Zhifeng Du

A novel nonenzymatic hydrogen peroxide sensor based on MnO2/graphene oxide nanocomposite

A new electrocatalyst, MnO(2)/graphene oxide hybrid nanostructure was successfully synthesized for the nonenzymatic detection of H(2)O(2). The morphological characterization was examined by scanning electron microscopy and transmission electron microscopy. The MnO(2)/graphene oxide based electrodes showed high electrochemical activity for the detection of H(2)O(2) in alkaline medium. The nonenzymatic biosensors displayed good performance along with low working potential, high sensitivity, low detection limit, and long-term stability, which could be attributed to the high surface area of graphene oxide providing for the deposition of MnO(2) nanoparticles. These results demonstrate that this new nanocomposite with the high surface area and electrocatalytic activity offers great promise for new class of nanostructured electrode for nonenzymatic biosensor and energy conversion applications.

Surface-depletion controlled gas sensing of ZnO nanorods grown at room temperature

The authors report on surface-depletion controlled gas sensing ZnO nanorods. These nanorods were synthesized through a simple wet chemical route at room temperature. The diameter of nanorods is about 15nm, which is close to two times of the Debye length of ZnO. In contrast to the previous report, the sensing is surface-depletion controlled rather than contact controlled and the sensitivity is up to 29.7 against 100ppm ethanol. Such high sensitivity is due to an almost complete depletion of the rods in air, which is confirmed from photoluminescence spectrum and x-ray photoelectron spectroscopy. The gas sensing mechanism controlled by surface depletion provides another approach to realize high-performance gas sensors.

A novel amperometric biosensor based on NiO hollow nanospheres for biosensing glucose

NiO hollow nanospheres were synthesized by controlled precipitation of metal ions with urea using carbon microspheres as templates, which were for the first time adopted to construct a novel amperometric glucose biosensor. Glucose oxidase was immobilized on the surface of hollow nanospheres through chitosan-assisted cross-linking technique. Due to the high specific active sites and high electrocatalytic activity of NiO hollow nanospheres, the constructed glucose biosensors exhibited a high sensitivity of 3.43 microA/mM. The low detection limit was estimated to be 47 microM (S/N=3), and the Michaelis-Menten constant was found to be 7.76 mM, indicating the high affinity of enzyme on NiO hollow nanospheres to glucose. These results show that the NiO hollow nanospheres are a promising material to construct enzyme biosensors.

Flexible morphology-controlled synthesis of mesoporous hierarchical α-Fe2O3 architectures and their gas-sensing properties

Mesoporous flower-like and urchin-like α-Fe2O3 nanostructures have been successfully synthesized by a simple solution-based reaction and sequential calcination. Detailed experiments demonstrated that the morphology of the hierarchical α-FeOOH precursors could be easily controlled by adjusting the experimental conditions including reactant concentration, solvent composition, reaction time, and reaction temperature. On the basis of time-dependent experiments, a multistage growth mechanism for the formation of the α-FeOOH super-architectures was proposed. In addition, by virtue of the unique hierarchical mesoporous structure and comparative high specific surface area, these obtained α-Fe2O3 nanostructures exhibited enhanced sensing performances to ethanol. This method is expected to be a useful technique for controlling the diverse morphologies of iron oxide superstructures that could meet the demands of a variety of applications, such as gas sensors, lithium-ion batteries, catalysis, waste-water treatment, and pigments.

Bandgap narrowing and ethanol sensing properties of In-doped ZnO nanowires

Indium doping effects on the optical and electrical properties of ZnO nanowires are investigated. The abnormal Raman spectrum shows only a peak centred at 439 cm−1 related to high E2 mode, which is due to In doping. The acceptor binding energy is estimated to be 93 meV from the results of temperature-dependent photoluminescence spectra. The redshift of the bandgap edge is attributed to a merging of donor and conduction bands. The sensitivity of the sensors fabricated from In-doped ZnO nanowires is about 3–1 ppm ethanol, and increases nearly linearly up to 27 as the ethanol concentration is raised to 100 ppm. Our results indicate that the In-doped ZnO nanowires have potential applications in fabricating optoelectrical devices and gas sensors.

Ultralow threshold field emission from ZnO nanorod arrays grown on ZnO film at low temperature

ZnO nanorod arrays have been synthesized on silicon substrate covered with ZnO film by thermal evaporation of zinc particles at a low temperature of 550 °C. Their field emission has been investigated: the turn-on electric field (at the current density of 1 µA cm−2) is about 3.8 V µm−1, and the threshold electric field (at the current density of 1 mA cm−2) is 6.3 V µm−1 at the working distance of 100 µm. In comparison, the turn-on and threshold electric fields of the not well-aligned ZnO nanorod arrays and ZnO film are 9.8, 15.8 V µm−1 and 13.7, 26.0 V µm−1 at 100 µm, respectively. These behaviors indicate that such an ultralow threshold field emission is attributed to the aligned structure, the good electric contact with the conducting substrate where they grow, and weaker field-screening effect. Our results demonstrate that well-aligned nanorod arrays with excellent field-emission performance grown at such a low temperature can provide the possibility of application in glass-sealed flat panel displays.

Electrocatalytic activity of horseradish peroxidase/chitosan/carbon microsphere microbiocomposites to hydrogen peroxide.

