Nitrogen Laser Research Articles

Fluorescence lifetime spectroscopy of glioblastoma multiforme.

Fluorescence spectroscopy of the endogenous emission of brain tumors has been researched as a potentially important method for the intraoperative localization of brain tumor margins. We investigated the use of time-resolved, laser-induced fluorescence spectroscopy for demarcation of primary brain tumors by studying the time-resolved spectra of gliomas. The fluorescence of human brain samples (glioblastoma multiforme, cortex and white matter: six patients, 23 sites) was induced ex vivo with a pulsed nitrogen laser (337 nm, 3 ns). The time-resolved spectra were detected in a 360-550 nm wavelength range using a fast digitizer and gated detection. Parameters derived from both the spectral- (intensities from narrow spectral bands) and the time domain (average lifetime) measured at 390 and 460 nm were used for tissue characterization. We determined that high-grade gliomas are characterized by fluorescence lifetimes that varied with the emission wavelength (>3 ns at 390 nm, <1 ns at 460 nm) and their emission is overall longer than that of normal brain tissue. Our study demonstrates that the use of fluorescence lifetime not only improves the specificity of fluorescence measurements but also allows a more robust evaluation of data collected from brain tissue. Combined information from both the spectral- and the time domain can enhance the ability of fluorescence-based techniques to diagnose and detect brain tumor margins intraoperatively.

Native fluorescence detection of flavin derivatives by microchip capillary electrophoresis with laser-induced fluorescence intensified charge-coupled device detection

To widen the scope of laser-induced fluorescence (LIF) for detection in microchip capillary electrophoresis (CE), a microchip CE LIF–ICCD (intensified charge-coupled device) system based on a tunable wavelength dye laser pumped by a pico-second pulse nitrogen laser for excitation and a spectrograph with ICCD for detection had developed to demonstrate the enhancement in detection sensitivity by the following three approaches: direct detection of native fluorescence, improvement of signal-to-noise ratio by pulse laser excitation and time delay detection, and selective spectral acquisition by multi-channel detection. Riboflavin, flavin mononucleotide (FMN) and flavin-adenine dinucleotide (FAD) have been selected as they are dietetically important and microchip CE provides a promising onsite detection method. The results indicate a strong effect of wavelength on detection sensitivity and the need to tune wavelength for direct detection. Under optimized conditions (excitation 450 nm, emission 520 nm, gate delay time 45 ns, 20 mM phosphate buffer at pH 7.1), the following results were obtained under static condition: Working ranges (0.6–350 μg/l, r>0.99), detection limits (0.15–1.0 μg/l) and peak height repeatability (1.8–2.2% R.S.D.), all within the applicability range for body fluids or beverages such as human urine and cow milk. Baseline separation of three flavins was obtained under dynamic condition and the fluorescence spectra acquired assist the identification of alkaline-degraded products of riboflavin. Thus, the capability to check peak purity and identify unknown peaks has been demonstrated.

Cluster formation in UV laser ablation plumes of ZnSe and ZnO studied by time-of-flight mass spectrometry

The composition of nitrogen laser (wavelength 337 nm, pulse width 3 ns) induced ablation plumes from ZnSe and ZnO targets was studied at different laser fluences using a time-of-flight mass spectrometer. In the case of ZnSe, abundant ion signals corresponding to Se and ZnSe clusters, some of which were Se-rich, were detected with fluence-dependent distributions. At a laser fluence of 1250 J m-2, clusters with elevated intensity were observed at sizes of 6, 13, 19, 23 and 33 ZnSe molecules (‘magic numbers’), which match quite well with the earlier observation by others of magic numbers of chemically similar ZnS produced by a conventional vaporization and quenching scheme. In the case of ZnO, we detected the presence of atomic Zn and molecular species of ZnO, as well as a series of (ZnO)n-type clusters with fluence-dependent distributions. Unlike the case of ZnSe, no magic numbers were observed for ZnO.

