Saichai Lin

Multi-walled carbon nanotube modified dummy-template magnetic molecularly imprinted microspheres as solid-phase extraction material for the determination of polychlorinated biphenyls in fish.

Novel multi-walled carbon nanotube modified dummy-template molecularly imprinted microspheres (MWCNTs@DMMIPs) were successfully synthesized as adsorbents for six kinds of polychlorinated biphenyls (PCBs). MWCNTs@DMMIPs were prepared by a surface molecular imprinting technique. Core-shell Fe3 O4 @SiO2 nanoparticles were employed as magnetic support. 3,4-Dichlorobenzene acetic acid was used as a dummy template instead of PCBs, methacrylic acid was used as functional monomer and ethylene glycol dimethacrylate was used as the cross-linker. The resulting absorbent was characterized by various methods. The adsorbent was employed for extracting PCBs and exhibited good selectivity and high adsorption efficiency. Furthermore, it was reusable and capable of magnetic separation. Adsorption kinetics fit well with a pseudo-second-order kinetic equation and also exhibited a three-stage intra-particle diffusion model. The Freundlich model was used to describe the adsorption isotherms. The materials were successfully applied to the magnetic dispersive solid-phase extraction of six kinds of PCBs followed by gas chromatography with mass spectrometry determination in fish samples, the limit of detection of six kinds of PCBs were 0.0028-0.0068 μg/L and spiked recoveries ranged between 73.41 and 114.21%. The prepared adsorbent was expected to be a new material for the removal and recovery of PCBs from contaminated foods.

Separation and enrichment of six indicator polychlorinated biphenyls from real waters using a novel magnetic multiwalled carbon nanotube composite absorbent

A novel and effective magnetic multiwalled carbon nanotube composite for the separation and enrichment of polychlorinated biphenyls was developed. Fe3 O4 @SiO2 core-shell structured nanoparticles were first synthesized, then the poly(sodium 4-styrenesulfonate) was laid on its surface to prepare the polyanionic magnetic nanoparticles. The above materials were then grafted with polycationic multiwalled carbon nanotubes, which were modified by polydiallyl dimethyl ammonium chloride through the layer-by-layer self-assembly approach. Its performance was tested by magnetic solid-phase extraction and gas chromatography with mass spectrometry for the determination of six kinds of indicator polychlorinated biphenyls in water samples. Under optimal conditions, the spiked recoveries of several real samples for six kinds of polychlorinated biphenyls (PCB28, PCB52, PCB101, PCB138, PCB153, PCB180) were in the range of 73.4-99.5% with relative standard deviations varying from 1.5 to 8.4%. All target compounds showed good linearities in the tested range with correlation coefficients higher than 0.9993. The limits of quantification for six kinds of indicator polychlorinated biphenyls were between 0.018 and 0.039 ng/mL. The proposed method was successfully applied to analyze polychlorinated biphenyls in real water samples. Satisfactory results were obtained using the effective magnetic absorbent.

A novel reductive graphene oxide-based magnetic molecularly imprinted poly(ethylene-co-vinyl alcohol) polymers for the enrichment and determination of polychlorinated biphenyls in fish samples

The novel reductive graphene oxide‐based magnetic molecularly imprinted poly(ethylene‐co‐vinyl alcohol) polymers (rGO@m‐MIPs) were successfully synthesized as adsorbents for six kinds of polychlorinated biphenyls (PCBs) in fish samples. rGO@m‐MIPs was prepared by surface molecular imprinting technique. Besides, Fe3O4 nanoparticles (NPs) were employed as magnetic supporters, and rGO@Fe3O4 was in situ synthesis. Different from functional monomer and cross‐linker in traditional molecularly imprinted polymer, here, 3,4‐dichlorobenzidine was employed as dummy molecular and poly(ethylene‐co‐vinyl alcohol) was adopted as the imprinted polymers. After morphology and inner structure of the magnetic adsorbent were characterized, the adsorbent was employed for disperse solid phase extraction toward PCBs and exhibited great selectivity and high adsorption efficiency. This material was verified by determination of PCBs in fish samples combined with gas chromatography‐mass spectrometry (GC‐MS) method. According to the detection, the low detection limits (LODs) of PCBs were 0.0035–0.0070 µg l−1 and spiked recoveries ranged between 79.90 and 94.23%. The prepared adsorbent can be renewable for at least 16 times and expected to be a new material for the enrichment and determination of PCBs from contaminated fish samples. Copyright

