Raman Spectroscopy For Monitoring Research Articles

LIBS for prospecting and Raman spectroscopy for monitoring: two feasibility studies for supporting in-situ resource utilization

Laser-induced breakdown spectroscopy (LIBS) and Raman spectroscopy are still rather new techniques for in-situ exploration of extraterrestrial planetary surfaces but have shown their suitability and great potential in several successful robotic missions already. Next to serving primary scientific applications, both methods can also be used in the context of in-situ resource utilization (ISRU) such as scouting for wanted substances and the surveillance of extraction processes. Here, we present two laboratory studies conducted in the context of ISRU with a focus on the chain from prospecting to extracting oxygen from lunar regolith. For LIBS, with optimized data processing and combined with state-of-the-art multivariate data analysis approaches, we show the potential of the technique for identifying samples with increased ilmenite content and for elemental quantification. The measurements were done using lunar regolith simulant and low pressures simulating vacuum on atmosphereless bodies such as the Moon. With Raman spectroscopy, we analyzed lunar regolith simulant samples that underwent electrochemical alteration for oxygen extraction and production of metal alloys demonstrating the potential of Raman spectroscopy for ISRU process monitoring. We also discuss the results in a broader context, evaluating the potential of both methods for other aspects of ISRU support.

Early stage ettringite and monosulfoaluminate carbonation investigated by in situ Raman spectroscopy coupled with principal component analysis

This study investigates the early stages of monosulfoaluminate and ettringite carbonation using non-destructive in situ Raman spectroscopy monitoring. Coupling this technique with Principal Components Analysis enables relevant information to be extracted from spectral data such as an accurate identification of the beginning of the reaction and of specific chemical phases. These two hydrates and some of their carbonation products can be well detected using this vibrational spectroscopy technique. Experiments were conducted on two pastes of hydrated yeelimite, in the presence and in the absence of gypsum respectively, during their carbonation. The results confirmed the detection of the beginning of the carbonation and allowed us to identify some consumed and formed chemical phases in the early stages of the reaction. These outcomes of in situ Raman spectroscopy monitoring study on cementitious phases could help understand the early chemical modifications occurring in complex environments such as cement pastes.

Illuminating milling mechanochemistry by tandem real-time fluorescence emission and Raman spectroscopy monitoring.

In pursuit of accessible and interpretable methods for direct and real-time observation of mechanochemical reactions, we demonstrate a tandem spectroscopic method for monitoring of ball-milling transformations combining fluorescence emission and Raman spectroscopy, accompanied by high-level molecular and periodic density-functional theory (DFT) calculations, including periodic time-dependent (TD-DFT) modelling of solid-state fluorescence spectra. This proof-of-principle report presents this readily accessible dual-spectroscopy technique as capable of observing changes to the supramolecular structure of the model pharmaceutical system indometacin during mechanochemical polymorph transformation and cocrystallisation. The observed time-resolved in situ spectroscopic and kinetic data are supported by ex situ X-ray diffraction and solid-state nuclear magnetic resonance spectroscopy measurements. The application of first principles (ab initio) calculations enabled the elucidation of how changes in crystalline environment, that result from mechanochemical reactions, affect vibrational and electronic excited states of molecules. The herein explored interpretation of both real-time and ex situ spectroscopic data through ab initio calculations provides an entry into developing a detailed mechanistic understanding of mechanochemical milling processes and highlights the challenges of using real-time spectroscopy.

Direct mechanocatalysis by resonant acoustic mixing (RAM).

We demonstrate the use of a metal surface to directly catalyse copper-catalysed alkyne-azide click-coupling (CuAAC) reactions under the conditions of Resonant Acoustic Mixing (RAM) - a recently introduced and scalable mechanochemical methodology that uniquely eliminates the need for bulk solvent, as well as milling media. By using a simple copper coil as a catalyst, this work shows that direct mechanocatalysis can occur in an impact-free environment, relying solely on high-speed mixing of reagents against a metal surface, without the need for specially designed milling containers and media. By introducing an experimental setup that enables real-time Raman spectroscopy monitoring of RAM processes, we demonstrate 0th-order reaction kinetics for several selected CuAAC reactions, supporting surface-based catalysis. The herein presented RAM-based direct mechanocatalysis methodology is simple, enables the effective one-pot, two-step synthesis of triazoles via a combination of benzyl azide formation and CuAAC reactions on a wide scope of reagents, provides control over reaction stoichiometry that is herein shown to be superior to that seen in solution or by using more conventional CuCl catalyst, and is applied for simple gram-scale synthesis of the anticonvulsant drug Rufinamide.

