chemical fixation

Chemical fixation is a method using chemicals to preserve the morphological structure of biological specimens such as cells and tissues extracted from living organisms, by keeping them close to their living states for scanning electron microscope (SEM) observation.
The method chemically fixes the proteins, lipids, etc., in cells and tissues. Immersion fixation is widely used, in which cells or tissues are directly immersed into a fixation solution. In addition, two other methods are often used: One is perfusion fixation in which a fixation solution is injected into a biological specimen through the vascular system. Another is vapor fixation in which a specimen is exposed to the vapor of a fixation solution.
Widely-used fixation solutions include glutalaldehyde and paraformaldehyde which can well fix proteins, and osmium tetroxide which can well fix phospholipids.
After chemical fixation, the specimen is subjected to ethanol dehydration. Then, the ethanol is substituted for t-butyl alcohol and is subjected to freeze drying, or the ethanol is substituted for isoamyl acetate and is subjected to critical-point drying. Finally, the specimen is observed with the SEM.