Journal of Raman Spectroscopy最新文献

In this work, aqueous nutrient solutions replicating bioreactor culture media for microalgae were analyzed using spontaneous Raman spectroscopy. Focusing on nitrate, sulfate, glucose, and phosphate, the study evaluated their potential for real-time monitoring in cell cultivations such as Chlorella vulgaris. Univariate analysis, based on Raman intensities of specific nutrient peaks, was conducted and compared to multivariate analysis results. Four multivariate calibration models were developed using partial least squares regression (PLSR), achieving high calibration and validation performance, with R² values above 0.99 and low RMSE_CV, indicating strong calibration accuracy. The study also examined the limit of detection (LOD) for each nutrient, finding that LODs for nitrate, sulfate, and glucose reached levels relevant for algae bioreactors even without the application of enhanced Raman techniques. To further validate the PLS models, independent real bioreactor samples were analyzed, showing strong predictive accuracy (R_P²: 0.9661–0.9892) and low RMSE_P values. Additional testing with five samples collected over a Chlorella vulgaris cultivation run (day 0 to day 9) confirmed the models' robust performance under real bioprocess conditions. Limitations in practical applications, such as phosphate's relatively high LOD, were also identified. The results suggest that Raman spectroscopy, combined with multivariate analysis, could deliver precise and reliable detection of critical nutrients and their concentrations in bioreactor culture media. This potential of the Raman technique, along with insights into nutrient LODs, PLS model accuracy, and practical application challenges, provides a solid foundation for future research and development in industrial bioprocess monitoring.

In this study, we utilized surface-enhanced Raman scattering (SERS) to examine the conformational changes of cysteamine on silver bumpy nanoshell (AgNS) in various solvents, including water, ethanol (EtOH), isopropyl alcohol (IPA), and acetonitrile (ACN). It was found that the interaction between cysteamine and solvent molecules could affect the conformational equilibrium of cysteamine on the AgNS surface, particularly the ratio between its trans and gauche conformations. Using the SERS bands at 630 and 720 cm⁻¹ assigned to S–C stretching modes of the gauche and trans conformations, respectively, and calculating the SERS intensity ratio of these bands (I_trans/I_gauche), we found that water stabilized the gauche conformation because of the strong hydrogen-bonding interactions with cysteamine, while solvents such as ACN favored the trans conformation. SERS measurements over time further indicated that cysteamine reached conformational equilibrium on AgNS slowly within hours in a single solvent environment. In mixed water/ACN solvents, the gauche conformation became increasingly dominant with higher water fractions. Conversely, introducing ACN into water-stabilized AgNS dispersion did not reverse the conformational shift, suggesting that the gauche to trans transition was limited by higher activation barrier due to irreversible stabilization of Ag–N bond in the gauche form and local solvent environment around surface-bound cysteamine. Conformational equilibrium of cysteamine on AgNS could be quantified using the degree of mixing (γ), a parameter reflecting the distribution and interaction of cysteamine in mixed solvent. This study shows that SERS is effective for monitoring solvent-mediated conformational changes in surface-bound cysteamine. This approach might help us optimize solvent selection for applications that leverage the reactive amine group of cysteamine on metal surfaces.

Pyrrhotite (Fe_1-xS; 0 < x < 0.125) is one of major iron sulfides found in sedimentary rocks. While it is sometimes considered merely a gangue for metal mining, it is geo/cosmochemically important mineral because its composition (x) and superstructure sensitively reflect an aqueous environment when it precipitated. Analyzing such properties presents difficulties, as pyrrhotite in natural rocks is often as small as micrometers and is embedded in silicate matrices. Micro-Raman spectroscopy is a powerful tool for analyzing the crystal structure with high spatial resolution. While several researchers had reported distinctly different Raman spectra for pyrrhotite, we recently revealed that the Raman bands of pyrrhotite are extremely weak and what appear to be intense peaks likely originate from its (hydro) oxides. However, at the time, we barely observed only one Raman band at ~120 cm⁻¹ so that even its fundamental properties such as its polarization dependence and relative intensity to other bands could not be obtained. In the present study, we optimized our lab-built Raman spectrometer to probe weak Raman bands in the low-wavenumber region (< 150 cm⁻¹) to provide a reliable dataset for the Raman spectra of pyrrhotite. As a result, we succeeded in finding lattice modes at ~68 ($�A_g$), ~87 ($�B_g$), ~117 ($�A_g$), and ~230 cm⁻¹ ($�A_g$) with a sufficiently low baseline level for the first time, enabling us to also determine polarization dependence of their intensity.

This work investigates the composition of the patina and state of preservation of an Etruscan bronze fibula from Tomb 129 of Vulci Archaeological Park (VT, Italy), dating back between the late eighth and early seventh centuries BC. Non-destructive analytical techniques, such as micro-Raman spectroscopy and energy-dispersive X-ray fluorescence (ED-XRF) combined with Monte Carlo simulations, were used to analyze the patina's mineralogy and the alloy's chemical composition. Monte Carlo simulation was applied to model the layered structure of the fibula accurately and distinguish between the alloy and the patina, allowing the elemental composition of the fibula to be known and excluding selective depletion phenomena. Innovative 3D reconstruction through X-ray microscopy (XRM) allowed the characterization of the internal structure of the artifact and its state of preservation. Micro-Raman results on the patina identified the occurrence of brochantite and sampleite due to interactions with the burial environment and the decomposition of organic matter. The fibula was a binary bronze alloy (Cu-Sn) with a low tin content and minimal lead concentration. XRM analysis detected fragility points and a small blind hole inside the fibula, probably related to the manufacturing processes. These findings provide insight into the artifact's conservation status and contribute to a better understanding of ancient Etruscan metalworking techniques. By integrating advanced analytical methods and non-invasive imaging, this study highlights the potential of combining scientific techniques to preserve cultural heritage and deepen our knowledge of metallurgical practices in ancient civilizations.

Emeralds frequently contain inclusions, and their study can provide valuable clues on their geological origin. For the present study, 11 emeralds containing elongated amphibole inclusions from four geographic origins (three from Austria, one from Russia, two from Zambia and five from Zimbabwe) were investigated with an optical microscope and Raman spectroscopy. The inclusions have various sizes and shapes; curved inclusions are frequently observed in emeralds from Zimbabwe and in one sample from Zambia. Most inclusions are of actinolite; tremolite is observed in Austrian samples and cummingtonite in samples from Zimbabwe. These subtle differences in amphibole inclusions in emeralds could help identify emeralds from these mining regions.