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Excitation Wavelength (excitation + wavelength)
Kinds of Excitation Wavelength Selected AbstractsControlling Light Oxidation Flavor in Milk by Blocking Riboflavin Excitation Wavelengths by InterferenceJOURNAL OF FOOD SCIENCE, Issue 9 2009J.B. Webster ABSTRACT:, Milk packaged in glass bottles overwrapped with iridescent films (treatments blocked either a single visible riboflavin [Rb] excitation wavelength or all visible Rb excitation wavelengths; all treatments blocked UV Rb excitation wavelengths) was exposed to fluorescent lighting at 4 °C for up to 21 d and evaluated for light-oxidized flavor. Controls consisted of bottles with no overwrap (light-exposed treatment; represents the light barrier properties of the glass packaging) and bottles overwrapped with aluminum foil (light-protected treatment). A balanced incomplete block multi-sample difference test, using a ranking system and a trained panel, was used for evaluation of light oxidation flavor intensity. Volatiles were evaluated by gas chromatography and Rb degradation was evaluated by fluorescence spectroscopy. Packaging overwraps limited production of light oxidation flavor over time but not to the same degree as the complete light block. Blocking all visible and UV Rb excitation wavelengths reduced light oxidation flavor better than blocking only a single visible excitation wavelength plus all UV excitation wavelengths. Rb degraded over time in all treatments except the light-protected control treatment and only minor differences in the amount of degradation among treatments was observed. Hexanal production was significantly higher in the light-exposed control treatment compared to the light-protected control treatment from day 7; it was only sporadically significantly higher in the 570 nm and 400 nm block treatments. Pentanal, heptanal, and an unidentified volatile compound also increased in concentration over time, but there were no significant differences in concentration among the packaging overwrap treatments for these compounds. [source] Epifluorescence microscopy and image analysis of high-level polycyclic aromatic hydrocarbon contamination in soilsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 12 2006J. Chadwick Roper Abstract Interactions between polycyclic aromatic hydrocarbons (PAHs) and soil are an important determinant of their chemical availability and transport. Laboratory examination of microscale PAH,soil interaction is limited by the availability of methods for particle-scale observation. Inverted epifluorescence microscopy, combined with digital photography and computer image analysis, was evaluated for specificity and linearity using dissolved PAHs. A pyrene filter (excitation wavelength, 360,400 nm; emission wavelength, 450,520 nm) gave nonspecific PAH fluorescence, and bias for fluoranthene, benzo[b]fluoranthene, benzo[g, h, i]perylene, and benz[a]anthracene was quantified in comparison to that for pyrene. Concentrations ranging from 1 to 10 mM for anthracene, fluoranthene, and pyrene and from 1 to 50 mM for naphthalene produced a linear response with low interpixel variability. Liquid-phase analyses validated use of the technique for the descriptive analysis of PAH distribution in solid samples, but liquid-phase calibration was not quantitative for spiked or field-contaminated soils. The mean luminance for three field soils was proportional to the values predicted from their chemically measured concentrations and to values from spiked, aged, uncontaminated materials. Image analysis of laboratory- and field-contaminated samples determined the area distribution of fluorescent intensity and the size of fluorescent areas exceeding a threshold luminance. These qualitative descriptions of the microscale spatial distribution of PAH contamination are presented as potential endpoints for future research on biogeochemical interactions in heavily contaminated solids. [source] A confocal micro-endoscopic investigation of the relationship between the microhardness of carious dentine and its autofluorescenceEUROPEAN JOURNAL OF ORAL SCIENCES, Issue 1 2010Avijit Banerjee Banerjee A, Cook R, Kellow S, Shah K, Festy F, Sherriff M, Watson T. A confocal micro-endoscopic investigation of the relationship between the microhardness of carious dentine and its autofluorescence. Eur J Oral Sci 2010; 118: 75,79. © 2010 The Authors. Journal compilation© 2010 Eur J Oral Sci This study aimed to investigate the null hypothesis that there is no relationship between the microhardness of carious dentine and its native autofluorescence (AF). Six extracted, carious molars were sectioned through natural lesions in the mesio-distal longitudinal plane. The Knoop microhardness (Knoop hardness number, KHN) of the cut surfaces of each sample was recorded at regular intervals through sound and