Molecularly Imprinted Polymer Microspheres Research Articles

Efficient Optosensing of Hippuric Acid in the Undiluted Human Urine with Hydrophilic "Turn-On"-Type Fluorescent Hollow Molecularly Imprinted Polymer Microparticles.

The development of complex biological sample-compatible fluorescent molecularly imprinted polymers (MIPs) with improved performances is highly important for their real-world bioanalytical and biomedical applications. Herein, we report on the first hydrophilic "turn-on"-type fluorescent hollow MIP microparticles capable of directly, highly selectively, and rapidly optosensing hippuric acid (HA) in the undiluted human urine samples. These fluorescent hollow MIP microparticles were readily obtained through first the synthesis of core-shell-corona-structured nitrobenzoxadiazole (NBD)-labeled hydrophilic fluorescent MIP microspheres by performing one-pot surface-initiated atom transfer radical polymerization on the preformed "living" silica particles and subsequent removal of their silica core via hydrofluoric acid etching. They showed "turn-on" fluorescence and high optosensing selectivity and sensitivity toward HA in the artificial urine (the limit of detection = 0.097 μM) as well as outstanding photostability and reusability. Particularly, they exhibited much more stable aqueous dispersion ability, significantly faster optosensing kinetics, and higher optosensing sensitivity than their solid counterparts. They were also directly used for quantifying HA in the undiluted human urine with good recoveries (96.0%-102.0%) and high accuracy (RSD ≤ 4.0%), even in the presence of several analogues of HA. Such fluorescent hollow MIP microparticles hold much promise for rapid and accurate HA detection in the clinical diagnostic field.

Preparation of Molecularly Imprinted Polymer Microspheres for Selective Solid-Phase Extraction of Capecitabine in Urine Samples.

Molecularly imprinted solid-phase extraction to treat biological samples has attracted considerable attention. Herein, molecularly imprinted polymer (MIP) microspheres with porous structures were prepared by a combined suspension-iniferter polymerization method using capecitabine (CAP) as a template molecule. This material was subsequently used as a solid-phase extraction agent to separate and enrich drug molecules in urine samples. UV analysis revealed that methacrylate (MAA) was an ideal functional monomer, and 1H Nuclear Magnetic Resonance (1H NMR), Ultraviolet (UV), and Fourier transform-infrared (FT-IR) spectroscopic analyses were used to study the interaction forces between MAA and CAP, demonstrating that hydrogen bonding was the primary interaction force. MIPs with outstanding selectivity were successfully prepared, and the analysis of their surface morphology and chemical structure revealed a spherical morphology with small holes distributed across a rough surface. This surface morphology significantly reduced the mass transfer resistance of template molecules, providing an ideal template recognition effect. Using the molecularly imprinted solid-phase extraction method, CAP and the structural analog cytidine (CYT) were pretreated in urine samples and quantified by HPLC. The results showed that CAP and CYT recoveries reached 97.2% and 39.8%, respectively, with a limit of detection of 10.0–50.0 µg·mL−1. This study provides a novel approach to drug molecule pretreatment that can be applied in drug separation and functional materials science fields.

The fabrication of molecularly imprinted polymer microspheres via Pickering emulsion polymerization stabilized with novel ferric hydroxide colloid

In this paper, the ferric hydroxide colloid was prepared firstly, which was found suitable for the stabilizer of Pickering emulsion because of proper hydrophilicity. Then, molecularly imprinted polymers (MIPs) microspheres were synthesized by means of facile Pickering emulsion polymerization using ferric hydroxide colloid as emulsifier. In the synthesis process, hydrophilic methacrylic acid was used for the functional monomer, and ethylene glycol dimethacrylate served as the crosslinking agent. Bisphenol A (BPA), a typical endocrine-disrupting chemical, was used for the template molecules. The whole synthesis was based on the hydrogen bonds interaction between the functional monomer and template molecule. The ferric hydroxide colloid could be removed from the surface of microspheres by gentle washing. The morphology of obtained MIPs microspheres were assessed through the optical microscope and field emission scanning electron microscope, respectively. The results suggested that the MIPs appeared the regular spherical form with relatively wide size distribution, whose diameter varied from 10 to 60 μm. The adsorptive property was studied detailedly through a series of rebinding experiments. The research showed that MIPs have fast binding kinetics, whose rebinding equilibrium in tested concentration could be achieved within 60 min, and the rebinding capacity in 0.3 mmol L−1 of BPA initial solution is 8.19 μmol g−1. Additionally, the binding capacities of MIPs were larger than that of non-imprinted polymers in the batch equilibrium binding experiments. The binding selectivity was investigated with 4, 4′-biphenol and hydroquinone, which played the role of the structurally similar compounds of template molecules. The result showed that the MIPs were highly selective for BPA, and the imprinting factor was calculated to be 1.63. Reusability experiment indicates that our prepared MIPs have good mechanical stability and could be reused at least 5 times. The MIPs microspheres would be valuable in the field of environmental protection.

