Guoyue Shi

A novel composite of SiO2-coated graphene oxide and molecularly imprinted polymers for electrochemical sensing dopamine.

A novel imprinting route based on graphene oxide (GO) was proposed for preparing a composite of SiO2-coated GO and molecularly imprinted polymers (GO/SiO2-MIPs). In this route, SiO2-coated GO sheets were synthesized in a water-alcohol mixture with sol-gel technique. Prior to polymerization, the vinyl groups were introduced onto the surface of GO/SiO2 through chemical modification with γ-methacryloxypropyl trimethoxysilane (γ-MAPS), which can direct the selective polymerization on the GO/SiO2 surface. Then a novel composite of GO/SiO2-MIPs was successfully obtained by the copolymerization in presence of vinyl groups functionalized GO/SiO2, dopamine (DA), methacrylic acid and ethylene glycol dimethacrylate. The GO/SiO2-MIPs composite was characterized by FTIR, TGA, Raman spectroscopy, SEM and AFM. The properties such as special binding, adsorption dynamics and selective recognition ability using differential pulse voltammetry (DPV) were evaluated. The DPV current response of GO/SiO2-MIPs sensor was nearly 3.2 times that of the non-imprinted polymers (NIPs). In addition, the GO/SiO2-MIPs sensor could recognize DA from its relatively similar molecules of norepinephrine and epinephrine, while the sensors based on GO/SiO2-NIPs and vinyl groups functionalized GO/SiO2 did not have the ability. The GO/SiO2-MIPs sensor had a wide linear range over DA concentration from 5.0 × 10(-8) to 1.6 × 10(-4)M with a detection limit of 3.0 × 10(-8)M (S/N=3). The sensor based on this novel imprinted composite was applied to the determination of DA in injections and human urine samples with satisfactory results.

A novel composite of graphene quantum dots and molecularly imprinted polymer for fluorescent detection of paranitrophenol

A novel fluorescent sensor based on graphene quantum dots (GQDs) was synthesized for determination of paranitrophenol (4-NP) in water sample, where molecularly imprinted polymer (MIP) was incorporated in GQDs-based sensing system for the first time. A simple hydrothermal method was used to fabricate silica-coated GQDs. The final composite was developed by anchoring the MIP layer on the silica-coated GQDs using 3-aminopropyltriethoxysilane as functional monomer and tetraethoxysilane as crosslinker. The combination of GQDs and MIP endows the composite with stable fluorescent property and template selectivity. Due to resonance energy transfer from GQDs (donor) to 4-NP (acceptor), the fluorescence of the MIP-coated GQDs composite can be efficiently quenched when 4-NP molecules rebound to the binding sites. The composite was applied to the detection of the non-emissive 4-NP and exhibited a good linearity in range of 0.02-3.00 µg mL(-1) with the detection limit of 9.00 ng mL(-1) (S/N=3). This work may open a new possibility for developing GQDs-based composite with selective recognition, and it is desirable for chemical sensing application.

A novel electrochemical sensor for determination of dopamine based on AuNPs@SiO2 core-shell imprinted composite

A novel core-shell composite of gold nanoparticles (AuNPs) and SiO(2) molecularly imprinted polymers (AuNPs@SiO(2)-MIPs) was synthesized through sol-gel technique and applied as a molecular recognition element to construct an electrochemical sensor for determination of dopamine (DA). Compared with previous imprinting recognition, the main advantages of this strategy lie in the introduction and combination of AuNPs and biocompatible porous sol-gel material (SiO(2)). The template molecules (DA) were firstly adsorbed at the AuNPs surface due to their excellent affinity, and subsequently they were further assembled onto the polymer membrane through hydrogen bonds and π-π interactions formed between template molecules and silane monomers. Cyclic voltammetry (CV) was carried out to extract DA molecules from the imprinted membrane, and as a result, DA could be rapidly and effectively removed. The AuNPs@SiO(2)-MIPs was characterized by ultraviolet visible (UV-vis) absorbance spectroscopy, transmission electron microscope (TEM) and Fourier transform infrared spectrometer (FT-IR). The prepared AuNPs@SiO(2)-MIPs sensor exhibited not only high selectivity toward DA in comparison to other interferents, but also a wide linear range over DA concentration from 4.8 × 10(-8) to 5.0 × 10(-5)M with a detection limit of 2.0 × 10(-8)M (S/N=3). Moreover, the new electrochemical sensor was successfully applied to the DA detection in dopamine hydrochloride injection and human urine sample, which proved that it was a versatile sensing tool for the selective detection of DA in real samples.

