Taking 'photographs' of individual molecules in action is probably not on the list of your next summer vacation. However, an international team of scientists from Australia, England and the U.S. has found a way to get full 3-D images of the interior of nanocrystals. Their technique, known as coherent X-ray diffraction imaging, "will help in the development of X-ray free-electron lasers, which will allow single-molecule imaging." But read more...
Here are some details from the Imperial College London (ICL) news release.
Professor Ian Robinson, of the UCL Department of Physics & Astronomy and the London Centre for Nanotechnology, who led the study, says: "This new imaging method shows that the interior structure of atomic displacements within single nanocrystals can be obtained by direct inversion of the diffraction pattern. We hope one day this will be applied to determine the structure of single protein molecules placed in the femtosecond beam of a free-electron laser.
"Coherent X-ray diffraction imaging emerged from the realisation that over-sampled diffraction patterns can be inverted to obtain real space images. It is an attractive alternative to electron microscopy because of the better penetration of the electromagnetic waves in materials of interest, which are often less damaging to the sample than electrons."
Now, let's look at some images. Below, you can see two perpendicular views of the three-dimensional reconstruction of the magnitude of the nanocrystal's complex density function (Credit: ICL, Nature).
The density function is shown as 50% density isosurfaces in a and c. The fitted facet planes of the equilibrium crystal shape have been coloured. b, Schematic model of a sphere (semi-transparent) and facet planes (disks) fitting the view of a. The diameter of the nanocrystal is 750 nm.
This second picture shows the "phase maps cutting through the crystal at three parallel planes" (Credit: ICL, Nature).
Schematic diagram of the sections, 138 nm apart. The translucent box is the support region used in the phasing calculations, which was rectangular before the coordinate transformation. The phase bulge is interpreted as a projection of strain fields in the crystal lattice arising from contact forces at the interface with the substrate.
This research work has been published by Nature under the title "Three-dimensional mapping of a deformation field inside a nanocrystal" (Volume 442 Number 7098, Pages 63-66, July 6, 2006). Here is a link to the editor's summary, Crystal mapping.
Synchrotron X-ray radiation, produced by electron accelerators at central facilities, can now be produced in extremely narrow coherent beams. When these X-rays illuminate a crystal of nanometre dimensions a diffraction pattern emerges that is highly resolved. This provides a powerful new tool for structural analysis, as the fine features of the diffraction pattern can be interpreted in terms of sub-atomic distortions within the crystal attributable to its contact with an external support.
And here are two more links to the abstract of this paper and to some figures and tables from which the above illustrations have been extracted.
Sources: University College London news release, via EurekAlert!, July 5, 2006; Nature, July 6, 2006
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