Development of a molecular imprinted electrochemiluminescence sensor for amitriptyline detection: From MD simulations to experimental implementation

Amitriptyline (AMT) frequent presence in environmental waters reflects the continuous consumption growth and raises issues on the importance of its monitorization. In this work, a sensitive and selective electrochemiluminescence (ECL) sensor was constructed using molecularly imprinted polymer (MIP) recognition element for AMT detection. Molecular dynamics (MD) simulations were performed to select the best functional monomer. Precipitation polymerization was followed to prepare the MIP microspheres using methacrylic acid (MAA) as functional monomer, ethylene glycol methacrylate (EGDMA) as crosslinker and chloroform (CHL) as solvent. The MIP sensor was then prepared on a low cost and disposable screen-printed electrodes (SPCEs), previously modified with single-walled carbon nanotubes (SWCNTs), by drop coating a solution containing the MIP microspheres synthesized. The mechanism of detection was based in the system Ru(bpy)32+/AMT, where AMT acts as co-reactor of Ru(bpy)32+ ECL. Several parameters controlling the preparation process of the sensor and AMT detection were optimised. The MIP/SWCNTs/SPCE ECL sensor showed good analytical performance with a linear correlation between ECL signal and the AMT concentration ranging from 0.1 to 200 µM (R2 = 0.9991). The limits of detection (LOD) and quantification (LOQ) were found to be 0.4 µM (S/N=3) and 1.5 µM (S/N = 10), respectively. The MIP ECL sensor displayed good selectivity to recognise AMT molecules when compared with analoge structures and it was successfully applied in real water samples with good recovery values (90 to 112%). The developed MIP ECL sensor is suitable for integration with portable devices for AMT detection in environmental waters.

Biological Sample-Compatible Ratiometric Fluorescent Molecularly Imprinted Polymer Microspheres by RAFT Coupling Chemistry.

Ratiometric fluorescent molecularly imprinted polymer (MIP) sensors hold great promise in many bioanalytical areas because of their high sensitivity and selectivity as well as excellent self-referencing and visual detection capability. However, their synthetic strategies are rather limited and the development of such optosensing MIPs that can directly and selectively quantify small organic analytes in complex biological samples remains a formidable challenge owing to the complexity of sample matrices. Herein, a versatile and modular strategy to obtaining well-defined ratiometric fluorescent MIP microspheres capable of directly and selectively detecting an organic herbicide [2,4-dichlorophenoxyacetic acid (2,4-D)] in undiluted pure milks is described. First, it involves the synthesis of uniform "living" polymer particles via RAFT precipitation polymerization, their successive well-controlled grafting of a polymer shell labeled with red CdTe QDs (being inert to 2,4-D) and an MIP shell labeled with green 4-nitrobenzo[c][1,2,5]oxadiazole (NBD) units (showing fluorescence "light-up" upon binding 2,4-D) via surface-initiated RAFT polymerization, and final grafting of hydrophilic poly(N-isopropylacrylamide) brushes via an efficient coupling reaction (i.e., RAFT coupling chemistry). The resulting hydrophilic dual fluorescent MIP particles showed excellent photostability and reusability. They exhibited obvious analyte binding-induced "turn-on"-type ratiometric fluorescence (and color) change and high 2,4-D optosensing selectivity and sensitivity in pure bovine milk (with a detection limit of 0.13 μM). Moreover, they were directly applied to 2,4-D determination in undiluted pure goat milk with good recoveries (96.0-103.2%) and high accuracy (RSD = 1.5-5.5%), even in the presence of several analogues of 2,4-D. The general applicability of our strategy was also demonstrated. This study paves the way for efficiently developing various advanced MIP optosensors (of easily tunable structures and desired properties) highly promising in many bioanalytical applications.

