Use Of Raman Microscopy Research Articles

Challenges and potential for detecting and quantifying titanium dioxide in food.

Titanium dioxide (TiO2) is banned in some countries but its use is still permitted in others. The global food supply chain is therefore challenged with the need to use rapid and reliable testing methods to either detect the presence of TiO2 or to quantify its concentration. The goal of this study was to determine the feasibility of using color, texture profile analysis, Raman microscopy, and X-ray fluorescence (XRF) spectroscopy to detect and quantify TiO2 in fillings used in the pastry and confectionery industry. In this study, two types of fillings were investigated: vanilla based and chocolate based. All fillings were prepared in four different variations - without TiO2 and with three concentrations as follows: 0.25 g*kg-1, 0.5 g*kg-1, or 0.75 g*kg-1 TiO2 per sample. The methods were selected for their ability to analyze the samples in a short period of time. All of the methods showed moderate to high potential for detecting TiO2 in the samples. The results reveal how TiO2 affects the food matrix color and texture. Use of Raman microscopy confirms its detectability, although concentrations of TiO2 do not follow a pattern. X-ray fluorescence spectroscopy showed the greatest potential as it can not only detect TiO2 but can also quantify its concentration in the samples. The highest potential for quantifying the concentration of this food additive was achieved with XRF. © 2024 Society of Chemical Industry.

High-throughput line-illumination Raman microscopy with multislit detection.

Raman microscopy is an emerging tool for molecular imaging and analysis of living samples. Use of Raman microscopy in life sciences is, however, still limited because of its slow measurement speed for spectral imaging and analysis. We developed a multiline-illumination Raman microscope to achieve ultrafast Raman spectral imaging. A spectrophotometer equipped with a periodic array of confocal slits detects Raman spectra from a sample irradiated by multiple line illuminations. A comb-like Raman hyperspectral image is formed on a two-dimensional detector in the spectrophotometer, and a hyperspectral Raman image is acquired by scanning the sample with multiline illumination array. By irradiating a sample with 21 simultaneous illumination lines, we achieved high-throughput Raman hyperspectral imaging of mouse brain tissue, acquiring 1108800 spectra in 11.4 min. We also measured mouse kidney and liver tissue as well as conducted label-free live-cell molecular imaging. The ultrafast Raman hyperspectral imaging enabled by the presented technique will expand the possible applications of Raman microscopy in biological and medical fields.

Raman imaging to capture microplastics and nanoplastics carried by smartphones

The sources of microplastics and nanoplastics can be found almost everywhere, including being released from the activities of our daily lives. Unfortunately, the process for determining the sources of microplastics and nanoplastics is hampered by the limited techniques available for characterisation. Herewith, we advance Raman imaging by combining it with logic-based, algebra-based, PCA-based algorithms and their hybrid, which can significantly increase the signal-noise ratio and the imaging certainty, to enable the characterisation of microplastics. Consequently, we can capture and identify the microplastics carried by our smartphones. That is because, due to the friction and fragmentation etc., our clothes and the decoration trinkets that might be made of plastic fibres can release microplastics. The released microplastics stick on the phone surface, or are trapped in the charging port, speaker ports etc., towards accumulation. We estimate hundreds or thousands of microplastics can be captured and carried by a smartphone, depending on the clothing materials, pocketing styles, user habits etc. Due to the complexity of the samples (which shields the weak signals emitted from nanoplastics), further methodological improvements are required, such as optimisation of sample preparation (for better isolation of nano-sized plastics), refinement of data processing algorithms and combined use of Raman microscopy and scanning electron microscopy (SEM).

Exploration of the Use of Raman Microscopy to the Identification of Extractables and Leachables from Polymeric Containers

In a follow-up to my February 2020 column, I started a more systematic study of extractables and leachables. Following a suggestion from Mark Witkowski of the FDA, I looked at three sets of centrifuge vials that were exposed to the following liquids in an effort to evaluate the potential of Raman microscopy to identify compounds exiting in polymers under particular conditions: saline, phosphate buffer, water, saline treatment at 100 0C, phosphate buffer treatment at 100 0C, water treatment at 100 0C, ethanol, chloroform, pH 5, and pH 9. Although all containers were made of polypropylene (PP), they didn’t behave similarly. Compounds that were extracted from PP vials from different manufacturers were not always the same. Although the number of spectral types that are recorded is large, this article focuses on a few whose interpretation is interesting. The goal was to figure out when it makes sense to employ Raman microscopy for such identification. The characteristics considered were ease of sample preparation, the minimum quantity of material amenable to analysis, and the quality of the identification.

