Time-resolved Laser-induced Fluorescence Research Articles

Laguerre-based method for analysis of time-resolved fluorescence data: application to in-vivo characterization and diagnosis of atherosclerotic lesions.

We report the application of the Laguerre deconvolution technique (LDT) to the analysis of in-vivo time-resolved laser-induced fluorescence spectroscopy (TR-LIFS) data and the diagnosis of atherosclerotic plaques. TR-LIFS measurements were obtained in vivo from normal and atherosclerotic aortas (eight rabbits, 73 areas), and subsequently analyzed using LDT. Spectral and time-resolved features were used to develop four classification algorithms: linear discriminant analysis (LDA), stepwise LDA (SLDA), principal component analysis (PCA), and artificial neural network (ANN). Accurate deconvolution of TR-LIFS in-vivo measurements from normal and atherosclerotic arteries was provided by LDT. The derived Laguerre expansion coefficients reflected changes in the arterial biochemical composition, and provided a means to discriminate lesions rich in macrophages with high sensitivity (>85%) and specificity (>95%). Classification algorithms (SLDA and PCA) using a selected number of features with maximum discriminating power provided the best performance. This study demonstrates the potential of the LDT for in-vivo tissue diagnosis, and specifically for the detection of macrophages infiltration in atherosclerotic lesions, a key marker of plaque vulnerability.

Distinction of brain tissue, low grade and high grade glioma with time-resolved fluorescence spectroscopy.

Neuropathology frozen section diagnoses are difficult in part because of the small tissue samples and the paucity of adjunctive rapid intraoperative stains. This study aims to explore the use of time-resolved laser-induced fluorescence spectroscopy as a rapid adjunctive tool for the diagnosis of glioma specimens and for distinction of glioma from normal tissues intraoperatively. Ten low grade gliomas, 15 high grade gliomas without necrosis, 6 high grade gliomas with necrosis and/or radiation effect, and 14 histologically uninvolved "normal" brain specimens are spectroscopicaly analyzed and contrasted. Tissue autofluorescence was induced with a pulsed Nitrogen laser (337 nm, 1.2 ns) and the transient intensity decay profiles were recorded in the 370-500 nm spectral range with a fast digitized (0.2 ns time resolution). Spectral intensities and time-dependent parameters derived from the time-resolved spectra of each site were used for tissue characterization. A linear discriminant analysis diagnostic algorithm was used for tissue classification. Both low and high grade gliomas can be distinguished from histologically uninvolved cerebral cortex and white matter with high accuracy (above 90%). In addition, the presence or absence of treatment effect and/or necrosis can be identified in high grade gliomas. Taking advantage of tissue autofluorescence, this technique facilitates a direct and rapid investigation of surgically obtained tissue.

Observation of aqueous Cm(III)/Eu(III) and UO 22+ nanoparticulates at concentrations approaching solubility limit by laser-induced fluorescence spectroscopy

Eu(III), Cm(III) and the uranyl ion display intense fluorescence spectra in the visible range and the spectroscopic characteristics are dependent on the composition and structure of the individual metal complexes. In this work, we demonstrate the application of laser-induced time-resolved fluorescence spectroscopy in identification of nanoparticles of (i) Eu(III) and Cm(III) in basic solutions (pH > 10) in the presence of organic chelates including EDTA, HEDTA, NTA and oxalate and (ii) sodium uranyl phosphate after equilibration with synthetic sodium uranyl phosphate suspensions. Fluorescence spectral and SEM results indicate that Eu(III) and Cm(III) can exist as colloidal nanoparticles in filtered 0.1 M NaOH solutions. Such nanoparticles, which display largely red-shifted fluorescence spectra as compared with the aqueous complexes and unusually short fluorescence lifetimes, contribute to the measured concentrations of Eu(III)/Cm(III) in the aqueous solutions. Similarly, uranyl spectroscopic signatures indicate that the determination of the solubility of uranium phosphate minerals is prone to the presence of uranyl phosphate nanoparticles. Due to the presence of such nanoparticles, the common solubility measurements may only indicate an upper limit of the “true” solubility.