In situ surface-enhanced Raman spectroscopy monitoring of molecular reorientation in plasmon-mediated chemical reactions

Understanding the molecular orientation is crucial for revealing the mechanism of chemical reactions. However, how to accurately monitor the molecular orientation remains a great challenge because of the motion of the molecules during the chemical reaction. Here, surface-enhanced Raman spectroscopy (SERS) was used to monitor the molecular reorientation from the plasmon-catalyzed conversion of p-aminothiophenol (PATP) to p,p'-dimercaptoazobenzene (DMAB). Spectral change due to molecular reorientation, which is often overlooked, is clearly extracted through the protonation of the PATP molecules to suppress the conversion of PATP to DMAB. Meanwhile, by monitoring the Raman features, the reaction process and molecular reorientation are simultaneously recorded, offering fresh insights on the long-standing puzzle that why the conversion to DMAB is suppressed with concentrated PATP: this is because the over-crowded PATP adsorbed on the substrate hampered its own space-taking reorientation (similar to the space-steric effect) which is a prerequisite for producing DMAB.

Localized Spectroelectrochemical Identification of Basal Plane and Defect-Related Charge-Transfer Processes in Graphene.

It is well-known that structural defects play a decisive role in electrochemical behavior of atomically thin materials, where all the defects are directly accessible by the electrolyte. However, the vast majority of experimental techniques do not allow disentanglement of the processes at the edges/defects from those at the intact basal plane. Therefore, to address this issue, we introduce a localized spectroelectrochemical method featuring a microdroplet electrochemical cell with simultaneous Raman spectroscopy monitoring. The electrochemical and spectral responses of the basal planes of monolayer graphene samples with varying levels of disorder were compared. Two contributions, stemming from the intact and defective areas on the surface, respectively, were discovered both in the Raman G band shifts and cyclic voltammetry using the hexaammineruthenium complex. Consequently, two independent electron transfer processes of slower and faster rates coexist in one sample, but they are restricted to the defect-free and defect-rich areas, respectively.

Au Nanoflowers for Catalyzing and In Situ Surface-Enhanced Raman Spectroscopy Monitoring of the Dimerization of p-Aminothiophenol.

In this work, we demonstrated a facile approach for fabrication of Au nanoflowers (Au NFs) using an amino-containing organosilane, 3-aminopropyltriethoxysilane (APTES), as a shape-directing agent. In this approach, the morphology of the Au particles evolved from sphere-like to flower-like with increasing the concentration of APTES, accompanied by a red shift in the localized surface plasmon resonance peak from 520 to 685 nm. It was identified that the addition of APTES is profitable to direct the preferential growth of the (111) plane of face-centered cubic gold and promote the formation of anisotropic Au NFs. The as-prepared Au NFs, with APTES on their surface, presented effective catalytic and surface-enhanced Raman scattering (SERS) performances, as evidenced by their applications in catalyzing the dimerization of p-aminothiophenol and monitoring the reaction process via in situ SERS analysis.

Raman spectroscopy for real-time and in situ monitoring of mechanochemical milling reactions.

