Toluidine staining

Toluidine staining (Fig. 3) is applied to semi thin sections of epoxy embedded tissue (section The stained sections can be used to determine the area of interest for further processing, but also for LM observations. Toluidine stock solution is obtained from commercial sources.

The 1 % toluidine blue and 2 % borate in distilled water needed is obtained by mixing:

  • 1 g  toluidine blue O
  • 2 g sodium borate (borax)
  • 100 ml distilled water

  1. Dissolve the sodium borate in the water
  2. Add the toluidine blue powder
  3. Stir until dissolved
  4. Filter the stain solution (use syringe filter) before use

   Note: The borax makes the stain alkaline so it will help penetrating to the epoxy sections

Staining process

  1. Cut semi-thin sections at 0.5 - 1.0 μm
  2. Transfer sections to a drop of distilled water on a glass slide.
  3. Dry sections on a glass slide on a slide warmer or over a 40 W lamp
  4. Cover section with staining solution (with the heat source still on) for 1-2 minutes
  5. Rinse off excess stain with distilled water and air dry


Fig. 3. Toluidine staining of a semi thin section of epoxy embedded ventricular tissue. Photo: I Fries.

Figure 3