Toluidine Blue is a basic thiazine metachromatic dye, which is used for selectively staining acidic tissue components such as carboxylates, sulfates, and phosphate radicals.
It is found to have affinity for nucleic acids, and therefore binds to nuclear material of tissues with a high DNA and RNA content.
Toluidine blue has been used in vivo to identify dysplasia and carcinoma of the oral cavity. Use of toluidine blue in tissue sections is done with the aim to highlight components, such as mast cells granules, mucins, and cartilage.