Time-of-flight Secondary Ion Mass Spectrometry Imaging Research Articles

ToF-SIMS 3D imaging unveils important insights on the cellular microenvironment during biomineralization of gold nanostructures

The biomolecular imaging of cell-nanoparticle (NP) interactions using time-of-flight secondary ion mass spectrometry (ToF-SIMS) represents an evolving tool in nanotoxicology. In this study we present the three dimensional (3D) distribution of nanomaterials within biomolecular agglomerates using ToF-SIMS imaging. This novel approach was used to model the resistance of human alveolar A549 cells against gold (Au) ion toxicity through intra- and extracellular biomineralization. At low Au concentrations (≤1 mM HAuCl4) 3D-ToF-SIMS imaging reveals a homogenous intracellular distribution of Au-NPs in combination with polydisperse spherical NPs biomineralized in different layers on the cell surface. However, at higher precursor concentrations (≥2 mM) supplemented with biogenic spherical NPs as seeds, cells start to biosynthesize partially embedded long aspect ratio fiber-like Au nanostructures. Most interestingly, A549 cells seem to be able to sense the enhanced Au concentration. They change the chemical composition of the extracellular NP agglomerates from threonine-O-3-phosphate aureate to an arginine-Au(I)-imine. Furthermore they adopt the extracellular mineralization process from spheres to irregular structures to nanoribbons in a dose-dependent manner with increasing Au concentrations. The results achieved regarding size, shape and chemical specificity were cross checked by SEM-EDX and single particle (sp-)ICP-MS. Our findings demonstrate the potential of ToF-SIMS 3D imaging to better understand cell-NP interactions and their impact in nanotoxicology.

Metabolic fingerprinting of cell types in mouse skeletal muscle by combining TOF-SIMS with immunofluorescence staining.

Skeletal muscle tissue is composed of various muscle cell types which differ in physiological functions. Changes in cell type composition of skeletal muscle are associated with the development of metabolic diseases. Skeletal muscle cell types are currently distinguished by immunofluorescence (IF) staining based on myosin heavy chain (MHC) isoform difference. However, it remains a challenge to provide metabolic fingerprints of different muscle cell types by IF staining. Therefore, in this study, we proposed a method to examine metabolite distribution within different cell types by time-of-flight secondary ion mass spectrometry (TOF-SIMS) with high spatial resolution. Skeletal muscle samples from C57/BL6 mice were obtained by slicing. Cell types in TOF-SIMS images were labelled corresponding to IF images from the same region of serially cut sections. Mass spectra corresponding to individual muscle cells were extracted to compare metabolic fingerprints among cell types. Skeletal muscle cells were classified into two clusters based on the mass spectra of individual cells. Unsaturated diacylglycerol (DG) and fatty acid (FA) species were found to be distributed in a cell-type dependent manner. Moreover, relative quantification showed that the content of unsaturated DGs, oleic acid and linoleic acid was higher in type I and type IIA cells than in type IIB cells. TOF-SIMS in combination with IF enables us to directly visualize metabolite distribution in different cell types, to find potential biomarkers for cell type classification. TOF-SIMS imaging coupled with IF staining has been proved to be a promising tool for metabolic fingerprinting of different skeletal muscle cell types.

Visualizing ToF-SIMS Hyperspectral Imaging Data Using Color-Tagged Toroidal Self-Organizing Maps.

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is a powerful surface characterization technique capable of producing high spatial resolution hyperspectral images, in which each pixel comprises an entire mass spectrum. Such images can provide insight into the chemical composition across a surface. However, issues arise due to the size and complexity of the data produced. Data are particularly complicated for biological samples, primarily due to overlapping spectra produced by similar components. The traditional approach of selecting individual ion peaks as representative of particular components is insufficient for such complex data sets. Multivariate analysis (MVA) can help to overcome this significant hurdle. We demonstrate that Kohonen self-organizing maps (SOMs) with a toroidal topology can be used to analyze a ToF-SIMS hyperspectral imaging data set and identify spectral similarities between pixels. We present a method for color-tagging the toroidal SOM output, which reduces the entire data set to a single RGB image in which similar pixels-based on their associated mass spectra-are assigned a similar color. This method was exemplified using a ToF-SIMS image of dried large multilamellar vesicles (LMVs), loaded with the antibiotic cefditoren pivoxil (CP). We successfully identified CP-loaded and empty LMVs without the need for any prior knowledge of the sample, despite their highly similar spectra. We also identified which specific ion peaks were most important in differentiating the two LMV populations. This approach is entirely unsupervised and requires minimal experimenter input. It was developed with the aim of providing a user-friendly yet sophisticated workflow for understanding complex biological samples using ToF-SIMS images.

