Micro-proton Induced X-ray Emission Research Articles

Localization of mercury and gold in cassava (Manihot esculenta Crantz).

The potential of cassava (Manihot esculenta Crantz.) for simultaneous Hg and Au phytoextraction was explored by investigating Hg and Au localization in cassava roots through Micro-Proton Induced X-Ray Emission, High-Resolution Transmission Electron Microscopy (HR-TEM) and X-Ray Diffractometry (XRD). The effect of Hg and Au in the cyanogenic glucoside linamarin distribution was also investigated using Matrix Assisted Laser Desorption Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (MALDI-FT-ICR-MS) imaging. Hg was located mainly in the root vascular bundle of plants grown in 50 or 100μmolL-1 Hg solutions. Au was localized in the epidermis and cortex or in the epidermis and endodermis for 50 and 100μmolL-1 Au solutions, respectively. For 50μmolL-1 solutions of both Hg and Au, the two metals were co-localized in the epidermis. When the Hg concentrations were increased to 100μmolL-1, Au was still localized to a considerable extent in the epidermis while Hg was located in all root parts. HR-TEM and XRD revealed that Au nanoparticles were formed in cassava roots. MALDI-FT-ICR-MS imaging showed linamarin distribution in the roots of control and plants and metal-exposed plants thus suggesting that linamarin might be involved in Hg and Au uptake and distribution.

NEW INSIGHTS INTO STRUCTURES AND COMPOSITION OF PLANT FOOD MATERIALS

The aim of this paper is to review principles and potential application of micro-proton induced X-ray emission (micro-PIXE), synchrotron-based micro-X-ray fluorescence (micro-XRF) and inductively coupled plasma-mass spectrometry (ICP-MS) hyphenated with pulsed laser ablation (LA) for analysing plants and plant materials to elucidate feature of constituensts of nutritional value. These are required in order to develop novel high-quality functional and other food products in view of the variability of properties of plant tissues and products.

Optical response of bismuth based thin films synthesized via unbalanced magnetron DC sputtering technique

Bismuth-based thin films were deposited on AISI 316L stainless steel and glass substrates via the unbalanced magnetron DC sputtering technique. Three different configurations of titanium pieces along the bismuth target race track were used in order to evaluate the influence of Ti content on the optical and electrical properties of the films. We used a reactive ambient mixture of Ar:O (80%:20%) and a constant flux of 9 sccm, along with a power of 40W. Results showed thin films with high homogeneity and smooth surfaces, with several bismuth droplets, in all the different configurations. It was also found that the optical and electrical properties of the thin films are strongly dependent on the preparation conditions, especially the Ti content. Titanium quantities in the parts-per-million range were found only through the micro-proton induced X-Ray emission technique. This small quantity of Ti, as well as the thickness of the thin films, affected the electrical and optical response of the bismuth-based thin films.

Fate of nickel and calcium in seedlings of the hyperaccumulator Berkheya coddii during germination

Little is known about Ni storage in seeds of hyperaccumulating plants and its possible role in the first stages of plant development. The aim of this study was to determine Ni distribution in seeds and seedlings during germination and to test its role during germination with and without an external Ni supply. Field-harvested seeds from the South African Ni-hyperaccumulator Berkheya coddii Roessler were germinated either in Ni-free deionised water or in ultramafic soil. Sections of seeds and seedlings were analyzed using micro-proton induced X-ray emission (micro-PIXE) in order to localise Ni and other elements. Results show that high amounts of Ni were stored within the seeds. In germinating seeds, Ni was located in different parts: the lower epidermis, margins of cotyledons, and the pericarp in the micropylar area. The Ni and Ca were not mobilised during germination sensu stricto. Emergence of the first leaf seemed to trigger the translocation of Ni and Ca within the seedling. Besides, no effect of Ni supply from soil on its redistribution could be established for the germination stage.

