Molecularly imprinted polymeric fibers for solid-phase microextraction

Solid-phase microextraction (SPME) is widely used in analytical laboratories for the analysis of organic compounds, thanks to its simplicity and versatility. However, the current commercially available fibers are based on nonselective sorbents, making difficult in some cases the final determination of target compounds by chromatographic techniques. Molecularly imprinted polymers (MIPs) are stable polymers with selective molecular recognition abilities, provided by the template used during their synthesis. In the present work, a simple polymerization strategy allowing the obtainment of molecularly imprinted polymeric fibers to be used in SPME is proposed. Such a strategy is based on the direct synthesis of molecularly imprinted polymeric fibers (monoliths) using silica capillaries as molds, with silica being etched away after polymerization. The system propazine:methacrylic acid was used as a model for the preparation of molecularly imprinted fibers, and its ability to selectively rebind triazines was evaluated. Variables affecting polymer morphology (i.e., polymerization time, fiber thickness) and binding-elution of target analytes (i.e., solvents, time, temperature) were studied in detail. The imprinted fiber showing the best performance in terms of selectivity and affinity for triazines was successfully applied to the extraction of target analytes from environmental and food samples.     

核-壳型罗丹明6G磁性分子印迹固相萃取材料的合成与表征

采用化学共沉淀法制备Fe3O4磁性纳米粒子,以3-氨丙基三乙氧基硅烷(APTES)对其表面进行氨基硅烷化改性,形成Fe3O4@SiO2-NH2纳米粒子。以其作为磁性核,采用表面印迹技术,以罗丹明6G为模板,丙烯酰胺(AM)为功能单体,三羟甲基丙烷三甲基丙烯酸酯(TRIM)为交联剂,在Fe3O4@SiO2-NH2表面形成罗丹明6G分子印迹聚合膜,制备了核-壳型罗丹明6G磁性分子印迹聚合物(Fe3O4@MIPs),对合成条件进行了优化。分别采用红外光谱(FT-IR)、场发射扫描电镜(FESEM)、振动样品磁强分析(VSM)和热重分析(TGA)等仪器分析手段,对Fe3O4@MIPs的结构进行表征。结果表明,所制备的核-壳型磁性分子印迹聚合物具有高吸附容量及显著选择性;在外加磁场作用下Fe3O4@MIPs可快速与样品基质分离,大大提高了实验效率。Fe3O4@MIPs作为一种新型固相萃取材料,可以从样品中选择性分离和富集违规添加的罗丹明6G,可应用于食品的安全检测。     

Surface-grafted molecularly imprinted polymers for protein recognition.

A technique for coating microplate wells with molecularly imprinted polymers (MIPs) specific for proteins is presented. 3-Aminophenylboronic acid was polymerized in the presence of the following templates: microperoxidase, horseradish peroxidase, lactoperoxidase, and hemoglobin, via oxidation of the monomer by ammonium persulfate. This process resulted in the grafting of a thin polymer layer to the polystyrene surface of the microplates. Imprinting resulted in an increased affinity of the polymer toward the corresponding templates. The influence of the washing procedure, template concentration, and buffer pH on the polymer affinity was analyzed. It was shown that the stabilizing function of the support and spatial orientation of the polymer chains and template functional groups are the major factors affecting the imprint formation and template recognition. Easy preparation of the MIPs, their high stability, and their ability to recognize small and large proteins, as well as to discriminate molecules with small variations in charge, make this approach attractive and broadly applicable in biotechnology, assays and sensors.     

Characterization of molecularly imprinted polymers with the Langmuir-Freundlich isotherm

The majority of binding models that have been applied to molecularly imprinted polymers (MIPs) have been homogeneous models. MIPs, on the other hand, are heterogeneous materials containing binding sites with a wide array of binding affinities and selectivities. Demonstrated is that the binding behavior of MIPs can be accurately modeled by the heterogeneous Langmuir-Freundlich (LF) isotherm. The applicability of the LF isotherm to MIPs was demonstrated using five representative MIPs from the literature, including both homogeneous and heterogeneous MIPs. Previously, such comparisons required the use of several different binding models and analyses, including the Langmuir model, the Freundlich model, and numerical approximation techniques. In contrast, the LF model enabled direct comparisons of the binding characteristics of MIPs that have very different underlying distributions and were measured under different conditions. The binding parameters can be calculated directly using the LF fitting coefficients that yield a measure of the total number of binding sites, mean binding affinity, and heterogeneity. Alternatively, solution of the Langmuir adsorption integral for the LF model enabled direct calculation of the corresponding affinity spectrum from the LF fitting coefficients from a simple algebraic expression, yielding a measure of the number of binding sites with respect to association constant Finally, the ability of the LF isotherm to model MIPs suggests that a unimodal heterogeneous distribution is an accurate approximation of the distribution found in homogeneous and heterogeneous MIPs.     