Improved ion imaging of slowly dried neurons and skin cells by graphene cover in time-of-flight secondary ion mass spectrometry.

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is a powerful tool to obtain both chemical information and spatial distribution of specific molecules of interest on a specimen surface. However, since the focused ion beam requires ultrahigh vacuum conditions for desorption and ionization of analytes, proper specimen preparation, such as drying, freeze-drying, and frozen dehydration, is required for ToF-SIMS analysis. In particular, biological specimens with high moisture content generally have a problem of specimen deformation during the normal drying process for a vacuum environment. In this study, the authors propose a cellular specimen preparation method to improve the ion imaging of cells by reducing the deformation of specimens in ToF-SIMS analysis. When the cells on the slide substrate are completely covered with single-layer graphene, the ToF-SIMS imaging is improved by reduced cell deformation due to slow drying. In addition, the graphene encapsulation also induces a reduction in the yield of secondary ions, thereby suppressing the background ion spectra generated by the unwanted organic residues on the substrate, resulting in the improvement of ToF-SIMS imaging. The authors also found that adding plasma treatment to this sample preparation can further improve ion imaging of cells. After cell dehydration is completed, the covered graphene layer can be peeled off by air-plasma treatment and the unwanted organic residues on the substrate can be removed due to plasma cleaning, thereby much improving ion imaging of cells.

3D Imaging of Nanoparticles in an Inorganic Matrix Using TOF-SIMS Validated with STEM and EDX.

Imaging nano-objects in complex systems such as nanocomposites using time-of-flight secondary ion mass spectrometry (TOF-SIMS) is a challenging task. Due to a very small amount of the material and a matrix effect, the number of generated secondary ions can be insufficient to represent a 3D elemental distribution despite being detected in a mass spectrum. Therefore, a model sample consisting of a ZrCuAg matrix with embedded Al nanoparticles is designed. A high mass difference between the light Al and heavy matrix components limits mass interference. The chemical structure measurements using a pulsed 60 keV Bi32+ beam or a continuous 30 keV Ga+ beam reveals distinct Al signal segregation. This can indicate a spatially resolved detection of single 10s of nanometer large particles and/or their agglomerates for the first time. However, TOF-SIMS images of 50 nm or smaller objects do not necessarily represent their exact size and shape but can rather be their convolutions with the primary ion beam shape. Therefore, the size of nanoparticles (25-64 nm) was measured using scanning transmission electron microscopy. Our studies prove the capability of TOF-SIMS to image chemical structure of nanohybrids which is expected to help building new functional materials and optimize their properties.

From the surface to the bulk: A comparison of methods for the microanalysis of an immiscible polymer blend

In this study, the morphology of an immiscible polymer blend system at various regions of interests was analyzed using different microanalytical methods with varying surface sensitivities. As a model immiscible polymer blend, a HDPE/PP (80/20 wt%) polymer film was used. The blend film was subjected to polarized light microscopy (PLM), scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM) and time of flight secondary ion mass spectrometry (ToF-SIMS). The obtained results were compared regarding the sensitivities, informational values and overall applicability of the analytical methods. It was evaluated which methods can be applied for a fast analysis of the morphology (surface and bulk) of the immiscible polymer blend with low preparation efforts, which is especially important for the analysis of new materials, for example materials manufactured via recycling. It was demonstrated that PLM, as well as SEM on wet-etched material, provide sufficient information to evaluate the bulk morphology. Additionally, the presented study shows the advantage of applying ToF-SIMS imaging for the characterization of the surface of immiscible polymer blend. As expected, the domain distribution of HDPE and PP varied between the bulk and the surface of the films. The proposed procedures can be taken as a guideline for other investigations concerning the morphology of heterogeneous polyolefin systems.

