Novel Fluorescence Switch for MicroRNA Imaging in Living Cells Based on DNAzyme Amplification Strategy.

MicroRNAs (miRNAs) play important roles in the regulation of target gene expression and cell development. Therefore, developing of accurate and visual detection methods for miRNAs is important for early diagnosis of cancer. In this study, we established a visual detection method for miRNA 155 based on DNAzyme amplification strategy in living cells. MnO2 nanosheets were employed to deliver locked DNAzyme and substrate DNA into cells. The gold nanoparticle (AuNP) probe was taken up by cells autonomously. Then, MnO2 nanosheets were reduced to Mn2+ by glutathione in cells and DNA modules were released. MiRNA 155 took away locker DNA by strand displacement reaction to activate the DNAzyme. Then, the DNAzyme cleaved the substrate DNA and released single-stranded DNA named key DNA. Then, Key DNA hybridized with the hairpin DNA, making cy5 far away from AuNP and turning on its fluorescence. One target miRNA led to plenty of released key DNA when lots of substrate DNA was added. Thus, the visual detection of miRNA 155 in living cells would be initiated. Under confocal laser microscopy, the fluorescence was obviously observed in tumor cells but not in normal cells. The method has a linear range from 0.1 to 10 nM and a low detection limit of 44 pM on in vitro detection.