Solid-state milling has emerged as an alternative, sustainable approach for preparing virtually all classes of compounds and materials. In situ reaction monitoring is essential to understanding the kinetics and mechanisms of these reactions, but it has proved difficult to use standard analytical techniques to analyze the contents of the closed, rapidly moving reaction chamber (jar). Monitoring by Raman spectroscopy is an attractive choice, because it allows uninterrupted data collection from the outside of a translucent milling jar. It complements the already established in situ monitoring based on powder X-ray diffraction, which has limited accessibility to the wider research community, because it requires a synchrotron X-ray source. The Raman spectroscopy monitoring setup used in this protocol consists of an affordable, small portable spectrometer, a laser source and a Raman probe. Translucent reaction jars, most commonly made from a plastic material, enable interaction of the laser beam with the solid sample residing inside the closed reaction jar and collection of Raman-scattered photons while the ball mill is in operation. Acquired Raman spectra are analyzed using commercial or open-source software for data analysis (e.g., MATLAB, Octave, Python, R). Plotting the Raman spectra versus time enables qualitative analysis of reaction paths. This is demonstrated for an example reaction: the formation in the solid state of a cocrystal between nicotinamide and salicylic acid. A more rigorous data analysis can be achieved using multivariate analysis.

Microdroplet extraction assisted ultrasensitive Raman detection in complex oil.

The Raman detection of trace substances in complex oil is still a great challenge at present because of the strong disturbance of background activity and the suppression of intensity in spectra caused by complicated components. In this work, a simple and robust approach based on microdroplet liquid-liquid extraction for the real-time Raman spectroscopy monitoring of trace substances in complex oil is reported. Based on unbalanced chemical potentials between water and oil on a microfluidic chip, a target trace molecule is extracted from complex mineral oil to a water microdroplet. Benefiting from the real-time fluorescence intensities of fluorescein in a water microdroplet, the extraction performance is investigated and optimized. The optimal water microdroplet is implemented for the Raman detection of furfural in a complex mineral oil, a typical trace performance marker in electric power equipment, and this exhibits excellent sensitivity with a limit of detection (LOD) of 26 ppb. Compared to traditional detection technology for trace substances in complex oil (high performance liquid chromatography, HPLC), this method greatly simplified the process of measurement, reduced the volume of sample required, had a fast measurement time, and exhibited the prospect of real-time monitoring applications with high sensitivity, which not only promotes the development of oil quality but also enlarges existing knowledge related to using Raman spectroscopy in chem-/bio-sensing.

Mechanochemical Metathesis between AgNO3 and NaX (X = Cl, Br, I) and Ag2XNO3 Double-Salt Formation.

Here we describe real-time, in situ monitoring of mechanochemical solid-state metathesis between silver nitrate and the entire series of sodium halides, on the basis of tandem powder X-ray diffraction and Raman spectroscopy monitoring. The mechanistic monitoring reveals that reactions of AgNO3 with NaX (X = Cl, Br, I) differ in reaction paths, with only the reaction with NaBr providing the NaNO3 and AgX products directly. The reaction with NaI revealed the presence of a novel, short-lived intermediate phase, while the reaction with NaCl progressed the slowest through the well-defined Ag2ClNO3 intermediate double salt. While the corresponding iodide and bromide double salts were not observed as intermediates, all three are readily prepared as pure compounds by milling equimolar mixtures of AgX and AgNO3. The in situ observation of reactive intermediates in these simple metathesis reactions reveals a surprising resemblance of reactions involving purely ionic components to those of molecular organic solids and cocrystals. This study demonstrates the potential of in situ reaction monitoring for mechanochemical reactions of ionic compounds as well as completes the application of these techniques to all major compound classes.

In-situ monitoring of seeded and unseeded stage III corrosion using Raman spectroscopy

Stage III glass dissolution, the occasionally observed tendency for accelerated aqueous corrosion after extensive time spent at low reaction rates, is a major area of technical uncertainty in long-term glass performance modeling for vitreous nuclear waste forms. Stage III dissolution behavior is thought to be caused by the precipitation of zeolite phases that lower the activity of the rate-controlling orthosilicic acid ion and cause the acceleration of glass dissolution. The uncertainty lies mainly in a poor understanding of the growth kinetics of these key crystalline phases. It is particularly important to understand the impact of temperature and pH conditions on Stage III behavior. Accurate analysis of this phenomenon is complicated by the typically very long (e.g., years), and variable length of the induction period preceding the onset of Stage III behavior. In this study of a high-sodium aluminoborosilicate glass, we demonstrate the ability to initiate the onset of Stage III behavior in a controllable fashion so as to both reduce the time delay of the incubation period, and to also be able to initiate Stage III dissolution in controlled conditions. In this case, we demonstrate that Stage III glass corrosion behavior is possible at 70 °C, a lower temperature than previously observed (90 °C), even in an unseeded experiment. We confirm, through a comparison study, that seeded and unseeded Stage III corrosion rates are equivalent. This enables wide-scale testing of Stage III corrosion rates for many glass compositions in relatively short times through this technique. We also report further development of the use of in situ Raman spectroscopy monitoring of boron concentration and pH through simple and chemometric analysis methods.

