Ming Ma

Synthesis of Ultrathin Nitrogen-Doped Graphitic Carbon Nanocages as Advanced Electrode Materials for Supercapacitor

Synthesis of nitrogen-doped carbons with large surface area, high conductivity, and suitable pore size distribution is highly desirable for high-performance supercapacitor applications. Here, we report a novel protocol for template synthesis of ultrathin nitrogen-doped graphitic carbon nanocages (CNCs) derived from polyaniline (PANI) and their excellent capacitive properties. The synthesis of CNCs involves one-pot hydrothermal synthesis of Mn3O4@PANI core-shell nanoparticles, carbonization to produce carbon coated MnO nanoparticles, and then removal of the MnO cores by acidic treatment. The CNCs prepared at an optimum carbonization temperature of 800 °C (CNCs-800) have regular frameworks, moderate graphitization, high specific surface area, good mesoporosity, and appropriate N doping. The CNCs-800 show high specific capacitance (248 F g(-1) at 1.0 A g(-1)), excellent rate capability (88% and 76% capacitance retention at 10 and 100 A g(-1), respectively), and outstanding cycling stability (~95% capacitance retention after 5000 cycles) in 6 M KOH aqueous solution. The CNCs-800 can also exhibit great pseudocapacitance in 0.5 M H2SO4 aqueous solution besides the large electrochemical double-layer capacitance. The excellent capacitance performance coupled with the facile synthesis of ultrathin nitrogen-doped graphitic CNCs indicates their great application potential in supercapacitors.

Synthesis and oxygen reduction properties of three-dimensional sulfur-doped graphene networks.

Novel three-dimensional sulfur-doped graphene networks were synthesized using an ion-exchange/activation combination method using a 732-type sulfonic acid ion exchange resin as the carbon precursor, which showed high electrocatalytic activity, good stability and excellent methanol tolerance for four-electron oxygen reduction in alkaline solution.

Improved GFP gene transfection mediated by polyamidoamine dendrimer-functionalized multi-walled carbon nanotubes with high biocompatibility

The multi-walled carbon nanotubes (MWCNTs)-polyamidoamine (PAMAM) hybrid was prepared by covalent linkage approach, and characterized by transmission electron microscopy, Fourier transform infrared spectroscopy and ultraviolet-visible spectrometry. The PAMAM dendrimers were present on the surface of MWCNTs in high density, and the MWCNT-PAMAM hybrid exhibited good dispersibility and stability in aqueous solution. The interaction between MWCNT-PAMAM with plasmid DNA of enhanced green fluorescence protein (pEGFP-N1), intracellular trafficking of the hybrid, transfection performance and cytotoxicity to HeLa cells were evaluated in detail. We found that the MWCNT-PAMAM hybrid possessed good pEGFP-N1 immobilization ability and could efficiently delivery GFP gene into cultured HeLa cells. The surface modification of MWCNTs with PAMAM improved the transfection efficiency 2.4 and 0.9 times, and simultaneously decreased cytotoxicity by about 38%, as compared with mixed acid-treated MWCNTs and pure PAMAM dendrimers. The MWCNT-PAMAM hybrid can be considered as a new carrier for the delivery of biomolecules into mammalian cells. Therefore, this novel system may have good potential applications in biology and therapy, including gene delivery systems.

Immobilization of enzymes at high load/activity by aqueous electrodeposition of enzyme-tethered chitosan for highly sensitive amperometric biosensing.

Electrodeposition has been so widely used to immobilize biomacromolecules, and it is always an important topic to increase the load and activity of the immobilized biomacromolecules. We report here on a new, simple and rather universal method for the highly efficient immobilization of enzymes by aqueous electrodeposition of enzyme-tethered chitosan (CS) for sensitive amperometric biosensing. Glucose oxidase (GOx) is chosen here to examine the proposed protocol in detail. GOx was crosslinked to CS with low-concentration glutaraldehyde (GA, 0.080 wt%), and the electroreduction of added H(2)O(2) increased the electrode-surface pH and triggered the electrodeposition of a GOx-GA-CS composite film. The GOx-GA-CS electrodeposition was monitored by an electrochemical quartz crystal microbalance and is theoretically discussed based on an electrogenerated base-to-acid titration model. The prepared first-generation enzyme electrode (CS-GA-GOx/Pt(nano)/Au) exhibits a current sensitivity as high as 102 microA mM(-1) cm(-2) at 0.70 V vs SCE, being 13 times that of the CS-GOx/Pt(nano)/Au prepared similarly but without the GOx-CS precrosslinking. UV-vis spectrophotometric determination of the GOx remains in the supernatant liquids after pH-induced CS precipitation suggested a high enzyme load in the GOx-GA-CS film, and amperometric measurements suggested a negligible decrease in the enzymatic activity of GOx after its reaction with the low-concentration GA. Also, the proposed protocol works well for the precrosslinking manner of 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide/N-hydroxysulfosuccinimide activation, the water-electroreduction-triggered CS electrodeposition, the second-generation biosensing mode, a 5.0-microm-radius Pt ultramicroelectrode, and immobilization of alkaline phosphatase for phenyl phosphate biosensing. The proposed protocol of pretethering the target biomacromolecules to the electrodeposition precusor for immobilization of the biomacromolecule at high load/activity is recommended for wide applications.

