Raman Imaging Research Articles

Raman imaging towards in-situ visualisation of perchlorate adsorption

Raman imaging can directly visualise perchlorate adsorption, and even enables in-situ monitoring, because water has a low Raman activity and generates almost no interference, which is demonstrated herein. The Raman signal enhancement of perchlorate on the porous silver surface provides a possibility to monitor the adsorption of perchlorate at low level. From this initial adsorption assembly of (i) porous silver-perchlorate, we test several more, including (ii) porous silver-perchlorate-sand, (iii) porous silver-perchlorate-microplastic-sand, (iv) porous silver-perchlorate-microplastic-sand-river water etc. The introduction of microplastic, another emerging contaminant, can provide extra insights into the co-adsorption process. Particularly the composite structure of microplastic-sand can simultaneously visualise the adsorption of perchlorate on the silver surface, the plastic/organic surface and the sand surface. We note that the water can modify the configuration of perchlorate in-situ towards the adsorption on silver surface; the adsorption of perchlorate can benefit from co-adsorption with organic matter, and the rough surface plays an important role as well. Overall, Raman imaging provides an effective approach to directly visualise the adsorption of emerging contaminants.

Versatile Confocal Raman Imaging Microscope Built from Off-the-Shelf Opto-Mechanical Components.

Confocal Raman microscopic (CRM) imaging has evolved to become a key tool for spatially resolved, compositional analysis and imaging, down to the μm-scale, and nowadays one may choose between numerous commercial instruments. That notwithstanding, situations may arise which exclude the use of a commercial instrument, e.g., if the analysis involves toxic or radioactive samples/environments; one may not wish to render an expensive instrument unusable for other uses, due to contamination. Therefore, custom-designed CRM instrumentation-being adaptable to hazardous conditions and providing operational flexibility-may be beneficial. Here, we describe a CRM setup, which is constructed nearly in its entirety from off-the-shelf optomechanical and optical components. The original aim was to develop a CRM suitable for the investigation of samples exposed to tritium. For increased flexibility, the CRM system incorporates optical fiber coupling to both the Raman excitation laser and the spectrometer. Lateral raster scans and axial profiling of samples are facilitated by the use of a motorized xyz-translation assembly. Besides the description of the construction and alignment of the CRM system, we also provide (i) the experimental evaluation of system performance (such as, e.g., spatial resolution) and (ii) examples of Raman raster maps and axial profiles of selected thin-film samples (such as, e.g., graphene sheets).

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).

Direct imaging of intracellular RNA, DNA, and liquid–liquid phase separated membraneless organelles with Raman microspectroscopy

Methodologies for direct intracellular imaging of RNA and DNA are necessary for the advancement of bioimaging. Here we show direct label-free imaging of RNA and DNA in single cells by isolating their accurate Raman spectra. Raman images of DNA from interphase cells show intact nucleus, while those from mitotic cells reveal condensed chromosome. The condensed chromosome images are accurate enough to assign the stage of mitotic cell division (e.g., metaphase). Raman spectral features indicate B-DNA double helical conformational form in all the cell lines investigated here. The Raman images of RNAs, on the other hand, reveal liquid-liquid phase separated (LLPS) membraneless organelles in interphase cells, which disappears during mitosis. Further, the Raman spectrum of proteins from the intracellular LLPS organelles indicates slight enrichment of amyloid-like secondary structural features. Vibrational imaging of intracellular DNA and RNA simultaneously would open myriad of opportunities for examining functional biochemical aspects of cells and organelles.

A comprehensive study on the ionomer properties of PFSA membranes with confocal Raman microscopy

The proton exchange membrane is the heart of many electrochemical energy systems, and their performance and longevity depend on a careful selection and processing of membrane materials. In this work, we use confocal Raman microscopy to investigate application-relevant properties of perfluorinated sulfonic acid (PFSA) membranes. Raman spectra of Nafion, Aquivion, and 3M Ionomer at different equivalent weights show differences in the spectral area and position of various Raman bands but reveal a clear trend of band intensities versus equivalent weight. Characteristics of these ionomers such as swelling and water uptake were determined with through-plane imaging. The technique offers advantages over conventional measurements, such as contact-free and non-destructive data acquisition. Calibration curves for the equivalent weight were derived for the different PFSAs with excellent linear fits that allow a quantification of the ionizable group content. The high spatial resolution of confocal Raman microscopy of less than 2 μm enables the local evaluation of all these ionomer properties. Furthermore, Raman imaging was employed to characterize composite membranes, which shows that it can resolve individual phases and features in multi-layered membranes. This study provides a comprehensive summary of confocal Raman microscopy as a powerful tool for the analysis of ionomer and membrane properties.

