Toluidine blue is also called toluidine blue; 2,2 '- [(9,10-dihydro-4,8-dihydroxy-9,10-dioxo-1,5-anthracenediyl) diamino] bis (5-methylbenzenesulfonic acid) disodium salt; Toluidine blue/toluidine blue; Toluidine blue O. Toluidine blue is a photosensitizer gel, which has the following advantages: gel preparation has certain viscosity and adhesion, which can make the drug stay at the diseased part to improve the treatment effect. On the other hand, toluidine blue is an acidophilic dye with a tendency of nucleic acid, which stays in tissues with more nuclear components. It has a good penetration depth in the tissue and can be effectively distributed in the infected target tissue, but can not penetrate the normal tissue, thus avoiding the photodynamic damage to the normal tissue, so toluidine blue has a good selectivity for the diseased area and bacteria. The most important point is that toluidine blue photosensitizer has no obvious toxic and side effects, which reduces the harm to human health system and is conducive to the promotion and application of photodynamic therapy. Oxidation-reduction indicator. Biological stain. In histochemistry, it is used to determine DNA and RNA. Diagnose diphtheria. Printing and dyeing of wool and silk.