Reference-free x-ray fluorescence analysis with a micrometer-sized incident beam

Spatially resolved x-ray fluorescence (XRF) based analysis employing incident beam sizes in the low micrometer range (μXRF) is widely used to study lateral composition changes of various types of microstructured samples. However, up to now the quantitative analysis of such experimental datasets could only be realized employing adequate calibration or reference specimen. In this work, we extent the applicability of the so-called reference-free XRF approach to enable reference-freeμXRF analysis. Here, no calibration specimen are needed in order to derive a quantitative and position sensitive composition of the sample of interest. The necessary instrumental steps to realize reference-freeμXRF are explained and a validation of ref.-freeμXRF against ref.-free standard XRF is performed employing laterally homogeneous samples. Finally, an application example from semiconductor research is shown, where the lateral sample features require the usage of ref.-freeμXRF for quantitative analysis.

Structural and chemical properties of anion exchanged CsPb(Br(1-x)Clx)3heterostructured perovskite nanowires imaged by nanofocused x-rays

Over the last years metal halide perovskites have demonstrated remarkable potential for integration in light emitting devices. Heterostructures allow for tunable bandgap depending on the local anion composition, crucial for optoelectronic devices, but local structural effects of anion exchange in single crystals is not fully understood. Here, we investigate how the anion exchange of CsPbBr3nanowires fully and locally exposed to HCl vapor affects the local crystal structure, using nanofocused x-rays. We study the nanoscale composition and crystal structure as function of HCl exposure time and demonstrate the correlation of anion exchange with changes in the lattice parameter. The local composition was measured by x-ray fluorescence and x-ray diffraction, with general agreement of both methods but with much less variation using latter. The heterostructured nanowires exhibit unintentional gradients in composition, both axially and radially. Ferroelastic domains are observed for all HCl exposure times, and the magnitude of the lattice tilt at the domain walls scales with the Cl concentration.

The feasibility of K XRF bone lead measurements in mice assessed using 3D-printed phantoms

This article describes the development of a system forin vivomeasurements of lead body burden in mice using109Cd K x-ray fluorescence (XRF). This K XRF system could facilitate early-stage studies on interventions that ameliorate or reverse organ tissue damage from lead poisoning by reducing animal numbers through a cross-sectional study approach. A novel mouse phantom was developed based on a mouse atlas and 3D-printed using PLA plastic with plaster of Paris 'bone' inserts. PLA plastic was found to be a good surrogate for soft tissue in XRF measurements and the phantoms were found to be good models of mice. As expected, lead detection limits varied with mouse size, mouse orientation, and mouse position with respect to the source and detector. The work suggests that detection limits of 10 to 20μg Pb per g bone mineral may be possible for a 2 to 3 hour XRF measurement in a single animal, an adequate limit for some pre-clinical studies. The109Cd K XRF mouse measurement system was also modeled using the Monte Carlo code MCNP. The combination of experiment and modeling found that contrary to expectation, accurate measurements of lead levels in mice required calibration using mouse-specific calibration standards due to the coherent scatter peak normalization failing when small animals are measured. MCNP modeling determined that this was because the coherent scatter signal from soft tissue, which until now has been assumed negligible, becomes significant when compared to the coherent scatter signal in bone in small animals. This may have implications for some human measurements. This work suggests that109Cd K x-ray fluorescence measurements of lead body burden are precise enough to make the system feasible for small animals if appropriately calibrated. Further work to validate the technology's measurement accuracy and performancein vivowill be required.

The effects of exogenous substances on the color of heated bones

OBJECTIVES

Burned bone coloration has been used for decades to help in the bioanthropological analysis of burned human bones. However, there is a variety of factors that can interfere with the coloration manifested by bones exposed to heat, resulting in colors that differ from the usual black to white gradient. In this study, we evaluated possible causes of unusual coloration changes and hues in burned bone.

MATERIALS AND METHODS

For that purpose, defleshed fresh pig (Sus scrofa) ribs as well as fresh and dry human clavicles were burned at four different temperatures (500, 700, 900 and 1100°C) in contact with different materials (CaO, Zn, Fe, Cu, Mn, and polyester cloth). Observable color changes were assessed through naked eye observation and description, Munsell color charts, and reflectance spectrophotometry. Additionally, chemical changes in bone were assessed using Fourier-transform infrared spectroscopy in attenuated total reflectance (FTIR-ATR) and x-ray fluorescence (XRF).

RESULTS

Our results showed that some materials did affect usual burned bone coloration (Fe, Mn, Cu, Zn) and correspondent FTIR-ATR and XRF spectra. As for other materials, although no effect on visual bone coloration was observed, they still affected FTIR-ATR and XRF spectra (CaO and cloth).

DISCUSSION

This study can contribute to the anthropological analysis of burned human remains, providing some answers to what can cause unusual types of heat-induced colorations.

