3D and Multimodal X-Ray Microscopy Reveals the Impact of Voids in CIGS Solar Cells.

Small voids in the absorber layer of thin-film solar cells are generally suspected to impair photovoltaic performance. They have been studied on Cu(In,Ga)Se2 cells with conventional laboratory techniques, albeit limited to surface characterization and often affected by sample-preparation artifacts. Here, synchrotron imaging is performed on a fully operational as-deposited solar cell containing a few tens of voids. By measuring operando current and X-ray excited optical luminescence, the local electrical and optical performance in the proximity of the voids are estimated, and via ptychographic tomography, the depth in the absorber of the voids is quantified. Besides, the complex network of material-deficit structures between the absorber and the top electrode is highlighted. Despite certain local impairments, the massive presence of voids in the absorber suggests they only have a limited detrimental impact on performance.

Cadmium and Zn hyperaccumulation provide efficient constitutive defense against Turnip yellow mosaic virus infection in Noccaea caerulescens.

To understand the role of Zn and Cd in anti-viral defence, Zn/Cd hyperaccumulator Noccaea caerulescens plants grown with deficient (0.3 µM), replete (10 µM) and excess (100 µM) Zn2+ and Cd (10 µM Zn2+ + 1 µM Cd2+) were infected with Turnip yellow mosaic virus (TYMV). Gas exchange and chlorophyll fluorescence kinetics analyses demonstrated direct TYMV effects on photosynthetic light reactions but N. caerulescens was more resistant against TYMV than the previously studied non-hyperaccumulator N. ochroleucum. Virus abundance and photosynthesis inhibition were the lowest in the high Zn and Cd treatments. RNAseq analysis of 10 µM Zn2+ plants revealed TYMV-induced upregulation of Ca transporters, chloroplastic ZTP29 and defence genes, but none of those that are known to be strongly involved in hyperaccumulation. Synchrotron µ-XRF tomography, however, showed that Zn hyperaccumulation remained strongest in vacuoles of epidermal storage cells regardless of infection. This was in contrast to N. ochroleucum, where apoplastic Zn drastically increased in response to TYMV. These results suggest that the antiviral response of N. caerulescens is less induced by the onset of this biotic stress, but it is rather a permanent resistant state of the plant. Real-time qPCR revealed upregulation of ferritin in Zn10 infected plants, suggesting Fe deprivation as a virus defence strategy under suboptimal Zn supply.

High-energy interference-free K-lines synchrotron X-ray fluorescence microscopy of rare earth elements in hyperaccumulator plants.

Synchrotron-based micro-X-ray fluorescence analysis (µXRF) is a nondestructive and highly sensitive technique. However, element mapping of rare earth elements (REEs) under standard conditions requires care, since energy-dispersive detectors are not able to differentiate accurately between REEs L-shell X-ray emission lines overlapping with K-shell X-ray emission lines of common transition elements of high concentrations. We aim to test REE element mapping with high-energy interference-free excitation of the REE K-lines on hyperaccumulator plant tissues and compare with measurements with REE L-shell excitation at the microprobe experiment of beamline P06 (PETRA III, DESY). A combination of compound refractive lens optics (CRLs) was used to obtain a micrometer-sized focused incident beam with an energy of 44 keV and an extra-thick silicon drift detector optimized for high-energy X-ray detection to detect the K-lines of yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), and neodymium (Nd) without any interferences due to line overlaps. High-energy excitation from La to Nd in the hyperaccumulator organs was successful but compared to L-line excitation less efficient and therefore slow (∼10-fold slower than similar maps at lower incident energy) due to lower flux and detection efficiency. However, REE K-lines do not suffer significantly from self-absorption, which makes XRF tomography of millimeter-sized frozen-hydrated plant samples possible. The K-line excitation of REEs at the P06 CRL setup has scope for application in samples that are particularly prone to REE interfering elements, such as soil samples with high concomitant Ti, Cr, Fe, Mn, and Ni concentrations.

Combining micro- and portable-XRF as a tool for fast identification of virus infections in plants: The case study of ASa-Virus in Fraxinus ornus L.

