<unk> <unk> <unk> <unk><unk><unk>  (PAS) is a staining method used to detect polysaccharides such as glycogen, and mucosubstances such as glycoproteins, glycolipids and mucins in tissues. The reaction of<unk> <unk>  oxidizes the vicinal diols in these sugars, usually breaking up the bond between two adjacent carbons not involved in the glycosidic linkage or ring closure in the ring of the monosaccharide units that are parts of the long polysaccharides, and creating a pair of aldehydes at the two free tips of each broken monosaccharide ring. The oxidation condition has to be sufficiently regulated so as to not oxidize the aldehydes further. These aldehydes then react with the<unk>  reagent to give a purple-magenta color. A suitable basic stain is often used as a counterstain. • PAS diastase stain (PAS-D) is PAS stain used in combination with diastase, an enzyme that breaks down glycogen. • Alcian blue/periodic<unk><unk><unk>  (AB/PAS or AB-PAS) uses alcian blue before the PAS step.
Periodic acid–Schiff stain
Mucicarmine stain
PAS diastase stain
Auramine phenol stain
HPS stain
Romanowsky stain
Alcian blue stain
Grocott's methenamine silver stain