Generally staining after embedding is better because:
Sometimes pre-embedded stain can make tissue hard and difficult to section
The reagent may affect the tissue and introduce artifacts
The reagent may interfere with subsequent cytochemical rxns.
Sufficiently electron dense
Is used during aldehyde fixation at physiological pH – causes reactive areas to become osmiophilic
Binds extracellular glycoproteins, mucins.
Avoid exposure to CO2 or precipitation occurs
OsO4 is a mordant for lead products.
Mixture with form/glut/osmium in phosphate buffer and kept at 4 C
Fix with glut and osmium, then in stoppered vial for 30-60 min at 70 C
high temp to stabilize.
Reacts strongly with Cacodylate buffer and phosphate buffers, so these should be rinsed extensively prior to exposure.
Incubate either before or after osmium fix.
usually aqueous, but some claim methanolic UA better at penetration.
Improves fixation with aldehydes of proteins and reacts with OsO4
Mix the glutaraldehyde with TA
Must be prepared fresh and filtered before use.