Journal of Raman Spectroscopy最新文献

Raman spectra of (As_1–xBi_x)₂S₃ glass samples with x ≤ 0.2 measured at the excitation with above-bandgap (532 nm) laser light at a relatively low power density (P_exc = 4 kW/cm²) clearly confirm the amorphous character, thereby markedly extending the known compositional interval of existence of the (As_1–xBi_x)₂S₃ glass previously known (x ≤ 0.06). Spectra measured at an increased P_exc (40 kW/cm²) reveal a photostructural transformation in the illuminated area of the glass leading to an additional contribution of Bi–S bonds as well as to an increasing number of cage-type As₄S₄ units with homopolar As–As bonds. A number of new features in a broad range up to about 1,000 cm⁻¹, which emerge in the Raman spectra of the (As_1–xBi_x)₂S₃ glasses with high (x ≥ 0.14) Bi content and increase in intensity with the exposure time, are related to a photochemical transformation, namely, oxidation of arsenic and sulphur on the (As_1–xBi_x)₂S₃ glass surface with formation of units containing arsenate AsO₄³⁻ and sulphate SO₄²⁻ ions. These processes are irreversible and occur only in the presence of a sufficient amount of bismuth.

Uranium dioxide (UO₂) is a widely studied material due to its use as fuel in pressurised water reactors (PWR), and Raman spectroscopy is a technique of choice to characterise the evolution of its microstructure. UO₂ crystallises in a fluorite CaF₂ (space group Fm-3m) structure that gives rise to a unique Raman signature, the T_2g band. However, several other bands are often detected whose attribution remains unclear. The present study gives new insights on the Raman spectrum of UO₂ thanks to the combination of isotopic labelling with ¹⁸O and Raman imaging. In addition to the expected T_2g, U₂ (LO), 2LO and U₃ bands, we have detected a doublet at 885 and 925 cm⁻¹, a U* band at 555 cm⁻¹ in some specific areas and two bands located at 367 and 1196 cm⁻¹. All Raman bands shift under the effect of the replacement of ¹⁶O by ¹⁸O, excepting for the U* band that could not be detected anymore. The isotopic shift ratio could be determined for 20% and 30% ¹⁸O labelling. No discrepancy in band position is observed between grains and grain boundaries, except for the U₂(LO) band. We also evidence a difference between the U defect bands and the 885 and 925 cm⁻¹ doublet bands evolution under labelling, although the latter also seems to be connected to the presence of defects in the material.

The examination and identification of silicate minerals are critical for advancing our understanding of the evolutionary journey of Earth-like bodies. To facilitate an efficient and productive process, it is imperative that these minerals be detected swiftly and accurately. This study is designed to explore the relationship between varying concentrations of cations and their corresponding Raman shifts. The focus is on primary silicate minerals in Earth-like bodies, specifically olivine, pyroxene, and feldspar, utilizing data from the RRUFF database. Employing a fitting formula, we identify distinct Raman peak ranges associated with different silicate minerals. Our research covers a wide array of mineral types, including five varieties of olivine (forsterite [Mg₂SiO₄], fayalite [Fe²⁺₂SiO₄], tephroite [Mn²⁺₂SiO₄], monticellite [CaMgSiO₄], and kirschsteinite [CaFe²⁺SiO₄]), four types of pyroxene (ferrosilite [Fe²⁺₂Si₂O₆], enstatite [Mg₂Si₂O₆], hedenbergite [CaFe²⁺Si₂O₆], and diopside [CaMgSi₂O₆]), and three varieties of feldspar (alkali feldspar [KAlSi₃O₈], albite [NaAlSi₃O₈], and anorthite [CaAl₂Si₂O₈]). The accuracy of matching Raman characteristics is exceptionally high for all olivine and pyroxene types (100%) and an impressive 86% for feldspar. The findings from this study highlight the crucial role of Raman spectroscopy in the field of silicate mineralogy and suggest significant implications for enhancing future exploration missions to Earth-like bodies.

