Jianshan Ye

Pt–Pb alloy nanoparticle/carbon nanotube nanocomposite: a strong electrocatalyst for glucose oxidation

A Pt–Pb alloy nanoparticle/multi-walled carbon nanotube (Pt–Pb/MWCNT) nanocomposite was prepared by electrodepositing Pt–Pb alloy onto MWCNTs that were vertically aligned on Ta plates. The 10–40 nm diameter Pt–Pb alloy nanoparticles were mainly deposited at the tips, and sparsely dispersed on the sidewalls of the bamboo-like MWCNTs, as demonstrated by scanning electron microscopy, transmission electron microscopy (TEM), and x-ray diffraction. The high resolution TEM (HRTEM) image showed a snowflake-like morphology for the Pt–Pb nanoparticles. This Pt–Pb/MWCNT nanocomposite exhibited much stronger electrocatalytic activity toward glucose oxidation than pristine MWCNTs, Pt–Pb on glassy carbon, and Pt/MWCNT and Au/MWCNT nanocomposites, in both neutral and alkaline solutions. This Pt–Pb/MWCNT nanocomposite electrode is hence promising for development as a nonenzymatic glucose sensor.

Nanostructured platinum-lipid bilayer composite as biosensor.

The present work describes the preparation of supported bilayer lipid membrane (s-BLM) doped with metal nanoparticles for the design of biosensors. Platinum (Pt) nanoparticles were deposited through s-BLM to build a hybrid device of nanoscale electrode array by potential cycling in 1 mM K(2)PtCl(6) solution containing 0.1 M KCl. The properties of Pt nanoparticle-doped s-BLM composite were then characterized by cyclic voltammetry, electrochemical impedance spectroscopy (EIS) and atomic force microscopy (AFM). Our results showed that Pt nanoparticles grew in voids of the s-BLMs, through which the underlying glassy carbon (GC) electrode was connected, with maximum length extended out of the lipid membrane around 40 nm. Doping of Pt nanoparticles through s-BLM increased the membrane capacitance and decreased the membrane resistance of s-BLM. Pt nanoparticles array in s-BLM electrocatalyzed the reduction of oxygen (O(2)) in phosphate buffer solution (PBS). Practical application of Pt nanoparticle-doped s-BLM for the construction of glucose biosensor was also demonstrated in terms of its dose-response curve, stability and reproducibility. Thus, lipid membrane doped with Pt nanoparticles is a novel electrode system at nanoscale that can penetrate through the insulating membrane to probe molecular recognition and catalytic events at the lipid membrane-solution interface.

Graphene as a Spacer to Layer-by-Layer Assemble Electrochemically Functionalized Nanostructures for Molecular Bioelectronic Devices

This study demonstrates the capability of graphene as a spacer to form electrochemically functionalized multilayered nanostructures onto electrodes in a controllable manner through layer-by-layer (LBL) chemistry. Methylene green (MG) and positively charged methylimidazolium-functionalized multiwalled carbon nanotubes (MWNTs) were used as examples of electroactive species and electrochemically useful components for the assembly, respectively. By using graphene as the spacer, the multilayered nanostructures of graphene/MG and graphene/MWNT could be readily formed onto electrodes with the LBL method on the basis of the electrostatic and/or π-π interaction(s) between graphene and the electrochemically useful components. Scanning electron microscopy (SEM), ultraviolet-visible spectroscopy (UV-vis), and cyclic voltammetry (CV) were used to characterize the assembly processes, and the results revealed that nanostructure assembly was uniform and effective with graphene as the spacer. Electrochemical studies demonstrate that the assembled nanostructures possess excellent electrochemical properties and electrocatalytic activity toward the oxidation of NADH and could thus be used as electronic transducers for bioelectronic devices. This potential was further demonstrated by using an alcohol dehydrogenase-based electrochemical biosensor and glucose dehydrogenase-based glucose/O(2) biofuel cell as typical examples. This study offers a simple route to the controllable formation of graphene-based electrochemically functionalized nanostructures that can be used for the development of molecular bioelectronic devices such as biosensors and biofuel cells.

