Qiaoli Yue

High-Resolution Separation of Graphene Oxide by Capillary Electrophoresis

Separation and purification of graphene oxide (GO) prepared from chemical oxidation of flake graphite and ultrasonication by capillary electrophoresis (CE) was demonstrated. CE showed the ability to provide high-resolution separations of GO fractionations with baseline separation. The GO fractionations after CE were collected for Raman spectroscopy, atomic force microscopy, and transmission electron microscopy characterizations. GO nanoparticles (unexfoliated GO) or stacked GO sheets migrated toward the anode, while the thin-layer GO sheets migrated toward the cathode. Therefore, CE has to be performed twice with a reversed electric field to achieve a full separation of GO. This separation method was suggested to be based on the surface charge of the GO sheets, and a separation model was proposed. This study might be valuable for fabrication of GO or graphene micro- or nanodevices with controlled thickness.

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.

How far can hydroxyl radicals travel? An electrochemical study based on a DNA mediated electron transfer process

Using photocatalytic reactive nanoparticles and DNA composite modified gold electrodes, exploiting the sensitivity of DNA-mediated electron transfer to base pair stacking, we examined the effects of DNA oxidation damage by photocatalytically generated hydroxyl radicals (˙OH) on charge transfer efficiency and proposed an electrochemical technique to read the effective diffusing distance of ˙OH.

Antioxidant Sensors Based on Iron Diethylenetriaminepentaacetic Acid, Hematin, and Hemoglobin Modified TiO2 Nanoparticle Printed Electrodes

Antioxidant amperometric sensors based on iron-containing complexes and protein modified electrodes were developed. Indium tin oxide glass was printed with TiO(2) nanoparticles, onto which iron-containing compounds and protein were adsorbed. When applied with negative potentials, the dissolved oxygen is reduced to H(2)O(2) at the electrode surface, and the H(2)O(2) generated in situ oxidizes Fe(II) to Fe(III), and then electrochemical reduction of Fe(III) therefore gives rise to a catalytic current. In the presence of antioxidants, H(2)O(2) was scavenged, the catalytic current was reduced, and the decreased current signal was proportional to the quantity of existing antioxidants. A kinetic model was proposed to quantify the H(2)O(2) scavenging capacities of the antioxidants. With the use of the sensor developed here, antioxidant measurements can be done quite simply: put the sensor into the sample solutions (in aerobic atmosphere), perform a cathodic polarization scan, and then read the antioxidant activity values. The present work can be complementary to the previous studies of antioxidant sensor techniques based on OH radicals and superoxide ions scavenging methods, but the sensor developed here is much easier to fabricate and use.

A reusable aptasensor of thrombin based on DNA machine employing resonance light scattering technique

The design of molecular nanodevices attracted great interest in these years. Herein, a reusable, sensitive and specific aptasensor was constructed based on an extension-contraction movement of DNA interconversion for the application of human thrombin detection. The present biosensor was based on resonance light scattering (RLS) using magnetic nanoparticles (MNPs) as the RLS probe. MNPs coated with streptavidin can combine with biotin labeled thrombin aptamers. The combined nanoparticles composite is monodispersed in aqueous medium. When thrombin was added a sandwich structure can form on the surface of MNPs, which induced MNPs aggregation. RLS signal was therefore enhanced, and there is a linear relationship between RLS increment and thrombin concentration in the range of 60pM-6.0nM with a limit of detection at 3.5pM (3.29SB/m, according to the recent recommendation of IUPAC). The present aptasensor can be repeatedly used for at least 6 cycling times by heat to transfer G-quadruplex conformation to single strand of DNA sequence and release thrombin. MNPs can be captured by applying the external magnetic field. Furthermore, the proposed biosensor was successfully applied to detect thrombin in human plasma.

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.