Photochemical Synthesis of Noble Metal (Ag, Pd, Au, Pt) on Graphene/ZnO Multihybrid Nanoarchitectures as Electrocatalysis for H2O2 Reduction

For the first time, a series of noble metal (Ag, Au, Pd, and Pt) nanoparticles (NPs) based on new functional graphene were successfully achieved via UV-assisted photocatalytic reduction by ZnO nanorods. The whole preparation strategy for constructing noble metal deposited graphene sheets/ZnO (GS/ZnO) was elucidated in detail in this work. First, graphene oxide based two-dimensional carbon nanostructures served as a support to disperse ZnO nanorods through a hydrothermal route. The ZnO nanorods were self-assembled onto the surface of graphene sheets, forming GS/ZnO nanocomposite, and the graphene oxide was reduced, yielding reduced graphene sheets in this synthetic procedure. Second, the GS/ZnO films were further employed as supporting materials for the dispersion of metal nanoparticles. Photogenerated electrons from UV-irradiated ZnO were transported across GS to stepwise and respectively reduce v μL metal ions (Ag(+), Pd(2+), AuCl4(-), PtCl6(2-), 20 mg/mL) into metal (Ag, Pd, Au, Pt) NPs at a location distinct from the ZnO anchored site, forming five graphene-based hybrid nanocomposites designated as GS/ZnO, GS/ZnO@Agv, GS/ZnO@Pdv, GS/ZnO@Auv, GS/ZnO@Ptv, respectively. The obtained mutihybrid nanoarchitectured materials were clearly characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). According to the diameters and distribution, the four metal NPs on GS/ZnO were divided into two categories: Ag&Au and Pd&Pt. Their difference was rooted in the rival abilities of gathering electron between graphene and different metal islands in the photochemical reduction process. The electrochemical behaviors of the five resultant hybrid nanocomposites were investigated in H2O2 as well as in potassium ferricyanide (Fe(CN)6(3-/4-)) and displayed distinct electrocatalytic activity.

Layer-by-Layer self-assembled acetylcholinesterase/PAMAM-Au on CNTs modified electrode for sensing pesticides

In this paper, an acetylcholinesterase (AChE)/dendrimers polyamidoamine (PAMAM)-Au/Carbon nanotubes (CNTs) multilayer modified electrode based on LbL self-assembled technique was employed in the detection of carbofuran in samples. The configuration of the nanostructure on the electrode provided a favorable environment to the immobilization of AChE. The modified films also improved the electrocatalytic characteristics and electron transfer speed between the films and the surface of electrode. The PAMAM-Au nanoparticles were characterized by SEM and UV-VIS methods. A set of experimental conditions were also optimized for the detection of the pesticides. A linear response over carbofuran concentration in the range of 4.8x10(-9)M to 0.9x10(-7)M was exhibited with a detection limit of 4.0x10(-9)M. The biosensor showed high sensitivity, good stability and reproducibility with promising application.

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.

Sensitive determination of dopamine on poly(aminobenzoic acid) modified electrode and the application toward an experimental Parkinsonian animal model

Recent research on the pathology and treatment of Parkinsons disease (PD) necessitates the development of methods for analysis of dopamine (DA), an electroactive substance whose content reduces in patients with PD. The concentration variation of dopamine in an experimental Parkinsonian animal model and a treatment model was studied in this paper. For the purpose of detecting dopamine sensitively, a poly(para-aminobenzoic acid) (P-pABA) electrochemically modified glassy carbon electrode was prepared. The electrochemical behavior of the modified electrode was studied by cyclic voltammetry. Under optimum conditions, the P-pABA modified electrode showed high sensitivity to DA oxidation. Coupled with high-performance liquid chromatography, the modified electrode was utilized to detect dopamine in rat brain dialysate with the linear range over three orders of magnitude and the detection limit of 2.0x10(-8) mol l(-1) (S/N=3). By treatment with reserpinum, an experimental Parkinsonian animal model was produced. Levodopa (L-dopa) and sodium nitroprusside (SNP) were used as drugs for treatment PD in this work. The dopamine level in PD model was only 22.4% that of the control one. PD rats could recover after therapy of L-dopa or SNP and the dopamine level increased sixfold compared with those not treated with drugs.

