An important component of progress in designing and making molecular machines and other nanostructures is a quick way to see the structures that have been produced. With quick feedback, rapid cycles of design-fabricate-test-redesign can be implemented. X-ray crystallography is the gold standard method of obtaining atomically precise structures from materials that can be prepared as micrometer scale crystals and larger. Now an international research collaboration centered in Germany has developed a method of automated electron diffraction tomography to give atomically precise information about nanostructures. Thanks to ScienceDaily for pointing to this news release from Johannes Gutenberg University Mainz. From “Researchers at Johannes Gutenberg University Mainz make visible the structure of the smallest crystals“:
A radical new way of making structures visible at the nano level has been developed at Johannes Gutenberg University Mainz (JGU). This new method makes it possible to determine with precision the arrangement of atoms and molecules in a diverse range of materials from cement to pharmaceuticals. The procedure, which is still in its infancy, comes from the field of electron microscopy and can resolve the structure of the tiniest crystals. The method was developed by Dr. Ute Kolb’s working group at the Institute of Physical Chemistry at Mainz University and is now receiving international attention. In cooperation with researchers from Spain and China, the method has now allowed the structure of a new type of fine-pore zeolite to be established, a study that the journal Science published in the end of August 2011 [abstract]. “We have opened a door to the world of nanostructures,” is how Dr. Ute Kolb describes her working group’s success.
The arrangement of atoms and molecules in a solid has a decisive influence on the physical properties of that material. Such structures were analyzed for the first time back in 1895 using X-rays, a method that has since become a standard procedure. The beginnings of the research in this area included the discovery in 1912 that crystals are made up of small grids, a characteristic that is responsible for the diversity of thermal, electrical, visual, and mechanical properties found in such substances. “The fact that this method had and still has a huge influence on our understanding of solids and their properties is reflected in the number of Nobel prizes awarded on the basis of structural analyses,” says Kolb, describing the success story that is X-ray structural analysis.
In the age of nanotechnology, however, science is focusing increasingly on very small particles, which can no longer be captured by way of X-ray structural analysis. For example, an X-ray structural analysis of a single crystal is only possible up to a crystal size of around 1 micrometer, i.e. one thousandth of a millimeter. Below this threshold, in the sphere of nanostructures, electron diffraction tomography or automated diffraction tomography (ADT) allows scientists to make a similar determination of the structure of individual crystallites for the first time. “It is as if we have switched on a light in the world of nanostructures,” says Kolb. As is the case with electron microscopy, the method is generally based on the concept of an electron beam being directed at an object and diffracted as a result. The diffraction behavior allows the location of the atoms to be established.
… In comparison with conventional electron microscopy characterizations, electron diffraction tomography is considerably faster, more accurate, and more complete. Whereas before, structures were researched for two years, using ADT a result can be obtained within just one day. Even beam-sensitive materials are, in principle, suitable for the method, which Kolb describes as “computer tomography for crystals”. ADT also shares a characteristic with computer tomography that has played a major role in its success: the experimental sample under the electron microscope is gradually tipped over in order to gather data from a wide variety of different positions. Using this trick, scientists can avoid the key problem found in this area: the strong interaction of the electron beam with the sample has, up to now, made the electron diffraction much more difficult.
It would be interesting to see these methods applied to structures made using structural DNA nanotechnology or RNA nanotechnology, and compared with images constructed using atomic force microscopy.