Xiaoru Wang

Synthesis of "Clean" and Well-Dispersive Pd Nanoparticles with Excellent Electrocatalytic Property on Graphene Oxide

Ultrafine Pd nanoparticles monodispersed on graphene oxide (GO) surfaces were successfully prepared by the redox reaction between PdCl(4)(2-) and GO. The as-made catalyst is very clean as a result of the surfactant-free formation process, allowing it to express high electrocatalytic ability in formic acid and ethanol oxidation relative to a commercial Pd/C catalyst. This simple and straightforward method is of significance for the facile preparation metal nanocatalysts with high catalytic activity on proper supporting materials.

Nonenzymatic amperometric sensing of glucose by using palladium nanoparticles supported on functional carbon nanotubes

A nonenzymatic electrochemical method was developed for glucose detection using an electrode modified with palladium nanoparticles (PdNPs)-functional carbon nanotubes (FCNTs). PdNPs were homogeneously modified on FCNTs through a facile spontaneous redox reaction and characterized by transmission electron microscopy. Based on the voltammetric and amperometric results, PdNPs efficiently catalyzed the oxidation of glucose at 0.40 V in the presence of 0.2M NaCl and showed excellent resistance towards poisoning from such interfering species as ascorbic acid, uric acid, and p-acetamidophenol. This anti-poisoning ability was investigated using analysis of the electrocatalytic products by in situ subtractively normalized interfacial Fourier transform infrared reflection spectroscopy, and the results indicated that no strongly adsorbed CO(ad) species could be found in the oxidation products, which was obviously different from the results obtained using Pt-based electrodes. In order to verify the sensor reliability, it was applied to the determination of glucose in urine samples. The results indicated that the proposed approach provided a highly sensitive, wide linear range, more facile method with good reproducibility for glucose determination, promising the development of Pd-based material in nonenzymatic glucose sensing.

Characterization of ormosil film for dissolved oxygen-sensing

Abstract An organically modified silicate (ormosil) as a matrix for the fabrication of dissolved oxygen-sensing film was produced. The process included taking tetramethoxysilane (TMOS) and dimethyldimethoxysilane (DiMe-DMOS) as precursor and running a reaction at 60xa0°C in an open vial, which accelerates hydrolysis and condensation and results in the formation of emulsion. The film doped with tris-(4,7-diphenyl-1,10-phenanthroline) ruthenium(II) ([Ru(dpp) 3 ] 2+ ) as an oxygen indicator exhibited a good linear relationship, fast response time, long-term stability and enhanced sensitivity to dissolved oxygen after optimizing the sol–gel processing parameters. The properties and the oxygen-sensing behavior of the film were investigated. The results presented here emphasized the significance of ormosil as a matrix for dissolved oxygen-sensing.

A quartz crystal microbalance sensor based on mussel-inspired molecularly imprinted polymer.

In this work, we describe a simple, inexpensive and fast method for the generation of molecularly imprinted polymer (MIP) film on quartz crystal microbalance (QCM) crystals using mussel-inspired polymer. Commonly known as a neurotransmitter, dopamine is also a small-molecule mimic of the adhesive proteins of mussels. Polymerization of dopamine in the presence of template molecule (1,3,5-pentanetricarboxylic acid, an analogue of domoic acid, in this case) could produce an adherent molecularly imprinted polydopamine film coating on QCM crystals. Advantages, such as high hydrophilicity, high biocompatibility and controllable thickness, make this molecularly imprinted polydopamine film an attractive recognition element for sensors. Selective rebinding of domoic acid on mussel-inspired molecularly imprinted polymer (m-MIP) coated crystal was observed as a frequency shift quantified by piezoelectric microgravimetry with the QCM system. The decreasing frequency shows a good linear relationship with the concentration of domoic acid. The quantitation limit of domoic acid was 5 ppb with the linear range of 0-100 ppb. The QCM sensor has high selectivity and was able to distinguish domoic acid from its analogous p-phthalic acid and o-phthalic acid owing to the molecular imprinting effect. In addition, the practical analytical performance of the sensor was examined by evaluating the detection of domoic acid in mussel extracts with satisfactory results. It is envisaged that m-MIP could be suitable as recognition element for sensors and the proposed m-MIP QCM sensor could be employed to detect analyte of interest in complex matrices.

Development of polymethylphenylsiloxane-coated fiber for solid-phase microextraction and its analytical application of qualitative and semi-quantitative of organochlorine and pyrethroid pesticides in vegetables

An approach to the synthesis of hydroxyl-terminated polymethylphenylsiloxane (PMPS-OH) was proposed and the synthesized PMPS-OH was successfully applied as a precursor to prepare a novel coating for solid-phase microextraction (SPME) via the sol-gel process. The thickness and length of the prepared coating was 70 microm and 1.5 cm, respectively. The extraction efficiency of the PMPS-coated fiber for selected pesticides was higher than that of commercial fibers including 100 microm polydimethylsiloxane (PDMS), 85 microm polyacrylate (PA) and 65 microm polydimethylsiloxane/divinylbenzene (PDMS/DVB). The influence of the extraction process, extraction temperature, extraction time, stirring rate, ionic strength, GC inlet conditions, desorption temperature and time for PMPS-coated fiber application was studied and optimized. Several experiments were carried out to evaluate the analytical characteristics of the proposed SPME-GC-ECD method under optimized conditions. The linearity was from 0.5 to 100 ng g(-1) for p,p-DDE, p,p-DDD and bifenthrin, and from 2 to 100 ng g(-1) for o,p-DDT, p,p-DDT, fenpropathrin, beta-cyfluthrin and cyhalothrin. The detection limits of these pesticides were between 0.13 and 1.45 ng g(-1). The recovery of the pesticides spiked in various vegetables at 4 ng g(-1) ranged from 42.9% to 105.3%, and the relative standard deviations were less than 16.2%.

