Target-triggered DNA nanoassembly on quantum dots and DNAzyme-modulated double quenching for ultrasensitive microRNA biosensing.

Herein, a simple and novel fluorescence biosensing strategy has been developed for ultrasensitive determination of microRNA (miRNA) by combining target-triggered DNA nanoassembly on quantum dots (QDs) with DNAzyme-modulated double quenching of QDs. In presence of miRNA target, the target triggered catalytic hairpin assembly (CHA) amplification and powered highly efficient DNA nanoassembly on the surface of QDs, leading to exhibition of numerous G-quadruplexes close to the QDs. The G-quadruplex folded properly and bound hemin to form a stable G-quadruplex/hemin complex. Then the luminescence of QDs was quenched via photoinduced electron transfer by hemin associated with the particles and the electron acceptor of O2 which was in situ generated with the horseradish peroxidase-mimicked G-quadruplex/hemin DNAzymes toward H2O2. Based on this target-triggered highly efficient DNA nanoassembly and DNAzyme-modulated double quenching mechanism, the proposed biosensing strategy showed admirable signal amplification capability. Using miRNA-21 as model analyte, the designed nanosensor could detect miRNA down to 37 fM with a wide linear detection range of 1×10-13M to 1.0×10-8M, and exhibited good selectivity, acceptable reproducibility and low matrix effect. This proposed strategy presented a simple, powerful platform toward ultrasensitive miRNA detection and had great potential for bioanalysis and clinic diagnostic application.