Study of the Spatial Distribution of Mercury in Roots of Vetiver Grass (Chrysopogon zizanioides) by Micro-Pixe Spectrometry

Localization of Hg in root tissues of vetiver grass (Chrysopogon zizanioides) was investigated by micro-Proton Induced X-ray Emission (PIXE) spectrometry to gain a better understanding of Hg uptake and its translocation to the aerial plant parts.Tillers of C. zizanioides were grown in a hydroponic culture for 3 weeks under controlled conditions and then exposed to Hg for 10 days with or without the addition of the chelators (NH4)2S2O3 or KI. These treatments were used to study the effects of these chelators on localization of Hg in the root tissues to allow better understanding of Hg uptake during its assisted-phytoextraction.Qualitative elemental micro-PIXE analysis revealed that Hg was mainly localized in the root epidermis and exodermis, tissues containing suberin in all Hg treatments. Hg at trace levels was localized in the vascular bundle when plants were treated with a mercury solution only. However, higher Hg concentrations were found when the solution also contained (NH4)2S2O3 or KI. This finding is consistent with the observed increase in Hg translocation to the aerial parts of the plants in the case of chemically induced Hg phytoextraction.

The fate of arsenic, cadmium and lead in Typha latifolia: A case study on the applicability of micro-PIXE in plant ionomics

Understanding the uptake, accumulation and distribution of toxic elements in plants is crucial to the design of effective phytoremediation strategies, especially in the case of complex multi-element pollution. Using micro-proton induced X-ray emission, the spatial distribution of Na, Mg, Al, Si, P, S, Cl, K, Ca, Mn, Fe, Zn, As, Br, Rb, Sr, Cd and Pb have been quantitatively resolved in roots and rhizomes of an obligate wetland plant species, Typha latifolia, treated with a mixture of 100μM each of As, Cd and Pb, together. The highest concentrations of As, Cd and Pb were found in the roots of the T. latifolia, with tissue-specific distributions. The As was detected in the root rhizodermis, and in the rhizome the majority of the As was within the vascular tissues, which indicates the high mobility of As within T. latifolia. The Cd was detected in the root exodermis, and in the vascular bundle and epidermis of the rhizome. The highest Pb concentrations were detected in the root rhizodermis and exodermis, and in the epidermis of the rhizome. These data represent an essential step in the resolution of fundamental questions in plant ionomics.

Use of micro-PIXE to determine spatial distributions of copper in Brassica carinata plants exposed to CuSO4 or CuEDDS

A better understanding of the mechanisms that govern copper (Cu) uptake, distribution and tolerance in Brassica carinata plants in the presence of chelators is needed before significant progress in chelate-assisted Cu phytoextraction can be made. The aims of this study were therefore to characterise (S,S)-N,N′-ethylenediamine disuccinic acid (EDDS)-assisted Cu uptake, and to compare the spatial distribution patterns of Cu in the roots and leaves of B. carinata plants. The plants were treated with 30μM or 150μM CuSO4 or CuEDDS in hydroponic solution. Quantitative Cu distribution maps and concentration profiles across root and leaf cross-sections of the desorbed plants were obtained by micro-proton induced X-ray emission. In roots, the 30μM treatments with both CuSO4 and CuEDDS resulted in higher Cu concentrations in epidermal/cortical regions. At 150μM CuSO4, Cu was mainly accumulated in root vascular bundles, whereas with 150μM CuEDDS, Cu was detected in endodermis and the adjacent inner cortical cell layer. Under all treatments, except with a H+-ATP-ase inhibitor, the Cu in leaves was localised mainly in vascular tissues. The incubation of plants with 150μM CuEDDS enhanced metal translocation to shoots, in comparison to the corresponding CuSO4 treatment. Inhibition of H+-ATPase activity resulted in reduced Cu accumulation in 30μM CuEDDS-treated roots and 150μM CuEDDS-treated leaves, and induced changes in Cu distribution in the leaves. This indicates that active mechanisms are involved in retaining Cu in the leaf vascular tissues, which prevent its transport to photosynthetically active tissues. The physiological significance of EDDS-assisted Cu uptake is discussed.

