Maia X-ray fluorescence imaging: Capturing detail in complex natural samples

Subventricular Accumulation of Cu in the Aging Mouse Brain Does Not Associate with Anticipated Increases in Markers of Oxidative Stress

Natural aging is associated with mild memory loss and cognitive decline, and age is the greatest risk factor for neurodegenerative diseases, such as Alzheimer's disease. There is substantial evidence that oxidative stress is a major contributor to both natural aging and neurodegenerative disease, and coincidently, levels of redox active metals such as Fe and Cu are known to be elevated later in life. Recently, a pronounced age-related increase in Cu content has been reported to occur in mice and rats around a vital regulatory brain region, the subventricular zone of lateral ventricles. In our study herein, we have characterized lateral ventricle Cu content in a unique murine model of accelerated aging, senescence accelerated mouse-prone 8 (SAMP8) mice. Our results confirm an age-related increase in ventricle Cu content, consistent with the studies by others in wild-type mice and rats. Specifically, we observed Cu content to increase over the time frame 1 to 5 months and 5 to 9 months, but interestingly, no significant increase occurred between 9 and 12 months (although brain Cu content at 12 months was significantly elevated relative to 1 and 5 month-old animals). Despite the magnitude of Cu increase observed within the cells that comprise the subventricular zone of lateral ventricles (average 3 mM Cu, with isolated subcellular concentrations of 17 mM), we did not detect spectroscopic markers of thiol oxidation, protein aggregation, or lipid oxidation. The lack of evidence for oxidative stress in ex vivo animal tissue is in contrast to in vitro studies demonstrating that thiol, protein, and lipid oxidation is pronounced at these Cu concentrations. We suggest that our findings most likely indicate that the Cu ions in this brain region are sequestered in an unreactive form, possibly extended chains of Cu-thiolate complexes, which do not readily redox cycle in the aqueous cytosol. These results also appear to partially challenge the long-held view that age-related increases in brain metal content drive oxidative stress as we did not observe a concomitant association between age-related Cu increase and markers of oxidative stress, nor did we observe a net increase in Cu content between mice aged 9 and 12 months.

Pure CO2 and impure CO2-SO2-NO-O2 reactions with carbon storage site underlying seals: Coaly mudstones and carbonate cemented sandstones

The transition to net zero emissions requires the capture of carbon dioxide from industrial point sources, and direct air capture (DAC) from the atmosphere for geological storage. Dissolved CO2 has reactivity to rock core, and while the majority of previous studies have concentrated on reservoir rock or cap-rock reactivity, the underlying seal formation may also react with CO2. Drill core from the underlying seal of a target CO2 storage site was reacted at in situ conditions with pure CO2, and compared with an impure CO2 stream with SO2, NO and O2 that could be expected from hard to abate industries. Argillaceous sandstones, mudstones, coaly mudstones, and carbonate cemented sandstones of the Moolayember Formation, Bowen Basin, had significant natural alteration of feldspar to kaolinite creating porosity, with clays, siderite and textured ankerite filling and rimming porosities of 3.5 to 15.8 %. Synchrotron XFM quantified Mn mainly hosted in siderite veins and cements, Sr and Rb in feldspar, and Pb, Th and Sr in monazite. Pb was also in siderite; with As mainly in pyrite and associated with ankerite. On pure CO2 or impure CO2 reaction, ankerite and siderite dissolution, Fe-chlorite leaching, and apatite or sulphide alteration occurred. With the impure CO2 stream Fe-oxides precipitated on rock surfaces especially in argillaceous sandstone. Ferroan carbonates, calcite, and Fe oxides containing Cr were also precipitated. Ankerite and siderite dissolution released increasing concentrations of dissolved Ca, Mg and Mn from carbonate cemented core that were higher with mixed gas injection. Argillaceous sandstone however released higher concentrations Si, Rb, Co and Zn. Dissolved Fe initially increased then decreased in impure gas experiments via Fe oxide precipitation, and Pb, Ni, Cr, REE also increased and subsequently decreased. Geochemical modelling predicted that Fe was mobilised mainly from reaction of siderite and Fe chlorite. Mainly carbonates (siderite, ankerite) and chlorite dissolution released trace metals, with several metals also initially mobilised by desorption and exchange. Precipitated Fe oxides provided adsorption sites to adsorb a portion of metals from solution. These reactions are also relevant to CO2 streams from DAC that could be expected to contain O2 and to potential reactions in overlying aquifers.

Metal mobilisation and fines migration in pure CO2 and impure CO2-SO2-NO reactions of carbon storage site core

Carbon dioxide geological storage is proposed as part of the solution to reach net zero emissions. The potential to mobilise heavy metals to low salinity groundwater through CO2 water rock geochemical reactions is a potential environmental risk factor, if CO2 migrates. Previous studies have focused on pure CO2 reactivity, however CO2 streams from hard to abate industries can contain gas impurities. Reservoir sandstone and mudstone drill cores from a proposed low salinity CO2 storage demonstration site were reacted at in situ conditions with pure CO2 or an impure NO-SO2-CO2 stream. Sandstones hosted Rb in illite analysed via synchrotron XFM. Arsenic (As) was hosted in pyrite; and Pb, Cr, Mn in siderite rimming intergranular pores. Mudstone contained Zn, Co, Ni, Cu, As, Pb in sphalerite, and Rb in illite and K-feldspar. In impure NO-SO2-CO2 experiments the lowered pH and oxidising conditions initially released higher concentrations of metals including Pb, Zn, Co into solution compared to pure CO2 reactions. Higher concentrations of Zn (Mn and Co) were released from sphalerite in the mudstone. Fe-chlorite, K-feldspar, and carbonate dissolution released Rb, Si, Fe, Ca, and Mg. Elevated dissolved Pb was mainly from siderite and sulphide mineral reaction in sandstones. Mobilised As was released prior to CO2 addition from desorption and ion exchange. Clay and fines migration into pores occurred in both pure and impure CO2 reactions that has the potential to impact fluid migration. A portion of metals including Fe, Ni, Cr were subsequently incorporated in precipitated Fe hydr(oxy)oxides where the co-injected NO induced oxidising conditions. Rock mineral content and the injected gas mix were the main controls on metal mobilisation to formation water. Further work should investigate new gas mixtures that may be expected in storage hubs, from blue hydrogen or from direct air capture.

Bulk and Mapping Speciation Analyses Unveil the Pattern and Heterogeneity of Cu Species during Organic Waste Treatment

Organic wastes (OWs) can be a common source of copper (Cu) contamination of agricultural soils. Here we conducted a comprehensive study of 22 raw and treated OWs sampled at 6 different full-scale OW treatment plants. Bulk XANES analysis findings indicated that the Cu oxidation state was subject to changes throughout the OW treatment process, mostly depending on the anaerobic/aerobic conditions prevailing in each treatment stage. These changes were independent of the OW origin (agricultural, urban or industrial). Cu(I) prevailed in raw OWs and digestates (88-100%), whereas Cu(II) dominated in composts (46-100%). Bulk EXAFS analysis confirmed these observations and revealed that Cu(I) species in raw OWs and digestates consisted mainly of Cu(I)-sulfide (76-100%), while Cu(II) species (60-100%) in composts were Cu(II)-citrate, Cu(II)-carbonate and amorphous Cu(II)-phosphate. Interestingly, we observed that anaerobic digestion was conducive to the formation of crystallized Cu(I)-sulfides at the expense of nanosized and poorly crystalline Cu(I)-sulfide species, and that the recalcitrant Cu(I) species in composts was always crystallized Cu(I)-sulfide. XANES imaging analysis revealed Cu(II) species present in low proportions (2-4%) that were not detected using bulk XAS analysis in raw OWs and digestates. This demonstrated the potential of XANES imaging for probing minor species in complex matrices.