An electrochemically enhanced solid-phase microextraction approach based on a multi-walled carbon nanotubes/Nafion composite coating.

In this paper, we proposed an approach using a multi-walled carbon nanotubes (MWCNTs)/Nafion composite coating as a working electrode for the electrochemically enhanced solid-phase microextraction (EE-SPME) of charged compounds. Suitable negative and positive potentials were applied to enhance the extraction of cationic (protonated amines) and anionic compounds (deprotonated carboxylic acids) in aqueous solutions, respectively. Compared to the direct SPME mode (DI-SPME) (without applying potential), the EE-SPME presented more effective and selective extraction of charged analytes primarily via electrophoresis and complementary charge interaction. The experimental parameters relating to extraction efficiency of the EE-SPME such as applied potentials, extraction time, ionic strength, sample pH were studied and optimized. The linear dynamic range of developed EE-SPME-GC for the selected amines spanned three orders of magnitude (0.005-1mugmL(-1)) with R(2) larger than 0.9933, and the limits of detection were in the range of 0.048-0.070ngmL(-1). All of these characteristics demonstrate that the proposed MWCNTs/Nafion EE-SPME is an efficient, flexible and versatile sampling and extraction tool which is ideally suited for use with chromatographic methods.

Optical colorimetric sensor strip for direct readout glucose measurement

A novel direct readout colorimetric optical glucose sensor strip was constructed based on a three-layer film, including a green-emitted CdTe/CdS quantum dots (QDs) layer as a stable color background, a red-fluorescent platinum-porphyrin oxygen-sensing layer and a glucose oxidase layer. The sensor achieved high resolution (up to 0.2 mmol L(-1)) glucose determination with a detection range from 0 to 3.0 mmol L(-1). A glucose ruler which acts as a glucose standard colorimetric card was obtained. Glucose concentration could easily be directly readout using the glucose ruler, which made the glucose determination rapid, convenient and easy. The effects of pH, salinity and temperature were systematically investigated. The prepared sensor was finally applied for glucose sample analysis, compared with the glucose ruler, accurate results could be directly readout.

Optical biosensor for the determination of BOD in seawater

An automatic sensing system was developed using an optical BOD sensing film. The sensing film consists of an organically modified silicate (ORMOSIL) film embedded with an oxygen-sensitive Ru complex. A multi-microorganisms immobilization method was developed for the BOD sensing film preparation. Three different kinds of microorganisms, Bacillus licheniformis, Dietzia maris and Marinobacter marinus from seawater, were immobilized on a polyvinyl alcohol ORMOSILs. After preconditioning, the BOD biosensor could steadily perform well up to 10 months. The linear fluctuant coefficients (R(2)) in the range of 0.3-40mgL(-1) was 0.985 when a glucose/glutamate BOD standard was applied. The reproducible response for the BOD sensing film could be obtained within +/-2.3% of the mean value in a series of 10 samples in 5.0mgL(-1) BOD standard GGA solution. The effects of temperature, pH and sodium chloride concentration on the two microbial films were studied as well. The BOD sensing system was tested and applied for the BOD determination of seawater.

Electronic nose based on SAWS array and its odor identification capability

Abstract The ability of odor identification by an electronic nose based on eight surface acoustic wave sensors (SAWS) was demonstrated in the present paper. The SAWS-based electronic nose was established first and its frequency stability was checked. Then, by applying appropriate polymers coating on SAW devices (SAWD), the prototype instrument was employed to collect data from its exposure to four kinds of organic reagents (ethanol, ether, acetone, ethyltate), four kinds of liquors (beer, spirit, samshu, wine) and five kinds of perfumes (phenethyl alcohol, ionone, vanillylalkohol, ethylisobutyrate, thymol). Data analysis was performed by three pattern recognition methods (principal component analysis (PCA), partial least squares (PLS), artificial neural network (ANN)). The results showed that the electronic nose was able to identify the above odors quite well.

Chemiluminescence of tryptophan and histidine in Ru(bpy)(3)(2+)-KMnO4 aqueous solution

Amino acids with different chemical structures have different abilities in terms of increasing the intensity of chemiluminescence (CL) of tris(2,2-bipyridine)ruthenium(II) [Ru(bpy)3(2+)]. In a flow system, CL caused by the reaction between Ru(bpy)3(3+) and 15 amino acids was observed, but only tryptophan (Trp) and histidine (His) enhanced the intensity obviously, and so the CL of Trp and His and their molecular groups was studied. A calculation of the ionization potentials (IPs) of their N atom indicated that the CL intensities of these compounds depended on their IPs. In addition, the flow system was used for the determination of Trp and His, and the detection limits were 3 x 10(-8) mol L(-1) for His and 2.5 x 10(-9) mol L(-1) for Trp. The calibration curves for the two amino acids were 1.0 x 10(-7) to 5.0 x 10(-3) mol L(-1) for His and 1.0 x 10(-8) to 1.0 x 10(-4) mol L(-1) for Trp. The proposed approach was applied to the determination of His in Ganoderma.