Surface topography reconstruction by stereo-PIXE

A method of sample surface topography reconstruction is described based on the asymmetry in the X-ray yields acquired by a pair of X-ray detectors positioned at opposite sides of the probing beam. The yield asymmetries in the two simultaneously acquired elemental maps are caused by differences in the X-ray absorption along the X-ray exit route in the sample with a topographically structured surface. The approach presented introduces an asymmetry factor of the X-ray intensity in each of the image pixels to obtain an image asymmetry matrix. The dependence of the asymmetry factor on the local target inclination in the detector plane is calculated for a flat sample surface model. The image asymmetry matrix is then converted into the local inclination angle matrix. As the last step, the surface topography is then reconstructed from the local inclination angle. The method is based on X-ray absorption phenomena and could be applied equivalently in X-ray elemental mapping methods using excitation beams with a well-defined direction in the sample. This includes micro-X-Ray Fluorescence analysis (micro-XRF) and micro-Proton Induced X-ray Emission (micro-PIXE). We demonstrated the method by topographic analysis of engraved metallic samples with stereo-PIXE and compared it with the results of stylus profilometry. The smallest value of the X-ray production depth and the characteristic X-ray attenuation length determines the lateral resolution of the proposed topography reconstruction method.

PIXE analysis of U and Pu from hot particles: K-lines vs L-lines

Transuranic nuclides have been released into the environment since the beginning of the nuclear age. In many of the areas so contaminated, a significant fraction of the plutonium appears under the form of radioactive particles (also called ‘hot’ particles). In previous works, García López et al. (2007) [1] and Jiménez-Ramos et al. (2010) [2], radioactive particles from aircraft accidents in Palomares and Thule have been characterized. Using micro-Proton Induced X-ray Emission (μ-PIXE) and confocal X-ray fluorescence microprobe (μ-XRF), the L-lines of the main components in these particles, U and Pu, were analyzed. In this work, the key goal is the possibility to determine elemental ratios and concentration of transuranic elements in hot particles from the same areas but using their K-lines, because of their advantages in comparison with the study of L-lines. Indeed, the U and Pu K-lines present not overlapping between the main peaks in the spectra and the X-ray absorption in the sample is much lower than for L-lines.

Micro-PIXE study of Ag in digestive glands of a nano-Ag fed arthropod (Porcellio scaber, Isopoda, Crustacea)

Micro-proton induced X-ray emission (micro-PIXE) method was applied to study the micro-localization of silver (Ag) in digestive glands of a terrestrial arthropod (Porcellio scaber) after feeding on silver nanoparticles (nano-Ag) dosed food. The aim of our work was to assess whether feeding on nano-Ag results in the assimilation of silver (Ag) in digestive gland cells. To study micro-localization and elemental distribution of Ag, the animals were fed on food dosed with nanoparticles for 14days under controlled laboratory conditions. At the end of the feeding exposure, the animals were dissected and digestive glands prepared for micro-PIXE analyses and TEM investigation. The results obtained by micro-PIXE documented high amounts of Ag inside S-cells of the digestive gland epithelium; however, TEM investigation did not show particle aggregates inside digestive gland cells. Also no adverse effect on feeding behavior was recorded what is a measure of toxic effects. We explain the presence of Ag inside the cells as a result of the assimilation of dissoluted Ag ions from ingested nano-Ag particles. Assimilation of excessive amounts of ingested metal ions in S-cells is a well known metal detoxification mechanism in isopods. We discuss the advantages of using micro-PIXE for the micro-localization of elements in biological tissue in studies of interactions between nanoparticles and biological systems.

Improved Lateral Discrimination in Screening the Elemental Composition of Buckwheat Grain by Micro-PIXE

The elemental composition of specific fractions of cereal and pseudocereal grains can be roughly estimated after milling. Alternatively, the elemental localization of cross-sectioned grains can be quantitatively analyzed by microproton induced X-ray emission (micro-PIXE), taking advantage of high elemental sensitivity and low lateral resolution. We present a micro-PIXE study on buckwheat (Fagopyrum esculentum) grain, with a detailed description of the elemental distributions. Elements such as Mg, P, S, K, Fe, Ni, Cu, and Zn were preferentially localized in the cotyledons and embryonic axis; however, significant amounts of K and Fe were also found in the pericarp. The aleurone layer covering the cotyledons was especially enriched in S and P, while testa, a thin layer above the aleurone did not show any significant element enrichments. The highest concentrations of Al, Si, Cl, Ca, and Ti were found in the pericarp. A detailed element localization study of pericarp layers revealed that the inner layer was enriched in K, Mn, Ca, and Fe, while the outer layer showed enrichments in Na, Mg, P, S, and Al. On the basis of the data obtained, milling techniques can be adapted to obtain milling fractions with targeted nutritional values.

