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Freeze-fracture electron microscopy reveals structures along a fracture through a frozen specimen, commonly within a biological membrane. The exposed surface is shadowed with a thin platinum-carbon deposit; supporting carbon stabilizes the replica, which is cleaned and examined by transmission electron microscopy. The image is of this replica, not a direct view through the original thick tissue.^[ref]

A practical preparation rapidly freezes tissue, fractures it in a cold vacuum apparatus, deposits the replica and transfers the cleaned film to a microscope grid. Membranes often split through their hydrophobic interior, exposing particles and complementary depressions associated with membrane proteins. The fracture plane is not generally the original outer cell surface.

This method is useful because it displays lateral membrane organization that a thin cross-section can hide. However, freezing artifacts, shadowing direction and fracture-path selection affect appearances. Combining replica structure with immunoelectron microscopy can help identify selected proteins, while an unlabeled intramembrane particle should not be assigned a molecular identity from shape alone.

Nicholas J. Severs is a researcher in cellular ultrastructure whose 2007 freeze-fracture electron microscopy protocol lists an affiliation with the National Heart and Lung Institute at Imperial College London. His methodological work explains how fracture planes reveal the internal organization of cell membranes.^[ref]

The protocol freezes a biological specimen, fractures it, deposits platinum and carbon to form a replica, and cleans that replica for transmission electron microscopy. The microscope thus examines a durable record of the exposed surface. Optional removal of ice by sublimation exposes additional relief. This makes preparation a scientific part of the measurement: the observed surface depends on where the specimen fractured and which material the procedure exposed.^[ref]