Phase-contrast tomography at the nanoscale using hard x rays

Synchrotron-based full-field tomographic microscopy established itself as a tool for noninvasive investigations. Many beamlines worldwide routinely achieve micrometer spatial resolution while the isotropic 100-nm barrier is reached and trespassed only by few instruments, mainly in the soft x-ray regime. We present an x-ray, full-field microscope with tomographic capabilities operating at 10 keV and with an isotropic resolution of 144 nm. Custom-designed optical components allow for ideal, aperture-matched sample illumination and very sensitive phase contrast imaging. We show here that the instrument has been successfully used for the nondestructive, volumetric investigation of single cells.

Figure 1

(Color online) (a) Schematic of the nanoscope setup installed at the TOMCAT beamline. The beam shaper (b) collects light coming from the source (located 20 m upstream) and produces a top-flat square illumination (d) at distance $q_{\text{beam}\text{shaper}}$. The Fresnel zone plate magnifies this region into the detector located at $q_{\text{lens}}=9\text{m}$ downstream. At the back-focal distance of the FZP the dot array (e) is aligned to the diffraction spots, generating Zernike phase contrast. An SEM image of the central part of the beam shaper is shown in (b) and the inset depicts the corner region, showing the $1\text{−}\mu \text{m}$-thick gold structures 100 nm apart. The central stop, obtained by laser cutting a $250\text{−}\mu \text{m}$-thick platinum/iridium foil is shown in (c).

Figure 2

Zernike phase contrast nanoimaging of different calibration samples. [(a)–(c)]: Radiographic image of a silicon Siemens star. (a) shows an image obtained by stitching $10\times 10$ single snapshots with a field of view of $35\times 35$ microns each. (b) illustrates the central part of the star and (c) illustrates the same region imaged with SEM. [(d)–(f)]: Nanotomographic investigation of a ${\text{SiO}}_2$ sphere with inclusions. (d) depicts a nanoradiographic projection. The dotted line marks the height of the axial cut shown in (e). (f) shows a sagittal cut through the sample at the position marked in (e).

Figure 3

Zernike phase contrast nanotomography of an unstained MC3 preosteoblast cell. (a) shows a nanoradiographic projection of the MC3 cell together with other cells which happened to be on the beam path during the snapshot. (b) and (c) show coronal and sagittal cut of the MC3 cell, respectively. A total of 251 angular projections over $180°$ have been collected within 10 min. Clearly visible are the nucleus (dark) with several intracellular structures.