... of cold 4% paraformaldehyde in PBS on ice for 15 min . Pro-Tip While 4% Paraformaldehyde fixation works...coated coverslips HeLa cells 24-well plate 4% Paraformaldehyde 5 mg/mL 4′,6-diamidino-2-phenylindole (DAPI...be better for some applications. Remove the paraformaldehyde and follow your institution's laboratory safety...