Detection of miRNA in Live Cells by Using Templated RuII-Catalyzed Unmasking of a Fluorophore

Reactions templated by cellular nucleic acids are attractive for nucleic acid sensing or responsive systems. Herein we report the use of a photocatalyzed reductive cleavage of an immolative linker to unmask a rhodamine fluorophore, and its application to miRNA imaging. The reaction was found to proceed with a very high turnover (>4000) and provided reliable detection down to 5 pM of template by using γ‐serine‐modified peptide nucleic acid (PNA) probes. The reaction was used for the selective detection of miR‐21 in BT474 cells and miR‐31 in HeLa cells following irradiation for 30 min. The probes were introduced by using reversible permeation with streptolysin‐O (SLO) or a transfection technique. Seeing is believing: Different miRNAs were used as templates for the photoreduction of an azide‐based immolative linker by RuII‐peptide nucleic acid (PNA) conjugates to uncage rhodamine (see figure). The method was validated by using two sets of γ‐serine‐modified PNA derivatives with varying affinities to their target (perfect match and mismatch).