Detection of U(VI) on the surface of altered depleted uranium by time-resolved laser-induced fluorescence spectroscopy (TRLFS)

Time-resolved laser-induced fluorescence spectroscopy (TRLFS) was applied to study the surface of a depleted uranium (DU) disc immersed in a Ca-phosphate solution for 182 days. The weathering solution contained 2.49·10 − 3 M calcium and 1.05·10 − 3 M phosphate, representing enhanced pore water concentrations of agricultural soils. The TRLFS results clearly show that meta-autunite, a U(VI) phosphate, has formed during low temperature alteration of the DU disc. This secondary U(VI) mineral phase was identified using a fingerprinting procedure by comparing it with TRLFS-spectra from an in-house U(VI) TRLFS database, including U(VI) oxides, U(VI) hydroxides, U(VI) sulphates and U(VI) phosphates. Its TRLFS spectrum is characterized by six fluorescence emission bands at 486, 501, 522, 546, 573, and 601 nm, and two fluorescence life times of 50 ± 5 ns and 700 ± 25 ns.

Two-point time-series measurements of minor-species concentrations in a turbulent nonpremixed flame

We report a technique that is capable of making simultaneous two-point time-series measurements of minor-species concentrations in turbulent flames. The experimental setup, which incorporates picosecond time-resolved laser-induced fluorescence, has a spatial resolution of less than 250 microm and a temporal resolution of less than 100 micros, which spatially and temporally resolve microscales in many turbulent flows. Two-point time-series data are given for a standard turbulent nonpremixed flame at Re= 10,000, including a discussion of potential implications.

A theoretical study on molecular structure of Eu(III)-salicylate complexes in aqueous system

The coordination geometry of Eu(III)-salicylate complexes in aqueous phase was obtained using a density functional theory (DFT) calculation. Geometry optimization with hybrid functional B3LYP revealed that the 1:1 carboxylate-coordinated complex takes uni-dentate coordination between carboxylate and central Eu(III), and holds eight coordination water molecules in its first coordination sphere, resulting in the constitution [Eu(HSA)·8H 2O] 2+, where (HSA) stands for salicylate with protonated OH group. Adopting a determination procedure including a continuum solvent using the CPCM model made a significant contribution. Namely, we found that the bi-dentate model with the constitution [Eu(HSA)·7H 2O] 2+ was the most stable structure of all models in the gas-phase, while the uni-dentate model [Eu(HSA)·8H 2O] 2+ became the most stable when using the CPCM solvent model. This agreed well with our recent experimental study using time-resolved laser-induced fluorescence spectroscopy (TRLIFS), where 5-sulfosalicylate forms a complex with Eu(III) via carboxyl group with uni-dentate coordination. The most stable geometry of the corresponding chelate complexes, Eu(SA) +, was obtained by the same procedure, and the constitution was identified as [Eu(SA)·6H 2O] +, where (SA) stands for salicylate with dissociated OH group. This suggests an important chemical finding that the following intra-molecular chelate ring closure reaction holds: [Eu(HSA)·8(H 2O)] 2+→[Eu(SA)·6(H 2O)] +H 3O +(H 2O). This means that two water molecules are dissociated with the penetration of the OH group into the first coordination sphere, and the coordination number of the central Eu(III) is reduced from nine to eight with the chelate ring closing reaction.

Two-photon laser-induced fluorescence of atomic hydrogen in a diamond-depositing dc arcjet

Atomic hydrogen in the plume of a dc-arcjet plasma is monitored by use of two-photon excited laser-induced fluorescence (LIF) during the deposition of diamond film. The effluent of a dc-arc discharge in hydrogen and argon forms a luminous plume as it flows through a converging-diverging nozzle into a reactor. When a trace of methane (< 2%) is added to the flow in the diverging part of the nozzle, diamond thin film grows on a water-cooled molybdenum substrate from the reactive mixture. LIF of atomic hydrogen in the arcjet plume is excited to the 3S and 3D levels with two photons near 205 nm, and the subsequent fluorescence is observed at Balmer-alpha near 656 nm. Spatially resolved LIF measurements of atomic hydrogen are made as a function of the ratio of hydrogen to argon feedstock gas, methane addition, and reactor pressure. At lower reactor pressures, time-resolved LIF measurements are used to verify our collisional quenching correction algorithm. The quenching rate coefficients for collisions with the major species in the arcjet (Ar, H, and H2) do not change with gas temperature variations in the plume (T < 2300 K). Corrections of the LIF intensity measurements for the spatial variation of collisional quenching are important to determine relative distributions of the atomic hydrogen concentration. The relative atomic hydrogen concentrations measured here are calibrated with an earlier calorimetric determination of the feedstock hydrogen dissociation to provide quantitative hydrogen-atom concentration distributions.

