Langxing Chen

A molecularly imprinted polymer-coated nanocomposite of magnetic nanoparticles for estrone recognition

In this study, we synthesized Fe(3)O(4) magnetic nanoparticles coated estrone-imprinted polymer with controlled size using a semi-covalent imprinting strategy. In this protocol, the estrone-silica monomer complex (EstSi) was synthesized by the reaction 3-(triethoxysilyl)propyl isocyanate with estrone, where the template was linked to the silica coating on the iron oxide core via a thermally reversible bond. The removal of the template by a simple thermal reaction produced specific estrone recognition sites on the surface of silica shell.The resulting estrone-imprinted polymer coating Fe(3)O(4) magnetic hybrid nanoparticles exhibit a much higher specific recognition and saturation magnetization. The hybrid nanoparticles have been used for biochemical separation of estrone.

Synthesis and characterization of the core-shell magnetic molecularly imprinted polymers (Fe3O4@MIPs) adsorbents for effective extraction and determination of sulfonamides in the poultry feed

In this study, we present a general method to prepare the core-shell magnetic molecularly imprinted polymers (MIPs) nanoparticles (NPs) for sulfamethazine (SMZ). The resulting Fe₃O₄@MIPs NPs possess a highly improved imprinting effect, fast adsorption kinetics and high adsorption capacity, and can be applied to extract sulfonamide in the poultry feed. In this protocol, the magnetite NPs were synthesized by co-precipitating Fe²⁺ and Fe³⁺ in an ammonia solution first. Silica was then coated on the Fe₃O₄ NPs using a sol-gel method to obtain silica shell magnetic NPs. Subsequently, the vinyl groups were grated onto silica-modified Fe₃O₄ surface by 3-methacryloyloxypropyltrimethoxysilane. Finally, the MIPs films were formed on the surface of Fe₃O₄@SiO₂ by the copolymerization of vinyl end groups with functional monomer, methacrylic acid, cross-linking agent, ethylene glycol dimethacrylate, the initiator azo-bis-isobutyronitrile and template molecule, sulfamethazine. The morphology, magnetic, adsorption and recognition properties of Fe₃O₄@MIPs NPs were characterized using transmission electron microscope (TEM), scanning electron microscope (SEM), Fourier transform infrared (FT-IR) spectrometer, vibrating sample magnetometer (VSM) and re-binding experiments. The results showed that the binding sites of Fe₃O₄@MIPs were good accessibility, fast adsorption rate and the maximum adsorption capacity of Fe₃O₄@MIPs to SMZ was 344.8 μg g⁻¹. The selectivity of the obtained Fe₃O₄@MIPs NPs were elucidated by the different rebinding capability of SMZ and structural related sulfonamides in the mixed solution. The results indicated that the Fe₃O₄@MIPs had high imprinting factor 9.5 and significant selectivity. A method was developed for enrichment and determination of SMZ in the poultry feed samples with recoveries of duck and chicken feed ranging from 63.3 to 76.5% and 68.7 to 74.7%, respectively and the relative standard deviations (RSD) (<6.7%).

Preparation and characterization of uniformly sized molecularly imprinted polymers functionalized with core–shell magnetic nanoparticles for the recognition and enrichment of protein

A general method to prepare thin, molecularly imprinted polymer (MIP) coatings on magnetic Fe3O4 nanoparticles (NPs) with a uniform core–shell structure for the recognition and enrichment of protein was developed. Four proteins (bovine serum albumin (BSA, pI = 4.9), bovine hemoglobin (BHb, pI = 6.9), bovine pancreas ribonuclease A (RNase A, pI = 9.4) and lysozyme (Lyz, pI = 11.2)) with different isoelectric points were chosen as the templates. The magnetic protein-MIPs were synthesized by combining surface imprinting and sol–gel techniques. The morphology, adsorption and recognition properties of the magnetic molecularly imprinted NPs were investigated by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FT-IR) spectroscopy and through the use of a vibrating sample magnetometer (VSM). In comparison with the use of Lyz, BSA and RNase A as template proteins, BHb-imprinted Fe3O4 showed the best imprinting effect and the highest adsorption capacity among the four proteins. The as-prepared Fe3O4@BHb-MIPs NPs with a mean diameter of 230 nm were coated with an MIP shell that was 10 nm thick, which enabled the Fe3O4@BHb-MIPs to easily reach adsorption equilibrium. A high magnetic saturation value of 25.47 emu g−1 for Fe3O4@BHb-MIPs NPs was obtained, which endowed the adsorbent with the convenience of magnetic separation under an external magnetic field. The resultant Fe3O4@BHb-MIPs NPs could not only selectively extract a target protein from mixed proteins but also specifically capture the protein BHb from a real sample of bovine blood. In addition, different batches of magnetic MIPs showed good reproducibility and reusability for at least six repeated cycles.

