Yuezhong Xian

Synthesis of water-soluble magnetic graphene nanocomposites for recyclable removal of heavy metal ions

In this work, graphene oxide/Fe3O4 (GO/Fe3O4) composites were synthesized via a copper catalyzed azide-alkyne cycloaddition reaction for the first time. After further modification with polyacrylic acid (PAA), water-soluble magnetic graphene nanocomposites were obtained. The PAA/GO/Fe3O4nanocomposites were characterized by atomic force microscopy, transmission electron microscopy, X-ray diffraction, Raman, Fourier transform infrared spectroscopy, thermogravimetric analysis and vibrating sample magnetometry. Due to the high surface area, excellent complex ability and superparamagnetism, the PAA/GO/Fe3O4 nanocomposites were used as nanoadsorbents for recyclable removal of Cu2+, Cd2+ and Pb2+ ions from aqueous solution. It is found that the PAA/GO/Fe3O4 nanocomposites show extraordinary removal capacity for Cu2+, Cd2+ and Pb2+ ions. Moreover, the PAA/GO/Fe3O4 nanocomposites are very easy to separate and recycle due to the superparamagnetism of Fe3O4. After five cycles, the removal efficacy of the nanoadsorbents for Cu2+, Cd2+ and Pb2+ ions is over 85%. All of the results demonstrate that the water-soluble magnetic graphene composites are effective adsorbents for removal of heavy metals and thus could provide a new platform for water cleanup.

Electrochemical sensor for bisphenol A based on magnetic nanoparticles decorated reduced graphene oxide

Bisphenol A (BPA), as one kind of endocrine-disrupting chemicals, has adverse impact on human health and environment. It is urgent to develop effective and simple methods for quantitative determination of BPA. In this work, an electrochemical sensor for BPA based on magnetic nanoparticles (MNPs)-reduced graphene oxide (rGO) composites and chitosan was presented for the first time. The MNPs-rGO composites were characterized by scanning electron microscopy, X-Ray diffraction and Fourier transform infrared spectroscopy. Electrochemical studies show that MNPs-rGO composites can lower the oxidation overpotential and enhance electrochemical response of BPA due to the synergetic effects of MNPs and rGO. Under the optimal experiment conditions, the oxidation peak current was proportional to the concentration of BPA over the range of 6.0×10(-8) to 1.1×10(-5)molL(-1) with the detection limit of 1.7×10(-8)molL(-1). Moreover, the MNPs-rGO based electrochemical sensor shows excellent stability, reproducibility and selectivity. The electrochemical sensor has been successfully applied to the determination of BPA in real samples with satisfactory results.

ZnO nanorods/Au hybrid nanocomposites for glucose biosensor

ZnO nanorods/Au hybrid nanocomposites (ZnO/Au) with Au nanocrystals growing on the surface of ZnO nanorods were synthesized via a simple and facile hydrothermal route. The prepared ZnO/Au nanocomposites were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM) for the morphology study. The composites had a good electron transferring and biocompatibility. The glucose biosensor was fabricated by entrapping glucose oxidase (GOx) in this composite matrix using cross-linking method with glutaraldehyde and Nafion solutions. The proposed biosensor responded to glucose linearly over concentration range of 0.1-33.0 μM (R(2)=0.9956), and the detection limit was 10nM (S/N=3) at an operating potential of +0.55 V in pH 7.4 phosphate buffered solution (PBS). The biosensor exhibited a high and reproducible sensitivity, short response time (within 5s), good storage stability and high affinity to GOx (K(M)(app)=0.41 mM). The effects of electroactive interferents at the testing conditions can be negligible which showed a good selectivity of the biosensor. It is estimated that this ZnO/Au is an attractive material for the fabrication of efficient amperometric biosensors.

Combining biofunctional magnetic nanoparticles and ATP bioluminescence for rapid detection of Escherichia coli.

A rapid, specific and sensitive method for assay of Escherichia coli (E. coli) using biofunctional magnetic nanoparticles (BMNPs) in combination with adenosine triphosphate (ATP) bioluminescence was proposed. The BMNPs were fabricated by immobilizing a specific anti-E. coli antibody on the surface of amine-functionalized magnetic nanoparticles (about 20nm in diameter), and then was applied to capture the target bacteria E. coli from samples. The BMNPs exhibited high capture efficiency to E. coli. Transmission electron microscope (TEM) images showed that the BMNPs were bound to the surface of entire E. coli cells. The target bacteria became magnetic so that could be isolated easily from the sample solution by employing an external magnetic field. The concentration of E. coli captured by the BMNPs was then detected by an ATP bioluminescence method. The optimization of ATP measurement was carried out to improve the detection sensitivity. The proposed method was applied to detect the E. coli inoculated into pasteurized milk with low detection limit (20 cfu/mL) and short detection time (about 1h).

Enzymatic biosensors based on the use of metal oxide nanoparticles

AbstractOver the past decades, various techniques have been developed to obtain materials at a nanoscale level to design biosensors with high sensitivity, selectivity and efficiency. Metal oxide nanoparticles (MONPs) are of particular interests and have received much attention because of their unique physical, chemical and catalytic properties. This review summarizes the progress made in enzymatic biosensors based on the use of MONPs. Synthetic methods, strategies for immobilization, and the functions of MONPs in enzymatic biosensing systems are reviewed and discussed. The article is subdivided into sections on enzymatic biosensors based on (a) zinc oxide nanoparticles, (b) titanium oxide nanoparticles, (c) iron oxide nanoparticles, and (d) other metal oxide nanoparticles. While substantial advances have been made in MONPs-based enzymatic biosensors, their applications to real samples still lie ahead because issues such as reproducibility and sensor stability have to be solved. The article contains 256 references. FigureA comprehensive and critical review on enzymatic biosensor based on metal oxide nanoparticles (MONPs) was provided. The progress and future perspectives of MONPs based enzymatic biosensing system were discussed.

