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1

Luciferase intramolecular dynamics studied by time-resolved fluorescence spectroscopy  

NASA Astrophysics Data System (ADS)

Earlier a comprehensive study of reaction substrate, product and their complexes with the enzyme has been carried out by means of stationary fluorescence spectroscopy. A hypothesis has been suggested according to which protein changes its conformation during the reaction. In this respect it is quite interesting to study both static and dynamic properties of the enzyme molecule. Luckily, according to genetic engineering data, luciferase molecule contains only one tryptophan residue, which makes it a very convenient object for the studies by means of time-resolved fluorescence spectroscopy. The scope of this paper is the study of luciferase tryptophan fluorescence. The methods applied were fluorescence spectrochronography and anisotropy decay analysis.

Brovko, Lubov Y.; Chikishev, Andrey Y.; Gandelman, Olga A.; Shkurinov, Aleksandr P.

1993-06-01

2

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

3

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

4

Picosecond time-resolved fluorescence spectroscopy of phytochrome and stentorin  

NASA Astrophysics Data System (ADS)

Phytochrome is a tetrapyrrole chromoprotein. It serves as a sensitive photosensor for red lightmediated gene expression and other developmental/morphological responses in plants. In this paper photochemical dynamics of the phytochrome molecule have been described in terms of photoisomerization of the tetrapyrrole chromophore in its singlet excited state and subsequent thermal processes in the Pr Pfr phototransformation of phytochrome. Stentorin acts as the photosensor molecule in the ciliate Stentor coeruleus. This unicellular protozoan is most sensitive to red light (610-620 urn). Stentor also senses the direction of light propagation as evidenced by their light-avoiding and negative phototactic swimming behaviors. This aneural photosensory phenomenon is triggered by the photoreceptor stentorin. The possible involvement of a light-induced transient proton release from the photoreceptor as the primary mechanism of light-signal processing has been discussed on the basis of picosecond fluorescence decays and time-resolved fluorescence spectra of stentorin in solution. An initial sensory signal generated by the primary photoprocess of stentorin then triggers subsequent transduction steps that include calcium ion influx from the extracellular medium. Calcium ion influx from the extracellular medium to the cytosol causes the Stentor cell to reverse its ciliary beating and subsequently steer away from the light trap. II.

Song, Pill-Soon

1991-05-01

5

Pitfalls and Their Remedies in Time-Resolved Fluorescence Spectroscopy and Microscopy  

Microsoft Academic Search

Time-resolved fluorescence spectroscopy and microscopy in both time and frequency domains provide very useful and accurate information on dynamic processes. Good quality data are essential in obtaining reliable parameter estimates. Distortions of the fluorescence response due to artifacts may have disastrous consequences. We provide here a concise overview of potential difficulties encountered under daily laboratory circumstances in the use of

Martin vandeVen; Marcel Ameloot; Bernard Valeur; Noël Boens

2005-01-01

6

Time-resolved fluorescence spectroscopy for chemical sensors  

NASA Astrophysics Data System (ADS)

A family of sensors is presented with fluorescence decay-time measurements used as the sensing technique. The concept is to take a single fluorophore with a suitably long fluorescence decay time as the basic building block for numerous different sensors. Analyte recognition can be performed by different functional groups that are necessary for selective interaction with the analyte. To achieve this, the principle of excited-state electron transfer is applied with pyrene as the fluorophore. Therefore the same instrumentation based on a small, ambient air-nitrogen laser and solid-state electronics can be used to measure different analytes, for example, oxygen, pH, carbon dioxide, potassium, ammonium, lead, cadmium, zinc, and phosphate.

Draxler, Sonja; Lippitsch, Max E.

1996-07-01

7

Characterization of fluorescence-labeled DNA by time-resolved fluorescence spectroscopy  

NASA Astrophysics Data System (ADS)

A strategy for DNA characterization was developed, which exploits the normally unwanted interactions of the dye with its environment. With a single suitable dye, acting as a sensitive probe, one can characterize the neighboring DNA-base by time-resolved fluorescence spectroscopy due to specific dynamic quenching reactions affecting the fluorescence lifetime. By specific coupling of the dye to a linker-group at the 3' terminus of DNA a one- label/one-lane concept for DNA sequencing seems to be possible and all problems with multiple dyes can be avoided. To study the feasibility of this concept, fluorescence lifetimes of various model phosphorothioate oligodeoxyribonucleotides, different in length and labelled with a specially synthesized coumarin derivative, were measured in different aqueous solutions with a DFDL-UV picosecond fluorescence spectrometer. The influence of nucleic acid-dye interactions on the lifetime and quantum yield of the coupled dye is investigated. In mononucleotides fluorescence lifetimes range between 5.3 and 1.4 ns. The order in the quenching efficiency of the bases is adenine (A) equals 0, cytosine (C) < thymine (T) < guanine (G). In labelled di- and oligonucleotides the order of quenching changes slightly: A equals 0, C < G fluorescence lifetime is small and depends on the diastereomer, sequence and solvent. Comparison of quantum yields and lifetimes shows an additional static quenching due to complex formation especially in oligonucleotides.

Seidel, Claus; Rittinger, K.; Cortes, J.; Goody, R. S.; Koellner, Malte; Wolfrum, Juergen M.; Greulich, Karl O.

1991-06-01

8

Design and evaluation of a device for fast multispectral time-resolved fluorescence spectroscopy and imaging  

NASA Astrophysics Data System (ADS)

The application of time-resolved fluorescence spectroscopy (TRFS) to in vivo tissue diagnosis requires a method for fast acquisition of fluorescence decay profiles in multiple spectral bands. This study focusses on development of a clinically compatible fiber-optic based multispectral TRFS (ms-TRFS) system together with validation of its accuracy and precision for fluorescence lifetime measurements. It also presents the expansion of this technique into an imaging spectroscopy method. A tandem array of dichroic beamsplitters and filters was used to record TRFS decay profiles at four distinct spectral bands where biological tissue typically presents fluorescence emission maxima, namely, 390, 452, 542, and 629 nm. Each emission channel was temporally separated by using transmission delays through 200 ?m diameter multimode optical fibers of 1, 10, 19, and 28 m lengths. A Laguerre-expansion deconvolution algorithm was used to compensate for modal dispersion inherent to large diameter optical fibers and the finite bandwidth of detectors and digitizers. The system was found to be highly efficient and fast requiring a few nano-Joule of laser pulse energy and <1 ms per point measurement, respectively, for the detection of tissue autofluorescent components. Organic and biological chromophores with lifetimes that spanned a 0.8-7 ns range were used for system validation, and the measured lifetimes from the organic fluorophores deviated by less than 10% from values reported in the literature. Multi-spectral lifetime images of organic dye solutions contained in glass capillary tubes were recorded by raster scanning the single fiber probe in a 2D plane to validate the system as an imaging tool. The lifetime measurement variability was measured indicating that the system provides reproducible results with a standard deviation smaller than 50 ps. The ms-TRFS is a compact apparatus that makes possible the fast, accurate, and precise multispectral time-resolved fluorescence lifetime measurements of low quantum efficiency sub-nanosecond fluorophores.

Yankelevich, Diego R.; Ma, Dinglong; Liu, Jing; Sun, Yang; Sun, Yinghua; Bec, Julien; Elson, Daniel S.; Marcu, Laura

2014-03-01

9

Design and evaluation of a device for fast multispectral time-resolved fluorescence spectroscopy and imaging.  

PubMed

The application of time-resolved fluorescence spectroscopy (TRFS) to in vivo tissue diagnosis requires a method for fast acquisition of fluorescence decay profiles in multiple spectral bands. This study focusses on development of a clinically compatible fiber-optic based multispectral TRFS (ms-TRFS) system together with validation of its accuracy and precision for fluorescence lifetime measurements. It also presents the expansion of this technique into an imaging spectroscopy method. A tandem array of dichroic beamsplitters and filters was used to record TRFS decay profiles at four distinct spectral bands where biological tissue typically presents fluorescence emission maxima, namely, 390, 452, 542, and 629 nm. Each emission channel was temporally separated by using transmission delays through 200 ?m diameter multimode optical fibers of 1, 10, 19, and 28 m lengths. A Laguerre-expansion deconvolution algorithm was used to compensate for modal dispersion inherent to large diameter optical fibers and the finite bandwidth of detectors and digitizers. The system was found to be highly efficient and fast requiring a few nano-Joule of laser pulse energy and <1 ms per point measurement, respectively, for the detection of tissue autofluorescent components. Organic and biological chromophores with lifetimes that spanned a 0.8-7 ns range were used for system validation, and the measured lifetimes from the organic fluorophores deviated by less than 10% from values reported in the literature. Multi-spectral lifetime images of organic dye solutions contained in glass capillary tubes were recorded by raster scanning the single fiber probe in a 2D plane to validate the system as an imaging tool. The lifetime measurement variability was measured indicating that the system provides reproducible results with a standard deviation smaller than 50 ps. The ms-TRFS is a compact apparatus that makes possible the fast, accurate, and precise multispectral time-resolved fluorescence lifetime measurements of low quantum efficiency sub-nanosecond fluorophores. PMID:24689603

Yankelevich, Diego R; Ma, Dinglong; Liu, Jing; Sun, Yang; Sun, Yinghua; Bec, Julien; Elson, Daniel S; Marcu, Laura

2014-03-01

10

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

PubMed

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. PMID:20459282

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

2010-01-01

11

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

Microsoft Academic Search

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

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

2004-01-01

12

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

13

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

14

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

15

TIME-RESOLVED VIBRATIONAL SPECTROSCOPY  

SciTech Connect

This document contains the Proceedings from the 14th International Conference on Time-Resolved Vibrational Spectroscopy, which was held in Meredith, NH from May 9-14, 2009. The study of molecular dynamics in chemical reaction and biological processes using time-resolved spectroscopy plays an important role in our understanding of energy conversion, storage, and utilization problems. Fundamental studies of chemical reactivity, molecular rearrangements, and charge transport are broadly supported by the DOE�s Office of Science because of their role in the development of alternative energy sources, the understanding of biological energy conversion processes, the efficient utilization of existing energy resources, and the mitigation of reactive intermediates in radiation chemistry. In addition, time-resolved spectroscopy is central to all five of DOE�s grand challenges for fundamental energy science. The Time-Resolved Vibrational Spectroscopy conference is organized biennially to bring the leaders in this field from around the globe together with young scientists to discuss the most recent scientific and technological advances. The latest technology in ultrafast infrared, Raman, and terahertz spectroscopy and the scientific advances that these methods enable were covered. Particular emphasis was placed on new experimental methods used to probe molecular dynamics in liquids, solids, interfaces, nanostructured materials, and biomolecules.

Andrei Tokmakoff, MIT (Conference Chair) [Conference Chair; Paul Champion, Northeastern University; Edwin J. Heilweil, NIST; Keith A. Nelson, MIT; Larry Ziegler, Boston University

2009-05-14

16

Time-resolved laser-induced fluorescence spectroscopy as a diagnostic instrument in head and neck carcinoma  

PubMed Central

OBJECTIVE 1) Determine differences in lifetime fluorescence between normal and malignant tissue of the upper aerodigestive tract. 2) Evaluate the potential of time-resolved laser-induced fluorescence spectroscopy (TR-LIFS) as a diagnostic instrument for head and neck squamous cell carcinoma (HNSCC). STUDY DESIGN Cross-sectional study. SETTING University-based medical center. SUBJECTS AND METHODS Nine patients with suspected HNSCC were included. In the operating room, a nitrogen pulse laser (337 nm, 700 ps pulse width) was used to induce tissue autofluorescence of normal tissue and suspected malignant lesions. Spectral intensities and time-domain measurements were obtained and compared to the histopathology at each site. A total of 53 sites were measured. The fluorescence parameters that provided the most discrimination were determined. RESULTS Differences in spectral intensities allowed for discrimination between malignant and normal tissue. The spectral intensity of malignant tissue was lower than the normal tissue, and a shift of peak intensity to a longer wavelength was observed in the normalized spectrum of malignant tissue in the range of 360~660 nm. Multiple time-resolved fluorescence parameters provided the best diagnostic discrimination between normal tissue and carcinoma, including average lifetimes (i.e., at 390 nm: 1.7±0.06 ns for normal and 1.3±0.06 ns for tumor, P=0.0025), and the Laguerre coefficients, LEC-2 (i.e., at 460 nm: 0.135±0.001 for normal and 0.155±0.007 for tumor, P<0.05). CONCLUSION These findings highlight some of the differences in lifetime fluorescence between normal and malignant tissue. TR-LIFS has potential as a non-invasive diagnostic technique for HNSCC.

Meier, Jeremy D.; Xie, Hongtao; Sun, Yang; Sun, Yinghua; Hatami, Nisa; Poirier, Brian; Marcu, Laura; Farwell, D. Gregory

2011-01-01

17

Picosecond time-resolved fluorescence spectroscopy of K-590 in the bacteriorhodopsin photocycle.  

PubMed Central

The fluorescence spectrum of a distinct isometric and conformational intermediate formed on the 10(-11) s time scale during the bacteriorhodopsin (BR) photocycle is observed at room temperature using a two laser, pump-probe technique with picosecond time resolution. The BR photocycle is initiated by pulsed (8 ps) excitation at 565 nm, whereas the fluorescence is generated by 4-ps laser pulses at 590 nm. The unstructured fluorescence extends from 650 to 880 nm and appears in the same general spectral region as the fluorescence spectrum assigned to BR-570. The transient fluorescence spectrum can be distinguished from that assigned to BR-570 by a larger emission quantum yield (approximately twice that of BR-570) and by a maximum intensity near 731 nm (shifted 17 nm to higher energy from the maximum of the BR-570 fluorescence spectrum). The fluorescence spectrum of BR-570 only is measured with low energy, picosecond pulsed excitation at 590 nm and is in good agreement with recent data in the literature. The assignment of the transient fluorescence spectrum to the K-590 intermediate is based on its appearance at time delays longer than 40 ps. The K-590 fluorescence spectrum remains unchanged over the entire 40-100-ps interval. The relevance of these fluorescence data with respect to the molecular mechanism used to model the primary processes in the BR photocycle also is discussed.

Atkinson, G H; Blanchard, D; Lemaire, H; Brack, T L; Hayashi, H

1989-01-01

18

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

19

Short-term light adaptation of a cyanobacterium, Synechocystis sp. PCC 6803, probed by time-resolved fluorescence spectroscopy.  

PubMed

In photosynthetic organisms, the interactions among pigment-protein complexes change in response to light conditions. In the present study, we analyzed the transfer of excitation energy from the phycobilisome (PBS) and photosystem (PS) II to PSI in the cyanobacterium Synechocystis sp. PCC 6803. After 20 min of dark adaptation, Synechocystis cells were illuminated for 5 min with strong light with different spectral profiles, blue, green, two kinds of red, and white light. After illumination, the energy-transfer characteristics were evaluated using 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, followed by spectral component analysis. Under illumination with strong light, the contribution of the energy transfer from the PSII to PSI (spillover) became greater, and that of the energy transfer from the PBS to PSI decreased; the former change was larger than the latter. The energy transfer pathway to PSI was sensitive to red light. We discuss the short-term adaptation of energy-transfer processes in Synechocystis under strong-light conditions. PMID:24495908

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

2014-08-01

20

An ultrafast time-resolved fluorescence spectroscopy system for metal ion complexation studies with organic ligands.  

PubMed

A dedicated spectrofluorimeter using ultrashort laser pulses as an excitation source was developed to measure the fluorescence properties of organic ligands for metal ion complexation with organic ligands. The laser system consists of an oscillator system for generation of femtosecond laser pulses, an amplifier system to increase the pulse energy of the generated pulses to about 2 mJ and an optical parametrical amplifier system to provide tunable laser pulses over a wide wavelength range (280 nm-10 microm). The laser pulses were applied to the sample and the emitted fluorescence was detected using a fast-gating intensified CCD camera-based spectrometer. To verify the performance of the laser, the well-known protonation constant [Pure Appl. Chem. 69 (1997) 329] of 2,3-dihydroxybenzoic acid was determined. The fluorescence lifetime of the excited species was determined as 375+/-32 ps in the pH range from 1.0 to 6.0, having a fluorescence emission maximum at 438 nm. The first protonation constant was determined from fluorescence data as log K(3)=3.17+/-0.05 at an ionic strength of 0.1 M and at 294 K exploiting the Stern-Volmer mechanism. The agreement of the protonation constant with literature data (log K(3)=3.10+/-0.20, I=0.1 M, T=298 K [Bull. Soc. Jpn. 44 (1971) 3459]) demonstrates the excellent performance of our system. Furthermore, we determined the complex formation constant log K(1)=-3.11+/-0.16 by measuring the fluorescence properties of the ligand for the 1:1 uranyldihydroxobenzoate complex in the pH range from 3.0 to 4.5 at ionic strength of 0.1 M and at 294 K. We also determined the complex formation constant via the fluorescence emission of the metal ion uranium(VI). The fluorescence of the uranyl ion is influenced by dynamic quenching of the non-dissociated ligand and by static quenching due to the complex formation. After correction of these effects using the determined fluorescence lifetime, the complex formation constant was calculated to be log K(1)=-3.99+/-0.44. A 1:1 metal:ligand stoichiometry was determined with both measurement methods. However, the difference of the obtained formation constants and the derived standard deviations indicate a superimposition of effects with the excited-state reactions of the ligand. PMID:14670508

Geipel, G; Acker, M; Vulpius, D; Bernhard, G; Nitsche, H; Fanghänel, Th

2004-01-01

21

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

22

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

23

A space- and time-resolved single photon counting detector for fluorescence microscopy and spectroscopy  

NASA Astrophysics Data System (ADS)

We have recently developed a wide-field photon-counting detector having high-temporal and high-spatial resolutions and capable of high-throughput (the H33D detector). Its design is based on a 25 mm diameter multi-alkali photocathode producing one photo electron per detected photon, which are then multiplied up to 10 7 times by a 3-microchannel plate stack. The resulting electron cloud is proximity focused on a cross delay line anode, which allows determining the incident photon position with high accuracy. The imaging and fluorescence lifetime measurement performances of the H33D detector installed on a standard epifluorescence microscope will be presented. We compare them to those of standard single-molecule detectors such as single-photon avalanche photodiode (SPAD) or electron-multiplying camera using model samples (fluorescent beads, quantum dots and live cells). Finally, we discuss the design and applications of future generation of H33D detectors for single-molecule imaging and high-throughput study of biomolecular interactions.

Michalet, X.; Siegmund, O. H. W.; Vallerga, J. V.; Jelinsky, P.; Millaud, J. E.; Weiss, S.

2006-03-01

24

Time resolved fluorescence of naproxen in organogel medium  

NASA Astrophysics Data System (ADS)

The interaction between non-steroidal anti-inflammatory drug naproxen and the self assembled fibrillar network created by a low molecular weight organogelator has been probed by means of time resolved fluorescence spectroscopy.

Burguete, M. Isabel; Izquierdo, M. Angeles; Galindo, Francisco; Luis, Santiago V.

2008-07-01

25

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

26

Interaction of europium and nickel with calcite studied by Rutherford Backscattering Spectrometry and Time-Resolved Laser Fluorescence Spectroscopy  

NASA Astrophysics Data System (ADS)

This study aims at elucidating the mechanisms regulating the interaction of Eu and Ni with calcite (CaCO3). Calcite powders or single crystals (some mm sized) were put into contact with Eu or Ni solutions at concentrations ranging from 10-3 to 10-5 mol L-1 for Eu and 10-3 mol L-1 for Ni. The sorption durations ranged from 1 week to 1 month. Rutherford Backscattering Spectrometry (RBS) well adapted to discriminate incorporation processes such as: (i) adsorption or co precipitation at the mineral surfaces or, (ii) incorporation into the mineral structure (through diffusion for instance), has been carried out. Moreover, using the fluorescence properties of europium, the results have been compared to those obtained by Time-Resolved Laser Fluorescence Spectroscopy (TRLFS) on calcite powders. For the single crystals, complementary SEM observations of the mineral surfaces at low voltage were also performed. Results showed that Ni accumulates at the calcite surface whereas Eu is also incorporated at a greater depth. Eu seems therefore to be incorporated into two different states in calcite: (i) heterogeneous surface accumulation and (ii) incorporation at depth greater than 160 nm after 1 month of sorption. Ni was found to accumulate at the surface of calcite without incorporation.

Sabau, A.; Pipon, Y.; Toulhoat, N.; Lomenech, C.; Jordan, N.; Moncoffre, N.; Barkleit, A.; Marmier, N.; Brendler, V.; Surblé, S.; Giffaut, E.

2014-08-01

27

Nanosecond time-resolved emission spectroscopy of a fluorescence probe adsorbed to L-alpha-egg lecithin vesicles.  

PubMed Central

Nanosecond time-resolved emission spectra (TRES) are fluorescence emission spectra obtained at discrete times during the fluorescence decay. The complete data-set obtainable is a surface representing the intensity at all wavelengths and times during the emission decay time. When 2-p-toluidinonaphthalene-6-sulfonate (2,6 p-TNS) is adsorbed to egg lecithin vesicles, an excited-state reaction associated with energetic changes of the emitting species occurs on the nanosecond time scale. Convolution of the fluorescence decay with the excitation response introduces an artifact in the time-dependent spectra. A precedure is described by which this artifact can be eliminated. The data for the generation of time-resolved emission spectra are obtained with a computer-interfaced instrument based on the single-photon counting method.

Easter, J H; DeToma, R P; Brand, L

1976-01-01

28

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

29

Time-resolved spectroscopy of wild-type and mutant Green Fluorescent Proteins reveals excited state deprotonation consistent with fluorophore-protein interactions  

Microsoft Academic Search

Recently steady-state and picosecond time-resolved absorption and fluorescence spectroscopy on the Green Fluorescent Protein (GFP) have been interpreted by a mechanism where the key process is an excited state deprotonation of the chromophore (M. Chattoraij, B.A. King, G.U. Bublitz and S.G. Boxer, Proc. Natl. Acad. Sci. USA, 93 (1996) 8362–8367). Such a conclusion was borne out by the mirror image

H. Lossau; A. Kummer; R. Heinecke; F. Pöllinger-Dammer; C. Kompa; G. Bieser; T. Jonsson; C. M. Silva; M. M. Yang; D. C. Youvan; M. E. Michel-Beyerle

1996-01-01

30

Study on the interaction of phthalate esters to human serum albumin by steady-state and time-resolved fluorescence and circular dichroism spectroscopy  

Microsoft Academic Search

Phthalate esters (PAEs) are globally pervasive contaminants that are considered to be endocrine disruptor chemicals and toxic environmental priority pollutants. In this paper, the interactions between PAEs and human serum albumin (HSA) were examined by molecular modelling, steady state and time-resolved fluorescence, ultraviolet–visible spectroscopy (UV–vis) and circular dichroism spectroscopy (CD). The association constants between PAEs and HSA were determined using

Xiaoyun Xie; Zhaowei Wang; Ximin Zhou; Xiaoru Wang; Xingguo Chen

2011-01-01

31

Photosystem II Does Not Possess a Simple Excitation Energy Funnel: Time-Resolved Fluorescence Spectroscopy Meets Theory  

PubMed Central

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.

2013-01-01

32

Complex formation of neptunium(V) with 4-hydroxy-3-methoxybenzoic acid studied by time-resolved laser-induced fluorescence spectroscopy with ultra-short laser pulses  

Microsoft Academic Search

The complex formation of neptunium(V) with 4-hydroxy-3-methoxybenzoic acid (vanillic acid) was studied by time-resolved laser-induced fluorescence spectroscopy with ultra-short laser pulses using the fluorescence properties of 4-hydroxy-3-methoxybenzoic acid. A 2:1 complex of neptunium(V) with 4-hydroxy-3-methoxybenzoic acid was found. The stability constant of this complex was determined to be log?210=7.33±0.10 at an ionic strength of 0.1mol\\/l (NaClO4) and at 21°C. The

D. Vulpius; G. Geipel; L. Baraniak; G. Bernhard

2006-01-01

33

Differences in excitation energy transfer of Arthrospira platensis cells grown in seawater medium and freshwater medium, probed by time-resolved fluorescence spectroscopy  

NASA Astrophysics Data System (ADS)

Excitation energy transfer of Arthrospira platensis cells grown in f/2 medium (a high salinity medium) and SOT medium (a control) was investigated by steady-state and time-resolved spectroscopies. Growth in f/2 medium induced changes in absorption and fluorescence spectra as well as in the energy transfer pathways. Excitation energy captured by phycobilisome (PBS) was transferred directly to photosystem (PS) I, instead of being first transferred to an intermediate (PBS ? PSII ? PSI), as observed in SOT medium. The respiration rate increased while photosynthetic rate reduced in f/2 medium. Possible causes of the differences in light-harvesting and energy-transfer processes between the two media are discussed.

Arba, Muhammad; Aikawa, Shimpei; Niki, Kenta; Yokono, Makio; Kondo, Akihiko; Akimoto, Seiji

2013-11-01

34

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

35

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

36

Time-resolved multiple probe spectroscopy.  

PubMed

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)(6)) monitored by IR absorption spectroscopy, following picosecond vibrational cooling of product formation through to slower bimolecular diffusion reactions on the microsecond time scale. PMID:23126751

Greetham, G M; Sole, D; Clark, I P; Parker, A W; Pollard, M R; Towrie, M

2012-10-01

37

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

38

Time-resolved fluorescence spectroscopy study of excited state dynamics of alkyl- and benzo-substituted triphyrin(2.1.1).  

PubMed

We have investigated the photophysical properties of alkyl-substituted triphyrin(2.1.1) (ATp) and benzotriphyrin(2.1.1) (BTp) by steady-state and time-resolved fluorescence spectroscopy. We focused on the effect of NH proton tautomerization, planarity of the macrocycles, and substituents on these properties. The fluorescence quantum yields (?y) of ATp did not depend on solvent viscosity, whereas those of BTp increased with solvent viscosity, reaching a maximum value of 0.17 in paraffin. Interestingly, analyzing ?y showed that the non-radiative rate constant of BTp decreased sharply as the solvent viscosity increased. These results suggest that the substituted phenyl groups play a crucial role in suppressing molecular distortion, thus leading to decreased non-radiative relaxation in triphyrin(2.1.1). The hydrogen bond formed in the inner cavity potentially contributes to the suppression of the structural distortion, whereas the pyrrole rings in the macrocycle are close, as in porphycene. PMID:24865987

Iima, Yusuke; Kuzuhara, Daiki; Xue, Zhao-Li; Akimoto, Seiji; Yamada, Hiroko; Tominaga, Keisuke

2014-06-11

39

Time-resolved Raman spectroscopy for in situ planetary mineralogy.  

PubMed

Planetary mineralogy can be revealed through a variety of remote sensing and in situ investigations that precede any plans for eventual sample return. We briefly review those techniques and focus on the capabilities for on-surface in situ examination of Mars, Venus, the Moon, asteroids, and other bodies. Over the past decade, Raman spectroscopy has continued to develop as a prime candidate for the next generation of in situ planetary instruments, as it provides definitive structural and compositional information of minerals in their natural geological context. Traditional continuous-wave Raman spectroscopy using a green laser suffers from fluorescence interference, which can be large (sometimes saturating the detector), particularly in altered minerals, which are of the greatest geophysical interest. Taking advantage of the fact that fluorescence occurs at a later time than the instantaneous Raman signal, we have developed a time-resolved Raman spectrometer that uses a streak camera and pulsed miniature microchip laser to provide picosecond time resolution. Our ability to observe the complete time evolution of Raman and fluorescence spectra in minerals makes this technique ideal for exploration of diverse planetary environments, some of which are expected to contain strong, if not overwhelming, fluorescence signatures. We discuss performance capability and present time-resolved pulsed Raman spectra collected from several highly fluorescent and Mars-relevant minerals. In particular, we have found that conventional Raman spectra from fine grained clays, sulfates, and phosphates exhibited large fluorescent signatures, but high quality spectra could be obtained using our time-resolved approach. PMID:20830184

Blacksberg, Jordana; Rossman, George R; Gleckler, Anthony

2010-09-10

40

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

2013-11-01

41

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

NASA Astrophysics Data System (ADS)

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 has previously been introduced. One limitation of this method, however, is the need to heuristically select two parameters that are crucial for the accurate estimation of the fluorescence decay: the Laguerre parameter ? and the expansion order. Here, a new implementation of the Laguerre deconvolution method is introduced, in which a nonlinear least-square optimization of the Laguerre parameter ? is performed, and the optimal expansion order is selected based on a minimum description length criterion (MDL). In addition, estimation of the zero-time delay between the recorded instrument response and fluorescence decay is also performed based on normalized mean square error criterion (NMSE). The method is validated on experimental data from fluorescence lifetime standards, endogenous tissue fluorophores, and human tissue. The proposed automated Laguerre deconvolution method will facilitate online applications of TRFS, such as real-time clinical tissue diagnosis.

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

2009-03-01

42

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

PubMed Central

Abstract. 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

2012-01-01

43

Time-Resolved Fluorescence Spectroscopy and Imaging of DNA Labeled with DAPI and Hoechst 33342 Using Three-Photon Excitation  

PubMed Central

We examined the fluorescence spectral properties of the DNA stains DAPI (4?,6-diamidino-2-phenylindole, hydrochloride) and Hoechst 33342 (bis-benzimide, or 2,5?-bi-1H-benzimidazole2?-(4-ethoxyphenyl)-5-(4-methyl-1-piperazinyl)) with two-photon (2h?) and three-photon (3h?) excitation using femtosecond pulses from a Ti:sapphire laser from 830 to 885 nm. The mode of excitation of DAPI bound to DNA changed from two-photon at 830 nm to three-photon at 885 nm. In contrast, Hoechst 33342 displayed only two-photon excitation from 830 to 885 nm. DAPI-DNA displayed the same emission spectra and decay times for 2h? and 3h? excitation. Hoechst 33342-DNA displayed the same intensity decay for excitation at 830 and 885 nm. Both probes displayed higher anisotropies for multiphoton excitation as compared to one-photon excitation with ultraviolet wavelengths, and DAPI-DNA displays a higher anisotropy for 3h? at 885 nm than for 2h? at 830 nm. We used 970-nm excitation of DAPI-stained chromosomes to obtain the first three-dimensional images with three-photon excitation. Three-photon excitation of DAPI-stained chromosomes at 970 nm was demonstrated by the power dependence in the fluorescence microscope. ImagesFIGURE 10FIGURE 11FIGURE 12

Lakowicz, Joseph R.; Gryczynski, Ignacy; Malak, Henryk; Schrader, Martin; Engelhardt, Peter; Kano, Hiroski; Hell, Stefan W.

1997-01-01

44

Complex formation of neptunium(V) with 4-hydroxy-3-methoxybenzoic acid studied by time-resolved laser-induced fluorescence spectroscopy with ultra-short laser pulses  

NASA Astrophysics Data System (ADS)

The complex formation of neptunium(V) with 4-hydroxy-3-methoxybenzoic acid (vanillic acid) was studied by time-resolved laser-induced fluorescence spectroscopy with ultra-short laser pulses using the fluorescence properties of 4-hydroxy-3-methoxybenzoic acid. A 2:1 complex of neptunium(V) with 4-hydroxy-3-methoxybenzoic acid was found. The stability constant of this complex was determined to be log ?210 = 7.33 ± 0.10 at an ionic strength of 0.1 mol/l (NaClO 4) and at 21 °C. The determination of the stability constant required an investigation of the excited-state proton transfer of 4-hydroxy-3-methoxybenzoic acid over the whole pH range. It was realized that 4-hydroxy-3-methoxybenzoic acid undergoes excited-state reactions only at pH values below 5. At pH values above 5 stability constants can be determined without kinetic calculation of the proton transfer.

Vulpius, D.; Geipel, G.; Baraniak, L.; Bernhard, G.

2006-03-01

45

Speciation of Eu3+ bound to humic substances by time-resolved laser fluorescence spectroscopy (TRLFS) and parallel factor analysis (PARAFAC)  

NASA Astrophysics Data System (ADS)

The bioavailability and toxicity of metal ions including radionuclides in the biosphere are greatly influenced by their speciation. Humic substances (HSs) are important constituents of various soil and water systems and have significant impact on the speciation and mobility of metal ions because of their high affinity to metal ions. In this study, the speciation of europium (Eu3+), a chemical homologue of trivalent actinides, with HSs collected from various origins was investigated by time-resolved laser fluorescence spectroscopy (TRLFS). The difficulties associated with the separation of the contribution of different Eu3+ species due to overlapping spectra or similar fluorescence lifetimes were addressed and mitigated by applying a multi-mode factor analysis, parallel factor analysis (PARAFAC), which resulted in the number, spectra, decay curves and relative fluorescence intensity profiles of different Eu3+ species. Subsequently, the interpretation of the Eu3+ species, was tackled by principal component analysis (PCA) and partial linear square (PLS) regression to deduce the nature of the Eu3+ species by taking into account the physicochemical properties of the HSs. Three factors corresponding to different Eu3+ species were obtained at 70 ?M Eu3+ for all HSs investigated except for one humic acid. One of the factors corresponded to free Eu3+ ion interacting with HSs via diffusion. The remaining two factors were thought to be Eu3+ bound to HSs: one bound to acidic functional groups of HSs and the other to the sites of HSs influenced by the carbon backbone structures. It was also found that the latter factor exhibited strong energy transfer from the excited Eu3+ center to HSs. At lower Eu3+ concentration (10 ?M), two factors having similar fluorescent characteristics to those of the second and third factors were obtained.

Lukman, Steven; Saito, Takumi; Aoyagi, Noboru; Kimura, Takaumi; Nagasaki, Shinya

2012-07-01

46

Time-Resolved Fluorescent Imaging of Glucose  

Microsoft Academic Search

A method for the fluorescent imaging of glucose is described that is based on the detection of enzymatically produced hydrogen peroxide, using the europium(III) tetracycline complex as the fluorescent probe incorporated into a hydrophilic polymer layer. Coadsorption of glucose oxidase (GOx) makes these sensor layers respond to the hydrogen peroxide produced by the GOx-assisted oxidation of glucose. The hydrogel layers

Michael Schäferling; Meng Wu; Otto S. Wolfbeis

2004-01-01

47

Time-resolved nanosecond fluorescence lifetime imaging and picosecond infrared spectroscopy of combretastatin A-4 in solution and in cellular systems  

NASA Astrophysics Data System (ADS)

Fluorescence lifetime images of intrinsic fluorescence obtained with two-photon excitation at 630 nm are shown following uptake of a series of E-combretastatins into live cells, including human umbilical vein endothelial cells (HUVECs) that are the target for the anticancer activity of combretastatins. Images show distribution of the compounds within the cell cytoplasm and in structures identified as lipid droplets by comparison with images obtained following Nile red staining of the same cells. The intracellular fluorescent lifetimes are generally longer than in fluid solution as a consequence of the high viscosity of the cellular environment. Following incubation, the intracellular concentrations of a fluorinated derivative of E-combretastatin A-4 in HUVECs are between two and three orders of magnitude higher than the concentration in the surrounding medium. Evidence is presented to indicate that at moderate laser powers (up to 6 mW), it is possible to isomerize up to 25% of the combretastatin within the femtolitre focal volume of the femtosecond laser beam. This suggests that it may be possible to activate the E-combretastatin (with low cellular toxicity) to the Z-isomer with high anticancer drug activity using two-photon irradiation. The isomerization of Z- and E-combretastatins by 266 nm irradiation has been probed by ultrafast time-resolved infrared spectroscopy. Results for the E-isomer show a rapid loss of excess vibrational energy in the excited state with a lifetime of 7 ps, followed by a slower process with a lifetime of 500 ps corresponding to the return to the ground state as also determined from the fluorescence lifetime. In contrast, the Z-isomer, whilst also appearing to undergo a rapid cooling of the initial excited state, has a much shorter overall excited state lifetime of 14 ps. DedicationThis paper is dedicated to the memory of Professor Christopher G Morgan (1949-2011). He was a valued colleague and friend at the University of Salford and made significant contributions to the development and applications of fluorescence lifetime imaging.

Bisby, Roger H.; Botchway, Stanley W.; Greetham, Greg M.; Hadfield, John A.; McGown, Alan T.; Parker, Anthony W.; Scherer, Kathrin M.; Towrie, Mike

2012-08-01

48

Thymine Dimer Formation probed by Time-Resolved Vibrational Spectroscopy  

NASA Astrophysics Data System (ADS)

Cyclobutane pyrimidine dimers are the major photoproducts formed when DNA is exposed to UV light. Femtosecond time-resolved vibrational spectroscopy reveals that thymine dimers are formed in thymidine oligonucleotides in an ultrafast photoreaction.

Schreier, Wolfgang J.; Schrader, Tobias E.; Roller, Florian O.; Gilch, Peter; Zinth, Wolfgang; Kohler, Bern

49

Conformational States of the Rapana thomasiana Hemocyanin and Its Substructures Studied by Dynamic Light Scattering and Time-Resolved Fluorescence Spectroscopy  

PubMed Central

Hemocyanins are dioxygen-transporting proteins freely dissolved in the hemolymph of mollusks and arthropods. Dynamic light scattering and time-resolved fluorescence measurements show that the oxygenated and apo-forms of the Rapana thomasiana hemocyanin, its structural subunits RtH1 and RtH2, and those of the functional unit RtH2e, exist in different conformations. The oxygenated respiratory proteins are less compact and more asymmetric than the respective apo-forms. Different conformational states were also observed for the R. thomasiana hemocyanin in the absence and presence of an allosteric regulator. The results are in agreement with a molecular mechanism for cooperative dioxygen binding in molluscan hemocyanins including transfer of conformational changes from one functional unit to another.

Georgieva, Dessislava; Schwark, Daniel; Nikolov, Peter; Idakieva, Krassimira; Parvanova, Katja; Dierks, Karsten; Genov, Nicolay; Betzel, Christian

2005-01-01

50

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

51

Seventh international conference on time-resolved vibrational spectroscopy  

SciTech Connect

The International Conference on Time-Resolved Vibrational Spectroscopy (TRVS) is widely recognized as the major international forum for the discussion of advances in this rapidly growing field. The 1995 conference was the seventh in a series that began at Lake Placid, New York, 1982. Santa Fe, New Mexico, was the site of the Seventh International Conference on Time-Resolved Vibrational Spectroscopy, held from June 11 to 16, 1995. TRVS-7 was attended by 157 participants from 16 countries and 85 institutions, and research ranging across the full breadth of the field of time-resolved vibrational spectroscopy was presented. Advances in both experimental capabilities for time-resolved vibrational measurements and in theoretical descriptions of time-resolved vibrational methods continue to occur, and several sessions of the conference were devoted to discussion of these advances and the associated new directions in TRVS. Continuing the interdisciplinary tradition of the TRVS meetings, applications of time-resolved vibrational methods to problems in physics, biology, materials science, and chemistry comprised a large portion of the papers presented at the conference.

Dyer, R.B.; Martinez, M.A.D.; Shreve, A.; Woodruff, W.H. [comps.] [comps.

1997-04-01

52

Time-resolved fluorescence of normal and atherosclerotic arteries  

NASA Astrophysics Data System (ADS)

Picosecond time-resolved fluorescence measurements were performed on fibrous and calcified atherosclerotic plaque and normal coronary artery with 351nm picosecond excitation of a mode-locked Nd-glass laser. Double exponential decay profiles were measured. The fast component of lifetimes of fibrous plaque is different than that of normal artery or calcified plaque and can be used to discriminate fibrous plaque from normal artery.

Pradhan, Asima; Das, Bidyut B.; Liu, C. H.; Alfano, Robert R.; O'Brien, Kenneth M.; Stetz, Mark L.; Scott, John J.; Deckelbaum, Lawrence I.

1991-05-01

53

Time resolved imaging microscopy. Phosphorescence and delayed fluorescence imaging.  

PubMed Central

An optical microscope capable of measuring time resolved luminescence (phosphorescence and delayed fluorescence) images has been developed. The technique employs two phase-locked mechanical choppers and a slow-scan scientific CCD camera attached to a normal fluorescence microscope. The sample is illuminated by a periodic train of light pulses and the image is recorded within a defined time interval after the end of each excitation period. The time resolution discriminates completely against light scattering, reflection, autofluorescence, and extraneous prompt fluorescence, which ordinarily decrease contrast in normal fluorescence microscopy measurements. Time resolved image microscopy produces a high contrast image and particular structures can be emphasized by displaying a new parameter, the ratio of the phosphorescence to fluorescence. Objects differing in luminescence decay rates are easily resolved. The lifetime of the long lived luminescence can be measured at each pixel of the microscope image by analyzing a series of images that differ by a variable time delay. The distribution of luminescence decay rates is displayed directly as an image. Several examples demonstrate the utility of the instrument and the complementarity it offers to conventional fluorescence microscopy. Images FIGURE 2 FIGURE 3 FIGURE 4 FIGURE 5 FIGURE 6

Marriott, G; Clegg, R M; Arndt-Jovin, D J; Jovin, T M

1991-01-01

54

Motor Oil Classification Based on Time-Resolved Fluorescence  

PubMed Central

A time-resolved fluorescence (TRF) technique is presented for classifying motor oils. The system is constructed with a third harmonic Nd:YAG laser, a spectrometer, and an intensified charge coupled device (ICCD) camera. Steady-state and time-resolved fluorescence (TRF) measurements are reported for several motor oils. It is found that steady-state fluorescence is insufficient to distinguish the motor oil samples. Then contour diagrams of TRF intensities (CDTRFIs) are acquired to serve as unique fingerprints to identify motor oils by using the distinct TRF of motor oils. CDTRFIs are preferable to steady-state fluorescence spectra for classifying different motor oils, making CDTRFIs a particularly choice for the development of fluorescence-based methods for the discrimination and characterization of motor oils. The two-dimensional fluorescence contour diagrams contain more information, not only the changing shapes of the LIF spectra but also the relative intensity. The results indicate that motor oils can be differentiated based on the new proposed method, which provides reliable methods for analyzing and classifying motor oils.

Mu, Taotao; Chen, Siying; Zhang, Yinchao; Guo, Pan; Chen, He; Meng, Fandong

2014-01-01

55

Time-resolved fluorescence detection of mosaic DNA chip.  

PubMed

We demonstrated a time-resolved fluorescence (TRF) label and detection of mosaic DNA chip in this paper. We synthesized oligonucleotide sequences in situ on glass slides directly, and then sliced them up into small pieces and patched up the pieces bearing different sequences to generate a mosaic DNA chip. With multiple 4, 7-bis(chlorosulfophenyl)-1, 10-phenanthroline-2, 9-dicarboxylic acid (BCPDA, abbreviated as BCPDA) labeling method based on avidin-biotin amplification, we established a TRF detection format on the mosaic DNA chip. The detection method allows discriminatory signals for perfect match, one-base mismatch, two-base mismatch, and three-base mismatch by TRF labeled DNA hybridization, whereby Europium (III, Eu3+) was captured and released on the principle of complexation and dissociation interaction between BCPDA and Eu3+ solution when the BCPDA-tagged avidin and biotin-capped oligonucleotide sequence linked. The fluorescence spectra and related lifetimes were determined. We also compared the TRF detection mode with the conventional fluorescence one. These results showed the former is a potential alternative replacement of the latter, especially for labeling the mosaic DNA chip. The discovery is of fundamental interest and has significant implications to biochips and biosensors based on time-resolved-fluorescence detection. PMID:16573071

He, Quanguo; Chen, Hong; Nie, Libo; Tang, Jianxin; Xiao, Pengfeng

2006-01-01

56

Ligand–receptor interactions and membrane structure investigated by AFM and time-resolved fluorescence microscopy  

Microsoft Academic Search

The atomic force microscope (AFM) and the associated dynamic force spectroscopy technique have been exploited to quantitatively assess the interaction between proteins and their binding to specific ligands and membrane surfaces. In particular, we have studied the specific interaction between lung surfactant protein D and various carbohydrates. In addition, we have used scanning AFM and time-resolved fluorescence microscopy to image

Esben Thormann; Adam C. Simonsen; Lars K. Nielsen; Ole G. Mouritsen

2007-01-01

57

Time resolved spectroscopy on Pigment Yellow 101 in solid state  

NASA Astrophysics Data System (ADS)

The photochemistry of the fluorescent Pigment Yellow 101 (P.Y.101) in the crystalline phase is investigated combining time resolved vibrational and electronic spectroscopy. The experiments reveal a complex reaction dynamics spanning several orders of magnitude in time and including excited state intramolecular proton transfer (ESIPT) from the initial trans-diol conformer. Following photoexcitation and the subsequent wavepacket motion out of the Franck-Condon region two tautomers, an excited trans-diol and trans-keto state are formed. The cis-trans isomerization of the keto form, which was experimentally observed and theoretically confirmed in DFT calculations in studies on P.Y.101 in solution is obstructed in the solid state, consequently the formation of the cis conformer is not directly observed. In addition, a long lived photoproduct with red shifted vibrational frequencies is identified. The life time of this intermediate is determined to be 50 ?s, although an unambiguous assignment to a specific molecular configuration cannot be given at present.

Staudt, H.; Köhler, T.; Lorenz, L.; Neumann, K.; Verhoefen, M.-K.; Wachtveitl, J.

2008-05-01

58

Time-resolved fluorescence spectroscopy measures clustering and mobility of a g protein-coupled receptor opsin in live cell membranes.  

PubMed

Determining membrane protein quaternary structure is extremely challenging, especially in live cell membranes. We measured the oligomerization of opsin, a prototypical G protein-coupled receptor with pulsed-interleaved excitation fluorescence cross-correlation spectroscopy (PIE-FCCS). Individual cell measurements revealed that opsin is predominantly organized into dimeric clusters. At low concentrations, we observed that the population of oligomers increased linearly with the square of the individual monomer populations. This finding supports a monomer-dimer equilibrium and provides an experimental measurement of the equilibrium constant. PMID:24831851

Comar, William D; Schubert, Sarah M; Jastrzebska, Beata; Palczewski, Krzysztof; Smith, Adam W

2014-06-11

59

Steady-state and time-resolved fluorometry of fluorescent pollutants and heavy metal complexes  

NASA Astrophysics Data System (ADS)

Time-resolved laser-induced fluorescence spectroscopy is one of the most sensitive optical methods which is well suited for on-line in situ analysis. Here, three examples for the steady- state and time-resolved fluorescence analysis of environmentally important analytes, the fluorescent monoaromatic hydrocarbons benzene, toluene, and xylene as well as non fluorescent heavy metal ions forming a fluorescent complex with a cation coordinating fluorescence probe, are presented and the potential of both methods is discussed. For BTX, various mixtures of the spectrally similar compounds B, T, and X showing different fluorescence lifetimes were studied with both methods. As an example for fluorometric metal ion analysis, the fluorescence probe BP(OH)2 (2,2'-bipyridyl- 3,3'-diol) was employed for the determination of d10 metal ions in water and the newly developed fluorescence probe APTA for the detection of Cu(II). Cation complexation of BP(OH2 yields spectrally very similar complexes which differ in their fluorescence lifetimes. Complexation of APTA to Cu(II) leads to small spectral changes and a strong increase in fluorescence quantum yield and lifetime. For the analytes studied, a comparison of the detection limits, standard deviations, and linear dynamic range of both methods clearly demonstrates the analytical potential of time-resolved fluorometry.

