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

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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.