Chromic Acid

Fluorescent Schiff

This method demonstrates fungi, and may also be called a Fluorescent Gridley or CAFS.

Solutions

Fluorescent Schiff reagent

Solution A
Chromium trioxide	50	g
Distilled water	500	mL

Solution B
Sodium sulphite	5	g
Distilled water	500	mL

Solution C
Ethanol, 70%	495	mL
Hydrochloric acid	5	mL

Tissue sample
5µ paraffin sections of neutral buffered formalin fixed tissue are suitable. Other fixatives are likely to be satisfactory.

Method

1. Bring sections to water via xylene and ethanol.
2. Place in solution A for 10 minutes.
3. Wash well with tap water.
4. Bleach with solution B for 1 minute.
5. Wash well with tap water.
6. Rinse with distilled water.
7. Place in fluorescent Schiff reagent for 20 minutes.
8. Wash well with tap water.
9. Place in solution C, two changes, 5 minutes each.
10. Wash well with tap water.
11. Dehydrate, clear and mount in a non fluorescent resinous medium.

Expected results
Using a BG 12 exciter filter, and OG 4 (yellow) and/or OG5 (orange) barrier filter.
Fungi fluoresce yellow with acriflavine and green-red with acridine orange.

Notes

1. This is most useful as a screening method.
2. If background fluorescence is too bright for fungi to be distinguished, it may be quenched with an alum hematoxylin for 1 minute, or 0.5% aqueous potassium permanganate for 1 minute. Quench immediately before the final dehydration step. This should be done with caution as it may reduce fungal fluorescence.

 

Reference
No specific reference is given for this method.
A similar technique using periodic acid as the oxidant is found in:–
  Culling C.F.A., (1974)
  Handbook of histopathological and histochemical techniques Ed. 3
  Butterworth, London, UK.

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