Preparation of MIP grafts for quercetin by tandem aryl diazonium surface chemistry and photopolymerization

The food antioxidant quercetin was used as a template in an ultrathin molecularly imprinted polymer (MIP) film prepared by photopolymerization. Indium tin oxide (ITO) plates were electrografted with aryl layers via a diazonium salt precursor bearing two terminal hydroxyethyl groups. The latter act as hydrogen donors for the photosensitizer isopropylthioxanthone and enabled the preparation of MIP grafts through radical photopolymerization of methacrylic acid (the functional monomer) and ethylene glycol dimethacrylate (the crosslinker) in the presence of quercetin (the template) on the ITO. The template was extracted, and the remaining ITO electrode used for the amperometric determination of quercetin at a working potential of 0.26 V (vs. SCE). The analytical range is from 5.10⁻⁸ to 10⁻⁴ mol L⁻¹, and the detection limit is 5.10⁻⁸ mol L⁻¹.

This work describes the grafting of a molecularly imprinted polymer (MIP) film by combining diazonium surface chemistry and surface-initiated photopolymerization. The MIP grafts specifically and selectively recognize quercetin in pure solution in THF and in real green tea infusion.

     

Development of a molecularly imprinted polymer-matrix solid-phase dispersion method for selective determination of β-estradiol as anabolic growth promoter in goat milk

A simple, fast, and sensitive method for determination of 17 β-estradiol (E2) in goat milk samples has been developed by combining selective molecularly imprinted matrix solid-phase dispersion (MIP–MSPD) and liquid chromatography with diode-array detection (DAD). The molecularly imprinted polymer was synthesized by use of 17β-estradiol as template molecule, methacrylic acid as functional monomer, ethylene glycol dimethacrylate as crosslinker monomer, azobisisobutyronitrile as initiator, and acetonitrile as porogen, and was used as selective solid support for matrix solid-phase dispersion. The selected dispersant had high affinity for E2 in the goat milk matrix and the extract obtained was sufficiently clean for direct injection for HPLC analysis without any interferences from the matrix. The proposed MIP–MSPD method was validated for linearity, precision, accuracy, decision limit (CCα) and detection capability (CCβ), in accordance with European Commission Decision 2002/657/EC criteria. Linearity ranged from 0.3–10 μg g^?1 (correlation coefficient r ²?>?0.999). Mean recovery of E2 from goat milk samples at different spiked levels was between 89.5 and 92.2%, with RSD values within 1.3–2%. CCα and CCβ values were 0.36 and 0.39 μg g^?1, respectively. The developed MIP–MSPD method was successfully applied to direct determination of E2 in goat milk samples.

Preparation of an amperometric sensor for norfloxacin based on molecularly imprinted grafting photopolymerization

A sensitive amperometric sensor for norfloxacin (NF) was introduced. The receptor layer was prepared by molecularly imprinted photopolymerization of acrylamide and trimethylolpropane trimethacrylate on the surface of a gold electrode. The binding mechanism of the molecularly imprinted polymer was explored by ultraviolet (UV) and infrared (IR) spectroscopy. The chemosensor was characterized by cyclic voltammetry (CV), differential pulse voltammetry (DPV), electrochemical impedance (EI), and scanning electron microscopy (SEM). The electrode prepared by photopolymerization has a better recognition ability to template molecules than that of electropolymerization and NIP. Some parameters affecting sensor response were optimized. Norfloxacin was detected by measurements of an amperometric i–t curve. The linear relationships between current and logarithmic concentration are obtained from 1.0?×?10^?9 to 1.0?×?10^?3?mol?L^?1. The detection limit of the sensor was 1.0?×?10^?10?mol?L^?1. The proposed method is sensitive, simple, and cheap, and is applied to detect NF in human urine successfully.

