A nucleic acid-specific fluorescent probe for nucleolus imaging in living cells

Nucleus imaging is of great importance for understanding cellular processes of genetic expression, proliferation and growth, etc. Although many nucleic-acid selective dyes for nucleus staining are available, few of them meet multiple standards. Herein, we report a cationic fluorescence dye FTI that possesses visible light excitation (436 nm), orange emission (571 nm) and a large Stokes shift (~135 nm) for nucleic-acid staining. FTI displays an obvious and sensitive fluorescent response to DNA in vitro with a 6.4-fold quantum yield increasing. Co-staining and nucleic acid digest experiments in live cells demonstrate that FTI exhibits an unexpected selectivity for the nucleolus of the cells due to the stronger affinity to RNA than DNA. Because of good photostability and low cytotoxicity, FTI can accomplish a promising stain for DNA recognition in vitro and nucleolus-specific imaging in cancer cells.