-pressure on model membranes have been investigated in great detail, high-pressure-induced structural changes in living cell membranes remain to be elucidated. Of the spectroscopic techniques available to date, fluorescence anisotropy measurement is a common useful method that provides information on dynamic membrane properties. This mini-review focuses on pressure-induced changes in natural cell membranes, analyzed by means of high-pressure time-resolved fluorescence anisotropy measurement (HP-TRFAM). Specifically, the role of eicosapentaenoic acid in deep-sea piezophiles is described in terms of the structural integrity of the membrane under high pressure. PMID:23790318

Abe, Fumiyoshi

2013-05-29

238

Time-autocorrelated two-photon counting technique for time-resolved fluorescence measurements  

NASA Astrophysics Data System (ADS)

We describe a new instrumental technique for the excitation, acquisition, and analysis of fluorescence decays from a variety of substances, in the present case plastic scintillators. The fluorescence is excited by ? particles from a radioactive source (100 ?Ci Sr-90). A random photon from the resulting fluorescence decay provides a trigger pulse to start a time-to-amplitude converter (TAC), while another random photon from the same ?-excitation event provides the stop pulse. The optical components and geometry for detecting these two photons, i.e., the two photomultipliers (PMT), the filters, and the pulse counting system, are identical. As a consequence, the measured fluorescence signal is the autocorrelation function of the fluorescence decay from the sample. A delay line of 50 ns is inserted between the ``stop'' signal PMT and the TAC so that those ``stop'' pulses which arrive before ``start pulses'' also are recorded. Thus the acquired fluorescence signal versus time is symmetric about the delay time and contains twice as many counts as without delay. We call the new technique the ``time-autocorrelated two-photon counting technique'' (TATPC) in distinction to the conventional ``time-correlated single-photon counting technique'' (TCSPC). We compared both techniques with the same equipment and scintillators, where in the TCSPC case, a ? particle is used for the start of the TAC instead of a random photon in the TATPC technique. We find that under similar experimental circumstances, the signal count rate with TATPC is about 50 times larger than with TCSPC. The new method is well suited for obtaining fluorescence decay times from plastic scintillators, which we use in this article to exemplify the technique. More generally, ?-particle excitation in combination with TATPC should prove useful for materials with high energy levels or band gaps, which cannot be excited with pulsed lasers in the visible region. The length of our excitation pulse is less than 20 ps and is negligible compared to the temporal response of about 1 ns of the rest of the apparatus. By employing mathematical deconvolution, we are able to measure fluorescence decays from the subnanosecond range and to longer times.

Borst, Walter L.; Liu, Lin-I.

1999-01-01

239

Characterization of the Dynamics of an Essential Helix in the U1A Protein by Time-Resolved Fluorescence Measurements†  

PubMed Central

The RNA recognition motif (RRM), one of the most common RNA-binding domains, recognizes single-stranded RNA. A C-terminal helix that undergoes conformational changes upon binding is often an important contributor to RNA recognition. The N-terminal RRM of the U1A protein contains a C-terminal helix (helix C) that interacts with the RNA-binding surface of a ?-sheet in the free protein (closed conformation), but is directed away from this ?-sheet in the complex with RNA (open conformation). The dynamics of helix C in the free protein have been proposed to contribute to binding affinity and specificity. We report here a direct investigation of the dynamics of helix C in the free U1A protein on the nanosecond time scale using time-resolved fluorescence anisotropy. The results indicate that helix C is dynamic on a 2–3 ns time scale within a 20° range of motion. Steady-state fluorescence experiments and molecular dynamics simulations suggest that the dynamical motion of helix C occurs within the closed conformation. Mutation of a residue on the ?-sheet that contacts helix C in the closed conformation dramatically destabilizes the complex (Phe56Ala) and alters the steady-state fluorescence, but not the time-resolved fluorescence anisotropy, of a Trp in helix C. Mutation of Asp90 in the hinge region between helix C and the remainder of the protein to Ala or Gly subtly alters the dynamics of the U1A protein and destabilizes the complex. Together these results show that helix C maintains a dynamic closed conformation that is stable to these targeted protein modifications and does not equilibrate with the open conformation on the nanosecond time scale.

Anunciado, Divina; Agumeh, Michael; Kormos, Bethany L.; Beveridge, David L.; Knee, Joseph L.; Baranger, Anne M.

2008-01-01

240

Low-temperature time-resolved vacuum UV spectroscopy of NH4H2PO4 crystals  

NASA Astrophysics Data System (ADS)

A complex investigation of the dynamics of electronic excitations in nonlinear optical crystals of ammonium dihydrophosphate NH4H2PO4 was performed using low-temperature vacuum UV luminescence spectroscopy with time resolution upon selective photoexcitation by synchrotron radiation. Data on the photoluminescence decay kinetics, time-resolved photoluminescence spectra (2-6.2 eV), and time-resolved photoluminescence excitation spectra (4-24 eV) were obtained for the first time for NH4H2PO4 crystals at 8 K. It is ascertained that the photoluminescence of NH4H2PO4 crystals in the vicinity of 4.7 eV has intrinsic character due to the radiative annihilation of self-trapped excitons. Possible channels of generation and decay of relaxed and unrelaxed electronic excitations in NH4H2PO4 crystals are discussed.

Ogorodnikov, I. N.; Pustovarov, V. A.; Kirm, M.; Cheremnykh, V. S.

2004-08-01

241

Time-resolved Raman spectroscopy applied to the photoinduced phenomena in NaV2O5  

NASA Astrophysics Data System (ADS)

Picosecond time resolved Raman scattering measurements were performed in a spin ladder system ?'-NaV2O5. We observed the decrease and recovery of the superstructure peak at 66 cm-1 in the low temperature phase by photoexcitation. The transient local temperature of the sample by photoexcitation was obtained from the intensity ratio of the anti-Stokes and Stokes scattering. It is found that the highest temperature of 23 K induced by the optical pumping is far below the phase transition temperature of 34 K. The temporal changes of the Raman scattering intensities are ascribed to the decrease of the order parameter in the superlattice structure induced by optical pumping in the low temperature phase. We demonstrate a high potentiality of time-resolved Raman scattering spectroscopy for investigating the photoinduced phenomena.

Nakajima, Makoto; Kazumi, Kenji; Isobe, Masahiko; Ueda, Yutaka; Suemoto, Tohru

2005-01-01

242

A dissociative fluorescence enhancement technique for one-step time-resolved immunoassays  

PubMed Central

The limitation of current dissociative fluorescence enhancement techniques is that the lanthanide chelate structures used as molecular probes are not stable enough in one-step assays with high concentrations of complexones or metal ions in the reaction mixture since these substances interfere with lanthanide chelate conjugated to the detector molecule. Lanthanide chelates of diethylenetriaminepentaacetic acid (DTPA) are extremely stable, and we used EuDTPA derivatives conjugated to antibodies as tracers in one-step immunoassays containing high concentrations of complexones or metal ions. Enhancement solutions based on different ?-diketones were developed and tested for their fluorescence-enhancing capability in immunoassays with EuDTPA-labelled antibodies. Characteristics tested were fluorescence intensity, analytical sensitivity, kinetics of complex formation and signal stability. Formation of fluorescent complexes is fast (5 min) in the presented enhancement solution with EuDTPA probes withstanding strong complexones (ethylenediaminetetra acetate (EDTA) up to 100 mM) or metal ions (up to 200 ?M) in the reaction mixture, the signal is intensive, stable for 4 h and the analytical sensitivity with Eu is 40 fmol/L, Tb 130 fmol/L, Sm 2.1 pmol/L and Dy 8.5 pmol/L. With the improved fluorescence enhancement technique, EDTA and citrate plasma samples as well as samples containing relatively high concentrations of metal ions can be analysed using a one-step immunoassay format also at elevated temperatures. It facilitates four-plexing, is based on one chelate structure for detector molecule labelling and is suitable for immunoassays due to the wide dynamic range and the analytical sensitivity. Figure  

Mukkala, Veli-Matti; Hakala, Harri H. O.; Makinen, Pauliina H.; Suonpaa, Mikko U.; Hemmila, Ilkka A.

2010-01-01

243

Equilibrium between quenched and nonquenched conformations of the major plant light-harvesting complex studied with high-pressure time-resolved fluorescence  

Microsoft Academic Search

Nonphotochemical quenching (NPQ) of chlorophyll fluorescence plays an important role in the protection of plants against excessive light. Fluorescence quenching of the major light-harvesting complex (LHCII) provides a model system to study the mechanism of NPQ. The existence of both quenched and nonquenched states of LHCII has been postulated. We used time-resolved fluorescence and hydrostatic pressure to study differences between

Oort van B. F; Arie van Hoek; Alexander V. Ruban; Herbert van Amerongen

2007-01-01

244

A Theoretical Distinction Between Time-Resolved Resonance Raman and Resonance Fluorescence  

NASA Astrophysics Data System (ADS)

Based on the time-dependent theory, an analysis of the distinction between resonance Raman (RR) and resonance fluorescence (RF) with pulse excitation was presented. The real population of the intermediate state gives two optical components-the independent time evolution of intermediate ket and bra states generates RR while RF originates from the phase coherent between ket and bra states. In cw limit, the transition probability of spontaneous emission with pulse excitation can be reduced to the classical theory.

Lu, Jing; Du, Si-De; Fan, Kang-Nian; Lee, Soo-Ying

2000-04-01

245

Gene expression analysis with an integrated CMOS microarray by time-resolved fluorescence detection  

PubMed Central

DNA microarrays have proven extraordinarily powerful for differential expression studies across thousands of genes in a single experiment. Microarrays also have the potential for clinical applications, including the detection of infectious and immunological diseases and cancer, if they can be rendered both reliable and cost-effective. Here we report the first practical application of an active microarray based on integrated circuit technology, completely obviating the need for external measurement instrumentation while employing protocols compatible with traditional fluorescence-based surface bioassays. In a gene-expression biodosimetry study, we determine the differential activity of genes from leucocytes in irradiated human blood. Quantum dots are used as fluorescence labels to realize filterless, time-gated fluorescence detection on an active complementary metal-oxide-semiconductor (CMOS) microarray with 100-pM sensitivity. Improvements in surface chemistry should allow sensitivities that approach the microarray hardware limit of less than 10 pM. Techniques for covalent attachment of DNA capture strands to the CMOS active microarrays allow integrated sensors to be placed in immediate proximity to hybridized analyte strands, maximizing photon collection efficiencies.

Huang, Ta-chien D.; Paul, Sunirmal; Gong, Ping; Levicky, Rastislav; Kymissis, John; Amundson, Sally A.; Shepard, Kenneth L.

2010-01-01

246

Time-resolved Ultraviolet Spectroscopy of the GJ 876 Exoplanetary System  

NASA Astrophysics Data System (ADS)

Extrasolar planets orbiting M-stars may represent our best chance to discover habitable worlds in the coming decade. The ultraviolet spectrum incident upon both Earth-like and Jovian planets is critically important for proper modeling of their atmospheric heating and chemistry. In order to provide a more realistic input for atmospheric models of planets orbiting low-mass stars, we present new near- and far-ultraviolet spectroscopy of the M-dwarf exoplanet host GJ 876 (M4V). Using the COS and STIS spectrographs aboard the Hubble Space Telescope, we have characterized the 1150-3140A spectrum of GJ 876. We have reconstructed the stellar HI LyA emission line profile, and find that the integrated LyA flux is roughly twice the rest of the integrated flux in the 1150-3140A ultraviolet bandpass (F(LyA)/F(FUV+NUV) 2). This LyA/(FUV+NUV) ratio is approximately four orders of magnitude greater than the solar value. We present a description of the ultraviolet line spectrum and report surprisingly strong fluorescent emission from hot H2 (T > 2000 K). We describe the light-curve of a chromospheric + transition region flare observed in several far-UV emission lines, with flare/quiescent ratios > 10. The strong far-ultraviolet radiation field of an M-star (and specifically LyA) may be important for determining the abundance of O2 in the lower atmosphere, and the formation of biomarkers, for Earth-like planets in the habitable zones of low-mass stars.

France, Kevin; Tian, F.; Linsky, J. L.; Froning, C. S.; Roberge, A.; Stocke, J. T.

2012-05-01

247

TIME-RESOLVED ULTRAVIOLET SPECTROSCOPY OF THE M-DWARF GJ 876 EXOPLANETARY SYSTEM  

SciTech Connect

Extrasolar planets orbiting M-stars may represent our best chance to discover habitable worlds in the coming decade. The ultraviolet spectrum incident upon both Earth-like and Jovian planets is critically important for proper modeling of their atmospheric heating and chemistry. In order to provide more realistic inputs for atmospheric models of planets orbiting low-mass stars, we present new near- and far-ultraviolet (NUV and FUV) spectroscopy of the M-dwarf exoplanet host GJ 876 (M4V). Using the COS and STIS spectrographs on board the Hubble Space Telescope, we have measured the 1150-3140 A spectrum of GJ 876. We have reconstructed the stellar H I Ly{alpha} emission line profile, and find that the integrated Ly{alpha} flux is roughly equal to the rest of the integrated flux (1150-1210 A + 1220-3140 A) in the entire ultraviolet bandpass (F(Ly{alpha})/F(FUV+NUV) Almost-Equal-To 0.7). This ratio is {approx}2500 Multiplication-Sign greater than the solar value. We describe the ultraviolet line spectrum and report surprisingly strong fluorescent emission from hot H{sub 2} (T(H{sub 2}) > 2000 K). We show the light curve of a chromospheric + transition region flare observed in several far-UV emission lines, with flare/quiescent flux ratios {>=}10. The strong FUV radiation field of an M-star (and specifically Ly{alpha}) is important for determining the abundance of O{sub 2}-and the formation of biomarkers-in the lower atmospheres of Earth-like planets in the habitable zones of low-mass stars.

France, Kevin; Froning, Cynthia S. [Center for Astrophysics and Space Astronomy, University of Colorado, 389 UCB, Boulder, CO 80309 (United States); Linsky, Jeffrey L. [JILA, University of Colorado and NIST, 440 UCB, Boulder, CO 80309 (United States); Tian, Feng [Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO 80309 (United States); Roberge, Aki, E-mail: kevin.france@colorado.edu [Exoplanets and Stellar Astrophysics Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)

2012-05-10

248

Time-resolved Ultraviolet Spectroscopy of the M-dwarf GJ 876 Exoplanetary System  

NASA Astrophysics Data System (ADS)

Extrasolar planets orbiting M-stars may represent our best chance to discover habitable worlds in the coming decade. The ultraviolet spectrum incident upon both Earth-like and Jovian planets is critically important for proper modeling of their atmospheric heating and chemistry. In order to provide more realistic inputs for atmospheric models of planets orbiting low-mass stars, we present new near- and far-ultraviolet (NUV and FUV) spectroscopy of the M-dwarf exoplanet host GJ 876 (M4V). Using the COS and STIS spectrographs on board the Hubble Space Telescope, we have measured the 1150-3140 Å spectrum of GJ 876. We have reconstructed the stellar H I Ly? emission line profile, and find that the integrated Ly? flux is roughly equal to the rest of the integrated flux (1150-1210 Å + 1220-3140 Å) in the entire ultraviolet bandpass (F(Ly?)/F(FUV+NUV) ? 0.7). This ratio is ~2500× greater than the solar value. We describe the ultraviolet line spectrum and report surprisingly strong fluorescent emission from hot H2 (T(H2) > 2000 K). We show the light curve of a chromospheric + transition region flare observed in several far-UV emission lines, with flare/quiescent flux ratios >=10. The strong FUV radiation field of an M-star (and specifically Ly?) is important for determining the abundance of O2—and the formation of biomarkers—in the lower atmospheres of Earth-like planets in the habitable zones of low-mass stars. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

France, Kevin; Linsky, Jeffrey L.; Tian, Feng; Froning, Cynthia S.; Roberge, Aki

2012-05-01

249

Fluorescence spectroscopy of peptides.  

PubMed

In peptides, steady-state fluorescence can be used to measure the intrinsic fluorescence of Trp, Tyr, and Phe residues, as well as associated dyes, which can change upon exposure to different environmental conditions. This technique can be thus used to detect changes in the conformational states of peptides. Time-resolved fluorescence can also be used to study fast motions of peptides and their interactions with fluorescence dyes. Data from several low-resolution spectroscopic techniques, including fluorescence, can be combined to generate an overall picture of peptide structure as a function of environmental conditions. PMID:24146408

Liyanage, Mangala R; Bakshi, Kunal; Volkin, David B; Middaugh, C Russell

2014-01-01

250

A novel luminescent terbium-3-carboxycoumarin probe for time-resolved fluorescence sensing of pesticides methomyl, aldicarb and prometryne.  

PubMed

The luminescence arising from lanthanide cations offers several advantages over organic fluorescent molecules: sharp, distinctive emission bands allow for easy resolution between multiple lanthanide signals; long emission lifetimes (?s-ms) make them excellent candidates for time-resolved measurements; and high resistance to photo bleaching allow for long or repeated experiments. A time-resolved (gated) luminescence-based method for determination of pesticides methomyl, aldicarb and prometryne in microtiterplate format using the long-lived terbium-3-carboxycoumarin in 1:3 metal:ligand ratio has been developed. The limit of detection is 1.20×10(6), 5.19×10(5) and 2.74×10(6)ng L(-1) for methomyl, prometryne and aldicarb, respectively. The quantum yield (QY=0.08) of Tb(III)-3-carboxycoumarin was determined using 3-(2-benzothiazolyl)-7-diethylamino-coumarin (coumarin 6). Stern-volmer studies at different temperatures indicate that collisional quenching dominates for methomyl, aldicarb and prometryne. Binding constants were determined at 303, 308 and 313 K by using Lineweaver-Burk equation. A thermodynamic analysis showed that the reaction is spontaneous with negative ?G. Effect of some relevant interferents on the detection of pesticides has been investigated. PMID:22906968

Azab, Hassan A; Duerkop, Axel; Saad, E M; Awad, F K; Abd El Aal, R M; Kamel, Rasha M

2012-07-31

251

A novel luminescent terbium-3-carboxycoumarin probe for time-resolved fluorescence sensing of pesticides methomyl, aldicarb and prometryne  

NASA Astrophysics Data System (ADS)

The luminescence arising from lanthanide cations offers several advantages over organic fluorescent molecules: sharp, distinctive emission bands allow for easy resolution between multiple lanthanide signals; long emission lifetimes (?s-ms) make them excellent candidates for time-resolved measurements; and high resistance to photo bleaching allow for long or repeated experiments. A time-resolved (gated) luminescence-based method for determination of pesticides methomyl, aldicarb and prometryne in microtiterplate format using the long-lived terbium-3-carboxycoumarin in 1:3 metal:ligand ratio has been developed. The limit of detection is 1.20 × 106, 5.19 × 105 and 2.74 × 106 ng L-1 for methomyl, prometryne and aldicarb, respectively. The quantum yield (QY = 0.08) of Tb(III)-3-carboxycoumarin was determined using 3-(2-benzothiazolyl)-7-diethylamino-coumarin (coumarin 6). Stern-volmer studies at different temperatures indicate that collisional quenching dominates for methomyl, aldicarb and prometryne. Binding constants were determined at 303, 308 and 313 K by using Lineweaver-Burk equation. A thermodynamic analysis showed that the reaction is spontaneous with negative ?G. Effect of some relevant interferents on the detection of pesticides has been investigated.

Azab, Hassan A.; Duerkop, Axel; Saad, E. M.; Awad, F. K.; Abd El Aal, R. M.; Kamel, Rasha M.

2012-11-01

252

Nanosecond time-resolved vacuum ultraviolet spectrometer for ion diode spectroscopy  

SciTech Connect

A 1-m normal incidence spectrometer has been modified for use as a diagnostic of ion diode plasmas. To improve instrumental sensitivity, an elliptical mirror images an anode surface plasma onto the entrance slit of an [ital f]/10 normal incidence spectrometer. The detector is a time-resolving copper iodide coated microchannel plate stripline framing camera with 60-[mu]m resolution, limiting instrumental resolution to 1 A with a 600 l/mm grating in first order. Reflectivity of optics and photoelectron efficiency limit the spectral range from 400 to 2000 A. With a 600-l/mm grating the detector spans a 600-A range. Applications of the instrument may include ion source divergence measurements from Doppler broadening, electric field measurements from Stark splittings or shifts, electron temperature from mean ionization state, and magnetic field measurements on high-power [ital Z] pinches from Zeeman splitting.

Nash, T.; Noack, D.; Filuk, A.B. (Sandia National Laboratory, Albuquerque, New Mexico 87185 (United States))

1993-09-01

253

High dynamic range streak camera for subpicosecond time-resolved x-ray spectroscopy  

SciTech Connect

The full characterization of a time resolved x-ray spectrometer is presented. It is based on the coupling of a conical crystal with a subpicosecond x-ray streak camera. The detector is designed to operate in accumulation mode at high repetition rate (up to 1 kHz) allowing signal to noise ratio as high as 10{sup 4}:1. Optical switches have been used to limit the jitter induced in the subpicosecond range, demonstrating the very long term stability (a few hours) of the entire device. The data analysis have been developed to get the spectral and temporal resolution of an ultrashort laser-plasma-based x-ray source.

Bonte, C.; Harmand, M.; Dorchies, F.; Magnan, S.; Pitre, V.; Kieffer, J.-C.; Audebert, P.; Geindre, J.-P. [Universite Bordeaux I, CNRS, CEA, CELIA UMR 5107, 351 cours de la Liberation, Talence, F-33405 (France); I.N.R.S.-Energie, Materiaux et Telecommunications, 1650 boul. Lionel-Boulet, Varennes, Qc, J3X 1S2 (Canada); Laboratoire pour l'Utilisation des Lasers Intenses (LULI), Ecole Polytechnique, 91128 Palaiseau (France)

2007-04-15

254

Time-resolved optical writing on a photosensitive and fluorescent polymer film  

NASA Astrophysics Data System (ADS)

Recently a melt-processed blend of 1,4-bis(?-cyano-4-octadecyloxystyryl)-2,5-dimethoxybenzene (C18-RG) dye and polyethylene terephthalate glycol (PETG) has been demonstrated as a promising 3-dimentional optical data storage (ODS) medium 1. ODS in this novel system relies on the laser-induced switching of the aggregation state of the excimerforming fluorescent dye in the inert host polymer. Here we investigate the mechanism and the time scales involved in the writing process. The optical writing was realized by the laser-induced localized excimer to monomer conversion and was characterized by the emergence of the monomer fluorescence. We obtained the dependence of the excimer to monomer conversion on the writing time. Our result indicates that the effective optical writing time is controlled by heating and cooling time of the host polymer and the excimer-to-monomer conversion time. The effective laser writing time, under the specific writing conditions employed in our experiments, is on the order of 10 ms.

Pan, Z.; Akrobetu, R.; Lott, J.; Ryan, C.; Saini, A.; Shan, J.; Mu, R.; Singer, K. D.; Weder, C.; Morgan, S. H.

2011-09-01

255

Time-resolved chlorophyll fluorescence for early detection of forest decline  

NASA Astrophysics Data System (ADS)

Aiming to an early detection of forest decline, prompt and delayed luminescence of spruce needles was studied from the picosecond to the second time range using novel laser diodes and highly sensitive detection systems. In particular, (1) subnanosecond fluorescence decay measurements showed a superposition of at least three exponentially decaying components, the largest of which (decay time (tau) equals 2.0 - 3.5 ns) represented some `dead' chlorophyll or closed reaction centers. This component is more pronounced in slightly damaged than in healthy spruces and can be used to monitor the early steps of photosynthesis. (2) Delayed luminescence -- which is supposed to report on the electron transport chain as a whole -- could also be correlated with the physiological state of the individual spruce. In general, healthy and declined spruces showed the highest photosynthetic efficiencies during the summer period, but also the most pronounced stress symptoms -- probably due to high irradiance, drought, and increased ozone concentrations.

Schneckenburger, Herbert; Schmidt, Werner

1993-06-01

256

Picosecond time-resolved microspectrofluorometry in live cells exemplified by complex fluorescence dynamics of popular probes ethidium and cyan fluorescent protein.  

PubMed

Time-resolved microspectrofluorometry in live cells, based on time- and space-correlated single-photon counting, is a novel method to acquire spectrally resolved fluorescence decays, simultaneously in 256 wavelength channels. The system is calibrated with a full width at half maximum (FWHM) of 90 ps for the temporal resolution, a signal-to-noise ratio of 10(6), and a spectral resolution of 30 (Deltalambda/Lambda). As an example, complex fluorescence dynamics of ethidium and cyan fluorescent protein (CFP) in live cells are presented. Free and DNA intercalated forms of ethidium are simultaneously distinguishable by their relative lifetime (1.7 ns and 21.6 ns) and intensity spectra (shift of 7 nm). By analysing the complicated spectrally resolved fluorescence decay of CFP, we propose a fluorescence kinetics model for its excitation/desexcitation process. Such detailed studies under the microscope and in live cells are very promising for fluorescence signal quantification. PMID:14731292

Tramier, M; Kemnitz, K; Durieux, C; Coppey-Moisan, M

2004-02-01

257

Using time-resolved fluorescence to measure serum venom-specific IgE and IgG.  

