Shuling Xu

Highly sensitive fluorescence assay of DNA methyltransferase activity by methylation-sensitive cleavage-based primer generation exponential isothermal amplification-induced G-quadruplex formation

Site-specific identification of DNA methylation and assay of MTase activity are imperative for determining specific cancer types, provide insights into the mechanism of gene repression, and develop novel drugs to treat methylation-related diseases. Herein, we developed a highly sensitive fluorescence assay of DNA methyltransferase by methylation-sensitive cleavage-based primer generation exponential isothermal amplification (PG-EXPA) coupled with supramolecular fluorescent Zinc(II)-protoporphyrin IX (ZnPPIX)/G-quadruplex. In the presence of DNA adenine methylation (Dam) MTase, the methylation-responsive sequence of hairpin probe is methylated and cleaved by the methylation-sensitive restriction endonuclease Dpn I. The cleaved hairpin probe then functions as a signal primer to initiate the exponential isothermal amplification reaction (EXPAR) by hybridizing with a unimolecular DNA containing three functional domains as the amplification template, producing a large number of G-quadruplex nanostructures by utilizing polymerases and nicking enzymes as mechanical activators. The G-quadruplex nanostructures act as host for ZnPPIX that lead to supramolecular complexes ZnPPIX/G-quadruplex, which provides optical labels for amplified fluorescence detection of Dam MTase. While in the absence of Dam MTase, neither methylation/cleavage nor PG-EXPA reaction can be initiated and no fluorescence signal is observed. The proposed method exhibits a wide dynamic range from 0.0002 to 20U/mL and an extremely low detection limit of 8.6×10(-5)U/mL, which is superior to most conventional approaches for the MTase assay. Owing to the specific site recognition of MTase toward its substrate, the proposed sensing system was able to readily discriminate Dam MTase from other MTase such as M.SssI and even detect the target in a complex biological matrix. Furthermore, the application of the proposed sensing strategy for screening Dam MTase inhibitors was also demonstrated with satisfactory results. This novel method not only provides a promising platform for monitoring activity and inhibition of DNA MTases, but also shows great potentials in biological process researches, drugs discovery and clinical diagnostics.

Te-template approach to fabricating ternary TeCuPt alloy nanowires with enhanced catalytic performance towards oxygen reduction reaction and methanol oxidation reaction

Fabricating ternary Pt-based alloys has emerged as a promising strategy to further enhance the catalytic performance of Pt catalysts in direct methanol fuel cells (DMFCs) for both the oxygen reduction reaction (ORR) and the methanol oxidation reaction (MOR). Herein, we reported for the first time the synthesis of ternary TeCuPt nanowires (NWs) by a Te-template-directed galvanic replacement reaction, in which Te NWs serve as both sacrificial templates and reducing agents. Compared with a binary TePt alloy and pure Pt catalysts, the ternary TeCuPt alloys exhibit a more positive half-wave potential and a higher specific area/mass activity for ORR, and also display a better CO tolerance ability and long-term stability for MOR. The enhanced catalytic performance for TeCuPt NWs is attributed to the electronic and geometric structure effects, originating from the Pt alloying with both Te and Cu components, which could weaken the binding strength between the Pt surface atoms and the intermediate species (e.g. OH*, CO*). Our studies have demonstrated a new alternative ternary Pt-based catalyst for both ORR and MOR, which could find application in DMFC.

One-pot synthesis of Ag@Cu yolk–shell nanostructures and their application as non-enzymatic glucose biosensors

In this report, Ag@Cu yolk–shell nanostructures have been synthesized through a facile one-pot hydrothermal method. The synthesis is based on the use of N,N-dimethylformamide (DMF) as both the reducing agent and solvent, in the presence of the polymer poly(vinylpyrrolidone) (PVP). The structure and composition of the yolk–shell nanostructures were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive spectrometry (EDS). To study the formation process of the Ag@Cu yolk–shell nanostructures, the samples obtained at various stages of the growth process were studied by TEM and XRD, and a rational growth mechanism for the Ag@Cu yolk–shell nanostructures was proposed. The as-prepared Ag@Cu yolk–shell nanostructures were used to construct non-enzymatic glucose sensors. The detecting results show that the designed sensors have well-defined, stable and fast amperometric responses to glucose.

