Raman-active Species Research Articles

Ultrabroadband two-beam coherent anti-Stokes Raman scattering and spontaneous Raman spectroscopy of organic fluids: A comparative study.

Spontaneous Raman spectroscopy is a well-established diagnostic tool, allowing for the identification of all Raman active species with a single measurement. Yet, it may suffer from low-signal intensity and fluorescent background. In contrast, coherent anti-Stokes Raman scattering (CARS) offers laser-like signals, but the traditional approach lacks the multiplex capability of spontaneous Raman spectroscopy. We present an ultrabroadband CARS setup which aims at exciting the full spectrum (300-3700 cm-1) of biological molecules. A dual-output optical parametric amplifier provides a ~7 fs pump/Stokes and a ~700 fs probe pulse. CARS spectra of DMSO, ethanol, and methanol show great agreement with spontaneous Raman spectroscopy and superiority in fluorescent environments. The spectral resolution proves sufficient to differentiate between the complex spectra of L-proline and hydroxyproline. Moreover, decay constants in the sub picosecond range are determined for individual Raman transitions, providing an additional approach for sample characterization.

Operando Raman Gradient Analysis for Temperature-Dependent Electrolyte Characterization.

Transport and thermodynamic properties are integral parameters to understand, model, and optimize state-of-the-art and next-generation battery electrolytes. The accurate measurement of these properties is experimentally challenging as well as time- and resource-intensive, and consequently, reports are scarce. Their dependence on temperature is explored even less and is commonly limited to a few temperature points. Recently, we introduced an operando Raman gradient analysis (ORGA) tool to extract transport and thermodynamic properties. Here, we expand the capabilities of ORGA by incorporating a temperature-sensitive external reference into the design. With this enhancement, we are able to visualize the local concentration of any Raman-active species in the electrolyte and detect lithium filament nucleation. We demonstrate and validate this new functionality of ORGA via an examination of lithium bis(fluorosulfonyl)imide (LiFSI) in tetraethylene glycol dimethyl ether (G4) as a function of temperature. All transport properties and activation energies are reported, and the effect of temperature is discussed.

Smart Surface-Enhanced Resonance Raman Scattering Nanoprobe for Monitoring Cellular Alkaline Phosphatase Activity during Osteogenic Differentiation.

High-efficiency induction of bone marrow mesenchymal stem cells (BMSCs) to osteogenic differentiation in vitro can help solve a series of bone diseases such as bone injury, fracture repair, and osteoporosis. In order to explore the optimal conditions for different chemical inducers to promote BMSCs differentiation and the possible differentiation mechanisms, we developed a smart nanoprobe that can achieve in situ alkaline phosphatase (ALP) activity detection during osteogenic differentiation in cells. The smart nanoprobe (Au@BCIP) was designed as the surface decoration of gold nanoparticles (AuNPs) with 5-bromo-4-chloro-3-indolyl phosphate (BCIP). The nanoprobe was co-cultured with differentiated BMSCs at different stages to monitor ALP activity based on an ALP-catalyzed hydrolysis reaction with BCIP as a substrate. The product can be quickly oxidized by dissolved oxygen to obtaina Raman-active species (5,5'-dibromo-4,4'-dichloro-1H,1H-[2,2'] biindolylidene-3,3'-dione). The SERS sensitivity was greatly improved by resonating the excitation wavelength of 632.8 nm. It is a new strategy for tracing bone disease-related ALP activity in an in vivo model with high sensitivity and selectivity and non-invasion. By using this nanoprobe, osteogenic differentiation of cells under osteogenic supplements was assessed and the p38 MAPK signaling pathway for osteogenic differentiation was experimentally evidenced, which are of significance for understanding BMSCs and regulating their osteogenic differentiation process.

Forming End-to-End Oligomers of Gold Nanorods Using Porphyrins and Phthalocyanines.

The illumination of aggregated metal nanospecies can create strong local electric fields to brighten Raman scattering. This study describes a procedure to self-assemble gold nanorods (NRs) through the use of porphyrin and phthalocyanine agents to create reproducibly stable and robust NR aggregates in the form of end-to-end oligomers. Narrow inter-rod gaps result, creating electric field "hot spots" between the NRs. The organic linker molecules themselves are potential Raman-based optical labels, and the result is significant numbers of Raman-active species located in the hot spots. NR polymerization was quenched by phospholipid encapsulation, which allows for control of the polydispersity of the aggregate solution, to optimize the surface-enhanced Raman scattering (SERS) enhancement and permitted the aqueous solubility of the aggregates. The increased presence of Raman-active species in the hot spots and the optimizing of solution polydispersity resulted in the observation of scattering enhancements by encapsulated porphyrins/phthalocyanines of up to 3500-fold over molecular chromophores lacking the NR oligomer host.

