Proton-Induced and Electron-Induced X-Ray Microanalysis of Insulin-Secreting Cells

Elemental redistribution induced by insulin secretion, was investigated by electron and proton probe X-ray microanalysis. In particular, ion fluxes following immediately upon stimulation were studied. As the sensitivity of the electron probe was insufficient, the proton microprobe was employed. In order to see whether the cell is asymmetric with respect to Ca2+ influx, the cells were stimulated in the presence of Sr2+ (as a Ca2+ analog). Insulin-secreting cells (RINm5F cells and isolated mouse β-cells) were cultured on grids and shock-frozen at 2-30 seconds after stimulation. In a large number of cells, the major elements and and large fluxes were analyzed by the electron microprobe. In the proton microprobe, selected cells were analyzed and elemental maps were compared with electron micrographs of the same cells. The proton microprobe, but not the electron microprobe, could detect an influx of Sr in response to K+-stimulation for 2 seconds, in RINm5F-cells. No polarization of Sr2+ uptake in RINm5F-cells could be detected, and the β-cells did not respond to high K+ by uptake of Sr. Momentary stimulation of β-cells also resulted in a significant increase in Na, detected by the electron probe. Spreading of the β-cells on the substrate appears to influence the subcellular elemental distribution. Thus, the proton probe has potential to detect small changes in elements such as those occurring after short-time stimulation

Simultaneous microbeam IBA and beam-induced luminescence analysis of strained doped silica fibre radiation dosimeters

We demonstrate that the simultaneous combination of ion beam analysis (IBA) and ion beam induced luminescence (IL) can reveal valuable information concerning the performance of strained doped silica fibre thermoluminescence microdosimeters. The micron scale spatial resolution and low detection limits of IBA allow the lateral distribution of dopant elements to be mapped and then correlated with the distribution of prompt radioluminescence. Measurement of the decay of the IL signal with dose provide information concerning the saturation of the subsequent TL signal at high doses. MeV ion beams can deposit relatively high energy in localized, well-quantified small volumes and so this method is valuable for studying high dose effects in TL dosimeters. We describe a simple modification of the target chamber microscope which enables sensitive low background light detection in two wavelength bands and present preliminary results from three types of germanium doped silica fibre dosimeter

An endogenous nanomineral chaperones luminal antigen and peptidoglycan to intestinal immune cells.

In humans and other mammals it is known that calcium and phosphate ions are secreted from the distal small intestine into the lumen. However, why this secretion occurs is unclear. Here, we show that the process leads to the formation of amorphous magnesium-substituted calcium phosphate nanoparticles that trap soluble macromolecules, such as bacterial peptidoglycan and orally fed protein antigens, in the lumen and transport them to immune cells of the intestinal tissue. The macromolecule-containing nanoparticles utilize epithelial M cells to enter Peyer's patches, small areas of the intestine concentrated with particle-scavenging immune cells. In wild-type mice, intestinal immune cells containing these naturally formed nanoparticles expressed the immune tolerance-associated molecule 'programmed death-ligand 1', whereas in NOD1/2 double knockout mice, which cannot recognize peptidoglycan, programmed death-ligand 1 was undetected. Our results explain a role for constitutively formed calcium phosphate nanoparticles in the gut lumen and show how this helps to shape intestinal immune homeostasis