Resch, Ute; Rurack, Knut

1997-05-01

60

Studies on the interaction of adriamycin with d-(TGATCA) 2 by proton nuclear magnetic resonance spectroscopy, time-resolved fluorescence measurement, diffusion ordered spectroscopy followed by structural refinement using restrained molecular dynamics approach  

NASA Astrophysics Data System (ADS)

Adriamycin is one of the most potent anticancer anthracycline drug having aromatic chromophore and an amino sugar moiety. We report here the solution structure of 2:1 adriamycin-d-(TGATCA) 2 complex which has been determined using restrained molecular dynamics. Sequential NOE (nuclear Overhauser effect) connectivities between T1pG2 and C5pA6 steps are not observed on the intercalation of the drug chromophore at these base pair steps. Presence of several other intermolecular NOEs, that is, T1CH 3sbnd 7H, T1CH 3sbnd 10eqH and C5H6 sbnd 4OCH 3 corroborate the same. The specificity of interaction arises from the O-glycosidic dihedral bond C7 sbnd O7 sbnd C1' sbnd C2' (133°), positioning of NH 3+ moiety in minor groove, conformation of ring A and daunosamine sugar. Besides this, diffusion ordered spectroscopy (DOSY) studies prove the formation of complex and time-resolved fluorescence measurement studies provide evidence for shortening of decay time on complex formation. The nonspecific interactions as well as those essential for molecular basis of drug action are discussed along with the specificity of interactions in the drug-DNA complex, which is responsible for the anticancer action of the drug.

Agrawal, Prashansa; Barthwal, Sudhir Kumar; Govil, Girjesh; Barthwal, Ritu

2009-08-01

61

Time-resolved fluorescence imaging in islet cell autoantibody quantitation.  

PubMed

The prodromal period of insulin-dependent diabetes mellitus (IDDM) is characterized by circulating islet cell autoantibodies (ICA) and other beta cell specific autoantibodies. Despite biochemical characterization of the major beta cell autoantigens insulin, glutamic acid decarboxylase and protein tyrosine phosphatase and development of the respective antibody assays, ICA has remained the standard in IDDM prediction. Conventional ICA quantitation using classic fluorochromes is prone to errors since fluorescence intensity is estimated subjectively using the human eye, which is also unable to differentiate specific signals from non-specific signals and autofluorescence. Using Eu(3+)-chelate labelled anti-human polyclonal IgG (decay time 1000 microseconds) as the secondary antibody in time-resolved fluorescence imaging (TRFI), the chelate and autofluorescence signals (typical decay time < 100 ns) are fully separated. The image is recorded using an optically gated cooled digital CCD camera. The specificity of the ICA signal is further improved by interactive analysis of the image. Signal detection is objective, the signal-to-background ratio improves, and ICA quantitation is possible using undiluted serum. Of 57 consecutive new-onset IDDM patients, 55 (96.5%) were ICA positive in the new assay while 51 (89.5%) were positive in the conventional assay suggesting that the sensitivity of TRFI exceeds that of the IAA, GAD65 and IA-2 autoantibody assays combined. For later comparisons, the stained slides may be stored in the light for years without any decrease in specific fluorescence. PMID:9433472

Rulli, M; Kuusisto, A; Salo, J; Kojola, H; Simell, O

1997-10-27

62

High resolution detection of fluorescently labeled microorganisms in environmental samples using time-resolved fluorescence microscopy  

Microsoft Academic Search

The high level of discrimination offered by fluorescence microscopy has led to its widespread use for the analysis of individual microbial cells. The major limitation of fluorescence microscopy in microbial ecology is that many types of environmental samples contain autofluorescent material that can obscure emission from a fluorescent label. Time-resolved fluorescence microscopy (TRFM) is a technique that greatly reduces background

Russell Connally; Duncan Veal; James Piper

2002-01-01

63

Time-resolved laser fluorescence spectroscopy and extended X-ray absorption spectroscopy investigations of the N3- complexation of Eu(III), Cm(III), and Am(III) in an ionic liquid: differences and similarities.  

PubMed

The complexation of the lanthanide Eu(III) and the actinides Cm(III) and Am(III) by N3- was investigated by application of time-resolved laser fluorescence spectroscopy (TRLFS) and X-ray absorption spectroscopy (XAFS) in the ionic liquid solution of C4mimTf2N (1-butyl-3-methylimidazolium-bis(trifluoromethylsulfonyl)imide). TRLFS measurements show that the interaction of azide with Eu(CF3SO3)3 and Eu(ClO4)3 results in both dynamic luminescence quenching by collisional encounters of N3- with Eu(III) and static luminescence quenching by inner-sphere complexation of Eu(III) by N3-. Hereby, the complexation of Eu-triflate by azide starts at a lower N3- concentration as compared to the perchlorate salt. The authors ascribe this phenomenon to a stronger bonding of ClO4- toward the metal ion than triflate, as well as to a stronger electrostatic repulsion of N3- by the perchlorate ligand. In both actinide samples (Cm(ClO4)3, Am(ClO4)3), the complexation with azide exhibits a clear kinetic hindrance. Nevertheless, mixed actinide-perchlorate-azide complexes are formed after several days in C4mimTf2N. The different reaction kinetics for the Ln- and An-complexation by azide may provide the opportunity for an effective separation of lanthanides from actinides in the nuclear fuel cycle by the use of N-based extractants in ionic liquid solution. PMID:18459761

Stumpf, S; Billard, I; Gaillard, C; Panak, P J; Dardenne, K

2008-06-01

64

Differential Hydration of Tricyanomethanide Observed by Time Resolved Vibrational Spectroscopy  

PubMed Central

The degenerate transition corresponding to asymmetric stretches of the D3h tricyanomethanide anion, C(CN)3-, in aqueous solution was investigated by linear FTIR spectroscopy, femtosecond pump-probe spectroscopy, and 2D IR spectroscopy. Time resolved vibrational spectroscopy shows that water induces vibrational energy transfer between the degenerate asymmetric stretch modes of tricyanomethanide. The frequency-frequency correlation function and the vibrational energy transfer show two significantly different ultrafast time scales. The system is modeled with molecular dynamics simulations and ab-initio calculations. A new model for theoretically describing the vibrational dynamics of a degenerate transition is presented. Microscopic models, where water interacts axially and radially with the ion, are suggested for the transition dipole reorientation mechanism.

Kuroda, Daniel G.; Singh, Prabhat K.; Hochstrasser, Robin M.

2012-01-01

65

Time-resolved microspectrofluorometry and fluorescence lifetime imaging using ps-pulsed diode lasers in laser scanning microscopes  

Microsoft Academic Search

A setup consisting on a laser scanning microscope equipped with appropriate detection units was developed for time-resolved intracellular fluorescence spectroscopy and fluorescence lifetime imaging (FLIM) for online detection of structural changes of various biomolecules. Short-pulsed excitation was performed with a diode laser which emits pulses at 398 nm with 70 ps duration. The laser was coupled to the laser scanning

Angelika Rück; Frank Dolp; Claudia Scalfi-Happ; Rudolf W. Steiner; Michael Beil

2003-01-01

66

Thermally activated delayed fluorescence of fluorescein derivative for time-resolved and confocal fluorescence imaging.  

PubMed

Compared with fluorescence imaging utilizing fluorophores whose lifetimes are in the order of nanoseconds, time-resolved fluorescence microscopy has more advantages in monitoring target fluorescence. In this work, compound DCF-MPYM, which is based on a fluorescein derivative, showed long-lived luminescence (22.11 ?s in deaerated ethanol) and was used in time-resolved fluorescence imaging in living cells. Both nanosecond time-resolved transient difference absorption spectra and time-correlated single-photon counting (TCSPC) were employed to explain the long lifetime of the compound, which is rare in pure organic fluorophores without rare earth metals and heavy atoms. A mechanism of thermally activated delayed fluorescence (TADF) that considers the long wavelength fluorescence, large Stokes shift, and long-lived triplet state of DCF-MPYM was proposed. The energy gap (?EST) of DCF-MPYM between the singlet and triplet state was determined to be 28.36 meV by the decay rate of DF as a function of temperature. The ?EST was small enough to allow efficient intersystem crossing (ISC) and reverse ISC, leading to efficient TADF at room temperature. The straightforward synthesis of DCF-MPYM and wide availability of its starting materials contribute to the excellent potential of the compound to replace luminescent lanthanide complexes in future time-resolved imaging technologies. PMID:24936960

Xiong, Xiaoqing; Song, Fengling; Wang, Jingyun; Zhang, Yukang; Xue, Yingying; Sun, Liangliang; Jiang, Na; Gao, Pan; Tian, Lu; Peng, Xiaojun

2014-07-01

67

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

68

Time-resolved infrared spectroscopy of RNA folding.  

PubMed

We introduce time-resolved infrared spectroscopy as a powerful method to study the kinetics of RNA folding and unfolding transitions. A laser-induced temperature jump is used to initiate a perturbation in the RNA structure. A probe laser, tuned to a specific infrared absorption of the RNA, is then used to monitor the subsequent relaxation kinetics. A 10-ns pump pulse permits the investigation of fast, nanosecond events. In this work we probe two vibrational transitions, one at 1620 cm(-1) and one at 1661 cm(-1). The former transition reports mainly on the dynamics of A and U interactions, the latter is attributed to mainly G and C interactions. Our results reveal three distinct kinetic phases for each vibrational transition probed. We propose two models to describe the data. In one mechanism, the unfolded state partitions into two separate populations; each is conformationally biased to proceed via one of two distinct pathways. In an alternative model, folding proceeds through a series of sequentially populated intermediates. In both cases, the first step in the proposed folding mechanism is rate limiting (hundreds of microseconds) and involves a collapse into incorrectly folded intermediate populations. Two faster kinetic phases (tens of microseconds and hundreds of nanoseconds) follow in which the intermediate populations undergo localized reorganizational motions in the search for native contacts. PMID:16126826

Brauns, Eric B; Dyer, R Brian

2005-11-01

69

Time Resolved Micro-Pl Spectroscopy of Individual Quantum Dots  

NASA Astrophysics Data System (ADS)

Experimental and theorectical investigations of the physics of self-assembled quantum dots (SADs) have focused largely on the nature of the individual dots, independent of their surroundings. However, the coupling of dots to each other, an external microcavity or nearby localized states is an important area of investigation, critical to issues of coherence and quantum information processing. For example, it has been found that the carriers may tunnel through the potential barrier of one QD to another QD via the localized states of the wetting layer(WL) [1]. We employ scanning SIL-confocal microscopy combined with time resolved photoluminescence(TRPL) spectroscopy to study small ensembles as well as individiual InGaAs/GaAs SADs. Due to high throughput of our experimental set-up we were able to observe state filling of individual dots. We explored the interaction between QDs and WL as well as the dynamics of the interband radiative recombination and intersublevel thermalization by determining the lifetimes of carriers in QDs and WL and then deduce the mechanism for carrier capture in the QDs. [1] H.D. Robinson, B.B. Goldberg, Physica E.6, 444 (2000)

Liu, Zhiheng; Bunea, G.; Robinson, H.; Goldberg, B.; Unlu, S.; Fafard, S.

2001-03-01

70

Time-resolved fluorescence studies of dye-polymers as excited by laser and beta-radiation  

Microsoft Academic Search

The fluorescence properties and energy transfer processes of dye-polymers have been investigated with time-resolved fluorescence spectroscopy. Based on an understanding of these characteristics, the new dye-polymers were optimized for potential applications in scintillators and wavelength shifters used in high energy particle detection. The two primary criteria for suitable samples were high quantum efficiencies and short fluorescence decay times. In this

Lin-I. Liu

1997-01-01

71

Preparation and characterization of phantom objects for optical imaging by time-resolved transmittance and fluorescence  

NASA Astrophysics Data System (ADS)

Well-characterized phantom objects are necessary for investigating the performances of optical imaging systems based on time-resolved transmittance and fluorescence. For this purposes we have prepared inhomogeneous phantoms made of gelatinous objects placed in aqueous solutions of 10% Intralipid with different concentrations. The gelatinous objects have been prepared using a mixture of 10% Intralipid with agar at which absorbing ink have been added for transmittance based optical imaging system. For fluorescence measurements proper fluorescent dyes (rhodamine6G and IR125) have been added. Conventional optical characterization by spectrophotometric and spectrofluorimetric measurements have been performed. In addition, time-resolved transmittance and fluorescence measurements have been carried out. In particular, time-correlated single photon counting system has been used for time-resolved transmittance measurements. For time-resolved fluorescence measurements an optical imaging system based on a Ti:Sa laser and streak camera has been employed.

Bottalico, Laura; Delfino, Ines; Esposito, Rosario; Lepore, Maria

2002-05-01

72

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

73

Time-resolved fluorescence spectroscopic investigation of cationic polymer/DNA complex formation  

NASA Astrophysics Data System (ADS)

Since DNA is not internalized efficiently by cells, the success of gene therapy depends on the availability of carriers to efficiently deliver genetic material into target cells. Gene delivery vectors can be broadly categorized into viral and non-viral ones. Non-viral gene delivery systems are represented by cationic lipids and polymers rely on the basics of supramolecular chemistry termed "self-assembling": at physiological pH, they are cations and spontaneously form lipoplexes (for lipids) and polyplexes (for polymers) complexing nucleic acids. In this scenario, cationic polymers are commonly used as non-viral vehicles. Their effectiveness is strongly related to key parameters including DNA binding ability and stability in different environments. Time-resolved fluorescence spectroscopy of SYBR Green I (DNA dye) was carried out to characterize cationic polymer/DNA complex (polyplex) formation dispersed in aqueous solution. Both fluorescence amplitude and lifetime proved to be very sensitive to the polymer/DNA ratio (N/P ratio, +/-).

D'Andrea, Cosimo; Bassi, Andrea; Taroni, Paola; Pezzoli, Daniele; Volonterio, Alessandro; Candiani, Gabriele

2011-06-01

74

Monitoring tissue metabolism via time-resolved laser fluorescence  

NASA Astrophysics Data System (ADS)

Most assays for drug screening are monitoring the metabolism of cells by detecting the NADH content, which symbolize its metabolic activity, indirectly. Nowadays, the performance of a LASER enables us to monitor the metabolic state of mammalian cells directly and on-line by using time-resolved autofluorescence detection. Therefore, we developed in combination with tissue engineering, an assay for monitoring minor toxic effects of volatile organic compounds (VOC), which are accused of inducing Sick Building Syndrome (SBS). Furthermore, we used the Laserfluoroscope (LF) for pharmacological studies on human bone marrow in vitro with special interest in chemotherapy simulation. In cancer research and therapy, the effect of chemostatica in vitro in the so-called oncobiogram is being tested; up to now without great success. However, it showed among other things that tissue structure plays a vital role. Consequently, we succeeded in simulating a chemotherapy in vitro on human bone marrow. Furthermore, after tumor ektomy we were able to distinguish between tumoric and its surrounding healthy tissue by using the LF. With its sensitive detection of metabolic changes in tissues the LF enables a wide range of applications in biotechnology, e.g. for quality control in artificial organ engineering or biocompatability testing.

Maerz, Holger K.; Buchholz, Rainer; Emmrich, Frank; Fink, Frank; Geddes, Clive L.; Pfeifer, Lutz; Raabe, Ferdinand; Marx, Uwe

1999-05-01

75

DEVELOPMENT OF TIME-RESOLVED LASER-INDUCED FLUORESCENCE SPECTROSCOPIC TECHNIQUE FOR THE ANALYSIS OF BIOMOLECULES UDC 539.2  

Microsoft Academic Search

Our developments of the time-resolved laser-induced fluorescence (TR-LIF) detection system for biomolecules are presented. This system is based on the tunable (320 nm to 475 nm) Nd:YAG laser pulses used to excite various biomolecules. The detection part is the Streak System for Fluorescence Lifetime Spectroscopy (Hamamatsu, Japan). The system consists of a C4334-01 streakscope, as a detector, DG 535 digital

M. Terzi?; B. P. Marinkovi?; D. Ševi?; J. Jureta; A. R. Milosavljevi?

76

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

77

Time-resolved fluorescence spectra of pyrene doped in amorphous silica glasses  

NASA Astrophysics Data System (ADS)

Steady-excitation fluorescence spectra of pyrene-doped amorphous silica glasses prepared by the sol—gel method were measured. A broad excimer-like emission was observed in higher dopant concentrations. The picosecond time-resolved fluorescence spectra and the fluorescence excitation spectra suggest that a ground-state dimer is responsible for the broad excimer-like emission.

Yamanaka, Takaya; Takahashi, Yoshihiro; Kitamura, Takashi; Uchida, Kenji

1990-08-01

78

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

79

Two-photon and time-resolved fluorescence conformational studies of aggregation in amyloid peptides.  

PubMed

The conformational changes associated with the aggregation of proteins are critical to the understanding of fundamental molecular events involved in early processes of neurodegenerative diseases. A detailed investigation of these processes requires the development of new approaches that allow for sensitive measurements of protein interactions. In this paper, we applied two-photon spectroscopy coupled with time-resolved fluorescence measurements to analyze amyloid peptide interactions through aggregation-dependent concentration effects. Labeled amyloid-beta peptide (TAMRA-Abeta1-42) was used in our investigation, and measurements of two-photon-excited fluorescence of the free and covalently conjugated peptide structure were carried out. The peptide secondary structure was correlated with a short fluorescence lifetime component, and this was associated with intramolecular interactions. Comparison of the fractional occupancy of the fluorescence lifetime measured at different excitation modes demonstrates the high sensitivity of the two-photon method in comparison to one-photon excitation (OPE). These results give strong justification for the development of fluorescence-lifetime-based multiphoton imaging and assays. PMID:20429591

Wang, Ying; Clark, Travis B; Goodson, Theodore

2010-05-27

80

Time-resolved spectroscopy of InGaN  

SciTech Connect

The authors have used time-resolved photoluminescence (PL), with 400 nm (3.1 eV) excitation, to examine In{sub x}Ga{sub 1{minus}x}N/GaN light-emitting diodes (LEDs) before the final stages of processing at room temperature. They have found dramatic differences in the time-resolved kinetics between dim, bright and super bright LED devices. The lifetime of the emission for dim LEDs is quite short, 110 {+-} 20 ps at photoluminescence (PL) maximum, and the kinetics are not dependent upon wavelength. This lifetime is short compared to bright and super bright LEDs, which the authors have examined under similar conditions. The kinetics of bright and super bright LEDs are clearly wavelength dependent, highly non-exponential, and are on the nanosecond time scale (lifetimes are in order of 1 ns for bright and 10 ns for super bright LED at the PL max). The nonexponential PL kinetics can be described by a stretched exponential function, indicating significant disorder in the material. Typical values for {beta}, the stretching coefficient, are 0.45--0.6 for bright LEDs, at the PL maxima at room temperature. The authors attribute this disorder to indium alloy fluctuations. From analysis of the stretched exponential kinetics they estimate the potential fluctuations to be approximately 75 meV in the super bright LED. Assuming a hopping mechanism, the average distance between indium quantum dots in the super bright LED is estimated to be 20 {angstrom}.

Pophristic, M.; Long, F.H.; Tran, C.; Ferguson, I.T.

2000-07-01

81

Integrated multimodal microscopy, time-resolved fluorescence, and optical-trap rheometry: toward single molecule mechanobiology  

PubMed Central

Cells respond to forces through coordinated biochemical signaling cascades that originate from changes in single-molecule structure and dynamics and proceed to large-scale changes in cellular morphology and protein expression. To enable experiments that determine the molecular basis of mechanotransduction over these large time and length scales, we construct a confocal molecular dynamics microscope (CMDM). This system integrates total-internal-reflection fluorescence (TIRF), epifluorescence, differential interference contrast (DIC), and 3-D deconvolution imaging modalities with time-correlated single-photon counting (TCSPC) instrumentation and an optical trap. Some of the structures hypothesized to be involved in mechanotransduction are the glycocalyx, plasma membrane, actin cytoskeleton, focal adhesions, and cell-cell junctions. Through analysis of fluorescence fluctuations, single-molecule spectroscopic measurements [e.g., fluorescence correlation spectroscopy (FCS) and time-resolved fluorescence] can be correlated with these subcellular structures in adherent endothelial cells subjected to well-defined forces. We describe the construction of our multimodal microscope in detail and the calibrations necessary to define molecular dynamics in cell and model membranes. Finally, we discuss the potential applications of the system and its implications for the field of mechanotransduction.

Gullapalli, Ramachandra R.; Tabouillot, Tristan; Mathura, Rishi; Dangaria, Jhanvi H.; Butler, Peter J.

2011-01-01

82

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

83

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

2013-12-01

84

Light-Harvesting Ability of the Fucoxanthin Chlorophyll a/c-Binding Protein Associated with Photosystem II from the Diatom Chaetoceros gracilis As Revealed by Picosecond Time-Resolved Fluorescence Spectroscopy.  

PubMed

The fucoxanthin chlorophyll a/c-binding protein (FCP) is a unique antenna complex possessed by diatoms. Although FCP complexes have been isolated from various diatoms, there is no direct evidence for the existence of FCP associated with photosystem II (FCPII). Here, we report the isolation and spectroscopic characterization of FCPII complex from the diatom Chaetoceros gracilis. The FCPII complex was purified using sucrose centrifugation and anion-exchange chromatography. Clear-native PAGE and SDS-PAGE analyses revealed that the FCPII complex was composed of FCP-A oligomer and FCP-B/C trimer. Time-resolved fluorescence spectra of the FCPII complex were measured at 77 K. The characteristic lifetimes and fluorescence components were determined using global fitting analysis, followed by the construction of fluorescence decay-associated spectra (FDAS). FDAS exhibited fluorescence rises and decays, reflecting excitation energy transfer, with the time constants of 150 ps, 800 ps, and 2.9 ns. The long time constants are most likely attributed to the intercomplex excitation energy transfer between FCP-A oligomer and FCP-B/C trimer in the FCPII complex. The 5.6 ns FDAS likely originates from the final energy traps. In contrast, the FDAS exhibited no quenching component with any time constant. These results indicate that the FCPII complex is efficient in light harvesting and excitation energy transfer. PMID:24773012

Nagao, Ryo; Yokono, Makio; Teshigahara, Ayaka; Akimoto, Seiji; Tomo, Tatsuya

2014-05-15

85

Enhanced excitation energy transfer in microdroplets — a study by time-resolved fluorescence microscopy  

Microsoft Academic Search

Time-resolved fluorescence microscopy was used to study the fluorescence quenching of rhodamine 6G (R6G) in single microdroplets with diameters equal to or larger than 2 ?m. The microdroplets were prepared by dispersing ethylene glycol solutions of R6G in silicone oil. The fluorescence lifetime of R6G was found to be independent of the size of the droplet at low concentrations (1.0

Krishna K. Pandey; Satoshi Hirayama

1996-01-01

86

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

87

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

88

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

2011-03-01

89

Localization of fluorescence marked prostate tumor with time- resolved diffuse optical tomography  

NASA Astrophysics Data System (ADS)

To increase prostate cancer diagnosis sensibility, we propose to add an optical modality to an US biopsy tool to localize fluorophore marked tumors. Optical signals are acquired on a time-resolved acquisition chain composed by a 770 nm femtosecond laser source and a four channels TCSPC device. The fluorescence concentration is reconstructed by using intensity and mean time of flight acquired from each time-resolved source-detector signal. Validation experiments are performed on a phantom mimicking prostate both on its optical and ultrasound properties with 10 ?mol/L ICG 1 cm deep double fluorescent inclusions to simulate marked tumors. An exhaustive search algorithm succeeded in reconstructing the two distinct fluorescence dots with correct locations.

Hervé, Lionel; Laidevant, Aurélie; Lecordier, Ludovic; Guyon, Laurent; Debourdeau, Mathieu; Boutet, Jérôme; Dinten, Jean-Marc

2010-02-01

90

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

91

Time-resolved fluorescence studies of flavodoxin. Fluorescence decay and fluorescence anisotropy decay of tryptophan in Desulfovibrio flavodoxins  

Microsoft Academic Search

The time-resolved fluorescence characteristics of tryptophan in flavodoxin isolated from the sulfate-reducing bacteria Desulfovibrio vulgaris and Desulfovibrio gigas have been examined. By comparing the results of protein preparations of normal and FMN-depleted flavodoxin, radiationless energy transfer from tryptophan to FMN has been demonstrated. Since the crystal structure of the D. vulgaris flavodoxin is known, transfer rate constants from the two

H. R. M. Leenders; J. Vervoort; A. van Hock; A. J. W. G. Visser

1990-01-01

92

Frame-Transfer Gating Raman Spectroscopy for Time-Resolved Multiscalar Combustion Diagnostics  

NASA Technical Reports Server (NTRS)

Accurate experimental measurement of spatially and temporally resolved variations in chemical composition (species concentrations) and temperature in turbulent flames is vital for characterizing the complex phenomena occurring in most practical combustion systems. These diagnostic measurements are called multiscalar because they are capable of acquiring multiple scalar quantities simultaneously. Multiscalar diagnostics also play a critical role in the area of computational code validation. In order to improve the design of combustion devices, computational codes for modeling turbulent combustion are often used to speed up and optimize the development process. The experimental validation of these codes is a critical step in accepting their predictions for engine performance in the absence of cost-prohibitive testing. One of the most critical aspects of setting up a time-resolved stimulated Raman scattering (SRS) diagnostic system is the temporal optical gating scheme. A short optical gate is necessary in order for weak SRS signals to be detected with a good signal- to-noise ratio (SNR) in the presence of strong background optical emissions. This time-synchronized optical gating is a classical problem even to other spectroscopic techniques such as laser-induced fluorescence (LIF) or laser-induced breakdown spectroscopy (LIBS). Traditionally, experimenters have had basically two options for gating: (1) an electronic means of gating using an image intensifier before the charge-coupled-device (CCD), or (2) a mechanical optical shutter (a rotary chopper/mechanical shutter combination). A new diagnostic technology has been developed at the NASA Glenn Research Center that utilizes a frame-transfer CCD sensor, in conjunction with a pulsed laser and multiplex optical fiber collection, to realize time-resolved Raman spectroscopy of turbulent flames that is free from optical background noise (interference). The technology permits not only shorter temporal optical gating (down to <1 s, in principle), but also higher optical throughput, thus resulting in a substantial increase in measurement SNR.

Nguyen, Quang-Viet; Fischer, David G.; Kojima, Jun

2011-01-01

93

Halide (Cl(super -)) Quenching of Quinine Sulfate Fluorescence: A Time-Resolved Fluorescence Experiment for Physical Chemistry  

ERIC Educational Resources Information Center

The time-resolved fluorescence experiment investigating the halide quenching of fluorescence from quinine sulfate in water is described. The objectives of the experiment include reinforcing student understanding of the kinetics of competing pathways, making connections with microscopic theories of kinetics through comparison of experimental and…

Gutow, Jonathan H.

2005-01-01

94

Optical characterization of Pseudomonas fluorescens on meat surfaces using time-resolved fluorescence  

NASA Astrophysics Data System (ADS)

A scanning optical system for the detection of bacteria on meat surfaces based on fluorescence lifetime and intensity measurements is described. The system detects autofluorescent light emitted by naturally occurring fluorophores in bacteria. The technique only requires minimal sample preparation and handling, thus the chemical properties of the specimen are preserved. This work presents the preliminary results obtained from a time-resolved fluorescence imaging system for the characterization of a nonpathogenic gram-negative bacteria, Pseudomonas fluorescens. Initial results indicate that the combination of fluorescence lifetime and intensity measurements provides a means for characterizing biological media and for detecting microorganisms on surfaces.

Bouchard, Alain; Frechette, Julie; Vernon, Marcia L.; Cormier, Jean-François; Beaulieu, Rene M.; Vallée, Réal; Mafu, Akier A.

2006-01-01

95

Time-resolved confocal fluorescence microscopy of trinitrobenzene-responsive organic nanofibers.  

PubMed

Time-resolved confocal fluorescence microscopy is used to image and analyze quantitatively the influence of 1,3,5-trinitrobenzene on the fluorescence of organic nanofibers. These nanofibers are formed by self-assembly of 2,3-didecyloxyanthracene in methanol or from solutions drop-casted onto glass surfaces. Amplification of the fluorescence quenching emerges in the nanofibers as compared to the constituting monomer thus leading to efficient detection of nanomolar concentrations of TNB. The emission of dry nanofibers on glass is also efficiently quenched by vapors of TNB. PMID:19838686

Giansante, Carlo; Olive, Alexandre G L; Schäfer, Christian; Raffy, Guillaume; Del Guerzo, André

2010-01-01

96

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

97

Identifying Fossil Biosignatures and Minerals in Mars Analog Materials Using Time-Resolved Raman Spectroscopy  

NASA Astrophysics Data System (ADS)

Mars sample return has been identified as a top priority in the planetary science decadal survey. A Mars sample selection and caching mission would be the likely first step in this endeavor. Such a mission would aim to select and prioritize for return to Earth aqueously formed geological samples present at a selected site on Mars, based upon their potential for biosignature capture and preservation. If evidence of past life exists and is found, it is likely to come via the identification of fossilized carbonaceous matter of biological origin (kerogen) found in the selected samples analyzed in laboratories after return to Earth. Raman spectroscopy is considered one of the primary techniques for analyzing materials in situ and selecting the most promising samples for Earth return. We have previously performed a pilot study to better understand the complexities of identifying kerogen using Raman spectroscopy. For the study, we examined a variety of Mars analog materials representing a broad range of mineral compositions and kerogen maturities. The study revealed that kerogen identification in many of the most promising lithologies is often impeded by background fluorescence that originates from long (>10 ns to ms) and short (<1 ns) lifetime fluorophores in both the mineral matrixes and preserved organic matter in the samples. This work explores the potential for time-gated Raman spectroscopy to enable clear kerogen and mineral identifications in such samples. The JPL time-resolved Raman system uses time gating to reduce background fluorescence. It uses a custom-built SPAD (single photon avalanche diode) detector, featuring a 1-ns time-gate, and electronically variable gate delay. Results for a range of fluorescent samples show that the JPL system reduces fluorescence, allowing the identification of both kerogen and mineral components more successfully than with conventional Raman systems. In some of the most challenging samples, the detection of organic matter is hindered by a combination of short lifetime fluorescence and weak Raman scattering coming from preserved kerogen grains. Fluorescence Lifetime Imaging Microscopy (FLIM) measurements were also performed to characterize the lifetimes of both components in the samples and to inform future system improvements such as shorter time gating. Here, we will discuss the results, along with identified challenges to the consistent and reliable in situ identification of kerogen in samples on Mars.

Shkolyar, S.; Farmer, J.; Alerstam, E.; Maruyama, Y.; Blacksberg, J.

2013-12-01

98

Modifying an enzyme immunoassay of immunoreactive trypsinogen to use time-resolved fluorescence.  

PubMed

A coated microtiter-well, enzyme-linked immunometric assay for quantifying immunoreactive trypsinogen in dried blood spots was modified to use time-resolved fluorescence of europium in place of end-point enzymatic color development as the quantification step. The streptavidin-horseradish peroxidase and color development solutions supplied as packaged reagents were replaced by europium-labeled avidin, and the signal was developed with commercially available enhancement solution and read by time-resolved fluorescence. The change of label from enzyme to europium increased the dynamic range of the assay by about 5-fold, reduced the detection limit 10-fold, and halved the intra- and interassay imprecision. The improved analytical precision and stability of the modified assay resulted in a more precise description of the population distribution of immunoreactive trypsinogen values in newborns, showing less variance in the upper centiles. This effect is of paramount importance when using this assay for neonatal screening for cystic fibrosis. PMID:8432010

Ryall, R G; Gjerde, E M; Gerace, R L; Ranieri, E

1993-02-01

99

Cubane radical cation in liquid hydrocarbons: Time-resolved fluorescence detected magnetic resonance study  

SciTech Connect

The authors report here a time-domain study of cubane{sup {center dot}}{sup +}, utilizing the time-resolved fluorescence detected magnetic resonance (FDMR) technique. They have observed a radical cation, which they assign to cubane {sup {center dot}+} in liquid hydrocarbon solution. The observed FDMR spectrum is consistent with the presence of eight protons (a{sub 8H} = 16.1 G) of the cation which are equivalent.

Qin, X.Z.; Trifunac, A.D. (Argonne National Lab., IL (USA)); Eaton, P.E.; Xiong, Y. (Univ. of Chicago, IL (USA))

1991-01-16

100

Time-Resolved Polarization Imaging By Pump-Probe (Stimulated Emission) Fluorescence Microscopy  

Microsoft Academic Search

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-?m orange

Ch. Buehler; C. Y. Dong; P. T. C. So; E. Gratton

2000-01-01

101

Residues determination of carbofuran in vegetables based on sensitive time-resolved fluorescence immunoassay  

Microsoft Academic Search

Using direct competitive time-resolved fluorescence immunoassay (TRFIA), a rapid, highly selective and sensitive method was developed for the determination of carbofuran residues in lettuce and carrot. The method was based on a direct competitive immunoassay using europium-labelled anti-carbofuran monoclonal antibody and carbofuran-ovalbumin as coated antigen. The sensitivity, estimated as the I50 value, was 34.54 ng\\/mL, with a detection limit (I10)

Wenjun Gui; Maojun Jin; Lifeng Sun; Yirong Guo; Guonian Zhu

2009-01-01

102

Combining precision spin-probe partitioning with time-resolved fluorescence quenching to study micelles  

Microsoft Academic Search

Micelles of lysomyristoylphosphatidylcholine (LMPC) and mixed micelles of LMPC with anionic detergent sodium dodecyl sulfate (SDS) have been characterized by spin-probe-partitioning electron paramagnetic resonance (SPPEPR) and time-resolved fluorescence quenching (TRFQ) experiments. SPPEPR is a novel new method to study structure and dynamics in lipid assemblies successfully applied here for the first time to micelles. Several improvements to the computer program

Miroslav Peric; Marilene Alves; Barney L. Bales

2006-01-01

103

Time-resolvable fluorescent conjugates for the detection of pathogens in environmental samples containing autofluorescent material  

NASA Astrophysics Data System (ADS)

Water is routinely monitored for environmental pathogens such a Cryptosporidium and Giardia using immunofluorescence microscopy (IFM). Autofluorescence can greatly diminish an operators capacity to resolve labeled pathogens from non-specific background. Naturally fluorescing components (autofluorophores) encountered in biological samples typically have fluorescent lifetimes (?) of less than 100 nanoseconds and their emissions may be excluded through use of time-resolved fluorescence microscopy (TRFM). TRFM relies on the large differences in ? between autofluorescent molecules and long-lived lanthanide chelates. In TRFM, targets labeled with a time-resolvable fluorescent immunoconjugate are excited by an intense (UV) light pulse. A short delay is imposed to permit the decay of autofluorescence before capture of luminescence from the excited chelate using an image intensified CCD camera. In our experience, autofluorescence can be reduced to insignificant levels with a consequent 30-fold increase in target visibility using TRFM techniques. We report conjugation of a novel europium chelate to a monoclonal antibody specific for Giardia lamblia and use of the immunoconjugate for TRFM studies. Initial attempts to conjugate the same chelate to a monoclonal antibody directed against Cryptosporidium parvum led to poorly fluorescent constructs that were prone to denature and precipitate. We successfully conjugated BHHCT to anti-mouse polyvalent immunoglobulin and used this construct to overcome the difficulties in direct labeling of the anti-Cryptosporidium antibody. Both Giardia and Cryptosporidium were labeled using the anti-mouse protocol with a subsequent 20-fold and 6.6-fold suppression of autofluorescence respectively. A rapid protocol for conjugating and purifying the immunoconjugate was found and methods of quantifying the fluorescence to protein ratio determined. Performance of our TRFM was dependent on the quality and brightness of the immunoconjugate and optimization of the conjugation process is necessary to reap the full benefit of time-resolved techniques.

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

2003-07-01

104

A new europium ?-diketone chelate for ultrasensitive time-resolved fluorescence immunoassays  

Microsoft Academic Search

4,4?-Bis(1?,1?,1?-trifluoro-2?,4?-butanedione-6?-yl)-chlorosulfo-o-terphenyl (BTBCT) was synthesized by modifying the structure of the reported BHHCT. In comparison with the original BHHCT, the detection sensitivity of BTBCT-Eu chelate in aqueous solution was improved ?8 times by time-resolved fluorescence measurement. To construct sensitive TRFIAs with the use of BTBCT-Eu chelate as the fluorescent label, streptavidin–BSA conjugate was prepared by the maleimide–thiol method and labeled by

Feng-Bo Wu; Chao Zhang

2002-01-01

105

Molecular diffusivity measurement through an alumina membrane using time-resolved fluorescence imaging  

NASA Astrophysics Data System (ADS)

We present a simple fluorescence imaging method for measuring the time-resolved concentration of a fluorescent molecule diffusing through an anodic alumina membrane with a pore diameter of 20 nm. From the concentration breakthrough curve, the molecular diffusivity of the fluorophore was extracted. The experimentally determined diffusivity was three orders of magnitude lower than reported bulk values. Due to the relative simplicity and ease of use, this method can be applied to provide fundamental information for biomolecular separations applications. One feature of this method is the high sensitivity at intercellular volumes broadening its application to drug delivery and controlled cell growth.

Kennard, Raymond; Desisto, William J.; Mason, Michael D.

2010-11-01

106

Initial Processes 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) and selected derivatives substituted in para-position of the anilino group has been investigated by femtosecond time-resolved photoelectron spectroscopy (TRPES) and time-dependent density functional theory (TDDFT). The planarity of the molecule was found to be a key parameter to describe ESIPT.

Sekikawa, Taro; Schalk, Oliver; Wu, Guorong; Boguslavskiy, Andrey E.; Stolow, Albert

2013-03-01

107

[Study of solid-phase time-resolved fluorescence label immunoassay].  

PubMed

This paper describes optimal conditions for HBsAbIgG labeling with a new fluorescence probe, 4,7-bis-chorosulfophenyl-1,10-phenanthroline-2,9-dicarboxylic acid (BCPDA) for the solid phase time-resolved fluorimmunoassay (TRFIA). The result of experiment under states clearly that BCPDA may react with protein under relative mild condition. The relative bioactivity of reacted protein was more than 80%. The labeling molar ratio of BCPDA for HBsAbIgG was 45-70. The recovery was higher than 80%. Protein-BCPDA-Eu3+ complex is stable. It can emit very high fluorescence intensity with very long fluorescence life times. The fluorescence of Protein-BCPDA-Eu3+ complex has a very large stokes shift (270 nm). The emission band at 611.2 nm is very narrow. The research provides the base for developing non-isotopic immunoassay technique and clinical medical diagnosis. PMID:15828337

Pan, Li-hua; Zhou, Si-hong; Sun, Wen-wei; Xie, Wen-bing; Zhao, Chao

2004-12-01

108

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

2012-10-22

109

Photophysical and Photochemical Properties of 4-Thiouracil: Time-Resolved IR Spectroscopy and DFT Studies.  

PubMed

Intensified research interests are posed with the thionucleobase 4-thiouracil (4-TU), due to its important biological function as site-specific photoprobe to detect RNA structures and nucleic acid-nucleic acid contacts. By means of time-resolved IR spectroscopy and density functional theory (DFT) studies, we have examined the unique photophysical and photochemical properties of 4-TU. It is shown that 4-TU absorbs UVA light and results in the triplet formation with a high quantum yield (0.9). Under N2-saturated anaerobic conditions, the reactive triplet undergoes mainly cross-linking, leading to the (5-4)/(6-4) pyrimidine-pyrimidone product. In the presence of O2 under aerobic conditions, the triplet 4-TU acts as an energy donor to produce singlet oxygen (1)O2 by triplet-triplet energy transfer. The highly reactive oxygen species (1)O2 then reacts readily with 4-TU, leading to the products of uracil (U) with a yield of 0.2 and uracil-6-sulfonate (U(SO3)) that is fluorescent at ?390 nm. The product formation pathways and product distribution are well rationalized by the joint B3LYP/6-311+G(d,p) calculations. From dynamics and mechanistic point of views, these results enable a further understanding for 4-TU acting as reactive precursors for photochemical reactions relevant to (1)O2, which has profound implications for photo cross-linking, DNA photodamage, as well as photodynamic therapy studies. PMID:24820207

Zou, Xiaoran; Dai, Xiaojuan; Liu, Kunhui; Zhao, Hongmei; Song, Di; Su, Hongmei

2014-06-01

110

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

111

Time-resolved tryptophan fluorescence in photosynthetic reaction centers from Rhodobacter sphaeroides  

NASA Technical Reports Server (NTRS)

Tryptophan fluorescence of reaction centers isolated from Rhodobacter sphaeroides, both stationary and time-resolved, was studied. Fluorescence kinetics were found to fit best a sum of four discrete exponential components. Half of the initial amplitude was due to a component with a lifetime of congruent to 60 ps, belonging to Trp residues, capable of efficient transfer of excitation energy to bacteriochlorophyll molecules of the reaction center. The three other components seem to be emitted by Trp ground-state conformers, unable to participate in such a transfer. Under the influence of intense actinic light, photooxidizing the reaction centers, the yield of stationary fluorescence diminished by congruent to 1.5 times, while the number of the kinetic components and their life times remained practically unchanged. Possible implications of the observed effects for the primary photosynthesis events are considered.

Godik, V. I.; Blankenship, R. E.; Causgrove, T. P.; Woodbury, N.

1993-01-01

112

Diffuse optical fluorescence tomography using time-resolved data acquired in transmission  

NASA Astrophysics Data System (ADS)

We present an algorithm using data acquired with a time-resolved system with the goal of reconstructing sources of fluorescence emanating from the deep interior of highly scattering biological tissues. A novelty in our tomography algorithm is the integration of a light transport model adapted to rodent geometries. For small volumes, our analysis suggest that neglecting the index of refraction mismatch between diffusive and non-diffusive regions, as well as the curved nature of the boundary, can have a profound impact on fluorescent images and spectroscopic applications relying on diffusion curve fitting. Moreover, we introduce a new least-squares solver with bound constraints adapted for optical problems where a physical non-negative constraint can be imposed. Finally, we find that maximizing the time-related information content of the data in the reconstruction process significantly enhances the quality of fluorescence images. Preliminary noise propagation and detector placement optimization analysis are also presented.

Leblond, Frederic; Fortier, Simon; Friedlander, Michael P.

2007-03-01

113

Steady-state and time-resolved fluorescence spectra for detection of colonic cancer  

NASA Astrophysics Data System (ADS)

The steady-state and time-resolved autofluorescence spectroscopic differences between normal and carcinomatous colonic tissues and the optimal excitation wavelengths were studied. The fluorescence excitation wavelengths varying form 260 to 540 nm were used to induce tissue autofluorescence, and the corresponding emission spectra were measured in the range from 280 to 800 nm. These spectra then can be assembled into an excitation -emission matrix (EEM). Significant changes in fluorescence intensity of excitation-emission matrices were observed between normal and tumor colonic tissues. Low NAD(P)H and FAD, and high protoporphyrin IX fluorescence characterize high-grade malignant tissue when compared with normal colonic tissue, and the most marked difference being at the excitation wavelengths of 340, 380, 460 and 540 nm. Furthermore, the average lifetimes for the normal and carcinomatous colonic tissues were about 4.12 and 18.8 ns, respectively. The promising applications of laser-induced autofluorescence for colonic tissue diagnosis are indicated.

Li, Buhong; Xie, Shusen; Zhang, Zhenxi

2005-07-01

114

Advanced Time-Resolved Fluorescence Microscopy Techniques for the Investigation of Peptide Self-Assembly  

NASA Astrophysics Data System (ADS)

The ubiquitous cross beta sheet peptide motif is implicated in numerous neurodegenerative diseases while at the same time offers remarkable potential for constructing isomorphic high-performance bionanomaterials. Despite an emerging understanding of the complex folding landscape of cross beta structures in determining disease etiology and final structure, we lack knowledge of the critical initial stages of nucleation and growth. In this dissertation, I advance our understanding of these key stages in the cross-beta nucleation and growth pathways using cutting-edge microscopy techniques. In addition, I present a new combined time-resolved fluorescence analysis technique with the potential to advance our current understanding of subtle molecular level interactions that play a pivotal role in peptide self-assembly. Using the central nucleating core of Alzheimer's Amyloid-beta protein, Abeta(16 22), as a model system, utilizing electron, time-resolved, and non-linear microscopy, I capture the initial and transient nucleation stages of peptide assembly into the cross beta motif. In addition, I have characterized the nucleation pathway, from monomer to paracrystalline nanotubes in terms of morphology and fluorescence lifetime, corroborating the predicted desolvation process that occurs prior to cross-beta nucleation. Concurrently, I have identified unique heterogeneous cross beta domains contained within individual nanotube structures, which have potential bionanomaterials applications. Finally, I describe a combined fluorescence theory and analysis technique that dramatically increases the sensitivity of current time-resolved techniques. Together these studies demonstrate the potential for advanced microscopy techniques in the identification and characterization of the cross-beta folding pathway, which will further our understanding of both amyloidogenesis and bionanomaterials.

Anthony, Neil R.

115

A new strategy based on aptasensor to time-resolved fluorescence assay for adenosine deaminase activity.  

PubMed

Quantitative protein bioanalysis in complex biological fluids presents considerable challenges in biological studies and medical diagnosis. The major obstacles are the background signals from the biological fluids and sensors themselves. Because the europium ion (Eu (III)) has the much longer fluorescence lifetime (1 ms) than that of the background (5 ns), time-resolved method can be widely used to eliminate the biological background. So, we report here an aptamer-based sensor (aptasensor) for time-resolved fluorescence assay of adenosine deaminase (ADA). This aptasensor employs two oligonucleotides labeled with DIG and biotin, respectively. The DNA1 (an oligonucleotide modified with biotin) is immobilized at a streptavidin-modified plate surface via the biotin-avidin bridge, and the DIG which is modified on the DNA2 serves as an affinity tag for the Eu(3+) labeled anti-DIG (Eu-anti-DIG) binding. If the adenosine is binding with DNA1, it will make the DNA1 in the closed state with a close-packed tight structure, which forbids the DNA2 approaching. And if the ADA is added into the mixture, the DNA1 unbends, because of the adenosine is transformed to inosine catalyzed by the ADA. Then DNA2 could hybridize with DNA1. Accordingly, the DIG finds Eu-anti-DIG and the Eu-anti-DIG will give a remarkable fluorescent signal. The detection limit of the aptasensor can be lowered to 2 UL(-1), which can meet the clinical requirement of ADA cutoff value (4 UL(-1)). Moreover, we were able to detect ADA in human serum quantitatively. Combined with time-resolved based measurements and aptasensor, this strategy holds great potential in protein analysis. PMID:22944024

Zhang, Kai; Xie, Minhao; Zhou, Bin; Hua, Yurong; Yan, Zihe; Liu, Haiyan; Guo, Li-Ning; Wu, Bing; Huang, Biao

2013-03-15

116

Implementation of intensity-modulated laser diodes in time-resolved, pump-probe fluorescence microscopy.  