Well-defined hydrophilic “turn-on”-type ratiometric fluorescent molecularly imprinted polymer microspheres for direct and highly selective herbicide optosensing in the undiluted pure milks

Molecularly imprinted polymer (MIP)-based optosensing materials capable of direct, reliable, and highly selective detection of small organic analytes in complex aqueous samples hold great promise in many bioanalytical applications, but their development remains a challenging task. Addressing this issue, well-defined hydrophilic “turn-on”-type ratiometric fluorescent MIP microspheres are developed via a versatile and modular strategy based on the controlled/“living” radical polymerization method. Its general principle was demonstrated by the synthesis of red CdTe quantum dot (QD)-labeled silica particles with surface-bound atom transfer radical polymerization (ATRP)-initiating groups via the one-pot sol-gel reaction and their successive grafting of a thin fluorescent 2,4-D (an organic herbicide)-MIP layer (labeled with green organic fluorophores bearing both nitrobenzoxadiazole (NBD) and urea interacting groups) and hydrophilic poly(glyceryl monomethacrylate) (PGMMA) brushes via surface-initiated ATRP. The introduction of PGMMA brushes and rationally selected dual fluorescence labeling (i.e., red CdTe QDs being inert to 2,4-D and green NBD showing fluorescence “light-up” upon binding 2,4-D) onto MIP particles afforded them excellent complex aqueous sample-compatibility (due to their largely enhanced hydrophilicity) and analyte binding-induced “turn-on”-type ratiometric fluorescence changes, respectively. Such advanced MIP particles proved to be promising optosensing materials, which had a detection limit of 0.13 μM and showed obvious fluorescent color change upon binding different concentrations of 2,4-D in the undiluted pure milk. Moreover, they were successfully applied for direct and highly selective quantification of 2,4-D in the undiluted pure goat and bovine milks with good recoveries (97.9%–104.5%), even in the presence of several analogues of 2,4-D.

Synthesis of Multi-mode Quantum Dots Encoded Molecularly Imprinted Polymers Microspheres and Application in Quantitative Detection for Dopamine

As the promising analytical strategy, multi-mode quantum dots (QDs) encoded molecularly imprinted fluorescent sensors have attracted considerable attention. Here, a novel encoding strategy for water-dispersed QDs molecularly imprinted polymers microspheres (MIPMs) with a high-performance fluorescence intensity and multi-color signal was established. The water-compatible MIPMs were firstly synthesized via integrating the reversible addition-fragmentation chain transfer and precipitation polymerization (RAFT-PP), which could improve the water compatibility by grafting the hydrophilic groups of poly(2-hydroxyrthyl methacrylate) (PHEMA). Then the water-compatible MIPMs were used as embedding matrix to separately incorporate with five different QDs, and a series of multi-color QDs encoded MIPs (five single-color and 10 dual-color fluorescent systems) were obtained. The fluorescent characterization of encoded MIPMs was studied in detail. Further, dual-mode fluorescence systems were fabricated as fluorescence sensors for the quantitative detection of dopamine; good linear response in the range of 5-300 μg L-1 and 1-100 μg L-1 and the limit of detection (LOD) with 2 μg L-1 and 0.5 μg L-1 were obtained for monochromatic and ratiometric sensor, respectively. It is the first time to introduce the optical encoding strategy into the fabrication of fluorescent MIPs, which not only greatly simplifies the preparation process of fluorescent imprinted sensor, but also provides more alternatives for the detection method of analyte and the potential of high-throughput multiple analytes at one time.

Selective Enrichment of Clenbuterol onto Molecularly Imprinted Polymer Microspheres with Tailor-made Structure and Oxygen Functionalities.

