Microprobe Imaging Research Articles

Large detector array and real-time processing and elemental image projection of X-ray and proton microprobe fluorescence data

A detector concept is described that integrates a large solid-angle detector array developed at Brookhaven National Laboratory and a high speed pipelined parallel processing engine developed at CSIRO for machine vision, with an embedded implementation of the Dynamic Analysis method for fluorescence spectra deconvolution and image projection, to yield a detection system capable of energy-dispersive detection, spectral deconvolution and real-time elemental imaging at ∼10 8 events per second for PIXE elemental imaging using the nuclear microprobe and SXRF elemental imaging using the synchrotron X-ray microprobe.

In situ measurements of Li isotopes in foraminifera

In situ measurement of Li isotope ratios in foraminifera has been developed using a Cameca ims 1270 ion microprobe. In situ δ7Li analyses have been performed in biogenic calcite of planktonic foraminifera from various locations. Results show that for west Pacific mixed Globigerinoides and Globorotalia (22°S161°E), the isotopic variability between tests and within a single test, respectively, is not significantly greater than estimated analytical uncertainty (∼1.5‰). Mean δ7Li for several planktonic foraminifera tests corresponds to the seawater value, strongly suggesting negligible Li isotope fractionation relative to seawater, as previously inferred by Hall et al. (2005) using thermo‐ionization mass spectrometer and multicollector‐inductively coupled plasma‐mass spectrometry techniques. Combined with scanning electron microscopy and ion microprobe imaging, micron‐sized grains, enriched in lithium, silica and aluminum have been found in the foraminifera calcite matrix. A simple mixing model shows that 0.3–2 wt % of marine clays incorporated within the analyzed calcite would lower the foraminifera δ7Li value, by 3‰ to 10‰ relative to the isotopic composition of the pure calcite. By comparison, no such grains have been detected in corals. The presence of micron‐sized silicate grains embedded within the foraminifera calcite is consistent with the Erez (2003) biomineralization model, involving calcite precipitation from seawater vacuoles. By contrast, coral calcium carbonate is instead precipitated from ions, which have been pumped or diffused through several membranes, impermeable to micrometric grains. Ion microprobe in situ δ7Li measurements in biogenic calcite present new methods for investigating both biomineralization processes and the past record of the ocean composition by exploring geochemical variations at a scale that is smaller in space and in time.

Chemical variability in chrome spinel grains from magnetically fractionated ilmenite concentrates: implications for processing

Detrital chrome spinels are contaminant grains within ilmenite rich heavy mineral concentrates found along the southeast coastline of Africa and in the Murray Basin region of southeastern Australia. Separation is often difficult because of overlaps of physical properties between the chrome spinels and ilmenite. The presence of even minor levels of chromia in the concentrates will downgrade their market value as potential feedstocks for the production of titania pigment. In the present paper, the chemistry and distribution of chrome spinels in magnetically fractionated ilmenite concentrates from both regions are characterised using electron microprobe imaging and analysis techniques to establish the chemical and mineralogical factors that impact on their separation behaviour. Results show that the South African sample contains two chemically and magnetically distinct chrome spinel groups. The first group is dominated by a strong trend that reflects the mutual substitution between Al3+ and Cr3+ while the second group is characterised by compositions containing abundant Fe3O4 magnetite component. The presence of these two spinel groups means that physical separation from the ilmenite is relatively straightforward using simple roasting and magnetic separation procedures. In comparison, the Murray Basin chrome spinels exhibit broad chemical variation that results in no clear separation based on magnetic response. The broad spread in composition and magnetic susceptibility of the chrome spinels is responsible for the previously observed difficulties in developing successful separation methods.