PubMed

We adapted DELFIA™ (dissociation-enhanced lanthanide fluoroimmunoassay), a time resolved fluorescence method, to quantitate whole venom specific and allergenic peptide-specific IgE (sIgE), sIgG(1) and sIgG(4) in serum from people clinically allergic to Australian native ant venoms, of which the predominant cause of allergy is jack jumper ant venom (JJAV). Intra-assay CV was 6.3% and inter-assay CV was 13.7% for JJAV sIgE. DELFIA and Phadia CAP JJAV sIgE results correlated well and had similar sensitivity and specificity for the detection of JJAV sIgE against intradermal skin testing as the gold standard. DELFIA was easily adapted for detecting sIgE to a panel of other native ant venoms. PMID:21304970

van Eeden, Pauline E; Wiese, Michael D; Aulfrey, Susan; Hales, Belinda J; Stone, Shelley F; Brown, Simon G A

2011-01-31

258

Photon counting technique applied to time-resolved laser-induced fluorescence measurements on a stabilized discharge.  

PubMed

A novel approach to perform time-resolved laser-induced fluorescence (LIF) measurements in plasma discharges is presented. The LIF technique relies on a photon counting method associated with a sinusoidal potential modulation on a floating electrode located in the plasma to ensure time coherence. By tuning the modulation frequency, resonance can be reached with the discharge current in order to guarantee repeatable measurement conditions. Time-averaged characteristics of the discharge (such as Te, ne, Vp, and Vion) remain unaffected by the modulation. As an example, the association of the photon counting method with the modulation system is employed to determine the time evolution of several ion velocity groups inside an E × B discharge. Interesting features of the velocity oscillations are examined and pave the way for more focused studies. PMID:23902068

Vaudolon, J; Balika, L; Mazouffre, S

2013-07-01

259

Photon counting technique applied to time-resolved laser-induced fluorescence measurements on a stabilized discharge  

NASA Astrophysics Data System (ADS)

A novel approach to perform time-resolved laser-induced fluorescence (LIF) measurements in plasma discharges is presented. The LIF technique relies on a photon counting method associated with a sinusoidal potential modulation on a floating electrode located in the plasma to ensure time coherence. By tuning the modulation frequency, resonance can be reached with the discharge current in order to guarantee repeatable measurement conditions. Time-averaged characteristics of the discharge (such as Te, ne, Vp, and Vion) remain unaffected by the modulation. As an example, the association of the photon counting method with the modulation system is employed to determine the time evolution of several ion velocity groups inside an E × B discharge. Interesting features of the velocity oscillations are examined and pave the way for more focused studies.

Vaudolon, J.; Balika, L.; Mazouffre, S.

2013-07-01

260

Using Time-Resolved Fluorescence to Measure Serum Venom-Specific IgE and IgG  

PubMed Central

We adapted DELFIA™ (dissociation-enhanced lanthanide fluoroimmunoassay), a time resolved fluorescence method, to quantitate whole venom specific and allergenic peptide-specific IgE (sIgE), sIgG1 and sIgG4 in serum from people clinically allergic to Australian native ant venoms, of which the predominant cause of allergy is jack jumper ant venom (JJAV). Intra-assay CV was 6.3% and inter-assay CV was 13.7% for JJAV sIgE. DELFIA and Phadia CAP JJAV sIgE results correlated well and had similar sensitivity and specificity for the detection of JJAV sIgE against intradermal skin testing as the gold standard. DELFIA was easily adapted for detecting sIgE to a panel of other native ant venoms.

van Eeden, Pauline E.; Wiese, Michael D.; Aulfrey, Susan; Hales, Belinda J.; Stone, Shelley F.; Brown, Simon G. A.

2011-01-01

261

Picosecond time-resolved pure-rotational coherent anti-Stokes Raman spectroscopy for N(2) thermometry.  

PubMed

Time-resolved pure-rotational coherent anti-Stokes Raman spectroscopy using picosecond-duration laser pulses is investigated for gas thermometry. The use of picosecond laser pulses significantly reduces background caused by scattering of the probe beam, and delayed probing of the Raman coherence enables elimination of interference from nonresonant four-wave mixing processes. Temperatures inferred from rotational spectra are sensitive to the probe delay because of the rotational-level dependence of collisional dephasing of Raman coherences. The sensitivity decreases, however, with increasing temperature, and accurate temperature measurements in a flame are demonstrated using a standard frequency-domain analysis of the spectra. PMID:19953185

Seeger, Thomas; Kiefer, Johannes; Leipertz, Alfred; Patterson, Brian D; Kliewer, Christopher J; Settersten, Thomas B

2009-12-01

262

Probing Reaction Dynamics of Transition-Metal Complexes in Solution via Time-Resolved X-ray Spectroscopy  

SciTech Connect

We report measurements of the photo-induced Fe(II) spin crossover reaction dynamics in solution via time-resolved x-ray absorption spectroscopy. EXAFS measurements reveal that the iron?nitrogen bond lengthens by 0.21+-0.03 Angstrom in the high-spin transient excited state relative to the ground state. XANES measurements at the Fe L-edge show directly the influence of the structural change on the ligand-field splitting of the Fe(II) 3d orbitals associated with the spin transition.

Huse, Nils; Khalil, Munira; Kim, Tae Kyu; Smeigh, Amanda L.; Jamula, Lindsey; McCusker, James K.; Schoenlein, Robert W.

2009-05-24

263

Time-resolving molecular vibration for microanalytics: single laser beam nonlinear Raman spectroscopy in simulation and experiment.  

PubMed

A single-beam implementation of coherent anti-Stokes Raman scattering (CARS) allows experimentally very much simplified and flexible approaches to time-resolved vibrational spectroscopy, with the additional benefit of microscopic spatial resolution. To achieve this, a broadband femtosecond laser is combined with a pulse shaper creating tailored pulse sequences by computer control. We discuss the theoretical foundations and technical issues of the technique in detail and show the successful implementation of different schemes for truly femtosecond time-resolved vibrational spectroscopy. Hereby, we elaborate all the details of the method shown earlier in a proof-of-principle study [Von Vacano and Motzkus, Opt. Comm., 2006, 264, 488] and greatly extend it by novel approaches relying on the use of identical double pulses or additional polarization control for background-free spectroscopy with superior robustness and signal-to-noise ratio. Perspectives and applications of the presented schemes for chemical microanalysis and high-contrast chemical imaging are examined. PMID:19791452

von Vacano, Bernhard; Motzkus, Marcus

2008-02-01

264

Time-resolved fluorescence and computational studies of adenylylated glutamine synthetase: analysis of intersubunit interactions.  

PubMed Central

Adenylylation of Tyr-397 of each subunit of Escherichia coli glutamine synthetase (GS) down-regulates enzymatic activity in vivo. The overall structure of the enzyme consists of 12 subunits arranged as two hexamers, face to face. Research reported in this paper addresses the question of whether the covalently attached adenylyl group interacts with neighboring amino acid residues to produce the regulatory phenomenon. Wild-type GS has two Trp residues (positions 57 and 158) and the adenylylation site lies within 7-8 A of the Trp-57 loop in the adjacent subunit of the same hexameric ring; Trp-158 is about 35 A from the site of adenylylation. Fluorescence lifetimes and quantum yields have been determined for two fluorophores with wild-type and mutant GS. One fluorophore is epsilon-AMP adenylylated GS (at Tyr-397), and the other fluorophore is the intrinsic protein residue Trp-57. These experiments were conducted in order to detect possible intersubunit interactions between adenylyl groups and the neighboring Trp-57 to search for a role for the Trp-57 loop in the regulation of GS. The fluorescence due to epsilon-AMP of two adenylylated enzymes, wild-type GS and the W158F mutant, exhibits heterogeneous decay kinetics; the data adequately fit to a double exponential decay model with recovered average lifetime values of 18.2 and 2.1 ns, respectively. The pre-exponential factors range from 0.66 to 0.73 for the long lifetime component, at five emission wavelengths. The W57L-epsilon-AMP enzyme yields longer average lifetime values of 19.5 and 2.4 ns, and the pre-exponential factors range from 0.82 to 0.85 for the long lifetime component. An additional residue in the Trp-57 loop, Lys-58, has been altered and the K58C mutant enzyme has been adenylylated with epsilon-AMP on Tyr-397. Lys-58 is near the ATP binding site and may represent a link by which the adenylyl group controls the activity of GS. The fluorescence of epsilon-AMP-adenylylated K58C mutant GS is best described by a triple exponential decay with average recovered lifetime values of 19.9, 4.6, and 0.58 ns, with the largest fraction being the median lifetime component. Relative quantum yields of epsilon-AMP-Tyr-397 were measured in order to determine if static quenching occurs from adenine-indole stacking in the wild-type GS. The relative quantum yield of the epsilon-AMP-adenylylated W57L mutant is larger than the wild-type protein by the amount predicted from the difference in lifetime values: thus, no static quenching is evident.(ABSTRACT TRUNCATED AT 400 WORDS)

Atkins, W. M.; Cader, B. M.; Hemmingsen, J.; Villafranca, J. J.

1993-01-01

265

Dynamics of nuclear receptor helix-12 switch of transcription activation by modeling time-resolved fluorescence anisotropy decays.  

PubMed

Nuclear hormone receptors (NRs) are major targets for pharmaceutical development. Many experiments demonstrate that their C-terminal Helix (H12) is more flexible in the ligand-binding domains (LBDs) without ligand, this increased mobility being correlated with transcription repression and human diseases. Crystal structures have been obtained in which the H12 is extended, suggesting the possibility of large amplitude H12 motions in solution. However, these structures were interpreted as possible crystallographic artifacts, and thus the microscopic nature of H12 movements is not well known. To bridge the gap between experiments and molecular models and provide a definitive picture of H12 motions in solution, extensive molecular dynamics simulations of the peroxisome proliferator-activated receptor-? LBD, in which the H12 was bound to a fluorescent probe, were performed. A direct comparison of the modeled anisotropy decays to time-resolved fluorescence anisotropy experiments was obtained. It is shown that the decay rates are dependent on the interactions of the probe with the surface of the protein, and display little correlation with the flexibility of the H12. Nevertheless, for the probe to interact with the surface of the LBD, the H12 must be folded over the body of the LBD. Therefore, the molecular mobility of the H12 should preserve the globularity of the LBD, so that ligand binding and dissociation occur by diffusion through the surface of a compact receptor. These results advance the comprehension of both ligand-bound and ligand-free receptor structures in solution, and also guide the interpretation of time-resolved anisotropy decays from a molecular perspective, particularly by the use of simulations. PMID:24094408

Batista, Mariana R B; Martínez, Leandro

2013-10-01

266

Molecular analysis of mitotic chromosome condensation using a quantitative time-resolved fluorescence microscopy assay  

PubMed Central

Chromosomes condense during mitotic entry to facilitate their segregation. Condensation is typically assayed in fixed preparations, limiting analysis of contributing factors. Here, we describe a quantitative method to monitor condensation kinetics in living cells expressing GFP fused to a core histone. We demonstrate the utility of this method by using it to analyze the molecular requirements for the condensation of holocentric chromosomes during the first division of the Caenorhabditis elegans embryo. In control embryos, the fluorescence intensity distribution for nuclear GFP:histone changes during two distinct time intervals separated by a plateau phase. During the first interval, primary condensation converts diffuse chromatin into discrete linear chromosomes. After the plateau, secondary condensation compacts the curvilinear chromosomes to form shorter bar-shaped structures. We quantitatively compared the consequences on this characteristic profile of depleting the condensin complex, the mitosis-specific histone H3 kinase Aurora B, the centromeric histone CENP-A, and CENP-C, a conserved protein required for kinetochore assembly. Both condensin and CENP-A play critical but distinct roles in primary condensation. In contrast, depletion of CENP-C slows but does not prevent primary condensation. Finally, Aurora B inhibition has no effect on primary condensation, but slightly delays secondary condensation. These results provide insights into the process of condensation, help resolve apparent contradictions from prior studies, and indicate that CENP-A chromatin has an intrinsic role in the condensation of holocentric chromosomes that is independent of its requirement for kinetochore assembly.

Maddox, Paul S.; Portier, Nathan; Desai, Arshad; Oegema, Karen

2006-01-01

267

Dynamics of Fluorescence Fluctuations in Green Fluorescent Protein Observed by Fluorescence Correlation Spectroscopy  

Microsoft Academic Search

We have investigated the pH dependence of the dynamics of conformational fluctuations of green fluorescent protein mutants EGFP (F64L\\/S65T) and GFP-S65T in small ensembles of molecules in solution by using fluorescence correlation spectroscopy (FCS). FCS utilizes time-resolved measurements of fluctuations in the molecular fluorescence emission for determination of the intrinsic dynamics and thermodynamics of all processes that affect the fluorescence.

Ulrich Haupts; Sudipta Maiti; Petra Schwille; Watt W. Webb

1998-01-01

268

Time resolved photoelectron spectroscopy of thioflavin T photoisomerization: a simulation study.  

PubMed

The excited state isomerization of thioflavin T (ThT) is responsible for the quenching of its fluorescence in a nonrestricted environment. The fluorescence quantum yield increases substantially upon binding to amyloid fibers. Simulations reveal that the variation of the twisting angle between benzothiazole and benzene groups (?1) is responsible for the subpicosecond fluorescence quenching. The evolution of the twisting process can be directly probed by photoelectron emission with energies ? ? 1.0 eV before the molecule reaches the ?1-twisted configuration (~300 fs). PMID:23517370

Ren, Hao; Fingerhut, Benjamin P; Mukamel, Shaul

2013-04-29

269

Speciation of europium (III) surface species on monocrystalline alumina using time-resolved laser-induced fluorescence-scanning near-field optical microscopy.  

PubMed

The aim of this work was to perform highly localized spectroscopic surface measurements by combining time-resolved laser spectroscopy and scanning near-field optical microscopy. The final purpose of that was to study surface sorption at the molecular level of trivalent ions in the framework of nuclear waste disposal assessment. Time-resolved laser spectroscopy presents the advantages of being selective, sensitive, and noninvasive and scanning near-field optical microscopy is a promising technique for high resolution surface speciation. Investigation of the interaction between trivalent europium and a monocrystalline alumina (1102) surface was made using different conditions of concentration and pH. We found that the distribution of sorbed europium was always homogeneous with a decay time of europium (III) equal to 350 micros+/-15 micros. On the other hand, carbonate species with a decay time of 210 micros+/-10 micros or other hydroxide species with a decay time of 180 micros+/-10 micros were detected on the surface when a higher concentration or a higher pH solution, respectively, were used. Distribution of these species was heterogeneous and their associated fluorescence signal was relatively high, evoking a precipitated form. X-ray photoelectron spectroscopy (XPS) was also used on the same samples as a complementary technique. A binding energy of 1135.1 eV was obtained for the sorbed europium and another binding energy of 1134.4 eV was obtained for the hydroxide species, thus confirming the presence of two kinds of species on the surface. PMID:18284798

Ghaleb, Khalil Abbas; Viala, François; Miserque, Frederic; Salmon, Laurent; Reiller, Pascal; Moutiers, Gilles

2008-02-01

270

Time-resolved high-performance liquid chromatography fluorescence detector using a nanosecond pulsed light source for detecting lanthanide-chelated compounds  

Microsoft Academic Search

We have constructed a time-resolved fluorescence detection (TRFD) system for the analysis of amino compounds with high-performance liquid chromatography (HPLC) using lanthanide ion chelates. In order to carry out time-resolved measurements, we have employed a nanosecond pulsed xenon-arc lamp as an excitation light source. Amino compounds derivatized by isothiocyanobenzyl-EDTA (IEDTA) with the lanthanide chelate are mixed with an enhancer solution

Tetsuo Iwata; Jun Koshoubu; Yasuyuki Kurosu; Tsutomu Araki

1999-01-01

271

Liquid film characterization in horizontal, annular, two-phase, gas–liquid flow using time-resolved laser-induced fluorescence  

Microsoft Academic Search

A non-intrusive optical technique was developed to provide time-resolved longitudinal and cross-sectional images of the liquid\\u000a film in horizontal annular pipe flow of air and water, revealing the interfacial wave behavior. Quantitative information on\\u000a the liquid film dynamics was extracted from the time-resolved images. The planar laser-induced fluorescence technique was\\u000a utilized to allow for optical separation of the light emitted

P. S. C. Farias; F. J. W. A. Martins; L. E. B. Sampaio; R. Serfaty; L. F. A. Azevedo

272

Time-resolved Spectroscopy of the Polar EU Cancri in the Open Cluster Messier 67  

NASA Astrophysics Data System (ADS)

We present time-resolved spectroscopic and polarimetric observations of the AM Her system EU Cnc. EU Cnc is located near the core of the old open cluster Messier 67; new proper motion measurements indicate that EU Cnc is indeed a member of the star cluster, and this system therefore is useful to constrain the formation and evolution of magnetic cataclysmic variables. The spectra exhibit two-component emission features with independent radial velocity variations as well as time-variable cyclotron emission indicating a magnetic field strength of 41 MG. The period of the radial velocity and cyclotron hump variations are consistent with the previously known photometric period, and the spectroscopic flux variations are consistent in amplitude with previous photometric amplitude measurements. The secondary star is also detected in the spectrum. We also present polarimetric imaging measurements of EU Cnc that show a clear detection of polarization, and the degree of polarization drops below our detection threshold at phases when the cyclotron emission features are fading or not evident. The combined data are all consistent with the interpretation that EU Cnc is a low-state polar in the cluster Messier 67. The mass function of the system gives an estimate of the accretor mass of M WD >= 0.68 M ? with M WD ? 0.83 M ? for an average inclination. We are thus able to place a lower limit on the progenitor mass of the accreting white dwarf of >=1.43 M ?. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

Williams, Kurtis A.; Howell, Steve B.; Liebert, James; Smith, Paul S.; Bellini, Andrea; Rubin, Kate H. R.; Bolte, Michael

2013-05-01

273

Time-resolved in situ measurement of mitochondrial malfunction by energy transfer spectroscopy  

NASA Astrophysics Data System (ADS)

To establish optical in situ detection of mitochondrial malfunction, nonradiative energy transfer from the coenzyme NADH to the mitochondrial marker rhodamine 123 (R123) was examined. Dual excitation of R123 via energy transfer from excited NADH molecules as well as by direct absorption of light results in two fluorescence signals whose ratio is a measure of mitochondrial NADH. A screening system was developed in which these signals are detected simultaneously using a time-gated (nanosecond) technique for energy transfer measurements and a frequency selective technique for direct excitation and fluorescence monitoring of R123. Optical and electronic components of the apparatus are described, and results obtained from cultivated endothelial cells are reported. The ratio of fluorescence intensities excited in the near ultraviolet and blue-green spectral ranges increased by a factor 1.5 or 1.35 after inhibition of the mitochondrial respiratory chain by rotenone at cytotoxic or noncytotoxic concentrations, respectively. Concomitantly the amount of mitochondrial NADH increased. Excellent linearity between the number of cells incubated with R123 and fluorescence intensity was found in suspension.

Schneckenburger, Herbert; Sailer, Reinhard; Strauss, Wolfgang S.; Lyttek, Marco; Stock, Karl; Zipfl, Peter

2000-10-01

274

Time-Resolved Atomic Spectroscopy With Fast-Ion Beams, Heavy-Ion Storage Ring and Ion Traps  

NASA Astrophysics Data System (ADS)

The understanding of the light received from astrophysical sources requires knowledge of atomic structure and dynamics, or of excitation cross sections and conditions, wavelengths and transition probabilities, f-values, branching ratios and level lifetimes. Fast ion beams (by beamfoil spectroscopy) and ion traps, as well as their cross-breed, the heavy-ion storage ring, can contribute to the field of X-ray astronomy. Fast-ion beam spectroscopy has a long track record in all spectral ranges, including Extreme Ultraviolet (XUV) and X-ray, with a plethora of data supporting astrophysics. In contrast, most of the time-resolved work with the ion trap techniques has been done in the Ultraviolet (UV) and Vacuum Ultraviolet (VUV)/Extreme Ultraviolet (EUV) above 100 Angstroms, but it can be extended into the region of interest.

Träbert, E.

2000-10-01

275

A homogeneous G protein-coupled receptor ligand binding assay based on time-resolved fluorescence resonance energy transfer.  

PubMed

Fluorescence resonance energy transfer (FRET) has emerged as a powerful tool to the study of protein-protein interactions, such as receptor-ligand binding. However, the application of FRET to the study of G protein-coupled receptors (GPCRs) has been limited by the method of labeling receptor with fluorescence probes. Here we described a novel time-resolved (TR)-FRET method to study GPCR-ligand binding by using human complement 5a (C5a) receptor (C5aR) as a model system. Human C5aR was expressed in human embryonic kidney 293 cells with a hemagglutinin (HA) epitope at the N-terminus. Purified human C5a was labeled with terbium chelate and used as the fluorescence donor. Monoclonal anti-HA antibody conjugated with Alexa Fluor 488 was used as the fluorescence acceptor. Robust FRET signal was observed when the labeled ligand and C5aR membrane were mixed in the presence of the conjugated anti-HA antibody. This FRET signal was specific and saturable. C5a binding affinity to C5aR measured by the FRET assay was consistent with the data as determined by competition binding analysis using radiolabeled C5a. The FRET assay was also used to determine affinity of C5aR antagonists by competition binding analysis, and the data are similar to those from radioligand binding studies. Compared to the commonly used radioligand binding assay, this TR-FRET-based assay provides a nonradioactive, faster, and sensitive homogeneous assay format that could be easily adapted to high-throughput screening. The principle of this assay should also be applicable to other GPCRs, especially to those receptors with peptide or protein ligands. PMID:18699727

Hu, Liaoyuan A; Zhou, Tian; Hamman, Brian D; Liu, Qingyun

2008-08-01

276

Time-Resolved Nonlinear Optical Spectroscopy of Magnetically Confined Quantum Well Excitons.  

NASA Astrophysics Data System (ADS)

The electronic states in a semiconductor quantum well undergo a transition from quasi-two-dimensional (2D) excitons to quasi-zero-dimensional (0D) magneto-excitons when subjected to a strong perpendicular magnetic field. In this transition, the band of free carrier states in the 2D quantum well breaks up into a series of isolated resonance peaks characteristic of systems in 0D. Using high intensity femtosecond broad-band continuum laser pulses, the time resolved nonlinear optical response of magneto-excitons is measured at fields as high as 12 Tesla. The results of these experiments demonstrate that at zero field, excitons interact with each other through a molecular potential similar to that in a hydrogen molecule. Magneto-excitons are strongly compressed by the high magnetic field, resulting in the quenching of their molecular interactions. At high fields, a gas of magneto-excitons in a semiconductor quantum well behaves as an ensemble of noninteracting two-level atoms. Coherent nonresonant excitation of quantum well magneto-excitons demonstrates that their nonlinear optical response is that of a Coulomb-enhanced two-level system. Excitation below the lowest magneto-exciton resonance results in a Rabi blue shift, while excitation above it results in a Rabi red shift, as expected for two-level atomic systems. Relaxation dynamics are also affected by the 0D confinement produced by a perpendicular magnetic field. At zero field, a distribution of carriers excited into the above-bandgap states of the semiconductor exhibit rapid scattering to achieve thermalization of the initially nonthermal distribution. At high field, however, the resonance peaks are widely separated, all low-energy scattering channels are eliminated, and relaxation of the initial distribution slows by orders of magnitude. Semiconductor quantum well magneto-excitons provide a unique laboratory in which to investigate the physics of excitonic systems during the transition from 2D to 0D. The experimental results demonstrate that this transition is accompanied by the elimination of Coulomb interactions, so that in the limit, the 0D system behaves as a noninteracting gas of two-level atoms. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617 -253-5668; Fax 617-253-1690.).

Stark, Jason Blain

277

Time-resolved reflectance spectroscopy for nondestructive assessment of fruit and vegetable quality  

Microsoft Academic Search

In the majority of food and feed, due to the microscopic spatial changes in the refractive index, visible (VIS) and near infrared (NIR) light undergoes multiple scattering events and the overall light distribution is determined more by scattering rather than absorption. Conventional steady state VIS\\/NIR reflectance spectroscopy can provide information on light attenuation, which depends both on light absorption and

Alessandro Torricelli; Lorenzo Spinelli; Maristella Vanoli; Anna Rizzolo; Paola Eccher Zerbini

2007-01-01

278

Time-resolved and steady-state FRET spectroscopy on commercial biocompatible quantum dots  

Microsoft Academic Search

Semiconductor nanocrystals (quantum dots - QDs) possess unique photophysical properties that make them highly interesting for many biochemical applications. Besides their common use as fluorophores in conventional spectroscopy and microscopy, QDs are well-suited for studying Förster resonance energy transfer (FRET). Size-dependent broadband absorption and narrow emission bands offer several advantages for the use of QDs both as FRET donors and

D. Wegner; D. Geißler; S. Stufler; H.-G. Löhmannsröben; N. Hildebrandt

2011-01-01

279

Time-resolved ultraviolet laser-induced breakdown spectroscopy for organic material analysis  

Microsoft Academic Search

Ultraviolet pulses (266 nm) delivered by a quadrupled Nd:YAG laser were used to analyze organic samples with laser-induced breakdown spectroscopy (LIBS). We present characteristics of the spectra obtained from organic samples with special attentions on the emissions of organic elements, O and N, and molecular bonds CN. The choice of these atomic or molecular species is justified on one hand, by

Matthieu Baudelet; Myriam Boueri; Jin Yu; Samuel S. Mao; Vincent Piscitelli; Xianglei Mao; Richard E. Russo

2007-01-01

280

Time-resolved reflectance spectroscopy for non-destructive assessment of food quality  

Microsoft Academic Search

In the majority of most food and feed, visible, and near infrared light undergoes multiple scattering events and the overall\\u000a light distribution is determined more by scattering rather than absorption due to the microscopic spatial changes in the refractive\\u000a index. Conventional steady state reflectance spectroscopy can provide information on light attenuation, which depends both\\u000a on light absorption and light scattering,

Alessandro Torricelli; Lorenzo Spinelli; Davide Contini; Maristella Vanoli; Anna Rizzolo; Paola Eccher Zerbini

2008-01-01

281

Time resolved spectroscopy and gain studies of Fullerenes C60 and C70  

NASA Astrophysics Data System (ADS)

The fluorescence decay time of Fullerenes C60 and C70 in pure form as well as in mixture with Coumarin C440 and Quinizarine dyes are studied. Results indicate that the decay of pure fullerenes is constant throughout the solute concentration and it is also independent of excitation wavelength, whereas in the case of mixture with dyes different behavior is noticed. We have also calculated the Stern-Volmer quenching constant and optical gain of both the fullerenes from which it is found that the optical gain is positive for Fullerene C70 only in a very narrow range of concentration.

