............................Physics on the Nanometer Scale
with a particular emphasis on the physics of biological systems
Group of Hans-Werner Fink
| last update: September 2008 |
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Properties and Applications of Electron and Ion Point Sources |
We employ Field Ion Microscopy and related techniques for fabricating and using electron and ion point sources. Coherent low energy electron beams are used to acquire and numerically reconstruct electron holograms of individual biological molecules. More recently, we combined dedicated electron optical devices with our coherent electron beams to obtain over sampled coherent diffraction patterns from a single molecule. We expect that both methods eventually lead to new tools for structural biology on a single molecule level, free from disturbing radiation damage effects inherent to other radiation with sufficient small wave lengths and thus potential for atomic resolution. For presenting a fragile single molecule to the coherent electron beam we structure free standing thin films with a focused gallium ion beam. Interfacing single molecules from the liquid phase to such nanometer-sized structures is another pre requisite before imaging by low energy electrons becomes possible. Fluorescent video microscopy allows us to observe and manipulate single DNA molecules already in the liquid phase and to explore the energetics of this important bio-polymer. Molecular biology expertise and tools for anchoring DNA and/or modifying the molecules according to our specific needs for imaging are provided to us by Clondiag Chip Technologies.
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Some of the major tools and methods we use are |
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Field Ion and Field Electron Microscopy to produce and characterize electron and ion sources. Low Energy Electron Point Source (LEEPS) Microscopy for electron holography. Focused Liquid Metal Ion Beams for structuring thin films and creating micron-sized electron optical devices for Coherent Diffraction Imaging (CDI). Scanning Electron Microscopy (SEM) for sample characterisation. Fluorescent Video Microscopy for single DNA experiments in the liquid phase. read more
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Nondestructive imaging of individual biomolecules by Matthias Germann, Tatiana Latychevskaia, Conrad Escher & Hans-Werner Fink, read more Radiation damage is considered to be the major problem that still prevents imaging an individual biological molecule for structural analysis. So far, all known mapping techniques using sufficient short wavelength radiation, be it x rays or high energy electrons, circumvent this problem by averaging over many molecules. Averaging, however, leaves conformational details uncovered. Here, we present direct experimental evidence for nondestructive imaging of individual DNA molecules. In fact, we show that DNA withstands coherent low energy electron radiation with deBroglie wavelength in the Ångstrom regime despite a vast dose of 100 million electrons/square-nanometer accumulated over more than one hour. See movie below for a description of the nondestructive DNA imaging experiment:
Electrons reveal DNA without destroying it, Physics World Magazine by James Dacey
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