Enzyme- and label-free fluorescence microRNA biosensor based on the distance-dependent photoinduced electron transfer of DNA/Cu nanoparticles

Herein, we report a convenient enzymeand label-free fluorescent biosensor for the quantitative detection of microRNA (miRNA). It is the first time that the distance-dependent property of photoinduced electron transfer (PET) has been observed between G-quadruplex/hemin (G/hemin) complexes and fluorescent DNA/Cu nano particles (NPs), accompanied by the change of the fluorescence intensity from DNA/Cu NPs. This innovative PET system could achieve the sensitive and specific determination of nucleic acids such as DNA and RNA based on the design of versatile detection sequences. With the existence of the target miRNA, the original flexible single-strand DNA detection probe becomes rigid DNA/RNA heteroduplexes. Therefore the PET could be hindered because of the prolonged distance from the electron donor-Cu NPs to electron acceptor-G/hemin complexes. Hence, a fluorescence light-up miRNA biosensor was established via the monitoring of the fluorescence signal of the formed DNA/Cu NPs. Compared to other reported PET-based miRNA determination methods, the distance dependent PET of Cu NPs-based biosensor only needs to adjust the detection probe sequences for various miRNAs assays. This strategy is effective for the determination of the miRNA let-7a over a linear range of 0.5 to 100 nM, with a relatively low limit of detection of 0.2 nM. Besides, this novel assay has been successfully employed for the enzymeand label-free fluorescence detection of miRNA from real samples.

Automated summary

This study presents a novel method for quantitative detection of miRNA, utilizing the distance-dependent property of photoinduced electron transfer between G-quadruplex/hemin complexes and DNA/Cu nano particles. The method enables the sensitive and specific determination of miRNA let-7a with a relatively low limit of detection, and has been successfully applied for enzymeand label-free fluorescence detection of miRNA from real samples.