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.

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 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.

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.

Rapid preparation of molecularly imprinted polymer by frontal polymerization

Frontal polymerization was successfully applied, for the first time, to obtain molecularly imprinted polymers (MIPs). The method provides a solvent-free polymerization mode, and the reaction can be completed in 30 min. By this approach, MIPs were synthesized using a mixture of levofloxacin (template), methacrylic acid, and divinylbenzene. The effect of template concentration and the amount of comonomer on the imprinting effect of the resulting MIPs was investigated. The textural and morphological parameters of the MIP particles were also characterized by mercury intrusion porosimetry, nitrogen adsorption isotherms, and scanning electron microscopy, providing evidence concerning median pore diameter, pore volumes, and pore size distributions. The levofloxacin-imprinted polymer formed in frontal polymerization mode showed high selectivity, with an imprinting factor of 5.78. The results suggest that frontal polymerization provides an alternative means to prepare MIPs that are difficult to synthesize and may open up new perspectives in the field of MIPs.

Molecular imprinting for anion recognition in aqueous media

Molecular imprinting technology is an attractive approach of creating recognition sites in polymeric materials by using the templating approach found in many natural systems. These recognition sites have memory to the target molecule that enables selective recognition of the template species. Molecularly imprinted polymers (MIPs) have been used in a wide range of areas including separation and isolation, catalysis, chemical sensing, and drug delivery. This review aims at highlight the recent advances in the application of molecular imprinting technology for inorganic and small organic anion recognition in aqueous media.

Surface molecular imprinting for chemiluminescence detection of the organophosphate pesticide chlorpyrifos

We report on a surface molecular imprinting strategy for synthesizing core-shell particles whose shell is imprinted with chlorpyrifos (CPF). The particles were prepared by copolymerization of the methacryloyl groups on the surface of silica particles modified with 3-methacryloxypropyl trimethoxysilane a functional monomer and a cross-linking agent. The imprinted particles exhibit larger binding capacity, faster binding kinetics, and higher recognition selectivity for CPF. Combined with highly sensitive chemiluminescence assay, the method was applied to the determination of CPF with a detection limit of 0.92?nM which is about 2 orders of magnitude lower than that by conventional CL method. The method also displays repeatability for more than 200 times.

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.

Transferrin recognition based on a protein imprinted material prepared by hierarchical imprinting technique

A novel kind of transferrin imprinted polymer particles was synthesized by a hierarchical strategy. First, transferrin was immobilized on silica beads by non-covalent absorption. Then, a pre-polymerization mixture, composed of 1,4-bis(acryloyl)piperazine, methacrylamide, methacrylic acid, ammonium sulfate and polyoxyethylene sorbitan monolaurate, was irrigated into the pores of silica particles, and polymerized at 25 °C. Finally, the silica matrix was etched with ammonium hydrogen fluoride, not only to remove the template protein, but also to expose protein recognition sites on the surface of the imprinted polymer. The binding capacity of the transferrin-imprinted particles is 6.3 mg of protein per gram of material, and the time required to reach adsorption equilibrium was less than 10 min. The imprinting factor of transferrin is ca. 3.3 in the presence of ribonuclease B, cytochrome c and β-lactoglobulin. The results indicate that these imprinted polymer particles can recognize transferrin with good selectivity, high binding capacity and fast mass transfer. They may be applied as an artificial antibody to remove the high abundance proteins in plasma.

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 %.

Piezoelectric atrazine sensor based on a molecularly imprinted film of titanium dioxide

We have developed a piezoelectric sensor for the determination of atrazine. It is based on the modification of a molecularly imprinted film of TiO₂ that was placed on a quartz crystal via a surface sol?Cgel process. The resulting sensor exhibits high selectivity for atrazine, a re-usability that is better than that of other sensors, a response time of 3?min, a wider linear range (0.0005?C8?mM), and a lower detection limit (0.1???M). The analytical application of the atrazine sensor confirms the feasibility of atrazine determination.

Development of a novel molecularly imprinted polymer for the retention of 4,6-dimethyldibenzothiophene

Several molecularly imprinted polymers (MIPs) for the retention of 4,6-dimethyldibenzothiophene (4,6-DMDBT) were prepared. The first was a polymer prepared non-covalently with methacrylic acid and ethylene glycol dimethacrylate polymerized in the presence of 4,6-DMDBT. After extraction of 4,6-DMDBT, the selectivity of the imprinted polymer was evaluated by HPLC and compared to a non-imprinted control polymer prepared without 4,6-DMDBT. The imprinted polymer retained 4,6-DMDBT slightly longer than the control polymer. The second polymer was prepared using nickel (II)-methacryloylhistidinedihydrate monomer which was combined with 4,6-DMDBT, and polymerized with ethylene glycol dimethacrylate. This is a novel use of this monomer for retention of sulfur-containing organic compounds. Selectivity for 4,6-DMDBT was much greater in this polymer compared to the first, and retention in acetonitrile was more than three times greater on the imprinted polymer compared to a control polymer. Results indicate the potential use of this novel MIP for the removal of organosulfur compounds from fuel.

