Year: 2009
Type: article
Abstract: We report our studies on X-ray diffraction microscopy (XDM) for biological samples.XDM requires no lenses, and a sample image is directly reconstructed from the coherent diffraction data.It is ideal X-ray phase-contrast imaging with no contrast degradation due to lenses.XDM is especially useful for observing internal structures of thick objects, such as cells or cell organelles, thanks to high penetrating power of X-rays.The first biological application of XDM was for Escherichia coli bacteria cells [1].The internal distribution of the proteins stained with manganese oxide was two-dimensionally imaged.In the image reconstruction, the Fourier transform of a lower-resolution sample image observed under a full-field soft X-ray transmission microscope was used to make up for missing coherent X-ray diffraction data near-forward direction.The missing data problem was later solved by improvements of microscope instruments to reduce parasitic scattering noise [2,3] and also by improvements of the phase retrieval algorithm, e.g. the iterative normalization algorithm [4].These improvements have made it possible to reconstruct a sample image only from the coherent diffraction data.Challenges remaining in biological application of XDM have been imaging of unstained samples and three-dimensional imaging.The both have been recently realized by observing an unstained human chromosome in three dimensions [5].This is the first successful threedimensional electron density mapping of a cell organelle by using hard X-rays.It is important because XDM is directly connected with X-ray crystallography, which is currently the most powerful method of the atomic structure analysis for proteins.The observed images reveal an axial structure with high electron-density in the chromosome, which other microscopic methods have been unable to visualize under unstained condition.Such mesoscopic-scale structures as cell organelle have been difficult to be observed, although molecular structures of their components like DNA and histone proteins could be studied by X-ray crystallography or electron microscopy.Our result experimentally demonstrates the high imaging ability of coherent X-ray diffraction for unstained biological specimens, which are almost transparent to X-rays, opening a novel and strong means of exploring cellular structures.
Language: English
Subfield: Radiation
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: bronze
OpenAlex ID: W2318658242