Label-free Raman spectroscopy monitoring of cytotoxic response induced by a telomerase inhibitor

We proposed a new approach to directly and quantitatively inspect cytotoxicity response at the unicellular scale based on Raman micro-spectroscopy. Variations of intracellular multicomponent caused by the telomerase inhibitor could be revealed by high-throughput Raman spectral screening simultaneously. The changes and modifications of the biochemical compositions including proteins and nucleic acids responded to the telomerase inhibitor were observed through Raman fingerprint assignment analysis of nucleic acids (570, 785, 1093, 1337 and 1484 cm−1) and proteins (570, 1001, 1231, 1337, 1484, 1662 and 2873 cm−1). HeLa cells stressed by different doses of telomerase inhibitor could be distinguished by unsupervised clustering analysis based on their Raman spectroscopy. Four Raman band ratios—I1093/1001, I1093/1032, I1093/1055, and I1093/1066—which were significantly correlated with the inhibitory rate of HeLa cells were identified, and nonlinear quantitative model for cell cytotoxicity was then established based on these Raman ratios. Furthermore, spatial distribution of intracellular important bio-chemical components was showed by Raman chemical imaging with these characteristics Raman ratios, indicating that the granules representing the corresponding substances first exhibited a significant degree of agglomeration (0.4 and 0.8 μM groups), which subsequently declined, becoming smaller and more divergent (1.6 and 4 μM groups) as cytotoxicity increased. This study provides a rapid and quantitative assessment for cytotoxicity induced by chemicals at the single-cell level. The ability to directly monitor chemically-induced cell cytotoxicity in situ promotes understanding of molecular level changes and improves knowledge of the molecular mechanisms involved, which has great application potential in pharmacological mechanism exploration and drug development.

Raman spectroscopy monitoring of MCF10A cells irradiated by protons at clinical doses

Purpose: Proton therapy has been recently proposed as a radiotherapy form for breast cancer treatment in view of its potentially decreased normal-tissue toxicity compared with conventional photon-based radiotherapy. However, the risks for the healthy tissue cannot be completely eliminated. In the present study, the suitability of Raman spectroscopy to monitor the radiosensitivity of normal cells exposed to clinical proton beam was investigated.Materials and methods: MCF10A normal human breast cells were irradiated at two different proton doses: 0.5 Gy and 4 Gy. They were fixed immediately after irradiation and measured by means of Raman spectroscopy technique. The obtained data were analyzed both by evaluating the intensity ratio of specific Raman spectral peaks and through Multivariate Distance Matrix Regression technique.Results: Certain Raman peaks associated with DNA showed a systematic suppression at both dose levels. In particular, the intensity of a Raman peak at 784 cm−1, related to a stretching mode inside the phosphate group of DNA, is very sensitive to the proton beam exposure, even at the lowest investigated dose. Therefore, it could be considered as a spectral marker of cytogenetic damage.Conclusions: The obtained results are encouraging for the future of Raman spectroscopy in radiobiology research, particularly for improving risk assessment in the field of proton radiotherapy. Specifically, these findings validate Raman spectroscopy to measure biological response in human breast cells exposed to standard proton therapy doses used in clinical setting.

Warming up for mechanosynthesis - temperature development in ball mills during synthesis.

We present a first direct measurement of the temperature during milling combined with in situ Raman spectroscopy monitoring. The data reveal a low temperature increase due to the mechanical impact and clear temperature increases as a consequence of the reaction heat. Based on the data, temperature rises as postulated in the magma plasma and hot spot theory can be excluded for soft matter milling syntheses.

