Spontaneous Raman Spectrum Research Articles

Robust Spontaneous Raman Flow Cytometry for Single-Cell Metabolic Phenome Profiling via pDEP-DLD-RFC.

A full-spectrum spontaneous single-cell Raman spectrum (fs-SCRS) captures the metabolic phenome for a given cellular state of the cell in a label-free, landscape-like manner. Herein a positive dielectrophoresis induced deterministic lateral displacement-based Raman flow cytometry (pDEP-DLD-RFC) is established. This robust flow cytometry platform utilizes a periodical positive dielectrophoresis induced deterministic lateral displacement (pDEP-DLD) force that is exerted to focus and trap fast-moving single cells in a wide channel, which enables efficient fs-SCRS acquisition and extended stable running time. It automatically produces deeply sampled, heterogeneity-resolved, and highly reproducible ramanomes for isogenic cell populations of yeast, microalgae, bacteria, and human cancers, which support biosynthetic process dissection, antimicrobial susceptibility profiling, and cell-type classification. Moreover, when coupled with intra-ramanome correlation analysis, it reveals state- and cell-type-specific metabolic heterogeneity and metabolite-conversion networks. The throughput of ≈30-2700 events min-1 for profiling both nonresonance and resonance marker bands in a fs-SCRS, plus the >5 h stable running time, represent the highest performance among reported spontaneous Raman flow cytometry (RFC) systems. Therefore, pDEP-DLD-RFC is a valuable new tool for label-free, noninvasive, and high-throughput profiling of single-cell metabolic phenomes.

SERS and DFT investigations of methyl 4‑bromo-1H-pyrrole-2-carboxylate adsorbed on silver and gold substrates: In perspective of biosensor applications

In the present study, the spontaneous Raman spectrum and surface-enhanced Raman scattering (SERS) spectra of Methyl 4‑bromo-1h-pyrrole-2-carboxylate (MBPC) were reported and validated using density functional theory (DFT) quantum chemical calculations. Initially, the molecular structure of MBPC, MBPC-Ag3 and MBPC-Au4 molecular systems were optimized. In order to attain the strong SERS enhancement, the SERS substrates such as silver-coated thin film (SCF) and gold-coated thin film (GCF) were fabricated. SEM images of SCF and GCF show that the silver and gold nanoparticles are spherical in shape with an average particle size of ~74 and ~56 nm, respectively. EDX spectra of SCF and GCF clearly evidences that only the silver and gold nanoparticles present in the respective films. The UV–visible spectral analysis shows a significant red-shift upon the MBPC molecule adsorbed on SCF and GCF surfaces, confirming that the MBPC molecule chemisorbed on SCF and GCF surfaces. Frontier molecular orbitals analysis shows that the charge transfer interaction occurs between the metal and molecule in the MBPC-Ag3 and MBPC-Au4 molecular systems. The molecular electrostatic potential surface and Fukui functions analysis further validated the charge transfer interaction in the investigated molecular systems. The spontaneous Raman and SERS spectral analysis strongly evidence that the title molecule chemisorbed on GCF with high affinity than SCF with tilted orientation through the lone pair electrons of the oxygen atom in the C = O functional group, pyrrole ring π electrons and lone pair electrons of bromine atom. Moroever, the experimentally observed results were correlated well with theoretical results. Hence, the present study paves the way for designing strong SERS active substrates, which will be useful for developing pyrrole related biosensors.