Characterization of Coarse Particles Formed by Laser Ablation of MALDI Matrixes

The quantity and size distribution of micrometer-sized particles ejected from thin crystalline films of organic molecules was measured with light scattering particle sizing. Four compounds that are commonly used as matrix materials in matrix-assisted laser desorption ionization (MALDI) were studied: 2,5-dihydroxybenzoic acid (DHB), sinapic acid, 4-nitroaniline, and 2-(4-hydroxyphenylazo)benzoic acid (HABA). Thin films of these matrixes were irradiated at atmospheric pressure with a 4 ns pulsed 337 nm nitrogen laser. Particulate resulting from the ablation was sampled directly into a particle sizing instrument. The mean aerodynamic diameter of the coarse particles formed at a laser fluence of 500 J/m2 was approximately 700 nm for all matrixes. This value does not include particles below 500 nm, which are not accurately measured by the particle sizing instrument. The threshold for detection of particles from the DHB matrix was found to be 300 J/m2 and it was estimated that an average of 1000 particles in the micrometer size range are ejected per laser shot. The fluence threshold and quantity of material ablated are similar to that observed for MALDI ion formation, suggesting that the role of large particle formation in this process is significant.

Stationary spectroscopy of biotissues in vivo: Fluorescent studies of some pathological states

The stationary spectra of autofluorescence, along with the reflection coefficient at the wavelength of excitation, are measured in vivo for some stomach tissues in the case of different pathological states (dysplasia, superficial gastritis, and cancer) using a nitrogen laser as the source of excitation (λrad=337.1 nm). The fluorescence spectra obtained are decomposed into Gaussian-Lorentzian components. It is found that, in development of dysplasia and tumor processes, at least seven groups of fluorophores can be distinguished that form the entire emission spectrum. The ratio between the fluorescence intensities of flavins and NAD(P)H is determined and the degree of respiratory activity of cells estimated for the states considered. The quantum yields of fluorescence of the biotissues under investigation are estimated.

Using the laser-induced fluorescence spectroscopy in the differentiation between normal and neoplastichuman breast tissue.

This article reports results of the in vitro study for potential evaluation of the laser-induced fluorescence spectroscopy in the differentiation between normal and neoplastic human breast tissue. A coumarine dye laser pumped by nitrogen laser generated an excitation light centered at 458 nm. In order to collect the fluorescence signal was used an optical fiber catheter coupled to a spectrometer and CCD detector. Fluorescence spectra were recorded from normal and neoplastic (benign and malignant) human breast tissue, adding up 94 different areas. The discrimination between normal and neoplasm groups reach a sensitivity and specificity of 100%.

Phase conjugation at the surfaces of optically excited CuI films

The possibility of realizing an optical phase conjugation in an excited semiconductor medium is shown theoretically and experimentally. A phase conjugation is revealed for the photon energy equal to half the energy of the radiative recombination of excitons in CuI films pumped by a nitrogen laser at room temperature. The dependences of the phase-conjugation signal intensity on its spectral composition are investigated. The quadratic interaction of light and exciton electromagnetic oscillations in the semiconductor medium is suggested as an explanation of this effect.

Second-order non-linear optical effects in BiB3O6 glass fibers

Abstract Photo-induced second harmonic generation was found in BiB3O6 (BiBO) glass fibers with diameters 0.7–1.9 mm. We have revealed that maximum of the output second-order optical susceptibility is achieved for the fibers having diameters about 1.1 mm. We have used a pulsed 3.5 MW nitrogen laser (λ=337 nm; τ=50 ps) as a source of photo-inducing laser beam. Fundamental (probing) laser beam was generated by pulsed Nd:YAG laser (λ=1.06 μm; τ=25 ps). Maximal value of the effective photo-induced second-order non-linear optical susceptibility deff was equal to about 1.5 pm/V.

