Molecularly imprinted polymer layer-coated silica nanoparticles toward dispersive solid-phase extraction of trace sulfonylurea herbicides from soil and crop samples

This paper reports the preparation of metsulfuron-methyl (MSM) imprinted polymer layer-coated silica nanoparticles toward analysis of trace sulfonylurea herbicides in complicated matrices. To induce the selective occurrence of surface polymerization, the polymerizable double bonds were first grafted at the surface of silica nanoparticles by the silylation. Afterwards, the MSM templates were imprinted into the polymer-coating layer through the interaction with functional monomers. The programmed heating led to the formation of uniform MSM-imprinted polymer layer with controllable thickness, and further improved the reproducibility of rebinding capacity. After removal of templates, recognition sites of MSM were exposed in the polymer layers. As a result, the maximum rebinding capacity was achieved with the use of optimal grafting ratio. There was also evidence indicating that the MSM-imprinted polymer nanoparticles compared with nonimprinted polymer nanoparticles had a higher selectivity and affinity to four structure-like sulfonylurea herbicides. Moreover, using the imprinted particles as dispersive solid-phase extraction (DSPE) materials, the recoveries of four sulfonylurea herbicides determined by high-performance liquid chromatography (HPLC) were 80.2-99.5%, 83.8-102.4%, 77.8-93.3%, and 73.8-110.8% in the spiked soil, rice, soybean, and corn samples, respectively. These results show the possibility that the highly selective separation and enrichment of trace sulfonylurea herbicides from soil and crop samples can be achieved by the molecular imprinting modification at the surface of silica nanoparticles.     

Molecularly imprinted polymer for monocrotophos and its binding characteristics for organophosphorus pesticides

In this study, molecular imprinting was used to develop a method based on noncovalent interaction for the synthesis of a monocrotophos-specific polymer. The selective binding characteristics of the template polymer were evaluated by 1H NMR study. The result was consistent with the existence of multi-molecular complexes formed by hydrogen-bonding interactions. Batch rebinding studies in acetonitrile were undertaken to quantitatively evaluate the affinity of the polymer for monocrotophos. The experimental binding isotherms were fitted to the Freundlich isotherm and the total number of binding sites of the polymer can be calculated to be 4.046 micromol g(-1). The induced affinity and selectivity by imprinting were examined chromatographically. The polymer gave more than 15 times longer retention for monocrotophos than the nonimprinted polymer with the same chemical composition. Other organophosphorus pesticides under study were eluted close to the void volume on the polymer column.     

Uniform-sized molecularly imprinted polymer for metsulfuron-methyl by one-step swelling and polymerization method

Uniform-sized molecularly imprinted polymer (MIP) beads for metsulfuron-methyl (MSM) were firstly prepared by one-step swelling and polymerization method using 4-vinylpyridine (4-VPY) and ethylene glycol dimethacrylate (EDMA) as functional monomer and cross-linker, respectively. The preparation was optimized by varying the ratio of MSM to 4-VPY. The chromatographic behaviors of MSM and other structurally related sulfonylureas (SUs) on the resultant MIP column were evaluated. The imprinted polymer revealed specific affinity to the template and the fair resolution of SUs was also obtained. Furthermore, the uniform-sized MSM-MIP was used as the solid phase extraction (SPE) material to enrich MSM in real water samples before reversed-phase HPLC (RP-HPLC) analysis. The recovery of MSM from 100 mL of drinking water at a 50 ng/L spike level was 99.59% with R.S.D. of 1.13%. The detection limit was about 6.0 ng/L of MSM when enriching a 100 mL water sample.     

分子印迹固相萃取牛奶中甲胺磷

以甲胺磷为印迹分子、α-甲基丙烯酸为功能单体及三羟甲基丙烷三丙烯酸酯为交联剂,通过悬浮聚合法制备甲胺磷分子印迹聚合物(MIP)微球,并用该聚合物进行了牛奶中甲胺磷残留的固相萃取研究.静态吸附实验表明,在结构相似物乙酰甲胺磷和水胺硫磷为竞争底物存在下,MIP对甲胺磷有良好的吸附识别能力.在优化条件下,印迹分子的固相萃取回收率达96.4%,能够用于甲胺磷的富集,而空白聚合物却不具备这样的特性.当实际牛奶样品中甲胺磷、乙酰甲胺磷和水胺硫磷加标水平为100μg/kg时,甲胺磷回收率达87.4%,乙酰甲胺磷和水胺硫磷的回收率低于15%.结果表明分子印迹固相萃取对甲胺磷有很好的专一选择性,且回收率能够满足农药残留分析要求.在相同实验条件下,与C18固相萃取柱进行比较,分子印迹固相萃取的选择性及样品净化能力优势明显.     

