Raman Scattering Research Articles

Amplification of the Surface-Enhanced Raman Scattering Signal from a Monolayer of Organic Molecules in Sandwich Structures Containing Plasmonic Silver Nanoplates

Amplification of the Surface-Enhanced Raman Scattering Signal from a Monolayer of Organic Molecules in Sandwich Structures Containing Plasmonic Silver Nanoplates

Temperature Dependence of Coherent versus Spontaneous Raman Scattering

Temperature Dependence of Coherent versus Spontaneous Raman Scattering

Toward video-rate compressive spontaneous Raman imaging via single-photon avalanche diode arrays.

Spontaneous Raman microscopy is well-known for its remarkable chemical contrast yet suffers from slow acquisition speeds. Recently, the compressive Raman microspectroscopy framework has shown that a significant speed advantage is brought by leveraging shot-noise-limited detection using a single-photon avalanche diode (SPAD). However, current imaging speeds of compressive Raman architectures are fundamentally limited by SPAD sensitivity and dead time. Here, we demonstrate an efficient and scalable compressive Raman parallelization scheme based on SPAD arrays. We show that parallelization using line excitation, instead of spatial multiplexing, allows to reach effective pixel dwell times (τ pdt ) of 0.8 µs. Such fast speed represents over one order-of-magnitude speed-up over previous demonstrations. This effective parallelization not only allows for demonstrating unprecedented chemical imaging speeds using the otherwise weak spontaneous Raman effect but also paves the way for true video-rate inexpensive molecular microspectroscopy.

Azo-Enhanced Raman Scattering Probing Proton Transfer between Water and Nanoscale Zero-valent Iron.

The interaction between a solid and water at their interface, especially proton transfer, impacts molecular-scale catalysis, macroscopic environmental science, and geoscience. Although being highly desired, directly probing proton transfer between a solid and water is a great challenge, given the subnanometer to nanometer scale of the interface. The fundamental challenge lies in the lack of a measurement tool to sensitively observe local proton concentration without introducing an exogenous electrode or nanoparticle with a minimum size of tens of nanometers. Here, we demonstrate an azo-enhanced Raman scattering strategy to design a 2 nm long small-molecule pH probe with a chelating group anchoring to the solid surface. Empowered by the intramolecular Raman enhancing sensitivity, the probe directly observes proton transfer between water and nanoscale zero-valent iron (nZVI), a famous environmental material for pollution control. This molecular-scale interfacial probing methodology offers a powerful tool to pave the way for advanced environmental and geochemical discernment and management.

Numerical Investigation of Raman-Assisted Four-Wave Mixing in Tapered Fiber Raman Fiber Amplifier

The generation of unwanted higher-order Raman effects is the main factor restricting the power scaling of Raman fiber amplifiers (RFAs). This phenomenon arises from an interplay of physical processes, including stimulated Raman scattering (SRS), four-wave mixing (FWM), and the intricate temporal and spectral dynamics. Tapered fibers have demonstrated excellent nonlinear effects suppression characteristics due to the varying core diameter along the fiber, which is widely used in ytterbium-doped fiber lasers. In this paper, a comprehensive numerical investigation is conducted on the core-pumping tapered fiber RFAs considering Raman-assisted FWM. The higher-order Raman power in the tapered fiber is always kept at a low level, showing a weak Raman-assisted FWM effect. A numerical investigation is conducted to study the impact of the tapering ratio, the lengths of the thin part, tapered region, and thick part on the higher-order Raman threshold of RFAs. Furthermore, the impact of phase mismatch variations caused by changes in the seed wavelength, on the output signal power and nonlinear effects is analyzed. This paper presents, for the first time, a study on core-pumped RFAs using tapered fibers, providing a novel perspective on enhancing the power of RFAs.

