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Nm Excitation (nm + excitation)
Selected AbstractsInduced SER-Activity in Nanostructured Ag,Silica,Au Supports via Long-Range Plasmon CouplingADVANCED FUNCTIONAL MATERIALS, Issue 12 2010Jiu-Ju Feng Abstract A novel Ag,silica,Au hybrid device is developed that displays a long-range plasmon transfer of Ag to Au leading to enhanced Raman scattering of molecules largely separated from the optically excited Ag surface. A nanoscopically rough Ag surface is coated by a silica spacer of variable thickness from ,1 to 21,nm and a thin Au film of ,25,nm thickness. The outer Au surface is further functionalized by a self-assembled monolayer (SAM) for electrostatic binding of the heme protein cytochrome c (Cyt c) that serves as a Raman probe and model enzyme. High-quality surface-enhanced resonance Raman (SERR) spectra are obtained with 413,nm excitation, demonstrating that the enhancement results exclusively from excitation of Ag surface plasmons. The enhancement factor is estimated to be 2,×,104,8,×,103 for a separation of Cyt c from the Ag surface by 28,47,nm, corresponding to an attenuation of the enhancement by a factor of only 2,6 compared to Cyt c adsorbed directly on a SAM-coated Ag electrode. Upon immobilization of Cyt c on the functionalized Ag,silica,Au device, the native structure and redox properties are preserved as demonstrated by time- and potential-dependent SERR spectroscopy. [source] Well-Aligned ZnO Nanowire Arrays Fabricated on Silicon Substrates ,ADVANCED FUNCTIONAL MATERIALS, Issue 6 2004C. Geng Abstract Arrays of well-aligned single-crystal zinc oxide (ZnO) nanowires of uniform diameter and length have been synthesized on a (100) silicon substrate via a simple horizontal double-tube system using chemical vapor transport and condensation method. X-ray diffraction and transmission electron microscopy (TEM) characterizations showed that the as-grown nanowires had the single-crystal hexagonal wurtzite structure with detectable defects and a <0002> growth direction. Raman spectra revealed phonon confinement effect when compared with those of ZnO bulk powder, nanoribbons, and nanoparticles. Photoluminescence exhibited strong ultraviolet emission at 3.29,eV under 355,nm excitation and green emission at 2.21,eV under 514.5,nm excitation. No catalyst particles were found at the tip of the nanowires, suggesting that the growth mechanism followed a self-catalyzed and saturated vapor,liquid,solid (VLS) model. Self-alignment of nanowires was attributed to the local balance and steady state of vapor flow at the substrate. The growth technique would be of particular interest for direct integration in the current silicon-technology-based optoelectronic devices. [source] Nondestructive Assessment of Lipid Oxidation in Minced Poultry Meat by Autofluorescence SpectroscopyJOURNAL OF FOOD SCIENCE, Issue 1 2000J.P. Wold ABSTRACT: To develop a rapid method to assess lipid oxidation, autofluorescence spectra (excitation wavelengths 365, 380, and 400 nm) from large samples (17 cm2) of minced poultry meat were collected by an optical system to determine directly lipid oxidation level. The same samples were also measured by 2-thiobarbituric acid method (TBARS). High correlations could be made between the TBARS method and autofluorescence spectra, especially those from 380 nm excitation. Partial least squares regression resulted in a root mean square error of 0.15 (R = 0.87) for chicken meat and 0.24 (R = 0.80) for mechanically recovered turkey meat. Classification analysis between fresh (TBARS < 0.25) and rancid (TBARS > 0.25) samples was done with high success rates. Autofluorescence spectroscopy might be well suited for rapid on-line determination of lipid oxidation level in minced poultry meat. [source] Raman spectra of organic acids obtained using a portable instrument at ,5 °C in a mountain area at 2000 m above sea levelJOURNAL OF RAMAN SPECTROSCOPY, Issue 4 2010J. Jehli Abstract Well-resolved Raman spectra of organic acids were obtained with 785 nm excitation using a portable Raman instrument (Ahura First Defender XL) under low temperature ,5 °C atmospheric conditions at an altitude of 2000 m (Axamer Lizum, Innental, Austria). The portable Raman spectrometer tested in this setting permits fast and unambiguous detection of solid forms of these organic