X-ray Microspectroscopy Research Articles

Water-dispersible PVA-based dry microballoons with potential for biomedical applications

This paper reports on the preparation and characterization of stable poly(vinyl alcohol) (PVA)-based dry hollow microparticles, readily convertible to gas-filled microballoons (MBs) in water suspension. The rehydrated MBs can be used as ultrasound contrast agents and for targeted drug delivery, while the dry MBs are suitable for encapsulation of biologically active gases. The MBs powder material is obtained by freeze-drying the as-prepared telechelic PVA-shelled MBs aqueous dispersion. The microstructure of the lyophilized MBs as well as of the starting and the reconstituted MBs in water suspension was examined using transmission electron microscopy (TEM), scanning electron microscopy (SEM), scanning transmission X-ray microspectroscopy (STXM) and confocal laser scanning microscopy (CLSM). STXM observations below and above the oxygen K-edge reveal that 80% of the MBs originating from the lyophilized particles are gas-filled. Moreover, local carbon K near-edge X-ray absorption fine structure spectroscopy (NEXAFS) measurements evidenced that the chemical composition of the polymeric shell is preserved during the freeze-drying process and subsequent shelf storage for at least more than one year.

Fluorescence X-ray micro-spectroscopy activities at ESRF

The X-ray Microscopy and Micro-analysis beamlines at ESRF operate complementary state-of-the-art instruments at ID21, ID22, ID18F and more recently ID22NI. Within a multi-modal strategy, these beamlines develop micro-imaging techniques with various contrast mechanisms (μXRF, μXANES, μXRD and phase contrast) and host experiments with scientific topics ranging from Geochemistry to Archeology, Environmental sciences, Biology and Material sciences. Future challenges include pushing spatial resolution down to the nano-scale and the development of innovative 3D micro-analysis techniques.

Investigations of clay colloid aggregates by scanning transmission X-ray microspectroscopy of suspensions

The environmental behaviour of colloidal clay in aquatic systems is linked to the properties of their aggregates. Earlier investigations of clay colloids were performed with electron microscope techniques which caused de-hydration of the particles. Information on the structure of colloid aggregates is needed for understanding their sedimentation behaviour, as well as colloid contaminant transport properties in natural systems. Scanning transmission X-ray microspectroscopy successfully produced images of montmorillonite colloid aggregates in a pseudo-equilibrium state in 1 mM NaCl suspensions equilibrated for more than a year. These clay aggregates were revealed at photon energies below the O absorption edges of clay and water. They were spherical or ellipsoidal with diameters of the order of 100-800 nm. The aggregates are porous and gel like with lower densities than the clay mineral. These investigations are important for modelling the occurrence of clay aggregates in aqueous environments.

Identification of L-ferritin in Neuromelanin Granules of the Human Substantia Nigra: A TARGETED PROTEOMICS APPROACH

In the pigmented dopaminergic neurons of the human substantia nigra pars compacta the system relevant in iron storage is the polymer neuromelanin (NM). Although in most cells this function is mainly accomplished by ferritin, this protein complex appears not to be expressed in NM-containing neurons. Nevertheless the conceivable presence of iron-storing proteins as part of the NM granules has recently been discussed on the basis of Mössbauer spectroscopy and synchrotron x-ray microspectroscopy. Intriguingly by combining subcellular fractionation of NM granules, peptide sequencing via tandem mass spectrometry, and the additional confirmation by multiple reaction monitoring and immunogold labeling for electron microscopy, L-ferritin could now be unambiguously identified and localized in NM granules for the first time. This finding not only supports direct evidence for a regulatory role of L-ferritin in neuroectodermal cell pigmentation but also integrates a new player within a complicated network governing iron homeostasis in the dopamine neurons of the human substantia nigra. Thus our finding entails far reaching implications especially when considering etiopathogenetic aspects of Parkinson disease.