Preparation of Core-shell Magnetic Molecularly Imprinted Polymer Nanoparticles for Recognition of Bovine Hemoglobin

Imprinting nanoparticles: Core-shell bovine hemoglobin (BHb) imprinted magnetic nanoparticles (MNPs) with a mean diameter of 210 nm have been synthesized for the first time. The imprinted magnetic nanoparticles could easily reach the adsorption equilibrium and magnetic separation under an external magnetic field, thus avoiding problems related to the bulk polymer. In this work, the core-shell bovine hemoglobin (BHb) imprinted magnetic nanoparticles (MNPs) with a mean diameter of 210 nm were synthesized for the first time. In this protocol, the initial step involved co-precipitation of Fe(2+) and Fe(3+) in an ammonia solution. Silica was then coated on the Fe(3)O(4) nanoparticles using a sol-gel method to obtain silica shell magnetic nanoparticles. Subsequently, 3-aminophenylboronic acid (APBA), which is the functional and cross-linking monomer, and poly(APBA) thin films were coated onto the silica-modified Fe(3)O(4) surface through oxidation with ammonium persulfate in an aqueous solution in the presence or absence of protein. The morphology, adsorption, and recognition properties of the magnetic molecularly imprinted nanomaterial were investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and vibrating sample magnetometer (VSM). Rebinding experiments were carried out to establish the equilibrium time and to determine the specific binding capacity and selective recognition. The protein adsorption results showed that poly(APBA) MIPs-coated magnetic nanoparticles have high adsorption capacity for template protein BHb and comparatively low non-specific adsorption. The imprinted magnetic nanoparticles could easily reach the adsorption equilibrium and magnetic separation under an external magnetic field, thus avoiding problems related to the bulk polymer. We believe that the imprinted polymer-coated magnetic nanoparticles can be one of the most promising candidates for various applications, which include chemical and biochemical separation, cell sorting, recognition elements in biosensors, and drug delivery.

Determination of tetracyclines in food samples by molecularly imprinted monolithic column coupling with high performance liquid chromatography.

A novel solid phase extraction (SPE) method for determination of tetracyclines (TCs) in milk and honey samples by molecularly imprinted monolithic column was developed. Using tetracycline (TC) as the template, methacrylic acid (MAA) as the functional monomer, ethylene glycol dimethacrylate (EGDMA) as the cross-linker, methanol as the solvent, cyclohexanol and dodecanol as the mixed porogenic solvents, a TC imprinted monolithic column was prepared by in situ molecular imprinting technique for the first time, and the optimal synthesis conditions and the selectivity of TC imprinted monolithic column were investigated. The interfering substances in food samples and TCs can be separated successfully on imprinted column. Molecularly imprinted solid phase extraction (MISPE) coupling with C18 column was used to determinate the TCs in milk and honey. The recoveries of this method for six tetracyclines antibiotics such as tetracycline (TC), oxytetracycline (OTC), minocycline (MINO), chlortetracycline (CTC), metacycline (MTC) and doxycycline (DTC) were investigated, and high recoveries of 73.3-90.6% from milk samples and 62.6-82.3% from honey samples were obtained. A method for determination of TCs at low concentration level in milk and honey samples was successfully developed by using the monolithic column as the precolumn for solid phase extraction of six TCs compounds.

Fabrication of mesoporous silica-coated CNTs and application in size-selective protein separation

In this study, we report a simple method to coat mesoporous silica onto carbon nanotubes (CNTs) via a two-step procedure. Mesoporous CNTs@SiO2 composites have been obtained by extracting cetyltrimethylammonium bromide (CTAB) via an ion-exchange procedure after silica-coated carbon nanotubes were synthesized with the aid of the cationic surfactant CTAB. The coating process was explicitly investigated, and a possible formation mechanism of the mesoporous CNTs@SiO2 was proposed, which reveals that the ratio of CTAB/CNTs plays a critical role in the coating process. Furthermore, the pore size of the as-prepared mesoporous silica could be exactly controlled by using different amounts of the bromide surfactant CTAB. The obtained mesoporous CNTs@SiO2 composite nanomaterial was evaluated with three typical proteins, cytochrome c (Cyt c), bovine serum albumin (BSA) and lysozyme (Lyz), with different molecular sizes. The adsorption and desorption of binary mixtures of Cyt c and BSA, Cyt c and Lyz, and a ternary mixture of Cyt c, BSA and Lyz showed that the mesoporous CNTs@SiO2 are effective and highly selective adsorbents for Cyt c. The as-prepared mesoporous CNTs@SiO2 composites have shown effective performance in size-selective adsorption of biomacromolecules, demonstrating great potential in biomacromolecular separation.

