Alcian blue, also known as Aixian blue or Alcian blue, is a copper-titanium anthocyanine conjugate dye, initially used for textile fiber dyeing. This cationic dye combines with acidic groups, i.e., Alcian blue forms insoluble complexes with anionic groups such as carboxylic acid groups and sulfate contained in tissues, and Alcian blue consists of the central copper-containing phthalocyanine ring and four isothiuronium groups linked by a thioether bond, which is moderately basic, causing Alcian blue to be cationic. The isothiourea groups are moderately basic, making Alisin Blue cationic. at pH 2.5 the carboxyl groups in the tissue ionize and carry a negative charge, forming a salt bond with the cations in Alisin Blue, which stains acidic mucus substances with carboxyl groups (mucin sulfate and salivary mucin).

Alisin blue staining solution (pH 1.0) using different pH value of the staining solution can distinguish the class of mucus substances, pH 2.5 when the carboxyl group stains well and the sulfate mucus coloring is not good; pH value of 1.0 when the tissue of the sulfate ionization, with a negative charge, and the cations in the Alisin blue to form a salt bond, so that tissues with sulfate (such as sulfate mucus substances) staining, neutral mucus proteins (such as gastric mucosa and Brunner's gland sites). Neutral mucins (such as those in the gastric mucosa and Brunner's gland sites) do not react with Alisin Blue.