Bio-metals imaging and speciation in cells using proton and synchrotron radiation X-ray microspectroscopy

The direct detection of biologically relevant metals in single cells and of their speciation is a challenging task that requires sophisticated analytical developments. The aim of this article is to present the recent achievements in the field of cellular chemical element imaging, and direct speciation analysis, using proton and synchrotron radiation X-ray micro- and nano-analysis. The recent improvements in focusing optics for MeV-accelerated particles and keV X-rays allow application to chemical element analysis in subcellular compartments. The imaging and quantification of trace elements in single cells can be obtained using particle-induced X-ray emission (PIXE). The combination of PIXE with backscattering spectrometry and scanning transmission ion microscopy provides a high accuracy in elemental quantification of cellular organelles. On the other hand, synchrotron radiation X-ray fluorescence provides chemical element imaging with less than 100 nm spatial resolution. Moreover, synchrotron radiation offers the unique capability of spatially resolved chemical speciation using micro-X-ray absorption spectroscopy. The potential of these methods in biomedical investigations will be illustrated with examples of application in the fields of cellular toxicology, and pharmacology, bio-metals and metal-based nano-particles.

Simultaneous soft X-ray transmission and emission microscopy

Novel low-energy X-ray fluorescence (LEXRF) system based on a multiple Si drift detector (SDD) configuration has been developed and implemented in the European TwinMic X-ray microspectroscopy station operating at the Italian synchrotron radiation facility ELETTRA. The setup, hosting up to eight large-area SDDs with specially adapted readout electronics, has demonstrated excellent performance for elemental analysis in the 280–2200 eV photon energy range, which covers the K and L edges of light elements, starting from C. The great advantage is the simultaneous acquisition of LEXRF, absorption and phase contrast maps, providing complementary information on elemental composition and morphology of specimen at submicrometer length scales.

On Source Identification and Alteration of Single Diesel and Wood Smoke Soot Particles in the Atmosphere; An X-Ray Microspectroscopy Study

Diesel and wood combustion are major sources of carbonaceous particles in the atmosphere. It is very hard to distinguish between the two sources by looking at soot particle morphology, but clear differences in the chemical structure of single particles are revealed by C(1s) NEXAFS (near edge X-ray absorption fine structure) microspectroscopy. Soot from diesel combustion has a dominant spectral signature at approximately 285 eV from aromatic pi-bonds, whereas soot from wood combustion has the strongest signature at approximately 287 eV from phenolic carbon bonds. To investigate if it is possible to use these signatures for source apportionment purposes, we collected atmospheric samples with either diesel or wood combustion as a dominant particle source. No spectra obtained from the atmospheric particles completely matched the emission spectra. Especially particles from the wood dominated location underwent large modifications; the phenolic spectral signature at approximately 287 eV is greatly suppressed and surpassed by the peak attributed to the aromatic carbon groups at approximately 285 eV. Comparison with spectra from diesel soot samples experimentally aged with ozone show that very fast modification of the carbon structure of soot particles occurs as soon as they enter the atmosphere. Source attribution of single soot particles with microspectroscopy is thus hardly possible, but NEXAFS remains a powerful tool to study aging effects.

Soft X-ray induced modifications of PVA-based microbubbles in aqueous environment: a microspectroscopy study

We use scanning-transmission X-ray microspectroscopy (STXM) for in situ characterization of the physicochemical changes in air-filled poly(vinyl alcohol) (PVA) based microbubbles upon soft X-ray irradiation. The microbubbles were illuminated directly in aqueous suspension with 520 eV X-rays and a continuous shrinkage of the particles with an illumination time/radiation dose was observed. Utilizing the intrinsic absorption properties of the species and the high spatial resolution of the STXM, the modifications of the particles' structure were simultaneously recognized. A thorough characterization of the microbubble volume, membrane thickness and absorption coefficient was performed by quantitative fitting of the radial transmittance profiles of the targeted microbubbles. Apart from the observed volume contraction, there was no significant change in the shell thickness. The chemical changes in the membranes were clarified via C K-edge near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. It was revealed that the observed structural alterations go along with a continuous degradation of the PVA network associated with formation of carbonyl- and carboxyl-containing species as well as an increased content of unsaturated bonds.

Synchrotron-induced X-ray fluorescence from rat bone and lumber vertebra of different age groups

The fluorescence spectra from rat bones of different age groups (8, 56 and 78 weeks) and lumber vertebra were measured with 8, 10 and 12 keV synchrotron X-rays. We have utilized the new hard X-ray micro-spectroscopy beamline facility, X27A, available at NSLS with a primary beam spot size of the order of ∼10 μm. With this spatial resolution and high flux throughput, X-ray fluorescent intensities for Ca and other trace elements were measured using a liquid-nitrogen-cooled 13-element energy-dispersive high-purity germanium detector. Regarding the lumber vertebra, we acquired the fluorescence spectra from the left, right and middle portions and calcium accumulation was evaluated and compared with the other samples. We have identified the major trace elements of Ca, Ni, Fe and Zn and minor trace elements of Ti, Cr and Mn in the sample. The percentage of scattered radiation and trace element contributions from these samples were highlighted at different energies.

