Osmium Ammine for Staining DNA in Electron Microscopy.

The osmium ammine staining allows the specific detection of DNA in the cell nucleus and represents one of the most used techniques for EM cytochemistry.The procedure is a Feulgen-type reaction, consisting of an acid hydrolysis to obtain free aldehyde groups on DNA followed by their binding to osmium ammine, a Schiff-type reagent. Osmium ammine is polyamminic electron-dense compound commercially available.Here, we describe the staining procedure for ultrathin sections and the different procedures for the preparation of the reagent for acrylic and epoxy sections.