Preparation of multiwall carbon nanotubes film modified electrode and its application to simultaneous determination of oxidizable amino acids in ion chromatography

A multiwall carbon nanotubes (MWNTs) film modified electrode was prepared and used as an amperometric sensor for the simultaneous determination of oxidizable amino acids including cysteine, tryptophane and tyrosine. The electrochemical behaviors of these amino acids at this modified electrode were studied by cyclic voltammetry (CV). The results indicated that the MWNTs chemically modified electrode (CME) exhibited efficient electrocatalytic activity towards the oxidation of these amino acids with relatively high sensitivity, stability and long-life. Following separation by ion chromatography (IC) with 2.0 x 10(-3) mol l(-1) citric acid buffer solution (pH 6.5) as eluent, cysteine, tryptophane and tyrosine could be determined by the MWNTs CME successfully. Under the optimal conditions, the detection limits were 7.0 x 10(-7) mol l(-1) for cysteine, 2.0 x 10(-7) mol l(-1) for tryptophane and 3.5 x 10(-7) mol l(-1) for tyrosine at the signal-to-noise of 3, respectively. The method was applied successfully to the determination of these substances in plasma.

Recyclable removal of bisphenol A from aqueous solution by reduced graphene oxide-magnetic nanoparticles: adsorption and desorption.

Reduced graphene oxide (rGO) nanosheets decorated with tunable magnetic nanoparticles (MNPs) were synthesized by a simple co-precipitation method and employed for recyclable removal of bisphenol A (BPA) from aqueous solution. The morphological characterization shows that Fe3O4 nanoparticles are uniformly deposited on rGO sheets. The magnetic characterization demonstrates that composites with various amounts of Fe3O4 nanoparticles are superparamagnetic. Due to the superparamagnetism, rGO-MNPs were used as recyclable adsorbents for BPA removal in aqueous solution. The kinetics of the adsorption process and the adsorption isotherm were investigated. The results indicate that the adsorption process is fitted to Langmuir model and the composites with lower density of MNPs represent better adsorption ability. In addition, its kinetics follows pseudo-second-order rate equation. Moreover, the adsorbents could be recovered conveniently by magnetic separation and recyclable used because of the easy desorption of BPA.

One-Step Synthesis of Water-Soluble MoS2 Quantum Dots via a Hydrothermal Method as a Fluorescent Probe for Hyaluronidase Detection

In this work, a bottom-up strategy is developed to synthesize water-soluble molybdenum disulfide quantum dots (MoS2 QDs) through a simple, one-step hydrothermal method using ammonium tetrathiomolybdate [(NH4)2MoS4] as the precursor and hydrazine hydrate as the reducing agent. The as-synthesized MoS2 QDs are few-layered with a narrow size distribution, and the average diameter is about 2.8 nm. The resultant QDs show excitation-dependent blue fluorescence due to the polydispersity of the QDs. Moreover, the fluorescence can be quenched by hyaluronic acid (HA)-functionalized gold nanoparticles through a photoinduced electron-transfer mechanism. Hyaluronidase (HAase), an endoglucosidase, can cleave HA into proangiogenic fragments and lead to the aggregation of gold nanoparticles. As a result, the electron transfer is blocked and fluorescence is recovered. On the basis of this principle, a novel fluorescence sensor for HAase is developed with a linear range from 1 to 50 U/mL and a detection limit of 0.7 U/mL.

ZnS quantum dots derived a reagentless uric acid biosensor

A reagentless amperometric uric acid biosensor based on zinc sulfide (ZnS) quantum dots (QDs) was firstly developed. It could detect uric acid without the presence of an electron mediator. The carboxyl group functionalized ZnS QDs were synthesized, and they were soluble biocompatible and conductive. ZnS QDs conjugates could provide increased enzyme binding sites, which may result in higher enzyme loading. Thus, the proposed uricase/ZnS QDs/l-cys biosensor exhibited higher amperometric response compared to the one without QDs (uricase/l-cys biosensor). In addition, there was little AA interference. It showed a linear dependence on the uric acid concentration ranging from 5.0x10(-6) to 2.0x10(-3)molL(-1) with a detection limit of 2.0x10(-6)molL(-1) at 3sigma.

Direct electrochemistry of horseradish peroxidase on TiO2 nanotube arrays via seeded-growth synthesis

Horseradish peroxidase (HRP) was successfully immobilized on vertically oriented TiO(2) nanotube arrays (NTAs), which was prepared by a seeded-growth mechanism. The nanotubular structure of TiO(2) was characterized by scanning electron microscope (SEM). After encapsulated HRP on TiO(2) nanotube arrays, the direct electron transfer of HRP was observed. Owing to the redox reaction of electroactive center of HRP, the HRP/TiO(2) NTAs modified electrode exhibited a pair of quasi-reversible peaks with the peak-to-peak separation of 70 mV and the formal potential of -0.122 V (vs. SCE) in 0.2mol L(-1) phosphate buffer solution (PBS, pH 7.0). The number of transference electron was 0.84 and the direct electron transfer (ET) constant (k(s)) was 3.82 s(-1). The HRP/TiO(2) NTAs modified electrode displayed an excellent electrocatalytic performance for H(2)O(2) and the formal Michaelis-Menten constant (K(m)(app)) was 1.9 mmol L(-1). The response currents had a good linear relation with the concentration of H(2)O(2) from 5.0 x 10(-7) mol L(-1) to 1.0 x 10(-5) mol L(-1) and 5.0 x 10(-5) mol L(-1) to 1.0 x10(-3) mol L(-1), respectively.