Soft X -ray Holography and Microscopy of Biological cells

Abstract

Some experimental results on soft X-ray microscopy and holography imaging of biological specimens are presented in the paper.As we know, due to diffraction effects, there exists a resolution limit determined by wavelength O and numerical aperture NA in conventional optical microscopy. In order to improve resolution, the numerical aperture should be made as large as possible and the wavelength as short as possible. Owing to the shorter wavelength, X-rays provide the potential of higher resolution in X-ray microscopy, holography image and allow for examination the interior structures of thicker specimens.In the experiments, we used synchrotron radiation source in Hefei as light source. Soft X-rays com e from a bending magnet in 800 MeV electron storage ring with characteristic wavelength of 2.4 nm. The continuous X-ray spectrum s are monochrom atized by a zone-plate and a pinhole with 300 Pm diameter. The experimental set-up is typical contact microscopic system, its main advantage is simplicity and no special optical element is needed.The specimens used in the experiments of microscopic imaging are the colibacillus, the gingko vascular hundle and the fritillaries ovary karyon. The specimen for holographic imaging is the spider filaments. The basic structures of plant cells such as the cell walls, the cytoplasm and the karyon especially the joint structures between the cells are observed clearly. An experimental study on a thick biological specimen that is a whole sporule with the thickness of about 30 Pm is perform ed.In the holographic experiments, the experimental setup is typical Gabor in-line holography. The specimen is placed in line with X-ray source, which provides both the reference waves and specimen illumination. The specimen is some spider filament, which adhere to a Si3N4 film. The recording medium is PM M A, which is placed at recording distance of about 400 Pm from the specimen. The hologram s were reconstructed by digital method with 300 nm resolutions.A novel method for recording in-line hologram is proposed which is called X-ray in-line holography with zone-plate magnification in this paper. The magnification factor of the micro zone plate imaging is about 103. The transverse resolution can be 48 nm in this method.