Raman Spectroscopy Research Articles

Combining Diffractometric and Spectroscopic Analysis of Artificial Stones from Palazzo Brasini (Taranto, Southern Italy) to Characterise Materials and Constructive Systems

ABSTRACT The aim of this work is to give a compositional characterisation of the artificial stones used in the building up of the Taranto (Apulia region, southern Italy) seaplane station, also better known as Palazzo Brasini (named after the architect who designed it), which represents an example of eclecticism from early 20th century monumental style. Diagnostic analyses applied to architecture, and specifically to “artificial stone” - carried out by combining diffractometric technique with spectroscopic ones, i.e. micro-Raman spectroscopy and micro-X-Ray fluorescence – provided information related to the compositional characterization of the material and its mechanical characteristics. They resulted to be compulsory to decode the specific production processes adopted by artisans other than to provide useful information on the interaction between the artefact and the conservation environment and the identification of degradation processes, thus allowing to plan any further restoring protocol. Besides, diagnostic analyses were necessary to highlight the technological know-how and the circulation of knowledge of artificial stone productions by identifying the lithocement components. The main artificial stone production features regard the use of saffron as a colouring agent in the production of the artificial stones of Palazzo Brasini due to its toxicological safety and stability to light. The use of this pigment is in line with the autarkic style that characterises the architecture of the 20th century, because it prefers the use of local or at least easily found raw materials. Grossularia, iron oxides, and carbon black were also used as pigment in the adopted artificial stones from Palazzo Brasini and their presence, together with that of saffron, can be likely considered a sort of “trademark” of manufacturing. Chloride ions have been found in the northern facade of the Palazzo Brasini as consequence of it being set in an environment where chloride rich aerosol is remarkable. It was found in samples from the external wall finishing layer from both the lower moulding and the upper moulding. The presence of chlorine in the layer of smooth plaster, suggests a slight penetration of the ion up to the smooth plaster. Besides, the penetration of sulphur into plaster layers (“arriccio” and smooth) – likely associated to the mineralogical phase gypsum as suggested by Raman spectroscopy – is responsible for the transformation reaction of calcite into anhydrite and may be related to the natural acidity of rainwater/aerosols and physical weathering from temperature change and erosion. The observation of white efflorescence, in between the sublayer A and B of the external wall finishing layer from lower moulding and upper moulding it is likely a consequence of the aggressive environment is which Palazzo Brasini is set. The proximity to the steel plant ILVA, responsible of high SO2 concentration levels in the aerosol, can be the triggering factor of the sulphate attack on the upper and lower moulding.

Measuring the Adhesion of Graphene Flake Networks via Button Shear Tests.

Graphene flake-based dispersions are attractive materials for various applications in microelectronics because of their ease of fabrication and the potential to deposit them on diverse substrates. The integration of these materials into conductive networks and microdevices requires thorough knowledge of their mechanical material properties, including adhesion. This paper presents quantitative adhesion measurements of graphene flake networks on silicon dioxide (SiO2) via button shear testing (BST). In this method, shear forces are applied to prefabricated micrometric buttons until they delaminate, providing information about the shear strength of the underlying graphene. We applied BST to graphene flake networks with different flake structures and defect densities. Flat flakes, a flat network structure, and a high flake defect density improve adhesion. We further demonstrate that graphene flake networks have stronger adhesion than chemical vapor-deposited (CVD) monolayer graphene grown on copper and transferred to SiO2. Hexamethyldisilazane (HMDS) increases the total adhesion force by improving flake network formation. Finally, we provide flake-type-specific delamination patterns by combining BST, optical microscopy, and Raman spectroscopy. We establish BST as a quantitative technique for measuring the adhesion of graphene dispersions and show the crucial role of interflake junctions in the overall adhesion of graphene flake networks.

Fabrication of highly efficient ZnO-Pt catalysts assisted by biomass-derived carboxymethyl cellulose for the photodegradation of diverse antibiotics.

Fabrication of highly efficient ZnO-Pt catalysts assisted by biomass-derived carboxymethyl cellulose for the photodegradation of diverse antibiotics.

Octahedral distortion induced photoluminescence in Cs2NaInxBi1-xCl6 halide double perovskites.