Measurements of pressure broadening of N2 in the anisotropic tensor component of spontaneous Raman spectra

Spontaneous Raman scattering from nitrogen is well-suited for temperature measurements in combustion experiments, especially at high pressure which increases the Raman signal because of the higher density in the measurement volume. In this work we investigate high density effects on the anisotropic tensor component of ro-vibrational spontaneous Raman scattering, which must be understood to obtain accurate thermometry in high pressure gases using high-fidelity Raman simulations. We measure the collision broadening for the anisotropic component of spontaneous Raman scattering from room temperature nitrogen over the pressure range 10–70 atm for three gas compositions: pure nitrogen, air, and nitrogen in argon. Line broadening coefficients inferred from these measurements were found to be 14 ± 5% larger than the corresponding broadening coefficients of the isotropic Q branch. Air broadening coefficients were found to be very similar and about 2.5% smaller than nitrogen self-broadening coefficients. Argon broadening coefficients were 25% smaller at rotational quantum number 7 and about 50% smaller at rotational quantum number 21. Additionally, we found that our unmixed line model for the O and S branches gave good fits for all pressures, which indicates that line mixing effects are not significant in the O and S branches over this range of pressures. Using indirect experimental evidence we infer that line mixing effects in the anisotropic component of the Q branch were below the threshold set by our experimental spectral resolution at pressures up to 70 atm at room temperature. Assuming that the anisotropic Q branch lines mix like the isotropic lines results in a small systematic error in the inferred temperature at flame temperatures, with the error increasing slowly with pressure. The bias can be easily removed by modeling the anisotropic spectrum separately from the isotropic spectrum. Line mixing effects should be included in the model of the isotropic part of the Raman spectrum, but can probably be neglected in the anisotropic part of the spontaneous Raman spectrum of N 2 for pressures below 400 atm at flame temperatures.

Highly efficient tunable picosecond deep ultraviolet laser system for Raman spectroscopy.

We present a narrowband laser system tunable from 219 to 236 nm for deep ultraviolet (DUV) Raman spectroscopy. The demonstrated laser system produces 6.7 ps nearly transform-limited pulses with energy up to 0.36 µJ at 100 kHz repetition rate. The system consists of a two-stage optical parametric amplifier (OPA) of a narrowband continuous wave diode laser and subsequent frequency conversion to the DUV radiation. We achieve more than 300 mW in the signal wave using ${{\rm LiB}_3}{{\rm O}_5}$LiB3O5 (LBO) and ${{\rm BaB}_2}{{\rm O}_4}$BaB2O4 (BBO) crystals, with the total 2.7 W pump after the two-stage OPA. We reach 12% conversion efficiency of the OPA signal wave into the DUV radiation using type-I phase matching in the BBO crystal. Finally, we demonstrate the applicability of the system for DUV Raman spectroscopy by collecting a high dynamic range, high spectral resolution spontaneous Raman spectrum of air.

Characterization of ZnWO_4 Raman crystal

Stimulated Raman scattering (SRS) is an important technique for broadening the laser spectra. The Raman crystals with large dimensions and high thermal conductivity are favorable by SRS. Zinc tungstate (ZnWO4) belonging to a monoclinic system has been grown by the Czochralski method with the dimensions of Φ 35 mm × 70 mm. The thermal properties were evaluated and analyzed in several aspects, including the density, specific heat, thermal expansion coefficient, and thermal conductivity. Thermal conductivity was calculated to be 5.412 Wm−1K−1 along the c-axis, which is about two times larger than the famous BaWO4 and SrWO4. Meanwhile, the optical properties including transmission and Raman spectra and Raman shift were measured and the stimulated Raman scattering performance of ZnWO4 crystal was demonstrated. The results show that the thermal conductivity decreases with increasing temperature. Furthermore, the thermal focal lengths were theoretically estimated. Along the a direction, the light with a wavelength of 532 nm can be shifted to the light at 558.95 nm, which is in good accordance with the spontaneous Raman spectrum. All the analyses and results above show that ZnWO4 is a promising solid-state Raman laser crystal.

