Abstract
Ptychographic coherent X-ray diffractive imaging (PCDI) has been combined with nano-focus X-ray diffraction to study the structure and density distribution of unstained and unsliced bacterial cells, using a hard X-ray beam of 6.2keV photon energy, focused to about 90nm by a Fresnel zone plate lens. While PCDI provides images of the bacteria with quantitative contrast in real space with a resolution well below the beam size at the sample, spatially resolved small angle X-ray scattering using the same Fresnel zone plate (cellular nano-diffraction) provides structural information at highest resolution in reciprocal space up to 2nm(-1). We show how the real and reciprocal space approach can be used synergistically on the same sample and with the same setup. In addition, we present 3D hard X-ray imaging of unstained bacterial cells by a combination of ptychography and tomography.
Highlights
To understand the important biophysical problem of DNA compactification in bacterial cells, ideally the three-dimensional density distribution at the sub-cellular level needs to be imaged with quantitative contrast values
We have previously shown that the projected electron density of unstained and unsliced freezedried cells of the bacterium Deinococcus radiodurans can be derived from coherent X-ray diffraction imaging (CDI) based on ptychographic phase retrieval [1]
Cells of the Deinococcus radiodurans wild-type strain were cultivated from freeze-dried cultures (DSM No 20539 by the German Collection of Microorganisms and Cell Cultures) for one day at 30◦C on petri dishes covered with nutrient medium
Summary
To understand the important biophysical problem of DNA compactification in bacterial cells, ideally the three-dimensional density distribution at the sub-cellular level needs to be imaged with quantitative contrast values. Determination of the mesoscopic density in the nucleoid would help to test these ideas and eventually to discriminate different models of DNA packing Towards this goal, we have previously shown that the projected electron density of unstained and unsliced freezedried cells of the bacterium Deinococcus radiodurans can be derived from coherent X-ray diffraction imaging (CDI) based on ptychographic phase retrieval [1]. Received 10 May 2012; revised 8 Jun 2012; accepted 13 Jun 2012; published 8 Aug 2012 13 August 2012 / Vol 20, No 17 / OPTICS EXPRESS 19235 diffraction observables This concept of scanning SAXS has been introduced first on the micron scale, with seminal work in the field of biological materials by Fratzl and co-workers [22,23,24,25] (see [26,27]), and can with further progress in X-ray focusing be extended to the nano-scale. The paper closes with some conclusions and a brief outlook
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