MicroRNAs (miRNAs) play important roles in cell differentiation, proliferation, and apoptosis and have been recognized as valuable biomarkers for clinical disease diagnosis. Here, we adopt for the first time zeolitic imidazolate framework-8 (ZIF-8) as a nanocarrier to efficiently deliver a nucleic acid probe to living cells and develop a novel ratiometric fluorescence strategy based on DNAzyme for miRNA-21 imaging. A Cy5-labeled 8-17 DNAzyme strand and a Cy3-labeled substrate strand containing a segment complementary to the target miRNA-21 first form a duplex probe, and fluorescence resonance energy transfer (FRET) takes place. After adsorption on the ZIF-8 surface and cellular uptake, the probe/ZIF-8 nanocomplex degrades in acidic endosome and releases duplex probes and Zn2+, and the latter can act as an effective cofactor for 8-17 DNAzyme. The intracellular miRNA-21 hybridizes with the complementary segment of the substrate strand and results in dissociation from the DNAzyme–substrate duplex probe after DNAzyme cleaves the substrate into two fragments, accompanied by the change in the FRET signal. The proposed method has been applied to image miRNA-21 expression levels in MCF-7, HeLa, and L02 cells with high contrast and reliability. The fluctuation of miRNA-21 expression level induced by miRNA-21 mimic or inhibitor can also be monitored through the obvious imaging color change. Taken together, the proposed method provides a powerful tool for cancer diagnosis and miRNA-associated biological study.

Developing non-expensive, highly active and highly stable electrocatalysts for hydrogen evolution has aroused extensive attention, owing to the necessity of novel clean and sustainable energy carriers. In this paper, we report a synthesis of free-standing three-dimensional hierarchical MoS2/CoS2 heterostructure arrays through a convenient process. The investigation of electrocatalytic HER performance suggests that the MoS2/CoS2 hybrid catalyst exhibits significant enhancement in HER (onsetpotential and potential at a current density of 100 mA cm−2 are 20 mV and 125 mV, respectively) and superior durability (no shift of current density is observed after a continuous scanning of 3000 times) compared with individual CoS2 and MoS2. The superior HER performance was attributed to the formation of the interface between CoS2 and MoS2 through the electrochemical characterization, Raman, XPS analysis, and the control experiment. The lower onsetpotential, higher current density, excellent durability, and the free-standing structure of the three-dimensional hierarchical MoS2/CoS2 heterostructure array make it a promising cathode catalyst suitable for widespread application.Free-standing hierarchical MoS2/CoS2 heterostructure arrays were fabricated through a convenient process, which are highly active and stable as HER catalysts.Download high-res image (199KB)Download full-size image

In this work, we report the synthesis of mesoporous carbon derived from nonporous MOFs without any heteroatom doping or residual metal, which is highly efficient for the electrocatalytic oxygen reduction reaction. The excellent ORR activity is attributed to both high specific surface area and mesoporous structure.

In this work, we report the synthesis of mesoporous carbon derived from nonporous MOFs without any heteroatom doping or residual metal, which is highly efficient for the electrocatalytic oxygen reduction reaction. The excellent ORR activity is attributed to both high specific surface area and mesoporous structure.