An insight into liquid water networks through hydrogen bonding halide anion: Stimulated Raman scattering

We have studied the interaction between water molecules and halide anions and acquired the influence of concentration by the spontaneous Raman spectrum. The results agreed well with the previous researches. To explore further, the stimulated Raman scattering of a halide–water binary solution is measured to study the nature of the hydrogen bonding between water molecules and halogen anions. Under the effect of laser-induced plasma, the OH stretching vibration spectra of aqueous solutions of halogen ions pretty exhibit different trend compared with that of spontaneous Raman spectrum. The frequency shifts of water OH vibration show different values and directions with adding different halide anions. The red shift of F−– and Cl−–water molecule clusters is due to the process of charge transfer, whereas the blue shift of Br−– and I−–water molecule cluster is due to polarization effect without charge transfer. The results demonstrate that F− and Cl− slightly weaken the hydrogen bond (HB), whereas Br− and I− enhance HB in the water cluster. The decrease of concentration of halogen ions aqueous solution can weaken the effect on the HB.

Influence of strong and weak hydrogen bonds in ices on stimulated Raman scattering.

Stimulated Raman scattering (SRS) in liquid water and ice Ih using Nd:YAG laser is investigated. The spectrum of backward SRS (BSRS) in water is acquired. The spectrum shows an unexpected SRS peak at around 3453 cm(-1) besides the normal peak, which is similar to the spontaneous Raman spectrum of ice VII. The ice VII phase will be formed by laser-induced shock compression in liquid water. Simultaneously, unlike the spontaneous Raman spectrum, the pre-resonance SRS of ice Ih at around 3110 and 3210 cm(-1) is observed. The Raman peaks appeared in liquid water and ice Ih are attributed to the effect of strong and weak hydrogen bonds (H bonds), which should be ubiquitous in other ice phases.

Stimulated Raman scattering properties of KDP crystal

In this paper the spontaneous Raman spectrum and stimulated Raman spectrum of potassium dihychogen phosphate (KDP) crystals were compared in detail. In the stimulated Raman spectrum three Stokes lines of the strongest vibration mode, which are 559.43 nm, 589.74 nm, 623.5 nm respectively, were observed. The Stokes lines for other vibration modes didnt appear due to the smaller stimulated Raman scattering (SRS) gain coefficient. In addition, we also compared the gain coefficients of KDP crystal grown by traditional growth method (including annealing and annealing samples) and rapid growth method (including the pyramidal and prismatic sectors samples). The results indicate that the growth method and annealing have no obvious impact on the SRS gain coefficient.

Growth and Raman spectrum of Ba2Mg(B3O6)2 crystal

Ba2Mg(B3O6)2 (BMBO) is a potential stimulated Raman scattering (SRS) crystal. In this work, a colorless transparent BMBO single crystal with a dimension of 32×23×7mm3 has been grown by the Kyropoulos method. A spontaneous Raman spectrum of the crystal was recorded at room temperature. Site group analysis and first-principles calculations were employed to interpret the Raman spectrum. The site group analysis results show that the total lattice modes are 10Ag+11Au+10Eg+11Eu, of which 10Ag+10Eg are Raman-active. The crystal Raman spectrum was computed in CASTEP (Cambridge Sequential Total Energy Package) using a hybrid method combining density functional perturbation theory with the finite displacement method. All of the Raman-active modes have been identified. The internal modes of the B3O6 ring in the crystal give rise to vibrations with Raman shifts above 220cm−1; the translations and the librations of the rings, as well as the translations of the Ba2+ cations, give rise to vibrations with Raman shifts below 220cm−1. The strongest peak at 645cm−1 in the experimental spectrum is assigned to the breathing mode of the B3O6 ring.

Use of the Gerchberg–Saxton algorithm in optimal coherent anti-Stokes Raman spectroscopy

We are utilizing recent advances in ultrafast laser technology and recent discoveries in optimal shaping of laser pulses to significantly enhance the stand-off detection of explosives via control of molecular processes at the quantum level. Optimal dynamic detection of explosives is a method whereby the selectivity and sensitivity of any of a number of nonlinear spectroscopic methods are enhanced using optimal shaping of ultrafast laser pulses. We have recently investigated the Gerchberg-Saxton algorithm as a method to very quickly estimate the optimal spectral phase for a given analyte from its spontaneous Raman spectrum and the ultrafast laser pulse spectrum. Results for obtaining selective coherent anti-Stokes Raman spectra (CARS) for an analyte in a mixture, while suppressing the CARS signals from the other mixture components, are compared for the Gerchberg-Saxton method versus previously obtained results from closed-loop machine-learning optimization using evolutionary strategies.