High-resolution MALDI imaging mass spectrometry allows localization of peptide distributions at cellular length scales in pituitary tissue sections

Matrix assisted laser desorption/ionization (MALDI) imaging mass spectrometry (IMS) has been used to determine peptide distributions directly from rat, mouse and human pituitary tissue sections. Since these organs are small (10 2–10 3 μm) the spatial resolution of IMS is a key issue in molecular imaging of pituitary tissue sections. Here we show that high-resolution IMS allows localization of neuropeptide distributions within different cell clusters of a single organ of a pituitary tissue section. The sample preparation protocol does not result in analyte redistribution and is therefore applicable to IMS experiments at cellular length scales. The stigmatic imaging mass spectrometer used in this study produces selected-ion-count images with pixel sizes of 500 nm and a resolving power of 4 μm, yielding superior spatial detail compared to images obtained in microprobe imaging experiments. Furthermore, we show that with imaging mass spectrometry a distinction can be made between different mammalian tissue sections based on differences in the amino acid sequence of neuropeptides with the same function. This example demonstrates the power of IMS for label-free molecular imaging at relevant biological length scales.

X‐ray fluorescence microprobe imaging in biology and medicine

Characteristic X-ray fluorescence is a technique that can be used to establish elemental concentrations for a large number of different chemical elements simultaneously in different locations in cell and tissue samples. Exposing the samples to an X-ray beam is the basis of X-ray fluorescence microscopy (XFM). This technique provides the excellent trace element sensitivity; and, due to the large penetration depth of hard X-rays, an opportunity to image whole cells and quantify elements on a per cell basis. Moreover, because specimens prepared for XFM do not require sectioning, they can be investigated close to their natural, hydrated state with cryogenic approaches. Until several years ago, XFM was not widely available to bio-medical communities, and rarely offered resolution better then several microns. This has changed drastically with the development of third-generation synchrotrons. Recent examples of elemental imaging of cells and tissues show the maturation of XFM imaging technique into an elegant and informative way to gain insight into cellular processes. Future developments of XFM-building of new XFM facilities with higher resolution, higher sensitivity or higher throughput will further advance studies of native elemental makeup of cells and provide the biological community including the budding area of bionanotechnology with a tool perfectly suited to monitor the distribution of metals including nanovectors and measure the results of interactions between the nanovectors and living cells and tissues.

Surface enhanced Raman scattering of organic sample powders spread over vacuum-evaporated silver thin film

Surface enhanced Raman scattering (SERS) from samples prepared by spreading para-nitrobenzoic acid (PNBA) and adenosine powders over silver thin films was achieved. The SERS intensities of the ionized PNBA on the silver film increase with increased applied pressure through a cover-glass and reach a maximum at 0.6 MPa. In contrast, the signals caused by adenosine remain nearly unchanged under applied pressures of 0–0.6 MPa. Beyond 0.6 MPa, the signals attributable to samples decrease in intensity. Atomic force microprobe images reveal that nanometer-scale surface morphology is changed by 0.8 MPa pressure, suggesting that the decrease in SERS intensity is related to pressure-induced morphological changes. Results obtained in this study indicate that SERS spectra are obtainable easily, without solvents, under ambient conditions using dispersion of the sample powder.

Surface-enhanced Raman spectral study of Au nano-particles/alkanethiol self-assembled monolayers/Au(1 1 1 ) heterostructures

This paper describes Raman spectroscopic investigations of octadecane–thiol (C 18H 37–SH; OD–mT) and octane–dithiol (HS–C 8H 16–SH; O–dT) self-assembled monolayers (SAMs) on an epitaxial Au(1 1 1 )/cleaved-mica substrate. The epitaxial Au(1 1 1 ) substrate having nanometer-scale domains increases the enhanced Raman signals of SAMs, whereas the Raman bands are much less intense on the micrometer-scale domains of Au(1 1 1 ). The Raman intensity of the ν s(CH 2) band is increased for depositions above 4 nm, and takes a maximum at a thickness of 9 nm when gold is vacuum-deposited on the OD–mT SAMs that are formed on micrometer-scale domains. For the O–dT SAMs, Raman band intensity profiles show two features at gold thicknesses of 2 and 9 nm; the latter intensity is about three times greater than that of the former. Atomic force microprobe (AFM) images reveal that 20–30-nanometer-scale islands are formed by 9 nm gold deposition for both SAMs. In contrast, 2 nm gold deposition onto the O–dT SAMs creates striped nanostructures (ca. 7 nm in spacing). The results suggest that the specific nanostructures formed by post-deposition of gold serve to enhance the SAMs Raman signals.