Production of small binary carbon clusters by laser ablation of thin films of derivatised fullerenes

The distribution of small carbon clusters derived by laser ablation (laser desorption/ionization) of thin films of derivatised fullerenes has been studied. The production of positive and negative ions has been monitored by time-of-flight (ToF) mass spectrometry. The materials under investigation included the [60]fullerene (C 60), hydrogenated and deuterated [60]fullerenes (C 60X 36 where X=H and D), fluorinated [60]fullerenes (C 60F x where x=46 and 48) and the aza[60]fullerene dimer ((C 59N) 2). Following laser ablation using a nitrogen laser, the efficient formation of small, negatively charged carbon clusters has been observed, while the corresponding positively charged clusters were not formed. Derivatised fullerenes display the co-formation of small binary carbon clusters of the type C n X −, where n shows odd/even alternation depending on X which represents the heteroatom initially linked to or networked with the fullerene cage. Although binary carbon clusters C n X − were formed where X=H, D and N, the ablation of fluorofullerene targets would not lead to the formation of C n F − clusters under the applied conditions, as confirmed by ablation experiments with chloro/fluoroalky-polymers. The formation of the binary carbon clusters has been also studied by laser fluence-dependent production of C n D − ions from C 60D 36, and by the production of C n P − ions using a composite C 60/P 4 target. Possible pathways leading to small binary carbon clusters are addressed.

O-Glycan Sialylation and the Structure of the Stalk-like Region of the T Cell Co-receptor CD8

Studies of mucins suggest that the structural effects of O-glycans are restricted to steric interactions between peptide-linked GalNAc residues and adjacent polypeptide residues. It has been proposed, however, that differential O-glycan sialylation alters the structure of the stalk-like region of the T cell co-receptor, CD8, and that this, in turn, modulates ligand binding (Daniels, M. A., Devine, L., Miller, J. D., Moser, J. M., Lukacher, A. E., Altman, J. D., Kavathas, P., Hogquist, K. A., and Jameson, S. C. (2001) Immunity 15, 1051-1061; Moody, A. M., Chui, D., Reche, P. A., Priatel, J. J., Marth, J. D., and Reinherz, E. L. (2001) Cell 107, 501-512). We characterize the glycosylation of soluble, chimeric forms of the alphaalpha- and alphabeta-isoforms of murine CD8 containing the O-glycosylated stalk of rat CD8alphaalpha, and we show that the stalk O-glycans are differentially sialylated in CHO K1 versus Lec3.2.8.1 cells (82 versus approximately 6%, respectively). Sedimentation analysis indicates that the Perrin functions, Pexp, which reflect overall molecular shape, are very similar (1.61 versus 1.54), whereas the sedimentation coefficients (s) of the CHO K1- and Lec3.2.8.1-derived proteins differ considerably (3.73 versus 3.13 S). The hydrodynamic properties of molecular models also strongly imply that the sialylated and non-sialylated forms of the chimera have parallel, equally highly extended stalks ( approximately 2.6 A/residue). Our analysis indicates that, as in the case of mucins, the overall structure of O-glycosylated stalk-like peptides is sialylation-independent and that the functional effects of differential CD8 O-glycan sialylation need careful interpretation.

Two-laser infrared and ultraviolet matrix-assisted laser desorption/ionization.

Matrix-assisted laser desorption/ionization (MALDI) was performed using two pulsed lasers with wavelengths in the IR and UV regions. A 10.6 micro m pulsed CO(2) laser was used to irradiate a MALDI target, followed after an adjustable delay by a 337 nm pulsed nitrogen laser. The sample consisted of a 2,5-dihydroxybenzoic acid matrix and bovine insulin guest molecule. The pulse energy for both of the lasers was adjusted so that the ion of interest, either the matrix or guest ion, was not produced by either of the lasers alone. The delay time for maximum ion yield occurs at 1 micro s for matrix and guest ions and the signal decayed to zero in approximately 400 micro s. A mechanism is presented for enhanced UV MALDI ion yield following the IR laser pulse based on transient heating.