Long-term stability of hydroxyapatite bone phantoms for the calibration ofin vivox-ray fluorescence spectrometry-based systems of bone lead and strontium quantification

Hydroxyapatite (HAp) phantoms have been proposed as an alternative to plaster of Paris (poP) phantoms for the calibration of x-ray fluorescence-based systems for thein vivoquantification of bone lead and strontium which employ a coherent normalization procedure. The chemical composition of the material becomes critical in the calculation, or omission, of the coherent correction factor (CCF) required in this normalization procedure. This study evaluated the long-term chemical stability of HAp phantoms. Phantoms were prepared and allowed to age for a two week period and over a seven year period in ambient conditions. The chemical composition of the phantoms was then assessed by powder x-ray diffraction. Two week old phantoms were found to be composed of HAp with only a small amount of contamination from CaHPO4·2H2O. Seven year old phantoms were found to have converted nearly completely to a carbonate-bearing apatite in the form of Ca10(PO4)6(CO3)0.75(OH)0.5indicating that the HAp phantom material likely reacts with carbon dioxide in air over time forming a carbonate-bearing apatite. The influence of this chemical conversion was assessed at the level of relevant cross-sections. Calibration under the assumption that the material is HAp when in fact it is a carbonate-bearing apatite would result in not more than a 0.2%-2% bias in the total mass attenuation coefficient within the photon energy range of 0-100 keV. Differential scattering cross-section for coherent scattering was found to differ between HAp and carbonate-bearing apatite by 0.9%-2% for both a 35.5 keV and 88.0 keVγ-ray. This variation in the differential scattering cross-section for coherent scattering may introduce a ca. 2% bias in the CCF used within the coherent normalization-based calibration procedure. Using HAp phantoms as calibrators thus requires acknowledgement of this conversion in chemical form and possible introduction of uncertainty into the calibration procedure.

Organ uptake, toxicity and skin clearance of ruthenium contrast agents monitored in vivo by x-ray fluorescence

Aims: To investigate the distribution and toxicity of ruthenium nanoparticles (Ru NPs) injected intravenously in mice. Methods: We synthesized Ru NPs, followed their biodistribution by x-ray fluorescence (XRF) imaging and evaluated organ toxicity by histopathology and gene expression. Results: Ru NPs accumulated, mainly in liver and spleen, where they were phagocyted by tissue macrophages, giving a transient inflammation and oxidative stress response that declined after 2 weeks. Ru NPs gradually accumulated in the skin, which was confirmed by microscopic examination of skin biopsies. Conclusion: Ru NP toxicity in recipient organs is transient. Particles are at least partially excreted by the skin, supporting a role for the skin as a nanoparticle clearing organ.

Microstructure and energy dispersive diffraction reconstruction of 3D patterns of crystallographic texture in a shark centrum

Purpose: Tomography using diffracted x-rays produces reconstructions mapping quantities such as crystal lattice parameter(s), crystallite size, and crystallographic texture, information quite different from that obtained with absorption or phase contrast. Diffraction tomography is used to map an entire blue shark centrum with its double cone structure (corpora calcerea) and intermedialia (four wedges). Approach: Energy dispersive diffraction (EDD) and polychromatic synchrotron x-radiation at 6-BM-B, the Advanced Photon Source, were used. Different, properly oriented Bragg planes diffract different x-ray energies; these intensities are measured by one of ten energy-sensitive detectors. A pencil beam defines the irradiated volume, and a collimator before each energy-sensitive detector selects which portion of the irradiated column is sampled at any one time. Translating the specimen along X , Y , and Z axes produces a 3D map. Results: We report 3D maps of the integrated intensity of several bioapatite reflections from the mineralized cartilage centrum of a blue shark. The c axis reflection's integrated intensities and those of a reflection with no c axis component reveal that the cone wall's bioapatite is oriented with its c axes lateral, i.e., perpendicular to the backbone's axis, and that the wedges' bioapatite is oriented with its c axes axial. Absorption microcomputed tomography (laboratory and synchrotron) and x-ray excited x-ray fluorescence maps provide higher resolution views. Conclusion: The bioapatite in the cone walls and wedges is oriented to resist lateral and axial deflections, respectively. Mineralized tissue samples can be mapped in 3D with EDD tomography and subsequently studied by destructive methods.

Sensitivity enhancement of an experimental benchtop x-ray fluorescence imaging system by deploying a single crystal cadmium telluride detector system optimized for high flux x-ray operations

