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SUMMARY:Quantitative elemental mapping in biological systems - Maria Arono
 va\, National Institute of Biomedical Imaging and Bioengineering\, Nationa
 l Institute of Health\, United States of America
DTSTART:20080630T140000Z
DTEND:20080630T150000Z
UID:TALK11215@talks.cam.ac.uk
CONTACT:Dr Jonathan Barnard
DESCRIPTION:Distributions of chemical elements within unstained sectioned 
 cells can provide important information about various classes of macromole
 cules.  For example\, phosphorus in nucleic acid enables determination of 
 the packing density of DNA within the chromatin of a cell’s nucleus\; va
 riations of calcium levels in mitochondrial and endoplasmic reticulum comp
 artments can help understand the mechanisms of calcium regulation and expl
 ain normal physiological as well as pathophysiological processes within ce
 lls.  Mapping of calcium/phosphorus distributions at ~10 nm spatial resolu
 tion in biological specimens is typically achieved using energy-dispersive
  x-ray spectroscopy or electron energy loss spectroscopy (EELS) in a scann
 ing transmission electron microscope (STEM).  Here\, we discuss a compleme
 ntary approach based on energy-filtered transmission electron microscopy (
 EFTEM) to map chemical elements in thin unstained sectioned cells. With EF
 TEM\, it is possible to obtain 2D elemental distributions from large cellu
 lar regions and combine it with conventional electron tomography to genera
 te 3D elemental maps. Using this technique we determine the 2D calcium dis
 tribution inside mitochondria as well as the 3D phosphorus distribution wi
 thin cell nuclei.  Although the detection limits for a given pixel are not
  as favorable as for STEM/EELS\, it is possible to improve the sensitivity
  of this method by averaging large number of pixels.  
LOCATION:Austin Lecture Theatre\, Materials Science and Metallurgy\, Depar
 tment of
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