Radiative Lifetimes of Doubly Ionized Terbium

Radiative lifetimes of two short-lived levels (i.e. 4f8(7F6)6p1/2 (6,1/2)11/2,13/2) in Tb III aremeasured by time-resolved laser-inducedfluorescence (LIF) technique with a two-step excitation process. FreeTb III ions are produced in a laser-induced plasma. Lifetimevalues are evaluated with a deconvolution procedure of the time-resolvedfluorescence signal with the temporal shape of second-step excitationpulse (about 1 ns). The lifetimes of the 4f8 (7F6)6p1/2(6,1/2)11/2 and 4f8 (7F6)6p1/2 (6,1/2)13/2levels are determined to be 1.9 (2) and 2.0 (2) ns, respectively.

Characterization and Comparison of Cm(III) and Eu(III) Complexed with 2,6-Di(5,6-dipropyl-1,2,4-triazin-3-yl)pyridine Using EXAFS, TRFLS, and Quantum-Chemical Methods

The complexation of Cm(III) and Eu(III) with 2,6-di(5,6-dipropyl-1,2,4-triazin-3-yl)pyridine (n-C3H7-BTP) in nonaqueous organic solution is studied with extended X-ray absorption spectroscopy. Bond lengths are the same in both complexes. Quantum-chemical calculations performed at different levels support this finding. On the other hand, the Cm.(n-C3H7-BTP)3 complex is formed at much lower ligand-to-metal concentration ratio than the Eu.(n-C3H7-BTP)3 complex, as shown by time-resolved laser-induced fluorescence spectroscopy. This is in good agreement with n-C3H7-BTP's high selectivity for trivalent actinides over lanthanides in liquid-liquid extraction.

Radiative lifetimes and transition probabilities in Ta I

Radiative lifetimes of 14 odd-parity Ta I levels, belonging to the 5d36s6p and 5d46p configurations in the energy range from 30 664 to 45 256 cm-1, have been measured using the time-resolved laser-induced fluorescence technique. Extensive calculations, taking configuration interactions and core-polarisation effects into account, are able to reproduce in a satisfying way the available experimental results but suffer from the rather fragmentary knowledge of the level structure of this atom. New transition probabilities are deduced for a set of strong lines depopulating the levels investigated experimentally in the present work.

Lifetimes along perturbed Rydberg series in neutral thallium

Radiative lifetimes of 15 Tl I levels belonging to the 6s2ns2S1/2 (n = 7–14) and 6s2nd2D3/2 Rydberg series (n = 6–12) have been measured using a time-resolved laser-induced fluorescence technique. All the measured levels have been excited from the ground state 6s26p2P01/2 (odd parity) with a single-step excitation process. The general perturbation of the ns series by the 6s6p2 configuration and the corresponding modification of the lifetimes are adequately reproduced by a theoretical model including core-polarization effects and combined with a least-squares fit to the observed energy levels. The general behaviour of the lifetime values for the 6s2np odd levels along the Rydberg series is also well reproduced. The use of the multiconfiguration quantum defect theory has allowed us to obtain lifetime values along the 6s2ns2S1/2 series up to levels with n = 31.

Uranyl sorption onto gibbsite studied by time-resolved laser-induced fluorescence spectroscopy (TRLFS)

Time-resolved laser-induced fluorescence spectroscopy (TRLFS) was combined with batch experiments to study the sorption of uranium(VI) onto gibbsite ( γ-Al(OH) 3). The experiments were performed under ambient conditions in 0.1 M NaClO 4 solution in the pH range from 5.0 to 8.5 using a total uranium concentration of 1 × 10 −5 M , and a solid concentration of 0.5 g/40 ml. Two uranyl surface species with fluorescence lifetimes of 330 ± 115 and 5600 ± 1640 ns , respectively, were identified. The first species was dominating the more acid pH region whereas the second one became gradually more prominent towards higher pH values. The fluorescence spectra of both adsorbed uranyl(VI) surface species were described with six characteristic fluorescence emission bands situated at 479.5 ± 1.1 , 497.4 ± 0.8 , 518.7 ± 1.0 , 541.6 ± 0.7 , 563.9 ± 1.2 , and 585.8 ± 2.1 nm . The surface species with the short-lived fluorescence lifetime of 330 ns is attributed to a bidentate mononuclear inner-sphere surface complex in which the uranyl(VI) is bound to two reactive OH − groups at the broken edge linked to one Al. The second surface species with the significant longer fluorescence lifetime of 5600 ns was attributed to small sorbed clusters of polynuclear uranyl(VI) surface species. The longer fluorescence lifetime of the long-lived uranyl surface species at pH 8.5 is explained with the growing average size of the adsorbed polynuclear uranyl surface species.