Ultra‐Broadband Visible‐DUV Supercontinuum Generation by Non‐Resonant Coherent Raman Scattering in Air

AbstractTo date, supercontinuum light in the visible and near‐infrared ranges is readily realizable by the optical Kerr effect through self‐phase modulation of ultrashort laser pulses in transparent media. However, it is still a challenge to extend the supercontinuum spectrum down to the deep‐ultraviolet (DUV) range, which is particularly needed for exploring ultrafast dynamics in chemistry, materials, and biology. Here, an approach of non‐resonant coherent Raman scattering is developed to generate ultra‐broadband visible‐DUV supercontinuum in ambient air with a spectral range spanning over 250 nm and a wavelength down to 220 nm. A rovibrational coherence is established in air molecules by filamentation of a near‐infrared femtosecond 800 nm pulse and two femtosecond Raman laser pulses at 267 and 400 nm are introduced into the coherent media to induce non‐resonant coherent Stokes and anti‐Stokes Raman scatterings, which serve as the spectral bridges to link the neighboring Raman pump laser spectra, resulting in ultra‐broadband supercontinuum light. The mechanism is further verified by examining the broadening of picosecond N2+ laser lines with narrow bandwidths (10–30 cm−1), which forms a supercontinuum spectrum spanning over 150 nm. The work provides a viable route for the establishment of coherent DUV supercontinuum in the gas media at designed wavelength ranges.

Effect of Deuteration on Raman Scattering in Single Crystals of Potassium Alum

ABSTRACTRaman spectra of KAl(SO4)2·12H2O and KAl(SO4)2·12D2O crystals in the range of 10–4000 cm−1 were experimentally obtained and studied. An increase in the number of sulfate ions, oriented by oxygen atoms towards the K+ ion, was detected upon deuteration of the sample. Low‐intensity Stokes components ν = 2485 cm−1 (ν = 1820 cm−1 for the deuterated crystal) were recorded, which indicates the formation of hydrogen bonds O–H•••SO42− (O–D•••SO42−), where the donors are water molecules of the [Al(H2O)6]3+ complex and the oxygen atoms of the sulfate ion act as acceptors. The decrease in the wavenumbers of internal vibrations of the sulfate ion during deuteration was explained by an increase in the strength of hydrogen bonds. The results obtained indicate the direct influence of deuteration on the degree of initial disordering of sulfate ions and on the stability of the crystal structure of potassium alum.

Precise Methylation Detection of Tumor Suppressor Gene Promoters by Magnetic Enrichment and Nano Silver Adduct-Promoted Surface-Enhanced Raman Scattering.

Noninvasive liquid biopsies can be used for early tumor diagnosis by identifying the methylation level of the tumor suppressor genes (TSGs)-a reliable index for cancer evaluation. However, identifying trace circulating genes from specimens remains challenging. This work introduces a novel method that combines magnetic isolation and surface-enhanced Raman scattering (SERS) to concentrate and detect the methylated TSG promotors. A superparamagnetic iron oxide nanoparticle modified with streptavidin is prepared as a universal magnetic bead. Biotin-terminated probe single-strand DNA (ssDNA) is immobilized on the magnetic beads through biotin-streptavidin bioconjugation. Artificial target ssDNA fragments with various methylation levels are applied as a promoter gene model. Concentrated double-strand DNA (dsDNA) is produced by a hybridizing probe and target ssDNA on magnetic nanobeads, as well as an additional magnetic isolation process. The well-prepared DNA adduct, which consists of 3nm cisplatin-modified Ag nanoclusters, can specifically bind with guanine-cytosine base pairs of dsDNA. Ag-nanoparticle-induced localized SERS amplified signals of 5-methylcytosine (5-mC) from the dsDNA in Raman spectra, enabling accurate methylation level measurement in mixtures of 0-1µm methylated DNA, with a detection limit of 0.05µm. This method shows promise for enabling the methylation level evaluation of various TSGs and promoters in early cancer liquid biopsies.

Impact of the host lattice on crystallographic, Raman, optical, and luminescent properties on the terbium ion

AbstractA comparative study of the Gd2O3:Tb and Y2O3:Tb nanoparticles (NPs) was presented to examine the influence of the host lattices on the crystallographic phase, surface characteristics, optical properties, Raman effect, and photoluminescence properties. Cubic shapes Gd2O3:Tb and Y2O3:Tb NPs with an estimated crystalline size of 17 and 11 nm were recorded from the X‐ray diffraction pattern, respectively. Comparative absorption spectra of both oxides NPs were presented to examine the dispersibility, colloidal stability, and optical behavior of the NPs. Energy bandgap values were estimated to monitor the optical characteristics of the metal oxides in the UV/Vis region. Fourier transform infrared was recorded to confirm the surface‐attached water and organic moieties. The Raman spectra of metal oxides were recorded to examine the symmetrical dis‐order and polarizability of the vibrational bands. The ionic radius of the atoms distorts the bond structure resulting in it greatly influenced the vibrational bands of the materials. The emission spectra certified the effective doping of the luminescent Tb3+‐ion in the metal oxide host lattices. Raman spectra and emission spectra validated the crystal symmetry imperfections; subsequently, the efficiency of the Raman active modes and emission transitions was greatly influenced. In a comparative analysis, Y2O3:Tb NPs exhibited higher luminescence intensity in comparison with the Gd2O3:Tb NPs.

