X-ray microscopy & cell structure

The x-ray microscope installed at the 3rd generation storage ring BESSY II is dedicated for applications in life, environmental and materials sciences. It covers the photon energy range between 250- 600 eV. Currently, the spatial resolution is about 25 nm. To protect biological cells from radiation damage caused by X-rays, imaging of the samples has to be performed at cryogenic temperatures, which makes it possible to take multiple images of a single cell as required for tomography [1]. Due to the small numerical aperture of zone plates, X-ray objectives have a depth of focus on the order of several microns. By treating the X-ray microscopic images as projections of the sample absorption, computed tomography can be performed [2,4]. Since cryogenic biological samples are resistant to radiation damage, it is possible to reconstruct frozen-hydrated cells imaged with a full-field X-ray microscope. This approach is used to obtain 3-D information about the location of specific proteins in cells. To localize proteins in cells, immunolabelling with strongly X-ray absorbing nanoparticles was performed [3]. To detect protein distributions inside of cells, X-ray microscopy tomography of immunolabelled frozen-hydrated cells was performed. As a first example, the distribution of the nuclear protein, male specifi