Using Ferrocenes to Assist in Voltammetric Characterization of Carbon Fiber Microelectrodes after Electrochemical and Laser Activation

AbstractIn this report the voltammetry of water‐soluble ferrocene derivatives is used to characterize the surface of carbon fiber microelectrodes before and after both electrochemical and laser activation procedures. Activation of carbon electrodes is necessary to produce a reproducible surface that will allow fast electron transfer. However, the activation method that is best suited for a given analysis can differ with analyte. In order to directly compare activation methods and characterize the resulting electrode performance, the voltammetry of a set of ferrocenes which have fast and well‐known electrochemistry has been used. As expected, electrochemical activation (0.000 to 2.000 V (vs. SSCE) at 500 V/s for 15 seconds) resulted in a hydrophilic surface with increased surface area. Laser pretreatment (20 Hz pulsed nitrogen laser irradiation for 15 seconds) appeared to remove surface oxides thereby producing a more hydrophobic surface that facilitates the adsorption of neutral analytes. In general, anionic ferrocene derivatives exhibited more quasi‐reversible voltammetry and were not as strongly adsorbed as the neutral analyte, particularly with electrochemically activated probes. In addition, neutral analytes show considerable adsorption, particularly at laser‐activated electrodes, while the cationic analyte shows significant adsorption at only the electrochemically‐pretreated electrodes, indicating surface‐specific interactions.

Laser beam studies of RPC behaviour in avalanche mode

Primary ionization is created inside the gas gap of a small size (10×20cm2) RPC, analogous to the RPC of the ATLAS muon detector, by focusing a pulsed (width ⩽0.5ns) nitrogen laser beam (transverse diameter ≈15μm). With this set-up we can characterize the behaviour of the RPC by measuring such parameters as drift velocity and gas amplification. For an ATLAS-like gas mixture (97% C2H2F4, 3% isobutane and a small addition of SF6), we have evidence of a space charge influence on RPC rate capability.

Photoinduced second harmonic generation in partially crystallized BiB 3O 6 glass

Photoinduced second harmonic generation was found in BiB 3O 6 (BiBO) glass having different degree of crystallinity. We have revealed that an increasing degree of crystallinity of BiBO glass leads to increase of the output second-order optical susceptibility. We have used a pulsed 35 MW nitrogen laser ( λ=337 nm ; τ=50 ps ) as a source of photoinducing laser beam. Fundamental laser beam was generated by pulsed Nd:YAG laser ( λ=1.06 μm ; time duration about 25 ps). Maximal value of the photoinduced second-order non-linear optical susceptibility d 222 was equal to about 5 pm/V, what is substantially higher than in case of BiBO single crystals (∼ 3 pm/ V ).

Intrinsic and Zn-, Ce-, Tb-, Er-, Sm-, and Eu-Activated photoluminescence of pseudoamorphous GaN and InGaN thin films

Thin films of pseudoamorphous GaN (a-nc-GaN), as well as of its alloys with indium, InxGa1−x N (x=0.04, 0.16), were prepared by magnetron sputtering of a metallic target in the plasma of a reactive nitrogen and argon mixture. The a-nc-GaN films were codoped by the Zn acceptor impurity and a set of rare-earth metal (REM) dopants, namely, Ce, Tb, Er, Sm, and Eu. Photoluminescence (PL) spectra excited by a nitrogen laser with wavelength λ=337 nm at room temperature and 77 K were measured for all compositions and a set of impurities. It was shown that the high-energy PL edge of the pseudoamorphous (a-nc) GaN matrix lies at the same energy as that of the crystalline (epitaxial) c-GaN. As in c-GaN, the Zn acceptor impurity stimulates blue luminescence; however, the PL spectrum is substantially more diffuse, with practically no temperature quenching of the PL present. Indium doping in an amount of 16 at. % results in strong PL with a diffuse peak at 2.1–2.2 eV; the PL of the alloy exhibits temperature quenching as high as a factor of three to four in the interval 77–300 K. The decay time of the PL response increases up to 50 µs. RE impurities enter the amorphous GaN host as trivalent ions and produce narrow-band (except Ce) high-intensity spectra, thus indicating both a high solubility of RE impurities in a-nc-GaN and the generation of an effective crystal field (by the GaN anion sublattice) whose local symmetry makes the intracenter f-f transitions partly allowed.