A Comparison of Electrode Surface Films Formed with Different Oxide Cathodes for Lithium-Ion Batteries

High-nickel, Li-rich, and high-voltage spinel electrodes are lithium-ion battery cathodes commonly considered as candidates for near-term commercialization. Each of these cathode materials can offer higher energy densities than conventional lithium cobalt oxide cathode materials, at least during initial cycles. High-Ni cathodes of the form LiNiaMnbCo1-a-bO2 have the same layered structure as current commercial cathodes with alternating transition metal and lithium layers between oxide slabs. With increasing Ni content, High-Ni cathode materials generally can provide higher discharge capacities, reaching upwards of 240 mAh g-1. Li-rich electrode materials (Li1+xMO) have a similar layered structure as High-Ni materials but include excess Li+ in the transition metal layer that can be accessed for much higher discharge capacities, even exceeding 300 mAh g-1. High-voltage spinel electrodes of the form LiMnaNi2-aO4 operate at high voltages providing high energy densities, though at much lower discharge capacities, ca. 140 mAh g-1. While all three of these electrode classes offer exciting possibilities for future lithium-ion battery development, they all suffer from the inherent instability of their surface reactivities. High-Ni cathodes suffer from high surface reactivity and a slow growth of the cubic rocksalt phase throughout cycling that impedes lithium intercalation. The activation of Li-rich electrodes involves a complex surface passivation involving the evolution of molecular oxygen and the formation of a spinel-like phase. High-voltage spinel electrodes operate outside the electrolyte stability region, so also suffer from rapid oxidative breakdown of electrolyte components and impedance growth. Aside from the cathode interphase, the solid electrolyte interphase formed at the anode can be affected by the surface chemistry of these various cathodes; for instance, transition-metal ions may dissolve from the cathode, migrate to the anode side where they are reduced, and act as a catalyst for further electrolyte reduction. This presentation describes our recent characterization of cathode and anode surface electrolyte interphases from cells with High-Ni, high-voltage spinel, and Li-rich electrodes. Half cells vs. lithium anodes, as well as full cells with up to 1,500 cycles are presented. For these studies, we employ time of flight – secondary ion mass spectrometry (TOF-SIMS), a powerful characterization technique pioneered by our group for characterization of battery materials. TOF-SIMS provides sub-nanometer depth resolution of specific chemical fragments over micron-sized image areas that can also be used in a depth profiling method, through layer-by-layer ablation of surface species to form a 3D image (Figure 1). TOF-SIMS is used in conjunction with standard characterization techniques, such as X-ray photoelectron spectroscopy (XPS), galvanostatic cycling data, and electrochemical impedance spectroscopy. Figure 1: A 3D TOF-SIMS image of cycled high-Ni cathode particles with transition metals indicated in green, as well as decomposed organics (C-, CH-, CH2 - ) indicated in red. Figure 1

Influence of post-treatment time of trivalent chromium protection coating on aluminium alloy 2024-T3 on improved corrosion resistance

Low corrosion protection performances of Trivalent Chromium Process (TCP) coatings with reference to Chromium Conversion Coatings (CCC) deposited on aluminium alloys can be overcome by application of post-treatment processes. This work shows the effect of post-treatment bath (containing hydrogen peroxide and lanthanum salt) on the chemical composition, structure and the corrosion performances of TCP coating deposited on AA 2024-T3 aluminium alloy. Different times of post-treatment bath were applied on the TCP coating and the samples were analyzed by Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), X-ray Photoelectron Spectroscopy (XPS) and Glow Discharge-Optical Emission Spectrometry (GD-OES). The ToF-SIMS and GD-OES depth profiles show that the post-treatment time has no influence on the thickness of the TCP coating and on its bi-layered structure. It is composed of an outer layer, rich in zirconium and chromium oxides and an inner layer rich in aluminium oxides and oxy-fluorides. 3D ToF-SIMS images reveal an enrichment of Cr and Zr-like species over the surface of intermetallic particles with reference to alloy matrix, whereas a homogenous distribution of La is observed. The analysis of in-depth distribution shows that La is present principally in the outer part of the TCP coating. The La concentration increases with increasing post-treatment time. The effect of post-treatment time on protection was evaluated by Electrochemical Impedance Spectroscopy (EIS) and Linear Sweep Voltammetry (LSV) in a 0.001 M NaCl + 0.1 M Na2SO4 electrolyte. The increased post-treatment time enhances the cathodic inhibition against oxygen reduction. The post-treatment provides improved coating homogeneity and sealing properties.