Radiation trapping of the Hg 254 nm resonance line

The decay rate of Hg 6 3P1 atoms, due primarily to the escape of trapped 254 nm resonance radiation, was measured as a function of both Hg and Ar density in cylindrical, sealed fused silica cells. Time-resolved laser-induced fluorescence at 254 nm was used to obtain the decay rates for Hg densities from 5 × 1013 to 7 × 1015 cm−3 (22–101°C cold spot temperatures) and Ar densities from 0 to 9.7 × 1017 cm−3 in a cell of inner radius 1.05 cm. These new experimental data are compared to Monte Carlo results from a highly realistic code for simulating radiation trapping. This code includes Voigt profiles from a combination of Doppler, resonance, buffer gas and radiative line broadening, as well as hyperfine and isotopic structure with proper collisional redistribution. Upper limits on the rate constants for the quenching of Hg 6 3 P1 atoms by collisions with ground level Ar and Hg atoms were derived. Additional Monte Carlo simulations covering cell radii from 0.1 to 3.0 cm were performed. A broadly applicable engineering formula is derived from this study, which predicts the Hg 6 3P1 decay rate from 254 nm resonance radiation trapping as a function of Hg and Ar densities and cell radius.

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

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 β 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.

Stabilities of the Aqueous Complexes Cm(CO3)33- and Am(CO3)33- in the Temperature Range 10−70 °C

The carbonate complexation of curium(III) in aqueous solutions with high ionic strength was investigated below solubility limits in the 10-70 degrees C temperature range using time-resolved laser-induced fluorescence spectroscopy (TRLFS). The equilibrium constant, K(3), for the Cm(CO(3))(2-) + CO(3)(2-) right harpoon over left harpoon Cm(CO(3))(3)(3-) reaction was determined (log K(3) = 2.01 +/- 0.05 at 25 degrees C, I = 3 M (NaClO(4))) and compared to scattered previously published values. The log K(3) value for Cm(III) was found to increase linearly with 1/T, reflecting a negligible temperature influence on the corresponding molar enthalpy change, Delta(r)H(3) = 12.2 +/- 4.4 kJ mol(-1), and molar entropy change, Delta(r)S(3) = 79 +/- 16 J mol(-1) K(-1). These values were extrapolated to I = 0 with the SIT formula (Delta(r)H(3) degrees = 9.4 +/- 4.8 kJ mol(-1), Delta(r)S(3) degrees = 48 +/- 23 J mol(-1) K(-1), log K(3) degrees = 0.88 +/- 0.05 at 25 degrees C). Virtually the same values were obtained from the solubility data for the analogous Am(III) complexes, which were reinterpreted considering the transformation of the solubility-controlling solid. The reaction studied was found to be driven by the entropy. This was interpreted as a result of hydration changes. As expected, excess energy changes of the reaction showed that the ionic strength had a greater influence on Delta(r)S(3) than it did on Delta(r)H(3).

Curium(III) species and the coordination states in concentrated LiCl-aqueous solutions studied by time-resolved laser-induced fluorescence spectroscopy

Study on Cm(III) species and the coordination states in concentrated LiCl-aqueous solutions were performed by using time-resolved laser-induced fluorescence spectroscopy. The inner-sphere hydration number, N H 2 O and average chloride coordination number, N Cl, of Cm(III) were determined from the luminescence lifetimes and emission spectra, respectively. While the inner-sphere coordination sites of Cm(III) was fully occupied by water molecules in the C LiCl range less than 4 M, the inner-sphere chloro complexation of Cm(III) was observed in the C LiCl range more than 6 M. The total coordination number, defined as the sum of N H 2 O and N Cl, was kept constant in the C LiCl range up to 10 M, and then decreased gradually with an increase of C LiCl. This indicates that one chloride ion excludes more than one water molecule through the inner-sphere chloro complexation in the extremely concentrated LiCl-aqueous solutions.

