Toluidine blue is a basic thiazine metachromatic dye with high affinity for acidic tissue components. It stains nucleic acids blue and polysaccharides purple and also increases the sharpness of histology slide images.
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.