The lab states fixation will trigger the dyes to leak with the cells. I believe the idea is fixation may hurt cell membranes. I did discover a paper which describes fixation utilizing methanol or acetic acid, just after staining using a DCFDA derivative. DCFDA will be the reagent that stains https://trentongsadf.blogdon.net/everything-about-2-fdck-hcl-44141275