A reusable and sensitive biosensor for total mercury in canned fish based on fluorescence polarization

In this work, we developed a sensitive and selective sensor technique for total mercury (Hg) detection in canned fish samples based on the fluorescence polarization (FP) method. The detection principle was that ssDNA containing thymine (T) bases was modified on magnetic nanoparticles (MNPs), which were used as enhancement probe. In the presence of Hg(2+), the ssDNA on MNPs can hybridize with the fluorophore labeled aptamer owing to the specific interaction between T bases and Hg(2+). The formation of thymine-Hg(2+)-thymine (T-Hg(2+)-T) complexes leads to the molar mass increase of fluorophore molecules, resulting in the enhancement of FP signal. The increase of FP was in a good linearity with the concentration of Hg(2+) in range of 2.0 nM-1.0 mM and the limit of detection was 0.49 nM (3.29 SB/m, according to the recent recommendation of IUPAC). Moreover, the proposed biosensor can be reused for 6 cycling times and was successfully applied in monitoring Hg(2+) in real samples.

Facet-dependent electrochemiluminescence spectrum of nanostructured ZnO

A facet-dependent electrochemiluminescence (ECL) behavior was found for nanostructured ZnO with different dominant exposing planes. The ECL spectrum of nanostructured ZnO was recorded by the emission scan mode with a fluorescence spectrometer and applied to investigate the difference of surface state for different crystal planes. Electronic structure calculations based on density functional theory were used to study the effect of crystal plane on the band structure and density of states. It revealed that the ECL emission was originated primarily from the recombination of electrons from Zn 4s and the hole from O 2p, which could be utilized to study the physical and chemical properties of surface structures of as-prepared nanostructured ZnO. A physical model was suggested to elucidate the differences of ECL spectra. A concept was proposed that the energy released as photons during ECL process of nanocrystalline semiconductor materials will be correlated with the energy level of active sites located at different crystal planes.

Study for the electrochemical deposition on single carbon fiber and electrochemiluminescence of ZnO nanostructures

In this work, ZnO nano-needles were electrochemically deposited onto the surface of single carbon fiber. The influence of deposition condition on the surface morphology of ZnO nanostructures was investigated. A growth mechanism was suggested to elucidate the deposition process. Electrochemiluminescence conducted in 0.1 M KOH solution containing 0.1 M K2S2O8 and 0.1 M KCl displayed the stable and sensitive luminescent property of as-prepared ZnO nano-needles. The electrochemiluminescence intensity per projection area from ZnO nano-needles deposited on single carbon fiber was almost five orders of magnitude larger than that from ZnO nanostructures deposited on ITO and ZnO dip-coated on ITO. It demonstrated the high electrochemiluminescence efficiency of ZnO nano-needles deposited on single carbon fiber and the remarkable electrical conductivity of carbon fiber. This work presented a new strategy to deposit oxides on carbon fiber with tunable coverage and nanostructure. Furthermore, the excellent electrochemiluminescence property of ZnO nano-needles on carbon fiber highlights the importance and potential utility of such nanostructures in the development of optoelectronic and biomedical devices.