Novel Ratiometric Surface-Enhanced Raman Scattering (SERS) Biosensor for Ultrasensitive Quantitative Monitoring of Human Carboxylesterase-1 in Hepatocellular Carcinoma Cells Using Ag-Au Nanoflowers as SERS Substrate.

In this study, we developed ratiometric surface-enhanced Raman scattering (SERS) biosensors using Ag-Au alloy nanoflowers as SERS substrates, molecules having amide bonds and alkyne groups (Tag A) as Raman reporters, and sodium thiocyanate as an internal standard molecule (Tag B) for the sensitive detection of human carboxylesterase-1 (hCE1) in HepG-2 cells. The correlation between HepG-2 cell damage and hCE1 activity levels was investigated. Both Tag A's alkyne group and Tag B's cyanide group produced characteristic SERS signals in the Raman-silent region (I2000cm-1 and I2115cm-1, respectively). The hydrolysis of the amide bond in Tag A via hCE1 and the shedding of the alkyne group led to a reduction in the SERS signal intensity observed at I2000cm-1. Conversely, the SERS signal intensity of Tag B at I2115cm-1 exhibited a consistent pattern. As the activity level of hCE1 and the ratiometric peak intensity (I2000cm-1/I2115cm-1) correlated negatively, hCE1 could be quantitatively detected within the range of 10-2 to 2 × 102 ng·mL-1, with a detection limit of 7.3 pg·mL-1. The ratiometric SERS probe strategy, in which a ratio response is employed, permits sensitive and reproducible SERS detection by facilitating intrinsic calibration to rectify signal fluctuations resulting from temporal and spatial variations in the detection conditions. Concurrently, the implementation of Raman-silent region reporter molecules mitigates the interference from endogenous biomolecules in SERS measurements and offers a novel approach for achieving highly sensitive and interference-free detection of intracellular hCE1.

Construction and Application of Au NRs/4-MBA/PAM Ratiometric Surface-Enhanced Raman Scattering Substrate for Fish Veterinary Drug Residue Detection

Surface-enhanced Raman scattering (SERS) is widely used for trace detection of substances, and the key to this technology lies in the preparation of the substrate material. In this study, a composite SERS material of Au NRs/4-MBA/PAM was constructed and characterized to better immobilize the reference molecule 4-mercaptobenzoic acid (4-MBA). Electron transmission microscopy results demonstrated that the PAM film helps Au NRs to pack closely, enhancing the stability of the material structure and reducing the interference of external environmental factors on the response of 4-MBA, thus improving the accuracy of quantitative determination. Comparative experimental results with the Au NRs/4-MBA substrate showed that the relative standard deviations (RSDs) of the detection results for MG on different batches of Au NRs/4-MBA/PAM were less than 8.0%, and the RSDs of different points on the same material were less than 10.0%, indicating that the Au NRs/4-MBA/PAM has higher uniformity, better reproducibility, and higher sensitivity in detecting malachite green (MG). Applying this material in the recovery determination of fish extract showed that the recovery rates of MG were between 75.60% and 83.24%. Therefore, the Au NRs/4-MBA/PAM substrate can accurately detect and quantify veterinary drug residue in complex matrices such as food tissue.

Deep Ultraviolet Excitation Photoluminescence Characteristics and Correlative Investigation of Al-Rich AlGaN Films on Sapphire.

