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Chiral selector-functionalized magnetic nanoparticles were achieved by self-assembly anchoring L-cysteine (L-Cys) on the surface of the Au/Fe 3 O 4 nanocomposites, which was synthesized via a facile in-situ reduction process. The as-prepared L-Cys-Au/Fe 3 O 4 magnetic nanoparticles (MNPs) were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, ultraviolet-visible spectroscopy, Fourier-transform infrared spectroscopy and electrochemical methods The typical MNPs with uniform globular morphology not only can provide the enhanced pore accessibility and excellent electrocatalytic active site for the guest species, but also effectively improve the load capacity of chiral selector of L-Cys. Based on magnetic field-induced assembly, a novel magnetic electrochemical chiral sensor (MECS) was first constructed by MNPs for the discrimination and determination of tyrosine (Tyr) enantiomers. Under the optimized experimental condition, the oxidation peak current ratio of L-Tyr to D-Tyr ( I L / I D ) and the difference between the peak potential of the two enantiomers (Δ E p = E D – E L ) was observed to be 1.85 and 84 mV according to square wave voltammetry (SWV). With the synergic effect of the magnetic Fe 3 O 4 NPs and the chiral electrocatalytic activity of L-Cys functionalized AuNPs, a linear relationship between the peak current and the concentration of the two enantiomers was obtained over the range of 1–125 μM, with the limit of detection of 0.021 μM and 0.084 μM for L- and D-Tyr, respectively. The preferential chiral recognition for L-Tyr was further verified by circular dichroism spectroscopy. Furthermore, the sensitive MECS has been successfully used for the practical determination of L- or D-enantiomer in the Tyr mixture solutions by continuously increasing the concentration of one isomer, showing the consistent and reproducible results. [ABSTRACT FROM AUTHOR]

The molecularly imprinted magnetic stir bar coatings were created based on graft-functional Fe 3 O 4 nanoparticles with magnetic field-induced self-assembly. The magnetic complex including clonazepam as template, the graft-functional Fe 3 O 4 nanoparticles and methacrylic acid as monomers was pre-assembled through π–π interaction and hydrogen bonding, then was directionally adsorbed on the surface of magnetic stir bar under the magnetic induction. The molecularly imprinted coating with well-ordered structure was generated by one-step copolymerization based on the cross linking of ethylene glycol dimethacrylate. The molecularly imprinted coating with multiple recognition sites could be manufactured and applied in polar solvents, and showed superior selectivity and fast binding kinetics for benzodiazepines. The analytes in herbal health foods, treated by stir bar sorptive extraction, were determined by HPLC-UV. Good linearity was observed in the range of 0.01–2 μg mL −1 . The content of clonazepam in the herbal health foods was found to be 44 ng g −1 , and the average recoveries were 89.8–103.3% with a relative standard deviation (RSD) <6.5%, demonstrating the successful application in real sample analysis. [ABSTRACT FROM AUTHOR]

Based on magnetic field directed self-assembly (MDSA) of the ternary Fe 3 O 4 @PANI/rGO nanocomposites, a facile and controllable molecularly imprinted electrochemical sensor (MIES) was fabricated through a one-step approach for detection of glutathione (GSH). The ternary Fe 3 O 4 @PANI/rGO nanocomposites were obtained by chemical oxidative polymerization and intercalation of Fe 3 O 4 @PANI into the graphene oxide layers via π–π stacking interaction, followed by reduction of graphene oxide in the presence of hydrazine hydrate. In molecular imprinting process, the pre-polymers, including GSH as template molecule, Fe 3 O 4 @PANI/rGO nanocomposites as functional monomers and pyrrole as both cross-linker and co-monomer, was assembled through N–H hydrogen bonds and the electrostatic interaction, and then was rapidly oriented onto the surface of MGCE under the magnetic field induction. Subsequently, the electrochemical GSH sensor was formed by electropolymerization. In this work, the ternary Fe 3 O 4 @PANI/rGO nanocomposites could not only provide available functionalized sites in the matrix to form hydrogen bond and electrostatic interaction with GSH, but also afford a promoting network for electron transfer. Moreover, the biomimetic sensing membrane could be controlled more conveniently and effectively by adjusting the magnetic field strength. The as-prepared controllable sensor showed good stability and reproducibility for the determination of GSH with the detection limit reaching 3 nmol L −1 (S/N = 3). In addition, the highly sensitive and selective biomimetic sensor has been successfully used for the clinical determination of GSH in biological samples. [ABSTRACT FROM AUTHOR]

A molecularly imprinted stir bar was constructed based on Fe 3 O 4 @Polyaniline nanoparticles with magnetic field-induced self-assembly process. The monomer, methacrylic acid, was pre-assembled into the pre-polymers with vanillin as template by the formation of hydrogen bonds. After that, the magnetic complexes were generated by the hydrogen bonding, the hydrophobic and π–π interaction between the pre-polymers and Fe 3 O 4 @Polyaniline. The complexes were adsorbed on the surface of magnetic stir bar under the magnetic induction, and the coating of vanillin-molecularly imprinted polymers was generated by the one-step copolymerization basing on the cross linking of ethylene glycol dimethacrylate. The molecular imprinting stir bar showed superior selectivity and fast binding kinetics for vanillin, and was used for the enrichment of vanilla-flavor enhancers (vanillin, ethyl maltol and methyl vanillin) in infant milk powders. The results measured by HPLC-UV exhibited good linear ranges of 0.01–100, 0.02–100 and 0.03–100 μg mL −1 with the limit of detection of 2.5–10.0 ng mL −1 , and the recoveries were 94.7–98.9%, 82.1–96.7% and 84.5–93.2% with RSD < 7.2% for the three enhancers, respectively. [ABSTRACT FROM AUTHOR]

