An improved acriflavine-Feulgen reagent for quantitative DNA cytofluorometry.

We have modified the acriflavine-Feulgen histochemical method for the quantitative determination of DNA by performing the staining of hydrolyzed cells affixed to cover slips with acriflavine dissolved in 90% ethanol. Compared to conventional techniques, in which the acriflavine is dissolved in aqueous HCl plus potassium metabisulfite, this method not only decreased non-Feulgen (background) staining in both the nucleus and the cytoplasm, but also increased the fluorescent intensity of Feulgen stained nuclei more than four-fold. Cells stained by our modified method exhibited a fluorescence maximum of 507 nm, which is similar to the 500 nm fluorescence maximum obtained with acriflavine bound to apurinic acid solution by a modification of the acriflavine-Feulgen method. These fluorescence maxima are in contrast to the 510 nm to 625 nm fluorescence maxima which are obtained when cells are stained according to conventional protocols. The fluorescence intensities of nuclei of synchronized cells stained by the modified method were proportional to DNA content. Thus, by the criteria of staining specificity, in situ and in solution fluorescence spectra agreement and quantitative staining, we conclude that our modified acriflavine-Feulgen method is more satisfactory for quantitatively measuring DNA in situ by cytofluorometry than the usual acriflavine-Feulgen method.