The noxious clenbuterol misapplied as the feed additive has posed an enormous threat to humans who actively rely on the food chains with high potential of contamination by clenbuterol, such as pork and beef. It is, therefore, highly desirable to develop novel materials and strategies for dealing with the clenbuterol. Herein, functional polymer microspheres prepared by Pickering emulsion polymerization were explored for the selective enrichment of the clenbuterol, and their structure and oxygen functionalities could be tailor-made by a molecular imprinting process. The clenbuterol imprinting was adequately demonstrated to not only increase the particle size (~52 nm vs. ~42 nm) and create cavities for the accommodation of the clenbuterol molecules, but also reduce the oxygen functionalities of the resulting molecularly imprinted polymer microspheres (MIPMs) by approximately 4 at.%, which is believed to correlate with the high specificity of the MIPMs. Various characterization methods were employed to evidence these findings, including scanning electron microscopy, BET measurements, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and elemental mapping examination. More importantly, the MIPMs showed a markedly superior enrichment capability towards clenbuterol to the counterpart, that is, non-molecularly imprinted polymer microspheres (NIPMs). Compared to the NIPMs without specificity for clenbuterol, the MIPMs exhibited an impressive selectivity to clenbuterol, with the relative selectivity coefficient (k′) values largely exceeding 1, thus corroborating that the useful molecular imprinting led to the generation of the binding sites complementary to the clenbuterol molecule in the size and functionalities. The MIPMs were also employed as the stationary phase to fabricate molecularly imprinting solid-phase extraction column, and the spike recovery was demonstrated to be not significantly decreased even after nine cycles. Furthermore, the reliability of the method was also evidenced through the comparison of the MIPMs prepared from different batches.

Application of paclitaxel-imprinted microparticles obtained using two different cross-linkers for prolonged drug delivery

Molecularly imprinted polymers (MIPs) are artificial materials processed to have cavities in the polymer structure which are capable of forming selective interactions with their molecular templates. Here, we report the synthesis of paclitaxel-imprinted microparticles and their application in prolonged drug delivery. Methacrylic acid was used as a functional monomer and 2-hydroxyethyl methacrylate was added to increase hydrophilicity of the obtained MIPs and therefore to improve compatibility with water solutions. The effect of two different cross-linkers, ethylene glycol dimethacrylate and trimethylolpropane trimethacrylate, on the final properties of obtained MIPs microspheres was examined. The influence of initial paclitaxel concentration as well as its contact time with MIPs microparticles on adsorption process was investigated. The release kinetics of paclitaxel from drug-loaded MIPs was found to be significantly depend upon the type of cross-linker used as well as the pH of the release medium. The highest cumulative release was observed at pH 7.4 for MIPs obtained using trimethylolpropane trimethacrylate as a cross-linker, reaching 85% in 50 h. The MIPs obtained using this cross-linker were characterized by IC50 comparable to the ones measured for pure paclitaxel. These results clearly indicate that the obtained MIPs microparticles have a large potential for prolonged drug delivery.

Preparation of Fluorescent Molecularly Imprinted Polymers via Pickering Emulsion Interfaces and the Application for Visual Sensing Analysis of Listeria Monocytogenes.

In this work, a novel molecularly imprinted polymer (MIP) with water-soluble CdTe quantum dots (QDs) was synthesized by oil-in-water Pickering emulsion polymerization using whole Listeria monocytogenes as the template. Listeria monocytogenes was first treated by acryloyl-functionalized chitosan with QDs to form a bacteria–chitosan network as the water phase. This was then stabilized in an oil-in-water emulsion comprising a cross-linker, monomer, and initiator, causing recognition sites on the surface of microspheres embedded with CdTe QDs. The resulting MIP microspheres enabled selective capture of the target bacteria via recognition cavities. The target bacteria Listeria monocytogenes was detected. Scanning electron microscopy (SEM) characterization showed that the MIPs had a rough spherical shape. There was visual fluorescence detection via quenching in the presence of the target molecule, which offered qualitative detection of Listeria monocytogenes in milk and pork samples. The developed method simplified the analysis process and did not require any sample pretreatment. In addition, the fluorescence sensor provided an effective, fast, and convenient method for Listeria monocytogenes detection in food samples.

