= Freeze-fracture electron microscopy
<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.<Freeze-fracture electron microscopy by Nicholas J. Severs>[Abstract and protocol, fracture, metal-carbon replica and TEM examination]{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.
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