Xiu-Chun Guo

Molecularly imprinted polymer as SPE sorbent for selective extraction of melamine in dairy products.

In this paper, a highly selective sample cleanup procedure combining molecular imprinting and solid-phase extraction (MI-SPE) was developed for the isolation of melamine in dairy products. The molecularly imprinted polymer (MIP) was prepared using melamine as the template molecule, methacrylic acid as the functional monomer and ethylene glycol dimethacrylate as the cross-linking monomer. The melamine imprinted polymer was used as selective sorbent for the solid-phase extraction of melamine from dairy products. An off-line MI-SPE method followed by high-performance liquid chromatography with diode-array detection for the detection of melamine was also established. The mean recoveries of melamine from ultra-heat treatment (UHT) milk and milk powders were 92.9-98.0% and 91.6-102.8%, respectively. Good linearity was obtained from 0.5 microM to 10 microM (r>0.999) with a quantitation limit of 0.5 micromol/L (0.06 ppm) which was sufficient to analyse melamine at the maximum level permitted by U.S. Food and Drug Administration (1 ppm) in dairy products. It was demonstrated that the proposed MI-SPE-HPLC method could be applied to direct determination of melamine in dairy products.

Molecularly imprinted polymer for selective extraction of domoic acid from seafood coupled with high-performance liquid chromatographic determination.

In this work, a highly selective sample cleanup procedure that combining molecular imprinting technique (MIT) and solid phase extraction (SPE) was developed for the isolation of domoic acid (a fascinating marine toxin) from seafood samples. The molecular imprinting polymer (MIP) for domoic acid was prepared using 1,3,5-pentanetricarboxylic acid as the template molecule instead of domoic acid. 4-Vinyl pyridine was used as the functional monomer and ethylene glycol dimethacrylate was used as the cross-linking monomer. The obtained imprinted polymer showed high affinity to domoic acid and was used as selective sorbent for the SPE of domoic acid from seafood samples. An off-line molecularly imprinted solid phase extraction (MISPE) method followed by high-performance liquid chromatography (HPLC) with diode-array detection for the detection of domoic acid was also established. Good linearity was obtained from 0.5 mg L(-1) to 25 mg L(-1) (R(2)>0.99) with a quantitation limit of 0.1 mg L(-1), which was sufficient to determine domoic acid at the maximum level permitted by several authorities. The mean recoveries of domoic acid from mussel extracts were 93.4-96.7%. It was demonstrated that the proposed MISPE-HPLC method could be applied to direct determination of domoic acid from seafood samples.

Molecularly imprinted solid phase extraction method for simultaneous determination of seven nitroimidazoles from honey by HPLC-MS/MS

In this work, a selective sample cleanup procedure that combined molecular imprinting technique with solid phase extraction was developed for the simultaneous extraction of the seven nitroimidazoles (NMZs) from honey samples. The molecular imprinting polymers for NMZs were prepared through bulk polymerization method using 2-methyl-5-nitroimidazole as template molecule, methacrylic acid as the functional monomer and ethylene glycol dimethacrylate as the cross linking agent. The obtained molecular imprinting polymers showed high affinity to template molecule and was used as selective sorbent for simultaneously selective extraction of the seven NMZs from honey matrix. An off-line molecularly imprinted solid phase extraction (MISPE) method followed by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS-MS) for simultaneous determination of the seven NMZs from honey samples was also established. The proposed method was validated at 1.0, 2.0 and 10.0μg/kg, obtaining recoveries in the range of 79.7-110%, with repeatability and interday precision values (expressed as relative standard deviation) ≤11.4% and ≤15.2%, respectively. Limits of quantification for different NMZs were 1.0μg/kg, which were always below the minimum required performance limits established by the European Community Reference Laboratories (Commission Decision 2002/657/EC). It was demonstrated that this proposed MISPE-HPLC-MS-MS method could be applied to direct determination of NMZs from honey samples.

