Comparison of two-dimensional fast Raman imaging versus point-by-point acquisition mode for human bone characterization.

Recent technical developments gave rise to a new technology for two-dimensional fast Raman imaging: the DuoScan averaging mode (DS-Avg). This technology allows the acquisition of a Raman spectrum over a rastered macro spot. The aim of this study was to evaluate the interest of the DS-Avg applied on trabecular human bone. The evaluation was based on the comparison of the DS-Avg versus the point-by-point mapping mode in real usage conditions. The signal-to-noise ratio, the spectral difference, and the physicochemical parameters were estimated for comparison of the efficiency of both modes. Principal component analysis was performed to explore the capacity of both modes to detect compositional variations. Results showed that the DS-Avg spectrum was equivalent to the average spectrum of individual spectra acquired with the point-by-point mode for the same sample area. The physicochemical parameters can be also determined from DS-Avg acquisition. The DS-Avg combined with an objective ×50 allows a drastic decrease of the acquisition time, but the information about the micrometric composition is lost. The combination of the DS-Avg with an objective ×100 is a good compromise between acquisition time and resolution. The DS-Avg is a useful technology for imaging mineral and organic phases of bones and for assessing their spatial distribution on large samples. The point-by-point imaging mode is more appropriate to assess the heterogeneous composition of bone within the micrometer scale. For the first time, this study compares the DuoScan averaging mode to the point-by-point imaging mode on a trabecular human bone.

Investigation of the chemical mixing state of individual Asian dust particles by the combined use of electron probe X-ray microanalysis and Raman microspectrometry.

In this work, quantitative electron probe X-ray microanalysis (EPMA) and Raman microspectrometry (RMS) were applied in combination for the first time to characterize the complex internal structure and physicochemical properties of the same ensemble of Asian dust particles. The analytical methodology to obtain the chemical composition, mixing state, and spatial distribution of chemical species within single particles through the combined use of the two techniques is described. Asian dust aerosol particles collected in Incheon, Korea, during a moderate dust storm event were examined to assess the applicability of the methodology to resolve internal mixtures within single particles. Among 92 individual analyzed particles, EPMA and RMS identified 53% of the particles to be internally mixed with two or more chemical species. Information on the spatial distribution of chemical compounds within internally mixed individual particles can be useful for deciphering the particle aging mechanisms and sources. This study demonstrates that the characterization of individual particles, including chemical speciation and mixing state analysis, can be performed more in detail using EPMA and RMS in combination than with the two single-particle techniques alone.

Optimisation of the chemical generation of singlet oxygen (1O2, 1Deltag) from the hydrogen peroxide-lanthanum(III) catalytic system using an improved NIR spectrometer.

A near-IR chemiluminescence spectrometer designed to study chemical sources of singlet oxygen ((1)O(2), (1)Delta(g)), was built by coupling a reactor compartment to a nitrogen-cooled Ge diode through a bundle of optical fibres. This device was used to optimise the generation of (1)O(2) from the hydrogen peroxide-lanthanum(iii) catalytic system. The reaction kinetics were studied with a 2(3)3(3)//12 screening experimental design comprising twelve experiments. The influence of six factors was examined: the nature of the lanthanum salt (hydroxide, oxide or nitrate) and its concentration (0.05 or 0.1 mol L(-1)), the pH value (5, 7 or 9), the concentration of H(2)O(2) (0.5, 1 or 2 mol L(-1)), the temperature (20 or 30 degrees C) and the concentration of EDTA (0 or 5 mmol L(-1)). Two responses were measured: the rate of H(2)O(2) disproportionation and the intensity of the luminescence of (1)O(2) at 1270 nm. The essential factor is the nature of the lanthanum salt since La(NO(3))(3) induces the disproportionation of H(2)O(2) about 60 x faster than La(2)O(3) or La(OH)(3). Other influencing factors are the pH value, the concentration of H(2)O(2), the temperature and the concentration of the lanthanum salt whereas the concentration of EDTA has no effect on the reaction. The catalytic activity of La(NO(3))(3) was then investigated in further detail by studying the influence of two factors (pH and [H(2)O(2)]) thanks to a Doehlert design.

Silicon nanowires coated with silver nanostructures as ultrasensitive interfaces for surface-enhanced Raman spectroscopy.