Elemental and structural studies at the bone–cartilage interface

Micro-Proton Induced X-ray Emission (μ-PIXE) and Proton Induced Gamma-ray Emission (PIGE) techniques were employed in the investigation of trace and essential elements distribution in normal and diseased human femoral head sections affected by osteoarthritis (OA). PIGE was exploited in the determination of elements of low atomic number z<15 such as Na and F whereas elements with z>15 viz Ca, Z, P and S were determined by PIXE. Accumulations of key elements in the bone and cartilage sections were observed, significant S and Na concentrations being found in the cartilage region particularly in normal tissues. Zn showed enhanced concentrations at the bone–cartilage interface. At a synchrotron facility, small angle X-ray scattering (SAXS) was utilized on a decalcified human femoral head section affected by OA, direct measurements being made of spatial alterations of collagen fibres. The SAXS results showed a slight decrease in the axial periodicity between normal collagen type I and that in diseased tissue in various sites, in contrast with the findings of others.

Nickel, Zn and Cd localisation in seeds of metal hyperaccumulators using μ-PIXE spectroscopy

Metal hyperaccumulators are a rare group of plant species that accumulate exceptionally high concentrations of metals in above ground tissues without showing symptoms of phytotoxicity. Quantitative localisation of the accumulated metals in seed tissues is of considerable interest to help understand the eco-physiology of these unique plant species. We investigated the spatial localisation of metals within seeds of Ni hyperaccumulating Hybanthus floribundus subsp. adpressus, H. floribundus subsp. floribundus and Pimelea leptospermoides and dual-metal (Cd and Zn) hyperaccumulating Thlaspi caerulescens using quantitative micro-proton induced X-ray emission (μ-PIXE) spectroscopy. Intact seeds were hand-sectioned, sandwiched between Formvar films and irradiated using the 3 MeV high energy heavy ion microprobe at ANSTO. Elemental maps of whole H. floribundus subsp. adpressus seeds showed an average Ni concentration of 5.1 × 10 3 mg kg −1 dry weight (DW) with highest Ni concentration in cotyledonary tissues (7.6 × 10 3 mg kg −1 DW), followed by the embryonic axis (4.4 × 10 3 mg kg −1 DW). Nickel concentration in whole H. floribundus subsp. floribundus seeds was 3.5 × 10 2 mg kg −1 DW without a clear pattern of Ni localisation. The average Ni concentration in whole P. leptospermoides seeds was 2.6 × 10 2 mg kg −1 DW, and Ni was preferentially localised in the embryonic axis (4.3 × 10 2 mg kg −1 DW). In T. caerulescens, Cd concentrations were similar in cotyledon (4.5 × 10 3 mg kg −1 DW) and embryonic axis (3.3 × 10 3 mg kg −1 DW) tissues, whereas Zn was highest in cotyledonary tissues (1.5 × 10 3 mg kg −1 DW). In all species, the presence of the accumulated metal within the cotyledonary and embryonic axis tissues indicates that the accumulated metal was able to move apoplastically within the seed.