TOF-SIMS study of morphology and chemical composition of wustite-based precursor and iron catalyst for ammonia synthesis

This study focuses on the application of time-of-flight secondary ion mass spectrometry (TOF-SIMS) for analysis of the morphology and chemical composition of a wustite-based precursor and iron catalyst for ammonia synthesis. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used as supplementary methods. TOF-SIMS imaging was capable of visualizing the micrometer-scale spatial distribution of elements on the surface of the catalyst precursor, which was composed of wustite crystallites separated by spaces, with high concentrations of K, Al and Ca used as promoters. Moreover, aluminum and calcium were detected in the wustite crystallites. Potassium, despite having a vanishingly low concentration in wustite phase, was able effectively to wet the wustite surfaces upon annealing at 350 °C.The potassium layer that formed on the surface of the wustite precursor had a different composition than that on the surface of the iron nanocrystallites of the iron catalyst. The most important finding concerns the composition of the surface of the iron catalyst.TOF-SIMS analysis showed a layer containing oxygen in the subsurface region of the iron catalyst obtained from the wustite-based precursor. This structure on the surface of the iron catalyst enabled the formation of active sites for the adsorption of nitrogen on iron atoms during ammonia synthesis.

3D Molecular ToF-SIMS Imaging of Artificial Lipid Membranes Using a Discriminant Analysis-Based Algorithm.

Artificial lipid membranes play a growing role in technical applications such as biosensors in pharmacological research and as model systems in the investigation of biological lipid films. In the standard procedure for displaying the distribution of membrane components, fluorescence microscopy, the fluorophores used can influence the distribution of the components and usually not all substances can be displayed at the same time. The discriminant analysis-based algorithm used in combination with scanning time-of-flight secondary ion mass spectrometry (ToF-SIMS) enables marker-free, quantitative, simultaneous recording of all membrane components. These data are used for reconstruction of distribution patterns. In the model system used for this survey, a tear fluid lipid layer, the distribution patterns of all lipids correlate well in calculated ToF-SIMS images and epi-fluorescence microscopic images. All epi-fluorescence microscopically viewable structures are visible when using both positive and negative secondary ions and can be reproduced with high lateral resolution in the submicrometer range despite the very low signal intensity and a very low signal-to-noise ratio. In addition, three-dimensional images can be obtained with a subnanometer depth resolution. Furthermore, structures and the distribution of substances that cannot be made visible by epi-fluorescence microscopy can be displayed. This enables new insights that cannot be gained by epi-fluorescence microscopy alone.

Mass Spectrometry Imaging Suggests That Cisplatin Affects Exocytotic Release by Alteration of Cell Membrane Lipids.

We used time-of-flight secondary ion mass spectrometry (TOF-SIMS) imaging to investigate the effect of cisplatin, the first member of the platinum-based anticancer drugs, on the membrane lipid composition of model cells to see if lipid changes might be involved in the changes in exocytosis observed. Platinum-based anticancer drugs have been reported to affect neurotransmitter release resulting in what is called the "chemobrain"; however, the mechanism for the influence is not yet understood. TOF-SIMS imaging was carried out using a high energy 40 keV (CO2)6000+ gas cluster ion beam with improved sensitivity for intact lipids in biological samples. Principal components analysis showed that cisplatin treatment of PC12 cells significantly affects the abundance of different lipids and their derivatives, particularly phosphatidylcholine and cholesterol, which are diminished. Treatment of cells with 2 μM and 100 μM cisplatin showed similar effects on induced lipid changes. Lipid content alterations caused by cisplatin treatment at the cell surface are associated with the molecular and bimolecular signaling pathways of cisplatin-induced apoptosis of cells. We suggest that lipid alterations measured by TOF-SIMS are involved, at least in part, in the regulation of exocytosis by cisplatin.

