Xiuying Liu

Determination of clenbuterol in pork and potable water samples by molecularly imprinted polymer through the use of covalent imprinting method

A novel molecularly imprinted polymer (MIP) for efficient separation and concentration of clenbuterol (CLB) was synthesized by covalent imprinting approach using CLB derivative as functional monomer. The MIPs synthesized were characterized by scanning electron microscope, nitrogen adsorption analysis, Fourier transform infrared spectrometer, and thermo-gravimetric analysis. The binding experimental results showed that the MIPs synthesized had fast adsorption kinetic (20 min at 25 mg L(-1)), high adsorption capacity and specific recognition ability for the analyte. In addition, the MIPs synthesized were successfully used as solid-phase sorbent for CLB sample preparation to be analyzed by high performance liquid chromatography with ultraviolet detector. Under optimized experimental conditions, the linear range of the calibration curve was 5-80 μg L(-1) (R(2) = 0.9938). The proposed method was also applied to the analysis of CLB in pork and potable water samples.

Upconversion particles coated with molecularly imprinted polymers as fluorescence probe for detection of clenbuterol

A novel fluorescence probe based on upconversion particles, YF3:Yb(3+), Er(3+), coating with molecularly imprinted polymers (MIPs@UCPs) has been synthesized for selective recognition of the analyte clenbuterol (CLB), which was characterized by scan electron microscope and X-ray powder diffraction. The fluorescence of the MIPs@UCPs probe is quenched specifically by CLB, and the effect is much stronger than the NIPs@UCPs (non-imprinting polymers, NIPs). Good linear correlation was obtained for CLB over the concentration range of 5.0-100.0 μg L(-1) with a detection limit of 0.12 μg L(-1) (S/N=3). The developed method was also used in the determination of CLB in water and pork samples, and the recoveries ranged from 81.66% to 102.46% were obtained with relative standard deviation of 2.96-4.98% (n=3). The present study provides a new and general tactics to synthesize MIPs@UCPs fluorescence probe with highly selective recognition ability to the CLB and is desirable for application widely in the near future.

Determination of ractopamine in pork using a magnetic molecularly imprinted polymer as adsorbent followed by HPLC

A new magnetic molecularly imprinted polymers (MMIPs) for separation and concentration of ractopamine (RAC) were prepared using surface molecular imprinting technique with methacryloyl chloride as functional monomer and RAC as template. The MMIPs were characterized using transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and vibrating sample magnetometer. The results of re-binding experiments indicated that the MMIPs had fast adsorption kinetics and could reach binding equilibrium within 20 min, and the adsorption capacity of the MMIPs was 2.87-fold higher than that of the corresponding non-imprinted polymer. The selectivity of the MMIPs was evaluated according to its recognition to RAC and its analogues. The synthesized MMIPs were successfully applied to extraction, followed by high performance liquid chromatography to determine RAC in real food samples. Spiked recoveries ranged from 73.60% to 94.5%, with relative standard deviations of <11.17%.

Magnetic molecularly imprinted polymers for spectrophotometric quantification of curcumin in food

Herein, we present a simple and rapid method for monitoring curcumin in food samples using a magnetic molecularly imprinted technique combined with ultraviolet-visible (UV-Vis) spectrophotometry. Magnetic molecularly imprinted polymers (mag-MIPs) were first synthesized by fabricating MIPs on to the surface of Fe3O4 nanobeads using curcumin as a template and methacrylic acid as a functional monomer. The obtained mag-MIPs were evaluated in detail with different techniques (such as binding isotherm, Scatchard analysis, and selectivity) and various adsorption experiments. Finally, mag-MIPs were constructed and UV-Vis spectrophotometry was used to quantify curcumin under optimized conditions. Good recoveries between 79.37% and 88.89% were obtained with the limits of detection and quantification of 1.31 and 4.38μg/mL, respectively.

Purification of six lignans from the stems of Schisandra chinensis by using high-speed counter-current chromatography combined with preparative high-performance liquid chromatography

A method for the preparative purification of lignans from Schisandra chinensis was established using a combination of high-speed counter-current chromatography (HSCCC) and preparative high-performance liquid chromatography (HPLC). The crude extracts obtained from S. chinensis by using 70% ethanol were separated on a macroporous resin column and then eluted with a graded ethanol series. A two-phase solvent system consisting of n-hexane-ethyl acetate-methanol-water (1:1:1:1, v/v) was used for HSCCC, and a mobile phase of acetonitrile-water (50:50, v/v) was used for preparative HPLC. The results obtained using HSCCC were compared with those obtained using preparative HPLC, and their advantages were further integrated to improve the separation efficiency. Six known lignans were identified by electrospray ionisation mass spectrometry and (1)H nuclear magnetic resonance (NMR) and (13)C NMR analyses; the purities of all the compounds were more than 91%.

