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

x射线接触光谱显微镜是一种基于x射线吸收特性来研究生物标本中分子和元素分布的方法。该系统由用于XANES测量生物分子的光谱切片和用于干燥标本的接触显微镜成像切片组成。电子变焦管是成像部分的主要组成部分，在处理标本和电磁线圈的操作方面得到了改进。该系统的性能在日本筑波KEK光子工厂使用同步辐射进行了评估。使用具有定义行间距至少0.5um的测试模式进行了解决。估计光子探测效率约为1%，这主要是由于金光电阴极的光电子产率。利用该系统研究了人体HeLa细胞中碳、氮、氧、钙、铁的元素分布，并利用最小二乘法编制了计算机程序。在光谱学部分，在组成元素的吸收边缘上对生物分子（如核酸、蛋白质和糖）的XANES谱进行了调查，以探索可用于细胞分子成像的分子特异性共振峰。磷k吸收边和氮k吸收边的共振峰被发现对细胞中DNA相关分子的成像有用。通过共振峰峰值波长上的图像与峰值波长下的图像相减，检测到有丝分裂HeLa细胞核区致密结构，提示是DNA相关分子如染色体的图像。

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.