Colloidal carbon microspheres (CMS) are dispersed in chitosan (CHIT) solution to form an organic-inorganic hybrid with excellent micro-environment for the immobilization of biomolecules. A novel amperometric biosensor for the determination of hydrogen peroxide (H(2)O(2)) has been constructed by entrapping horseradish peroxidase (HRP) in as-synthesized CMS/CHIT hybrid. The modification of glassy carbon electrode is made by a simple solution-evaporation method. The electrochemical properties of the biosensor are characterized in electrochemical methods. The proposed biosensor shows high sensitive determination and fast response to H(2)O(2) at -0.15 V. The constructed HRP/CHIT/CMS/GC electrode also exhibits a fine linear correlation with H(2)O(2) concentration. The calculated value of the apparent Michaelis-Menten constant, 2.33 mM, suggests that the HRP in CMS/CHIT hybrid keeps its native bioactivity and has high affinity for H(2)O(2).

Fast Synthesis of Graphene Sheets with Good Thermal Stability by Microwave Irradiation

In recent years, considerable attention has been focused on graphene, because it has shown to possess a wealth of exceptional properties and various promising applications. To realize this promise, reliable methods for the large-scale production of high-quality graphene are required. Epitaxial growth on polycrystalline nickel is being actively pursued, but achieving large graphene domains with uniform properties remains a challenge. The mechanical cleavage of graphite originally led to the discovery of graphene sheets and this method is the process currently used in most fundamental research on graphene. However, the low productivity of this method makes it unsuitable for synthesizing graphene on a large-scale. Instead, the chemical conversion from graphite appears to be a muchmore-efficient approach to bulk production of graphene sheets (GSs). Most chemical syntheses of GSs from graphite begin with graphite oxide (GO) and usually need a reductant. GO can be reduced by H2. [16] However, it is highly explosive and flammable. Hydrazine can also be used to reduce GO. In view of its toxicity and combustibility, precautions must be taken when large quantities of hydrazine are used to prepare GSs on a large-scale. NaBH4 is known to reduce GO in aqueous solution. Owing to its hygroscopic and flammable properties, the secure preservation of sodium borohydride is a difficult task. Furthermore, reducing GO by traditional heating systems (such as an oil bath) is time-consuming. Therefore, those methods are inefficient and not fit for preparing GSs on a large-scale. On the other hand, the thermal stability of carbon materials is an important aspect of their properties. The synthesis of graphene with good thermal stability would provide greater potential for commercial applications. A study reported by Wu et al. found that GSs synthesized by hydrogen-arc discharge exfoliation were of good thermal stability. Unfortunately, to the best of our knowledge, there are only a few papers that have investigated the thermal stability of graphene. As such, the development of a method for synthesizing GSs with good thermal stability from widely available graphite on a large-scale is of great significance. Although various methods for the synthesis of graphene under microwave irradiation have been reported, they all employed either organic solution or poisonous reagents. In this study, GSs with upper thermal stability were rapidly synthesized in aqueous media by a method based on microwave-assisted and ascorbic acid (AA) as a reductant. Microwave adsorption of GO increased its local temperature and pressure, resulting in the elevation of the thermal stability of GSs. It should be noted that the reducing time of GO by using microwave irradiation was shortened to 30 minutes and the reductant of GO was nontoxic and tractable. AA is naturally employed as a reductant in living things, and has also been used to synthesize nanomaterials. Herein, we report the use of this nontoxic and tractable reductant for the preparation of GSs. The synthesis of GSs is shown in Scheme 1. Firstly, GO was dispersed in deionized water with the help of sonication. Secondly, the temperature of the solution around the GO rose drastically under microwave irradiation, becoming evidently higher than other regions, because GO could strongly absorb the energy of microwave irradiation. With the help of a local elevated temperature, GO was reduced by AA within 0.5 hours. In addition, the local high pressure of GO resulting from microwave irradiation may contribute to the good thermal stability of the GSs. For comparison, we also prepared GSs with an oil bath (marked as GSOB). Figure 1 a shows typical FTIR spectra obtained for GO and GSs. The FTIR spectra of GO confirmed the presence of oxygen-containing groups, including C OH (nC OH = 3390 cm ), C O C (nC O C =1230 cm ), and C=O in car[a] M. Zhang , S. Liu, X. M. Yin, Z. F. Du, Q. Y. Hao, D. N. Lei, Prof. Q. H. Li, Prof. T. H. Wang Key Laboratory for Micro-Nano Optoelectronic Devices of Ministry of Education and State Key Laboratory for Chemo/Biosensing and Chemometrics, Hunan University Changsha 410082 (China) Fax: (+86) 0731-88823407 E-mail : thwang@hnu.cn liqiuhon2004@hotmail.com Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/asia.201000776.

Electrografted Poly(N-mercaptoethyl acrylamide) and Au Nanoparticles-Based Organic/Inorganic Film: A Platform for the High-Performance Electrochemical Biosensors

In this study, we describe the use of the combination of eletrografting poly(N-mercaptoethyl acrylamide) and Au nanoparticles in the construction of high-performance biosensors. The poly(N-mercaptoethyl acrylamide) was electrografted onto the glassy carbon electrode surface, which provided a strongly adhering primer film for the stable attachment of Au nanoparticles and horseradish peroxidase (HRP) enzymes. The performances of the biosensors based on the HRP immobilized in the Au/poly(N-mercaptoethyl acrylamide) composite film were investigated. A couple of redox peaks were obtained, indicating that the Au nanoparticles could facilitate the direct-electron transfer between HRP and the underlying electrode. The biosensor showed an excellent electrocatalytic activity toward the reduction of hydrogen oxide and long-term stability, owing to the stable electrografted film and biocompatible Au nanoparticles. Our results demonstrate that the combination of electrografting and Au nanoparticles provides a promising platform for the immobilization of biomolecules and analysis of redox enzymes for their sensing applications.