Intelligent assembly of Y-shaped DNA nanostructures for intracellular microRNA imaging

Highly sensitive and specific imaging of low-level microRNAs (miRNAs) in cytoplasm is vital for early diagnosis of cancers. In this work, we have developed the amplification strategies for miRNA-155 detection based on the combination the nicked rolling circle amplification (N-RCA) and catalyzed hairpin assembly (CHA). In this system, the target miRNA-155 acts as a polymerase primer to activate N-RCA to produce nicked fragment1 (NF1) and NF2. NF1 acted as new primer could further initiate a new N-RCA reaction over and over. Then, the NF2s could serve as triggers to induce the CHA reaction, and the Y-shaped DNA nanostructure (Y-SDN) was formed. Thus, an amplified fluorescence signal was obtained based on the multiple amplification. Under the optimized experimental conditions, a high sensitivity with a detection limit as low as 1.8 pM at 3σ miRNA-155 and excellent specificity in buffer condition have been achieved by applying this method. Meanwhile, the proposed method enables the application in miRNA-155 detection in human serum. Moreover, we have shown that the method performs well for the intracellular miRNA-155 imaging in cellular environments. Therefore, the present strategy was expected to apply into the clinical disease diagnosis effectively.