Plant viruses can affect micro- and macro-nutrients homeostasis in woody plants, with fluctuation in the concentration of some elements at the leaf level due to the pathogen activity and/or the plant physiological response to the infection.Leaves of Fraxinus ornus L. (flowering ash) were sampled for three consecutive years in the city of Hamburg (Germany), from both trees showing the typical symptoms of the ash shoestring associated virus infection (ASaV+) and healthy trees (ASaV-). Such leaves were analyzed by µ-XRF, using both laboratory and synchrotron X-ray sources, and large differences between symptomatic and not symptomatic leaves were observed: ASaV+ samples showed uneven element distribution and regions of the lamina with severe depletions of P, S, and Ca. Differently, K appeared more concentrated. Thus, 139 leaflets sampled from various healthy and infected ash trees over the three-year period were analyzed for K and Ca concentration with a portable XRF instrument. We found that the K:Ca concentration ratio was always significantly higher in ASaV+ samples, and this trend was verified for all the samplings over the tree years. We conclude that the K:Ca ratio parameter has potential in the frame of trendsetting diagnostics and could be used, together with visual symptoms, for a rapid, non-destructive, on-site and cheap indirect ASaV detection.

Sublethal and lethal Cd toxicity in soybean roots specifically affects the metabolome, Cd binding to proteins and cellular distribution of Cd.

Soybean (Glycine max (L.) Merr.) plants were exposed to various Cd concentrations from background and low non-toxic (0.5-50 nM) via sublethally toxic (< 550 nM) to highly, ultimately lethally toxic (3 µM) concentrations. Plants were cultivated hydroponically for 10 weeks until pod development stage of the control plants. The threshold and mechanism of sublethal Cd toxicity was investigated by metabolomics and metalloproteomics (HPLC-ICP-MS) measuring metal binding to proteins in the harvested roots. Spatial distribution of Cd was revealed by µXRF-CT. Specific binding of Cd to proteins already at 50 nM Cd revealed the likely high-affinity protein binding targets in roots, identified by protein purification from natural abundance. This revealed allantoinase, aquaporins, peroxidases and protein disulfide isomerase as the most likely high-affinity targets of Cd binding. Cd was deposited in cortex cell vacuoles at sublethal and bound to the cell walls of the outer cortex and the vascular bundle at lethal Cd. Cd binding to proteins likely inhibits them, and possibly induces detoxification mechanisms, as verified by metabolomics: allantoic acid and allantoate increased due to sublethal Cd toxicity. Changes of the Cd binding pattern indicated a detoxification strategy at lower Cd, but saturated binding sites at higher Cd concentrations.

X-ray diffraction with micrometre spatial resolution for highly absorbing samples.

X-ray diffraction with high spatial resolution is commonly used to characterize (poly)crystalline samples with, for example, respect to local strain, residual stress, grain boundaries and texture. However, the investigation of highly absorbing samples or the simultaneous assessment of high-Z materials by X-ray fluorescence have been limited due to the utilization of low photon energies. Here, a goniometer-based setup implemented at the P06 beamline of PETRA III that allows for micrometre spatial resolution with a photon energy of 35 keV and above is reported. A highly focused beam was achieved by using compound refractive lenses, and high-precision sample manipulation was enabled by a goniometer that allows up to 5D scans (three rotations and two translations). As experimental examples, the determination of local strain variations in martensitic steel samples with micrometre spatial resolution, as well as the simultaneous elemental distribution for high-Z materials in a thin-film solar cell, are demonstrated. The proposed approach allows users from the materials-science community to determine micro-structural properties even in highly absorbing samples.

Gadolinium and Bio-Metal Association: A Concentration Dependency Tested in a Renal Allograft and Investigated by Micro-Synchrotron XRF.

