Molecularly imprinted polymers by reversible addition-fragmentation chain transfer precipitation polymerization for preconcentration of atrazine in food matrices

Novel magnetic bimetallic AuCu catalyst for reduction of nitroarenes and degradation of organic dyes

Herein, core-shell magnetic nanoparticles are modified with imidazolium-tagged phosphine and propylene glycol moieties and used for the stabilization of bimetallic AuCu nanoparticles. The structure and morphology of the prepared material are identified with SEM, TEM, XRD, XPS, atomic absorption spectroscopy, Fourier translation infrared spectroscopy, and a vibrating sample magnetometer. This hydrophilic magnetic bimetallic catalyst is applied in the reduction of toxic nitroarenes and reductive degradation of hazardous organic dyes such as methyl orange (MO), methyl red (MR), and rhodamine B (RhB), as well as in the degradation of tetracycline (TC). This magnetic AuCu catalyst indicated superior activity in all three mentioned reactions in comparison with its single metal Au and Cu analogs. This catalyst is recycled for 17 consecutive runs in the reduction of 4-nitrophenol to 4-aminophenol without a significant decrease in catalytic activity and recycled catalyst is characterized.

Molecularly imprinted polymers via reversible addition-fragmentation chain-transfer synthesis in sensing and environmental applications

Molecularly imprinted polymers (MIP) have shown their potential as artificial and selective receptors for environmental monitoring. These materials can be tailor-made to achieve a specific binding event with a template through a chosen mechanism. They are capable of emulating the recognition capacity of biological receptors with superior stability and versatility of integration in sensing platforms. Commonly, these polymers are produced by traditional free radical bulk polymerization (FRP) which may not be the most suitable for enhancing the intended properties due to the poor imprinting performance. To improve the imprinting technique and the polymer capabilities, controlled/living radical polymerization (CRP) has been used to overcome the main drawbacks of FRP. Combining CRP techniques such as RAFT (reversible addition-fragmentation chain transfer) with MIP has achieved higher selectivity, sensitivity, and sorption capacity of these polymers when implemented as the transductor element in sensors. The present work focuses on RAFT-MIP design and synthesis strategies to enhance the binding affinities and their implementation in environmental contaminant sensing applications.

Recent application of molecular imprinting technique in food safety

Due to the extensive use of chemical substances such as pesticides, antibiotics and food additives, food safety issues have gradually attracted people's attention. The extensive use of these chemicals seriously damages human health. In order to detect trace chemical residues in food, researchers have to find several simple, economical and effective tools for qualitative and quantitative analysis. As a kind of material that specifically and selectively recognize template molecules from real samples, molecular imprinting technique (MIT) has widely applied in food samples analysis. This article mainly reviews the application of molecularly imprinted polymer (MIP) in the detection of chemical residues from food in the past five years. Some recent and novel methods for fabrication of MIP are reviewed. Their application of sample pretreatment, sensors, etc. in food analysis is reviewed. The application of molecular imprinting in chromatographic stationary phase is referred. Additionally, the challenges faced by MIP are discussed.

Microsphere Polymers in Molecular Imprinting: Current and Future Perspectives

Molecularly imprinted polymers (MIPs) are specific crosslinked polymers that exhibit binding sites for template molecules. MIPs have been developed in various application areas of biology and chemistry; however, MIPs have some problems, including an irregular material shape. In recent years, studies have been conducted to overcome this drawback, with the synthesis of uniform microsphere MIPs or molecularly imprinted microspheres (MIMs). The polymer microsphere is limited to a minimum size of 5 nm and a molecular weight of 10,000 Da. This review describes the methods used to produce MIMs, such as precipitation polymerisation, controlled/'Living' radical precipitation polymerisation (CRPP), Pickering emulsion polymerisation and suspension polymerisation. In addition, some green chemistry aspects and future perspectives will also be given.

Molecular imprinted polymers for the controlled uptake of sinapic acid from aqueous media

Molecularly imprinted polymers (MIPs) were synthesized via a precipitation polymerization method using 4-vinylpyridine as a functional monomer and ethylene glycol dimethacrylate as a cross-linker for selective separation of sinapic acid from water.