The First Step in Glycine Solvation: The Glycine−Water Complex

The jet-cooled spontaneous Raman spectrum of a glycine-water complex (Gly + H(2)O), the first step in amino acid hydration, is reported. The low-frequency vibrational spectrum (below 500 cm(-1)) of the solvated molecule is recorded and assigned using quantum chemical data calculated from ab initio (MP2) and DFT (B3LYP, BLYP, PBE0 = PBE1PBE). Anharmonic corrections or Raman and infrared (IR) active vibrations are calculated using second-order perturbation theory at the MP2/6-31+G(d) level. The acquired spectra at medium resolution (hwhm of ~4 cm(-1)) allow different conformers of the glycine-water heterodimer to be distinguished. Three different dimer conformations are observed and identified; selective collision-induced relaxation processes are used to estimate their relative stability. The results are compared with recent theoretical predictions and microwave (MW) spectroscopy data. The premise that the acidic character of the OH group of the carboxylic acid dominates the interaction between water and glycine is confirmed. The addition of a water molecule is found to greatly change the potential energy surface and conformational preferences of H(2)NCH(2)COOH. Water stabilizes conformations in which formation of a closed-ring, H-bonded structure is possible. Simultaneous participation by the carboxyl oxygen of the amino acid in two hydrogen bonds is found to be unfavorable. It may be expected that the addition of extra water molecules could ultimately lead to the stabilization of the Gly zwitterion.

The identification of the two missing conformers of gas-phase alanine: a jet-cooled Raman spectroscopy study

The jet-cooled spontaneous Raman spectrum of an amino acid-alanine (Ala, 2-aminopropanoic acid; H(2)NCH(CH(3))COOH)-is reported. The low-frequency vibrational spectrum (below 500 cm(-1)) was recorded and assigned using quantum chemical data: ab initio (MP2) and DFT (BLYP, B3LYP, and PBE0). Band polarization measurements were used to confirm the vibrational assignments. The acquired medium resolution spectra (HWHM of approximately 4 cm(-1)) allow the different alanine conformations to be distinguished. Four alanine conformers were observed and identified: two previously reported by microwave spectroscopy studies and two that were previously unreported. A set of reasons for why these conformers eluded previous studies are discussed. Selective collisional relaxation processes in the jet (associated with low interconversion barriers between different alanine conformations) that depopulate the high-energy conformers were experimentally demonstrated.

Conformational Equilibrium in Glycine: Experimental Jet-Cooled Raman Spectrum

The first observation of a gas-phase spontaneous Raman spectrum of an amino acid, glycine (Gly, H2NCH2COOH), is reported. A molecular beam source was combined with a high-sensitivity Raman setup to record a low-frequency (below 500 cm−1) vibrational spectrum. Ab initio (MP2) and density functional theory (DFT) (BLYP, B3LYP, and PBE0) calculations with the aug-cc-pVTZ basis set were used to support vibrational assignments. Jet-cooling of glycine molecules was observed by varying the laser-nozzle distance. The acquired medium resolution spectra (4 cm−1) allow the different glycine conformations to be distinguished. The structures of the two most stable glycine conformers, previously observed by electron diffraction and microwave spectroscopy, have been confirmed. Evidence is reported for a third conformation (gauche−trans−trans), which has not been previously experimentally reported. Band polarization measurements were used to confirm the vibrational assignments.