Qaiser, Darakhshan; Khan, Mohd. Shahid; Singh, R. D.; Khan, Zahid H.

2013-09-01

282

Time-resolved terahertz spectroscopy and Hall measurement on chromium vanadium thin films  

NASA Astrophysics Data System (ADS)

We have measured the low-frequency dynamical conductivity of Cr1-xVx thin films through the quantum phase transition at x 0.35 using terahertz time-domain spectroscopy. From Drude model fits we have determined the plasma frequency ?p of samples over concentrations x=0-0.1 and temperatures 10--300 K. We have compared these to the Hall resistance RH on the same samples and found that both reveal the opening of the spin-density wave gap. At high temperatures ?p^21/RH, but as the temperature is lowered below 75 K, 1/RH falls more rapidly than ?p^2. We will relate these observations to a theoretical model based on a realistic Fermi surface.

Farahani, Amir; Kamal, Saeid; Fullerton, Eric; Dodge, J. Steven

2010-03-01

283

Complete momentum and energy resolved TOF electron spectrometerfor time-resolved photoemission spectroscopy  

SciTech Connect

Over the last decade, high-resolution Angle-Resolved Photoemission Spectroscopy (ARPES) has emerged as a tool of choice for studying the electronic structure of solids, in particular, strongly correlated complex materials such as cuprate superconductors. In this paper we present the design of a novel time-of-flight based electron analyzer with capability of 2D in momentum space (kx and ky) and all energies (calculated from time of flight) in the third dimension. This analyzer will utilize an improved version of a 2D delay linedetector capable of imaging with<35 mm (700x700 pixels) spatial resolution and better than 120 ps FWHM timing resolution. Electron optics concepts and optimization procedure are considered for achieving an energy resolution less than 1 meV and an angular resolution better than 0.11.

Hussain, Zahid; Lebedev, G.; Tremsin, A.; Siegmund, O.; Chen, Y.; Shen, Z.X.; Hussain, Z.

2007-08-12

284

Complete assignment of spin sublevels in the lowest excited triplet state of corrole compounds by time-resolved EPR spectroscopy  

NASA Astrophysics Data System (ADS)

The lowest excited triplet state of free-base 5,10,15-trispentafluorophenylcorrole (H3Cor) was studied in rigid glass by time-resolved electron paramagnetic resonance (TR-EPR) spectroscopy. Triplet sublevels were experimentally determined by using magnetophotoselection and liquid crystal. Quantum chemical calculations of zero-field splitting parameters D and E were used for the sublevel assignment. The out-of-plane sublevel Tz was found to be the lowest; namely, D is positive for H3Cor, in contrast to previous reports. The origin of the difference is discussed in detail. Preliminary TR-EPR experiments on rhodium corrole, accompanied by the quantum chemical calculations, emphasize the important contribution of spin-orbit couplings.

Yamauchi, Seigo; Tanabe, Mana; Ohba, Yasunori; Sugisaki, Kenji; Toyota, Kazuo; Sato, Kazunobu; Takui, Takeji; Saltsman, Irena

2012-01-01

285

Photoluminescence and time-resolved spectroscopy in multiferroic BiFeO3: Effects of electric fields and sample aging  

NASA Astrophysics Data System (ADS)

We report photoluminescence and time-resolved spectroscopy in bismuth ferrite excited with a 325 nm source. The direct-bandgap recombinations near 2.55 eV and indirect-bandgap transitions near 2.67 eV are presented as functions of applied in-plane electric field with recombination time in the microsecond regime. The applied field moves some conduction electrons away from the Brillouin zone center, increasing significantly the intensity of indirect-gap recombination. An aging phenomenon is manifest in specimens stored for more than twelve months under ambient conditions. Effect of external magnetic field on the surface phase transition is negligible up to H = 0.5 T.

Anshul, Avneesh; Kumar, Ashok; Gupta, Bipin K.; Kotnala, R. K.; Scott, J. F.; Katiyar, R. S.

2013-06-01

286

A time-resolved fluorescence-resonance energy transfer assay for identifying inhibitors of hepatitis C virus core dimerization.  

PubMed

Binding of hepatitis C virus (HCV) RNA to core, the capsid protein, results in the formation of the nucleocapsid, the first step in the assembly of the viral particle. A novel assay was developed to discover small molecule inhibitors of core dimerization. This assay is based on time-resolved fluorescence resonance energy transfer (TR-FRET) between anti-tag antibodies labeled with either europium cryptate (Eu) or allophycocyanin (XL-665). The N-terminal 106-residue portion of core protein (core106) was tagged with either glutathione-S-transferase (GST) or a Flag peptide. Tag-free core106 was selected as the reference inhibitor. The assay was used to screen the library of pharmacologically active compounds (LOPAC) consisting of 1,280 compounds and a 2,240-compound library from the Center for Chemical Methodology and Library Development at Boston University (CMLD-BU). Ten of the 28 hits from the primary TR-FRET run were confirmed in a secondary amplified luminescent proximity homogeneous assay (ALPHA screen). One hit was further characterized by dose-response analysis yielding an IC(50) of 9.3 microM. This 513 Da compound was shown to inhibit HCV production in cultured hepatoma cells. PMID:20035614

Kota, Smitha; Scampavia, Louis; Spicer, Timothy; Beeler, Aaron B; Takahashi, Virginia; Snyder, John K; Porco, John A; Hodder, Peter; Strosberg, Arthur Donny

2010-02-01

287

Determination of the energy transfer rate in photosynthetic systems by means of time-resolved spectroscopy  

NASA Astrophysics Data System (ADS)

This report addresses the energy migration problem in the light-harvesting antenna systems of photosynthetic objects. Both linear and nonlinear relaxation cases are discussed. In the linear case, the spectral inhomogeneity is taken into account by averaging the Master equation for the excitation over the spectrally inhomogeneous distribution of pigment molecules. That reformulates the Master equation as the excitation diffusion in the energy space. The stationary solution of this equation enables the determination of the Stokes shift dependence on homogeneous and inhomogeneous spectral bandwidths. The nonlinear relaxation is considered at the singlet-singlet annihilation conditions. The analysis of the fluorescence quantum yield, the excitation delay kinetics as well as the changes of spectral properties of the object under consideration as a function of the excitation intensity, demonstrates the possibility to determine the energy migration parameters. An important conclusion of this analysis is that the real pulse-shape of the excitation as well as the population of higher excited states during the nonlinear annihilation have to be taken into account.

Valkunas, Leonas; Trinkunas, Gediminas

1993-06-01

288

Dynamics of Long-Lived Exciton-Polaritons in Cadmium - Probed by Time-Resolved Edge Luminescence Excitation Spectroscopy  

NASA Astrophysics Data System (ADS)

Low temperature time-resolved edge luminescence excitation spectroscopy has bene used to probe the polariton transport properties in CdS. Long-lived polaritons with lifetimes exceeding 400 ns, which propagate from their origin at the front sample surface to the rear surface, have been directly observed as delayed luminescence peaks in the temporal response of edge luminescence. From the delay time of these peaks, a group velocity minimum of 6.5 times 10^5 cm/s, corresponding to the "bottleneck" energy, has been obtained in ultra high purity samples. By slightly detuning from the polariton resonance, the group velocity as a function of polariton excitation energy in the region at and below the bottleneck has been measured and analysed. Important properties of polaritons have been deduced from our experimental results. First, the process of polariton thermal relaxation down to the bottleneck region is very fast since the propagating time from front to rear surface is almost independent of the excitation photon energies for polaritons created above the bottleneck value. Second, the interactions between polaritons and other entities (electrons, phonons, defects, etc.) is very small at the interior of the CdS crystal since the attenuation coefficient is very small. Third, surfaces are the most important regions for generating polaritons as well as edge luminescence. Additionally, several new features have been observed from time-resolved excitation spectroscopy of edge luminescence using improved apparatus and spectral resolution. A delay -time-dependent spectral feature around the I_1 bound exciton resonance, which appears as a peak at short delay time and reverses to a dip at longer delay time, has been interpreted in terms of the faster decay of DAP luminescence generated at the I_1 excitation resonance since DA centers nearer the surface region are the ones excited. For the doubly etched e-e surface condition, new spectral features were seen under the high resolution excitation conditions. Dependence of excitation spectra on different combinations of surface treatments and excitation intensities in the time-resolved mode also provide important new information. (Abstract shortened with permission of author.).

Lin, Jingyu

289

DNA binding induces dissociation of the multimeric form of HIV-1 integrase: A time-resolved fluorescence anisotropy study  

PubMed Central

Self-assembly of HIV-1 integrase (IN) in solution has been studied previously by time-resolved fluorescence, using tryptophan anisotropy decay. This approach provides information on the size of macromolecules via the determination of rotational correlation times (?). We have shown that, at submicromolar concentration, IN is characterized by a long rotational correlation time (?20°C = 90–100 ns) corresponding to a high-order oligomeric form, likely a tetramer. In the present work, we investigated the self-assembly properties of the DNA-bound IN by using three independent fluorophores. Under enzymatic assay conditions (10?7 M IN, 2 × 10?8 M DNA), using either fluorescein-labeled or fluorescent guanosine analog-containing oligonucleotides that mimic a viral end long terminal repeat sequence, we found that the DNA–IN complex was characterized by shorter ?20°C values of 15.5–19.5 and 23–27 ns, calculated from experiments performed at 25°C and 37°C, respectively. These results were confirmed by monitoring the Trp anisotropy decay as a function of the DNA substrate concentration: the ? of IN shifted from 90–100 ns to lower values (<30 ns) upon increasing the DNA concentration. Again, the normalized ?20°C values were significantly higher when monitored at 37°C as compared with 25°C. These results indicate that upon binding the viral DNA end, the multimeric enzyme undergoes a dissociation, most likely into a homogenous monomeric form at 25°C and into a monomer–dimer equilibrium at 37°C.

Deprez, Eric; Tauc, Patrick; Leh, Herve; Mouscadet, Jean-Francois; Auclair, Christian; Hawkins, Mary E.; Brochon, Jean-Claude

2001-01-01

290

Time-resolved x-ray absorption spectroscopy: Watching atoms dance  

NASA Astrophysics Data System (ADS)

The introduction of pump-probe techniques to the field of x-ray absorption spectroscopy (XAS) has allowed the monitoring of both structural and electronic dynamics of disordered systems in the condensed phase with unprecedented accuracy, both in time and in space. We present results on the electronically excited high-spin state structure of an Fe(II) molecular species, [FeII(bpy)3]2+, in aqueous solution, resolving the Fe-N bond distance elongation as 0.2 Å. In addition an analysis technique using the reduced ?2 goodness of fit between FEFF EXAFS simulations and the experimental transient absorption signal in energy space has been successfully tested as a function of excited state population and chemical shift, demonstrating its applicability in situations where the fractional excited state population cannot be determined through other measurements. Finally by using a novel ultrafast hard x-ray 'slicing' source the question of how the molecule relaxes after optical excitation has been successfully resolved using femtosecond XANES.

Milne, Chris J.; Pham, Van-Thai; Gawelda, Wojciech; van der Veen, Renske M.; El Nahhas, Amal; Johnson, Steven L.; Beaud, Paul; Ingold, Gerhard; Lima, Frederico; Vithanage, Dimali A.; Benfatto, Maurizio; Grolimund, Daniel; Borca, Camelia; Kaiser, Maik; Hauser, Andreas; Abela, Rafael; Bressler, Christian; Chergui, Majed

2009-11-01

291

Structural dynamics of membrane proteins - time-resolved and surface-enhanced IR spectroscopy  

NASA Astrophysics Data System (ADS)

Membrane proteins are the target of more than 50% of all drugs and are encoded by about 30% of the human genome. Electrophysiological techniques, like patch-clamp, unravelled many functional aspects of membrane proteins but suffer from structural sensitivity. We have developed Surface Enhanced Infrared Difference Absorption Spectroscopy (SEIDAS) to probe potential-induced structural changes of a protein on the level of a monolayer. A novel concept is introduced to incorporate membrane proteins into solid supported lipid bilayers in an orientated manner via the affinity of the His-tag to the Ni-NTA terminated gold surface. General applicability of the methodological approach is shown by tethering photosystem II to the gold surface. In conjunction with hydrogenase, the basis is set towards a biomimetic system for hydrogen production. Recently, we succeeded to record IR difference spectra of a monolayer of sensory rhodopsin II under voltage-clamp conditions. This approach opens an avenue towards mechanistic studies of voltage-gated ion channels with unprecedented structural and temporal sensitivity. Initial vibrational studies on the novel light-gated channelrhodopsin-2 (ChR2) will be presented. ChR2 represents a versatile tool in the new field of optogenetics where physiological reactions are controlled by light.

Heberle, Joachim

2013-03-01

292

Analytical performances of a DNA-ligand system using time-resolved fluorescence for the determination of ochratoxin A in wheat.  

PubMed

The analytical performances of a novel DNA-ligand system using the time-resolved fluorescence (TRF) response of ochratoxin A (OTA)-terbium-DNA aptamer interaction were tested for the quantitative determination of OTA in wheat. Wheat was extracted with acetonitrile/water (60:40, v/v) followed by clean-up through affinity columns containing a DNA-aptamer-based oligosorbent. Then, OTA was detected by TRF spectroscopy after reaction with a terbium fluorescent solution containing the DNA-aptamer probe. The entire procedure was performed in less than 30 min, including sample preparation, and allowed analysis of several samples simultaneously with a 96-well microplate reader. The average recovery from samples spiked with 2.5-25 ?g kg(-1) OTA was 77%, with a relative standard deviation lower than 6% and a quantification limit of 0.5 ?g kg(-1). Comparative analyses of 29 naturally contaminated (up to 14 ?g kg(-1)) wheat samples using the aptamer-affinity column/TRF method or the immunoaffinity column/high-performance liquid chromatography method showed good correlation (r = 0.985) in the range tested. The trueness of the aptamer-based method was additionally assessed by analysis of two quality control wheat materials for OTA. The DNA-ligand system is innovative, simple and rapid, and can be used to screen large quantities of samples for OTA contamination at levels below the EU regulatory limit with analytical performances satisfying EU criteria for method acceptability. PMID:22576657

De Girolamo, Annalisa; Le, Linda; Penner, Gregory; Schena, Roberto; Visconti, Angelo

2012-05-12

293

Rotational and Translational Dynamics of Rhodamine 6G in a Pyrrolidinium Ionic Liquid: A Combined Time-Resolved Fluorescence Anisotropy Decay and NMR Study  

SciTech Connect

NMR spectroscopy and time-resolved fluorescence anisotropy decay (TRFAD) are two of the most commonly used methods to study solute-solvent interactions. However, only a few studies have been reported to date using a combined NMR and TRFAD approach to systematically investigate the overall picture of diffusional and rotational dynamics of both the solute and solvent. In this paper, we combined NMR and TRFAD to probe fluorescent rhodamine dyes in a pyrrolidinium-based room temperature ionic liquid (RTIL), an emergent environmentally-friendly solvent type used in several energy-related applications. A specific interaction of the R6G cation and [Tf2N]- anion was identified, resulting in near-stick boundary condition rotation of R6G in this RTIL. The diffusional rates of the R6G solute and [C4mpyr][Tf2N] solvent derived from 1H NMR suggest the rates are proportional to their corresponding hydrodynamic radii. The 1H and 13C NMR studies of self-rotational dynamics of [C4mpyr][Tf2N] showed that the self-rotational correlation time of [C4mpyr]+ is 47 2 ps at 300 K. At the same temperature, we find that the correlation time for N-CH3 rotation in [C4mpyr]+ is 77 2 ps, comparable to overall molecular reorientation. This slow motion is attributed to properties of the cation structure.

Guo, Jianchang [ORNL; Han, Kee Sung [ORNL; Mahurin, Shannon Mark [ORNL; Baker, Gary A [ORNL; Hillesheim, Patrick C [ORNL; Dai, Sheng [ORNL; Hagaman, Edward {Ed} W [ORNL; Shaw, Robert W [ORNL

2012-01-01

294

Ultrafast time-resolved absorption spectroscopy of geometric isomers of carotenoids  

NASA Astrophysics Data System (ADS)

The structures of a number of stereoisomers of carotenoids have been revealed in three-dimensional X-ray crystallographic investigations of pigment-protein complexes from photosynthetic organisms. Despite these structural elucidations, the reason for the presence of stereoisomers in these systems is not well understood. An important unresolved issue is whether the natural selection of geometric isomers of carotenoids in photosynthetic pigment-protein complexes is determined by the structure of the protein binding site or by the need for the organism to accomplish a specific physiological task. The association of cis isomers of a carotenoid with reaction centers and trans isomers of the same carotenoid with light-harvesting pigment-protein complexes has led to the hypothesis that the stereoisomers play distinctly different physiological roles. A systematic investigation of the photophysics and photochemistry of purified, stable geometric isomers of carotenoids is needed to understand if a relationship between stereochemistry and biological function exists. In this work we present a comparative study of the spectroscopy and excited state dynamics of cis and trans isomers of three different open-chain carotenoids in solution. The molecules are neurosporene ( n = 9), spheroidene ( n = 10), and spirilloxanthin ( n = 13), where n is the number of conjugated ?-electron double bonds. The spectroscopic experiments were carried out on geometric isomers of the carotenoids purified by high performance liquid chromatography (HPLC) and then frozen to 77 K to inhibit isomerization. The spectral data taken at 77 K provide a high resolution view of the spectroscopic differences between geometric isomers. The kinetic data reveal that the lifetime of the lowest excited singlet state of a cis-isomer is consistently shorter than that of its corresponding all- trans counterpart despite the fact that the excited state energy of the cis molecule is typically higher than that of the trans molecule. Quantum theoretical calculations on an n = 9 linear polyene were carried out to examine this process. The calculations indicate that the electronic coupling terms are significantly higher for the cis isomer, and when combined with the Franck-Condon factors, predict internal conversion rates roughly double those of the all- trans species. The electronic effects more than offset the decrease in coupling efficiencies associated with the higher system origin energies and explain the observed shorter cis isomer lifetimes.

Niedzwiedzki, Dariusz M.; Sandberg, Daniel J.; Cong, Hong; Sandberg, Megan N.; Gibson, George N.; Birge, Robert R.; Frank, Harry A.

2009-02-01

295

Time-resolved Fluorescence Resonance Energy Transfer (TR-FRET) to Analyze the Disruption of EGFR/HER2 Dimers  

PubMed Central

In oncology, simultaneous inhibition of epidermal growth factor receptor (EGFR) and HER2 by monoclonal antibodies (mAbs) is an efficient therapeutic strategy but the underlying mechanisms are not fully understood. Here, we describe a time-resolved fluorescence resonance energy transfer (TR-FRET) method to quantify EGFR/HER2 heterodimers on cell surface to shed some light on the mechanism of such therapies. First, we tested this antibody-based TR-FRET assay in NIH/3T3 cell lines that express EGFR and/or HER2 and in various tumor cell lines. Then, we used the antibody-based TR-FRET assay to evaluate in vitro the effect of different targeted therapies on EGFR/HER2 heterodimers in the ovarian carcinoma cell line SKOV-3. A simultaneous incubation with Cetuximab (anti-EGFR) and Trastuzumab (anti-HER2) disturbed EGFR/HER2 heterodimers resulting in a 72% reduction. Cetuximab, Trastuzumab or Pertuzumab (anti-HER2) alone induced a 48, 44, or 24% reduction, respectively. In contrast, the tyrosine kinase inhibitors Erlotinib and Lapatinib had very little effect on EGFR/HER2 dimers concentration. In vivo, the combination of Cetuximab and Trastuzumab showed a better therapeutic effect (median survival and percentage of tumor-free mice) than the single mAbs. These results suggest a correlation between the extent of the mAb-induced EGFR/HER2 heterodimer reduction and the efficacy of such mAbs in targeted therapies. In conclusion, quantifying EGFR/HER2 heterodimers using our antibody-based TR-FRET assay may represent a useful method to predict the efficacy and explain the mechanisms of action of therapeutic mAbs, in addition to other commonly used techniques that focus on antibody-dependent cellular cytotoxicity, phosphorylation, and cell proliferation.

Gaborit, Nadege; Larbouret, Christel; Vallaghe, Julie; Peyrusson, Frederic; Bascoul-Mollevi, Caroline; Crapez, Evelyne; Azria, David; Chardes, Thierry; Poul, Marie-Alix; Mathis, Gerard; Bazin, Herve; Pelegrin, Andre

2011-01-01

296

Time-resolved fluorescence emission measurements of photosystem I particles of various cyanobacteria: a unified compartmental model.  

PubMed Central

Photosystem I (PS-I) contains a small fraction of chlorophylls (Chls) that absorb at wavelengths longer than the primary electron donor P700. The total number of these long wavelength Chls and their spectral distribution are strongly species dependent. In this contribution we present room temperature time-resolved fluorescence data of five PS-I core complexes that contain different amounts of these long wavelength Chls, i.e., monomeric and trimeric photosystem I particles of the cyanobacteria Synechocystis sp. PCC 6803, Synechococcus elongatus, and Spirulina platensis, which were obtained using a synchroscan streak camera. Global analysis of the data reveals considerable differences between the equilibration components (3.4-15 ps) and trapping components (23-50 ps) of the various PS-I complexes. We show that a relatively simple compartmental model can be used to reproduce all of the observed kinetics and demonstrate that the large kinetic differences are purely the result of differences in the long wavelength Chl content. This procedure not only offers rate constants of energy transfer between and of trapping from the compartments, but also well-defined room temperature emission spectra of the individual Chl pools. A pool of red shifted Chls absorbing around 702 nm and emitting around 712 nm was found to be a common feature of all studied PS-I particles. These red shifted Chls were found to be located neither very close to P700 nor very remote from P700. In Synechococcus trimeric and Spirulina monomeric PS-I cores, a second pool of red Chls was present which absorbs around 708 nm, and emits around 721 nm. In Spirulina trimeric PS-I cores an even more red shifted second pool of red Chls was found, absorbing around 715 nm and emitting at 730 nm.

Gobets, B; van Stokkum, I H; Rogner, M; Kruip, J; Schlodder, E; Karapetyan, N V; Dekker, J P; van Grondelle, R

2001-01-01

297

Determination of NADH in the rat brain during sleep-wake states with an optic fibre sensor and time-resolved fluorescence procedures  

Microsoft Academic Search

The present paper reports a nanosecond time-resolved fluorescence derived from the cortex and the area of the periaqueductal gray including the nucleus raphe dorsalis (PAG-nRD) in unanaesthetized freely moving rats. The measurements were acquired through a single optic fibre transmitting a subnanosecond nitrogen laser pulse (337nm, 15Hz) and collecting the brain fluorescence occurring at 460nm which might depend on mitochondrial

S. Mottin; P. Laporte; M. Jouvet; R. Cespuglio

1997-01-01

298

Design of the optical system for a new time-resolved X-ray absorption spectroscopy apparatus  

NASA Astrophysics Data System (ADS)

Calculations of total reflection mirror optics and analyzing crystal polychromator optics are done to design a new time-resolved soft X-ray absorption spectroscopy apparatus. This apparatus utilizes pulsed soft X-rays of pseudo-continuum energy which are generated by a pulsed laser-induced metal plasma, and covers an energy range of 90 eV similar to 3 keV. An optimal design of the optical system, i.e., optimal dimensions, setting positions and materials of the mirror and polychromator, is proposed based on the calculations of the reflectivity of the material, efficiency of the X-ray acceptance and ray-tracing. Calculations are also made on the reflectivity of several mirror materials commonly used for the X-ray diffraction and spectroscopy in the energy range up to 50 keV. Data of the reflectivity in this energy region are necessary to design an X-ray apparatus using synchrotron radiation as an X-ray source. Numerical results of the reflectivity are available.

Miyashita, Atsumi; Yoda, Osamu

1988-10-01

299

Probing the hydrogen-bond network of water via time-resolved soft x-ray spectroscopy  

SciTech Connect

We report time-resolved studies of hydrogen bonding in liquid H2O, in response to direct excitation of the O-H stretch mode at 3 mu m, probed via soft x-ray absorption spectroscopy at the oxygen K-edge. This approach employs a newly developed nanofluidic cell for transient soft x-ray spectroscopy in liquid phase. Distinct changes in the near-edge spectral region (XANES) are observed, and are indicative of a transient temperature rise of 10K following transient laser excitation and rapid thermalization of vibrational energy. The rapid heating occurs at constant volume and the associated increase in internal pressure, estimated to be 8MPa, is manifest by distinct spectral changes that differ from those induced by temperature alone. We conclude that the near-edge spectral shape of the oxygen K-edge is a sensitive probe of internal pressure, opening new possibilities for testing the validity of water models and providing new insight into the nature of hydrogen bonding in water.

