Fig. 2.

STEM-HAADF images of ferritin molecule cores within thin sections of fixed and unstained tissue. (a) Ferritin cores located in a hereditary haemochromatosis human liver biopsy. Strongly scattering iron-rich cores are visible as bright spots in the image and occur throughout the cytoplasm. Some cellular structures can be identified: A: endoplasmic reticulum; B: ribosome; C: organelle (probably mitochondrion). (b) Intermediate magnification HAADF image within the tissue section showing clear and regular subunit structure to the cytosolic ferritin cores with a line profile of the signal to background across a core inset. (c) Bright field STEM image of the same area as (b); note the significant decrease in signal to background of the inset line profile across a core compared to the HAADF image. (d) High magnification image of cytosolic ferritin cores from the same biopsy showing atomic lattice resolution of a subunit within a core. While other parts of the core may also be crystalline, only the bottom-right corner of the core is oriented along a crystallographic zone axis such that iron atom columns are resolvable/visible in the image. Note the non-facetted nature of the core edges. The lattice d-spacings (0.273 nm for spacing 1 and 0.272 nm for spacing 2, and 0.276 nm for spacing 3) and angles between the spacings (58.7° and 60.2°) are consistent with a ferrihydrite crystal structure (Drits et al., 1993). (e) Corresponding bright field STEM image of the core shown in (d) here the image is dominated by phase contrast effects such as the granularity in the embedded tissue surrounding the core and the lattice fringes in the subunit of the core that is lying on a crystallographic zone axis. i.e., the size and shape of the core is not clear here in comparison to the HAADF image because the parts of the core that are not lying on a crystallographic zone axis are partially obscured.