The halide perovskite materials have shown broadband light emission and there are multiple strategies to tweak the photoluminescence. Here in this work, we report a class of halide double perovskites Cs2NaxIn1-xCl6 that are chemically tuned via trivalent cation engineering to introduce octahedral distortion. This distortion leads to improved light emission properties where the photoluminescence quantum yield improved from <1% for a symmetric-octahedra containing parent compounds to > 6.5 % in distorted-octahedra containing mixed-trivalent compounds. Using structural and optical studies including Raman spectroscopy, far-infrared absorption, and steady-state photoluminescence, the role of octahedral distortion in improving light emission in halide double perovskites is demonstrated. In addition, to emphasize the role of distortion, electric bias was intentionally applied to symmetric-octahedra containing parent compounds, and their role in the emission properties was investigated.

Raman spectroscopy based diagnosis of pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma is currently the 12th most frequent form of cancer worldwide, characterized by a very low 5-year survival rate. Although several therapeutic approaches have been proposed to treat this form of pancreatic cancer, surgical resection is still commonly recognized as the most effective technique to slow down the disease progression and maximize the 5-year survival rate. Analogously, one critical issue is the ability of current diagnostic methodologies to distinguish between irregular growth of the tumor mass and surrounding inflammatory tissues. In this pilot study, we apply Raman spectroscopy, supported by a series of machine learning techniques, to distinguish among healthy, pancreatitis and ductal adenocarcinoma tissues, respectively, for a total of 15 cases. Raman spectroscopy is a label-free, non-destructive spectral technique exploiting Raman scattering. In turn, by applying a combination of principal component analysis and random forest classifier on the Raman spectral dataset, we achieved a maximum accuracy of up to ∼96%. Our findings clearly indicate that Raman spectroscopy could become a powerful spectral technique to support pathologists in improving pancreatic cancer diagnosis.

Prediction of Secondary Structure Content of Proteins Using Raman Spectroscopy and Self-Organizing Maps.

Proteins are biomolecules with characteristic three-dimensional (3D) arrangements that render them different vital functions. In the last 20 years, there has been a growing interest in biopharmaceutical proteins, especially antibodies, due to their therapeutic application. The functionality of a protein depends on the preservation of its native form, which under certain stressing conditions can undergo changes at different structural levels that cause them to lose their activity.1 Although mass spectrometry is a powerful technique for primary structure determination, it often fails to give information at higher order levels. Like infrared (IR), Raman spectra are well known to contain bands (especially the amide I from 1625-1725cm-1) that correlate with secondary structure (SS) content. However, unlike circular dichroism (CD), the most well-established technique for SS analysis, Raman spectroscopy allows a much wider ranges of optical density, making possible the analysis of highly concentrated samples with no prior dilution. Moreover, water is a weak scatterer below 3000 cm-1, which confers Raman an advantage over IR for the analysis of complex aqueous pharmaceutical samples as the signal from water dominates the amide I region. The most traditional procedure to extract information on SS content is band-fitting. However, in most cases, we found the method to be ambiguous, limited by spectral noise and subjected to the judgment of the analyzer. Self-organizing maps (SOM) is a type of self-learning algorithm that organizes data in a two-dimensional (2D) space based on spectral similarity and class with no bias from the analyzer and very little effect from noise. In this work, a set of protein spectra with known SS content were collected in both solid and aqueous state with back-scatter Raman spectroscopy and used to train a SOM algorithm for SS prediction. The results were compared with those by partial least squares (PLS) regression, band-fitting, and X-ray data in the literature. The prediction errors observed by SOM were comparable to those by PLS and far from those obtained by band-fitting, proving Raman-SOM as viable alternative to the aforementioned methods.

Characterization of Cr implanted GaAs processed with ArF+ and Nd-YAG laser melting

Abstract We present a detailed investigation on the properties of supersaturated GaAs using Cr implantation followed by nanosecond Pulsed Laser Melting (PLM). A comparison between two different lasers was carried out (ArF+ and Nd-YAG). We have analyzed supersaturated samples by means of structural, electrical, optical, and optoelectronic techniques. Raman spectroscopy and transmission electron microscopy (TEM) results show a recovery of crystallinity after the PLM process. ToF-SIMS results reveal a Cr concentration above the solid solubility limit after the PLM process, featuring depth distribution depending on the type of laser used. The sheet resistance results obtained using van der Pauw configuration measurements show an activation of the implanted Cr in semi-insulating GaAs after PLM. Optical transmittance and Reflectance measurements show a sub-bandgap absorption (up to 10% for = 1250 nm) of the supersaturated GaAs:Cr related to the Cr incorporation, besides absorption induced by the PLM process itself. The origin of this sub-bandgap absorption has been analyzed by means of opto-electronic measurements revealing sub-bandgap photoresponsivity related to the absorption analyzed. The photoresponsivity measured below the bandgap originates from both the defects introduced by the PLM process and the states within the bandgap associated to the implanted Cr.