Contrasting morphology and growth habits of Frutexites in Late Devonian reef complexes of the Canning Basin, northwestern Australia

Frutexites-like microstructures are described from the exhumed Late Devonian reef complexes of the northern Canning Basin, Western Australia. Several high-resolution imaging techniques, including X-ray microcomputerised tomography, scanning electron microscopy and X-ray fluorescence microscopy, were used to investigate morphology and composition in two samples. Three types of Frutexites-like microstructures (Types I-III) have been identified. Type I, found lining an early marine cement-filled cavity in fore-reef grainstone facies, consists of dendritic structures formed primarily of coccoid bacteria with filamentous bacteria embedded in sheets of amorphous extracellular polymeric substances (EPS). These ferromanganiferous dendrites have laminated to spheroidal textures. Types II and III are from a toe-of-slope hardground. Type II grew in a crypt between two corals, is also dendritic and composed of bacilliform and filamentous bacteria embedded in an amorphous EPS sheet. The opaqueness of these ferriferous dendrites precludes more detailed description of textures. Type III grew as branching columnar microstromatolites and is composed of entwined filaments of Girvanella, Rothpletzella and Wetheredella with Fe-enriched outer walls that generate Frutexites-like microstructures. Types I and II resemble Frutexites sensu stricto as defined by Maslov (Stromatolites, Trudy Instituta geologicheskikh nauk Akademiya nauk SSR, 1960) and are the result of the consecutive growth and permineralisation of biofilms composed of mixed bacterial communities growing in cryptic habitats. Type III superficially resembles Frutexites sensu stricto based on macroscopic field observations, however, detailed microscopic analysis reveals that it is composed of Fe-enriched tubular walls surrounded by Mn-enriched calcite.

Elemental Mapping in a Preclinical Animal Model Reveals White Matter Copper Elevation in the Acute Phase of Central Nervous System Trauma

Understanding the chemical events following trauma to the central nervous system could assist in identifying causative mechanisms and potential interventions to protect neural tissue. Here, we apply a partial optic nerve transection model of injury in rats and use synchrotron X-ray fluorescence microscopy (XFM) to perform elemental mapping of metals (K, Ca, Fe, Cu, Zn) and other related elements (P, S, Cl) in white matter tracts. The partial optic nerve injury model and spatial precision of microscopy allow us to obtain previously unattained resolution in mapping elemental changes in response to a primary injury and subsequent secondary effects. We observed significant elevation of Cu levels at multiple time points following the injury, both at the primary injury site and in neural tissue near the injury site vulnerable to secondary damage, as well as significant changes in Cl, K, P, S, and Ca. Our results suggest widespread metal dyshomeostasis in response to central nervous system trauma and that altered Cu homeostasis may be a specific secondary event in response to white matter injury. The findings highlight metal homeostasis as a potential point of intervention in limiting damage following nervous system injury.

Demonstration of an AI-driven workflow for autonomous high-resolution scanning microscopy

Modern scanning microscopes can image materials with up to sub-atomic spatial and sub-picosecond time resolutions, but these capabilities come with large volumes of data, which can be difficult to store and analyze. We report the Fast Autonomous Scanning Toolkit (FAST) that addresses this challenge by combining a neural network, route optimization, and efficient hardware controls to enable a self-driving experiment that actively identifies and measures a sparse but representative data subset in lieu of the full dataset. FAST requires no prior information about the sample, is computationally efficient, and uses generic hardware controls with minimal experiment-specific wrapping. We test FAST in simulations and a dark-field X-ray microscopy experiment of a WSe2 film. Our studies show that a FAST scan of <25% is sufficient to accurately image and analyze the sample. FAST is easy to adapt for any scanning microscope; its broad adoption will empower general multi-level studies of materials evolution with respect to time, temperature, or other parameters.

Accelerated mineral bio-carbonation of coarse residue kimberlite material by inoculation with photosynthetic microbial mats

Microbiological weathering of coarse residue deposit (CRD) kimberlite produced by the Venetia Diamond Mine, Limpopo, South Africa enhanced mineral carbonation relative to untreated material. Cultures of photosynthetically enriched biofilm produced maximal carbonation conditions when mixed with kimberlite and incubated under near surface conditions. Interestingly, mineral carbonation also occurred in the dark, under water-saturated conditions. The examination of mineralized biofilms in ca. 150 µm-thick-sections using light microscopy, X-ray fluorescence microscopy (XFM) and backscatter electron-scanning electron microscopy-energy dispersive x-ray spectrometry demonstrated that microbiological weathering aided in producing secondary calcium/magnesium carbonates on silicate grain boundaries. Calcium/magnesium sulphate(s) precipitated under vadose conditions demonstrating that evaporites formed upon drying. In this system, mineral carbonation was only observed in regions possessing bacteria, preserved within carbonate as cemented microcolonies. 16S rDNA molecular diversity of bacteria in kimberlite and in natural biofilms growing on kimberlite were dominated by Proteobacteria that are active in nitrogen, phosphorus and sulphur cycling. Cyanobacteria based enrichment cultures provided with nitrogen & phosphorus (nutrients) to enhance growth, possessed increased diversity of bacteria, with Proteobacteria re-establishing themselves as the dominant bacterial lineage when incubated under dark, vadose conditions consistent with natural kimberlite. Overall, 16S rDNA analyses revealed that weathered kimberlite hosts a diverse microbiome consistent with soils, metal cycling and hydrocarbon degradation. Enhanced weathering and carbonate-cemented microcolonies demonstrate that microorganisms are key to mineral carbonation of kimberlite.

Locked up Inside the Vessels: Rare Earth Elements Are Transferred and Stored in the Conductive Tissues of the Accumulating Fern Dryopteris erythrosora

Rare earth elements (REEs) are strategic metals strongly involved in low-carbon energy conversion. However, these emerging contaminants are increasingly disseminated into ecosystems, raising concern regarding their toxicity. REE-accumulating plants are crucial subjects to better understand REE transfer to the trophic chain but are also promising phytoremediation tools. In this analysis, we deciphered REE accumulation sites in the REE-accumulating fern Dryopteris erythrosora by synchrotron X-ray μfluorescence (μXRF). This technique allows a high-resolution and in situ analysis of fresh samples or frozen-hydrated cross sections of different organs of the plant. In the sporophyte, REEs were translocated from the roots to the fronds by the xylem sap and were stored within the xylem conductive system. The comparison of REE distribution and accumulation levels in the healthy and necrotic parts of the frond shed light on the differential mobility between light and heavy REEs. Furthermore, the comparison emphasized that necrotized areas were not the main REE-accumulating sites. Finally, the absence of cell-to-cell mobility of REEs in the gametophyte suggested the absence of REE-compatible transporters in photosynthetic tissues. These results provide valuable knowledge on the physiology of REE-accumulating ferns to understand the REE cycle in biological systems and the expansion of phytotechnologies for REE-enriched or REE-contaminated soils.

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.

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.