PubMed

We present the implementation of intensity-modulated laser diodes for applications in frequency-domain pump-probe fluorescence microscopy. Our technique, which is based on the stimulated-emission approach, uses two sinusoidally modulated laser diodes. One laser (635 nm) excites the chromophores under study, and the other laser (680 nm) is responsible for inducing stimulated emission from excited-state molecules. Both light sources are modulated in the 80-MHz range but with an offset of 5 kHz between them. The result of the interaction of the pump and the probe beams is that a cross-correlation fluorescence signal at 5 kHz is generated primarily at the focal volume. Microscope imaging at the cross-correlation signal results in images with high contrast, and time-resolved high-frequency information can be acquired without high-speed detection. A detailed experimental arrangement of our methodology is presented along with images acquired from a 4.0-mum-diameter fluorescent sphere and TOTO-3-labeled mouse STO cells. (TOTO-3 is a nucleic acid stain.) Our results demonstrate the feasibility of using sinusoidally modulated laser diodes for pump-probe imaging, creating the exciting possibility of high-contrast time-resolved imaging with low-cost laser-diode systems. PMID:18357095

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

2001-03-01

117

A CTRW-based model of time-resolved fluorescence lifetime imaging in a turbid medium.  

PubMed

We develop an analytic model of time-resolved fluorescent imaging of photons migrating through a semi-infinite turbid medium bounded by an infinite plane in the presence of a single stationary point fluorophore embedded in the medium. In contrast to earlier models of fluorescent imaging in which photon motion is assumed to be some form of continuous diffusion process, the present analysis is based on a continuous-time random walk (CTRW) on a simple cubic lattice, the object being to estimate the position and lifetime of the fluorophore. Such information can provide information related to local variations in pH and temperature with potential medical significance. Aspects of the theory were tested using time-resolved measurements of the fluorescence from small inclusions inside tissue-like phantoms. The experimental results were found to be in good agreement with theoretical predictions provided that the fluorophore was not located too close to the planar boundary, a common problem in many diffusive systems. PMID:21057657

Chernomordik, Victor; Gandjbakhche, Amir H; Hassan, Moinuddin; Pajevic, Sinisa; Weiss, George H

2010-12-01

118

A CTRW-based model of time-resolved fluorescence lifetime imaging in a turbid medium  

NASA Astrophysics Data System (ADS)

We develop an analytic model of time-resolved fluorescent imaging of photons migrating through a semi-infinite turbid medium bounded by an infinite plane in the presence of a single stationary point fluorophore embedded in the medium. In contrast to earlier models of fluorescent imaging in which photon motion is assumed to be some form of continuous diffusion process, the present analysis is based on a continuous-time random walk (CTRW) on a simple cubic lattice, the objective being to estimate the position and lifetime of the fluorophore. This can provide information related to local variations in pH and temperature with potential medical significance. Aspects of the theory were tested using time-resolved measurements of the fluorescence from small inclusions inside tissue-like phantoms. The experimental results were found to be in good agreement with theoretical predictions provided that the fluorophore was not located too close to the planar boundary, a common problem in many diffusive systems.

Chernomordik, Victor; Gandjbakhche, Amir H.; Hassan, Moinuddin; Pajevic, Sinisa; Weiss, George H.

2010-12-01

119

Time-resolved imaging of fluorescent inclusions in optically turbid medium — phantom study  

NASA Astrophysics Data System (ADS)

We present results of application of a time-resolved optical system for imaging of fluorescence excited in an inclusion containing indocyanine green (ICG), and located in optically turbid medium. The developed imaging system enabled simultaneous acquisition of fluorescence and diffusive reflectance. Eight independent time-resolved measurement channels based on time-correlated single photon counting technique were applied. In four of these channels, used for the fluorescence detection, sets of filters were applied in order to block the excitation light. Fast optomechanical switches allowed us to illuminate sequentially nine different spots on the surface of the studied object and finally 4×4 pixels maps at excitation and emission wavelengths were obtained. A liquid phantom used in this study consists of the fish tank filed with a solution ofmilk and water with black ink added to obtain optical properties in the range of the optical properties typical for the living tissue. A gel ball of a diameter of 5 mm with precisely controlled concentration of ICG was immersed in the liquid. The measurements were performed for inclusion located at different depths and for various ICG concentrations in the gel ball and in the surrounding liquid. The recorded distributions of times of arrival (DTA) of fluorescence photons and times of flight (DTOF) of diffusely reflected photons were analyzed by calculation of their statistical moments. We observed specific changes in moments of the measured DTAs as a function of depth of immersion of the fluorescent inclusion in the medium. We noted also that the changes of moments depend significantly on concentration of the dye in the fluorescence inclusion as well as in the surrounding liquid.

Kacprzak, M.; Liebert, A.; Sawosz, P.; ?o?ek, N.; Milej, D.; Maniewski, R.

2010-03-01

120

A time-resolved 128x128 SPAD camera for laser Raman spectroscopy  

NASA Astrophysics Data System (ADS)

In this paper we present a time-gated single-photon avalanche diode (SPAD) array, the first of its kind to be integrated with a newly developed time-resolved laser Raman spectrometer. Time-resolved Raman spectra from various highly fluorescent minerals were successfully observed using our SPAD array; these spectra were obscured by an overwhelming fluorescence background when measured using a traditional continuous wave green laser. The system has photon detection efficiency (PDE) of 5 % at 5 V excess bias with on-chip microlenses. The dark count rate (DCR) of this SPAD is 1.8 kHz at 5 V excess bias. However, thanks to the nanosecond scale time-gating, noise rate per frame is effectively reduced to ~10-3 counts at 40 kHz laser repetition rate.

Maruyama, Yuki; Blacksberg, Jordana; Charbon, Edoardo

2012-05-01

121

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

122

Probing local secondary structure by fluorescence: time-resolved and circular dichroism studies of highly purified neurotoxins.  

PubMed Central

The relationship between beta-sheet secondary structure and intrinsic tryptophan fluorescence parameters of erabutoxin b, alpha-cobratoxin, and alpha-bungarotoxin were examined. Nuclear magnetic resonance and x-ray crystallography have shown that these neurotoxins have comparable beta-sheet, beta-turn, and random coil secondary structures. Each toxin contains a single tryptophan (Trp) residue within its beta-sheet. The time-resolved fluorescence properties of native erabutoxin b and alpha-cobratoxin are best described by triple exponential decay kinetics, whereas native alpha-bungarotoxin exhibits more than four lifetimes. The disulphide bonds of each toxin were reduced to facilitate carboxymethylation and amidocarboxymethylation. The two different toxin derivatives of all three neurotoxins displayed triple exponential decay kinetics and were completely denatured as evidenced by circular dichroism (random coil). The concentration (c) values of the three fluorescence decay times (time-resolved fluorescence spectroscopy (TRFS)) were dramatically different from those of the native toxins. Each neurotoxin, treated with different concentrations of guanidinium hydrochloride (GuHCl), was studied both by circular dichroism and TRFS. Disappearance of the beta-sheet secondary structural features with increasing concentrations of GuHCl was accompanied by a shift in the relative contribution (c value) of each fluorescence decay time (TRFS). It was found that certain disulphide residues confer added stability to the beta-sheet secondary structure of these neurotoxins and that the center of the beta-sheet is last to unfold. These titrations show that Trp can be used as a very localized probe of secondary structure. Images FIGURE 1

Dahms, T E; Szabo, A G

1995-01-01

123

Development of Time Resolved Fluorescence Resonance Energy Transfer-based Assay for FXR Antagonist Discovery  

PubMed Central

FXR (farnesoid X receptor, NRIH4), a nuclear receptor, plays a major role in the control of cholesterol metabolism. FXR ligands have been investigated in preclinical studies for targeted therapy against metabolic diseases, but have shown limitations. Therefore, there is a need for new agonist or antagonist ligands of FXR, both for potential clinical applications, as well as to further elucidate its biological functions. Here we describe the use of the X-ray crystal structure of FXR complexed with the potent small molecule agonist GW4064 to design and synthesize a novel fluorescent, high-affinity probe (DY246) for time resolved fluorescence resonance energy transfer (TR-FRET) assays. We then used the TR-FRET assay for high throughput screening of a library of over 5,000 bioactive compounds. From this library, we identified 13 compounds that act as putative FXR transcriptional antagonists.

Yu, Donna D.; Lin, Wenwei; Chen, Taosheng; Forman, Barry M.

2013-01-01

124

Polar solvation dynamics of coumarin 153 by ultrafast time-resolved fluorescence  

NASA Astrophysics Data System (ADS)

Polar solvation dynamics of coumarin 153 in acetonitrile, methanol, and butanol are investigated by dynamic Stokes shift function, S(t). In small protic solvents, it is known that an initial ultrafast component below 50 fs constitutes more than half of the total solvation process. We use fluorescence up-conversion technique via two-photon absorption process, which can provide 40 fs time resolution for the whole emission wavelength range. Moreover, time-resolved fluorescence spectra are recorded directly without the spectral reconstruction. We observe a temporal oscillation in frequency of whole emission spectrum in the solvation curve. In the obtained S(t), initial solvation time scale is 120 fs, invariant to solvents used in this experiment, although its amplitude varies in different solvents.

Eom, Intae; Joo, Taiha

2009-12-01

125

Time-resolved high-harmonic spectroscopy of nonadiabatic dynamics in NO2  

NASA Astrophysics Data System (ADS)

Time-resolved high-harmonic spectroscopy is an emerging approach to measuring coupled electronic and nuclear dynamics in photochemical reactions. A general conceptual and theoretical model for the technique is derived from first principles and applied to study the sensitivity of the technique to nonadiabatic dynamics. By comparing the model with detailed experimental data on photoexcited NO2 molecules, we find that time-resolved high-harmonic spectroscopy is primarily sensitive to electronic population dynamics. The coordinate dependence of the vertical ionization potential and photorecombination matrix elements contribute also, but much less significantly, to the observed dynamics because of the rapid spreading of the wave packet in the excited state. We discuss the extension of the method to larger polyatomic molecules in light of this insight.

Kraus, P. M.; Arasaki, Y.; Bertrand, J. B.; Patchkovskii, S.; Corkum, P. B.; Villeneuve, D. M.; Takatsuka, K.; Wörner, H. J.

2012-04-01

126

Near-infrared time-resolved fluorescence lifetime determinations in poly(methylmethacrylate) microchip electrophoresis devices.  

PubMed

High aspect-ratio microstructures were hot-embossed in polymer substrates with a molding tool fabricated using lithography/electroplating/forming (LIGA). The resulting devices were used for the electrophoretic separation of oligonucleotides labeled with near-infrared (near-IR) dyes. Near-IR time-resolved fluorescence was used as an identification method for the labeling dyes. The detection apparatus consisted of a pulsed laser diode operating at 680 nm, a single-photon avalanche diode, an integrated microscope, and a PC-board incorporating time-correlated single photon counting electronics. Investigation of the optical quality and amount of autofluorescence generated from different polymer substrates was carried out in the near-IR region for determining compatibility with time-resolved fluorescence. Our results revealed that of several poly(methylmethacrylate)(PMMA) substrates, brand Plexiglas offered minimal replication errors in the embossed features using appropriate embossing conditions with low background fluorescence contributions to the observed decay. Near-IR dye-labeled oligonucleotides were separated to determine the applicability of fluorescence lifetime discrimination between Cy5.5 (tauf = 930 ps) and IRD700 (tauf = 851 ps) labeling dyes during the microchip separation. These dyes were used to label T-fragments (thymine) of an M13mp18 ssDNA template. The DNA ladders were electrophoresed at 130 V/cm in a 4% linear polyacrylamide gel (LPA) gel matrix in a 9.5 cm long serpentine channel heated to 50 degrees C. The electropherogram revealed that the lifetimes could be accurately read well beyond 450 bases, although single-base pair resolution in the electropherogram was difficult to achieve due to potential solute-wall interactions in the polymer microdevice or the electroosmotic flow (EOF) properties of the device. The relative standard deviations secured for individual bands in the electropherogram were similar to those obtained using capillary gel electrophoresis, in spite of the lower load volume. PMID:15565677

Llopis, Shawn D; Stryjewski, Wieslaw; Soper, Steven A

2004-11-01

127

Properties of Liquid Silicon Observed by Time-Resolved X-Ray Absorption Spectroscopy  

NASA Astrophysics Data System (ADS)

Time-resolved x-ray spectroscopy at the Si L edges is used to probe the electronic structure of an amorphous Si foil as it melts following absorption of an ultrafast laser pulse. Picosecond temporal resolution allows observation of the transient liquid phase before vaporization and before the liquid breaks up into droplets. The melting causes changes in the spectrum that match predictions of molecular dynamics and ab initio x-ray absorption codes.

Johnson, S. L.; Heimann, P. A.; Lindenberg, A. M.; Jeschke, H. O.; Garcia, M. E.; Chang, Z.; Lee, R. W.; Rehr, J. J.; Falcone, R. W.

2003-10-01

128

Time resolved spectroscopy of the dwarf nova VY Aquarii in superoutburst and quiescence  

Microsoft Academic Search

Time resolved spectroscopy is presented of the SU UMa type dwarf nova VY Aqr in superoutburst and quiescence. From the radial velocity variations found in outburst I derive on the basis of the value for the superhump period an orbital period of 0.06348 (12) days (or possibly 0.06787(13) days). The radial-velocity amplitude is 29(5) km\\/s. In the outburst spectra taken

T. Augusteijn

1994-01-01

129

Developments of widely tunable light sources for picosecond time-resolved resonance Raman spectroscopy  

Microsoft Academic Search

Two systems of widely tunable light sources for picosecond time-resolved resonance Raman (ps-TR3) spectroscopy have been constructed using a 1 kHz ps-Ti:sapphire laser\\/regenerative amplifier system. Performance of the systems was examined in terms of pulse duration, spectral width, pulse energy, and shot-to-shot stability. One system, consisting of white light continuum seeder and ?-barium borate optical parametric amplifier, demonstrated tunability in

Yuki Uesugi; Yasuhisa Mizutani; Teizo Kitagawa

1997-01-01

130

Superconducting gap excitations, acoustic and optical phonons probed with femtosecond time-resolved and Raman spectroscopy  

Microsoft Academic Search

Spontaneous Raman scattering and femtosecond time-resolved pump-probe spectroscopy are used to study and characterize material properties in superconductors, bulk semiconductors and semiconducting quantum dots. Superconducting gap oscillations are observed for the first time in MgB 2 (Tc = 39 K) and 2H-NbSe2 ( Tc = 7 K). In MgB2, multiple superconducting gap oscillations are observed at 24 cm-1, 103 cm

Cynthia Aku-Leh

2005-01-01

131

Steady-state and time-resolved fluorescence spectroscopic characterization of urine of healthy subjects and cervical cancer patients.  

PubMed

Steady-state and time-resolved fluorescence spectroscopy were employed in the discrimination of cervical cancer patients from healthy subjects using urine samples. Fluorescence emission at 390 and 440 nm was considered to monitor the fluorescence of indoxyl sulfate and neopterin. Significant spectral differences were observed between healthy and cancer subjects. Different ratio parameters were calculated from the spectral intensity at 280- and 350-nm excitation and were subjected to stepwise linear discriminant analysis. In total, 84.0% of samples were correctly classified at 280 nm and 96.4% were correctly classified at 350 nm. The fluorescence decay kinetics of urine samples at 390-nm emission was best described by bi- exponential fits, whereas the decay characteristics at 440 nm of urine samples was best explained by bi-exponential fits and, in some cases, by tri-exponential fits. However, the decay kinetics of both indoxyl sulfate and neopterin standards was well described by bi-exponential decays. Based on the fluorescence emission characteristics and statistical analysis, the fluorophores indoxyl sulfate, neopterin, and riboflavin may be considered as potential biomarkers for cervical cancer diagnosis. PMID:24647974

Rajasekaran, Ramu; Aruna, Prakasa Rao; Koteeswaran, Dornadula; Bharanidharan, Ganesan; Baludavid, Munusamy; Ganesan, Singaravelu

2014-03-01

132

Protein self-association in crowded protein solutions: a time-resolved fluorescence polarization study.  

PubMed

The self-association equilibrium of a tracer protein, apomyoglobin (apoMb), in highly concentrated crowded solutions of ribonuclease A (RNase A) and human serum albumin (HSA), has been studied as a model system of protein interactions that occur in crowded macromolecular environments. The rotational diffusion of the tracer protein labeled with two different fluorescent dyes, 8-anilinonaphthalene-1-sulfonate and fluorescein isothiocyanate, was successfully recorded as a function of the two crowder concentrations in the 50-200 mg/mL range, using picosecond-resolved fluorescence anisotropy methods. It was found that apoMb molecules self-associate at high RNase A concentration to yield a flexible dimer. The apparent dimerization constant, which increases with RNase A concentration, could also be estimated from the fractional contribution of monomeric and dimeric species to the total fluorescence anisotropy of the samples. In contrast, an equivalent mass concentration of HSA does not result in tracer dimerization. This different effect of RNase A and HSA is much larger than that predicted from simple models based only on the free volume available to apoMb, indicating that additional, nonspecific interactions between tracer and crowder should come into play. The time-resolved fluorescence polarization methods described here are expected to be of general applicability to the detection and quantification of crowding effects in a variety of macromolecules of biological relevance. PMID:15459331

Zorrilla, Silvia; Rivas, Germán; Acuña, A Ulises; Lillo, M Pilar

2004-11-01

133

Capturing molecular structural dynamics by 100 ps time-resolved X-ray absorption spectroscopy  

PubMed Central

An experimental set-up for time-resolved X-ray absorption spectroscopy with 100?ps time resolution at beamline NW14A at the Photon Factory Advanced Ring is presented. The X-ray positional active feedback to crystals in a monochromator combined with a figure-of-merit scan of the laser beam position has been utilized as an essential tool to stabilize the spatial overlap of the X-ray and laser beams at the sample position. As a typical example, a time-resolved XAFS measurement of a photo-induced spin crossover reaction of the tris(1,10-phenanthrorine)iron(II) complex in water is presented.

Sato, Tokushi; Nozawa, Shunsuke; Ichiyanagi, Kohei; Tomita, Ayana; Chollet, Matthieu; Ichikawa, Hirohiko; Fujii, Hiroshi; Adachi, Shin-ichi; Koshihara, Shin-ya

2009-01-01

134

Noninvasive assessment of breast cancer risk using time-resolved diffuse optical spectroscopy  

NASA Astrophysics Data System (ADS)

Breast density is a recognized strong and independent risk factor for breast cancer. We propose the use of time-resolved transmittance spectroscopy to estimate breast tissue density and potentially provide even more direct information on breast cancer risk. Time-resolved optical mammography at seven wavelengths (635 to 1060 nm) is performed on 49 subjects. Average information on breast tissue of each subject is obtained on oxy- and deoxyhemoglobin, water, lipids, and collagen content, as well as scattering amplitude and power. All parameters, except for blood volume and oxygenation, correlate with mammographic breast density, even if not to the same extent. A synthetic optical index proves to be quite effective in separating different breast density categories. Finally, the estimate of collagen content as a more direct means for the assessment of breast cancer risk is discussed.

Taroni, Paola; Pifferi, Antonio; Quarto, Giovanna; Spinelli, Lorenzo; Torricelli, Alessandro; Abbate, Francesca; Villa, Anna; Balestreri, Nicola; Menna, Simona; Cassano, Enrico; Cubeddu, Rinaldo

2010-11-01

135

Time-resolved high-harmonic spectroscopy of valence electron dynamics  

NASA Astrophysics Data System (ADS)

Time-resolved high-harmonic spectroscopy (TRHHS) is an emerging technique for probing valence electron dynamics in molecules undergoing photochemical reactions. A general description of the technique including experimental and theoretical aspects is given. The relation of TRHHS to other time-resolved techniques is discussed, with particular emphasis on the specificities of TRHHS. Coherence endows TRHHS with two of its original properties: the interference of excited and unexcited molecules makes it highly sensitive to small excitation fractions and to the phase of photorecombination matrix elements. The technique is also sensitive to the variation of the vertical ionization potential, providing additional insights into the photochemical dynamics. The principles of the technique are discussed in relation to recent results on the photochemistry of Br2 and NO2, revealing its sensitivity to different aspects of the dynamics, most notably electronic dynamics occurring in non-adiabatic dynamics.

Kraus, Peter M.; Wörner, Hans Jakob

2013-03-01

136

Capturing molecular structural dynamics by 100 ps time-resolved X-ray absorption spectroscopy.  

PubMed

An experimental set-up for time-resolved X-ray absorption spectroscopy with 100 ps time resolution at beamline NW14A at the Photon Factory Advanced Ring is presented. The X-ray positional active feedback to crystals in a monochromator combined with a figure-of-merit scan of the laser beam position has been utilized as an essential tool to stabilize the spatial overlap of the X-ray and laser beams at the sample position. As a typical example, a time-resolved XAFS measurement of a photo-induced spin crossover reaction of the tris(1,10-phenanthrorine)iron(II) complex in water is presented. PMID:19096182

Sato, Tokushi; Nozawa, Shunsuke; Ichiyanagi, Kohei; Tomita, Ayana; Chollet, Matthieu; Ichikawa, Hirohiko; Fujii, Hiroshi; Adachi, Shin Ichi; Koshihara, Shin Ya

2009-01-01

137

Noninvasive assessment of breast cancer risk using time-resolved diffuse optical spectroscopy.  

PubMed

Breast density is a recognized strong and independent risk factor for breast cancer. We propose the use of time-resolved transmittance spectroscopy to estimate breast tissue density and potentially provide even more direct information on breast cancer risk. Time-resolved optical mammography at seven wavelengths (635 to 1060 nm) is performed on 49 subjects. Average information on breast tissue of each subject is obtained on oxy- and deoxyhemoglobin, water, lipids, and collagen content, as well as scattering amplitude and power. All parameters, except for blood volume and oxygenation, correlate with mammographic breast density, even if not to the same extent. A synthetic optical index proves to be quite effective in separating different breast density categories. Finally, the estimate of collagen content as a more direct means for the assessment of breast cancer risk is discussed. PMID:21198142

Taroni, Paola; Pifferi, Antonio; Quarto, Giovanna; Spinelli, Lorenzo; Torricelli, Alessandro; Abbate, Francesca; Villa, Anna; Balestreri, Nicola; Menna, Simona; Cassano, Enrico; Cubeddu, Rinaldo

2010-01-01

138

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

139

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

140

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

141

Ultrasensitive detection of microRNA with isothermal amplification and a time-resolved fluorescence sensor.  

PubMed

MicroRNAs (miRNAs) play important roles in a plethora of biological and cellular processes. The levels of miRNAs can be useful biomarkers for cellular events or disease diagnosis, thus the method for sensitive and selective detection of miRNAs is imperative to miRNA discovery, study, and clinical diagnosis. Here we develop a novel method to quantify miRNA expression levels as low as attomolar sensitivity by two-stage exponential amplification reaction (EXPAR) and a time-resolved fluorescence sensor in real samples. The method reveals superior sensitivity with a detection limit of miRNA of 0.1 aM under pure conditions. The method also shows the high selectivity for discriminating differences between miRNA family members, thus providing a promising alternative to standard approaches for quantitative detection of miRNA. PMID:24561522

Wang, Ke; Zhang, Kai; Lv, Zhuwu; Zhu, Xue; Zhu, Ling; Zhou, Fanfan

2014-07-15

142

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

143

Cerenkov radiation as a UV and visible light source for time-resolved fluorescence.  

PubMed

We demonstrate the first use of Cerenkov radiation for the measurement of fluorescence lifetimes. Relativistic beta particles from the nuclear decay of 90 Sr and 90Y generate a spectral continuum in a quartz waveguide. Light flashes of < 100-ps duration are delivered simultaneously to a sample cell and a reference photomultiplier. A simple, digitally based cross-correlation signal processor allows extraction of the sample fluorescence decay kinetics without distortions which can result from the random excitation pulse sequence. We characterize both the pulse duration and the pulse intensity of the light that is emitted from the waveguide. Although the excitation intensity is very weak, we demonstrate that accurate lifetime measurements are possible with only a few hundred seconds of integration time. Tests on a variety of compounds illustrate the utility of the light source throughout the UV and blue regions of the spectrum. We also discuss future design improvements and potential applications of this new approach to time-resolved fluorescence. PMID:9726168

Burden, D L; Hieftje, G M

1998-08-15

144

Non-contact characterization of bacteria by time-resolved fluorescence  

NASA Astrophysics Data System (ADS)

Accurate real-time methods for the detection of pathogenic microorganisms in the agri-food industry would represent an improvement over standard methods of analysis. We are currently developing a non-contact, scanning optical system for the detection of bacteria on meat surfaces based on fluorescence lifetime and intensity measurements. The system detects autofluorescent light emitted by the naturally occurring fluorophores in bacteria. Potential expected advantages of this system include accurate and efficient 2D real-time mapping of bacterial contamination of surfaces, and elimination of sample-to-sample cross-contamination. Furthermore, as the technique only requires minimal sample preparation and handling, the chemical properties of the specimen are preserved. This article presents the preliminary results obtained from a time-resolved fluorescence imaging system for the characterization of a non-pathogenic gram-negative bacteria, Pseudomonas fluorescens. Additionally we present a particular application of the system of interest to the agri-food industry, demonstrating its potential as a real-time macroscopic imaging system for mapping bacterial contamination on meat surfaces. Initial results indicate that the combination of fluorescence lifetime and intensity measurements provides a means for characterizing biological media and for detecting microorganisms on surfaces.

Bouchard, Alain; Frechette, Julie; Long, William F.; Vernon, Marcia; Cormier, Jean-Francois; Vallee, Real; Mafu, Akier A.; Lemay, Marie-Josee

2004-07-01

145

Generalized magic angle for time-resolved spectroscopy with laser pulses of arbitrary ellipticity  

NASA Astrophysics Data System (ADS)

We present a general approach for calculating the magic-angle condition for time-resolved spectroscopy of isotropic samples. Allowing for arbitrary static polarizations and propagation directions of each pulse enables us to retrieve not only the known magic-angle conditions for linear and circular polarization, but also analogous conditions for anisotropy-free spectroscopy using elliptically polarized laser pulses. The results are exemplified on transient absorption and transferred to coherent two-dimensional spectroscopy. Furthermore we derive for transient absorption spectroscopy the relation between the measurable anisotropy and the molecular structure, i.e., the angle between the pumped and probed transition dipole moments (TDMs). The impact of multiple spectrally overlapping signals is considered and discussed on the example of a molecule with a two-fold degenerate TDM.

Schott, Sebastian; Steinbacher, Andreas; Buback, Johannes; Nuernberger, Patrick; Brixner, Tobias

2014-06-01

146

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

147

Pump-Probe Fluorescence Microscopy: A New Method for Time-Resolved Imaging with High Spatial and Temporal Resolution  

Microsoft Academic Search

We present a unique time-resolved, fluorescence microscope using the pump-probe technique. In this microscope, two laser sources with different repetition frequencies are focused onto the fluorescent sample. The wavelengths of the lasers are chosen such that one laser excites the sample, and another laser induces stimulated emission from the molecules in the excited states or excite the ground state molecules.

Chen Y. Dong; Peter T. C. So; Enrico Gratton

1996-01-01

148

Serological Responses to Experimental Norwalk Virus Infection Measured Using a Quantitative Duplex Time-Resolved Fluorescence Immunoassay ?  

PubMed Central

A quantitative duplex time-resolved fluorescence assay, dissociation-enhanced lanthanide fluorescent immunoassay (DELFIA), was developed to measure Norwalk virus (NV)-specific IgA and IgG antibodies simultaneously. The duplex assay showed superior performance by detecting seroconversion following experimental NV infection at an earlier time point than a reference total immunoglobulin enzyme-linked immunosorbent assay (ELISA).

Kavanagh, Owen; Estes, Mary K.; Reeck, Amanda; Raju, Ravikiran M.; Opekun, Antone R.; Gilger, Mark A.; Graham, David Y.; Atmar, Robert L.

2011-01-01

149

Photodissociation of thioglycolic acid studied by femtosecond time-resolved transient absorption spectroscopy  

SciTech Connect

Steady-state and time-resolved spectroscopies were employed to study the photodissociation of both the neutral (HS-CH{sub 2}-COOH) and doubly deprotonated ({sup -}S-CH{sub 2}-COO{sup -}) forms of thioglycolic acid (TGA), a common surface-passivating ligand used in the aqueous synthesis and organization of semiconducting nanostructures. Room temperature UV-Vis absorption spectroscopy indicated strong absorption by the S{sub 1} and S{sub 2} excited states at 250 nm and 185 nm, respectively. The spectrum also contained a weaker absorption band that extended to approximately 550 nm, which was assigned to the {pi}{sub CO}{sup *}(leftarrow)n{sub O} transition. Femtosecond time-resolved transient absorption spectroscopy was performed on TGA using 400 nm excitation and a white-light continuum probe to provide the temporally and spectrally resolved data. Both forms of TGA underwent a photoinduced dissociation from the excited state to form an {alpha}-thiol-substituted acyl radical ({alpha}-TAR, S-CH{sub 2}-CO). For the acidic form of TGA, radical formation occurred with an apparent time constant of 60 {+-} 5 fs; subsequent unimolecular decay took 400 {+-} 60 fs. Similar kinetics were observed for the deprotonated form of TGA (70 {+-} 10 fs radical formation; 420 {+-} 40 fs decay). The production of the {alpha}-TAR was corroborated by the observation of its characteristic optical absorption. Time-resolved data indicated that the photoinduced dissociation of TGA via cleavage of the C-OH bond occurred rapidly ({<=}100 fs). The prevalence of TGA in aqueous semiconducting nanoparticles makes its absorption in the visible spectral region and subsequent dissociation key to understanding the behavior of nanoscale systems.

Attar, Andrew R.; Blumling, Daniel E.; Knappenberger, Kenneth L. Jr. [Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306 (United States)

2011-01-14

150

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

151

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

152

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

153

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

154

A new method for the detection of adenosine based on time-resolved fluorescence sensor.  

PubMed

In this work, we report a thrombin binding aptamer complex based time-resolved fluorescence sensor for small molecule detection. The sensor employs two strands (DNA1 and DNA2) of oligonucleotides. This two strands of oligonucleotides contain two aptamer (?-aptamer and ?-aptamer) respectively. DNA1 and DNA2 were labeled with biotin and DIG at the 3'-end, respectively. Binding of the ?-aptamer and ?-aptamer to the thrombin promotes the hybridization between the complementary stem sequences attached to the two oligonucleotide sequences. The hybridization then brings biotin to be hidden in the shield part on DNA1, shielding biotin from being approached by the streptavidin modified on the microplate due to the steric hindrance effect of the shield part of DNA1. Result in the thrombin-aptamer complex cannot be modified on the surface of microplate which further leads to no signal reported. The strategy integrates the distinguishing features of aptamer and fluorescent techniques. As a proof-of-principle, adenosine in serum was detected with a detection limit of 0.5 nM. A nice detection limit and linear relationship were obtained. PMID:23770393

Zhang, Kai; Wang, Ke; Xie, Minhao; Xu, Lan; Zhu, Xue; Pan, Shiyang; Zhang, Qun; Huang, Biao

2013-11-15

155

Time resolved single molecule spectroscopy of semiconductor quantum dot/conjugated organic hybrid nanostructures  

NASA Astrophysics Data System (ADS)

Single molecule studies on CdSe quantum dots functionalized with oligo-phenylene vinylene ligands (CdSe-OPV) provide evidence of strong electronic communication that facilitate charge and energy transport between the OPV ligands and the CdSe quantum dot core. This electronic interaction greatly modify, the photoluminescence properties of both bulk and single CdSe-OPV nanostructure thin film samples. Size-correlated wide-field fluorescence imaging show that blinking suppression in single CdSe-OPV is linked to the degree of OPV coverage (inferred from AFM height scans) on the quantum dot surface. The effect of the complex electronic environment presented by photoexcited OPV ligands on the excited state property of CdSe-OPV is measured with single photon counting and photon-pair correlation spectroscopy techniques. Time-tagged-time-resolved (TTTR) single photon counting measurements from individual CdSe-OPV nanostructures, show excited state lifetimes an order of magnitude shorter relative to conventional ZnS/CdSe quantum dots. Second-order intensity correlation measurements g(2)(tau) from individual CdSe-OPV nanostructures point to a weak multi-excitonic character with a strong wavelength dependent modulation depth. By tuning in and out of the absorption of the OPV ligands we observe changes in modulation depth from g(2) (0) ? 0.2 to 0.05 under 405 and 514 nm excitation respectively. Defocused images and polarization anisotropy measurements also reveal a well-defined linear dipole emission pattern in single CdSe-OPV nanostructures. These results provide new insights into to the mechanism behind the electronic interactions in composite quantum dot/conjugated organic composite systems at the single molecule level. The observed intensity flickering , blinking suppression and associated lifetime/count rate and antibunching behaviour is well explained by a Stark interaction model. Charge transfer from photo-excitation of the OPV ligands to the surface of the CdSe quantum dot core, mixes electron/holes states and lifts the degeneracy in the band edge bright exciton state, which induces a well define linear dipole behaviour in single CdSe-OPV nanostructures. The shift in the electron energies also affects Auger assisted hole trapping rates, suppress access to dark states and reduce the excited state lifetime.

Odoi, Michael Yemoh

156

Quantitative Determination of the Radius of Gyration of Poly(methy1 methacrylate) in the Amorphous Solid State by Time-Resolved Fluorescence Depolarization Measurements of Excitation Transport  

Microsoft Academic Search

Excitation transport among naphthyl chromophores in low concentration on isolated coils of poly(2-vinylnaphthalene-co-methyl methacrylate) in a poly(methy1 methacrylate) host is monitored by time-resolved fluorescence depolarization spectroscopy. Comparison of the experimental results to a recently developed theory for excitation transport in finite volume systems employing Gaussian segmental distribution functions allows the quantitative evaluation of the copolymer root-mean-square radius of gyration (

K. A. Peterson; M. B. Zimmt; S. Linse; R. P. Domingue; M. D. Fayer

157

Fluorescence multiplexing with time-resolved and spectral discrimination using a near-IR detector.  

PubMed

We report on the design and performance of a two-color, time-resolved detector for the acquisition of both steady-state and time-resolved fluorescence data acquired in real time during the capillary gel electrophoresis separation of DNA sequencing fragments. The detector consisted of a pair of pulsed laser diodes operating at 680 and 780 nm. The diode heads were coupled directly to single-mode fibers, which were terminated into a single fiber mounted via a FC/PC connector to the detector body. The detector contained a dichroic filter, which directed the dual-laser beams to an objective. The objective focused the laser light into a capillary gel column and also collected the resulting fluorescence emission. The dual-color emission was transmitted through the dichroic and focused onto a multimode fiber (core diameter 50 microm), which carried the luminescence to a pair of single-photon avalanche diodes (SPADs). The emission was sorted spectrally using a second dichroic onto one of two SPADs and isolated using appropriate interference filters (710- or 810-nm channel). The dual-color detector demonstrated a time response of 450 and 510 ps (fwhm) for the 710- and 810-nm channels, respectively. The mass detection limits for two near-IR dye-labeled sequencing primers electrophoresed in a capillary gel column were found to be 7.1 x 10(-21) and 3.2 x 10(-20) mol (SNR = 3) for the 710- and 810-nm detector channels, respectively. In addition, no leakage of luminescence excited at 680 nm was observed in the 810-nm channel or 780-nm excited luminescence into the 710-nm channel. An M13mp18 template was sequenced in a single capillary gel column using a two-color, two-lifetime format. The read length was found to be 650 base pairs for the test template at a calling accuracy of 95.1% using a linear poly(dimethylacrylamide) (POP6) gel column, with the read length determined primarily by the electrophoretic resolution produced by the sieving gel. PMID:12918968

Zhu, Li; Stryjewski, Wieslaw; Lassiter, Suzanne; Soper, Steven A

2003-05-15

158

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.

Group, Kansas S.; Zollman, Dean A.

2004-03-05

159

ULTRAFAST CHEMISTRY: Using Time-Resolved Vibrational Spectroscopy for Interrogation of Structural Dynamics  

NASA Astrophysics Data System (ADS)

Time-resolved infrared (IR) and Raman spectroscopy elucidates molecular structure evolution during ultrafast chemical reactions. Following vibrational marker modes in real time provides direct insight into the structural dynamics, as is evidenced in studies on intramolecular hydrogen transfer, bimolecular proton transfer, electron transfer, hydrogen bonding during solvation dynamics, bond fission in organometallic compounds and heme proteins, cis-trans isomerization in retinal proteins, and transformations in photochromic switch pairs. Femtosecond IR spectroscopy monitors the site-specific interactions in hydrogen bonds. Conversion between excited electronic states can be followed for intramolecular electron transfer by inspection of the fingerprint IR- or Raman-active vibrations in conjunction with quantum chemical calculations. Excess internal vibrational energy, generated either by optical excitation or by internal conversion from the electronic excited state to the ground state, is observable through transient frequency shifts of IR-active vibrations and through nonequilibrium populations as deduced by Raman resonances.

Nibbering, Erik T. J.; Fidder, Henk; Pines, Ehud

2005-05-01

160

Radiative lifetime measurements of some La I and La II levels by time-resolved laser spectroscopy  

NASA Astrophysics Data System (ADS)

Natural radiative lifetimes for 60 excited levels of La I and La II were measured using time-resolved laser-induced fluorescence spectroscopy in laser-induced plasma. The lifetimes of 40 excited levels of La I, in the energy range from 24 507.87 to 52 030.4 cm-1, and 20 levels of La II, from 26 414.01 to 56 035.70 cm-1, were measured in this work. The results of lifetimes range from 4.2 to 330 ns with the uncertainties within 10 per cent. To our best knowledge, 34 lifetimes of La I and 17 lifetimes of La II are reported for the first time.

Shang, Xue; Tian, Yanshan; Wang, Qian; Fan, Shuang; Bai, Wanshuang; Dai, Zhenwen

2014-07-01

161

Time-Resolved Photoluminescence Spectroscopy and Imaging: New Approaches to the Analysis of Cultural Heritage and Its Degradation  

PubMed Central

Applications of time-resolved photoluminescence spectroscopy (TRPL) and fluorescence lifetime imaging (FLIM) to the analysis of cultural heritage are presented. Examples range from historic wall paintings and stone sculptures to 20th century iconic design objects. A detailed description of the instrumentation developed and employed for analysis in the laboratory or in situ is given. Both instruments rely on a pulsed laser source coupled to a gated detection system, but differ in the type of information they provide. Applications of FLIM to the analysis of model samples and for the in-situ monitoring of works of art range from the analysis of organic materials and pigments in wall paintings, the detection of trace organic substances on stone sculptures, to the mapping of luminescence in late 19th century paintings. TRPL and FLIM are employed as sensors for the detection of the degradation of design objects made in plastic. Applications and avenues for future research are suggested.

Nevin, Austin; Cesaratto, Anna; Bellei, Sara; D'Andrea, Cosimo; Toniolo, Lucia; Valentini, Gianluca; Comelli, Daniela

2014-01-01

162

Validation and evaluation of a novel time-resolved laser-induced fluorescence technique  

NASA Astrophysics Data System (ADS)

We present a novel technique to measure time-resolved laser-induced fluorescence signals in plasma sources that have a relatively constant Fourier spectrum of oscillations in steady-state operation, but are not periodically pulsed, e.g., Hall thrusters. The technique uses laser modulation of the order of MHz and recovers signal via a combination of band-pass filtering, phase-sensitive detection, and averaging over estimated transfer functions calculated for many different cycles of the oscillation. Periodic discharge current oscillations were imposed on a hollow cathode. Measurements were validated by comparison with independent measurements from a lock-in amplifier and by comparing the results of the transfer function average to an independent analysis technique triggering averaging over many oscillation cycles in the time domain. The performance of the new technique is analyzed and compared to prior techniques, and it is shown that this new technique has a niche in measurements where the analog photomultiplier signal has a nonwhite noise spectral density and cycles of oscillation are not sufficiently repeatable to allow for reliable triggering or a meaningful average waveform in the time domain.

Durot, C. J.; Gallimore, A. D.; Smith, T. B.

2014-01-01

163

Validation and evaluation of a novel time-resolved laser-induced fluorescence technique.  

PubMed

We present a novel technique to measure time-resolved laser-induced fluorescence signals in plasma sources that have a relatively constant Fourier spectrum of oscillations in steady-state operation, but are not periodically pulsed, e.g., Hall thrusters. The technique uses laser modulation of the order of MHz and recovers signal via a combination of band-pass filtering, phase-sensitive detection, and averaging over estimated transfer functions calculated for many different cycles of the oscillation. Periodic discharge current oscillations were imposed on a hollow cathode. Measurements were validated by comparison with independent measurements from a lock-in amplifier and by comparing the results of the transfer function average to an independent analysis technique triggering averaging over many oscillation cycles in the time domain. The performance of the new technique is analyzed and compared to prior techniques, and it is shown that this new technique has a niche in measurements where the analog photomultiplier signal has a nonwhite noise spectral density and cycles of oscillation are not sufficiently repeatable to allow for reliable triggering or a meaningful average waveform in the time domain. PMID:24517766

Durot, C J; Gallimore, A D; Smith, T B

2014-01-01

164

Time-resolved fluorescence of intramolecular charge-transfer systems: experimental results and theoretical predictions  

NASA Astrophysics Data System (ADS)

The time-resolved emission spectrum of dual fluorescent pyrrolidino-benzonitrile in glycerol acetate is interpreted by employing a stochastic model. The model system is made up of an internal coordinate describing the intramolecular adiabatic charge-transfer reaction and a polarization coordinate describing the dynamic behaviour of the polar solvent. The time evolution of the system is governed by a coupled Smoluchowski equation plus source and sink terms to account for the excitation from the ground state and subsequent decay. The model reproduces the dynamic Stokes shift of the frequency maximum of the emission band related to the charge-transfer (CT) state towards the red region, and it provides interpretation of the kinetic behaviour manifested by the system after pulse excitation at the short-wavelength absorption band, corresponding to the locally excited (LE) state. The observation of a dynamic Stokes shift accompanying the time evolution of the CT band implies a kinetic pathway which deviates from steepest descent to the CT state, the rate-determining step being the solvent relaxation.

Braun, David; Nordio, Pier Luigi; Polimeno, Antonino; Saielli, Giacomo

1996-07-01

165

H-bond sensing with 3-hydroxyflavones: steady-state and time-resolved fluorescence studies  

NASA Astrophysics Data System (ADS)

The 4'-dialkylamino derivatives of 3-hydroxyflavone find many applications as molecular probes, since their two-band fluorescence spectra produce a strong response to different intermolecular interactions including H-bonding. The results of our steady-state and time-resolved studies in neat and mixed solvents reveal an important and probably unique property of these dyes: their ground-state equilibrium between H-bonded and non H-bonded forms is not changed significantly on excitation to the normal (N*) excited state. In the excited state, new H-bonds do not form but those already existing in the ground state can disrupt on a slow time scale. This last process is probably coupled with the slow excited-state intramolecular proton transfer (ESIPT) reaction of the H-bonded form of the dye. These dyes do not change significantly the distribution between H-bonded and non H-bonded species in their environment and therefore they can provide a measure of the H-bonding potential of their environment. Due to this feature, they can serve as unique sensors of the H-bonding potential in unknown media. This sensing can be provided by the dramatic change of the relative intensities of their two separated emission bands.

Shynkar, Vasyl V.; Klymchenko, Andrey S.; Demchenko, Alexander P.; Mely, Yves

2004-09-01

166

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

2011-11-01

167

Time-resolved pulsed-plasma characterization using broadband terahertz pulses correlated with fluorescence imaging  

SciTech Connect

Near-monocycle terahertz (THz)-bandwidth electromagnetic pulses have been used to probe pulsed-discharge argon plasmas at various pressures from 10 to 50 Torr. Time-resolved electric field measurements were made of the THz pulse with and without plasma allowing a full characterization of the real and imaginary parts of the plasma index of refraction. Electron densities n{sub e}{>=}10{sup 13} cm{sup -3} and collision rates {gamma}{sub p}{>=}10{sup 11} s{sup -1} were deduced by applying a simple Lorentz model to the measured time-domain pulse with no plasma and comparing it to the measured pulse with the plasma present. Minimizing the rms error between these in the two-dimensional parameter space (n{sub e},{gamma}{sub p}) fixed the values for each point in time of the plasma evolution. Optical fluorescence imaged transverse to the THz beam path was used to estimate the density profile used in the propagation model.

Kolner, B.H.; Conklin, P.M.; Buckles, R.A.; Fontaine, N.K.; Scott, R.P. [Department of Applied Science, University of California, Davis, One Shields Avenue, Davis, California 95616 (United States)

2005-10-10

168

Simultaneous use of time-resolved fluorescence and anti-stokes photoluminescence in a bioaffinity assay.  

PubMed

A bioaffinity assay is described where anti-Stokes photoluminescence of inorganic lanthanide phosphors and time-resolved fluorescence of lanthanide chelates are measured from a single microtitration well without any disturbance from these label technologies to each other. Up-converting phosphor (UPC-phosphor) bioconjugate was produced by grinding the commercial, micrometer-sized UPC-phosphors to colloidal, submicrometer-sized phosphor particles and by attaching these phosphors to biomolecules. Experiments were carried out in standard 96-well microtitration plates to determine detection limits, linearity, and cross-talk of UPC-phosphor and europium chelate. In numbers of molecules the lower limits of detection for UPC-phosphor were roughly 3 x 10(3) particles in solution and 1 x 10(4) particles in solid phase, and for europium label same values were 9 x 10(6) and 9 x 10(7) molecules. Linearity of detection was for UPC-phosphor 5 orders of magnitude in solution and over 4 orders of magnitude in solid phase and for europium label over 5 orders of magnitude in solution and over 4 orders of magnitude in solid phase. The cross-talk between the two labels was practically nonexistent. In this study we show that up-converting anti-Stokes photoluminescent phosphors could be employed in bioaffinity assays as very potential labels with significant advantages either alone or together with long-lifetime lanthanide chelates. PMID:15859599

Kuningas, Katri; Rantanen, Terhi; Karhunen, Ulla; Lövgren, Timo; Soukka, Tero

2005-05-01

169

Triiodothyronine uptake measurement in serum by time-resolved fluorescence immunofluorometry.  