The use of molecularly imprinted polymers for extraction of sulfonylurea herbicides

Molecularly imprinted polymers (MIPs) possessing a good binding ability for the family of sulfonylurea herbicides were prepared using 4- or 2-vinyl pyridine as functional monomers and ethylene glycol dimethylacrylate as a crosslinker. Metsulfuron methyl was used as a template. It was found that MIP prepared in a polar organic solvent (acetonitrile) showed good recognition of the template and five other sulfonylurea herbicides (thifensulfuron methyl, chlorsulfuron, prosulfuron, chlorimuron ethyl, triflusulfuron methyl). The binding capacity was 0.08-0.1 mg g⁻¹ of the polymer. It was found that the polymer could be used for quantitative enrichment (>75%) of five sulfonylurea herbicides from water.     

Molecularly imprinted polyethersulfone microspheres for the binding and recognition of bisphenol A

BPA-imprinted polyethersulfone (PES) microspheres for the binding and recognition of bisphenol A (BPA) were fabricated by means of a liquid-liquid phase separation technique. The imprinted novel PES microspheres had a porous structure with a skin layer, under which was followed by a finger-like structure. The recognition experiments with the BPA-imprinted microspheres were carried out by applying the microspheres to various BPA solutions. In water, high binding amounts of BPA were observed in the range of 19-42 μmol/g capacity, but the recognition was low in the BPA water solution. With the increase of the concentration in BPA solution, the binding amounts and the recognition coefficient increased. However, 1,4-butylene glycol/water media showed high recognition of the imprinted microspheres with a low binding capacity of BPA. In addtion, with the increase of the BPA amounts in the PES solution used to prepare the imprinted microspheres, the specific recognition sites increased, and the recognition ability increased. Evidence revealed that microsphere recognition was effective for BPA due to the binding to specific recognition sites [S]_(sites). The imprinted microspheres showed the selectivity for BPA in the wine including BPA and other organic compounds. Charge transfer and special cavities could be employed to explain the mechanism.     

Molecularly imprinted hydrogel displaying reduced non‐specific binding and improved protein recognition

A novel approach for enhancing protein recognition in molecularly imprinted hydrogel (MIH) is presented. This approach was developed based on the hypothesis that the number of specific binding sites created in the previously described MIH is very small, thus attempts to enhance the capacity result in most cases in additional non‐specific binding and loss of selectivity. Thus, blocking the non‐specific binding sites could lead to higher capacities and better selectivity. To test this hypothesis, MIH interpenetrating networks designed to block non‐specific binding sites were synthesized using two separate stages of polymerization. Re‐binding of the template protein (lysozyme) and a competitor protein (cytochrome C) was measured, and the results were compared with the similar experiment performed using a control non‐imprinted hydrogel and a “conventional” MIH. The imprinting efficacy of the MIH interpenetrating network was found to be much higher than that of the controls. Furthermore, competitive adsorption assays have demonstrated the superiority of the new formulation.     

Molecularly imprinted supermacroporous cryogels for cytochrome c recognition

Molecular imprinting is an attractive biomimetic approach that creates specific recognition sites for the shape and functional group arrangement to template molecules. The purpose of this study is to prepare cytochrome c-imprinted poly(hydroxyethyl methacrylate) (PHEMA)-based supermacroporous cryogel which can be used for the separation of cytochrome c from protein mixtures. N-Methacryloyl-(L)-histidinemethylester (MAH) was used as the metal-coordinating monomer. In the first step, Cu(2+) was complexed with MAH, and the cytochrome c imprinted PHEMA (MIP) cryogel was prepared by free radical cryopolymerization initiated by N,N,N',N'-tetramethylene diamine at -12°C. After polymerization is completed, the template cytochrome c molecules were removed from the MIP cryogel using 0.5 M NaCl solution. The maximum cytochrome c binding amount was 126 mg/g polymer. Selective binding studies were performed in the presence of lysozyme and bovine serum albumin. The relative selectivity coefficients of MIP cryogel for cytochrome c/lysozyme and cytochrome c/bovine serum albumin were 1.7 and 5.2 times greater than those of the non-imprinted PHEMA cryogel, respectively. The selectivity of MIP cryogel for cytochrome c was also confirmed with fast protein liquid chromatography. The MIP cryogel could be used many times with no remarkable decrease in cytochrome c binding capacity.     

