title: Three-dimensional mass density mapping of cellular ultrastructure by ptychographic X-ray nanotomography.
abstract: We demonstrate absolute quantitative mass density mapping in three dimensions of frozen-hydrated biological matter with an isotropic resolution of 180 nm. As model for a biological system we use Chlamydomonas cells in buffer solution confined in a microcapillary. We use ptychographic X-ray computed tomography to image the entire specimen, including the 18 μm-diameter capillary, thereby providing directly an absolute mass density measurement of biological matter with an uncertainty of about 6%. The resulting maps have sufficient contrast to distinguish cells from the surrounding ice and several organelles of different densities inside the cells. Organelles are identified by comparison with a stained, resin-embedded specimen, which can be compared with established transmission electron microscopy results. For some identified organelles, the knowledge of their elemental composition reduces the uncertainty of their mass density measurement down to 1% with values consistent with previous measurements of dry weight concentrations in thin cellular sections by scanning transmission electron microscopy. With prospects of improving the spatial resolution in the near future, we expect that the capability of non-destructive three-dimensional mapping of mass density in biological samples close to their native state becomes a valuable method for measuring the packing of organic matter on the nanoscale.
authors.affiliation: Paul Scherrer Institut, 5232 Villigen PSI, Switzerland. Electronic address: ana.diaz@psi.ch.
authors.forename: Ana
authors.initials: A
authors.lastname: Diaz
authors.affiliation: Paul Scherrer Institut, 5232 Villigen PSI, Switzerland.
authors.forename: Barbora
authors.initials: B
authors.lastname: Malkova
authors.affiliation: Paul Scherrer Institut, 5232 Villigen PSI, Switzerland.
authors.forename: Mirko
authors.initials: M
authors.lastname: Holler
authors.affiliation: Paul Scherrer Institut, 5232 Villigen PSI, Switzerland.
authors.forename: Manuel
authors.initials: M
authors.lastname: Guizar-Sicairos
authors.affiliation: Brookhaven National Laboratory, 11973 Upton, NY, USA.
authors.forename: Enju
authors.initials: E
authors.lastname: Lima
authors.affiliation: Paul Scherrer Institut, 5232 Villigen PSI, Switzerland.
authors.forename: Valerie
authors.initials: V
authors.lastname: Panneels
authors.affiliation: Max Planck Institute of Molecular Cell Biology and Genetics, 01307 Dresden, Germany.
authors.forename: Gaia
authors.initials: G
authors.lastname: Pigino
authors.affiliation: Scientific Center for Optical and Electron Microscopy, ETH Zürich, 8093 Zurich, Switzerland.
authors.forename: Anne Greet
authors.initials: AG
authors.lastname: Bittermann
authors.affiliation: Paul Scherrer Institut, 5232 Villigen PSI, Switzerland.
authors.forename: Larissa
authors.initials: L
authors.lastname: Wettstein
authors.affiliation: Paul Scherrer Institut, 5232 Villigen PSI, Switzerland.
authors.forename: Takashi
authors.initials: T
authors.lastname: Tomizaki
authors.affiliation: Paul Scherrer Institut, 5232 Villigen PSI, Switzerland.
authors.forename: Oliver
authors.initials: O
authors.lastname: Bunk
authors.affiliation: Paul Scherrer Institut, 5232 Villigen PSI, Switzerland.
authors.forename: Gebhard
authors.initials: G
authors.lastname: Schertler
authors.affiliation: Paul Scherrer Institut, 5232 Villigen PSI, Switzerland.
authors.forename: Takashi
authors.initials: T
authors.lastname: Ishikawa
authors.affiliation: Scientific Center for Optical and Electron Microscopy, ETH Zürich, 8093 Zurich, Switzerland.
authors.forename: Roger
authors.initials: R
authors.lastname: Wepf
authors.affiliation: Paul Scherrer Institut, 5232 Villigen PSI, Switzerland.
authors.forename: Andreas
authors.initials: A
authors.lastname: Menzel
mesh_terms: D016825:Chlamydomonas reinhardtii / Q000502:physiology* / Q000648:ultrastructure*; D005615:Freezing; D021621:Imaging, Three-Dimensional / Q000379:methods*; D015388:Organelles / Q000648:ultrastructure*; D014057:Tomography, X-Ray Computed / Q000379:methods*
keywords: Chlamydomonas; Ptychography; X-ray microscopy