Researchers achieved this high 3-D resolution by illuminating the minute structures of the frozen-hydrated 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 coherent light generates significantly higher contrast for small object details compared to incoherent illumination. Combining this approach with a high-resolution lens, the researchers were able to visualize the ultrastructures of cells at hitherto unattained contrast.
The new X-ray microscope also allows for more space around the sample, which leads to a better spatial view. This space has always been greatly limited by the setup for the sample illumination. The required monochromatic X-ray light was created using a radial grid and then, from this light, a diaphragm would select the desired range of wavelengths. The diaphragm had to be placed so close to the sample that there was almost no space to turn the sample around. The researchers modified this setup: Monochromatic light is collected by a new type of condenser which directly illuminates the object, and the diaphragm is no longer needed. This allows the sample to be turned by up to 158 degrees and observed in three dimensions. These developments provide a new tool in structural biology for the better understanding of the cell structure.
|Contact: Dr. Gerd Schneider|
Helmholtz Association of German Research Centres