acids (formic, acetic, valeric, hexanoic, heptanoic, isophthalic, ascorbic and mellitic) under field conditions. This demonstrates the possibility to use a miniaturized Raman spectrometer as a key instrument for investigating the presence of organic compounds and biomolecules under low temperature conditions. These results are important for future missions focusing not only on Mars, where Raman spectroscopy will be a key non-destructive analytical tool for the in situ identification of organic compounds relevant to life detection on planetary surfaces or near sub-surfaces. Copyright © 2009 John Wiley & Sons, Ltd. [source] UV resonance Raman spectroscopy probes the localization of tryptophan-containing antimicrobial peptides in lipid vesiclesJOURNAL OF RAMAN SPECTROSCOPY, Issue 3 2009Bryan Quan Abstract In this work we employed UV resonance Raman spectroscopy with 229 nm excitation to study two tryptophan-containing antimicrobial peptides with a broad-spectrum activity against Gram-positive and Gram-negative bacteria: lactoferricin B (LfB, RRWQWRMKKLG) and pEM-2 (KKWRWWLKALAKK). UV resonance Raman spectra of both peptides are dominated by tryptophan bands. Raman spectra of LfB and pEM-2 in D2O and 2,2,2-trifluoro ethanol (TFE) have been measured and used to identify the hydrogen-bond strength marker bands W6 and W17. The tryptophan doublet, W7, at 1340 and 1360 cm,1 was used to detect an increase in the hydrophobicity of Trp environment in TFE. The spectra of LfB in complex with model cell membranes composed of zwitterionic dipalmitoylglycero-phosphocholine (DPPC) or anionic dipalmitoyglycero-phosphoglycerol (DPPG) lipid vesicles revealed a more hydrophobic Trp environment in DPPG, suggesting stronger interactions between the cationic peptide and anionic model cell membrane. Copyright © 2008 John Wiley & Sons, Ltd. [source] The relaxations of temporal bond polarizabilities of methylviologen adsorbed on the Ag electrode by 514.5 nm excitation: a Raman intensity studyJOURNAL OF RAMAN SPECTROSCOPY, Issue 3 2009Chao Fang Abstract An algorithm to elucidate the temporal bond polarizabilities from the surface enhanced Raman (SERS) intensities was employed to the case of methylviologen (MV) adsorbed on the Ag electrode. This enables us to obtain the properties of its SERS mechanisms and the effect of its adsorption. The analysis shows that the charge transfer and electromagnetic mechanisms involving in this MV SERS system possess different relaxation times for its various temporal bond polarizabilities. The physics is that the process involved in the charge transfer mechanism will take longer time than that involved in the electromagnetic mechanism since it needs more time to redistribute the charges during relaxation. The time division between these two mechanisms is figured out to be around 3 ps for this system. Adsorption also enhances the relaxation of the temporal bond polarizabilities, in general. The adsorption effect is indicated by the temporal bond polarizabilities close to the final stage of relaxation. They are, in fact, the quantities parallel to the bond electronic densities in the molecular orbital (MO) concept. For comparison, the case of MV solid was also analyzed. Copyright © 2008 John Wiley & Sons, Ltd. [source] Indole ring orientations of Trp189 in the ground and M intermediate states of bacteriorhodopsin as studied by polarized UV resonance Raman spectroscopy,JOURNAL OF RAMAN SPECTROSCOPY, Issue 1-3 2006Kazuhiro Asakawa Abstract Polarized resonance Raman spectroscopy provides a means for orientation analysis of proteins in aligned samples. Previously, we developed a Raman linear intensity difference (RLID) method to determine the orientations of aromatic amino acid side chains in flow-oriented or membrane-bound proteins. In this study, we have applied the RLID method to Trp189 in bacteriorhodopsin (BR), a transmembrane protein that acts as a light-driven proton pump. Among the eight Trp residues in BR, the Raman spectrum of Trp189 has been extracted by subtracting the spectrum of the Trp189 , Phe mutant from that of wild-type BR. By examining the 251.3-nm-exited polarized resonance Raman intensities of two indole ring vibrations of Trp189, the directions of the La and Bb transition moments have been determined with respect the membrane normal in the light-adapted ground state (BR568) and a photo-excited intermediate (M). Comparison of the orientations of the Trp189 indole ring derived from the La and Bb inclination angles has shown that the indole ring slightly but significantly reorients toward the ionone ring of the retinal chromophore in the M intermediate. The reorientation of Trp189 is consistent with the previous observation that helix F, on which Trp189 is located, undergoes an outward tilt and the hydrophobic interaction of Trp189 increases in the M intermediate. The RLID method combined with 251.3 nm excitation and point mutation is useful for detecting even a small reorientation of a targeted Trp residue. Copyright © 2006 John Wiley & Sons, Ltd. [source] Photoluminescent Properties of SrTiO3:Pr, Al Nanophosphors Synthesized by Microemulsion,Microwave HeatingJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2007Qi Pang A novel approach for the preparation of SrTiO3:Pr, Al nanophosphors by microemulsion,microwave heating is reported in this paper. In comparison with the conventional solid-state sintering processes, this novel method provides a limited small space in a micelle for the formation of nanosized precursors and requires a very short heating time, thus reducing the energy consumption. As a result, small-sized particles with a narrow size distribution and high purity were produced. Transmission electron microscopy characterizations indicated that the synthesized particles were almost spherical with an averaging diameter of ,24 nm and agglomerates slightly. The X-ray diffraction analysis revealed the perovskite cubic structure of SrTiO3:Pr3+ nanoparticles. The luminescent of SrTiO3:Pr, Al phosphors were investigated by photoluminescence. Under 350 nm excitation, SrTiO3:Pr, Al showed a strong red emission, peaking at around 615 nm. The photoluminescence excitation intensity was enhanced by the addition of Al3+ ions. [source] Fluorescence Spectroscopy of Color Centers Generated in Phosphate Glasses after Exposure to Femtosecond Laser PulsesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2002James W. Chan A confocal fluorescence microscopy setup was used to observe, in situ, spectral changes in phosphate glasses which were modified using 0.3 ,J of tightly focused 800 nm, 130 fs laser pulses. On 488 nm excitation, the modified glass shows a broad fluorescence centered at roughly 600 nm, which decays with prolonged exposure to the 488 nm light. The decay behavior is dependent on the 488 nm power, with a faster decay rate for higher powers. A mechanism whereby color centers, formed by the femtosecond pulses, fluoresce when excited by the 488 nm light and are simultaneously photobleached is proposed to explain the observed behavior. [source] Temporally and spectrally resolved fluorescence spectroscopy for the detection of high grade dysplasia in Barrett's esophagusLASERS IN SURGERY AND MEDICINE, Issue 1 2003T. Joshua Pfefer PhD Abstract Background and Objectives Temporal and spectral fluorescence spectroscopy can identify adenomatous colonic polyps accurately. In this study, these techniques were examined as a potential means of improving the surveillance of high grade dysplasia (HGD) in Barrett's esophagus (BE). Study Design/Materials and Methods Using excitation wavelengths of 337 and 400 nm, 148 fluorescence spectra, and 108 transient decay profiles (at 550,±,20 nm) were obtained endoscopically in 37 patients. Corresponding biopsies were collected and classified as carcinoma, HGD, or low risk tissue (LRT) [non-dysplastic BE, indefinite for dysplasia (IFD), and low grade dysplasia (LGD)]. Diagnostic algorithms were developed retrospectively using linear discriminant analysis (LDA) to separate LRT from HGD. Results LDA produced diagnostic algorithms based solely on spectral data. Moderate levels of sensitivity (Se) and specificity (Sp) were obtained for both 337 nm (Se,=,74%, Sp,=,67%) and 400 nm (Se,=,74%, Sp,=,85%) excitation. Conclusions In the diagnosis of HGD in BE, steady-state fluorescence was more effective than time-resolved data, and excitation at 400 nm excitation was more effective than 337 nm. While fluorescence-targeted biopsy is approaching clinical usefulness, increased sensitivity to dysplastic changes,possibly through modification of system parameters,is needed to improve accuracy levels. Lasers Surg. Med. 32:10,16,2003. © 