Development of an active packaging with molecularly imprinted polymers for beef preservation

To develop molecularly imprinted polymers (MIPs) for new food packaging material, a new active antibacterial packaging material was prepared with allyl isothiocyanate MIPs (AITC‐MIPs) and chitosan (CS) for beef preservation. AITC‐MIPs were prepared with AITC as template, β‐CD as the functional monomer, and TDI as the cross‐linker by the non‐covalent method, and the release characteristics were evaluated under different relative humidities and temperatures. The AITC‐MIPs active packaging film was obtained by uniform coating with CS coating solution and AITC‐MIPs based on the surface of the original low‐density polyethylene packaging film, and its role in delaying muscle metamorphism was thoroughly explored. According to the N‐hexane extraction method, the AITC content in AITC‐MIPs was determined to be 73.9 μL/g. The release behaviors of AITC‐MIPs under different humidities could be obtained by fitting with Avrami's Equation. The release of AITC‐MIPs under the relative humidities of 98% and 75% is a restricted dynamic diffusion process, while the release behaviors of AITC‐MIPs under the relative humidity of 50% are between those of a diffusion process and those of a first‐order mode dynamic process. The AITC‐MIPs could endure the heat stress, and the lower temperature was conducive to the stability of the AITC‐MIPs. A series of physicochemical and microbiological indicators fully illustrated that muscle deterioration could be significantly (P < 0.05) postponed by AITC‐MIPs active packaging film compared with the original low‐density polyethylene packaging film.     

分子印迹聚合物在分离领域的应用

分子印迹技术是近年来集高分子合成、分子设计、分子识别、仿生生物工程等众多学科优势发展起来的一种应用广泛的新型技术.阐述了分子印迹方法的基本原理,介绍了分子印迹聚合物在分离领域的应用.综述了该技术的研究现状,并展望了其发展趋势.     

Optical detection of chloramphenicol using molecularly imprinted polymers

A practical optical sensing system for the determination of chloramphenicol (CAP), utilizing molecularly imprinted polymers (MIPs) and HPLC, has been developed. The method is based on competitive displacement of a chloramphenicol-methyl red (CAP-MR) dye conjugate from specific binding cavities in an imprinted polymer by the analyte. The best of these polymers was obtained using (diethylamino)ethyl methacrylate as functional monomer at a monomer:template ratio of 2:1. HPLC with a mobile phase containing CAP-MR was used as the detection system, and injection of CAP and, to a lesser degree, thiamphenicol resulted in proportional displacement of the conjugate, which was detected at 460 nm. The detection system showed a linear response over a range of 3-1000 μg/mL and effectively detected CAP extracted from serum. This system offers a tailor-made, selective, and rapid method for CAP detection, is able to discriminate between similar molecules, and is effective below and above the therapeutic range (10-20 μg/mL serum, potentially toxic above 25 μg/mL). This technique is quite general and should enable the use of MIPs in a wide variety of applications involving the detection of families of molecules which possess a distinct arrangement of functional groups.     

Nanosphere molecularly imprinted polymers doped with gold nanoparticles for high selectivity molecular sensors

We report the first attempt of using molecularly imprinted polymers (MIPs) in the shape of nanoparticles that were doped with gold nanoparticles (AuNPs) for surface enhanced Raman scattering (SERS)-based sensing of molecular species.Specifically,AuNPs doped molecularly imprinted nano-spheres (AuNPs@nanoMIPs) were synthesized by one-pot precipitation polymerization using Sudan Ⅳ as the template for the SERS sensing.The AuNPs@nanoMIPs were characterized by various modes of scanning transmission electron microscopy (STEM) that showed the exact location of the AuNPs inside the MIP particles.The effects of Au concentration and solution stirring on the shape and the polydispersity of the particles were studied.Significant enhancement of the Raman signals was observed only when the MIP particles were doped with the AuNPs.The SERS signal improved significantly with increase in the Au concentration inside the AuNPs@nanoMIPs.Selectivity measurements of the Sudan Ⅳ imprinted AuNPs@nanoMIPs carried out with different Sudan derivatives showed high selectivity of the AuNPs-doped MIP particles.     