carious dentine. Confocal fibre-optic micro-endoscopic (CFOME) examination of the carious dentine and the sound dentine was carried out at the same intervals using the Cellvizio system (600 ,m wide, flat-end probe) with an excitation wavelength of 488 nm. The blindly collected numerical data were analysed using the original microhardness KHN. The data analysis indicated that the autofluorescence signals increased significantly when the microhardness of dentine dropped below 25 KHN. Therefore, the null hypothesis was disproved, and it was concluded from this investigation that the autofluorescent signal intensity recorded using CFOME could produce an objective and reproducible correlation to the microhardness of carious dentine. Confocal fibre-optic micro-endoscopic examination could have clinical potential as a technology to help delineate the carious dentine that might be excavated in a clinical procedure in vivo. [source] Generic Method of Preparing Multifunctional Fluorescent Nanoparticles Using Flash NanoPrecipitationADVANCED FUNCTIONAL MATERIALS, Issue 5 2009Mustafa Akbulut Abstract There is increased demand for nanoparticles with a high fluorescence yield that have the desired excitation wavelength, surface functionalization, and particle size to act as biological probes. Here, a simple, rapid, and robust method, Flash NanoPrecipitation (FNP), to produce such fluorescent nanoparticles is described. This process involves encapsulation of a hydrophobic fluorophore with an amphiphilic biocompatible diblock copolymer in a kinetically frozen state. FNP is used to produce nanoparticles ranging from 30 to 800,nm with fluorescence emission peaks ranging from, but not limited to, 370,nm to 720,nm. Such fluorescent nanoparticles remain stable in aqueous solutions, and, in contrast to soluble dyes, show no photobleaching. Fluorophores and drugs are incorporated into a single nanoparticle, allowing for simultaneous drug delivery and biological imaging. In addition, functionalization of nanoparticle surfaces with disease-specific ligands permits precise cell targeting. These features make FNP-produced fluorescent nanoparticles highly desirable for various biological applications. [source] Red,Yellow Fluorescence Patterning of a Polymer Film Containing Phthalimido Carbamate GroupsADVANCED FUNCTIONAL MATERIALS, Issue 17 2007H. Chae Abstract Bicolor fluorescent micro-patterns in the polymer film are prepared through the use of a new group of photobase generator containing phthalimido carbamate groups. The photobase generation from phthalimide carbamates is studied by examining the changes in pH, fluorescence intensity, and photo-crosslinking of poly(glycidyl methacrylate). The product analysis of a model compound indicates that amine groups are produced from the photolytic cleavage of the C,N bond of the phthalimide carbamate groups. A copolymer containing phthalimide carbamate groups is applied to a bicolor fluorescent imaging material. Red-yellow fluorescent micropatterns are obtained by treating the copolymer film, which is irradiated with 254 nm UV light through a photomask, with fluorescamine and rhodamine, consecutively. Various colored fluorescent micropatterns , green, red, or red-yellow, are obtained on a single polymer film by varying the excitation wavelength. [source] Photoresponse Properties of CdSe Single-Nanoribbon Photodetectors,ADVANCED FUNCTIONAL MATERIALS, Issue 11 2007Y. Jiang Abstract Photodetectors are fabricated from individual single-crystal CdSe nanoribbons, and the photoresponse properties of the devices are studied systematically. The photodetector shows a high sensitivity towards excitation wavelength with a sharp cut-off at 710,nm, corresponding to the bandgap of CdSe. The device exhibits a high photo-to-dark current ratio of five orders of magnitude at 650,nm, and can function with excellent stability, reproducibility, and high response speed (<,1,ms) in a wide range of switching frequency (up to 300,Hz). The photocurrent of the device shows a power-law dependence on light intensity. This finding together with the analysis of the light intensity-dependent response speed reveals the existence of various traps at different energy levels (shallow and deep) in the bandgap. Coating with a thin SiO2 isolating layer increases the photocurrent but decreases the response speed of the CdSe nanoribbon, which is attributed to reduction of recombination centers on ribbon surface. [source] Fluorescence Modulation in Polymer Bilayers Containing Fluorescent and Photochromic Dopants,ADVANCED FUNCTIONAL MATERIALS, Issue 5 2005M. Tomasulo Abstract We have identified viable operating principles for the modulation of optical signals under the influence of optical stimulations. They are based on the overlap between the emission bands of a fluorescent compound and the absorption bands of one of the two