Event
MSE Seminar - Dr. Richard Leapman, National Institute of Biomedical Imaging and Bioengineering, NIH
Friday, November 14, 2008
1:00 p.m.
Rm. 2108, Chemical and Nuclear Engineering Bldg.
Annette Mateus
301 405 5207
amateus@umd.edu
"Quantitative Nanoscale Imaging of Biological Structures in the Electron Microscope"
By combining imaging techniques with spectroscopy in the transmission electron microscope, it is now possible to obtain compositional information about biological structures on a nanometer scale. Electron energy loss spectroscopy (EELS) provides a sensitive and quantitative tool for determining elemental distributions, based on detection of characteristic atomic core shell excitations. Elemental mapping can be performed using two complementary techniques to measure the inelastic scattering: energy-filtering transmission electron microscopy (EFTEM), using broad-beam illumination of the specimen; and scanning transmission electron microscopy (STEM), using a nanometer-diameter focused probe, which yields detection limits as low as a few atoms. By recording EFTEM images in electron tomographic tilt series, we have shown that it is possible to reconstruct quantitative 3D distributions of chemical elements within sectioned cells, although sensitivity is ultimately limited by radiation damage. In addition, electron tomography can be combined with STEM imaging, based on detection of the elastic scattering signal, to obtain quantitative 3D distributions of heavy atom clusters that have been developed to label specific proteins within cells. These compositional imaging techniques can also be applied to characterize non-biological systems, including soft materials.