Three-Dimensional Graphene Networks as a New Substrate for Immobilization of Laccase and Dopamine and Its Application in Glucose/O2 Biofuel Cell

We report here three-dimensional graphene networks (3D-GNs) as a novel substrate for the immobilization of laccase (Lac) and dopamine (DA) and its application in glucose/O2 biofuel cell. 3D-GNs were synthesized with an Ni(2+)-exchange/KOH activation combination method using a 732-type sulfonic acid ion-exchange resin as the carbon precursor. The 3D-GNs exhibited an interconnected network structure and a high specific surface area. DA was noncovalently functionalized on the surface of 3D-GNs with 3,4,9,10-perylene tetracarboxylic acid (PTCA) as a bridge and used as a novel immobilized mediating system for Lac-based bioelectrocatalytic reduction of oxygen. The 3D-GNs-PTCA-DA nanocomposite modified glassy carbon electrode (GCE) showed stable and well-defined redox current peaks for the catechol/o-quinone redox couple. Due to the mediated electron transfer by the 3D-GNs-PTCA-DA nanocomposite, the Nafion/Lac/3D-GNs-PTCA-DA/GCE exhibited high catalytic activity for oxygen reduction. The 3D-GNs are proven to be a better substrate for Lac and its mediator immobilization than 2D graphene nanosheets (2D-GNs) due to the interconnected network structure and high specific surface area of 3D-GNs. A glucose/O2 fuel cell using Nafion/Lac/3D-GNs-PTCA-DA/GCE as the cathode and Nafion/glucose oxidase/ferrocence/3D-GNs/GCE as the anode can output a maximum power density of 112 μW cm(-2) and a short-circuit current density of 0.96 mA cm(-2). This work may be helpful for exploiting the popular 3D-GNs as an efficient electrode material for many other biotechnology applications.

Facile fabrication of network film electrodes with ultrathin Au nanowires for nonenzymatic glucose sensing and glucose/O2 fuel cell.

We report here on the facile fabrication of network film electrodes with ultrathin Au nanowires (AuNWs) and their electrochemical applications for high-performance nonenzymatic glucose sensing and glucose/O2 fuel cell under physiological conditions (pH 7.4, containing 0.15M Cl(-)). AuNWs with an average diameter of ~7 or 2 nm were prepared and can self-assemble into robust network films on common electrodes. The network film electrode fabricated with 2-nm AuNWs exhibits high sensitivity (56.0 μA cm(-2)mM(-1)), low detection limit (20 μM), short response time (within 10s), excellent selectivity, and good storage stability for nonenzymatic glucose sensing. Glucose/O2 fuel cells were constructed using network film electrodes as the anode and commercial Pt/C catalyst modified glassy carbon electrode as cathode. The glucose/O2 fuel cell using 2-nm AuNWs as anode catalyst output a maximum power density of is 126 μW cm(-2), an open-circuit cell voltage of 0.425 V, and a short-circuit current density of 1.34 mA cm(-2), respectively. Due to the higher specific electroactive surface area of 2-nm AuNWs, the network film electrode fabricated with 2-nm AuNWs exhibited higher electrocatalytic activity toward glucose oxidation than the network film electrode fabricated with 7-nm AuNWs. The network film electrode exhibits high electrocatalytic activity toward glucose oxidation under physiological conditions, which is helpful for constructing implantable electronic devices.

Sulfur-doped porous carbon nanosheets as an advanced electrode material for supercapacitors

Direct carbonization and simultaneous chemical activation of a cobalt ion-impregnated sulfonic acid ion exchange resin is found to be an efficient approach to the large-scale synthesis of sulfur-doped porous carbon nanosheets (S-PCNS) for supercapacitors with high specific energy and excellent rate capability. The as-prepared S-PCNS showed a three-dimensional interconnected structure, high graphitization degree, high C/O atomic ratio (22.9 : 1), high-level sulfur doping (9.6 wt%), high specific surface area (2005 m2 g−1), and good porosity. The S-PCNS serving as an electrode material for supercapacitors exhibited a specific capacitance as high as 312 F g−1 at 0.5 A g−1, excellent rate capability (78% of capacitance retention at 50 A g−1), high energy density (11.0 W h kg−1 at 0.5 A g−1), and outstanding cycling stability (∼97% of its initial capacitance after 10 000 cycles at 2 A g−1) in 6.0 M aqueous KOH electrolyte. Due to the unique structure of S-PCNS, the specific capacitance of S-PCNS is higher than that of sulfur-doped activated carbon. The excellent capacitance performance coupled with the facile synthesis of S-PCNS indicates a potential electrode material for supercapacitors.