forms of a bistable photochromic switch. Under these conditions, the photoinduced interconversion of the two states of the photochrome modulates efficiently the emission intensity of the fluorophore. We have implemented this mechanism for intermolecular fluorescence modulation with multilayer structures. They consist of two quartz plates sandwiching two overlapping polymer layers. One of the polymers is doped with a fluorescent benzofurazan. The other contains a photochromic spiropyran. The multilayer assembly is operated with two light sources. One of them is centered at the excitation wavelength of the fluorophore, where neither of the two states of the photochrome absorbs. The other light source is switched between ultraviolet and visible wavelengths to induce the interconversion between the two states of the photochrome. The light emitted by the fluorescent component has to propagate through the photochromic layer before reaching a detector. It can do so efficiently for only one of the two states of the photochrome. It follows that a measurement of the light intensity reaching the detector can read the state of the photochromic switch, which in turn is written and erased with optical stimulations. Thus, our strategy for all-optical processing can be used to store and retrieve binary digits, as well as to implement optical inversion, with the aid of engineered molecule-based components. [source] Autofluorescence imaging analysis of gastric cancerJOURNAL OF DIGESTIVE DISEASES, Issue 3 2002Shu Dong XIAO AIMS: To investigate the characteristics of gastric cancer in autofluorescence images. METHODS: A double-channel laser scanning confocal microscope with an argon ion laser (excitation wavelength 488 nm) and helium,neon laser (excitation wavelength 543 nm) were used to detect autofluorescence from 16 gastric cancer tissue specimens and corresponding normal gastric tissue. RESULTS: Autofluorescence from normal gastric tissue produced a green-colored image. The intensity of red color increased obviously in all gastric cancer tissues (100%) after illumination and the tissues produced a reddish-brown-colored image. CONCLUSIONS: A reddish-brown image is characteristic of autofluorescence in gastric cancer detected by an argon ion laser and helium,neon laser with a double-channel laser scanning confocal microscope. Autofluorescence imaging analysis is useful in the diagnosis of gastric cancer. [source] Controlling Light Oxidation Flavor in Milk by Blocking Riboflavin Excitation Wavelengths by InterferenceJOURNAL OF FOOD SCIENCE, Issue 9 2009J.B. Webster ABSTRACT:, Milk packaged in glass bottles overwrapped with iridescent films (treatments blocked either a single visible riboflavin [Rb] excitation wavelength or all visible Rb excitation wavelengths; all treatments blocked UV Rb excitation wavelengths) was exposed to fluorescent lighting at 4 °C for up to 21 d and evaluated for light-oxidized flavor. Controls consisted of bottles with no overwrap (light-exposed treatment; represents the light barrier properties of the glass packaging) and bottles overwrapped with aluminum foil (light-protected treatment). A balanced incomplete block multi-sample difference test, using a ranking system and a trained panel, was used for evaluation of light oxidation flavor intensity. Volatiles were evaluated by gas chromatography and Rb degradation was evaluated by fluorescence spectroscopy. Packaging overwraps limited production of light oxidation flavor over time but not to the same degree as the complete light block. Blocking all visible and UV Rb excitation wavelengths reduced light oxidation flavor better than blocking only a single visible excitation wavelength plus all UV excitation wavelengths. Rb degraded over time in all treatments except the light-protected control treatment and only minor differences in the amount of degradation among treatments was observed. Hexanal production was significantly higher in the light-exposed control treatment compared to the light-protected control treatment from day 7; it was only sporadically significantly higher in the 570 nm and 400 nm block treatments. Pentanal, heptanal, and an unidentified volatile compound also increased in concentration over time, but there were no significant differences in concentration among the packaging overwrap treatments for these compounds. [source] Synthesis of 4-(7-diethylaminocoumarin-3-yl)benzeneisocyanate (DACB-NCO): A highly sensitive fluorescent derivatization reagent for alcohols in high-performance liquid chromatography,JOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 2 2001Haruko Takechi 4-(7-Diethylaminocoumarin-3-yl)benzeneisocyanate (DACB-NCO) was synthesized as a new fluorescent derivatization reagent for alcohols for use in high-performance liquid chromatography (hplc). Saturated alcohols (C6 -C22) were derivatized in good