Tianshu Zhou

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.

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.

Amperometric determination of morphine on cobalt hexacyanoferrate modified electrode in rat brain microdialysates

The analysis of morphine in biological fluids is of vital interest in monitoring opiate abuse and in drug abuse research. In this paper, a cobalt hexacyanoferrate (CoHCF) chemically modified electrode (CME) was prepared. The electrochemical behavior of morphine at this modified electrode has been studied by cyclic voltammetry (CV). The results indicated that the modified electrode exhibited efficiently electrocatalytic oxidation for morphine with relatively high sensitivity and stability. The CoHCF CME was employed as the detector of high-performance liquid chromatography (HPLC). The peak current was linearly related to the morphine concentration in the range of 1.0x10(-6) M to 5.0x10(-4) M at +0.60 V (vs. Ag/AgCl) with a detection limit of 5.0x10(-7) M (S/N of 3). Typical intra-day reproducibility (n=5) of 2.0% and inter-day reproducibility (n=5) of 3.8% were obtained at the 2.0x10(-5) M level. This method was for the first time applied to study the pharmacokinetics of morphine in rat brain after an intravenous administration of morphine (25 mgkg(-1)).

Differential pulse voltammetric determination of methyl parathion based on multiwalled carbon nanotubes-poly(acrylamide) nanocomposite film modified electrode

A sensitive electrochemical differential pulse voltammetry method was developed for detecting methyl parathion based on multiwalled carbon nanotubes-poly(acrylamide) (MWCNTs-PAAM) nanocomposite film modified glassy carbon electrode. The novel MWCNTs-PAAM nanocomposite, containing high content of amide groups, was synthesized by PAAM polymerizing at the vinyl group functionalized MWCNTs surface using free radical polymerization. The MWCNTs-PAAM nanocomposite was characterized by Fourier transform infrared spectroscopy, thermal gravimetric analysis and scanning electron microscopy. Electrochemical behavior and interference studies of MWCNTs-PAAM/GCE for methyl parathion were investigated. The experimental results demonstrated that the MWCNTs-PAAM/GCE exhibited a high adsorption and strong affinity toward methyl parathion compared with some metal ions and nitroaromatic compounds, which exist in environmental samples. The adsorbed amount of methyl parathion on the MWCNTs-PAAM/GCE approached the equilibrium value upon 5 min adsorption time. A linear calibration curve for methyl parathion was obtained in the concentration range from 5.0×10(-9) to 1.0×10(-5) mol L(-1), with a detection limit of 2.0×10(-9) mol L(-1). The MWCNTs-PAAM/GCE was proved to be a suitable sensing tool for the fast, sensitive and selective determination of methyl parathion in environmental water samples.

Determination of Parathion in Vegetables by Electrochemical Sensor Based on Molecularly Imprinted Polyethyleneimine/Silica Gel Films

A novel sensor for the determination of parathion based on coupled grafting of the functional macromolecule polyethyleneimine on surfaces of silica gel particles via a surface imprinting method using molecular imprinting technology was fabricated. The electrochemical behavior of parathion at the imprinted sensor was characterized by cyclic voltammetry and linear sweeping voltammetry. The imprinted films showed high selectivity toward parathion in comparison to similar organophosphates. A linear response over parathion concentration in the range of 0.015-15 mg kg(-1) was exhibited with a detection limit of 0.003 mg kg(-1) (S/N = 3). The imprinted film sensor has been applied to the determination of parathion in spiked vegetable samples and shows promise for fast and selective determination of trace levels of parathion in real samples.

Composites of Polyaniline Nanofibers and Molecularly Imprinted Polymers for Recognition of Nitroaromatic Compounds

This paper reports a monomer strategy for imprinting of 1,3-dinitrobenzene (DNB) molecules at the surface of conductive functional polyaniline nanofibers (PANI) for the first time. It has been demonstrated that the vinyl functional monomer layer on the PANI surface can not only direct the selective occurrence of imprinting polymerization, but can also drive DNB templates into the polymer through charge-transfer complexing interactions between DNB and functionalized PANI. These two basic processes lead to the formation of DNB-imprinted polymers at the surface of polyaniline nanofibers. The capacity to uptake DNB shows that selectivity coefficient in the nanofibers polymers is nearly three times as high as that of traditional imprinted materials and the nanofibers polymers also possess high selectivity toward DNB in comparison to similar nitroaromatic compounds. A linear response of DNB concentration between 2.20×10(-8) and 3.08×10(-6) M was exhibited with a detection limit of 7.33×10(-9) M (S/N=3). These results reported here could form the basis of a new strategy for preparing various polymer-coating layers on polyaniline supports and the molecular imprinting techniques discussed could also find applications in the fields of separation, trace detection, and environmental monitoring.

Quantum dot-DNA aptamer conjugates coupled with capillary electrophoresis: A universal strategy for ratiometric detection of organophosphorus pesticides.

Based on the highly sensitivity and stable-fluorescence of water-soluble CdTe/CdS core-shell quantum dots (QDs) with broad-specificity DNA aptamers, a novel ratiometric detection strategy was proposed for the sensitive detection of organophosphorus pesticides by capillary electrophoresis with laser-induced fluorescence (CE-LIF). The as-prepared QDs were first conjugated with the amino-modified oligonucleotide (AMO) by amidation reaction, which is partial complementary to the DNA aptamer of organophosphorus pesticides. Then QD-labeled AMO (QD-AMO) was incubated with the DNA aptamer to form QD-AMO-aptamer duplex. When the target organophosphorus pesticides were added, they could specifically bind the DNA aptamer, leading to the cleavage of QD-AMO-aptamer duplex, accompany with the release of QD-AMO. As a result, the ratio of peak height between QD-AMO and QD-AMO-aptamer duplex changed in the detection process of CE-LIF. This strategy was subsequently applied for the detection of phorate, profenofos, isocarbophos, and omethoate with the detection limits of 0.20, 0.10, 0.17, and 0.23μM, respectively. This is the first report about using QDs as the signal indicators for organophosphorus pesticides detection based on broad-specificity DNA aptamers by CE-LIF, thus contributing to extend the scope of application of QDs in different fields. The proposed method has great potential to be a universal strategy for rapid detection of aptamer-specific small molecule targets by simply changing the types of aptamer sequences.