Soft X-ray Nanotomography of Cryo Specimens

为了了解生物样本内结构之间的空间关系，需要三维成像。软X射线断层扫描提供了在30-100纳米体素分辨率下对几微米厚的标本进行成像的可能性，独特的对比机制，以及检查水合标本的能力。 将通过将层析成像能力添加到具有液氮温度阶段的软X射线扫描透射显微镜来开发具有软X射线光学的纳米层析成像。菲涅耳波带片将用于将软X射线波荡器光束聚焦到30-50纳米分辨率探头（任何波长的电磁辐射的最小聚焦点），并且将通过该探头以一定范围的倾斜角扫描样本。景深是这样的，每个图像将代表通过标本的投影，至少在最初的研究选择的问题。在对冻干标本进行初步研究后，将在液氮温度下对已玻璃化的水合标本进行成像。 这些新的纳米断层扫描功能将在我们的x射线显微镜用户设施与我们的生物学合作者正在进行的和新的跨学科研究中使用。这些合作包括中期染色体中染色质折叠的研究，疟疾寄生虫恶性疟原虫的成像，蛋白质和DNA浓度的定量映射以了解精子中的染色体包装，软骨和骨中的钙化（与关节炎和骨质疏松症的影响），以及细胞核中RNA转录位点的定位。

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.