Extraction of tributyltin by magnetic molecularly imprinted polymers

We have prepared core-shell magnetic molecularly imprinted polymer nanoparticles for recognition and extraction of tributyl tin (TBT). The use of particles strongly improves the imprinting effect and leads to fast adsorption kinetics and high adsorption capacities. The functional monomer acrylamide was grafted to the surface of Fe₃O₄ nanospheres in two steps, and MIP layers were then formed on the surface by creating a MIP layer on the surface consisting of poly(ethyleneglycol dimethacrylate) with a TBT template. The particles were characterized in terms of morphological, magnetic, adsorption, and recognition properties. We then have developed a method for the extraction of TBT from spiked mussel (Mytilidae), and its determination by liquid chromatography-tandem mass spectrometry. The method has a limit of detection of 1.0 ng?g^?1 (n?=?5) of TBT, with a linear response between 5.0 and 1,000 ng?g^?1. The proposed method was successfully applied to the determination of trace TBT in marine food samples with recoveries in the range of 78.3–95.6 %.

A molecularly imprinted polymer for solid phase extraction of allantoin

We describe a molecularly imprinted polymer (MIP) for the solid-phase extraction of the skin protectant allantoin. The MIP was deposited on the surface of monodisperse silica microspheres possessing acroyl groups on the surface (MH-SiO₂). The resulting MIP microspheres (MH-SiO₂@MIP) showed a 3.4-fold higher adsorption capacity and a 1.9-fold better selectivity for allantoin than the respective non-imprinted polymer (MH-SiO₂@NIP). The monolayer adsorption capacities of the MH-SiO₂@MIP and the MH-SiO₂@NIP were calculated with the help of the Langmuir model and found to be 6.8 and 1.9 mg?g^?1, respectively. Adsorption kinetics fit a pseudo-second order rate mechanism, with an initial adsorption rate of 1.44 for the MH-SiO₂@MIP, and of 0.07 mg?g^?1?min^?1 for the MH-SiO₂@NIP. The material can be regenerated, and its adsorption capacity for allantoin remains stable for at least five regeneration cycles. It was successfully used as a sorbent for the selective solid-phase extraction of allantoin from Rhizoma dioscoreae.

Chiral separation of racemic mandelic acids by use of an ionic liquid-mediated imprinted monolith with a metal ion as self-assembly pivot

A new chiral stationary phase based on molecularly imprinted polymers (MIP) was prepared in ionic liquid by use of the metal pivot concept. Imprinted monoliths were synthesized by use of a mixture of R-mandelic acid (template), 4-vinylpyridine, ethylene glycol dimethacrylate, and several metal ions as pivot between the template and functional monomer. A ternary mixture of dimethyl sulfoxide–dimethylformamide–[BMIM]BF₄ containing metal ions was used as the porogenic system. Separation of the enantiomers of rac-mandelic acid was successfully achieved on the MIP thus obtained, with resolution of 1.87, whereas no enantiomer separation was observed on the imprinted monolithic column in the absence of metal ions. The effects of polymerization conditions, including the nature of the metal ion and the ratios of template to metal ions and template to functional monomer, on the chiral separation of mandelic acid were investigated. The results reveal that use of metal ions as a pivot, in combination with ionic liquid, is an effective method for preparation of a highly efficient MIP stationary phase for chiral separation.

Determination of sulfamethoxazole in milk using molecularly imprinted polymer monolith microextraction coupled to HPLC

We report on a new method for the selective extraction of the antibiotic sulfamethoxazole (SMO) in milk that is making use of a molecularly imprinted polymer (MIP) monolith as the sorbent. The monolith was synthesized in the tip of a micropipette using SMO as the template and a combination of acrylamide and 4-vinylpyridine as the co-functional monomers. The monolith was connected to syringes in different sizes and used for microextraction without any other treatment and showed high selectivity and enrichment ability for SMO. It was applied to the selective extraction and sensitive determination of SMO in milk. The linear range is from 5–600?μg?L^?1, the correlation coefficient (r²) is 0.9984, and the detection limit (at S/N?=?3) is 1?μg?L^?1. Recoveries range from 93.6 to 101.7?%, with relative standard deviations of <6.1?%.

