Which stain is used to demonstrate acid mucopolysaccharides?

• A. Alcian blue
• B. Schiff reagent
• C. Thioflavin T
• D. Best Carmine

Answer: (A)

Acid mucopolysaccharides carry negative charges from sulfate and carboxyl groups, so a stain that binds to these charges is used to visualize them. Alcian blue is a cationic dye that binds to the negatively charged acidic mucopolysaccharides, turning them blue. When used at a pH around 2.5, Alcian blue stains both sulfated and carboxylated mucopolysaccharides, making it the standard method to demonstrate acid mucopolysaccharides in tissue sections. Other stains don’t target these negative charges specifically: Schiff reagent (PAS) detects carbohydrates in general after oxidation, not just acidic mucins; Thioflavin T highlights amyloid; and Best Carmine has other staining targets and is not the preferred method for acid mucopolysaccharides.