Hairpin/DNA ring ternary probes for highly sensitive detection and selective discrimination of microRNA among family members.

The detection and quantification of microRNA (miRNA) plays essential roles in clinical and biomedical research. Yet, it is of major challenge to sense miRNA with high degree of selectivity and sensitivity due to its unique characteristics of short length, similarity of sequence among family members and low abundance. Here, with the design of a new hairpin/DNA ring ternary probe, we describe the development of a rolling circle amplification (RCA) method for sensitively and selectively sensing miRNA from cancer cells. The target miRNA binds the hairpin/DNA ring probes through toehold-mediated strand displacement (TSD) to form the ternary structures, in which the bound miRNA and DNA ring are respectively used as the primer and template to realize RCA, leading to the generation of many repeated metal ion-dependent DNAzyme sequences. The fluorescently quenched hairpin signal probes can be cyclically cleaved by these DNAzyme sequences with co-existence of the corresponding metal ions in buffer to show drastically enhanced fluorescence recovery for highly sensitive sensing of miRNA in the range between 10 fM and 10 nM with a detection limit of 1.51 fM. Besides, owing to the high base variation discrimination ability of TSD, selective detection of the target miRNA among the corresponding family members can be achieved by this method. Moreover, such a method can also be employed to differentiate miRNA expression variations in cancer cells for screening potential therapeutic drugs.