Preparation and characterization of molecularly imprinted microspheres for selective extraction of trace melamine from milk samples

We describe molecularly imprinted microspheres (MIMs) for the selective extraction of melamine from milk. The MIMs were made from melamine as the template molecule, methacrylic acid as the functional monomer, and ethylene glycol dimethacrylate as the linking agent. The MIMs were synthesized by suspension polymerization and characterized by rebinding experiments. They displayed high adsorption capacity, fast rebinding kinetics, and highly specific rebinding of melamine. The imprinting factor is 4.1. Scatchard analysis revealed a one-type rebinding behavior, the dissociation constant and maximum rebinding capacity being 37.59 g L^?1 and 30.85 μmol g^?1, respectively. The MIMs exhibited a 25% cross-reactivity towards atrazine, but less than 3.0% towards prometryn, clenbuterol and metronidazole. In addition, a MIM-based solid phase extraction (MISPE) column for melamine was prepared by packing MIMs into a common SPE cartridge. The MISPE extraction gave recoveries of 89.8 to 100.6% of melamine, with relative standard deviations of 5.9 to 7.5%. There was no significant loss of rebinding capacity after more than 60 repeated uses, thus demonstrating the high stability of the MISPE column. The MSPE column also was applied to the extraction of melamine from spiked liquid and powdered milk with satisfying accuracy and precision.

Molecularly imprinted dispersive solid-phase microextraction for determination of sulfamethazine by capillary electrophoresis

We have developed a rapid, selective and efficient method for dispersive solid-phase microextraction (DSPME) using microbeads of a molecularly imprinted polymer (MIP). It enables the pre-concentration of sulfamethazine and sample clean-up prior to capillary electrophoresis with UV detection. The microbeads were synthesized via precipitation polymerization using sulfamethazine, methacrylic acid and ethylene glycol dimethacrylate (EGDMA) as the template molecule, the functional monomer and the cross-linking monomer, respectively. Characterization by SEM displayed the high uniformity and dispersibility of the MIP microbeads. The adsorption and desorption of sulfamethazine and the parameters for CE were optimized to result in a limit of detection of 1.1?μg?L^?1, which is 373-fold lower than that of direct CE detection. The equilibration time of extraction was reduced to 5?min, and the selectivity of the microbeads was significantly improved compared to the non-imprinted polymer. The method was successfully applied to the determination of trace sulfamethazine in several milk samples, with recoveries in the range of 89?% to 110?%.

A molecular imprint-coated stirrer bar for selective extraction of caffeine, theobromine and theophylline

We have prepared a novel caffeine imprinted polymer on a stir bar that can be used for selective extraction of caffeine, theobromine and theophylline from beverages. The polymerization time and quantities of reagents (template, cross-linker, porogenic solvent) were optimized. The morphology of the molecularly imprinted polymer-coating was studied by scanning electron microscopy and Fourier transform IR spectroscopy. A rapid and sensitive method was worked out for the extraction of caffeine, theobromine and theophylline from beverages by using the molecularly imprinted stir bar followed by HPLC analysis. The effects of extraction solvent, stirring speed, desorption solvent, adsorption and desorption time were optimized. The method displays a linear response in the 5–150 μg L^?1 caffein concentration range, with a correlation coefficient of >0.9904. The recoveries for three analytes in tea, carbonated and functional beverages were 91–108 %, 90–110 % and 93–109 %, with relative standard deviations ranging from 3.6–5.7 %, 3.5–7.9 % and 3.2–7.9 %, respectively.

Enhancement of the chemiluminescence of permanganate-formaldehyde system by gold/silver nanoalloys and its application to trace determination of melamine

We have examined the specificity of electrosynthesized poly-o-phenylenediamine as a kind of material molecularly imprinted with metal chelates. Molecularly imprinted polymers (MIPs) were prepared in situ by an electrochemical method. The EDTA chelate complexes of Cu(II), Zn(II), Fe(III) and Cd(II) ions were used as templates of the MIPs deposited on a gold electrode of a quartz crystal microbalance (QCM). The binding ability and specificity of the MIPs were investigated via the frequency response of the QCM to the adsorption of the template chelates and their analogs. Linear relationships are observed between the frequency shift and the concentration of the template chelates over a typical range of ~10^?6 to ~10^?4?mol·L^?1. The results reveal good binding specificity of such MIPs for their templates over structurally related analogs, but the selectivity coefficients are less significant than that for enantiomers. The results also suggest no significant correlation between binding specificity and the ionic (or atomic) radius of the investigated metal ions. The observed specificity is qualitatively attributed to the overall conformational difference of the metal-EDTA complexes resulting from their difference in both ionic radius and electronic structures.