In this work, an energy-resolving thermoelectrically cooled single crystal cadmium telluride (CdTe) detector system upgraded with the latest firmware was optimized for high x-ray flux operations using high bias voltage and fast peaking time. This detector system was deployed into an experimental benchtop x-ray fluorescence (XRF) imaging/computed tomography (XFCT) system developed for quantitative imaging of metal nanoprobes such as gold nanoparticles (GNPs). Using the firmware-upgraded and existing/old CdTe detector systems, the Compton/XRF spectra from small (8 mm diameter) GNP-containing phantoms were acquired. The phantoms were irradiated with 1.8 mm Sn-filtered 125 kVp cone beam x-rays at 24 mA. The firmware-upgraded detector system produced relatively lower dead time under high x-ray flux, compared with the old detector system, and performed well with the spectral resolution of ~0.7 keV (in full width at half maximum) at 69 keV photon energy. Given the same 2 mm aperture detector collimator and irradiation time of 10 s, this detector system managed to score nearly 50% more gold XRF signals than the existing one at all GNP concentrations tested. This improvement resulted in the GNP detection limit of 0.02 wt. % which was lower than that (0.03 wt. %) achievable with the existing detector system. When combined with the detector collimator containing a larger (3 mm) aperture, the firmware-upgraded detector system produced drastically more gold XRF signal at a given GNP concentration (e.g., 9 times more for 1 wt. % GNP solution and irradiation time of 10 s), leading to further reduction in the GNP detection limit (i.e., 0.01 wt. %). The present investigation showed that the firmware upgraded CdTe detector system optimized for high x-ray flux operations allowed for better photon counting efficiency, thus leading to sensitivity enhancement of an experimental benchtop XRF/XFCT imaging system.

A novel calibration for L-shell x-ray fluorescence measurements of bone lead concentration using the strontium Kβ/Kαratio

Objective. Lead (Pb) is a well-known toxic element.In vivobone Pb concentration measurement is a long-term exposure metric complementary to blood Pb concentration measurement which is a metric of recent exposure.In vivohuman tibia bone Pb measurements using Pb K-shell or L-shell x-ray fluorescence (KXRF or LXRF) emissions were developed in the 1980s. KXRF bone Pb measurements using Cd-109 gamma rays and coherent-to-fluorescence ratio to account for differences between phantom andin vivomeasurements, was employed in human studies. Bone Pb LXRF method employed x-ray tubes. However, calibration procedures using ultrasound measurements of the soft tissue thickness (STT) proved inaccurate.Approach. In this study, bone and soft tissue (ST) phantoms simulatedin vivobone Pb measurements. Seven plaster-of-Paris cylindrical bone phantoms containing 1.01 mg g-1of strontium (Sr) were doped with Pb in 0, 8, 16, 29, 44, 59, and 74 μg g-1concentrations. Polyoxymethylene (POM), resin, and wax were each used to fabricate four ST phantoms in the approximate 1-4 mm thickness range. Pb LXRF measurements were performed using a previously developed optimal grazing incidence position method.Main results. Linear attenuation coefficients measurements of ST materials indicated that POM and resin mimicked well attenuation of Pb x-rays in skin and adipose tissue, respectively. POM and resin data indicated a bone Pb detection limit of 20 μg g-1for a 2 mm STT. Derived relationships between the Pb concentration, Pb LXRF and Sr Kβ/Kαratio data did not require STT knowledge. Applied to POM and resin data, the new calibration method yielded unbiased results.Significance.In vivobone Pb measurements in children were suggested following considerations of radiation dose, STT, detectability and distribution of Pb and Sr in bone. This research meets with the concerns regarding the negative effects of low levels of Pb exposure on neurodevelopment of children.

Characterization of a Pixelated Cadmium Telluride Detector System Using a Polychromatic X-Ray Source and Gold Nanoparticle-Loaded Phantoms for Benchtop X-Ray Fluorescence Imaging

Pixelated semi-conductor detectors providing high energy resolution enable parallel acquisition of x-ray fluorescence (XRF) signals, potentially leading to performance enhancement of benchtop XRF imaging or computed tomography (XFCT) systems utilizing ordinary polychromatic x-ray sources. However, little is currently known about the characteristics of such detectors under typical operating conditions of benchtop XRF imaging/XFCT. In this work, a commercially available pixelated cadmium telluride (CdTe) detector system, HEXITEC (High Energy X-ray Imaging Technology), was characterized to address this issue. Specifically, HEXITEC was deployed into our benchtop cone-beam XFCT system, and used to detect gold Kα XRF photons from gold nanoparticle (GNP)-loaded phantoms. To facilitate the detection of XRF photons, various parallel-hole stainless steel collimators were fabricated and coupled with HEXITEC. A pixel-by-pixel spectrum merging algorithm was introduced to obtain well-defined XRF + scatter spectra with parallel-hole collimators. The effect of charge sharing addition (CSA) and discrimination (CSD) algorithms was also investigated for pixel-level CS correction. Finally, the detector energy resolution, in terms of the full-width at half-maximum (FWHM) values at two gold Kα XRF peaks (~68 keV), was also determined. Under the current experimental conditions, CSD provided the best energy resolution of HEXITEC (~1.05 keV FWHM), compared with CSA and no CS correction. This FWHM value was larger (by up to ~0.35 keV) than those reported previously for HEXITEC (at ~60 keV Am-241 peak) and single-crystal CdTe detectors (at two gold Kα XRF peaks). This investigation highlighted characteristics of HEXITEC as well as the necessity for application-specific detector characterization.