Optical gain characteristics of C 460 and C 450

Dye concentration dependent gain spectra for Coumarin 460 (C 460) and Coumarin 450 (C 450) in ethanol have been studied using Amplified Spontaneous Emission (ASE) technique under Nitrogen laser (337.1 nm) excitation in the concentration range 10 −2–10 −5 m/l. The dependence of lasing wavelength and peak gain on concentration have been understood in terms of variation of fluorescence lifetime, which is due to photo-physical processes such as radiation trapping and concentration-quenching. Pump intensity dependence of efficiency is also explained in terms of fluorescence lifetime. A comparison of the stability of the two dyes has also been made on the basis of the functional groups at different positions of the basic coumarin.

Mapping fast flows over micrometer-length scales using flow-tagging velocimetry and single-molecule detection.

This paper describes a technique of characterizing microfluidic flow profiles from slow laminar flow to fast near-turbulent flow. Using a photo-activated fluorophore, nanosecond-duration photolysis pulses from a Nitrogen laser, and high-sensitivity single-molecule detection with Ar+ laser excitation, we report the measurement of flow speeds up to 47 m/s in a 33-microm-wide straight channel and the mapping of flow profiles in a 55-microm-wide microchamber. Sensitive single-molecule detection is necessary both because of the short time delay (submicrosecond) between laser photolysis and fluorescence detection and the fast transit times (as low as 10 ns) of the fluorescent molecules across the diffraction-limited beam waist of the Ar+ laser focus. This technique permits the high-resolution three-dimensional mapping and analysis of a wide range of velocity profiles in confined spaces that measure a few micrometers in dimension.

Correlation between the chemical bonding and the physical properties of the CN x films obtained by pulsed laser deposition from C targets in low-pressure N 2

Carbon–nitride thin films were deposited by XeCl* ( λ=308 nm, τ FWHM≅30 ns) multipulse excimer laser irradiation of graphite targets in low-pressure (1–100 Pa) nitrogen atmosphere. We investigated the chemical bonding formation between the C and N atoms, and its influence upon the optical and mechanical properties of the obtained structures. We found that these properties strongly depend on the deposition parameters. These in turn determine the nitrogen content and the sp 3/sp 2/sp carbon atoms hybridization ratio of the synthesized material. According to our results, the increase of the nitrogen pressure or laser fluence in an attempt to obtain CN x thin films with higher N/C ratio does not lead to the formation of the theoretically predicted low-compressibility, high density, extremely hard β-C 3N 4 structure with the C atoms in the sp 3 hybridization state.

Chemiluminescence of Luminol Induced by NpO2F4OH3- Complexes Excited with Nitrogen Laser Radiation (λ = 337.1 nm)

Chemiluminescence of luminol induced by NpO22+ complexes excited with nitrogen laser radiation was studied in 42% solutions of CsF with different pH. The absorption spectra of solutions of NpO2F4OH3- complexes and the chemiluminescence spectra of these solutions containing luminol and having different pH were recorded.

Band bending near the surface in GaN as detected by a charge sensitive probe

ABSTRACTWe measured the absolute value of the surface band bending in GaN layers grown by molecular beam epitaxy with a charge sensitive surface microprobe. Surface potential measurements showed an upward band bending from 0.7 to 1.4 eV in undoped and Si-doped GaN. The samples stored in dark for one week showed an increase in band bending by up to 0.1 eV. The effect of ultraviolet (UV) exposure (with a lamp or a pulsed nitrogen laser) on band bending was also studied. Typically, the surface barrier decreased by about 0.2 – 0.5 eV under UV light. The barrier was restored very slowly (by a logarithmic law) in the dark at room temperature. These and other similar phenomena are tentatively attributed to thermionic transfer of free electrons from the bulk to the surface states. Photo-induced desorption of oxygen may also play a role in the observed effects.