Jan Garrevoet

Perfect X-ray focusing via fitting corrective glasses to aberrated optics

Due to their short wavelength, X-rays can in principle be focused down to a few nanometres and below. At the same time, it is this short wavelength that puts stringent requirements on X-ray optics and their metrology. Both are limited by todays technology. In this work, we present accurate at wavelength measurements of residual aberrations of a refractive X-ray lens using ptychography to manufacture a corrective phase plate. Together with the fitted phase plate the optics shows diffraction-limited performance, generating a nearly Gaussian beam profile with a Strehl ratio above 0.8. This scheme can be applied to any other focusing optics, thus solving the X-ray optical problem at synchrotron radiation sources and X-ray free-electron lasers.

A novel calibration strategy for the quantitative imaging of iron in biological tissues by LA-ICP-MS using matrix-matched standards and internal standardisation

The development of a novel and straightforward procedure for the preparation of matrix-matched calibration standards for the quantitative imaging of iron (Fe) in biological tissues by laser ablation (LA)-ICP-MS with on-tissue internal standard addition is described. This simple approach enabled on-tissue addition of Rh as internal standard to samples (with heterogeneous Fe distribution) and calibrants (with homogeneous Fe distribution). This is achieved without altering the original Fe distribution of the sample. Calibration standards were prepared by full horizontal immersion of slides with mounted homogenised sheep brain tissue section into the corresponding solution containing 0.5, 0.75, 1, 5, 10 and 20 mg kg−1 Fe (each also containing 250 µg kg−1 Rh as IS) in pure methanol for 30 minutes (6 immersions, each for 5 minutes). Subsequent air-drying (bench drying at room temperature) for approximately 5 minutes was undertaken in between consecutive immersions, to prevent long-term exposure of the tissue to lipid degradation. Tissue-matched standards were characterised in-house for Fe composition, homogeneity and stability (at storage temperatures of −80 °C, −20 °C, 4 °C and 25 °C for up to 2 months) in order to investigate their suitability as calibrants for quantitative LA-ICP-MS. The homogeneity data suggested that the materials are homogeneous in terms of Fe and Rh distribution with RSDs (n = 30) of 8.3% and 4.7%, respectively. The Fe measurement precision was improved by approximately a factor of 2 when normalising 56Fe intensities to 103Rh intensities; the RSD (n = 30) for 56Fe/103Rh was 3.6%. The produced calibration standards were found to be stable when stored at room temperature for approximately 50 days, suggesting that they can be reused for multiple batches. Using LA coupled to double-focusing sector field ICP-MS in medium resolution mode (m/Δm = 4000), linear calibration over a range of 107 to 1519 mg kg−1 Fe (R2 = 0.99) was achieved with a limit of detection of 1.84 mg kg−1 Fe. Assessment of the accuracy of the method for the quantitative imaging of Fe in tissues was undertaken by comparison of the LA-ICP-MS data with that obtained by micro-XRF; the average Fe concentrations in selected tissue regions obtained by using XRF fell within the window defined by the LA-ICP-MS values and their associated standard deviations.

High spectral and spatial resolution X-ray transmission radiography and tomography using a Color X-ray Camera

High resolution X-ray radiography and computed tomography are excellent techniques for non-destructive characterization of an object under investigation at a spatial resolution in the micrometer range. However, as the image contrast depends on both chemical composition and material density, no chemical information is obtained from this data. Furthermore, lab-based measurements are affected by the polychromatic X-ray beam, which results in beam hardening effects. New types of X-ray detectors which provide spectral information on the measured X-ray beam can help to overcome these limitations. In this paper, an energy dispersive CCD detector with high spectral resolution is characterized for use in high resolution radiography and tomography, where a focus is put on the experimental conditions and requirements of both measurement techniques.

The combined effect of dissolved organic carbon and salinity on the bioaccumulation of copper in marine mussel larvae.

Larvae of Mytilus spp. are among the most Cu sensitive marine species. In this study we assessed the combined effect of salinity and dissolved organic carbon (DOC) on Cu accumulation on mussel larvae. Larvae were exposed for 48 h to three Cu concentrations in each of nine salinity/DOC treatments. Synchrotron radiation X-ray fluorescence was used to determine the Cu concentration in 36 individual larvae with a spatial resolution of 10 × 10 μm. Cu body burden concentrations varied between 1.1 and 27.6 μg/g DW larvae across all treatments and Cu was homogeneously distributed at this spatial resolution level. Our results indicate decreasing Cu accumulation with increasing DOC concentrations which can be explained by an increase in Cu complexation. In contrast, salinity had a nonlinear effect on Cu. This cannot be explained by copper speciation or competition processes and suggests a salinity-induced alteration in physiology.

Nanoscopic X-ray fluorescence imaging of meteoritic particles and diamond inclusions

The new ESRF ID16B-NA Nanoanalysis beamline has been applied for the first time for XRF imaging with a resolution level down to a few tens of nanometers on rare geological materials: meteoritic fragments from achondrite NWA 6693 and diamond inclusions. The instrument proved to be an extremely valuable tool for mapping samples containing submicrometer heterogeneities. It was discovered that the track of bubblelike inclusions in NWA 6693 consists mainly of Cr-rich phases. Some inclusions containing Ni and Ca were also detected. In diamond SL05, originating from the Juina region in Brazil, multiple inclusions were analyzed with dimensions smaller than 1 μm. Raman spectrometry measurements indicated the presence of a ringwoodite inclusion in this diamond; the detection of several iron-rich inclusions justifies further investigation of this material.