Huse, Nils; Wen, Haidan; Nordlund, Dennis; Szilagyi, Erzsi; Daranciang, Dan; Miller, Timothy A.; Nilsson, Anders; Schoenlein, Robert W.; Lindenberg, Aaron M.

2009-04-24

300

Time-resolved Spectroscopy and Multi-color Photometry Of The Pulsating and Short-period Binary Subdwarf B Star Feige 48  

NASA Astrophysics Data System (ADS)

Pulsating subdwarf B (sdB) stars can be used as probes of the helium fusing cores of horizontal branch stars. To probe these stars, asteroseismology must be able to observationally associate pulsation frequencies with modes. Time-resolved spectroscopy and multicolor photometry have been employed with mixed results for short-period pulsating sdB stars. Time-resolved spectroscopy has successfully measured radial velocity, temperature, and gravity variations in six pulsators, yet interpreting results is far from straightforward. Multicolor photometry requires extremely high precision to discern between low-degree modes, yet has been used effectively to eliminate high-degree modes. Combining RV and multicolor measurements has also been shows as an effective means of constraining mode identifications. I will present results for Feige 48 using both time-resolved spectroscopy and multicolor photometry and attempts to constrain their pulsation modes using the atmospheric codes BRUCE and KYLIE.

Reed, Mike; Baran, A.; O'Toole, S.

2012-05-01

301

Solvatochromism and time-resolved fluorescence of the antitumor agent mitoxantrone and its analogues in solution and in DNA  

SciTech Connect

The electronic spectroscopy and fluorescence kinetics of 1,4-dihydroxy-5,8-(2-(2-((2-hydroxyethyl)amino)ethyl)amino)-9,10-anthracenedione (mitoxantrone) and three closely related analogues have been studied in several solvents. The small solvatochromic blue shifts of their visible charge-transfer absorption bands in protic solvents are dominated by interactions with a solvent H-bonding donor, rather than by dipole-dielectric solute-solvent electrostatics. These interactions are unrelated to the phenolic hydroxy groups or the distal N atoms on the side chains but must be localized to the carbonyl groups. The fluorescence decays of all four anthraquinones are controlled by subnanosecond nonradiative relaxation in all solvents studied. At least two decay mechanisms contribute to the observed fluorescence kinetics in solution: (a) subnanosecond internal conversion that is accelerated relative to that in 1,4-diaminoanthraquinone by the presence of the flexible 1,4-side chains in mitoxantrone and its analogues; (b) an additional decay mode that is accentuated in H-bonding solvents. A substantial normal isotope effect occurs in the fluorescence lifetimes of mitoxantrone in perdeuterated water and methanol but not in aprotic solvents. When bound to double-stranded calf thymus DNA, mitoxantrone displays a fluorescence lifetime similar to that in aprotic solvents, suggesting that H-bonding interactions with water are precluded by chromophore intercalation. DNA-bound ametantrone exhibits a lifetime longer than that in either H-bonding or aprotic solvents, indicating that immobilization of the side chains through binding of the distal N atoms to the DNA backbone may influence the decay kinetics. This technique therefore shows potential for elucidating the DNA binding modes for a large class of intercalative drugs.

Su Lin; Struve, W.S. (Ames Lab., IA (United States))

1991-03-21

302

Testing the Physical Mechanisms of Gamma-Ray Bursts with Multi-Instrument Time-Resolved Spectroscopy  

NASA Astrophysics Data System (ADS)

We have continued the project of time-resolved spectral analyses of gamma-ray bursts observed jointly by the BATSE and the Wide-Field Camera on board BeppoSAX. We are making progress understanding the systematic differences between the two data sets. These data comprise the most important joint analysis set for our project. In several meetings, we have reported on metal efforts to understand the blackbody portion of the time series of spectra from GRB970111. Clearly, a fading thermal component can provide a 'seed' spectrum for Compton upscattering. It is very likely the X-ray excess that has been observed previously in BATSE data alone continues into the X-ray band observed by the WFC. We have also made progress in joint fitting of BATSE Large Area Detector and Spectroscopy Detector data with that of the Total Absorption Scintillation Calorimeter (TASC) of the EGRET experiment on CGRO. The TASC data are important to understanding the high-energy response of the BATSE data. We have produced time-sequences of spectra for two important GRB with data from both instruments. The Summer workshop on GRBs at the Aspen Center for Physics provided an opportunity for in-depth discussion of our on-going work. To aid our effort, we continue to make improvements in our spectral analysis software, RMFIT (rewritten from WINGSPAN).

Briggs, Michael S.; Preece, Robert E.

2001-12-01

303

Direct observation of a sulfonyl azide excited state and its decay processes by ultrafast time-resolved IR spectroscopy.  

PubMed

The photochemistry of 2-naphthylsulfonyl azide (2-NpSO(2)N(3)) was studied by femtosecond time-resolved infrared (TR-IR) spectroscopy and with quantum chemical calculations. Photolysis of 2-NpSO(2)N(3) with 330 nm light promotes 2-NpSO(2)N(3) to its S(1) state. The S(1) excited state has a prominent azide vibrational band. This is the first direct observation of the S(1) state of a sulfonyl azide, and this vibrational feature allows a mechanistic study of its decay processes. The S(1) state decays to produce the singlet nitrene. Evidence for the formation of the pseudo-Curtius rearrangement product (2-NpNSO(2)) was inconclusive. The singlet sulfonylnitrene (1)(2-NpSO(2)N) is a short-lived species (? ? 700 ± 300 ps in CCl(4)) that decays to the lower-energy and longer-lived triplet nitrene (3)(2-NpSO(2)N). Internal conversion of the S(1) excited state to the ground state S(0) is an efficient deactivation process. Intersystem crossing of the S(1) excited state to the azide triplet state contributes only modestly to deactivation of the S(1) state of 2-NpSO(2)N(3). PMID:22462556

Kubicki, Jacek; Luk, Hoi Ling; Zhang, Yunlong; Vyas, Shubham; Peng, Huo-Lei; Hadad, Christopher M; Platz, Matthew S

2012-04-13

304

Time-resolved Fourier transform emission spectroscopy of He/CH4 in a positive column discharge.  

PubMed

Time-resolved Fourier transform infrared emission spectroscopy was applied to the study of a pulsed discharge in a He/CH(4) mixture. The dynamics of the formation and decay of acetylene ?(3) (3289 cm(-1)), methane ?(3) (3019 cm(-1)) and ?(1) (2917 cm(-1)), the CH radical electronic ground state X(2)?(r) (2309-2953 cm(-1)), C(2) Bernath electronic transition B(1)?(g)-A(1)?(u) (3337-3606 cm(-1)), molecular hydrogen emission transitions 5g-4f and 2p-2s, atomic hydrogen, and atomic helium were monitored in the 1800-4000 cm(-1) region. The time profile of the rotational and vibrational temperature of the CH radical was obtained for a 30 ?s time interval during and after the discharge pulse. A kinetic model was used for the study of the chemical dynamics of the formation and decay of the individual fragments. The results from the model were compared to the experimental emission spectra. PMID:22375598

Civiš, Svatopluk; Kubelík, Petr; Ferus, Martin

2012-03-13

305

Photoexcited State Properties of H2-Porphyrin/C60-Based Rotaxanes as Studied by Time-Resolved EPR Spectroscopy  

PubMed Central

Light-driven intramolecular electron transfer (ET) and energy transfer (EnT) processes in two rotaxanes, the first containing two free base porphyrins and C60 fullerene moieties incorporated around a Cu(I)bisphenanthroline core ((H2P)2-Cu(I)(phen)2-C60) and a second rotaxane lacking the fullerene moiety ((H2P)2-Cu(I)(phen)2) were studied by X-band (9.5 GHz) time-resolved electron paramagnetic resonance (TREPR) spectroscopy. The experiments were performed in a frozen toluene and ethanol, and different phases of the nematic liquid crystal (E-7). It is demonstrated that the ET and EnT processes in the (H2P)2-Cu(I)(phen)2-C60 rotaxane in different media result in formation of the same charge separated state, namely (H2P)2•+-Cu(I)(phen)2•?-C60, while photoexcitation of the (H2P)2-Cu(I)(phen)2 rotaxane does not induce noticeable transfer processes in these matrices. The results are discussed in terms of the high conformational mobility of the rotaxanes, which enables changes in the molecular topography and resultant modification of the rates and routes of photoinduced processes occurring in these systems. The parameters of the transfer processes are compared with those obtained in our previous study of (ZnP)2-Cu(I)(phen)2-C60 and (ZnP)2-Cu(I)(phen) rotaxanes under the same experimental conditions.

Jakob, Manuela; Berg, Alexander; Levanon, Haim; Schuster, David I.; Megiatto, Jackson D.

2011-01-01

306

Aqueous solutions of uranium(VI) as studied by time-resolved emission spectroscopy: a round-robin test.  

PubMed

Results of an inter-laboratory round-robin study of the application of time-resolved emission spectroscopy (TRES) to the speciation of uranium(VI) in aqueous media are presented. The round-robin study involved 13 independent laboratories, using various instrumentation and data analysis methods. Samples were prepared based on appropriate speciation diagrams and, in general, were found to be chemically stable for at least six months. Four different types of aqueous uranyl solutions were studied: (1) acidic medium where UO2(2+)aq is the single emitting species, (2) uranyl in the presence of fluoride ions, (3) uranyl in the presence of sulfate ions, and (4) uranyl in aqueous solutions at different pH, promoting the formation of hydrolyzed species. Results between the laboratories are compared in terms of the number of decay components, luminescence lifetimes, and spectral band positions. The successes and limitations of TRES in uranyl analysis and speciation in aqueous solutions are discussed. PMID:14661847

Billard, Isabelle; Ansoborlo, Eric; Apperson, Kathleen; Arpigny, Sylvie; Azenha, M Emilia; Birch, David; Bros, Pascal; Burrows, Hugh D; Choppin, Gregory; Couston, Laurent; Dubois, Veronique; Fanghänel, Thomas; Geipel, Gerhard; Hubert, Solange; Kim, Jae I; Kimura, Takaumi; Klenze, Reinhardt; Kronenberg, Andreas; Kumke, Michael; Lagarde, Gerard; Lamarque, Gerard; Lis, Stefan; Madic, Charles; Meinrath, Gunther; Moulin, Christophe; Nagaishi, Ryuji; Parker, David; Plancque, Gabriel; Scherbaum, Franz; Simoni, Eric; Sinkov, Sergei; Viallesoubranne, Carole

2003-08-01

307

Iron-carbonyl bond geometries of carboxymyoglobin and carboxyhemoglobin in solution determined by picosecond time-resolved infrared spectroscopy.  

PubMed Central

The iron-carbonyl geometries in carboxymyoglobin (MbCO) and carboxyhemoglobin (HbCO) in ambient temperature solution have been investigated using picosecond time-resolved infrared spectroscopy. Polarized infrared and visible beams were used to monitor the change in infrared absorbance of the bound CO stretch bands on photodissociation of the ligand. The ratio of the change in absorbance for perpendicular and parallel relative polarizations of the photolysis and infrared probe beams is directly related to the angle between the ligand bond axis and the normal to the heme plane. Ratios, and hence the angles, have been obtained for the configurations giving rise to the principal CO stretch infrared absorption bands of HbCO and MbCO: 18 degrees for the 1951 cm-1 band of HbCO; 20 degrees and 35 degrees, respectively, for the 1944 cm-1 and 1933 cm-1 bands of MbCO. Structures consistent with x-ray diffraction and the picosecond experiments reported here are proposed for MbCO and HbCO in which the Fe-C bond tilts to the heme normal and the Fe-C-O angle differs significantly from 180 degrees.

Moore, J N; Hansen, P A; Hochstrasser, R M

1988-01-01

308

Time-Resolved Energy-Momentum Spectroscopy of Electric and Magnetic Dipole Transitions in Cr(3+):MgO.  

PubMed

Due to the recent interest in magnetic light-matter interactions, the magnetic dipole (MD) transitions in lanthanide ions have been studied for potential applications in nano-optics. Similar to lanthanide ions, transition-metal ions also exhibit strong MD emission at room temperature, but their prominent MD zero-phonon lines are often accompanied by significant electric dipole (ED) sideband emission. Here, we extend energy-momentum spectroscopy to time-resolved measurements, and use this technique to quantify the ED and MD contributions to light emission from trivalent chromium doped magnesium oxide (Cr(3+):MgO). This allows us to differentiate the MD (2)E ? (4)A2 zero-phonon line from phonon-assisted (2)E ? (4)A2 and (4)T2 ? (4)A2 ED sidebands. We also demonstrate how the relative intensities of the sharp MD zero-phonon line and the broad ED sidebands can be used as a qualitative measure of the MD and ED local density of optical states. PMID:23879390

Karaveli, Sinan; Wang, Shutong; Xiao, Gang; Zia, Rashid

2013-07-26

309

Two-photon resonances in femtosecond time-resolved four-wave mixing spectroscopy: {beta}-carotene  

SciTech Connect

Femtosecond time-resolved pump-degenerate four-wave mixing (pump-DFWM) spectroscopy has been used to study the ultrafast dynamics of {beta}-carotene involving several electronic and vibrational states. An initial pump pulse, resonant with the S{sub 0}-to-S{sub 2} transition, excites the molecular system and a DFWM process, resonant with the S{sub 1}-to-S{sub n} transition, is used to probe the relaxation pathways. The transient shows a peculiar decay behavior, which is due to the contributions of resonant DFWM signal of the excited S{sub 1} state, nonresonant DFWM signal of the ground S{sub 0} state and vibrational hot S{sub 0}{sup *} state, and the two-photon resonant DFWM signal of the ground S{sub 0} state. We have used a kinetic model including all the signal contributions to successfully fit the transient. The time constants extracted are in very good agreement with the known values for {beta}-carotene. For comparison, a two-pulse pump-probe experiment was performed measuring the transient absorption at the wavelength of the DFWM experiment.

Namboodiri, V.; Namboodiri, M.; Flachenecker, G.; Materny, A. [Center of Functional Materials and Nanomolecular Science, Jacobs University Bremen, Campus Ring 1, 28759 Bremen (Germany)

2010-08-07

310

Time-resolved vibrational spectroscopy detects protein-based intermediates in the photosynthetic oxygen-evolving cycle  

PubMed Central

Photosynthetic oxygen production by photosystem II (PSII) is responsible for the maintenance of aerobic life on earth. The production of oxygen occurs at the PSII oxygen-evolving complex (OEC), which contains a tetranuclear manganese (Mn) cluster. Photo-induced electron transfer events in the reaction center lead to the accumulation of oxidizing equivalents on the OEC. Four sequential photooxidation reactions are required for oxygen production. The oxidizing complex cycles among five oxidation states, called the Sn states, where n refers to the number of oxidizing equivalents stored. Oxygen release occurs during the S3-to-S0 transition from an unstable intermediate, known as the S4 state. In this report, we present data providing evidence for the production of an intermediate during each S state transition. These protein-derived intermediates are produced on the microsecond to millisecond time scale and are detected by time-resolved vibrational spectroscopy on the microsecond time scale. Our results suggest that a protein-derived conformational change or proton transfer reaction precedes Mn redox reactions during the S2-to-S3 and S3-to-S0 transitions.

Barry, Bridgette A.; Cooper, Ian B.; De Riso, Antonio; Brewer, Scott H.; Vu, Dung M.; Dyer, R. Brian

2006-01-01

311

Dynamic insight into the interaction between porphyrin and G-quadruplex DNAs: time-resolved fluorescence anisotropy study.  

PubMed

Understanding the nature of the interaction between small molecules and G-quadruplex DNA is crucial for the development of novel anticancer drugs. In this paper, we present the first data on time-resolved fluorescence anisotropy study on the interaction between a water-soluble cationic porphyrin H(2)TMPyP4 and four distinct G-quadruplex DNAs, that is, AG(3)(T(2)AG(3))(3), thrombin-binding aptamer (TBA), (G(4)T(4)G(4))2, and (TG(4)T)4. The anisotropy decay curves show the monoexponential for free H(2)TMPyP4 and the biexponential upon binding to the excess amount of G-quadruplex DNAs. The biexponential anisotropy decay can be well interpreted using a wobbling-in-the-cone model. The orientational diffusion of the bound H(2)TMPyP4 is initially restricted to a limited cone angle within the G-quadruplex DNAs, and then an overall orientational relaxation of the G-quadruplex DNA-H(2)TMPyP4 complexes occurs in a longer time scale. It was found that the dynamics of the restricted internal rotation of bound H(2)TMPyP4 strongly depends on the ending structures of the G-quadruplex DNAs. According to the order parameter (Q) calculated from the wobbling-in-the-cone model, we deduce that the degree of restriction around the bound H(2)TMPyP4 follows the order of TBA > (TG(4)T)4 > AG(3)(T(2)AG(3))(3) > (G(4)T(4)G(4))2. Especially, based on the maximum order parameter (Q) of bound H(2)TMPyP4 within TBA, a new sandwich-type binding mode for TBA-H(2)TMPyP4 complex was proposed in which both terminal G-quartet and T*T base pair stack on the porphyrin ring through pi-pi interaction. This study thus provides a new insight into the interaction between G-quadruplex DNAs and H(2)TMPyP4. PMID:19924868

Jia, Guoqing; Feng, Zhaochi; Wei, Chunying; Zhou, Jun; Wang, Xiuli; Li, Can

2009-12-17

312

Fast CCD camera for x-ray photon correlation spectroscopy and time-resolved x-ray scattering and imaging  

SciTech Connect

A new, fast x-ray detector system is presented for high-throughput, high-sensitivity, time-resolved, x-ray scattering and imaging experiments, most especially x-ray photon correlation spectroscopy (XPCS). After a review of the architectures of different CCD chips and a critical examination of their suitability for use in a fast x-ray detector, the new detector hardware is described. In brief, its principal component is an inexpensive, commercial camera - the SMD1M60 - originally designed for optical applications, and modified for use as a direct-illumination x-ray detector. The remainder of the system consists of two Coreco Imaging PC-DIG frame grabber boards, located inside a Dell Power-edge 6400 server. Each frame grabber sits on its own PCI bus and handles data from 2 of the CCD's 4 taps. The SMD1M60 is based on a fast, frame-transfer, 4-tap CCD chip, read out at12-bit resolution at frame rates of up to 62 Hz for full frame readout and up to 500 Hz for one-sixteenth frame readout. Experiments to characterize the camera's suitability for XPCS and small-angle x-ray scattering (SAXS) are presented. These experiments show that single photon events are readily identified, and localized to within a pixel index or so. This is a sufficiently fine spatial resolution to maintain the speckle contrast at an acceptable value for XPCS measurements. The detective quantum efficiency of the SMD1M60 is 49% for directly-detected 6.3 keV x rays. The effects of data acquisition strategies that permit near-real-time data compression are also determined and discussed. Overall, the SMD1M60 detector system represents a major improvement in the technology for time-resolved x-ray experiments, that require an area detector with time-resolutions in few-milliseconds-to-few-seconds range, and it should have wide applications, extending beyond XPCS.

Falus, P.; Borthwick, M.A.; Mochrie, S.G.J. [Department of Physics, Yale University, New Haven, Connecticut 06520 and Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Departments of Physics and Applied Physics, Yale University, New Haven, Connecticut 06520 (United States)

2004-11-01

313

DETECTION OF FECAL CONTAMINATION ON APPLES USING NANOSECOND-SCALE TIME-RESOLVED IMAGING OF LASER INDUCED FLUORESCENCE  

Technology Transfer Automated Retrieval System (TEKTRAN)

Detection of apples contaminated with feces is a public health concern. In this study, time resolved imaging of apples artificially contaminated with feces allowed optimization of timing parameters for detection. Dairy feces were applied to Red Delicious apples and Golden Delicious apples. Laser-ind...

314

Phonon relaxation in CdSSe semiconductor quantum dots studied by femtosecond time-resolved resonant four-wave mixing spectroscopy  

Microsoft Academic Search

We have observed coherent longitudinal optical phonons in CdSSe quantum dots embedded in a glass matrix by femtosecond time-resolved coherent anti-Stokes Raman spectroscopy (CARS). The LO phonon mode is identified by the frequency of the oscillations on the CARS signal. The phase relaxation time is directly deduced from the decay of the signal.

P. Waltner; A Materny; W Kiefer

2000-01-01

315

Liquid-ordered microdomains in lipid rafts and plasma membrane of U-87 MG cells: a time-resolved fluorescence study  

Microsoft Academic Search

Lipid rafts, the functional microdomains in the cell membrane, are believed to exist as liquid-ordered (L o) phase domains along with the liquid-disordered (L d) phase of the bulk of the cell membranes. We have examined the lipid order in model and natural membranes by time-resolved fluorescence of trimethylammonium-1,6-diphenylhexatriene incorporated into the membranes. The lipid phases were discerned by the

Mau Sinha; Sudha Mishra; Preeti G. Joshi

2003-01-01

316

A time-resolved, internally quenched fluorescence assay to characterize inhibition of hepatitis C virus nonstructural protein 3–4A protease at low enzyme concentrations  

Microsoft Academic Search

The hepatitis C virus (HCV) nonstructural protein 3 (NS3) with its cofactor NS4A is a pivotal enzyme for the replication of HCV. Inhibition of NS3–4A protease activity has been validated as an antiviral target in clinical studies of inhibitors of the enzyme. We have developed a sensitive time-resolved fluorescence (TRF) assay capable of detecting very low NS3–4A concentrations. A depsipeptide

Shi-Shan Mao; Jillian DiMuzio; Carolyn McHale; Christine Burlein; David Olsen; Steven S. Carroll

2008-01-01

317

Time-resolved fluorescence studies of the interactions between the thermoresponsive polymer host, poly( N-isopropylacrylamide), and a hydrophobic guest, pyrene  

Microsoft Academic Search

The time-resolved fluorescence anisotropy behaviour of pyrene solubilized (10?6M) in ultra-dilute (10?3wt%) aqueous solutions of the thermoresponsive polymer poly(N-isopropylacrylamide), PNIPAM, shows unusual characteristics. Rather than decay to zero (as expected of a freely rotating species in a homogeneous fluid environment) the anisotropy of the emission from the probe attains a minimum but finite value, some 40ns after excitation of the

C. K. Chee; K. P. Ghiggino; T. A. Smith; S. Rimmer; I. Soutar; L. Swanson

2001-01-01

318

Effect of sphere to rod transition on the probe microenvironment in sodium dodecyl sulphate micelles: A time resolved fluorescence anisotropy study  

Microsoft Academic Search

The effect of different hydrotropic salts on the microenvironment at the anionic head group region of sodium dodecyl sulphate (SDS) micelle has been studied through time-resolved fluorescence anisotropy measurements of a solubilized probe, coumarin-153 (C153). The organic cations of the hydrotropic salts used in this study, i.e. aniline hydrochloride (AHC) and o-, m- and p-toluidine hydrochlorides (OTHC, MTHC and PTHC,

Teena Goel; Manoj Kumbhakar; Tulsi Mukherjee; Haridas Pal

2010-01-01

319

Chromophore-anion interactions in halorhodopsin from Natronobacterium pharaonis probed by time-resolved resonance Raman spectroscopy.  

PubMed

Halorhodopsin of Natronobacterium pharaonis which acts as a light-driven chloride pump is studied by time-resolved resonance Raman spectroscopy. In single-beam experiments, resonance Raman spectra were obtained of the parent state HR578 and the first thermal intermediate HR520. The parent state is structural heterogeneous including ca. 80% all-trans and 20% 13-cis isomers. The resonance Raman spectra indicate that the all-trans conformer exhibits essentially the same chromophoric structure as in the parent states of bacteriorhodopsin or halorhodopsin from Halobacterium salinarium. Special emphasis of the resonance Raman spectroscopic analysis was laid on the C=C and C=N stretching region in order to probe the interactions between the protonated Schiff base and various bound anions (chloride, bromide, iodide). These investigations were paralleled by spectroscopic studies of retinal Schiff base model complexes in different solvents in an attempt to determine the various parameters which control the C=C and C=N stretching frequencies. From these data, it was concluded that in the parent state the anion is not involved in hydrogen bonding interactions with the Schiff base proton but is presumably bound to a nearby (positively charged) amino acid residue. On the other hand, the anion still exerts an appreciable effect on the chromophore structure which is, for instance, reflected by the variation of the isomer composition in the presence of different anions and in the anion-depleted form. In contrast to the parent state, the intermediate HR520 reveals frequency shifts of the C=N stretching in the presence of different anions. These findings indicate a closer proximity of the bound anion to the Schiff base proton which is sufficient for hydrogen bonding interactions. These changes of the anion-chromophore interaction upon transition from HR578 to HR520 may be related to the coupling of the chromophore movement with the anion translocation. PMID:9283093

Gerscher, S; Mylrajan, M; Hildebrandt, P; Baron, M H; Müller, R; Engelhard, M

1997-09-01

320

Diffusion of water in Nafion using time-resolved Fourier transform infrared-attenuated total reflectance spectroscopy.  