Radial distribution of wood extractives in European larch Larix decidua by TOF-SIMS imaging

Wood extractives in the xylem of European larch Larix decidua were mapped by time-of-flight secondary ion mass spectrometry (TOF-SIMS) imaging, which allows the radial distribution of both mineral and lipophilic extractives in the xylem to be scrutinized with high spatial resolution for the first time. Results show that all the components are inhomogeneously distributed across the annual ring. Mineral nutrients including Na+, K+, Ca+, and Cl− ions exhibit no preferential localization between earlywood and latewood, whereas PO3− ion is exclusively present in the ray cells, indicating it may be related to acid phosphatase. Lipophilic extractives were found to be more abundant in the inner secondary xylem. Ion images with 400 nm spatial resolution reveal that fatty acids, triglycerides and phytosterols are co-localized principally in the earlywood within the first annual ring. Resin acids prove to be the main components in the resin canal of the secondary xylem and are distributed in the outer of it.

Combined ToF-SIMS and AFM protocol for accurate 3D chemical analysis and data visualization

In dual-beam time-of-flight secondary ion mass spectrometry (ToF-SIMS) depth profiling, a succession of two-dimensional chemical images is acquired. These can be used to generate a three-dimensional (3D) visualization of the sputtered volume. However, standard reconstruction methods do not take into account the initial sample topography or lateral variations in sputter rates. For heterogeneous, nonplanar samples, the resulting 3D chemical visualization may be distorted. To address this issue, ToF-SIMS analysis was combined with atomic force microscopy (AFM). This correlation provides the missing sample topography and allows the calculation of sputter rates. The protocol to achieve an accurate 3D ToF-SIMS reconstruction comprises AFM topographical images, crater depth measurements, and sequences of ToF-SIMS images, all acquired on the same area of the sample. As a result, a 3D overlay between AFM and ToF-SIMS images at each interface can be made. In addition, the morphological information can be used to map the local sputter rate. Finally, the authors developed an accurate data processing for the correction of the 3D ToF-SIMS reconstruction within the rendered volume defined by successive AFM imaging.

Compositional study of a corrosion protective layer formed by leachable lithium salts in a coating defect on AA2024-T3 aluminium alloys

Organic primer coatings loaded with environmentally harmful Cr(VI) corrosion inhibitive pigments still play an important role in corrosion protection of aluminium alloys for the aerospace industry. A potential “green” alternative coating system has recently been developed, loaded with lithium salt corrosion inhibitors. Under exposure to neutral salt spray, lithium salts leach from the organic coating into coating defects to induce the formation of a corrosion protective layer. In this work the composition and growth of this protective layer is investigated by time-of-flight secondary ion mass spectrometry (ToF-SIMS). ToF-SIMS imaging is successfully applied to monitor the lateral spread of leaching lithium salts in artificial 1-mm-wide scribes. The chemical composition of the protective layer is revealed by comparing the mass spectra of salt spray exposed scribe areas to the mass spectra of pseudoboehmite and aluminium-lithium layered double hydroxide reference samples. The insights obtained in this work have led to a thorough understanding of the formation mechanism of the protective layer and provide local chemical and structural information which can be linked to corrosion protection behavior.

A Time-of-Flight Secondary Ion Mass Spectrometry/Multivariate Analysis (ToF-SIMS/MVA) Approach To Identify Phase Segregation in Blends of Incompatible but Extremely Similar Resins.

This work presents a data analysis extension to a well-established methodology for the assessment of organic coatings using imaging time-of-flight secondary ion mass spectrometry (ToF-SIMS). Such an approach produced results that can be analyzed using a multivariate analysis (MVA) procedure that performs the simultaneous processing of spatially and chemically related datasets. The coatings consist of two commercial resins that yield extremely similar spectra, and there are no peaks of sufficient intensity that are uniquely diagnostic of either material to provide an unambiguous identification of each. In order to resolve the problem, in addition to microtome-based sample preparation steps of tapers for the analysis through sample thickness, standard samples in cured and uncured conditions are introduced and measured in the same fashion as the specimens under investigation. The resulting ToF-SIMS imaging datasets have been processed using non-negative matrix factorization (NMF), which enabled identification of phase separation in the cured coatings.