Ultrasensitive detection of clenbuterol by a covalent imprinted polymer as a biomimetic antibody

As an ideal biomimetic antibody, molecularly imprinted polymer (MIP) has shown great promise in immunoassays. Here, we developed a covalent imprinting method to prepare MIP artificial antibody towards clenbuterol on the well surface of a microtiter plate. Template molecule (clenbuterol) was splited by hydrolysis with functional monomer and removed by methanol/acetic acid solution, and then three-dimensional cavities were fabricated in the MIP, which can rebind template molecule via hydrogen bond interaction. Using this artificial antibody, we developed a novel biomimetic enzyme-linked immunosorbent assay (ELISA) with excellent sensitivity and specificity. The linear range for clenbuterol was 10-5 to 1000μgL-1, with a detection limit of 10-7μgL-1. Cross reactivity of this MIP artificial antibody to other four structural analogs was less than 0.93%. This method was applied to determine clenbuterol in real samples with satisfactory result, suggesting a promising application of the biomimetic ELISA in food and environmental analysis.

Advantage of Eu3+-Doped Polystyrene Microspheres Compared with Colloidal Gold Used in Immunochromatographic Assays for the Detection of Melamine in Milk: Advantages of fluorescent NPs in ICTS…

Colloidal gold and Eu3+ -doped fluorescent microspheres were applied as labels to develop the immunochromatographic strips for detecting melamine in milk. Under the optimized condition, the visual detection limit of colloidal gold-immunochromatographic test strip (ICTS) was 150 μg/L of melamine in phosphate-buffered saline (PBS), although the visual detection limit of fluorescent nanoparticles (FN)-ICTS was 75 μg/L in PBS. As thermal acceleration test, FN-ICTS could be stored at 37 °C for at least 11 d before sample testing, but the color of the lines on colloidal gold-ICTS faded away after 7-d storage. The visual result of FN-ICTS was more stable than that of colloidal gold-ICTS, and the fluorescence intensity of the line on FN-ICTS could be maintained up to 30 d at 22 °C after sample testing. Once the immunochromatographic strips were used to detect melamine in milk, no negative effect of milk components on the performance of FN-ICTS was identified, whereas the performance of colloidal gold-ICTS was significantly influenced by milk matrix.

Visual flow-through column biomimetic immunoassay using molecularly imprinted polymer as artificial antibody for rapid detection of clenbuterol in water sample

ABSTRACT A novel visual flow-through column biomimetic immunoassay using horseradish peroxidase-labeled clenbuterol (HRP-CLB) as a tracer and molecularly imprinted polymers (MIPs) with high specificity as the artificial antibody has been developed for rapid detection of CLB. Different intensities of blue color products on test layer of the column could be observed after reaction. This optimized assay provided a preliminary qualitative result in the concentration range of 0 to 1000 μg/L by judging color density of the test layer without any equipment, and the detection could be finished within 15 min. This assay was evaluated using CLB spiked water samples and results were comparable to high performance liquid chromatography method. The visual detection limit of 5 μg/L in water sample was obtained. This developed flow-through column biomimetic immunoassay was demonstrated as a suitable tool for rapid, sensitive, low-cost, and qualitative determination of CLB residues on site.

The influence of combination mode on the structure and properties of graphene quantum dot-porphyrin composites

As a rising star in the family of fluorescent material, graphene quantum dots (GQDs) have attracted great attention because of their excellent properties such as high photostability against photobleaching and blinking, biocompatibility, and low toxicity. Herein, strongly fluorescent GQDs have been prepared by one-step solvothermal method. Then three kinds of GQDs-porphyrin composites were assembled by means of noncovalent interaction. It was found that the functional groups on the peripheries of the porphyrin were important on the combination mode of porphyrin and GQDs. The fluorescence of GQDs was quenched in the presence of the porphyrin. The suggested quenching mechanism is through Förster resonance energy transfer (FRET). Tetrasodium-meso-tetra(4-sulfonatophenyl) porphine dodecahydrate (NaTSPP) was easy to react with GQDs and flat on the GQDs due to the strong hydrogen bond and π-π interaction. The photoelectronic activity of the GQDs-NaTSPP composite was higher than those of the other two GQDs-porphyrin composites. These results provided some hints for how to adjust the properties of the GQDs-porphyrin composites by modifying the combination mode between porphyrins and GQDs. These novel GQDs-porphyrin composites hold promise for various optical and luminescence-based applications.