Special Stains - Masson Fontana

Melanin possesses the ability to bind silver from silver solutions and reduce it directly to metallic silver without the use of an external reducer.

The masson fontana stain uses the reducing property of melanin pigment to reduce silver salts found in the staining solution.  This is called an argentaffin reaction where the tissue component reduces the silver as opposed to argyrophic reaction where an external reducing agent is required  to reduce the silver. This is a useful stain used for diagnosis of malignant melanomas.

Method

If bleaching step is required :

 

Use 2 control sections and 2 test sections.  One control and one test with bleach and one control and one test without bleach.

 

1. Take sections to distilled water
2. Stain with 0.5% potassium permanganate for 5 minutes
3. Wash in water
4. Decolourise with 5% oxalic acid for 1 minute
5. Wash in distilled water
6. Carry on from step 2 below

 

If no bleaching required :

 

1. Take sections to distilled water.
2. Treat with working solution, in a dark container, at 56ºC for 40-60 minutes, or overnight at room temperature
3. Wash well in several changes of distilled water.
4. Treat with 0.2% gold chloride for 5 minutes
5. Wash in water
6. Treat with 0.5% sodium thiosulphate for 2 minutes
7. Wash in water
8. Counterstain in 0.1% aqueous nuclear fast red in 5% aluminium sulphate for 5 minutes
9. Wash, dehydrate, clear and mount

Result

Melanin, argentaffin, chromaffin, some lipfuscin pigment	Black
Nuclei	Red

Photo - x10 Masson Fontana