Effects of exogenous citric acid on the concentration and spatial distribution of Ni, Zn, Co, Cr, Mn and Fe in leaves of Noccaea caerulescens grown on a serpentine soil

The aim of this study was to show the potential of citric acid in increasing the concentration of Ni, Zn, Co, Cr, Mn and Fe in leaves of the hyperaccumulator Noccaea caerulescens. Synchrotron x-ray fluorescence (μ-XRF) images were collected to assess the distribution of metals in leaves. Applying citric acid (20 mmol kg^-1) to soil increased in 14-, 10-, 7-, 2- and 1.4- fold the concentration of Mn, Fe, Co, Ni, and Cr, respectively, compared to the control. The μ-XRF imaging revealed that Ni and Zn were not spatially correlated across the leaf. We observed a clear partitioning of Zn between veins and surrounding leaf cells while Ni was more evenly distributed between veins and leaf blade. The accumulation of metals in citric acid treated plants did not change the Ni and Zn distribution pattern in leaves but altered the Mn distribution. It seems that Mn reached toxic concentrations in leaves and we hypothesize that a mechanism driven by transpiration through the xylem was used to excrete the metal. Our results show that citric acid can enhance metal accumulation by N. caerulescens and have impact for soil remediation by either decreasing the time for clean up or increasing the access to non-labile pools of metals in soil.

The feasibility of NaGdF4 nanoparticles as an x-ray fluorescence computed tomography imaging probe for the liver and lungs

PURPOSE

As a novel imaging modality, x-ray fluorescence computed tomography (XFCT) can provide distribution and concentration information of contrast agents containing high atomic number elements, such as iodine, gadolinium, barium, gold, and platinum. Since XFCT has a better sensitivity and detection limit of high-Z elements compared with traditional and spectral CT, it becomes a powerful quantitative imaging tool for biological studies. The main problem of current XFCT imaging is its low emission and detection efficiency of x-ray fluorescence (XRF) photons. Increasing XRF photons generation by choosing a high atomic element as a contrast agent is essential to improve the imaging quality of XFCT. Gadolinium emits at least a few times more of XRF photons than gold under the same x-ray excitation condition, leading to a detection limit at a level of sub-mg/mL as the next generation of clinical imaging modality. However, most current XFCT studies have utilized gadolinium salt as the contrast agent, which could not accumulate in organs or tumors efficiently, making in vivo XFCT imaging quite difficult. In this study, we present NaGdF₄ nanoparticles with ultra-small size as nanoprobes to test the feasibility for in vivo XFCT application for the first time.

METHODS

NaGdF₄ nanoparticles with different sizes (3-10 nm) were successfully synthesized via a coprecipitation process by controlling the reaction time at temperature of 290 °C. The morphology, crystal phase, chemical composition, and size of such NPs were further characterized with HR-TEM, XRD, and EDX. The abilities of XRF photons from different sizes of NPs were quantified by our customized XFCT imaging system. To access the in vivo application of as-synthesized NPs, such hydrophobic NPs capped OA molecules were further modified with AEP via a ligand-exchange process and characterized with FT-IR. For in vivo XFCT imaging, 0.1 mL of 30 mg/mL NPs were injected into nude mice via the tail vein. The Varian G-297 x-ray tube was set to 150 kV and 0.5 mA. The XRF photons were captured by a Kromek eV-3500 photon counting detector at each 8° for 10 s.

RESULT

The successfully synthesized NaGdF₄ nanoparticles (3-10 nm) were monodisperse, highly uniform spherical morphology and hexagonal crystalline phases. No significant influence on XRF photons yields or XFCT imaging quality were found by varying the nanoparticle size. The XRF photons were 2.5 times more emitted from NaGdF₄ nanoparticles (NPs) compared to gold nanoparticles, thereby leading to a better image quality. With the AEP surface modification, such NPs were readily adapted for use in in vivo XFCT applications with monodispersity in aqueous solution and negligible cytotoxicity. With the tail-vein injection, the liver, spleen, and lungs could be clearly imaged with XFCT at a sub-mg/mL level.

CONCLUSIONS

Such NaGdF₄ NPs, which were synthesized with coprecipitation process, were modified with AEP for in vivo XFCT applications. With both the phantom and in vivo experiments, such NPs were proved to be appropriate probes for XFCT application with the detection limit at a sub-mg/mL level. In the future research, such NPs could be further functionalized with targeting molecules for early-phase cancer detection.

Phylogenetic and geographic distribution of nickel hyperaccumulation in neotropical Psychotria

PREMISE

Hyperaccumulation of heavy metals in plants has never been documented from Central America or Mexico. Psychotria grandis, P. costivenia, and P. glomerata (Rubiaceae) have been reported to hyperaccumulate nickel in the Greater Antilles, but they also occur widely across the neotropics. The goals of this research were to investigate the geographic distribution of hyperaccumulation in these species and explore the phylogenetic distribution of hyperaccumulation in this clade by testing related species.