Mineralogical and magnetic characterisation of iron titanium oxides in soils developed on two various basaltic rocks under temperate climate

The objective of this study was to characterize alteration processes of iron titanium oxides in andic soils developed on basaltic rocks under temperate climate. Among the magnetic minerals, titanomagnetites are the most abundant and represent the major spinel in basalts. In order to understand processes involved in the alteration of iron titanium oxides from basaltic rocks associated to soils, two pedons developed on Tertiary massive basaltic formations submitted to temperate climate were considered. The magnetic minerals have been characterized by studying rock and soil magnetic parameters i.e. magnetic susceptibility and Curie temperature. Chemical composition was investigated by optical and electron microscopy (EMPA, SEM-EDS) and by micro-proton induced X-ray emission (µPIXE). Because mineralogy of the parent rocks controls those of the soils, we have first studied the rocks. The thermomagnetic curves obtained on the two studied rocks show that initial titanomagnetite is preserved in one sample (MC-rock) while the other (PC-rock) contains near-pure magnetite possibly issued from exsolution process. Microscopic observations confirm the exsolution lamellae on titanomagnetites and show a Cr content gradient in chromian spinel partially enclosed in olivine. These observations suggest a deuteric alteration. The two profiles exhibit increasing Curie temperature between the rocks and soil horizons, indicating a transformation of magnetic minerals. Results emphasize the maghemitization of iron titanium oxides in andic soils in a temperate climate.

Application of X-ray fluorescence analytical techniques in phytoremediation and plant biology studies

Phytoremediation is an emerging technology that employs the use of higher plants for the clean-up of contaminated environments. Progress in the field is however handicapped by limited knowledge of the biological processes involved in plant metal uptake, translocation, tolerance and plant–microbe–soil interactions; therefore a better understanding of the basic biological mechanisms involved in plant/microbe/soil/contaminant interactions would allow further optimization of phytoremediation technologies. In view of the needs of global environmental protection, it is important that in phytoremediation and plant biology studies the analytical procedures for elemental determination in plant tissues and soil should be fast and cheap, with simple sample preparation, and of adequate accuracy and reproducibility. The aim of this study was therefore to present the main characteristics, sample preparation protocols and applications of X-ray fluorescence-based analytical techniques (energy dispersive X-ray fluorescence spectrometry—EDXRF, total reflection X-ray fluorescence spectrometry—TXRF and micro-proton induced X-ray emission—micro-PIXE). Element concentrations in plant leaves from metal polluted and non-polluted sites, as well as standard reference materials, were analyzed by the mentioned techniques, and additionally by instrumental neutron activation analysis (INAA) and atomic absorption spectrometry (AAS). The results were compared and critically evaluated in order to assess the performance and capability of X-ray fluorescence-based techniques in phytoremediation and plant biology studies. It is the EDXRF, which is recommended as suitable to be used in the analyses of a large number of samples, because it is multi-elemental, requires only simple preparation of sample material, and it is analytically comparable to the most frequently used instrumental chemical techniques. The TXRF is compatible to FAAS in sample preparation, but relative to AAS it is fast, sensitive and multi-elemental. The micro-PIXE technique requires rather expensive instrumentation, but offers multi-elemental analysis on the tissue and cellular level.

Early Calcifications in Human Coronary Arteries As Determined with a Proton Microprobe

The current paradigm reads that calcifications characterize the advanced and complex lesions in the atherosclerotic process. To explore the possibility that coronary artery wall calcifications already commence at an early stage of atherosclerosis, a combination of proton beam techniques with a (sub-) micrometer resolution, i.e., micro-proton induced X-ray emission, backward and forward scattering spectroscopy, was applied on human coronary arteries with lesions preceding overt atheromas. The detection limits of phosphorus and calcium in each separate pixel, 0.88*0.88 microm2 in size, were approximately 150 and 80 microg/g dry weight, respectively. Calcium distributions of entire coronary artery cross section were obtained, and calcifications were demonstrated at a preatheroma stage of the atherosclerotic process. The size of the microcalcifications varied between 1 and 10 microm. The composition of the microcalcifications was deduced from the calcium-to-phosphorus ratio. In order to quantify this ratio, the thickness of the specific X-ray absorber used for PIXE had to be accurately determined. Also, thick target PIXE calculations were performed and the method was validated. The calcium-to-phosphorus ratios of the microcalcifications were assessed with good accuracy and varied from 1.62 to 2.79, which corresponds with amorphous calcium phosphate.

