Confocal Raman Imaging Research Articles

In situ Raman imaging of high-temperature solid-state reactions in the CaSO4\u2013SiO2 system

The deposition of mineral phases on the heat transfer surfaces of brown coal power plants may have a negative effect on power plant boilers. The paragenesis of these deposits contains information about the actual temperature prevailed during the combustion of lignite, if the temperature-dependences of distinct mineral transformations or reactions are known. Here, we report results of a sintering study (to ~ 1100 °C) with samples containing anhydrite, quartz, and gehlenite, which are typical components of Rhenish lignite ashes. Thermal decompositions and solid-state reactions were analyzed (1) in situ and (2) both in situ and after quenching using confocal hyperspectral Raman imaging. This novel application of confocal Raman spectroscopy provides temperature- and time-resolved, 2-dimensional information about sintering processes with a micrometer-scale resolution. In the course of the sintering experiments with anhydrite and quartz with a weight ratio of 2:1 both polymorphs wollastonite and pseudowollastonite were identified in situ at about 920 and 1000 °C, respectively. The formation of pseudowollastonite was thus observed about 120 °C below the phase transition temperature, demonstrating that it can form metastably. In addition, alpha_{L}^{prime }-Ca2SiO4 was identified at about 1100 °C. In samples containing equal weight fractions of anhydrite and quartz that were quenched after firing for 9 h at about 1100 °C, β-Ca2SiO4 (larnite) crystallized as rims around anhydrite grains and in direct contact to wollastonite. We furthermore observed that, depending on the ratio between quartz and anhydrite, wollastonite replaced quartz grains between 920 and 1100 °C., i.e., the higher the quartz content, the lower the formation temperature of wollastonite.

Coupling SEM-EDS and confocal Raman-in-SEM imaging: A new method for identification and 3D morphology of asbestos-like fibers in a mineral matrix.

Asbestos consists in natural minerals crystallized in a specific habit and possessing in particular properties. In the case of Naturally Occurring Asbestos, usual methods applied to the identification of mineral fibers and the determination of their possible asbestiform nature seems not efficient, especially in the case of mineral fibers included in mineral matrix. We present a new in-situ method based on the use of confocal Raman-in-SEM imaging implemented in a Scanning Electron Microscope as an efficient method for in-situ mineralogy. The limitation of conventional methods is discussed. We applied 2D-Raman imaging to the identification of sub-micrometric fibers included in different mineral matrix. We were able to identify actinolite fibers down to 400 nm in diameter, included in feldspar, quartz and/or calcite matrix. Moreover, Confocal Raman allows the collection of 3D data that would provide access to critical information on the morphology of the amphibole fibers in the volume, such as aspect ratio, fibers distribution and amphibole volume fraction. We performed this method on various examples of rocks containing actinolite fibers of mean structural formula is: Na0,04-0,12 Mg2,79-3,73 Al0,29-0,58 K0,01 Ca1,79-1,98 Mn0,01-0,09 Fe2+0,99-1,91 Fe3+Si7,64-7,73 O22(OH)2. We demonstrated that coupling confocal Raman imaging and SEM is a new and efficient in-situ method for identification and morphological characterization of amphibole fibers.

Microstructural and magnetic properties of rGO/MnFe2O4 nanocomposites; relaxation dynamics

In the present investigation, nanocomposite (NC) of reduced graphene oxide (rGO) and manganese ferrite (MnFe2O4) with three different (rGO/MnFe2O4) weight-ratio of rGO have been synthesized using a simple and efficient one-step hydrothermal route. The crystallinity, morphology and magnetic studies were conducted using X-ray diffraction (XRD), confocal Raman imaging and vibrating sample magnetometry (VSM).Detailed ferromagnetic resonance (FMR) studies were performed in the field-sweep mode at different applied frequencies ranging from 5 to 30 GHz using a vector network analyzer (VNA). We have realized a nano-composite layer of rGO/MnFe2O4 NC on top of coplanar waveguide (CPW) transmission lines to perform FMR experiments. The largest ferromagnetic resonance (FMR) absorption of −28 dB was observed for 0.06 g GO doped MnFe2O4 at the 22 GHz frequency. This absorption at FMR is found to be tunable by rGO concentration in manganese ferrite. We have also evaluated various relaxation/damping parameters of the nanocomposites. The experimental values of FMR linewidths were fitted using two micromagnetic models, and hence intrinsic and extrinsic damping parameters were obtained for nanocomposite samples. The damping parameters were observed to influenced by the rGO weight ratio. Therefore the developed nanocomposite can find various applications in the area of microwave monolithic devices and circuits like filters, phase shifters, circulators, etc.