PubMed

Hydrogen fuel cells are attractive alternative power sources for applications such as transportation; however, fuel cell performance is a strong function of water equilibrium content and water sorption and desorption kinetics in polymer electrolyte membranes (e.g., Nafion). Although similar water sorption isotherms for Nafion have been reproduced in many laboratories, reported diffusion coefficients of water in Nafion vary by 4 orders of magnitude. In this study, sorption and desorption dynamics of water vapor in Nafion were measured as a function of water vapor activity and flow rate using time-resolved Fourier transform infrared-attenuated total reflectance (FTIR-ATR) spectroscopy. Both integral and differential experiments were performed, where integral experiments consisted of increasing the vapor activity from 0% RH to one of five values (22, 43, 56, 80, or 100% RH), while in differential experiments the activity was sequentially increased in smaller steps from 0 to 22 to 43 to 56 to 80 to 100% RH. For integral experiments, non-Fickian behavior was observed at both low and high vapor activities, while Fickian behavior was observed at moderate vapor activities. For differential experiments, Fickian behavior was observed at all vapor activities except at low vapor activities (0-22% RH). Sorption kinetics was found to be a function of flow rate, where mass transfer resistance at the vapor/polymer interface was significant at low flow rates but was insignificant at high flow rates. Accurate sorption and desorption diffusion coefficients were calculated in this study (measured at high flow rates with no mass transfer resistance) and were similar, on the order of 10(-7) cm(2)/s, and weak functions of water vapor activity. PMID:19320522

Hallinan, Daniel T; Elabd, Yossef A

2009-04-01

321

Time resolved infrared spectroscopy: kinetic studies of weakly binding ligands in an iron-iron hydrogenase model compound.  

PubMed

Solution photochemistry of (?-pdt)[Fe(CO)(3)](2) (pdt = ?(2)-S(CH(2))(3)S), a precursor model of the 2-Fe subsite of the H-cluster of the hydrogenase enzyme, has been studied using time-resolved infrared spectroscopy. Following the loss of CO, solvation of the Fe center by the weakly binding ligands cyclohexene, 3-hexyne, THF, and 2,3-dihydrofuran (DHF) occurred. Subsequent ligand substitution of these weakly bound ligands by pyridine or cyclooctene to afford a more stable complex was found to take place via a dissociative mechanism on a seconds time scale with activation parameters consistent with such a pathway. That is, the ?S(‡) values were positive and the ?H(‡) parameters closely agreed with bond dissociation enthalpies (BDEs) obtained from DFT calculations. For example, for cyclohexene replacement by pyridine, experimental ?H(‡) and ?S(‡) values were determined to be 19.7 ± 0.6 kcal/mol (versus a theoretical prediction of 19.8 kcal/mol) and 15 ± 2 eu, respectively. The ambidentate ligand 2,3-DHF was shown to initially bind to the iron center via its oxygen atom followed by an intramolecular rearrangement to the more stable ?(2)-olefin bound species. DFT calculations revealed a transition state structure with the iron atom almost equidistant from the oxygen and one edge of the olefinic bond. The computed ?H(‡) of 10.7 kcal/mol for this isomerization process was found to be in excellent agreement with the experimental value of 11.2 ± 0.3 kcal/mol. PMID:22680284

Muhammad, Sohail; Moncho, Salvador; Brothers, Edward N; Darensbourg, Marcetta Y; Darensbourg, Donald J; Bengali, Ashfaq A

2012-06-08

322

Monitoring changes of cellular metabolism and microviscosity in vitro based on time-resolved endogenous fluorescence and its anisotropy decay dynamics  

NASA Astrophysics Data System (ADS)

Reduced nicotinamide adenine dinucleotide (NADH) is a well-known metabolic coenzyme and endogenous fluorophore. In this study, we develop a system that simultaneously measures time- and wavelength-resolved fluorescence to extract free and protein-bound NADH signals from total cellular fluorescence. We analyze temporal characteristics of NADH fluorescence in a mixture of NADH and lactate dehydrogenase (LDH) as well as in living cell samples. The results show that in both the NADH/LDH mixture and cell samples, a fraction of free NADH and protein-bound components can be identified. The extracted free and bound NADH signals are confirmed by time-resolved measurement of anisotropy decay of NADH fluorescence, based on the fact that free NADH is a small fluorescent molecule with much shorter rotational diffusion time than bound NADH. The ratio of free NADH signal to bound NADH signal is very different between normal and cancer cervical epithelial cells. In addition, the ratio changes significantly when the cell samples are treated with a mitochondrial inhibitor or uncoupler, demonstrating that the method is sensitive to monitor cellular metabolic activity. Finally, we demonstrate that the microviscosity for relatively small molecules such as NADH in cells could be extracted from wavelength- and time-resolved NADH fluorescence of living cell samples.

Zheng, Wei; Li, Dong; Qu, Jianan Y.

2010-05-01

323

Monitoring changes of cellular metabolism and microviscosity in vitro based on time-resolved endogenous fluorescence and its anisotropy decay dynamics.  

PubMed

Reduced nicotinamide adenine dinucleotide (NADH) is a well-known metabolic coenzyme and endogenous fluorophore. In this study, we develop a system that simultaneously measures time- and wavelength-resolved fluorescence to extract free and protein-bound NADH signals from total cellular fluorescence. We analyze temporal characteristics of NADH fluorescence in a mixture of NADH and lactate dehydrogenase (LDH) as well as in living cell samples. The results show that in both the NADH/LDH mixture and cell samples, a fraction of free NADH and protein-bound components can be identified. The extracted free and bound NADH signals are confirmed by time-resolved measurement of anisotropy decay of NADH fluorescence, based on the fact that free NADH is a small fluorescent molecule with much shorter rotational diffusion time than bound NADH. The ratio of free NADH signal to bound NADH signal is very different between normal and cancer cervical epithelial cells. In addition, the ratio changes significantly when the cell samples are treated with a mitochondrial inhibitor or uncoupler, demonstrating that the method is sensitive to monitor cellular metabolic activity. Finally, we demonstrate that the microviscosity for relatively small molecules such as NADH in cells could be extracted from wavelength- and time-resolved NADH fluorescence of living cell samples. PMID:20615042

Zheng, Wei; Li, Dong; Qu, Jianan Y

324

Time-resolved fluorescence anisotropy studies show domain-specific interactions of calmodulin with IQ target sequences of myosin V  

Microsoft Academic Search

Single cysteine mutants of calmodulin, Cam(S38C) and Cam(N111C), have been specifically labelled with Alexa488 maleimide to study the effects of calcium on the structural dynamics of calmodulin complexed with IQ3, IQ4 and IQ34 target peptide motifs of mouse unconventional myosin-V. Using phase fluorometry, the time-resolved anisotropy shows well-separated global and segmental correlation times. The calcium-sensitive global motion of either calmodulin

Peter Bayley; Stephen Martin; Peter Browne; Catherine Royer

2003-01-01

325

Strongly nonexponential time-resolved fluorescence of quantum-dot ensembles in three-dimensional photonic crystals  

Microsoft Academic Search

We observe experimentally that ensembles of quantum dots in three-dimensional (3D) photonic crystals reveal strongly nonexponential time-resolved emission. These complex emission decay curves are analyzed with a continuous distribution of decay rates. The log-normal distribution describes the decays well for all studied lattice parameters. The distribution width is identified with variations of the radiative emission rates of quantum dots with

Ivan S. Nikolaev; Peter Lodahl; Driel van A. Floris; A. Femius Koenderink; Willem L. Vos

2007-01-01

326

Time-resolved FTIR spectroscopy for monitoring protein dynamics exemplified by functional studies of Ras protein bound to a lipid bilayer  

NASA Astrophysics Data System (ADS)

Time-resolved Fourier transform infrared (FTIR) difference spectroscopy is a valuable tool for monitoring the dynamics of protein reactions and interactions. Absorbance changes can be monitored with time resolutions down to nanoseconds and followed for time periods that range over nine orders of magnitude. Membrane proteins bound to solid supported lipid bilayers can be investigated in near physiological conditions with the attenuated total reflection (ATR) technique. Here, we review the basics of time-resolved FTIR with a focus on Ras, a GTPase that is mutated in 25% of human tumors. We show the first time-resolved measurements of membrane anchored Ras and observed the switching between its activated and its inactivated state. We compared those measurements with measurements of the truncated Ras in solution. We found that both the kinetics and the functional groups involved were very similar. This suggested that the membrane did not have a major influence on the hydrolysis reaction.

Kötting, Carsten; Güldenhaupt, Jörn; Gerwert, Klaus

2012-03-01

327

Electrochemical control of the conductivity in an organic memristor: a time-resolved X-ray fluorescence study of ionic drift as a function of the applied voltage.  

PubMed

Grazing-incidence X-ray fluorescence measurements were applied for a time-resolved study of an organic memristor conductivity variation mechanism. A comparison of these results with electrical measurements has allowed us to conclude that the variation of the fluorescence intensity of Rb ions is directly connected to the ionic charge transferred between the conducting polymer and the solid electrolyte, which made up the device. In addition, the conductivity of the memristor was shown to be a function of the transferred ionic charge. PMID:20355843

Berzina, Tatiana; Erokhina, Svetlana; Camorani, Paolo; Konovalov, Oleg; Erokhin, Victor; Fontana, M P

2009-10-01

328

Model-independent time-resolved fluorescence depolarization from ordered biological assemblies applied to restricted motion of myosin cross-bridges in muscle fibers.  

PubMed

We formulate a model-independent description of time-dependent restricted molecular rotational motion and apply it to the time-resolved fluorescence depolarization signal from fluorescence-labeled molecules following polarized excitation. In this treatment, the time-dependent molecular orientation distribution is equal to the operation of a linear time-development operator on the initial orientation distribution. The formula for the time-development operator is derived from the equation of motion for the orientation distribution. The time-development operator is then expanded in time in terms of a complete set of orthonormal polynomials. When this expression for the orientation distribution is used to calculate the time-resolved fluorescence depolarization signal, properties of the orthonormal polynomials allow the signal to be quantitated uniquely in terms of matrix elements of the differential operators from the equation of motion. We demonstrate how to obtain the experimental value of the matrix elements directly from the fluorescence depolarization signal. In this paper, we also describe the application of the model-independent formalism to fluorescence-labeled myosin cross-bridges in muscle fibers when the fibers are in a variety of physiological states. We show that the analysis of time-resolved fluorescence depolarization data with the new formalism and the rotational diffusion in a potential model results in a slight revision of our previous estimate of the relaxed cross-bridge rotational diffusion constant and the determination of rank 6 order parameters that were ignored in the previous analysis [Burghardt, T. P., & Thompson, N. L. (1985) Biochemistry 24, 3731-3735]. The rank 6 order parameters are shown to make a significant contribution to the proposed steady-state angular distribution of the relaxed cross-bridges. Order parameters of rank 6 do not contribute to the steady-state fluorescence polarization signal and can only be detected with the time-resolved signal [Burghardt, T. P. (1984) Biopolymers 23, 2383-2406]. We have also applied the model-independent formalism to new data from fibers in rigor when the fibers are in a configuration such that the excitation light polarization is perpendicular to the fiber axis and the light propagates along the fiber axis, so that the fluorescence depolarization signal is sensitive to probe rotational motions about the fiber axis.(ABSTRACT TRUNCATED AT 400 WORDS) PMID:3730371

Burghardt, T P; Ajtai, K

1986-06-01

329

Fluorescence correlation spectroscopy.  

PubMed

Fluorescence correlation spectroscopy (FCS) is a powerful technique to measure concentrations, mobilities, and interactions of fluorescent biomolecules. It can be applied to various biological systems such as simple homogeneous solutions, cells, artificial, or cellular membranes and whole organisms. Here, we introduce the basic principle of FCS, discuss its application to biological questions as well as its limitations and challenges, present an overview of novel technical developments to overcome those challenges, and conclude with speculations about the future applications of fluorescence fluctuation spectroscopy. PMID:22415816

Ries, Jonas; Schwille, Petra

2012-03-13

330

Local structures in ionic liquids probed and characterized by microscopic thermal diffusion monitored with picosecond time-resolved Raman spectroscopy  

NASA Astrophysics Data System (ADS)

Vibrational cooling rate of the first excited singlet (S1) state of trans-stilbene and bulk thermal diffusivity are measured for seven room temperature ionic liquids, C2mimTf2N, C4mimTf2N, C4mimPF6, C5mimTf2N, C6mimTf2N, C8mimTf2N, and bmpyTf2N. Vibrational cooling rate measured with picosecond time-resolved Raman spectroscopy reflects solute-solvent and solvent-solvent energy transfer in a microscopic solvent environment. Thermal diffusivity measured with the transient grating method indicates macroscopic heat conduction capability. Vibrational cooling rate of S1 trans-stilbene is known to have a good correlation with bulk thermal diffusivity in ordinary molecular liquids. In the seven ionic liquids studied, however, vibrational cooling rate shows no correlation with thermal diffusivity; the observed rates are similar (0.082 to 0.12 ps-1 in the seven ionic liquids and 0.08 to 0.14 ps-1 in molecular liquids) despite large differences in thermal diffusivity (5.4-7.5 × 10-8 m2 s-1 in ionic liquids and 8.0-10 × 10-8 m2 s-1 in molecular liquids). This finding is consistent with our working hypothesis that there are local structures characteristically formed in ionic liquids. Vibrational cooling rate is determined by energy transfer among solvent ions in a local structure, while macroscopic thermal diffusion is controlled by heat transfer over boundaries of local structures. By using ``local'' thermal diffusivity, we are able to simulate the vibrational cooling kinetics observed in ionic liquids with a model assuming thermal diffusion in continuous media. The lower limit of the size of local structure is estimated with vibrational cooling process observed with and without the excess energy. A quantitative discussion with a numerical simulation shows that the diameter of local structure is larger than 10 nm. If we combine this lower limit, 10 nm, with the upper limit, 100 nm, which is estimated from the transparency (no light scattering) of ionic liquids, an order of magnitude estimate of local structure is obtained as 10 nm < L < 100 nm, where L is the length or the diameter of the domain of local structure.

Yoshida, Kyousuke; Iwata, Koichi; Nishiyama, Yoshio; Kimura, Yoshifumi; Hamaguchi, Hiro-O.

2012-03-01

331

Local structures in ionic liquids probed and characterized by microscopic thermal diffusion monitored with picosecond time-resolved Raman spectroscopy.  

PubMed

Vibrational cooling rate of the first excited singlet (S(1)) state of trans-stilbene and bulk thermal diffusivity are measured for seven room temperature ionic liquids, C(2)mimTf(2)N, C(4)mimTf(2)N, C(4)mimPF(6), C(5)mimTf(2)N, C(6)mimTf(2)N, C(8)mimTf(2)N, and bmpyTf(2)N. Vibrational cooling rate measured with picosecond time-resolved Raman spectroscopy reflects solute-solvent and solvent-solvent energy transfer in a microscopic solvent environment. Thermal diffusivity measured with the transient grating method indicates macroscopic heat conduction capability. Vibrational cooling rate of S(1) trans-stilbene is known to have a good correlation with bulk thermal diffusivity in ordinary molecular liquids. In the seven ionic liquids studied, however, vibrational cooling rate shows no correlation with thermal diffusivity; the observed rates are similar (0.082 to 0.12 ps(-1) in the seven ionic liquids and 0.08 to 0.14 ps(-1) in molecular liquids) despite large differences in thermal diffusivity (5.4-7.5 × 10(-8) m(2) s(-1) in ionic liquids and 8.0-10 × 10(-8) m(2) s(-1) in molecular liquids). This finding is consistent with our working hypothesis that there are local structures characteristically formed in ionic liquids. Vibrational cooling rate is determined by energy transfer among solvent ions in a local structure, while macroscopic thermal diffusion is controlled by heat transfer over boundaries of local structures. By using "local" thermal diffusivity, we are able to simulate the vibrational cooling kinetics observed in ionic liquids with a model assuming thermal diffusion in continuous media. The lower limit of the size of local structure is estimated with vibrational cooling process observed with and without the excess energy. A quantitative discussion with a numerical simulation shows that the diameter of local structure is larger than 10 nm. If we combine this lower limit, 10 nm, with the upper limit, 100 nm, which is estimated from the transparency (no light scattering) of ionic liquids, an order of magnitude estimate of local structure is obtained as 10 nm < L < 100 nm, where L is the length or the diameter of the domain of local structure. PMID:22423845

Yoshida, Kyousuke; Iwata, Koichi; Nishiyama, Yoshio; Kimura, Yoshifumi; Hamaguchi, Hiro-o

2012-03-14

332

Testing the Physical Mechanisms of Gamma-Ray Bursts with Multi-Instrument Time-Resolved Spectroscopy.  

National Technical Information Service (NTIS)

We have continued the project of time-resolved spectral analyses of gamma-ray bursts observed jointly by the BATSE and the Wide-Field Camera on board BeppoSAX. We are making progress understanding the systematic differences between the two data sets. Thes...

M. S. Briggs R. E. Preece

2001-01-01

333

Time-resolved rapid-scan Fourier transform infrared difference spectroscopy on a noncyclic photosystem: rhodopsin photointermediates from Lumi to Meta II.  

PubMed

The visual pigment rhodopsin has been extensively studied for the kinetics of its photointermediates by various spectroscopic methods. Unlike such archaeal retinal proteins as bacteriorhodopsin, visual rhodopsin does not thermally recover its dark state after photoexcitation, which precludes repeated excitation of a single sample and thereby complicates time-resolved experiments. Kinetic data on the late rhodopsin photointermediates have so far been available mainly from time-resolved ultraviolet (UV)-visible spectroscopy, but not from Fourier transform infrared (FTIR) spectroscopy. The latter has the advantage of being informative of structural changes of both chromophore and protein, but does not allow the highly reproducible, automated sample exchange procedures available to UV-visible spectroscopy. Using rapid-scan FTIR difference spectroscopy, we obtained time-resolved data sets that were analyzed by a maximum entropy inverse Laplace-transform. Covering the time range from 8 ms to 15 s at temperatures of 0 and -7 degrees C, the transitions from the Lumi to the Meta I and from the Meta I to the Meta II photoproduct states could be resolved. In the transition from Meta I to Meta II, our data reveal a partial deprotonation of the retinal Schiff base preceding the conformational change of the receptor protein to Meta II. The technique and the results are discussed in regard to its advantages as well as its limitations. PMID:16721790

Lüdeke, Steffen; Lórenz Fonfría, Víctor A; Siebert, Friedrich; Vogel, Reiner

2006-10-01

334

Optical studies of Cr3+ in KMgF3: Time-resolved site-selective spectroscopy and experimental evidence of spin-orbit coupling  

Microsoft Academic Search

Three different sites of the Cr3+ ions in the fluoride perovskite KMgF3 have been identified by absorption, selective optical excitation, and time-resolved emission spectroscopy of the 4T24A2 transition. High-pressure measurements showing the crossover from low-crystal field to high-crystal field, allows us to situate the Dq\\/B values of the different chromium sites clearly below 2.3. The different spin-orbit components associated with

M. Mortier; Q. Wang; J. Y. Buzaré; M. Rousseau; B. Piriou

1997-01-01

335

Time-resolved photoluminescence spectroscopy of InAs quantum dots on InP with various InAlGaAs barrier thicknesses  

Microsoft Academic Search

The Optical characteristics of InAs quantum dots (QDs) embeded in InAlGaAs on InP have been investigated by photoluminescence (PL) spectroscopy and time-resolved PL. Four different QD samples are grown by using molecular beam epitaxy, and all the QD samples have five-stacked InAs quantum dot layers with a different InAlGaAs barrier thickness. The PL yield from InAs QDs was increased with

J. J. Yoon; S. I. Jung; H. J. Park; H. K. Suh; M. H. Jeon; J. Y. Leem; E. T. Cho; J. I. Lee; H. K. Cho; Y. G. Mo; J. S. Kim; J. S. Son; I. K. Han

2005-01-01

336

Femtosecond time-resolved optical pump-probe spectroscopy at kilohertz-scan-rates over nanosecond-time-delays without mechanical delay line  

Microsoft Academic Search

We demonstrate a technique for femtosecond time-resolved optical pump-probe spectroscopy that allows to scan over a nanosecond time delay at a kilohertz scan rate without mechanical delay line. Two mode-locked femtosecond lasers with approximately 1 GHz repetition rate are linked at a fixed difference frequency of DeltafR=11 kHz. One laser delivers the pump pulses, the other provides the probe pulses.

A. Bartels; F. Hudert; C. Janke; T. Dekorsy; K. Köhler

2006-01-01

337

Kinetics of the F + NO 2 + M ? FNO 2 + M reaction studied by pulse radiolysis combined with time-resolved IR and UV spectroscopy  

Microsoft Academic Search

The title reaction was initiated by the pulse radiolys ofSF6NO2 gas mixtures, and the formation of FNO2 was studied by time-resolved infrared spectroscopy employing strong rotational transitions within the?1and?4 bands of FNO2. The pressure dependence of the formation kinetics was studied with SF6 pressures of 5–1000 mbar at 298 K. Comparative studies were carried out by monitoring the decay kinetics

Palle Pagsberg; Alfred Sillesen; Jerzy T. Jodkowski; Emil Ratajczak

1996-01-01

338

Tryptophan dynamics in the exploration of micro-conformational changes of refolded ?-lactoglobulin after thermal exposure: a steady state and time-resolved fluorescence approach.  

PubMed

Refolding intermediates of proteins, including molten globules, are likely to undergo dynamic conformational transitions. In this work, thermal unfolding and refolding of bovine ?-lactoglobulin (?-lg) have been revisited to encounter such intermediate states. Lower thermal range (< 80°C) was selected to avoid irreversible aggregate formation. The gross kinetic refolding as monitored with the fluorophore, Trp19, was likely to be reversible but alteration in time resolved fluorescence parameters ruled out the possibility of micro-structural reversibility for the refolded partner. Time resolved fluorescence showed that the refolded protein still lacks some intact native conformation. Far-UV CD signals lack the signature of any secondary structural distortion in global structural context whereas near-UV CD signals were strongly indicative of perturbation in micro-structure surrounding the aromatic moieties which hardly revives after cooling. Steady state anisotropy results showed successfully the break-down of dimer to monomer form of ?-lg within 50°C temperature range and augmentation in anisotropy up on further thermal stress reflected the reorganization of tryptophan residues into more restricted and rigid micro-environment as well as irreversible disulfide-linked dimer formation. Reliability of conformational reversibility in the thermal unfolding-refolding is still enigmatic on micro and global structural perspectives. Intermediate state prior to the completion of refolding of thermally exposed ?-lg was identified through fluorescence studies. PMID:22342029

Halder, Umesh C; Chakraborty, Jishnu; Das, Niloy; Bose, Sayantan

2012-02-01

339

Time-resolved Raman spectroscopy applied to the photoinduced phenomena in NaV2O5  

Microsoft Academic Search

Picosecond time resolved Raman scattering measurements were performed in a spin ladder system alpha'-NaV2O5. We observed the decrease and recovery of the superstructure peak at 66 cm-1 in the low temperature phase by photoexcitation. The transient local temperature of the sample by photoexcitation was obtained from the intensity ratio of the anti-Stokes and Stokes scattering. It is found that the

Makoto Nakajima; Kenji Kazumi; Masahiko Isobe; Yutaka Ueda; Tohru Suemoto

2005-01-01

340

NS-SCALE TIME-RESOLVED LASER INDUCED FLUORESCENCE IMAGING FOR DETECTION OF FECAL CONTAMINATION ON APPLES  

Technology Transfer Automated Retrieval System (TEKTRAN)

Our laboratory has been utilizing fluorescence techniques as a potential means for detection of quality and wholesomeness of food products. A system with a short pulse light source such as a laser coupled with a gated detector can be used to harvest fluorescence in ambient light conditions from bio...

341

Simultaneously reconstructing fluorescent yield and lifetime from time-resolved transmittances of a small-animal-sized phantom  

NASA Astrophysics Data System (ADS)

A full three-dimensional, featured-data algorithm for time-domain diffuse fluorescence tomography is presented, which inverts the Laplace-transformed time-domain coupled diffusion equations and employs a pair of real-domain transform-factors to effectively separate the fluorescent yield and lifetime parameters. By use of a multi-channel time-correlation single photon counting system and a normalized Born formulation for the inversion, the proposed scheme is experimentally validated to achieve simultaneous reconstruction of the fluorescent yield and lifetime distributions with a reasonable accuracy.

Gao, Feng; Zhang, Limin; Poulet, Patrick; Li, Jiao; Zhao, Huijuan; Yamada, Yukio

2009-07-01

342

Design of peptide substrates for nanosecond time-resolved fluorescence assays of proteases: 2,3-diazabicyclo[2.2.2]oct-2-ene as a noninvasive fluorophore.  