yields into the corresponding fluorescent DACB-carbamic esters by treating with DACB-NCO. The DACB-carbamic esters of these alcohols were clearly separated on a reversed-phase hplc column (Inertsil ODS-2, mobile phase: methanol-water, excitation wavelength 402 nm; emission wavelength 488 nm). The detection limit (S/N = 3) of cetyl alcohol, as a test compound, was 5 fmol/10 ,l. [source] Characterisation of carbonaceous materials using Raman spectroscopy: a comparison of carbon nanotube filters, single- and multi-walled nanotubes, graphitised porous carbon and graphiteJOURNAL OF RAMAN SPECTROSCOPY, Issue 3 2009H. M. Heise Abstract Multi-walled carbon nanotube (MWCNT) filters have been recently synthesised which have specific molecular filtering capabilities and good mechanical strength. Optical and scanning electron microscopy (SEM) reveals the formation of highly aligned arrays of bundles of carbon nanotubes having lengths up to 500 µm. The Raman spectra of this material along with four other carbonaceous materials, commercially available single-walled carbon nanotubes (SWCNTs) and MWCNTs, graphitised porous carbon (Carbotrap) and graphite have been recorded using two-excitation wavelengths, 532 and 785 nm, and analysed for band positions and shape with special emphasis paid to the D-, G- and G,-bands. A major difference between the different MWCNT varieties analysed is that G-bands in the MWCNT filters exhibit almost no dispersion, whereas the other MWCNTs show a noticeable dispersive behaviour with a change in the excitation wavelength. Spectral features similar to those of the MWCNT filter varieties were observed for the Carbotrap material. From the line shape analysis, the intensity ratio, ID/IG, of the more ordered MWCNT filter material using the integral G-band turns out to be two times lower than that of the less ordered MWCNT filter product at both excitation wavelengths. This parameter can, therefore, be used as a measure of the degree of MWCNT alignment in filter varieties, which is well supported also by our SEM study. Copyright © 2008 John Wiley & Sons, Ltd. [source] Optical probing and imaging of live cells using SERS labelsJOURNAL OF RAMAN SPECTROSCOPY, Issue 1 2009Janina Kneipp Abstract During surface-enhanced Raman scattering (SERS), molecules exhibit a significant increase in their Raman signals when attached, or in very close vicinity, to gold or silver nanostructures. This effect is exploited as the basis of a new class of optical labels. Here we demonstrate robust and sensitive SERS labels as probes for imaging live cells. These hybrid labels consist of gold nanoparticles with Rose Bengal or Crystal Violet attached as reporter molecules. These new labels are stable and nontoxic, do not suffer from photobleaching, and can be excited at any excitation wavelength, even in the near infrared. SERS labels can be detected and imaged through the specific Raman signatures of the reporters. In addition, surface-enhanced Raman spectroscopy in the local optical fields of the gold nanoparticles also provides sensitive information on the immediate molecular environment of the label in the cell and allows imaging of the native constituents of the cell. This is demonstrated by images based on a characteristic Raman line of the reporter as well as by displaying lipids based on the SERS signal of the CH deformation/bending modes at ,1470 cm,1. Copyright © 2008 John Wiley & Sons, Ltd. [source] Surface-enhanced Raman sensors: early history and the development of sensors for quantitative biowarfare agent and glucose detectionJOURNAL OF RAMAN SPECTROSCOPY, Issue 6-7 2005Christy L. Haynes Abstract Surface-enhanced Raman spectroscopy (SERS) is a powerful technique for the sensitive and selective detection of low-concentration analytes. This paper includes a discussion of the early history of SERS, the concepts that must be appreciated to optimize the intensity of SERS and the development of SERS-based sensors. In order to achieve the lowest limits of detection, both the relationship between surface nanostructure and laser excitation wavelength, as well as the analyte/surface binding chemistry, must be carefully optimized. This work exploits the highly tunable nature of nanoparticle optical properties to establish the first set of optimization conditions. The SERS enhancement factor, EFSERS, is optimized when the energy of the localized surface plasmon resonance (LSPR) lies between the energy of the excitation wavelength and the energy of the vibrational band of interest. With the narrow LSPRs used in this work, it is straightforward to achieve EFSERS , 108. These optimization conditions were exploited to develop SERS-based sensors for two important target molecules: a Bacillus anthracis biomarker and glucose in a serum protein mixture. Using these optimized film-over-nanosphere surfaces, an inexpensive, portable