Journal of Raman Spectroscopy最新文献

Raman spectroscopy basically probes the changes in polarizability induced by lattice vibration, popularly known as Raman tensor which is highly sensitive to the interatomic distances. The question is how precisely this can be probed. Can Raman spectroscopy sense very small atomic displacement, say femtometer displacement? The answer is yes; now, it is a reality, thanks to the light polarization dependence of the Raman scattering. In this review, we discuss the working principles of the atomic displacement detection protocol using angle resolved polarized Raman spectroscopy and theoretical formulation of the relation between the directional atomic displacement (strain) and spectral parameters along with some experimental results on different classes of materials like multiferroic and ferroelectric. The very high detection capability of this technique enables one to unearth the microscopic mechanism of the electric polarization in Type II multiferroic material CuO and resolve the long-standing debate on crystal symmetry of the popularly used substrate material NdGaO₃ and detection of Ti displacement in classical ferroelectric BaTiO₃. Remarkably, the required apparatus is very simple; it includes a polarization analysis capable Raman spectrometer to probe a specific Raman tensor element, a sample rotation stage to adjust the polarization of the incident and scattered light with respect to crystallographic orientations, and of course sample should be single crystals or epitaxial thin film. The simple instrumental requirements, straightforward direct method of atomic displacement detection, high sensitivity for the low atomic number elements, and microscopic special resolution make it highly useful in future applications where small atomic displacement (particularly from the center of symmetry) to external factors like temperature, pressure, and electric or magnetic field plays pivotal in shaping physical properties.

Raman spectroscopy, especially Raman imaging, has become a popular technique for fluid inclusion studies. Raman imaging is particularly useful for the study of tiny inclusions appearing in high or ultrahigh pressure (UHP) metamorphic minerals. The small size of daughter phases, as well as the presence of liquid or gas phases, precludes the application of microprobe analysis for unexposed inclusions. Nontransparent inclusions, usually assigned as “opaque”, “ore,” or “black” accessory minerals, are rarely studied by Raman spectroscopy due to the high absorbance of laser energy by black materials, their unstable behavior at the laser beam, and low Raman signal. Despite these difficulties, a number of documented examples show that multiphase inclusions in these metamorphic rocks may persist. These inclusions provide valuable information on the composition of fluids in deeply subducted environments. For the first time, we demonstrate that “opaque” or “black” inclusions in UHP rocks are multiphase. They contain CO₂ + CH₄ gas bubbles ± calcite and graphite with different degrees of crystallinity. These multiphase fluid inclusions coexist side by side with “classical” inclusions which also contain CO₂ and CH₄ gases, as well as liquid water, but no graphite. Our findings demonstrate that Raman imaging of “classical” and “black” fluid inclusions and subsequent data treatment by different techniques may bring important information about their composition.

Raman spectroscopy is a powerful optical tool that provides nondestructive analysis with minimal sample preparation and structural information, making it widely used in planetary and deep-sea research. Although Raman spectroscopy has shown potential for estimating Mg/Ca ratios in Mg-calcites, data for biogenic Mg-calcites from diverse marine regions remain limited. Here, we investigated the relationship between Raman spectral parameters (peak position and width) and chemical composition (Mg/Ca molar ratios) in 50 biogenic Mg-calcites in methane-derived authigenic carbonate (MDAC) from Site 16GH-P3 in the Ulleung Basin, Korea. Using electron probe microanalysis, we obtained Mg# (=Mg/[Mg + Ca], mol%) values ranging from 0 to 13.8 mol% in biogenic Mg-calcites (foraminifera, coccolithophore, and unidentified species). By combining chemical composition data with Raman spectral results, we derived positive correlation equations for CO₃²⁻ vibrational modes, consistent with previous studies. These equations demonstrate a strong correlation between Raman spectral features and Mg/Ca ratios, highlighting the usefulness of Raman spectroscopy in estimating Mg/Ca ratios in biogenic Mg-calcites. Through analysis of foraminifera from MDAC with Mg# of 0.1 mol%, we propose to use both peak widths and positions in estimating Mg/Ca ratios in biogenic Mg-calcites. Our study expands the data set for using Raman spectral features to estimate Mg/Ca ratios in biogenic Mg-calcites, providing a valuable reference for future Raman applications.