METHODS

Portable x-ray fluorescence (XRF) spectroscopy was used to analyze 565 specimens representing eight species of Psychotria from the Missouri Botanical Garden herbarium.

RESULTS

Nickel hyperaccumulation was found in specimens of Psychotria costivenia ranging from Mexico to Costa Rica and in specimens of P. grandis from Guatemala to Ecuador and Venezuela. Among related species, nickel hyperaccumulation is reported for the first time in P. lorenciana and P. papantlensis, but no evidence of hyperaccumulation was found in P. clivorum, P. flava, or P. pleuropoda. Previous reports of hyperaccumulation in P. glomerata appear to be erroneous, resulting from taxonomic synonymy and specimen misidentification.

CONCLUSIONS

Hyperaccumulation of nickel by Psychotria is now known to occur widely from southern Mexico through Central America to northwestern South America, including some areas not known to have ultramafic soils. Novel aspects of this research include the successful prediction of new hyperaccumulator species based on molecular phylogeny, use of XRF technology to nondestructively obtain elemental data from herbarium specimens, and documentation of previously unknown areas of ultramafic or nickel-rich soil based on such data.

Sheet beam x-ray fluorescence computed tomography (XFCT) imaging of gold nanoparticles

PURPOSE

X-ray fluorescence computed tomography (XFCT) experiments have typically used pencil beams for data acquisition, which yielded good quality images of gold nanoparticles (AuNP) but prolonged the imaging time. Here we propose three novel collimator geometries for use with faster sheet beam XFCT data acquisition. The feasibility of a multipinhole, parallel, and converging collimator was investigated in a Monte Carlo study.

METHODS

A cylindrical water phantom with 2 cm in diameter and 3 cm in height containing 0.5-2 mm diameter vials with 0.4%-1.6% AuNP concentrations was modelled by FLUKA. A 15 and 81 keV monoenergetic x-ray sheet beam of 0.4 mm in width was used to image the phantom with L-shell and K-shell XFCT, respectively, with a dose of 30 mGy. The collimator thickness for L-shell and K-shell data acquisition was 3.3 and 5.1 mm, respectively. The XFCT images resulting from three collimator geometries were generated using the maximum likelihood expectation maximization (MLEM) iterative reconstruction method. With a resolution of 0.4 mm they were corrected for x-ray attenuation. The sheet beam XFCT images were compared against pencil beam geometry images that were generated using 55 translations. To assess image quality, the contrast-to-noise ratio (CNR) was evaluated for each vial. The Rose criterion was used to determine the lowest AuNP concentration detectable for each image.

RESULTS

Among the three collimator geometry types, the sheet beam L-shell and K-shell parallel collimator XFCT images yielded AuNP sensitivity limits at 0.09% and 0.08%, respectively, for a 2 mm diameter vial. The AuNP sensitivity limits of the pencil beam XFCT images were 0.07% and 0.01% for L-shell and K-shell XFCT, respectively. The L-shell parallel collimator AuNP imaging sensitivity approached that of the pencil beam geometry with a 55-fold reduction in imaging time. The AuNP sensitivity limits for the 1 mm diameter vial for the L-shell and K-shell parallel collimator XFCT images were 0.19% and 0.16%, respectively, and those of the pencil beam XFCT images were 0.08% and 0.01% for L-shell and K-shell XFCT, respectively. The remaining two collimator geometries resulted in a lower CNR and poorer image quality. For a 2 mm diameter vial, the AuNP sensitivity limits for the L-shell and K-shell multipinhole collimator XFCT images were 0.23% and 0.52%, respectively, while for the L-shell and K-shell converging collimator XFCT images the AuNP sensitivity limits were 0.38% and 0.13%, respectively.

CONCLUSION

This work demonstrates the feasibility of sheet beam L-shell XFCT imaging for small animal studies using parallel-oriented lead collimators which can detect AuNP concentrations approaching the level of pencil beam images with reduced imaging time.

A microbeam grazing-incidence approach to L-shell x-ray fluorescence measurements of lead concentration in bone and soft tissue phantoms

OBJECTIVE

L-shell x-ray fluorescence (LXRF) is a non-invasive approach to lead (Pb) concentration measurements in the human bone. The first studies were published in the early 1980s. In the same period the K-shell x-ray fluorescence (KXRF) method using a Cd-109 radionuclide source was developed and later improved and refined. Lower sensitivity and calibration difficulties associated with the LXRF method led the KXRF to be the most adopted method for in vivo human bone Pb studies. In the present study a microbeam-based grazing-incidence approach to Pb LXRF measurements was investigated.