A molecularly imprinted polymer for the determination of neopterin

A molecularly imprinted polymer (MIP) for the specific retention of neopterin has been developed. A set of 6 polymers was prepared by radical polymerization under different experimental condition using methacrylic acid as functional monomer and ethylene glycol dimethacrylate as crosslinker, with the aim to understand their influence on the efficiency of the MIP. The performance of each MIP was tested in batch experiments via their binding capacity. The MIP prepared in the presence of nickel ions in dimethylsulfoxide-acetonitrile mixture (P4) exhibited the highest binding capacity for neopterin (260 μmol per gram of polymer). A selectivity study with two other pteridines demonstrated the polymer P4 also to possess the best selectivity.

Determination of t,t-muconic acid in urine samples using a molecular imprinted polymer combined with simultaneous ethyl chloroformate derivatization and pre-concentration by dispersive liquid–liquid microextraction

The present communication describes the preparation and evaluation of a molecularly imprinted polymer (MIP) as a solid-phase extraction (SPE) sorbent and simultaneous ethyl chloroformate (ECF) derivatization and pre-concentration by dispersive liquid–liquid microextraction (DLLME) for the analysis of t,t-muconic acid (t,t-MA) in urine samples using gas chromatography–mass spectrometry. The imprinting polymer was prepared using methacrylic acid as a functional monomer, ethylene glycol dimethacrylate as a cross-linker, 2,2-azobisisobutyronitrile as the initiator and t,t-MA as a template molecule. The imprinted polymer was evaluated for its use as a SPE sorbent by comparing both imprinted and non-imprinted polymers in terms of the recovery of t,t-MA from urine samples. Molecular modelling studies were performed in order to estimate the binding energy and efficiency of the MIP complex formed between the monomer and the t,t-MA. Various factors that can affect the extraction efficiency of MIP, such as the loading, washing and eluting conditions, were optimized; other factors that can affect the derivatization and DLLME pre-concentration were also optimized. MIP in combination with ECF derivatization and DLLME pre-concentration for t,t-MA exhibits good linearity, ranging from 0.125 to 2 μg?mL^?1 (R ²?=?0.9971), with limit of detection of 0.037 μg?mL^?1 and limit of quantification of 0.109 μg?mL^?1. Intra- and inter-day precision was found to be <6 %. The proposed method has been proven to be effective and sensitive for the selective pre-concentration and determination of t,t-MA in urine samples of cigarette smokers.

Preparation of monodisperse curcumin-imprinted polymer by precipitation polymerization and its application for the extraction of curcuminoids from Curcuma longa L.

A monodisperse molecularly imprinted polymer (MIP) for curcumin was first prepared by precipitation polymerization using methacrylamide (MAM) and 4-vinylpyridine as functional co-monomers, divinylbenzene as a crosslinker, and a mixture of acetonitrile and toluene as a porogen. The use of MAM as the co-monomer resulted in the formation of a monodisperse MIP and non-imprinted polymer (NIP). MIP and NIP, respectively, were monodispersed with a narrow particle size distribution (3.3?±?0.09 and 3.5?±?0.10 μm). In addition to shape recognition, hydrophobic and hydrogen-bonding interactions affected the retention and molecular-recognition of curcumin on the MIP. The MIP for curcumin could extract curcuminoids (curcumin, demethoxycurcumin, and bisdemethoxycurcumin) in Curcuma longa L.