Preservation of Terrestrial Microorganisms and Organics Within Alteration Products of Chondritic Meteorites from the Nullarbor Plain, Australia

Meteorites that fall to Earth quickly become contaminated with terrestrial microorganisms. These meteorites are out of chemical equilibrium in the environments where they fall, and equilibration promotes formation of low-temperature alteration minerals that can entomb contaminant microorganisms and thus preserve them as microfossils. Given the well-understood chemistry of meteorites and their recent discovery on Mars by rovers, a similarly weathered meteorite on Mars could preserve organic and fossil evidence of a putative past biosphere at the martian surface. Here, we used several techniques to assess the potential of alteration minerals to preserve microfossils and biogenic organics in terrestrially weathered ordinary chondrites from the Nullarbor Plain, Australia. We used acid etching of ordinary chondrites to reveal entombed fungal hyphae, modern biofilms, and diatoms within alteration minerals. We employed synchrotron X-ray fluorescence microscopy of alteration mineral veins to map the distribution of redox-sensitive elements of relevance to chemolithotrophic organisms, such as Mn-cycling bacteria. We assessed the biogenicity of fungal hyphae within alteration veins using a combination of Fourier-transform infrared spectroscopy and pyrolysis gas chromatography-mass spectrometry, which showed that alteration minerals sequester and preserve organic molecules at various levels of decomposition. Our combined analyses results show that fossil microorganisms and the organic molecules they produce are preserved within calcite-gypsum admixtures in meteorites. Furthermore, the distributions of redox-sensitive elements (e.g., Mn) within alteration minerals are localized, which qualitatively suggests that climatically or microbially facilitated element mobilization occurred during the meteorite's residency on Earth. If returned as part of a sample suite from the martian surface, ordinary chondrites could preserve similar, recognizable evidence of putative past life and/or environmental change.

Trace-element XAFS sensitivity: a stress test for a new XRF multi-detector

X-ray absorption fine-structure (XAFS) spectroscopy can assess the chemical speciation of the elements providing their coordination and oxidation state, information generally hidden to other techniques. In the case of trace elements, achieving a good quality XAFS signal poses several challenges, as it requires high photon flux, counting statistics and detector linearity. Here, a new multi-element X-ray fluorescence detector is presented, specifically designed to probe the chemical speciation of trace 3d elements down to the p.p.m. range. The potentialities of the detector are presented through a case study: the speciation of ultra-diluted elements (Fe, Mn and Cr) in geological rocks from a calcareous formation related to the dispersal processes from Ontong (Java) volcanism (mid-Cretaceous). Trace-elements speciation is crucial in evaluating the impact of geogenic and anthropogenic harmful metals on the environment, and to evaluate the risks to human health and ecosystems. These results show that the new detector is suitable for collecting spectra of 3d elements in trace amounts in a calcareous matrix. The data quality is high enough that quantitative data analysis could be performed to determine their chemical speciation.

Scanning Compton X-ray microscopy

X-ray microscopy offers the opportunity to image biological and radiosensitive materials without special sample preparations, bridging optical and electron microscopy capabilities. However, the performance of such microscopes, when imaging radiosensitive samples, is not limited by their intrinsic resolution, but by the radiation damage induced on such samples. Here, we demonstrate a novel, to the best of our knowledge, radio-efficient microscope, scanning Compton X-ray microscopy (SCXM), which uses coherently and incoherently (Compton) scattered photons to minimize the deposited energy per unit of mass for a given imaging signal. We implemented SCXM, using lenses capable of efficiently focusing 60 keV X-ray photons into the sub-micrometer scale, and probe its radio-efficient capabilities. SCXM, when implemented in high-energy diffraction-limited storage rings, e.g., European Synchrotron Radiation Facility Extremely Brilliant Source and PETRA IV, will open the opportunity to explore the nanoscale of unstained, unsectioned, and undamaged radiosensitive materials.

Trace element catalyses mineral replacement reactions and facilitates ore formation

Reaction-induced porosity is a key factor enabling protracted fluid-rock interactions in the Earth’s crust, promoting large-scale mineralogical changes during diagenesis, metamorphism, and ore formation. Here, we show experimentally that the presence of trace amounts of dissolved cerium increases the porosity of hematite (Fe₂O₃) formed via fluid-induced, redox-independent replacement of magnetite (Fe₃O₄), thereby increasing the efficiency of coupled magnetite replacement, fluid flow, and element mass transfer. Cerium acts as a catalyst affecting the nucleation and growth of hematite by modifying the Fe²⁺(aq)/Fe³⁺(aq) ratio at the reaction interface. Our results demonstrate that trace elements can enhance fluid-mediated mineral replacement reactions, ultimately controlling the kinetics, texture, and composition of fluid-mineral systems. Applied to some of the world’s most valuable orebodies, these results provide new insights into how early formation of extensive magnetite alteration may have preconditioned these ore systems for later enhanced metal accumulation, contributing to their sizes and metal endowment.

Trace amounts of Cerium can act as a catalyst by enhancing fluid-mediated magnetite alteration, which preconditions ore systems and could contribute to the large size and metal content of world-class ore deposits.

Biogenicity of Spicular Geyserite from Te Kopia, New Zealand: Integrated Petrography, High-Resolution Hyperspectral and Elemental Analysis

Hyperspectral and micro X-ray fluorescence (μXRF) imagery were used to derive maps of mineralogy and elemental chemistry from a sample of a siliceous hot spring deposit, or sinter, collected from a landslide breccia deposit at the base of the Paeroa fault, which bounds the eastern Taupo Rift at Te Kopia, Taupo Volcanic Zone, New Zealand. The sample is of a known biogenic sinter layer from a paleo-vent area of a recently extinct alkali chloride hot spring. The aim of the study was to distinguish it from other horizons derived from nonbiogenic sources, which is of relevance to early and extraterrestrial life research, specifically to help assess the potential reliability of morphology as an indicator of biology in the geological record. In particular, the distribution of opal, a common mineral in hot springs deposits that is known to preserve microbial features, and the relative abundances of Al-OH clay and water (OH and H₂O) were mapped from hyperspectral imagery and element distributions defined by μXRF element mapping. Layers within the sinter sample composed of spicular geyserite-a type of micro-columnar stromatolite-showed contrasting mineralogy and water content in comparison with interspicular clastic sediment. Whereas clay was found to be concentrated in the interspicular sediment, high water contents characterized the spicules. μXRF imagery also showed differences in the composition of the two components of the spicule-bearing layers, with interspicular sediment being enriched in K, Ti, Fe, and Rb relative to the spicules, which are enriched in Ga. The contrasting nature of the mapped components highlights the detailed upward-branching nature of the spicules, identical to those found in living microstromatolites. These discriminants show that the spicular component can be discerned from the geological background through hyperspectral and μXRF mapping and used to define morphological features that may survive burial diagenesis and metamorphism as a biosignature in deep time rocks.