Time-of-flight secondary ion mass spectrometry analyses of vancomycin.

As an antibiotic that prevents and treats infections caused by Gram-positive bacteria such as Staphylococcus aureus, vancomycin incorporated in a biodegradable polymer poly(lactide-co-glycolide) provides opportunities to construct controlled-release drug delivery systems. Developments associated with this promising system have been largely concentrated on areas of drug delivery kinetics and biodegradability. In order to provide surface analytical approaches to this important system, the authors demonstrate applicability of time-of-flight secondary ion mass spectrometry (TOF-SIMS) in three-dimensional molecular imaging for a model system consisting of alternating layers of ploy(lactide-co-glycolide) and vancomycin. TOF-SIMS imaging clarified that the two chemicals can undergo phase separation when dimethyl sulfoxide is used as the solvent. The authors identified two diagnostic ions that are abundant and structural moieties of vancomycin. The results on TOF-SIMS imaging and depth profiling vancomycin provide useful information for further applications of TOF-SIMS in the development of antibiotic drug delivery systems involving the use of vancomycin.

Secondary ion mass spectrometry imaging and multivariate data analysis reveal co-aggregation patterns of Populus trichocarpa leaf surface compounds on a micrometer scale.

Spatially resolved analysis of a multitude of compound classes has become feasible with the rapid advancement in mass spectrometry imaging strategies. In this study, we present a protocol that combines high lateral resolution time-of-flight secondary ion mass spectrometry (TOF-SIMS) imaging with a multivariate data analysis (MVA) approach to probe the complex leaf surface chemistry of Populus trichocarpa. Here, epicuticular waxes (EWs) found on the adaxial leaf surface of P. trichocarpa were blotted on silicon wafers and imaged using TOF-SIMS at 10μm and 1μm lateral resolution. Intense M+● and M-● molecular ions were clearly visible, which made it possible to resolve the individual compound classes present in EWs. Series of long-chain aliphatic saturated alcohols (C21 -C30 ), hydrocarbons (C25 -C33 ) and wax esters (WEs; C44 -C48 ) were clearly observed. These data correlated with the 7 Li-chelation matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) analysis, which yielded mostly molecular adduct ions of the analyzed compounds. Subsequently, MVA was used to interrogate the TOF-SIMS dataset for identifying hidden patterns on the leaf's surface based on its chemical profile. After the application of principal component analysis (PCA), a small number of principal components (PCs) were found to be sufficient to explain maximum variance in the data. To further confirm the contributions from pure components, a five-factor multivariate curve resolution (MCR) model was applied. Two distinct patterns of small islets, here termed 'crystals', were apparent from the resulting score plots. Based on PCA and MCR results, the crystals were found to be formed by C23 or C29 alcohols. Other less obvious patterns observed in the PCs revealed that the adaxial leaf surface is coated with a relatively homogenous layer of alcohols, hydrocarbons and WEs. The ultra-high-resolution TOF-SIMS imaging combined with the MVA approach helped to highlight the diverse patterns underlying the leaf's surface. Currently, the methods available to analyze the surface chemistry of waxes in conjunction with the spatial information related to the distribution of compounds are limited. This study uses tools that may provide important biological insights into the composition of the wax layer, how this layer is repaired after mechanical damage or insect feeding, and which transport mechanisms are involved in deploying wax constituents to specific regions on the leaf surface.