ZnO nanotubes supported molecularly imprinted polymers arrays as sensing materials for electrochemical detection of dopamine

In this study, ZnO nanotubes (ZNTs) were prepared onto fluorine-doped tin oxide (FTO) glass and used as supports for MIPs arrays fabrication. Due to the imprinted cavities are always located at both inner and outer surface of ZNTs, these ZNTs supported MIPs arrays have good accessibility towards template and can be used as sensing materials for chemical sensors with high sensitivity, excellent selectivity and fast response. Using K3[Fe(CN)6] as electron probe, the fabricated electrochemical sensor shows two linear dynamic ranges (0.02-5μM and 10-800μM) towards dopamine. This proposed electrochemical sensor has been applied for dopamine determination with satisfied recoveries and precision. More complex human urine samples also confirmed that the proposed method has good accuracy for dopamine determination in real biological samples. These results suggest potential applicability of the proposed method and sensor in important molecule analysis.

One Step Electrodeposition of Graphene-Au Nanocomposites for Highly Sensitive Electrochemical Detection of Salbutamol

A simple and available strategy was developed for one step electrodeposition of graphene-Au (G-Au) nanocomposites which could be used for highly sensitive electrochemical detection of salbutamol. GAu nanocomposites were simultaneously deposited on glassy carbon electrode by one step electrodeposition method. This resulting G-Au nanocomposites modified electrode was characterized by different methods. Compared to graphene or Au nanoparticles (AuNPs) modified electrodes, this GAu nanocomposites modified electrode dramatically promote the electrooxidation of salbutamol on electrode surface and significantly enhance the differential pulse voltammetry (DPV) current response towards salbutamol. In addition, this one step electrodeposition method improved the stability of the modified G-Au nanocomposites layer. This constructed G-Au nanocomposites based electrochemical sensor exhibits high sensitivity and good selectivity for salbutamol, which may introduce by the synergistic effect of G-Au nanocomposites. Under optimized conditions, the constructed salbutamol sensor showed two linear dynamic ranges (0.05-10 μM and 20200 μM). The linear range and sensitivity of the proposed salbutamol electrochemical sensors are better than other reported values. Moreover, this electrochemical sensor has been successfully applied to the determination of salbutamol in salbutamol sulfate injections with satisfied recoveries (95.4 % to 103.1 %) and precision (1.5 % to 4.6 % of RSD).

Controlled Synthesis and Optical Properties of CuInS2 Nanocrystals

A facile method for the synthesis of size-and shape-controlled CuInS2 semiconductor nanocrystals was developed by thermolysis of a mixed solution of Cu (acac)2, In (acac)3 and dodecanethiol at 200 °C. By adjusting the reaction time, CuInS2 nanocrystals with size of ~2 to ~6 nm were obtained. The as-prepared nanocrystals were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-vis absorption and photoluminescence (PL) spectroscopy. The nanocrystals solutions exhibit tunable absorption and PL spectra with the absorption edge ranging from 450 to 750 nm while the PL emission peaks from 660 to 700, indicting a strong size-dependent quantum confinement effect. The proposed synthesis strategy developed in this work may be used as a general process for other metal chalcogenides nanocrystals and may have a bright application prospects in different areas, such photovoltaic application, in the future.

Synthesis of Single-Crystal Copper Indium Gallium Diselenide (CIGS) Nanotubes Using AAO Templates

A facile solution method for the synthesis of single-crystal copper indium gallium diselenide (CIGS) nanotubes was developed by using anodic aluminum oxide (AAO) as morphology directing template and triethylenetetramine as both reducing agent and effective chelating agent. The crystal structure, morphology, elemental composition of the as-obtained CIGS nanotubes were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM). The as-obtained CIGS nanotubes have a diameter about 200 nm and a thickness of 30 nm. The proposed synthesis strategy developed in this work may be used as a general process for other metal chalcogenides nanotubes and may have a bright application prospects in high efficiency, yet low cost photovoltaic areas in the future.