Preparation of porous magnetic molecularly imprinted polymers for fast and specifically extracting trace norfloxacin residue in pork liver

Here, magnetic molecularly imprinted polymers were designed for norfloxacin via oil-in-water emulsifier-free emulsion method. It was prepared by simply mixing norfloxacin, methacrylic acid-co-ethylene glycol dimethacrylate copolymer, and Fe₃ O₄ together at room temperature. Characterized by multiple analytical tools, the particle size, pore size, pore volume, specific surface area, and saturation magnetization of the product were about 30 µm, 10-500 nm, 2.92 mL/g, 105.84 m² /g, and 3.052 emu/g, respectively. And the adsorption capacity was high at 27.04 mg/g towards norfloxacin. Combined with ultra high performance liquid chromatography, it was used to determine norfloxacin in real samples. Average recoveries were above 77.44% with relative standard deviations between 1.21 and 6.85% at three spiked levels (n = 3) for lake water and pork liver. The determination was achieved for the most complex biosample pork liver spiked with norfloxacin low to 30 ng/g, about 100 times less than the maximum residue limit regulated by Commission of the European Communities. All evidences demonstrated that the magnetic molecularly imprinted polymers can be used in practice for monitoring norfloxacin either in environmental water or meat product with high accuracy and reliability.

Optimization and validation of the kinetic spectrophotometric method for quantitative determination of the pesticide atrazine and its application in infant formulae and cereal-based baby food

BACKGROUND

Pesticides are potentially toxic to humans and can produce both acute and chronic health effects, depending on the quantity and the ways in which a person is exposed. Exposure to pesticides can cause serious health problems. Infants and young children are particularly sensitive to these contaminants because their brains and organ systems are not fully developed. For this reason, it is important to determine the quantities of pesticides in baby food.

RESULTS

The aim of this study was to develop a kinetic-spectrophotometric method for atrazine determination and to apply it to determine pesticide in baby-food samples, using solid-phase extraction (SPE) followed by the kinetic-spectrophotometric method and the high-performance liquid chromatography (HPLC) method. This method is based on the inhibition effect of atrazine (the oxidation of sulfanilic acid (SA) by hydrogen peroxide in the alkaline medium in the presence of the Co²⁺ ion). Under the experimental conditions used, atrazine showed a linear dynamic range of 0.5 to 5.0 μg mL^-1 , and from 5.0 to 70.00 μg mL^-1 with relative standard deviations (RSD) from 1.91% to 9.41%. The limit of detection and the limit of quantification were 0.074 and 0.225 μg mL^-1 , respectively. The kinetic method was successfully applied to determine the atrazine concentration in spiked samples after SPE of samples. High-performance liquid chromatography was used to verify the results.

CONCLUSION

The proposed method is highly sensitive, simple, easy, requires cheap reagents, and leads to good recovery levels. It is linear, precise, and accurate. It can be used successfully for the routine analysis of atrazine in infant formulae and cereal-based food samples. © 2019 Society of Chemical Industry.

Post-imprinting modification based on multilevel mesoporous silica for highly sensitive molecularly imprinted fluorescent sensors

p-MIFPs based on multilevel mesoporous silica exhibited improved sensitivity as compared to those prepared by the doping method due to their well-maintained fluorescence intensity and low background.

Automated Protein Biomarker Analysis: on-line extraction of clinical samples by Molecularly Imprinted Polymers

Robust biomarker quantification is essential for the accurate diagnosis of diseases and is of great value in cancer management. In this paper, an innovative diagnostic platform is presented which provides automated molecularly imprinted solid-phase extraction (MISPE) followed by liquid chromatography-mass spectrometry (LC-MS) for biomarker determination using ProGastrin Releasing Peptide (ProGRP), a highly sensitive biomarker for Small Cell Lung Cancer, as a model. Molecularly imprinted polymer microspheres were synthesized by precipitation polymerization and analytical optimization of the most promising material led to the development of an automated quantification method for ProGRP. The method enabled analysis of patient serum samples with elevated ProGRP levels. Particularly low sample volumes were permitted using the automated extraction within a method which was time-efficient, thereby demonstrating the potential of such a strategy in a clinical setting.

Assessment of the binding performance of histamine-imprinted microspheres by frontal analysis capillary electrophoresis

Frontal analysis capillary electrophoresis was used to evaluate the binding performance of molecularly imprinted microspheres (MIM) toward its template histamine and analogs at pH 7, and compared to the high performance liquid chromatographic method. In both methods, batch binding was employed and the binding parameters were calculated from the measured concentration of unbound amine analytes and afforded comparable histamine equilibrium dissociation constants (K_d ∼ 0.4 mM). FACE was easily carried out at shorter binding equilibration time (i.e. 30 min) and without the need to separate the microspheres, circumventing laborious and, in the case of the system under study, inefficient sample filtration. It also allowed for competitive binding studies by virtue of its ability to distinctly separate intact microspheres and all tested amines which could not be resolved in HPLC. K_d 's for nonimprinted (control) microspheres (NIM) from FACE and HPLC were also comparable (∼ 0.6 mM) but at higher histamine concentrations, HPLC gave lower histamine binding. This discrepancy was attributed to inefficient filtration of the batch binding samples prior to HPLC analysis resulting in an over-estimation of the concentration of free histamine brought about by the presence of unfiltered histamine-bound microspheres.

