pH-responsive ZnO nanoprobe mediated DNAzyme signal amplification strategy for sensitive detection and live cell imaging of multiple microRNAs

Here, a pH-responsive ZnO nanoprobe mediated DNAzyme signal amplification strategy was proposed for sensitive detection and live cell imaging of multiple microRNAs. The nanoprobe including ZnO nanoparticles (ZnO NPs) core as carrier and cofactor provider and polydopamine shell for adsorption the functional hairpin DNAs was designed. When nanoprobe entered the cell through endocytosis, the acidic environment of the cell could decompose the ZnO NPs core to release the functional hairpin DNAs and Zn2+. The Zn2+ could act as cofactor for the DNAzyme cleavage amplification reaction, avoiding additional cell delivery processes. The recognition hairpin DNAs (H1 and H3) recognized microRNA and exposed the DNAzyme. The DNAzyme cleaved cyclically the reporter hairpin DNAs (H2 and H4), producing enhanced fluorescent signal for miR-21 and miR-373 detection with the detection limit of 54 pM and 38 pM, respectively. Expression levels of miR-21 in Hela, HepG-2 and L02 cells were differentiated. Furthermore, simultaneous imaging of miR-21 and miR-373 in same living cells was achieved. These results indicated this strategy could have a potential application in microRNAs assays for the accurate diagnosis and therapy of cancer.