Baseline correction is a critical yet challenging task in Raman spectroscopy analysis of low-maturity organic matter (organic material with minimal thermal alteration or metamorphism, generally with apparent peak metamorphic temperatures < 280°C), especially due to the difficulty in accurately identifying the true shape of the baseline when the spectra exhibit broad and overlapping bands. In this study, we present a novel approach to evaluate baseline correction methods by comparing the correlation of Raman spectral parameters obtained at two different excitation wavelengths (514 and 633 nm). We applied four baseline correction methods (linear, polynomial, spline, and IFORS) to the spectra of organic microfossils from a section in South China as examples and evaluated their performance based on the correlation of eight key Raman parameters between the two wavelengths. The results show that for 633 nm excitation, the linear method causes the largest errors, while the optimal baseline correction method varies among different parameters. For 514 nm excitation, all baseline methods performed similarly, with the linear method showing slightly better results. The comparative analysis of spectral parameters at two wavelengths provides a new and practical strategy for evaluating baseline correction methods in Raman spectroscopy. This methodology provides insights for improving the reliability of spectral analysis in studies of low-maturity organic matter, offering a clearer understanding of how different baseline correction methods affect the interpretation of Raman data.

Gem-quality emeralds—the green color variety of beryl (Be₃Al₂Si₆O₁₈)—from some of the most important world localities (Australia, Austria, Brazil, China, Colombia, Egypt, Madagascar, Nigeria, Russia, South Africa, and Zambia) were characterized using micro-Raman spectroscopy. There are three main characteristic Raman shift regions in emeralds: the fingerprint region (150–1500 cm⁻¹) representative of Si-O, Be-O, and Al-O bonds; the water region (3500–3900 cm⁻¹), and the nitrogen and hydrocarbons regions (~2325 cm⁻¹ and ~2914 cm⁻¹, respectively). This study examined crystals and gemstones representing 11 major localities along with one synthetic. The analysis involved a systematic study of crystal orientation effects (parallel and perpendicular to the c-axis) and peak finding and fitting of Raman shift center and full width half maximum of main peaks using Fourier self-deconvolution and Lorentz functions, respectively. Peak intensity was found to be strongly influenced by crystal polarization effects, with the bands around 1070 cm⁻¹, due to Si-O and/or Be-O stretching, being the most affected. Colombian emeralds, found in carbonaceous black shales and low in alkalis, exhibited a dominant type-I water peak (3608 cm⁻¹) in both orientations and showed the highest intensity of the N₂ molecule (~2325 cm⁻¹). In contrast, Madagascar and Zambian emeralds had a dominant type-II water peak (3598 cm⁻¹) and the highest alkali concentrations. Preliminary linear discriminant analysis (LDA) applied to Raman spectroscopy and LA-ICPMS datasets demonstrates a distinct clustering pattern for Colombian emeralds. Furthermore, the analysis effectively differentiates Pan-African deposits, specifically distinguishing Madagascan samples from Zambian ones. Including additional combined datasets from other localities would enhance the potential of using Raman spectroscopy as a provenance tool.

Raman spectroscopy analysis has been used successfully to distinguish normal from neoplastic tissue during surgical resection of tumors. However, microscopic Raman spectroscopy is typically time-consuming and restricted to examining only a small, specific region of the tissue. Recently developed handheld Raman probes have shown promise to overcome these limitations and thus be developed as an intraoperative tool to categorize and identify various types of tissues. In this paper, we evaluated the use of Raman spectroscopy by a handheld probe in feasibility studies of fresh samples of normal human white adipose tissue (WAT) taken from adjacent to four sarcomas to determine the accuracy and consistency of measurements under varying ex vivo conditions. We also studied if the results are affected by freezing the samples, a common practice in ex vivo protocols, or by covering the probe with polyethylene, which could be used under sterile conditions during surgery. Our findings showed that the handheld probe provided consistent Raman measurements in white adipose samples and that exposing fat tissue to different freezing protocols does not significantly affect the integrity and representation of prominent peaks for the tissue, resulting in consistent identification of tissue spectra. We also found that covering the probe with polyethylene had minimal effects on measurement of the WAT spectra, which suggests that sterile polyethylene could be used to cover the probe in the operating room to maintain sterility. Our findings suggest that Raman spectroscopy with a handheld probe has potential to be developed for use in the OR to identify normal adipose tissue in a surgical bed.