Synthetically Directed Self-Assembly and Enhanced Surface-Enhanced Raman Scattering Property of Twinned Crystalline Ag/Ag Homojunction Nanoparticles

A synthetically directed self-assembly strategy to the aqueous-phase synthesis of twinned crystalline silver/silver homojunction nanoparticles (Ag/Ag HJNPs) is demonstrated. In the self-assembly, ethylenediamine tetraacetic acid disodium (EDTA) and solution pH values play a crucial role in the formation of Ag/Ag HJNPs while the sizes of Ag nanoparticles (NPs) in the Ag/Ag HJNPs depend on the reductant concentrations of ascorbic acid. Surface-enhanced Raman scattering (SERS) measurements indicate that the SERS intensity acquired from the Ag/Ag HJNP colloidal solution is about 200 times stronger than that obtained from isolated Ag NP colloid solution. The plasmonic and SERS behaviors of Ag/Ag HJNPs were simulated by discrete-dipole approximation (DDA) and three-dimensional finite-difference time domain (3D-FDTD) methods, respectively. Theoretical calculation results disclose that surface plasmon resonance (SPR) properties of the Ag/Ag HJNPs are different from those of isolated Ag nanospheres, and their maximal SERS enhancement is about 2 orders of magnitude higher than that of isolated Ag nanospheres, which is in good agreement with the experimental results. The extra SERS enhancement can be explained by the hot spots at homojunction structures between Ag particles because of near-field coupling effect.

Transition metal sulfides grown on graphene fibers for wearable asymmetric supercapacitors with high volumetric capacitance and high energy density

Fiber shaped supercapacitors are promising candidates for wearable electronics because they are flexible and light-weight. However, a critical challenge of the widespread application of these energy storage devices is their low cell voltages and low energy densities, resulting in limited run-time of the electronics. Here, we demonstrate a 1.5 V high cell voltage and high volumetric energy density asymmetric fiber supercapacitor in aqueous electrolyte. The lightweight (0.24 g cm−3), highly conductive (39 S cm−1), and mechanically robust (221 MPa) graphene fibers were firstly fabricated and then coated by NiCo2S4 nanoparticles (GF/NiCo2S4) via the solvothermal deposition method. The GF/NiCo2S4 display high volumetric capacitance up to 388 F cm−3 at 2 mV s−1 in a three-electrode cell and 300 F cm−3 at 175.7 mA cm−3 (568 mF cm−2 at 0.5 mA cm−2) in a two-electrode cell. The electrochemical characterizations show 1000% higher capacitance of the GF/NiCo2S4 as compared to that of neat graphene fibers. The fabricated device achieves high energy density up to 12.3 mWh cm−3 with a maximum power density of 1600 mW cm−3, outperforming the thin-film lithium battery. Therefore, these supercapacitors are promising for the next generation flexible and wearable electronic devices.

Microfluidic Chip-Based Online Electrochemical Detecting System for Continuous and Simultaneous Monitoring of Ascorbate and Mg2+ in Rat Brain

This study demonstrates a microfluidic chip-based online electrochemical detecting system for in vivo continuous and simultaneous monitoring of ascorbate and Mg(2+) in rat brain. In this system, a microfluidic chip is used as the detector for both species. To fabricate the detector, a single-channel microfluidic chip is developed into an electrochemical flow cell by incorporating the chip with an indium-tin oxide (ITO) electrode as working electrode, an Ag/AgCl wire as reference electrode, and a stainless steel tube as counter electrode. Selective detection of ascorbate and Mg(2+) is achieved by drop-coating single-walled carbon nanotubes (SWNTs) and polymerizing toluidine blue O (polyTBO) film onto the ITO electrode, respectively. Moreover, the alignment of SWNT-modified and polyTBO-modified electrodes and the solution introduction pattern are carefully designed to avoid any cross talk between two electrodes. With the microfluidic chip-based electrochemical flow cell as the detector, an online electrochemical detecting system is successfully established by directly integrating the microfluidic chip-based electrochemical flow cell with in vivo microdialysis. The microfluidic system exhibits sensing properties with a linear relationship from 5 to 100 μM for ascorbate and from 100 to 2000 μM for Mg(2+). Moreover, this system demonstrates a high selectivity and stability and good reproducibility for simultaneous measurements of ascorbate and Mg(2+) in a continuous-flow system. These excellent properties substantially render this system great potential for continuous and simultaneous online monitoring of ascorbate and Mg(2+) in rat brain.

Electrochemical functionalization of vertically aligned carbon nanotube arrays with molybdenum oxides for the development of a surface-charge-controlled sensor

The modification of inorganic polymeric oxides at the surface of carbon nanotubes is of paramount importance for developing new sensors. In this study, molybdenum oxide (MoOx) film was electrodeposited on the surface of multi-walled carbon nanotubes (MWNTs) by cycling the potential between +0.20 and ?0.80?V (versus 3?M KCl?Ag|AgCl) in Na2MoO4 solution. The MoOx-modified nanotube (MoOx/MWNT) electrode displays well-defined redox transitions in 5?mM H2SO4 or in phosphate buffer solution (PBS), which can be attributed to the reductive formation and the re-oxidation of hydrogen molybdenum oxides. X-ray photoelectron spectra (XPS) showed that the deposited MoOx films are mainly Mo6+ complexes. Both MWNT and MoOx/MWNT electrodes have ideal reversibility in 5?mM K3[Fe(CN)6] in 1?M KCl as supporting electrolytes at all sweep rates (0.02?1.00?V?s?1) by cyclic voltammetry. The negatively charged surface of MoOx/MWNTs can further attract molecular cations such as Ru(NH3)63+. The MoOx/MWNT electrode exhibited electrocatalytic ability towards the reduction of bromate due to high surface area and the fast electron transfer rate of nanotubes. Thus, electrochemical modification of inorganic polymeric oxides on the carbon nanotube provides a simple method for the preparation of novel sensors.