Hydrophilic molecularly imprinted polymers for bisphenol A prepared in aqueous solution

We have prepared a hydrophilic molecularly imprinted polymer (MIP) for the hydrophobic compound bisphenol A (BPA) in aqueous solution using 3-acrylamido-N,N,N-trimethylpropan-1-aminium chloride (AMTC) as the functional monomer. Under redox-polymerization conditions, BPA forms an ion-pair with AMTC, which was confirmed by ¹H-NMR titration. The imprinting effect in aqueous solution was evaluated by comparison of this material with the corresponding non-imprinted polymer (NIP) and with a control polymer (CP) bearing no AMTC. The MIP showed the highest activity among the three polymers, and the imprinting factors as calculated from the amount of BPA bound to the MIP divided by the amounts bound to NIP and CP, respectively, are 1.8 and 6.0. The MIP was selective for BPA in aqueous solution, while structurally related compounds are not recognized. Such a selectivity for a hydrophobic compound is rarely observed in aqueous medium because non-specific binding of BPA inevitably leads to hydrophobic interaction.

A microvolume molecularly imprinted polymer modified fiber-optic evanescent wave sensor for bisphenol A determination

A fiber-optic evanescent wave sensor for bisphenol A (BPA) determination based on a molecularly imprinted polymer (MIP)-modified fiber column was developed. MIP film immobilized with BPA was synthesized on the fiber column, and the sensor was then constructed by inserting the optical fiber prepared into a transparent capillary. A microchannel (about 2.0 μL) formed between the fiber and the capillary acted as a flow cell. BPA can be selectively adsorbed online by the MIP film and excited to produce fluorescence by the evanescent wave produced on the fiber core surface. The conditions for BPA enrichment, elution, and fluorescence detection are discussed in detail. The analytical measurements were made at 276 nm/306 nm (λ _ex/λ _em), and linearity of 3?×?10^?9–5?×?10^?6 g mL^?1 BPA, a limit of detection of 1.7?×?10^?9 g mL^?1 BPA (3σ), and a relative standard deviation of 2.4 % (n?=?5) were obtained. The sensor selectivity and MIP binding measurement were also evaluated. The results indicated that the selectivity and sensitivity of the proposed fiber-optic sensor could be greatly improved by using MIP as a recognition and enrichment element. Further, by modification of the sensing and detection elements on the optical fiber, the proposed sensor showed the advantages of easy fabrication and low cost. The novel sensor configuration provided a platform for monitoring other species by simply changing the light source and sensing elements. The sensor presented has been successfully applied to determine BPA released from plastic products treated at different temperatures.

Preparation of guanidinium terminus-molecularly imprinted polymers for selective recognition and solid-phase extraction (SPE) of [arginine]-microcystins

About 70 % of microcystin (MC) congeners reported in literature consist of l-arginine amino acid (R) with its guanidinium terminal extending out of the cyclic moiety of these MCs. Molecularly imprinted polymer (MIP) bearing guanidinium terminus cavities was successfully synthesised using l-arginine as a template. Non-imprinted polymer (NIP; without template) was also synthesised for control purposes. The surface area, total pore volume and average pore diameter of MIP and NIP were 267.13 m²/g, 0.63 cm³/g and 88.39 Å; 249.39 m²/g; 0.54 cm³/g and 87.14 Å, respectively. The polymers were investigated for selective recognition and extraction of [arginine]-MCs in water using solid-phase extraction/liquid chromatography-electrospray ionisation–mass spectrometry (SPE/LC-ESI-MS) method. Representative model standard solutions (0.5–10.0 μg/L) of MC-LR and MC-LY were spiked in distilled water, recovered by SPE and quantified by LC-ESI-MS. In this study, Oasis Waters? HLB cartridges served as positive control SPE sorbents. The MIP recognised MC-LR with high recoveries (70.8–91.4 %; r ² ?=?0.9962) comparable to HLB cartridges (71.0–91.85 %; r ² ?=?0.9993), whereas the NIP did not recognise or retain MC-LR. Also, neither MIP nor NIP recognised or retained MC-LY. Extracts of environmental toxic Microcystis aeruginosa were subjected to SPE procedure employing MIP, NIP and HLB cartridges. Microcystin-LR, -YR, -RR, -WR, -(H₄)YR and (D-Asp³, Dha⁷)MC-RR were extracted by MIP and HLB cartridges only as confirmed by LC-ESI-MS. This study demonstrated that the prepared MIP have potential applications for the removal in water and LC-ESI-MS identifications of MCs consisting the guanidinium moiety, i.e.[arginine]-MCs, and in particular targeting commonly encountered toxic congeners, MC-LR, -YR and -RR.