In-tube moleculary imprinted polymer solid-phase microextraction for the selective determination of propranolol

A molecularly imprinted polymer (MIP) material was synthesized for use as an in-tube solid-phase microextraction (SPME) adsorbent. The inherent selectivity and chemical and physical robustness of the MIP material was demonstrated as an effective stationary-phase material for in-tube SPME. An automated and on-line MIP SPME extraction method was developed for propranolol determination in biological fluids. This simplified the sample preparation process and the chromatographic separation of several beta-blocker compounds. The method developed for propranolol showed improved selectivity in comparison to alternative in-tube stationary-phase materials, overcoming the limitations of existing SPME coating materials. Preconcentration of the sample by the MIP adsorbent increased the sensitivity, yielding a limit of detection of 0.32 microg/mL by UV detection. Excellent method reproducibility (RSD < 5.0%) and column reusability (> 500 injections) were observed over a fairly wide linear dynamic range (0.5-100 microg/mL) in serum samples. To our knowledge, this is the first report on the automated application of a MIP material for in-tube SPME. The method was inexpensive, simple to set up, and simplified the choice of SPME adsorbent for in-tube extraction. The approach can potentially be extended to other MIPs for the determination of a wide range of chemically significant analytes.     

Preparation of molecularly imprinted polymers for the detection of aromatic hydrocarbons

In this study, the molecularly imprinted polymers (MIPs) are designed to improve their sensitivity and selectivity for specific aromatic hydrocarbons such as benzene, toluene, and xylene isomers. The MIPs based on methyl acrylate (MA) monomer are prepared using toluene and ethylene glycol dimetacrylate (EGDMA) as a template and a cross linking agent, respectively. The binding sites on the MIPs are characterized by using Fourier transform infrared spectrometry (FT-IR), nitrogen adsorption isotherms, and transmission electron microscopy (TEM). The selective behaviors of the MIPs are evaluated by their adsorption properties on a gravimetric apparatus. It is found that the performance is strongly influenced by the composition ratios of cross-linker, functional monomer, and template molecule. The molecular recognition ability can be assessed on the basis of an imprinting effect. The results indicate that the prepared MIPs can be used for the aromatic hydrocarbon sensor materials with high sensitivity and selectivity.     

Determination of theophylline in serum by molecularly imprinted solid-phase extraction with pulsed elution

The technique of molecular imprinting is used to produce an extensively cross-linked poly(methacrylic acid-co-ethylene dimethacrylate) material that contains theophylline as a print molecule. After Soxhlet extraction of the theophylline, binding sites are formed in the polymer with complementary size, shape, and positioning of chemical functionalities. The molecularly imprinted polymer's (MIP) high theophylline selectivity, chemical stability, and physically robust nature make it an ideal stationary-phase material in columns for HPLC separation of theophylline from other structurally related drug compounds. Mobile-phase tests confirm that a retention mechanism typical of normal-phase chromatography governs the separation, and selectivity of the MIP column can be controlled by a combination of the mobile phase and the sample solvent. Under optimal conditions, the MIP column functions like a solid-phase sorbent for theophylline extraction. Rapid elution of the bound theophylline can be accomplished in a pulsed format through injection of 20 μL of a solvent that has the proper polarity and protic nature to disrupt the electrostatic interactions and hydrogen bonding between theophylline and binding sites. A concentration detection limit of 120 ng/mL is obtained using direct UV absorption detection at 270 nm, which corresponds to a mass detection limit of 2.4 ng. This new technique, molecularly imprinted solid-phase extraction with pulsed elution (MISPE-PE), permits on-line preconcentration of theophylline from a large volume of dilute sample solution. Using a sample volume of 300 μL, a 40 ng/mL standard solution produces a detectable peak signal. Application of MISPE-PE in serum analysis further demonstrates the high capability of the MIP column to selectively isolate theophylline from other matrix components for fast, accurate determination.     

Method for synthesis and screening of large groups of molecularly imprinted polymers

A technique for the synthesis of molecularly imprinted polymers (MIPs) in small scale (～55 mg) coupled with direct in situ processing and batch rebinding evaluation is reported. The primary assessment is based on quantification by HPLC or UV absorbance measurement of the amount of template released from the polymer in a given solvent. This method allows a rapid screening of the parameters of importance to reach a desired level of binding affinity capacity and selectivity for a given target molecule. This was demonstrated for the triazine herbicide terbutylazine, where an initial screening was performed for the type of functional monomer used in the MIP preparation. Thus among the six functional monomers tested, methyl methacrylate, 4-vinylpyridine, and N-vinyl-α-pyrrolidone led to rapid and quantitative extraction whereas methacrylic acid and (trifluoromethyl)acrylic acid led to polymers that retained the template the most. After having established useful functional monomers, a secondary screening for selectivity was performed. In this, nonimprinted blank polymers were prepared and a normal batch rebinding evaluation was performed. The polymer showing the highest selectivity was the one prepared using methacrylic acid as functional monomer. This polymer was shown to strongly retain chlorotriazines including atrazine when a normal-scale batch of the polymer was evaluated in chromatography.     