Preparation and characterization of an imprinted monolith by atom transfer radical polymerization assisted by crowding agents

A method based on reverse atom transfer radical polymerization (R-ATRP) and molecular crowding has been used for design and synthesis of monolithic molecularly imprinted polymers (MIPs) capable of recognizing ibuprofen (IBU). 4-Vinylpyridine (4-VP) was used as the functional monomer, and ethylene glycol dimethacrylate (EDMA) was the crosslinking monomer. Azobisisobutyronitrile (AIBN)–CuCl₂–N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA) was used as the initiating system. Compared with conventional radical polymerization-based IBU-MIPs, the imprinting effects of the obtained IBU-MIPs was enhanced, suggesting the merit of combination of reverse ATRP and molecular crowding. In addition, it was found that the polymerization time of the molecularly imprinted monolithic column, the amount of template, the degree of crosslinking, and the composition of mobile phase greatly affected retention of the template and the performance of molecular recognition .

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?%.

Towards a synthetic avidin mimic

A series of streptavidin-mimicking molecularly imprinted polymers has been developed and evaluated for their biotin binding characteristics. A combination of molecular dynamics and NMR spectroscopy was used to examine potential polymer systems, in particular with the functional monomers methacrylic acid and 2-acrylamidopyridine. The synthesis of copolymers of ethylene dimethacrylate and one or both of these functional monomers was performed. A combination of radioligand binding studies and surface area analyses demonstrated the presence of selectivity in polymers prepared using methacrylic acid as the functional monomer. This was predicted by the molecular dynamics studies showing the power of this methodology as a prognostic tool for predicting the behavior of molecularly imprinted polymers.

First example of a molecularly imprinted polymer incorporating a difunctionalized alloxazine flavin isomer

High-quality alloxazine (a flavin isomer) imprinted polymers have been made for the first time. A molecularly imprinted polymer (MIP) for the N1,N3-di-functionalized alloxazine template 2 was made. The MIP prepared for 2 exhibited excellent, highly selective molecular recognition for template 2, as determined by HPLC analysis using columns prepared with the MIP. This has also demonstrated that the core flavin structure can survive the imprinting process.     

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.

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.

Heat-transfer-based detection of l-nicotine, histamine, and serotonin using molecularly imprinted polymers as biomimetic receptors

In this work, we will present a novel approach for the detection of small molecules with molecularly imprinted polymer (MIP)-type receptors. This heat-transfer method (HTM) is based on the change in heat-transfer resistance imposed upon binding of target molecules to the MIP nanocavities. Simultaneously with that technique, the impedance is measured to validate the results. For proof-of-principle purposes, aluminum electrodes are functionalized with MIP particles, and l-nicotine measurements are performed in phosphate-buffered saline solutions. To determine if this could be extended to other templates, histamine and serotonin samples in buffer solutions are also studied. The developed sensor platform is proven to be specific for a variety of target molecules, which is in agreement with impedance spectroscopy reference tests. In addition, detection limits in the nanomolar range could be achieved, which is well within the physiologically relevant concentration regime. These limits are comparable to impedance spectroscopy, which is considered one of the state-of-the-art techniques for the analysis of small molecules with MIPs. As a first demonstration of the applicability in biological samples, measurements are performed on saliva samples spiked with l-nicotine. In summary, the combination of MIPs with HTM as a novel readout technique enables fast and low-cost measurements in buffer solutions with the possibility of extending to biological samples.

Molecularly imprinted polystyrene–titania hybrids with both ionic and π–π interactions: a case study with pyrenebutyric acid

We present hybrid films consisting of a composite prepared from polystyrene (PS) and titanium dioxide (titania; TiO₂) and molecularly imprinted with 1-pyrenebutyric acid (PBA). The interaction of PBA with the polymer is shown to occur via binding of the carboxylic group to TiO₂ and hydrophobic interaction of the pyrene moiety with the PS network. We investigated the effects of the PS fraction on morphology, imprinting properties, and guest binding. The template could be completely removed by incubating the films in an acetonitrile solution of pyrene, which is due to the stronger π–π interaction between PBA and pyrene than the interaction between PBA and its binding site. A guest binding study with pyrene, 1-aminopyrene, pyrenemethanol, and anthracene-9-carboxylic acid showed that the hybrid films possessed selectivity and much higher binding capacity for PBA. This study demonstrates the first case of clear PS-assisted imprinting, where the π–π interaction of the template with a linear (non-crosslinked) polymer creates selective binding sites and enhances the binding capacity. This is a driving force for guest binding in addition to the interaction of the template/analyte with TiO₂. All molecularly imprinted films displayed better binding, repeatability and reversibility compared to the respective non-imprinted films.