Which staining technique is used to demonstrate acid mucopolysaccharides in tissues?

• A. Colloidal iron
• B. Giemsa
• C. Periodic acid-Schiff (PAS)
• D. Hematoxylin and eosin

Answer: (A)

Acid mucopolysaccharides (glycosaminoglycans) are negatively charged components of the extracellular matrix, so a stain that binds these substances will specifically highlight them in tissue. Colloidal iron works by using iron-containing particles that attach to the acidic carboxyl and sulfate groups of these mucopolysaccharides, producing blue deposits where they are abundant. This makes it the best choice among the options for demonstrating acid mucopolysaccharides.

The other stains serve different purposes: Giemsa is used mainly for cellular detail and parasites, H&E provides general tissue architecture, and the Periodic acid–Schiff stain detects neutral carbohydrates and some glycoproteins rather than specifically the acidic mucopolysaccharides.