Exposure of the nuclear counterstain DAPI to just a few seconds of UV excitation light during fluorescence imaging can photoconvert the dye to stable green- and red-emitting forms, resulting in imaging artifacts in multi-color staining experiments. This article reviews the published literature on photoconversion and compares the effect of different mounting media on photoconversion of DAPI in stained tissue sections. Once photoconversion is recognized as a potential source of non-specific fluorescence, careful imaging practices or reagent selection can be used to avoid it.
