DNAzyme-functionalized porous carbon nanospheres serve as a fluorescent nanoprobe for imaging detection of microRNA-21 and zinc ion in living cells

The present study shows that a dual-signal nanoprobe consisting of DNAzyme-functionalized porous carbon nanospheres (PCNs) responds to microRNA-21 and zinc ion (Zn 2+ ). The fluorescent probe undergoes an increase in the fluorescence intensity of fluorescein isothiocyanate (FITC) (with excitation/emission wavelengths at 488/517 nm) and the fluorescence intensity of cyanine-5 (Cy5) (with excitation/emission wavelengths at 633/670 nm) in the presence of microRNA-21 and Zn 2+ . The recognition between microRNA-21 and its complementary strand in the PCNs induces the separation of Zn 2+ -specific DNAzyme from PCNs, thus resulting in the increase of green fluorescence, and the exogenous Zn 2+ triggers the rupture of cleavage strand of DNAzyme and recovery of red fluorescence. This nanoprobe allows us to acquire in vitro the determination of microRNA-21 in the range of 2–300 nM with a detection limit of 0.57 nM and the determination of Zn 2+ in the range 2–100 nM with a detection limit of 0.43 nM, and in situ simultaneous imaging in MCF-7 breast cancer cells. Therefore, this strategy permits to obtain the expression levels of different biomarkers in living cells, providing a useful tool for diagnosis of cancers and understanding their biological process. Schematic representation of the DNAzyme-functionalized porous carbon nanospheres for the imaging analysis of microRNA-21 and Zn2+ in living cells.