Permanent fluorescent staining of nucleic acids in isolated cells.

Staining of fixed cells, blood smears and chromosomes with 0.1% w/v of 3, 5, 7, 2', 4'-pentahydroxyflavanol (morin dehydrate) in 70% ethanol after brief mordanting with 5% w/v aluminum ammonium sulfate results in permanent fluorescence of cellular nucleic acids. Incubation in ribonuclease solution before mordanting, or 5-min hydrolysis with INHCL at 60 degrees C selectively abolishes RNA fluorescence, while the incubation in deoxyribonuclease solution abolishes DNA fluorescence. The morin-mordant complex bound to nucleic acids is stable to photodegradation and up to five years of storage.