The Importance of Osmiophilia in the Production of Stable Azoindoxyl Complexes of High Contrast for Combined Enzyme Cytochemistry and Electron Microscopy

The versatility of dye methods for locating cellular enzymes gives them great potentialities as alternatives to metal salt precipitation techniques for electron microscopy, although their use has many attendant difficulties. For example, gross diffusion of the organic dye occurs in embedding media when indigogenic or certain azonaphthol methods are used in attempts to determine the cellular locations of lysosomal or microsomal esterases (13, 14). Such dyes also have relatively poor contrast in the electron microscope. In attempts to overcome these limitations, Hanker et al. have exploited their finding that certain sulphur-containing dyes are able to reduce osmium tetroxide to "osmium black," a product that is opaque to both light and electrons, and have