The XFM beamline at the Australian Synchrotron

The X-ray fluorescence microscopy (XFM) beamline is an in-vacuum undulator-based X-ray fluorescence (XRF) microprobe beamline at the 3 GeV Australian Synchrotron. The beamline delivers hard X-rays in the 4-27 keV energy range, permitting K emission to Cd and L and M emission for all other heavier elements. With a practical low-energy detection cut-off of approximately 1.5 keV, low-Z detection is constrained to Si, with Al detectable under favourable circumstances. The beamline has two scanning stations: a Kirkpatrick-Baez mirror microprobe, which produces a focal spot of 2 µm × 2 µm FWHM, and a large-area scanning `milliprobe', which has the beam size defined by slits. Energy-dispersive detector systems include the Maia 384, Vortex-EM and Vortex-ME3 for XRF measurement, and the EIGER2 X 1 Mpixel array detector for scanning X-ray diffraction microscopy measurements. The beamline uses event-mode data acquisition that eliminates detector system time overheads, and motion control overheads are significantly reduced through the application of an efficient raster scanning algorithm. The minimal overheads, in conjunction with short dwell times per pixel, have allowed XFM to establish techniques such as full spectroscopic XANES fluorescence imaging, XRF tomography, fly scanning ptychography and high-definition XRF imaging over large areas. XFM provides diverse analysis capabilities in the fields of medicine, biology, geology, materials science and cultural heritage. This paper discusses the beamline status, scientific showcases and future upgrades.

Concentrations of toxic metals and essential trace elements vary among individual neurons in the human locus ceruleus

Objective

Damage to locus ceruleus neurons could play a part in the pathogenesis of neurodegenerative disorders such as Alzheimer’s disease, Parkinson’s disease, and multiple sclerosis because of impairment of the blood-brain barrier and enhanced neuroinflammation. The locus ceruleus has connections throughout the brain and spinal cord, so the characteristic widespread multifocal pathology in these disorders could be due to damage to different subsets of locus ceruleus neurons. Previous studies have shown that only certain locus ceruleus neurons accumulate the neurotoxic metal mercury. To find out if concentrations of other toxic metals or of essential trace elements also vary between individual locus ceruleus neurons, we used synchrotron X-ray fluorescence microscopy on frozen sections of locus ceruleus neurons taken from people with multiple sclerosis, in whom the locus ceruleus is structurally intact.

Materials and methods

Paraffin embedded sections containing the locus ceruleus from seven people with multiple sclerosis were stained with autometallography that demonstrates accumulations of mercury, silver and bismuth. These were compared to maps of multiple elements obtained from frozen sections of locus ceruleus neurons from the same people using X-ray fluorescence microscopy. Neurons in the anterior pons from three of these donors were used as internal controls.

Results

Autometallography staining was observed in scattered locus ceruleus neurons from three of the seven donors. X-ray fluorescence microscopy showed variations among individual locus ceruleus neurons in levels of mercury, selenium, iron, copper, lead, bromine, and rubidium. Variations between donors of locus ceruleus neuronal average levels of mercury, iron, copper, and bromine were also detected. Anterior pons neurons contained no mercury, had varied levels of iron, and had lower copper levels than locus ceruleus neurons.

Conclusions

Individual human locus ceruleus neurons contain varying levels of toxic metals and essential trace elements. In contrast, most toxic metals are absent or at low levels in nearby anterior pons neurons. The locus ceruleus plays a role in numerous central nervous system functions, including maintaining the blood-brain-barrier and limiting neuroinflammation. Toxic metals, or alterations in essential trace metals within individual locus ceruleus neurons, could be one factor determining the non-random destruction of locus ceruleus neurons in normal aging and neurodegenerative diseases, and subsequently the sites of the widespread multifocal central nervous system pathology in these disorders.

Assessing radiation dose limits for X-ray fluorescence microscopy analysis of plant specimens

BACKGROUND AND AIMS

X-ray fluorescence microscopy (XFM) is a powerful technique to elucidate the distribution of elements within plants. However, accumulated radiation exposure during analysis can lead to structural damage and experimental artefacts including elemental redistribution. To date, acceptable dose limits have not been systematically established for hydrated plant specimens.

METHODS

Here we systematically explore acceptable dose rate limits for investigating fresh sunflower (Helianthus annuus) leaf and root samples and investigate the time-dose damage in leaves attached to live plants.

KEY RESULTS

We find that dose limits in fresh roots and leaves are comparatively low (4.1 kGy), based on localized disintegration of structures and element-specific redistribution. In contrast, frozen-hydrated samples did not incur any apparent damage even at doses as high as 587 kGy. Furthermore, we find that for living plants subjected to XFM measurement in vivo and grown for a further 9 d before being reimaged with XFM, the leaves display elemental redistribution at doses as low as 0.9 kGy and they continue to develop bleaching and necrosis in the days after exposure.

CONCLUSIONS

The suggested radiation dose limits for studies using XFM to examine plants are important for the increasing number of plant scientists undertaking multidimensional measurements such as tomography and repeated imaging using XFM.

Characterization of Ionic and Lipid Gradients within Corpus Callosum White Matter after Diffuse Traumatic Brain Injury in the Rat

There is increased recognition of the effects of diffuse traumatic brain injury (dTBI), which can initiate yet unknown biochemical cascades, resulting in delayed secondary brain degeneration and long-term neurological sequela. There is limited availability of therapies that minimize the effect of secondary brain damage on the quality of life of people who have suffered TBI, many of which were otherwise healthy adults. Understanding the cascade of biochemical events initiated in specific brain regions in the acute phase of dTBI and how this spreads into adjacent brain structures may provide the necessary insight into drive development of improved therapies. In this study, we have used direct biochemical imaging techniques (Fourier transform infrared spectroscopic imaging) and elemental mapping (X-ray fluorescence microscopy) to characterize biochemical and elemental alterations that occur in corpus callosum white matter in the acute phase of dTBI. The results provide direct visualization of differential biochemical and ionic changes that occur in the highly vulnerable medial corpus callosum white matter relative to the less vulnerable lateral regions of the corpus callosum. Specifically, the results suggest that altered ionic gradients manifest within mechanically damaged medial corpus callosum, potentially spreading to and inducing lipid alterations to white matter structures in lateral brain regions.

Confocal Volumetric μXRF and Fluorescence Computed μ-Tomography Reveals Arsenic Three-Dimensional Distribution within Intact Pteris vittata Fronds

The fern Pteris vittata has been the subject of numerous studies because of its extreme arsenic hyperaccumulation characteristics. However, information on the arsenic chemical speciation and distribution across cell types within intact frozen-hydrated Pteris vittata fronds is necessary to better understand the arsenic biotransformation pathways in this unusual fern. While 2D X-ray absorption spectroscopy imaging studies show that different chemical forms of arsenic, As(III) and As(V), occur across the plant organs, depth-resolved information on arsenic distribution and chemical speciation in different cell types within tissues of Pteris vittata have not been reported. By using a combination of planar and confocal μ-X-ray fluorescence imaging and fluorescence computed μ-tomography, we reveal, in this study, the localization of arsenic in the endodermis and pericycle surrounding the vascular bundles in the rachis and the pinnules of the fern. Arsenic is also accumulated in the vascular bundles connecting into each sporangium, and in some mature sori. The use of 2D X-ray absorption near edge structure imaging allows for deciphering arsenic speciation across the tissues, revealing arsenate in the vascular bundles and arsenite in the endodermis and pericycle. This study demonstrates how different advanced synchrotron X-ray microscopy techniques can be complementary in revealing, at tissue and cellular levels, elemental distribution and chemical speciation in hyperaccumulator plants.