PubMed

Fluorescence protease assays were investigated with peptide substrates containing a 2,3-diazabicyclo[2.2.2]oct-2-ene-labeled asparagine (Dbo) as a fluorescent amino acid. The special characteristic of the fluorophore Dbo is its exceedingly long fluorescence lifetime (ca. 300 ns in water under air), which allows the use of nanosecond time-resolved fluorescence (Nano-TRF) detection to efficiently suppress shorter-lived background emission. In addition, the natural amino acids tryptophan and tyrosine can be employed as intramolecular fluorescence quenchers, which facilitates substrate design. Fourteen synthetic peptide substrates (composed of 2-19 amino acids) and five enzymes (trypsin, pepsin, carboxypeptidase A, leucine aminopeptidase, and chymotrypsin) were investigated and, in all 28 examined combinations, enzymatic activity was detected by monitoring the increase in steady state fluorescence with time and determining the reaction rates as kcat/Km values, which ranged from 0.2 to 80x10(6) M-1 min-1. The results suggest an excellent compatibility of the very small and hydrophilic fluorescent probe Dbo with solid-phase peptide synthesis and the investigated proteases. For all 14 peptides the fluorescence lifetimes before and after enzymatic cleavage were measured and Nano-TRF measurements were performed in 384-well microplates. The fluorescence lifetimes of the different peptides provide the basis for the rational design of Dbo-based fluorescent substrates for protease assays. Measurements in Nano-TRF mode revealed, in addition to efficient suppression of background fluorescence, an increased differentiation between cleaved and uncleaved substrate. The Dbo-based assays can be adapted for high-throughput screening. PMID:17134673

Hennig, Andreas; Florea, Mara; Roth, Doris; Enderle, Thilo; Nau, Werner M

2006-11-03

343

Multichannel, time-resolved picosecond laser ultrasound imaging and spectroscopy with custom complementary metal-oxide-semiconductor detector  

SciTech Connect

This paper presents a multichannel, time-resolved picosecond laser ultrasound system that uses a custom complementary metal-oxide-semiconductor linear array detector. This novel sensor allows parallel phase-sensitive detection of very low contrast modulated signals with performance in each channel comparable to that of a discrete photodiode and a lock-in amplifier. Application of the instrument is demonstrated by parallelizing spatial measurements to produce two-dimensional thickness maps on a layered sample, and spectroscopic parallelization is demonstrated by presenting the measured Brillouin oscillations from a gallium arsenide wafer. This paper demonstrates the significant advantages of our approach to pump probe systems, especially picosecond ultrasonics.

Smith, Richard J.; Light, Roger A.; Johnston, Nicholas S.; Pitter, Mark C.; Somekh, Mike G. [Institute of Biophysics, Imaging and Optical Science, University of Nottingham, Nottinghamshire NG7 2RD (United Kingdom); Sharples, Steve D. [Applied Optics Group, Electrical Systems and Optics Research Division, University of Nottingham, Nottinghamshire NG7 2RD (United Kingdom)

2010-02-15

344

Enhancement of the high-order harmonic generation from the gold plume using the time-resolved plasma spectroscopy  

SciTech Connect

We present systematic time-resolved investigations of plasma conditions for achieving the maximum cutoff and maximum conversion efficiency of high-order harmonic generation from gold plasma within the plateau. We analyzed harmonic generation under different laser-plasma conditions. We also performed simulations to calculate the ionization state of the gold plasma, the free electron density, and singly charged ion density at different prepulse intensities. By optimizing the plasma conditions, we observed a harmonic cutoff at the 53rd order ({lambda}=15.09 nm). We estimate the conversion efficiency of the harmonics within the plateau region to be 2x10{sup -6}.

Ganeev, Rashid A.; Elouga Bom, Luc B.; Ozaki, Tsuneyuki [Institut National de la Recherche Scientifique, Energie, Materiaux et Telecommunications, 1650 Lionel-Boulet, Varennes, Quebec J3X 1S2 (Canada) and Scientific Association Akadempribor, Academy of Sciences of Uzbekistan, Akademgorodok, Tashkent 100125 (Uzbekistan); Institut National de la Recherche Scientifique, Energie, Materiaux et Telecommunications, 1650 Lionel-Boulet, Varennes, Quebec J3X 1S2 (Canada)

2007-10-01

345

Time-Resolved X-ray Absorption Spectroscopy of Carbon Monoxide-Myoglobin Recombination After Laser Photolysis.  

PubMed

Results are presented for the first time-resolved x-ray absorption measurements with a time resolution of 300 microseconds on a dynamically evolving chemical system. By synchronizing a neodymium: yttrium-aluminum-garnet pulsed laser with the bursts of x-rays emitted from the Cornell High Energy Synchrotron Source, it was possible to monitor at room temperature the recombination of carbon monoxide with myoglobin after laser photolysis. Changes in the pre-edge structure and in the position of the iron edge of this protein were detected as a function of time. PMID:17737757

Mills, D M; Lewis, A; Harootunian, A; Huang, J; Smith, B

1984-02-24

346

Separation of indocyanine green boluses in the human brain and scalp based on time-resolved in-vivo fluorescence measurements  

NASA Astrophysics Data System (ADS)

Non-invasive detection of fluorescence from the optical tracer indocyanine green is feasible in the adult human brain when employing a time-domain technique with picosecond resolution. A fluorescence-based assessment may offer higher signal-to-noise ratio when compared to bolus tracking relying on changes in time-resolved diffuse reflectance. The essential challenge is to discriminate the fluorescence originating from the brain from contamination by extracerebral fluorescence and hence to reconstruct the bolus kinetics; however, a method to reliably perform the necessary separation is missing. We present a novel approach for the decomposition of the fluorescence contributions from the two tissue compartments. The corresponding sensitivity functions pertaining to the brain and to the extracerebral compartment are directly derived from the in-vivo measurement. This is achieved by assuming that during the initial and the late phase of bolus transit the fluorescence signal originates largely from one of the compartments. Solving the system of linear equations allows one to approximate time courses of a bolus for each compartment. We applied this method to repetitive measurements on two healthy subjects with an overall 34 boluses. A reconstruction of the bolus kinetics was possible in 62% of all cases.

Jelzow, Alexander; Wabnitz, Heidrun; Obrig, Hellmuth; Macdonald, Rainer; Steinbrink, Jens

2012-05-01

347

Microfluidic space-domain time-resolved emission spectroscopy of terbium(III) and europium(III) chelates with pyridine-2,6-dicarboxylate.  

PubMed

This article describes the utilization of laminar microflows for time-resolved emission measurements with steady-state excitation and detection. Passing a laminar flow through a short illuminated section of a microchannel provided a means for pulsed-like photoexcitation of the moieties carried by the fluid. Imaging the microchannel flows carrying thus photoexcited chelates of lanthanide ions allowed us to extract their excited-state lifetimes from the spatial distribution of the changes in the emission intensity. The lifetime values obtained using this space-domain approach agreed well with the lifetimes from time-domain measurements. This validated space-domain microfluidic approach reveals a means for miniaturization of time-resolved emission spectroscopy. PMID:23550512

Nuñez, Vicente; Upadhyayula, Srigokul; Millare, Brent; Larsen, Jillian M; Hadian, Ali; Shin, Sanghoon; Vandrangi, Prashanthi; Gupta, Sharad; Xu, Hong; Lin, Adam P; Georgiev, Georgi Y; Vullev, Valentine I

2013-04-17

348

Improvements in signal acquisition and processing for time-resolved step-scan FT-IR spectroscopy  

NASA Astrophysics Data System (ADS)

A broadband amplifier with a short rise time was developed for the acquisition of the time dependent part of the interferogram in time-resolved step-scan measurements. Amplification of this portion of the interferogram by about 40 dB is necessary to digitize signal and noise with adequate amplitude resolution. Therefore, the transient ac-signal from the detector has to be separated from the static dc-signal being larger by a factor of thousand. We describe here a way to avoid the currently used ac-coupling of the signal which is always related to the disadvantage of a low frequency limit for time-dependent signals. Since the recorded interferogram shows distortions caused by nonlinear response of the MCT-detector, especially, when a photoconductive detector is used, we implemented a software nonlinearity correction method proposed by Keens and Simon (1). The effects of the nonlinearity correction on the time-resolved step-scan difference spectra of biological samples are demonstrated.

Rödig, C.; Siebert, F.

1998-06-01

349

Nanosecond fluorescence spectroscopy  

SciTech Connect

This article is a summary of a short course lecture given in conjunction with the 1984 Nuclear Science Symposium. Measuring systems for nanosecond fluorescence spectroscopy using single-photon counting techniques are presented. These involve systems based on relaxation-type spark gap light pulser and synchronously pumped mode-locked dye lasers. Furthermore, typical characteristics and optimization of operating conditions of the critical components responsible for the system time resolution are discussed. A short comparison of the most important deconvolution methods for numerical analysis of experimental data is given particularly with respect to the signal-to-noise ratio of the fluorescence signal. 22 refs., 8 figs.

Leskovar, B.

1985-03-01

350

Radiation-induced polymerization monitored in situ by time-resolved fluorescence of probe molecules in methyl methacrylate  

NASA Astrophysics Data System (ADS)

A technique is presented for monitoring radiation-induced polymerizations in situ based on the measurement of the fluorescence lifetime of molecular probes dissolved in the polymerizing medium. This method is illustrated with results on methyl methacrylate (MMA) using two fluorogenic probe molecules; N-(2-anthracene)methacrylamide (AnMA) and maleimido-fluoroprobe (MFP), a molecule which has a highly dipolar excited state.

Frahn, Mark S.; Abellon, Ruben D.; Luthjens, Leonard H.; Vermeulen, Martien J. W.; Warman, John M.

2003-08-01

351

Deriving Intrinsic Parameters of Photoinduced Electron Transfer Reaction from the Transient Effect Probed by Picosecond Time-Resolved Fluorescence Quenching  

Microsoft Academic Search

Fluorescence quenching of a pyrylium salt (PDP2+) by toluene in acetonitrile gives rise to a nonexponential decay. This behavior is ascribed to the so-called transient effect occurring at high quencher concentrations for diffusion-controlled reactions. First, the Kalman filter was used to deconvolute the original signal from the experimental decay curve and the response function of the apparatus. This treatment led

X. Allonas; P. Jacques; A. Accary; M. Kessler; F. Heisel

2000-01-01

352

Time Resolved Detection of Native Molecular Emissions and Recombination using Femtosecond Laser Induced Breakdown Spectroscopy from Organic Compounds  

NASA Astrophysics Data System (ADS)

Laser induced breakdown plasmas are ``dirty'' events yielding a mixture of ionized species, electrons, and non-ionized matter of various size. Molecular emissions have been detected in excited nanosecond plasmas microseconds after the ablation event. However, with these molecular signatures it is difficult to distinguish between native emissions and atmospheric recombination with respect to the sample probed. A time resolved study during and after the continuum of the plasma event produced from specific organic materials can yield a possible insight in identifying native molecular emission and recombination. In this study, a plasma was formed by interacting a femtosecond beam with Nitrobenzoic acid, Ammonium Nitrate, Benzylacetonitrile, Nitrophenol, and Phthalimide. Molecular spectral signatures of NO, OH+, CN, C2, and NH were monitored as a function of plasma lifetime, with a 50 nanosecond gate window, delineating a trend of growth and decay. Use of a buffer gas, Argon, has been observed suppressing the impact of atmospheric oxygen, nitrogen, and hydrogen on plasma assisted recombination.

Martinez, Jorge; Akpovo, Charlemagne; Bullock, Nathan; Allen, Susan; Johnson, Lewis

2011-06-01

353

Detection of short-lived intermediates in electrochemical reactions using time-resolved surface-enhanced Raman spectroscopy  

SciTech Connect

p-Nitrobenzoic acid (PNBA) is studied by real-time detection of SERS spectra during time-resolved optical multichannel recording following the application of a double potential step to a Ag electrode. The spectral bands of three stable intermediate products, p-nitrosobenzoate, hydroxylamine, and azoxy compounds are observed. In addition, the transient bands of an unstable intermediate are seen at 996, 1233, and 1580 cm{sup {minus}1} with a lifetime of about 70 ms during the oxidation process of the hydroxylamine compound which itself is generated electrochemically by a 200-ms potential pulse. We suggest these bands represent the p-nitrosobenzoate free-radical anion intermediate formed during the oxidation of the hydroxylamine compound.

Shi, Chongtie,; Zhang, Wei; Birke, R.L.; Lombardi, J.R. (The City College of The City Univ. of New York, NY (USA))

1990-06-14

354

Quantitative time-resolved vibrational sum frequency generation spectroscopy as a tool for thin film kinetic studies: new insights into oleic Acid monolayer oxidation.  

PubMed

Environmental air-water interfaces are often covered by thin films of surface-active organic substances that play an important role for air-sea gas exchange and aerosol aging. Surface-sensitive vibrational sum frequency generation (VSFG) spectroscopy has been widely used to study the static structure of organic monolayers serving as simple model systems of such films. Probably due to the difficulties to correlate the SFG signal intensity with the surface concentration, corresponding time-resolved studies of surface reactions are scarce. In this study, quantitative time-resolved measurements have been performed on the oleic acid monolayer ozonolysis, which is considered a benchmark system for investigating the reactivity and fate of unsaturated natural organics. Surface concentration calibration data have been obtained by combining the pressure-area isotherm and VSFG spectra acquisition such that the 2D phase behavior of the oleic acid film could be properly taken into account. In contrast to literature reports, surface-active oxidation products were found to be negligible and do not interfere with the VSFG measurements. A pseudo-first-order kinetic analysis of the time-resolved data yielded a bimolecular rate constant of k2(oleic acid + O3 ? products) = (1.65 ± 0.64) × 10(-16) cm(3) molecules(-1) s(-1), corresponding to an uptake coefficient of ? = (4.7 ± 1.8) × 10(-6). This result is in very good agreement with most recent monolayer measurements based on alternative methods and underlines the reliability of the time-resolved VSFG approach. PMID:23808968

Kleber, Joscha; Laß, Kristian; Friedrichs, Gernot

2013-08-07

355

Homodimerization of Amyloid Precursor Protein at the Plasma Membrane: A homoFRET Study by Time-Resolved Fluorescence Anisotropy Imaging  

PubMed Central

Classical FRET (Förster Resonance Energy Transfer) using two fluorescent labels (one for the donor and another one for the acceptor) is not efficient for studying the homodimerization of a protein as only half of the homodimers formed can be identified by this technique. We thus resorted to homoFRET detected by time-resolved Fluorescence Anisotropy IMaging (tr-FAIM). To specifically image the plasma membrane of living cells, an original combination of tr-FAIM and Total Internal Reflection Fluorescence Lifetime Imaging Microscope (TIRFLIM) was implemented. The correcting factor accounting for the depolarization due to the high numerical aperture (NA) objective, mandatory for TIRF microscopy, was quantified on fluorescein solutions and on HEK293 cells expressing enhanced Green Fluorescence Protein (eGFP). Homodimerization of Amyloid Precursor Protein (APP), a key mechanism in the etiology of Alzheimer’s disease, was measured on this original set-up. We showed, both in epifluorescence and under TIRF excitation, different energy transfer rates associated with the homodimerization of wild type APP-eGFP or of a mutated APP-eGFP, which forms constitutive dimers. This original set-up thus offers promising prospects for future studies of protein homodimerization in living cells in control and pathological conditions.

Devauges, Viviane; Marquer, Catherine; Lecart, Sandrine; Cossec, Jack-Christophe; Potier, Marie-Claude; Fort, Emmanuel; Suhling, Klaus; Leveque-Fort, Sandrine

2012-01-01

356

Homogeneous time-resolved fluorescence-based assay to screen for ligands targeting the growth hormone secretagogue receptor type 1a.  

PubMed

The growth hormone secretagogue receptor type 1a (GHS-R1a) belongs to class A G-protein-coupled receptors (GPCR). This receptor mediates pleiotropic effects of ghrelin and represents a promising target for dysfunctions of growth hormone secretion and energy homeostasis including obesity. Identification of new compounds which bind GHS-R1a is traditionally achieved using radioactive binding assays. Here we propose a new fluorescence-based assay, called Tag-lite binding assay, based on a fluorescence resonance energy transfer (FRET) process between a terbium cryptate covalently attached to a SNAP-tag fused GHS-R1a (SNAP-GHS-R1a) and a high-affinity red fluorescent ghrelin ligand. The long fluorescence lifetime of the terbium cryptate allows a time-resolved detection of the FRET signal. The assay was made compatible with high-throughput screening by using prelabeled cells in suspension under a 384-well plate format. K(i) values for a panel of 14 compounds displaying agonist, antagonist, or inverse agonist properties were determined using both the radioactive and the Tag-lite binding assays performed on the same batches of GHS-R1a-expressing cells. Compound potencies obtained in the two assays were nicely correlated. This study is the first description of a sensitive and reliable nonradioactive binding assay for GHS-R1a in a format amenable to high-throughput screening. PMID:20937574

Leyris, Jean-Philippe; Roux, Thomas; Trinquet, Eric; Verdié, Pascal; Fehrentz, Jean-Alain; Oueslati, Nadia; Douzon, Stéphanie; Bourrier, Emmanuel; Lamarque, Laurent; Gagne, Didier; Galleyrand, Jean-Claude; M'kadmi, Céline; Martinez, Jean; Mary, Sophie; Banères, Jean-Louis; Marie, Jacky

2010-09-24

357

An enzyme substrate binding aptamer complex based time-resolved fluorescence sensor for the adenosine deaminase detection.  

PubMed

In this work, we report an enzyme substrate binding aptamer complex based fluorescence sensor for an enzyme activity detection of adenosine deaminase (ADA). The sensor employs a DNA probe containing an adenosine aptamer region dually labeled with biotin and digoxigenin (DIG). The probe is immobilized in a streptavidin-modified 96-well micro plate via biotin-avidin bridge, and the DIG serves as an affinity tag for an Anti-DIG antibody conjugated with horseradish peroxidase (anti-DIG-HRP). The principle of our sensor is as follows: the aptamer forms a coiled structure making the DNA in a "closed" state in the presence of adenosine, which shields the DIG tag from the bulky anti-DIG-HRP due to a proper steric effect. After adding ADA in the test solution, adenosine will be converted to inosine regardless of the aptamer binding. Then, the inosine release causes the DNA to relax and consequently, the DIG becomes accessible to the bulky anti-DIG-HRP which will further conjugate a Eu³? labeled anti-horseradish peroxidase (Eu-anti-HRP). The Eu-anti-HRP can give a fluorescence signal when an enhancement solution is added. In the result of the experiment, we found the sensor signal can reflect the enzyme activity accurately and the detection limit is lowered to 0.5 U L?¹ of ADA not only in buffer solution, but also in serum, and an enzyme inhibitor erythro-9-(2-hydroxy-3-nonyl) adenine hydrochloride is studied. With a concentration of 0.01 nM it is enough to cause a distinct difference of the sensor response. PMID:23202335

Zhang, Kai; Yang, Qianlu; Zhang, Jue; Fu, Lixin; Zhou, Yan; Wu, Bing; Xie, Minhao; Huang, Biao

2012-11-02

358

Segmental dynamics of the cytoplasmic domain of erythrocyte band 3 determined by time-resolved fluorescence anisotropy: sensitivity to pH and ligand binding.  

PubMed Central

Interactions between the erythrocyte membrane and its skeleton are mediated primarily by binding of cytoskeletal components to a conformationally sensitive structure, the cytoplasmic domain of band 3 (cdb3). To examine the nanosecond segmental motions of cdb3, band 3 was labeled selectively by fluorescein maleimide at Cys-201 near the proposed hinge in cdb3 about which pH-dependent conformational changes occur. Time-resolved anisotropy of labeled cdb3 in isolated form and in stripped erythrocyte membranes was measured by parallel-acquisition frequency-domain microfluorimetry. Samples had a single-component fluorescein lifetime of approximately 4 ns. Multifrequency phase and modulation data (5-200 MHz) fitted well to a segmental motion model containing two correlation times (tau 1c and tau 2c) and two limiting anisotropies (r1infinity and r2infinity). Measurements in protease-cleaved and denatured samples indicated that tau 1c (100-150 ps) corresponded to rapid rotation of bound fluorescein and tau 2c (2-5 ns) corresponded to segmental motion of cdb3. Both motions were hindered as quantified by nonzero r1infinity and r2infinity. The strong pH dependence of segmental motion correlated with that of cdb3 conformation measured by intrinsic tryptophan fluorescence. Significant changes in cdb3 segmental motion occurred upon interactions with the small ligands 2,3-bisphosphoglycerate and calcium and several glycolytic enzymes known to bind to the N terminus of band 3. These time-resolved fluorescence measurements of the nanosecond segmental dynamics of a labeled membrane protein provide evidence for the sensitivity of cdb3 conformation to ligand binding and suggest long-range structural communication through cdb3. Images

Thevenin, B J; Periasamy, N; Shohet, S B; Verkman, A S

1994-01-01

359

Time-Resolved FT-IR Spectroscopy of CO Hydrogenation overSupported Ru Catalyst at 700K  

SciTech Connect

Time-resolved FT-IR spectra of carbon monoxide hydrogenation over alumina-supported ruthenium were recorded on the millisecond timescale at 703 K using various H{sub 2} concentrations (1 atm total pressure). Adsorbed carbon monoxide was detected along with gas phase products methane (3016 and 1306 cm{sup -1}), water (sharp bands from 1900 - 1300 cm{sup -1}), and carbon dioxide (2348 cm{sup -1}). No other surface species were detected other than adsorbed carbon monoxide. The rate of formation of methane (2.5 {+-} 0.4 s{sup -1}) coincides with the rate of formation of carbon dioxide (3.4 {+-} 0.6 s{sup -1}), and bands due to water are observed to grow in over time. These results establish that methane and carbon dioxide originate from the same intermediate. The adsorbed carbon monoxide band is broad and unsymmetrical with a maximum at 2010 cm{sup -1} in spectra observed at 36 ms that shifts over 3000 ms to 1960 cm{sup -1} due to decreasing amounts of adsorbed carbon monoxide. Kinetic analysis of the adsorbed carbon monoxide band reveals that only a portion of the band can be temporally linked to gas phase products that we observe over the first 1000 ms of catalysis. This result suggests that we are observing dispersive kinetics, which is most likely due to heterogeneity of the surface environment.

Wasylenko, Walter; Frei, Heinz

2006-02-13

360

IR transition moments and collisional dynamics of vibrationally excited OH radicals via time-resolved laser absorption spectroscopy  

NASA Astrophysics Data System (ADS)

A high resolution, IR laser flash kinetic spectrometer has been constructed for time-resolved study of reactive kinetics, energy transfer, and radiative properties of atmospheric OH radicals. Theoretical efforts predict a dramatic J dependence to OH vibrational radiative rates, which are exploited experimentally in the flash kinetic spectrometer to infer an empirical dipole moment function. The accuracy of this dipole moment function is extended to include the turning points of up to OH(v=9) by use of rotationally resolved emission from FTIR studies of the H + O3 chemiluminescent reaction. The explicit knowledge of the state-to-state radiative rates permits an absolute measurement of the quantum yields for 193 and 248 nm photolysis production of OH from HNO3 and H2O2. Reaction rates of OH with atmospheric hydrocarbons are investigated, as well as the relaxation processes of highly rotationally excited OH formed by excimer laser photolysis of HNO3. This information bears directly on the characterization of highly vibrationally and rotationally excited OH airglow emission from the stratosphere.

Nesbitt, David J.

1990-03-01

361

Elucidating Charge Delocalization in the High-Spin State of aqueous FeII Spin-Crossover Compounds via Time-Resolved Spectroscopy in the X-ray Water Window  

NASA Astrophysics Data System (ADS)

We report the first time-resolved spectroscopy of aqueous solution in the Xray water window. Nitrogen K-edge spectra, combined with ab initio calculations, reveal distinct charge delocalization, shedding light on the origins of ultrafast spin crossover.

Huse, Nils; Van Kuiken, Benjamin E.; Cho, Hana; Strader, Matthew L.; Kim, Tae Kyu; Khalil, Munira; Schoenlein, Robert W.

2013-03-01

362

The Near-Earth Encounter of 2005 YU55: Time-Resolved Visible and Near-Infrared Spectroscopy  

NASA Astrophysics Data System (ADS)

We will present visible and near-IR spectroscopy of near-Earth asteroid 2005 YU55 obtained during its close encounter with the Earth in November of 2011. We will focus on compositional analysis and modeling of thermal emission at near-IR wavelengths.

Moskovitz, N. A.; Yang, B.; Lim, L. F.; Willman, M.; Rivkin, A. S.; Emery, J. P.; Granvik, M.; Sheppard, S. S.

2012-05-01

363

Evaluation of the time resolved fluorescence immunoassay (TRFIA) for the detection of varicella zoster virus (VZV) antibodies following vaccination of healthcare workers.  