AIMS: This study aimed to investigate gadolinium (Gd) and bio-metals in a renal allograft of a patient who was shortly after transplantation repeatedly exposed to a Gd-based contrast agent (GBCA), with the purpose of determining whether Gd can be proven and spatially and quantitatively imaged. Further elemental associations between Gd and bio-metals were also investigated. MATERIALS AND METHODS: Archival paraffin-embedded kidney tissue (eight weeks after transplantation) was investigated by microscopic synchrotron X-ray fluorescence (µSRXRF) at the DORIS III storage ring, beamline L, at HASYLAB/DESY (Hamburg, Germany). For the quantification of elements, X-ray spectra were peak-fitted, and the net peak intensities were normalized to the intensity of the incoming monochromatic beam intensity. Concentrations were calculated by fundamental parameter-based program quant and external standardization. RESULTS: Analysis of about 15,000 µSRXRF spectra (comprising allograft tissue of four cm2) Gd distribution could be quantitatively demonstrated in a near histological resolution. Mean Gd resulted in 24 ± 55 ppm with a maximum of 2363 ppm. The standard deviation of ±55 ppm characterized the huge differences in Gd and not in detection accuracy. Gd was heterogeneously but not randomly distributed and was mostly found in areas with interstitial fibrosis and tubular atrophy. Concentrations of all other investigated elements in the allograft resembled those found in normal kidney tissue. No correlations between Gd and bio-metals such as calcium, strontium or zinc below ~40 ppm Gd existed. In areas with extremely high Gd, Gd was associated with iron and zinc. CONCLUSIONS: We could show that no dose-dependent association between Gd and bio-metals exists-least in renal tissue-at Gd concentrations below ~40 ppm Gd. This was proven compared with a GBCA-exposed end-stage renal failure in which the mean Gd was ten-fold higher. Our results could shed additional light on Gd metabolism.

Synchrotron XFM tomography for elucidating metals and metalloids in hyperaccumulator plants.

Visualizing the endogenous distribution of elements within plant organs affords key insights in the regulation of trace elements in plants. Hyperaccumulators have extreme metal(loid) concentrations in their tissues, which make them useful models for studying metal(loid) homeostasis in plants. X-ray-based methods allow for the nondestructive analysis of most macro and trace elements with low limits of detection. However, observing the internal distributions of elements within plant organs still typically requires destructive sample preparation methods, including sectioning, for synchrotron X-ray fluorescence microscopy (XFM). X-ray fluorescence microscopy-computed tomography (XFM-CT) enables "virtual sectioning" of a sample thereby entirely avoiding artefacts arising from destructive sample preparation. The method can be used on frozen-hydrated samples, as such preserving "life-like" conditions. Absorption and Compton scattering maps obtained from synchrotron XFM-CT offer exquisite detail on structural features that can be used in concert with elemental data to interpret the results. In this article we introduce the technique and use it to reveal the internal distribution of hyperaccumulated elements in hyperaccumulator plant species. XFM-CT can be used to effectively probe the distribution of a range of different elements in plant tissues/organs, which has wide ranging applications across the plant sciences.

Assessing Cellular Uptake of Exogenous Coenzyme Q10 into Human Skin Cells by X-ray Fluorescence Imaging.

X-ray fluorescence (XRF) imaging is a highly sensitive non-invasive imaging method for detection of small element quantities in objects, from human-sized scales down to single-cell organelles, using various X-ray beam sizes. Our aim was to investigate the cellular uptake and distribution of Q10, a highly conserved coenzyme with antioxidant and bioenergetic properties. Q10 was labeled with iodine (I2-Q10) and individual primary human skin cells were scanned with nano-focused beams. Distribution of I2-Q10 molecules taken up inside the screened individual skin cells was measured, with a clear correlation between individual Q10 uptake and cell size. Experiments revealed that labeling Q10 with iodine causes no artificial side effects as a result of the labeling procedure itself, and thus is a perfect means of investigating bioavailability and distribution of Q10 in cells. In summary, individual cellular Q10 uptake was demonstrated by XRF, opening the path towards Q10 multi-scale tracking for biodistribution studies.

Altered SOD1 maturation and post-translational modification in amyotrophic lateral sclerosis spinal cord.