APPROACH

The microbeam produced by an integrated x-ray tube and polycapillary x-ray lens (PXL) unit was used to excite cylindrical plaster-of-Paris (poP) bone phantoms doped with Pb in seven concentrations: 0, 8, 16, 29, 44, 59, and 74 µg g-1. Two 1 mm- and 3 mm-thick cylindrical shell soft tissue phantoms were made out of polyoxymethylene (POM) plastic. Three bone-soft tissue phantom sets corresponding to the 0, 1, and 3 mm POM thickness values resulted. Each phantom was placed between the microbeam and the detector; its position was controlled using a positioning stage. Small steps (0.1-0.5 mm) and short 30 s x-ray spectra acquisitions were used to find the optimal phantom position according to the maximum observed Sr Kα peak height. At the optimal geometry, five 180 s x-ray spectra were acquired for each phantom set. Calibration lines were obtained using the fitted peak heights of the two observed Pb Lα and Pb Lβ peaks.

MAIN RESULTS

The lowest detection limit (DL) values were (2.9  ±  0.2), (4.9  ±  0.3), and (23  ±  3) µg g-1, respectively. The order of magnitude of the absorbed radiation dose in the POM plastic for the 180 s irradiation was estimated to be  <1 mGy.

SIGNIFICANCE

The results are superior to a relatively recently published LXRF phantom study and show promise for future designs of in vivo LXRF measurements.

Experimental validation of L-shell x-ray fluorescence computed tomography imaging: phantom study

Thanks to the current advances in nanoscience, molecular biochemistry, and x-ray detector technology, x-ray fluorescence computed tomography (XFCT) has been considered for molecular imaging of probes containing high atomic number elements, such as gold nanoparticles. The commonly used XFCT imaging performed with K-shell x rays appears to have insufficient imaging sensitivity to detect the low gold concentrations observed in small animal studies. Low energy fluorescence L-shell x rays have exhibited higher signal-to-background ratio and appeared as a promising XFCT mode with greatly enhanced sensitivity. The aim of this work was to experimentally demonstrate the feasibility of L-shell XFCT imaging and to assess its achievable sensitivity. We built an experimental L-shell XFCT imaging system consisting of a miniature x-ray tube and two spectrometers, a silicon drift detector (SDD), and a CdTe detector placed at [Formula: see text] with respect to the excitation beam. We imaged a 28-mm-diameter water phantom with 4-mm-diameter Eppendorf tubes containing gold solutions with concentrations of 0.06 to 0.1% Au. While all Au vials were detectable in the SDD L-shell XFCT image, none of the vials were visible in the CdTe L-shell XFCT image. The detectability limit of the presented L-shell XFCT SDD imaging setup was 0.007% Au, a concentration observed in small animal studies.

Spectrometric analysis of mercury content in 549 skin-lightening products: is mercury toxicity a hidden global health hazard?

BACKGROUND

Cosmetic skin lightening is practiced worldwide. Mercury is a well-documented melanotoxin added to some lightening products. However, mercury can cause many dermatologic, renal, and neurologic problems. The Food and Drug Administration limits the amount of mercury in cosmetic products to trace amounts, 1 ppm.

OBJECTIVE

The objective of this study was to quantitatively evaluate a large international sample of lightening products for mercury content, focusing on products available to US consumers either online or in stores.

METHODS

A total of 549 skin-lightening products, manufactured in 32 countries, were purchased online in the United States, Taiwan, and Japan and in stores in the United States, China, Taiwan, Thailand, Japan, and Sri Lanka. Cosmetics were screened for mercury content above 200 ppm using a low-cost portable x-ray fluorescence spectrometer.

RESULTS

Of the 549 tested products, 6.0% (n = 33) contained mercury above 1000 ppm. In all, 45% of mercury-containing samples contained mercury in excess of 10,000 ppm. Of lightening products purchased in the United States, 3.3% were found to contain mercury in excess of 1000 ppm.

LIMITATIONS

Our study did not evaluate creams for other melanosuppressive ingredients. Only 1 sample of each product was tested.

CONCLUSION

Our study confirms the national and global presence of mercury in skin-lightening products.

Friedreich ataxia: metal dysmetabolism in dorsal root ganglia

BACKGROUND

Friedreich ataxia (FA) causes distinctive lesions of dorsal root ganglia (DRG), including neuronal atrophy, satellite cell hyperplasia, and absorption of dying nerve cells into residual nodules. Two mechanisms may be involved: hypoplasia of DRG neurons from birth and superimposed iron (Fe)- and zinc (Zn)-mediated oxidative injury. This report presents a systematic analysis of DRG in 7 FA patients and 13 normal controls by X-ray fluorescence (XRF) of polyethylene glycol-embedded DRG; double-label confocal immunofluorescence microscopy of Zn- and Fe-related proteins; and immunohistochemistry of frataxin and the mitochondrial marker, ATP synthase F1 complex V β-polypeptide (ATP5B).