PubMed

A solid phase competition-type fluoroimmunoassay for triiodothyronine (T3) uptake in serum is described. In the assay, exogenous free T3 binds to the unoccupied binding sites on serum thyroxine binding proteins while the remaining unbound T3 competes with immobilized T3 for binding to a soluble biotinylated anti-T3 monoclonal antibody. The bound biotinylated antibody is quantitated by the addition of streptavidin labeled with the europium chelator 4,7-bis(chlorosulfophenyl-1,10 phenanthroline-2,9-bicarboxylic acid (BCPDA) in the presence of excess europium. The fluorescence signal of the final complex, which is directly proportional to the number of unoccupied binding sites on thyroxine binding proteins, is then measured on the dried solid-phase with a pulsed-laser time-resolved fluorometer. The assay requires a 10 microliters serum sample and a total incubation time of 90 minutes. The coefficients of variation for within-run and between-run assays ranged from 2.0 to 5.7%. Results obtained by the present method compared well with those determined by two commercial radioimmunoassays (r greater than 0.9). PMID:2112159

Tan, Y K; Bhayana, V; Papanastasiou-Diamandi, A; Khosravi, M J

1990-01-01

170

Fluorescence dynamics of poly (N-vinylcarbazole) in fluid solution. Multivariate analysis of time-resolved fluorescence spectra  

NASA Astrophysics Data System (ADS)

Time-resolved fluorescence spectra of poly(N-vinylcarbazole) in solution were analyzed by using a principal multicomponent spectral estimation method. It was clearly indicated that the spectra were composed of only three component fluorescence (monomer, partial overlap excimer, and sandwich excimer). Rise as well as decay curves of this component fluorscence were nonexponential and depended upon tacticity of the polymer. The partial overlap is formed not only by ultrafast trapping in the pre-existing site but also through dynamic processes such as energy migration. In tens of ns time range the excited monomer as well as the partial overlap excimer are produced via dissociation and re-activation of the sandwich excimer

Sakai, Hisashi; Itaya, Akira; Masuhara, Hiroshi; Sasaki, Keiji; Kawata, Satoshi

1993-06-01

171

Time-resolved fluorescence microscopy to study biologically related applications using sol-gel derived and cellular media  

NASA Astrophysics Data System (ADS)

Fluorescence microscopy provides a non-invasive means for visualising dynamic protein interactions. As well as allowing the calculation of kinetic processes via the use of time-resolved fluorescence, localisation of the protein within cells or model systems can be monitored. These fluorescence lifetime images (FLIM) have become the preferred technique for elucidating protein dynamics due to the fact that the fluorescence lifetime is an absolute measure, in the main independent of fluorophore concentration and intensity fluctuations caused by factors such as photobleaching. In this work we demonstrate the use of a time-resolved fluorescence microscopy, employing a high repetition rate laser excitation source applied to study the influence of a metal surface on fluorescence tagged protein and to elucidate viscosity using the fluorescence lifetime probe DASPMI. These were studied in a cellular environment (yeast) and in a model system based on a sol-gel derived material, in which silver nanostructures were formed in situ using irradiation from a semiconductor laser in CW mode incorporated on a compact time-resolved fluorescence microscope (HORIBA Scientific DeltaDiode and DynaMyc).

Toury, Marion; Chandler, Lin; Allison, Archie; Campbell, David; McLoskey, David; Holmes-Smith, A. Sheila; Hungerford, Graham

2011-02-01

172

Nanosecond time-resolved polarization spectroscopies: tools for probing protein reaction mechanisms.  

PubMed

Polarization methods, introduced in the 1800s, offered one of the earliest ways to examine protein structure. Since then, many other structure-sensitive probes have been developed, but circular dichroism (CD) remains a powerful technique because of its versatility and the specificity of protein structural information that can be explored. With improvements in time resolution, from millisecond to picosecond CD measurements, it has proven to be an important tool for studying the mechanism of folding and function in many biomolecules. For example, nanosecond time-resolved CD (TRCD) studies of the sub-microsecond events of reduced cytochrome c folding have provided direct experimental evidence of kinetic heterogeneity, which is an inherent property of the diffusional nature of early folding dynamics on the energy landscape. In addition, TRCD has been applied to the study of many biochemical processes, such as ligand rebinding in hemoglobin and myoglobin and signaling state formation in photoactive yellow protein and prototropin 1 LOV2. The basic approach to TRCD has also been extended to include a repertoire of nanosecond polarization spectroscopies: optical rotatory dispersion (ORD), magnetic CD and ORD, and linear dichroism. This article will discuss the details of the polarization methods used in this laboratory, as well as the coupling of time-resolved ORD with the temperature-jump trigger so that protein folding can be studied in a larger number of proteins. PMID:20438842

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

2010-09-01

173

Microcontroller based resonance tracking unit for time resolved continuous wave cavity-ringdown spectroscopy measurements  

NASA Astrophysics Data System (ADS)

We present in this work a new tracking servoloop electronics for continuous wave cavity-ringdown absorption spectroscopy (cw-CRDS) and its application to time resolved cw-CRDS measurements by coupling the system with a pulsed laser photolysis set-up. The tracking unit significantly increases the repetition rate of the CRDS events and thus improves effective time resolution (and/or the signal-to-noise ratio) in kinetics studies with cw-CRDS in given data acquisition time. The tracking servoloop uses novel strategy to track the cavity resonances that result in a fast relocking (few ms) after the loss of tracking due to an external disturbance. The microcontroller based design is highly flexible and thus advanced tracking strategies are easy to implement by the firmware modification without the need to modify the hardware. We believe that the performance of many existing cw-CRDS experiments, not only time-resolved, can be improved with such tracking unit without any additional modification to the experiment.

Votava, Ondrej; Mašát, Milan; Parker, Alexander E.; Jain, Chaithania; Fittschen, Christa

2012-04-01

174

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

175

Raman spectroscopy and time-resolved photoluminescence of BN and BxCyNz nanotubes  

SciTech Connect

We report Raman and time-resolved photoluminescence spectroscopic studies of multiwalled BN and B{sub x}C{sub y}N{sub z} nanotubes. The Raman spectroscopy shows that the as-grown B{sub x}C{sub y}N{sub z} charge recombination, respectively. Comparison of the photoluminescence of BN nanotubes to that decay process is characterized by two time constants that are attributed to intra- and inter-BN sheet nanotubes as predicted by theory. nanotubes are radially phase separated into BN shells and carbon shells. The photoluminescence of hexagonal BN is consistent with the existence of a spatially indirect band gap in multi-walled BN.

Wu, J.; Han, Wei-Qiang; Walukiewicz, W.; Ager III, J.W.; Shan, W.; Haller,E.E.; Zettl, A.

2004-01-21

176

Thermal decomposition study of nitropyrazoles based on time-resolved pulsed photoacoustic spectroscopy  

NASA Astrophysics Data System (ADS)

The paper reports the study of thermal decomposition of 3(5)-nitropyrozole, 4-nitropyrazole and 1-nitropyrazole using time-resolved pulsed photoacoustic spectroscopy technique for the first time. The second harmonic, i.e., ? = 532 nm, 7 ns pulse width at 10 Hz repetition rate, obtained from Q-switched Nd: YAG laser has been employed. In addition, we have studied the effect of pressure, temperature and incident laser energy on the thermal decomposition mechanism of nitropyrazoles. The strength of photoacoustic signal provides significant information about the multistep thermal decomposition mechanism of 3(5)-nitropyrazole and 4-nitropyrazole, while 1-nitropyrazole follows the path of direct decomposition based on single reaction, which is also verified by the thermal gravimetric-differential thermal analysis (TG-DTA) technique. We have also experimentally demonstrated the presence of free NO2 before the melting point, which is due to the thermal dissociation of solid nitropyrazole compounds.

Yehya, F.; Chaudhary, A. K.

2013-01-01

177

Study of singlet and triplet 2,6-difluorophenylnitrene by time-resolved infrared spectroscopy.  

PubMed

The solution-phase photochemistry of 2,6-difluorophenyl azide was studied by time-resolved infrared (TRIR) spectroscopy. A vibrational band of singlet 2,6-difluorophenyl nitrene (1N) was observed at 1404 cm(-1) between 243 and 283 K. At ambient temperature, it was not possible to detect this intermediate. At 298 K, only the decay products of the singlet nitrene, the isomerized products ketenimine (K) and triplet-2,6-difluorophenyl nitrene (3N), were observed at 1576 and 1444 cm(-1), respectively. The assignments are consistent with density functional theory calculations and previous studies of this system by laser flash photolysis techniques with UV-visible detection. PMID:16833595

Mandel, Sarah; Liu, Jin; Hadad, Christopher M; Platz, Matthew S

2005-03-31

178

Least-squares support vector machines modelization for time-resolved spectroscopy  

NASA Astrophysics Data System (ADS)

By use of time-resolved spectroscopy it is possible to separate light scattering effects from chemical absorption effects in samples. In the study of propagation of short light pulses in turbid samples the reduced scattering coefficient and the absorption coefficient are usually obtained by fitting diffusion or Monte Carlo models to the measured data by use of numerical optimization techniques. In this study we propose a prediction model obtained with a semiparametric modeling technique: the least-squares support vector machines. The main advantage of this technique is that it uses theoretical time dispersion curves during the calibration step. Predictions can then be performed by use of data measured on different kinds of sample, such as apples.

Chauchard, Fabien; Roussel, Sylvie; Roger, Jean-Michel; Bellon-Maurel, Véronique; Abrahamsson, Christoffer; Svensson, Tomas; Andersson-Engels, Stefan; Svanberg, Sune

2005-11-01

179

Time-resolved fluorescence and FCS studies of dye-doped DNA  

NASA Astrophysics Data System (ADS)

Fluorescence lifetime, anisotropy and intensity dependent single molecule fluorescence correlation spectroscopy (I-FCS) are used to investigate the mechanism of fluorescence saturation in a free and nucleotide bound fluorophore (NR6104) in an antioxidising ascorbate buffer. Nucleotide attachment does not appreciably affect the fluorescence lifetime of the probe and there is a decrease in the rate of intersystem crossing relative to that of triplet state deactivation. The triplet state fraction is seen to plateau at 72% (G-attached) and 80% (free fluorophore) in agreement with these observations. Measurements of translational diffusion times show no intensity dependence for excitation intensities between 1 and 105kW cm-2 and photobleaching is therefore negligible. The dominant mechanism of fluorescence saturation is thus triplet state formation. I-FCS measurements for Rhodamine 6G in water were compared with those in the ascorbate buffer. In water the triplet fraction was saturated at considerably higher powers (45% at ca. 1.5 × 103kW cm-2) than in the ascorbate buffer (55%ca. 1 1kW cm-2)

Nicolaou, N.; Marsh, R. J.; Blacker, T.; Armoogum, D. A.; Bain, A. J.

2009-08-01

180

Time-resolved laser-induced fluorescence of atomic nitrogen in a free-burning arc discharge  

Microsoft Academic Search

An experiment to detect ground-state atomic nitrogen in an atmospheric-pressure argon-nitrogen free-burning 200 A arc by time-resolved two-photon laser-induced fluorescence is described. The time decay of the fluorescence pulses showed that quenching of the laser-excited state is rapid. Upper bound estimates of the pulse-decay time were determined as a function of radius, and were found to be on the order

Stuart C. Snyder; Anna M. LeRoux

1997-01-01

181

Rapid homogenous time-resolved fluorescence (HTRF) immunoassay for anthrax detection.  

PubMed

Infection with Bacillus anthracsis spores induces an acute anthrax disease that can cause casualties and death in untreated cases. Thus rapid diagnosis of anthrax at early stage of the disease is essential to allow an effective treatment. Here we present the development of rapid and sensitive homogenous time-resolved fluorescence (HTRF) immunoassays based on the energy transfer process of europium cryptate (EuK) donor to AlexaFluor647 acceptor. The energy transfer process is limited to d?

Cohen, Noam; Mechaly, Adva; Mazor, Ohad; Fisher, Morly; Zahavy, Eran

2014-05-01

182

Time-resolved tuned diode laser absorption spectroscopy of pulsed plasma  

NASA Astrophysics Data System (ADS)

A novel method for time-resolved tuned diode laser absorption spectroscopy has been developed. In this paper, we describe in detail developed electronic module that controls time-resolution of laser absorption spectroscopy system. The TTL signal triggering plasma pulse is used for generation of two signals: the first one triggers the fine tuning of laser wavelength and second one controls time-defined signal sampling from absorption detector. The described method and electronic system enable us to investigate temporal evolution of sputtered particles in technological low-temperature plasma systems. The pulsed DC planar magnetron sputtering system has been used to verify this method. The 2" in diameter titanium target was sputtered in pure argon atmosphere. The working pressure was held at 2 Pa. All the experiments were carried out for pulse ON time fixed at 100 (is. When changing OFF time the discharge has operated between High Power Impulse Magnetron Sputtering regime and pulsed DC magnetron regime. The effect of duty cycle variation results in decrease of titanium atom density during ON time while length of OFF time elongates. We believe that observed effect is connected with higher degree of ionization of sputtered particles. As previously reported by Bohlmark et al., the measured optical emission spectra in HiPIMS systems were dominated by emission from titanium ions [1].

Adámek, P.; Do, H. T.; ?ada, M.; Hubi?ka, Z.; Hippler, R.

2014-05-01

183

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

184

Time-resolved fluorescence measurements using microlens array and area imaging devices.  

PubMed

Time-resolved fluorescence (TRF) assay formats are frequently used technologies in high-throughput screening. In this article, we have characterised the novel Plate::Vision(2) 96-microlens array reader (Carl Zeiss Jena GmbH, Germany) and compared it to the novel LEADseeker Generation IV multimodality imaging system (LEADseeker Gen IV; Amersham Biosciences UK Ltd., UK) for applications in the TRF mode. In europium measurements using the TRF mode, the Plate::Vision displayed a limit of detection for europium of approximately 3 pM, which was comparable to two established TRF readers, the Discovery and the Victor V (both PerkinElmer Life Sciences Inc., USA). The LEADseeker's limit of detection only extended down to europium concentrations of approximately 10 pM in these experiments. For TRF resonance energy transfer (TR-FRET) experiments, a europium-biotin (Eu-biotin) conjugate was titrated with a streptavidin-allophycocyanin (SA-APC) conjugate. The Plate::Vision produced Z' values larger than 0.5 for the acceptor fluorophor emission with concentrations of Eu-biotin as low as 3 nM combined with 175 pM SA-APC. To achieve Z' values of at least 0.5 with the LEADseeker, concentrations of 10 nM Eu-biotin combined with SA-APC of at least 0.8 nM were required. In a drug screening application using TR-FRET, the energy transfer from a europium-labelled protein X (Eu-protein X) to a complex of biotinylated peptide Y with SA-APC was measured. Using the Plate::Vision, a Z' factor larger than 0.5 for the acceptor fluorophor emission was only obtained for a Eu-protein X concentration of at least 10 nM in combination with biotinylated peptide Y/SA-APC at saturating concentrations. Both the Plate::Vision and the LEADseeker show good quality results for applications in the TRF mode and enable an increased throughput based on their shortened measurement time in comparison to classic photomultiplier tube-based readers. PMID:14965260

Merk, Susanne; Lietz, Achim; Kroner, Margareta; Valler, Martin; Heilker, Ralf

2004-02-01

185

In vivo time-resolved spectroscopy of the human bronchial early cancer autofluorescence  

NASA Astrophysics Data System (ADS)

Time-resolved measurements of tissue autofluorescence (AF) excited at 405 nm were carried out with an optical-fiber-based spectrometer in the bronchi of 11 patients. The objectives consisted of assessing the lifetime as a new tumor/normal (T/N) tissue contrast parameter and trying to explain the origin of the contrasts observed when using AF-based cancer detection imaging systems. No significant change in the AF lifetimes was found. AF bronchoscopy performed in parallel with an imaging device revealed both intensity and spectral contrasts. Our results suggest that the spectral contrast might be due to an enhanced blood concentration just below the epithelial layers of the lesion. The intensity contrast probably results from the thickening of the epithelium in the lesions. The absence of T/N lifetime contrast indicates that the quenching is not at the origin of the fluorescence intensity and spectral contrasts. These lifetimes (6.9 ns, 2.0 ns, and 0.2 ns) were consistent for all the examined sites. The fact that these lifetimes are the same for different emission domains ranging between 430 and 680 nm indicates that there is probably only one dominant fluorophore involved. The measured lifetimes suggest that this fluorophore is elastin.

Uehlinger, Pascal; Gabrecht, Tanja; Glanzmann, Thomas; Ballini, Jean-Pierre; Radu, Alexandre; Andrejevic, Snezana; Monnier, Philippe; Wagnières, Georges

2009-03-01

186

Three-dimensional time-resolved fluorescence imaging by multifocal multiphoton microscopy for a photosensitizer study in living cells  

NASA Astrophysics Data System (ADS)

Two-photon fluorescence microscopy is widely applied to biology and medicine to study both the structure and dynamic processes in living cells. The main issue is the slow acquisition rate due to the point scanning approach limiting the multimodal detection (x,y,z,t). To extend the performances of this powerful technique, we present a time-resolved multifocal multiphoton microscope (MMM) based on laser amplitude splitting. An array of 8×8 foci is created on the sample that gives a direct insight of the fluorescence localization. Four-dimensional (4D) imaging is obtained by combining simultaneous foci scanning, time-gated detection, and z displacement. We illustrate time-resolved MMM capabilities for 4D imaging of a photosensitizer inside living colon cancer cells. The aim of this study is to have a better understanding of the photophysical processes implied in the photosensitizer reactivity.

Deniset-Besseau, A.; Lévêque-Fort, S.; Fontaine-Aupart, M. P.; Roger, G.; Georges, P.

2007-11-01

187

Two-photon resonances in femtosecond time-resolved four-wave mixing spectroscopy: ?-carotene  

NASA Astrophysics Data System (ADS)

Femtosecond time-resolved pump-degenerate four-wave mixing (pump-DFWM) spectroscopy has been used to study the ultrafast dynamics of ?-carotene involving several electronic and vibrational states. An initial pump pulse, resonant with the S0-to-S2 transition, excites the molecular system and a DFWM process, resonant with the S1-to-Sn 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 S1 state, nonresonant DFWM signal of the ground S0 state and vibrational hot S0* state, and the two-photon resonant DFWM signal of the ground S0 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 ?-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.

2010-08-01

188

The vinyl + NO reaction : determining the products with time-resolved Fourier transform spectroscopy.  

SciTech Connect

We have studied the vinyl + NO reaction using time-resolved Fourier transform emission spectroscopy, complemented by electronic structure and microcanonical RRKM rate coefficient calculations. To unambiguously determine the reaction products, three precursors are used to produce the vinyl radical by laser photolysis: vinyl bromide, methyl vinyl ketone, and vinyl iodide. The emission spectra and theoretical calculations indicate that HCN + CH{sub 2}O is the only significant product channel for the C{sub 2}H{sub 3} + NO reaction near room temperature, in contradiction to several reports in the literature. Although CO emission is observed when vinyl bromide is used as the precursor, it arises from the reaction of NO with photofragments other than vinyl. This conclusion is supported by the absence of CO emission when vinyl iodide or methyl vinyl ketone is used. Prompt emission from vibrationally excited NO is evidence of the competition between back dissociation and isomerization of the initially formed nitrosoethylene adduct, consistent with previous work on the pressure dependence of this reaction. Our calculations indicate that production of products is dominated by the low energy portion of the energy distribution. The calculation also predicts an upper bound of 0.19% for the branching ratio of the H{sub 2}CNH + CO channel, which is consistent with our experimental results.

Osborn, David L; Zou, Peng; Klippenstein, Stephen J.

2005-01-01

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

Unraveling photoexcited conformational changes of bacteriorhodopsin by time resolved electron paramagnetic resonance spectroscopy.  

PubMed Central

By means of time-resolved electron paramagnetic resonance (EPR) spectroscopy, the photoexcited structural changes of site-directed spin-labeled bacteriorhodopsin are studied. A complete set of cysteine mutants of the C-D loop, positions 100-107, and of the E-F loop, including the first alpha-helical turns of helices E and F, positions 154-171, was modified with a methanethiosulfonate spin label. The EPR spectral changes occurring during the photocycle are consistent with a small movement of helix C and an outward tilt of helix F. These helix movements are accompanied by a rearrangement of the E-F loop and of the C-terminal turn of helix E. The kinetic analysis of the transient EPR data and the absorbance changes in the visible spectrum reveals that the conformational change occurs during the lifetime of the M intermediate. Prominent rearrangements of nitroxide side chains in the vicinity of D96 may indicate the preparation of the reprotonation of the Schiff base. All structural changes reverse with the recovery of the bacteriorhodopsin initial state.

Rink, T; Pfeiffer, M; Oesterhelt, D; Gerwert, K; Steinhoff, H J

2000-01-01

191

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.

192

[Photodissociation of Acetylene and Acetone using Step-Scan Time-Resolved FTIR Emission Spectroscopy  

NASA Technical Reports Server (NTRS)

The photodissociation of acetylene and acetone was investigated as a function of added quenching gas pressures using step-scan time-resolved FTIR emission spectroscopy. Its main components consist of Bruker IFS88, step-scan Fourier Transform Infrared (FTIR) spectrometer coupled to a flow cell equipped with Welsh collection optics. Vibrationally excited C2H radicals were produced from the photodissociation of acetylene in the unfocused experiments. The infrared (IR) emission from these excited C2H radicals was investigated as a function of added argon pressure. Argon quenching rate constants for all C2H emission bands are of the order of 10(exp -13)cc/molecule.sec. Quenching of these radicals by acetylene is efficient, with a rate constant in the range of 10(exp -11) cc/molecule.sec. The relative intensity of the different C2H emission bands did not change with the increasing argon or acetylene pressure. However, the overall IR emission intensity decreased, for example, by more than 50% when the argon partial pressure was raised from 0.2 to 2 Torr at fixed precursor pressure of 160mTorr. These observations provide evidence for the formation of a metastable C2H2 species, which are collisionally quenched by argon or acetylene. Problems encountered in the course of the experimental work are also described.

McLaren, Ian A.; Wrobel, Jacek D.

1997-01-01

193

Monitoring brain temperature by time-resolved near-infrared spectroscopy: pilot study.  

PubMed

Mild hypothermia (HT(32°C-33°C)) is an effective neuroprotective strategy for a variety of acute brain injuries. However, the wide clinical adaptation of HT(32-33°C) has been hampered by the lack of a reliable noninvasive method for measuring brain temperature, since core measurements have been shown to not always reflect brain temperature. The goal of this work was to develop a noninvasive optical technique for measuring brain temperature that exploits both the temperature dependency of water absorption and the high concentration of water in brain (80%-90%). Specifically, we demonstrate the potential of time-resolved near-infrared spectroscopy (TR-NIRS) to measure temperature in tissue-mimicking phantoms (in vitro) and deep brain tissue (in vivo) during heating and cooling, respectively. For deep brain tissue temperature monitoring, experiments were conducted on newborn piglets wherein hypothermia was induced by gradual whole body cooling. Brain temperature was concomitantly measured by TR-NIRS and a thermocouple probe implanted in the brain. Our proposed TR-NIRS method was able to measure the temperature of tissue-mimicking phantoms and brain tissues with a correlation of 0.82 and 0.66 to temperature measured with a thermometer, respectively. The mean difference between the TR-NIRS and thermometer measurements was 0.15°C ± 1.1°C for the in vitro experiments and 0.5°C ± 1.6°C for the in vivo measurements. PMID:24817622

Bakhsheshi, Mohammad Fazel; Diop, Mamadou; St Lawrence, Keith; Lee, Ting-Yim

2014-05-01

194

Monitoring brain temperature by time-resolved near-infrared spectroscopy: pilot study  

NASA Astrophysics Data System (ADS)

Mild hypothermia (HT) is an effective neuroprotective strategy for a variety of acute brain injuries. However, the wide clinical adaptation of HT has been hampered by the lack of a reliable noninvasive method for measuring brain temperature, since core measurements have been shown to not always reflect brain temperature. The goal of this work was to develop a noninvasive optical technique for measuring brain temperature that exploits both the temperature dependency of water absorption and the high concentration of water in brain (80%-90%). Specifically, we demonstrate the potential of time-resolved near-infrared spectroscopy (TR-NIRS) to measure temperature in tissue-mimicking phantoms (in vitro) and deep brain tissue (in vivo) during heating and cooling, respectively. For deep brain tissue temperature monitoring, experiments were conducted on newborn piglets wherein hypothermia was induced by gradual whole body cooling. Brain temperature was concomitantly measured by TR-NIRS and a thermocouple probe implanted in the brain. Our proposed TR-NIRS method was able to measure the temperature of tissue-mimicking phantoms and brain tissues with a correlation of 0.82 and 0.66 to temperature measured with a thermometer, respectively. The mean difference between the TR-NIRS and thermometer measurements was 0.15°C±1.1°C for the in vitro experiments and 0.5°C±1.6°C for the in vivo measurements.

Bakhsheshi, Mohammad Fazel; Diop, Mamadou; St. Lawrence, Keith; Lee, Ting-Yim

2014-05-01

195

"Live" Prussian blue fading by time-resolved X-ray absorption spectroscopy  

NASA Astrophysics Data System (ADS)

Prussian blue (PB) is an artists' pigment that has been frequently used in many artworks but poses several problems of conservation because of its fading under light and anoxia treatment. PB fading is due to the reduction of iron(III) into iron(II) and depends a lot on the object investigated. Due to the complexity of the structure, the precise physico-chemical mechanisms behind the redox process remain obscure. In this paper, we present a procedure to investigate light- and anoxia-induced fading of PB-paper samples by means of time resolved X-ray absorption spectroscopy performed at the Fe K-edge. A system composed of a visible light source and a flux-controlled environmental cell allowed light, gas and humidity to be modified in situ. The synchrotron X-ray beam was evidenced to induce a reduction of PB and to play a major role in the kinetics. The analysis of the PB fading kinetics of a sample submitted to various gas and light environments showed that both synchrotron beam and anoxia were influencing PB reduction in a correlated way. In comparison, light was found to play a minor role. Finally, we have demonstrated that the type of paper substrate could influence significantly the kinetics of reduction. Several hypotheses to explain the correlation between PB reduction mechanism and substrate are presented.

Gervais, Claire; Languille, Marie-Angélique; Reguer, Solenn; Gillet, Martine; Vicenzi, Edward P.; Chagnot, Sébastien; Baudelet, François; Bertrand, Loïc

2013-04-01

196

Time-resolved wavelength modulation spectroscopy measurements of HO{sub 2} kinetics  

SciTech Connect

High-frequency wavelength modulation spectroscopy (WMS) has been applied to the detection of the hydroperoxyl radical (HO{sub 2}) in a laser photolysis and long-path absorption pump-probe kinetics reactor with a near-infrared distributed feedback diode laser. The HO{sub 2} is formed by the 355-nm photolysis of Cl{sub 2} in the presence of CH{sub 3}OH and O{sub 2} and monitored by a phase-sensitive detection of the second-harmonic (2f) signal in the 2{nu}{sub 1} band with a 1.5-{mu}m diode laser directly modulated at 5 MHz. The measured 2f WMS signal is calibrated by direct absorption and converted to an absolute number density with the known absorption line strength of the HO{sub 2} line at 6625.80 cm{sup {minus}1}. The utility of time-resolved WMS as a second-order kinetics probe is demonstrated through the measurement of the HO{sub 2} self-reaction rate constant at 295 K. {copyright} 1997 Optical Society of America

Taatjes, Craig A. [Combustion Research Facility, Mail Stop 9055, Sandia National Laboratories, Livermore, California 94551-0969 (United States)] Oh, Daniel B. [Southwest Sciences, Incorporated, 1570 Pacheco Street, Suite E-11, Santa Fe, New Mexico 87505 (United States)

1997-08-01

197

a Study of the Hydroxycyclohexadienyl Radical Absorption Using Time-Resolved Resonance Raman Spectroscopy  

NASA Astrophysics Data System (ADS)

Thus far there has been little understanding of the vibrational spectra, structure and electronic absorption of hydroxycyclohexadienyl radicals in water. They are primary chemical species formed on interaction of radiation with aqueous solutions containing aromatic molecules. We have applied time- resolved resonance Raman (TR-RR) spectroscopy to structurally identify isomers of cyclohexadienyl radicals formed in the pulse radiolysis, using aqueous benzoate solutions as a model system. An early ESR study ((Eiben, K; Fessenden, R.W.; J. Phys. Chem. 1971, 75, 1186-1201) has shown that a mixture of three benzoate hydroxycyclohexadienyl radical isomers: ortho-, meta- and para- are formed upon electron irradiation of N_{2}O saturated benzoate solution. Their collective transient absorption is believed to exhibit a single broad band in the near UV region (?_{max} = 330 nm, ?_{330} = 3800 M^{-1}cm^{-1}). To extract the single isomeric contribution to this collective absorption, we applied TR-RR at various wavelengths within the broad transient absorption range looking for the characteristic indication of each individual isomer. Raman signals of various para-substituted benzoates were also collected to aid in the vibrational studies of the aforementioned benzoate hydroxycyclohexadienyl radicals.

O'Donnell, Deanna M.; Tripathi, G. N. R.; Brinkmann, Nicole R.

2009-06-01

198

Probing Non-equilibrium Phonon Dynamics in Graphite by Time-Resolved Raman Spectroscopy  

NASA Astrophysics Data System (ADS)

Time-resolved Raman spectroscopy has been applied to obtain direct information about phonon lifetimes in graphite. A non-equilibrium population of zone-center optical phonons was produced by the rapid relaxation of charge carriers following photoexcitation of the sample with a femtosecond laser pulse. The subsequent evolution of the phonon population was recorded using the strength of G-mode anti-Stokes Raman scattering from a time-delayed femtosecond probe pulse. A population lifetime for the G-mode phonons of approximately 2 ps was found. Analogous measurements of optical-phonon lifetimes were also conducted in few-layer graphene samples produced by mechanical exfoliation of bulk graphite. Results obtained for graphite and few-layer graphene will be compared with one another, as well as with earlier data on the lifetime of G-mode phonons in single-walled carbon nanotubes [1]. [1] D. Song, F. Wang, G. Dukovic, M. Zheng, E. D. Semke, L. E. Brus, and T. F. Heinz, submitted.

Yan, Hugen; Song, Daohua; Mak, Kin Fai; Chatzakis, Ioannis; Maultzsch, Janina; Heinz, Tony

2008-03-01

199

Hexamethylcyclopentadiene: time-resolved photoelectron spectroscopy and ab initio multiple spawning simulations.  

PubMed

Progress in our understanding of ultrafast light-induced processes in molecules is best achieved through a close combination of experimental and theoretical approaches. Direct comparison is obtained if theory is able to directly reproduce experimental observables. Here, we present a joint approach comparing time-resolved photoelectron spectroscopy (TRPES) with ab initio multiple spawning (AIMS) simulations on the MS-MR-CASPT2 level of theory. We disentangle the relationship between two phenomena that dominate the immediate molecular response upon light absorption: a spectrally dependent delay of the photoelectron signal and an induction time prior to excited state depopulation in dynamics simulations. As a benchmark molecule, we have chosen hexamethylcyclopentadiene, which shows an unprecedentedly large spectral delay of (310 ± 20) fs in TRPES experiments. For the dynamics simulations, methyl groups were replaced by "hydrogen atoms" having mass 15 and TRPES spectra were calculated. These showed an induction time of (108 ± 10) fs which could directly be assigned to progress along a torsional mode leading to the intersection seam with the molecular ground state. In a stepladder-type approach, the close connection between the two phenomena could be elucidated, allowing for a comparison with other polyenes and supporting the general validity of this finding for their excited state dynamics. Thus, the combination of TRPES and AIMS proves to be a powerful tool for a thorough understanding of ultrafast excited state dynamics in polyenes. PMID:24817114

Wolf, T J A; Kuhlman, T S; Schalk, O; Martínez, T J; Møller, K B; Stolow, A; Unterreiner, A-N

2014-06-21

200

Effects of Nonequilibrium Dynamical Screening on Femtosecond Time-resolved Spectroscopy of Semiconductors  

NASA Astrophysics Data System (ADS)

We present here the theory of ultrafast carrier-carrier scattering in semiconductors and apply it to study the thermalization of carriers and to understand femtosecond time-resolved spectroscopy. The main feature of our approach is the theoretically sound treatment of collisions. We abandon Fermi's Golden rule in favor of the Schwinger-Bakshi-Mahantappa-Keldysh (nonequilibrium field theoretical) formalism as the former is applicable only in the long-time regime. Explicit formulas are derived for the screened coulomb interaction in terms of the external time-varying classical electromagnetic fields that are assumed to be present. The formulas are contrasted with the traditional random phase approximation. The polarization dephasing rates are computed as a function of the excited carrier density and it is found that the dephasing rate for carrier-carrier scattering is proportional to the carrier density at low densities, which enables a comparison with experiment. We also demonstrate the dramatic effects of carrier-carrier scattering on the momentum-density distribution of carriers. For resonant pumping we find an overall broadening of the probability distribution. For pump frequencies above the band gap we find a pronounced depletion of carriers at the pump wavevector and a corresponding enhancement at lower momenta. Work supported by ONR N00014-90-J-1267 and NSF/DMR-89-20539.

Setlur, G. S.; Chang, Y. C.

1996-03-01

201

Resting hypofrontality in schizophrenia: A study using near-infrared time-resolved spectroscopy.  

PubMed

Hypofrontality has been a major finding obtained from functional neuroimaging studies on schizophrenia, although there have also been contradictory results that have questioned the reality of hypofrontality. In our previous study, we confirmed the existence of activation hypofrontality by using a 2-channel continuous-wave-type (CW-type) near-infrared spectroscopy (NIRS) instrument. In this study, we employed a single-channel time-resolved spectroscopy (TRS) instrument, which can quantify hemoglobin (Hb) concentrations based on the photon diffusion theory, to investigate resting hypofrontality. A pair of incident and detecting light guides was placed on either side of the forehead at approximately Fp2-F8 or Fp1-F7 alternately in 14 male schizophrenic patients and 16 age-matched male control subjects to measure Hb concentrations at rest. The patients were also measured with a 2-channel CW-type NIRS instrument during the performance of a random number generation (RNG) task. A reduced total hemoglobin concentration (t-Hb) less than 60 microM (the mean value of the control subjects-1.5 SD) was observed bilaterally in 4 patients and only in the left side in 3 patients. Activation hypofrontality was more manifest in these patients than in the remaining 7 patients despite the same task performance. This decreased t-Hb was related to the duration of illness, and it was not observed in patients whose duration of illness was less than 10 years. These results indicate that resting hypofrontality is a chronically developed feature of schizophrenia. This does not necessarily represent frontal dysfunction, but may reflect anatomical and/or functional changes in frontal microcirculation. PMID:16626944

Hoshi, Yoko; Shinba, Toshikazu; Sato, Chie; Doi, Nagafumi

2006-06-01

202

Time-resolved pulsed-plasma characterization using broadband terahertz pulses correlated with fluorescence imaging  

Microsoft Academic Search

Near-monocycle terahertz (THz)-bandwidth electromagnetic pulses have been used to probe pulsed-discharge argon plasmas at various pressures from 10 to 50 Torr. Time-resolved electric field measurements were made of the THz pulse with and without plasma allowing a full characterization of the real and imaginary parts of the plasma index of refraction. Electron densities ne>=1013 cm-3 and collision rates gammap>=1011 s-1

B. H. Kolner; P. M. Conklin; R. A. Buckles; N. K. Fontaine; R. P. Scott

2005-01-01

203

Structural characteristic of folding/unfolding intermediate of pokeweed anti-viral protein revealed by time-resolved fluorescence.  

PubMed

The structural feature of unfolding intermediate of pokeweed anti-viral protein (PAP) was characterized using time-resolved fluorescence spectroscopic methods to elucidate protein folding/unfolding process. CD and fluorescence spectra consistently demonstrated that the unfolding of PAP completed at 4 M of guanidine hydrochloride (GuHCl). The fluorescence resonance energy transfer (FRET) and time-resolve fluorescence depolarization analysis of Trp208 and Trp237 located in the C-terminal domain of PAP suggested that peculiar unfolding intermediate populated before reaching to the unfolding state. The FRET distance of Trp237 to Tyr182 was extended to more than 28 Å with keeping the compact conformation in the unfolding intermediate state populated in the presence of 2 M GuHCl. On the other hand, Trp208 maintained the energy transfer pair with Tyr72 near the active site, although the rotational freedom was increased a little. There results suggest that the most distinguished structural feature of the unfolding intermediate of PAP is the separation of C-terminal domain from N-terminal domain. FRET and fluorescence depolarization studies also showed that C-terminal domain would be more separated to liberate the segmental motions of Trp208 and Trp237 distinctly at the unfolding state. PMID:23319009

Matsumoto, Shuzo; Taniguchi, Yuka; Fukunaga, Yukihiro; Nakashima, Hiromichi; Watanabe, Keiichi; Yamashita, Shoji; Nishimoto, Etsuko

2013-05-01

204

Time-resolved stand-off UV-Raman spectroscopy for planetary exploration  

NASA Astrophysics Data System (ADS)

The exploration of Mars, Europa and Enceladus has provided evidence that support the existence of present or past potentially habitable environments, which may shelter signatures of extinct or extant life. A search for further evidence for habitability or for life requires the development of sophisticated instruments and techniques that enable detailed investigations of locations, which are of great interest to planetary scientists and astrobiologists. Raman spectroscopy is a powerful and versatile technique; a rover based Raman Laser Spectrometer (RLS) operating at 532 nm excitation wavelength has been selected for the 2018 ExoMars mission. In this study, we demonstrate the feasibility of the utilisation of a time-resolved stand-off UV-Raman prototype for the detection and identification of pure organics, organics mixed in a quartz matrix and minerals that have been selected based on their potential relevance to astrobiology and planetary exploration. The samples of organics (?-carotene, L-ascorbic acid, thiamine hydrochloride, L-alanine, L-serine, thymine), carbonates (calcite, dolomite), sulfates (gypsum), silicates (quartz), and natural rock (an altered meta-volcanic rock featuring quartz inclusions) were analyzed at a distance of 6 m using a 355 nm excitation source and a gated intensified charged-coupled device (ICCD) as the detector. We were able to obtain spectra with clear Raman signals enabling unequivocal identification of all selected samples. We assert for the first time, that such an instrument can effectively identify minerals and a wide range of organics that may serve as geo- and biomarkers thus showing great potential for the exploration of planets and astrobiology.

Skulinova, M.; Lefebvre, C.; Sobron, P.; Eshelman, E.; Daly, M.; Gravel, J.-F.; Cormier, J.-F.; Châteauneuf, F.; Slater, G.; Zheng, W.; Koujelev, A.; Léveillé, R.

2014-03-01

205

Site-Specific Measurement of Water Dynamics in the Substrate Pocket of Ketosteroid Isomerase Using Time-Resolved Vibrational Spectroscopy  

PubMed Central

Little is known about the reorganization capacity of water molecules at the active sites of enzymes and how this couples to the catalytic reaction. Here, we study the dynamics of water molecules at the active site of a highly proficient enzyme, ?5-3-ketosteroid isomerase (KSI), during a light-activated mimic of its catalytic cycle. Photo-excitation of a nitrile containing photo-acid, coumarin183 (C183), mimics the change in charge density that occurs at the active site of KSI during the first step of the catalytic reaction. The nitrile of C183 is exposed to water when bound to the KSI active site, and we used time-resolved vibrational spectroscopy as a site-specific probe to study the solvation dynamics of water molecules in the vicinity of the nitrile. We observed that water molecules at the active site of KSI are highly rigid, during the light-activated catalytic cycle, compared to the solvation dynamics observed in bulk water. Based upon this result we hypothesize that rigid water dipoles at the active site might help in the maintenance of the pre-organized electrostatic environment required for efficient catalysis. The results also demonstrate the utility of nitrile probes in measuring the dynamics of local (H-bonded) water molecules in contrast to the commonly used fluorescence methods which measure the average behavior of primary and subsequent spheres of solvation.

Jha, Santosh Kumar; Ji, Minbiao; Gaffney, Kelly J.; Boxer, Steven G.

2012-01-01

206

Evaluating steady-state and time-resolved fluorescence as a tool to study the behavior of asphaltene in toluene.  

PubMed

A combination of steady-state fluorescence, fluorescence lifetime measurements and the determination of time-resolved emission spectra were employed to characterize asphaltene toluene solutions. Lifetime measurements were shown to be insensitive to the source of asphaltene or the alkane solvent from which asphaltene was precipitated. This insensitivity suggests that either the composition of Athabasca and Cold Lake asphaltene is very similar or that the fluorescence behavior is dominated by the same sub-set of fluorophores for the different samples. These results highlight the limitations in using fluorescence to characterize asphaltene solutions. Different dependencies were observed for the average lifetimes with the asphaltene concentration when measured at two different emission wavelengths (420 nm and 520 nm). This result suggests that different fluorophores underwent diverse interactions with other asphaltene molecules as the asphaltene concentration was raised, suggesting that models for asphaltene aggregation need to include molecular diversity. PMID:24722727

Zhang, Hui Ting; Li, Rui; Yang, Zixin; Yin, Cindy-Xing; Gray, Murray R; Bohne, Cornelia

2014-05-21

207

Time-resolved fluorescence for breast cancer detection using an octreotate-indocyanine green derivative dye conjugate  

NASA Astrophysics Data System (ADS)

Time-resolved fluorescence was used to investigate malignant and normal adjacent breast tissues stained with a conjugate of indocyanine green and octreotate. A marked increase in fluorescence lifetime intensity was seen in the breast cancer sample compared to the normal sample. The fluorescent lifetimes were also investigated and showed similar fluorescence decay curves in stained malignant and normal breast tissue. These results confirm that somatostatin receptors occur on human breast carcinomas, suggest that the presence of somatostatin receptors should be investigated as a marker of breast cancer aggressiveness, and suggest that this conjugate might be used to detect the presence of residual breast cancer after surgery, allowing better assessment of tumor margins and reducing the need for second or repeat biopsies in selected patients. These results may also provide clues for designing future treatment options for breast cancer patients.

Sordillo, Laura A.; Das, B. B.; Pu, Yang; Liang, Kexian; Milione, Giovanni; Sordillo, Peter P.; Achilefu, Sam; Alfano, R. R.

208

Construction of time-resolved fluorescence detector for amino compounds after high-performance liquid chromatography using europium chelate  

SciTech Connect

We have constructed a simple, low-cost, time-resolved fluorescence detector (TRFD) for analysis of amino compounds with high-performance liquid chromatography using europium (Eu{sup 3+}) chelates, which consists of a dc-operated xenon lamp, two synchronized mechanical choppers, and spectroscopic filters. Amino compounds derivatized by isothiocyanobenzyl EDTA with Eu{sup 3+} chelate are mixed with an enhancer solution postcolumn and detected by the long TRFD. Taking advantage of the long fluorescence lifetime of the Eu{sup 3+} chelates, high selectivity against background fluorescein is achieved. To demonstrate the usefulness of the TRFD, fundamental performance test comparison with the conventional fluorescence detector was carried our. Details of the system are also described. 12 refs., 5 figs., 1 tab.

Iwata, Tetsuo; Senda, Masaaki; Kurosu, Yasuyuki [JASCO Technical Research Laboratories Corporation, Tokyo (Japan)] [JASCO Technical Research Laboratories Corporation, Tokyo (Japan); Tsuji, Akio; Maeda, Masako [Showa Univ., Tokyo (Japan)] [Showa Univ., Tokyo (Japan)

1997-05-15

209

Eclipse Reappearance Of Io: Time-resolved Spectroscopy (1.9 4.2 ?M)  

NASA Astrophysics Data System (ADS)

We obtained time-resolved, near-infrared spectra of Io during the 60-90 minutes following its reappearance from eclipse by Jupiter on five occasions in 2004. The purpose was to search for spectral changes, particularly in the well-known SO2 frost absorption bands, that would indicate surface-atmosphere exchange of gaseous SO2 induced by temperature changes during eclipse. These observations were a follow-on to eclipse spectroscopy observations in which Bellucci et al. (2004 Icarus 172, 141-148) reported significant changes in the strengths of two strong SO2 bands in data acquired with the VIMS instrument on Cassini. One band (4.07 µm [?1 + ?3]) observed by Bellucci et al. is visible from ground-based observatories and is included in our data. We detected no changes in Io’s spectrum at any of the five observed events during the 60-90 minutes following Io’s emergence from Jupiter’s shadow. The areas of the three strongest SO2 bands in the region 3.5-4.15 µm were measured for each spectrum; the variation of the band areas with time does not exceed that which can be explained by Io’s axial rotation during the intervals of observation, and in no case does the change in band strength approach that seen in the Cassini VIMS data. Our data are of sufficient quality and resolution to show the weak 2.198 ?m (4549.6 cm-1) 4?1 band of SO2 frost on Io for what we believe is the first time. At one of the events (June 22, 2004), we began the acquisition of spectra 6 min before Io reappeared from Jupiter’s shadow, during which time it was detected through its own thermal emission. No SO2 bands were superimposed on the purely thermal spectrum on this occasion, suggesting that the upper limit to condensed SO2 in the vertical column above Io’s surface was 4 X 10-5 g cm-2.

Kornei, Katherine; Cruikshank, D. P.; Emery, J. P.; Bellucci, G.; D'Aversa, E.; Formisano, V.; Brown, R. H.

2006-12-01

210

Transient Absorption and Time-Resolved Fluorescence Studies of Solvated Ruthenium Di-Bipyridine Pseudo-Halide Complexes  

NASA Astrophysics Data System (ADS)

Time-resolved IR and fluorescence measurements were performed to probe the vibrational and electronic properties, respectively, of ruthenium di-bipyridine pseudo-halide (Ru(Bpy){_2}(X){_2} (where X = CN, N{_3} or NCS)) complexes. Vibrational energy relaxation (VER) times were determined for the complexes dissolved in dimethyl sulfoxide (DMSO) with a trend in VER time of NCS > CN > N{_3}. A similar trend and comparable absolute rates for NCS- and N3- were previously observed by our group and others for simple inorganic anions in solution, suggesting a minimal contribution due to complexation. Measurements of the VER time of the CN complex in various solvents provide VER times in ethanol (42.3 ps) and DMSO (53.3 ps), which shows that protic solvents promote the relaxation. Time-resolved fluorescence measurements indicate a strong ligand dependence, with a factor of five decrease in the excited electronic state decay time from the CN (215 ns) to the NCS (39 ns) complex. A solvent dependence of the CN complex reveals a nearly 3-fold increase in the fluorescence decay time from acetonitrile (70 ns) to DMSO (215 ns).

Compton, R.; Weidinger, D.; Owrutsky, J. C.

2012-06-01

211

Time resolved optical emission spectroscopy of an inductively coupled plasma in argon and oxygen  

Microsoft Academic Search

We present the space-time resolved excitation data for a single coil inductively coupled plasma (ICP) reactor operating in collision dominated regime in argon and oxygen at 13.56 MHz. Robot assisted scanning was used in order to obtain Abel inverted radial profiles of emission and subsequently of the net excitation rate as well as the number density of excited states. The

Masahiro Tadokoro; Hajime Hirata; Nobuhiko Nakano; Zoran Lj. Petrovic; Toshiaki Makabe

1998-01-01

212

Time-resolved optical double resonance spectroscopy of the G 2 ? + state of BaCl  

Microsoft Academic Search

A time-resolved optical double resonance experiment is presented in which the BaCl G2?+ state is studied by the delayed coincidence method. The lifetime of the G2?+ state was determined to be 42±2 ns, where the given error is one standard deviation.

