Hemicyanine dyes linked with quaternary ammonium group: Near-infrared probes for the detection of nucleic acid

Two hemicyanine dyes (1a-b) linked with tetraalkyl ammonium group were prepared, and they were evaluated as near-infrared probes for the detection of nucleic acid. Fluorescent responses were observed from 643 to 850 nm when probes 1a-b was titrated with commercially available DNA and RNA. The dimethylaminophenyl containing hemicyanine (1a) gave a 32.8-fold and 33.5-fold emission enhancement towards DNA and RNA, while the dimethylaminonaphthalen containing hemicyanine (1b) gave a 33.0-fold and 38.8-fold emission enhancement respectively. They also show large fluorescence Stokes shifts. The fluorescence of 1a-b distinguishes clear nucleoli staining accompanied by faint cytoplasm in cellular environment, and nucleic acid digest test of ribonuclease indicates their markedly higher affinity for RNA. These results prove that probes 1a-b are very attractive staining reagents for visualizing RNA in fixed cells.