Sudan III (Solvent Red 23) is a solvent dye used to color nonpolar substances.

Tissue lipid staining
1. Material preparation:
1) Sudan III working solution: Prepare 0.5–1% Sudan III in ethanol or ethanol-acetone mixture (70% ethanol and 30% acetone).
2) Sections: frozen sections or paraffin sections.
3) Distilled water and hematoxylin (optional, as contrast stain).
2. Staining steps:
1) Tissue fixation and preparation
2) Fix tissue with 10% neutral buffered formaldehyde (no dewaxing is required for frozen sections).
3) Prepare sections using a cryostat (recommended thickness 5–10 μm).
4. Staining
1) Immerse sections in Sudan III working solution and stain for 5–15 minutes (time can be adjusted according to lipid content).
2) Wash off excess dye with distilled water.
5. Contrast staining (optional): Nuclei can be stained with hematoxylin, and rinse with water after staining for 1–2 minutes.
6. Sealing: Use a sealing medium containing glycerol to seal the slides. Avoid using a sealing medium containing organic solvents to avoid discoloration.
7. Microscope observation: Use an optical microscope to observe the orange-red staining signal of lipids.