Metal-enhanced fluorescence/visual bimodal platform for multiplexed ultrasensitive detection of microRNA with reusable paper analytical devices.

Convenient biosensor for simultaneous multi-analyte detection was increasingly required in biological analysis. A novel flower-like silver (FLS)-enhanced fluorescence/visual bimodal platform for the ultrasensitive detection of multiple miRNAs was successfully constructed for the first time based on the principle of multi-channel microfluidic paper-based analytical devices (µPADs). Fluorophore-functionalized DNA (DNA-N-CDs) was combined with FLS, which was hybridized with quencher-carrying strand (DNA-CeO) to form FLS-enhanced fluorescence biosensor. Upon the addition of the target miRNA, the fluorescent intensity of DNA-N-CDs within the proximity of the FLS was strengthened. The disengaged DNA/CeO complex could result in color change after joining HO, leading to real-time visual detection of miRNA firstly. If necessary, then the fluorescence method was applied for a accurate determination. In this strategy, the growth of FLS in µPADs not only reduced the background fluorescence but also provided an enrichment of "hot spots" for surface enhanced fluorescence detection of miRNAs. Results also showed versatility of the FLS in the enhancement of sensitivity and selectivity of the miRNA biosensor. Remarkably, this biosensor could detect as low as 0.03fM miRNA210 and 0.06fM miRNA21. Interestingly, the proposed biosensor also possessed good capability of recycling in three cycles upon change of the supplementation of DNA-CeO and visual substitutive device. This method opened new opportunities for further studies of miRNA related bioprocesses and will provide a new instrument for simultaneous detection of multiple low-level biomarkers.