H. Ludwigs; N. Gador; L. E. Berg; P. Royen; L. Vikor

1998-01-01

213

Self-association of the polyene antibiotic nystatin in dipalmitoylphosphatidylcholine vesicles: a time-resolved fluorescence study.  

PubMed Central

The interaction between Nystatin and small unilamellar vesicles of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine, both in gel (T = 21 degrees C) and in liquid-crystalline (T = 45 degrees C) phases, was studied by steady-state and time-resolved fluorescence measurements by taking advantage of the intrinsic tetraene fluorophore present in this antibiotic. It was shown that Nystatin aggregates in aqueous solution with a critical concentration of 3 microM. The enhancement in the fluorescence intensity of the antibiotic was applied to study the membrane binding of Nystatin, and it was shown that the antibiotic had an almost fivefold higher partition coefficient for the vesicles in a gel (P = (1.4 +/- 0.1) x 10(3)) than in a liquid-crystalline phase (P = (2.9 +/- 0.1) x 10(2)). Moreover, a time-resolved fluorescence study was used to examine Nystatin aggregation in the membrane. The emission decay kinetics of Nystatin was described by three and two exponentials in the lipid membrane at 21 degrees C and 45 degrees C, respectively. Nystatin mean fluorescence lifetime is concentration-dependent in gel phase lipids, increasing steeply from 11 to 33 ns at an antibiotic concentration of 5-6 microM, but the fluorescence decay parameters of Nystatin were unvarying with the antibiotic concentration in fluid lipids. These results provide evidence for the formation of strongly fluorescent antibiotic aggregates in gel-phase membrane, an interpretation that is at variance with a previous study. However, no antibiotic self-association was detected in a liquid-crystalline lipid bilayer within the antibiotic concentration range studied (0-14 microM).

Coutinho, A; Prieto, M

1995-01-01

214

Time resolved inner-shell spectroscopy of laser produced plasmas using a HOPG crystal in Von Hamos geometry  

Microsoft Academic Search

Time resolved heat transport in warm dense matter, an essential component of the Fast Ignition concept, has been studied using inner-shell spectra from Ti and Al\\/Ti\\/Al foils. Thermal emission is generated by irradiation with either 527 nm and 1ns or 1053 nm and 5 ps pulses using the Vulcan laser at RAL. Fluorescence emission was recorded with a ZYA grade

R. L. Weber; R. R. Freeman; L. van Woerkom; A. J. MacKinnon; A. G. Macphee; R. Dickson; D. Hey; F. Khattak; E. Garcia Saiz; D. Riley; S. N. Chen; F. Beg; R. B. Stephens; M. Notley; D. Neely; G. Gregori

2006-01-01

215

Time-resolved laser-induced fluorescence lifetime measurements and relativistic Hartree Fock calculations of transition probabilities in Sm II  

NASA Astrophysics Data System (ADS)

Radiative lifetime measurements were performed with time-resolved laser-induced fluorescence techniques for 47 levels of the astrophysically important ion Sm1+ over the energy range 21 000-36 000 cm-1. The new results have been compared with previous measurements but also with theoretical calculations taking configuration interactions and core-polarization effects into account, and a satisfying agreement has been found for many levels of this complex ion. New calculated transition probabilities are deduced from the experimental lifetimes and from the theoretical branching fractions for 162 transitions of astrophysical interest. These results will help astrophysicists in the quantitative investigation of the chemical composition of CP stars.

Xu, H. L.; Svanberg, S.; Quinet, P.; Garnir, H. P.; Biémont, E.

2003-12-01

216

Characterization of crude oil and condensate by time-resolved laser fluorescence microscopy - preliminary study  

Microsoft Academic Search

To determine the type and maturity of normal and biodegraded crude oil and condensates, 13 samples from diverse types of Tertiary and Cretaceous reservoirs from Alabama, California, Texas, and Venezuela were characterized utilizing pulsed laser fluorescence microscopy (developed by Borst for coal characterization). Parameters such as fluorescence lifetime in nanoseconds (ns) for three resolved fluorophores and percent contribution of each

P. K. Mukhopadhyay; C. L. Gangopadhyay; M. Pheil; W. L. Borst

1987-01-01

217

Time-resolved fluorescence microscopy for quantitative Ca2+ imaging in living cells.  

PubMed

Calcium (Ca(2+)) is a ubiquitous intracellular second messenger and involved in a plethora of cellular processes. Thus, quantification of the intracellular Ca(2+) concentration ([Ca(2+)]i) and of its dynamics is required for a comprehensive understanding of physiological processes and potential dysfunctions. A powerful approach for studying [Ca(2+)]i is the use of fluorescent Ca(2+) indicators. In addition to the fluorescence intensity as a common recording parameter, the fluorescence lifetime imaging microscopy (FLIM) technique provides access to the fluorescence decay time of the indicator dye. The nanosecond lifetime is mostly independent of variations in dye concentration, allowing more reliable quantification of ion concentrations in biological preparations. In this study, the feasibility of the fluorescent Ca(2+) indicator Oregon Green Bapta-1 (OGB-1) for two-photon fluorescence lifetime imaging microscopy (2P-FLIM) was evaluated. In aqueous solution, OGB-1 displayed a Ca(2+)-dependent biexponential fluorescence decay behaviour, indicating the presence of a Ca(2+)-free and Ca(2+)-bound dye form. After sufficient dye loading into living cells, an in situ calibration procedure has also unravelled the Ca(2+)-free and Ca(2+)-bound dye forms from a global biexponential fluorescence decay analysis, although the dye's Ca(2+) sensitivity is reduced. Nevertheless, quantitative [Ca(2+)]i recordings and its stimulus-induced changes in salivary gland cells could be performed successfully. These results suggest that OGB-1 is suitable for 2P-FLIM measurements, which can gain access to cellular physiology. PMID:23975087

Sagolla, Kristina; Löhmannsröben, Hans-Gerd; Hille, Carsten

2013-10-01

218

Superconducting gap excitations, acoustic and optical phonons probed with femtosecond time-resolved and Raman spectroscopy  

NASA Astrophysics Data System (ADS)

Spontaneous Raman scattering and femtosecond time-resolved pump-probe spectroscopy are used to study and characterize material properties in superconductors, bulk semiconductors and semiconducting quantum dots. Superconducting gap oscillations are observed for the first time in MgB 2 (Tc = 39 K) and 2H-NbSe2 ( Tc = 7 K). In MgB2, multiple superconducting gap oscillations are observed at 24 cm-1, 103 cm -1 and ˜44 cm-1. These frequencies are in reasonable agreement with other reported experimental results and published theoretical models. Spontaneous Raman measurements on MgB2 show a single strong resonance at 107 cm-1 near the superconducting gap. Consistent with spontaneous Raman measurement, coherent superconducting gap oscillations in 2H-NbSe2 are observed at 18 cm-1 (E symmetry) and 14 cm-1 ( A symmetry). The analysis suggests that a non-Raman mechanism or impurities are responsible for the observed oscillations in MgB2. Spontaneous Raman spectra of MgB2 show a large frequency shift in the optical E2g phonon from 580 cm-1 at 300 K to 630 cm-1 at 3 K due to anharmonicity. The resonance at the superconducting gap frequency shows a strong asymmetric lineshape near Tc, becoming Lorentzian-like near 3 K due to spectral weight gain at low frequencies. In ZnO, a study of the anharmonic properties of the low-frequency E2 optical phonon, using pump-probe spectroscopy, show an unusually long lifetime ˜2 orders of magnitude larger for most optical modes in semiconductors. At 5 K, the frequency and lifetime are (2.9787 +/- 0.0002) THz and (211 +/- 7) ps. The temperature dependence of the lifetime is determined by up-conversion decay contributions, which vanish at zero temperature. The results show that the lifetime is limited by isotopic disorder and that nanosecond lifetimes may be achievable in isotopically-pure samples. In CdTe1-xSex quantum dots, two longitudinal optical phonons and a mixed mode are identified. The amplitude of the optical modes as a function of the laser wavelength agrees with the impulsive stimulated Raman scattering mechanism. At low power densities, the frequency of the optical phonons deviates from spontaneous Raman scattering behavior, which is attributed to impurity state trapping. Size-selective excitation effects for the acoustic phonons are more noticeable in time-domain studies. The difference between the time-domain and spontaneous Raman studies is not understood. Acoustic phonons are observed in CdSe quantum dots at 37 cm-1, 22 cm-1 and 5 cm-1 at 560 nm. The linewidth of the mode at 37 cm-1 shows a strong dependence on dot size and a linear dependence with temperature.

Aku-Leh, Cynthia

2005-12-01

219

Characterization of time-resolved fluorescence response measurements for distributed optical-fiber sensing.  

PubMed

A distributed optical-fiber sensing system based on pulsed excitation and time-gated photon counting has been used to locate a fluorescent region along the fiber. The complex Alq3 and the infrared dye IR-125 were examined with 405 and 780 nm excitation, respectively. A model to characterize the response of the distributed fluorescence sensor to a Gaussian input pulse was developed and tested. Analysis of the Alq3 fluorescent response confirmed the validity of the model and enabled the fluorescence lifetime to be determined. The intrinsic lifetime obtained (18.2±0.9 ns) is in good agreement with published data. The decay rate was found to be proportional to concentration, which is indicative of collisional deactivation. The model allows the spatial resolution of a distributed sensing system to be improved for fluorophores with lifetimes that are longer than the resolution of the sensing system. PMID:21102661

Sinchenko, Elena; Gibbs, W E Keith; Davis, Claire E; Stoddart, Paul R

2010-11-20

220

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

221

Time-resolved fluorescence spectra of naphthalene doped in amorphous silica glasses  

NASA Astrophysics Data System (ADS)

Fluorescence spectra of naphthalene doped in amorphous silica glasses were measured by a picosecond time-correlated single-photon counting technique. The fluorescence with a peak at 375 nm, observed in the initial time region of the spectra at 5 × 10 -1 M of naphthalene, is ascribed to the second excimer formed from the ground-state dimer in amorphous silica glasses within 6 ps.

Yamanaka, Takaya; Takahashi, Yoshihiro; Uchida, Kenji

1990-09-01

222

Characterization of crude oil and condensate by time-resolved laser fluorescence microscopy - preliminary study  

SciTech Connect

To determine the type and maturity of normal and biodegraded crude oil and condensates, 13 samples from diverse types of Tertiary and Cretaceous reservoirs from Alabama, California, Texas, and Venezuela were characterized utilizing pulsed laser fluorescence microscopy (developed by Borst for coal characterization). Parameters such as fluorescence lifetime in nanoseconds (ns) for three resolved fluorophores and percent contribution of each fluorophore were correlated with organic geochemical and bulk chemical data on crude oils and condensates. The fluorescence lifetime (ns) of the intermediate component has been correlated with ratios of aromatics to the heterocomponents (fluorescence emitters). This relationship, when compared with the ratio of aromatics to asphaltenes (fluorescence quenchers), revealed characteristic distribution of oils derived from two different reservoirs: (1) marine source-derived oil from Lovetts Creek field (Smackover), Alabama, and (2) terrestrial source-derived oil from Charamousca field (Wilcox), south Texas. These data are supported by geochemical fingerprinting. The above-mentioned ratios and the ratios of the fluorescence lifetimes of two individual fluorophores also show characteristic patterns for biodegraded (alteration in reservoir) and nonbiodegraded crude oils from the Wilcox, Duval County, south Texas, and the Oficina reservoir, Venezuela. These ratios also suggest the possible maturity of two biodegraded crude oils from the Wilcox, south Texas, that coincides with the results of a biomarker study. The above parameters indicate the similarity in origin of two crude oils and one condensate from the Travis Peak Formation, Chapel Hill field, east Texas.

Mukhopadhyay, P.K.; Gangopadhyay, C.L.; Pheil, M.; Borst, W.L.

1987-05-01

223

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

224

Helix formation in a photoswitchable peptide tracked from picoseconds to microseconds by time-resolved IR spectroscopy  

Microsoft Academic Search

Photo-triggered -helix formation of a 16-residue peptide featuring a built-in conformational photoswitch is monitored by time-resolved IR spectroscopy. An experimental approach with 2-ps time resolution and a scanning range up to 30 µs is used to cover all time scales of the peptide dynamics. Experiments are carried out at different temperatures between 281 and 322 K. We observe single-exponential kinetics

Jens Bredenbeck; Jan Helbing; Janet R. Kumita; G. Andrew Woolley; Peter Hamm

2005-01-01

225

Time-resolved temperature measurements of radiatively heated tamped MgO foils by K? absorption spectroscopy  

Microsoft Academic Search

In this paper we present time-resolved temperature measurements of a radiatively heated, thin tamped foil via K? absorption spectroscopy. The sample foil was 1500 Å MgO, tamped on both sides with 1000 Å paralyene, and was heated by soft x-rays transmitted through the back side of a separate laser-irradiated 1500 Å Au foil. The resulting plasma was then backlit by

J. A. Koch; C. A. Back; C. A. Iglesias; D. L. McWilliams; R. C. Cauble; E. J. Hsieh; H. N. Kornblum; N. C. Woolsey; J. C. Moreno; A. Asfaw; J. K. Nash; F. J. Rogers; R. W. Lee

1995-01-01

226

Picosecond time-resolved resonance Raman spectroscopy of the charge separated state of Mg-free base diporphyrins  

Microsoft Academic Search

The photoinduced charge separated state of a covalently linked magnesium porphyrin and free base porphyrin heterodimer complex (Mg?H2) was investigated by picosecond time-resolved, two-color, pump-probe resonance Raman spectroscopy. The charge separated state is detected within 30 ps of laser excitation; recombination occurs within 500 ps. In the charge separated state of the Mg?H2 diporphyrin complex, vibrational mode correlations showed that

H. Zhang; E. Schmidt; W. Wu; C. K. Chang; G. T. Babcock

1995-01-01

227

Fast CCD camera for x-ray photon correlation spectroscopy and time-resolved x-ray scattering and imaging  

Microsoft Academic Search

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

P. Falus; M. A. Borthwick; S. G. J. Mochrie

2004-01-01

228

Time-resolved spectroscopy in ZnWO4 and ZnWO4 : Fe  

Microsoft Academic Search

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.

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

2003-01-01

229

Time resolved photoluminescence spectroscopy of surface-plasmon-enhanced light emission from conjugate polymers  

NASA Astrophysics Data System (ADS)

The authors have experimentally verified that the light emission from conjugated polymers can be enhanced through the use of surface plasmon coupling layers. Carrier dynamics of such plasmon-enhanced organic light emitters were studied and a recombination rate increase due to surface plasmon polaritons was experimentally observed. Internal quantum efficiency data from the polyfluorenes studied follow the trend supported by the time resolved photoluminescence measurements.

Neal, Terrell D.; Okamoto, Koichi; Scherer, Axel; Liu, Michelle S.; Jen, Alex K.-Y.

2006-11-01

230

Time-resolved visible spectroscopy of laser-produced lithium plasmas  

Microsoft Academic Search

We have measured time-resolved visible spectra emitted from a plasma formed when the output from a dye laser irradiates solid lithium. Such a plasma has potential as a source of lithium ions for ion-driven inertial confinement fusion, and it also provides a useful source for developing diagnostics. The laser delivered 0.5 J onto a 2--7-mm-diam spot, with a 900-ns pulse

J. Bailey; G. C. Tisone; M. J. Hurst; R. L. Morrison; K. W. Bieg

1988-01-01

231

Time-resolved visible spectroscopy of laser-produced lithium plasmas  

Microsoft Academic Search

We have measured time-resolved visible spectra emitted from a plasma formed when the output from a dye laser irradiates solid lithium. Such a plasma has potential as a source of lithium ions for ion-driven inertial confinement fusion, and it also provides a useful source for developing diagnostics. The laser delivered 0.5 J onto a 2–7-mm-diam spot, with a 900-ns pulse

J. Bailey; G. C. Tisone; M. J. Hurst; R. L. Morrison; K. W. Bieg

1988-01-01

232

Time-resolved visible spectroscopy of laser-produced lithium plasmas  

Microsoft Academic Search

We have measured time-resolved visible spectra emitted from a plasma formed when the output from a dye laser irradiates solid lithium. Such a plasma has potential as a source of lithium ions for ion-driven inertial confinement fusion, and it also provides a useful source for developing diagnostics. The laser delivered 0.5 Joules onto a 2 to 7 mm diameter spot,

J. Bailey; G. C. Tisone; M. J. Hurst; R. L. Morrison; K. W. Bieg

1988-01-01

233

Hyperfast time-resolved spectroscopy of electron correlation in excited states  

NASA Astrophysics Data System (ADS)

As a consequence of continuing developments in the science and technology of techniques that produce and control electromagnetic pulses with frequencies that are found in a broad part of the spectrum, from the ir to the soft X-rays, it is possible to have hyperfast pump-probe time delay spectroscopic techniques capable of time resolving the dynamics of various atomic and molecular systems involving excited states. In this context, it has been demonstrated via first principles solution of the time-dependent Schr"odinger equation (TDSE), that effects which are caused by strong electron correlations in excited states, including the process of autoionization and the formation of resonances, can be time-resolved on a time scale of attoseconds [1-3]. By extending the investigations to polyelectronic atoms, we have obtained new results for various time resolved processes associated with the photo-ejection of inner (2s) electrons and of two electrons (LM) from the thirteen electron atom of Aluminum and with the electron correlation beats in bound and autoionizind states of N^+3 and Al. The theory and computations account for the interference of direct double ionization, inner hole states and Auger decay [4]. [1] C. A. Nicolaides et al, J. Phys. B 35, L271 (2002). [2] Th. Mercouris et al, Phys. Rev. A 69, 032502 (2004). [3] Th. Mercouris, et al, Phys. Rev. A 75, 013407 (2007). [4] Th. Mercouris, Y. Komninos and C. A. Nicolaides, unpublished.

Nicolaides, Cleanthes A.

2007-06-01

234

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

235

Fast photomultiplier tube gating technique for time-resolved fluorescence measurements  

Microsoft Academic Search

A nanosecond gating technique applied to conventional, 'off the shelf', photomultiplier tubes (PMTs) is described. This technique is most suitable for detection and analysis of fluorescence, induced by pulsed lasers. A high voltage square wave generator is applied to 3 dynodes of the PMT. The result is a fast time-gated optical detector with a high dynamic range of approximately 80

Peter Zipfl; Herbert Schneckenburger; Lars Schoch

1999-01-01

236

Conformational heterogeneity of the copper binding site in azurin. A time-resolved fluorescence study.  

PubMed Central

Comparison of the fluorescence spectra and the effect of temperature on the quantum yields of fluorescence of Azurin (from Pseudomonas fluorescens ATCC-13525-2) and 3-methylindole (in methylcyclohexane solution) provides substantive evidence that the tryptophan residue in azurin is completely inaccessible to solvent molecules. The quantum yields of azurin (CuII), azurin (CuI), and apoazurin (lambda ex = 291 nm) were 0.052, 0.054, and 0.31, respectively. Other evidence indicates that there is no energy transfer from tyrosine to tryptophan in any of these proteins. The fluorescence decay behavior of each of the azurin samples was found to be invariant with emission wavelength. The fluorescences of azurin (CuII) and azurin (CuI) decay with dual exponential kinetics (tau 1 = 4.80 ns, tau 2 = 0.18 ns) while that of apoazurin obeys single exponential decay kinetics (tau = 4.90). The ratio of pre-exponentials of azurin (CuII), alpha 1/alpha 2, is found to be 0.25, and this ratio increases to 0.36 on reduction to azurin (CuI). The results are interpreted as originating from different interactions of the tryptophan with two conformers of the copper-ligand complex in azurin.

Szabo, A G; Stepanik, T M; Wayner, D M; Young, N M

1983-01-01

237

Optical characterization of Pseudomonas fluorescens on meat surfaces using time-resolved fluorescence  

Microsoft Academic Search

A scanning optical system for the detection of bacteria on meat surfaces based on fluorescence lifetime and intensity measurements is described. The system detects autofluorescent light emitted by naturally occurring fluorophores in bacteria. The technique only requires minimal sample preparation and handling, thus the chemical properties of the specimen are preserved. This work presents the preliminary results obtained from a

Alain Bouchard; Julie Frechette; Marcia L. Vernon; Jean-François Cormier; Rene M. Beaulieu; Réal Vallée; Akier Assanta Mafu

2006-01-01

238

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

239

Implementation of Intensity-Modulated Laser Diodes in Time-Resolved, Pump Probe Fluorescence Microscopy  

Microsoft Academic Search

We present the implementation of intensity-modulated laser diodes for applications in frequency-domain pump-probe fluorescence microscopy. Our technique, which is based on the stimulated-emission ap- proach, uses two sinusoidally modulated laser diodes. One laser ~635 nm! excites the chromophores under study, and the other laser ~680 nm! is responsible for inducing stimulated emission from excited- state molecules. Both light sources are

Chen-Yuan Dong; Christof Buehler; Peter T. C. So; Todd French; Enrico Gratton

2001-01-01

240

Non-contact characterization of bacteria by time-resolved fluorescence  

Microsoft Academic Search

Accurate real-time methods for the detection of pathogenic microorganisms in the agri-food industry would represent an improvement over standard methods of analysis. We are currently developing a non-contact, scanning optical system for the detection of bacteria on meat surfaces based on fluorescence lifetime and intensity measurements. The system detects autofluorescent light emitted by the naturally occurring fluorophores in bacteria. Potential

Alain Bouchard; Julie Frechette; William F. Long; Marcia Vernon; Jean-Francois Cormier; Real Vallee; Akier A. Mafu; Marie-Josee Lemay

2004-01-01

241

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

242

Application of time-resolved fluorescence to the determination of metabolites.  

PubMed

A simple fluorescent methodology for the simultaneous determination of two major metabolites of acetylsalicylic acid - salicylic and gentisic acids - in pharmaceutical preparations and human urine is proposed. Due to the overlapping between the fluorescence spectra of both analytes, the use of the more selective fluorescence decay curves is proposed. Values of dependent instrumental variables affecting the signal-to-noise ratio were fixed with a simplex optimization procedure. A calibration matrix of thirteen standards plus two blank samples was processed using a partial least-squares (PLS) analysis. To assess the goodness of the proposed method, a prediction set of nine synthetic samples was analyzed, obtaining recovery percentages between 95% and 106%. Limits of detection, calculated by means of a new criterion, were 3.49?gL(-1) and 1.66?gL(-1) for salicylic and gentisic acids, respectively. The method was also tested in three pharmaceutical preparations containing salicylic acid, obtaining recovery percentages close to 100%. Finally, the simultaneous determination of both analytes in human urine samples was successfully carried out by the PLS-analysis of a matrix of thirteen standards plus five analyte blanks. Although spectra of analytes and urine overlap strongly, no extraction method neither prior separation of the analytes were needed. PMID:24662756

Murillo Pulgarín, J A; Alañón Molina, A; Martínez Ferreras, F

2014-07-15

243

Application of time-resolved fluorescence to the determination of metabolites  

NASA Astrophysics Data System (ADS)

A simple fluorescent methodology for the simultaneous determination of two major metabolites of acetylsalicylic acid - salicylic and gentisic acids - in pharmaceutical preparations and human urine is proposed. Due to the overlapping between the fluorescence spectra of both analytes, the use of the more selective fluorescence decay curves is proposed. Values of dependent instrumental variables affecting the signal-to-noise ratio were fixed with a simplex optimization procedure. A calibration matrix of thirteen standards plus two blank samples was processed using a partial least-squares (PLS) analysis. To assess the goodness of the proposed method, a prediction set of nine synthetic samples was analyzed, obtaining recovery percentages between 95% and 106%. Limits of detection, calculated by means of a new criterion, were 3.49 ?g L-1 and 1.66 ?g L-1 for salicylic and gentisic acids, respectively. The method was also tested in three pharmaceutical preparations containing salicylic acid, obtaining recovery percentages close to 100%. Finally, the simultaneous determination of both analytes in human urine samples was successfully carried out by the PLS-analysis of a matrix of thirteen standards plus five analyte blanks. Although spectra of analytes and urine overlap strongly, no extraction method neither prior separation of the analytes were needed.

Murillo Pulgarín, J. A.; Alañón Molina, A.; Martínez Ferreras, F.

2014-07-01

244

Development of time resolved x-ray spectroscopy in high intensity laser-plasma interactions  

NASA Astrophysics Data System (ADS)

This article discusses the design of a novel time resolved von Hamos Bragg spectrometer to provide spectra in the region around the titanium K-? and He-? lines. The instrument consists of a highly oriented pyrolitic graphite mosaic crystal coupled to a picosecond x-ray streak camera. Measurements of the time dependent behavior from Ti foils illuminated with intense laser pulses can be used to improve the understanding of recombination dynamics, electron transport, and phase transitions in strongly coupled dense plasma. This is important for the modeling of the compression phase in inertial confinement fusion research and the study of astrophysical environments.

Notley, M. M.; Weber, R. L.; Fell, B.; Jeffries, J.; Freeman, R. R.; MacKinnon, A. J.; Dickson, R.; Hey, D.; Khattak, F.; Saiz, E. Garcia; Gregori, G.

2006-10-01

245

Time-Resolved Suppression of Fluorescence in Raman Spectrometry By Continuous Wave Laser Amplitude Modulation and Phase-Sensitive Detection  

Microsoft Academic Search

Raman spectroscopy applied to biological systems is often dominated by interfering fluorescence background. In this report Raman scattering of benzene in the presence of strong fluorescence was obtained via phase sensitive detection upon sinusoidally modulating the continous wave laser beam at tens of MHz. Extended detectability of the 992 cm frequency was obtained, but the signal enhancement is greatly dependent

Arie van Hoek; Antonie J. W. G. Visser

1985-01-01

246

In vivo optical characterization of human tissues from 610 to 1010 nm by time-resolved reflectance spectroscopy.  

PubMed

A fully automated system for time-resolved reflectance spectroscopy based on tunable mode-locked laser sources and on time-correlated single-photon counting for the detection of time-resolved reflectance data was applied to the evaluation of the optical properties of biological tissues (arm, abdomen and forehead) in vivo from 610 to 1010 nm. The scattering decreases progressively with increasing wavelength, while the absorption line shapes show the typical spectral features of the principal tissue components (haemoglobin, water and lipid), with different weights depending on the tissue type. The best fit of the absorption spectra measured in vivo with the spectra of the pure constituents yielded information on the percentage composition of the different tissues. The interpretation of transport scattering spectra with Mie theory provided information on tissue structure. PMID:11512621

Torricelli, A; Pifferi, A; Taroni, P; Giambattistelli, E; Cubeddu, R

2001-08-01

247

Label-free and time-resolved measurements of cell volume changes by surface plasmon resonance (SPR) spectroscopy.  

PubMed

Cell volume and its regulation is one of the key players for cellular integrity and a strong indicator for several cell pathologies. But time-resolved volume measurements of adherently grown mammalian cells using established methods, such as extracellular impedance analysis or light microscopy, are complex and time-consuming. In this study, we demonstrate that surface plasmon resonance spectroscopy (SPR) is a powerful transducer device capable of reporting volume changes of cells that are directly grown on the SPR sensor surface. The approach is label-free, non-invasive and provides an outstanding time resolution. In proof-of-principle studies we recorded the volume change of confluent MDCK II cells induced by hypo- or hypertonic stimulation in a time-resolved manner. Comparison of the SPR-based experiments reported here with more recent studies using different approaches suggests a direct correlation between SPR signal shift and cell volume changes. PMID:19818594

Robelek, R; Wegener, J

2010-01-15

248

Time resolved laser-induced fluorescence of electrosprayed ions confined in a linear quadrupole trap  

SciTech Connect

We have designed and constructed a linear quadrupole ion trap for the measurement of laser-induced fluorescence (LIF) of mass selected gas-phase ions produced by electrospray ionization. The instrument consists of a simple electrospray source, radiofrequency octopole guide, a dc quadrupole bender, a quadrupole mass filter, the linear quadrupole trap (which is equipped with optics for LIF collection and a channeltron ion detector), and several multielement focusing lenses. With this instrument, the LIF decay lifetime of gas-phase Rhodamine 640 radical cations is determined for the first time.

Friedrich, Jochen; Fu Jinmei; Hendrickson, Christopher L.; Marshall, Alan G.; Wang Yisheng [Ion Cyclotron Resonance Program, National High Magnetic Field Laboratory, Florida State University, 1800 East Paul Dirac Drive, Tallahassee, Florida 32310-4005 (United States); Institute of Atomic and Molecular Sciences, Academia Sinica, P. O. Box 23-166, Taipei, Taiwan (China)

2004-11-01

249

Time resolved optical emission spectroscopy of an inductively coupled plasma in argon and oxygen  

NASA Astrophysics Data System (ADS)

We present the space-time resolved excitation data for a single coil inductively coupled plasma (ICP) reactor operating in collision dominated regime in argon and oxygen at 13.56 MHz. Robot assisted scanning was used in order to obtain Abel inverted radial profiles of emission and subsequently of the net excitation rate as well as the number density of excited states. The net excitation rate in argon has modulation close to the walls due to the azimuthal field time dependence and a large bulk value independent of the time presumably due to low energy electron-metastable atom collisions. The time resolved profile in oxygen shows a much more pronounced modulation due to the azimuthal field and a much lower degree of excitation for the center of the tube. At low pressures a structure is observed in the temporal dependence of the net excitation rate that is consistent with two different mechanisms of electron acceleration with phase shift of ?/4: (I) by azimuthal field and (II) due to the drift motion in crossed electric and magnetic fields that leads to a motion in the azimuthal or radial direction and consequently to energy gain.

Tadokoro, Masahiro; Hirata, Hajime; Nakano, Nobuhiko; Petrovi?, Zoran Lj.; Makabe, Toshiaki

1998-01-01

250

Time-resolved femtosecond photoelectron spectroscopy by field-induced surface hopping.  

PubMed

We present the extension of our field-induced surface hopping method for the description of the photoionization process and the simulation of time-resolved photoelectron spectra (TRPES). This is based on the combination of nonadiabatic molecular dynamics "on the fly" in the framework of TDDFT generalized for open shell systems under the influence of laser fields with the approximate quantum mechanical description of the photoionization process. Since arbitrary pulse shapes can be employed, this method can be also combined with the optimal control theory in order to steer the photoionization or to shape the outgoing electronic wavepackets. We illustrate our method for the simulation of TRPES on the prototype system of Ag(3), which involves excitation from the equilibrium triangular geometry, as well as excitation from the linear transition state, where in both cases nonadiabatic relaxation takes place in a complex manifold of electronic states. Our approach represents a generally applicable method for the prediction of time-resolved photoelectron spectra and their analysis in systems with complex electronic structure as well as many nuclear degrees freedom. This theoretical development should serve to stimulate new ultrafast experiments. PMID:20939619

Mitri?, Roland; Petersen, Jens; Wohlgemuth, Matthias; Werner, Ute; Bona?i?-Koutecký, Vlasta; Wöste, Ludger; Jortner, Joshua

2011-04-28

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

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

2012-11-01

253

Time-resolved fluorescence of 2-aminopurine as a probe of base flipping in M.HhaI-DNA complexes  

PubMed Central

DNA base flipping is an important mechanism in molecular enzymology, but its study is limited by the lack of an accessible and reliable diagnostic technique. A series of crystalline complexes of a DNA methyltransferase, M.HhaI, and its cognate DNA, in which a fluorescent nucleobase analogue, 2-aminopurine (AP), occupies defined positions with respect the target flipped base, have been prepared and their structures determined at higher than 2 ? resolution. From time-resolved fluorescence measurements of these single crystals, we have established that the fluorescence decay function of AP shows a pronounced, characteristic response to base flipping: the loss of the very short (?100 ps) decay component and the large increase in the amplitude of the long (?10 ns) component. When AP is positioned at sites other than the target site, this response is not seen. Most significantly, we have shown that the same clear response is apparent when M.HhaI complexes with DNA in solution, giving an unambiguous signal of base flipping. Analysis of the AP fluorescence decay function reveals conformational heterogeneity in the DNA–enzyme complexes that cannot be discerned from the present X-ray structures.

Neely, Robert K.; Daujotyte, Dalia; Grazulis, Saulius; Magennis, Steven W.; Dryden, David T. F.; Klimasauskas, Saulius; Jones, Anita C.

2005-01-01

254

Correlation of conformational heterogeneity of the tryptophyl side chain and time-resolved fluorescence intensity decay kinetics  

NASA Astrophysics Data System (ADS)

The time-resolved fluorescence properties of a tryptophan residue should be useful for probing protein structure, function, and dynamics. To date, however, the non-single exponential fluorescence intensity decay kinetics for numerous peptides and proteins having a single tryptophan residue have not been adequately explained. Many possibilities have been considered and include: (1) contributions from the 1La and 1Lb states of indole; (2) excited-state hydrogen exchange; and (3) environmental heterogeneity from (chi) 1 and (chi) 2 rotamers. In addition, it has been suggested that generally many factors contribute to the decay and a distribution of probabilities may be more appropriate. Two recent results support multiple species due to conformational heterogeneity as the major contributor to complex kinetics. First, a rotationally constrained tryptophan analogue has fluorescence intensity decay kinetics that can be described by the sum of two exponentials with amplitudes comparable to the relative populations of the two rotational isomers. Second, the multiple exponentials observed for tyrosine-containing model compounds and peptides correlate with the (chi) 1 rotamer populations independently determined by 1H NMR. We now report similar correlations between rotamer populations and fluorescence intensity decay kinetics for a tryptophan analogue of oxytocin. It appears for this compound that either (chi) 2 rotations do not appreciably alter the indole environment, (chi) 2 rotations are rapid enough to average the observed dependence, or only one of two possible (chi) 2 populations is associated with each (chi) 1 rotamer.

Laws, William R.; Ross, J. B.

1992-04-01

255

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

256

Cellular Oxygen and Nutrient Sensing in Microgravity Using Time-Resolved Fluorescence Microscopy  

NASA Technical Reports Server (NTRS)

Oxygen and nutrient sensing is fundamental to the understanding of cell growth and metabolism. This requires identification of optical probes and suitable detection technology without complex calibration procedures. Under this project Microcosm developed an experimental technique that allows for simultaneous imaging of intra- and inter-cellular events. The technique consists of frequency-domain Fluorescence Lifetime Imaging Microscopy (FLIM), a set of identified oxygen and pH probes, and methods for fabrication of microsensors. Specifications for electronic and optical components of FLIM instrumentation are provided. Hardware and software were developed for data acquisition and analysis. Principles, procedures, and representative images are demonstrated. Suitable lifetime sensitive oxygen, pH, and glucose probes for intra- and extra-cellular measurements of analyte concentrations have been identified and tested. Lifetime sensing and imaging have been performed using PBS buffer, culture media, and yeast cells as a model systems. Spectral specifications, calibration curves, and probes availability are also provided in the report.

Szmacinski, Henryk

2003-01-01

257

Time-Resolved Ultraviolet Spectroscopy of The M-Dwarf GJ 876 Exoplanetary System  

NASA Technical Reports Server (NTRS)

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 H1 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) equals approximately 0.7). This ratio is approximately 2500x greater than the solar value. We describe the ultraviolet line spectrum and report surprisingly strong fluorescent emission from hot H2 (T(H2) greater than 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 greater than or equal to 10. The strong FUV radiation field of an M-star (and specifically Ly alpha) 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.

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

2012-01-01

258

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

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

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

SciTech Connect

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 T{sub e}, n{sub e}, V{sub p}, and V{sub ion}) 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. [ICARE Laboratory - CNRS, 1C Av. de la Recherche Scientifique, Orleans (France)] [ICARE Laboratory - CNRS, 1C Av. de la Recherche Scientifique, Orleans (France)

2013-07-15

261

Tracking of tuning effects in bis-cyclometalated iridium complexes: a combined time resolved infrared spectroscopy, electrochemical, and computational study.  

PubMed

Electronic structure and photophysical properties have been investigated for a new series of fluorinated iridium complexes with the parent [Ir(ppy)2(deeb)](PF6) (deeb is 4,4'-diethylester-2,2'-bipyridine). Time resolved infrared spectroscopy (TRIR) has been used to observe the long-lived triplet excited state of each complex confirming its mixed charge transfer character. Supplementary evidence of charge transfer in the triplet state is provided via emission spectroscopy, transient absorption spectroscopy, and density functional theory (DFT) calculations. Both computational and spectroscopic assignments reveal consistency in the first excitation throughout the series of complexes. Electrochemical measurements meanwhile show that increasing fluorination still induces expected shifting of frontier orbitals. Excited states beyond the lowest lying triplet are probed for the complexes via UV-vis spectroscopy which reveals three distinct features. These features are assigned via time-dependent DFT (TD-DFT) to build a broader understanding of electronic structure. PMID:23844761

Chirdon, Danielle N; McCusker, Catherine E; Castellano, Felix N; Bernhard, Stefan

2013-08-01

262

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

263

Shock-to-detonation transition of nitromethane: Time-resolved emission spectroscopy measurements  

SciTech Connect

The objective of this work is to improve the knowledge of the shock-to-detonation transition of nitromethane. The study is based on a spectral analysis in the range 0.3-0.85 {mu}m, with a 28-nm resolution, during experiments of plane shock impacts on explosive targets at 8.6 GPa. The time-resolved radiant spectra show that the detonation front, the reaction products produced during the superdetonation, and the detonation products are semitransparent. The temperature and absorption coefficient profiles are determined from the measured spectra by a mathematical inversion method based on the equation of radiative transfer with Rayleigh scattering regime. Shocked nitromethane reaches at least 2500 K, showing the existence of local chemical reactions after shock entrance. Levels of temperature of superdetonation and steady-state detonation are also determined.

Bouyer, Viviane; Darbord, Isabelle; Herve, Philippe [Laboratoire d'energetique et d'economie d'energie, Universite Paris X, 1 Chemin Desvallieres, F-92410 Ville d'Avray (France); Baudin, Gerard; Le Gallic, Christian [Centre d'etudes de Gramat, DGA/DCE/CEG, F-46500 Gramat (France); Clement, Francois; Chavent, Guy [INRIA-Rocquencourt, BP105, F-78153 Le Chesnay Cedex (France)

2006-01-01

264

Time-Resolved X-ray Spectroscopy of the Massive Binary delta Ori  

NASA Astrophysics Data System (ADS)

We have obtained 500 ks of Chandra HETG observations of the massive binary delta Ori (O9.5II+unseen companion), one of the fundamental calibrators of the mass-luminosity-radius relation in the upper HR diagram. The program is intended to map the emission line parameters as the secondary moves through the wind of the primary star. Custom extraction techniques have been developed to create 12 time-resolved 40 ks spectra from these observations, each of which is properly calibrated for time and temperature effects. Emission line fluxes for these time slice spectra are presented, as well as phase analysis of the variability of the fluxes. We discuss the interpretation of the resulting data, such as colliding winds and occultation of various temperature regimes of the primary wind by the secondary.

Nichols, Joy S.; Naze, Y.; Corcoran, M. F.; Pollock, A.; Moffat, A. F.; Ignace, R.; Waldron, W. L.; Evans, N. R.

2014-01-01

265

Time-resolved infrared spectroscopy of superconducting NbTiN films  

NASA Astrophysics Data System (ADS)

Time-resolved, pump-probe measurements of superconducting thin NbTiN films were performed at the National Synchrotron Light Source, Brookhaven National Laboratory. Near-infrared Ti:sapphire laser pulses break Cooper pairs, producing an excess of non-thermal quasiparticles. The recombinations of these excess quasiparticles are probed by time-synchronized, far-infrared, synchrotron pulses, with a time resolution of order 200 picoseconds. The main process probed is the bottleneck between gap-edge quasiparticles and excess 2? phonons. (The phonons, generated by recombination of quasiparticles into Cooper pairs, are pairbreaking, producing gap-edge quasiparticles.) We will report the temperature, magnetic field, and laser fluence dependence of the spectrum-averaged far-infrared photoinduced transmission and reflection. We will also report the changes in the photoinduced far-infrared transmission spectrum.

Zhang, H.; Reitze, D. H.; Stanton, C. J.; Tanner, D. B.; Lobo, R. P. S. M.; Carr, G. L.

2006-03-01

266

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

NASA Astrophysics Data System (ADS)

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 (e.g., S2 and S1) correlations correspond to the same ionic continua, presumably an unfavorable case. We use ultrafast internal conversion in the polyaromatic hydrocarbons phenanthrene and naphthalene as examples. In this situation, the geometry changes (displacements) upon nonadiabatic crossing and upon ionization will strongly affect the ability to disentangle electronic from vibrational dynamics. Particularly, phenanthrene and naphthalene are both very rigid molecules and have small displacements upon internal conversion and ionization, still allowing for direct monitoring of the S2 state internal conversion rate.

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

2001-01-01

267

Direct observation of the "special" salt effect in the dynamics of transient ion pairs by time-resolved spectroscopy  

NASA Astrophysics Data System (ADS)

Intimate ion pairs [A +,T -] are generated by specific excitation of the charge transfer band of the electron donor—acceptor complex of anthracene and tetranitromethane. Time-resolved spectroscopy in three distinct time regimes (ps, ns and ?s) reveals the presence of a second "loose" or solvent-separated ion pair [A +//T -], the dynamic behavior of which is strongly modulated by added salts. The "special" salt effect is quantitatively evaluated, together with all the rate constants involved in ion-pair dynamics.

Masnovi, J. M.; Levine, A.; Kochi, J. K.

1985-09-01

268

Time-resolved luminescent VUV-spectroscopy of pure and doped by rare earth ions crystals of strontium fluoride  

Microsoft Academic Search

The spectroscopic properties SrF2–Eu(1%), SrF2–Er(1%) and nominal pure SrF2 crystals have been studied using time-resolved vacuum ultraviolet (VUV) spectroscopy under pulsed synchrotron radiation excitation. The 4fk?4fk?15d (f–d) and 4fk?4fk (f?f) excitation spectra and emission spectra (with and without of time resolution) have been investigated in the wide energy region at 8 and 295K. Moreover, the emission and excitation behaviors of

K. V. Ivanovskikh; V. A. Pustovarov; B. V. Shulgin

2005-01-01

269

Time-resolved spectroscopy at the picosecond laser-triggered electron accelerator ELYSE  

NASA Astrophysics Data System (ADS)

ELYSE is a fast kinetics center created for pulse radiolysis with picosecond time-resolution. The facility is a 4-9 MeV electron accelerator using a subpicosecond laser pulse to produce an electron pulse from a Cs 2Te semiconductor photocathode and RF gun technology for the electron acceleration. The pulse duration is around 5 ps at low charge (<2 nC) and high energy (9 MeV), and is under routine conditions 10 ps at higher charge (5 nC) and >8 MeV. The dark current at the target is less than 1% of the pulse photocurrent. Time-resolved absorbance measurements in cells placed in front of the electron beam are achieved using pulsed laser diodes, or a xenon flash lamp as light sources, and photodiodes connected to a 3 GHz transient digitizer or a streak camera (250-800 nm range and 3.7 ps time resolution) as detection instruments. In addition, the synchronization between the laser beam and the electron beam is exploited to measure the absorbance by a pump-probe set-up, the pump being the electron pulse produced by the laser pulse, and the probe being part of the laser beam (120 fs-3 ps) delayed by a variable optical line.

Marignier, J.-L.; de Waele, V.; Monard, H.; Gobert, F.; Larbre, J.-P.; Demarque, A.; Mostafavi, M.; Belloni, J.

2006-09-01

270

Spectroscopy and optically stimulated luminescence of Al2O3:C using time-resolved measurements  

NASA Astrophysics Data System (ADS)

This paper reports the observation of ultraviolet (UV) emission at 335 nm in the optically stimulated luminescence (OSL) of carbon-doped aluminum oxide (Al2O3:C) and presents results on the investigation of the OSL properties of this band, including its dose response, time dependence after irradiation, and dependence of the OSL signal on the type of radiation. Time-resolved OSL measurements were used to separate the UV emission band from the dominant OSL emission band of Al2O3:C, namely, the F-center luminescence at 420 nm. A comparison of the OSL properties of the UV and F-center emission bands is important for various dosimetric applications because the relative contribution of the UV and F-center emissions to the OSL signal varies with readout technique and optical filters used in the readout equipment. The UV emission band is found to show an ionization density dependence that is different from the dependence observed for the F-center emission, and an increase in intensity with time elapsed after beta irradiation. These results are relevant for OSL dosimetry of radiation fields containing heavy charged particles, such as the space radiation field and the secondary fields created by interactions of matter with energetic neutrons, as well as for understanding of the basic OSL mechanism in Al2O3:C.

Yukihara, E. G.; McKeever, S. W. S.

2006-10-01

271

Diffusion optical spectroscopy of cancerous and normal prostate tissues in time-resolved and frequency domain  

NASA Astrophysics Data System (ADS)

It is well-known that light transport can be well described using Maxwell's electromagnetic theory. In biological tissue, the scattering particles cause the interaction of scattered waves from neighboring particles. Since such interaction cannot be ignored, multiple scattering occurs. The theoretical solution of multiple scattering is complicated. A suitable description is that the wavelike behavior of light is ignored and the transport of an individual photon is considered to be absorbed or scattered. This is known as the Radiative Transfer Equation (RTE) theory. Analytical solutions to the RTE that explicitly describes photon migration can be obtained by introducing some proper approximations. One of the most popular models used in the field of tissue optics is the Diffusion Approximation (DA). In this study, we report on the results of our initial study of optical properties of ex vivo normal and cancerous prostate tissues and how tissue parameters affect the near infrared light transporting in the two types of tissues. The time-resolved transport of light is simulated as an impulse isotropic point source of energy within a homogeneous unbounded medium with different absorption and scattering properties of cancerous and normal prostate tissues. Light source is also modulated sinusoidally to yield a varied fluence rate in frequency domain at a distant observation point within the cancerous and normal prostate tissues. Due to difference of the absorption and scattering coefficients between cancerous and normal tissues, the expansion of light pulse, intensity, phase are found to be different.

Zhou, Kenneth J.; Pu, Yang; Chen, Jun

2014-03-01

272

Time-resolved infrared spectroscopy of the lowest triplet state of thymine and thymidine  

NASA Astrophysics Data System (ADS)

Vibrational spectra of the lowest energy triplet states of thymine and its 2'-deoxyribonucleoside, thymidine, are reported for the first time. Time-resolved infrared (TRIR) difference spectra were recorded over seven decades of time from 300 fs to 3 ?s using femtosecond and nanosecond pump-probe techniques. The carbonyl stretch bands in the triplet state are seen at 1603 and ˜1700 cm -1 in room-temperature acetonitrile- d3 solution. These bands and additional ones observed between 1300 and 1450 cm -1 are quenched by dissolved oxygen on a nanosecond time scale. Density-functional calculations accurately predict the difference spectrum between triplet and singlet IR absorption cross sections, confirming the peak assignments and elucidating the nature of the vibrational modes. In the triplet state, the C4 dbnd O carbonyl exhibits substantial single-bond character, explaining the large (˜70 cm -1) red shift in this vibration, relative to the singlet ground state. Femtosecond TRIR measurements unambiguously demonstrate that the triplet state is fully formed within the first 10 ps after excitation, ruling out a relaxed 1n? ? state as the triplet precursor.