RESULTS

XRF revealed normal total Zn- and Fe-levels in the neural tissue of DRG in FA (mean ± standard deviation): Zn=5.46±2.29 μg/ml, Fe=19.99±13.26 μg/ml in FA; Zn=8.16±6.19 μg/ml, Fe=23.85±12.23 μg/ml in controls. Despite these unchanged total metal concentrations, Zn- and Fe-related proteins displayed major shifts in their cellular localization. The Zn transporter Zip14 that is normally expressed in DRG neurons and satellite cells became more prominent in hyperplastic satellite cells and residual nodules. Metallothionein 3 (MT3) stains confirmed reduction of neuronal size in FA, but MT3 expression remained low in hyperplastic satellite cells. In contrast, MT1/2 immunofluorescence was prominent in proliferating satellite cells. Neuronal ferritin immunofluorescence declined but remained strong in hyperplastic satellite cells and residual nodules. Satellite cells in FA showed a larger number of mitochondria expressing ATB5B. Frataxin immunohistochemistry in FA confirmed small neuronal sizes, irregular distribution of reaction product beneath the plasma membrane, and enhanced expression in hyperplastic satellite cells.

CONCLUSIONS

The pool of total cellular Zn in normal DRG equals 124.8 μM, which is much higher than needed for the proper function of Zn ion-dependent proteins. It is likely that any disturbance of Zn buffering by Zip14 and MT3 causes mitochondrial damage and cell death. In contrast to Zn, sequestration of Fe in hyperplastic satellite cells may represent a protective mechanism. The changes in the cellular localization of Zn- and Fe-handling proteins suggest metal transfer from degenerating DRG neurons to activated satellite cells and connect neuronal metal dysmetabolism with the pathogenesis of the DRG lesion in FA.

Spatial resolution of confocal XRF technique using capillary optics

XRF (X-ray fluorescence) is a powerful technique for elemental analysis with a high sensitivity. The resolution is presently limited by the size of the primary excitation X-ray beam. A test-bed for confocal-type XRF has been developed to estimate the ultimate lateral resolution which could be reached in chemical mapping using this technique. A polycapillary lens is used to tightly focus the primary X-ray beam of a low power rhodium X-ray source, while the fluorescence signal is collected by a SDD detector through a cylindrical monocapillary. This system was used to characterize the geometry of the fluorescent zone. Capillary radii ranging from 50 μm down to 5 μm were used to investigate the fluorescence signal maximum level This study allows to estimate the ultimate resolution which could be reached in-lab or on a synchrotron beamline. A new tool combining local XRF and scanning probe microscopy is finally proposed.

A hard X-ray nanoprobe beamline for nanoscale microscopy

The Hard X-ray Nanoprobe Beamline (or Nanoprobe Beamline) is an X-ray microscopy facility incorporating diffraction, fluorescence and full-field imaging capabilities designed and operated by the Center for Nanoscale Materials and the Advanced Photon Source at Sector 26 of the Advanced Photon Source at Argonne National Laboratory. This facility was constructed to probe the nanoscale structure of biological, environmental and material sciences samples. The beamline provides intense focused X-rays to the Hard X-ray Nanoprobe (or Nanoprobe) which incorporates Fresnel zone plate optics and a precision laser sensing and control system. The beamline operates over X-ray energies from 3 to 30 keV, enabling studies of most elements in the periodic table, with a particular emphasis on imaging transition metals.

Quantitative performance measurements of bent crystal Laue analyzers for X-ray fluorescence spectroscopy

Third-generation synchrotron radiation sources pose difficult challenges for energy-dispersive detectors for XAFS because of their count rate limitations. One solution to this problem is the bent crystal Laue analyzer (BCLA), which removes most of the undesired scatter and fluorescence before it reaches the detector, effectively eliminating detector saturation due to background. In this paper experimental measurements of BCLA performance in conjunction with a 13-element germanium detector, and a quantitative analysis of the signal-to-noise improvement of BCLAs are presented. The performance of BCLAs are compared with filters and slits.

Functional characterisation of metal(loid) processes in planta through the integration of synchrotron techniques and plant molecular biology

Functional characterisation of the genes regulating metal(loid) homeostasis in plants is a major focus for phytoremediation, crop biofortification and food security research. Recent advances in X-ray focussing optics and fluorescence detection have greatly improved the potential to use synchrotron techniques in plant science research. With use of methods such as micro X-ray fluorescence mapping, micro computed tomography and micro X-ray absorption near edge spectroscopy, metal(loids) can be imaged in vivo in hydrated plant tissues at submicron resolution, and laterally resolved metal(loid) speciation can also be determined under physiologically relevant conditions. This article focuses on the benefits of combining molecular biology and synchrotron-based techniques. By using molecular techniques to probe the location of gene expression and protein production in combination with laterally resolved synchrotron techniques, one can effectively and efficiently assign functional information to specific genes. A review of the state of the art in this field is presented, together with examples as to how synchrotron-based methods can be combined with molecular techniques to facilitate functional characterisation of genes in planta. The article concludes with a summary of the technical challenges still remaining for synchrotron-based hard X-ray plant science research, particularly those relating to subcellular level research.

