cryoultramicrotome

A cryoultramicrotome is a specialized ultramicrotome equipped with a cryogenic cooling system that enables the production of ultrathin sections from frozen specimens. It is used in sample preparation for cryo-electron microscopy (cryo-EM) and related techniques, providing sections of vitrified, near-native material by maintaining the specimen at cryogenic temperatures during cutting.

In operation, specimens are rapidly frozen and mounted on cryo-holders inside a chamber kept at low temperature, often using liquid nitrogen. A diamond knife slices the frozen block as the stage advances, producing ultrathin ribbons typically in the range of 50 to 100 nanometers. Sections are collected on grids with support films under cryogenic conditions and then transferred to the imaging stage with minimal warming. The instrument is designed to minimize frost and contamination and to control temperature, vibration, and cutting parameters.

There are various instrument designs optimized for vitreous-ice sectioning or for cryo-immunolabeling workflows. Achieving good quality sections requires precise control of temperature, knife angle, cutting speed, and environmental conditions. Common artefacts include compression, chatter, crevasses, and thinning of the sections, which can affect interpretability.

Applications include visualization of cellular ultrastructure, organelles, and macromolecular complexes by transmission electron microscopy and cryo-electron tomography, with the aim of observing native conformations and arrangements in situ. Cryoultramicrotomy complements other cryo-preparation methods such as plunge freezing and Tokuyasu cryosectioning. It remains technically demanding and is primarily used in specialized structural biology laboratories.