Layer-by-layer self-assembly of functionalized graphene nanoplates for glucose sensing in vivo integrated with on-line microdialysis system

In this work, a novel amperometric biosensor for hydrogen peroxide was fabricated through the layer-by-layer (LBL) self-assembling of amine-terminated ionic liquid (IL-NH(2)), and sulfonic acid (SO(3)(-)) functionalized graphene by covalent bonding. The modification of the two functionalities introduced positive and negative charge onto the surface of graphene respectively, thus facilitating the formation of a multilayer film denoted with {IL-RGO/S-RGO}(n) through electrostatic interaction and further immobilization of glucose oxidase (GOx). The resulting {IL-RGO/S-RGO}(n)/GOx/Nafion biosensor displayed an excellent response to glucose at a potential of -200 mV. Combined with on-line microdialysis system, the glucose biosensor in the on-line system showed good linear range from 10 μM to 500 μM with the detection limit of 3.33 μM (S/N=3). Consequently, the basal level of glucose in the striatum of anesthetic rats was calculated to be 0.376 ± 0.028 mM (mean ± s.d., n=3). The {IL-RGO/S-RGO}(n)/GOx/Nafion biosensor was further applied for in vivo sensing of the glucose level in the striatum when rats received intraperitoneal (i.p.) injection of 30 μL insulin, which resulted in an obvious decrease in the extracellular concentration of glucose within 30 min. The method was proved to be sensitive and reproducible, which enabled its promising application in physiology and pathology.

Study of carbon nanotubes-HRP modified electrode and its application for novel on-line biosensors.

In this paper, multi-walled carbon nanotubes (MWCNTs) were successfully immobilized on the surface of a glassy carbon electrode by mixing with horse-radish peroxidase (HRP). The electrochemical behavior of H2O2 was also studied with the MWCNTs-HRP modified electrode as a working electrode. The MWCNTs-HRP modified electrode showed excellent response of reduction current for the determination of H2O2 at the potential of -300 mV (vs. Ag/AgCl). We assembled the MWCNTs-HRP modified electrode in a thin-layer flow cell and the H2O2 solution was continuously introduced into the cell with a syringe pump. We optimized the sensitivity of the H2O2 sensor by adjusting the working potential and the pH of the buffer solution. The peak current increased linearly with the concentration of H2O2 in the range 3.0 x 10(-7) to approximately 2.0 x 10(-4) mol L(-1). The detection limit is 1.0 x 10(-7) mol L(-1) (S/N = 3). The interferences from ascorbic acid, uric acid and other electroactive substances can be greatly excluded since the sensor can be operated at -300 mV. Stability and reproducibility of the MWCNTs-HRP chemically modified electrode were also studied in this paper. Fabricated with glucose and lactate oxidase, the MWCNTs-HRP electrode was also applied to prepare the on-line glucose and lactate biosensors because of the high sensitivity for the determination of H2O2.

Preparation and photoelectrocatalytic activity of ZnO nanorods embedded in highly ordered TiO2 nanotube arrays electrode for azo dye degradation

In this article, the ZnO nanorods embedded in highly ordered TiO(2) nanotube arrays (ZnO/TiO(2) NR/Ts) electrodes were fabricated through two steps: (1) electrosynthesis of TiO(2) nanotube arrays (TiO(2) NTs) in HF solution by anodization method; (2) followed by cathodic electrodeposition of ZnO embedded in the TiO(2) nanotube arrays. The morphological characteristics and structures of ZnO/TiO(2) NR/Ts electrodes were examined by field-emission scanning electron microscopy (FE-SEM), energy dispersive X-ray (EDX) spectroscopy, X-ray diffraction (XRD) analysis, and UV-vis spectra. The linear-sweep photovoltammetry response on the ZnO/TiO(2) NR/Ts electrode was presented and the photocurrent was dramatically enhanced on the ZnO/TiO(2) NR/Ts electrode, comparing with that on bare TiO(2) NTs electrode. The photocatalytic and photoelectrocatalytic activity of ZnO/TiO(2) NR/Ts electrode was evaluated in degradation of methyl orange (MO) in aqueous solution.