Cyclic voltammetry insights into Ni/Al-carbonate hydrotalcite catalysis for methanol oxidation

The catalytic performance of Ni/Al-carbonate-based layered double hydroxide (Ni-LDH) for methanol oxidation reaction (MOR) was investigated using spectro-electrochemical techniques. Ni-Al hydrotalcite containing carbonate anions was synthesized and characterized by XRD, SEM, FTIR, and Raman spectroscopy. A glassy carbon electrode modified with Ni-LDH (NLGC) showed optimal catalytic activity under alkaline conditions (pH 13). Cyclic voltammetry (CV) of NLGC exhibited anodic and cathodic peak current densities at 0.62 V and 0.42 V, corresponding to quasi-reversible redox behavior of Ni(II)/Ni(III) centers. The linear correlation of peak current with scan rate in the non-faradaic region (0.1–0.3 V) suggests an adsorption mechanism involving the NiII-(OH)2/NiIII-OOH redox couple, while a square-root relationship indicates diffusion-controlled MOR. Hysteresis at 0.60 V and peak shifts further highlighted efficient charge transport, enhanced by the brucite layer of Ni-LDH. The electrochemically active surface area was calculated to be 0.042 cm², and linear sweep voltammetry revealed a 5.2 V onset potential. Double potential chronoamperometry confirmed a one-electron redox process, with a Tafel slope of 24.2 mV/dec. Raman analysis supported these findings, showing a redshift of NiII-O at 474 cm⁻¹ and formate ion vibrations, confirming NiIII-OOH’s role in MOR catalysis on NLGC.

Tracing the source of the Mineralization Fluid, and metamorphism of the Nampala Gold Deposit, southern Mali: Constraints from stable (oxygen and hydrogen) isotopes and Raman Spectroscopy

Tracing the source of the Mineralization Fluid, and metamorphism of the Nampala Gold Deposit, southern Mali: Constraints from stable (oxygen and hydrogen) isotopes and Raman Spectroscopy

Ternary composite of unzipped multiwalled carbon nanotubes (curved graphenes) for next-generation capatteries.

Ternary composite of unzipped multiwalled carbon nanotubes (curved graphenes) for next-generation capatteries.

Arc erosion behaviour of Ag–La2Sn2O7/SnO2 electrical contact composites in SF6, N2, and CO2

ABSTRACT Ag-La2Sn2O7/SnO2 composites (with a mass ratio of 88:4:8) were prepared by powder metallurgy using Ag powder and La2Sn2O7/SnO2 composite powder (synthesised by chemical co-precipitation). The arc erosion behaviour under discharging atmospheres of SF6, N2, and CO2 at a constant voltage of 7 kV was investigated by analysing arc parameters, erosion morphology, and compositional variation. Results indicated that the arc duration and arc energy increased in the order of SF6, N2, and CO2, with the highest breakdown current observed in CO2. The erosion area in SF6 exhibited fewer bulges and splash particles owing to its shorter arc duration and lower energy. In contrast, the erosion in N2 and CO2 was more severe, with microcracks being observed particularly in CO₂. Raman and X-ray photoelectron spectroscopy (XPS) analyses revealed that the erosion area in SF6 was primarily composed of LaF3, while in N2 and CO2, partial decomposition of La2Sn2O7 formed La2O3 and SnO2. The addition of La2Sn2O7 positively influenced the arc erosion resistance by increasing the viscosity of the molten pool, hindering the flow and splashing of Ag liquid. Under high arc energy conditions, La2Sn2O7 underwent partial decomposition, effectively protecting the Ag matrix from further damage.

Methodologies for label free Raman microspectroscopic monitoring of viral replication processes in vitro.

Methodologies for label free Raman microspectroscopic monitoring of viral replication processes in vitro.

Characterization and differentiation of myocardial remodeling using artificial intelligence‐assisted confocal Raman spectroscopy imaging

Characterization and differentiation of myocardial remodeling using artificial intelligence‐assisted confocal Raman spectroscopy imaging

Reversible phase transitions and enhanced electrostrain in BNST-xFN ceramics under electric and thermal stimuli