Raman spectrometer was used successfully to detect the infectious dose of Bacillus subtilis spores with only a 5-s data collection. The biomarker used to detect the Bacillus subtilis spores binds irreversibly to SERS substrates, whereas other important biomolecules, such as glucose, do not have any measurable binding affinity to a bare silver surface. To overcome this difficulty, a biocompatible partition layer was self-assembled on the SERS substrate before exposure to the analyte solution. Using the partition layer approach to concentrate glucose near the SERS-active substrate, physiological glucose concentrations can be detected even in the presence of interfering serum proteins. Copyright © 2005 John Wiley & Sons, Ltd. [source] Surface-enhanced Raman scattering study of the adsorption of the anthraquinone pigment alizarin on Ag nanoparticlesJOURNAL OF RAMAN SPECTROSCOPY, Issue 11 2004M. V. Cańamares Abstract FT-Raman and surface-enhanced Raman scattering (SERS) spectroscopy were applied in the vibrational characterization and study of the adsorption and acidity behavior of the highly fluorescent anthraquinone dye alizarin on Ag colloids prepared by chemical reduction with hydroxylamine hydrochloride. The SERS spectra were obtained at different conditions of pH, excitation wavelength and pigment concentration in order to deduce the adsorption mechanism of this molecule. On the basis of the results found we propose an adsorption model for alizarin, which has a different acidic behavior on the metal surface to that in solution. On the metal the deprotonation order of the OH groups changes with respect to the aqueous solution, the OH in position 1 being the first to be ionized instead of that in position 2 as occurs in solution. The two main alizarin forms identified on the metal surface correspond to the mono- and dianionic alizarin species. Copyright © 2004 John Wiley & Sons, Ltd. [source] Spectroscopic studies on origination of the peak at 730 nm in delayed fluorescence of chloroplastsLUMINESCENCE: THE JOURNAL OF BIOLOGICAL AND CHEMICAL LUMINESCENCE, Issue 4 2007Lizhang Zeng Abstract The origination of the peak at 730 nm in the delayed fluorescence (DF) spectrum of chloroplasts was studied using various optical analysis methods. The DF spectrum showed that the main emission peak was at about 685 nm, with a small shoulder at 730 nm when the chloroplast concentration was < 7.8 µg/mL. The intensity of the peak at 685 nm decreased, while the intensity of the peak at 730 nm increased, when the chloroplast concentrations were increased from 7.8 to 31.2 µg/mL. With the concentration increasing, the peak at 730 nm became dominant while the peak at 685 nm finally disappeared. The DF decay kinetic curves showed that the intensity of the peak at 730 nm decayed as the same speed as the intensity of the peak at 685 nm during the entire relaxation process (0.5,30.5 s). With the excitation wavelength at 685 nm, the emission intensity was stronger in the excitation spectrum at 730 nm. The absorption spectrum demonstrated that the ratio A685:A730 remained almost constant when the chloroplast concentration increased. The results suggest that the peak at 730 nm appearing in DF is mainly contributed by the fluorescence of photosystem I (PSI), generated by the re-absorption of 685 nm band DF. Copyright © 2007 John Wiley & Sons, Ltd. [source] Tuning the Photoluminescence of Silsesquioxanes with Short Substituted Urea BridgesMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 6 2008María L. Gómez Abstract The polycondensation of a precursor synthesized by the reaction of 3-(anilinepropyl)trimethoxysilane with 3-(isocyanatopropyl)triethoxysilane led to a silsesquioxane bearing a substituted urea group in the short organic bridge. The self-assembly of organic bridges, analyzed by SAXS and FTIR spectra, could be controlled by varying the conditions of the synthesis. Depending on the size of organic clusters, the silsesquioxane exhibited photoluminescence either in the green or red regions of the spectra, or an emission that could be tuned in the whole visible region by the excitation wavelength. [source] Practical limits of resolution in confocal and non-linear microscopyMICROSCOPY RESEARCH AND TECHNIQUE, Issue 1 2004Guy Cox Abstract Calculated and measured resolution figures are presented for confocal microscopes with different pinhole sizes and for nonlinear (2-photon and second harmonic) microscopes. A modest degree of super-resolution is predicted for a confocal microscope but in practice this is not achievable and confocal fluorescence gives little resolution improvement over widefield. However, practical non-linear microscopes do approach their theoretical resolution and therefore show no resolution disadvantage relative to confocal microscopes in spite of the longer excitation wavelength. Microsc. Res. Tech. 