Raman imaging studies on the stability of Paracetamol tablets under different storage conditions

The applicability of Raman imaging for pharmaceutics production ranges from the characterization of pharmaceutical formulations, kinetic processes in drug delivery to the rapid detection and identification of counterfeit drugs/contaminants. Acetaminophen (Paracetamol, APAP) is an analgesic and antipyretic drug and one of the most consumed medicines worldwide. On the other hand, the compound 4-aminophenol (4-AP) is a hydrolytic product of APAP with nephrotoxicity and teratogenic effects. In this work, we have explored for the first time Raman imaging methods to characterize the main components of commercial APAP tablets (APAP-tablets) and to inquire about the potential of this optical technique to identify 4-AP in APAP tablets, which have been previously spiked with such contaminant. The laboratorial treated APAP-tablet samples were subjected to different temperature, humidity and sunlight exposure conditions, mimicking storage conditions, and then the Raman spectra and images were collected to monitor changes that might occur in those conditions. Although the lower limit of detection of 4-AP in APAP-tablets is above the minimum levels established by Pharmacopoeias (0.005 %), this research demonstrates that Raman imaging still allows the detection of small amounts of the contaminant, thus opening perspectives for exploring this technique for characterizing APAP products.

Mycelial differentiation linked avermectin production in Streptomyces avermitilis studied with Raman imaging

Streptomyces avermitilis is a gram-positive bacterium that undergoes complex physiological and morphological differentiation during its life cycle, which has implications in secondary metabolite production. Avermectin, produced by S. avermitilis, is widely used as an anthelmintic and insecticidal agent. In this study, we have applied Raman microspectroscopic imaging to elucidate the correlation between production of avermectin and the morphological differentiation in S. avermitilis. We demonstrate distinctive variations in the localization of secondary metabolites at various stages of morphological differentiation. Under solid culture, avermectin was detected in the mycelia formed at the later stages of morphological differentiation (e.g., spore-bearing mycelium and spiral spore chains), but not in the early-stage substrate mycelium. On the contrary, under liquid culture condition, avermectin was found concentrated in the mycelial pellet formed at the early MII stage of differentiation. Furthermore, the chemical profiles of the mycelia were substantially different depending on the culture condition. Raman spectra corresponding to proteins, lipids, and cytochrome were observed in the mycelia irrespective of the stage of morphological differentiation, however, carotenoid was observed under solid culture condition particularly in spore-bearing mycelium and spiral spore chains. KEY POINTS: • Avermectin production is regulated during mycelial differentiation • Liquid and solid culture conditions affects mycelial differentiation • Raman microspectroscopic analysis reveals localization profiles of avermectin.

Synchrotron Radiation μ-XRF Imaging Reveals Mn Zoning in Freshwater Pearls

Chemical zoning is commonly seen in inorganic minerals, and it holds implications for magmatic processes, hydrothermal evolution, or metal mineralization. However, few studies are available on oscillatory zoning in biominerals, which carries the most direct and unique information on the biomineralization mechanism. This study investigates spatial and temporal resolution of trace element distributions in pearls that were cultivated in the Hyriopsis cumingii mantle (non-nucleated pearls and nucleated Akoya pearls) or visceral mass (nucleated Edison pearls) for 1–5 years. Using synchrotron radiation micro-X-ray fluorescence imaging, we find a variety of trace elements such as Sc, Cr, Mn, Cu, Zn, Ge, and Ba. The types of trace elements are slightly different for individuals. For the first time, submillimeter-scale Mn zoning is identified ubiquitously, concentric with the pearl, and exhibits increased concentrations toward the pearl margin. In non-nucleated pearls and nucleated Akoya pearls, the Mn zones are superposed with a spatially damped pattern with a decrease in the interzones. In contrast, no damped trends are observed in the Mn zones in nucleated Edison pearls. This difference may be due to different cultivation sites within mollusks that have different requirements for Mn during pearl growth. We suggest a growth model of dissipative structure for the Mn zoning in pearls, which depends upon the coupling between the interface kinetics and the diffusion of chemical species in the environment. The trace elements (including Mn) substitute Ca in aragonite isomorphically, based on Raman imaging. The scanning electron microscopy images show a periodic structure of aragonite platelets and organic matter of pearls. Locally in the Mn zones, there are minor defects on platelets, which may arise from the enrichment of trace elements. This study would develop a new research field for chemical zoning in minerals and introduce a new angle in understanding trace element incorporation in biominerals and the biomineralization processes.

