Mark R. Davidson

In situ characterization and mapping of iron compounds in Alzheimer's disease tissue.

There is a well-established link between iron overload in the brain and pathology associated with neurodegeneration in a variety of disorders such as Alzheimers (AD), Parkinsons (PD) and Huntingtons (HD) diseases [1]. This association was first discovered in AD by Goodman in 1953 [2], where, in addition to abnormally high concentrations of iron in autopsy brain tissue, iron has also been shown to accumulate at sites of brain pathology such as senile plaques [3]. However, since this discovery, progress in understanding the origin, role and nature of iron compounds associated with neurodegeneration has been slow. Here we report, for the first time, the location and characterisation of iron compounds in human AD brain tissue sections. Iron fluorescence was mapped over a frontal-lobe tissue section from an Alzheimers patient, and anomalous iron concentrations were identified using synchrotron X-ray absorption techniques at 5 mum spatial resolution. Concentrations of ferritin and magnetite, a magnetic iron oxide potentially indicating disrupted brain-iron metabolism, were evident. These results demonstrate a practical means of correlating iron compounds and disease pathology in-situ and have clear implications for disease pathogenesis and potential therapies.

High field magnetic resonance microscopy of the human hippocampus in Alzheimer's disease: quantitative imaging and correlation with iron

We report R(2) and R(2) in human hippocampus from five unfixed post-mortem Alzheimers disease (AD) and three age-matched control cases. Formalin-fixed tissues from opposing hemispheres in a matched AD and control were included for comparison. Imaging was performed in a 600MHz (14T) vertical bore magnet at MR microscopy resolution to obtain R(2) and R(2) (62 μm×62 μm in-plane, 80 μm slice thickness), and R(1) at 250 μm isotropic resolution. R(1), R(2) and R(2) maps were computed for individual slices in each case, and used to compare subfields between AD and controls. The magnitudes of R(2) and R(2) changed very little between AD and control, but their variances in the Cornu Ammonis and dentate gyrus were significantly higher in AD compared for controls (p<0.001). To investigate the relationship between tissue iron and MRI parameters, each tissue block was cryosectioned at 30 μm in the imaging plane, and iron distribution was mapped using synchrotron microfocus X-ray fluorescence spectroscopy. A positive correlation of R(2) and R(2)* with iron was demonstrated. While studies with fixed tissues are more straightforward to conduct, fixation can alter iron status in tissues, making measurement of unfixed tissue relevant. To our knowledge, these data represent an advance in quantitative imaging of hippocampal subfields in unfixed tissue, and the methods facilitate direct analysis of the relationship between MRI parameters and iron. The significantly increased variance in AD compared for controls warrants investigation at lower fields and in-vivo, to determine if this parameter is clinically relevant.

Effect of Mn concentration on the structural, optical, and magnetic properties of GaMnN

The room temperature magnetization of GaMnN films grown by molecular beam epitaxy on (0001) sapphire substrates with Mn concentrations varying from 0 to 9 at. % was found to depend on Mn concentration, with a maximum magnetization found at ∼3 at. % Mn. High-resolution x-ray diffraction measurements show that the c-plane lattice constant initially decreases with increasing Mn concentration, then increases when the Mn content increases above ∼3 at. %. This increase is accompanied by a decrease in the full width at half maximum of the rocking curves. Extended x-ray absorption fine structure results indicate that the nonsubstitutional Mn is not present in the form of GaxMny clusters and thus is most likely present in the form of an interstitial. Optical absorption measurements show only a slight increase in the band gap for material with 3 at. % Mn, relative to undoped GaN.

Evidence of alloy formation during reduction of platinized tin oxide surfaces

Ion scattering spectroscopy, Auger electron spectroscopy, and electron spectroscopy for chemical analysis have been used to examine a platinized tin oxide catalyst surface before, during, and after reduction by annealing under vacuum at 250 to 450 C. These techniques were then used to examine the reduced surface after a room-temperature, low-pressure oxygen exposure. The spectral results and the behavior of the reduced surface toward oxygen exposure both indicate that a Pt/Sn alloy is produced during reduction.

Three-Dimensional Self-Assembled Hierarchical Architectures of Gamma-Phase Flowerlike Bismuth Oxide

Three-dimensional (3D) self-assembled hierarchical bismuth oxide architectures were prepared via a solution precipitation synthesis at 85 degrees C in 45 min with the aid of polyethylene glycol-8000 (PEG-8000) as a capping agent. The morphology and crystalline phase evolution was studied versus reaction time and capping agent concentration and interpreted in terms of growth mechanisms. At higher capping agent concentrations, the as-grown 3D hierarchical flowerlike bismuth oxide was crystalline cubic gamma-phase that was previously formed only at temperature > or =640 degrees C. The morphology and crystal structure of these 3D cubic gamma-phase bismuth oxide flowers were not changed with calcining up to 600 degrees C. Photoluminescence was attributed to emission from the Bi(3+) ion by a (3)P(0),(1) --> (1)S(0) transition and from defects. The gamma-phase flowerlike bismuth oxide shows better ion conductivity than that of rodlike bismuth oxide formed without the capping agent. The flowerlike morphology was attributed to modification of the nucleation and growth kinetics by the capping agent.

