acridine orange
<chemical, molecular biology> 3, 6-bis(dimethylamino)acridinium chloride.
A toxic, fluorescing dye that stains DNA and RNA and is typically used to identify cancerous tumour 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.