Near-infrared modulation by means of GeTe/SOI-based metamaterial.

Today, nanophotonics still lacks components for modulation that can be easily implementable in existing silicon-on-insulator (SOI) technology. Chalcogenide phase change materials (PCMs) are promising candidates for tuning in the near infrared: at the nanoscale, thin layers can provide enough contrast to control the optical response of a nanostructure. Moreover, all-dielectric metamaterials allow for resonant behavior without having ohmic losses in the telecom range. Here, a novel hybridization of a SOI-based metamaterial with PCM GeTe is experimentally investigated. A metamaterial based on Si nanorods, covered by a thin layer of GeTe, is designed and fabricated. Switching GeTe from amorphous to crystalline leads to a rather high resonance-governed reflection contrast at 1.55μm. Additional confocal Raman imaging is done to differentiate the crystallized zones of the metamaterials' unit cell. The findings are in good agreement with numerical analysis and show good perspectives of all-dielectric tunable near-infrared nanophotonics.

Random and aligned electrospun PLGA nanofibers embedded in microfluidic chips for cancer cell isolation and integration with air foam technology for cell release

BackgroundCirculating tumor cells (CTCs) comprise the high metastatic potential population of cancer cells in the blood circulation of humans; they have become the established biomarkers for cancer diagnosis, individualized cancer therapy, and cancer development. Technologies for the isolation and recovery of CTCs can be powerful cancer diagnostic tools for liquid biopsies, allowing the identification of malignancies and guiding cancer treatments for precision medicine.MethodsWe have used an electrospinning process to prepare poly(lactic-co-glycolic acid) (PLGA) nanofibrous arrays in random or aligned orientations on glass slips. We then fabricated poly(methyl methacrylate) (PMMA)-based microfluidic chips embedding the PLGA nanofiber arrays and modified their surfaces through sequential coating with using biotin–(PEG)7–amine through EDC/NHS activation, streptavidin (SA), and biotinylated epithelial-cell adhesion-molecule antibody (biotin-anti-EpCAM) to achieve highly efficient CTC capture. When combined with an air foam technology that induced a high shear stress and, thereby, nondestructive release of the captured cells from the PLGA surfaces, the proposed device system operated with a high cell recovery rate.ResultsThe morphologies and average diameters of the electrospun PLGA nanofibers were characterized using scanning electron microscopy (SEM) and confocal Raman imaging. The surface chemistry of the PLGA nanofibers conjugated with the biotin–(PEG)7–amine was confirmed through time-of-flight secondary ion mass spectrometry (ToF–SIMS) imaging. The chip system was studied for the effects of the surface modification density of biotin–(PEG)7–amine, the flow rates, and the diameters of the PLGA nanofibers on the capture efficiency of EpCAM-positive HCT116 cells from the spiked liquid samples. To assess their CTC capture efficiencies in whole blood samples, the aligned and random PLGA nanofiber arrays were tested for their abilities to capture HCT116 cells, providing cancer cell capture efficiencies of 66 and 80%, respectively. With the continuous injection of air foam into the microfluidic devices, the cell release efficiency on the aligned PLGA fibers was 74% (recovery rate: 49%), while it was 90% (recovery rate: 73%) on the random PLGA fibers, from tests of 200 spiked cells in 2 mL of whole blood from healthy individuals. Our study suggests that integrated PMMA microfluidic chips embedding random PLGA nanofiber arrays may be suitable devices for the efficient capture and recovery of CTCs from whole blood samples.

