Advances in fluorescence imaging of RNAs in living cells based on functional nucleic acid probes

RNA is an essential biomolecule that determines and regulates numerous biological process in cells. The sensitive and specific imaging of the expression level, localization and dynamic change of RNAs in living cells possesses great significance in biological and medicine. The fluorescence functional nucleic acid probes with well-designed sequences are increasingly reported to be applied for living cell imaging, ascribing to their exceptional sensitivity and designability. In this review, the importance and examples of the living cell imaging of different types of RNAs are discussed. The fluorescence imaging methods based on functional nucleic acid probes, including non-amplification and amplification methods, are detailedly introduced. Especially, the combination of different amplification methods to achieve superior imaging performance is an advanced strategy to overcome the disadvantages of single amplification methods, so these methods are also introduced in detail. Finally, the downstream applications including subcellular imaging, in-depth disease mechanism investigation and disease diagnosis are demonstrated. In general, functional nucleic acid probe is a promising tool for imaging of RNAs in living cells, and this technique is rapidly improving ascribing to the emerging advances in functional nucleic acid and microscopy technology.