Preparation of Monodisperse Enrofloxacin Molecularly Imprinted Polymer Microspheres and Their Recognition Characteristics.

This study presents a new strategy for the detection of enrofloxacin (ENR) in food samples by the use of monodisperse ENR molecularly imprinted polymers (MIPs). Using enrofloxacin as template molecule, methacrylic acid as functional monomer, and ethylene diglycidyl ether as cross-linker, surface molecularly imprinted polymers (MIPs) were prepared on the surface of polymeric glycidyl methacrylate-ethylene glycol dimethacrylate (PGMA-EDMA) microspheres. The surface morphology and imprinting behavior of PGMA-EDMA@MIPs were investigated and optimized. Synthesized PGMA-EDMA@MIPs showed good physical and chemical stability and specific recognition toward fluoroquinolones. The introduction of PGMA-EDMA microspheres greatly increased the adsorption area of PGMA-EDMA@MIPs and increased the adsorption capacity of target molecules. The core shell structure increased the adsorption rate, and adsorption equilibrium was achieved within 6 min, much higher than that of MIPs synthesized by traditional methods. Enrofloxacin in milk samples was detected by molecular imprinting solid phase extraction (MISPE) combined with high performance liquid chromatography (HPLC). Implementing this method resulted in a recovery rate of 94.6~109.6% with a relative standard deviation (RSD) of less than 3.2%. The limit of detection (LOD) of this method was identified as three times the signal-to-noise ratio (10 μg/L). In summary, this work proposed a sensitive, rapid, and convenient method for the determination of trace ENR in food samples.

Improvement of surface hydrophilicity and biological sample-compatibility of molecularly imprinted polymer microspheres by facile surface modification with α-cyclodextrin

Molecularly imprinted polymers (MIPs) compatible with complex biological samples hold much promise in many bioanalytical and biomedical applications and development of new strategies for obtaining such advanced synthetic receptors is thus of high interest. Herein, a facile and efficient new approach is presented for the preparation of MIP microspheres capable of selectively recognizing small organic analyte in the complex biological sample, which involves the simple surface modification of MIP particles bearing polyethylene glycol (PEG) brushes with α-cyclodextrin (α-CD). The proof-of-principle was demonstrated by the first synthesis of propranolol-imprinted polymer microspheres bearing PEG brushes of different molecular weights (Mn = 2000 and 5000) via our previously developed reversible addition-fragmentation chain transfer (RAFT) coupling chemistry, their supramolecular inclusion complexation with α-CD, and subsequent chemical crosslinking. The chain length of the surface-grafted PEG brushes showed much influence on the water-compatibility of MIPs. Whereas the MIP particles bearing PEG brushes of Mn = 2000 hardly showed specific template bindings in both pure water and pure milk, those bearing PEG brushes of Mn = 5000 exhibited moderate specific template bindings in pure water. Nevertheless, the latter MIP particles still failed to show enough specific template bindings in pure milk. The inclusion of α-CD onto PEG brushes proved to largely enhance the surface hydrophilicity of MIPs and lead to their much improved water-compatibility. In particular, the MIP microspheres bearing α-CD-modified PEG brushes of Mn = 5000 showed excellent specific template bindings in both pure water and pure milk. The above strategy not only paves the way for efficiently preparing biological sample-compatible MIPs, but also opens the possibility of generating many other advanced biomaterials with high antifouling properties.

Controlled preparation of molecularly imprinted polymer microspheres with surface uncrosslinked glycoprotein binding cavities