Hare, Patrick M.; Middleton, Chris T.; Mertel, Kristin I.; Herbert, John M.; Kohler, Bern

2008-05-01

273

Time-resolved fluorescence imaging of slab gels for lifetime base-calling in DNA sequencing applications.  

PubMed

A compact time-resolved near-IR fluorescence imager was constructed to obtain lifetime and intensity images of DNA sequencing slab gels. The scanner consisted of a microscope body with f/1.2 relay optics onto which was mounted a pulsed diode laser (repetition rate 80 MHz, lasing wavelength 680 nm, average power 5 mW), filtering optics, and a large photoactive area (diameter 500 microns) single-photon avalanche diode that was actively quenched to provide a large dynamic operating range. The time-resolved data were processed using electronics configured in a conventional time-correlated single-photon-counting format with all of the counting hardware situated on a PC card resident on the computer bus. The microscope head produced a timing response of 450 ps (fwhm) in a scanning mode, allowing the measurement of subnano-second lifetimes. The time-resolved microscope head was placed in an automated DNA sequencer and translated across a 21-cm-wide gel plate in approximately 6 s (scan rate 3.5 cm/s) with an accumulation time per pixel of 10 ms. The sampling frequency was 0.17 Hz (duty cycle 0.0017), sufficient to prevent signal aliasing during the electrophoresis separation. Software (written in Visual Basic) allowed acquisition of both the intensity image and lifetime analysis of DNA bands migrating through the gel in real time. Using a dual-labeling (IRD700 and Cy5.5 labeling dyes)/two-lane sequencing strategy, we successfully read 670 bases of a control M13mp18 ssDNA template using lifetime identification. Comparison of the reconstructed sequence with the known sequence of the phage indicated the number of miscalls was only 2, producing an error rate of approximately 0.3% (identification accuracy 99.7%). The lifetimes were calculated using maximum likelihood estimators and allowed on-line determinations with high precision, even when short integration times were used to construct the decay profiles. Comparison of the lifetime base calling to a single-dye/four-lane sequencing strategy indicated similar results in terms of miscalls, but reduced insertion and deletion errors using lifetime identification methods, improving the overall read accuracy. PMID:11080890

Lassiter, S J; Stryjewski, W; Legendre, B L; Erdmann, R; Wahl, M; Wurm, J; Peterson, R; Middendorf, L; Soper, S A

2000-11-01

274

Imaging time-resolved electrothermal atomization laser-excited atomic fluorescence spectrometry for determination of mercury in seawater.  

PubMed

In this study, direct determination of mercury at the nanogram per liter level in the complex seawater matrix by imaging time-resolved electrothermal atomization laser-excited atomic fluorescence spectrometry (ITR-ETA-LEAFS) is described. In the case of mercury, the use of a nonresonant line for fluorescence detection with only one laser excitation is not possible. For measurements at the 253.652 nm resonant line, scattering phenomena have been minimized by eliminating the simultaneous vaporization of salts and by using temporal resolution and the imaging mode of the camera. Electrothermal conditions (0.1 M oxalic acid as matrix modifier, low atomization temperature) have been optimized in order to suppress chemical interferences and to obtain a good separation of specific signal and seawater background signal. For ETA-LEAFS, a specific response has been obtained for Hg with the use of time resolution. Moreover, an important improvement of the detection limit has been obtained by selecting, from the furnace image, pixels collecting the lowest number of scattered photons. Using optimal experimental conditions, a detection limit of 10 ng L(-1) for 10 ?L of sample, close to the lowest concentration level of total Hg in the open ocean, has been obtained. PMID:21524139

Le Bihan, Alain; Cabon, Jean-Yves; Deschamps, Laure; Giamarchi, Philippe

2011-06-15

275

Limitations of Time-Resolved Fluorescence Suggested by Molecular Simulations: Assessing the Dynamics of T cell Receptor Binding Loops  

PubMed Central

Time-resolved fluorescence anisotropy (TRFA) has a rich history in evaluating protein dynamics. Yet as often employed, TRFA assumes that the motional properties of a covalently tethered fluorescent probe accurately portray the motional properties of the protein backbone at the probe attachment site. In an extensive survey using TRFA to study the dynamics of the binding loops of a ?? T cell receptor, we observed multiple discrepancies between the TRFA data and previously published results that led us to question this assumption. We thus simulated several of the experimentally probed systems using a protocol that permitted accurate determination of probe and protein time correlation functions. We found excellent agreement in the decays of the experimental and simulated correlation functions. However, the motional properties of the probe were poorly correlated with those of the backbone of both the labeled and unlabeled protein. Our results warrant caution in the interpretation of TRFA data and suggest further studies to ascertain the extent to which probe dynamics reflect those of the protein backbone. Meanwhile, the agreement between experiment and computation validates the use of molecular dynamics simulations as an accurate tool for exploring the molecular motion of T cell receptors and their binding loops.

Scott, Daniel R.; Vardeman, Charles F.; Corcelli, Steven A.; Baker, Brian M.

2012-01-01

276

Identifiability analysis of rotational diffusion tensor and electronic transition moments measured in time-resolved fluorescence depolarization experiment  

NASA Astrophysics Data System (ADS)

The subject of this paper is studies of the deterministic identifiability of molecular parameters, such as rotational diffusion tensor components and orientation of electronic transition moments, resulting from the time-resolved fluorescence anisotropy experiment. In the most general case considered, a pair of perpendicularly polarized emissions enables the unique determination of all the rotational diffusion tensor's principal components. The influence of the tensor's symmetry and the associated degeneration of its eigenvalues on the identifiability of the electronic transitions moments is systematically investigated. The analysis reveals that independently of the rotational diffusion tensor's symmetry, the transition moments involved in photoselection and emission processes cannot be uniquely identified without a priori information about their mutual orientation or their orientation with respect to the principal axes of the tensor. Moreover, it is shown that increasing the symmetry of the rotational diffusion tensor deteriorates the degree of the transition moments identifiability. To obtain these results analytically, a novel approach to solve bilinear system of equations for Markov parameters is applied. The effect of the additional information, obtained from fluorescence measurements for different molecular mobilities, to improve the identifiability at various levels of analysis is shown. The effectiveness and reliability of the target analysis method for experimental determination of the molecular parameters is also discussed.

Szubiakowski, Jacek P.

2014-06-01

277

TIME-RESOLVED SPECTROSCOPY OF THE POLAR EU CANCRI IN THE OPEN CLUSTER MESSIER 67  

SciTech Connect

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{sub WD} {>=} 0.68 M{sub Sun} with M{sub WD} Almost-Equal-To 0.83 M{sub Sun} 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{sub Sun }.

Williams, Kurtis A. [Department of Physics and Astronomy, Texas A and M University-Commerce, P.O. Box 3011, Commerce, TX 75429 (United States); Howell, Steve B. [NASA Ames Research Center, P.O. Box 1, M/S 244-30, Moffett Field, CA 94035 (United States); Liebert, James; Smith, Paul S. [Steward Observatory, University of Arizona, Tucson, AZ (United States); Bellini, Andrea [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Rubin, Kate H. R. [Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, D-69117 Heidelberg (Germany); Bolte, Michael, E-mail: kurtis.williams@tamuc.edu, E-mail: steve.b.howell@nasa.gov, E-mail: jamesliebert@gmail.com, E-mail: psmith@as.arizona.edu, E-mail: bellini@stsci.edu, E-mail: rubin@mpia.de, E-mail: bolte@ucolick.org [UCO/Lick Observatory, University of California, 1156 High St., Santa Cruz, CA 95064 (United States)

2013-05-15

278

Time-resolved visible spectroscopy of laser-produced lithium plasmas  

NASA Astrophysics Data System (ADS)

We have measured time-resolved visible spectra emitted from a plasma formed when the output from a dye laser irradiates solid lithium. Such a plasma has potential as a source of lithium ions for ion-driven inertial confinement fusion, and it also provides a useful source for developing diagnostics. The laser delivered 0.5 Joules onto a 2 to 7 mm diameter spot, with a 900-ns pulse length. Experiments were performed with the wavelength tuned to the Li I 2s-2p resonance line at 6708 A and off resonance at 6728 A. The target was a 500 to 1000 A thick Li film, vacuum evaporated in situ onto a substrate. The light from the plasma was coupled into the entrance slit of a 1-m Czerny-Turner spectrometer, and the output from the spectrometer was focused onto the input slit of a steak camera. The electron density was obtained from Stark broadened widths of Li I 2p-4d, 2p-5d, 2p-4s, and H I 2p-4d. An irradiance of 2 x 10(6) W/sq cm at 6708 A resulted in a peak electron density of 3.9 x 10(17)/cu cm. The density decreased at lower irradiance, with an intensity threshold of 5 x 10(5) W/sq cm for producing an ionized plasma. The threshold for producing a plasma was higher with the laser tuned off resonance, although high density lithium plasmas could still be formed at relatively lower laser irradiance.

Bailey, J.; Tisone, G. C.; Hurst, M. J.; Morrison, R. L.; Bieg, K. W.

279

A comparative study on bulk and nanoconfined water by time-resolved optical Kerr effect spectroscopy.  

PubMed

The low frequency (nu < 500 cm(-1)) vibrational spectra of hydrated porous silica are specifically sensitive to the hydrogen bond interactions and provide a wealth of information on the structural and dynamical properties of the water contained in the pores of the matrix. We investigate systematically this spectral region for a series of Vycor porous silica samples (pore size approximately equal 4 nm) at different levels of hydration, from the dry matrix to completely filled pores. The spectra are obtained as the Fourier transforms of time-resolved heterodyne detected optical Kerr effect (HD-OKE) measurements. The comparison of these spectra with that of bulk water enables us to separately extract and analyze the spectral contributions of the first and second hydration layers, as well as that of bulk-like inner water. We conclude that the extra water entering the pores above approximately equal 10% water/silica weight ratio behaves very similarly to bulk water. At lower levels of hydration, corresponding to two complete superficial water layers or less, the H-bond bending and stretching bands, characteristic of the tetrahedral coordination of water in the bulk phase, progressively disappear: clearly in these conditions the H-bond connectivity is very different from that of liquid water. A similar behavior is observed for the structural relaxation times measured from the decay of the time-dependent HD-OKE signal. The value for the inner water is very similar to that of the bulk liquid; that of the first two water layers is definitely longer by a factor approximately equal 4. These findings should be carefully taken into account when employing pore confinement to extend towards lower temperatures the accessible temperature range of supercooled water. PMID:24640497

Taschin, Andrea; Bartolini, Paolo; Marcelli, Agnese; Righini, Roberto; Torre, Renato

2013-01-01

280

Time-resolved spectroscopy of laser emission from dye-doped droplets  

SciTech Connect

Micrometer-sized droplets of Rhodamine 6G solution in water and ethanol are irradiated by high-intensity nanosecond pulses from a frequency-doubled Nd:YAG laser. Coupling of the spontaneous fluorescence emission with natural resonant modes of the spherical droplets results in stimulated emission, with each droplet behaving like a laser cavity. Spectral observations suggest that droplet lasing emission is supported by resonances of a single mode order. The emission exhibits faster rise times and is shorter lived than corresponding bulk-liquid fluorescence. Lasing in droplets is generally initiated almost simultaneously with elastic scattering, unlike stimulated Raman scattering, which is significantly delayed.

Biswas, A.; Latifi, H.; Armstrong, R.; Pinnick, R.G.

1989-02-15

281

Time-resolved spectroscopy of laser emission from dye-doped droplets.  

PubMed

Micrometer-sized droplets of Rhodamine 6G solution in water and ethanol are irradiated by high-intensity nanosecond pulses from a frequency-doubled Nd:YAG laser. Coupling of the spontaneous fluorescence emission with natural resonant modes of the spherical droplets results in stimulated emission, with each droplet behaving like a laser cavity. Spectral observations suggest that droplet lasing emission is supported by resonances of a single mode order. The emission exhibits faster rise times and is shorter lived than corresponding bulk-liquid fluorescence. Lasing in droplets is generally initiated almost simultaneously with elastic scattering, unlike stimulated Raman scattering, which is significantly delayed. PMID:19749873

Biswas, A; Latifi, H; Armstrong, R L; Pinnick, R G

1989-02-15

282

Quantitative measurement of optical parameters in normal breasts using time-resolved spectroscopy: in vivo results of 30 Japanese women  

NASA Astrophysics Data System (ADS)

Previous investigation has proved time-resolved spectroscopy to be applicable to measurement of optical parameters in the human breast. To increase knowledge of these properties in vivo, the optical parameters of healthy breasts were measured using time-resolved reflectance spectroscopy. A time-correlated single-photon counting method was used to obtain time-response curves for the breasts of 30 Japanese women. Values of (mu) a and (mu) s$' were analyzed by fitting the curves to the diffusion equation. The relationships of optical parameters to age, body mass index, thickness of the breast, number of pregnancies, and menstrual status were examined. The (mu) a and (mu) s' ranged from 0.0024 to 0.0078/mm and from 0.63 to 1.08/mm, respectively. The values of (mu) a and (mu) s' showed a high correlation with properties may be strongly influenced by changes in tissue components related to aging, menstrual status, and so on. This optical information will contribute to the investigation of photon migration in the human breast.

Suzuki, Kazunori; Yamashita, Yutaka; Ohta, Kazuyoshi; Kaneko, Masao; Yoshida, Masayuki; Chance, Britton

1996-07-01

283

Time-resolved autofluorescence spectroscopy of the bronchial mucosa for the detection of early cancer: clinical results  

NASA Astrophysics Data System (ADS)

Time-resolved measurements of endogenous tissue autofluorescence were carried out on the bronchial mucosa of 18 patients during endoscopy by the means of a optical fibre-based spectrometer. The objective was to assess the fluorescence lifetime as a new contrast parameter between normal and malignant tissue and to explain the origin of a previously observed contrast in fluorescence intensity. The intra- and interpatient variation of tissue autofluorescence intensity and decay on normal tissue was determined with the outcome that a strong fluctuation in autofluorescence intensity but not in lifetime was observed on the normal tissue. Preliminary results were obtained by comparing fluorescence decays on normal mucosa and dysplasia/carcinoma in situ. No significant change in fluorescence decay nor in spectrum between 510 and 650 nm was found. Measurements in parallel with an endoscopic autofluorescence imaging device, on the other hand, indicated a contrast in intensity and spectrum on the same lesions. This suggests that the spectral contrast might be due to an enhanced blood concentration in deeper lying layers of the lesion the optical fibre-based contact measurements are less sensitive to. The difference in intensity might be due to a lower concentration in fluorophores or to the thickening of the epithelium in the neoplastic mucous membrane. However, no indication for fluorescence quenching in the upper layers of the mucous membrane as the reason for the reduced fluorescence intensity was found. The fluorescence decays showed a quite stable behaviour with three decay times of 6.9 ns, 2.0 ns and 0.2 ns in the spectral range between 430 and 680 nm. This can be an indication that there is one dominant fluorophore involved, the calculated decay times suggest that it might be elastin. However, a slight spectral dependence of the fluorescence decays let presume that there is a contribution from other fluorophores, probably flavins and NADH.

Glanzmann, Thomas M.; Uehlinger, Pascal; Ballini, Jean-Pierre; Radu, Alexandre; Gabrecht, Tanja; Monnier, Philippe; van den Bergh, Hubert; Wagnieres, Georges A.

2001-10-01

284

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

285

Time resolved single molecule spectroscopy of semiconductor quantum dot\\/conjugated organic hybrid nanostructures  

Microsoft Academic Search

Single molecule studies on CdSe quantum dots functionalized with oligo-phenylene vinylene ligands (CdSe-OPV) provide evidence of strong electronic communication that facilitate charge and energy transport between the OPV ligands and the CdSe quantum dot core. This electronic interaction greatly modify, the photoluminescence properties of both bulk and single CdSe-OPV nanostructure thin film samples. Size-correlated wide-field fluorescence imaging show that blinking

Michael Yemoh Odoi

2010-01-01

286

Time-resolved spectroscopy of laser emission from dye-doped droplets  

Microsoft Academic Search

Micrometer-sized droplets of Rhodamine 6G solution in water and ethanol are irradiated by high-intensity nanosecond pulses from a frequency-doubled Nd:YAG laser. Coupling of the spontaneous fluorescence emission with natural resonant modes of the spherical droplets results in stimulated emission, with each droplet behaving like a laser cavity. Spectral observations suggest that droplet lasing emission is supported by resonances of a

A. Biswas; H. Latifi; R. L. Armstrong; R. G. Pinnick

1989-01-01

287

Time-resolved imaging and spatially-resolved spectroscopy of electrical discharge machining plasma  

Microsoft Academic Search

The plasma created during electrical discharge machining is investigated with imaging and spatially-resolved optical emission spectroscopy. Analysis of the pre-breakdown duration shows that the breakdown is of stochastic nature. Due to the presence of gas bubbles created by electrolysis, the breakdown mechanism in water could be different from the one in oil. After the breakdown, the plasma develops very fast

A. Descoeudres; Ch Hollenstein; G. Wälder; R. Perez

2005-01-01

288

Time-resolved X-ray spectroscopy of photoreduced base-off Cob(II)alamin compared to the Co(II) species in Clostridium thermoaceticum  

SciTech Connect

We have made significant improvements in pump-probe time-resolved X-ray absorption spectroscopy that enable us to structurally describe chemical intermediates with short lifetimes. We demonstrate that X-ray pre-edge data for a 1 mM compound can be acquired with a high signal-to-noise ratio by time-resolved discrimination of fluorescent signals from a 13-element germanium detector. With the utilization of this novel time-multiplexed laser photolysis system coupled to a flow cell, we characterized the structure of the initial photoproduct of five-coordinate base-off Co(III) methylcobalamin. The X-ray pre-edge spectra of five- and six-coordinate species have a strong 1s-3d transition at about 10 eV below the edge. In four-coordinate, square-planar species the 1s-3d intensity is significantly reduced, but they show a 1s-4p peak at about 6 eV below the edge. We used this `fingerprint` to monitor the structural change upon photolysis. Since the quantum yield of the base-off species is 0.48, the observed spectrum upon photolysis is a mixture of photoproduct and initial states. The photoproduct of the base-off methylcobalamin shows a substantial decrease in the 1s-3d peak and significant increase in the 1s-4p peak. This indicates the formation of a four-coordinate species. The four-coordinate species in the free cobalamin is very unstable and can only be detected by time-resolved methods. This indicates a special role for the protein in maintaining an unusual four-coordinate Co(II) corrinoid. 23 refs., 5 figs.

Scheuing, E.M.; Clavin, W.; Wirt, M.D. [Albert Einstein College of Medicine of Yeshiva Univ., Bronx, NY (United States)] [Albert Einstein College of Medicine of Yeshiva Univ., Bronx, NY (United States); [Brookhaven National Lab., Upton, NY (United States); and others.

1996-02-29

289

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

290

Dynamics of intramolecular vibrational redistribution in terminal acetylene molecules studies by time-resolved Raman spectroscopy  

NASA Astrophysics Data System (ADS)

We report the first direct investigations of vibrational dynamics in isolated polyatomic molecules by means of Raman spectroscopy. A pump-probe experimental scheme is applied where laser pumping of one mode of a molecule is followed by probing its anti-Stokes Raman spectrum, so that a decrease ofRaman signal with the probe-pump delay time tells us about intramolecular vibrational redistribution (IVR) of the energy from the initially excited mode to the other modes. Experimental results for terminal acetylene molecules are presented and discussed. The principal observation is that IVR times in our studies are much shorter than those estimated previously for the same molecules from high-resolution spectroscopy ofthe cold molecular beams. We analyze this difference assuming that the rotational degrees of freedom, which are highly populated in our case of gas at room temperature, play an important role in mediating IVR in the molecules under consideration.

Malinovsky, Alexander L.; Makarov, Alexander A.; Ryabov, Evgeny A.

2006-12-01

291

Space and time resolved coherent optical spectroscopy of single quantum dots  

Microsoft Academic Search

A novel experimental technique, combining near-field optics and femtosecond pump-probe spectroscopy, is demonstrated to analyse the coherent nonlinear optical response of single quantum dots on ultrafast time scales. The technique is used to study the effects of strong non-resonant light fields on the optical spectra of single excitons in interface quantum dots. Transient reflectivity spectra show dispersive line shapes reflecting

Thomas Unold; Kerstin Mueller; Christoph Lienau; Thomas Elsaesser

2004-01-01

292

Time resolved inner-shell spectroscopy of laser produced plasmas using a HOPG crystal in Von Hamos geometry  

NASA Astrophysics Data System (ADS)

Time resolved heat transport in warm dense matter, an essential component of the Fast Ignition concept, has been studied using inner-shell spectra from Ti and Al/Ti/Al foils. Thermal emission is generated by irradiation with either 527 nm and 1ns or 1053 nm and 5 ps pulses using the Vulcan laser at RAL. Fluorescence emission was recorded with a ZYA grade HOPG crystal used in mosaic focusing mode and Von Hamos geometry. The crystal was coupled with a Kentech Low Magnification Streak Camera, fitted with a fluffy CsI photocathode, providing a temporal resolution of about 50 ps. Although the small dynamic range of the streak camera restricts measurement of the full duration of He-alpha emission, our data indicates that the FWHM duration of the resonance line is approximately 1.5 ns when the Ti foil is irradiated with 1 ns pulses.

Weber, R. L.; Freeman, R. R.; van Woerkom, L.; MacKinnon, A. J.; Macphee, A. G.; Dickson, R.; Hey, D.; Khattak, F.; Garcia Saiz, E.; Riley, D.; Chen, S. N.; Beg, F.; Stephens, R. B.; Notley, M.; Neely, D.; Gregori, G.

2006-10-01

293

Nanosecond dynamics of calmodulin and ribosome-bound nascent chains studied by time-resolved fluorescence anisotropy.  

PubMed

We report a time-resolved fluorescence anisotropy study of ribosome-bound nascent chains (RNCs) of calmodulin (CaM), a prototypical member of the EF-hand family of calcium-sensing proteins. As shown in numerous studies, in vitro protein refolding can differ substantially from biosynthetic protein folding, which takes place cotranslationally and depends on the rate of polypeptide chain elongation. A challenge in this respect is to characterize the adopted conformations of nascent chains before their release from the ribosome. CaM RNCs (full-length, half-length, and first EF-hand only) were synthesized in vitro. All constructs contained a tetracysteine motif site-specifically incorporated in the first N-terminal helix; this motif is known to react with FlAsH, a biarsenic fluorescein derivative. As the dye is rotationally locked to this helix, we characterized the structural properties and folding states of polypeptide chains tethered to ribosomes and compared these with released chains. Importantly, we observed decelerated tumbling motions of ribosome-tethered and partially folded nascent chains, compared to released chains. This indicates a pronounced interaction between nascent chains and the ribosome surface, and might reflect chaperone activity of the ribosome. PMID:24644265

Lamprou, Paraskevas; Kempe, Daryan; Katranidis, Alexandros; Büldt, Georg; Fitter, Jörg

2014-05-01

294

Triplet excimer formation of dibromocarbazole chromophores in methacrylate copolymer films measured by time-resolved phosphorescence and transient absorption spectroscopy  

SciTech Connect

Time-resolved phosphorescence and transient absorption spectroscopy have been carried out for studying the triplet states of the 3,6-dibromocarbazole (DBCz) chromophore in a solid matrix of methacrylate copolymer. poly[2-(3,6-dibromo-9-carbazoyl)ethyl methacrylate-co-methyl methacrylate]. The sample film containing 10% DBCz units showed critical behavior in the time-resolved phosphorescence spectra which altered the shape from the monomer state [sup 3]M* to two kinds of excimer states: E1 and E2 (460 and 510 nm at the maximum intensity, respectively). These excimeric species have identical profiles with those reported for poly(3,6-dibromo-9-vinylcarbazole), although the polymer structures are totally different. This result shows that the DBCz chromophores tend to take some preferential geometry which results in the formation of two distinct excimer sites in the polymer film. The spectral alteration with time was drastically accelerated by thermal activation in the temperature range 25-77 K. Iterative trapping and detrapping processes determine the rate of relaxation to the deeper traps, E1 and E2. 15 refs., 8 figs., 1 tab.

Ito, Shinzaburo; Yamamoto, Masahide (Kyoto Univ. (Japan)); Liebe, W.R.; Burkhart, R.D. (Univ. of Nevada, Reno, NV (United States)); Wada, Yoshio (Kyoto Inst. of Technology (Japan))

1994-08-04

295

Time-resolved imaging and spatially-resolved spectroscopy of electrical discharge machining plasma  

NASA Astrophysics Data System (ADS)

The plasma created during electrical discharge machining is investigated with imaging and spatially-resolved optical emission spectroscopy. Analysis of the pre-breakdown duration shows that the breakdown is of stochastic nature. Due to the presence of gas bubbles created by electrolysis, the breakdown mechanism in water could be different from the one in oil. After the breakdown, the plasma develops very fast (<50 ns) and then remains stable. The plasma excites a broad volume around the electrode gap, between 50 and 400 µm in diameter depending on the discharge current. The H? line is emitted from the whole plasma, since the hydrogen atoms originate from the dielectric. On the other hand, spatially-resolved spectroscopy shows that plasma contamination from the electrodes is concentrated in their vicinity. After the discharge, light is still emitted by incandescent metallic particles coming from erosion of the workpiece. Profiles between the electrodes of electron density and of electron temperature have been estimated from spatially-resolved emission spectra. The density is found to slightly increase towards the plasma centre, whereas the temperature is quite constant across the plasma (~0.7 eV).

Descoeudres, A.; Hollenstein, Ch; Wälder, G.; Perez, R.

2005-11-01

296

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

297

On the intrinsic photophysics of indigo: a time-resolved photoelectron spectroscopy study of the indigo carmine dianion.  

PubMed

The intrinsic photophysics of indigo has been studied using gas-phase time-resolved photoelectron imaging of the indigo carmine dianion (InC(2-)). The action spectrum reveals that the gas-phase absorption spectrum arising from the S(1) <-- S(0) transition in InC(2-) has a similar solvent shift to that of neutral indigo. Femtosecond spectroscopy shows that the S(1) state decays on a 1.4 ps timescale. Through isotopic substitution, the primary mechanism on the S(1) excited state can be assigned to an intra-molecular proton transfer, which is the same as that which has been observed in solution. However, the excited state lifetime is significantly shorter in vacuum. These similarities and differences are discussed in terms of recent theoretical investigations of the S(1) excited state of indigo. PMID:24734261

Chatterley, Adam S; Horke, Daniel A; Verlet, Jan R R

2012-12-14

298

Photoinduced Neutral-to-Ionic Phase Transition in Tetrathiafulvalene-p-chloranil Studied by Time-Resolved Vibrational Spectroscopy  

NASA Astrophysics Data System (ADS)

We studied the photoinduced neutral-to-ionic phase transition in tetrathiafulvalene-p-chloranil (TTF-CA) using time-resolved infrared (IR) vibrational spectroscopy with a broadband femtosecond IR laser pulse and a linear IR detector array. After photoexcitation, the strength of the TTF ag?3 band increased, indicating that dimerization is activated within ˜1 ps. In contrast, the strength of the CA b1u?10 band, whose frequency is proportional to the degree of charge transfer (?), decreased, and a broad weak band appeared in the lower-frequency region. This implies that large fluctuations in charge transfer continued until about 20 ps after the photoexcitation. These results indicate a large difference between the electronic structures of the ionic phases generated by thermalexcitation and photoexcitation, although a dimerized structure was observed in both cases.

Matsubara, Yoshitaka; Okimoto, Yoichi; Yoshida, Tatsushi; Ishikawa, Tadahiko; Koshihara, Shin-ya; Onda, Ken

2011-12-01

299

Femtosecond time-resolved reflection spectroscopy of photoinduced ionic-neutral phase transition in TTF-CA crystals  

NASA Astrophysics Data System (ADS)

We study the dynamics of photoinduced transition from ionic to neutral phases in tetrathiafulvalen- p -chloranil crystals by means of the fs time-resolved reflection spectroscopy at 6K . We find that the phase transition consists of three sequential steps: (1) Precursor neutral regions form within 20ps after excitation; (2) local neutral pairs aggregate to proliferate neutral clusters at 20-100ps after excitation; (3) three-dimensional order of the neutral phase forms around 400ps after excitation. Temporal oscillations in the reflectivity, characterized by two modes with different frequencies, are observed and assigned to impulsive acoustic phonons associated with phase transition. We discuss the mechanism of the phase transition based on these results.

Tanimura, Katsumi

2004-10-01

300

Time-resolved luminescent VUV-spectroscopy of pure and doped by rare earth ions crystals of strontium fluoride  

NASA Astrophysics Data System (ADS)

The spectroscopic properties SrF 2-Eu(1%), SrF 2-Er(1%) and nominal pure SrF 2 crystals have been studied using time-resolved vacuum ultraviolet (VUV) spectroscopy under pulsed synchrotron radiation excitation. The 4f k?4f k-15d (f-d) and 4f k?4f k (f-f) excitation spectra and emission spectra (with and without of time resolution) have been investigated in the wide energy region at 8 and 295 K. Moreover, the emission and excitation behaviors of intrinsic luminescence SrF 2 have been studied at 8 K, when the fast and slow components given by singlet and triplet relaxation of self-trapped excitons (STE) are observed. Special attention is devoted to VUV emission of Er 3+-doped SrF 2 due to spin-allowed and spin-forbidden 4f 105d?4f 11 transitions.

Ivanovskikh, K. V.; Pustovarov, V. A.; Shulgin, B. V.

2005-05-01

301

Local structure of reaction intermediates probed by time-resolved x-ray absorption near edge structure spectroscopy  

SciTech Connect

A method for the analysis of time-resolved x-ray absorption near edge structure (XANES) spectra is proposed. It combines principal component analysis of the series of experimental spectra, multidimensional interpolation of theoretical XANES as a function of structural parameters, and ab initio XANES calculations. It allows to determine the values of structural parameters for intermediates of chemical reactions and the concentrations of different states as a function of time. This approach is tested using numerically generated data and its possibilities and limitations are discussed. The application of this method to a reaction with methylrhenium trioxide catalyst in solution, for which experimental data were measured using stopped-flow energy-dispersive x-ray absorption spectroscopy technique, is demonstrated. Possibilities and limitations of this experimental technique are also discussed.

Smolentsev, G.; Soldatov, A. V. [Center for Nanoscale Structure of Matter and Faculty of Physics, Southern Federal University, Rostov-on-Don 344090 (Russian Federation); Guilera, G. [ALBA Synchrotron, Barcelona 08193 (Spain); Tromp, M. [University of Southampton, Southampton SO17 1BJ (United Kingdom); Pascarelli, S. [European Synchrotron Radiation Facility, Grenoble 38000 (France)

2009-05-07

302

Time resolved diagnostics in CF4 / H2 plasmas by electron attachment mass spectrometry and optical emission spectroscopy.  

NASA Astrophysics Data System (ADS)

In the case of a parallel plate symmetrical 50 kHz low pressure discharge in CF4 - H2 mixtures (discharge current 10 - 40 mA, total pressure 10 - 30 Pa , hydrogen admixture 0 - 80 %, closed system) the main stable products (e.g. F_2, CF_4, C_2F_6, C_3F_8) of plasma chemical reactions have been time resolved investigated by the electron attachment mass spectrometry (EAMS), investigating them according their resonant electron attachment cross sections. The EAMS was realised by means of a HAL EQP 300 Hiden Analytical system, extended by the (-) RGA mode. The plasma chemical reaction kinetics is characterised by the time dependent consumption of molecular hydrogen and the production of higher molecular fluorocarbons. These measurements were completed by optical emission spectroscopy of electronic excited species (e.g. atomic fluorine, molecular hydrogen).

Wagner, Hans-Erich; Meichsner, Juergen; Kroutilina, Valja; Lerch, Rene

2000-10-01

303

Monoclonal Antibody-Based Time-Resolved Fluorescence Immunoassays for Daidzein, Genistein, and Equol in Blood and Urine: Application to the Isoheart Intervention Study  

Microsoft Academic Search

Background: Time-resolved fluorescence immunoas- says (TR-FIAs) for phytoestrogens in biological samples are an alternative to mass spectrometric methods. These immunoassays were used to test urine and plasma samples from individuals in a dietary intervention trial aimed at determining the efficacy of dietary isoflavones in reducing the risk of coronary heart disease in post- menopausal women. Methods: We established murine monoclonal

Duncan C. S. Talbot; Richard M. Ogborne; Tony Dadd; Herman Adlercreutz; Geoff Barnard; Susanne Bugel; Fortune Kohen; Sandra Marlin; Jerry Piron; Aedin Cassidy; Jonathan Powell

304

Ultrafast time-resolved absorption spectroscopy of geometric isomers of xanthophylls  

NASA Astrophysics Data System (ADS)

This paper presents an ultrafast optical spectroscopic investigation of the excited state energies, lifetimes and spectra of specific geometric isomers of neoxanthin, violaxanthin, lutein, and zeaxanthin. All- trans- and 15,15'- cis-?-carotene were also examined. The spectroscopy was done on molecules purified by HPLC frozen immediately to inhibit isomerization. The spectra were taken at 77 K to maintain the configurations and to provide better spectral resolution than seen at room temperature. The kinetics reveal that for all of the molecules except neoxanthin, the S 1 state lifetime of the cis isomers is shorter than that of the all- trans isomers. The S 1 excited state energies of all the isomers were determined by recording S 1 ? S 2 transient absorption spectra. The results obtained in this manner at cryogenic temperatures provide an unprecedented level of precision in the measurement of the S 1 energies of these xanthophylls, which are critical components in light-harvesting pigment-protein complexes of green plants.

Niedzwiedzki, Dariusz M.; Enriquez, Miriam M.; LaFountain, Amy M.; Frank, Harry A.

2010-07-01

305

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

306

A new angle into time-resolved photoacoustic spectroscopy: A layered prism cell increases experimental flexibility  

NASA Astrophysics Data System (ADS)

A new pulsed photoacoustic calorimetry cell that uses transmission of light through a pair of dovetail prisms is discussed. The layered prism cell (LPC) combines the enhanced time-resolution capabilities of the ``layered'' front-face irradiation geometry with the zero-background and broadband flexibility of the classical cuvette geometry. This work provides a phenomenological description of photoinduced pressure changes to yield an analytical expression to calculate the magnitude of the photoinduced acoustic pressure wave in a series of solvents. The mechanical to electrical conversion efficiency for an ultrasonic transducer coupled to the LPC is presented to provide a comparison of the experimentally observed photoinduced acoustic signal amplitudes to the empirically calculated acoustic signal amplitudes. An analysis of the background signals due to absorption and electrostriction of the media provides insight into the issues of sensitivity and limitations of pulsed photoacoustic experiments. The LPC provides several benefits to increase the flexibility of the photoacoustic spectroscopy: (1) greater sensitivity, (2) enhanced time resolution, and (3) the ability to obtain kinetic data in complex solvent mixtures. Under optically dilute conditions in the layered cell geometry, the acoustic transient time, ?a, approaches zero because the photoinduced acoustic wave homogeneously expands against the walls of the photoacoustic cell. To demonstrate the unique capabilities of the LPC, rates of hydrogen abstraction by tert-butoxyl radical from solvent mixtures containing ethyl and methyl alcohol are presented.

Autrey, Tom; Foster, Nancy S.; Klepzig, Kim; Amonette, James E.; Daschbach, John L.

1998-06-01

307

Development of a High Harmonic Beamline for Time-Resolved XUV Spectroscopy  

NASA Astrophysics Data System (ADS)

In order to better understand bond breaking and other photochemical processes it is critical to determine the valence electron dynamics occurring during such phenomena. Extreme ultraviolet (XUV) light induces transitions between narrowly confined core electronic states and valence states. Thus ultrafast XUV absorption provides a route to determine electron distributions during chemical change. We present the design of our new femtoseconds XUV absorption spectrometer. The XUV pulses are generated in a rare gas cell in a high harmonic generation (HHG) process. Strong laser field HHG yields a promising probe source in the 10-100 eV spectral range, making it an ideal tool for XUV absorption spectroscopy of molecules containing 3d transition metals with M2,3 edges between 40-70 eV. The femtosecond duration pulses intrinsically produced by HHG allow for the necessary temporal resolution. We plan to study organometallic molecules such as the transition metal carbonyls which undergo ligand dissociation under the influence of ultraviolet light. After UV excitation a radiationless non-Born-Oppenheimer processes occur before dissociation. The understanding of these non-Born-Oppenheimer dynamics is important to the general field of photocatalysis. This work is supported by the Office of Science Early Career Research Program.

Sistrunk, Emily; Grilj, Jakob; Guehr, Markus

2012-06-01

308

Valence tautomerism in co-dioxolene complexes: static and time-resolved infrared spectroscopy study.  

PubMed

In this work, we studied the valence tautomerism process on two different Co-dioxolene complexes by means of transient infrared spectroscopy (TRIR). The molecules investigated are ls-Co(III)(Cat-N-BQ)(Cat-N-SQ) (DQ2) and [ls-Co(III)(tpy)(Cat-N-SQ)]PF6 (tpy), where Cat-NBQ = 2-(2-hydroxy-3,5-ditert-butylphenyl-imino)-4,6-ditert-butylcyclohexa-3,5-dienone, Cat-N-SQ is the dianionic radical analogue, and tpy = 2,2'-6-2?-terpyridine. DFT calculations of the harmonic frequencies for the two complexes allow us to pinpoint the normal modes to be used as markers of the semiquinonate and benzoquinonate isomers. The photoinduced one-electron charge transfer process from the radical semiquinonate ligand to the metal center leads to a ls-Co(II)(x)(Cat-N-BQ) electronic state (where x is the other ligand). Following this first step, an ultrafast ISC process (? < 200 fs) takes places, yielding the benzoquinonate isomer (hs-Co(II)(x)(Cat-N-BQ)). In the experiments, we employed different excitation wavelengths on resonance with different absorption bands of the two samples. Excitation in the ligand-to-metal charge transfer (LMCT) band at ?520 nm and in the semiquinonate band at ?1000 nm induces the valence tautomerism (VT) in both samples. From the time evolution of the TRIR spectra, we determine the time constants of the vibrational cooling in the tautomeric state (7-14 ps) and the ground state recovery times (?350 ps for tpy and ?450 ps for DQ2). In contrast, when the pump frequency is set at 712 nm, on resonance with the benzoquinonate absorption band of the second active ligand of the DQ2, no electron transfer takes place: the TRIR spectra basically show only ground state bleaching bands and no marker band of the tautomeric conversion shows up. PMID:23888870

Azzaroli, Nicolò; Lapini, Andrea; Di Donato, Mariangela; Dei, Andrea; Righini, Roberto

2013-12-12

309

Time-resolved fluorescence and fourier transform infrared spectroscopic investigations of lateral packing defects and superlattice domains in compositionally uniform cholesterol/phosphatidylcholine bilayers.  

PubMed

Time-resolved fluorescence and Fourier transform infrared spectroscopies were used to investigate the lateral organization of lipids in compositionally uniform and fully equilibrated 1-palmitoyl-2-oleoyl-phosphatidylcholine/cholesterol (POPC/CHOL) liposomes prepared by a recently devised low-temperature trapping method. Independent fluorescence decay lifetime and rotational dynamics parameters of diphenylhexatriene (DPH) chain-labeled phosphatidylcholine (DPH-PC) in these liposomes were recovered from the time-resolved fluorescence measurements as a function of cholesterol molar fraction (X(CHOL)) at 23 degrees C. The results indicate significantly greater lifetime heterogeneity, shorter average lifetime, rotational correlation time, and lower order parameter of the DPH moiety at X(CHOL) approximately 0.40 and 0.50 as compared to the adjacent cholesterol concentrations. Less prominent changes were also detected at, for example, X(CHOL) approximately 0.20 and 0.33. These X(CHOL)'s coincide with the "critical" X(CHOL)'s predicted by the previously proposed superlattice (SL) model, thus indicating that POPC and cholesterol molecules tend to form SL domains where the components tend to be regularly distributed. The data also support another prediction of the SL model, namely that lateral packing defects coexist with the ordered SL domains. It appears that unfavorable interaction of the DPH-moiety of DPH-PC with cholesterol results in a preferential partition of DPH-PC to the defect regions. Fourier transform infrared analysis of the native lipid O=P=O, C=O, and C-H vibrational bands of POPC/CHOL liposomes in the absence of DPH-PC revealed an increase in the conformational order of the acyl chains and a decrease in the conformational order (or increased hydration) of the interfacial and headgroup regions at or close to the predicted critical X(CHOL)'s. This provides additional but probe-independent evidence for SL domain formations in the POPC/CHOL bilayers. We propose that the defect regions surrounding the putative SL domains could play an important role in modulating the activity of various membrane-associated enzymes, e.g., those regulating the lipid compositions of cell membranes. PMID:12770884

Cannon, Brian; Heath, Garrett; Huang, Juyang; Somerharju, Pentti; Virtanen, Jorma A; Cheng, Kwan Hon

2003-06-01

310

Use of a Phosphotyrosine-Antibody Pair as a General Detection Method in Homogeneous Time-Resolved Fluorescence: Application to Human Immunodeficiency Viral Protease  

Microsoft Academic Search

A homogeneous time-resolved fluorescence (HTRF) assay has been developed for human immunodeficiency viral (HIV) protease. The assay utilizes a peptide substrate, differentially labeled on either side of the scissile bond, to bring two detection components, streptavidin-cross-linked XL665 (SA\\/XL665) and a europium cryptate (Eu(K))-labeled antiphosphotyrosine antibody, into proximity allowing fluorescence resonance energy transfer (FRET) to occur. Cleavage of the doubly labeled

Richard T. Cummings; Heather M. McGovern; Song Zheng; Young Whan Park; Jeffrey D. Hermes

1999-01-01

311

Detection of anthrax protective antigen (PA) using europium labeled anti-PA monoclonal antibody and time-resolved fluorescence.  

PubMed

Inhalation anthrax is a rare but acute infectious disease following adsorption of Bacillus anthracis spores through the lungs. The disease has a high fatality rate if untreated, but early and correct diagnosis has a significant impact on case patient recovery. The early symptoms of inhalation anthrax are, however, non-specific and current anthrax diagnostics are primarily dependent upon culture and confirmatory real-time PCR. Consequently, there may be a significant delay in diagnosis and targeted treatment. Rapid, culture-independent diagnostic tests are therefore needed, particularly in the context of a large scale emergency response. The aim of this study was to evaluate the ability of monoclonal antibodies to detect anthrax toxin proteins that are secreted early in the course of B. anthracis infection using a time-resolved fluorescence (TRF) immunoassay. We selected monoclonal antibodies that could detect protective antigen (PA), as PA83 and also PA63 and LF in the lethal toxin complex. The assay reliable detection limit (RDL) was 6.63×10(-6)?M (0.551ng/ml) for PA83 and 2.51×10(-5)?M (1.58ng/ml) for PA63. Despite variable precision and accuracy of the assay, PA was detected in 9 out of 10 sera samples from anthrax confirmed case patients with cutaneous (n=7), inhalation (n=2), and gastrointestinal (n=1) disease. Anthrax Immune Globulin (AIG), which has been used in treatment of clinical anthrax, interfered with detection of PA. This study demonstrates a culture-independent method of diagnosing anthrax through the use of monoclonal antibodies to detect PA and LF in the lethal toxin complex. PMID:24857756

Stoddard, Robyn A; Quinn, Conrad P; Schiffer, Jarad M; Boyer, Anne E; Goldstein, Jason; Bagarozzi, Dennis A; Soroka, Stephen D; Dauphin, Leslie A; Hoffmaster, Alex R

2014-06-01

312

Time-resolved visible and extreme ultraviolet spectroscopy of laser-produced tin plasma  

NASA Astrophysics Data System (ADS)

Previous experimental studies of laser-matter interactions have often been conducted without sufficient accuracy or attention to critical laser parameters. Moreover, much of the work published in the open literature lacks the essential theoretical underpinnings necessary to explain observations and provide predictive capability for future experiments. In this study, we use nanosecond-resolved spectroscopic techniques to investigate fundamental physics in laser-produced tin plasma, and overcome these shortcomings by implementing several metrological innovations to ensure the accuracy of experimental data. Furthermore, we present a side-by-side comparison of experimental results with computational modeling to advance our understanding of the many nonlinear, interrelated processes that occur within transient tin plasma. This dissertation is divided into three primary sections. In the first section, we study the physics governing the generation and early-time evolution of tin plasma in the low-irradiance regime: IL ˜ 4 x 1011 - 1 x 1012W/cm2 . A two-channel XUV photodiode spectrometer has been developed to measure tin plasma temperature, as well as diagnose radiation transport processes during the laser irradiation phase. During laser heating, the radiation spectrum from semi-infinite tin targets was found to approach the blackbody limit in the 10--80 nm spectral range. Through one-dimensional numerical modeling, this is shown to be due to the penetration of a radiative diffusion wave beyond the critical depth. Analysis of the time-dependent tin emission spectrum has shown that nearly 30% of the incident laser energy is converted to energetic photons in the spectral range of 15 < hv < 120 eV. The equilibrium radiation temperature, characteristic of the optically thick ablation front, has shown reasonable agreement with numerical predictions despite the model's limited dimensionality. The second part of this work examines the late-time hydrodynamics associated with the radiative plasma phase studied in the preceding section. Nanosecond-gated optical emission spectroscopy is employed to diagnose electron temperature, electron density, and propagation velocity of the ablation plume. In contrast to the large change in radiation temperature observed for a factor of three increase in laser intensity, it is found that the post-pulse plume hydrodynamics is not significantly affected for the same variation in irradiation conditions. At late times, the ion kinetic energy is found to exceed electron thermal energy by more than 100 times, which serves as a lower bound on the ratio to the ion thermal counterpart. The expanding laser-produced tin plasma is well described by a cylindrical hydrodynamic transport model; a comparison between time-integrated experimental and numerical plasma energy density has shown convergence to within a factor of two. At distances > 3 mm from the target, it was found that the heavy ion tin plasma transitions from Boltzmann to coronal equilibrium, rendering LTE assumptions in the spectral deconvolution procedure invalid. In the final section of this study, we investigate the radiative properties of tin ablation plasma as the laser irradiance is varied by more than an order of magnitude. The effect of increased focused laser energy is manifested in a weak scaling of radiation temperature, and a significant broadening of the emission lifetime at the highest laser intensities. It is found that the resulting radiation conversion efficiency is not a strong function of laser intensity within the parameter regime of this work. It is shown that agreement between experimental and simulated plasma conditions becomes progressively worse in the high-irradiance regime as the ionization and radiative transfer models play increasingly dominant roles in the plasma energetics.

