High resolution imaging analysis of elements and molecules in a cell with an X-ray contact microscope.

基于X射线吸收特性，发展了X射线接触光谱显微镜，用于研究生物样品中的分子和元素分布。该系统由生物分子的XANES测量光谱学部分和干燥样品的接触显微镜成像部分组成。电子变焦管是成像部分的主要组成部分，在处理样品和操作电磁线圈方面得到了改进。该系统的性能是在日本筑波KEK的光子工厂使用同步辐射进行评估的。使用具有定义的线间距至少0.5um的测试图案已被解决。光子探测效率估计约为1%，主要是由于金光电阴极的光电子产额。用该系统研究了碳、氮、氧、钙、铁在人HeLa细胞中的元素分布，并用最小二乘法编制了计算机程序。在光谱学部分，研究了核酸、蛋白质和糖等生物分子在组成元素吸收边的XANES谱，以探索可用于细胞中分子成像的分子特定共振峰。磷钾吸收边和氮钾吸收边的共振峰被发现对细胞中的DNA相关分子进行成像是有用的。有丝分裂HeLa细胞核区的致密结构通过共振峰峰值波长与峰值波长下图像之间的减法检测到，这表明这是染色体等DNA相关分子的图像。

X-ray contact spectromicroscopy has been developed for the study of molecular and elemental distribution in biological specimens based on X-ray absorption characteristics. The system consists of a spectroscopy section for XANES measurements of biomolecules and an imaging section of a contact microscopy of dried specimens. An electronic zooming tube, a major component of the imaging section, has been improved in handling of specimens and in the operation of electromagnetic coils. The performance of the system was evaluated using synchrotron radiation at the Photon Factory, KEK,Tsukuba, Japan. Using a test pattern with defined line spacings at least 0.5um was resolved. The efficiency of photon detection was estimated as about 1% mainly due to the photoelectron yield of gold photocathode. With this system we have studied the elemental distribution of carbon, nitrogen, oxygen, calcium and iron in a human HeLa cell with the development of computer program using the least square method. At the spectroscopy section XANES profiles of biomolecules such as nucleic acids, proteins, and sugar were surveyed over the absorption edges of constituent elements to explore molecular specific resonance peaks which are available to molecular imaging in a cell. Resonance peaks at the phosphorus K-absorption edge and at the nitrogen K-absorption edge were found to be useful for imaging DNA related molecules in a cell. The dense structure in a nuclear area of mitotic HeLa cell has been detected by the subtraction between images on the peak wavelength of the resonance peak and below the peak wavelength, suggesting the image of DNA related molecules such as chromosomes.