Transition from positive to negative electrical resistance response under humidity conditions for PEDOT:PSS-MoS2 nanocomposite thin films

Here, we report the preparation of PEDOT:PSS-MoS2 nanocomposite thin films and their electrical resistance response under humidity conditions revealing their promising properties as humidity sensor materials. One of the most interesting features of our samples is the transition from positive to a negative electrical resistance response to humidity conditions with increasing MoS2 additions. Our confocal Raman imaging studies revealed that the presence of MoS2 yields a local charge rearrangement in the thiophenyl rings of PEDOT:PSS, in relation to the enhancement of the electrical resistance negative response as observed by impedance spectroscopy analysis. The enhancement on the negative response with increasing MoS2 additions could be explained through the increment of hole carriers in MoS2 nanosheets under humidity conditions, thus leading to an enhancement in the electrical transport along the PEDOT:PSS chains.

Manipulation of Recrystallization and Network Formation of Oil-Dispersed Micronized Fat Crystals.

A detailed investigation was carried out on the modulation of the coupling between network formation and the recrystallization of oil-dispersed micronized fat crystal (MFC) nanoplatelets by varying oil composition, shear, and temperature. Sunflower (SF) and bean (BO) oils were used as dispersing media for MFC nanoplatelets. During MFC dispersion production at high shear, a significant increase in the average crystal thickness (ACT) could be observed, pointing to recrystallization of the MFC nanoplatelets. More rapid recrystallization of MFC occurred in the SF dispersion than in the BO dispersion, which is attributed to higher solubility of MFC in the SF oil. When the dispersions were maintained under low shear in narrow gap Couette geometry, we witnessed two stages of recrystallization (measured via rheo-SAXD) and the development of a local yield stress (measured via rheo-MRI). In the first stage, shear-enabled mass transfer induces rapid recrystallization of randomly distributed MFC nanoplatelets, which is reflected in a rapid increase in ACT (rheo-SAXD). The formation of a space-filling weak-link MFC network explains the increase in yield stress (assessed in real time by rheo-MRI). In this second stage, recrystallization slows down and yield stress decreases as a result of the formation of MFC aggregates in the weak link network, as observed by confocal Raman imaging. The high fractal dimension of the weak-link network indicates that aggregation takes place via a particle-cluster mechanism. The effects of oil type and shear on the recrystallization rate and network strength could be reproduced in a stirred bowl with a heterogeneous shear stress field, which opens perspectives for the rational manipulation of MFC thickness and network strength under industrial processing conditions.

Tunicamycin induced endoplasmic reticulum changes in endothelial cells investigated in vitro by confocal Raman imaging

This paper describes how tunicamycin (Tu), the most widely used pharmacological agent for inducing endoplasmic reticulum (ER) stress, interacts with endothelial cells. Our results show that tunicamycin enters the cells and accumulates within the ER area. ER stress takes place when improperly folded or damaged proteins begin to accumulate; however, spectroscopic markers of these changes have not been identified as yet. In this work, Raman spectroscopy and scanning electron microscopy imaging of individual endothelial cells treated with Tu were performed. The changes in the biochemical composition of endothelial cells induced by Tu attributed to ER stress were studied in detail. A main feature of the Tu impact on the cells was a decrease of the phospholipid content in the area of ER, and the most abundant lipid with phosphorus groups found there, was identified as sphingomyelin.

Standardized Estimation of Spatial Resolution of Confocal Raman Imaging

Standardized Estimation of Spatial Resolution of Confocal Raman Imaging

Confocal Raman imaging of skin sections containing hair follicles using classical least squares regression and multivariate curve resolution – alternating least squares

Confocal Raman microscopy (CRM) is applied ex vivo for imaging of the spatial distribution of different skin components in skin sections containing hair follicles. For multivariate data analysis, different methods are used in order to spectrally decompose the reference spectra of the skin components (dermis, viable epidermis, stratum corneum and hair). Classical least squares regression (CLS) and multivariate curve resolution–alternating least squares (MCR-ALS) are chosen as suitable methods. In comparison to other optical methods, the advantage of CRM is molecular specificity and dispensability of labelling dyes, which is e.g. necessary in fluorescence microscopy. Therefore, a useful future application of CRM in combination with multivariate data analysis lies in the analysis of penetration routes of topically applied substances, such as cosmetic formulations or drugs into the skin, which is particularly interesting in and around hair follicles.