Preparation of IDA-Cu functionalized core–satellite Fe3O4/polydopamine/Au magnetic nanocomposites and their application for depletion of abundant protein in bovine blood

In this study, we report a method to synthesize core–satellite structured Fe3O4/polydopamine/Au composite nanoparticles (NPs). Firstly, the Fe3O4/polydopamine composite NPs with a well-defined core–shell structure are obtained using dopamine self-polymerization to form thin, surface-adherent polydopamine films onto the surface of a Fe3O4 “core”. The polydopamine shell could be adjusted by controlling the experimental parameters such as reaction time and the reactant concentrations. Then, numerous “satellites” of gold nanoparticles were assembled on the surface of Fe3O4/polydopamine by reducing Au3+ between the Fe3O4/polydopamine solid and HAuCl4 solution. Next, 11-mercaptoundecanoic acid (11-MUA) forms a self-assembled monolayer of MUA on the surface of the Au NPs and polydopamine layer. Finally, IDA-Cu functionalized Fe3O4/polydopamine/Au composite NPs are obtained by the carboxyl groups of MUA reacting with iminodiacetic acid (IDA), charged with Cu2+. The IDA-Cu groups, acting as an “anchor”, are attached on the gold and the polydopamine surface is designed for capturing target molecules. The morphology, structure and composition of the nanocomposites are characterized by transmission electron microscopy (TEM), X-ray powder diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectrometry (XPS). The resulting Fe3O4/polydopamine/Au composite NPs show not only a strong magnetic response to an externally applied magnetic field, but are also highly specific to protein bovine hemoglobin (BHb), and removal of abundant protein BHb in the bovine blood as well. This opens a novel route for future application in removing abundant protein in proteomic analysis.

Synthesis and application of a macroporous boronate affinity monolithic column using a metal-organic gel as a porogenic template for the specific capture of glycoproteins

A macroporous boronate affinity monolithic column was prepared and applied to specifically capture glycoproteins using metal-organic gels (MOGs) as a porogenic template. This newly explored application of MOGs has proven to be a more convenient method for the formation of macropores in contrast to traditional porogenic methods. The poly (3-acrylamidophenylboronic acid-co-ethylene dimethacrylate) monolithic columns were synthesized in stainless columns by in situ polymerization. To fabricate the macroporous formation with a uniformed open-channel network, the preparation conditions, such as reaction temperature, the concentration of the MOGs and the ratio of monomers were systematically investigated. The prepared macroporous monoliths were characterized by scanning electron microscope (SEM) and mercury intrusion porosimetry. Furthermore, horseradish peroxidase (HRP) and transferrin (TF) were chosen as test glycoproteins, and the chromatographic analysis demonstrated that the macroporous boronate affinity monoliths exhibited a higher selectivity and better dynamic binding capacity toward glycoproteins compared with non-glycoproteins. The resulted affinity monolithic column was successfully employed to specifically capture TF from a bovine serum sample.

Boronic acid modified magnetic nanoparticles for enrichment of glycoproteins via azide and alkyne click chemistry

In this study, a novel approach was developed to synthesize aminophenylboronic acid functionalized magnetic nanoparticles (NPs) via Cu(I)-catalyzed azide–alkyne cycloaddition (CuAAC) ‘click’ chemistry. Firstly, azide-functional Fe3O4 NPs were obtained by a two-step chemical modification process. Then, an alkyne-phenylboronic acid molecule was connected onto the surface of magnetite by the CuAAC reaction. The morphology, structure and composition of the synthesized nanocomposites were characterized by transmission electron microscopy (TEM), X-ray powder diffraction (XRD), vibrating sample magnetometer (VSM), Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectrometry (XPS). Five proteins, including ovalbumin (OB), transferrin (Trf), as glycoprotein templates and lysozyme (Lyz), bovine serum albumin (BSA), horse heart cytochrome c (Cyt C) as nonglycoprotein templates are chosen as target proteins. The as-prepared click-Fe3O4@APBA NPs with a mean diameter of 23.2 nm showed a strong magnetic response to an externally applied magnetic field and exhibited a high adsorption capacity and excellent specificity towards glycoproteins in comparison with nonglycoproteins. The click-Fe3O4@APBA NPs showed the higher adsorption capacity towards glycoproteins than the nonclick-Fe3O4@APBA NPs which were synthesized through a common nucleophilic substitution reaction. The greatly enhanced adsorption capacity towards glycoproteins demonstrated that the ‘click’ method presented great superiority in ligand immobilization. Finally, the click-Fe3O4@APBA NPs could efficiently enrich glycoproteins from real egg white samples as well.

Synthesis and evaluation of molecularly imprinted core-shell carbon nanotubes for the determination of triclosan in environmental water samples

Synthetic core-shell molecularly imprinted polymers (MIPs) were prepared for the extraction of trace triclosan in environmental water samples. The synthesis process combined a surface molecular imprinting technique with a sol-gel process based on carbon nanotubes (CNTs) coated with silica. The morphology and structure of the products were characterized by transmission electron microscopy and Fourier transform infrared spectroscopy. The adsorption properties of the polymers were demonstrated by equilibrium rebinding experiments and Scatchard analysis. The prepared imprinted materials exhibited fast kinetics, high capacity and favorable selectivity. The process of synthesis was quite simple and different batches of MIPs and non-imprinted polymers (NIPs) showed good reproducibility in the template binding. The feasibility of determination of triclosan from real samples was testified using spiked river and lake water samples. The recoveries of river water and lake water samples were ranged from 92.1 to 95.3% and 90.7 to 93.6%, respectively, when the environmental water samples were spiked with 0.1, 0.3, and 0.5 μg L(-1) of TCS. In addition, the reusability of MIPs and NIPs without any deterioration in capacity was demonstrated for at least 10 repeated cycles.