Periodic Acid-Schiff (PAS): Counterstaining with Fast Green

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Periodic Acid-Schiff (PAS): Counterstaining with Fast Green

Fast green should be used as a counterstain when using PAS staining procedures to demonstrate the presence of fungal organisms in tissue sections. 

For a fast green counterstain, continue any of the PAS staining protocols with the following step:
  • Fast green (0.02% solution) for 30 seconds

Expected result: The PAS-negative background elements will stain green.

Post staining procedure:
  • After counterstain, tissue sections should be rinsed quickly in distilled water, as fast green is easily rinsed out of tissue sections.
  • Following the quick water rinse, sections should be dehydrated with 95% alcohol, followed by 100% alcohols, cleared with xylene (or xylene substitute), and cover-slipped.

PAS fungal stain; fast green counterstain