X-ray fluorescence analysis of metal distributions in cryogenic biological samples using large-acceptance-angle SDD detection and continuous scanning at the Hard X-ray Micro/Nano-Probe beamline P06 at PETRA III

A new Rococo 2 X-ray fluorescence detector was implemented into the cryogenic sample environment at the Hard X-ray Micro/Nano-Probe beamline P06 at PETRA III, DESY, Hamburg, Germany. A four sensor-field cloverleaf design is optimized for the investigation of planar samples and operates in a backscattering geometry resulting in a large solid angle of up to 1.1 steradian. The detector, coupled with the Xspress 3 pulse processor, enables measurements at high count rates of up to 106 counts per second per sensor. The measured energy resolution of ∼129 eV (Mn Kα at 10000 counts s-1) is only minimally impaired at the highest count rates. The resulting high detection sensitivity allows for an accurate determination of trace element distributions such as in thin frozen hydrated biological specimens. First proof-of-principle measurements using continuous-movement 2D scans of frozen hydrated HeLa cells as a model system are reported to demonstrate the potential of the new detection system.

Nanoparticle Size and Coating Chemistry Control Foliar Uptake Pathways, Translocation, and Leaf-to-Rhizosphere Transport in Wheat

Nanoenabled foliar-applied agrochemicals can potentially be safer and more efficient than conventional products. However, limited understanding about how nanoparticle properties influence their interactions with plant leaves, uptake, translocation through the mesophyll to the vasculature, and transport to the rest of the plant prevents rational design. This study used a combination of Au quantification and spatial analysis to investigate how size (3, 10, or 50 nm) and coating chemistry (PVP versus citrate) of gold nanoparticles (AuNPs) influence these processes. Following wheat foliar exposure to AuNPs suspensions (∼280 ng per plant), adhesion on the leaf surface was increased for smaller sizes, and PVP-AuNPs compared to citrate-AuNPs. After 2 weeks, there was incomplete uptake of citrate-AuNPs with some AuNPs remaining on the outside of the cuticle layer. However, the fraction of citrate-AuNPs that had entered the leaf was translocated efficiently to the plant vasculature. In contrast, for similar sizes, virtually all of the PVP-AuNPs crossed the cuticle layer after 2 weeks, but its transport through the mesophyll cells was lower. As a consequence of PVP-AuNP accumulation in the leaf mesophyll, wheat photosynthesis was impaired. Regardless of their coating and sizes, the majority of the transported AuNPs accumulated in younger shoots (10-30%) and in roots (10-25%), and 5-15% of the NPs <50 nm were exuded into the rhizosphere soil. A greater fraction of larger sizes AuNPs (presenting lower ζ potentials) was transported to the roots. The key hypotheses about the NPs physical-chemical and plant physiology parameters that may matter to predict leaf-to-rhizosphere transport are also discussed.

Biofortification of field-grown cassava by engineering expression of an iron transporter and ferritin

Less than 10% of the estimated average requirement (EAR) for iron and zinc is provided by consumption of storage roots of the staple crop cassava (Manihot esculenta Crantz) in West African human populations. We used genetic engineering to improve mineral micronutrient concentrations in cassava. Overexpression of the Arabidopsis thaliana vacuolar iron transporter VIT1 in cassava accumulated three- to seven-times-higher levels of iron in transgenic storage roots than nontransgenic controls in confined field trials in Puerto Rico. Plants engineered to coexpress a mutated A. thaliana iron transporter (IRT1) and A. thaliana ferritin (FER1) accumulated iron levels 7-18 times higher and zinc levels 3-10 times higher than those in nontransgenic controls in the field. Growth parameters and storage-root yields were unaffected by transgenic fortification in our field data. Measures of retention and bioaccessibility of iron and zinc in processed transgenic cassava indicated that IRT1 + FER1 plants could provide 40-50% of the EAR for iron and 60-70% of the EAR for zinc in 1- to 6-year-old children and nonlactating, nonpregnant West African women.

Recent advances in analysis of trace elements in environmental samples by X-ray based techniques (IUPAC Technical Report)

Trace elements analysis is a fundamental challenge in environmental sciences. Scientists measure trace elements in environmental media in order to assess the quality and safety of ecosystems and to quantify the burden of anthropogenic pollution. Among the available analytical techniques, X-ray based methods are particularly powerful, as they can quantify trace elements in situ. Chemical extraction is not required, as is the case for many other analytical techniques. In the last few years, the potential for X-ray techniques to be applied in the environmental sciences has dramatically increased due to developments in laboratory instruments and synchrotron radiation facilities with improved sensitivity and spatial resolution. In this report, we summarize the principles of the X-ray based analytical techniques most frequently employed to study trace elements in environmental samples. We report on the most recent developments in laboratory and synchrotron techniques, as well as advances in instrumentation, with a special attention on X-ray sources, detectors, and optics. Lastly, we inform readers on recent applications of X-ray based analysis to different environmental matrices, such as soil, sediments, waters, wastes, living organisms, geological samples, and atmospheric particulate, and we report examples of sample preparation.

Garnet peridotites reveal spatial and temporal changes in the oxidation potential of subduction

Changes in the oxygen fugacity (fO₂) of the Earth's mantle have been proposed to control the spatial and temporal distribution of arc-related ore deposits, and possibly reflect the evolution of the atmosphere over billions of years. Thermodynamic calculations and natural evidence indicate that fluids released from subducting slabs can oxidise the mantle, but whether their oxidation potential varied in space and time remains controversial. Here, we use garnet peridotites from western Norway to show that there is a linear decrease in maximum fO₂ with increasing depth in the mantle wedge. We ascribe this relation to changes in the speciation of sulfur released in slab fluids, with sulfate, controlling maximum oxidation, preferentially released at shallow depths. Even though the amount of sulfate in the Precambrian oceans, and thus in subducted lithologies, is thought to have been dramatically lower than during the Phanerozoic, garnet peridotites metasomatised during these two periods have a comparable fO₂ range. This opens to the possibility that an oxidised mantle with fO₂ similar to modern-day values has existed since the Proterozoic and possibly earlier. Consequently, early magmas derived from partial melting of metasomatised mantle may have had suitable fO₂ to generate porphyry Cu-Au and iron-oxide Cu-Au deposits.

A comparison of parametric and integrative approaches for X-ray fluorescence analysis applied to a Stroke model

Synchrotron X-ray fluorescence imaging enables visualization and quantification of microscopic distributions of elements. This versatile technique has matured to the point where it is used in a wide range of research fields. The method can be used to quantitate the levels of different elements in the image on a pixel-by-pixel basis. Two approaches to X-ray fluorescence image analysis are commonly used, namely, (i) integrative analysis, or window binning, which simply sums the numbers of all photons detected within a specific energy region of interest; and (ii) parametric analysis, or fitting, in which emission spectra are represented by the sum of parameters representing a series of peaks and other contributing factors. This paper presents a quantitative comparison between these two methods of image analysis using X-ray fluorescence imaging of mouse brain-tissue sections; it is shown that substantial errors can result when data from overlapping emission lines are binned rather than fitted. These differences are explored using two different digital signal processing data-acquisition systems with different count-rate and emission-line resolution characteristics. Irrespective of the digital signal processing electronics, there are substantial differences in quantitation between the two approaches. Binning analyses are thus shown to contain significant errors that not only distort the data but in some cases result in complete reversal of trends between different tissue regions.