63:18,22, 2004. © 2003 Wiley-Liss, Inc. [source] Time-Resolved and Steady-State Fluorescence Spectroscopy of Eumelanin and Indolic PolymersPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 6 2007Stephen P. Nighswander-Rempel Eumelanin plays a variety of important physiological roles in human skin. However, its structure and fundamental properties still remain poorly understood. Although the absorbance of eumelanin is broad and reveals little about its structure, a variety of techniques have revealed the presence of a disordered array of chromophores within the melanin compound. In order to examine the fluorescence decay dynamics of these chromophores, time-resolved spectroscopy was applied to solutions of synthetic eumelanin and a melanin-like polymer of N-methyl,5-hydroxy,6-methoxyindole (N-Me-5H6MI). Solutions were excited with 80 fs laser pulses at 355, 370, 390 and 400 nm, and decay time courses were acquired at 20 nm intervals between 400 and 600 nm for each excitation wavelength. Decay profiles for both eumelanin and the polymer exhibited a characteristic multiexponential behavior with decay times between 0.5 and 15 ns, although steady-state spectra for the polymer exhibited only two peaks. The long-decay component in the polymer showed a significant decrease in both amplitude (30,5%) and decay time (14,6 ns) with increasing emission wavelength. In contrast, the amplitude and decay time in melanin increased slightly (10,15% and 7,10 ns, respectively) from 400 to 520 nm emission, at which point they leveled off. These trends were consistent for all excitation wavelengths. These results suggest that the multiexponential behavior of melanin fluorescence is characteristic of each oligomer within the eumelanin compound, and is consistent with the assertion that the diversity of constituents within eumelanin provides it with a robustness in spectral properties. [source] Porphyrin Bleaching and PDT-induced Spectral Changes are Irradiance Dependent in ALA-sensitized Normal Rat Skin In Vivo,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 1 2001Jarod C. Finlay ABSTRACT Photobleaching kinetics of aminolevulinic acid,induced protoporphyrin IX (PpIX) were measured in the normal skin of rats in vivo using a technique in which fluorescence spectra were corrected for the effects of tissue optical properties in the emission spectral window through division by reflectance spectra acquired in the same geometry and wavelength interval and for changes in excitation wavelength optical properties using diffuse reflectance measured at the excitation wavelength. Loss of PpIX fluorescence was monitored during photodynamic therapy (PDT) performed using 514 nm irradiation. Bleaching in response to irradiances of 1, 5 and 100 mW cm,2 was evaluated. The results demonstrate an irradiance dependence to the rate of photobleaching vs irradiation fluence, with the lowest irradiance leading to the most efficient loss of fluorescence. The kinetics for the accumulation of the primary fluorescent photoproduct of PpIX also exhibit an irradiance dependence, with greater peak accumulation at higher irradiance. These findings are consistent with a predominantly oxygen-dependent photobleaching reaction mechanism in vivo, and they provide spectroscopic evidence that PDT delivered at low irradiance deposits greater photodynamic dose for a given irradiation fluence. We also observed an irradiance dependence to the appearance of a fluorescence emission peak near 620 nm, consistent with accumulation of uroporphyrin/coproporphyrin in response to mitochondrial damage. [source] Green photoluminescence of SrGa2S4:Sn phosphorsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 11 2009Mutsumi Nagata Abstract The phosphor SrGa2S4:Sn exhibits a new green photoluminescence (PL) whose spectrum peaks at 534,nm. The phosphor also exhibits yellow and orange PL with very broad spectral bands when the excitation wavelength of the UV light is changed. These emissions are caused by the 5p,5s transition in the 5s2 configuration of Sn2+ ions occupying Sr2+ sites. The origin of the green emission was investigated by analyzing the PL excitation spectra and the electronic states of Sn2+ substituting at three different Sr2+ sites. The electronic states were analyzed in a first-principles calculation of the density of states. [source] Analysis of Raman modes in Mn-doped ZnO nanocrystalsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 10 2009Shuxia Guo Abstract Mn-doped ZnO was synthesized using a co-precipitation technique. X-ray diffraction (XRD) measurements and photoluminescence (PL) spectra show that Mn ions are doped into the lattice positions of ZnO. The modes at 202, 330, and 437,cm,1 in the Raman spectrum are assigned as 2E2 (low), E2 (high),E2 (low), and E2 (high) modes of ZnO base, respectively. The mode at 528,cm,1 is ascribed