Fluorescent turn-on detection of cysteine using a molecularly imprinted polyacrylate linked to allylthiol-capped CdTe quantum dots

CdTe quantum dots capped with thioglycolic acid (TGA) display a strong turn-on fluorescence response if exposed to solutions of cysteine (Cys). In order to exploit this effect, a molecularly imprinted polymer (MIP) for Cys was covalently linked to the QDs via allyl mercaptan. The resulting nanomaterials (QDs, MIP-coated QDs, and nonimprint-coated QDs) were characterized by FTIR and scanning electron microscopy. The adsorption of Cys was studied in phosphate buffer (pH 7.4) with respect to equilibration times (5, 15, and 40 min, respectively), binding constants [2.98, 2.42, and 0.96 (×10⁴ M^?1)], and Langmuir isotherms (R²?=?0.9995, 0.9999, and 0.9983) in the Cys concentration range between 3.33 μM to 500 μM. The method has a detection limit of 0.85 μM (3σ, blank, for n?=?10). The selectivity of the MIP-coated QDs for Cys over 19 other amino acids is similar to that of bare QDs, but MIP-QDs afford better recoveries of Cys from solutions also containing bovine serum albumin (90 %) and fetal bovine serum (97 %), respectively, when compared to the recoveries that are obtained with bare (non-imprinted) QDs (135 % and 120 %). This is probably due to the fact that the outer MIP shell largely reduces protein wrapping, dot aggregation, and matrix inclusion.

Solid phase extraction of penicillins from milk by using sacrificial silica beads as a support for a molecular imprint

We have prepared molecularly imprinted beads with molecular recognition capability for target molecules containing the penicillanic acid substructure. They were prepared by (a) grafting mesoporous silica beads with 6-aminopenicillanic acid as the mimic template, (b) filling the pores with a polymerized mixture of methacrylic acid and trimethylolpropane trimethacrylate, and (c) removing the silica support with ammonium fluoride. The resulting imprinted beads showed good molecular recognition capability for various penicillanic species, while antibiotics such as cephalosporins or chloramphenicol were poorly recognized. The imprinted beads were used to extract penicillin V, nafcillin, oxacillin, cloxacillin and dicloxacillin from skimmed and deproteinized milk in the concentration range of 5–100 μg·L^?1. The extracts were then analyzed by micellar electrokinetic chromatography by applying reverse polarity staking as an in-capillary preconcentration step, and this resulted in a fast and affordable method within the MRL levels, characterized by minimal pretreatment steps and recoveries of 64–90 %.

Micro-solid phase extraction of ochratoxin A, and its determination in urine using capillary electrophoresis

We describe a simple, environmentally friendly and selective technique for the determination of ochratoxin A (OTA) in urine. It involves (a) the use of a molecularly imprinted polymer as a sorbent in micro-solid-phase extraction in which the sorbent is contained in a propylene membrane envelope, and (b) separation and detection by capillary electrophoresis (CE). Under optimized conditions, response is linear in the range between 50 and 300 ng mL^?1 (with a correlation coefficient of 0.9989), relative standard deviations range from 4 to 8 %, the detection limit for OTA in urine is 11.2 ng mL^?1 (with a quantification limits of 32.5 ng mL^?1) which is lower than those of previously reported methods for solid-phase extraction combined with CE. The recoveries of OTA from urine spiked at levels of 50, 150 and 300 ng mL^?1 ranged from 93 to 97 %.