Development and characterization of molecularly imprinted polymers for controlled release of citalopram

In this work, the use of molecularly imprinted polymers (MIPs) for citalolpram as anti-depressant drug was studied. Imprinted polymers were prepared from methacrylic acid (MAA; functional monomer), ethylene glycol dimethacrylate (EGDMA; cross-linker), and citalopram (as a drug template) using bulk polymerization method. The polymeric devices were further characterized by FT-IR, thermogravimetric analysis, scanning electron microscopy, and binding experiments. The dissolution media employed in controlled release studies were hydrochloric acid at the pH level of 4.3 and phosphate buffers, at pH levels of 7.2 and 10.1, maintained at 37.0 and 25.0 ± 0.5°C. Results showed the ability of MIP polymers to control the release of citalopram. In all cases, the imprinted polymers showed a higher affinity for citalopram and a slower release rate than the nonimprinted polymers. At the pH level of 4.3 and at the temperature of 25°C, slower release of citalopram imprinted polymer occurred.     

Potentiometric immunosensor using artificial antibody based on molecularly imprinted polymers

A potentiometric artificial immunosensor based on a molecularly imprinted polymer was prepared as a detecting element in micro total analysis systems with the intent of providing easy clinical analysis. As the structure and transducing mechanism of this sensor are very simple, construction of a single microsensor should be quite easy. Multimicrosensor arrays applicable to several kinds of analytes will be attainable by both changing the template molecule to be imprinted and reducing the sensor size. The response characteristics of this sensor were evaluated by measuring the response potential to serotonin, which was used as a model material. The obtained sensor was highly responsive to serotonin in water but not to tryptamine, acetaminophen, or procainamide. This phenomenon confirms that the sensor recognizes serotonin and that it functions as a specific artificial immunosensor. Quick measurement is possible because the response time, defined as the time required to achieve 95% of the magnitude of the equilibrated signal, correspond to approximately 12 s. The sensor's determination and detection limits were found to be 1 mumol/L and 100 pmol/L, respectively. These results suggest that our strategy can be applied to construction of a potentiometric artificial immunosensor.     

Quartz crystal microbalance sensor for organic vapor detection based on molecularly imprinted polymers

Molecularly imprinted polymers on quartz crystal microbalances (QCM) are examined for their ability to detect vapors of small organic molecules with greater sensitivity and selectivity than the traditional amorphous polymer coatings. Hydroquinone and phenol serve as noncovalently bound templates that generate shape-selective cavities in a poly(acrylic) or poly(methacrylic) polymer matrix. The imprinted polymers are immobilized on the piezoelectric crystal surface via a precoated poly(isobutylene) layer. The behavior of the imprinted polymer films is characterized by the dynamic and steady-state response of the QCM frequency to pulses of organic vapors in dry air. The apparent partition coefficients are determined for imprinted and nonimprinted polymers prepared by two synthetic methods and for varying mole ratios of template to monomer. The hydroquinone-imprinted polymers and, to a lesser extent, the phenol-imprinted polymers exhibit greater sensitivity and higher selectivity than the nonimprinted polymers toward organic vapors that are structurally related to the templates. These results indicate that molecularly imprinted polymers are promising for the development of selective piezoelectric sensors for organic vapor detection.     

On-line solid-phase extraction of triazine herbicides using a molecularly imprinted polymer for selective sample enrichment

A coupled-column system, consisting of a combination of a molecularly imprinted polymer (MIP) and a C(18)-silica column, was used for selective triazine detection in the HPLC mode. Complex aqueous samples, spiked with triazines, were selectively extracted by the MIP followed by subsequent identification by analytical reversed-phase chromatography. The MIP showed good performance for selectively discriminating triazines from humic acid, whereas urine and apple extract had some tendency to be retained by the MIP. Enrichment was observed in all cases, and triazine-enrichment factors of up to 100 could be recorded, with good extraction efficiency (74-77%). The results indicate that the high selectivity of MIPs can be favorably used for selective sample enrichment in conjunction with reversed-phase HPLC.     