RISE-микроскопия в оценке качества многокомпонентных порошкообразных дезинфицирующих средств

Multicomponent powdered disinfection products with in situ generation of biocidal substances are stable in long-term storage and therefore well suited for emergency preparedness stockpiling to use in outbreaks of infectious diseases. Certain structural and chemical characteristics of the powdered biocidal mixtures might alter their efficacy, safety, or handling properties. The RISE microscopy is a new non-destructive method for comprehensive evaluation of pharmaceutical samples by combining confocal Raman imaging with scanning electron microscopy. The RISE microscopy can be used for evaluation of compounded disinfection products.

291 - Impact of glucose on the absorption, transport and metabolism of dietary polyphenols

Polyphenol-rich food can protect against type 2 diabetes. However, how the hyperglycaemia affects the bioavailability of dietary polyphenols is not clear. In this study, anin vitro model was established to investigate the impact of glucose on the absorption, transport and metabolism of polyphenols. Human endothelial cells, monocytes and macrophages were incubated either with polyphenols in the presence and absence of glucose according to our previous methods. A Confocal Raman Imaging System was used to visualize cells exposed to high level of glucose. At distinct time points, samples were analyzed by UPLC-MS/MS. The impact of high level glucose on the uptake of polyphenols into cells was explored. Human Caco-2 cell monolayer is a popular intestinal epithelial model to evaluate the transport of polyphenols and determine the effect of processing and in vitro digestion on its absorption. Caco-2 cells were provided an attractive option for initial screening of polyphenols bioavailability[3]. The uptake characteristics of polyphenols in Caco-2 cells with high and low levels of glucose will be compared to investigate the influence of glucose on Caco-2 cells transporting polyphenols. Quantitative and qualitative analysis of polyphenols and their metabolites were achieved applied the UPLC-MS/MS. Impact of glucose on the content and species of metabolites was investigated.

Impact of cell cycle dynamics on pathology recognition: Raman imaging study.

Confocal Raman imaging combined with fluorescence-activated cell sorting was used for in vitro studies of cell cultures to look at biochemical differences between the cells in different cell phases. To answer the question what is the impact of the cell cycle phase on discrimination of pathological cells, the combination of several factors was checked: a confluency of cell culture, the cell cycle dynamics and development of pathology. Confluency of 70% and 100% results in significant phenotypic cell changes that can be also diverse for different batches. In 100% confluency cultures, cells from various phases become phenotypically very similar and their recognition based on Raman spectra is not possible. For lower confluency, spectroscopic differences can be found between cell cycle phases (G0 /G1 , S and G2 /M) for control cells and cells incubated with tumor necrosis factor alpha (TNF-α), but when the mycotoxin cytochalasin B is used the Raman signatures of cell phases are not separable. Generally, this work shows that heterogeneity between control and inflamed cells can be bigger than heterogeneity between cell cycle phases, but it is related to several factors, and not always can be treated as a rule.

Highly Selective Mitochondrial Targeting by a Ruthenium(II) Peptide Conjugate: Imaging and Photoinduced Damage of Mitochondrial DNA

AbstractMitochondrial DNA (mtDNA) plays a crucial but incompletely understood role in cellular biochemistry and etiology of numerous disease states. Thus, there is an urgent need for targeted probes that can dynamically respond to changes to mtDNA such as copy number in live cells, but it is difficult to permeate the mitochondrial membrane of the living cell. Now, a ruthenium(II) light‐switching probe targeted by peptide vectorization selectively to mitochondrial nucleoids is presented. Evidence for DNA binding by the probe in live cells is derived from confocal fluorescence microscopy, resonance Raman, and luminescence lifetime imaging. While viable under imaging conditions, specific staining of mitochondrial DNA permitted efficient and selective photoinduced toxicity on a cell‐by‐cell basis under higher excitation intensities. This powerful combination of imaging and photocytotoxicity is an important step towards realizing phototheranostic application of such RuII probes.