The production and properties of holographic diffraction gratings

The techniques for producing high quality holographic diffraction gratings are investigated. These gratings are formed by recording the fringes of an optical interference pattern in such a way as to give grooves in a highly reflecting surface, and have been found to be superior to ruled gratings in terms of resolving power, although the sinusoidal groove profile means that the efficiency cannot be controlled easily. In order to produce gratings of high quality, care must be taken in the design of the apparatus used to form the fringes. It is shown that the two interfering wavefronts must be identical in curvature and accurately plane (r ≫ 20m) in order to form an accurate plane grating. The effects of the light source and environmental changes on the quality of the pattern are investigated, and the apparatus is designed to minimise these effects. Stability tests of the fringe system show that it is satisfactory. The fringes are recorded in positive photoresist (Shipley AZ1350), which becomes soluble on exposure to light. The techniques for preparing the blanks by spin coating and developing the exposed gratings are discussed. The exposure characteristics of the photoresist are measured and the groove profile for various combinations of exposure and development time is calculated. It is found that the minimum distortion from a sinusoidal groove profile results when the gratings are given a small, constant exposure to the fringes and the groove depth is changed by varying the development time. The resist surface is metallised to give a high quality reflection grating. The efficiency of the gratings as a function of angle of incidence, wavelength and groove depth is investigated in various configurations. It is found that for coarse gratings (λ/d ≲0.25) with highly reflecting surfaces, simple scalar theory is sufficient to explain the observed behaviour. For gratings with larger values of λ/d, there are fewer propagating orders and a corresponding increase in the intensity of the high orders. This introduces Wood's anomalies, which are rapid variations of efficiency occurring when one of the orders passes off the grating. These are polarisation dependant and cannot be explained on simple theories. The basic properties of rigorous theories which assume a perfect metal are considered. These are found to be inaccurate in the region of the S polarised (E perpendicular to the grooves) anomaly. The recent theories which take account of the optical properties of the metal are shown to predict accurately the observed variation of efficiency even in the region of the anomalies. The dependence of the grating properties on the metal coating has been shown to be due to an interaction between the radiation field and the electrons of the metal coating. This surface plasmon resonance is investigated in detail. The phenomena caused by the resonance are found to be: i) A net absorption of energy by the grating; ii) Redistribution of energy between the orders of the grating; iii) An increase in the scattered light from the grating; iv) A well defined angular distribution of scattered light. The phenomena only occur with S-polarised incident light. The conditions under which the resonance occurs are investigated and the effects are observed. The dependence of the resonance on groove depth is also investigated. It is shown how observations of the surface plasmon resonance may provide information concerning the properties of electron waves on periodic surfaces. Finally, some applications of the holographic gratings made during this work are discussed. These are: i) Radiation resistant gratings for use in synchrotron radiation; ii) Gratings for tunable lasers; iii) A multichannel spectrometer using a composite grating; iv) Holographic zone plates as imaging elements.</p

Simultaneous microbeam IBA and beam-induced luminescence analysis of strained doped silica fibre radiation dosimeters

We demonstrate that the simultaneous combination of ion beam analysis (IBA) and ion beam induced luminescence (IL) can reveal valuable information concerning the performance of strained doped silica fibre thermoluminescence microdosimeters. The micron scale spatial resolution and low detection limits of IBA allow the lateral distribution of dopant elements to be mapped and then correlated with the distribution of prompt radioluminescence. Measurement of the decay of the IL signal with dose provide information concerning the saturation of the subsequent TL signal at high doses. MeV ion beams can deposit relatively high energy in localized, well-quantified small volumes and so this method is valuable for studying high dose effects in TL dosimeters. We describe a simple modification of the target chamber microscope which enables sensitive low background light detection in two wavelength bands and present preliminary results from three types of germanium doped silica fibre dosimeter

Simultaneous microbeam IBA and beam-induced luminescence analysis of strained doped silica fibre radiation dosimeters

We demonstrate that the simultaneous combination of ion beam analysis (IBA) and ion beam induced luminescence (IL) can reveal valuable information concerning the performance of strained doped silica fibre thermoluminescence microdosimeters. The micron scale spatial resolution and low detection limits of IBA allow the lateral distribution of dopant elements to be mapped and then correlated with the distribution of prompt radioluminescence. Measurement of the decay of the IL signal with dose provide information concerning the saturation of the subsequent TL signal at high doses. MeV ion beams can deposit relatively high energy in localized, well-quantified small volumes and so this method is valuable for studying high dose effects in TL dosimeters. We describe a simple modification of the target chamber microscope which enables sensitive low background light detection in two wavelength bands and present preliminary results from three types of germanium doped silica fibre dosimeter

Preliminary Applications of the Surrey External Beam Facility

ABSTRACT The new external microbeam at the University of Surrey is capable of mapping areas of 3mm x3 mm. In this study it has been used to map the metal composition of 2 inks in a German 1920&apos;s bank note. The major constituents of the red ink are mercury and barium, while those in the green ink, which was applied first, are lead and chromium. The analysis took 10 minutes and there was no detectable mark left on the paper as a result of the analysis. RBS and PIXE analysis of lines drawn on cartridge paper using a lead metalpoint enabled the fine structure and the depth distribution of lead in the paper to be determined

MgF(3)(-) as a transition state analog of phosphoryl transfer

AbstractThe formation of complexes between small G proteins and certain of their effectors can be facilitated by aluminum fluorides. Solution studies suggest that magnesium may be able to replace aluminum in such complexes. We have determined the crystal structure of RhoA.GDP bound to RhoGAP in the presence of Mg2+ and F− but without Al3+. The metallofluoride adopts a trigonal planar arrangement instead of the square planar structure of AlF4−. We have confirmed that these crystals contain magnesium and not aluminum by proton-induced X-ray emission spectroscopy. The structure adopted by GDP.MgF− possesses the stereochemistry and approximate charge expected for the transition state. We suggest that MgF3− may be the reagent of choice for studying phosphoryl transfer reactions