Microscopic imaging of biological samples using soft X-ray synchrotron radiation from within the ‚water window’

Thomas Gorniak, Universität Heidelberg, Heidelberg/D; Tobias Senkbeil, Universität Heidelberg, Heidelberg/D; Mike Beckers, Universität Heidelberg, Heidelberg/D; Andreas Buck, Universität Heidelberg, Heidelberg/D; Maria Alles, Universität Heidelberg, Heidelberg/D; Klaus Giewekemeyer, Universität Göttingen, Göttingen/D; Tim Salditt, Universität Göttingen, Göttingen/D; Axel Rosenhahn, Universität Heidelberg, Heidelberg/D

Coherent X-ray microscopy of hydrated biological samples – especially in the ‚water window’ of 284—540 eV – is of tremendous interest for life sciences due to the high contrast of organic matter with respect to the aqueous background  [1]. We present micrographs of vitrified marine biofouling organisms Navicula perminuta recorded ptychographically at a photon energy of 517 eV. Ptychography uses coherent diffraction images at different sample positions while maintaining a fixed spatial overlap between the fields of view  [2]. By introducing this spatial redundancy to the data an additional constraint for the iterative reconstruction algorithm is achieved. This enhances the convergence of phase retrieval drastically and allows for imaging of virtually infinitely extended samples. We supplement these results with resonant ptychographic imaging of dehydrated test particles where both, absorption and phase shifts, revealed information about the samples’ chemical composition in the vicinity of core level resonances near the oxygen K-edge  [3]. Both results show that resonant imaging of hydrated biological material is within reach.

Literature

[1] G. Schneider, Ultramicroscopy 75, 85-104 (1998).

[2] P. Thibault, M. Dierolf, A. Menzel, O. Bunk, C. David, and F. Pfeiffer, Science 321, 379-82 (2008).

[3] M. Beckers, T. Senkbeil, T. Gorniak, M. Reese, S.-C. Gleber, T. Salditt, and A. Rosenhahn, Physical Review Letters 107, 1-4 (2011).