Soft X-ray Nanotomography of Cryo Specimens

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To understand the spatial relationships among structures within biological specimens, three-dimensional imaging is required. Soft x-ray tomography offers the possibility to image several micrometer thick specimens at 30-100 nanometer voxel resolution, unique contrast mechanisms, and the ability to examine hydrated specimens. Nanotomography with soft x-ray optics will be developed by adding tomography capabilities to a soft x-ray scanning transmission microscope with a liquid nitrogen temperature stage. Fresnel zone plates will be used to focus a soft x-ray undulator beam to a 30-50 nanometer resolution probe (the smallest focused spot of electromagnetic radiation of any wavelength), and the specimen will be scanned through this probe at a range of tilt angles. The depth of field is such that each image will represent a projection through the specimen, at least in problems selected for initial studies. After initial studies of freeze-dried specimens, hydrated specimens which have been vitrified will be imaged at liquid nitrogen temperatures. These novel nanotomography capabilities will be employed in ongoing and new interdisciplinary studies with our biology collaborators at our x-ray microscope user facility. These collaborations have included the study of chromatin folding in metaphase chromosomes, imaging of the malarial parasite P. falciparum, quantitative mapping of protein and DNA concentrations to understand chromosome packing in sperm, calcification in cartilage and bone (with implications for arthritis and osteoporosis), and the localization of RNA transcription sites in the nucleus.