Aberrant self-assembly and toxicity of wild-type and mutant superoxide dismutase 1 (SOD1) has been widely examined in silico, in vitro and in transgenic animal models of amyotrophic lateral sclerosis. Detailed examination of the protein in disease-affected tissues from amyotrophic lateral sclerosis patients, however, remains scarce. We used histological, biochemical and analytical techniques to profile alterations to SOD1 protein deposition, subcellular localization, maturation and post-translational modification in post-mortem spinal cord tissues from amyotrophic lateral sclerosis cases and controls. Tissues were dissected into ventral and dorsal spinal cord grey matter to assess the specificity of alterations within regions of motor neuron degeneration. We provide evidence of the mislocalization and accumulation of structurally disordered, immature SOD1 protein conformers in spinal cord motor neurons of SOD1-linked and non-SOD1-linked familial amyotrophic lateral sclerosis cases, and sporadic amyotrophic lateral sclerosis cases, compared with control motor neurons. These changes were collectively associated with instability and mismetallation of enzymatically active SOD1 dimers, as well as alterations to SOD1 post-translational modifications and molecular chaperones governing SOD1 maturation. Atypical changes to SOD1 protein were largely restricted to regions of neurodegeneration in amyotrophic lateral sclerosis cases, and clearly differentiated all forms of amyotrophic lateral sclerosis from controls. Substantial heterogeneity in the presence of these changes was also observed between amyotrophic lateral sclerosis cases. Our data demonstrate that varying forms of SOD1 proteinopathy are a common feature of all forms of amyotrophic lateral sclerosis, and support the presence of one or more convergent biochemical pathways leading to SOD1 proteinopathy in amyotrophic lateral sclerosis. Most of these alterations are specific to regions of neurodegeneration, and may therefore constitute valid targets for therapeutic development.

Evidence of hexavalent chromium formation and changes of Cr speciation after laboratory-simulated fires of composted tannery sludges long-term amended agricultural soils.

Controlled or accidental fires can impact agricultural soils amended with composted organic materials since high temperatures cause fast organic matter (OM) mineralization and soil properties modifications. During these events, potentially toxic elements (PTEs) associated with OM can be released and change their distribution and speciation thus becoming a threat to the environment and to crops. In this study, we investigated the changes of distribution and speciation of chromium in soils long-term amended with compost obtained from tannery sludges, after simulating fires of different intensity (300, 400 and 500 °C) likely to occur on agricultural soils. A combination of conventional soil chemical analyses and bulk and (sub)micro X-ray analyses allowed the observation of the formation of hexavalent chromium and changes of chromium speciation. Specifically, a strong decrease of Cr-OM associations was found with increasing temperature in favour of Cr-iron (hydr)oxides interactions and CaCrO4 formation. These data provide first evidence that fires can transform OM-stabilized Cr into more mobile, available and toxic Cr-forms potentially accessible for plant uptake, thus posing a risk for the food chain and the environment.

Spatial Distribution of Intracellular Ion Concentrations in Aggregate-Forming HeLa Cells Analyzed by µ-XRF Imaging.

Protein aggregation is a hallmark of several severe neurodegenerative disorders such as Huntington's, Parkinson's, or Alzheimer's disease. Metal ions play a profound role in protein aggregation and altered metal-ion homeostasis is associated with disease progression. Here we utilize µ-X-ray fluorescence imaging in combination with rapid freezing to resolve the elemental distribution of phosphorus, sulfur, potassium, and zinc in huntingtin exon-1-mYFP expressing HeLa cells. Using quantitative XRF analysis, we find a threefold increase in zinc and a 10-fold enrichment of potassium that can be attributed to cellular stress response. While the averaged intracellular ion areal masses are significantly different in aggregate-containing cells, a local intracellular analysis shows no different ion content at the location of intracellular inclusion bodies. The results are compared to corresponding experiments on HeLa cells forming pseudoisocyanine chloride aggregates. As those show similar results, changes in ion concentrations are not exclusively linked to huntingtin exon-1 amyloid formation.

Synchrotron XRF Analysis Identifies Cerium Accumulation Colocalized with Pharyngeal Deformities in CeO2 NP-Exposed Caenorhabditis elegans.