Single‐cell Raman microscopy of microengineered cell scaffolds

AbstractStudying cells in a three‐dimensional (3D) environment has great potential in understanding cell behaviours such as morphology, proliferation, differentiation, and migration. Microengineered 3D cell scaffolds with precise defined geometries have offered a new approach to study cell behaviour and its interactions with scaffolds. The use of Raman spectroscopy to characterise biomolecules is a rapidly expanding area and has been implemented in numerous fields including pharmacology, microbiology, toxicology, and single‐cell studies. However, one area where it remains unexploited despite the vast potential of the technique is in the investigation of 3D cell scaffolds. A combination of Raman microscopy and chemometric approaches have employed to investigate the structure and biochemistry of nanofabricated scaffolds and a cell–scaffold complex. The 3D Raman mapping combined with the use of nanofabricated 3D scaffolds offers a unique opportunity to assess the influence of scaffold architecture on cell body and cell nuclei morphology and biochemistry. For the first time, we have cultured a human epithelial colorectal adenocarcinoma cell line on OrmoComp scaffolds and determined the structure and biochemistry of nanofabricated scaffolds and a cell–scaffold complex with the use of Raman microscopy combined with appropriate data analysis protocols. The results demonstrate the potential of 3D Raman mapping for identifying biochemical and physical variation within single cells as they grow and adhere to 3D scaffolds.

Quantification of Polyphosphate in Microalgae by Raman Microscopy and by a Reference Enzymatic Assay.

Polyphosphates have occurred in living cells early in evolution and microalgae contain these important polymers in their cells. Progress in research of polyphosphate metabolism of these ecologically as well as biotechnologically important microorganisms is hampered by the lack of rapid quantification methods. Experiments with the green alga Chlorella vulgaris presented here compared polyphosphate extraction in water, methanol-chloroform, and phenol-chloroform followed by polyphosphate purification by binding to silica columns or ethanol precipitation. The phenol-chloroform extraction of C. vulgaris followed by ethanol precipitation of polyphosphate was shown to be superior to the other tested method variants. Recovery test of added polyphosphate standard to algal biomass showed that the method is accurate. Using this biochemical assay as a validated reference, we show that 2-dimensional, confocal Raman microscopy can serve as a linear proxy for polyphosphate in C. vulgaris with R2 up to 0.956. With this, polyphosphate quantification can be shortened by use of Raman microscopy from days to hours and, additionally, information about intracellular distribution of polyphosphate and heterogeneity among individual cells in algal culture can be obtained. This offers new insights into the dynamics and role of these polymers crucial for phosphorus uptake and storage. This analytical capability is of particular practical importance because algae aid phosphorus sequestration from wastewater and the thus enriched biomass may serve as organic fertilizer. Both these applications have a strong potential in a future sustainable, circular bioeconomy.

On the use of Raman microscopy for sulfation analysis in lead-acid battery research

Enhanced flooded batteries were studied by means of spatially resolved Raman spectroscopy. Negative plate sulfation as an important failure mode in partial state of charge cycling was characterized. Raman spectroscopy turned out to be an appropriate method for sulfation analysis. The data were correlated with results from elementary analysis and EDX. A lead sulfate specific mapping along electrode cross-section was possible with a spatial resolution of ∼50μm.

Feasibility of the quantification of respirable crystalline silica by mass on aerosol sampling filters using Raman microscopy

Airborne respirable crystalline silica (RCS) is a hazard that can affect the health of workers, and more sensitive measurements are needed for the assessment of worker exposure. To assess the use of Raman microscopy for the analysis of RCS particulate collected on filters, aliquots of quartz or cristobalite suspended in isopropanol were pipetted onto silver filters. Samples were measured by arbitrarily selecting positions along the filter and collecting spectra at 50 discrete points. The calculated limits of quantification on test samples were between 0.066–0.161 and 0.106–0.218 μg for quartz and cristobalite, respectively. Three respirable quartz calibration dusts (A9950, NIST 1878 and Quin 1B) with different mass median aerodynamic particle sizes obtained similar Raman response relationships per unit mass. The difference between NIST 1878 and Quin 1B was not significant (p = 0.22). The intermediate measurement precision of replicate samples was 10–25% over the measured range for quartz (0.25–10 μg) and could potentially be improved. Results from mixtures of quartz and cristobalite were mostly within 10% of their theoretical values. Results from samples of 6% quartz in calcite were close to the theoretical quartz mass. The upper measurement limit for a mixture of 20% RCS in the light absorbing mineral hematite (Fe2O3) was 5 μg. These data show that Raman spectroscopy is a viable option for the quantification of the mass of respirable crystalline silica on filters with a limit of detection approaching 1/10th of that obtained with other techniques. The improvement in sensitivity may enable the measurement of particulate in samples from low concentration environments (e.g. inside a mask) or from miniature samplers operating at low flow rates. ©2017 Crown copyright. Journal of Raman Spectroscopy published by John Wiley & Sons, Ltd. © 2017 Crown copyright. Journal of Raman Spectroscopy published by John Wiley & Sons, Ltd.