Zircaloy-2 secondary phase precipitate analysis by X-ray microspectroscopy

Secondary phase precipitates of a Zircaloy sample have been characterised by X-ray microspectroscopy. In Zircaloy-2 X-ray microscopy reveals pictures with a 40 nm resolution identifying Fe, Cr and to a lower occurrence Ni phases up to size of the micrometer. Analysis by X-ray spectroscopy defines the structure of specific secondary phase precipitates. The feasibility tests demonstrate that the characterisation of Fe and Cr can be performed on 100 nm size phases allowing the analysis of the Fe or Cr atoms environment in these secondary phase precipitates.

Soft x-ray spectroscopy and microspectroscopy of correlated materials: photoemission andmagnetic circular dichroism

Spectroscopy and microspectroscopy of strongly correlated systems, ferromagneticmaterials and magnetic microstructures by means of photoemission and magnetic circulardichroism using soft x-rays are presented. Bulk-sensitive high-resolution soft x-rayphotoemission has revealed the real bulk electronic states of rare-earth compounds withvarious degrees of electronic correlation. Soft x-ray magnetic circular dichroism (XMCD)has enabled element-specific measurements of the system dependence of the orbitalcontribution to the magnetic moment, which has been shown to be enhanced when themagnetic electrons are more localized. XMCD microspectroscopy has been carried out formagnetic microstructures, which, by fully utilizing the spectroscopic aspect, has yielded notonly the magnetic domain structures but also the distribution of the spin and orbitalmagnetic moment.

Plutonium Oxidation and Subsequent Reduction by Mn(IV) Minerals in Yucca Mountain Tuff

Plutonium oxidation state distribution on Yucca Mountain tuff and synthetic pyrolusite (beta-MnO2) suspensions was measured using synchrotron X-ray micro-spectroscopy and microimaging techniques as well as ultrafiltration/solventextraction techniques. Plutonium sorbed to the tuff was preferentially associated with manganese oxides. For both Yucca Mountain tuff and synthetic pyrolusite, Pu(IV) or Pu(V) was initially oxidized to more mobile Pu(V/VI), but over time, the less mobile Pu(IV) became the predominant oxidation state of the sorbed Pu. The observed stability of Pu(IV) on oxidizing surfaces (e.g., pyrolusite), is proposed to be due to the formation of a stable hydrolyzed Pu(IV) surface species. These findings have important implications in estimating the risk associated with the geological burial of radiological waste in areas containing Mn-bearing minerals, such as at the Yucca Mountain or the Hanford Sites, because plutonium will be predominantly in a much less mobile oxidation state (i.e., Pu(IV)) than previously suggested (i.e., Pu(V/VI).

Technical Report: Monte Carlo Simulations for Soft X-ray Microspectroscopy Using the Upgraded EGS4 Code System

X-ray microspectroscopy became a very common synchrotron-based method during the last decade. Soft X-ray microspectroscopy is an imaging technique based on penetration of very thin samples by a monoenergetic, parallel intense beam. The typical samples examined contain a suspension of microscopic organic bodies in emulsion. Since soft X-rays in the energy range of 100–1000eV have a very short wavelength compared to visible light, high-resolution images can be obtained with soft X-rays. In general, the field of view for most of the samples must be on the order of a few tens of microns. Usually, submicron spatial resolution is desired to obtain images of the objects. The experimental setup for soft X-ray microscopy was described in detail by Jacobsen et al. [1]

X27A—A new hard X-ray micro-spectroscopy facility at the National Synchrotron Light Source

A new hard X-ray micro-spectroscopy beamline has recently been installed at bending-magnet beamline X27A at the National Synchrotron Light Source, where the focus of research is primarily directed towards the environmental, geological and materials science communities. This instrument delivers moderate, ∼10 μm spatial resolution using achromatic dynamically bent Kirkpatrick–Baez mirrors, in addition to providing high X-ray flux throughput and selectable energy resolution. The balance between moderate spatial resolution and high flux throughput, in combination with a liquid nitrogen-cooled 13-element energy-dispersive high-purity germanium detector, is particularly well suited to the investigation of dilute and thin-film systems using the fluorescence X-ray absorption fine-structure mode of detection. In this paper, we report on the design and performance of this instrument and highlight a recent experimental study undertaken at this facility.