A combination of synchrotron radiation-based elemental imaging, in vivo redox status analysis, histology, and toxic responses was used to investigate the uptake, biodistribution, and adverse effects of Ce nanoparticles (CeO2 NP; 10 nm; 0.5-34.96 mg Ce L-1) or Ce(NO3)3 (2.3-26 mg Ce L-1) in Caenorhabditis elegans. Elemental mapping of the exposed nematodes revealed Ce uptake in the alimentary canal prior to depuration. Retention of CeO2 NPs was low compared to that of Ce(NO3)3 in depurated individuals. X-ray fluorescence (XRF) mapping showed that Ce translocation was confined to the pharyngeal valve and foregut. Ce(NO3)3 exposure significantly decreased growth, fertility, and reproduction, caused slightly reduced fecundity. XRF mapping and histological analysis revealed severe tissue deformities colocalized with retained Ce surrounding the pharyngeal valve. Both forms of Ce activated the sod-1 antioxidant defense, particularly in the pharynx, whereas no significant effects on the cellular redox balance were identified. The CeO2 NP-induced deformities did not appear to impair the pharyngeal function or feeding ability as growth effects were restricted to Ce(NO3)3 exposure. The results demonstrate the utility of integrated submicron-resolution SR-based XRF elemental mapping of tissue-specific distribution and adverse effect analysis to obtain robust toxicological evaluations of metal-containing contaminants.

Distribution of Pb and Se in mouse brain following subchronic Pb exposure by using synchrotron X-ray fluorescence.

Lead (Pb) is a well-known neurotoxicant and environmental hazard. Recent experimental evidence has linked Pb exposure with neurological deterioration leading to neurodegenerative diseases, such as Alzheimer's disease. To understand brain regional distribution of Pb and its interaction with other metal ions, we used synchrotron micro-x-ray fluorescence technique (µ-XRF) to map the metal distribution pattern and to quantify metal concentrations in mouse brains. Lead-exposed mice received oral gavage of Pb acetate once daily for 4 weeks; the control mice received sodium acetate. Brain tissues were cut into slices and subjected for analysis. Synchrotron µ-XRF scans were run on the PETRA III P06 beamline (DESY). Coarse scans of the entire brain were performed to locate the cortex and hippocampus, after which scans with higher resolution were run in these areas. The results showed that: a) the total Pb intensity in Pb-exposed brain slices was significantly higher than in control brain; b) Pb typically deposited in localized particles of <10 um2 in both the Pb-exposed and control brain slices, with more of these particles in Pb-exposed samples; c) selenium (Se) was significantly correlated with Pb in these particles in the cortex and hippocampus/corpus callosum regions in the Pb-exposed samples, and the molar ratio of the Se and Pb in these particles is close to 1:1. These results indicated that Se may play a crucial role in Pb-induced neurotoxicity. Our findings call for further studies to investigate the relationship between Pb exposure and possible Se detoxification responses, and the implication in the etiology of Alzheimer's disease.

Copper and Trace Elements in Gallbladder form Patients with Wilson's Disease Imaged and Determined by Synchrotron X-ray Fluorescence.

Investigations about suspected tissue alterations and the role of gallbladder in Wilson's disease (WD)-an inherited genetic disease with impaired copper metabolism-are rare. Therefore, tissue from patients with genetically characterised WD was investigated by microscopic synchrotron X-ray fluorescence (µSRXRF). For two-dimensional imaging and quantification of elements, X-ray spectra were peak-fitted, and the net peak intensities were normalised to the intensity of the incoming monochromatic beam intensity. Concentrations were calculated by fundamental parameter-based program quant and external standardisation. Copper (Cu), zinc (Zn) and iron (Fe) along with sulphur (S) and phosphorus (P) mappings could be demonstrated in a near histological resolution. All these elements were increased compared to gallbladder tissue from controls. Cu and Zn and Fe in WD-GB were mostly found to be enhanced in the epithelium. We documented a significant linear relationship with Cu, Zn and sulphur. Concentrations of Cu/Zn were roughly 1:1 while S/Cu was about 100:1, depending on the selected areas for investigation. The significant linear relationship with Cu, Zn and sulphur let us assume that metallothioneins, which are sulphur-rich proteins, are increased too. Our data let us suggest that the WD gallbladder is the first in the gastrointestinal tract to reabsorb metals to prevent oxidative damage caused by metal toxicity.

Determination of the through-plane profile of vanadium species in hydrated Nafion studied with micro X-ray absorption near-edge structure spectroscopy - proof of concept.

