Observation Of Human Chromosomes With Soft X-Ray Contact Microscopy

Soft X-ray contact microscopy was applied to human chromosomes. Chromosomes of human lymphocytes were spread on a clean surface of distilled water, attached on a X-ray resist, polymethylmethacrylate (PMMA), and dried with no fixatives. The specimens were exposed without staining to the 2.98 nm monochromatic undulator radiation at the Photon Factory, National Laboratory for High Energy Physics, Japan. The developed images on PMMA were observed either with differential interference optical microscope or with transmission electron microscope by the use of replica method with a plasma polymerization-film in a glow discharge. The results showed that soft X-ray contact microscopy visualized chromosomes with the contrast produced by their components themselves at high resolution. The images were composed of highly entangled parts and stretched portions. From the stretched portions, particle like structures were recognized in a chromosomal fiber. The minimum size observed was 10-20 nm of fibers with 20-40 nm particles. Three dimensional observation will reveal the structure of highly entangled parts. The present results suggest the big potential of X-ray microscopy in biology.