to a local vibrational mode related to Mn. The mode at 580,cm,1 should be an intrinsic mode of ZnO and assigned to E1 longitudinal optical (LO). Its reinforcement should result from a combination of resonance at the excitation wavelength and impurity-induced scattering. [source] G-mode behaviour of closed ended single wall carbon nanotubes under pressurePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2009Ahmad J. Ghandour Abstract We have performed high pressure Raman experiments on closed-ended single wall carbon nanotubes using two different excitation wavelengths: 632.8 nm and 514 nm. We found that the shape of the G-mode spectrum changes while changing the excitation wavelength at lower pressures, while it becomes similar at 3.5 GPa. In addition we record that the value of the transition pressure, associated with the structural transitions in the tubes, has also changed with changing the excitation wavelength even though we are examining tubes from the same produced sample. We attribute these results to the tubes having different electronic nature (metallic; semi-conducting) and different diameters in resonance with each excitation wavelength. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Surface phonons in CdS1,xSex nanoparticles embedded in a dielectric mediumPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 9 2009Yu. M. Azhniuk Abstract Raman scattering by surface phonons in CdS1,xSex nanocrystals grown in a borosilicate glass matrix, is studied. CdSe-like and CdS-like surface phonon frequencies are shown to increase with the relevant component content in the nanocrystal composition. No clear size dependence of the surface phonon frequencies has been observed. On the other hand, surface phonons in CdS1,xSex nanocrystals exhibit resonant dependence on the Raman excitation wavelength. It is emphasized that measurements of Raman scattering by surface phonons in CdS1,xSex nanocrystals give no reason to judge upon the nanocrystal shape. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Development of a fluorimetric detection method for cinnabarinic acid using ortho -tolyl hydrazine as the derivatization reagentBIOMEDICAL CHROMATOGRAPHY, Issue 3 2010Hideaki Iizuka Abstract A fluorimetric detection method for one of the tryptophan metabolites, cinnabarinic acid (CA), which has recently been reported to have the ability to induce apoptosis in thymocytes, was developed using o -tolyl hydrazine (TH) as the derivatization reagent. The carbonyl group at position 3 in CA was tagged with the hydrazino moiety of TH at 100°C for 30 min, and the generated derivative, CA tagged with TH, fluoresced at 412 nm with a 316 nm excitation wavelength. The CA tagged with TH was separated on a reversed-phase HPLC and detected fluorometrically. The relative standard deviation was in the range of 1.1,8.9% (n = 3), and the detection limit was approximately 12?fmol (signal-to-noise ratio, 3). The proposed HPLC method can be useful for the sensitive detection of CA. Copyright © 2009 John Wiley & Son, Ltd. [source] A new HPLC method for serum neopterin measurement and relationships with plasma thiols levels in healthy subjectsBIOMEDICAL CHROMATOGRAPHY, Issue 6 2004Ciriaco Carru Abstract Neopterin, a pyrazinopyrimidine compound, serves as a marker of cellular immune system activation, and it can be used as a prognostic predictor for certain types of diseases. We propose a new simple HPLC method to measure serum neopterin with highly sensitive ,uorimetric detection. After TCA serum protein precipitation, the supernatant was diluted ,ve times, injected into a C18 reversed-phase column and eluted at a ,ow rate of 1.5 mL/min by an isocratic water,acetonitrile (99:1) mobile phase. The natural ,uorescence of the molecule was detected at excitation wavelength 353 nm and emission 438 nm. In these conditions the neopterin retention time was about 4 min. Our proposed method was compared with a validated chromatographic separation, and the obtained data of the serum neopterin from 35 healthy volunteers were analysed by Passing,Bablok regression and Bland,Altman test. Neopterin measurement in healthy subjects was also employed to investigate on its potential relationships with plasma thiols levels. Copyright © 2004 John Wiley & Sons, Ltd. [source] Synthesis and Photophysical Properties of C60 -carbazole AdductsCHINESE JOURNAL OF CHEMISTRY, Issue 9 2001Gui Yin Abstract Three C60 -carbazole adducts have been synthesized by 1, 3-dipolar cycloaddition reaction. Intramolecular energy/electron transfer from carbazole to C60 was observed by steady-state absorption and fluorescence spectra. The fluorescence spectra of these adducts were similar to each other and dependent on the excitation wavelength and solvent. [source] Controlling Light Oxidation Flavor in Milk by Blocking Riboflavin Excitation Wavelengths by