Paraformaldehyde (PFA) for HCR (4%)

4% paraformaldehyde (PFA)

1× phosphate-buffered saline (PBS) for HCR (DEPC-treated; pH 7.4)

In a fume hood, weigh 1.6 g of crystalline PFA (Sigma-Aldrich P6148) into a 50-mL conical tube. Add 1× DEPC-treated PBS (pH 7.4) until the final volume is 40 mL. Heat the solution in a water bath (<60°C) until all of the PFA powder is completely dissolved. Cool the solution on ice and store at −20°C until use. Thaw and use the fixative only once; dispose of the remaining fixative according to local ordinances.

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