O'Shay, Joseph Fred

313

Application of near-infrared time-resolved spectroscopy to rat liver--a preliminary report for surgical application.  

PubMed

The applicability of near-infrared time-resolved spectroscopy to rat liver surgery was investigated. First, the technical reliability in determining the absorption coefficient (mu(a)) and reduced scattering coefficient (mu'(s)) of the liver was checked. Next, boundary effects in determining mu(a) and mu'(s) of the rat liver were examined. Finally, changes in mu(a) and mu'(s) of rat liver with ischaemia were directly measured by TRS. Our TRS system showed that the mu(a) value held a linear correlation with the ink concentration in a lipid emulsion until mu(a) reached 1.2 cm(-1), while the mu'(s) was fairly independent. The mu(a) values of blood-free rat liver and blood-containing rat liver at 780 nm were observed to be 0.43 cm(-1) and 0.67 cm(-1) by using the matching method, indicating that TRS is reliable in determining mu(a) and mu'(s) of the liver. Possible errors in mu(a) and mu'(s) determination due to the boundary effects of the rat liver were as small as 7%, when the mu(a) value was as high as observed for the liver. The oxygen saturation of haemoglobin (SO2) was changed from 64.9% to 8.0%, and the haemoglobin content (THB) from 189.1 microM to 131.6 microM by ischaemia. Mu'(s) dynamically changed in the range 7.06 cm(-1) to 11.36 cm(-1). We conclude that time-resolved measurement is applicable in the high-mu(a) region observed in the liver, and can give quantitative estimations of SO2 and THB in the liver. PMID:10473213

Kitai, T; Miwa, M; Liu, H; Beauvoit, B; Chance, B; Yamaoka, Y

1999-08-01

314

Excited state dynamics in SO2. I. Bound state relaxation studied by time-resolved photoelectron-photoion coincidence spectroscopy.  

PubMed

The excited state dynamics of isolated sulfur dioxide molecules have been investigated using the time-resolved photoelectron spectroscopy and time-resolved photoelectron-photoion coincidence techniques. Excited state wavepackets were prepared in the spectroscopically complex, electronically mixed (B?)(1)B1/(Ã)(1)A2, Clements manifold following broadband excitation at a range of photon energies between 4.03 eV and 4.28 eV (308 nm and 290 nm, respectively). The resulting wavepacket dynamics were monitored using a multiphoton ionisation probe. The extensive literature associated with the Clements bands has been summarised and a detailed time domain description of the ultrafast relaxation pathways occurring from the optically bright (B?)(1)B1 diabatic state is presented. Signatures of the oscillatory motion on the (B?)(1)B1/(Ã)(1)A2 lower adiabatic surface responsible for the Clements band structure were observed. The recorded spectra also indicate that a component of the excited state wavepacket undergoes intersystem crossing from the Clements manifold to the underlying triplet states on a sub-picosecond time scale. Photoelectron signal growth time constants have been predominantly associated with intersystem crossing to the (c?)(3)B2 state and were measured to vary between 750 and 150 fs over the implemented pump photon energy range. Additionally, pump beam intensity studies were performed. These experiments highlighted parallel relaxation processes that occurred at the one- and two-pump-photon levels of excitation on similar time scales, obscuring the Clements band dynamics when high pump beam intensities were implemented. Hence, the Clements band dynamics may be difficult to disentangle from higher order processes when ultrashort laser pulses and less-differential probe techniques are implemented. PMID:24880274

Wilkinson, Iain; Boguslavskiy, Andrey E; Mikosch, Jochen; Bertrand, Julien B; Wörner, Hans Jakob; Villeneuve, David M; Spanner, Michael; Patchkovskii, Serguei; Stolow, Albert

2014-05-28

315

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

316

Noninvasive observation of skeletal muscle contraction using near-infrared time-resolved reflectance and diffusing-wave spectroscopy  

NASA Astrophysics Data System (ADS)

We introduce a method for noninvasively measuring muscle contraction in vivo, based on near-infrared diffusing-wave spectroscopy (DWS). The method exploits the information about time-dependent shear motions within the contracting muscle that are contained in the temporal autocorrelation function g(1)(?,t) of the multiply scattered light field measured as a function of lag time, ?, and time after stimulus, t. The analysis of g(1)(?,t) measured on the human M. biceps brachii during repetitive electrical stimulation, using optical properties measured with time-resolved reflectance spectroscopy, shows that the tissue dynamics giving rise to the speckle fluctuations can be described by a combination of diffusion and shearing. The evolution of the tissue Cauchy strain e(t) shows a strong correlation with the force, indicating that a significant part of the shear observed with DWS is due to muscle contraction. The evolution of the DWS decay time shows quantitative differences between the M. biceps brachii and the M. gastrocnemius, suggesting that DWS allows to discriminate contraction of fast- and slow-twitch muscle fibers.

Belau, Markus; Ninck, Markus; Hering, Gernot; Spinelli, Lorenzo; Contini, Davide; Torricelli, Alessandro; Gisler, Thomas

2010-09-01

317

Quantum theory of time-resolved femtosecond stimulated Raman spectroscopy: Direct versus cascade processes and application to CDCl3  

NASA Astrophysics Data System (ADS)

We present a quantum mechanical wave packet treatment of time-resolved femtosecond stimulated Raman spectroscopy (FSRS), or two-dimensional (2D) FSRS, where a vibrational coherence is initiated with an impulsive Raman pump which is subsequently probed by FSRS. It complements the recent classical treatment by Mehlenbacher et al. [J. Chem. Phys. 131, 244512 (2009)]. In this 2D-FSRS, two processes can occur concurrently but with different intensities: a direct fifth-order process taking place on one molecule, and a cascade process comprising two third-order processes on two different molecules. The cascade process comprises a parallel and a sequential cascade. The theory is applied to the 2D-FSRS of CDCl3 where calculations showed that: (a) the cascade process is stronger than the direct fifth-order process by one order of magnitude, (b) the sidebands assigned to C-Cl E and A1 bends, observed on both sides of the Stokes C-D stretch frequency, are not due to anharmonic coupling between the C-D stretch and the C-Cl bends, but are instead due to the coherent anti-Stokes Raman spectroscopy (CARS) and coherent Stokes Raman spectroscopy (CSRS) fields produced in the first step of the cascade process, (c) for each delay time between the femtosecond impulsive pump and FSRS probe pulses, the line shape of the sidebands shows an inversion symmetry about the C-D stretch frequency, and this is due to the 180? phase difference between the CARS and CSRS fields that produced the left and right sidebands, and (d) for each sideband, the line shape changes from positive Lorentzian to dispersive to negative Lorentzian, then to negative dispersive and back to positive Lorentzian with the period of the bending vibration, and it is correlated with the momentum of the wave packet prepared on the ground-state surface by the impulsive pump along the sideband normal coordinate.

Zhao, Bin; Sun, Zhigang; Lee, Soo-Y.

2011-01-01

318

Picosecond dynamics of G-protein coupled receptor activation in rhodopsin from time-resolved UV resonance Raman spectroscopy.  

PubMed

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, tryptophan modes W18, W16, and W3 exhibit decreased Raman scattering intensity. At longer pump-probe time delays of +5 and +20 ps, both tryptophan (W18, W16, W3, and W1) and tyrosine (Y1 + 2xY16a, Y7a, Y8a) peak intensities drop by up to 3%. These intensity changes are attributed to decreased hydrophobicity in the microenvironment near at least one tryptophan and one tyrosine residue that likely arise from weakened interaction with the beta-ionone ring of the chromophore following cis-to-trans isomerization. Examination of the crystal structure suggests that W265 and Y268 are responsible for these signals. These UV Raman spectral changes are nearly identical to those observed for the rhodopsin-to-Meta I transition, implying that impulsively driven protein motion by the isomerizing chromophore during the 200 fs primary transition drives key structural changes that lead to protein activation. PMID:12731857

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

2003-05-13

319

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

320

Experimental Investigation of Coronal Plasma Conditions in Direct-Drive ICF Using Time-Resolved X-Ray Spectroscopy  

NASA Astrophysics Data System (ADS)

The ne and Te of planar plasmas generated with six beams of the OMEGA laser are diagnosed with time-resolved K-shell spectroscopy of microdot tracer layers. Plastic foils (125 ?m thick) with buried microdots (Al, KCl) were irradiated with a high-intensity, 100-ps Gaussian pulse (5 × 10^14 W/cm^2) or a low-intensity (3 × 10^13 W/cm^2), 1-ns square pulse, corresponding to the initial stages of direct-drive implosions with and without a short, high-intensity picket at the beginning of the drive pulse. The microdot buried depth was varied (0.1 to 0.5 ?m) to probe the plasma at different times. Simulated spectra generated by post-processing hydrocode output (1-D LILAC, 2-D SAGE) with the FLY atomic physics code will be compared with the measured spectra. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC03-92SF19460.

Sawada, H.; Regan, S. P.; Goncharov, V. N.; Knauer, J. P.; Epstein, R.; Craxton, R. S.; Delettrez, J. A.; Marshall, F. J.; Yaakobi, B.; Meyerhofer, D. D.; Radha, P. B.; Sangster, T. C.; Seka, W.

2003-10-01

321

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

NASA Technical Reports Server (NTRS)

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.

2001-01-01

322

Reaction Mechanism of Adenylyltransferase DrrA from Legionella pneumophila Elucidated by Time-Resolved Fourier Transform Infrared Spectroscopy.  

PubMed

Modulation of the function of small GTPases that regulate vesicular trafficking is a strategy employed by several human pathogens. Legionella pneumophila infects lung macrophages and injects a plethora of different proteins into its host cell. Among these is DrrA/SidM, which catalyzes stable adenylylation of Rab1b, a regulator of endoplasmatic reticulum to Golgi trafficking, and thereby alters the function and interactions of this small GTPase. We employed time-resolved FTIR-spectroscopy to monitor the DrrA-catalyzed AMP-transfer to Tyr77 of Rab1b. A transient complex between DrrA, adenylylated Rab1b, and the pyrophosphate byproduct was resolved, allowing us to analyze the interactions at the active site. Combination of isotopic labeling and site-directed mutagenesis allowed us to derive the catalytic mechanism of DrrA from the FTIR difference spectra. DrrA shares crucial residues in the ATP-binding pocket with similar AMP-transferring enzymes such as glutamine synthetase adenylyltransferase or kanamycin nucleotidyltransferase, but provides the complete active site on a single subunit. We determined that Asp112 of DrrA functions as the catalytic base for deprotonation of Tyr77 of Rab1b to enable nucleophilic attack on the ATP. The study provides detailed understanding of the Legionella pneumophila protein DrrA and of AMP-transfer reactions in general. PMID:24950229

Gavriljuk, Konstantin; Schartner, Jonas; Itzen, Aymelt; Goody, Roger S; Gerwert, Klaus; Kötting, Carsten

2014-07-01

323

Interaction of Eu3+ with N,N,N',N'-tetraoctyl diglycolamide: A time resolved luminescence spectroscopy study  

NASA Astrophysics Data System (ADS)

N,N,N',N'-tetraoctyl diglycolamide (TODGA) has been identified as one of the promising extractants for the partitioning of minor actinides from high-level nuclear waste solutions. Solvent extraction studies have shown that stoichiometry of the extracted species of Eu3+ with TODGA depend on the nature of diluent. Time resolved luminescence spectroscopy (TRLS) has been employed to investigate the complexation of Eu3+ with TODGA under different experimental conditions. The effects of different experimental parameters such as aqueous phase acidity, nature of diluent, and TODGA concentration on the luminescence lifetime of Eu3+ ions have been investigated. The lifetime measurements of the complexed fraction of Eu3+ with TODGA suggested the absence of water molecules in the inner coordination sphere of the metal ion in different solvents. In ethanol-water (60/40%) mixture, the complexation of Eu3+ with TODGA under varying ligand-to-metal ratios suggested the formation of 1:1, 1:2, and 1:3 species, viz., Eu(TODGA)3+, Eu(TODGA)23+, and Eu(TODGA)33+, respectively. The conditional stability constants log ?1, log ?2, and log ?3 were calculated as 6.1 ± 0.5, 10.8 ± 0.7, and 14.3 ± 0.6, respectively. The nature of diluent did not influence the luminescence spectra of Eu3+ in the presence of TODGA.

Pathak, P. N.; Ansari, S. A.; Godbole, S. V.; Dhobale, A. R.; Manchanda, V. K.

2009-07-01

324

Time-resolved spectroscopy of the M15 X-ray binary AC211/X2127+119  

NASA Astrophysics Data System (ADS)

We present time-resolved spectroscopy acquired during two epochs (spaced apart by ~15 d) of the eclipsing low-mass X-ray binary AC211/X2127+119 in the globular cluster M15. The spectra show variations in the HeII?4686 emission line not only modulated on the orbital period, but also on time-scales of a few days. During the first epoch of observation, the emission line shows a strong S-wave superimposed on the average double-peaked profile. The line exhibits no evidence of rotational disturbance at the orbital phases when the eclipse is observed in the optical continuum. During the second epoch, no double-peak or S-wave component is present. The HeI absorption lines detected by other authors are not present in our spectra. A Doppler image of HeII?4686 for the first epoch supports the presence of the accretion disc. No hotspot is detected, although enhanced emission at VX= 30 km s-1, VY= 160 km s-1 is observed. We discuss the implications of this emission in the context of an X-ray heated donor star, in which case a high mass ratio and neutron star primary are implied. Finally, we speculate on the possibility of a misaligned secondary star in AC211.

Torres, M. A. P.; Callanan, P. J.; Garcia, M. R.

2003-06-01

325

Fast CCD camera for x-ray photon correlation spectroscopy and time-resolved x-ray scattering and imaging  

NASA Astrophysics Data System (ADS)

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.

2004-11-01

326

A cell-based time-resolved fluorescence assay for selection of antibody reagents for G protein-coupled receptor immunohistochemistry  

Microsoft Academic Search

A cell-based time-resolved fluorescence (celTRF) immunoassay is described for pre-screening antibodies to G protein-coupled receptor (GPCR) peptides that predicts suitability for immunohistochemistry (IHC). Rat GPCRs were expressed in Saos-2 human osteosarcoma cells via recombinant baculoviruses designed for mammalian cell expression, i.e., the transduced cells were used as a “screening lawn”. The lawn was fixed and permeabilized similarly to IHC tissue.

Jui-Lan Su; Jim Fornwald; Philip Rivers; Susan Goldsworthy; Noeleen A. Looney; Jeff Hanvey; Chris Plumpton; Janet Parham; Michael Romanos; Thomas A. Kost; Frederick C. Kull

2004-01-01

327

Profiling of dynamics in protein–lipid–water systems: a time-resolved fluorescence study of a model membrane protein with the label BADAN at specific membrane depths  

Microsoft Academic Search

Profiles of lipid-water bilayer dynamics were determined from picosecond time-resolved fluorescence spectra of membrane-embedded\\u000a BADAN-labeled M13 coat protein. For this purpose, the protein was labeled at seven key positions. This places the label at\\u000a well-defined locations from the water phase to the center of the hydrophobic acyl chain region of a phospholipid model membrane,\\u000a providing us with a nanoscale ruler

Rob B. M. Koehorst; Sergey Laptenok; Bart van Oort; Arie van Hoek; Ruud B. Spruijt; Ivo H. M. van Stokkum; Herbert van Amerongen; Marcus A. Hemminga

2010-01-01

328

Profiling of dynamics in protein-lipid-water systems: a time- resolved fluorescence study of a model membrane protein with the label BADAN at specific membrane depths  

Microsoft Academic Search

Profiles of lipid-water bilayer dynamics were determined from picosecond time-resolved fluorescence spectra of membrane-embedded BADAN-labeled M13 coat protein. For this purpose, the protein was labeled at seven key positions. This places the label at well-defined locations from the water phase to the center of the hydro- phobic acyl chain region of a phospholipid model mem- brane, providing us with a

Rob B. M. Koehorst; Sergey Laptenok; Bart van Oort; Arie van Hoek; Ruud B. Spruijt; Herbert van Amerongen; Marcus A. Hemminga

2009-01-01

329

Fluorescence Correlation Spectroscopy  

NSDL National Science Digital Library

This paper, which was previously published as part of an online biophysics textbook, provides detailed information about concepts related to fluorescence correlation spectroscopy. Sections of the document include writing on experimental realization, theoretical concepts, and applications of this technology.

Haustein, Elke; Schwille, Petra

2011-06-17

330

Multiplexed fluorescence detection in microfabricated devices with both time-resolved and spectral-discrimination capabilities using near-infrared fluorescence.  

PubMed

We examined the feasibility of using a two-color time-resolved detection scheme with microdevices for DNA sequencing applications. A home-built dual-color optical-fiber-based time-resolved near-infrared (IR) fluorescence microscope successfully coupled lifetime discrimination with color discrimination, increasing fluorescence multiplexing capabilities. The instrument was constructed by using two pulsed-diode lasers (680/780-nm excitation) and two avalanche photodiodes as the basic building blocks. The data were processed using electronics configured in a time-correlated single-photon counting format. The use of near-IR fluorescence detection greatly simplified the hardware and allowed low detection limits (< 0.1nM). We examined the separation of a single-base tract on a microchip and compared the performance with that of conventional capillary gel electrophoresis. The microchip was fabricated in glass and contained an effective separation length of 7.0 cm. It was found that, without incorporating a solid-phase reversible immobilization cleanup procedure, the calculated lifetime of the dye label on the microchip was longer and the standard deviation was larger than those of the same sample analyzed using capillary electrophoresis. Using cleanup steps, the accuracy and precision of the measurements improved. Lifetimes of four near-IR dyes (AlexaFluor680, IRD700, IRD800, and IRD40) used in this study were determined to be 986 ps (RSD=2.1%), 1551 ps (RSD=1.8%), 520 ps (RSD=3.3%), and 788 ps (RSD=4.9%), respectively, in a microchannel filled with poly(dimethylacrylamide) (POP-6) gel. The lifetimes calculated using maximum likelihood estimators provided favorable precision on the microchip, where small numbers of photocounts were collected. An M13mp18 template was sequenced on the microchip using a two-color two-lifetime format with POP-6 as the sieving polymer. Read lengths of 294 bp with calling accuracies of 90.8 and 83.7% were achieved in each color channel. The relatively low calling accuracy and the short read length resulted primarily from the short separation channel, which yielded low electrophoretic resolution. PMID:15203326

Zhu, Li; Stryjewski, Wieslaw J; Soper, Steven A

2004-07-15

331

Combined small angle X-ray scattering (SAXS) and Fourier transform infrared (FT-IR) spectroscopy in a time resolved mode using synchrotron radiation  

Microsoft Academic Search

The simultaneous time resolved study of structure development and reaction kinetics during materials processing is an experimental method which has great potential in developing a deeper understanding of the parameters which govern the formation of various material structures and their final properties. A novel combination of synchrotron radiation small angle X-ray scattering and Fourier transform infrared spectroscopy has been developed,

D. Bogg; G. E. Derbyshire; W. Bras; J. Cooke; M. J. A. Elwell; S. Naylor; A. J. Ryan

1995-01-01

332

Intra- and extra-cortical activation during a working memory task assessed by time-resolved near-infrared spectroscopy (fNIRS)  

NASA Astrophysics Data System (ADS)

We evaluated the vascular response correlated to neural activity within a working memory "n-back" task in a population of healthy volunteers by means of time-resolved near-infrared functional spectroscopy and Generalized Linear Models. Moreover, we attempted a separation of purely cortical activation from non-cerebral contribution.

Molteni, Erika; Bianchi, Anna M.; Baselli, Giuseppe; Caffini, Matteo; Contini, Davide; Spinelli, Lorenzo; Torricelli, Alessandro; Cerutti, Sergio; Cubeddu, Rinaldo

2009-07-01

333

Microsecond Time-Resolved Absorption Spectroscopy Used to Study CO Compounds of Cytochrome bd from Escherichia coli  

PubMed Central

Cytochrome bd is a tri-heme (b558, b595, d) respiratory oxygen reductase that is found in many bacteria including pathogenic species. It couples the electron transfer from quinol to O2 with generation of an electrochemical proton gradient. We examined photolysis and subsequent recombination of CO with isolated cytochrome bd from Escherichia coli in one-electron reduced (MV) and fully reduced (R) states by microsecond time-resolved absorption spectroscopy at 532-nm excitation. Both Soret and visible band regions were examined. CO photodissociation from MV enzyme possibly causes fast (?<1.5 µs) electron transfer from heme d to heme b595 in a small fraction of the protein, not reported earlier. Then the electron migrates to heme b558 (??16 µs). It returns from the b-hemes to heme d with ??180 µs. Unlike cytochrome bd in the R state, in MV enzyme the apparent contribution of absorbance changes associated with CO dissociation from heme d is small, if any. Photodissociation of CO from heme d in MV enzyme is suggested to be accompanied by the binding of an internal ligand (L) at the opposite side of the heme. CO recombines with heme d (??16 µs) yielding a transient hexacoordinate state (CO-Fe2+-L). Then the ligand slowly (??30 ms) dissociates from heme d. Recombination of CO with a reduced heme b in a fraction of the MV sample may also contribute to the 30-ms phase. In R enzyme, CO recombines to heme d (??20 µs), some heme b558 (??0.2–3 ms), and finally migrates from heme d to heme b595 (??24 ms) in ?5% of the enzyme population. Data are consistent with the recent nanosecond study of Rappaport et al. conducted on the membranes at 640-nm excitation but limited to the Soret band. The additional phases were revealed due to differences in excitation and other experimental conditions.

Siletsky, Sergey A.; Zaspa, Andrey A.; Poole, Robert K.; Borisov, Vitaliy B.

2014-01-01

334

Ultrafast excited-state dynamics in photochromic N-salicylideneaniline studied by femtosecond time-resolved REMPI spectroscopy  

NASA Astrophysics Data System (ADS)

Ultrafast processes in photoexcited N-salicylideneaniline have been investigated with femtosecond time-resolved resonance-enhanced multiphoton ionization spectroscopy. The ion signals via the S1(n,?*) state of the enol form as well as the proton-transferred cis-keto form emerge within a few hundred femtoseconds after photoexcitation to the first S1(?,?*) state of the enol form. This reveals that two ultrafast processes, excited-state intramolecular proton transfer (ESIPT) reaction and an internal conversion (IC) to the S1(n,?*) state, occur on a time scale less than a few hundred femtoseconds from the S1(?,?*) state of the enol form. The rise time of the transient corresponding to the production of the proton-transferred cis-keto form is within 750 fs when near the red edge of the absorption is excited, indicating that the ESIPT reaction occurs within 750 fs. The decay time of the S1(?,?*) state of the cis-keto form is 8.9 ps by exciting the enol form at 370 nm, but it dramatically decreases to be 1.5-1.6 ps for the excitation at 365-320 nm. The decrease in the decay time has been attributed to the opening of an efficient nonradiative channel; an IC from S1(?,?*) to S1(n,?*) of the cis-keto form promotes the production of the trans-keto form as the final photochromic products. The two IC processes may provide opposite effect on the quantum yield of photochromic products: IC in the enol form may substantially reduce the quantum yield, but IC in the cis-keto form increase it.

Okabe, Chie; Nakabayashi, Takakazu; Inokuchi, Yoshiya; Nishi, Nobuyuki; Sekiya, Hiroshi

2004-11-01

335

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

2012-07-01

336

Time-resolved optical emission spectroscopy on three-dimensionally integrated micro solution plasma in He/H2O mixture  

NASA Astrophysics Data System (ADS)

We have performed time-averaged and time-resolved optical emission spectroscopy (OES) on three-dimensionally integrated micro solution plasma (3D IMSP) in He/H2O mixture. The results of time-resolved OES on 3D IMSP in He/H2O mixture have shown that duration of the optical emission of OH(A2?+ ? X2? around 309 nm) is shorter than that in Ar/H2O mixture. Possible causes of this difference are discussed by means of difference in the energy of metastable states of Ar and He.

Himeno, Y.; Ogura, Y.; Shirafuji, T.

2014-06-01

337

Observation of ultrafast NH3 (Ã) state relaxation dynamics using a combination of time-resolved photoelectron spectroscopy and photoproduct detection.  

PubMed

The ultrafast excited state relaxation of ammonia is investigated by resonantly exciting specific vibrational modes of the electronically excited NH(3) (Ã) state using three complementary femtosecond (fs) pump-probe techniques: time-resolved photoelectron, ion-yield and photofragment translational spectroscopy. Ammonia can be seen as a prototypical system for studying non-adiabatic dynamics and therefore offers a benchmark species for demonstrating the advantages of combining the aforementioned techniques to probe excited state dynamics, whilst simultaneously illuminating new aspects of ammonia's photochemistry. Time-resolved photoelectron spectroscopy (TRPES) provides direct spectroscopic evidence of ?* mediated relaxation of the NH(3) (Ã) state which manifests itself as coupling of the umbrella (?(2)) and symmetric N-H stretch (?(1)) modes in the photoelectron spectra. Time-resolved ion yield (TRIY) and time-resolved photofragment translation spectroscopy (TRPTS) grant a measure of the dissociation dynamics through analysis of the H and NH(2) photodissociation co-fragments. Initial vibrational level dependent TRIY measurements reveal photoproduct formation times of between 190 and 230 fs. Measurement of H-atom photoproduct kinetic energies enables investigation into the competition between adiabatic and non-adiabatic dissociation channels at the NH(3) (Ã)/NH(3) (X?) conical intersection and has shown that upon non-adiabatic dissociation into NH(2) (X?) + H, the NH(2) (X[combining tilde]) fragment is predominantly generated with significant fractions of internal vibrational energy. PMID:22499282

Evans, Nicholas L; Yu, Hui; Roberts, Gareth M; Stavros, Vasilios G; Ullrich, Susanne

2012-08-14

338

Flash lamp-excited time-resolved fluorescence microscope suppresses autofluorescence in water concentrates to deliver an 11-fold increase in signal-to-noise ratio.  

PubMed

The ubiquity of naturally fluorescing components (autofluorophores) encountered in most biological samples hinders the detection and identification of labeled targets through fluorescence-based techniques. Time-resolved fluorescence (TRF) is a technique by which the effects of autofluorescence are reduced by using specific fluorescent labels with long fluorescence lifetimes (compared with autofluorophores) in conjunction with time-gated detection. A time-resolved fluorescence microscope (TRFM) is described that is based on a standard epifluorescence microscope modified by the addition of a pulsed excitation source and an image-intensified time-gateable CCD camera. The choice of pulsed excitation source for TRFM has a large impact on the price and performance of the instrument. A flash lamp with rapid discharge characteristics was selected for our instrument because of the high spectral energy in the UV region and short pulse length. However, the flash output decayed with an approximate lifetime of 18 micros and the TRFM required a long-lived lanthanide chelate label to ensure that probe fluorescence was 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 waterborne parasite Giardia lamblia. For a 600-nm bandpass filter set and a gate delay of 60 micros, the TRFM provided an 11.3-fold improvement in the signal-to-noise ratio (S/N) of labeled Giardia over background. A smaller gain in an SNR of 9.69-fold was achieved with a 420-nm longpass filter set; however, the final contrast ratio between labeled cyst and background was higher (11.3 versus 8.5). Despite the decay characteristics of the light pulse, flash lamps have many practical advantages compared with optical chopper wheels and modulated lasers for applications in TRFM. PMID:15250759

Connally, Russell; Veal, Duncan; Piper, James

2004-01-01

339

Time-resolved Fourier transform infrared spectroscopy of the polarizable proton continua and the proton pump mechanism of bacteriorhodopsin.  

PubMed Central

Nanosecond-to-microsecond time-resolved Fourier transform infrared (FTIR) spectroscopy in the 3000-1000-cm(-1) region has been used to examine the polarizable proton continua observed in bacteriorhodopsin (bR) during its photocycle. The difference in the transient FTIR spectra in the time domain between 20 ns and 1 ms shows a broad absorption continuum band in the 2100-1800-cm(-1) region, a bleach continuum band in the 2500-2150-cm(-1) region, and a bleach continuum band above 2700 cm(-1). According to Zundel (G., J. Mol. Struct. 322:33-42), these continua appear in systems capable of forming polarizable hydrogen bonds. The formation of a bleach continuum suggests the presence of a polarizable proton in the ground state that changes during the photocycle. The appearance of a transient absorption continuum suggests a change in the polarizable proton or the appearance of new ones. It is found that each continuum has a rise time of less than 80 ns and a decay time component of approximately 300 micros. In addition, it is found that the absorption continuum in the 2100-1800-cm(-1) region has a slow rise component of 190 ns and a fast decay component of approximately 60 micros. Using these results and those of the recent x-ray structural studies of bR(570) and M(412) (H. Luecke, B. Schobert, H.T. Richter, J.-P. Cartailler, and J. K., Science 286:255-260), together with the already known spectroscopic properties of the different intermediates in the photocycle, the possible origins of the polarizable protons giving rise to these continua during the bR photocycle are proposed. Models of the proton pump are discussed in terms of the changes in these polarizable protons and the hydrogen-bonded chains and in terms of previously known results such as the simultaneous deprotonation of the protonated Schiff base (PSB) and Tyr185 and the disappearance of water molecules in the proton release channel during the proton pump process.

Wang, J; El-Sayed, M A

2001-01-01

340

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

341

In-situ analysis of fruit anthocyanins by means of total internal reflectance, continuous wave and time-resolved spectroscopy  

NASA Astrophysics Data System (ADS)

In sweet cherry (Prunus avium), the red pigmentation is correlated with the fruit maturity stage and can be measured by non-invasive spectroscopy. In the present study, the influence of varying fruit scattering coefficients on the fruit remittance spectrum (cw) were corrected with the effective pathlength and refractive index in the fruit tissue obtained with distribution of time-of-flight (DTOF) readings and total internal reflection fluorescence (TIRF) analysis, respectively. The approach was validated on fruits providing variation in the scattering coefficient outside the calibration sample set. In the validation, the measuring uncertainty when non-invasively analyzing fruits with cw method in comparison with combined application of cw, DTOF, and TIRF measurements showed an increase in r2 up to 22.7 % with, however, high errors in all approaches.

Zude, Manuela; Spinelli, Lorenzo; Dosche, Carsten; Torricelli, Alessandro

2009-08-01

342

Multiemission wavelength picosecond time-resolved fluorescence decay data obtained on the millisecond time scale: application to protein--DNA interactions and protein-folding reactions  

Microsoft Academic Search

One of the major aspects of fluorescence spectroscopy which differentiates this technique from many other spectroscopic approaches is the inherent multidimensional nature of the data. For instance, the basic pulsed-laser fluorescence data set is characterized by fluorescence versus: emission wavelength, polarization state (parallel and perpendicular intensities), time of emission (picoseconds to nanoseconds), and time of biological reaction (milliseconds to minutes).

Joseph M. Beechem

1992-01-01

343

Non-invasive measurement of blood glucose level by time-resolved transmission spectroscopy: A feasibility study  

NASA Astrophysics Data System (ADS)

An optical spectroscopic method is investigated theoretically for in vivo measurement of blood glucose concentration. This method is based on dynamic dual wavelength (610 nm and 810 nm) time-resolved measurements under a condition of artificial blood flow kinetics in a human finger. The influence of glucose concentration on absorption and reduced scattering coefficients of the whole blood is simulated using the T-matrix method. The scattering centers, RBC aggregation, under the artificial — kinetics condition are modeled as spheroid. The modified parametric slopes were derived from the Laplace transformed data of the time-resolved transmittance. The results show that an appropriate selection of the Laplace parameter can lead to enhanced sensitivity for glucose measurement.

Sun, Meixiu; Chen, Nanguang

2012-03-01

344

Conformation Transition in Silk Protein Films Monitored by Time-Resolved Fourier Transform Infrared Spectroscopy:  Effect of Potassium Ions on Nephila Spidroin Films †  

Microsoft Academic Search

We used time-resolved Fourier transform infrared spectroscopy (FTIR) to follow a conformation transition in Nephila spidroin film from random coil and\\/or helical structures to ‚-sheet induced by the addition of KCl from 0.01 to 1.0 mol\\/L in D2O. Time series difference spectra showed parallel increases in absorption at 1620 and 1691 cm-1, indicating formation of ‚-sheet, together with a coincident

Xin Chen; David P. Knight; Zhengzhong Shao; Fritz Vollrath

2002-01-01

345

Investigation of Cu-doped Li2B4O7 single crystals by electron paramagnetic resonance and time-resolved optical spectroscopy  

Microsoft Academic Search

A low-temperature study of the thermoluminescent dosimeter material, lithium tetraborate (Li2B4O7) doped by Cu, has been carried out by the methods of electron paramagnetic resonance (EPR) and time-resolved polarization spectroscopy using 4-20 eV synchrotron radiation and 1 µs Xe flash lamp pulses in the region 3-6 eV. The observed EPR spectra of an unpaired hole with strong d-character and characteristic

G. Corradi; V. Nagirnyi; A. Kotlov; A. Watterich; M. Kirm; K. Polgár; A. Hofstaetter; M. Meyer

2008-01-01

346

Time-resolved infrared diode laser spectroscopy of the ? 1 (C–O stretch) band of the CoCO radical  

Microsoft Academic Search

Infrared spectrum of the cobalt carbonyl radical CoCO produced by the 193nm excimer laser photolysis of cobalt tricarbonyl nitrosyl Co(CO)3NO was observed by time-resolved diode laser spectroscopy. More than 600 lines were identified as belonging to the ?1 (C–O stretch) fundamental band, consisting of the ?=5\\/2 and 3\\/2 subbands, and the associated hot bands 112, 101211, 101311, and 101222. The

Seiki Ikeda; Toshihide Hikida; Takehiko Tanaka; Keiichi Tanaka

2008-01-01

347

Time resolved luminescence spectroscopy of alkaline earth oxides after pulsed electron beam irradiation. II. Spectra and thresholds of MgO  

Microsoft Academic Search

Time-resolved luminescence spectroscopy has been used to study the emissions occurring in MgO in the time range 100 ns to 100 ..mu..s after irradiation with nanosecond duration pulses of electrons of energy between 0.2 and 3.0 MeV. An emission at approx.380 nm with a threshold energy of 0.28 +- 0.01 MeV is attributed to processes resulting from the displacement of

Janice L. Grant; Ronald Cooper; Phillip Zeglinski; John F. Boas

1989-01-01

348

Time resolved luminescence spectroscopy of alkaline earth oxides after pulsed electron beam irradiation. II. Spectra and thresholds of MgO  

Microsoft Academic Search

Time-resolved luminescence spectroscopy has been used to study the emissions occurring in MgO in the time range 100 ns to 100 ?s after irradiation with nanosecond duration pulses of electrons of energy between 0.2 and 3.0 MeV. An emission at ?380 nm with a threshold energy of 0.28±0.01 MeV is attributed to processes resulting from the displacement of oxygen anions

Janice L. Grant; Ronald Cooper; Phillip Zeglinski; John F. Boas

1989-01-01

349

Time-resolved emission spectroscopy in laser-generated argon plasmas—determination of Stark broadening parameters  

Microsoft Academic Search

We have investigated time-resolved emission spectra of neutral argon lines in a pulsed laser-generated argon plasma source at atmospheric pressure. Depending on time after spark ignition, electronic excitation tempera- tures between roughly 5600 and 9600 K are observed. Electron density values between 0.6 and 2:3×1016 cm?3 are determined from Griem's theory of Stark-broadened line shapes as applied to the 703:025

L. Cadwella

350

Fluorescence Spectroscopy of Neoplastic and Non-Neoplastic Tissues  

PubMed Central

Abstract Fast and non-invasive, diagnostic techniques based on fluorescence spectroscopy have the potential to link the biochemical and morphologic properties of tissues to individual patient care. One of the most widely explored applications of fluorescence spectroscopy is the detection of endoscopically invisible, early neoplastic growth in epithelial tissue sites. Currently, there are no effective diagnostic techniques for these early tissue transformations. If fluorescence spectroscopy can be applied successfully as a diagnostic technique in this clinical context, it may increase the potential for curative treatment, and thus, reduce complications and health care costs. Steady-state, fluorescence measurements from small tissue regions as well as relatively large tissue fields have been performed. To a much lesser extent, time-resolved, fluorescence measurements have also been explored for tissue characterization. Furthermore, sources of both intrinsic (endogenous fluorophores) and extrinsic fluorescence (exogenous fluorophores) have been considered. The goal of the current report is to provide a comprehensive review on steady-state and time-resolved, fluorescence measurements of neoplastic and non-neoplastic, biologic systems of varying degrees of complexity. First, the principles and methodology of fluorescence spectroscopy are discussed. Next, the endogenous fluorescence properties of cells, frozen tissue sections and excised and intact bulk tissues are presented; fluorescence measurements from both animal and human tissue models are discussed. This is concluded with future perspectives.

Ramanujam, Nirmala

2000-01-01

351

Picosecond time-resolved fluorescence of ribonuclease T1. A pH and substrate analogue binding study.  

PubMed Central

The tryptophyl fluorescence of ribonuclease T1 decays monoexponentially at pH 5.5, tau = 4.04 ns but on increasing pH, a second short-lived component of 1.5 ns appears with a midpoint between pH 6.5 and 7.0. Both components have the same fluorescence spectrum. Acrylamide quenches both fluorescence components, and the short-lived component is quenched fivefold faster than the predominant long component. Binding of the substrate analogue 2'-guanylic acid at pH 5.5 quenches the fluorescence by 20% and introduces a second decay component, tau = 1.16 ns. Acrylamide quenches both tryptophyl decay components, with similar quenching rates. The fluorescence anisotropy decay of ribonuclease T1 was consistent with a molecule the size of ribonuclease T1 surrounded by a single layer of water at pH 7.4, even though the anisotropy decay at pH 5.5 deviated from Stokes-Einstein behavior. The fluorescence data were interpreted with a model where the tryptophyl residue exists in two conformations, remaining in a hydrophobic pocket. The acrylamide quenching is interpreted with electron transfer theory and suggests that one conformer has the nearest atom approximately 3 A from the protein surface, and the other, approximately 2 A.

Chen, L X; Longworth, J W; Fleming, G R

1987-01-01

352

Time-resolved spectroscopy of 5d-4f transitions in Pr3+ doped alkali-earth fluorides  

Microsoft Academic Search

We measured time-resolved spectra and emission decay times under pulsed X-ray and synchrotron excitation in alkali-earth fluorides doped with Pr3+ ions. Two fast decay components were found in the emission spectra of BaF2-Pr3+ and SrF2-Pr3+ . These were 4 ns and 21 ns in BaF2-Pr3+ and 8 and 24 ns in SrF2-Pr3+. The intensity of the faster components 4 ns

R. Shendrik; E. Radzhabov; V. Nagirnyi

2010-01-01

353

Time-resolved in situ investigations of reactive sputtering processes by grazing incidence X-ray absorption spectroscopy  

NASA Astrophysics Data System (ADS)

We have applied the time-resolved grazing incidence X-ray absorption fine structure technique to study in situ the atomic short range order and the electronic structure of reactively sputter deposited thin films. Results obtained during the reactive deposition of amorphous Ta-pentoxide thin films deposited in oxygen containing atmospheres will be presented. A new calculation scheme for a detailed reflection mode EXAFS data analysis giving bond distances, coordination numbers and Debye-Waller factors is presented. The atomic short range structure of the amorphous Ta 2O 5 thin films is compared to that of crystalline ?-Ta 2O 5.

Lützenkirchen-Hecht, Dirk; Frahm, Ronald

2006-09-01

354

A high-throughput time-resolved mini-silicon photomultiplier with embedded fluorescence lifetime estimation in 0.13 ?m CMOS.  

PubMed

We describe a miniaturized, high-throughput, time-resolved fluorescence lifetime sensor implemented in a 0.13 m CMOS process, combining single photon detection, multiple channel timing and embedded pre-processing of fluorescence lifetime estimations on a single device. Detection is achieved using an array of single photon avalanche diodes (SPADs) arranged in a digital silicon photomultiplier (SiPM) architecture with 400 ps output pulses and a 10% fill-factor. An array of time-to-digital converters (TDCs) with ?50 ps resolution records up to 8 photon events during each excitation period. Data from the TDC array is then processed using a centre-of-mass method (CMM) pre-calculation to produce fluorescence lifetime estimations in real-time. The sensor is believed to be the first reported implementation of embedded fluorescence lifetime estimation. The system is demonstrated in a practical laboratory environment with measurements of a variety of fluorescent dyes with different single exponential lifetimes, successfully showing the sensor's ability to overcome the classic pile-up limitation of time-correlated single photon counting (TCSPC) by over an order of magnitude. PMID:23853257

Tyndall, David; Rae, Bruce R; Li, David Day-Uei; Arlt, Jochen; Johnston, Abigail; Richardson, Justin A; Henderson, Robert K

2012-12-01

355

Dual probe solubilisation in two distinct regions of pure and mixed micelles: a pico-second time resolved fluorescence study  

Microsoft Academic Search

Photophysical parameters of a newly synthesised fluorescence probe, 2-[3-(N-methyl-N-phenyl amino)-2-propenylidene] indanone, have been studied in three different micellar media formed by the surfactants sodium dodecyl sulphate (SDS), cetyl trimethyl ammonium bromide (CTAB) and triton X-100 (TX100) and their binary mixtures (SDS–TX100, CTAB–TX100). Our study indicates that the probe molecules are distributed between the core and Stern\\/palisade layer of the micelle.

Mrinmoy Shannigrahi; Sanjib Bagchi

2004-01-01

356

Excited states of C{sub 70} and the intersystem crossing process studied by picosecond time-resolved spectroscopy in the visible and near-IR region  

SciTech Connect

The photophysical properties of C{sub 70} excited states were investigated by some time-resolved spectroscopic techniques. The absorption bands of singlet excited state ({sup 1}C{sub 70}{sup *}) and triplet excited state ({sup 3}C{sub 70}{sup *}) in the visible region were observed by time-resolved absorption spectroscopy using a streak camera. The intersystem crossing rate constant k{sub isc} from {sup 1}C{sub 70}{sup *} to {sup 3}C{sub 70}{sup *} was determined to be 1.25 x 10{sup 9} s{sup -1} by the analysis of the absorption-time profiles considering the overlap of the decay of {sup 1}C{sub 70}{sup *} and the growth of {sup 3}C{sub 70}{sup *}, where the curve fitting was carried out by using the decay rate constant of {sup 1}C{sub 70}{sup *} (1.61 x 10{sup 9} s{sup -1}) determined by the picosecond time-resolved emission spectroscopy. The picosecond time-resolved near-IR spectra of {sup 3}C{sub 70}{sup *} were obtained by the pump-probe technique, using a probe beam based on the broad-band optical parametric generation (OPG) of a {beta}-barium borate (BBO) crystal pumped by 532-nm laser pulse. The lowest transition band of the T-T absorption of {sup 3}C{sub 70}{sup *} was found in the near-IR region (960 nm) by the new technique. 28 refs., 10 figs.

Watanabe, Akira; Ito, Osamu [Tohoku Univ., Sendai (Japan)] [Tohoku Univ., Sendai (Japan); Watanabe, Motoyuki; Saito, Haruhisa; Koishi, Musubu [Hamamatsu Photonics K.K. (Japan)] [Hamamatsu Photonics K.K. (Japan)

1996-06-20

357

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

358

Critical evaluation of the two-state model describing the equilibrium unfolding of the PI3K SH3 domain by time-resolved fluorescence resonance energy transfer.  

PubMed

It appears that equilibrium unfolding transitions of many small proteins can be described as two-state transitions, because the probes commonly used to measure such transitions cannot detect the underlying heterogeneity inherent in protein folding and unfolding reactions. Time-resolved fluorescence or Forster resonance energy transfer (TRFRET) measurements have the potential to uncover such heterogeneity and to test the cooperativity of protein folding reactions. Here, TRFRET measurements have been used to study the equilibrium unfolding of the SH3 domain of PI3 kinase. The single tryptophan residue (W53) was used as the FRET donor, and a covalently attached thionitrobenzoate moiety at either of two sites (C17 and C70) was used as the FRET acceptor. The individual lifetime and amplitude components estimated from fitting the fluorescence decay kinetics to the sum of three or four exponentials were determined over a range of denaturant concentrations. The equilibrium unfolding transitions reported by these components were found to be noncoincident, suggesting the presence of multiple conformations in equilibrium during the course of unfolding. Fluorescence lifetime distributions were also generated by the model-free maximum entropy method of analysis. Different segments of the protein were found to show differences in the expansion of the native state at low denaturant concentrations, suggestive of gradual structural transitions. The unfolded protein was found to swell at increasingly high denaturant concentrations. The evolution of the fluorescence lifetime distributions with increasing denaturant concentration was also found to be incompatible with a two-state equilibrium unfolding model. PMID:24325755

Kishore, Megha; Krishnamoorthy, G; Udgaonkar, Jayant B

2013-12-31

359

Immunosuppressor binding to the immunophilin FKBP59 affects the local structural dynamics of a surface beta-strand: time-resolved fluorescence study.  

PubMed

The interaction of the immunophilin domain of FKBP59 (FKBP59-I) with immunosuppressant drugs was investigated by steady-state and time-resolved fluorescence of tryptophan. One of the two Trp residues present in this protein (W89), conserved in almost all immunophilins, is buried in the hydrophobic core and participates in the immunosuppressant binding. By comparison with the highly homologous protein FKBP12, containing only the buried Trp, it has been concluded that its weak fluorescence is due to an atypical H-bond interaction involving the indole nitrogen and the Phe129 benzene ring. The second Trp residue (W59) in FKBP59-I is located on the external hydrophilic side of the 50-60 beta-sheet [Craescu, C. T., Rouvière, N., Popescu, A., Cerpolini, E., Lebeau, M.-C., Baulieu, E.-E., & Mispelter, J. (1996) Biochemistry 35, 11045-11052] and is responsible for >95% of the fluorescence emission. The long lifetime of the major excited state, the large activation energy of thermal quenching, and the rotational correlation time distribution pattern suggest that its environment is not highly mobile. Binding of the immunosuppressant drugs FK506 and rapamycin leads to a approximately 60% decrease of the fluorescence intensity without any change in the fluorescence emission maximum. Time-resolved measurements show that this "quenching" is due to a conformational change which depletes the long excited-state lifetime population to the profit of a more quenched minor excited state, which becomes prominent in the complexes. This is accompanied by a strong slowing of the indole ring dynamics in the case of FK506 and by a complete immobilization in the case of rapamycin, as shown by two-dimensional (tau, theta) maximum entropy analysis of the polarized fluorescence decays. Binding of the immunosuppressant drugs therefore modifies the structure and the dynamics of the external side of the 50-60 beta-sheet in FKBP59-I, which could be relevant for the formation of ternary complexes with other protein targets. PMID:9200682

Rouviere, N; Vincent, M; Craescu, C T; Gallay, J

1997-06-17

360

Investigation of verbal and visual working memory by multi-channel time-resolved functional near-infrared spectroscopy  

NASA Astrophysics Data System (ADS)

Working memory (WM) is fundamental for a number of cognitive processes, such as comprehension, reasoning and learning. WM allows the short-term maintenance and manipulation of the information selected by attentional processes. The goal of this study was to examine by time-resolved fNIRS neural correlates of the verbal and visual WM during forward and backward digit span (DF and DB, respectively) tasks, and symbol span (SS) task. A neural dissociation was hypothesised between the maintenance and manipulation processes. In particular, a dorsolateral/ventrolateral prefrontal cortex (DLPFC/VLPFC) recruitment was expected during the DB task, whilst a lateralised involvement of Brodmann Area (BA) 10 was expected during the execution of the DF task. Thirteen subjects were monitored by a multi-channel, dual-wavelength (690 and 829 nm) time-resolved fNIRS system during 3 minutes long DF and DB tasks and 4 minutes long SS task. The participants' mean memory span was calculated for each task: DF: 6.46+/-1.05 digits; DB: 5.62+/-1.26 digits; SS: 4.69+/-1.32 symbols. No correlation was found between the span level and the heart rate data (measured by pulse oximeter). As expected, DB elicited a broad activated area, in the bilateral VLPFC and the right DLPFC, whereas a more localised activation was observed over the right hemisphere during either DF (BA 10) or SS (BA 10 and 44). The robust involvement of the DLPFC during DB, compared to DF, is compatible with previous findings and with the key role of the central executive subserving in manipulating processes.

