Alcian blue, also known as Aixian blue or Alisin blue or Alcian blue, is a copper-titanium anthocyanine conjugate dye, initially used for textile fiber dyeing. This cationic dye is combined with acidic groups, i.e., Alcian blue forms insoluble complexes with anionic groups such as carboxylic acid groups and sulfate contained in tissues, and is formed by the central copper-containing phthalocyanine ring and four isothiuric carbamoyl groups connected through a thioether bond. When the pH is 2.5, the carboxyl group in the tissue is ionized and carries a negative charge, forming a salt bond with the cation in Alisin Blue, which stains the acidic mucus substances with carboxyl groups (mucin sulfate and salivary mucin). pH 1.0, the sulfate in the tissue is ionized and carries a negative charge, forming a salt bond with the cation in Alisin Blue, which stains the acidic mucus substances with sulfate groups (mucin sulfate and salivary mucin); at pH 1.0, the sulfate in the tissue is ionized and carries a negative charge, forming a salt bond with the cation in Alisin Blue. form a salt bond that stains tissues with sulfate (e.g., sulfated mucus material).

Cartilage staining solution (Alisin blue method, pH 1.0) can distinguish the class of mucus substances by using different pH values of the staining solution. At pH 1, carboxylic acid group (-COOH) does not stain, and sulfate group (-OSO3H) stains; at pH 2.5, carboxylic acid group stains well, but sulfate mucus does not stain well, and sulfate mucus and saliva mucus proteins are stained.