Visual characterization of microplastics in corn flour by near field molecular spectral imaging and data mining

As potential hazard to human health, microplastics have attracted increasing attention. Most current studies have addressed the characterization of microplastics from the environment. For microplastics in food, most detections focused on liquid systems such as alcohol, beverages, etc., while there has been quite rare research on microplastics in solid foods with complex matrices. Thus, this study attempted to use three molecular spectral imaging approaches, namely, Fourier transform infrared (FTIR), optical photothermal resonance infrared (O-PTIR), and confocal Raman spectral imaging, combined with chemometrics to characterize the presence of microplastics in corn flour. The results demonstrated that O-PTIR imaging can rapidly sense the presence of microplastics, but its data integrity and visualization were limited. By decomposing the image, FTIR and Raman acquired a more integral distribution. Wherein, microplastics were well depicted by Raman imaging coupled with independent component analysis. Moreover, O-PTIR imaging can quickly detect contaminants at low concentrations but with a low detection rate. Raman imaging underperformed in low-concentration samples but provided a better visualization in mid-concentration samples. Overall, the results confirmed that the visual detection of microplastics in powdered food can be realized by molecular spectral imaging coupled with data mining, which can provide a reference for the detection of microplastics in other foods.

Sensing soluble molecules through SERS substrates in one-step procedure: unrevealing the Meiji woodblock printing materials

Ultrasensitive SERS substrates allowed us to detect complex mixtures of coloring components from Meiji Japanese woodblock prints (1868–1912). In museum settings, compositional analyses have limitations due to restrictions to sampling advised by conservators and curators for the adequate preservation of the objects. An additional layer of complexity is brought by the high heterogeneity of heritage materials, usually not resolved with commercial portable instruments. High-performance instruments for in situ analyses are seldom available in museums. Furthermore, the chambers of most instruments for morphological or chemical characterization accommodate small samples rather than large or medium-sized objects. The innovative sampling strategy herein proposed comprises the gentle touch-dry removal of small coloring molecules weakly bound to the surface of heritage objects, transferred through a silicone sampler to planar SERS substrates with selected solvents in a one-step procedure. The analytical protocol reduces the amount of sample necessary for reliable identification of color components down to nanograms. The selectivity of the solvents combined with the geometry of the planar SERS sensing devices produces reliable signals for molecular identification, with no need for incision or wetting of the printed material. Further, 3D Raman imaging allowed us to reach an unprecedented degree of molecular discrimination, advancing previously available minimally-invasive instrumental methods used in heritage science research. The validation with historical inks from Meiji woodblock prints led to the identification of soluble synthetic azo β-naphthols, barium sulfonic lakes, purple anilines, Prussian blue, glass arsenic sulfides and other traditional coloring media.

Graphene Oxide-Carbon Nanotube (GO-CNT) Hybrid Mixed Matrix Membrane for Pervaporative Dehydration of Ethanol.

The pervaporation process is an energy-conservative and environmentally sustainable way for dehydration studies. It efficiently separates close boiling point and azeotrope mixtures unlike the distillation process. The separation of ethanol and water is challenging as ethanol and water form an azeotrope at 95.6 wt.% of ethanol. In the last few decades, various polymers have been used as candidates in membrane preparation for pervaporation (PV) application, which are currently used in the preparation of mixed matrix membranes (MMMs) for ethanol recovery and ethanol dehydration but have not been able to achieve an enhanced performance both in terms of flux and selectivity. Composite membranes comprising of poly (vinyl alcohol) (PVA) incorporated with carboxylated carbon nanotubes (CNT-COOH), graphene oxide (GO) and GO-CNT-COOH mixtures were fabricated for the dehydration of ethanol by pervaporation (PV). The membranes were characterized with Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), Raman spectroscopy, Raman imaging, contact angle measurement, and water sorption to determine the effects of various nanocarbons on the intermolecular interactions, surface hydrophilicity, and degrees of swelling. The effects of feed water concentration and temperature on the dehydration performance were investigated. The incorporation of nanocarbons led to an increase in the permeation flux and separation factor. At a feed water concentration of 10 wt.%, a permeation flux of 0.87 kg/m2.h and a separation factor of 523 were achieved at 23 °C using a PVA-GO-CNT-COOH hybrid membrane.