Vanadium-ion transport through the polymer membrane results in a significant decrease in the capacity of vanadium redox flow batteries. It is assumed that five vanadium species are involved in this process. Micro X-ray absorption near-edge structure spectroscopy (micro-XANES) is a potent method to study chemical reactions during vanadium transport inside the membrane. In this work, protocols for micro-XANES measurements were developed to enable through-plane characterization of the vanadium species in Nafion 117 on beamline P06 of the PETRA III synchrotron radiation facility (DESY, Hamburg, Germany). A Kapton tube diffusion cell with a diameter of 3 mm was constructed. The tube diameter was chosen in order to accommodate laminar flow for cryogenic cooling while allowing easy handling of the cell components by hand. A vertical step size of 2.5 µm and a horizontal step size of 5 µm provided sufficient resolution to resolve the profile and good statistics after summing up horizontal rows of scan points. The beam was confined in the horizontal plane to account for the waviness of the membrane. The diffusion of vanadium ions during measurement was inhibited by the cryogenic cooling. Vanadium oxidation, e.g. by water radiolysis (water percentage in the hydrated membrane ∼23 wt%), was mitigated by the cryogenic cooling and by minimizing the dwell time per pixel to 5 ms. Thus, the photo-induced oxidation of V3+ in the focused beam could be limited to 10%. In diffusion experiments, Nafion inside the diffusion cell was exposed on one side to V3+ electrolyte and on the other side to VO2+. The ions were allowed to diffuse across the through-plane orientation of the membrane during one of two short defrost times (200 s and 600 s). Subsequent micro-XANES measurements showed the formation of VO2+ from V3+ and VO2+ inside the water body of Nafion. This result proves the suitability of the experimental setup as a powerful tool for the determination of the profile of vanadium species in Nafion and other ionomeric membranes.

Native Separation and Metallation Analysis of SOD1 Protein from the Human Central Nervous System: a Methodological Workflow.

Studies of the metal content of metalloproteins in tissues from the human central nervous system (CNS) can be compromised by preparative techniques which alter levels of, or interactions between, metals and the protein of interest within a complex mixture. We developed a methodological workflow combining size exclusion chromatography, native isoelectric focusing, and either proton or synchrotron X-ray fluorescence within electrophoresis gels to analyze the endogenous metal content of copper-zinc superoxide dismutase (SOD1) purified from minimal amounts (<20 mg) of post-mortem human brain and spinal cord tissue. Abnormal metallation and aggregation of SOD1 are suspected to play a role in amyotrophic lateral sclerosis and Parkinson's disease, but data describing SOD1 metal occupancy in human tissues have not previously been reported. Validating our novel approach, we demonstrated step-by-step metal preservation, preserved SOD1 activity, and substantial enrichment of SOD1 protein versus confounding metalloproteins. We analyzed tissues from nine healthy individuals and five CNS regions (occipital cortex, substantia nigra, locus coeruleus, dorsal spinal cord, and ventral spinal cord). We found that Cu and Zn were bound to SOD1 in a ratio of 1.12 ± 0.28, a ratio very close to the expected value of 1. Our methodological workflow can be applied to the study of endogenous native SOD1 in a pathological context and adapted to a range of metalloproteins from human tissues and other sources.

Nanofocusing with aberration-corrected rotationally parabolic refractive X-ray lenses. Corrigendum.

A correction in the paper by Seiboth et al. [(2018). J. Synchrotron Rad. 25, 108-115] is made.

Erratum: Ossig, C., et al. Four-Fold Multi-Modal X-ray Microscopy Measurements of a Cu(In, Ga)Se2 Solar Cell. Materials 2021, 14, 228.

In the original version of our article [...].

Micro x-ray fluorescence analysis of trace element distribution in frozen hydrated HeLa cells at the P06 beamline at Petra III.

X-ray fluorescence analysis enables the study of trace element distributions in biological specimens. When this analysis is done under cryogenic conditions, cells are cryofixed as closely as possible to their natural physiological state, and the corresponding intracellular elemental densities can be analyzed. Details about the experimental setup used for analysis at the P06 beamline at Petra III, DESY and the used cryo-transfer system are described in this work. The system was applied to analyze the elemental distribution in single HeLa cells, a cell line frequently used in a wide range of biological applications. Cells adhered to silicon nitride substrates were cryoprotected within an amorphous ice matrix. Using a continuous scanning scheme and a KB x-ray focus, the distribution of elements in the cells was studied. We were able to image the intracellular potassium and zinc levels in HeLa cells as two key elements relevant for the physiology of cells.