At-Line Monitoring of Conversion in the Inverse Miniemulsion Polymerization of Acrylamide by Raman Spectroscopy

This work studied the at-line Raman spectroscopy monitoring for the inverse miniemulsion polymerization of acrylamide. The conversion was determined from the Raman spectra without previous calibration using the peaks corresponding to —CH2— and C═C functional groups of acrylamide. Gravimetric data was used to validate the results of conversion obtained with the Raman spectra. Dynamic light scattering was used to measure the particle size. The results show that high energy in the homogenization step increases the surface area of the droplets and generates a lack of surfactant, which results in larger diameters. It is possible to make at-line monitoring of monomer conversion directly from the Raman spectra without using calibration models. The data obtained show an incomplete conversion that is also confirmed by gravimetric analysis.

From Jellylike Phase to Crystal: Effects of Solvent on Self-Assembly of Cefotaxime Sodium

Jellylike phase (JLP) is usually harmful to the process of crystallization. The special state of cefotaxime sodium (CTX) jellylike phase and its spontaneous transition to crystals is investigated in this paper. The crystals transformed from JLPs containing different solvents have distinct habits and forms. The solvent used in JLP formation and crystallization was very important. The results show that the polarity and hydrogen bonding ability of the solvent plays a decisive role in the JLP formation and its crystallization. Combined with Fourier transform infrared spectra, in situ Raman spectroscopy monitoring experiment indicates that the orientational hydrogen bonding between the solvent and CTX molecule facilitates the construction of the CTX crystal structure. JLP crystallization offers a new way for novel polymorph development and crystal habit modification, especially for drugs that are difficult to crystallize from solution.

Oxidizing dissolution mechanism of an irradiated MOX fuel in underwater aerated conditions at slightly acidic pH

The (U,Pu)O2 matrix behavior of an irradiated MIMAS-type (MIcronized MASter blend) MOX fuel, under radiolytic oxidation in aerated pure water at pH 5–5.5 was studied by combining chemical and radiochemical analyses of the alteration solution with Raman spectroscopy characterizations of the surface state. Two leaching experiments were performed on segments of irradiated fuel under different conditions: with or without an external γ irradiation field, over long periods (222 and 604days, respectively). The gamma irradiation field was intended to be representative of the irradiation conditions for a fuel assembly in an underwater interim storage situation.The data acquired enabled an alteration mechanism to be established, characterized by uranium (UO22+) release mainly controlled by solubility of studtite over the long-term. The massive precipitation of this phase was observed for the two experiments based on high uranium oversaturation indexes of the solution and the kinetics involved depended on the irradiation conditions. External gamma irradiation accelerated the precipitation kinetics and the uranium concentrations (2.9×10−7mol/l) were lower than for the non-irradiated reference experiment (1.4×10−5mol/l), as the quantity of hydrogen peroxide was higher. Under slightly acidic pH conditions, the formation of an oxidized UO2+x phase was not observed on the surface and did not occur in the radiolysis dissolution mechanism of the fuel matrix. The Raman spectroscopy performed on the heterogeneous MOX fuel matrix surface, showed that the fluorite structure of the mainly UO2 phase surrounding the Pu-enriched aggregates had not been particularly impacted by any major structural change compared to the data obtained prior to leaching. For the plutonium, its behavior in solution involved a continuous release up to concentrations of approximately 3×10−6molL−1 with negligible colloid formation. This data appears to support a predominance of the +V oxidation state for plutonium in solution under highly oxidizing conditions.Furthermore, the Raman spectroscopy monitoring of the sample surface oxidation states did not point to any significant effect from the high Pu content of the aggregates (10–15%) and therefore did not indicate a better aggregate stability under radiolysis compared to the mainly UO2 matrix. This is because acidic pH conditions do not favor the development of oxidized layers on a fuel surface, with the exception of secondary phases.