Molecularly imprinted polymers (MIPs) are synthetic receptors with tailor-made recognition sites for target molecules. Their high affinity and selectivity, excellent stability, easy preparation, and low cost make them promising substitutes to biological receptors (e.g., antibody and enzyme) in many applications where molecular recognition is important. Despite significant progress made in the imprinting of small templates, the imprinting of biomacromolecules (e.g., proteins) remains a big challenge because of their large sizes, complexed structures, and conformational variability. These inherent characteristics of biomacromolecules lead to many significant problems for the resulting macromolecularly imprinted polymers (mMIPs) such as laborious removal of large templates and their slow access to the binding sites. Recent years have witnessed much efforts being devoted to the development of mMIPs due to their great potential in proteome analysis, clinical diagnostics, and biomedicine. So far, some useful strategies have been developed for the imprinting of proteins, mainly including the bulk polymerization method, epitope imprinting strategy, and surface imprinting approach. Among them, the surface imprinting approach has been most widely used because it can readily lead to mMIPs with higher efficiency for removing large templates and more rapid template binding kinetics. Nevertheless, the presently developed mMIPs normally have crosslinked template binding sites, whose rigid structures might have negative influence on the removal of large templates and template binding kinetics. In this sense, the development of mMIPs with more flexible biomacromolecular binding cavities (e.g., uncrosslinked ones) should be useful for solving the above problems. To our knowledge, however, only rather limited numbers of publications relating to mMIPs with uncrosslinked binding sites have been disclosed, which are all based on the use of self-assembled monolayer strategy. The development of versatile new approaches for preparing mMIPs with uncrosslinked binding sites and good molecular imprinting effect is still highly desirable. We demonstrate a facile and efficient new approach for the controlled preparation of MIP microspheres with surface uncrosslinked glycoprotein binding sites. It involves the first one-pot synthesis of uniform “living” polymer microspheres with both surface-bound epoxy groups and alkyl halide groups (i.e., atom transfer radical polymerization (ATRP)-initiating groups) via atom transfer radical precipitation polymerization, their surface modification with 3-aminophenylboronic acid (APBA) for introducing surface phenylboronic acid moieties and surface immobilization of a glycoprotein (ovalbumin (OVA)), subsequent use of the “living” polymer microspheres with surface-immobilized OVA as the ATRP initiator for the controlled grafting of poly( N -isopropylacrylamide) (PNIPAAm) brushes, and final removal of OVA. A series of MIP microspheres with surface uncrosslinked OVA binding sites were readily obtained following the above procedure by just changing the polymerization time for grafting PNIPAAm brushes, and their morphologies, chemical structures, surface hydrophilicity, water dispersion stability, and template binding properties were characterized in detail. The experimental results demonstrated that the above approach could effectively provide MIPs with excellent recognition ability toward OVA in the aqueous medium. The surface hydrophilicity and water dispersion stability of MIP microspheres were largely improved due to their surface-grafting of hydrophilic polymer brushes. Moreover, the chain length of PNIPAAm brushes showed significant influence on the template binding properties of MIP microspheres, and the best template binding capacity and specific binding were achieved for MIPs only when the thickness of PNIPAAm layers was close to the total length of the diameter of OVA plus the length of the surface-attached phenylboronic acid unit. Furthermore, the optimal MIP also exhibited good selectivity toward OVA over other proteins. The strategy presented here paves a new way for controlled and efficient preparation of glycolprotein-imprinted polymer microspheres with good molecular recognition capability.

Functionalization of Molecularly Imprinted Polymer Microspheres for the Highly Selective Removal of Contaminants from Aqueous Solutions and the Analysis of Food-Grade Fish Samples.

The proliferation of pollution in aquatic environments has become a growing concern and calls for the development of novel adsorbents capable of selectively removing notorious and recalcitrant pollutants from these ecosystems. Herein, a general strategy was developed for the synthesis and functionalization of molecularly imprinted polymer microspheres (MIPs) that could be optimized to possess a significant adsorption selectivity to an organic pollutant in aqueous media, in addition to a high adsorption capacity. Considering that the molecular imprinting alone was far from satisfactory to produce a high-performance MIPs-based adsorbent, further structural engineering and surface functionalization were performed in this study. Although the more carboxyl groups on the surfaces of the MIPs enhanced the adsorption rate and capacity toward an organic pollutant through electrostatic interactions, they did not strengthen the adsorption selectivity in a proportional manner. Through a systematic study, the optimized sample exhibiting both impressive selectivity and capacity for the adsorption of the organic pollutant was found to possess a small particle size, a high specific surface area, a large total pore volume, and an appropriate amount of surface carboxyl groups. While the pseudo-second-order kinetic model was found to better describe the process of the adsorption onto the surface of MIPs as compared to the pseudo-first-order kinetic model, neither Langmuir nor Freundlich isothermal model could be used to well fit the isothermal adsorption data. Increased temperature facilitated the adsorption of the organic pollutant onto the MIPs, as an endothermic process. Furthermore, the optimized MIPs were also successfully employed as a stationary phase for the fabrication of a molecularly imprinted solid phase extraction column, with which purchased food-grade fish samples were effectively examined.

