Toluidine blue is widely used in histology and pathology for staining tissues to enhance the visibility of cellular structures under a microscope. It is particularly effective in highlighting nucleic acids, making it valuable for identifying nuclei in tissue samples. The stain is also used in the detection of mast cells, which are crucial in immune responses, due to its metachromatic properties. In addition, toluidine blue is employed in the diagnosis of oral cancers and precancerous lesions, as it selectively stains abnormal tissues, aiding in early detection. Its application extends to microbiology for staining bacteria and other microorganisms, providing clear visualization for analysis.