Which staining method is used to specifically visualize sulfated mucopolysaccharides at a very low pH?

• A. Alcian blue at pH 0
• B. Periodic acid Schiff
• C. Giemsa
• D. Mayer mucicarmine

Answer: (A)

Sulfated mucopolysaccharides are visualized specifically with a positively charged dye that binds to their sulfate groups, and this binding is made selective by using an extremely low pH. At very low pH, carboxyl groups on mucopolysaccharides lose their negative charge by protonation, so they no longer bind the dye. The sulfate groups remain negatively charged and attract the cationic Alcian blue, producing a blue stain that highlights sulfated mucopolysaccharides while non-sulfated (or less sulfated) mucins do not stain. This selective demonstration helps distinguish sulfomucins from other mucins in tissue sections. The other stains work on different chemical principles: PAS targets neutral carbohydrates; Giemsa is for general cellular morphology; and Mayer mucicarmine stains acidic mucins but does not rely on pH-driven selectivity for sulfation.