Microscale controls on the fate of contaminant uranium in the vadose zone, Hanford Site, Washington

An alkaline brine containing uranyl (UO 2 2+) leaked to the thick unsaturated zone at the Hanford Site. We examined samples from this zone at microscopic scale to determine the mode of uranium occurrence—microprecipitates of uranyl (UO 2 2+) silicate within lithic-clast microfractures—and constructed a conceptual model for its emplacement, which we tested using a model of reactive diffusion at that scale. The study was driven by the need to understand the heterogeneous distribution of uranium and the chemical processes that controlled it. X-ray and electron microprobe imaging showed that the uranium was associated with a minority of clasts, specifically granitic clasts occupying less than four percent of the sediment volume. XANES analysis at micron resolution showed the uranium to be hexavalent. The uranium was precipitated in microfractures as radiating clusters of uranyl silicates, and sorbed uranium was not observed on other surfaces. Compositional determinations of the 1–3 μm precipitates were difficult, but indicated a uranyl silicate. These observations suggested that uranyl was removed from pore waters by diffusion and precipitation in microfractures, where dissolved silica within the granite-equilibrated solution would cause supersaturation with respect to sodium boltwoodite. This hypothesis was tested using a reactive diffusion model operating at microscale. Conditions favoring precipitation were simulated to be transient, and driven by the compositional contrast between pore and fracture space. Pore–space conditions, including alkaline pH, were eventually imposed on the microfracture environment. However, conditions favoring precipitation were prolonged within the microfracture by reaction at the silicate mineral surface to buffer pH in a solubility limiting acidic state, and to replenish dissolved silica. During this time, uranyl was additionally removed to the fracture space by diffusion from pore space. Uranyl is effectively immobilized within the microfracture environment within the presently unsaturated Vadose Zone.

Development and applications of an epifluorescence module for synchrotron x-ray fluorescence microprobe imaging

Synchrotron x-ray fluorescence (XRF) microprobe is a valuable analysis tool for imaging trace element composition in situ at a resolution of a few microns. Frequently, epifluorescence microscopy is beneficial for identifying the region of interest. To date, combining epifluorescence microscopy with x-ray microprobe has involved analyses with two different microscopes. We report the development of an epifluorescence module that is integrated into a synchrotron XRF microprobe beamline, such that visible fluorescence from a sample can be viewed while collecting x-ray microprobe images simultaneously. This unique combination has been used to identify metal accumulation in Alzheimer’s disease plaques and the mineral distribution in geological samples. The flexibility of this accessory permits its use on almost any synchrotron x-ray fluorescence microprobe beamline and applications in many fields of science can benefit from this technology.

Enhanced scanning ion microprobe image analysis for rough surface samples as an alternative to SIMS depth profiling

AbstractThe usefulness of scanning ion microprobe (SIM) image analysis by a gallium focused ion beam (FIB) on a bevelled sample surface is investigated. To improve the low secondary ionization yields of elements caused by the gallium bombardment, the oxygen ions for the positive ion detection and the caesium ions for the negative ion detection were in‐situ implanted with a dose of 1016–1017 atoms/cm2 prior to imaging analysis. A significant enhancement of ion image sensitivity in the ion‐implanted area compared with that in the non‐implanted area was observed. The enhanced SIM image analysis for the highly magnified bevel is especially useful for multilayered structures with rough surfaces. That is because the secondary ion mass spectrometry (SIMS) depth profiles for the rough surface samples do not give accurate depth information due to the significant distortion and degradation of the profiles caused by uneven etching. This technique can be an alternative to the SIMS depth profiling for rough surface samples. Copyright © 2004 John Wiley & Sons, Ltd.

