Xuecai Tan

Synthesis and characterization of core–shell magnetic molecularly imprinted polymers for solid-phase extraction and determination of Rhodamine B in food

Core-shell magnetic molecularly imprinted polymers (MIPs) nanoparticles (NPs), in which a Rhodamine B-imprinted layer was coated on Fe3O4 NPs. were synthesized. First, Fe3O4 NPs were prepared by a coprecipitation method. Then, amino-modified Fe3O4 NPs (Fe3O4@SiO2-NH2) was prepared. Finally, the MIPs were coated on the Fe3O4@SiO2-NH2 surface by the copolymerization with functional monomer, acrylamide, using a cross-linking agent, ethylene glycol dimethacrylate; an initiator, azobisisobutyronitrile and a template molecule, Rhodamine B. The Fe3O4@MIPs were characterized using a scanning electron microscope, Fourier transform infrared spectrometer, vibrating sample magnetometer, and re-binding experiments. The Fe3O4@MIPs showed a fast adsorption equilibrium, a highly improved imprinting capacity, and significant selectivity; they could be used as a solid-phase extraction material and detect illegal addition Rhodamine B in food. A method was developed for the selective isolation and enrichment of Rhodamine B in food samples with recoveries in the range 78.47-101.6% and the relative standard deviation was <2%.

Amperometric hydrogen peroxide biosensor based on immobilization of hemoglobin on a glassy carbon electrode modified with fe(3)o(4)/chitosan core-shell microspheres.

Novel magnetic Fe3O4/chitosan (CS) microspheres were prepared using magnetic Fe3O4 nanoparticles and the natural macromolecule chitosan. Then, using an easy and effective hemoglobin (Hb) immobilization method, an innovative biosensor with a Fe3O4/CS-Hb-Fe3O4/CS “sandwich” configuration was constructed. This biosensor had a fast (less than 10 s) response to H2O2 and excellent linear relationships were obtained in the concentration range of 5.0 × 10−5 to 1.8 × 10−3 M and 1.8 × 10−3 to 6.8 × 10−3 M with a detection limit of 4.0 × 10−6 M (s/n = 3) under the optimum conditions. The apparent Michaelis-Menten constant Km was 0.29 mM and it showed the excellent biological activity of the fixed Hb. Moreover, the biosensor had long-time stability and good reproducibility. The method was used to determine H2O2 concentration in real samples.

Room-temperature synthesis, growth mechanism and properties of uniform CdMoO4 nano-octahedra

Large-scale, uniform and single-crystalline CdMoO4 nano-octahedra have been successfully synthesized via a reverse-microemulsion route at room temperature. The structures and morphologies of the as-prepared products were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). The effect of various reaction conditions on the morphology and size of CdMoO4 products was investigated. The results show that the water content (ω), initial concentration of reagents and reaction temperature play important roles in governing the final product. A possible four-step growth mechanism was proposed for the formation of CdMoO4 nano-octahedra. Room-temperature photoluminescence (PL) spectra of CdMoO4 crystallites were measured, indicating that their optical properties obviously depend on the particle sizes and morphologies. Moreover, temperature-dependent photoluminescence and electrochemical behavior of CdMoO4 nano-octahedra were tested for the first time. The results suggest their prospective applications for optoelectronic devices and sensor construction.

Synthesis and characterization of molecularly imprinted polymers with modified rosin as a cross-linker and selective SPE-HPLC detection of basic orange II in foods

Basic orange II (BOII) is an alkaline azo dye that is listed as a prohibited substance in food additives. In order to develop a novel molecularly imprinted polymer (MIP) with modified rosin as a cross-linker for the selective solid-phase extraction (SPE) of BOII in foods, MIP was synthesized using BOII as the template molecule, acrylamide as the functional monomer, and maleic rosin glycol acrylate (MRGA) as the cross-linking agent. MIP was characterized using scanning electron microscopy, Fourier transform infrared spectroscopy and thermogravimetric analysis. Compared to the imprinted polymers prepared by the traditional cross-linker, MIP showed a highly imprinting capacity, significant selectivity, hardness and toughness, and it could be used as a SPE material, as well as for the detection of illegal addition of BOII in food. In the sample with a spiked level of 5–11 mg kg−1, BOII in foods revealed an average recovery rate of 68.43–80.25% with a precision (relative standard deviation) of less than 1.2%.