Leading–Edge Portable Biosensors and Biomarkers Development for Raman Biospectroscopy and Imaging in Cancer Diagnosis

Raman spectroscopy is an important method for identifying molecules, which is widely used in determining the chemical and structural characteristics of various substances. Many materials have a special Raman spectrum, so that this phenomenon has turned the Raman device into an efficient tool for studying the structural and chemical properties of molecules. Since it is possible to obtain detailed information about the chemical and structural characteristics of biological compounds from Raman spectroscopy, the use of this method is rapidly expanding in the field of life sciences, especially in biological and medical studies. There is no need for special, time–consuming and expensive preparations in the study of materials with the help of a Raman device. In the protein Raman spectrum, distinct bands arise from the vibrational states of the peptide backbone and amino acid side chains. Therefore, based on the position and intensity of the protein's Raman spectrum, it is possible to obtain valuable information about its second, third, and fourth structures. Also, the Raman spectrum of the protein contains information about the orientation and surrounding environment of the amino acid side chains. The correct formation of the disulfide bond in the protein structure can also be studied with the help of the Raman device. In general, the Raman spectrum of proteins contains multiple discrete bands that represent the vibrational states of the molecule and is used as a selective fingerprint to accurately determine the three–dimensional structure of proteins, intramolecular dynamics, and intermolecular interactions.

CBMS-5 STEAROYL-COA DESATURASE INHIBITOR INDUCES APOPTOSIS VIA ENHANCING LIPOLYSIS IN IDH MUTANT GLIOMA

Abstract Background Little is known about the antineoplastic effect and the mechanism of Stearoyl-CoA desaturase (SCD) inhibitor which catalyzes the biosynthesis of monounsaturated fatty acids (MUFA). Mutant isocitrate dehydrogenase (IDH) catalyzes the NADPH-mediated reduction of α-ketoglutarate (αKG) to 2-hydroxyglutarate (2HG) and causes metabolic reprograming of lipid. In this study, to develop a feasible drug for IDH mutant glioma, we have investigated the changes of the lipid distribution and the mechanism of antineoplastic effect of SCD inhibition in IDH mutant glioma. Materials and Methods We prepared genetically engineered glioma cell lines (U251 wild type: U251WT and U251 IDH mutant: U251mut) and patient derived cell lines (TS603 and GSC923). Lipid metabolic analysis was conducted by using Raman imaging spectroscopy and LC-MS, and functional analysis for the role of SCD expression in IDH mutant glioma was investigated by RNA sequence and Western-blotting. Results: In LC-MS analysis of the extracted Endoplasmic Reticulum, MUFAs were distributed significantly higher in IDH mutant than wild type. SCD expression was increased in IDH mutant compared to wild type due to 2HG-mediated upregulation of SCD. Therefore, IDH mutant in which SCD expression level was high indicated high sensitivity to SCD inhibitor, and apoptosis was highly induced in IDH mutant compared to wild type. RNA sequencing was performed in U251mut treated with SCD inhibitor compared to U251mut treated with DMSO, and lipid droplet metabolism-associated RNA expression was significantly changed in U251mut treated with SCD inhibitor. We checked lipid droplet in U251mut with presence or absence of SCD inhibitor, and lipolysis was induced by SCD inhibitor treatment, suggesting that SCD inhibition is associated with the apoptosis in IDH mutant via enhanced lipolysis mechanism. Conclusions 2HG produced in IDH mutant glioma directly induces SCD expression and enhances sensitivity to SCD inhibitor, which suggests that SCD inhibitor is an IDH mutant glioma-specific treatment strategy.

Enhanced extraction assisted by pressure and ultrasound for targeting RG-I enriched pectin from citrus peel wastes: A mechanistic study

