Contrast of biological cryosections in scanning transmission electron microscopy

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Abstract
SUMMARY: Ultrathin (70–100 nm thick) frozen‐hydrated cryosections of yeast cells were studied by scanning transmission electron microscopy (STEM). Generally, the contrast is very poor in brightfield and increases slightly by use of the darkfield signal in imaging. The contrast can either be enhanced by selective staining before cryofixation or by mass loss caused either by freeze‐drying or by radiation damage. Partial freeze‐drying by superficial ice sublimation seems to be the most efficient method to increase the contrast in cryosections in the frozen‐hydrated state. The highest contrast in cryosections is achieved after complete freeze‐drying.