Abstract: A novel electrochemical sensing platform based on magnetic field-induced self-assembly of Fe3O4@Polyaniline nanoparticles (Fe3O4@PANI NPs) has been for the first time fabricated for the sensitive detection of creatinine in biological fluids. The template molecule, creatinine, was self-assembled on the surface of Fe3O4@PANI NPs together with the functional monomer aniline by the formation of N–H hydrogen bonds. After pre-assembled, through the magnetic-induction of the magnetic glassy carbon electrode (MGCE), the ordered structure of molecularly imprinted polymers (MIPs) were established by the electropolymerization and assembled on the surface of MGCE with the help of magnetic fields by a simple one-step approach. The structural controllability of the MIPs film established by magnetic field-induced self-assembly was further studied. The stable and hydrophilic Fe3O4@PANI can not only provide available functionalized sites with which the template molecule creatinine can form hydrogen bond by the abundant amino groups in PANI matrix, but also afford a promoting pathway for electron transfer. The as-prepared molecularly imprinted electrochemical sensor (MIES) shows good stability and reproducibility for the determination of creatinine with the detection limit reached 0.35nmolL−1 (S/N=3). In addition, the highly sensitive and selective MIES has been successfully used for the clinical determination of creatinine in human plasma and urine samples. The average recoveries were 90.8–104.9% with RSD lower than 2.7%. [Copyright &y& Elsevier]

Abstract: Based on magnetic field directed self-assembly (MDSA) of Fe3O4@rGO composites, a novel magnetic molecularly imprinted electrochemical sensor (MIES) was fabricated and developed for the determination of the azo dye amaranth. Fe3O4@rGO composites were obtained by a one-step approach involving the initial intercalating of iron ions between the graphene oxide layers via the electrostatic interaction, followed by the reduction with hydrazine hydrate to deposit Fe3O4 nanoparticles onto the reduced oxide graphene nanosheets. In molecular imprinting, the complex including the function monomer of aniline, the template of amaranth and Fe3O4@rGO was pre-assembled through π–π stacking and hydrogen bonding interactions, and then was self-assembled on the surface of magnetic glassy carbon electrode (MGCE) with the help of magnetic field induction before electropolymerization. The structures and morphologies of Fe3O4@rGO and the doped molecularly imprinted polymers (MIPs) were investigated by Fourier transform infrared spectrometer (FT-IR), Raman spectra and scanning electron microscope (SEM). Besides, the characterization by differential pulse voltammetry (DPV) showed that Fe3O4@rGO composites promoted the electrical conductivity of the imprinted sensors when doped into the MIPs. The adsorption isotherms and adsorption kinetics were employed to evaluate the performances of MIES. The detection of amaranth was achieved via the redox probe K3[Fe(CN)6] by blocking the imprinted cavities, which avoided the interferences of oxidation products and analogs of amaranth. Furthermore, the prepared MIES exhibited good sensitivity, selectivity, reproducibility and efficiency for detecting amaranth in fruit drinks. The average recoveries were 93.15–100.81% with the RSD <3.0%. [Copyright &y& Elsevier]

Abstract: Graphene/gold nanoparticle multilayer films composed of polysodium 4-styrenesulfonate (PSS) functionalized reduced graphene oxide (RGO) and polyamidoamine (PAMAM) dendrimer stabilized gold nanoparticles (AuNPs) were built up using the electrostatic layer-by-layer (LBL) self-assembly technique on a glassy carbon electrode (GCE) modified with a first layer of poly(diallyldimethylammonium chloride) (PDDA). The film assembly, the electrochemical property as well as the electrocatalytic activity toward the oxidation of dopamine were investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV). Electrochemical studies exhibit that the LBL assembled RGO/AuNPs films possess an excellent sensing performance for the detection of dopamine with a linear range from 1μM to 60μM and a limit of detection (LOD) as low as 0.02μM based on S/N =3. In addition, this electrochemical sensor was applied to the simultaneous detection of dopamine and uric acid by using DPV with high sensitivity and selectivity. The good analytical performance and long-term stability of the proposed sensor can be attributed to the combination of the reduced graphene oxide and gold nanoparticles in the LBL assembly films and the synergistic effect on the electrochemical oxidation of dopamine. [Copyright &y& Elsevier]

Abstract: This paper reports a surface molecular self-assembly strategy for molecular imprinting on magnetic nanoparticles for selective separation and detection of estrogens in feeds. First, γ-methacryloxypropyltrimethoxysilane (MEMO) was successfully assembled at the surface magnetic nanoparticles through simple free radical polymerization, and subsequently, the copolymerization was further assembled between methacrylic acid (MAA) and ethylene glycol dimethacrylate (EGDMA) in the presence of templates 17β-estradiol (E2). The synthesized magnetic molecularly imprinted polymers for E2 (E2-MMIPs) showed quick separation, large adsorption capacity, high selectivity and fast binding kinetics for E2. Meanwhile, a dispersive solid-phase extraction (DSPE) based on E2-MMIPs has been established for efficient separation and fast enrichment of estrogens from the feeds. The assay exhibited a linear range of 0.1–4μM for E2 and estriol (E3) with the correlation coefficient above 0.9996 and 0.9994, respectively. Recoveries of E2 from three kinds of feeds spiked at different concentration levels ranged from 92.7% to 97.0% with RSD<4.7%, and recoveries of E3 ranged from 71.9% to 83.1% with RSD<4.9%, respectively. The method is simple and sensitive, and can be used as an alternative tool to effectively separate and enrich the trace of estrogens in agricultural products by HPLC–UV. [Copyright &y& Elsevier]