PubMed

Determination of varicella zoster virus (VZV) immunity in healthcare workers without a history of chickenpox is important for identifying those in need of vOka vaccination. Post immunisation, healthcare workers in the UK who work with high risk patients are tested for seroconversion. To assess the performance of the time-resolved fluorescence immunoassay (TRFIA) for the detection of antibody in vaccinated as well as unvaccinated individuals, a cut-off was first calculated. VZV-IgG specific avidity and titres six weeks after the first dose of vaccine were used to identify subjects with pre-existing immunity among a cohort of 110 healthcare workers. Those with high avidity (? 60%) were considered to have previous immunity to VZV and those with low or equivocal avidity (<60%) were considered naive. The former had antibody levels ? 400 mIU/mL and latter had levels < 400 mIU/mL. Comparison of the baseline values of the naive and immune groups allowed the estimation of a TRFIA cut-off value of > 130 mIU/mL which best discriminated between the two groups and this was confirmed by ROC analysis. Using this value, the sensitivity and specificity of TRFIA cut-off were 90% (95% CI 79-96), and 78% (95% CI 61-90) respectively in this population. A subset of samples tested by the gold standard Fluorescence Antibody to Membrane Antigen (FAMA) test showed 84% (54/64) agreement with TRFIA. PMID:21192976

McDonald, S L R; Maple, P A C; Andrews, N; Brown, K E; Ayres, K L; Scott, F T; Al Bassam, M; Gershon, A A; Steinberg, S P; Breuer, J

2010-12-28

364

Direct observation of surface oxide formation and reduction on platinum clusters by time-resolved X-ray absorption spectroscopy  

Microsoft Academic Search

Dispersive X-ray absorption fine structure (XAFS) spectroscopy was used to monitor changes in the Pt charge and the number of O and Pt nearest neighbors during the electrochemical oxidation and reduction of a dispersed Pt catalyst in real time. The oxidation at 1.20 V\\/SHE follows logarithmic kinetics over a period of 5 min with all three XAFS features (NO, NPt

P. G. Allen; S. D. Conradson; M. S. Wilson; S. Gottesfeld; I. D. Raistrick; J. Valerio; M. Lovato

1995-01-01

365

Femtosecond time-resolved core-level photoelectron spectroscopy tracking surface photovoltage transients on p GaAs  

Microsoft Academic Search

Visible-pump\\/extreme ultraviolet (EUV)-probe spectroscopy using spectrally selected high harmonics of intense laser pulses is utilised for tracking the charge carrier dynamics on semiconductor surfaces. The time evolution of the electric field in the surface layer of p-GaAs(100) is probed with 70 eV femtosecond EUV pulses by measuring the kinetic-energy shifts of Ga-3d core-level photoelectrons after excitation with 3.1 eV femtosecond

P. Siffalovic; M. Drescher; U. Heinzmann

2002-01-01

366

Kinetic study of the absolute rate constant for the reaction between K + N/sub 2/O by time-resolved atomic resonance absorption spectroscopy  

SciTech Connect

The authors present a kinetic study of the reaction K + N/sub 2/O ..-->.. KO + N/sub 2/ across the temperature range 701-903K by direct monitoring of atomic potassium in the time-resolved mode. K(4/sup 2/S/sub 1/2/) was generated by the pulsed irradiation of KI vapor at elevated temperatures and studied by time-resolved atomic resonance absorption spectroscopy in the ''single-shot mode'' using the Rydberg doublet at lambda = 404 nm (K(5/sup 2/P/sub J/) left arrow K(4/sup 2/S/sub 1/2/)). Measurements of the rate constant, k/sub R/, at different temperatures yielded the following Arrhenius form: k/sub R/ = (1.4 +- 0.10) x 10/sup -10/ exp ( -8.6 +- 1.2 kJ mol/sup -1//RT) cm/sup 3/ molecule/sup -1/ s/sup -1/, a result similar to that for the analogous reaction between Na + N/sub 2/O, and permitting the reaction to be employed as a titration technique for the quantitative preparation of KO and the subsequent kinetic study of this diatomic species. The reaction also provides a kinetic standard for atomic potassium at elevated temperatures.

Husian, D.; Lee, Y.H.

1987-05-01

367

Hydrogen transfer dynamics in a photoexcited phenol/ammonia (1:3) cluster studied by picosecond time-resolved UV-IR-UV ion dip spectroscopy.  

PubMed

The picosecond time-resolved IR spectra of phenol/ammonia (1:3) cluster were measured by UV-IR-UV ion dip spectroscopy. The time-resolved IR spectra of the reaction products of the excited state hydrogen transfer were observed. From the different time evolution of two vibrational bands at 3180 and 3250 cm(-1), it was found that two isomers of hydrogenated ammonia radical cluster .NH(4)(NH(3))(2) coexist in the reaction products. The time evolution was also measured in the near-IR region, which corresponds to 3p-3s Rydberg transition of .NH(4)(NH(3))(2); a clear wavelength dependence was found. From the observed results, we concluded that (1) there is a memory effect of the parent cluster, which initially forms a metastable product, .NH(4)-NH(3)-NH(3), and (2) the metastable product isomerizes successively to the most stable product, NH(3)-.NH(4)-NH(3). The time constant for OH cleaving, the isomerization, and its back reaction were determined by rate-equation analysis to be 24, 6, and 9 ps, respectively. PMID:18154379

Ishiuchi, Shun-ichi; Sakai, Makoto; Daigoku, Kota; Hashimoto, Kenro; Fujii, Masaaki

2007-12-21

368

Hydrogen transfer dynamics in a photoexcited phenol/ammonia (1:3) cluster studied by picosecond time-resolved UV-IR-UV ion dip spectroscopy  

SciTech Connect

The picosecond time-resolved IR spectra of phenol/ammonia (1:3) cluster were measured by UV-IR-UV ion dip spectroscopy. The time-resolved IR spectra of the reaction products of the excited state hydrogen transfer were observed. From the different time evolution of two vibrational bands at 3180 and 3250 cm{sup -1}, it was found that two isomers of hydrogenated ammonia radical cluster {center_dot}NH{sub 4}(NH{sub 3}){sub 2} coexist in the reaction products. The time evolution was also measured in the near-IR region, which corresponds to 3p-3s Rydberg transition of {center_dot}NH{sub 4}(NH{sub 3}){sub 2}; a clear wavelength dependence was found. From the observed results, we concluded that (1) there is a memory effect of the parent cluster, which initially forms a metastable product, {center_dot}NH{sub 4}-NH{sub 3}-NH{sub 3}, and (2) the metastable product isomerizes successively to the most stable product, NH{sub 3}-{center_dot}NH{sub 4}-NH{sub 3}. The time constant for OH cleaving, the isomerization, and its back reaction were determined by rate-equation analysis to be 24, 6, and 9 ps, respectively.

Ishiuchi, Shun-ichi; Sakai, Makoto; Daigoku, Kota; Hashimoto, Kenro; Fujii, Masaaki [Chemical Resources Laboratoty, Tokyo Institute of Technology, 4259, Nagatsuta, Yokohama 226-8503 (Japan); Department of Chemistry and Biological Science, Aoyama Gakuin University, 5-10-1 Fuchinobe, Sagamihara 229-8585 (Japan); Department of Chemistry, Tokyo Metropolitan University, Minami-Ohsawa, Hachioji, Tokyo 192-0397 (Japan); Integrated Research Institute, Tokyo Institute of Technology, 4259 Nagatsuta, Yokohama 226-8503 (Japan)

2007-12-21

369

Hydrogen transfer dynamics in a photoexcited phenol/ammonia (1:3) cluster studied by picosecond time-resolved UV-IR-UV ion dip spectroscopy  

NASA Astrophysics Data System (ADS)

The picosecond time-resolved IR spectra of phenol/ammonia (1:3) cluster were measured by UV-IR-UV ion dip spectroscopy. The time-resolved IR spectra of the reaction products of the excited state hydrogen transfer were observed. From the different time evolution of two vibrational bands at 3180 and 3250 cm-1, it was found that two isomers of hydrogenated ammonia radical cluster .NH4(NH3)2 coexist in the reaction products. The time evolution was also measured in the near-IR region, which corresponds to 3p-3s Rydberg transition of .NH4(NH3)2 a clear wavelength dependence was found. From the observed results, we concluded that (1) there is a memory effect of the parent cluster, which initially forms a metastable product, .NH4-NH3-NH3, and (2) the metastable product isomerizes successively to the most stable product, NH3-.NH4-NH3. The time constant for OH cleaving, the isomerization, and its back reaction were determined by rate-equation analysis to be 24, 6, and 9 ps, respectively.

Ishiuchi, Shun-Ichi; Sakai, Makoto; Daigoku, Kota; Hashimoto, Kenro; Fujii, Masaaki

2007-12-01

370

Intersubunit Communication via Changes in Hemoglobin Quaternary Structures Revealed by Time-Resolved Resonance Raman Spectroscopy: Direct Observation of the Perutz Mechanism.  

PubMed

Time-resolved resonance Raman spectroscopy was used to investigate intersubunit communication of hemoglobin using hybrid hemoglobin in which nickel was substituted for the heme iron in the ? subunits. Changes in the resonance Raman spectra of the ? heme and the ? Ni-heme groups in the hybrid hemoglobin were observed upon CO photolysis in the ? subunit using a probe pulse of 436 and 418 nm, respectively. Temporal evolution of the frequencies of the ?(Fe-His) and the ?7 band of ? heme was similar to that of unsubstituted hemoglobin, suggesting that substitution with Ni-heme did not perturb the allosteric dynamics of the hemoglobin. In the ? subunits, no structural change in the Ni-heme was observed until 1 ?s. In the microsecond regime, temporal evolution of the frequencies of the ?(Ni-His) and the ?7 band of ? Ni-heme was observed concomitant with an R ? T quaternary change at about 20 ?s. The changes in the ?(Fe-His) and ?(Ni-His) frequencies of the ? and ? subunits with the common time constant of ?20 ?s indicated that the proximal tension imposed on the bond between the heme and the proximal histidine strengthened upon the quaternary changes in both the ? and the ? subunits concertedly. This observation is consistent with the Perutz mechanism for allosteric control of oxygen binding in hemoglobin and, thus, is the first real-time observation of the mechanism. Protein dynamics and allostery based on the observed time-resolved spectra also are discussed. PMID:24067234

Yamada, Kenta; Ishikawa, Haruto; Mizuno, Misao; Shibayama, Naoya; Mizutani, Yasuhisa

2013-10-09

371

Time-resolved formation of excitons and electron-hole droplets in si studied using terahertz spectroscopy.  

PubMed

We investigated the formation dynamics of excitons and electron-hole (e-h) droplets (EHDs) in Si by using broadband terahertz time-domain spectroscopy. The formation of indirect excitons in Si was studied by observing their 1S-2P transition. Changes in surface plasmon resonance of the EHDs showed a gradual condensation from homogeneous e-h plasma at e-h densities above the exciton-Mott transition. Excitonic correlations were shown to exist prior to EHD condensation even above the Mott density. PMID:19792534

Suzuki, Takeshi; Shimano, Ryo

2009-07-31

372

Femtosecond time-resolved photoelectron spectroscopy with a vacuum-ultraviolet photon source based on laser high-order harmonic generation  

NASA Astrophysics Data System (ADS)

A laser-based tabletop approach to femtosecond time-resolved photoelectron spectroscopy with photons in the vacuum-ultraviolet (VUV) energy range is described. The femtosecond VUV pulses are produced by high-order harmonic generation (HHG) of an amplified femtosecond Ti:sapphire laser system. Two generations of the same setup and results from photoelectron spectroscopy in the gas phase are discussed. In both generations, a toroidal grating monochromator was used to select one harmonic in the photon energy range of 20-30 eV. The first generation of the setup was used to perform photoelectron spectroscopy in the gas phase to determine the bandwidth of the source. We find that our HHG source has a bandwidth of 140 +/- 40 meV. The second and current generation is optimized for femtosecond pump-probe photoelectron spectroscopy with high flux and a small spot size at the sample of the femtosecond probe pulses. The VUV radiation is focused into the interaction region with a toroidal mirror to a spot smaller than 100 × 100 ?m2 and the flux amounts to 1010 photons/s at the sample at a repetition rate of 1 kHz. The duration of the monochromatized VUV pulses is determined to be 120 fs resulting in an overall pump-probe time resolution of 135 +/- 5 fs. We show how this setup can be used to map the transient valence electronic structure in molecular dissociation.

Wernet, Philippe; Gaudin, Jérôme; Godehusen, Kai; Schwarzkopf, Olaf; Eberhardt, Wolfgang

2011-06-01

373

Femtosecond time-resolved photoelectron spectroscopy with a vacuum-ultraviolet photon source based on laser high-order harmonic generation.  

PubMed

A laser-based tabletop approach to femtosecond time-resolved photoelectron spectroscopy with photons in the vacuum-ultraviolet (VUV) energy range is described. The femtosecond VUV pulses are produced by high-order harmonic generation (HHG) of an amplified femtosecond Ti:sapphire laser system. Two generations of the same setup and results from photoelectron spectroscopy in the gas phase are discussed. In both generations, a toroidal grating monochromator was used to select one harmonic in the photon energy range of 20-30 eV. The first generation of the setup was used to perform photoelectron spectroscopy in the gas phase to determine the bandwidth of the source. We find that our HHG source has a bandwidth of 140 ± 40 meV. The second and current generation is optimized for femtosecond pump-probe photoelectron spectroscopy with high flux and a small spot size at the sample of the femtosecond probe pulses. The VUV radiation is focused into the interaction region with a toroidal mirror to a spot smaller than 100 × 100 ?m(2) and the flux amounts to 10(10) photons/s at the sample at a repetition rate of 1 kHz. The duration of the monochromatized VUV pulses is determined to be 120 fs resulting in an overall pump-probe time resolution of 135 ± 5 fs. We show how this setup can be used to map the transient valence electronic structure in molecular dissociation. PMID:21721681

Wernet, Philippe; Gaudin, Jérôme; Godehusen, Kai; Schwarzkopf, Olaf; Eberhardt, Wolfgang

2011-06-01

374

Femtosecond time-resolved photoelectron spectroscopy with a vacuum-ultraviolet photon source based on laser high-order harmonic generation  

SciTech Connect

A laser-based tabletop approach to femtosecond time-resolved photoelectron spectroscopy with photons in the vacuum-ultraviolet (VUV) energy range is described. The femtosecond VUV pulses are produced by high-order harmonic generation (HHG) of an amplified femtosecond Ti:sapphire laser system. Two generations of the same setup and results from photoelectron spectroscopy in the gas phase are discussed. In both generations, a toroidal grating monochromator was used to select one harmonic in the photon energy range of 20-30 eV. The first generation of the setup was used to perform photoelectron spectroscopy in the gas phase to determine the bandwidth of the source. We find that our HHG source has a bandwidth of 140 {+-} 40 meV. The second and current generation is optimized for femtosecond pump-probe photoelectron spectroscopy with high flux and a small spot size at the sample of the femtosecond probe pulses. The VUV radiation is focused into the interaction region with a toroidal mirror to a spot smaller than 100 x 100 {mu}m{sup 2} and the flux amounts to 10{sup 10} photons/s at the sample at a repetition rate of 1 kHz. The duration of the monochromatized VUV pulses is determined to be 120 fs resulting in an overall pump-probe time resolution of 135 {+-} 5 fs. We show how this setup can be used to map the transient valence electronic structure in molecular dissociation.

Wernet, Philippe; Gaudin, Jerome; Godehusen, Kai; Schwarzkopf, Olaf; Eberhardt, Wolfgang [Helmholtz-Zentrum Berlin fuer Materialien und Energie GmbH, Albert-Einstein-Strasse 15, 12489 Berlin (Germany)

2011-06-15

375

Nonresonant ionization of oxygen molecules by femtosecond pulses: plasma dynamics studied by time-resolved terahertz spectroscopy.  

PubMed

We show that optical pump-terahertz probe spectroscopy is a direct experimental tool for exploring laser-induced ionization and plasma formation in gases. Plasma was produced in gaseous oxygen by focused amplified femtosecond pulses. The ionization mechanisms at 400- and 800-nm excitation wavelengths differ significantly being primarily of a multiphoton character in the former case and a strong-field process in the latter case. The generation of the plasma in the focal volume of the laser and its expansion on subnanosecond time scale is directly monitored through its density-dependent susceptibility. A Drude model used to evaluate the plasma densities and electron-scattering rates successfully captures the observations for a wide range of pump intensities. In addition, rotational fingerprints of molecular and ionic species were also observed in the spectra. PMID:16178600

Mics, Zoltan; Kadlec, Filip; Kuzel, Petr; Jungwirth, Pavel; Bradforth, Stephen E; Apkarian, V Ara

2005-09-01

376

Nonresonant ionization of oxygen molecules by femtosecond pulses: Plasma dynamics studied by time-resolved terahertz spectroscopy  

SciTech Connect

We show that optical pump-terahertz probe spectroscopy is a direct experimental tool for exploring laser-induced ionization and plasma formation in gases. Plasma was produced in gaseous oxygen by focused amplified femtosecond pulses. The ionization mechanisms at 400- and 800-nm excitation wavelengths differ significantly being primarily of a multiphoton character in the former case and a strong-field process in the latter case. The generation of the plasma in the focal volume of the laser and its expansion on subnanosecond time scale is directly monitored through its density-dependent susceptibility. A Drude model used to evaluate the plasma densities and electron-scattering rates successfully captures the observations for a wide range of pump intensities. In addition, rotational fingerprints of molecular and ionic species were also observed in the spectra.

Mics, Zoltan; Kadlec, Filip; Kuzel, Petr; Jungwirth, Pavel; Bradforth, Stephen E.; Apkarian, V. Ara [Institute of Physics, Academy of Sciences of the Czech Republic, and Center for Biomolecules and Complex Molecular Systems, Na Slovance 2, 182 21 Prague 8 (Czech Republic); Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic (Czech Republic); Center for Biomolecules and Complex Molecular Systems, Flemingovo nam. 2, 166 10 Prague 6 (Czech Republic); Department of Chemistry, University of Southern California, Los Angeles, California 90089 (United States); Department of Chemistry, University of California, Irvine, California 92697 (United States)

2005-09-08

377

VLT/SINFONI time-resolved spectroscopy of the central, luminous, H-rich WN stars of R136  

NASA Astrophysics Data System (ADS)

Using the Very Large Telescope's Spectrograph for INtegral Field Observation in the Near-Infrared, we have obtained repeated adaptive-optics-assisted, near-infrared spectroscopy of the six central luminous, Wolf-Rayet (WR) stars in the core of the very young (~1 Myr), massive and dense cluster R136, in the Large Magellanic Cloud (LMC). We also de-archived available images that were obtained with the Hubble Space Telescope's Space Telescope Imaging Spectrograph, and extracted high-quality, differential photometry of our target stars to check for any variability related to binary motion. Previous studies, relying on spatially unresolved, integrated, optical spectroscopy, had reported that one of these stars was likely to be a 4.377-d binary. Our study set out to identify the culprit and any other short-period system among our targets. However, none displays significant photometric variability, and only one star, BAT99-112 (R136c), located on the outer fringe of R136, displays a marginal variability in its radial velocities; we tentatively report an 8.2-d period. The binary status of BAT99-112 is supported by the fact that it is one of the brightest X-ray sources among all known WR stars in the LMC, consistent with it being a colliding wind system. Followup observations have been proposed to confirm the orbital period of this potentially very massive system. Based on observations collected at the European Organization for Astronomical Research in the Southern Hemisphere, Chile, under programme ID 076.D-0563, and on observations made with the Hubble Space Telescope (HST) obtained from the European Southern Observatory (ESO)/Space Telescope-European Coordinating Facility (ST-ECF) Science Archive. E-mail: o.schnurr@sheffield.ac.uk

Schnurr, O.; Chené, A.-N.; Casoli, J.; Moffat, A. F. J.; St-Louis, N.

2009-08-01

378

Time-Resolved Spectral Studies of Blue?Green Fluorescence of Artichoke ( Cynara cardunculus L. Var. Scolymus ) Leaves:  Identification of Chlorogenic Acid as One of the Major Fluorophores and Age-Mediated Changes  

Microsoft Academic Search

Synchrotron radiation and the time-correlated single-photon counting technique were used to investigate the spectral and time-resolved characteristics of blue-green fluorescence (BGF) of artichoke leaves. Leaves emitted BGF under ultraviolet (UV) excitation; the abaxial side was much more fluorescent than the adaxial side, and in both cases, the youngest leaves were much more fluorescent than the oldest ones. The BGF of

FERMI ÄN MORALES; AURE Ä LIE CARTELAT; Ana Álvarez-Fernández; Ismael Moya; Zoran G. Cerovic

2005-01-01

379

Direct Observation of the Surface Segregation of Cu in Pd by Time-Resolved Positron-Annihilation-Induced Auger Electron Spectroscopy  

SciTech Connect

Density functional theory calculations predict the surface segregation of Cu in the second atomic layer of Pd which has not been unambiguously confirmed by experiment so far. We report measurements on Pd surfaces covered with three and six monolayers of Cu using element selective positron-annihilation-induced Auger electron spectroscopy (PAES) which is sensitive to the topmost atomic layer. Moreover, time-resolved PAES, which was applied for the first time, enables the investigation of the dynamics of surface atoms and hence the observation of the segregation process. The time constant for segregation was experimentally determined to {tau}=1.38(0.21) h, and the final segregated configuration was found to be consistent with calculations. Time-dependent PAES is demonstrated to be a novel element selective technique applicable for the investigation of, e.g., heterogeneous catalysis, corrosion, or surface alloying.

Mayer, J.; Hugenschmidt, C.; Schreckenbach, K. [ZWE FRM II, Lichtenbergstrasse 1, 85747 Garching (Germany); Physik Department E21, Technische Universitaet Muenchen, James Franck Strasse, 85748 Garching (Germany)

2010-11-12

380

Direct measurement of S-branch N2-H2 Raman linewidths using time-resolved pure rotational coherent anti-Stokes Raman spectroscopy.  

PubMed

S-branch N(2)-H(2) Raman linewidths have been measured in the temperature region 294-1466 K using time-resolved dual-broadband picosecond pure rotational coherent anti-Stokes Raman spectroscopy (RCARS). Data are extracted by mapping the dephasing rates of the CARS signal temporal decay. The J-dependent coherence decays are detected in the time domain by following the individual spectral lines as a function of probe delay. The linewidth data set was employed in spectral fits of N(2) RCARS spectra recorded in binary mixtures of N(2) and H(2) at calibrated temperature conditions up to 661 K using a standard nanosecond RCARS setup. In this region, the set shows a deviation of less than 2% in comparison with thermocouples. The results provide useful knowledge for the applicability of N(2) CARS thermometry on the fuel-side of H(2) diffusion flames. PMID:22920115

Bohlin, A; Nordström, E; Patterson, B D; Bengtsson, P-E; Kliewer, C J

2012-08-21

381

Duration of bubble rearrangements in a coarsening foam probed by time-resolved diffusing-wave spectroscopy: Impact of interfacial rigidity  

NASA Astrophysics Data System (ADS)

In aqueous foams, the diffusive gas transfer among neighboring bubbles drives a coarsening process which is accompanied by intermittent rearrangements of the structure. Using time-resolved diffusing-wave spectroscopy, we probe the dynamics of these events as a function of the rigidity of the gas-liquid interfaces, liquid viscosity, bubble size, and confinement pressure. We present in detail two independent techniques for analyzing the light scattering data, from which we extract the rearrangement duration. Our results show that interfacial rheology has a major impact on this duration. In the case of low interfacial rigidity, the rearrangements strongly slow down as the pressure is decreased close to the value zero where the bubble packing unjams. In contrast, if the interfaces are rigid, rearrangement durations are independent of the confinement pressure in the same investigated range. Using scaling arguments, we discuss dissipation mechanisms that may explain the observed dependency of the rearrangement dynamics on foam structure, pressure, and physicochemical solution properties.

Le Merrer, Marie; Cohen-Addad, Sylvie; Höhler, Reinhard

2013-08-01

382

Intra-molecular mobility of charge carriers along oligogermane backbones studied by flash photolysis time-resolved microwave conductivity and transient optical spectroscopy techniques  

NASA Astrophysics Data System (ADS)

Time-resolved microwave conductivity (TRMC) measurement has been performed for fullerene-doped thin films of oligo (dimethylgermane) at different excitation energies to evaluate the intra-molecular mobility of holes along their Ge backbones. Photo-induced electron transfer reaction between oligogermane and fullerene has been observed in the solution with a variety of solvent polarity using transient optical spectroscopy (TOS). The transient spectrum at 391 nm can be attributed to the radical cation of the oligomer under an excitation at 532-nm light, whereas the same spectrum (391 nm) is the overlapping of absorptions of radical cations and neutral radicals of oligogermanes upon exposure of 355-nm light in polar solvent. A combined TRMC and TOS experiments on the solutions of oligomer confirms the conductive transients originate from the radical cations on the backbone chains.

Seki, Shu; Saeki, Akinori; Acharya, Anjali; Koizumi, Yoshiko; Tagawa, Seiichi; Mochida, Kunio

2008-10-01

383

Atomic resolution mapping of the excited-state electronic structure of Cu2O with time-resolved x-ray absorption spectroscopy  

SciTech Connect

We have used time-resolved soft x-ray spectroscopy to investigate the electronic structure of optically excited cuprous oxide at the O K-edge and the Cu L3-edge. The 400 nm optical excitation shifts the Cu and O absorptions to lower energy, but does not change the integrated x-ray absorption significantly for either edge. The constant integrated x-ray absorption cross-section indicates that the conduction-band and valence-band edges have very similar Cu 3d and O 2p orbital contributions. The 2.1 eV optical band gap of Cu2O significantly exceeds the one eV shift in the Cu L3- and O K-edges absorption edges induced by optical excitation, demonstrating the importance of core-hole excitonic effects and valence electron screening in the x-ray absorption process.

Hillyard, P. W.; Kuchibhatla, S. V. N. T.; Glover, T. E.; Hertlein, M. P.; Huse, Nils; Nachimuthu, P.; Saraf, L. V.; Thevuthasan, S.; Gaffney, K. J.

2010-05-02

384

OH density measurement by time-resolved broad band absorption spectroscopy in an Ar-H2O dielectric barrier discharge  

NASA Astrophysics Data System (ADS)

We report results of a novel time-resolved broad-band absorption spectroscopy experiment for OH density measurement applied to a pulsed dielectric barrier discharge in Ar/H2O mixtures. The measurement is aimed at the calibration of our previous OH LIF measurements in the same discharge. The apparatus is simple and cheap, being based on a UV LED light source and a non-intensified, non-cooled, gateable linear CCD array as a detector. The set-up is capable of ruling out both medium/long-term drifts of the UV source and of the discharge, and discharge emission from the measurement. Performances of the set-up are discussed, together with possible improvements for its use as a standalone technique.

Dilecce, G.; Ambrico, P. F.; Simek, M.; De Benedictis, S.

