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Difference between 2% PFA and 4% PFA - (Feb/15/2013 )

Any immunocytochemistry experts out there who can clarify what exactly does PFA do when used as a fixative? Why are there two preferred concentrations which people use when fixing cells/tissue?

Also, the fixation times vary from protocol to protocol. Some recommend 10-15 min, some more than 30 min. What will over-fixing do to the cells?

-science noob-

we are using PFA 4% for brain tissue for maximum 30 min. Usually between 10-30min should be ok


over-fixing of tissue can inactivate some antigens


Check out this reference: Fox et al., The Journal of Histochemistry and Cytochemistry Vol. 33, No. 8, pp. 845-853, 1985