High-Pressure Synthesis, Structural, and Spectroscopic Studies of the Ni-U-O System

The first comprehensive structural study of the Ni-U-O system is reported. Single crystals of α-NiUO₄, β-NiUO₄, and NiU₃O₁₀ were synthesized, and their structures were refined-using synchrotron single-crystal X-ray diffraction data supported by X-ray absorption spectroscopic measurements. α-NiUO₄ adopts an orthorhombic structure in space group Pbcn and is isostructural to CrUO₄ containing corrugated two-dimensional (2D) layers of corner-sharing UO₆ polyhedra and edge-sharing one-dimensional (1D) zigzag α-PbO₂ rutile-like chains of NiO₆ polyhedra in the [001] direction. β-NiUO₄ is isostructural to MgUO₄ and has an orthorhombic structure in space group Ibmm, which contains alternating 1D chains of edge-sharing UO₆ and NiO₆ polyhedra in the [001] direction as in regular TiO₂ rutile. NiU₃O₁₀ forms a triclinic structure in space group P1̅ and is isostructural with CuU₃O₁₀, where it forms a three-dimensional (3D) framework structure built through a mixture of UO₆ and UO₇ polyhedra in which the NiO₆ polyhedra sit isolated within the framework. X-ray absorption near-edge structure (XANES) measurements, conducted using XANES mapping of single crystals, support the presence of hexavalent uranium in the three structures. The polymorphs of NiUO₄ were found to only form under high-pressure and high-temperature conditions (≥4 GPa and 700 °C). It is argued that this is a consequence of the relative size difference between the Ni²⁺ and U⁶⁺ cations, where the Ni²⁺ cation is effectively too small for the Ibmm structure and too large for the Pbcn structure to form under ambient pressure conditions. This does not appear to be an issue for NiU₃O₁₀, which forms under ambient pressure conditions, where NiO₆ polyhedra sit isolated within the framework of 3D connected UO₆/UO₇ polyhedra. Synthesis conditions indicate that β-NiUO₄ is the preferred higher-pressure phase and that the transformation to this occurs irreversibly at a temperature between 950 and 1000 °C, when P = 4 GPa. The routes toward the synthesis of the oxides and the associated structural and spectroscopic results are described with respect to the structural chemistry of the Ni-U-O system, the larger AUO₄ family of oxides (A = divalent or trivalent cation), and also their relation to the rutile-related family of oxides.

CuII(atsm) Attenuates Neuroinflammation

Background: Neuroinflammation and biometal dyshomeostasis are key pathological features of several neurodegenerative diseases, including Alzheimer’s disease (AD). Inflammation and biometals are linked at the molecular level through regulation of metal buffering proteins such as the metallothioneins. Even though the molecular connections between metals and inflammation have been demonstrated, little information exists on the effect of copper modulation on brain inflammation.

Methods: We demonstrate the immunomodulatory potential of the copper bis(thiosemicarbazone) complex Cu^II(atsm) in an neuroinflammatory model in vivo and describe its anti-inflammatory effects on microglia and astrocytes in vitro.

Results: By using a sophisticated in vivo magnetic resonance imaging (MRI) approach, we report the efficacy of Cu^II(atsm) in reducing acute cerebrovascular inflammation caused by peripheral administration of bacterial lipopolysaccharide (LPS). Cu^II(atsm) also induced anti-inflammatory outcomes in primary microglia [significant reductions in nitric oxide (NO), monocyte chemoattractant protein 1 (MCP-1), and tumor necrosis factor (TNF)] and astrocytes [significantly reduced NO, MCP-1, and interleukin 6 (IL-6)] in vitro. These anti-inflammatory actions were associated with increased cellular copper levels and increased the neuroprotective protein metallothionein-1 (MT1) in microglia and astrocytes.

Conclusion: The beneficial effects of Cu^II(atsm) on the neuroimmune system suggest copper complexes are potential therapeutics for the treatment of neuroinflammatory conditions.

Temporal Evolution of Copper Distribution and Speciation in Roots of Triticum aestivum Exposed to CuO, Cu(OH)2, and CuS Nanoparticles

Utilization of nanoparticles (NP) in agriculture as fertilizers or pesticides requires an understanding of the NP properties influencing their interactions with plant roots. To evaluate the influence of the solubility of Cu-based NP on Cu uptake and NP association with plant roots, wheat seedlings were hydroponically exposed to 1 mg/L of Cu NPs with different solubilities [CuO, CuS, and Cu(OH)₂] for 1 h then transferred to a Cu-free medium for 48 h. Fresh, hydrated roots were analyzed using micro X-ray fluorescence (μ-XRF) and imaging fluorescence X-ray absorption near edge spectroscopy (XANES imaging) to provide laterally resolved distribution and speciation of Cu in roots. Higher solubility Cu(OH)₂ NPs provided more uptake of Cu after 1 h of exposure, but the lower solubility materials (CuO and CuS) were more persistent on the roots and continued to deliver Cu to plant leaves over the 48 h depuration period. These results demonstrate that NPs, by associating to the roots, have the potential to play a role in slowly providing micronutrients to plants. Thus, tuning the solubility of NPs may provide a long-term slow delivery of micronutrients to plants and provide important information for understanding mechanisms responsible for plant uptake, transformation, and translocation of NPs.

A color x-ray camera for 2-6 keV using a mass produced back illuminated complementary metal oxide semiconductor sensor

There are several reports in the scientific literature of the use of mass-produced charge coupled device or complementary metal oxide semiconductor (CMOS) sensors as x-ray detectors that combine high spatial resolution with significant energy resolution. Exploiting a relatively new especially favorable ambient-temperature back-illuminated CMOS sensor, we report the development of a spectroscopic x-ray camera having particularly impressive performance for 2-6 keV photons. This instrument has several beneficial characteristics for advanced x-ray spectroscopy studies in the laboratory, at synchrotron light sources, at x-ray free electron lasers, or when using pulsed x-ray sources such as for laser plasma physics research. These characteristics include fine position and energy resolution for individual photon events, high saturation rates, frame rates above 100 Hz, easy user maintenance for damaged sensors, and software for real-time processing. We evaluate this camera as an alternative to traditional energy-dispersive solid-state detectors, such as silicon drift detectors, and also illustrate its use in a very high resolution wavelength-dispersive x-ray fluorescence spectrometer (i.e., x-ray emission spectrometer) that has recently been reported elsewhere [W. M. Holden et al., Rev. Sci. Instrum. 88(7), 073904 (2017)].

Recovery of Degraded-Beyond-Recognition 19th Century Daguerreotypes with Rapid High Dynamic Range Elemental X-ray Fluorescence Imaging of Mercury L Emission

A daguerreotype image, the first commercialized photographic process, is composed of silver-mercury, and often silver-mercury-gold amalgam particles on the surface of a silver-coated copper plate. Specular and diffuse reflectance of light from these image particles produces the range of gray tones that typify these 19^th century images. By mapping the mercury distribution with rapid-scanning, synchrotron-based micro-X-ray fluorescence (μ-XRF) imaging, full portraits, which to the naked eye are obscured entirely by extensive corrosion, can be retrieved in a non-invasive, non-contact, and non-destructive manner. This work furthers the chemical understanding regarding the production of these images and suggests that mercury is retained in the image particles despite surface degradation. Most importantly, μ-XRF imaging provides curators with an image recovery method for degraded daguerreotypes, even if the artifact’s condition is beyond traditional conservation treatments.