A novel hydrogen peroxide biosensor based on sol–gel poly (vinyl alcohol) (PVA)/(titanium dioxide)TiO2 hybrid material

A novel hydrogen peroxide biosensor has been fabricated based on Hb entrapped poly(vinyl alcohol) (PVA)/Titanium dioxide (TiO2) hybrid material. Multi-walled carbon nanotubes (MWCNTs) were then dispersed into the composite matrix. It was found that such hybrid material could retain the native biocatalytic activity of the entrapped Hb by electrochemical experiments. In addition, MWCNTs enhanced catalytic performance of hydrogen peroxide and promoted electronic transfer. Effects of some experimental variables such as the amount of MWCNTs, concentration of enzyme, amounts of modifier on the current response of the biosensor were investigated. A linear calibration graph was obtained in the concentration range of H2O2 from 0.5 to 2.7 μM (linear regression coefficient = 0.997) with a detection limit of 0.01 μM (S/N = 3). The apparent Michaelis-Menten constant Km was 0.997 μM. The biosensor displayed excellent repeatability, high sensitivity, long-term stability, and good selectivity. The recovery of H2O2 in samples was testified with satisfactory results.

Morphology Effect on the Kinetic Parameters and Surface Thermodynamic Properties of Ag3PO4 Micro-/Nanocrystals

Considerable effort has been exerted using theoretical calculations to determine solid surface energies. Nanomaterials with high surface energy depending on morphology and size exhibit enhanced reactivity. Thus, investigating the effects of morphology, size, and nanostructure on the surface energies and kinetics of nanomaterials is important. This study determined the surface energies of silver phosphate (Ag3PO4) micro-/nanocrystals and their kinetic parameters when reacting with HNO3 by using microcalorimetry. This study also discussed rationally combined thermochemical cycle, transition state theory, basic theory of chemical thermodynamics with thermokinetic principle, morphology dependence of reaction kinetics, and surface thermodynamic properties. Results show that the molar surface enthalpy, molar surface entropy, molar surface Gibbs free energy, and molar surface energy of cubic Ag3PO4 micro-/nanocrystals are larger than those of rhombic dodecahedral Ag3PO4 micro-/nanocrystals. Compared with rhombic dodecahedral Ag3PO4, cubic Ag3PO4 with high surface energy exhibits higher reaction rate and lower activation energy, activation Gibbs free energy, activation enthalpy, and activation entropy. These results indicate that cubic Ag3PO4 micro-/nanocrystals can overcome small energy barrier faster than rhombic dodecahedral Ag3PO4 micro-/nanocrystals and thus require lower activation energy.

An electrochemical sensor for the determination of phoxim based on a graphene modified electrode and molecularly imprinted polymer

Graphene and a novel cross-linker (ethylene glycol maleic rosinate acrylate) for preparing highly sensitive, molecularly imprinted sensors were proposed for phoxim determination. A molecularly imprinted polymer (MIP) film was created on a graphene-modified electrode for the determination of phoxim using a free radical polymerization method. The electrochemical properties of the MIP and non-molecularly imprinted polymer (NIP) sensors were investigated via cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). The surface morphology of the imprinted film was characterized by scanning electron microscopy (SEM). Under the optimal experimental conditions, the peak currents were proportional to the concentrations of phoxim in the range of 8.0 × 10−7 to 1.4 × 10−4 mol L−1 with a detection limit of 2.0 × 10−8 mol L−1 (S/N = 3). The imprinted electrochemical sensor was employed to determine phoxim in cucumber samples with recovery ranging from 98.06% to 101.13%. An adsorption model for the imprinted sensor was investigated, and the measured imprinting factor β of the sensor was found to be 7.23, with the binding rate constant k being 14.2247 s. The developed electrochemical sensor based on the graphene modified electrode and the molecularly imprinted polymer exhibited good repeatability and stability, and can be successfully used to determine phoxim in cucumber samples.