Ferroelectric materials based on (Bi0.5Na0.5)TiO3 are well-known for their outstanding chemical stability and exceptional electrical properties, particularly their large electrostrain response under applied electric fields, positioning them as promising candidates for precision actuator applications. In this study, we investigate the electrical and structural responses of lead-free (Bi0.38Na0.38Sr0.24)Ti1-x (Fe0.5Nb0.5)x O3 (BNST-x FN) ferroelectric ceramics under the combined effects of temperature and electric field. Using in-situ electric field and variable-temperature Raman spectroscopy, piezoelectric force microscopy, and comprehensive dielectric and ferroelectric property evaluations, we explore the evolution of structural transformations, polarization behavior, and macroscopic property changes in ceramics with different initial phase structures under thermal and electrical stimuli. Notably, the BNST-0.01FN composition, located near the boundary between the non-ergodic relaxor and ergodic relaxor phases, exhibits a remarkable room-temperature electrostrain of 0.37%, driven by a reversible electric field-induced nonpolar-to-polar phase transition. Upon heating, as the BNST ceramic approaches the phase boundary, a prominent electrostrain (~0.38%) is observed near the temperature of the ferroelectric-to-relaxor phase transition (T FR, ~60 °C) under the electric field. This study combines in-situ microstructural analysis with macroscopic ferroelectric characterization, providing a deeper understanding of the dynamic coupling between microscopic fields and macroscopic electrical properties, and offering valuable insights for the design of high-performance lead-free ferroelectric ceramics.

DIELECTRIC PROPERTIES OF GLASS CERAMIC COMPOSITES FABRICATED VIA MICROWAVE TECHNIQUE

The investigations and enhancement of dielectric ceramics have been studied for decades in order to improve their performance of sustainable management in energy. To increase dielectric constant, dielectric breakdown strength and to decrease dielectric loss have been generally focused. In this study, Ti0.98(Ni0.01, Nb0.01)O2, using as ceramics phase, and borosilicate glass powder were fabricated to glass ceramic composites with different concentration via microwave heating technique. X-ray diffraction technique and Raman spectroscopy revealed the crystalline phase existence in the glass ceramic composites. The results were also confirmed by Scanning Electron Microscope. Moreover, as the content of ceramic phase increased it was found that the dielectric constant increased and dielectric loss decreased.

Ultrafast Laser-Induced 1T'/2H-MoTe2 Nanopattern with Au-Nanoclusters for Raman Monitoring of Cellular Drug Metabolism.

The development of surface-enhanced Raman spectroscopy (SERS) as an ultrasensitive fingerprint analysis technique in precision medicine requires high-performance SERS substrates with controllable nanostructure (hot-spot) distribution, simple fabrication, superior stability, biocompatibility, and extraordinary optical responses. Unfortunately, fabrication of arbitrary nanostructures with high homogeneity on a large scale for SERS is still challenging. Herein, we report an ultrafast laser parallel fabrication protocol for Au/2D-transition-metal dichalcogenide hybrid SERS biosensors. The leveraged photonic nanojets (PNJs) are generated by a micron-sized microsphere monolayer to simultaneously trigger localized phase transition in 2H-MoTe2, achieving a 1T'-MoTe2 nanopattern array with a density of 1 million per mm2 by a single laser shot. The Au nanoparticle clusters (AuNCs) are subsequently grown in situ from the 1T' regions, creating a AuNCs on 1T'/2H-MoTe2 (AuNCs@1T'/2H-MoTe2) hybrid SERS substrate. The fabricated feature diameter and overlay accuracy of the patterned AuNCs are 210.1 ± 3.4 and 9.2 ± 1.7 nm, respectively. To eliminate background noise, we designed dimer-AuNCs@1T'/2H-MoTe2 (dAuNCs@1T'/2H-MoTe2), achieving a detection limit of 10-13 M with an enhancement factor of 4.9 × 108 for the methylene blue (MB) analyte. The strong localized surface plasmon resonances in the dAuNCs as well as efficient charge transfers between Au, 2H-MoTe2, and MB contribute to the majority of Raman enhancement. The multiscale dAuNCs@1T'/2H-MoTe2 array provides a powerful SERSome (comprising multiple SERS spectra) platform for therapeutic drug monitoring, by which we successfully identified the metabolic behaviors of living gastric adenocarcinoma cells administered with two drugs, i.e., capecitabine, oxaliplatin, and their combination. The present work establishes opportunities for creating a highly ordered nanopattern array for ultrasensitive SERSome analysis of cell metabolism in cancer therapy.