High‐resolution narrowband CARS spectroscopy in the spectral fingerprint region

AbstractCoherent anti‐Stokes Raman scattering (CARS) spectroscopy is an important technique for spectroscopy and chemically selective microscopy, but wider implementation requires dedicated versatile tunable sources. We describe an optical parametric oscillator (OPO) based on a magnesium oxide‐doped periodically poled lithium niobate crystal, with a novel variable output coupler, used as a tunable coherent light source. The OPO's signal wavelength ranges from 880 to 1040 nm and its idler wavelength from 1090 to 1350 nm.We use this OPO to demonstrate high‐resolution narrowband CARS spectroscopy on bulk polystyrene from 900 to 3600 cm−1, covering a large part of the molecular fingerprint region. Recording vibrational spectra using narrowband CARS spectroscopy has several advantages over spontaneous Raman spectroscopy, which we discuss. We isolate the resonant part of the CARS spectrum and compare it to the spontaneous Raman spectrum of polystyrene using the maximum entropy method of phase retrieval; we find them to be in extremely good agreement. Copyright © 2009 John Wiley & Sons, Ltd.

Background free CARS imaging by phase sensitive heterodyne CARS

In this article we show that heterodyne CARS, based on a controlled and stable phase-preserving chain, can be used to measure amplitude and phase information of molecular vibration modes. The technique is validated by a comparison of the imaginary part of the heterodyne CARS spectrum to the spontaneous Raman spectrum of polyethylene. The detection of the phase allows for rejection of the non-resonant background from the data. The resulting improvement of the signal to noise ratio is shown by measurements on a sample containing lipid.

Coherent anti-Stokes Raman scattering microscopy.

Coherent anti-Stokes Raman scattering microscopy.

Continuous‐wave solid‐state Raman laser for spectroscopic applications

AbstractThe experimental and theoretical investigations of a solid‐state Raman laser operating in the continuous‐wave regime are described. The Raman laser represents the single resonant cavity with a Raman crystal. The theoretically predicted operation threshold is in agreement with that observed experimentally. The Raman conversion efficiency of the Stokes radiation is close to 5%. The analysis of temporal fluctuations of the output Stokes signal shows its super‐Gaussian statistics near the threshold. The output Stokes radiation was used for the measurement of the spontaneous Raman spectrum of CCl4. Copyright © 2006 John Wiley & Sons, Ltd.

Four‐photon coherent spectroscopy of orientational motion of H2O molecules in liquid water

AbstractThe unexpectedly narrow structure of Rayleigh wing spectra from 5 to 50 cm−1 was detected using four‐photon coherent laser spectroscopy. The observed features were compared with the IR water vapor absorption (from the HITRAN database) and with the spontaneous Raman spectrum in the vapor phase. The fairly good resemblance between our recorded four‐photon spectrum and the pure rotational spectra of H2O molecules in the gas phase allows the suggestion that a discernible proportion of water molecules may exhibit virtually free rotation in the liquid phase. Copyright © 2005 John Wiley & Sons, Ltd.

Detection of Bacillus subtilis spores in water by means of broadband coherent anti-Stokes Raman spectroscopy

Broadband coherent anti-Stokes Raman scattering (CARS) spectroscopy is used for detection of bacterial spores in aqueous solution. Polarization CARS spectroscopy is employed to suppress the non-resonant background. CARS spectrum recorded in the spectral region from 700 to 1900 cm(-1) exhibits all the characteristic features of spontaneous Raman spectrum taken for a solid powder and resembles that one of the dipicolinic acid, which is considered to be the major component of bacterial spores, including anthrax.

Coherent anti-Stokes Raman scattering spectral interferometry: determination of the real and imaginary components of nonlinear susceptibility χ^(3) for vibrational microscopy

We demonstrate coherent anti-Stokes Raman scattering (CARS) heterodyne spectral interferometry for retrieval of the real and imaginary components of the third-order nonlinear susceptibility (chi(3)) of molecular vibrations. Extraction of the imaginary component of chi(3) allows a straightforward reconstruction of the vibrationally resonant signal that is completely free of the electronic nonresonant background and resembles the spontaneous Raman spectrum. Heterodyne detection offers potential for signal amplification and enhanced sensitivity for CARS microscopy.