Quantitative acetylene measurements in laminar and turbulent flames using 1D Raman/Rayleigh scattering

This work presents the extension of the established detection of seven major species in 1D Raman/Rayleigh measurements to incorporate acetylene (C2H2) as an eighth species. Acetylene is an important soot precursor which is generated in hydrocarbon flames as an intermediate species following decomposition. It occurs over a broad temperature range in flames and has been identified as a potentially detectable species in 1D Raman/Rayleigh measurements. In this paper, we discuss the Raman spectral signature of acetylene, its temperature dependence, calibration procedures, and the interference with other Raman-active species, C2 and broadband interferences, all of which are essential to quantify for accurate data processing. In this regard, Raman measurements in laminar and turbulent dimethyl ether flames were acquired. The data are spectrally analyzed and low-temperature calibrations of the Raman response are combined with an extrapolation model for high temperatures in order to place the acetylene signals on an absolute scale. Single-shot and conditional-mean values are presented as a function of mixture fraction for a laminar partially-premixed DME/air flame. Measurements from the laminar flame are compared to a 1D laminar flame calculation to assess the accuracy of the calibration and analysis procedures. Finally, detection limits, signal-to-noise, and signal-to-interference ratio of the C2H2 measurement are discussed, and single-shot measurements of acetylene in a turbulent DME/air jet flame are demonstrated.

A strong N[sbnd]H…Br vibrational behaviour studied through X-ray, vibrational spectra and quantum chemical studies in an isomorphous crystal: 2-Nitroanilinium bromide

A needle shaped transparent light brown crystals of 2-nitroanilinium bromide were successfully synthesized and crystallized from an aqueous mixture by slow evaporation technique. Single crystal XRD studies confirm the crystalline phase of this isomorphous compound which contains a positively charge 2-nitroanilinium cation and a negatively charged bromide anion. The solid phase FT-IR and FT-Raman spectra of the compound have been recorded in the range of 4000–400cm−1. The observed modes are correlated by the factor group theory analysis and different IR and Raman active species were identified. Geometrical optimisations were carried out and harmonic vibrational wave numbers were computed for the minimum energy molecular structure at RHF level invoking 6-311++G(d,p) and SDD basis sets. Optimised molecular geometry was compared with the crystallographic data. The calculated wavenumbers were compared with the experimental values. The NH vibrational bands are shifted from its normal range and the shifting is associated with the influence of the intermolecular hydrogen bonds in the crystal. A strong intensity peak in theoretical and corresponding band in experimental confirms the presence of NH…Br interaction as predicted in crystalline state.

Nanofabricated SERS-active substrates for single-molecule to virus detection in vitro: A review

The surface-enhanced Raman scattering (SERS) method has great potential for the detection of Raman-active species, ranging from single molecules to biomolecules. In the last five years, various approaches have been developed to fabricate SERS-active substrates with high sensitivity using noble metal nanostructures via top-down, bottom-up, combination, or template-assisted routes. Nanostructured substrates with high average SERS enhancement factors (EFs) can now be easily produced, with the EF depending strongly on the size and shape of the nanostructures that give rise to the effect. For SERS substrates to be used as a platform for applications such as trace detection and bio-sensing, several issues, including sensitivity, intensity-concentration dependency, and selectivity, need to be addressed. Although several challenges remain before SERS-active substrates become consistent analytical tools, many successful examples have been demonstrated with promising results.

Phospholipid Membrane Encapsulation of Nanoparticles for Surface-Enhanced Raman Scattering

Lipid-encapsulated surface-enhanced Raman scattering (SERS) nanoparticles, with promising applications in biomedical diagnostics, were produced. Gold nanoparticles, 60 nm in diameter, were coated with a ternary mixture of DOPC, sphingomyelin, and cholesterol. The lipid layer is versatile for engineering the chemical and optical properties of the particles. The stability of the lipid-encapsulated particles is demonstrated over a period of weeks. The versatility of the layer is demonstrated by the incorporation of three different Raman-active species using three different strategies. The lipid layer was directly observed by TEM, and the SERS spectrum of the three dye species was confirmed by Raman spectroscopy. UV-vis absorption and dynamic light scattering provide additional evidence of lipid encapsulation. The encapsulation is achieved in aqueous solution, avoiding phase transfer and possible contamination from organic solvents. Furthermore, when fluorescent dye-labeled lipids were employed in the encapsulant, the fluorescence and SERS activity of the particles were controlled by the use of dissolved ions in the preparation solution.