Oxidative modification of neurogranin by nitric oxide: an amperometric study

Neurogranin (Ng) is a neuron-specific protein kinase C (PKC) substrate, which contains four cysteine (Cys) residues. Recently, it has been shown that Ng is a redox-sensitive protein and is a likely target of nitric oxide (NO) and other oxidants [F.-S. Sheu, C.W. Mahoney, K. Seki, K.-P. Huang, Nitric oxide modification of rat brain neurogranin affects its phosphorylation by protein kinase C and affinity for calmodulin, J. Biol. Chem. 271 (1996) 22407-22413: J. Li, J.H. Pak, F.L. Huang, K.-P. Huang, N-methyl-D-aspartate induces neurogranin/RC3 oxidation in rat brain slices, J. Biol. Chem. 274 (1999) 1294-1300]. In this study, we directly examine the redox reactions between dissolved NO and Cys as well as between NO and bacterial expressed Ng in its reduced form, at concentrations approximate to the physiological levels in phosphate buffer solution (PBS) under aerobic conditions. The reaction kinetics are measured directly by our newly developed electrochemical sensor. Our sensor is based on the chemical modification of electrode with immobilized nanoparticles of transition metal palladium (Pd) which serves as catalytic centers for the electrochemical oxidation of thiol and NO selectively and quantitatively at different potentials. It detects Cys and Ng in a linear range from nano to micromolar concentration at + 450 mV, vs. a saturated calomel reference electrode (SCE), while the detection of NO at the sensor can be optimally achieved at + 700 mV (vs. SCE) with a linear current-to-concentration range of nM to microM. It thus provides a selective control to monitor two reactants independently. With this sensor as a detector, we found that (1) the oxidation of either Cys or Ng by NO is a fast reaction which reaches a near completion within 1-2 min at its physiological concentration; and (2) after the completion of reaction, NO is mostly, if not all, regenerated, an observation consistent with the reaction mechanism involving the formation of S-nitrosothiol as an intermediate. The reaction kinetics of both NO to Cys and NO to Ng implies that NO can achieve local action on cellular proteins in addition to its effect on targets located in neighboring cells via concentration-gradient-dependent diffusion.

A spinneret as the key component for surface-porous graphene fibers in high energy density micro-supercapacitors

A metal needle spinneret was found to be the key component to synthesize neat graphene fibers with a porous surface in the wet spinning process. Flexible solid-state micro-supercapacitors (micro-SCs) based on the neat graphene fibers were then designed and fabricated. The as-prepared graphene fibers with an impressive specific surface area up to 839 m2 g−1 achieved an excellent specific capacitance of 228 mF cm−2 at 39.7 μA cm−2. The assembled micro-SCs exhibited excellent performance such as high energy densities of 7.9 μW h cm−2 (or 4.0 mW h cm−3) approaching those of lithium thin film batteries and excellent long life stability. This research opens the door to the synthesis of surface-porous neat graphene fibers and these fibers are promising as electrode materials in high-performance micro-SCs.

Nitric oxide enhances the capacitance of self-assembled, supported bilayer lipid membranes

The effect of nitric oxide (NO) at biologically relevant concentrations on the electrochemical features of the membrane was investigated by cyclic voltammetry (CV) at self-assembled, stainless steel supported lipid bilayer membranes (s-BLMs) using a three-electrode system. The results showed that the membrane capacitance (Cm) of s-BLMs was dramatically enhanced by the presence of increasing NO concentration from 0 to 70 μM. For comparison, fullerene C60 doped s-BLMs (C60@s-BLMs) was also studied. The Cm of C60@s-BLMs increased with NO concentration from 0 to 16 μM and gradually reached a plateau value when NO concentration was over 16 μM. We concluded that (i) NO accumulated inside lipid bilayer increases the Cm of s-BLMs, and (ii) C60 inside s-BLMs changes the dielectric constant of lipid bilayer, thus reducing the effect of NO on the Cm of C60@s-BLMs. This novel self-assembled lipid modified probe provides a simple yet interesting model to study the effect of NO on the electrical conductance of the membrane.