Highly Selective Mitochondrial Targeting by a Ruthenium(II) Peptide Conjugate: Imaging and Photoinduced Damage of Mitochondrial DNA.

Mitochondrial DNA (mtDNA) plays a crucial but incompletely understood role in cellular biochemistry and etiology of numerous disease states. Thus, there is an urgent need for targeted probes that can dynamically respond to changes to mtDNA such as copy number in live cells, but it is difficult to permeate the mitochondrial membrane of the living cell. Now, a ruthenium(II) light-switching probe targeted by peptide vectorization selectively to mitochondrial nucleoids is presented. Evidence for DNA binding by the probe in live cells is derived from confocal fluorescence microscopy, resonance Raman, and luminescence lifetime imaging. While viable under imaging conditions, specific staining of mitochondrial DNA permitted efficient and selective photoinduced toxicity on a cell-by-cell basis under higher excitation intensities. This powerful combination of imaging and photocytotoxicity is an important step towards realizing phototheranostic application of such RuII probes.

Confocal Raman-in-SEM Imaging: a New Method for 3D Morphology of Asbestos like Fibers in a Mineral Matrix - Complementarity with SEM-FIB.

Asbestos consists of natural mineral fibers crystallized in a specific way with specific properties including flexibility, high tensile strength, resistance to heat and chemical degradation. The term refers to one fibrous serpentine, and five asbestiform varieties of amphiboles [1][2]. Asbestos is considered a Category 1 human carcinogen (e.g. [1][3][4][5][6]), as inhalation of fibers causes respiratory diseases, in particular asbestosis, lung cancers and malignant mesothelioma. Due to the pathogenicity of fibers, their use has been banned in most countries around the world. The classification as asbestos comprises three main characteristics: sub-micrometric fibrous morphology (so-called asbestiform), chemistry and crystallography (i.e. mineralogy). The ban applies to natural materials, which are quarried and used for public works projects. Compliance with existing rules requires accurate diagnosis of the or non-asbestos nature of the materials likely to be exploited in a quarry or involved in the opening of a construction site. Conventional methods for diagnosis, mainly based on the use of TEM, are hard to apply to massive materials as the sample preparation protocol is complex, it is likely to release artifacts like cleavage fragments, or sample-piece thinning is costly and hard to achieve and thus not applicable in routine analysis. The use of a LV-FE-SEM-EDS (Low vacuum field emission gun scannning electron microscope equiped with energy dispersive spectroscopy) coupled to confocal Raman-in-SEM imaging (RISE) is a new and efficient method for identifying the mineral nature of sub-micrometer fibers or fibrous bundles. SEM coupled to EDS provides a qualitative or semi-quantitative composition of the fiber. The crystal structure is determined by confocal Raman spectroscopy (with lateral resolution down to 360 nm [7]). Thus the combination of these two kinds of information allows for accurate identification of both the nature and the morphology of the mineral. The combination of SEM, EDS and confocal Raman imaging in a unique analytical system (RISE) allows precise location of the same area / fiber and identification of its mineral nature. In addition, RISE allows the acquisition of 3D data, which is able to provide morphological information of the mineral distribution in the sample volume and leading to the determination of the aspect ratio, a critical parameter for (i.e. asbestiform or non-asbestiform). Moreover, this combination of techniques is not destructive. The coupling of SEM-EDS with RISE is a powerful analytical system that simplifies and reinforces existing analytical procedures. For highest resolution studies of fibers in the sample volume (3 D imaging), the RISE can be connected to a FIB-SEM [7]. Although FIB volume reconstruction is a destructive method, the resolution of the voxel can be extended to below 100 nm [8]-a resolution sufficient for visualizing even the thinnest fibers. Furthermore, Raman 3D view is an efficient tool for sampling TEM slices using the FIB.