A new insight into polyurethane foam deterioration – the use of Raman microscopy for the evaluation of long‐term storage conditions

This research aims at bringing new contributions for lowering the polyether‐based polyurethane (PUR) flexible foam high deterioration rate by studying selected storage conditions. With a life expectancy of 20–50 years, many PUR objects show severe deterioration signs that, so far, cannot be prevented. To establish a preservation strategy, a natural ageing experiment in the dark (12 months, 45–55% relative humidity) has been carried out for the study of four storage conditions: open air at room temperature (T) and sealed enclosures at room T (with/without oxygen) and low T (11–13 °C). For this research, unaged (model PUR) and naturally pre‐aged (commercial PUR) references were included. The samples were analysed every 3 months by colourimetry, optical microscopy (visible and UV light), infrared and Raman microspectroscopies. Further statistical data treatment was carried out in order to identify significant spectral variations (ANOVA) and to uncover correlations between molecular spectral lines and physical aspects. Raman proved to be a powerful tool in the detection of early stage PUR molecular deterioration. For both model and commercial samples, open‐air storage proved to be the most harmful condition, while anoxic storage showed the best results. In general, this experiment has enabled new contributions for lowering PUR high deterioration rate. Copyright © 2016 John Wiley & Sons, Ltd.

The use of Raman microscopy and laser desorption ionization mass spectrometry in the examination of synthetic organic pigments in modern works of art

Synthetic organic pigments are widely used in modern and contemporary works of art. They have been examined by a variety of techniques including spectroscopic methods such as Fourier transform infrared spectroscopy, Raman, and X‐ray powder diffraction as well as chromatographic or mass spectrometric techniques such as pyrolysis‐gas chromatography/mass spectrometry and laser desorption ionization mass spectrometry (LDI–MS). Often, a combination of techniques has been used to examine these pigments. This paper describes use of Raman spectroscopy to create a database of colorants including two pigments not previously reported, PO1 and PO2. Then, using Raman spectroscopy in combination with LDI–MS, samples from modern works of art by artists including Mark Rothko, Barnett Newman, and José de Rivera were examined in order to identify the pigments present. One finding was that Rothko used a variety of red pigments over the course of his career including PR11 which has not been previously reported in artwork, and PO2 found with its positional isomer PR1. Knowledge of the colorants serves to inform conservators about display and treatment decisions. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.

Hyperspectral imaging with stimulated Raman scattering by chirped femtosecond lasers.

Raman microscopy is a quantitative, label-free, and noninvasive optical imaging technique for studying inhomogeneous systems. However, the feebleness of Raman scattering significantly limits the use of Raman microscopy to low time resolutions and primarily static samples. Recent developments in narrowband stimulated Raman scattering (SRS) microscopy have significantly increased the acquisition speed of Raman based label-free imaging by a few orders of magnitude, at the expense of reduced spectroscopic information. On the basis of a spectral focusing approach, we present a fast SRS hyperspectral imaging system using chirped femtosecond lasers to achieve rapid Raman spectra acquisition while retaining the full speed and image quality of narrowband SRS imaging. We demonstrate that quantitative concentration determination of cholesterol in the presence of interfering chemical species can be achieved with sensitivity down to 4 mM. For imaging purposes, hyperspectral imaging data in the C-H stretching region is obtained within a minute. We show that mammalian cell SRS hyperspectral imaging reveals the spatially inhomogeneous distribution of saturated lipids, unsaturated lipids, cholesterol, and protein. The combination of fast spectroscopy and label-free chemical imaging will enable new applications in studying biological systems and material systems.

Trends in Raman chemical imaging

The use of Raman microscopy (or Raman chemical imaging) has grown enormously in the last few decades and it has become a valuable tool for a range of applications. Raman microscopy presents several unique features such as ability to provide chemical and spatial information with resolution of a few micrometers in a rapid and non-destructive fashion, requir- ing little or no sample preparation and the ability to probe aqueous materials. Instrumentation, data processing methods and computer technology advances have made a renaissance of Raman microscopy and the number of applications has continu- ously growing. Furthermore, other spectroscopic derivatives aimed to improve Raman sensitivity have been recently applied to imaging: coherent anti-Stokes Raman spectroscopy (CARS), stimulated Raman spectroscopy (SRS), surface enhanced Raman spectroscopy (SERS), tip enhanced Raman spectroscopy (TERS) and imaging with carbon nanotubes (CNTs). These methods provide a significant improvement in sensitivity in relation to traditional spontaneous Raman microscopy, allowing faster data acquisition and therefore the study of in-vitro, ex-vivo and in-vivo dynamic systems in an unprecedented manner. This paper will discuss recent papers applying the techniques above mentioned and discuss trends for future Raman chemical imaging.

