3,6-bis(dimethylamino)acridinium chloride.

A toxic, fluorescing dye that stains DNA and RNA and is typically used to identify cancerous tumor cells. When it binds to double-stranded DNA, it fluoresces green; when it binds with the phosphate groups of single-stranded DNA or RNA, it fluoresces orange. The chemical also causes frameshift mutations.

From the BioTech Dictionary at http://biotech.icmb.utexas.edu/. For further information see the BioTech homenode.