Observation of human chromosome fibers in a water layer by laser-plasma x-ray contact microscopy

Abstract

Soft x-ray contact microscopy was applied to hydrated human chromosomes. Chromosomes of human lymphocytes were spread on a clean surface of distilled water, attached on an x-ray resist, polymethylmethacrylate (PMMA), immediately covered with a silicon nitride window, and mounted in a simple hydrated chamber. The specimens were exposed to a single shot of laser-produced gold plasma x rays (600 ps) in a vacuum chamber. The developed images were observed with transmission electron microscope using the replica method with a plasma polymerization-film in a glow discharge. The results show that we have imaged the complicated entanglement of chromosome fibers in a hydrated condition. The thickness was estimated as 10 nm in an average of four narrow parts of these fibers. Particle like structures were observed in many places. The present results prove that a hydrated biological specimen is observable with the contrast produced by its components themselves using soft x-ray microscopy at the resolution of 10 nm. During this imaging exposure, however, the silicon nitride (SiN) window was broken. We have studied the reason for this evidence and found that the energy absorbed by the SiN window or water layer was very high. The estimated temperature increase was 870 -1470°C for SiN and 43°C for the water layer. These results suggest that the temperature increase may be responsible for the breakage of SiN window. Show more