What is the correct sequence for performing the Alcian blue mucosubstance stain?

• A. 3% acetic acid; Alcian blue; Nuclear Fast Red
• B. Alcian blue; 3% acetic acid; Nuclear Fast Red
• C. Nuclear Fast Red; Alcian blue; 3% acetic acid
• D. 3% acetic acid; Nuclear Fast Red; Alcian blue

Answer: (A)

Staining acidic mucosubstances with Alcian blue works best when the tissue environment is prepared under acidic conditions, so the dye binds specifically to sulfated and carboxylated mucopolysaccharides. Starting with 3% acetic acid acidifies the tissue and helps remove interfering substances, creating the proper low pH that promotes selective binding of Alcian blue to the mucosubstances. After this pre-treatment, applying Alcian blue lets the dye attach to the negatively charged mucosubstances, giving a vivid blue result where these substances are present. Finally, Nuclear Fast Red serves as a counterstain to color nuclei and provide contrast, making the blue mucosubstances easier to distinguish. Staining Alcian blue first or counterstaining before the blue would reduce specificity and contrast, so the acid pre-step, then Alcian blue, then Nuclear Fast Red is the correct sequence.