Azure A is a basic cationic dye, a polycyclic aromatic compound. Azure A is formed by the oxidation of methylene blue and has strong heterochromatic properties. It can be used in dyeing agents, redox media studies for electrochemical biosensing. Soluble in water as blue solution, slightly soluble in ethanol. With concentrated sulfuric acid shows yellow-green, dilution is blue to blue-purple, aqueous solution with sodium hydroxide shows dark purple and dark purple precipitate. Eosin is a chemically synthesized acidic dye, under certain conditions can make the cell plasma coloring, when the pH value of the staining solution in the cytoplasmic proteins below the isoelectric point (4.7-5.0), the cytoplasmic proteins to the alkaline ionization, then the cytoplasm is positively charged, it can be stained by negatively charged acidic dyes, presenting a red color.

The azure A-eosin staining solution consists of azure A, eosin, acetate, differentiation solution, etc. It is mainly used for staining of plasma cells, which have dark blue nuclei and grayish blue cytoplasm.