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nanotimes News in Brief

11-01 :: December 2010 / January 2011

Microscopes // German HZB Researchers Can Take Images of Small Cellular Components in Their Natural Environment

D

r. Gerd Schneider and his microscopy team at the Institute for Soft Matter and Functional

Materials at German Helmholtz-Zentrum Berlin (HZB) have developed a new X-ray nanotomography microscope. Using their new system, they can reveal the structures on the smallest components of mam- malian cells in three dimensions. For the first time, there is no need to chemically fix, stain or cut cells in order to study them. Instead, whole living cells are fast-frozen and studied in their natural environment. The new method delivers an immediate 3-D image, thereby closing a gap between conventional micro- scopic techniques.

The new microscope delivers a high-resolution 3-D image of the entire cell in one step. This is an advan- tage over electron microscopy, in which a 3-D image is assembled out of many thin sections. This can take up to weeks for just one cell. Also, the cell need not to be labelled with dyes, unlike in fluorescence mi- croscopy, where only the labelled structures become visible. The new X-ray microscope instead exploits the natural contrast between organic material and water to form an image of all cell structures.

With the high resolution achieved by their micro- scope, the researchers, in cooperation with col- leagues of the National Cancer Institute in the USA, have reconstructed mouse adenocarcinoma cells in

three dimensions. The smallest of details were visi- ble: the double membrane of the cell nucleus, nucle- ar pores in the nuclear envelope, membrane chan- nels in the nucleus, numerous invaginations of the inner mitochondrial membrane and inclusions in cell organelles such as lysosomes. Such insights will be crucial for shedding light on inner-cellular processes: such as how viruses or nanoparticles penetrate into cells or into the nucleus, for example.

This is the first time the so-called ultrastructure of cells has been imaged with x-rays to such precisi- on, down to 30nm. Ten nanometres are about one ten-thousandth of the width of a human hair. Ul- trastructure is the detailed structure of a biological specimen that is too small to be seen with an optical microscope.

Researchers achieved this high 3-D resolution by illuminating the minute structures of the frozen-hy- drated object with partially coherent light. This light is generated by BESSY II, the synchrotron source at HZB. Partial coherence is the property of two waves whose relative phase undergoes random fluctuations which are not, however, sufficient to make the wave completely incoherent. Illumination with partial co- herent light generates significantly higher contrast for small object details compared to incoherent illumina- tion. Combining this approach with a high-resolution