Use of Raman Microscopy and Multivariate Data Analysis to Observe the Biomimetic Growth of Carbonated Hydroxyapatite on Bioactive Glass

In the present contribution, the biomimetic growth of carbonated hydroxyapatite (HA) on bioactive glass were investigated by Raman microscopy. Bioactive glass samples were immersed in simulated body fluid (SBF) buffered solution at pH 7.40 up to 17 days at 37 degrees C. Raman microscopy mapping was performed on the bioglass samples immersed in SBF solution for different periods of time. The collected data was then analyzed using the band-target entropy minimization technique to extract the observable pure component Raman spectral information. In this study, the pure component Raman spectra of the precursor amorphous calcium phosphate, transient octacalcium phosphate, and matured HA were all recovered. In addition, pure component Raman spectra of calcite, silica glass, and some organic impurities were also recovered. The resolved pure component spectra were fit to the normalized measured Raman data to provide the spatial distribution of these species on the sample surfaces. The current results show that Raman microscopy and multivariate data analysis provide a sensitive and accurate tool to characterize the surface morphology, as well as to give more specific information on the chemical species present and the phase transformation of phosphate species during the formation of HA on bioactive glass.

Use of Raman Microscopy and Band-Target Entropy Minimization Analysis To Identify Dyes in a Commercial Stamp. Implications for Authentication and Counterfeit Detection

Raman microscopy was used in mapping mode to collect more than 1000 spectra in a 100 microm x 100 microm area from a commercial stamp. Band-target entropy minimization (BTEM) was then employed to unmix the mixture spectra in order to extract the pure component spectra of the samples. Three pure component spectral patterns with good signal-to-noise ratios were recovered, and their spatial distributions were determined. The three pure component spectral patterns were then identified as copper phthalocyanine blue, calcite-like material, and yellow organic dye material by comparison to known spectral libraries. The present investigation, consisting of (1) advanced curve resolution (blind-source separation) followed by (2) spectral data base matching, readily suggests extensions to authenticity and counterfeit studies of other types of commercial objects. The presence or absence of specific observable components form the basis for assessment. The present spectral analysis (BTEM) is applicable to highly overlapping spectral information. Since a priori information such as the number of components present and spectral libraries are not needed in BTEM, and since minor signals arising from trace components can be reconstructed, this analysis offers a robust approach to a wide variety of material problems involving authenticity and counterfeit issues.

Use of Raman microscopy and band-target entropy minimization technique to differentiate physical mixture from chemical mixture in mixed metal oxides

Raman microscopy has been applied to characterize physical and chemical mixtures of mixed metal oxides. The obtained Raman mapping data were first subjected to singular value decomposition to obtain the right singular vectors, and the right singular vectors were then subjected to band-target entropy minimization (BTEM) to recover the pure component spectra of the observed species present in the sample. Subsequently, these resolved pure component spectral information was used to differentiate the physical and chemical mixtures. In addition, BTEM is also able to recover the pure component spectra of both unstable compound and its degradation product due to laser irradiation. In current study, the physical mixture of Mn 2O 3 and Co 3O 4, and the chemical mixture of CoMn 2O 4 spinel oxide were investigated.

The use of Raman microscopy to determine and localize vitamin E in biological samples

Alpha-tocopherol (aT), the predominant form of vitamin E in mammals, is thought to prevent oxidation of polyunsaturated fatty acids. In the lung, aT is perceived to be accumulated in alveolar type II cells and secreted together with surfactant into the epithelial lining fluid. Conventionally, determination of aT and related compounds requires extraction with organic solvents. This study describes a new method to determine and image the distribution of aT and related compounds within cells and tissue sections using the light-scattering technique of Raman microscopy to enable high spatial as well as spectral resolution. This study compared the nondestructive analysis by Raman microscopy of vitamin E, in particular aT, in biological samples with data obtained using conventional HPLC analysis. Raman spectra were acquired at spatial resolutions of 2-0.8 microm. Multivariate analysis techniques were used for analyses and construction of corresponding maps showing the distribution of aT, alpha-tocopherol quinone (aTQ), and other constituents (hemes, proteins, DNA, and surfactant lipids). A combination of images enabled identification of colocalized constituents (heme/aTQ and aT/surfactant lipids). Our data demonstrate the ability of Raman microscopy to discriminate between different tocopherols and oxidation products in biological specimens without sample destruction. By enabling the visualization of lipid-protein interactions, Raman microscopy offers a novel method of investigating biological characterization of lipid-soluble compounds, including those that may be embedded in biological membranes such as aT.