AlGaN is attractive for fabricating deep ultraviolet (DUV) optoelectronic and electronic devices of light-emitting diodes (LEDs), photodetectors, high-electron-mobility field-effect transistors (HEMTs), etc. We investigated the quality and optical properties of AlxGa1-xN films with high Al fractions (60-87%) grown on sapphire substrates, including AlN nucleation and buffer layers, by metal-organic chemical vapor deposition (MOCVD). They were initially investigated by high-resolution X-ray diffraction (HR-XRD) and Raman scattering (RS). A set of formulas was deduced to precisely determine x(Al) from HR-XRD data. Screw dislocation densities in AlGaN and AlN layers were deduced. DUV (266 nm) excitation RS clearly exhibits AlGaN Raman features far superior to visible RS. The simulation on the AlGaN longitudinal optical (LO) phonon modes determined the carrier concentrations in the AlGaN layers. The spatial correlation model (SCM) analyses on E2(high) modes examined the AlGaN and AlN layer properties. These high-x(Al) AlxGa1-xN films possess large energy gaps Eg in the range of 5.0-5.6 eV and are excited by a DUV 213 nm (5.8 eV) laser for room temperature (RT) photoluminescence (PL) and temperature-dependent photoluminescence (TDPL) studies. The obtained RTPL bands were deconvoluted with two Gaussian bands, indicating cross-bandgap emission, phonon replicas, and variation with x(Al). TDPL spectra at 20-300 K of Al0.87Ga0.13N exhibit the T-dependences of the band-edge luminescence near 5.6 eV and the phonon replicas. According to the Arrhenius fitting diagram of the TDPL spectra, the activation energy (19.6 meV) associated with the luminescence process is acquired. In addition, the combined PL and time-resolved photoluminescence (TRPL) spectroscopic system with DUV 213 nm pulse excitation was applied to measure a typical AlGaN multiple-quantum well (MQW). The RT TRPL decay spectra were obtained at four wavelengths and fitted by two exponentials with fast and slow decay times of ~0.2 ns and 1-2 ns, respectively. Comprehensive studies on these Al-rich AlGaN epi-films and a typical AlGaN MQW are achieved with unique and significant results, which are useful to researchers in the field.

Insights into pharmaceutical co-crystallization using coherent Raman microscopy

Formulating active pharmaceutical ingredients (APIs) as co-crystals requires a thorough understanding of co-crystallization behavior under different process conditions. This study employs two forms of coherent Raman microscopy, narrowband coherent anti-Stokes Raman scattering (CARS) and stimulated Raman scattering (SRS) with spectral focusing, to study co-crystallization via liquid-assisted ball milling. Indomethacin and nicotinamide served as the model API and co-former, and the results were compared with established analytical methods. Narrowband CARS, with univariate peak position analysis, was useful to visualize co-crystal formation, but suffered some degree of signal mixing that affected component identification. Hyperspectral SRS imaging, combined with classical least squares multivariate analysis, separated the different components with high confidence and proved to be a robust and rapid tool to qualitatively and quantitatively image co-crystallization. The coherent Raman imaging results explained divergent co-crystallization endpoints obtained with the conventional solid-state analysis methods. CARS and SRS microscopies also revealed the presence of otherwise undetected trace forms. Finally, we also demonstrated the dramatic reversal of partial co-crystal formation during milling, depending on ethanol content. Overall, the study demonstrates the added value coherent Raman microscopy can provide for analysis of co-crystallization processes.

Mid-Infrared Lasers and Supercontinuum Sources Based on Stimulated Raman Scattering in Gas-Filled Hollow-Core Fibers

Mid-Infrared Lasers and Supercontinuum Sources Based on Stimulated Raman Scattering in Gas-Filled Hollow-Core Fibers

Modeling Surface-Enhanced Raman Scattering of Au-Pyrazine and Au-Pyrazine-Au Nanorod Dimer Systems with the TD-DFTB Method

Modeling Surface-Enhanced Raman Scattering of Au-Pyrazine and Au-Pyrazine-Au Nanorod Dimer Systems with the TD-DFTB Method

Dendritic copper nanostructures for ultrasensitive detection of rhodamine 6G and Congo red

Surface-Enhanced Raman Scattering (SERS) is a fast-responding and non-destructive ultra-sensitive detection technique that can replace traditional chromatographic and spectroscopic analysis techniques. In this experiment, dendritic copper nanostructures were prepared by the solid-state ionics method and the vacuum hot evaporation process with an applied current of I=9μA. Using them as a SERS substrate, Raman detection was performed on the dye molecules Rhodamine 6G (R6G) and Congo Red (CR) to determine SERS enhancement performance. It is found that the growth of the prepared copper nanostructures has a top-end dominant phenomenon. The fractal dimension of the copper nanostructure was calculated using fractal theory, and it was revealed to be 1.560. Scanning electron microscopy (SEM) results showed that a large number of 60-80 nm regularly arranged copper nanoparticles were attached to the surface of the dendritic copper nanostructure. This is beneficial to increase the surface roughness of the substrate and improve the detection level of dye molecules. Subsequently, copper nanostructures can sensitively detect R6G and CR solutions as low as 1×10-13 mol/L and 1×10-7 mol/L, reaching single-molecule levels. The Raman mapping experiment showed that the mean relative standard deviation (RSD) values of R6G and CR were 12.3% and 12.9%, indicating high uniformity and reproducibility of the structure. This structure effectively achieves the fusion of uniformity, repeatability, and sensitivity, and shows broad application prospects in food detection.