2003 Wiley-Liss, Inc. [source] Combustion synthesis of Na2Sr(PO4)F:Dy3+ white light emitting phosphorLUMINESCENCE: THE JOURNAL OF BIOLOGICAL AND CHEMICAL LUMINESCENCE, Issue 1 2010I. M. Nagpure Abstract The synthesis, X-ray diffraction, photoluminescence, TGA/DTA and FTIR techniques in Dy3+ activated Na2Sr(PO4)F phosphor are reported in this paper. The prepared phosphor gave blue, yellow and red emission in the visible region of the spectrum at 348 nm excitation. CIE color co-ordinates of Na2Sr(PO4)F:Dy3+ are suitable as white light-emitting phosphors. Copyright © 2009 John Wiley & Sons, Ltd. [source] Real-time cellular uptake of serotonin using fluorescence lifetime imaging with two-photon excitationMICROSCOPY RESEARCH AND TECHNIQUE, Issue 4 2008Stanley Walter Botchway Abstract The real-time uptake of serotonin, a neurotransmitter, by rat leukemia mast cell line RBL-2H3 and 5-hydroxytryptophan by Chinese hamster V79 cells has been studied by fluorescence lifetime imaging microscopy (FLIM), monitoring ultraviolet (340 nm) fluorescence induced by two-photon subpicosecond 630 nm excitation. Comparison with two-photon excitation with 590 nm photons or by three-photon excitation at 740 nm shows that the use of 630 nm excitation provides optimal signal intensity and lowered background from auto-fluorescence of other cellular components. In intact cells, we observe using FLIM three distinct fluorescence lifetimes of serotonin and 5-hydroxytryptophan according to location. The normal fluorescence lifetimes of both serotonin (3.8 ns) and 5-hydroxytryptophan (3.5 ns) in solution are reduced to ,2.5 ns immediately on uptake into the cell cytosol. The lifetime of internalized serotonin in RBL-2H3 cells is further reduced to ,2.0 ns when stored within secretory vesicles. Microsc. Res. Tech., 2008. © 2007 Wiley-Liss, Inc. [source] Tryptophan Fluorescence in the Bacillus subtilis Phototropin-related Protein YtvA as a Marker of Interdomain Interaction,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 1 2004Aba Losi ABSTRACT The Bacillus subtilis protein YtvA, related to plant phototropins (phot), binds flavin mononucleotide (FMN) within the N-terminal light, oxygen and voltage (LOV) domain. The blue light-triggered photocycle of YtvA and phot involves the reversible formation of a covalent photoadduct between FMN and a cysteine (cys) residue. YtvA contains a single tryptophan, W103, localized on the LOV domain and conserved in all phot-LOV domains. In this study, we show that the fluorescence parameters of W103 in YtvA-LOV are markedly different from those observed in the full-length YtvA. The fluorescence quantum yields are ca 0.03 and 0.08, respectively. In YtvA-LOV, the maximum is redshifted (ca 345 vs 335 nm) and the average fluorescence lifetime shorter (2.7 vs 4.7 ns). These data indicate that W103 is located in a site of tight contact between the two domains of YtvA. In the FMN-cys adduct, selective excitation of W103 at 295 nm results in minimal changes of the fluorescence parameters with respect to the dark state. On 280 nm excitation, however, there is a detectable decrease in the fluorescence emitted from tyrosines, with concomitant increase in W103 fluorescence. This effect is reversible in the dark and might arise from a light-regulated energy transfer process from a yet unidentified tyrosine to W103. [source] High pressure Raman study of the second-order vibrational modes of single- and double-walled carbon nanotubesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 11 2007K. Papagelis Abstract The pressure response of the second-order Raman G, band of bundled double- (DWCNTs) and single-wall carbon nanotubes (SWCNTs) has been investigated by means of Raman spectroscopy using the 632.8 nm excitation. The different pressure responses of the G, peak in SWCNTs and its corresponding components associated with the inner and the outer tubes in DWCNTs can be attributed to the different diameters of the resonantly probed tubes and the strength of the inner-outer tube interaction. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Improving detection in capillary electrophoresis with laser induced fluorescence via a bubble cell capillary and laser power adjustmentBIOMEDICAL CHROMATOGRAPHY, Issue 1 2009Audrey Rodat Abstract Bubble cells have been frequently employed in capillary electrophoresis (CE) to increase the light path length with UV detection to provide an increase in the observed sensitivity of CE; however this approach has not been commonly used for laser-induced fluorescence detection (LIF) with CE. In this paper we study the influence of laser power on the sensitivity of detection in using conventional and enlarged fused silica capillaries for CE with LIF. When using the bubble cell capillary, the laser power must be decreased relative to use of the conventional capillary to reduce the effects of photodegradation of the species being illuminated by the laser. Even though the light intensity was decreased, an increase in sensitivity of detection was observed for most compounds when a bubble cell was used. This increase ranged from a factor of 8 for riboflavin (410 nm excitation) to 3.2 for most aromatic compounds (266 nm excitation), when using a 3× bubble cell compared with a conventional capillary. The bubble cell capillary was used for native detection of IgG by LIF at 266 nm. A limit of detection of 60 ng mL,1 was obtained from a 20 pg injection, which was 40 times more sensitive than silver staining in conventional SDS/PAGE. Copyright © 2008 John Wiley & Sons, Ltd. [source] Development and application of an excitation ratiometric optical pH sensor for bioprocess monitoringBIOTECHNOLOGY PROGRESS, Issue 6 2008Ramachandram Badugu Abstract The development of a fluorescent excitation ratiometric pH sensor (AHQ-PEG) using a novel allylhydroxyquinolinium (AHQ) derivative copolymerized with polyethylene glycol dimethacrylate (PEG) is described. The AHQ-PEG sensor film is shown to be suitable for real-time, noninvasive, continuous, online pH monitoring of bioprocesses. Optical ratiometric measurements are generally more reliable, robust, inexpensive, and insensitive to experimental errors such as fluctuations in the source intensity and fluorophore photobleaching. The sensor AHQ-PEG in deionized water was shown to exhibit two excitation maxima at 375 and 425 nm with a single emission peak at 520 nm. Excitation spectra of AHQ-PEG show a decrease in emission at the 360 nm excitation and an increase at the 420 nm excitation with increasing pH. Accordingly, the ratio of emission at 420:360 nm excitation showed a maximum change between pH 5 and 8 with an apparent pKa of 6.40. The low pKa value is suitable for monitoring the fermentation of most industrially important microorganisms. Additionally, the AHQ-PEG sensor was shown to have minimal sensitivity to ionic strength and temperature. Because AHQ is covalently attached to PEG, the film shows no probe leaching and is sterilizable by steam and alcohol. It shows rapid (,2 min) and reversible response to pH over many cycles without any photobleaching. Subsequently, the AHQ-PEG sensor film was tested for its suitability in monitoring the pH of S. cereviseae (yeast) fermentation. The observed pH using AHQ-PEG film is in agreement with a conventional glass pH electrode. However, unlike the glass electrode, the present sensor is easily adaptable to noninvasive monitoring of sterilized, closed bioprocess environments without the awkward wire connections that electrodes require. In addition, the AHQ-PEG sensor is easily miniaturized to fit in microwell plates and microbioreactors for high-throughput cell culture applications. [source] Mechanico-chemical interaction of SWNTs with different host matrices evidenced by SERS spectroscopyPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 13 2006Serge Lefrant Abstract Surface enhanced Raman scattering (SERS) performed with 676.4 and 1064 nm excitations were used to investigate single-walled carbon nanotubes (SWNTs) thin films prepared from platelets obtained by non-hydrostatic compression at 0.58 GPa. SWNTs were compressed alone or dispersed into chemical reactive and non-reactive host matrices. SERS spectra indicate that by compression, SWNTs break into fragments of different sizes, which in turn can react or not with the host matrix. In inorganic hosts (KI, Ag) donor-acceptor complexes are formed. The appearance of short fragments of SWNTs with a closed-shell fullerenes behaviour is revealed in SERS spectra. This typical signature appears in the Raman spectrum as a line at ca. 1460 cm,1 associated with a pentagonal pinch mode. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||||||||