New insights into globoids of protein storage vacuoles in wheat aleurone using synchrotron soft X-ray microscopy

Mature developed seeds are physiologically and biochemically committed to store nutrients, principally as starch, protein, oils, and minerals. The composition and distribution of elements inside the aleurone cell layer reflect their biogenesis, structural characteristics, and physiological functions. It is therefore of primary importance to understand the mechanisms underlying metal ion accumulation, distribution, storage, and bioavailability in aleurone subcellular organelles for seed fortification purposes. Synchrotron radiation soft X-ray full-field imaging mode (FFIM) and low-energy X-ray fluorescence (LEXRF) spectromicroscopy were applied to characterize major structural features and the subcellular distribution of physiologically important elements (Zn, Fe, Na, Mg, Al, Si, and P). These direct imaging methods reveal the accumulation patterns between the apoplast and symplast, and highlight the importance of globoids with phytic acid mineral salts and walls as preferential storage structures. C, N, and O chemical topographies are directly linked to the structural backbone of plant substructures. Zn, Fe, Na, Mg, Al, and P were linked to globoid structures within protein storage vacuoles with variable levels of co-localization. Si distribution was atypical, being contained in the aleurone apoplast and symplast, supporting a physiological role for Si in addition to its structural function. These results reveal that the immobilization of metals within the observed endomembrane structures presents a structural and functional barrier and affects bioavailability. The combination of high spatial and chemical X-ray microscopy techniques highlights how in situ analysis can yield new insights into the complexity of the wheat aleurone layer, whose precise biochemical composition, morphology, and structural characteristics are still not unequivocally resolved.

Adult lead exposure: time for change

We have assembled this mini-monograph on adult lead exposure to provide guidance to clinicians and public health professionals, to summarize recent thinking on lead biomarkers and their relevance to epidemiologic research, and to review two key lead-related outcomes, namely, cardiovascular and cognitive. The lead standards of the U.S. Occupational Safety and Health Administration are woefully out of date given the growing evidence of the health effects of lead at levels of exposure previously thought to be safe, particularly newly recognized persistent or progressive effects of cumulative dose. The growing body of scientific evidence suggests that occupational standards should limit recent dose to prevent the acute effects of lead and separately limit cumulative dose to prevent the chronic effects of lead. We hope this mini-monograph will motivate renewed discussion of ways to protect lead-exposed adults in the United States and around the world.

Impact of occupational exposure on lead levels in women

In 1994, 207 women participated in a study designed to examine the effects of occupational exposure and various lifestyle factors on bone and blood lead levels. In vivo measurements of Pb concentrations in tibia were performed by X-ray fluorescence. All 108 former smelter employees and 99 referents provided blood samples and answered a questionnaire on lifestyle characteristics and the relevant medical history. Lead concentrations in tibia and blood were significantly higher in the exposed group. The difference in mean bone Pb concentrations of the two groups is markedly greater than the difference in the mean blood Pb concentrations, supporting the view that bone Pb measurements are a more reliable determinant of Pb body burden. Chronic exposure did not result in any statistically significant differences in adverse pregnancy outcomes. A significantly lower age at the onset of menopause in occupationally exposed women may suggest that Pb causes adverse changes in the pattern of estrus and menses. The exposed women had lower bone Pb concentrations than those found in most studies on predominantly male workers. Blood Pb concentrations remain increased in women long after the cessation of occupational exposure, reflecting the importance of the endogenous exposure. The endogenous exposure relation found for postmenopausal exposed women is consistent with data on male smelter workers, whereas the relation found for premenopausal women is significantly lower. This suggests that sex plays an important role in the metabolism of lead, and current models of exposure extrapolated from male data may be inappropriate for use on women.

Determinants of bone and blood lead levels among minorities living in the Boston area

We measured blood and bone lead levels among minority individuals who live in some of Boston's neighborhoods with high minority representation. Compared with samples of predominantly white subjects we had studied before, the 84 volunteers in this study (33:67 male:female ratio; 31-72 years of age) had similar educational, occupational, and smoking profiles and mean blood, tibia, and patella lead levels (3 microg/dL, 11.9 microg/g, and 14.2 microg/g, respectively) that were also similar. The slopes of the univariate regressions of blood, tibia, and patella lead versus age were 0.10 microg/dL/year (p < 0.001), 0.45 microg/g/year (p < 0.001), and 0.73 microg/g/year (p < 0.001), respectively. Analyses of smoothing curves and regression lines for tibia and patella lead suggested an inflection point at 55 years of age, with slopes for subjects greater than or equal to 55 years of age that were not only steeper than those of younger subjects but also substantially steeper than those observed for individuals > 55 years of age in studies of predominantly white participants. This apparent racial disparity at older ages may be related to differences in historic occupational and/or environmental exposures, or possibly the lower rates of bone turnover that are known to occur in postmenopausal black women. The higher levels of lead accumulation seen in this age group are of concern because such levels have been shown in other studies to predict elevated risks of chronic disease such as hypertension and cognitive dysfunction. Additional research on bone lead levels in minorities and their socioeconomic and racial determinants is needed.