Molecularly imprinted beads by surface imprinting

Molecular imprinting is a state-of-the-art technique for imparting molecular recognition properties to a synthetic polymeric matrix. Conventionally, the technique is easily carried out using bulk imprinting, where molecularly imprinted polymers (MIPs) are prepared in large chunks and post-treatment processes like grinding and sieving are then required. However, this strategy tends to produce sharp-edged, irregular MIP bits with a limited scope of direct application. In addition, due to the creation of binding sites within the polymeric bulk, the issue of the hindrance of adsorbate diffusion (especially in the case of macromolecules) during template rebinding makes the MIPs prepared through this approach unsuitable for practical applications. Thus over the years, many efforts to address the limitations of conventional molecular imprinting techniques have resulted in new imprinting methodologies. Systems like suspension and precipitation polymerization, where MIPs with tunable morphologies can be prepared, have been developed. Additionally, strategies like surface imprinting have also been employed. Ultimately, both of these approaches have been combined to prepare regularly shaped surface-imprinted MIP beads. Such an approach incorporates the advantages of both methodologies at the same time. Given their desirable physical morphologies and favorable adsorption kinetics, MIPs prepared in this manner show significant promise for industrial applications. Therefore, they will be the main focus of this review.     

Molecularly imprinted polymers for sample preparation: A review

In spite of the huge development of analytical instrumentation during last two decades, sample preparation is still nowadays considered the bottleneck of the whole analytical process. In this regard, efforts have been conducted towards the improvement of the selectivity during extraction and/or subsequent clean-up of sample extracts. Molecularly imprinted polymers (MIPs) are stable polymers with molecular recognition abilities, provided by the presence of a template during their synthesis and thus are excellent materials to provide selectivity to sample preparation. In the present review, the use of MIPs in solid-phase extraction and solid-phase microextraction as well as its recent incorporation to other extraction techniques such as matrix-solid phase dispersion and stir bar sorptive extraction, among others, is described. The advantages and drawbacks of each methodology as well as the future expected trends are discussed.     

Molecularly imprinted polymer grafted to porous polyethylene frits: a new selective solid-phase extraction format

In this paper, a novel format for selective solid-phase extraction based on a molecularly imprinted polymer (MIP) is described. A small amount of MIP has been synthesized within the pores of commercial polyethylene (PE) frits and attached to its surface using benzophenone (BP), a photo-initiator capable to start the polymerisation from the surface of the support material. Key properties affecting the obtainment of a proper polymeric layer, such as polymerisation time and kind of cross-linker were optimised. The developed imprinted material has been applied as a selective sorbent for cleaning extracts of thiabendazole (TBZ), as model compound, from citrus samples. The use of different solvents for loading the analyte in the imprinted frits was investigated, as well as the binding capacity of the imprinted polymer. Imprinted frits showed good selectivity when loads were performed using toluene and a linear relationship was obtained for the target analyte up to 1000 ng of loaded analyte. Prepared composite material was applied to the SPE of TBZ in real samples extracts, showing an impressive clean-up ability. Calibrations showed good linearity in the concentration range of 0.05-5.00 μg g(-1), referred to the original solid sample, and the regression coefficients obtained were greater than 0.996. The calculated detection limit was 0.016 μg g(-1), low enough to satisfactory analysis of TBZ in real samples. RSDs at different spiking levels ranged below 15% in all the cases and imprinted frits were reusable without loss in their performance.     