2012-03-01

385

Time-resolved soft-x-ray spectroscopy of a magnetic octupole transition in nickel-like xenon, cesium, and barium ions  

SciTech Connect

A microcalorimeter with event mode capability for time-resolved soft-x-ray spectroscopy, and a high-resolution flat-field EUV spectrometer have been employed at the Livermore EBIT-I electron beam ion trap for observations and wavelength measurements of M1, E2, and M3 decays of long-lived levels in the Ni-like ions Xe{sup 26+}, Cs{sup 27+}, and Ba{sup 28+}. Of particular interest is the lowest excited level, 3d{sup 9}4s {sup 3}D{sub 3}, which can only decay via a magnetic octupole (M3) transition. For this level in Xe an excitation energy of (590.40 {+-} 0.03eV) and a level lifetime of (11.5 {+-} 0.5 ms) have been determined.

Tr?bert, E; Beiersdorfer, P; Brown, G V; Boyce, K; Kelley, R L; Kilbourne, C A; Porter, F S; Szymkowiak, A

2005-11-11

386

Time-Resolved Quantum Cascade Laser Absorption Spectroscopy of Pulsed Plasma Assisted Chemical Vapor Deposition Processes Containing BCl3  

NASA Astrophysics Data System (ADS)

In situ measurements are reported giving insight into the plasma chemical conversion of the precursor BCl3 in industrial applications of boriding plasmas. For the online monitoring of its ground state concentration, quantum cascade laser absorption spectroscopy (QCLAS) in the mid-infrared spectral range was applied in a plasma assisted chemical vapor deposition (PACVD) reactor. A compact quantum cascade laser measurement and control system (Q-MACS) was developed to allow a flexible and completely dust-sealed optical coupling to the reactor chamber of an industrial plasma surface modification system. The process under the study was a pulsed DC plasma with periodically injected BCl3 at 200 Pa. A synchronization of the Q-MACS with the process control unit enabled an insight into individual process cycles with a sensitivity of 10-6 cm-1\\cdotHz-1/2. Different fragmentation rates of the precursor were found during an individual process cycle. The detected BCl3 concentrations were in the order of 1014 molecules\\cdotcm-3. The reported results of in situ monitoring with QCLAS demonstrate the potential for effective optimization procedures in industrial PACVD processes.

Lang, Norbert; Hempel, Frank; Strämke, Siegfried; Röpcke, Jürgen

2011-08-01

387

A laser produced plasma as a pulsed source of continuum infrared radiation for time resolved absorption spectroscopy  

NASA Astrophysics Data System (ADS)

The focussed beam from the 20 ns pulse of an amplified Nd glass laser produces a high temperature plasma in air or other media. Such plasmas, while well known as phenomena, seem not to have been investigated as a source of infrared radiation. We find the emission in the chemical infrared region, 2100-1700/CM, to be a continuum or white, and at least twenty five times more intense than that from a typical glow bar used in conventional infrared absorption spectroscopy. Emission from the plasma formed in air decays with a wavelength dependent lifetime, about 150 ns for the visible portion, and 2 microsecond for the infrared portion. When formed in argon, the plasma emission is more intense, and the decay time of the infrared emission rises to 4 microsec. Use of this source is demonstrated in a measurement of the carbonyl stretching absorption for W(C0)6 and plans are to apply the method to the determination of infrared absorption spectra of thermally equilibrated excited states of organic molecules and of coordination compounds.

Adamson, A. W.; Cimolino, M. C.

1983-06-01

388

Time-resolved study of actyl radical in zeolite NaY by step-scan FT-IR spectroscopy  

SciTech Connect

Step-scan FT-infrared spectroscopy of 1-naphthyl acetate and pinacolone photodissociation in zeolite NaY revealed a transient at 2125 cm{sup {minus}1} assigned to acetyl radical. Comparison of the intensities of transient and final product absorptions, 2-acetyl-1-naphthol in the case of naphthyl acetate and acetaldehyde for pinacolone, indicates that the acetyl radical represents the main, and probably only, reaction channel. The decay of the radical at room temperature is best described by a single-exponential law with a lifetime of 71 {+-} 15 {micro}s (1-naphthyl acetate) and 315 {+-} 30 {micro}s (pinacolone). This constitutes the first detection and kinetic study of a small transient radical in a zeolite. The kinetic result is interpreted in terms of complete separation of the photogenerated pairs from the parent supercage, followed by random walks in subspaces of the zeolite lattice imposed by the much less mobile precursor molecules. These force the geminate radicals to react and thereby contribute to the high selectivity of these photoreactions.

Vasenkov, S.; Frei, H.

2000-05-11

389

Picosecond time-resolved resonance Raman spectroscopy of bacteriorhodopsin: structure and kinetics of the J, K, and KL intermediates  

NASA Astrophysics Data System (ADS)

Picosecond resonance Raman spectroscopy has been used to obtain structural information on the primary photointermediates of bacteriorhodopsin. A synchronously pumped dye laser was amplified at 50 Hz to produce a probe pulse at 589 nm. A second, spectrally distinct, pump pulse at 550 nm was generated by amplification of a 10 nm portion of a continuum produced from the probe pulse. This apparatus was used to record spectra of the J, K, and KL intermediates. The J spectrum exhibits strong hydrogen out-of-plane (HOOP) intensity and the fingerprint region consists of a broad series of lines centered at 1180 cm-1. By 3 ps, K has formed and the relative HOOP intensity decreases while the fingerprint collapses to a single mode at 1190 cm-1, characteristic of a 13-cis chromophore. These results argue that J contains a highly twisted chromophore which relaxes upon conversion to K and that isomerization is complete within 3 ps. Between 3 ps and 3.7 ns there is a resurgence in HOOP intensity and the ethylenic frequency rises from 1518 to 1521 cm-1 indicating the conversion of K to KL.

Doig, Stephen J.; Reid, Philip J.; Mathies, Richard A.

1991-06-01

390

A Set of Time-Resolved Fluorescence Resonance Energy Transfer Assays for the Discovery of Inhibitors of Estrogen Receptor-Coactivator Binding  

PubMed Central

Therapeutic block of estrogen action is typically achieved with conventional antagonists (CAs), compounds that displace estradiol from the estrogen receptor (ER) and induce formation of an ER conformation that cannot bind to coactivator proteins, such as the steroid receptor coactivators (SRCs). As an alternative mode for blocking estrogen action, we are seeking small molecules that act as coactivator binding inhibitors (CBIs), i.e., they compete directly with SRC3 for interaction with estradiol-bound ER. CBIs would be interesting mechanistic probes of estrogen action and might also provide an alternative, more durable endocrine therapy for hormone-responsive breast cancer, where cellular adaptations lead to resistance to CAs. We have designed and optimized a set of time-resolved fluorescence resonance energy transfer (TR-FRET) assays to monitor the interaction of ER with SRC3 and ligands, and we have used them in high-throughput screens to discover small molecule CBIs that are able to disrupt this interaction. These assays also distinguish CBIs from CAs. These robust and sensitive “mix and measure” assays use low concentrations of ER labeled with a europium chelate as FRET donor and a Cy5-labeled SRC as acceptor. This multiplexed protocol produces excellent signal to noise ratios (> 100) and Z' values (> 0.8).

Gunther, Jillian R.; Du, Yuhong; Rhoden, Eric; Lewis, Iestyn; Revennaugh, Brian; Moore, Terry W.; Kim, Sung Hoon; Dingledine, Raymond; Fu, Haian; Katzenellenbogen, John A.

2009-01-01

391

Development of an immunomagnetic bead-based time-resolved fluorescence immunoassay for rapid determination of levels of carcinoembryonic antigen in human serum.  

PubMed

A novel immunoassay for the determination of tumor markers in human serum was established by combining a time-resolved fluoroimmunoassay (TRFIA) and immunomagnetic separation. Based on a sandwich-type immunoassay format, analytes in samples were captured by magnetic beads coated with one monoclonal antibody and "sandwiched" by another monoclonal antibody labeled with europium chelates. The immunocomplex was separated and washed by exposure to a magnetic field and treatment with enhancement solution; fluorescence was then measured according to the number of europium ions dissociated. Levels of the model analyte, carcinoembryonic antigen (CEA), were determined in a linear range (1-1000 ng mL(-1)) with a limit of detection of 0.5 ng mL(-1) under optimal conditions. The reproducibility, recovery, and specificity of the immunoassay were demonstrated to be acceptable. To evaluate this novel assay for clinical applications, 239 serum samples were evaluated. Compared with the conventional TRFIA and chemiluminescence immunoassay (CLIA), the correlation coefficients of the developed immunoassay were 0.985 and 0.975, respectively. These results showed good correlation and confirmed that our method is feasible and could be used for the clinical determination of CEA (or other tumor antigens) in human serum. PMID:22704477

Hou, Jing-Yuan; Liu, Tian-Cai; Lin, Guan-Feng; Li, Zhi-Xiong; Zou, Li-Ping; Li, Ming; Wu, Ying-Song

2012-05-14

392

Pulse laser photolysis of aqueous ozone in the microsecond range studied by time-resolved far-ultraviolet absorption spectroscopy.  

PubMed

Chemical dynamics of an ozone (O3) pulse-photolytic reaction in aqueous solutions were studied with pump-probe transient far-ultraviolet (FUV) absorption spectroscopy. With a nanosecond pulse laser of 266 nm as pump light, transient spectra of O3 aqueous solutions (78-480 ?M, pH 2.5-11.3) were acquired in the time range from -50 to 50 ?s in the wavelength region from 190 to 225 nm. The measured transient spectra were linearly decomposed into the molar absorption coefficients and the concentration-time profiles of constituted chemical components with a multivariate curve resolution method. From the dependences of the time-averaged concentrations for 20 ?s of the constituted chemicals on the initial concentration of O3, it was found that the transient spectra involve the decomposition of O3 and the formation of hydrogen peroxide (H2O2) and a third component that is assigned to hydroxyl radical (OH) or perhydroxyl radical (HO2). Furthermore, the pH dependence of the time-averaged concentration of the third components indicates that HO2 is more probable than OH as the third component. The time-averaged concentration ratio of each chemical component to the initial O3 concentration depends on the pH conditions from -0.95 to -0.60 for O3, 0.98 to 1.2 for H2O2, 0.002 to 0.29 for OH, and 0.012 to 0.069 for HO2. PMID:23560681

Goto, Takeyoshi; Morisawa, Yusuke; Higashi, Noboru; Ikehata, Akifumi; Ozaki, Yukihiro

2013-04-17

393

Time-Resolved Fluorescent Resonance Energy Transfer Assay for Simple and Rapid Detection of Anti-Brucella Antibodies in Ruminant Serum Samples?  

PubMed Central

Brucellosis is a globally significant zoonosis, the control of which is difficult and resource intensive. Serological tests form a vital part of a multifactorial approach to control and are often performed in large numbers. The aim of the present study was to develop a new assay to improve the efficiency, ease, and effectiveness of serological testing. An existing competitive enzyme-linked immunosorbent assay (cELISA) was adapted to a completely homogeneous time-resolved fluorescent resonance energy transfer (TR-FRET) assay. This was achieved by labeling an anti-Brucella monoclonal antibody with a long-lifetime donor fluorophore and Brucella smooth lipopolysaccharide with a compatible acceptor and optimizing the reading conditions. The assay was performed in a 96-well plate with a single 30-min incubation period and no separation (wash) steps and was concluded by a single plate-reading step. The performance of the assay was evaluated with a panel of serum samples from infected (n = 73) and uninfected (n = 480) sources and compared to the performance of the parent cELISA, an indirect ELISA (iELISA), and fluorescence polarization assay (FPA). The performance of the TR-FRET assay matched the performance of the iELISA, which had 100% diagnostic sensitivity and specificity, and surpassed the performance of the cELISA and the FPA. The results also demonstrated that the TR-FRET technique is effective with poor-quality serum samples from the field. To the knowledge of the authors, this is the first homogeneous TR-FRET assay to detect antibodies raised against an infectious disease. The technique appears to be sufficiently adaptable to meet the needs of many other similar testing requirements to identify infectious diseases.

McGiven, John A.; Thompson, Iain J.; Commander, Nicola J.; Stack, Judy A.

2009-01-01

394

Transmission Electron Microscopy and Time Resolved Optical Spectroscopy Study of the Electronic and Structural Interactions of ZnO Nanorods with Bovine Serum Albumin.  

PubMed

The adsorption behavior and electronic interactions of bovine serum albumin (BSA) with ZnO nanorod surfaces were investigated using high-resolution transmission electron microscopy as well as stationary and time-resolved optical spectroscopy techniques. Transmission electron microscopy shows that ZnO nanorod surfaces are surrounded by a homogeneous amorphous BSA film with thicknesses between ?2.5 and 5.0 nm. The electronic structure and adsorption geometry of BSA were examined using high-angle annular dark field scanning transmission electron microscopy combined with electron energy loss spectroscopy. The adsorption process was observed to result into an unfolded conformation of BSA becoming predominantly bound in the side-on orientation at the ZnO surface. This adsorption mode of the BSA molecules allows for a strong interaction with surface states of the ZnO nanorods. This is obvious from its efficient quenching of the defect-center photoluminescence of ZnO. Complementary information of electronic interactions across the ZnO nanorod interface was obtained from femtosecond transient absorption spectroscopy experiments. The rise dynamics of the measured transients revealed altered hole trapping dynamics and, thus, indicated to heterogeneous charge transfer as emerging from adsorbed BSA molecules to defect centers of the ZnO interface. PMID:23889004

Klaumünzer, M; Weichsel, U; Ma?kovi?, M; Spiecker, E; Peukert, W; Kryschi, C

2013-08-07

395

Understanding the photophysical properties of coumarin-based Pluronic-silica (PluS) nanoparticles by means of time-resolved emission spectroscopy and accurate TDDFT/stochastic calculations.  

PubMed

The photophysical properties of two 7-aminocoumarin molecules with flexible and rigid alkyl moieties at the 7-nitrogen atom have been investigated in ethanol and in Pluronic-silica nanoparticles (PluS NPs) by means of time-resolved emission spectroscopy (TRES) and time-dependent density functional theory (TDDFT). Although the two coumarin derivatives have very different photophysical properties in solution, they show quite similar photophysical behaviour when embedded into the NPs, where an increase in the fluorescence quantum yield of about 10 times was observed for the more flexible molecule. TDDFT calculations employing long-range corrected functionals and with proper account of environmental effects reveal that the formation of an accessible twisted-intramolecular charge transfer state (TICT) is possible for 7-aminocoumarin molecules with flexible alkyl groups in fluid solution, where a conical intersection between the S1 and S0 states is observed at a dihedral angle of about 80°. The excited state dynamics of the population density of this reaction coordinate in ethanol and in silica NPs investigated through the resolution of a generalized Smoulochowsky equation shows that this deactivation mechanism is drastically hampered in a silica matrix, in good agreement with experimental evidence. Steady state and time resolved measurements also suggest that at high concentration for both the dyes intermolecular interactions into the silica matrix lead to fluorescence quenching. TDDFT/PCM calculations clearly indicate that the strong quenching and red shift observed is imputable to the formation of excimers with CT character after absorption of the monomeric species. PMID:23783271

Pedone, Alfonso; Gambuzzi, Elisa; Barone, Vincenzo; Bonacchi, Sara; Genovese, Damiano; Rampazzo, Enrico; Prodi, Luca; Montalti, Marco

2013-06-20

396

Time-resolved Fourier Transform Infrared Spectroscopy of the Nucleotide-binding Domain from the ATP-binding Cassette Transporter MsbA  

PubMed Central

MsbA is an essential Escherichia coli ATP-binding cassette (ABC) transporter involved in the flipping of lipid A across the cytoplasmic membrane. It is a close homologue of human P-glycoprotein involved in multidrug resistance, and it similarly accepts a variety of small hydrophobic xenobiotics as transport substrates. X-ray structures of three full-length ABC multidrug exporters (including MsbA) have been published recently and reveal large conformational changes during the transport cycle. However, how ATP hydrolysis couples to these conformational changes and finally the transport is still an open question. We employed time-resolved FTIR spectroscopy, a powerful method to elucidate molecular reaction mechanisms of soluble and membrane proteins, to address this question with high spatiotemporal resolution. Here, we monitored the hydrolysis reaction in the nucleotide-binding domain of MsbA at the atomic level. The isolated MsbA nucleotide-binding domain hydrolyzed ATP with Vmax = 45 nmol mg?1 min?1, similar to the full-length transporter. A Hill coefficient of 1.49 demonstrates positive cooperativity between the two catalytic sites formed upon dimerization. Global fit analysis of time-resolved FTIR data revealed two apparent rate constants of ?1 and 0.01 s?1, which were assigned to formation of the catalytic site and hydrolysis, respectively. Using isotopically labeled ATP, we identified specific marker bands for protein-bound ATP (1245 cm?1), ADP (1101 and 1205 cm?1), and free phosphate (1078 cm?1). Cleavage of the ?-phosphate–?-phosphate bond was found to be the rate-limiting step; no protein-bound phosphate intermediate was resolved.

Syberg, Falk; Suveyzdis, Yan; Kotting, Carsten; Gerwert, Klaus; Hofmann, Eckhard

2012-01-01

397

Gas-phase photodissociation of CH3CHBrCOCl at 248 nm: detection of molecular fragments by time-resolved FT-IR spectroscopy.  

PubMed

By employing time-resolved Fourier transform infrared emission spectroscopy, the fragments HCl (v=1-3), HBr (v=1), and CO (v=1-3) are detected in one-photon dissociation of 2-bromopropionyl chloride (CH(3)CHBrCOCl) at 248 nm. Ar gas is added to induce internal conversion and to enhance the fragment yields. The time-resolved high-resolution spectra of HCl and CO were analyzed to determine the rovibrational energy deposition of 10.0±0.2 and 7.4±0.6 kcal mol(-1), respectively, while the rotational energy in HBr is evaluated to be 0.9±0.1 kcal mol(-1). The branching ratio of HCl(v>0)/HBr(v>0) is estimated to be 1:0.53. The bond selectivity of halide formation in the photolysis follows the same trend as the halogen atom elimination. The probability of HCl contribution from a hot Cl reaction with the precursor is negligible according to the measurements of HCl amount by adding an active reagent, Br(2), in the system. The HCl elimination channel under Ar addition is verified to be slower by two orders of magnitude than the Cl elimination channel. With the aid of ab initio calculations, the observed fragments are dissociated from the hot ground state CH(3)CHBrCOCl. A two-body dissociation channel is favored leading to either HCl+CH(3)CBrCO or HBr+CH(2)CHCOCl, in which the CH(3)CBrCO moiety may further undergo secondary dissociation to release CO. PMID:21226203

Liu, Chia-Yun; Tsai, Ming-Tsang; Tsai, Po-Yu; Liu, Yu-Ting; Chen, Si Ying; Chang, Agnes Hsiu Hwa; Lin, King-Chuen

2010-12-29

398

Ultrafast time-resolved transient absorption and resonance raman spectroscopy study of the photodeprotection and rearrangement reactions of p-hydroxyphenacyl caged phosphates.  

PubMed

The kinetics and mechanism of the photodeprotection and rearrangement reactions for the pHP phototrigger compounds p-hydroxyphenacyl diethyl phosphate (HPDP) and diphenyl phosphate (HPPP) were studied using transient absorption (TA) and picosecond time-resolved resonance Raman (ps-TR(3)) spectroscopy. TA spectroscopy was employed to detect the dynamics of the triplet precursor decay as well as to investigate the influence of the solvent and leaving group on the triplet quenching process. Ps-TR(3) spectroscopy was used to directly monitor the formation dynamics for the photosolvolytic rearrangement product and its solvent and leaving group dependence. The TA and TR(3) spectroscopy experiments were also used to characterize the structural and electronic properties of the triplet precursor to the HPDP and HPPP deprotection reactions. The solvent effect observed in conjunction with the leaving group dependence of the triplet decay dynamics are consistent with a concerted solvent assisted triplet cleavage through a heterolytic mechanism for the HPDP and HPPP photodeprotection process. Correlation of the dynamics between the deprotection and rearrangement processes reveals there is a consecutive mechanism and the involvement of an intermediate between the two reaction steps. The reaction rate of the deprotection and rearrangement steps and the influence of the solvent and leaving group were determined and evaluated based on kinetic modeling of the dynamical data obtained experimentally for HPDP and HPPP in H(2)O/MeCN mixed solvents with varying water concentration in the solvent system. A solvation complex with a contact ion pair character was proposed to be the intermediate involved in the deprotection and rearrangement pathway. The results here combined with our previous study on the photophysical events occurring on the early picosecond time scale (Ma; et al. J. Am. Chem. Soc. 2005, 127, 1463-1472) provide a real time overall mechanistic description for the photodeprotection and rearrangement reactions of pHP caged phosphate phototrigger compounds. PMID:16492039

Ma, Chensheng; Kwok, Wai Ming; Chan, Wing Sum; Du, Yong; Kan, Jovi Tze Wai; Toy, Patrick H; Phillips, David Lee

2006-03-01

399

Ligand Regulation of the Quaternary Organization of Cell Surface M3 Muscarinic Acetylcholine Receptors Analyzed by Fluorescence Resonance Energy Transfer (FRET) Imaging and Homogeneous Time-resolved FRET*  

PubMed Central

Flp-InTM T-RExTM 293 cells expressing a wild type human M3 muscarinic acetylcholine receptor construct constitutively and able to express a receptor activated solely by synthetic ligand (RASSL) form of this receptor on demand maintained response to the muscarinic agonist carbachol but developed response to clozapine N-oxide only upon induction of the RASSL. The two constructs co-localized at the plasma membrane and generated strong ratiometric fluorescence resonance energy transfer (FRET) signals consistent with direct physical interactions. Increasing levels of induction of the FRET donor RASSL did not alter wild type receptor FRET-acceptor levels substantially. However, ratiometric FRET was modulated in a bell-shaped fashion with maximal levels of the donor resulting in decreased FRET. Carbachol, but not the antagonist atropine, significantly reduced the FRET signal. Cell surface homogeneous time-resolved FRET, based on SNAP-tag technology and employing wild type and RASSL forms of the human M3 receptor expressed stably in Flp-InTM TRExTM 293 cells, also identified cell surface dimeric/oligomeric complexes. Now, however, signals were enhanced by appropriate selective agonists. At the wild type receptor, large increases in FRET signal to carbachol and acetylcholine were concentration-dependent with EC50 values consistent with the relative affinities of the two ligands. These studies confirm the capacity of the human M3 muscarinic acetylcholine receptor to exist as dimeric/oligomeric complexes at the surface of cells and demonstrate that the organization of such complexes can be modified by ligand binding. However, conclusions as to the effect of ligands on such complexes may depend on the approach used.

Alvarez-Curto, Elisa; Ward, Richard J.; Pediani, John D.; Milligan, Graeme

2010-01-01

400

Ligand regulation of the quaternary organization of cell surface M3 muscarinic acetylcholine receptors analyzed by fluorescence resonance energy transfer (FRET) imaging and homogeneous time-resolved FRET.  

PubMed

Flp-In(TM) T-REx(TM) 293 cells expressing a wild type human M(3) muscarinic acetylcholine receptor construct constitutively and able to express a receptor activated solely by synthetic ligand (RASSL) form of this receptor on demand maintained response to the muscarinic agonist carbachol but developed response to clozapine N-oxide only upon induction of the RASSL. The two constructs co-localized at the plasma membrane and generated strong ratiometric fluorescence resonance energy transfer (FRET) signals consistent with direct physical interactions. Increasing levels of induction of the FRET donor RASSL did not alter wild type receptor FRET-acceptor levels substantially. However, ratiometric FRET was modulated in a bell-shaped fashion with maximal levels of the donor resulting in decreased FRET. Carbachol, but not the antagonist atropine, significantly reduced the FRET signal. Cell surface homogeneous time-resolved FRET, based on SNAP-tag technology and employing wild type and RASSL forms of the human M(3) receptor expressed stably in Flp-In(TM) TREx(TM) 293 cells, also identified cell surface dimeric/oligomeric complexes. Now, however, signals were enhanced by appropriate selective agonists. At the wild type receptor, large increases in FRET signal to carbachol and acetylcholine were concentration-dependent with EC(50) values consistent with the relative affinities of the two ligands. These studies confirm the capacity of the human M(3) muscarinic acetylcholine receptor to exist as dimeric/oligomeric complexes at the surface of cells and demonstrate that the organization of such complexes can be modified by ligand binding. However, conclusions as to the effect of ligands on such complexes may depend on the approach used. PMID:20489201

Alvarez-Curto, Elisa; Ward, Richard J; Pediani, John D; Milligan, Graeme

2010-05-19

401

Multimodal fluorescence imaging spectroscopy.  

PubMed

Multimodal fluorescence imaging is a versatile method that has a wide application range from biological studies to materials science. Typical observables in multimodal fluorescence imaging are intensity, lifetime, excitation, and emission spectra which are recorded at chosen locations at the sample. This chapter describes how to build instrumentation that allows for multimodal fluorescence imaging and explains data analysis procedures for the observables. PMID:24108642

Stopel, Martijn H W; Blum, Christian; Subramaniam, Vinod

2014-01-01

402

Time-Resolved Spectroscopic Studies of the AppA Blue-Light Receptor BLUF Domain from Rhodobacter sphaeroides †  

Microsoft Academic Search

AppA is a blue-light and redox-responding regulator of photosynthesis gene expression in Rhodobacter sphaeroides . Detailed time-resolved fluorescence spectroscopy and subpicosecond transient absorption spectroscopy study of the BLUF domain is presented for wild-type AppA (AppAwt) and a photoinactive Y21F mutant of AppA. The main findings discussed here are that (1) time-resolved laser excitation studies on dark-adapted protein show that AppAwt

Vladimira Dragnea; Matthias Waegele; Septimiu Balascuta; Carl Bauer; Bogdan Dragnea

2005-01-01