The localization of the SERS effect from air nitrogen molecules over nanostructured self-assembled silver films has been experimentally investigated. In our previous experiments on surface-enhanced Raman scattering from myoglobin on such SERS substrates, the intensity of the scattering spectrum depended on the thickness of the analyte. At very low analyte concentrations, giving an estimated monolayer on the substrate, little or no SERS was observed; at higher concentrations, analyte crystallites as thick as 0.5 to 1 μm gave an intense SERS spectrum. Since the plasmon resonance field of a single nanoparticle is mainly localized near its surface on the scale of a few nanometers, the electromagnetic and chemical mechanisms of SERS are localized at the same distances. We hypothesized that for a rough metal with a developed surface consisting of crystallites of noble metals with subwavelength sizes, the total field of these particles can localize the SERS effect at larger distances from the substrate. While the literature data on this issue for continuous films are contradictory, we present the results of a systematic study of our hypothesis. Experiments with the SERS effect from air nitrogen molecules exclude any volume or chemical effects from the analyte. The measured scale of the long-range SERS contrasts with the traditional idea of the extremely fast attenuation of SERS at distances of units to tens of nanometers. The observed characteristic space scale of ~140 nm exceeds the characteristic scales of inhomogeneities in the substrate nanostructure. An explanation of this fact should apparently be sought in terms of the mechanism of excitation, scattering, and localization of hybrid plasmon–polariton waves under conditions of a real optical scheme, taking into account the morphology and structure of silver films. The experimental methods (Z-Scan) used in the work allow measuring the real point distribution function for confocal microscopes.

Plasma proteins are considered an important indicator for cancer diagnosis and prognosis. Currently, commonly used detection methods are unable to achieve rapid and highly sensitive detection of plasma proteins, making them insufficient to meet the demands of high-sensitivity cancer screening. To address this issue, we propose a rapid detection method for plasma proteins using surface-enhanced Raman spectroscopy (SERS) based on particulate triacetate cellulose (TCA), referred to as TCA-SERS. To verify the feasibility of TCA-SERS for liver cancer (LC) screening, we analyzed the SERS spectra of plasma samples from 60 LC patients and 60 healthy individuals using two multivariate statistical algorithms: PCA-LDA and PLS-SVM. The classification accuracy of PCA-LDA in distinguishing LC patients from healthy individuals was 84.2%, with a sensitivity of 81.7%, specificity of 86.7%, and an AUC value of 0.911. In contrast, the classification accuracy of PLS-SVM was 95.8%, with a sensitivity of 96.7%, specificity of 95%, and an AUC value of 0.999. The diagnostic performance of PLS-SVM surpassed that of PCA-LDA, indicating that TCA-SERS demonstrates excellent potential for LC detection. Moreover, the results highlight the greater potential of the PLS-SVM algorithm in analyzing SERS spectra of plasma samples in TCA-SERS. These findings are of great significance for developing label-free, noninvasive LC screening methods.

The Indian scientist Sir C.V. Raman, in 1928 has used sun light to perform an inelastic light scattering experiment, which later became known as the Raman effect. In preview of the centennial of the discovery of this effect in 2028, a similar experiment has been made, however, in an “inverted” arrangement, whereby wavelength sections of the sun light between a few Fraunhofer lines were used simultaneously for Raman excitation. A single, narrowband Raman line of high intensity had been employed for this purpose. The latter has been accomplished with the 1048 cm-¹ Raman transition of a barium nitrate (Ba[NO₃]₂) single crystal. As a consequence, the selected Fraunhofer lines appear in a spectral region shifted to longer wavelengths by 1048 cm-¹.