Alcian Blue stain solution [pH 2.5]

Alcian blue is a copper-titanium cyanine conjugate dye, originally used for textile fiber dyeing. When the pH value is 2.5, the carboxyl group in the tissue is ionized and has a negative charge, forming a salt bond with the cation in Alcian blue, so that tissues with carboxyl groups (such as proteoglycan/hyaluronic acid and epithelial acidic mucin) are stained. Neutral mucin (such as neutral mucin in gastric mucosa and Brunner glands) cannot react with Alcian blue. At pH 2.5, both the carboxyl group and the sulfate group are ionized, and both carboxylic acid mucus and sulfate mucus can be dyed blue-green.