Reduction-triggered fluorescent amplification probe for the detection of endogenous RNAs in living human cells

Oligonucleotide-templated reactions are attracting attention as a method for RNA detection in living cells. Previously, a reduction-triggered fluorescence probe has been reported that is based on azide reduction to switch fluorescence on. In this article, we report a more advanced probe, a reduction-triggered fluorescent amplification probe that is capable of amplifying a target signal. Azidomethyl fluorescein was newly synthesized and introduced into a probe. Azido-masked fluorescein on the probe showed a strong turn-on fluorescence signal upon oligonucleotide-templated Staudinger reduction. The catalytic reaction of the probe offered a turnover number of 50 as fluorescence readout within 4 h. Finally, probes were introduced into human leukemia HL-60 cells by use of streptolysin O pore-forming peptide. We successfully detected and quantitated the 28S rRNA and beta-Actin mRNA signal above the background by flow cytometry. In addition, the same RNA targets were imaged by fluorescence microscopy. The data suggest that a reduction-triggered amplification probe may be a powerful tool in analyzing the localization, transcription, or processing of RNA species in living eukaryotic cells.