Sulfur accumulation in the timbers of King Henry VIII's warship Mary Rose : A pathway in the sulfur cycle of conservation concern

In marine-archaeological oak timbers of the Mary Rose large amounts of reduced sulfur compounds abound in lignin-rich parts such as the middle lamella between the cell walls, mostly as thiols and disulfides, whereas iron sulfides and elemental sulfur occur in separate particles. Synchrotron-based x-ray microspectroscopy was used to reveal this environmentally significant accumulation of organosulfur compounds in waterlogged wood. The total concentration of sulfur in reduced forms is approximately 1 mass % throughout the timbers, whereas iron fluctuates up to several mass %. Conservation methods are being developed aiming to control acid-forming oxidation processes by removing the reactive iron sulfides and stabilizing the organosulfur compounds.

An x-ray microspectroscopy study of hemochromatosis liver and diabetic mice kidney tissues: preliminary observations

We report preliminary observations of tissue images and micro-XAFS using x-ray microscopy techniques. Tissue specimens from hemocromatosis liver and knockout mice kidney were the subjects of the investigation. The x-ray microprobe experiments were conducted with a micro beam from an undulator beamline equipped with a set of K–B mirrors. Microbeam XAFS studies at selected pixels of interest from the metal images were conducted. These techniques, together with optical and IR imaging provide a powerful tool for tissue analysis using synchrotron radiation. Preliminary Fe and Cu K-edge XAFS results from these experiments are reported and discussed.

04/02687 A study of diesel PM with X-ray microspectroscopy: Braun, A. et al. Fuel, 2004, 83, (7–8), 997–1000

04/02687 A study of diesel PM with X-ray microspectroscopy: Braun, A. et al. Fuel, 2004, 83, (7–8), 997–1000

Beamline 10.3.2 at ALS: a hard X-ray microprobe for environmental and materials sciences.

Beamline 10.3.2 at the ALS is a bend-magnet line designed mostly for work on environmental problems involving heavy-metal speciation and location. It offers a unique combination of X-ray fluorescence mapping, X-ray microspectroscopy and micro-X-ray diffraction. The optics allow the user to trade spot size for flux in a size range of 5-17 microm in an energy range of 3-17 keV. The focusing uses a Kirkpatrick-Baez mirror pair to image a variable-size virtual source onto the sample. Thus, the user can reduce the effective size of the source, thereby reducing the spot size on the sample, at the cost of flux. This decoupling from the actual source also allows for some independence from source motion. The X-ray fluorescence mapping is performed with a continuously scanning stage which avoids the time overhead incurred by step-and-repeat mapping schemes. The special features of this beamline are described, and some scientific results shown.

A study of diesel PM with X-ray microspectroscopy

Carbonaceous particulate matter from diesel fuel combustion was studied with Scanning Transmission X-ray Microspectroscopy, a novel synchrotron radiation-based technique, which combines X-ray absorption spectroscopy and microscopy. Single soot particles were chemically identified with a spatial resolution of better than 100 nm. Near-edge X-ray Absorption Fine Structure spectra from the carbon K-absorption edge could be assigned to specific particle regions, making it possible to distinguish graphitic carbon in the soot particles from hydrocarbons, such as residual lubricating oil and diesel fuel and their reaction products.

X-ray microspectroscopy of sulfur in basaltic glass inclusions. Inference on the volcanic sulfur emissions

It is commonly accepted that sulfur is carried out as sulfide (S $\rm ^{II-}$) or/and sulfate (S $\rm ^{VI}$) by Earth mantlederived melts, before being released as SO 2 and/or H 2S in volcanic emissions. By analyzing reference compounds and a selection of minute glass inclusions in olivine crystals using $\mu$XANES (X-ray Near Edge Structure) spectroscopy at the sulfur K-edge, we demonstrated the ubiquitous presence of sulfite (S $\rm ^{IV}$) in addition to sulfate (S $\rm ^{VI}$) in these rare inclusions representative of oxidized and water rich-basaltic magmas, prior to loss of sulfur and water. The sulfide (S $\rm ^{II-}$) when exists is minor. We proposed that sulfite (S $\rm ^{IV}$) acts as an intermediate, metastable species which results in partitioning of sulfur into the volcanic gas emissions.