Transition metal complexes, such as the low-spin bis (phenylterpyridine) (A) and bis (pyridylterpyrazine)iron (II) (B) complexes, provide didactic chromophore species for demonstrating the Raman, resonance Raman, and the surface-enhanced Raman scattering (SERS) behavior in coordination chemistry, as well as for elucidating the nature of inner-sphere and outer-sphere association with plasmonic nanoparticles. Their electrostatically stabilized ion pairs with citrate–gold nanoparticles have been studied in an aqueous solution, from the pronounced changes in the plasmonic band at 540 nm. Complex A, lacking any coordinating site, can only generate outer-sphere complexes with citrate–gold nanoparticles, but they are stable enough to give a strong SERS response, even at 10⁻⁸ M. At 10⁻⁶ M, agglomeration accompanies the decrease of the electrostatic repulsion, resulting in a sharp decay of the plasmon resonance band at 540 nm. This is followed by the rise of a plasmon coupling band above 700 nm. However, at 10⁻⁴ M, the excess of the complex in the adsorption layer produces a reverse effect, decreasing agglomeration. The observed Raman spectra are essentially similar for the several concentrations employed because the outer-sphere interaction implies a SERS electromagnetic mechanism. In contrast, complex B exhibits several pyridine and pyrazine N-atoms available to form inner-sphere-associated species. A selective enhancement of the SERS signals is observed at 10⁻⁸ M, clearly indicating a chemical mechanism, consistent with a bridging mode. At 10⁻⁶ M and above, the agglomeration leads to a plasmon coupling band at 800 nm, while the SERS response indicates a change in the binding modes dictated by the excess of the complexing molecules.

Raman hyperspectral imaging (RHSI) is a valuable tool for gaining crucial information about the chemical composition of materials. However, obtaining clear Raman signals is not always a trivial task. Raw Raman signals can be susceptible to photoluminescence interference and noise. Hence, the preprocessing of RHSI is a required step for an effective and reliable chemical analysis. The main challenge is splitting the measured RHSI into separate Raman photoluminescence signals. Since no golden-standard exists, it is non-trivial to validate the correctness of the separated signals. While current state-of-the-art preprocessing methods are effective, they require expert knowledge and involve unintuitive hyperparameters. Current approaches also lack generalizability, requiring extensive hyperparameter tuning on a case-by-case basis, while even then results are not always as expected. To this end, this work proposes a novel iterative RHSI preprocessing pipeline for splitting raw Raman signals and noise removal based on linear spline and radial basis function regression (IlsaRBF). The proposed method involves hyperparameters based on the physical properties of Raman spectroscopy, making them intuitive to use. This leads to more robust and stable hyperparameters, reducing the necessity for extensive hyperparameter tuning. A thorough evaluation shows that the proposed method outperforms the current state-of-the-art. Additionally, a cosmic ray identification and removal algorithm (CRIR) and dynamic PCA for noise reduction are introduced. A standalone tool containing our proposed methods is provided, making RHSI preprocessing available to a broader audience, aiding further research and advancements in the field of Raman spectroscopy.

Microporous materials containing hydrated silanol groups Si–OH as well as hydrated proton complexes, H_2n+1O_n⁺, including hydronium (n = 1), Zundel (n = 2), and Eigen (n = 4) cations, are of practical importance as potential ion exchangers and ion conductors. In this paper, we provide data on crystal-chemical features, hydrogen bonding and Raman spectra of alkaline microporous titano-, niobo-, zircono-, and aluminosilicate minerals belonging to the labuntsovite, lovozerite, eudialyte, and sodalite groups in which a part of sodium was substituted by hydrated proton complexes under low-temperature hydrothermal or supergene conditions. Most minerals studied in this work do not have synthetic analogues and are considered as possible natural prototypes of microporous materials with technologically important properties. The obtained experimental data and their comparison with the results of ab initio theoretical calculations published elsewhere show that Raman spectroscopy is an effective tool for the precise identification of hydrated proton complexes with extremely strong hydrogen bonds and estimation of corresponding O···O distances in the range of 2.37–2.68 Å. The presence of hydrated proton complexes in microporous silicates is a clear and sensitive geological indicator showing that a rock underwent the low-temperature alteration.