Polyamidoamine dendrimer and oleic acid-functionalized graphene as biocompatible and efficient gene delivery vectors.

Functionalized graphene has good potential in biomedical applications. To address a better and multiplex design of graphene-based gene vectors, the graphene-oleate-polyamidoamine (PAMAM) dendrimer hybrids were synthesized by the oleic acid adsorption and covalent linkage of PAMAM dendrimers. The micromorphology, electrical charge property, and amount of free amine groups of the graphene-oleate-PAMAM hybrids were characterized, and the peripheral functional groups were identified. The PAMAM dendrimers could be tethered onto graphene surface in high density. The graphene-oleate-PAMAM hybrids exhibit relatively good dispersity and stability in aqueous solutions. To evaluate the potential application of the hybrids in gene delivery vectors, cytotoxicity to HeLa and MG-63 cells and gene (plasmid DNA of enhanced green fluorescent protein) transfection capacity of the hybrids were investigated in detail. The graphene-oleate-PAMAM hybrids show mammalian cell type- and dose-dependent in vitro cytotoxicity. Under the optimal condition, the hybrids possess good biocompatibility and gene transfection capacity. The surface modification of graphene with oleic acid and PAMAM improves the gene transfection efficiency 13 times in contrast to the ultrasonicated graphene. Moreover, the hybrids show better transfection efficiency than the graphene oxide-PAMAM without the oleic acid modification.

Carrier-mediated liquid phase microextraction coupled with high performance liquid chromatography for determination of illicit drugs in human urine

A new method was developed for the analysis of illicit drugs in human urine by coupling carrier-mediated liquid phase microextraction (LPME) to high performance liquid chromatography (HPLC). By adding an appropriate carrier in organic phase, simultaneous extraction and enrichment of hydrophilic (morphine and ephedrine) and hydrophobic (pethidine) drugs were achieved. Effects of the types of organic solvents and carriers, the carrier concentration in the organic phase, the HCl concentration in the acceptor solution, the stirring rate, and the extraction time on the enrichment factor of analytes were investigated. Under the optimal experimental conditions, high enrichment factors (202-515) were obtained. The linear detection ranges were 0.1-10mgL(-1) for the studied drugs. The limits of detection (LOD) at signal-to-noise ratio of 3 were 0.05mgL(-1) for both morphine and ephedrine, and 0.02mgL(-1) for pethidine. This method was successfully applied to analysis of ephedrine in real urine specimens, revealing that the determination of illicit drugs in urine was feasible.

Electrochemical quartz crystal microbalance studies on enzymatic specific activity and direct electrochemistry of immobilized glucose oxidase in the presence of sodium dodecyl benzene sulfonate and multiwalled carbon nanotubes.

The electrochemical quartz crystal microbalance (EQCM) technique was utilized to monitor in situ the adsorption of glucose oxidase (GOD) and the mixture of GOD and sodium dodecyl benzene sulfonate (SDBS) onto Au electrodes with and without modification of multiwalled carbon nanotubes (MWCNTs) or SDBS/MWCNTs composite, and the relationship between enzymatic specific activity (ESA) and direct electrochemistry of the immobilized GOD was quantitatively evaluated for the first time. Compared with the bare gold electrode at which a little GOD was adsorbed and the direct electrochemistry of the adsorbed GOD was negligible, the amount and electroactivity of adsorbed GOD were greatly enhanced when the GOD was mixed with SDBS and then adsorbed onto the SDBS/MWCNTs modified Au electrode. However, the ESA of the adsorbed GOD was fiercely decreased to only 16.1% of the value obtained on the bare gold electrode, and the portion of adsorbed GOD showing electrochemical activity exhibited very low enzymatic activity, demonstrating that the electroactivity and ESA of immobilized GOD responded oppositely to the presence of MWCNTs and SDBS. The ESA results obtained from the EQCM method were well supported by conventional UV-vis spectrophotometry. The direct electrochemistry of redox proteins including enzymes as a function of their biological activities is an important concern in biotechnology, and this work may have presented a new and useful protocol to quantitatively evaluate both the electroactivity and ESA of trace immobilized enzymes, which is expected to find wider applications in biocatalysis and biosensing fields.