InterferenceJOURNAL OF FOOD SCIENCE, Issue 9 2009J.B. Webster ABSTRACT:, Milk packaged in glass bottles overwrapped with iridescent films (treatments blocked either a single visible riboflavin [Rb] excitation wavelength or all visible Rb excitation wavelengths; all treatments blocked UV Rb excitation wavelengths) was exposed to fluorescent lighting at 4 °C for up to 21 d and evaluated for light-oxidized flavor. Controls consisted of bottles with no overwrap (light-exposed treatment; represents the light barrier properties of the glass packaging) and bottles overwrapped with aluminum foil (light-protected treatment). A balanced incomplete block multi-sample difference test, using a ranking system and a trained panel, was used for evaluation of light oxidation flavor intensity. Volatiles were evaluated by gas chromatography and Rb degradation was evaluated by fluorescence spectroscopy. Packaging overwraps limited production of light oxidation flavor over time but not to the same degree as the complete light block. Blocking all visible and UV Rb excitation wavelengths reduced light oxidation flavor better than blocking only a single visible excitation wavelength plus all UV excitation wavelengths. Rb degraded over time in all treatments except the light-protected control treatment and only minor differences in the amount of degradation among treatments was observed. Hexanal production was significantly higher in the light-exposed control treatment compared to the light-protected control treatment from day 7; it was only sporadically significantly higher in the 570 nm and 400 nm block treatments. Pentanal, heptanal, and an unidentified volatile compound also increased in concentration over time, but there were no significant differences in concentration among the packaging overwrap treatments for these compounds. [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] A white light confocal microscope for spectrally resolved multidimensional imagingJOURNAL OF MICROSCOPY, Issue 3 2007J. H. FRANK Summary Spectrofluorometric imaging microscopy is demonstrated in a confocal microscope using a supercontinuum laser as an excitation source and a custom-built prism spectrometer for detection. This microscope system provides confocal imaging with spectrally resolved fluorescence excitation and detection from 450 to 700 nm. The supercontinuum laser provides a broad spectrum light source and is coupled with an acousto-optic tunable filter to provide continuously tunable fluorescence excitation with a 1-nm bandwidth. Eight different excitation wavelengths can be simultaneously selected. The prism spectrometer provides spectrally resolved detection with sensitivity comparable to a standard confocal system. This new microscope system enables optimal access to a multitude of fluorophores and provides fluorescence excitation and emission spectra for each location in a 3D confocal image. The speed of the spectral scans is suitable for spectrofluorometric imaging of live cells. Effects of chromatic aberration are modest and do not significantly limit the spatial resolution of the confocal measurements. [source] Characterisation of carbonaceous materials using Raman spectroscopy: a comparison of carbon nanotube filters, single- and multi-walled nanotubes, graphitised porous carbon and graphiteJOURNAL OF RAMAN SPECTROSCOPY, Issue 3 2009H. M. Heise Abstract Multi-walled carbon nanotube (MWCNT) filters have been recently synthesised which have specific molecular filtering capabilities and good mechanical strength. Optical and scanning electron microscopy (SEM) reveals the formation of highly aligned arrays of bundles of carbon nanotubes having lengths up to 500 µm. The Raman spectra of this material along with four other carbonaceous materials, commercially available single-walled carbon nanotubes (SWCNTs) and MWCNTs, graphitised porous carbon (Carbotrap) and graphite have been recorded using two-excitation wavelengths, 532 and 785 nm, and analysed for band positions and shape with special emphasis paid to the D-, G- and G,-bands. A major difference between the different MWCNT varieties analysed is that G-bands in the MWCNT filters exhibit almost no dispersion, whereas the other MWCNTs show a noticeable dispersive behaviour with a change in the excitation wavelength. Spectral features similar to those of the MWCNT filter varieties were observed for the Carbotrap material. From the line shape analysis, the intensity ratio, ID/IG, of the more ordered MWCNT filter material using the integral G-band turns out to be two times lower than that of the less ordered MWCNT filter product at both excitation wavelengths. This parameter can, therefore, be used as a measure of the degree of MWCNT alignment in filter varieties, which is well supported also by our SEM study. Copyright © 2008 John Wiley & Sons, Ltd. [source] | ||||||||||||||||||||||