Probing calcium and sulfur distribution and pattern in hairs using micro-proton induced X-ray emission (MPIXE)

More than 20 hair strands obtained from several people are analyzed by non-invasive micro-proton induced X-ray emission (PIXE) for probing calcium and sulfur distribution and pattern. The sulfur content in woman’s hair along the longitudinal axis shows a monthly rhythm whereas the level of Ca is much higher in the medulla core and exhibits a daily rhythm both in male and female hair. The Ca content gradually decreases from the tip to the root position in the shedding process and more Ca can be found in black hair compared to white hair.

Origins of PM10 Determined by the Micro-Proton Induced X-Ray Emission Spectra of Single Aerosol Particles

The micro-proton induced X-ray emission (micro-PIXE) spectrum of a single aerosol particle (SAP) was considered as its fingerprint for tracing its origin. A proton microprobe was used to extract fingerprints of SAPs. Environmental monitoring samples of PM(10) were collected from a heavy industrial area of Shanghai and were analyzed by proton microprobe for finding their pollution sources. In order to find the sources of SAPs collected from environmental monitoring sites, a fingerprint database of SAPs collected from various pollution sources was established. The origins of samples collected through environmental monitoring were identified by comparison of the micro-PIXE spectra of SAPs with those of SAPs in the fingerprint database using a pattern recognition technique. The results of this study show that most of the measured PM(10) is derived from metallurgic industry, soil dust, coal combustion, automobile exhaust, and motorcycle exhaust. The study also shows that the proton microprobe is an ideal tool for the analysis of SAPs. The unidentified particles of PM(10) are classified into seven classes by hierarchical cluster analysis based on the element peak intensity in the spectra.

The distribution of Ag in Ag-doped YBa2Cu3O7- thin film prepared by dual-beampulsed-laser deposition

<P>The Ag distribution in Ag-doped YBa<SUB>2</SUB>Cu<SUB>3</SUB>O<SUB>7-<IMG SRC="common/delta.gif" ALT="delta" ALIGN="TOP"/></SUB> (YBCO) thin films fabricated by dual-beam pulsed-laser deposition on SrTiO<SUB>3</SUB> (100) substrates has been studied by Auger electron spectroscopy, microproton-induced x-ray emission, atomic force microscopy and scanning electron microscopy. All the results consistently show that Ag aggregated in the bar-like structures observed in the film. These bars are aligned along the <I>a</I>-<I>b</I>-axis or at 45° to the <I>a</I>-<I>b</I>-axis of the YBCO thin film. The main body of the long bars aligned with the <I>a</I>-<I>b</I>-axes of the film was found to be a combination of metallic Ag with other precipitates of YBCO film that may grow from the substrate surface to the YBCO film surface. There were other precipitates aggregating as well at the surface of these bars, such as oxides of Cu and Ba. The short bars that aligned along 45° to the <I>a</I>-<I>b</I>-axes of the film were found to be deficient in Ag but rich in Cu, Ba and O, which could be oxide precipitates of YBCO. The growth mechanisms of the two types of bars seem quite different.</P>

Concentration and Distribution of Metal Elements at the Surface of Balsam Fir Foliage by Micro-Proton Induced X-ray Emission

Metal contaminations at the surface of balsam fir (Abies balsamea (L.) Mill.) needles collected at two locations in southern Quebec were determined by micro-PIXE (micro-proton induced X-ray emission) with scanning depth of 3−4 or 45−50 μm and scanning spacing from 15 to 250 μm. At adaxial surfaces, concentrations of Al, Si, Ca, Ti, Fe, and Zn were significantly (P < 0.05) higher at the near-urban site than at the mountainous location. Accumulation of Mg, Al, Si, K, Mn, Fe, and Zn was significantly (P < 0.01) higher at surfaces of unwashed needles as compared to chloroform-washed needles, which shows significant metal accumulation in/on epicuticular wax layers. Metal deposits, except Mn, in epicuticular wax layers were significantly affected by washing with acidic solution. Distributions of Mg, K, Mn, and Zn deposits at the surface were lower around central regions than near foliar edges, while Si was higher around the central area. Scanning to the 45−50 μm depth showed significant accumulation of Ni on ei...