Crystalline Form Information from Multiwell Plate Salt Screening by Use of Raman Microscopy

The purpose of this study was to establish a useful methodology, possibly providing information on the stoichiometry of pharmaceutical drug salts obtained from salt screening by using a multiwell plate and a Raman microscope. Tamoxifen salt screening was conducted with monobasic and polybasic acids on 96-well quartz plates with a Raman microscope. Appearance and crystalline forms of salts prepared on 96-well plates were observed by polarizing light microscope and Raman microscope, respectively. Based on the results of the salt screening, tamoxifen citrate and fumarate salts were prepared on a large scale. The salts prepared were characterized by powder X-ray diffractometry (PXRD) and ion chromatography. The results of the multiwell salt screening indicated that tamoxifen has a tendency toward the formation of mono salt as opposed to hemi salt with polybasic acid, and that most of tamoxifen salts gave several potential polymorphic forms. PXRD patterns of scaled-up tamoxifen citrate and fumarate salts suggested that the same crystalline form was obtained from the binary mixture regardless of molar ratios of 2:1 or 1:1 (tamoxifen/acid). The crystalline forms obtained were tamoxifen monocitrate and monofumarate salts as measured by ion chromatography. Salt screening on multiwell plates with a Raman microscope provided novel insight into the characteristics prediction of the stoichiometrical salts in addition to potential polymorph information. Based on the stoichiometrical information of salts, the amount of compound and time required for crystalline form selection of drug candidates would be significantly reduced.

An investigation into the use of Raman microscopy for the detection of labelled compounds in living human cells

AbstractWe report on the first detection of vibrationally labelled compounds by Raman micro‐spectroscopy in living cells and demonstrate the feasibility of this technique for bioanalysis. Copyright © 2004 John Wiley & Sons, Ltd.

Raman microscopy in archaeological science

Improvements in the instrumentation for dispersive and interferometric Fourier transform (FT) Raman microscopy have overcome many of the earlier limitations of these techniques, thus opening the way for their widespread and routine utilisation in archaeometry laboratories. The use of Raman spectroscopy for identifying and studying archaeological materials has flourished in recent years, but the resulting articles have seldom been published in the archaeology literature, thus limiting their impact on the field. Therefore, this article covers concisely the theory and instrumentation of Raman microscopy and then comprehensively reviews the many applications of this technique in archaeometric research. The significant advances made in archaeological science through the use of Raman microscopy are highlighted, but many areas requiring further research, such as the generation of more extensive and reliable spectral libraries and the surmounting of obstacles in the analysis of certain classes of historical materials, are also revealed.

Thermal decomposition of metazeunerite—a high-resolution thermogravimetric and hot-stage Raman spectroscopic study

A combination of high-resolution thermogravimetric analysis coupled to a gas evolution mass spectrometer has been used to study the thermal decomposition of metazeunerite {Cu(H 2O) 4}(H 2O) 4[(UO 2)(AsO 4)] 2. Five stages of weight loss are observed at 48, 88, 125, 882 and 913 °C. In the first three stages 2, 4 and 2 mol of water are lost. In stages 4 and 5, some As 2O 5 units are lost and it is probable that reduction of the anhydrous phase Cu[(UO 2)(AsO 4)] 2 occurs. The stages of dehydration were confirmed by the use of evolved water vapour mass spectroscopy. Changes in the structure of metazeunerite were followed by the use of Raman microscopy in conjunction with a thermal stage. Two Raman bands are observed at 818 and 811 cm −1 and are assigned to the ν 1 symmetric stretching modes of the UO 2 units. The UO 2 Raman antisymmetric stretching mode was observed at 890 cm −1. No AsO 4 stretching vibrations were observed until after two stages of dehydration of the metazeunerite. The AsO 4 ν 4 bending modes show complexity with bands observed at 463, 446, 396 and 380 cm −1. Thermal treatment results in the removal of this degeneracy. The ν 2 band of the AsO 4 units is observed at 320 cm −1. Raman bands at 275 and 235 cm −1 are attributed to the ν 2 bending modes of the (UO 2) 2+ units. The use of the hot-stage Raman microscope enables low-temperature phase changes brought about through dehydration to be studied.