Interactions of rare earth elements with bacteria and organic ligands

We investigated the interactions of rare earth elements (REEs) Eu(III) and/or Ce(III, IV) with the common soil bacterium Pseudomonas fluorescens and organic ligands, such as malic acid, citric acid, a siderophore (DFO), cellulose, chitin, and chitosan. Malic acid formed complexes with Eu(III), but degradation of malic acid was observed when the ratio of malic acid to Eu(III) was higher than 100. Citric acid formed a stoichiometric complex with Eu(III) that was not degraded by P. fluorescens. Adsorption of Eu(III) from the DFO complex occurred as a free ion dissociated from DFO and not as the Eu(III)–DFO complex. Cerium(III) was oxidized to Ce(IV) during complexation with DFO to form the Ce(IV)–DFO complex. Time-resolved laser-induced fluorescence spectroscopy (TRLFS) analysis showed that cellulose, chitin, and chitosan, respectively, formed a weak complex, an inner-spherical complex, and an outer-spherical complex with Eu(III). This method also demonstrated that the coordination environment of Eu(III) adsorbed on P. fluorescens possessed similar characteristics to that of chitin, and revealed that adsorption of Eu(III) on P. fluorescens was through a multidentate and predominantly inner-spherical coordination.

NO Reburn and Formation Chemistry in Methane Diffusion Flames

Abstract We have applied time-resolved picosecond linear laser-induced fluorescence to obtain spatially resolved profiles of NO in laminar methane/air and methane/nitric oxide/air counterflow diffusion flames at atmospheric pressure. Temperature profiles have been measured with broadband CARS of nitrogen. Flames at strain rates from 59 s−1 to 269 s−1 were studied to characterize the strain rate dependence of the NO concentration. The work shows that NO concentrations decrease with increasing strain rate. Comparisons have been made with predicted NO levels obtained using two different chemical kinetic mechanisms (Lindstedt and co-workers and GRI-Mech. 3.0). Computed concentrations are shown to be in good agreement with experimental data. The addition of up to 600 ppm NO to the fuel did permit an assessment of differences in the reburn chemistry between the two mechanisms.

In vivo detection of macrophages in a rabbit atherosclerotic model by time-resolved laser-induced fluorescence spectroscopy

Accumulation of numerous macrophages in the fibrous cap is a key identifying feature of plaque inflammation and vulnerability. This study investigates the use of time-resolved laser-induced fluorescence spectroscopy (TR-LIFS) as a potential tool for detection of macrophage foam cells in the intima of atherosclerotic plaques. Experiments were conducted in vivo on 14 New Zealand rabbits (6 control, 8 hypercholesterolemic) following aortotomy to expose the intimal luminal surface of the aorta. Tissue autofluorescence was induced with a nitrogen pulse laser (337 nm, 1 ns). Lesions were histologically classified by the percent of collagen or macrophage foam cells as well as thickness of the intima. Using parameters derived from the time-resolved fluorescence emission of plaques, we determined that intima rich in macrophage foam cells can be distinguished from intima rich in collagen with high sensitivity (>85%) and specificity (>95%). This study demonstrates, for the first time, that a time-resolved fluorescence-based technique can differentiate and demark macrophage content versus collagen content in vivo. Our results suggest that TR-LIFS technique can be used in clinical applications for identification of inflammatory cells important in plaque formation and rupture.

On the Use of Spectroscopic Techniques for Interaction Studies, Part I: Complexation between Europium and Small Organic Ligands

In the framework of environmental studies, it is important to understand the interaction of humic substances with cations (heavy metals, radionuclides) and to determine their complexation constants in order to evaluate their potential impact on their fate. For this purpose, two techniques have been used: electrospray ionization mass spectrometry, a newly used technique in speciation studies, and time-resolved laser-induced fluorescence spectrometry, a well-known technique for such studies. As a first step, for simplification purposes and to compare both techniques, simple molecules having functional groups present in humic substances have been selected, such as acetic, glycolic, and 4-hydroxyphenylacetic acids. Both techniques have been used to obtain stoichiometries and complexation constants between these simple molecules and europium (III).