title: Feasibility of imaging living cells at subnanometer resolutions by ultrafast X-ray diffraction.
abstract: Detailed structural investigations on living cells are problematic because existing structural methods cannot reach high resolutions on non-reproducible objects. Illumination with an ultrashort and extremely bright X-ray pulse can outrun key damage processes over a very short period. This can be exploited to extend the diffraction signal to the highest possible resolution in flash diffraction experiments. Here we present an analysis of the interaction of a very intense and very short X-ray pulse with a living cell, using a non-equilibrium population kinetics plasma code with radiation transfer. Each element in the evolving plasma is modeled by numerous states to monitor changes in the atomic populations as a function of pulse length, wavelength, and fluence. The model treats photoionization, impact ionization, Auger decay, recombination, and inverse bremsstrahlung by solving rate equations in a self-consistent manner and describes hydrodynamic expansion through the ion sound speed. The results show that subnanometer resolutions could be reached on micron-sized cells in a diffraction-limited geometry at wavelengths between 0.75 and 1.5 nm and at fluences of 1011-1012 photons microm-2 in less than 10 fs. Subnanometer resolutions could also be achieved with harder X-rays at higher fluences. We discuss experimental and computational strategies to obtain depth information about the object in flash diffraction experiments.
authors.affiliation: Laboratory of Molecular Biophysics, Institute of Cell and Molecular Biology, Uppsala University, Uppsala, Sweden.
authors.forename: Magnus
authors.initials: M
authors.lastname: Bergh
authors.forename: Gösta
authors.initials: G
authors.lastname: Huldt
authors.forename: Nicusor
authors.initials: N
authors.lastname: Tîmneanu
authors.forename: Filipe R N C
authors.initials: FR
authors.lastname: Maia
authors.forename: Janos
authors.initials: J
authors.lastname: Hajdu
mesh_terms: D055592:Biophysical Phenomena; D002477:Cells / Q000737:chemistry* / Q000528:radiation effects / Q000648:ultrastructure*; D022082:Cellular Structures / Q000737:chemistry / Q000528:radiation effects / Q000648:ultrastructure; D017709:Fractals; D021621:Imaging, Three-Dimensional / Q000379:methods; D007477:Ions; D008954:Models, Biological; D012542:Scattering, Radiation; D055471:Thermal Diffusion; D014961:X-Ray Diffraction / Q000379:methods*
chemical_list: D007477:Ions