Hollow Fibre Membrane-Protected Molecularly Imprinted Microsolid-Phase Extraction (HFM-Protected-MI-MSPE) of Triazines from Soil Samples

In this work, a combination of molecularly imprinted polymer (MIP) technology with micro solid-phase extraction in a hollow fibre device is described. MIP microspheres were synthesized and packed into polypropylene hollow fibre (HF) segments. The proposed device was used directly for trace enrichment and clean-up of triazines in soil sample extracts by hollow-fibre membrane-protected molecularly imprinted micro solid-phase extraction (HFM-protected-MI-MSPE). Analytes were extracted from soil by ultrasonic assisted extraction, evaporated to dryness and reconstituted in toluene. The proposed device was immersed in the toluene extracts, and migrations of analytes through the walls of the hollow fibre was achieved with the help of external agitation. Then, selective recognition of the target analytes by MIP-microspheres took place in the inner part of the HF. All parameters affecting the extraction were optimized. Under optimum conditions, quantitative recoveries were obtained for simazine, cyanazine, atrazine, propazine and terbutylazine in soil samples, with relative standard deviations lower than 11%. The detection limits (LODs) were lower than 5 ng g−1 in all cases.

Combining Pickering Emulsion Polymerization with Molecular Imprinting to Prepare Polymer Microspheres for Selective Solid-Phase Extraction of Malachite Green.

Malachite green (MG) is currently posing a carcinogenic threat to the safety of human lives; therefore, it is highly desirable to develop an effective method for fast trace detection of MG. Herein, for the first time, this paper presents a systematic study on polymer microspheres, being prepared by combined Pickering emulsion polymerization and molecular imprinting, to detect and purify MG. The microspheres, molecularly imprinted with MG, show enhanced adsorption selectivity to MG, despite a somewhat lowered adsorption capacity, as compared to the counterpart without molecular imprinting. Structural features and adsorption performance of these microspheres are elucidated by different characterizations and kinetic and thermodynamic analyses. The surface of the molecularly imprinted polymer microspheres (M-PMs) exhibits regular pores of uniform pore size distribution, endowing M-PMs with impressive adsorption selectivity to MG. In contrast, the microspheres without molecular imprinting show a larger average particle diameter and an uneven porous surface (with roughness and a large pore size), causing a lower adsorption selectivity to MG despite a higher adsorption capacity. Various adsorption conditions are investigated, such as pH and initial concentration of the solution with MG, for optimizing the adsorption performance of M-PMs in selectively tackling MG. The adsorption kinetics and thermodynamics are deeply discussed and analyzed, so as to provide a full picture of the adsorption behaviors of the polymer microspheres with and without the molecular imprinting. Significantly, M-PMs show promising solid-phase extraction column applications for recovering MG in a continuous extraction manner.

Selective isolation of gonyautoxins 1,4 from the dinoflagellate Alexandrium minutum based on molecularly imprinted solid-phase extraction

Gonyautoxins 1,4 (GTX1,4) from Alexandrium minutum samples were isolated selectively and recognized specifically by an innovative and effective extraction procedure based on molecular imprinting technology. Novel molecularly imprinted polymer microspheres (MIPMs) were prepared by double-templated imprinting strategy using caffeine and pentoxifylline as dummy templates. The synthesized polymers displayed good affinity to GTX1,4 and were applied as sorbents. Further, an off-line molecularly imprinted solid-phase extraction (MISPE) protocol was optimized and an effective approach based on the MISPE coupled with HPLC-FLD was developed for selective isolation of GTX1,4 from the cultured A. minutum samples. The separation method showed good extraction efficiency (73.2–81.5%) for GTX1,4 and efficient removal of interferences matrices was also achieved after the MISPE process for the microalgal samples. The outcome demonstrated the superiority and great potential of the MISPE procedure for direct separation of GTX1,4 from marine microalgal extracts.