Fast XANES fluorescence imaging using a Maia detector

A new fast X-ray absorption spectroscopy scanning method was recently implemented at the Hard X-ray Microprobe endstation P06, PETRA III, DESY, utilizing a Maia detector. Spectromicroscopy maps were acquired with spectra for X-ray absorption near-edge structure (XANES) acquisition in the sub-second regime. The method combines XANES measurements with raster-scanning of the sample through the focused beam. The order of the scanning sequence of the axes, one beam energy axis and two (or more) spatial axes, is a variable experimental parameter and, depending on it, the dwell at each location can be either single and continuous (if the energy axis is the inner loop) or in shorter discontinuous intervals (if a spatial axis is innermost). The combination of improved spatial and temporal resolution may be necessary for rapidly changing samples, e.g. for following in operando chemical reactions or samples highly susceptible to beam damage where the rapid collection of single XANES spectra avoids issues with the emergence of chemical changes developing from latent damage. This paper compares data sets collected on a specially designed test pattern and a geological thin-section scanning the energy as inner, middle and outer axis in the sequence. The XANES data of all three scanning schemes is found to show excellent agreement down to the single-pixel level.

X-ray elemental mapping techniques for elucidating the ecophysiology of hyperaccumulator plants

Contents Summary 432 I. Introduction 433 II. Preparation of plant samples for X-ray micro-analysis 433 III. X-ray elemental mapping techniques 438 IV. X-ray data analysis 442 V. Case studies 443 VI. Conclusions 446 Acknowledgements 449 Author contributions 449 References 449 SUMMARY: Hyperaccumulators are attractive models for studying metal(loid) homeostasis, and probing the spatial distribution and coordination chemistry of metal(loid)s in their tissues is important for advancing our understanding of their ecophysiology. X-ray elemental mapping techniques are unique in providing in situ information, and with appropriate sample preparation offer results true to biological conditions of the living plant. The common platform of these techniques is a reliance on characteristic X-rays of elements present in a sample, excited either by electrons (scanning/transmission electron microscopy), protons (proton-induced X-ray emission) or X-rays (X-ray fluorescence microscopy). Elucidating the cellular and tissue-level distribution of metal(loid)s is inherently challenging and accurate X-ray analysis places strict demands on sample collection, preparation and analytical conditions, to avoid elemental redistribution, chemical modification or ultrastructural alterations. We compare the merits and limitations of the individual techniques, and focus on the optimal field of applications for inferring ecophysiological processes in hyperaccumulator plants. X-ray elemental mapping techniques can play a key role in answering questions at every level of metal(loid) homeostasis in plants, from the rhizosphere interface, to uptake pathways in the roots and shoots. Further improvements in technological capabilities offer exciting perspectives for the study of hyperaccumulator plants into the future.

Characterization of uranium redox state in organic-rich Eocene sediments

The presence of organic matter (OM) has a profound impact on uranium (U) redox cycling, either limiting or promoting the mobility of U via binding, reduction, or complexation. To understand the interactions between OM and U, we characterised U oxidation state and speciation in nine OM-rich sediment cores (18 samples), plus a lignite sample from the Mulga Rock polymetallic deposit in Western Australia. Uranium was unevenly dispersed within the analysed samples with 84% of the total U occurring in samples containing >21 wt % OM. Analyses of U speciation, including x-ray absorption spectroscopy and bicarbonate extractions, revealed that U existed predominately (∼71%) as U(VI), despite the low pH (4.5) and nominally reducing conditions within the sediments. Furthermore, low extractability by water, but high extractability by a bi-carbonate solution, indicated a strong association of U with particulate OM. The unexpectedly high proportion of U(VI) relative to U(IV) within the OM-rich sediments implies that OM itself does not readily reduce U, and the reduction of U is not a requirement for immobilizing uranium in OM-rich deposits. The fact that OM can play a significant role in limiting the mobility and reduction of U(VI) in sediments is important for both U-mining and remediation.

2D/3D Microanalysis by Energy Dispersive X-ray Absorption Spectroscopy Tomography

X-ray spectroscopic techniques have proven to be particularly useful in elucidating the molecular and electronic structural information of chemically heterogeneous and complex micro- and nano-structured materials. However, spatially resolved chemical characterization at the micrometre scale remains a challenge. Here, we report the novel hyperspectral technique of micro Energy Dispersive X-ray Absorption Spectroscopy (μED-XAS) tomography which can resolve in both 2D and 3D the spatial distribution of chemical species through the reconstruction of XANES spectra. To document the capability of the technique in resolving chemical species, we first analyse a sample containing 2-30 μm grains of various ferrous- and ferric-iron containing minerals, including hypersthene, magnetite and hematite, distributed in a light matrix of a resin. We accurately obtain the XANES spectra at the Fe K-edge of these four standards, with spatial resolution of 3 μm. Subsequently, a sample of ~1.9 billion-year-old microfossil from the Gunflint Formation in Canada is investigated, and for the first time ever, we are able to locally identify the oxidation state of iron compounds encrusting the 5 to 10 μm microfossils. Our results highlight the potential for attaining new insights into Precambrian ecosystems and the composition of Earth's earliest life forms.

Scanning X-ray diffraction on cardiac tissue: automatized data analysis and processing

A scanning X-ray diffraction study of cardiac tissue has been performed, covering the entire cross section of a mouse heart slice. To this end, moderate focusing by compound refractive lenses to micrometer spot size, continuous scanning, data acquisition by a fast single-photon-counting pixel detector, and fully automated analysis scripts have been combined. It was shown that a surprising amount of structural data can be harvested from such a scan, evaluating the local scattering intensity, interfilament spacing of the muscle tissue, the filament orientation, and the degree of anisotropy. The workflow of data analysis is described and a data analysis toolbox with example data for general use is provided. Since many cardiomyopathies rely on the structural integrity of the sarcomere, the contractile unit of cardiac muscle cells, the present study can be easily extended to characterize tissue from a diseased heart.

Impact of Surface Charge on Cerium Oxide Nanoparticle Uptake and Translocation by Wheat (Triticum aestivum)

Nanoparticle (NP) physiochemical properties, including surface charge, affect cellular uptake, translocation, and tissue localization. To evaluate the influence of surface charge on NP uptake by plants, wheat seedlings were hydroponically exposed to 20 mg/L of ∼4 nm CeO₂ NPs functionalized with positively charged, negatively charged, and neutral dextran coatings. Fresh, hydrated roots and leaves were analyzed at various time points over 34 h using fluorescence X-ray absorption near-edge spectroscopy to provide laterally resolved spatial distribution and speciation of Ce. A 15-20% reduction from Ce(IV) to Ce(III) was observed in both roots and leaves, independent of NP surface charge. Because of its higher affinity with negatively charged cell walls, CeO₂(+) NPs adhered to the plant roots the strongest. After 34 h, CeO₂(-), and CeO₂(0) NP exposed plants had higher Ce leaf concentrations than the plants exposed to CeO₂(+) NPs. Whereas Ce was found mostly in the leaf veins of the CeO₂(-) NP exposed plant, Ce was found in clusters in the nonvascular leaf tissue of the CeO₂(0) NP exposed plant. These results provide important information for understanding mechanisms responsible for plant uptake, transformation, and translocation of NPs, and suggest that NP coatings can be designed to target NPs to specific parts of plants.