Melt inclusions from the deep Slave lithosphere: implications for the origin and evolution of mantle-derived carbonatite and kimberlite

Melt inclusions in clinopyroxenes from lherzolitic xenoliths from the deep lithospheric mantle beneath the Slave Craton (Lac de Gras area, Canada) reveal multiple origins for carbonatitic melts. One type of inclusions consists of a series of silicate–carbonate–silicate concentric layers, interpreted to have unmixed under disequilibrium conditions during rapid ascent to the surface. Bulk major- and trace-element compositions are typical of Group 1 kimberlites and quantitative nuclear microprobe imaging of the globules reveals fractionation of related elements (e.g. F–Br, Nb–Ta) between the silicate and carbonate components. The globules probably formed by partial melting of carbonated peridotite, consistent with results of melting experiments and some models for the generation of kimberlite magmas. They provide evidence for a genetic relationship between some carbonate-rich magmas and ultramafic silicate magmas, and for the possibility of unmixing processes of these melts during their evolution.The second inclusion type comprises carbonate-rich globules interpreted as samples of Mg-carbonatite melt that quenched on ascent to the surface. Bulk major- and trace-element compositions indicate that the melts were derived from a carbonate-rich source and oxygen, carbon, and strontium isotope data are consistent with the involvement of recycled crustal material and suggest that some mantle-derived carbonatites are unrelated to kimberlites.

Electron microprobe imaging for the characterization of polymer matrix composites

Traditionally, image analysis of polymer matrix composite (PMC) materials has been achieved through optical microscopy and, to a lesser extent, scanning electron microscopy. In this study, image analysis using an electron microprobe in backscatter mode is introduced as a method to provide a qualitative comparison of void content and fiber packing in PMC materials. Composite parts were fabricated using a vacuum-assisted resin transfer molding (VARTM) process and another process known as the composites pressure resin infusion system (ComPRIS). Voids were observed in the composite specimens fabricated by the VARTM process, where resin infusion is driven by vacuum. No significant voids were observed in the composite specimens fabricated by the ComPRIS process, where resin infusion is driven by pressure. The apparent difference in void content is attributed to the difference in the resin infusion driving force, i.e. vacuum versus pressure. Backscattered electron imaging of samples using an electron microprobe proved to be a suitable technique for imaging PMC surfaces.

Enhanced Raman microprobe imaging of single-wall carbon nanotubes

We explore Raman microprobe capabilities of visualizing single-wall carbonnanotubes (SWCNTs). Although this technique is limited to the micron scale, wedemonstrate that images of individual SWCNTs, bundles, or their agglomerates canbe generated by mapping Raman active elementary excitations. We measuredthe Raman response from carbon vibrations in SWCNTs excited by confocalscanning of a focused laser beam. Carbon vibrations reveal key characteristics ofSWCNTs such as the nanotube diameter distribution (radial breathing modes (RBM),100–300 cm−1), the presence of defects and functional groups (D-mode,1300–1350 cm−1), strain and oxidation states of SWCNTs, as well as the metallic orsemiconducting character of the tubes encoded in the lineshape of the G-modes at1520–1600 cm−1. In addition, SWCNTs are highly anisotropic scatterers. The Raman response from aSWCNT is maximal for incident light polarization parallel to the tube axis and vanishingfor perpendicular directions. We show that the SWCNT bundle shape or direction can bedetermined, with some limitations, from a set of Raman images taken for two orthogonaldirections of the incident light polarization.

Nuclear microprobe imaging of gallium nitrate in cancer cells

Gallium nitrate is used in clinical oncology as treatment for hypercalcemia and for cancer that has spread to the bone. Its mechanism of antitumor action has not been fully elucidated yet. The knowledge of the intracellular distribution of anticancer drugs is of particular interest in oncology to better understand their cellular pharmacology. In addition, most metal-based anticancer compounds interact with endogenous trace elements in cells, altering their metabolism. The purpose of this experiment was to examine, by use of nuclear microprobe analysis, the cellular distribution of gallium and endogenous trace elements within cancer cells exposed to gallium nitrate. In a majority of cellular analyses, gallium was found homogeneously distributed in cells following the distribution of carbon. In a smaller number of cells, however, gallium appeared concentrated together with P, Ca and Fe within round structures of about 2–5 μm diameter located in the perinuclear region. These intracellular structures are typical of lysosomial material.