Preparation and characterization of molecularly imprinted polymers for the selective separation of 2,4-dichlorophenoxyacetic acid

As a method of preparing ligand-selective cavities in a synthetic polymer matrix, molecular imprinting technique has been attracting significant interest from a large number of areas in chemistry and analytical sciences. In this study, molecularly imprinted polymers (MIPs) were prepared with styrene, 4-vinylpyridine (4-VPy), and divinylbenzene (DVB) for the separation of hazardous 2,4-dichlorophenoxyacetic acid (2,4-D), and the selectivity of MIPs as adsorbed 2,4-D and structurally similar materials was evaluated. The template was removed through the swelling process of toluene/ethanol, and the removal ratio was about 95–99%, respectively. MIPs synthesized in this study had good adsorption selectivity in the presence of other materials, although there was a difference of adsorption quantities (uptake) in the functional monomer (4-VPy contents) and the cross-linker (DVB contents). The results exhibit that the selectivity of MIPs was improved significantly by controlling the cross-linker. We expect that molecular imprinting technique will serve as a novel method for selective separation of specific materials in various fields, especially in the fields of environment and pharmaceutics.     

Study of prepolymerization complex formation in the synthesis of steroid-based molecularly imprinted polymers

The preparation of steroid-based molecularly imprinted polymers (MIPs) based upon noncovalent interaction is particularly suited for selective capture of steroid hormones in biological and environmental samples. The success of this method lies in the optimization of the interaction between steroids (template) and methacrylic acid (functional monomer) in the prepolymerization mixture. NMR techniques coupled with DFT calculations were used to evaluate the capacity of the methacrylic acid to bind a steroid for future applications. The androstane derivative steroids considered in the present study have two functional groups at C(3) and C(17), which may interact with the methacrylic acid. These can be hydroxyl or ketone groups. Experimental results show that the steroids can be divided in three groups corresponding to the ketone type at C(3), the H-bond strength increasing with the number of double bonds. DFT calculations are in very good agreement with experimental results, showing increasing binding energy from no bonds, a single bond, and two double bond steroids. For steroids holding a hydroxyl group the binding energy obtained in the solvent model is comparable to the binding energy of single bond ketone steroids.     

Evaluation of a multidimensional solid-phase extraction platform for highly selective on-line cleanup and high-throughput LC-MS analysis of triazines in river water samples using molecularly imprinted polymers

A novel highly selective sample cleanup procedure based on the use of molecularly imprinted polymers (MIPs) as solid-phase extraction materials has been evaluated with respect to its applicability and routine use in environmental analysis. The method comprises the combination of a restricted access material (RAM) and a MIP allowing a selective sample preparation to be achieved in the online mode. This combination is called the size-selective sample separation and solvent switch (six-SPE). The RAM column combines size exclusion and adsorption chromatography, reducing the concentration of matrix molecules by a cutoff of 15 kDa. The MIP column selectively retains the triazine analytes whereas the residual matrix is not retained and separated completely. Thus, the automated RAM-MIP is capable of excluding all matrix and nontarget compounds. The cleaned and enriched extract is subsequently eluted to an HPLC column and analyzed by LC-MS. A complete on-line analysis cycle including multidimensional solid-phase extraction, separation, and detection takes less than 15 min. Terbuthylazine, atrazine, propazine, simazine, ametryn, prometryn, irgarol, and also the metabolites deethylatrazine and deisopropylatrazine can be determined without any matrix interferences, e.g., by humic acids. The whole setup is fully automated and may be continuously operated. Nonspecific interactions with the polymer are below 1% in all cases. The accuracy of the LC-MIP-LC-MS system was controlled using a certified reference material (Aquacheck). The applicability of the method to the cleanup of real samples was demonstrated by injection of contaminated river water samples. The stability of different polymers was tested by consecutive injections, and it was shown that the performance of the materials did not vary even after more than 300 enrichment and desorption cycles.     

Computational approach to the rational design of molecularly imprinted polymers for voltammetric sensing of homovanillic acid

A methodology based on density functional theory calculations for the design of molecularly imprinted polymers (MIPs) is described. The method allows the rational choice of the most suitable monomer and polymerization solvent among a set of chemicals traditionally used in MIP formulations for the molecular imprinting of a given template. It is based on the comparison of the stabilization energies of the prepolymerization adducts between the template and different functional monomers. The effect of the polymerization solvent is included using the polarizable continuum model. A voltammetric sensor for homovanillic acid was constructed using different MIPs as recognition element, confirming that the solvent (toluene) and functional monomer (methacrylic acid) selected according to the theoretical predictions lead to the most efficient molecular recognition sensing phase. With the voltammetric sensor prepared using the MIP designed according to the theoretical predictions, a linear response for concentrations of homovanillic acid between 5 x 10(-8) and 1 x 10(-5) M can be obtained. The limit of detection is 7 x 10(-9) M. The selectivity obtained for homovanillic acid over other structurally related compounds buttresses the validity of this strategy of design.