Three‐Dimensional Raman Tomographic Microspectroscopy: A Novel Imaging Technique

AbstractChemical constituents and their spatial distributions in terrestrial and extraterrestrial samples may provide clues to their formation histories and secondary processes they were subjected to. Most analytical tools are either limited in imaging the interior of samples or they are destructive such that the sample is chemically modified. In this work, we have conducted three‐dimensional Raman tomographic imaging experiments on both terrestrial and extraterrestrial samples. The in situ nondestructive analytical technique presented here provides spatial distribution of various chemical constituents from the interior of the samples with high spatial and depth resolution. Raman data were first collected from two‐dimensional layers at the surface and at various depths inside the samples by means of confocal Raman imaging. Individual chemical distribution maps were generated for each layer, which were then stacked to form and visualize the three‐dimensional distributions. In addition to three‐dimensional distributions, Raman spectral information was also collected from each pixel within the measured areas, thus allowing us to also perform detailed spectral investigations of the samples.

Surface enhanced Raman spectroscopy-detection of the uptake of mannose-modified nanoparticles by macrophages in vitro: A model for detection of vulnerable atherosclerotic plaques.

Atherosclerosis is a process of thickening and stiffening of the arterial walls through the accumulation of lipids and fibrotic material, as a consequence of aging and unhealthy life style. However, not all arterial plaques lead to complications, which can lead to life-threatening events such as stroke and myocardial infarction. Diagnosis of the disease in early stages and identification of unstable atherosclerotic plaques are still challenging. It has been shown that the development of atherosclerotic plaques is an inflammatory process, where the accumulation of macrophages in the arterial walls is immanent in the early as well as late stages of the disease. We present a novel surface enhanced Raman spectroscopy (SERS)-based strategy for the detection of early stage atherosclerosis, based on the uptake of tagged gold nanoparticles by macrophages and subsequent detection by means of SERS. The results presented here provide a basis for future in vivo studies in animal models.The workflow of tracing the SERS-active nanoparticle uptake by macrophages employing confocal Raman imaging.

The impact of oxalate ions on barium sulfate crystallization

In this manuscript we investigate the impact of oxalate ions on the crystallization of barium sulfate. The organic anion, oxalate, was found to inhibit both nucleation and growth according to atomic force microscopy measurements and dynamic light scattering data. Raman confocal imaging was used to try and determine how the oxalate interacts with the barium sulfate surface. It was found that barium oxalate is only seen at very high oxalate concentrations. At lower concentrations no direct evidence for the presence of oxalate was observed, however, the most probable mode of action for oxalate is via adsorption onto the barium sulfate surface including into key kink or step sites, impacting growth.

UV irradiation of biomarkers adsorbed on minerals under Martian-like conditions: Hints for life detection on Mars

Laboratory simulations of Martian conditions are essential to develop quantitative models for the survival of organic biomarkers for future Mars exploration missions.In this work, we report the results of ultraviolet (UV) irradiation processing of biomarkers adsorbed on minerals under Martian-like conditions. Specifically, we prepared Mars soil analogues by doping forsterite, lizardite, antigorite, labradorite, natrolite, apatite and hematite minerals with organic compounds considered as potential biomarkers of extant terrestrial life such as the nucleotides adenosine monophosphate (AMP) and uridine monophosphate (UMP). We characterized such Mars soil analogues by means of Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) and Confocal Raman Imaging Spectroscopy (CRIS), in order to get insights into the specific molecule-mineral interactions and explore the capabilities of different techniques to reveal diagnostic features of these biomarkers. Then, we performed irradiation experiments in the mid-UV spectral region under simulated Martian conditions and under terrestrial ambient conditions for comparison, monitoring the degradation process through DRIFTS.We observed that degradation under Martian-like conditions occurs much slower than in terrestrial ambient conditions. The minerals labradorite and natrolite mainly promote photodegradation of nucleotides, hematite and forsterite exhibit an intermediate degrading effect, while apatite, lizardite and antigorite do not show any significant catalytic effect on the degradation of the target organic species.