Biological Imaging

The majority of biological x-ray microscopy studies are done in the water window, which is for photon energies between the K shell absorption edges of Oxygen (543 eV, 2.3 nm) and Carbon (284 eV, 4.4 nm). For x-ray energies just below the Oxygen edge (e.g., 517 eV, 2.4 nm), the absorption of mostly carbon-containing organic material is about an order of magnitude less than the absorption of water, permitting a natural contrast. The penetration depth of these soft x-rays is also ideally suited to image intact cells with a thickness of a few microns. The photoelectric absorption, which provides contrast in soft x-ray microscopy, is also responsible for significant radiation damage to biological samples However, it is possible to prepare samples in different stages of development and then make conclusions based on statistical methods; a common method used with electron microscopy.

Cells which are sensitive to radiation damage can be chemically fixed to maintain cell structure during x-ray imaging. In addition, a labeling technique for localizing specific proteins within cellular structure can be used. Natural antibodies are utilized to attach dense silver and gold particles to the protein of interest. A computerized process is used after the imaging to locate the sharp increases in intensity to identify the regions of labeling.

For other types of experiments, we have a sample holder for imaging cryogenically frozen cells, which mitigates the effects of radiation damage. Because of this, chemical fixation is not needed, which results in images with remarkable detail.

Tubulin Network in Epithelial Cell

W. Meyer-Ilse, A. Nair/ CXRO
C. Larabell, S. Lelièvre, D. Hamamoto, M. Bissell / Life Sciences Division



X-ray images of malaria infected blood cells obtained at 2.4nm wavelength.
Left: uninfected cell, Center: newly infected cell, Right: cell 36h after infection.

C. Magowan, W. Meyer-Ilse and J.Brown, LBNL


Recording a series of images of a specimen mounted in a rotational stage with the rotation axis perpendicular to the photon beam direction opens the avenue for X-ray tomography at high lateral resolution to study 3-dim structures in cells. A new X-ray microscope is currently being set-up by the National Center for X-ray tomography at the ALS.


Problems? Contact the webmaster.

DHTML Menu / JavaScript Menu - Created Using NavStudio (OpenCube Inc.)