Characterization of corrosion products on Han Dynasty iron swords excavated from Tuchengpo Cemetery in Wushan, Chongqing, China

Six iron sword samples dated to the Western Han to Xinmang period (206 BC–24 AD) of the Han Dynasty excavated from Tuchengpo Cemetery in Wushan, Chongqing, were characterized by Raman spectroscopy combined with SEM-EDS technology. The results showed that corrosion products on the iron swords were mainly divided into two corrosion layers. In the external layer, mineralized wood residue of scabbard was observed, and calcite, goethite, lepidocrocite, hematite, and carbon were detected. Different dense products were distinguished by color, including goethite (orange), lepidocrocite (reddish-brown), akaganeite (yellowish-brown), magnetite (black), and hematite (red), which formed rust sublayers in the internal layer. Chloride was mainly distributed in the internal layer, which had almost the same structure as the rust sublayers. This study provided the basic insights into the corrosion products of iron artifacts excavated from the Three Gorges region of Chongqing, as well as the comprehensive scientific information for protection of iron artifacts.

Mechanical Transitions in Crystals: The Low-Temperature Thermosalient Transition of a Mesogenic Polyphenyl.

Thermosalient transitions are a subset of single-crystal-to-single-crystal (SCSC) transitions, in which the change of lattice parameters is highly anisotropic and very fast. As a result, crystals at the transition undergo macroscopic dynamical effects (hopping, jumping, and shattering). These transitions feature a conversion of heat to mechanical energy that can be exploited in the realization of advanced materials. Most thermosalient transitions are observed at temperatures higher than room temperature. Examples of low-temperature thermosalient transitions are rare. We describe a new example of a low-temperature thermosalient transition in a sexiphenyl compound. At about -40 °C, the parent single crystal (phase I) shatters into single crystal fragments of the new phase (phase II). The two phases have been studied by single-crystal X-ray analysis using a synchrotron source, variable-temperature Raman spectroscopy, and computational analysis of lattice normal vibration modes. A mechanism of the transition is proposed. We confirm colossal thermal expansion coefficients and supercells as reliable features of thermosalient transitions and add as a third feature a low-frequency principal optical vibration of the crystal lattice prompting the transition. Based on this, a roadmap for the automated prediction of thermosalient transitions in molecular crystals is also outlined.

Kinetically arrested SERS-Active aggregates for biosensing.

There is a demand for biosensors capable of long-term, non-invasive monitoring of low analyte concentrations in various biofluids for diagnostics, personalized healthcare, and disease monitoring. Biofluids present challenges to biosensor sensing and stability on account of their complex composition and dynamic nature. Surface Enhanced Raman Spectroscopy (SERS) offers ultra-high sensitivity, non-destructive, real-time monitoring and non-invasive detection, ideal for sensing in complex media. Plasmonic gold nanoparticle (AuNP) SERS-active assemblies have been widely explored owning to their biocompatibility and tuneable sensitivity based on AuNP morphology. Controlled aggregation of AuNPs has been achieved by incorporating a 'molecular-glue', cucurbit[7]uril (CB[7]), to produce AuNP:CB[7] aggregates containing robust nanogaps (ca. 1 nm) and displaying strong, reproducible SERS signals at low concentrations, but eventually leads to irreversible precipitation. Here we employ thiolated poly(ethylene glycol) (PEG-SH) to produce kinetically trapped metastable AuNP:CB[7]:PEG aggregates. The aggregates maintain SERS-activity, are highly tuneable through facile modification of the PEG chain length and grafting density, and possess improved stability. Moreover, the AuNP:CB[7]:PEG aggregates demonstrate low concentration detection of a common Raman reporter alongside a bioanalyte in a range of biofluids highlighting the potential application of these aggregates for non-invasive in vivo long-term monitoring alongside future customized SERS biosensing applications.

Single-Molecule SERS Discrimination of Proline from Hydroxyproline Assisted by a Deep Learning Model.

Discriminating low-abundance hydroxylation is a crucial and unmet need for early disease diagnostics and therapeutic development due to the small hydroxyl group with 17.01 Da. While single-molecule surface-enhanced Raman spectroscopy (SERS) sensors can detect hydroxylation, subsequent data analysis suffers from signal fluctuations and strong interference from citrates. Here, we used our plasmonic particle-in-pore sensor, occurrence frequency histogram of the single-molecule SERS spectra, and a one-dimensional convolutional neural network (1D-CNN) model to achieve single-molecule discrimination of hydroxylation. The histogram extracted spectral features of the whole data set to overcome the signal fluctuations and helped the citrate-replaced particle-in-pore sensor to generate clean signals of the hydroxylation for model training. As a result, the discrimination of single-molecule SERS signals of proline and hydroxyproline was successful by the 1D-CNN model with 96.6% accuracy for the first time. The histogram further validated that the features extracted by the 1D-CNN model corresponded to hydroxylation-induced spectral changes.