Abstract

MiRNAs have long been regarded as reliable biomarkers for the early diagnosis of various diseases including cancer. By combining catalytic hairpin assembly (CHA) and DNA walking cascade amplification, we constructed a 3D DNA walker and turn-on fluorescence sensing system for an ultrasensitive detection of miRNA-21 (miR-21). The presence of miR-21 triggers the CHA among three exquisitely designed hairpins (HP1, HP2, and HP3) to form the tripedal DNA walkers. As the walking trajectories, FAM-labeled hairpins (HP4) were attached on gold nanoparticles (AuNPs), the fluorescence of which was initially quenched due to its close proximity to AuNPs. After binding/cleaving/walking process between tripedal DNA walkers and HP4 driven by nuclease, a number of ssDNAs will be generated with FAM fluorescence recovered.

Benefiting from the cascade amplification, the strategy shows a remarkably low detection limit at atto-molar level. The precise design of the system enables excellent specificity in distinguishing miR-21 from its single-, double-mismatched and non-complementary sequences, demonstrating great versatility and potential for the early diagnostics and clinical analysis.