Study on the morphology-controlled synthesis of MnCO3 materials and their enhanced electrochemical performance for lithium ion batteries

In this work, monodispersed and high quality crystalline MnCO3 micro-peanuts and MnCO3 nano-shuttles were prepared by a simple hydrothermal method. A growth mechanism was proposed to elucidate the influence of reactant components on the morphology and size of the prepared MnCO3 samples. Both structures were employed as active electrode materials in lithium ion batteries. The electrochemical performance of the obtained MnCO3 samples was examined by analyzing the cyclic voltammograms, galvanostatic charge–discharge, rate performance and electrochemical impedance. At a current rate of 250 mA h g−1, the reversible capacity of the MnCO3 nano-shuttle electrode after 500 cycles was 605 mA h g−1, while that of the MnCO3 micro-peanut electrode was 463.4 mA h g−1. The results indicated that the MnCO3 samples synthesized by this method presented wonderful electrochemical properties, which could be used as promising active materials in lithium ion batteries.

CTAB-reduced synthesis of urchin-like Pt–Cu alloy nanostructures and catalysis study towards the methanol oxidation reaction

Urchin-like PtCu alloy nanostructures were fabricated using a facile co-reduction approach, and the cationic surfactant cetyltrimethylammonium bromide (CTAB) served as the reducing agent. The reaction temperature highly influenced the reducing activity of CTAB, and no reducing activity was exhibited when the reaction temperature was below 120 °C. During the formation process of urchin-like PtCu alloy nanostructures, partial CTAB firstly reacted with H2PtCl6 to produce a yellow colloid precipitation, which could reduce the generation rate of Pt atoms and benefit the alloying of Cu with metallic Pt to form the PtCu alloy. Compared with pure Pt, the PtCu alloy catalyst exhibited a much higher catalytic efficiency and stability towards the methanol oxidation reaction. It was proposed that the enhanced catalytic activity of the PtCu alloy was attributed to the downshift of the d-band center of Pt, which greatly reduced the affinity energy with CO* intermediate species.

Construction of a controllable Förster resonance energy transfer system based on G-quadruplex for DNA sensing.

Conjugations of oligonucleotides, chromophores, and gold nanoparticles (GNPs) can be used for energy transfer assays to detect DNA. Herein, a homogenous Förster resonance energy transfer (FRET) system employing two-step modification of oligonucleotide on GNPs was reported. The distance between the donor (fluorescein attached onto DNA) and the acceptor (GNPs) was controlled by using the G-rich DNA. In the presence of porphyrin or berberine, which can act as ligands of G-quadruplexes, the G-rich DNA spacer can result into G-quadruplex structure. Therefore, the intimate contact between the fluorophore and the GNP results in efficient energy transfer and fluorescence quenching. After hybridization with target DNA, the G-quadruplex stretched and resulted in an enhancement of fluorescence. So the present FRET system can be used for target DNA sensing with detection limit as low as 40 pM (S/N=3). In this study, a relation between the fluorescence quenching efficiency and GNP sizes was found and bigger GNPs had higher fluorescence enhancement after hybridization with target DNA.

Electrocatalytic study of a 1,10-phenanthroline–cobalt(II) metal complex catalyst supported on reduced graphene oxide towards oxygen reduction reaction

A new class of oxygen reduction reaction (ORR) catalyst was fabricated by loading a 1,10-phenanthroline–cobalt(II) metal-complex onto reduced graphene oxide (rGO) surfaces by π–π interaction. The Co(II)–N4 was the active center of the metal-complex catalyst and catalyzed the ORR via a highly efficient four-electron reduction pathway. The introduction of the nitro-group substituent in 1,10-phenanthroline highly boosted the catalytic activity of the metal complex in terms of half-wave potential (E1/2) and kinetic current density (JK), due to the downshift of the eg-orbital energy level for central Co(II) resulting from the electron-withdrawing effect of the nitro group. Considering the configuration of the metal complex on rGO surfaces, a single cobalt center-mediated catalytic mechanism was proposed to elucidate the ORR process. Compared with the commercial Pt/C catalyst, the as-prepared metal-complex catalyst exhibited a superior methanol tolerance and catalytic durability for the ORR. Our study provides more information about the relationship between the molecular structure and catalytic activity towards the ORR.