Preparation and Binding Evaluation of Histamine-Imprinted Microspheres via Conventional Thermal and RAFT-Mediated Free-Radical Polymerization

Elevated histamine (HTM) levels are closely linked to food poisoning as well as to pathophysiological allergic diseases. In this study, HTM-imprinted, solution-processable microspheres were prepared via high-dilution conventional thermal polymerization (CTP) and controlled radical polymerization (CRP) using ethylene glycol dimethacrylate (80 or 90 wt %) and methacrylic acid at 60 °C in acetonitrile and evaluated as recognition materials for sensing applications. The polymers were selective to HTM in binding studies, cross-rebinding, and competitive binding assays against the HTM analogues histidine, imidazole, and tryptamine. The selective binding capacity was significantly higher with CTP-80 (on the basis of mass: 21.0 μmol/g and surface area: 8.08 × 10^-2 μmol/m²) than that with both CTP-90 (8.47 μmol/g, 4.49 × 10^-2 μmol/m²) and CRP-80 (9.00 μmol/g, 1.19 × 10^-2 μmol/m²).

Preparation of Magnetic Hollow Molecularly Imprinted Polymers for Detection of Triazines in Food Samples

Novel magnetic hollow molecularly imprinted polymers (M-H-MIPs) were proposed for highly selective recognition and fast enrichment of triazines in food samples. M-H-MIPs were prepared on the basis of multi-step swelling polymerization, followed by in situ growth of magnetic Fe3O4 nanoparticles on the surface of hollow molecularly imprinted polymers (H-MIPs). Transmission electron microscopy and scanning electron microscopy confirmed the successful immobilization of Fe3O4 nanoparticles on the surface of H-MIPs. M-H-MIPs could be separated simply using an external magnet. The binding adsorption results indicated that M-H-MIPs displayed high binding capacity and fast mass transfer property and class selective property for triazines. Langmuir isotherm and pseudo-second-order kinetic models fitted the best adsorption models for M-H-MIPs. M-H-MIPs were used to analyze atrazine, simazine, propazine, and terbuthylazine in corn, wheat, and soybean samples. Satisfactory recoveries were in the range of 80.62-101.69%, and relative standard deviation was lower than 5.2%. Limits of detection from 0.16 to 0.39 μg L(-1) were obtained. When the method was applied to test positive samples that were contaminated with triazines, the results agree well with those obtained from an accredited method. Thus, the M-H-MIP-based dispersive solid-phase extraction method proved to be a convenient and practical platform for detection of triazines in food samples.

Polymeric Colloidal Nanostructures Fabricated via Highly Controlled Convective Assembly and Their Use for Molecular Imprinting

In this work, the formation of various polystyrene (PS) colloidal structures on striped PS patterns is demonstrated based on a simple and novel convective assembly method that controls the electrostatic interactions between the PS colloidal particles and sodium dodecyl sulfate (SDS). Under the optimal conditions (different withdrawal speeds, channel dimensions, suspension concentrations, etc.), highly ordered structures such as highly close-packed, zigzag, and linear colloidal aggregates are observed. In addition, these colloidal arrangements are used for development of molecularly imprinted polymer (MIP) sensors with highly improved sensing properties. Using PDMS replicas, three hemispherical poly(methacrylic acid-ethylene glycol dimethacrylate) (poly(MAA-EGDMA)) MIP films, including planar MIP and non-imprinted polymer (NIP) films, are photopolymerized for detection of trace atrazine in an aqueous solution. From gravimetric quartz crystal microbalance (QCM) measurements, a non-close-packed MIP film exhibits highest sensing response (Δf = 932 Hz) to atrazine detection among hemispherical MIP films and shows 6.5-fold higher sensing response than the planar MIP film. In addition, the sensitivity of the MIP sensor is equivalent to -119 Hz/(mol L(-1)). From the ratio of slopes of the calibration curves for the hemispherical MIP and NIP films, the imprinting factor (If) is as high as 11.0. The hemispherical MIP film also shows excellent selectivity in comparison with the sensing responses of other analogous herbicides. As a result, this molecular surface imprinting using PS colloidal arrays is highly efficient for herbicide detection.

Molecular imprinting: perspectives and applications

This critical review presents a survey of recent developments in technologies and strategies for the preparation of MIPs, followed by the application of MIPs in sample pretreatment, chromatographic separation and chemical sensing.

Precipitation polymerization: a versatile tool for preparing molecularly imprinted polymer beads for chromatography applications

Minireview on recent advances of application of MIPs prepared by precipitation polymerization for recognition of target analytes in complex matrices.