Synthesis optimization of Li 1 + x[Mn 0.45Co 0.40Ni 0.15]O 2 with different spherical sizes via co-precipitation

Li 1 + x [Mn 0.45Co 0.40Ni 0.15]O 2 spherical cathode materials with different sizes (about 2 and 5 μm) were fabricated by calcining uniform spherical metal carbonate, [Mn 0.45Co 0.40Ni 0.15]CO 3 with lithium hydroxide at high temperature. The precursor of spherical metal carbonate, [Mn 0.45Co 0.40Ni 0.15]CO 3, was obtained via co-precipitation method at room temperature, which was significantly dependent on synthetic conditions, such as the reaction temperature, the concentration of NH 4HCO 3, and stirring speed, etc. The optimized condition resulted in [Mn 0.45Co 0.40Ni 0.15]CO 3, of which the particle size distribution was uniform and the particle shape was spherical. The final products, Li 1 + x [Mn 0.45Co 0.40Ni 0.15]O 2, had a well-ordered layered structure and uniform homogeneity. Raman spectroscopy analysis showed the Raman-active species E g and A 1g modes were observed at 488, 473 cm − 1 and 597, 590 cm − 1 , respectively, for the obtained spherical cathode materials.

Smart Nanostructured Polymeric Coatings for Use as Remote optical Strain Sensors

Nanostructured polyurethane coatings have been developed with opto-mech. properties which make them suitable for performing stress-strain measurements via Raman spectroscopy. Two types of coatings were developed: microphase-sepd. copolyurethanes (DA-coPU) where the Raman active species are nanoscale-dispersed diacetylene-contg. hard segments (DA) that are produced in situ, and polyurethane nanocompositesfilled with dispersed HiPco single-wall carbon nanotubes. The use of SWNTs as strain sensitive Raman-active material has shown great potential compared to PbO coatings or even diacetylene crystals of DA-coPU. The use of polarized Raman spectroscopy on isotropic SWNT-PU and Da-coPU coatings which contain isotropic dispersions of resp. SWNTs or diacetylene crystals, allows the selection of species lying along the polarization direction. [on SciFinder (R)]

Diffraction-Limited Photogeneration and Characterization of Silver Nanoparticles

Visible-light-induced photogeneration of silver nanoparticles in a diffraction-limited focal region is demonstrated. The photochemical growth depends quadratically on illumination intensity indicative of a multiphoton generation process, with the identity of the silver nanoparticles confirmed by UV/vis absorption spectroscopy. Mie simulations of the absorption spectrum reveal a size distribution dominated by Ag particles with radii in the range of a few nanometers. Spectrally resolved laser excitation and emission studies demonstrate that the likely luminescence source is surface-enhanced Raman scattering from silver nanoparticles, with spectral jumps occurring on a time scale comparable to that of fluctuations in the total luminescence intensity. Possible routes for the photogeneration process as well as identity of the Raman-active species are discussed. Such diffraction-limited photoproduction methods for luminescent silver nanoparticles offer novel routes toward optical data storage and nanometer-scal...

Selective functionalisation of TNT for sensitive detection by SERRS.

Selective chemical functionalisation of 2,4,6-trinitrotoluene to a surface enhanced resonance Raman active species for sensitive detection.

Raman spectra of aqueous solutions of strong electrolytes: evolving-factor analysis