Silver nanoparticles (Ag NPs) were chemically deposited on silicon nanowires (SiNWs), prepared using the vapor-liquid-solid (VLS) growth mechanism, using an in situ electroless metal deposition technique. The resulting SiNWs/Ag NPs composite interfaces showed large Raman scattering enhancement for rhodamine 6G (R6G) with a detection limit of 10(-14) M and an enhancement factor of 2.3 x 10(8). This large enhancement factor was attributed to the presence of "hot" spots on the SiNWs/Ag NPs substrate.

Correlated fluorescence lifetime and spectral measurements in living cells.

Studies of proteins' interaction in cells by FRET can take benefit from two important photo-physical properties describing fluorescent proteins: fluorescence emission spectrum and fluorescence lifetime. These properties provide specific and complementary information about the tagged proteins and their environment. However, none of them taken individually can completely quantify the involved fluorophore characteristics due to their multiparametric dependency with molecular environment, experimental conditions, and interpretation complexity. A solution to get a better understanding of the biological process implied at the cellular level is to combine the spectral and temporal fluorescence data acquired simultaneously at every cell region under investigation. We present the SLiM-SPRC160, an original temporal/spectral acquisition system for simultaneous lifetime measurements in 16 spectral channels directly attached to the descanned port of a confocal microscope with two-photon excitation. It features improved light throughput, enabling low-level excitation and minimum invasivity in living cells studies. To guarantee a fairly good level of accuracy and reproducibility in the measurements of fluorescence lifetime and spectra on living cells, we propose a rigorous protocol for running experiments with this new equipment that preserves cell viability. The usefulness of SLiM approach for the precise determination of overlapping fluorophores is illustrated with the study of known solutions of rhodamine. Then, we describe reliable FRET experiments in imaging mode realized in living cells using this protocol. We also demonstrate the benefit of localized fluorescence spectrum-lifetime acquisitions for the dynamic study of fluorescent proteins. proteins.

Lanthanum(III)-catalyzed disproportionation of hydrogen peroxide: a heterogeneous generator of singlet molecular oxygen-1O2 (1Deltag)-in near-neutral aqueous and organic media for peroxidation of electron-rich substrates.

The decomposition of hydrogen peroxide into singlet molecular oxygen-(1)O(2) ((1)Delta(g))-in the presence of lanthanum(iii) salts was studied by monitoring its characteristic IR luminescence at 1270 nm. The process was found to be heterogeneously catalyzed by La(III), provided that the heterogeneous catalyst is generated in situ. The yield of (1)O(2) generation was assessed as 45+/-5 % both in water and in methanol. The pH-dependence on the rate of (1)O(2) generation corresponds to a bell-shaped curve from pH 4.5 to 13 with a maximum around pH 8. The study of the influence of H(2)O(2) showed that the formation of (1)O(2) begins as soon as one equivalent of H(2)O(2) is introduced. It then increases drastically up to two equivalents and more smoothly above. Unlike all other metal salt catalyst systems known to date for H(2)O(2) disproportionation, this chemical source of (1)O(2) is able to generate (1)O(2) not only in basic media, but also under neutral and slightly acidic conditions. In addition, this La-based catalyst system has a very low tendency to induce unwanted oxygenating side reactions, such as epoxidation of alkenes. These two characteristics of the heterogeneous lanthanum catalyst system allow non-photochemical (i.e., "dark") singlet oxygenation of substrate classes that cannot be peroxidized successfully with conventional molybdate catalysts, such as allylic alcohols and alkenyl amines.

Calcium peroxide diperoxohydrate as a storable chemical generator of singlet oxygen for organic synthesis.

Calcium peroxide diperoxohydrate (CaO(2).2H(2)O(2)) is an environmentally friendly generator of singlet oxygen ((1)O(2), (1)Delta(g)) that can be used in organic synthesis as an alternative to the regular photochemical method. This compound produces (1)O(2) in various solvents and can be easily recovered by filtration for further regeneration. Both monitoring of (1)O(2) luminescence at 1270 nm and specific trapping have shown that CaO(2).2H(2)O(2) can be stored for several days at -80 degrees C and that the yield of (1)O(2) is equal to 25%. Oxidation of typical organic substrates in methanol or THF through [4 + 2] or [2 + 2] cycloaddition and ene reaction have been carried out on a preparative scale with total conversion and selectivity.