osmium fixation

Osmium fixation is one of chemical fixation methods for scanning electron microscope (SEM) observation of biological specimens.
To fix phospholipids of biological membranes, cells or tissues extracted from living organisms are immersed in an osmium tetroxide solution (concentration: about 1%) for approximately one hour. If a high-concentration solution is used or the specimen is immersed in the solution for long hours, proteins in the specimen can be destroyed or melted. To prevent this phenomenon, it is required to properly control the concentration of the fixation solution and the time spent for fixation. For mycelia and spores of molds or mushrooms, the phospholipids in the specimen are fixed by exposing them to the vapor of osmium tetroxide (aqueous solution concentration: about 2 to 4%) for several hours to all night (vapor fixation). This chemical fixation method is also called “post-fixation” because the fixation is carried out after the perfusion fixation using aldehyde.