In histochemistry and histological research, the Periodic-Acid Schiff (PAS) staining technique is used to show the presence of carbohydrates and carbohydrate molecules such polysaccharides, mucin, glycogen, and components of fungal cell walls.
It has been used to find glycogen in tissues including the heart, liver, and skeletal muscles.
It makes use of frozen tissue sections, paraffin-embedded tissue sections, and formalin-fixed tissue sections.
Principle of Periodic Acid-Schiff (PAS) Staining
Some polysaccharides interact with the periodic acid in Schiff's reaction with carbohydrates, which is an oxidative process that results in an oxidised molecule called an aldehyde.
The fixation of the colourless Schiffs fuchsin results in the red, pink, or magenta colouring, which indicates the presence of aldehydes.
The interaction of PAS with the diastase enzymes, which convert starch to maltose and then to glucose, is thought to be the cause of PAS.
The stain becomes pink after glucose conversion, defining the persistence of intracellular or extracellular mucins.
Nuclei are stained with methyl green or hematoxylin.
Preparation of Solutions and Reagents
Periodic Acid solution (0.5%)
Periodic acid- 0.5g
Distilled water- 100ml
Testing Schiff’s Reagent
10 ml of 37% formalin
Add Schiff’s reagent to be tested.
A good Schiffs reagent turns red-purple in color while a poor Schiffs reagent will have a delayed reaction producing deep blue-purple coloration
Mayer’s Hematoxylin Solution
Procedure for Periodic Acid-Schiff (PAS) Staining
Hydrate and deparaffinize water.
Oxidation: For oxidation, add 0.5% Periodic acid solution and let it sit for 5 minutes.
In distilled water, rinse.
Aldehydration: For 15 minutes, immerse the stain in Schiff reagent, which becomes bright pink.
Washing: Let the stain sit in lukewarm tap water for 5 minutes to turn it dark pink.
Add Mayer's Hematoxylin for 1 minute to counterstain.
Spend five minutes washing with hot, running water.
Dehydrate and mount with a synthetic mount medium.
Results and Interpretation
Pink or purple stains are produced by glycogen, mucin, elastic fibres, thyroid colloids, basophilic granules of the pituitary gland, reticular fibres, basement membranes, bone cartilage, and other carbohydrate components.
Depending on the dye employed, the nuclei stain green or blue.
The background stains blue.
Applications of Periodic Acid-Schiff (PAS) Staining
Cytology: The diagnosis of glandular carcinomas (adenocarcinomas) has also been made using this stain, which has also been employed in the undifferentiated identification of tumours.
Pathology: The diagnosis of liver and renal diseases also use it.
Fungal studies: It is used to diagnose Candida albicans, Aspergillus fumigatus, and Cryptococcus neoformans infections by showing the fungal hyphae and yeast forms of fungus in tissue samples.
Gastrointestinal pathology: To detect the presence of mucins in the gastrointestinal tract.
Lung studies: the stain studies the amorphous or granular globules of the pulmonary alveolar proteinosis.
Skin: to study the eosinophilic globoid bodies or Kamino bodies.
Muscle biopsies: to demonstrate glycogen components.
To detect prostate cancer, pancreatic pathologies, effects of the small intestines, testis.
Application in the identification of granules in enzymatic cytochemistry.
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