Electro-deposited poly-luminol molecularly imprinted polymer coating on carboxyl graphene for stir bar sorptive extraction of estrogens in milk

Electrochemical polymerization of luminol molecularly imprinted polymer on carboxyl graphene (MIP/CG) was developed as stir bar sorptive extraction (SBSE) coating for selective pre-concentration and specific recognition of bisphenol A (BPA), hexoestrol and diethylstilbestrol in milk samples. Luminol was employed as monomer and BPA as the template to prepare MIP under 0-0.6V electro-polymerization. Carboxyl graphene was modified on pencil lead as the substrate to increase extraction capacity. The preparation and extraction conditions affecting the extraction efficiency were optimized. Under the optimized conditions, a good linearity of three estrogens was obtained in the range of 4-1000ngmL(-1). The average recoveries at the three spiked levels of the three estrogens ranged from 83.4% to 96.3% with the relative standard deviations (RSD)≤7.1%. The limits of detection were in the range of 0.36-1.09ngmL(-1). The developed method with low cost, high selectivity and good reproducibility can be potentially applied for determining trace estrogens in complex food samples.

Amperometric Immunosensor for Determination of Clenbuterol Based on Enzyme-Antibody Coimmobilized ZrO2 Nano Probes as Signal Tag

Abstract A novel amperometic immunosensor for Clenbuterol (CLB) detection based on enzyme-antibody co-immobilized zirconium dioxide (ZrO2) nanoprobes for signal amplification was developed. First, ZrO2 nanoparticles (ZNPs) were used to adsorb glucose oxidase (GOD) enzyme and CLB antibody (anti-CLB) to prepare the signal tag (ZNPs/GOD-anti CLB). While poly(diallyldimethylammonium chloride) (PDDA), Hemin and Au nanoparticles (AuNPs) were assembled layer by layer on the surface of multi-walled carbon nanotubes (MWCNTs) which was modified by screen-printed electrodes (SPCE). By this means, the sensor (SPCE|WCNTs/PDDA/Hemin/AuNPs), which can catalyze H2O2 into generate reduction current, was obtained. When CLB was detected, the samples and ZNPG were embedded to the bottom of the 96-well plate in advance. On the basis of the reaction mechanism of competitive enzyme-linked immunoassay, CLB in samples would compete with slab CLB for the combination with the nanoprobe ZNPG. After reaction, glucose (Glu) was added to the 96-well plate, and then the GOD catalyze Glu to generate H2O2, which could be detected by the immunosensor for quantification. Current decline in value (δI) was inversely proportional to a certain concentration range of CLB. Under the optimal conditions (pH 7.0, incubation time 30 min at 37 °C), the immunosensor provided an excellent response for CLB ranging from 0.003 to 100 μg L−1 with a detection limit of 1 ng L−1 (3σ). The sensitivity of this method was 2 orders of magnitude higher than that of the ELISA method due to the high density of GOD on the signal tag, which could greatly amplify the detection signal. The average recovery of the samples was 93.6%, the coefficient of intragroup variation was less than 2.5%, which confirmed that the amperometic immunosensor prepared had a high precision. The immunosensor was reusable, sensitive and rapid for the analysis of ultra trace amounts of CLB in food samples in real time.

Novel method for the rapid and specific extraction of multiple β2 -agonist residues in food by tailor-made Monolith-MIPs extraction disks and detection by gas chromatography with mass spectrometry.

A quick and specific pretreatment method based on a series of extraction clean-up disks, consisting of molecularly imprinted polymer monoliths and C18 adsorbent, was developed for the specific enrichment of salbutamol and clenbuterol residues in food. The molecularly imprinted monolithic polymer disk was synthesized using salbutamol as a template through a one-step synthesis process. It can simultaneously and specifically recognize salbutamol and clenbuterol. The monolithic polymer disk and series of C18 disks were assembled with a syringe to form a set of tailor-made devices for the extraction of target molecules. In a single run, salbutamol and clenbuterol can be specifically extracted, cleaned, and eluted by methanol/acetic acid/H2 O. The target molecules, after a silylation derivatization reaction were detected by gas chromatography-mass spectrometry. The parameters including solvent desorption, sample pH, and the cycles of reloading were investigated and discussed. Under the optimized extraction and clean-up conditions, the limits of detection and quantitation were determined as 0.018-0.022 and 0.042-0.049 ng/g for salbutamol and clenbuterol, respectively. The assay described was convenient, rapid, and specific; thereby potentially efficient in the high-throughput analysis of β2 -agonists residues in real food samples.