The rhamnogalacturonan I (RG-I) region of pectin shows health benefits and novel gel applications. Commercial pectin is extracted from citrus peel in most instances, whereas they are homogalacturonan (HG)-dominated productions and the methods to extract pectin targeting RG-I are limited. To take full advantage of citrus wastes and upgrading this pectin resources, a new extraction method based on a diluted NaOH assisted by a combination of ultrasound (US) and pressure, namely manosonication (MS), was established for RG-I enriched pectin extraction. MS significantly enhanced the pectin yield (21.47 ± 0.11%) while reducing the use of NaOH reagents (50 mmol/L) and processing time (50 min). Structurally, the MS (300 kPa) resulting products achieved nearly a 2-fold greater RG-I content (58.61 mol%) than that of commercial pectin (30.12 mol%). Moreover, for the investigation of the extraction mechanism, external pressure enhanced the cavitation effect, as the calorimetric intensity increased from 1.28 W/mL (100 kPa) to 3.3 W/mL (350 kPa). A sufficient ultrasonic mechanical action allowed for obtaining RG-I enriched products with large molecular weight (9.506×10 4 –2.813 × 10 5 ) and low degree of methoxylation. Transmission electron microscopy (TEM) and scanning electron microscopies (SEM) verified the increased disintegration of the cell wall tissue by MS. Raman imaging and immunofluorescence labeling suggested the synergistic effect of pressure and ultrasound on enhancing the yields and RG-I content. This new method provided alternations in functional polysaccharides extraction, and the yield and structure of citrus RG-I enriched pectin strongly indicates the potentials of MS in other RG-I rich vegetables applications. • Chemical compositions of extracted pectin between different methods were compared. • Manosonication extraction improved pectin yield and RG-I region content. • External pressure enhanced the ultrasonic cavitation effect. • Mechanical action was the dominating factor in cellulose network destruction. • Immunolabeling suggested the synergistic extraction mechanism on RG-I dissolution.

Visualization of wood cell structure during cellulose purification via high resolution X-ray CT and spectroscopy

Wood is a heterogeneous material with multiple scales. Revealing the three-dimensional structure of wood tissue in multiple dimensions works as a prerequisite for the reorganization, modification and high-value utilization of wood. By adopting high resolution X-ray micro computed tomography (XμCT), the three-dimensional structural changes during cellulose purification were reconstructed. In the meantime, the changing process in the chemical composition of wood cell wall was demonstrated in situ using laser Raman spectroscopy imaging technology. Moreover, cellular changes on a two-dimensional scale were observed by ordinary optical, fluorescence, and polarizing microscopes respectively. XμCT results indicated that the disruption of the cell structure of chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) by purification treatment started between the diameter walls of the tracheids, while that of the poplar (Populus sp.) cell structure started between the vessels or between the vessels and the wood rays. Such kind of disruption in cell structure was more pronounced after the hemicellulose was removed, with adjacent cells scattered and deformed. In the first step of matrix removal, the cell wall got thinner primarily out of lignin removal, while in the process of hemicellulose removal, the cell wall swelled with the lye. The Raman images illustrated that the distribution of purified cellulose in the cell wall was related to the degree of cell disruption. In undeformed cell walls, the cellulose was evenly distributed, whereas in shrunken and deformed cell walls, it was unevenly scattered.

Raman Spectroscopy Reveals Phase Separation in Imine-Based Covalent Adaptable Networks.

The introduction of dynamic covalent bonds into cross-linked polymer networks enables the development of strong and tough materials that can still be recycled or repurposed in a sustainable manner. To achieve the full potential of these covalent adaptable networks (CANs), it is essential to understand-and control-the underlying chemistry and physics of the dynamic covalent bonds that undergo bond exchange reactions in the network. In particular, understanding the structure of the network architecture that is assembled dynamically in a CAN is crucial, as exchange processes within this network will dictate the dynamic-mechanical material properties. In this context, the introduction of phase separation in different network hierarchies has been proposed as a useful handle to control or improve the material properties of CANs. Here we report-for the first time-how Raman confocal microscopy can be used to visualize phase separation in imine-based CANs on the scale of several micrometers. Independently, atomic force microscopy (AFM) confirmed the phase-separated domains inside the polymer. Remarkably, the materials were found to undergo phase separation despite being built up from miscible monomers, which arguably should yield homogeneous materials. We found that the phase separation not only affected the appearance of the material but-more notably-also had a noticeable effect on the thermal-mechanical properties of the material: CANs (of equal aliphatic/aromatic monomer composition) that displayed phase separation had both a higher crossover temperature (T cross, where tan(δ) = 1, and where the material transits from a rubbery to a viscous state) and an increased elastic modulus (G'). By modifying the CAN architecture, we were able to either suppress or enhance the phase separation, and we propose that the phase separation is driven by favorable π-π interactions between the aromatic components. Our work further shows the importance of phase separation in CANs, including in networks built from miscible components, and provides a handle to control the dynamic material properties. Moreover, our work underlines the suitability of Raman imaging as a method to visualize phase separation in CANs.