Molecularly imprinted polyaniline-polyvinyl sulphonic acid composite based sensor for para-nitrophenol detection

We report results of the studies relating to the fabrication and characterization of a conducting polymer based molecularly imprinted para-nitrophenol (PNP) sensor. A water pollutant, para-nitrophenol is electrochemically imprinted with polyvinyl sulphonic acid (PVSA) doped polyaniline onto indium tin oxide (ITO) glass substrate. This PNP imprinted electrode (PNPI-PANI-PVSA/ITO) prepared via chronopotentiometric polymerization and over-oxidation is characterized by Fourier transform infra-red spectroscopy (FT-IR), UV–visible (UV–vis) spectroscopy, contact angle (CA), scanning electron microscopy (SEM), cyclic voltammetry (CV) and differential pulse voltammetry (DPV) studies. The response studies of PNPI-PANI-PVSA/ITO electrode carried out using DPV reveal a lower detection limit of 1 × 10⁻³ mM, improved sensitivity as 1.5 × 10⁻³ A mM⁻¹ and stability of 45 days. The PNPI-PANI-PVSA/ITO electrode shows good precision with relative standard deviation of 2.1% and good reproducibility with standard deviation of 3.78%.     

Noncovalently galactose imprinted polymer for the recognition of different saccharides

Molecularly imprinted polymers (MIPs) represent a new class of materials possessing high selectivity and affinity for the target molecule. The main goal of this study was to prepare a galactose imprinted polymer and its potential application for the recognition of different saccharides. The selectivity of galactose imprinted polymer for several saccharides; glucose, mannose, fructose, maltose, lactose, sucrose and raffinose was investigated. Macroporous polymer was prepared utilizing ethyleneglycoldimethacrylate as a crosslinking agent, in the presence of galactose as a template molecule with acrylamide as a functional monomer. After the synthesis of polymer, galactose was removed by methanol:acetic acid washing. The selectivity of galactose imprinted polymer for other saccharides was utilized by batch rebinding assay. The arrangement of functional groups within cavities versus shape selectivity is discussed. The results showed that, the orientation of the functional groups was the dominating factor for the selectivity of galactose imprinted polymer. The dissociation constants of polymer were determined by Scatchard analysis.     

Silica nanoparticle supported molecularly imprinted polymer layers with varied degrees of crosslinking for lysozyme recognition

Surface imprinting over nanosized support materials is particularly suitable for protein templates, considering the problems with mass transfer limitation and low binding capacity. Previously we have demonstrated a strategy for surface protein imprinting over vinyl-modified silica nanopartiles with lysozyme as a model template by polymerization in high-dilution monomer solution to prevent macrogelation. Herein, the synthesis process was further studied toward enhancement of the imprinting performance by examining the effect of several synthesis conditions. Interestingly, the feed crosslinking degree was found to have a great impact on the thickness of the formed imprinting polymer layers and the recognition properties of the resulting imprinted materials. The imprinted particles with a crosslinking degree up to 50% showed the best imprinting effect. The imprinting factor achieved 2.89 and the specific binding reached 23.3 mg g⁻¹, which are greatly increased compared to those of the lowly crosslinked imprinted materials reported previously. Moreover, the relatively high crosslinking degree led to no significant retarding of the binding kinetics to the imprinted particles, and the saturated adsorption was reached within 10 min. Therefore, this may be a promising method for protein imprinting.     

Molecularly imprinted polymers with assistant recognition polymer chains for bovine serum albumin

A new protein molecularly imprinted polymer (MIP) was prepared with grafting polyvinyl alcohol as assistant recognition polymer chains (ARPCs). The ARPCs and acrylamide monomers were interpenetrated and then polymerized on the surface of macroporous acrylate adsorbent spheres. The template BSA was removed by treatment with 2.00 mol L-1 potassium chloride (KCl) solution and the adsorbed proteins were detected with sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). 0.150, 0.500, and 2.00 mo...     

Molecularly imprinted polymer for the determination of trace ractopamine in pork using SPE followed by HPLC with fluorescence detection

In this study, a molecularly imprinted functionalized polymer for the selective separation of ractopamine (RAC) was prepared by combining a surface molecular imprinting technique with a sol–gel method process. The polymer was evaluated by static, kinetic adsorption, and selective experiments. Results indicated that the molecularly imprinted polymer had high adsorption capacity, selective ability, and fast mass transfer rate. The polymer was applied for the determination of trace RAC through online SPE‐HPLC. With a sample loading flow rate of 2 mL/min, the enhancement factor of 516.26 and the LOD (S/N = 3) of 4.6 ng/L were achieved, respectively, and the linear range of the calibration curve was 0.04–18 μg/L with r² >0.99. The RAC in pork was determined at three spiked levels (0.5, 1, and 2 ng/g) with recoveries ranging from 55.86 to 67.28%.     