Salinity and dissolved organic carbon both affect copper toxicity in mussel larvae: Copper speciation or competition cannot explain everything

Predicting copper (Cu) toxicity in marine and estuarine environments is challenging because of the influence of anions on Cu speciation, competition between Cu(2+) and other cations at the biotic ligand and the effect of salinity on the physiology of the organism. In the present study the combined effect of salinity and dissolved organic carbon (DOC) on Cu toxicity to larvae of Mytilus galloprovincialis was assessed. Two statistical models were developed and used to elucidate the relationship between Cu toxicity, salinity, and DOC. All models based on dissolved Cu indicate a decrease in Cu toxicity with increasing DOC concentrations, which can partly be explained by complexation of Cu(2+) ions with DOC. These models also indicate an increase in Cu toxicity (modeled with dissolved Cu or Cu(2+) activity) with increasing salinity, suggesting a salinity-induced alteration in the physiology of the mussel larvae. When based on Cu body burdens, neither of the models indicates an effect of salinity or DOC. This shows that the Cu body burden is a more constant predictor of Cu toxicity, regardless of the water chemistry influencing Cu speciation or competition and possible physiological alterations or changes in Cu speciation or competition.

Full-field fluorescence mode micro-XANES imaging using a unique energy dispersive CCD detector.

X-ray absorption near-edge structure (XANES) spectroscopy is a well-known nondestructive technique that allows for chemical state and local structure determination. Spatially resolved oxidation state imaging is possible performing full-field transmission mode XANES experiments, providing chemical state information on the illuminated sample area, but these experiments are limited to thin, concentrated samples. Here we present the use of a unique energy dispersive (ED) pnCCD detector, the SLcam, for full-field fluorescence mode XANES experiments, thereby significantly relaxing the constraints on sample thickness. Using this new detection methodology, spatially resolved chemical state information on millimeter-sized sample areas can be obtained with microscopic resolution in moderate measuring times (less than 15 h), obtaining a XANES profile for each of nearly 70,000 points in a single measurement without the need of scanning the sample through the beam. Besides a description of the use of this detector for micro-XANES applications, we also present the proof of concept for fluorescence mode micro-XANES using a Fe(0)/Fe2O3 model sample and a Nitisol soil sample, which was measured to obtain iron chemical state distribution information.

Methodology toward 3D micro X-ray fluorescence imaging using an energy dispersive charge-coupled device detector.

A new three-dimensional (3D) micro X-ray fluorescence (μXRF) methodology based on a novel 2D energy dispersive CCD detector has been developed and evaluated at the P06 beamline of the Petra-III storage ring (DESY) in Hamburg, Germany. This method is based on the illumination of the investigated sample cross-section by a horizontally focused beam (vertical sheet beam) while fluorescent X-rays are detected perpendicularly to the sheet beam by a 2D energy dispersive (ED) CCD detector allowing the collection of 2D cross-sectional elemental images of a certain depth within the sample, limited only by signal self-absorption effects. 3D elemental information is obtained by a linear scan of the sample in the horizontal direction across the vertically oriented sheet beam and combining the detected cross-sectional images into a 3D elemental distribution data set. Results of the 3D μXRF analysis of mineral inclusions in natural deep Earth diamonds are presented to illustrate this new methodology.

In vivo X-ray elemental imaging of single cell model organisms manipulated by laser-based optical tweezers

We report on a radically new elemental imaging approach for the analysis of biological model organisms and single cells in their natural, in vivo state. The methodology combines optical tweezers (OT) technology for non-contact, laser-based sample manipulation with synchrotron radiation confocal X-ray fluorescence (XRF) microimaging for the first time. The main objective of this work is to establish a new method for in vivo elemental imaging in a two-dimensional (2D) projection mode in free-standing biological microorganisms or single cells, present in their aqueous environment. Using the model organism Scrippsiella trochoidea, a first proof of principle experiment at beamline ID13 of the European Synchrotron Radiation Facility (ESRF) demonstrates the feasibility of the OT XRF methodology, which is applied to study mixture toxicity of Cu-Ni and Cu-Zn as a result of elevated exposure. We expect that the new OT XRF methodology will significantly contribute to the new trend of investigating microorganisms at the cellular level with added in vivo capability.

Development and Applications of a Laboratory Micro X-ray Fluorescence (μXRF) Spectrometer Using Monochromatic Excitation for Quantitative Elemental Analysis.

The analytical characterization and an application example of a novel laboratory X-ray fluorescence (μXRF) microprobe is presented, which combines monochromatic, focused X-ray beam excitation with a high-performance silicon drift detector (SDD) and two-dimensional/three-dimensional (2D/3D) scanning capability. Because of the monochromatic excitation, below the (multiple) Compton/Rayleigh scattering peak region, the XRF spectra obtained by this laboratory spectrometer has similarly high peak-to-background ratios as those which can be obtained at synchrotron sources. However, the flux density difference between the proposed laboratory instrument and current synchrotron end stations is on the order of several orders of magnitude. As a result, sub-ppm minimum detection limits (MDL) for transition metals are obtained for a variety of sample matrices. The monochromatic excitation also allows for the efficient use of an iterative Monte Carlo simulation algorithm to obtain quantitative information on the analyzed samples. The analytical characteristics of this instrument and quantitative results, in combination with an iterative reverse Monte Carlo simulation algorithm, will be demonstrated using measurements conducted on an iron-containing meteorite.