CCD camera as feasible large-area-size x-ray detector for x-ray fluorescence spectroscopy and imaging

As X-ray fluorescence radiation isotropically spreads from the sample, one of the most important requirements for spectrometers for many years has been a large solid angle. Charge-coupled device (CCD) cameras are quite promising options because they have a fairly large area size, usually larger than 150 mm². The present work has examined the feasibility of a commercially available camera with an ordinary CCD chip (1024 × 1024 pixels, the size of one pixel is 13 μm × 13 μm, designed for visible light) as an X-ray fluorescence detector. As X-ray photons create charges in the CCD chip, reading very quickly the amount is the key for this method. It is very simple if the charges always go into one pixel. As the charges quite often spread to several pixels, and sometimes can be lost, it is important to recover the information by filtering out the unsuccessful events. For this, a simple, versatile, and reliable scheme has been proposed. It has been demonstrated that the energy resolution of the present camera is 150 eV at Mn Kα, and also that its overall achievement in seeing minor elements is almost compatible with conventional X-ray fluorescence detectors. When the CCD camera is combined with a micro-pinhole collimator, full field X-ray fluorescence imaging with a spatial resolution of 20 μm becomes possible. Further feasibility in practical X-ray fluorescence analysis is discussed.

Application toward Confocal Full-Field Microscopic X-ray Absorption Near Edge Structure Spectroscopy

Using X-ray absorption near edge structure (XANES) spectroscopy, information on the local chemical structure and oxidation state of an element of interest can be acquired. Conventionally, this information can be obtained in a spatially resolved manner by scanning a sample through a focused X-ray beam. Recently, full-field methods have been developed to obtain direct 2D chemical state information by imaging a large sample area. These methods are usually in transmission mode, thus restricting the use to thin and transmitting samples. Here, a fluorescence method is displayed using an energy-dispersive pnCCD detector, the SLcam, characterized by measurement times far superior to what is generally applicable. Additionally, this method operates in confocal mode, thus providing direct 3D spatially resolved chemical state information from a selected subvolume of a sample, without the need of rotating a sample. The method is applied to two samples: a gold-supported magnesia catalyst (Au/MgO) and a natural diamond containing Fe-rich inclusions. Both samples provide XANES spectra that can be overlapped with reference XANES spectra, allowing this method to be used for fingerprinting and linear combination analysis of known XANES reference compounds.

Fast X-ray microfluorescence imaging with submicrometer-resolution integrating a Maia detector at beamline P06 at PETRA III

The high brilliance of third-generation synchrotron sources increases the demand for faster detectors to utilize the available flux. The Maia detector is an advanced imaging scheme for energy-dispersive detection realising dwell times per image-pixel as low as 50 µs and count rates higher than 10 × 10⁶ s^-1. In this article the integration of such a Maia detector in the Microprobe setup of beamline P06 at the storage ring PETRA III at the Deutsches Elektronen-Synchrotron (DESY) in Hamburg, Germany, is described. The analytical performance of the complete system in terms of rate-dependent energy resolution, scanning-speed-dependent spatial resolution and lower limits of detection is characterized. The potential of the Maia-based setup is demonstrated by key applications from materials science and chemistry, as well as environmental science with geological applications and biological questions that have been investigated at the P06 beamline.

Fate of Plutonium at a Former Nuclear Testing Site in Australia

A series of the British nuclear tests conducted on mainland Australia between 1953 and 1963 dispersed long-lived radioactivity and nuclear weapons debris including plutonium (Pu), the legacy of which is a long-lasting source of radioactive contamination to the surrounding biosphere. A reliable assessment of the environmental impact of Pu contaminants and their implications for human health requires an understanding of their physical/chemical characteristics at the molecular scale. In this study, we identify the chemical form of the Pu remaining in the local soils at the Taranaki site, one of the former nuclear testing sites at Maralinga, South Australia. We herein reveal direct spectroscopic evidence that the Pu legacy remaining at the site exists as particulates of Pu(IV) oxyhydroxide compounds, a very concentrated and low-soluble form of Pu, which will serve as ongoing radioactive sources far into the future. Gamma-ray spectrometry and X-ray fluorescence analysis on a collected Pu particle indicate that the Pu in the particle originated in the so-called "Minor trials" that involved the dispersal of weapon components by highly explosive chemicals, not in the nuclear explosion tests called "Major trials". A comprehensive analysis of the data acquired from X-ray fluorescence mapping (XFM), X-ray absorption near-edge structure (XANES), and extended X-ray absorption fine structure (EXAFS) suggests that the collected Pu particle forms a "core-shell" structure with the Pu(IV) oxyhydroxide core surrounded by an external layer containing Ca, Fe, and U, which further helps us to deduce a possible scenario of the physical/chemical transformation of the original Pu materials dispersed in the semiarid environment at Maralinga more than 50 years ago. These findings also highlight the importance of the comprehensive physical/chemical characterization of Pu contaminants for reliable environmental- and radiotoxicological assessment.

Mapping Alterations to the Endogenous Elemental Distribution within the Lateral Ventricles and Choroid Plexus in Brain Disorders Using X-Ray Fluorescence Imaging

The choroid plexus and cerebral ventricles are critical structures for the production of cerebral spinal fluid (CSF) and play an important role in regulating ion and metal transport in the brain, however many aspects of its roles in normal physiology and disease states, such as psychiatric illness, remain unknown. The choroid plexus is difficult to examine in vivo, and in situ ex vivo, and as such has typically been examined indirectly with radiolabeled tracers or ex vivo stains, making measurements of the endogenous K+, Cl-, and Ca+ distributions unreliable. In the present study, we directly examined the distribution of endogenous ions and biologically relevant transition metals in the choroid plexus and regions surrounding the ventricles (ventricle wall, cortex, corpus callosum, striatum) using X-ray fluorescence imaging (XFI). We find that the choroid plexus was rich in Cl- and Fe while K+ levels increase further from the ventricle as Cl- levels decrease, consistent with the known role of ion transporters in the choroid plexus CSF production. A polyI:C offspring displayed enlarged ventricles, elevated Cl- surrounding the ventricles, and intraventricular calcifications. These observations fit with clinical findings in patients with schizophrenia and suggest maternal treatment with polyI:C may lead to dysfunctional ion regulation in offspring. This study demonstrates the power of XFI for examining the endogenous elemental distributions of the ventricular system in healthy brain tissue as well as disease models.

Spatiotemporal distribution of essential elements through Populus leaf ontogeny

We examined the spatiotemporal distribution and accumulation of calcium (Ca), potassium (K), and zinc (Zn) during the growth and maturation of grey poplar (Populus tremula × alba) leaves covering plastochrons 01 through 10. This period spans the sugar sink-to-source transition and requires coordinated changes of multiple core metabolic processes that likely involve alterations in essential and non-essential element distributions as tissues mature and effect a reversal in phloem flow direction. Whole-leaf elemental maps were obtained from dried specimens using micro X-ray fluorescence spectroscopy. Additional cross-sections of fresh leaves were scanned to check for tissue specificity in element accumulation. The anatomical distribution of Zn and K remains relatively consistent throughout leaf development; Ca accumulation varied across leaf developmental stages. The basipetal allocation of Ca to the leaf mesophyll matched spatially and temporally the sequence of phloem maturation, positive carbon balance, and sugar export from leaves. The accumulation of Ca likely reflects the maturation of xylem in minor veins and the enhancement of the transpiration stream. Our results independently confirm that xylem and phloem maturation are spatially and temporally coordinated with the onset of sugar export in leaves.