Investigating the structure of biomolecules on the atomic scale has always been of utmost importance for healthcare, medicine and life science in general, since the three-dimensional shape of proteins, for example, relates to their function. At present, these structural data are predominantly obtained by X-ray crystallography, cryo-electron microscopy and NMR. Although an impressive database (www.pdb.org) has been obtained with these methods, they all require large quantities of a particular protein. This leads to averaging over fine conformational details in the recovered structure.
The goal of modern imaging techniques is to visualize an individual biomolecule at atomic resolution. A direct visualization of an individual molecule at Ångstrom resolution can be achieved by using electron or X-ray waves which have a wavelength of about 1 Å. However, the resolution achieved is largely limited by damage caused by both types of radiation. It has been shown  that individual DNA molecules can withstand low-energy electron radiation with energy of 60 eV (corresponding to a wavelength of 1.58 Å) for at least 70 minutes.
We  employ holography  and coherent diffractive imaging  with low-energy electrons (with kinetic energies of 50-250 eV, corresponding to wavelengths of 0.78-1.73 Å) for imaging single biological molecules . The experimental set-ups for both holographic and CDI recording with low-energy electrons designed and built in our laboratory [6-7] are sketched in the figure. Retrieval of the object structure is achieved by numerical reconstruction of the recorded holograms .In summary: we believe that radiation damage-free observation of a single molecule by coherent low-energy electron imaging, i.e. holography and CDI and their combination (HCDI) could constitute the first tool for structural biology on the single molecule level [9-10].
- M. Germann, T. Latychevskaia, C. Escher, and H.-W. Fink, “Nondestructive imaging of individual biomolecules”, Phys. Rev. Lett. 104, 095501 (2010).
- For further details see the web-site of group of Prof. Hans-Werner Fink at University of Zurich http://www.physik.uzh.ch/groups/fink/
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- T. Latychevskaia, J.-N. Longchamp, C. Escher, and H.-W. Fink, “Coherent diffraction and holographic imaging of individual biomolecules using low-energy electrons”, in Present and Future Methods for Biomolecular Crystallography (Springer, 2013), pp. 331–342.
- H.-W. Fink, W. Stocker, and H. Schmid, “Holography with low-energy electrons”, Phys. Rev. Lett. 65, 1204–1206 (1990).
- J.-N. Longchamp, T. Latychevskaia, C. Escher, and H.-W. Fink, “Graphene unit cell imaging by holographic coherent diffraction”, Phys. Rev. Lett. 110, 255501 (2013).
- T. Latychevskaia and H.-W. Fink, “Practical algorithms for simulation and reconstruction of digital in-line holograms”, Applied Optics 54(9), 2424-2434 (2015).
- T. Latychevskaia, J.-N. Longchamp and H.-W. Fink, “When holography meets coherent diffraction imaging”, Optics Express 20(27), 28871-28892 (2012).
- T. Latychevskaia, J.-N. Longchamp, C. Escher and H.-W. Fink, “Holography and coherent diffraction with low-energy electrons: A route towards structural biology at the single molecule level”, Ultramicroscopy 159, 395-402 (2015).