Thermometry of Spatially Inhomogeneous Methane–Air Flame Using Two-Color Planar Laser-Induced Fluorescence and Coherent Anti-Stokes Raman Scattering Spectroscopy

Thermometry of Spatially Inhomogeneous Methane–Air Flame Using Two-Color Planar Laser-Induced Fluorescence and Coherent Anti-Stokes Raman Scattering Spectroscopy

Recent Progress in Deep Learning for Improving Coherent Anti‐Stokes Raman Scattering Microscopy (Laser Photonics Rev. 18(11)/2024)

Recent Progress in Deep Learning for Improving Coherent Anti‐Stokes Raman Scattering Microscopy (Laser Photonics Rev. 18(11)/2024)

Deciphering the Ce3+to Ce4+Evolution: Insight from X-ray Raman Scattering Spectroscopy at Ce N4,5Edges.

Cerium oxide, or ceria, (CeO2) is one of the most studied materials for its wide range of applications in heterogeneous catalysis and energy conversion technologies. The key feature of ceria is the remarkable oxygen storage capacity linked to the switch between Ce4+ and Ce3+ states, in turn creating oxygen vacancies. Changes in the electronic structure occur with oxygen removal from the lattice. Accordingly, the two valence electrons can be accommodated by the reduction of support cations where the electrons can be localized in empty f states of Ce4+ ions nearby.Quantifying the different oxidation states in situ is crucial to understand and model the reaction mechanism. Beside the different techniques to quantify Ce3+ and Ce4+ states, we discuss the use of X-ray Raman Scattering (XRS) spectroscopy as an alternative method. In particular, we show that XRS can observe the oxidation state changes of cerium directly in the bulk of the materials under realistic environmental conditions. The Hilbert++ code is used to simulate the XRS spectra and quantify accurately the Ce3+ and Ce4+ content. These results are compared to those obtained from in situ X-ray Diffraction (XRD) collected in parallel and the differences arising from the two different probes are discussed.

Versatile hybrid magnetic core silver-shell (Fe3O4@PEI@Ag) microspheres based SERS substrates for detection of organic dyes pollutant

In recent years, the development of highly sensitive and versatile substrates for Surface-Enhanced Raman Scattering (SERS) has become pivotal in environmental monitoring. This study introduces a hybrid SERS substrate designed to enhance the detection and discrimination of organic dyes in aqueous environments. In this report, we present silver shell magnetic core (Fe3O4@PEI@Ag) microspheres as a versatile SERS substrate for the detection and differentiation of organic dyes, specifically malachite green (MG), crystal violet (CV), Rhodamine 6G (R6G), and Safranin O (S.O), which are often overlooked water pollutants. The core-shell structure of Fe3O4@PEI@Ag microspheres have been synthesized via seed-mediated growth method. The microspheres, integrates a magnetic core of iron oxide (Fe3O4) through a polymeric layer of polyethyleneimine (PEI) with silver shell (Ag), are optimized to act as magnetic separator and show SERS activity. The SEM measurements confirm the spherical shape of grown nano-particles whereas magnetization experiments confirm the presence of magnetic cores as well non-magnetic layers coating in the end products. These microspheres with aluminium (Al) base combination demonstrate high SERS sensitivity with enhancement factor of 1 × 105, 5.6 × 106, 6.4 × 106, and 4.2 × 105 for MG, CV, R6G, and S.O respectively. The detection limits have been found in the range between 10–8–10–10 for all four dyes. A linear relationship between Raman intensity and concentrations of dyes make it suitable for quantitative analysis of unknown concentration. Principal component analysis (PCA), a multivariate analysis has been adopted to discrimination of dyes. These dyes have been effectively detected quantitative in tap water to express substrate's suitability in real-world application. Their dual functionality, as SERS-active substrate and as magnetic separator, enhances their utility in real-world applications such as organic contaminants in aquatic environments.