The preparation of ultrathin frozen sections for immunocytochemistry at the electron microscope level

A description of ultrathin frozen sectioning is presented. Small pieces of lightly‐fixed but unembedded tissue are cryoprotected in 80% sucrose, mounted on chucks and frozen in liquid nitrogen. Frozen sections approximately 100 nm thick for electron microscopy are cut at about −90°C, using a cryosectioning unit mounted on a conventional ultramicrotome. Sections are picked up from the surface of the knife with a droplet of 80% sucrose, and are applied to membrane‐coated EM grids at room temperature. The mounted sections are then used for EM immunocytochemistry. Essentially the same sectioning procedure can provide frozen sections 1 μm thick for light microscope immunocytochemistry.