A genetically encoded fluorescent biosensor for detecting nitroreductase activity in living cancer cells.

Genetically encoded fluorescent biosensors are particularly promising sensors to examine biochemical processes in a complex cellular context. RNA mimics of GFP are RNA-fluorophore complexes that emit green fluorescence comparable in brightness to fluorescent proteins. The fluorophore is non-fluorescent until it binds with specific RNA. We designed and developed a dual activated fluorescent probe based on RNA mimics of GFP for the detection of an intracellular nitroreductase. Our probe only fluoresces in the presence of both the specific RNA and nitroreductase. Since we used RNA to tag cells, our probe only fluoresces when nitroreductase exists in such cells. Our detection system should benefit the study of cell biomarkers in heterogeneous cell populations. More importantly, the strategy of quenching the RNA/DFHBI complex by alkylation of the hydroxyl group in DFHBI opens new possibilities for developing various genetically encoded fluorescent biosensors based on RNA/DFHBI complexes.