Strand displacement-triggered G-quadruplex/rolling circle amplification strategy for the ultra-sensitive electrochemical sensing of exosomal microRNAs

Emerging evidence suggests that exosomal microRNAs are potential biomarkers for the early diagnosis and prognostic assessment of tumor. Here, we design a strand displacement-initiated G-quadruplex/rolling circle amplification (RCA) strategy for highly specific and sensitive electrochemical sensing of exosomal microRNAs. In the presence of exosomal miRNA-21, a locked nucleic acid (LNA)-labeled toehold mediated strand displacement reaction (TMSDR) is initiated, releasing output P2 to trigger the subsequent RCA reaction by hybridizing with the C-rich circular template. Then the obtained G-rich RCA products can bind to the probe anchored on the surface of gold electrode and generate G-quadruplex conformations. Based on the TMSDR-triggered G-quadruplex/RCA strategy, the detection limit of this electrochemical biosensor is down to 2.75 fM. Moreover, our biosensor exhibits excellent repeatability, stability, and high consistency compared to RT-PCR for clinical detection. In conclusion, this assay is expected to provide a hopeful strategy for the early non-invasive diagnosis and prognostic estimation of cancer.