Pyronin-phosphotungstic acid: spectral characteristics and staining pattern on Epon semithin sections

Phosphotungstic acid (PTA) binds to the basic dye pyronin Y to give a non fluorescent complex with absorption characteristics which are different from those of the free dye. The use of this complex on different cells and Epon embedded tissues revealed no staining affinity and only certain hydrated tissue components as starch showed a light reaction with the pyronin-PTA. The role played by the hydratation degree of certain components from epoxy-embedded tissues on the reaction mechanisms observed with some dyes and electron contrasting agents is briefly discussed.