Selectivity and recovery performance of phosphate-selective molecularly imprinted polymer

A phosphate-selective molecularly imprinted polymer was prepared using 1-allyl-2-thiourea as a functional monomer, and the binding ability and selectivity of the polymer were evaluated. The imprinted polymer showed high binding ability to and selectivity for phosphate in aqueous media. The recoverability of phosphate from the imprinted polymer was also examined, and nearly 70% of highly concentrated phosphate could be recovered.     

Molecularly imprinted stir bars for selective extraction of thiabendazole in citrus samples

Stir‐bar sorptive extraction is based on the partitioning of target analytes between the sample (mostly aqueous‐based liquid samples) and a stationary phase‐coated magnetic stir bar. Until now, only PDMS‐coated stir bars are commercially available, restricting the range of applications to the non‐selective extraction of hydrophobic compounds due to the apolar character of PDMS. In this work, a novel stir bar coated with molecularly imprinted polymer as selective extraction phase for sorptive extraction of thiabendazole (TBZ) was developed. Two different procedures, based on physical or chemical coating, were assessed for the preparation of molecularly imprinted stir bars. Under optimum conditions, recoveries achieved both in imprinted and non‐imprinted polymer stir bars obtained by physical coating were very low, whereas TBZ was favourably retained by imprinted over non‐imprinted polymer stir bars obtained by chemical coating and thus the latter approach was used in further studies. Different parameters affecting both stir‐bars preparation (i.e. cross‐linker, porogen, polymerization time) and the subsequent selective extraction of TBZ (i.e. washing, loading and elution solvents, extraction time) were properly optimized. The molecularly imprinted coated stir bars were applied to the extraction of TBZ from citrus samples (orange, lemon and citrus juices) allowing its final determination at concentrations levels according to current regulations.     

Molecularly imprinted poly (methacrylamide-co-methacrylic acid) composite membranes for recognition of curcumin

In this study, molecularly imprinted poly (methacrylamide-co-methacrylic acid) composite membranes with different ratio of methacrylamide (MAM) versus methacrylic acid (MAA) were prepared via UV initiated photo-copolymerization on the commercial filter paper. Curcumin was chosen as the template molecule. Infra-red (IR) spectroscopy was used to study the binding mechanism between the imprinted sites and the templates. The morphology of the resultant membranes was visualized by scanning electron microscopy (SEM). Static equilibrium binding and recognition properties of the imprinted composite membranes to curcumin (cur-I) and its analogues demethoxycurcumin (cur-II) or bisdemethoxycurcumin (cur-III) were tested. The results showed that curcumin-imprinted membranes had the best recognition ability to curcumin compared to its analogues. From the results, the biggest selectivity factor of α_cur-I/cur-II and α_{cur-I/cur-III} were 1.50 and 5.94, and they were obtained from the composite membranes in which MAM/MAA were 1:4 and 0:1, respectively. The results of this study implied that the molecularly imprinted composite membranes could be used as separation membranes for curcumin enrichment.     

Molecularly imprinted polymer for selective extraction of domoic acid from seafood coupled with high-performance liquid chromatographic determination

In this work, a highly selective sample cleanup procedure that combining molecular imprinting technique (MIT) and solid phase extraction (SPE) was developed for the isolation of domoic acid (a fascinating marine toxin) from seafood samples. The molecular imprinting polymer (MIP) for domoic acid was prepared using 1,3,5-pentanetricarboxylic acid as the template molecule instead of domoic acid. 4-Vinyl pyridine was used as the functional monomer and ethylene glycol dimethacrylate was used as the cross-linking monomer. The obtained imprinted polymer showed high affinity to domoic acid and was used as selective sorbent for the SPE of domoic acid from seafood samples. An off-line molecularly imprinted solid phase extraction (MISPE) method followed by high-performance liquid chromatography (HPLC) with diode-array detection for the detection of domoic acid was also established. Good linearity was obtained from 0.5 mg L⁻¹ to 25 mg L⁻¹ (R² > 0.99) with a quantitation limit of 0.1 mg L⁻¹, which was sufficient to determine domoic acid at the maximum level permitted by several authorities. The mean recoveries of domoic acid from mussel extracts were 93.4-96.7%. It was demonstrated that the proposed MISPE-HPLC method could be applied to direct determination of domoic acid from seafood samples.