Exposing intracellular molecular changes during the differentiation of human-induced pluripotent stem cells into erythropoietin-producing cells using Raman spectroscopy and imaging

The objective of this study was to explore intracellular molecular changes during the differentiation of human-induced pluripotent stem cells (iPSCs) into erythropoietin (EPO)-producing cells using Raman spectroscopy and imaging. Raman imaging data of fixed cells at four stages of cell differentiation were analyzed by a partial least squares (PLS) regression model, and the variations in the intracellular molecular compositions with cell differentiation were investigated. As a result, three biomarkers characterizing the cell phases were identified: dimethyl sulfoxide (DMSO), fatty acids with a low grade of unsaturation, and glycoproteins. The uptake of DMSO by EPO-producing cells, which was added into a culture medium as an inducer for cell differentiation, was detected, and the increase in unsaturated fatty acid concentrations was revealed that lipid metabolism changed over the course of cell differentiation. The decrease in the glycoprotein concentration after the cell phase during which iPSCs differentiated into EPO-producing cells was also made clear. Raman imaging successfully visualized chemical images of these three biomarkers in two dimensions, where the biomarker concentrations independently varied during cell differentiation. These results demonstrated the application potential of the proposed method to regenerative medicine for monitoring cell differentiation and discriminating cell maturation in situ at the molecular level.

Decoding the role of cytochrome c in metabolism of human spermatozoa by Raman imaging.

The normal functioning of sperm cells requires cytochrome c in the redox balanced forms: reduced and oxidized. The oxidized form of cytochrome c is localized in the mitochondrial intermembrane space and is a part of the electron transport chain. This ensures that electron shuttling between the complex III, cytochrome c, and complex IV can occur leading to controlled effective oxidative phosphorylation (respiration) and ATP production needed for most steps in spermatozoal maturation, motility, hyperactivation and fertilization. We studied the biochemical composition of specific organelles in sperm cells by Raman imaging. The structures of the head consisting of the nucleus and acrosome, the midpiece representing mitochondria, and the tail characterized by the sperm axoneme surrounded by outer dense fiber and covered by the membrane were measured. Metabolic biochemical analysis of mitochondria, head and tail of sperm cells, and seminal plasma by using Raman imaging combined with chemometric classification method of Cluster Analysis has been obtained. Our results show that cytochrome c, which is a key protein that is needed to maintain life (respiration) and cell death (apoptosis), is located in sperm mitochondria in the oxidized or reduced form of the heme group. This work demonstrated that an application of Raman micro-spectroscopy can be extended to monitoring the redox state of mitochondrial cytochrome c in sperm cells.

Accelerated transformation of plastic furniture into microplastics and nanoplastics by fire

Numerous plastic items are known to gradually degrade and release microplastics and nanoplastics under certain conditions, which can be significantly accelerated by fire combustion. Unfortunately there is a limited knowledge about this burning process because the characterisation on microplastics and nanoplastics is still a challenge. In this study, an outdoor plastic chair is subjected to a combustion process, the change in the surface functional groups (due to different degree of burning) and the release of microplastics and nanoplastics are investigated. During the combustion process, the plastic is molten, burned and deposited on solid surfaces including concrete, stone and glass. Scanning electron microscopy (SEM) results show that the peeling off the deposited plastic generates a large number of fragments. Through Raman imaging, these fragments are characterised as polypropylene (PP) microplastics and nanoplastics due to appearance of characteristic peaks. To further increase the sensitivity, several algorithms are tested and optimised, including logic-based, non-supervised principal component analysis (PCA)-based, algebra-based and their hybrids (to intentionally correct the non-supervised PCA) to enable the effective extraction of the key information towards plastics characterisation, particularly by distinguishing the signal from the background noise towards the visualisation of the different degrees of burning. Based on the findings from Raman imaging and SEM, it is estimated that tens of microplastics and nanoplastics are created per μm2. Overall Raman imaging can be a suitable approach to characterise the microplastics and nanoplastics in a complex background, such as the fire-burned plastic items.

Fast Compressive Raman Imaging of Polymorph Molecules and Excipients in Pharmaceutical Tablets.

We implement a near-infrared (NIR) version of compressive Raman imaging that incorporates a digital micromirror device (DMD) and a single-pixel detector for fast chemometric analysis and microscopic imaging. The NIR compressive Raman system is successfully used to detect and image active pharmaceutical ingredients exhibiting polymorphism within compact pharmaceutical tablets. We report the chemical imaging of a mixture of two clopidogrel polymorphs and three excipients in solid tablets with a pixel dwell time of 2.5 ms (0.5 ms per species). These results open the road to fast pharmaceutical tablet quality control imaging using compressive Raman technology.