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Frozen, glasslike samples for electron microscopy

Published on
October 1, 2012

The freezing of wet samples (cryofixation) for use in electron microscopy is such specialised work that Professor Martien Cohen Stuart’s Laboratory of Physical Chemistry and Colloid Science used to have its samples prepared in Bayreuth, Germany – 600 kilometres away. “It was the nearest group that could provide the required quality”, says Cohen Stuart. Fortunately, that has changed since CAT-AgroFood recently installed a Vitrobot at the Wageningen Electron Microscopy Centre (WEMC).

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The Vitrobot freezes wet samples very rapidly. It rids samples off excess water and then immerses them in liquid ethane for instant freezing. This process, known as cryofixation or vitrification, prevents the formation of ice crystals and results in samples that are clear as glass. Transmission Electron Microscopy and Scanning Electron Microscopy make it possible to perfectly analyse the structure of these samples. It is humanly impossible to produce – and reproduce – such extremely thin “glassy” films of a wide variety of wet samples at constant and user-definable physical and mechanical conditions.

Nanostructures that have to stay wet

Cohen Stuart: “Cryofixation enables us to study special molecules or nanoparticles that have to stay in water. If you were to dry these objects they would crumble or clot and lose their structure and functionalities.” His group studies and designs molecules that function well in a wet environment, like the human body. For diagnostic or therapeutic purposes it is very useful to design something that could be injected in a patient and be monitored, for example via the MRI-scanner. The Colloid Science group also works on the design of novel soft and wet materials in which human cells are happy to grow; it is important to know what the structure of such materials is in the wet state, inside the human body.

The picture above is a sample that was prepared with the Vitrobot and analysed by Transmission Electron Microscope in Bayreuth, Germany. “These nano strings have a very unusual structure, much like railway tracks”, says Cohen Stuart. They are designed in Beijing University by Professor Yan, a former postdoc of Cohen Stuart. An application for this amazing material has not been found, yet.