Colloidal iron staining is used for demonstration of which substances?

• A. Acid mucopolysaccharides
• B. Proteins
• C. Lipid
• D. Nucleic acids

Answer: (A)

Colloidal iron staining targets acidic mucopolysaccharides because the negative carboxyl and sulfate groups on glycosaminoglycans attract and bind the iron-containing colloid. When sections are treated with the ferric hydroxide colloid, these acidic polysaccharides in the extracellular matrix and mucins bind the iron, producing a blue deposit that highlights areas rich in glycosaminoglycans such as hyaluronic acid, chondroitin sulfate, dermatan sulfate, and heparan sulfate. This makes structures like cartilage matrix, basement membranes, and mucinous secretions stand out.

Proteins don’t have the same abundant negative charges that the iron colloid targets in these contexts, so this stain isn’t used to demonstrate proteins. Lipids require different stains (such as Sudan dyes) in frozen sections, not colloidal iron. Nucleic acids are detected by other methods (like Feulgen reaction), not by colloidal iron staining.