Are metabolites of Fusarium oxysporum responsible for fungal skin invasion? A morphological and Raman spectroscopy monitoring

Fusarium is an emerging pathogen with high levels of morbidity and mortality. A significant tissue response is observed in infected patients, and the condition has been associated with the production of toxic metabolites. The aim of the present study was to identify a major fraction of crude metabolic extract of Fusarium oxysporum and investigate its effects on the skin of healthy rats. Fraction F1 was obtained from the cultivation of F. oxysporum in Czapek–Dox. In the treatment groups, fraction F1 (0.05 mg/ ml) was injected intradermally, while (50 µl) 0.9% of saline solution was injected in the control groups. The animals were killed 3, 6, 12, and 24 h after inoculation. The skin was fixed for inclusion in paraffin to obtain histological sections and stained with hematoxylin and eosin, Sirius red, and terminal deoxynucleotidyl transferase‐mediated dUTP nick‐end labeling. Samples were analyzed using Fourier transform Raman spectroscopy. The tissue reactions were classified and compared over time and by treatment. In the treatment group, inflammatory reaction peaked at 6 h, being classified as moderate, with infiltrate composed mainly of neutrophils. terminal deoxynucleotidyl transferase‐mediated dUTP nick‐end labeling staining was negative. The area occupied by types I and III collagen in the treatment group increased over time. There was a change in the area occupied by amide I and the ratios of the –CH2 and –CH3 molecules. It can be argued that the fraction F1 contains elements that contribute to the invasion of Fusarium in the skin, destructurizing the organization of the extracellular matrix. Copyright © 2014 John Wiley & Sons, Ltd.

Sci-Fri AM: Mountain - 04: Label-free Raman spectroscopy of single tumour cells detects early radiation-induced glycogen synthesis associated with increased radiation resistance

Purpose: To use label-free Raman spectroscopy (RS) for early treatment monitoring of tumour cell radioresistance. Methods: Three human tumour cell lines, two radioresistant (H460, SF2 = 0.57 and MCF7, SF2 = 0.70) and one radiosensitive (LNCaP, SF2 = 0.36), were irradiated with single fractions of 2, 4, 6, 8 or 10 Gy. In additional experiments, H460 and MCF7 cells were irradiated under co-treatment with the anti-diabetic drug metformin, a known radiosensitizing agent. Treated and control cultures were analyzed with RS daily for 3 days post-treatment. Single-cell Raman spectra were acquired from 20 live cells per sample, and experiments were repeated in triplicate. The combined data sets were analyzed with principal component analysis using standard algorithms. Cells from each culture were also subjected to standard assays for viability, proliferation, cell cycle, and radiation clonogenic survival. Results: The radioresistant cells (H460, MCF7) exhibited a RS molecular radiation response signature, detectable as early as 1 day post-treatment, of which radiation-induced glycogen synthesis is a significant contributor. The radiosensitive cells (LNCaP) exhibited negligible glycogen synthesis. Co-treatment with metformin in MCF7 cells blocked glycogen synthesis, reduced viability and proliferation, and increased radiosensitivity. Conversely, metformin co-treatment in H460 cells did not produce these same effects; importantly, both radiation-induced synthesis of glycogen and radiosensitivity were unaffected. Conclusions: Label-free RS can detect early glycogen synthesis post-irradiation, a previously undocumented metabolic mechanism associated with tumour cell radioresistance that can be targeted to increase radiosensitivity. RS monitoring of intratumoral glycogen may provide new opportunities for personalized combined modality radiotherapy treatments.

Effect of rough surface patterning on the tribology of W–S–C–Cr self-lubricant coatings

In this work, self-lubricant W–S–C films were alloyed with Cr by co-sputtering chromium and composite WS2–C targets. Besides the usual physical, chemical and mechanical characterization, including the evaluation of the chemical composition, the structure, the morphology, the hardness and the cohesion/adhesion, special attention was paid to the friction and wear analyses of the film deposited on intentionally roughened surfaces. The substrates were steel polished disks with different types of patterns produced by micromachining. To analyze the sliding process, in-situ techniques were applied, such as optical microscopy and Raman spectroscopy monitoring of the wear track. The surfaces in the contact were then analyzed by scanning electron microscopy (SEM) and 3D profilometry.The results showed that W–S–C–Cr coating exhibited remarkable ability to reduce the detrimental effect of deep grooves with irregular shape. For specific patterns on the substrate the friction and wear was even slightly lower compared to a polished sample. The grooves were filled with self-lubricant material and acted as reservoirs supporting formation of a low-friction tribolayer.