ToF-SIMS study of differentiation of human bone-derived stromal cells: new insights into osteoporosis

Lipids have numerous important functions in the human body, as they form the cells' plasma membranes and play a key role in many disease states, presumably also in osteoporosis. Here, the fatty acid composition of the outer plasma membranes of cells differentiated into the osteogenic and adipogenic direction is studied with surface-sensitive time-of-flight secondary ion mass spectrometry (ToF-SIMS). For data evaluation, principal component analysis (PCA) is applied. Human (bone-derived) mesenchymal stromal cells (hMSCs) from an osteoporotic donor and a control donor are compared to reveal differences in the fatty acid composition of the membranes. The chemical information is correlated to staining and real-time quantitative polymerase chain reaction (rt-qPCR) results to provide insight into the gene expression of several differentiation markers on the RNA level. Adipogenic differentiation of hMSCs from a non-osteoporotic donor correlates with increased relative intensities of all fatty acids under investigation. After osteogenic differentiation of non-osteoporotic cells, the relative mass signal intensities of unsaturated fatty acids such as oleic and linoleic acids are increased. However, the osteoporotic cells show increased levels of palmitic acid in the plasma membrane after exposure to osteogenic differentiation conditions, which correlates to an immature differentiation state relative to non-osteoporotic osteogenic cells. This immature differentiation state is confirmed by increased early osteogenic differentiation factor Runx2 on RNA level and by less calcium mineralization spots seen in von Kossa staining and ToF-SIMS images. Graphical abstract Time-of-flight secondary ion mass spectrometry is applied to analyze the fatty acid composition of the outer plasma membranes of cells differentiated into the adipogenic and osteogenic direction. Cells from an osteoporotic and a control donor are compared to reveal differences due to differentiation and disease stage of the cells.

Fatty acids penetration into human skin ex vivo: A TOF-SIMS analysis approach.

Linoleic, oleic, palmitoleic, palmitic, and stearic fatty acids (FAs) are commonly used in dermatological formulations. They differ by their structure, presence in the skin, and mode of application in pharmaceuticals and cosmetics compounding. These FAs are also known as chemical penetration enhancers, but their mechanisms of penetration enhancement and effect on barrier characteristics of the skin require additional study. In this study, the authors conducted an ex vivo analysis of the distribution of lipid components in the epidermis and dermis of human skin after applying individual FAs. The goal was to elucidate possible mechanisms of penetration enhancement and FA effects on barrier characteristics of the skin. FA penetration studies were conducted ex vivo on human skin and time-of-flight secondary ion mass spectrometry (TOF-SIMS) bioimaging analysis was performed to visualize and analyze distribution of FAs in skin sections. The current study demonstrated that TOF-SIMS imaging was effective in visualizing the distribution of linoleic, oleic, palmitoleic, palmitic, and stearic acid in the human skin ex vivo after the skin penetration experiment of individual FAs. The integration of the obtained TOF-SIMS images allowed a semiquantitative comparison of the effects induced by individual FA applications on the human skin ex vivo. FAs showed varying abilities to penetrate the skin and disorder the FAs within the skin, based on their structures and physicochemical properties. Linoleic acid penetrated the skin and changed the distribution of all the analyzed FAs. Skin treatment with palmitoleic or oleic acid increased the amounts of singular FAs in the skin. Penetration of saturated FAs was low, but it increased the detected amounts of linoleic acid in both skin layers. The results indicate that application of FAs on the skin surface induce redistribution of native FAs not only in the stratum corneum layer of epidermis but also in the lipid content of full epidermis and dermis layers. The results indicate that topically applied pharmaceutical products should be evaluated for potential chemical penetration enhancement and lipid component redistribution effects during formulation.

Nanoscale imaging of alteration layers of corroded international simple glass particles using ToF-SIMS

Glass particles with dimensions typically ranging from tens to hundreds of microns are often used in glass corrosion research in order to accelerate testing. Two-dimensional and three-dimensional nanoscale imaging techniques are badly needed to characterize the alteration layers at the surfaces of these corroded glass particles. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) can provide a lateral resolution as low as ∼100nm, and, compared to other imaging techniques, is sensitive to elements lighter than carbon. In this work, we used ToF-SIMS to characterize the alteration layers of corroded international simple glass (ISG) particles. At most particle surfaces, inhomogeneous or no alteration layers were observed, indicating that the thickness of the alterations layers may be too thin to be observable by ToF-SIMS imaging. Relatively thick (e.g., 1–10µm) alteration layers were inhomogeneously distributed at a small portion of surfaces. More interestingly, some large-size (tens of microns) glass particles were fully altered. Above observations suggest that weak attachment and the defects on ISG particle surfaces play an important role in ISG glass corrosion.