Periodic Acid-Schiff: Chemistry
The Periodic Acid-Schiff (PAS) staining technique is the most widely used procedure for the demonstration of glycogen and certain glycoconjugates. The PAS reaction is a result of aldehyde groups being formed via oxidation using periodic acid. The tissue section is then incubated in a Schiff reagent (a colorless concoction of basic fuchsin, HCl, and sodium metabisulfite). The section is finally rinsed with running water, which causes the fuchsin molecules bound to the glycogen in the tissue to turn pinkish red.
Hematoxylin or fast green may be used as counterstains.