Ion image enhancement using in-situ implantation of Cs + and O 2+ ions

Scanning ion microprobe (SIM) image using a gallium focused ion beam (FIB) is greatly improved in sensitivity by the in-situ implantation of cesium or oxygen ions with the dose of 10 15–10 17 atoms/cm 2. When the cesium ions are implanted into the imaging area prior to gallium beam analysis, the brightness of the SIM images in negative ion mode is greatly enhanced. In the same way, the implantation of oxygen ions causes the remarkable enhancement of the brightness of SIM images in positive ion mode. A layered structured sample is beveled and polished mechanically with a slope angle of 0.5°, which magnifies the thickness of a layer at about 110 times on the slope. By implanting cesium ions into the beveled surface, an SiO 2 layer of 30 nm thickness is clearly distinguished by the enhanced O − image.

Quantitative, high sensitivity, high resolution, nuclear microprobe imaging of fluids, melts and minerals

Samples of fluids and melts trapped and preserved as inclusions in growing minerals or healed fractures provide unique windows on a range of geological processes from mantle melting and metasomatism through to economic ore formation and remobilization. Recent advances in nuclear microprobe (NMP) technology at the CSIRO provide powerful tools for the study of these inclusions and associated mineral assemblages. These tools include a new NMP designed for high resolution and high sensitivity, PIXE analytical methods for quantitative imaging and analysis, and simultaneous PIGE imaging. The quantitative imaging and analysis methods are based on the dynamic analysis approach, which generates a fast matrix transform for projection of list-mode PIXE data onto pure elemental images. Recent advances provide rapid pixel-by-pixel correction for matrix and absorption effects in different (mineral) compositions across the image area to yield true quantitative images. These methods are combined in a software package called GeoPIXE II.

X-ray microprobe imaging and X-ray microspectroscopy in biology

X-ray microprobe imaging and X-ray microspectroscopy in biology

A new mechanism of formation of the silver-rim structure on primary gold grains

Gold minerals in the Baochun skarn-type gold deposit are Au-Ag alloys with Ag contents within the range of 15–35. 5 wt% and the minerals vary from 5μm to 50μm in size. As viewed from the electron microprobe images, most gold grains show silver rims with a high Ag content as compared with the core, ranging generally from 2 to 3μm in width. From dynamic calculations based on the mass action and mass balance constraints on the crystallization of native gold, it is considered that the enrichment of silver in the rim of gold minerals is due to gradual enrichment of silver in the ore-forming solutions with its evolution from the early to the late metallogenic stage.

Oscillatory zinc distribution in Arctic char ( Salvelinus alpinus) otoliths: : The result of biology or environment?

Scanning proton microprobe (SPM) analysis and imaging was used to map the distribution of zinc in otoliths of anadromous and non-anadromous Arctic char ( Salvelinus alpinus) from the Canadian Arctic. Zinc distribution patterns were oscillatory with concentrations ranging from 35 to 240 ppm. Superimposition of the zinc distribution on optical images of the otoliths permitted correlation of zinc uptake with annular structure in the otoliths and with strontium patterns from the same otolith. Well defined oscillations of zinc concentrations were observed in the otoliths, particularly in the first few years in all samples. In anadromous fish, these overlapped with the onset of the strontium oscillations that were indicative of anadromy and then declined; in non-anadromous fish the oscillations generally continued to later years. Oscillatory zoning of zinc may indicate: (1) variations in the concentration of zinc in water; (2) variations in nutrient availability in the environment; (3) temperature variations in the habitat occupied; or (4) a combination of zinc concentration, nutrient availability or temperature changes. As such, the systematic distribution of zinc in otoliths has the potential to provide temporally constrained information on fish habitat and/or fish biology.

The use of molecular beams in nuclear microprobe imaging

Molecular hydrogen ions were first used in nuclear microprobe STIM imaging to enhance contrast. These beams have also been used for PIXE and other techniques of microprobe imaging, although the high-energy electrons associated with the molecules caused problems with charge integration. This paper discusses the use of asymmetric molecular ion beams, to utilise the properties of molecular break-up for enhanced materials analysis. In particular the use of the deuterium-hydrogen (DH+) molecule for STIM imaging to provide increased image contrast and improved density measurement for specimens of widely varying areal densities is discussed.