Electrochemical Sensor for the Determination of Theophylline Based on Molecularly Imprinted Polymer with Ethylene Glycol Maleic Rosi- nate Acrylate as Cross-linker

A novel electrochemical sensor for the determination of theophylline based on ethylene glycol maleic rosinate acrylate as the cross linking agent and acrylic acid as functional monomer was fabricated by molecularly imprinted technology. A molecularly imprinted polymers (MIPs) membrane was synthesized on the surface of a glassy carbon electrode in vacuum drying oven by free radical polymerization method. The electrochemical behavior of the membrane was characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronoamperometry. Under optimum conditions, it was found that the response of peak currents was linear to the concentration of theophylline in range of 2.00×10

Selective separation and determination of glucocorticoids in cosmetics using dual-template magnetic molecularly imprinted polymers and HPLC

Molecularly imprinting polymers (MIPs) are typically prepared using a single template molecule, which allows selective separation and enrichment of only one target analyte. It is not suitable for determination of complex real samples containing multiple analytes. In order to expand the practical application of imprinted polymers, novel dual-template magnetic molecularly imprinted polymers (MMIPs) were synthesized by surface polymerization using hydrocortisone and dexamethasone as the dual-template molecules in this study. The dual-template MMIPs were prepared by copolymerization on the surface of Fe3O4@ SiO2-NH2, the template molecules, the functional monomer acrylamide (AM), the cross-linking agent ethylene glycol dimethacrylate (EGDMA), and the initiator 2,2-azobisisobutyronitrile. The morphology, magnetic properties and adsorption characteristics of the obtained dual-template MMIPs were studied by field emission scanning electron microscopy, dynamic light scattering, Fourier transform infrared spectroscopy, thermal gravimetric analysis, and vibrating sample magnetometry, and re-binding experiments. The results indicated that dual-template MMIPs had uniform particle size, strong magnetic properties, high thermal stability, and good mass transfer rate. To investigate the selectivity of dual-template MMIPs, the template molecules were mixed along with their structural analogs. The dual-template MMIPs revealed a significantly higher adsorption amount for the template molecule than its structure analog. The dual-template MMIPs can be used for the enrichment and determination of hydrocortisone and dexamethasone in cosmetic products with the recoveries of spiked cosmetic samples ranging from 86.8-107.5% and 91.2-104.3%, respectively. The relative standard deviation (RSD) for hydrocortisone was <2.89%, and RSD for dexamethasone was <2.62%.

Ru(bpy) 3 2+ -Silica@Poly- L -lysine-Au as labels for electrochemiluminescence lysozyme aptasensor based on 3D graphene

In this work, the feasibility of a novel sensitive electrochemiluminescence aptasensor for the detection of lysozyme using Ru(bpy)32+-Silica@Poly-L-lysine-Au (RuSiNPs@PLL-Au) nanocomposites labeling as an indicator was demonstrated. The substrate electrode of the aptasensor was prepared by depositing gold nanoparticles (AuNPs) on 3D graphene-modified electrode. The lysozyme binding aptamer (LBA) was attached to the 3D graphene/AuNPs electrode through gold-thiol affinity, hybridized with a complementary single-strand DNA (CDNA) of the lysozyme aptamer labeled by RuSiNPs@PLL-Au as an electrochemiluminescence intensity amplifier. Thanks to the synergistic amplification of the 3D graphene, the AuNPs and RuSiNPs@PLL-Au NPs linked to Ru(bpy)32+-ECL further enhanced the ECL intensity of the aptasensor. In presence of lysozyme, the CDNA segment of the self-assembled duplex was displaced by the lysozyme, resulting in decreased electrochemiluminescence signal. Under the optimized conditions, the decrease in electrochemiluminescence intensity varied proportionally with the logarithmic concentration of the lysozyme from 2.25 × 10-12 to 5.0 × 10-8 mol L-1, and the detection limit was estimated to 7.5 × 10-13 mol L-1. The aptasensor was further tested in real samples and found reliable for the detection of lysozyme, thus holding great potential application in food safety researches and bioassay analysis.