Surface-enhanced Raman scattering nanoparticles (SERS NPs) offer powerful optical contrast features for imaging assays. Their gold core enhances the inelastic scattering cross section, allowing highly sensitive and rapid detection, and their characteristic sets of narrow spectral bands give them unsurpassed multiplexing capabilities. Multiplexed hyperspectral images are commonly unmixed using a compensation matrix of reference spectra to produce quantitative image channels illustrating the distribution of each material. It is these unmixed channels that are fit for interpretation from assays utilizing SERS NP contrast agents. Some factors that may impact SERS NP quantitative and dynamic range capabilities may include endogenous background heterogeneity, the ability of unmixing algorithms to account for signal variances, and linear system conditioning imposed by contrast agent signals. We report on hyperspectral Raman imaging of mixtures of SERS NPs from an expanded library of contrast agents. We study increasing plexity and varying degrees of system conditioning as inputs to a diverse set of classical, non-negatively constrained, and regularized regression algorithms to investigate which signal features and unmixing methods deliver the most promising quantitation performance with the least error. Raman imaging of SERS NP mixtures is performed on controlled substrates and representative biological specimens, and experimental results are compared against ground truth data. We evaluate spectral fitting fidelity, quantitation, and specificity correlations with system conditioning. Spectral unmixing with a regularized hybrid of least squares regression with principal component analysis (HLP) algorithm approximated spectra with 3.5× better fitting fidelity and 3× better quantitation robustness with tissue background compared with simpler unmixing routines.

Helicobacter pylori and Epstein–Barr Virus (EBV) are Group 1 carcinogens that can enhance gastric cancer progression. Bioactive substances extracted from plants can be effective therapeutic agents in cancer treatment. For example, Withania somnifera extract-WSE reduces the Gankyrin oncoprotein, which is upregulated in the presence of H. pylori and EBV. The various biochemical and metabolic changes upon 24 hrs post-infection followed by W. somnifera extract (WSE) treatment on gastric epithelial cells (AGS) can be studied using spectroscopic techniques. In the biomedical sciences, Raman and NMR spectroscopy have been extensively employed to interpret cellular alterations contributing to the onset of infection and the severity of gastric cancer. More specifically, alterations in cellular biochemical homeostasis are linked to the moieties of cholesterol, collagen, choline, carbohydrate, lipids, tyrosine, and phenylalanine. Further, we have found significantly elevated FWHM for carbohydrates, tumor associated protein, collagen, cholesterol, and cholesterol ester in the co-infection model. We also looked into the potential correlation between these molecules using molecular network analysis and found several related factors that can be modulated through biomolecular levels. These molecules are crucial in several physiological functions, including cell division, cell proliferation, apoptosis, necrosis, cell migration, and lipid transport. Our study paves the pathway to study H. pylori and EBV co-infection in human gastric epithelial cells and the therapeutic interventions of WSE in this scenario and highlights specific biomolecular alterations, which can be focused for further mechanistic investigations.

Although the potential of Raman Optical Activity (ROA) spectroscopy in the field of organic and inorganic materials research has been well demonstrated, its practical application is still limited. This work shows historical background, current state of the art and challenges of ROA spectroscopy facing scientists today. Expectations and development prospects for the coming years are also discussed. Efforts have already been made to improve but also to properly interpret the ROA signal when the ROA technique is combined with other spectroscopies (i.e., ROA/Electronic Circular Dichroism and ROA/Circularly Polarized Luminescence). The paper shows how to intensify the ROA effect to shorten the spectrum accumulation time, control possible artefacts and support the analysis of ROA spectra with actual and new theoretical approaches. However, the challenge is to increase the interest in this technique among the academic community, develop reliable protocols and adapt them for practical use. National and international research networks can significantly contribute to the growth of methodologies and standardization in areas in which the ROA has so far been little used. This paper presents a perspective vision for the future progress of ROA alongside other chiroptical methods.

We summarize the current knowledge on crystal structures, synthesis, applications, and Raman spectroscopy of Wadsley phases of vanadium oxide, including VO₂ (B), V₆O₁₃, V₄O₉, V₃O₇, and V₂O₅. While these oxides have garnered significant attention for potential energy storage applications and have been studied for decades, there remains inconsistency in data regarding their characteristic Raman spectra. To address this, we synthesized a series of Wadsley phases by physical vapor deposition of amorphous vanadium oxide films and subsequent annealing in a controlled environment. X-ray diffraction studies confirmed the formation of VO₂ (B), V₆O₁₃, V₄O₉, and V₃O₇. We meticulously measured the room-temperature Raman spectra of these phases, offering robust reference data for the easy identification of vanadium oxides in unknown samples. Finally, we studied low-temperature phase transitions in VO₂ (B) and V₆O₁₃.