Oxygen transport through high-purity, large-grain Ag

The permeability of oxygen through pure, large-grain Ag membrames has been found to be linear and repeatable over the 400-800 C range, but only at a magnitude that is a factor of 3.2 smaller than ascribed by prior research. AES data indicate the pertinence of grain-boundary considerations, due to the virtual undetectability of intragranular oxygen. Vacuum-desorption of oxygen-saturated Ag is found to occur at the critical temperature of 630 C; this is consistent with the increased mobility of oxygen atoms in the higher temperature regime.

The 2005 MARTE Robotic Drilling Experiment in Río Tinto, Spain: Objectives, Approach, and Results of a Simulated Mission to Search for Life in the Martian Subsurface

The Mars Astrobiology Research and Technology Experiment (MARTE) simulated a robotic drilling mission to search for subsurface life on Mars. The drill site was on Peña de Hierro near the headwaters of the Río Tinto river (southwest Spain), on a deposit that includes massive sulfides and their gossanized remains that resemble some iron and sulfur minerals found on Mars. The mission used a fluidless, 10-axis, autonomous coring drill mounted on a simulated lander. Cores were faced; then instruments collected color wide-angle context images, color microscopic images, visible-near infrared point spectra, and (lower resolution) visible-near infrared hyperspectral images. Cores were then stored for further processing or ejected. A borehole inspection system collected panoramic imaging and Raman spectra of borehole walls. Life detection was performed on full cores with an adenosine triphosphate luciferin-luciferase bioluminescence assay and on crushed core sections with SOLID2, an antibody array-based instrument. Two remotely located science teams analyzed the remote sensing data and chose subsample locations. In 30 days of operation, the drill penetrated to 6 m and collected 21 cores. Biosignatures were detected in 12 of 15 samples analyzed by SOLID2. Science teams correctly interpreted the nature of the deposits drilled as compared to the ground truth. This experiment shows that drilling to search for subsurface life on Mars is technically feasible and scientifically rewarding.

SOLID2: an antibody array-based life-detector instrument in a Mars Drilling Simulation Experiment (MARTE).

A field prototype of an antibody array-based life-detector instrument, Signs Of LIfe Detector (SOLID2), has been tested in a Mars drilling mission simulation called MARTE (Mars Astrobiology Research and Technology Experiment). As one of the analytical instruments on the MARTE robotic drilling rig, SOLID2 performed automatic sample processing and analysis of ground core samples (0.5 g) with protein microarrays that contained 157 different antibodies. Core samples from different depths (down to 5.5 m) were analyzed, and positive reactions were obtained in antibodies raised against the Gram-negative bacterium Leptospirillum ferrooxidans, a species of the genus Acidithiobacillus (both common microorganisms in the Río Tinto area), and extracts from biofilms and other natural samples from the Río Tinto area. These positive reactions were absent when the samples were previously subjected to a high-temperature treatment, which indicates the biological origin and structural dependency of the antibody-antigen reactions. We conclude that an antibody array-based life-detector instrument like SOLID2 can detect complex biological material, and it should be considered as a potential analytical instrument for future planetary missions that search for life.

Detection, identification and mapping of iron anomalies in brain tissue using X-ray absorption spectroscopy.

This work describes a novel method for the detection, identification and mapping of anomalous iron compounds in mammalian brain tissue using X-ray absorption spectroscopy. We have located and identified individual iron anomalies in an avian tissue model associated with ferritin, biogenic magnetite and haemoglobin with a pixel resolution of less than 5 μm. This technique represents a breakthrough in the study of both intra- and extra-cellular iron compounds in brain tissue. The potential for high-resolution iron mapping using microfocused X-ray beams has direct application to investigations of the location and structural form of iron compounds associated with human neurodegenerative disorders—a problem which has vexed researchers for 50 years.

Improved brightness, efficiency, and stability of sputter deposited alternating current thin film electroluminescent ZnS:Mn by codoping with potassium chloride

Electroluminescent ZnS:Mn thin films have been codoped with KCl via an ex situ deposition and diffusion process. The brightness, efficiency, and stability of sputter deposited ZnS:Mn alternating current thin film electroluminescent devices have been greatly improved over untreated devices. Potassium chloride doping is shown to have a modest fluxing effect on the grain size of ZnS:Mn films, particularly in the region of the film where nucleation occurs. However, improved electroluminescence is postulated to be strongly influenced by doping control of electric fields and injected charge.