Ion association in aqueous solutions of varied concentrations of LiNO3, Mg(NO3)2, Co(NO3)2, Li2SO4 and MgSO4 was studied by means of Raman spectrometry assisted by principal-components (PCA) and evolving-factor (EFA) analyses. Formation of one Raman-active associated species, {M···L(R)} (M=Li+, Mg2+, Co2+; L=NO3−, SO42−), was detected at higher salt concentrations (≳2 mol dm−3 for LiNO3, ≳1 mol dm−3 for Co(NO3)2, ≳0.2 mol dm−3 for Li2SO4, ≳0.5 mol dm−3 for MgSO4). Spectral profiles of L(aq) and {M···L(R)} species were computed by means of EFA, as well as their equilibrium concentrations in each solution. Maximum fractions of anions engaged in {M···L(R)} species amounted (at highest salt concentrations) to ≈0.6 (LiNO3), ≈0.4 (Co(NO3)2), ≈0.60 (Li2SO4) and ≈0.3 (MgSO4). Since, for a given salt concentration, the eqilibrium concentration of Raman-active species, [M···L(R)], was always lower than the concentration of analogous UV-active species, [M···L(UV)] (reported in a previous paper) it is suggested that {M···L(UV)} could be a precursor of {M···L(R)}. In all instances, apparent stability constants of {M···L(R)} species, falling into the range of (0.01≲K1/dm3 mol−1≲1), have a progressively upward trend with increasing salt concentration.

Accurate Procedure for Determining the Calibration Curve of High-Temperature Molten Salt Systems via Raman Spectroscopy

The measurement of the intensity of a Raman spectral peak presents one particular difficulty which does not appear in the measurement of absorption spectra of any kind. It is possible in absorption measurements to establish the absorption of the investigated substance by a direct comparison with the unimpaired beam which emerges from the same light source at any wavelength, continuously in two-beam instruments. A direct comparison is not possible for various reasons in case of the usually very weak intensity of the Raman emission, so the determination of a calibration curve in Raman scattering spectroscopy is difficult. The conventional method for obtaining a calibration curve of a Raman-active species is by the addition of an internal standard or by the use of solvent Raman signals as an internal standard. The former method is not suitable for molten salt systems at high temperature. For a molten salt system having no Raman signals other than Rayleigh scattering, the latter method is not applicable either. Here, we want to give a simple yet accurate method of determining calibration curves in such systems. The essence of the method is the use of the shoulder of the Rayleigh line as the normalization point, i.e., the internal standard. We illustrate here the basic principle of the method via the determination of a calibration curve for MgCl2 in a four-component composite melt at 720°C. However, the general method can be extended to determine calibration curves for other molten salt systems.

Distance dependence of surface-enhanced resonance Raman enhancement in Langmuir-Blodgett dye multilayers

Monolayers of a surface-active dye incorporated into inert matrix material were transferred onto structurally defined silver island films by the Langmuir-Blodgett technique. The dye-containing monolayers were spaced from the surface by accurately known increments by deposition of inert spacer monolayers. Surface-enhanced resonance Raman spectra were observed from dye molecules spaced as distant as six spacer increments (ca. 16 nm) from the silver surface. These results indicate an electromagnetic mechanism is operative in this system in contradiction to a chemical mechanism which would require direct contact between the Raman-active species and the metal surface.

Resonance Raman spectra of octaethylporphyrinato-Ni(II) and m e s o-deuterated and 15N substituted derivatives. II. A normal coordinate analysis

Normal coordinate calculations are carried out for all the in-plane modes of octaethylporphyrinato-Ni (II) and its meso-deuterated and 15N substituted derivatives. With 37 constants of a modified Urey–Bradley force field and a structural model with D4h symmetry, 59 resonance Raman lines (A1g+B1g +A2g+B2g) and 38 infrared bands (Eu) of these three molecules are assigned. The vibrational modes of the Raman active species are represented in terms of the Cartesian atomic displacement vectors. Based on the present results, some important resonance Raman lines of hemoproteins are interpreted. The so-called ’’oxidation state maker’’ (Band IV) is due to an in-phase breathing-like mode of four pyrrole rings although being somewhat deformed by the large contribution of the Cα–N symmetric stretching term. The spin state sensitive Raman lines, namely, Band I and III, are associated mainly with methine bridge (Cα–Cm) stretching modes. Two prominent anomalously-polarized Raman lines of hemoproteins around 1580 and 1300 cm−1 are primarily due to the Cα–Cm stretching and Cm–H bending modes, respectively.

Laser Induced Raman Spectra of Some Tungstates and Molybdates.

The Raman spectra of single crystals of CaWO4, CaMoO4, PbWO4, and PbMoO4 have been recorded using a He-Ne laser (λ = 6328 Å) and an Argon ion laser (λ = 4880 Å) as the exciting radiation sources. The polarization data have enabled us to classify unambiguously the observed fundamentals into the Raman active species of the point group C4h to which these crystals belong. The comparison of the spectra of these crystals in the low frequency region has also enabled us to make a rough classification of the bands into the rotational and the translational lattice vibrations.