Turn-on fluorescent probes that can light up endogenous RNA in nucleoli and cytoplasm of living cells under a two-photon microscope

We have synthesized two-photon organic molecule probes (IMT-E and IMT-M), which selectively stain endogenous RNA in the nucleolus and cytoplasm of living cells in a short incubation time. Using these probes, bright two-photon excitation fluorescence (TPEF) images of living cells have been developed. Titrations and digest tests of ribonuclease indicate the markedly higher affinity of these probes for RNA, especially when using IMT-E. Upon binding to RNA, the fluorescence intensity of IMT-E increases by about 15-fold, showing that IMT-E is a turn-on probe for the detection of RNAs. MTT assays demonstrate that the mitochondria of cells maintain their electron mediating ability after being stained with the probes. These results demonstrate that IMT-E is an attractive two-photon turn-on fluorescent probe for visualizing RNA in living cells.