Synthesis of magnetic molecularly imprinted polymers by reversible addition fragmentation chain transfer strategy and its application in the Sudan dyes residue analysis

Magnetic molecularly imprinted polymers (MMIPs) have become a hotspot owing to the dual functions of target recognition and magnetic separation. In this study, the MMIPs were obtained by the surface-initiated reversible addition fragmentation chain transfer (RAFT) polymerization using Sudan I as the template. The resultant MMIPs were characterized by transmission electron microscope, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, vibrating sample magnetometer, and X-ray diffraction. Benefiting from the controlled/living property of the RAFT strategy, the uniform MIP layer was successfully grafted on the surface of RAFT agent-modified Fe3O4@SiO2 nanoparticles, favoring the fast mass transfer and rapid binding kinetics. The developed MMIPs were used as the solid-phase extraction sorbents to selectively extract four Sudan dyes (Sudan I, II, III, and IV) from chili powder samples. The recoveries of the spiked samples in chili powder samples ranged from 74.1 to 93.3% with RSD lower than 6.4% and the relative standard uncertainty lower than 0.029. This work provided a good platform for the extraction and removal of Sudan dyes in complicated matrixes and demonstrated a bright future for the application of the well-constructed MMIPs in the field of solid-phase extraction.

Development of a selective sorbent for the solid-phase extraction of terbuthylazine in olive oil samples: a molecular imprinting strategy

Aiming to implement an analytical methodology that is highly selective for the extraction and quantification of terbuthylazine from olive oil, we successfully achieved: (i) the development of a molecularly imprinted polymer by bulk polymerization using terbuthylazine as template molecule, methacrylic acid as functional monomer, ethylene glycol dimethacrylate as cross-linker, and dichloromethane as porogen; (ii) characterization of the imprinting material using Fourier transform infrared spectroscopy, thermogravimetric analysis, nitrogen adsorption at 77 K, and scanning electron microscopy; (iii) their molecular recognition for the template molecule using high-performance liquid chromatography, and (iv) optimization of a solid-phase extraction procedure using as sorbent the synthesized molecularly imprinted polymer for the selective extraction and clean-up of terbuthylazine from spiked organic olive oil and further quantification of the pesticide levels by high-performance liquid chromatography. The suitability of the implemented analytical methodology was demonstrated, as concentrations of terbuthylazine below the tolerated maximum residue limits in the spiked organic olive oil samples could be satisfactorily analyzed with good precision/accuracy with high recovery rates (96%). Overall, the implemented methodology has proven to be reliable and robust and is highly promising in the field of sample preparation, particularly for the isolation/preconcentration of terbuthylazine in complex food samples.

Exploiting β-cyclodextrin in molecular imprinting for achieving recognition of benzylparaben in aqueous media

The molecularly imprinted polymer (MIP) based on methacrylic acid functionalized β-cyclodextrin (MAA-β-CD) monomer was synthesized for the purpose of selective recognition of benzylparaben (BzP). The MAA-β-CD monomer was produced by bridging a methacrylic acid (MAA) and β-cyclodextrin (β-CD) using toluene-2,4-diisocyanate (TDI) by reacting the –OH group of MAA and one of the primary –OH groups of β-CD. This monomer comprised of triple interactions that included an inclusion complex, π–π interaction, and hydrogen bonding. To demonstrate β-CD performance in MIPs, two MIPs were prepared; molecularly imprinted polymer-methacrylic acid functionalized β-cyclodextrin, MIP(MAA-β-CD), and molecularly imprinted polymer-methacrylic acid, MIP(MAA); both prepared by a reversible addition fragmentation chain transfer polymerization (RAFT) in the bulk polymerization process. Both MIPs were characterized using the Fourier Transform Infrared Spectroscopy (FTIR), Field Emission Scanning Electron Microscopy (FESEM), and Brunauer-Emmett-Teller (BET). The presence of β-CD not only influenced the morphological structure, it also affected the specific surface area, average pore diameter, and total pore volume of the MIP. The rebinding of the imprinting effect was evaluated in binding experiments, which proved that the β-CD contributed significantly to the enhancement of the recognition affinity and selective adsorption of the MIP.

One-pot synthesis of magnetic molecularly imprinted microspheres by RAFT precipitation polymerization for the fast and selective removal of 17β-estradiol

A one-pot synthesis strategy was developed to prepare magnetic molecularly imprinted microspheres for the selective recognition and fast removal of 17-beta-estradiol.

Magnetic mesoporous imprinted adsorbent based on Fe3O4-modified sepiolite for organic micropollutant removal from aqueous solution

A novel magnetic molecularly imprinted polymer adsorbent based on a magnetic sepiolite composite was successfully prepared for the first time. It has a maximum adsorption capacity of 69.53 mg g⁻¹for atrazine.