Contini, D.; Caffini, M.; Re, R.; Zucchelli, L.; Spinelli, L.; Basso Moro, S.; Bisconti, S.; Ferrari, M.; Quaresima, V.; Cutini, S.; Torricelli, A.

2013-03-01

361

Dual probe solubilisation in two distinct regions of pure and mixed micelles: a pico-second time resolved fluorescence study  

NASA Astrophysics Data System (ADS)

Photophysical parameters of a newly synthesised fluorescence probe, 2-[3-( N-methyl- N-phenyl amino)-2-propenylidene] indanone, have been studied in three different micellar media formed by the surfactants sodium dodecyl sulphate (SDS), cetyl trimethyl ammonium bromide (CTAB) and triton X-100 (TX100) and their binary mixtures (SDS-TX100, CTAB-TX100). Our study indicates that the probe molecules are distributed between the core and Stern/ palisade layer of the micelle. The extent of distribution depends on the nature of the micelle. The radiative decay constant ( kr) for the excited S 1 state has been found to be independent of the nature of micellar media. However, the non-radiative decay constant ( knr) exhibits significant medium dependence in the order SDS > CTAB ? TX100. Non-linear variation of knr with component surfactant composition in the mixed micelle has been observed and has been explained in terms of synergistic interaction between the surfactant molecules.

Shannigrahi, Mrinmoy; Bagchi, Sanjib

2004-10-01

362

Steady-state and time-resolved fluorescence studies of reverse micelles in liquids and supercritical solvents  

SciTech Connect

The authors investigate the effects of temperature, salt concentration, and water loading on the internal dynamics of AOT Aerosol-OT, sodium bis (2-ethylhexyl sulfosuccinate) micelles in liquid heptane, using ANS-like (anilino-naphthalene sulfate) fluorescent probes. The important results from these experiments are that: (1) the molecular geometry of the probe is the predominant factor controlling partitioning even at high water loadings; (2) the photophysics of ANS is strongly dependent on the water content and temperature and corresponds to changes in local polarity and viscosity; (3) addition of electrolytes changes the dynamic fluorescence which is in turn related to the changes in internal microenvironments; and (4) a nanosecond solvent relaxation process occurs within reverse micelles. It was wondered if the continuous phase (alkane) density could be used to control the internal dynamics within a reverse micelle. To answer this question, research focused on: (1) the effects of water loading, temperature, and fluid density on solute partitioning and determination of the density effects on micellar aggregates; (2) the effects of solute structure on the distribution of probe molecules within reverse micelles; and (3) the effects of fluid density, water concentration, and temperature on the reorganizational dynamics within AOT reverse micelles. Simple thermodynamic measurements and nanosecond solvent relaxation experiments are used to account for this partitioning and water reorganization in AOT reverse micelles, respectively. Results on excited-state deprotonation reactions in AOT reverse micelles maintained in sub-critical propane, provides a useful model for density-controlled deprotonation reactions within reverse micelles. Preliminary work shows that the continuous phase density can be used to control reactions within reverse micelles formed in near- and supercritical alkanes.

Zhang, Jing.

1992-01-01

363

Direct on-strip analysis of size- and time-resolved aerosol impactor samples using laser induced fluorescence spectra excited at 263 and 351 nm.  

PubMed

We report a novel atmospheric aerosol characterization technique, in which dual wavelength UV laser induced fluorescence (LIF) spectrometry marries an eight-stage rotating drum impactor (RDI), namely UV-LIF-RDI, to achieve size- and time-resolved analysis of aerosol particles on-strip. The UV-LIF-RDI technique measured LIF spectra via direct laser beam illumination onto the particles that were impacted on a RDI strip with a spatial resolution of 1.2mm, equivalent to an averaged time resolution in the aerosol sampling of 3.6 h. Excited by a 263 nm or 351 nm laser, more than 2000 LIF spectra within a 3-week aerosol collection time period were obtained from the eight individual RDI strips that collected particles in eight different sizes ranging from 0.09 to 10 ?m in Djibouti. Based on the known fluorescence database from atmospheric aerosols in the US, the LIF spectra obtained from the Djibouti aerosol samples were found to be dominated by fluorescence clusters 2, 5, and 8 (peaked at 330, 370, and 475 nm) when excited at 263 nm and by fluorescence clusters 1, 2, 5, and 6 (peaked at 390 and 460 nm) when excited at 351 nm. Size- and time-dependent variations of the fluorescence spectra revealed some size and time evolution behavior of organic and biological aerosols from the atmosphere in Djibouti. Moreover, this analytical technique could locate the possible sources and chemical compositions contributing to these fluorescence clusters. Advantages, limitations, and future developments of this new aerosol analysis technique are also discussed. PMID:24745745

Wang, Chuji; Pan, Yong-Le; James, Deryck; Wetmore, Alan E; Redding, Brandon

2014-04-11

364

Zeptomole detection sensitivity of prostate-specific antigen in a rapid microtitre plate assay using time-resolved fluorescence.  

PubMed

Prostate-specific antigen (PSA) was detected in microtitre wells coated with a PSA-specific antibody using biotinylated antibody and streptavidin-coated, highly fluorescent 107 nm nanoparticles, which contained more than 30000 europium ions entrapped by beta-diketones. PSA was monitored directly on the surface of a well without any additional enhancement step. The sensitivity of the assay was 1.6 ng/L, corresponding to 50 fmol/L or 250 zeptomoles (250 x 10(-21) mol/L) of PSA. The high specific activity and low non-specific binding of the streptavidin-coated nanoparticles improved the sensitivity of the PSA assay 100-fold compared to the conventional europium-labelled streptavidin tracer in the same assay format. Additionally, the streptavidin-coated nanoparticle label made very rapid assays possible, due to the high affinity of the streptavidin-biotin complex and a high number of binding sites available for tracing the biotinylated antibody on the surface. Due to the inherent problems of tracing analyte with a complex of biotinylated antibody and streptavidin-coated nanoparticles, the streptavidin-coated nanoparticles reacting with the surface-captured analyte and biotinylated antibody was favoured and factors influencing this are discussed. This universal labelling technology can be applied to detect any biotinylated molecule, either in solution or on a solid phase, in order to improve detection sensitivities in many areas of biochemical analysis, such as cyto- and histochemistry, multianalyte DNA-chip assays and single-particle assays. PMID:11114110

Härmä, H; Soukka, T; Lönnberg, S; Paukkunen, J; Tarkkinen, P; Lövgren, T

2000-01-01

365

Tracking Local Conformational Changes of Ribonuclease A Using Picosecond Time-Resolved Fluorescence of the Six Tyrosine Residues  

PubMed Central

The six tyrosine residues of ribonuclease A (RNase A) are used as individual intrinsic probes for tracking local conformational changes during unfolding. The fluorescence decays of RNase A are well described by sums of three exponentials with decay times (?1 = 1.7 ns, ?2 = 180 ps, and ?3 = 30 ps) and preexponential coefficients (A1 = 1, A2 = 1, and A3 = 4) at pH 7, 25°C. The decay times are controlled by photo-induced electron transfer from individual tyrosine residues to the nearest disulphide (–SS–), bridge, which is distance (R) dependent. We assign ?1 to Tyr-76 (R = 12.8 Å), ?2 to Tyr-115 (R = 6.9 Å), and ?3 to Tyr-25, Tyr-73, Tyr-92, and Tyr-97 (all four at R = 5.5 ± 0.3 Å) at 23°C. On the basis of this assignment, the results show that, upon thermal or chemical unfolding only Tyr-25, Tyr-92, and Tyr-76 undergo significant displacement from their nearest –SS– bridge. Despite reporting on different regions of the protein, the concordance between the transition temperatures, Tm, obtained from Tyr-76 (Tm = 59.2°C) and Tyr-25 and Tyr-92 (Tm = 58.2°C) suggests a single unfolding event in this temperature range that affects all these regions similarly.

Noronha, Melinda; Lima, Joao C.; Paci, Emanuele; Santos, Helena; Macanita, Antonio L.

2007-01-01

366

Direct observation of back energy transfer in blue phosphorescent materials for organic light emitting diodes by time-resolved optical waveguide spectroscopy  

NASA Astrophysics Data System (ADS)

We demonstrate a high-sensitive transient absorption technique for detection of excited states in an organic thin film by time-resolved optical waveguide spectroscopy. By using a laser beam as a probe light, we detect small change in the transient absorbance which is equivalent to 10-7 absorbance unit in a conventional method. This technique was applied to organic thin films of blue phosphorescent materials for organic light emitting diodes. We directly observed the back energy transfer from emitting guest molecules to conductive host molecules.

Hirayama, H.; Sugawara, Y.; Miyashita, Y.; Mitsuishi, M.; Miyashita, T.

2013-02-01

367

Time-resolved surface-enhanced IR-absorption spectroscopy of direct electron transfer to cytochrome c oxidase from R. sphaeroides.  

PubMed

Time-resolved surface-enhanced IR-absorption spectroscopy triggered by electrochemical modulation has been performed on cytochrome c oxidase from Rhodobacter sphaeroides. Single bands isolated from a broad band in the amide I region using phase-sensitive detection were attributed to different redox centers. Their absorbances changing on the millisecond timescale could be fitted to a model based on protonation-dependent chemical reaction kinetics established previously. Substantial conformational changes of secondary structures coupled to redox transitions were revealed. PMID:24359742

Schwaighofer, Andreas; Steininger, Christoph; Hildenbrandt, David M; Srajer, Johannes; Nowak, Christoph; Knoll, Wolfgang; Naumann, Renate L C

2013-12-17

368

Direct observation of back energy transfer in blue phosphorescent materials for organic light emitting diodes by time-resolved optical waveguide spectroscopy  

PubMed Central

We demonstrate a high-sensitive transient absorption technique for detection of excited states in an organic thin film by time-resolved optical waveguide spectroscopy. By using a laser beam as a probe light, we detect small change in the transient absorbance which is equivalent to 10?7 absorbance unit in a conventional method. This technique was applied to organic thin films of blue phosphorescent materials for organic light emitting diodes. We directly observed the back energy transfer from emitting guest molecules to conductive host molecules.

Hirayama, H.; Sugawara, Y.; Miyashita, Y.; Mitsuishi, M.; Miyashita, T.

2013-01-01

369

Time-Resolved IR-Absorption Spectroscopy of Hot-Electron Dynamics in Satellite and Upper Conduction Bands in GaP  

NASA Technical Reports Server (NTRS)

The relaxation dynamics of hot electrons in the X6 and X7 satellite and upper conduction bands in GaP was directly measured by femtosecond UV-pump-IR-probe absorption spectroscopy. From a fit to the induced IR-absorption spectra the dominant scattering mechanism giving rise to the absorption at early delay times was determined to be intervalley scattering of electrons out of the X7 upper conduction-band valley. For long delay times the dominant scattering mechanism is electron-hole scattering. Electron transport dynamics of the upper conduction band of GaP has been time resolved.

Cavicchia, M. A.; Alfano, R. R.

1995-01-01

370

A cGMP-dependent protein kinase assay for high throughput screening based on time-resolved fluorescence resonance energy transfer.  

PubMed

Activation of cyclic GMP-dependent protein kinase (cGK) is an important event in the regulation of blood pressure and platelet function. Upstream signals are the generation of nitric oxide (NO) by NO synthases and the subsequent rise in cyclic GMP levels mediated by NO-dependent guanylyl cyclases (GCs). The identification of new cGK activators by high throughput screening (HTS) may lead to the development of a novel class of therapeutics for the treatment of cardiovascular diseases. Therefore, a homogeneous, nonradioactive assay for cGK activity was developed using a biotinylated peptide derived from vasodilator-stimulated phosphoprotein (VASP), a well-characterized natural cGK substrate. The phosphorylated peptide could be detected by a VASP-specific monoclonal phosphoserine antibody and a fluorescent detection system consisting of a europium-labeled secondary antibody and allophycocyanin (APC)-labeled streptavidin. Fluorescence resonance energy transfer (FRET) from europium to APC was detected in a time-resolved fashion (TR-FRET). Activation and inhibition constants for known substances determined by this new fluorescence-based assay correlated well with published results obtained by conventional radioactive cGK activity assays. The assay proved to be sensitive, robust, highly specific for cGK, and suitable for HTS in 96- and 384-well formats. This assay is applicable to purified enzymes as well as to complex samples such as human platelet extracts. PMID:11689125

Bader, B; Butt, E; Palmetshofer, A; Walter, U; Jarchau, T; Drueckes, P

2001-08-01

371

A space- and time-resolved single photon counting detector for fluorescence microscopy and spectroscopy  

Microsoft Academic Search

We have recently developed a wide-field photon-counting detector having high-temporal and high-spatial resolutions and capable of high-throughput (the H33D detector). Its design is based on a 25 mm diameter multi-alkali photocathode producing one photo electron per detected photon, which are then multiplied up to 107 times by a 3-microchannel plate stack. The resulting electron cloud is proximity focused on a

X. Michalet; O. H. W. Siegmund; J. V. Vallerga; P. Jelinsky; J. E. Millaud; S. Weiss

2006-01-01

372

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

373

Sensitive time-resolved fluorometer  

NASA Astrophysics Data System (ADS)

With the use of lanthanide trivalence ion and its chelates for marking substance, Time-resolved Fluorescence Immunoassay (TRFIA) is superior to RIA in sensitivity, speciality, stability. And it has become one of the hotspots in the field of labeled immunoassay application. In this paper, a sensitive time-resolved fluorescence immunoassay instrument made by us was presented. In the device, a pulsed Xenon lamp of flash frequency 1kHz was adopted as exciting light, and the peculiarities of long lifetime and big Stokes about lanthanide trivalence ion and its chelates was utilized for the application of time-resolved and spectra-resolved technique. Thus the influence of scattering light and short-lifetime fluorescence was removed. By testing, 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=99.9%(p=0.0001). In a word, the instrument is advanced for ultrasensitive detection of antigen and antibody, and many other aspects.

Tian, Zhen; Guo, Zhouyi

2005-02-01

374

Time-resolved plasma spectroscopy of thin foils heated by a relativistic-intensity short-pulse laser  

NASA Astrophysics Data System (ADS)

Time-resolved K-shell x-ray spectra are recorded from sub-100 nm aluminum foils irradiated by 150-fs laser pulses at relativistic intensities of I?2=2×1018 W ?m2/cm2. The thermal penetration depth is greater than the foil thickness in these targets so that uniform heating takes place at constant density before hydrodynamic motion occurs. The high-contrast, high-intensity laser pulse, broad spectral band, and short time resolution utilized in this experiment permit a simplified interpretation of the dynamical evolution of the radiating matter. The observed spectrum displays two distinct phases. At early time, ?500 fs after detecting target emission, a broad quasicontinuous spectral feature with strong satellite emission from multiply excited levels is seen. At a later time, the He-like resonance line emission is dominant. The time-integrated data is in accord with previous studies with time resolution greater than 1 ps. The early time satellite emission is shown to be a signature of an initial large area, high density, low-temperature plasma created in the foil by fast electrons accelerated by the intense radiation field in the laser spot. We conclude that, because of this early time phenomenon and contrary to previous predictions, a short, high-intensity laser pulse incident on a thin foil does not create a uniform hot and dense plasma. The heating mechanism has been studied as a function of foil thickness, laser pulse length, and intensity. In addition, the spectra are found to be in broad agreement with a hydrodynamic expansion code postprocessed by a collisional-radiative model based on superconfiguration average rates and on the unresolved transition array formalism.

Audebert, P.; Shepherd, R.; Fournier, K. B.; Peyrusse, O.; Price, D.; Lee, R. W.; Springer, P.; Gauthier, J.-C.; Klein, L.

2002-12-01

375

Time-resolved plasma spectroscopy of thin foils heated by a relativistic-intensity short-pulse laser.  

PubMed

Time-resolved K-shell x-ray spectra are recorded from sub-100 nm aluminum foils irradiated by 150-fs laser pulses at relativistic intensities of Ilambda(2)=2 x 10(18) W microm(2)/cm(2). The thermal penetration depth is greater than the foil thickness in these targets so that uniform heating takes place at constant density before hydrodynamic motion occurs. The high-contrast, high-intensity laser pulse, broad spectral band, and short time resolution utilized in this experiment permit a simplified interpretation of the dynamical evolution of the radiating matter. The observed spectrum displays two distinct phases. At early time, < or =500 fs after detecting target emission, a broad quasicontinuous spectral feature with strong satellite emission from multiply excited levels is seen. At a later time, the He-like resonance line emission is dominant. The time-integrated data is in accord with previous studies with time resolution greater than 1 ps. The early time satellite emission is shown to be a signature of an initial large area, high density, low-temperature plasma created in the foil by fast electrons accelerated by the intense radiation field in the laser spot. We conclude that, because of this early time phenomenon and contrary to previous predictions, a short, high-intensity laser pulse incident on a thin foil does not create a uniform hot and dense plasma. The heating mechanism has been studied as a function of foil thickness, laser pulse length, and intensity. In addition, the spectra are found to be in broad agreement with a hydrodynamic expansion code postprocessed by a collisional-radiative model based on superconfiguration average rates and on the unresolved transition array formalism. PMID:12513417

Audebert, P; Shepherd, R; Fournier, K B; Peyrusse, O; Price, D; Lee, R W; Springer, P; Gauthier, J-C; Klein, L

2002-12-01

376

Depth profiling for the identification of unknown substances and concealed content at remote distances using time-resolved stand-off Raman spectroscopy.  

PubMed

Time-resolved stand-off Raman spectroscopy was used to determine both the position and identity of substances relative to each other at remote distances (up to tens of meters). Spectral information of three xylene isomers, toluene, and sodium chlorate was obtained at a distance of 12 m from the setup. Pairs and triplets of these samples were placed at varying distances (10-60 cm) relative to each other. Via the photon time of flight the distance between the individual samples was determined to an accuracy of 7% (corresponding to a few cm) of the physically measured distance. Furthermore, at a distance of 40 m, time-resolved Raman depth profiling was used to detect sodium chlorate in a white plastic container that was non-transparent to the human eye. The combination of the ranging capabilities of Raman LIDAR (sample location usually determined using prior knowledge of the analyte of interest) with stand-off Raman spectroscopy (analyte detection at remote distances) provides the capability for depth profile identification of unknown substances and analysis of concealed content in distant objects. To achieve these results, a 532 nm laser with a pulse length of 4.4 ns was synchronized to an intensified charge-coupled device camera with a minimum gate width of 500 ps. For automated data analysis a multivariate curve resolution algorithm was employed. PMID:22800681

Zachhuber, Bernhard; Gasser, Christoph; Ramer, Georg; Chrysostom, Engelene t H; Lendl, Bernhard

2012-08-01

377

A time-resolved fluorescence resonance energy transfer assay suitable for high-throughput screening for inhibitors of immunoglobulin E-receptor interactions  

PubMed Central

The interaction of immunoglobulin E (IgE) antibodies with the high-affinity receptor, Fc?RI, plays a central role in initiating most allergic reactions. The IgE–receptor interaction has been targeted for treatment of allergic diseases, and many high-affinity macromolecular inhibitors have been identified. Small molecule inhibitors would offer significant advantages over current anti-IgE treatment, but no candidate compounds have been identified and fully validated. Here, we report the development of a time-resolved fluorescence resonance energy transfer (TR–FRET) assay for monitoring the IgE–receptor interaction. The TR–FRET assay measures an increase in fluorescence intensity as a donor lanthanide fluorophore is recruited into complexes of site-specific Alexa Fluor 488-labeled IgE-Fc and His-tagged Fc?RI? proteins. The assay can readily monitor classic competitive inhibitors that bind either IgE-Fc or Fc?RI? in equilibrium competition binding experiments. Furthermore, the TR–FRET assay can also be used to follow the kinetics of IgE-Fc–Fc?RI? dissociation and identify inhibitory ligands that accelerate the dissociation of preformed complexes, as demonstrated for an engineered DARPin (designed ankyrin repeat protein) inhibitor. The TR–FRET assay is suitable for high-throughput screening (HTS), as shown by performing a pilot screen of the National Institutes of Health (NIH) Clinical Collection Library in a 384-well plate format.

Kim, Beomkyu; Tarchevskaya, Svetlana S.; Eggel, Alexander; Vogel, Monique; Jardetzky, Theodore S.

2013-01-01

378

Study of the laser-induced decomposition of energetic materials at static high-pressure by time-resolved absorption spectroscopy  

NASA Astrophysics Data System (ADS)

The reactivity of laser-initiated energetic materials has been studied at high-pressure using time-resolved absorption spectroscopy in a diamond anvil cell (DAC). The results obtained for nitromethane (NM) are presented in this paper. A change in reactivity is clearly seen around 25 GPa. Below this pressure, a one-step reaction is found to occur. The decomposition products formed behind the combustion front are essentially carbon residues as shown by Raman spectroscopy. At higher pressure, a two-step mechanism is observed. The first step, which is similar to the reaction observed below 25 GPa, leads to the formation of carbonaceous products. It is followed by a slower step which leads to the formation of a transparent amorphous product. This product remains stable in the DAC after reaction.

Hébert, P.; Saint-Amans, C.

2014-05-01

379

Spatial density profile of electrons near the LaAlO3/SrTiO3 heterointerface revealed by time-resolved photoluminescence spectroscopy  

NASA Astrophysics Data System (ADS)

The depth profile of the electron density near the LaAlO3/SrTiO3 heterointerface has been studied by means of time-resolved photoluminescence (PL) spectroscopy. A broad blue PL band is observed at 2.9 eV, originating from the two-carrier radiative recombination of interface-induced electrons and photoexcited holes. The PL lifetime of LaAlO3/SrTiO3 heterointerface is dominated by the three-carrier Auger recombination of electrons and holes and is sensitive to electron density. We tuned the probing depth by changing the excitation photon energy and evaluated the carrier-density profile using the relation between the carrier density and the PL lifetime. Our non-contact probe method based on PL spectroscopy indicates that the carriers are confined within several nanometers in depth near the LaAlO3/SrTiO3 heterostructures.

Yamada, Yasuhiro; Sato, Hiroki K.; Hikita, Yasuyuki; Hwang, Harold Y.; Kanemitsu, Yoshihiko

2014-04-01

380

Concentration Measurement of Gas Embedded in Scattering Media by Employing Absorption and Time-Resolved Laser Spectroscopy  

NASA Astrophysics Data System (ADS)

Diode-laser-based absorption spectroscopy for the evaluation of embedded gas concentrations in porous materials is demonstrated in measurements of molecular oxygen dispersed throughout scattering polystyrene foam, used here as a generic test material. The mean path length of light scattered in the material is determined with the temporal characteristics of the radiation transmitted through the sample. This combined with sensitive gas-absorption measurements employing wavelength-modulation spectroscopy yields an oxygen concentration in polystyrene foam of 20.4% corresponding to a foam porosity of 98%, which is consistent with manufacturing specifications. This feasibility study opens many possibilities for quantitative measurements by using the method of gas-in-scattering-media absorption spectroscopy.

Somesfalean, Gabriel; Sjöholm, Mikael; Alnis, Janis; Klinteberg, Claes Af; Andersson-Engels, Stefan; Svanberg, Sune

2002-06-01

381

Concentration measurement of gas embedded in scattering media by employing absorption and time-resolved laser spectroscopy.  

PubMed

Diode-laser-based absorption spectroscopy for the evaluation of embedded gas concentrations in porous materials is demonstrated in measurements of molecular oxygen dispersed throughout scattering polystyrene foam, used here as a generic test material. The mean path length of light scattered in the material is determined with the temporal characteristics of the radiation transmitted through the sample. This combined with sensitive gas-absorption measurements employing wavelength-modulation spectroscopy yields an oxygen concentration in polystyrene foam of 20.4% corresponding to a foam porosity of 98%, which is consistent with manufacturing specifications. This feasibility study opens many possibilities for quantitative measurements by using the method of gas-in-scattering-media absorption spectroscopy. PMID:12078678

Somesfalean, Gabriel; Sjöholm, Mikael; Alnis, Janis; af Klinteberg, Claes; Andersson-Engels, Stefan; Svanberg, Sune

2002-06-20

382

Time-resolved x-ray photoelectron spectroscopy techniques for real-time studies of interfacial charge transfer dynamics  

SciTech Connect

X-ray based spectroscopy techniques are particularly well suited to gain access to local oxidation states and electronic dynamics in complex systems with atomic pinpoint accuracy. Traditionally, these techniques are applied in a quasi-static fashion that usually highlights the steady-state properties of a system rather than the fast dynamics that often define the system function on a molecular level. Novel x-ray spectroscopy techniques enabled by free electron lasers (FELs) and synchrotron based pump-probe schemes provide the opportunity to monitor intramolecular and interfacial charge transfer processes in real-time and with element and chemical specificity. Two complementary time-domain xray photoelectron spectroscopy techniques are presented that are applied at the Linac Coherent Light Source (LCLS) and the Advanced Light Source (ALS) to study charge transfer processes in N3 dye-sensitized ZnO semiconductor nanocrystals, which are at the heart of emerging light-harvesting technologies.

Shavorskiy, Andrey; Hertlein, Marcus; Guo Jinghua; Tyliszczak, Tolek [Advanced Light Source, Lawrence Berkeley National Laboratory (United States); Cordones, Amy; Vura-Weis, Josh [Department of Chemistry, University of California Berkeley (United States); Siefermann, Katrin; Slaughter, Daniel; Sturm, Felix; Weise, Fabian; Khurmi, Champak; Belkacem, Ali; Weber, Thorsten; Gessner, Oliver [Ultrafast X-ray Science Laboratory, Chemical Sciences Division, Lawrence Berkeley National Laboratory (United States); Bluhm, Hendrik [Chemical Sciences Division, Lawrence Berkeley National Laboratory (United States); Strader, Matthew; Cho, Hana; Coslovich, Giacomo; Kaindl, Robert A. [Materials Sciences Division, Lawrence Berkeley National Laboratory (United States); Lin, Ming-Fu [Department of Chemistry, University of California Berkeley (United States); Ultrafast X-ray Science Laboratory, Chemical Sciences Division, Lawrence Berkeley National Laboratory (United States); and others

2013-04-19

383

Time-resolved spectrofluorometer for clinical tissue characterization during endoscopy  

NASA Astrophysics Data System (ADS)

Time-resolved fluorescence spectroscopy has the potential to provide more information for the detection of early cancer than continuous wave spectroscopy. A new optical fiber-based spectrofluorometer for time-resolved fluorescence spectroscopy of biological tissue during clinical endoscopy is presented. The apparatus is based on a nitrogen laser pumping a dye laser as excitation source and a streak camera coupled with a spectrograph as time-resolved spectrometer. The excitation and fluorescence light is carried by an optical fiber to the tissue under investigation and back to the detector, respectively. This optical fiber can be inserted into the biopsy channel of a conventional endoscope. Hence, the apparatus can be used to perform in situ tissue characterization during endoscopy. The instrument enables the measurement of the decays of entire fluorescence spectra within 15 s with a dynamic range of the spectro-temporal images of up to three orders of magnitude. Luminescence lifetimes from the sub ns up to the ms range can be measured. Spectral and temporal resolution, sensitivity, and dynamic range of the instrumentation were determined. The accuracy of the apparatus was checked by the measurement of the fluorescence lifetimes of various fluorophores with known lifetimes. For the first time, two-dimensional time-resolved spectra with sub-ns temporal resolution of tissue fluorescence of the human bladder, the bronchi, and the esophagus taken during endoscopy are presented as a demonstration of performance of the instrumentation. The excitation wavelengths were 337 nm in the case of the bladder and the esophagus and 480 nm in the case of the bronchi. Lifetime contrasts between normal and neoplastic tissue were found in all three organs. The spectral analysis of the fluorescence decays showed that the fluorescence between 370 and 490 nm, excited at 337 nm, consisted in several overlapping spectra. In the case of the esophagus, the contrast between normal and tumoral tissue was inverse in two different spectral bands proving the importance of the choice of the appropriate spectral range for time-resolved autofluorescence measurements for an optimal contrast. The in vivo fluorescence decay of the photosensitizers 5-aminolevulinic acid hexylester hydrochloride-induced protoporphyrin IX was measured in the human bladder and found to be mono-exponential with a lifetime of 15.9 (+/-1.2) ns. An in vivo fluorescence lifetime of 8.5 (+/-0.8) ns was found in the case of the photosensitizer 5, 10, 15, 20-tetra(m-hydroxyphenyl)chlorin (mTHPC) in the esophagus.

Glanzmann, Thomas; Ballini, Jean-Pierre; van den Bergh, Hubert; Wagnières, Georges

1999-10-01

384

Time-Resolved and Backward-Wave Oscillator Submillimetre Spectroscopy of Some Ferroelectric Ceramics and Thin Films  

Microsoft Academic Search

Backward-wave oscillator spectroscopy was applied to the transmission measurements of the complex dielectric spectra in the frequency range 8-33 cm m 1 at temperatures from 10 K to 300 K. The samples under investigation were relaxor PLZT 9.5\\/65\\/35 ceramics, antiferroelectric PbZrO 3 ceramics and thin films of Ba x Sr 1 m x TiO 3 (x = 0; 0.1; 1)

Alexey Pashkin; Petr Kužel; Jan Petzelt; Boris Gorshunov; Martin Dressel

2002-01-01

385

Time-Resolved X-Ray Absorption Spectroscopy Data for the Study of Chemical Reaction Intermediate States  

SciTech Connect

Energy-dispersive X-ray absorption Spectroscopy is an increasingly powerful tool for the investigation of kinetic processes in chemical systems as an element-specific local structure and electronic-state probe. In this paper we present a study of the structural evolution of the inner-sphere electron transfer reaction between [IrCl6]2- and [Co(CN)5]3-. The experimental requirements necessary for the extraction of maximal structural and electronic information are discussed.

Diaz Moreno, Sofia [Diamond Light Source, Chilton, Didcot, OX11 ODE (United Kingdom); Bowron, Daniel T. [ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0QX (United Kingdom); Evans, John [School of Chemistry, University of Southampton, Southampton S017 1BJ (United Kingdom)

2007-02-02

386

Femtosecond-laser-induced Ablation of an Aluminum Target Probed by Space- and Time-resolved Soft X-ray Absorption Spectroscopy  

NASA Astrophysics Data System (ADS)

Laser ablation involves phase transitions that produce an ablation plume consisting of various states of matter, namely solid, liquid, vapor, and plasma. This plume plays an important role in the deposition of thin films [1], the formation of nanoparticles [2], and other processes. It is important to investigate this ablation plume at the atomic level not only for a basic study of laser ablation dynamics but also to provide a better understanding of such processes. Because the plume evolves spatially over time, space- and time-resolved measurements are also required. One atomic-level diagnostic method is X-ray absorption spectroscopy (XAS). This involves an element-specific probe of the local structure in a material and provides information about its electronic and atomic structure. An important advantage of this technique is that a wide variety of solid, liquid, and gaseous samples can be examined directly and nondestructively. Furthermore, we can combine this technique with an ultrafast X-ray probe generated by femtosecond-laser-induced plasma [3]-[6], and this makes time-resolved XAS suitable for the study of laser ablation processes.

Okano, Yasuaki; Oguri, Katsuya; Nishikawa, Tadashi; Nakano, Hidetoshi

387

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

388

Implementation of Time-Resolved Step-Scan Fourier Transform Infrared (FT-IR) Spectroscopy Using a kHz Repetition Rate Pump Laser  

PubMed Central

Time-resolved step-scan Fourier transform infrared (FT-IR) spectroscopy has been shown to be invaluable for studying excited-state structures and dynamics in both biological and inorganic systems. Despite the established utility of this method, technical challenges continue to limit the data quality and more wide ranging applications. A critical problem has been the low laser repetition rate and interferometer stepping rate (both are typically 10 Hz) used for data acquisition. Here we demonstrate significant improvement in the quality of time-resolved spectra through the use of a kHz repetition rate laser to achieve kHz excitation and data collection rates while stepping the spectrometer at 200 Hz. We have studied the metal-to-ligand charge transfer excited state of Ru(bipyridine)3Cl2 in deuterated acetonitrile to test and optimize high repetition rate data collection. Comparison of different interferometer stepping rates reveals an optimum rate of 200 Hz due to minimization of long-term baseline drift. With the improved collection efficiency and signal-to-noise ratio, better assignments of the MLCT excited-state bands can be made. Using optimized parameters, carbonmonoxy myoglobin in deuterated buffer is also studied by observing the infrared signatures of carbon monoxide photolysis upon excitation of the heme. We conclude from these studies that a substantial increase in performance of ss-FT-IR instrumentation is achieved by coupling commercial infrared benches with kHz repetition rate lasers.

MAGANA, DONNY; PARUL, DZMITRY; DYER, R. BRIAN; SHREVE, ANDREW P.

2011-01-01

389

Intraluminal fluorescence spectroscopy catheter with ultrasound guidance  

PubMed Central

We demonstrate the feasibility of a time-resolved fluorescence spectroscopy (TRFS) technique for intraluminal investigation of arterial vessel composition under intravascular ultrasound (IVUS) guidance. A prototype 1.8-mm (5.4 Fr) catheter combining a side-viewing optical fiber (SVOF) and an IVUS catheter was constructed and tested with in vitro vessel phantoms. The prototype catheter can locate a fluorophore in the phantom vessel wall, steer the SVOF in place, perform blood flushing under flow conditions, and acquire high-quality TRFS data using 337-nm wavelength excitation. The catheter steering capability used for the coregistration of the IVUS image plane and the SVOF beam produce a guiding precision to an arterial phantom wall site location of 0.53±0.16 mm. This new intravascular multimodal catheter enables the potential for in vivo arterial plaque composition identification using TRFS.

Stephens, Douglas N.; Park, Jesung; Sun, Yang; Papaioannou, Thanassis; Marcu, Laura

2014-01-01

390

Intraluminal fluorescence spectroscopy catheter with ultrasound guidance  

NASA Astrophysics Data System (ADS)

We demonstrate the feasibility of a time-resolved fluorescence spectroscopy (TRFS) technique for intraluminal investigation of arterial vessel composition under intravascular ultrasound (IVUS) guidance. A prototype 1.8-mm (5.4 Fr) catheter combining a side-viewing optical fiber (SVOF) and an IVUS catheter was constructed and tested with in vitro vessel phantoms. The prototype catheter can locate a fluorophore in the phantom vessel wall, steer the SVOF in place, perform blood flushing under flow conditions, and acquire high-quality TRFS data using 337-nm wavelength excitation. The catheter steering capability used for the coregistration of the IVUS image plane and the SVOF beam produce a guiding precision to an arterial phantom wall site location of 0.53+/-0.16 mm. This new intravascular multimodal catheter enables the potential for in vivo arterial plaque composition identification using TRFS.

Stephens, Douglas N.; Park, Jesung; Sun, Yang; Papaioannou, Thanassis; Marcu, Laura

2009-05-01

391

Lifetime fluorescence spectroscopy for in situ investigation of osteogenic differentiation  

NASA Astrophysics Data System (ADS)

Time-Resolved Laser-Induced Fluorescence Spectroscopy (TR-LIFS) represents a potential tool for the in-situ characterization of bioengineered tissues. In this study, we evaluate the application of TR-LIFS to non-intrusive monitoring of matrix composition during osteogenetic differentiation. Human adipose-derived stem cells, harvested from 3 patients, were induced in osteogenic media for 3, 5, and 7 weeks. Samples were subsequently collected and probed for time-resolved fluorescence emission with a pulsed nitrogen laser. Fluorescence parameters, derived from both spectral- and time-domain, were used for sample characterization. The samples were further analyzed using Western blot analysis and computer-based densitometry. A significant change in the fluorescence parameters was detected for samples beyond 3 weeks of osteogenic differentiation. The spectroscopic observations: 1) show increase of collagen I when contrasted against the time-resolved fluorescence spectra of commercially available collagens; and 2) are in agreement with Western blot analysis that demonstrated significant increase in collagen I content between 3- vs. 5-weeks and 3- vs. 7-weeks and no changes for collagens III, IV, and V. Our results suggest that TR-LIFS can be used as a non-invasive means for the detection of specific collagens in maturing connective tissues.

Marcu, Laura; Elbarbary, Amir; Zuk, Patricia; De Ugarte, Daniel A.; Benhaim, Prosper; Kurt, Hamza; Hedrick, Marc H.; Ashjian, Peter

2003-07-01

392

Subunit-Selective Interrogation of CO Recombination in Carbonmonoxy Hemoglobin by Isotope-Edited Time-resolved Resonance Raman Spectroscopy  

PubMed Central

Hemoglobin is an allosteric tetrameric protein made up of ?? hetero-dimers. The ? and ? chains are similar, but are chemically and structurally distinct. To investigate dynamical differences between the chains, we have prepared tetramers in which the chains are isotopically distinguishable, via reconstitution with 15N-heme. Ligand recombination and heme structural evolution, following HbCO dissociation, was monitored with chain selectivity by resonance Raman (RR) spectroscopy. For ? but not for ? chains, the frequency of the ?4 porphyrin breathing mode increased on the microsecond time scale. This increase is a manifestation of proximal tension in the Hb T-state, and its time course is parallel to the formation of T contacts, as determined previously by UVRR spectroscopy. Despite the localization of proximal constraint in the ? chains, geminate recombination was found to be equally probable in the two chains, with yields of 39 ± 2 %. We discuss the possibility that this equivalence is coincidental, in the sense that it arises from the evolutionary pressure for cooperativity, or that it reflects mechanical coupling across the ?? interface, evidence for which has emerged from UVRR studies of site-mutants.

Balakrishnan, Gurusamy; Zhao, Xiaojie; Podstawska, Edyta; Proniewicz, Leonard M.; Kincaid, James R.; Spiro, Thomas G.

2009-01-01

393

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

394

Identification of small molecule inhibitors of the mitotic kinase haspin by high-throughput screening using a homogeneous time-resolved fluorescence resonance energy transfer assay.  

PubMed

Haspin/Gsg2 is a kinase that phosphorylates histone H3 at Thr-3 (H3T3ph) during mitosis. Its depletion by RNA interference results in failure of chromosome alignment and a block in mitosis. Haspin, therefore, is a novel target for development of antimitotic agents. We report the development of a high-throughput time-resolved fluorescence resonance energy transfer (TR-FRET) kinase assay for haspin. Histone H3 peptide was used as a substrate, and a europium-labeled H3T3ph phosphospecific monoclonal antibody was used to detect phosphorylation. A library of 137632 small molecules was screened at K(m) concentrations of ATP and peptide to allow identification of diverse inhibitor types. Reconfirmation of hits and IC( 50) determinations were carried out with the TR-FRET assay and by a radiometric assay using recombinant histone H3 as the substrate. A preliminary assessment of specificity was made by testing inhibition of 2 unrelated kinases. EC( 50) values in cells were determined using a cell-based ELISA of H3T3ph. Five compounds were selected as leads based on potency and chemical structure considerations. These leads form the basis for the development of specific inhibitors of haspin that will have clear utility in basic research and possible use as starting points for development of antimitotic anticancer therapeutics. PMID:18978305

Patnaik, Debasis; Jun Xian; Glicksman, Marcie A; Cuny, Gregory D; Stein, Ross L; Higgins, Jonathan M G

2008-12-01

395

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

2012-07-13

396

Time-resolved transconductance spectroscopy on self-assembled quantum dots: Spectral evolution from single- into many-particle states  

NASA Astrophysics Data System (ADS)

Using transconductance spectroscopy we study the tunneling dynamics of electrons from a two-dimensional electron gas (2DEG) into excited and ground states of a layer of self-assembled InAs quantum dots (QDs). From an initially selected nonequilibrium condition, we observe the charging dynamics of the QD states and their spectral evolution for one- and two-electron configurations. Furthermore, we measure the electron emission from the QD states into the 2DEG for the corresponding evolution of the QD-hydrogen and QD-helium spectra. The comparison with theoretically predicted energies, as well as the evaluation of the dynamics in charging and emission, allows us to separate and identify ground and excited electron configurations in the spectral evolution and discuss in detail the observed maxima in the different spectra.

Beckel, A.; Ludwig, A.; Wieck, A. D.; Lorke, A.; Geller, M.

2014-04-01

397

H-Bonding vs Non-H-Bonding in 100% Pyrene Methacrylate Comb Polymers: Self-Assembly Probed by Time-Resolved Emission Spectra and Temperature Dependent Fluorescence.  

PubMed

The differences in self-organization behavior in novel 100% pyrene labeled comb methacrylate polymers probed as a function of their varied origins of excimer formation are presented. The different structural variations in the polymers included the presence or absence of hydrogen bonding interactions in the form of urethane linkages, short or long alkyl spacer segments separating the pyrene units from the polymer backbone and linear versus kinked urethane linkage. The effect of variable concentration and temperature on the chemical shift of the NH proton of the urethane linkage was probed using (1)H NMR experiments conducted at temperatures varying from 25 to 70 °C at two different concentrations (2.5 and 25 mmol) in DMSO-d6 as solvent. The photophysical properties of the polymers in dilute DMF solutions were investigated by steady state emission, fluorescence decay studies, time-resolved emission spectra (TRES), and variable temperature emission studies. It was observed that the polymer poly(PBH) having a non-hydrogen-bondable ester linkage in the pendant chains formed an excimer completely via a static mechanism and the ground state aggregate species were not broken even at higher temperatures. The polymer poly(PIC) having a short hydrogen-bondable urethane linkage formed an excimer via a static as well as dynamic mechanism. The other hydrogen-bondable urethane methacrylate polymers having a linear linker poly(PHH) and kinked linker (PIHP) formed excimer mostly via a dynamic mechanism with a very small contribution from the static route. The TRES studies carried out for the polymers provided significant insight into the excimer formation mechanism in these polymers. The variable temperature fluorescence studies highlighted the differences in the H-bonded vs non-H-bonded polymer as a function of their excimer recovery upon cooling. PMID:24734783

Kaushlendra, K; Asha, S K

2014-05-01

398

A cell-based time-resolved fluorescence assay for selection of antibody reagents for G protein-coupled receptor immunohistochemistry.  

PubMed

A cell-based time-resolved fluorescence (celTRF) immunoassay is described for pre-screening antibodies to G protein-coupled receptor (GPCR) peptides that predicts suitability for immunohistochemistry (IHC). Rat GPCRs were expressed in Saos-2 human osteosarcoma cells via recombinant baculoviruses designed for mammalian cell expression, i.e., the transduced cells were used as a "screening lawn". The lawn was fixed and permeabilized similarly to IHC tissue. The celTRF, a dissociation-enhanced lanthanide fluorescence immunoassay (DELFIA), employed Eu-labelled goat anti-rabbit IgG. It exhibited a broad dynamic range upon which enzyme-linked immunosorbant assay (ELISA)-positive affinity-purified anti-peptide antibody reagents were examined for specificity and potency. Over 150 anti-peptide reagents to 27 GPCRs were characterized. All celTRF-positive antibodies were found to be suitable for IHC, whereas ELISA alone did not predict IHC utility. Examples are illustrated with five rabbit anti-neuropeptide FF receptor 1 (NPFF1) antibodies, where a strong correlation between celTRF potency and IHC utility was observed in both applications. In contrast, two high anti-peptide ELISA titer but celTRF-negative antibodies failed to recognize the NPFF1 receptor in IHC. The celTRF assay was performed manually and in an automated fashion, in our case, using a Biomek FX station and Sami scheduling software. The celTRF is the first in vitro automated assay that offers confident pre-selection of antibodies for IHC and the versatility to accommodate the rapid screening of large numbers of GPCRs. The celTRF is readily applicable to other protein target classes. PMID:15345311

Su, Jui-Lan; Fornwald, Jim; Rivers, Philip; Goldsworthy, Susan; Looney, Noeleen A; Hanvey, Jeff; Plumpton, Chris; Parham, Janet; Romanos, Michael; Kost, Thomas A; Kull, Frederick C

2004-08-01

399

Applications of immunomagnetic capture and time-resolved fluorescence to detect outbreak Escherichia coli O157 and Salmonella in alfalfa sprouts  

NASA Astrophysics Data System (ADS)

Commercially available alfalfa seeds were inoculated with low levels (~ 4 CFU/g) of pathogenic bacteria. The inoculated seeds were then allowed to sprout in sterile tap water at 22°C. After 48 hours, the irrigation water and sprouts were separately transferred to bovine heart infusion (BHI) media. The microbes in the BHI samples were allowed to grow for 4 hours at 37°C and 160 rpm. Specific immunomagnetic beads (IMB) were then applied to capture the E.coli O157 and/or Salmonella in the growth media. Separation and concentration of IMB-captured pathogens were achieved using magnetic separators. The captured E. coli O157:H7 and Salmonella spp were further tagged with europium (Eu) labeled anti-E. coli O157 antibodies and samarium (Sm) labeled anti-Salmonella antibodies, respectively. After washing, the lanthanide labels were extracted out from the complexes by specific chelators to form strongly fluorescent chelates. The specific time-resolved fluorescence (TRF) associated with Eu or Sm was measured to estimate the extent of capture of the E. coli O157 and Salmonella, respectively. The results indicated that the approach could detect E. coli O157 and Salmonella enterica from the seeds inoculated with ~ 4 CFU/g of the pathogens. Non-targeted bacteria, e.g., Aeromonas and Citrobacter exhibited essentially no cross reactivity. Since the pathogen detection from the sprouts was achieved within 6 hours, the developed methodology could be use as a rapid, sensitive and specific screening process for E. coli O157 and Salmonella enterica in this popular salad food.

Tu, Shu-I.; Gordon, Marsha; Fett, William F.; Gehring, Andrew G.; Irwin, Peter L.