Toluidine Blue 0.1%, in sodium tetraborate, is an aqueous staining solution used in histology and cytology. The solution contains 0.1% toluidine blue, a basic dye dissolved in a buffer of sodium tetraborate.

This stain is used to highlight various cell structures and tissue types in microscopic specimens. Toluidine blue selectively binds to acidic components, such as nucleic acids and proteoglycans, and stains them blue. Because of these properties, toluidine blue is ideal for imaging cell nuclei, cartilage, and mast cells.

In histology, toluidine blue is often used as a frozen section stain to allow rapid diagnosis and differentiation of tissue types intraoperatively. In addition, it is used in cytology to examine cell smears and cell cultures.

The use of sodium tetraborate as a buffer solution helps maintain the optimal pH for staining and ensures good color binding and differentiation of cell structures.