The use of tannic acid fixation for the electron microscope visualization of fluorochrome-labelled antibodies attached to cell surface antigens.

Tannic acid as a prefixative for EM purposes was introduced by Futaesaku et al. (1972). The fixative creates conditions for enhancing electron density of different protein materials. By using a mixture of tannic acid and glutaraldehyde as prefixative, followed by a routine procedure of postfixation (OsO4) and poststaining (uranylacetate and lead citrate), membrane bound antibodies not conjugated with electron dense markers are made visible under the electron microscope.