Enzyme-linked immunoassay based on imprinted microspheres for the detection of sulfamethazine residue

This study attempts to develop an enzyme-linked immunoassay (ELISA) using a molecularly imprinted polymer (MIP) as an artificial recognition element. The MIP microspheres were prepared using precipitation polymerization with SM2 as the template molecule, methacrylic acid as the functional monomer and ethylene glycol dimethacrylate as the cross-linker. After the microspheres were coated in microtiter plate wells, the molecular imprinting ELISA (MI-ELISA) method was established based on the direct competition between free SM2 and horseradish peroxidase (HRP)-labelled SM2 in heterogeneous mode. The linear regression analysis data for the calibration curve showed a good linear relationship with a regression coefficient of 0.999 in the concentration range of 100μgL−1–3200μgL−1. Furthermore, following the selective solid-phase extraction (SPE) with bulk SM2 MIPs as the sorbent and MI-ELISA detection, the limits of detection and quantification were 6.8μgkg−1 and 20.4μgkg−1, respectively, for SM2 in swine muscle. For the first time, MI-ELISA combined with molecular imprinting SPE was developed to determine trace SM2 in real samples, and the results show that it can be a useful analytical tool for quick detection in residue analysis.

Preparation and evaluation of paclitaxel-imprinted polymers with a rosin-based crosslinker as the stationary phase in high-performance liquid chromatography

In this study, molecularly imprinted polymer (MIP) microspheres for paclitaxel (PTX) were prepared by microsuspension polymerization and used as a stationary phase in high-performance liquid chromatography (HPLC) for the separation of PTX and its structural analog docetaxel (DOC). For MIP synthesis, ethylene glycol maleic rosinate acrylate and 2-vinylpyridine were used as the cross-linker and functional monomer, respectively. MIP microspheres were characterized by scanning electron microscopy, laser granulometry, nitrogen sorption porosimetry, and thermogravimetric analysis. Results indicated the formation of regular MIPs with an even pore size distribution; furthermore, these MIPs exhibited excellent thermal stability. These MIP microspheres were packed into a stainless steel column for the selective separation of PTX and DOC. Under optimum chromatographic conditions, a separation factor of 2.54 and an imprinting factor of 2.37 were obtained. In addition, thermodynamic data obtained from van’t Hoff plots revealed enthalpy-driven separation and higher contribution from functional group interactions as compared with that from steric complementary interactions. Microcalorimetry was employed to investigate the binding mechanisms of the analytes on the MIP surface.

A Porphyrin Molecularly Imprinted Biomimetic Electrochemical Sensor Based on Gold Nanoparticles and Carboxyl Graphene Composite for the Highly Efficient Detection of Methyl Parathion

A highly sensitive and selective biomimetic sensor based on zinc porphyrin molecularly imprinted Polymer microspheres (MIPMs), gold nanoparticles (AuNPs) and carboxyl graphene (CG) nanomaterials was successfully developed for direct electrochemical detection of methyl parathion (MP). The novel strategy emphasized the fabrication of a porphyrin zinc-based sensor via attaching MIPMs on AuNPs/CG nanocomposites. MIPMs was prepared by free radical polymerization using MP as the template, Zinc porphyrin as the functional monomer, ethylene glycol dimethacrylate (EGDMA) as the cross-linking reagent and azobisisobutyronitrile (AIBN) as the initiator. The introduction of AuNPs/CG significantly increased the effective electrode area, and amplified the sensor signal. The modified electrode was characterized by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The parameters of the detection process were also optimized. The biomimetic sensor exhibits a much wider linear dynamic range between 1.0[Formula: see text][Formula: see text][Formula: see text]10[Formula: see text][Formula: see text]mol L[Formula: see text] and 8.0[Formula: see text][Formula: see text][Formula: see text]10[Formula: see text][Formula: see text]mol L[Formula: see text] and the limit of detection (LOD) down to 3.16[Formula: see text][Formula: see text][Formula: see text]10[Formula: see text][Formula: see text]mol L[Formula: see text] based on S/N [Formula: see text] 3. The sensor had good reproducibility, stability and selectivity for MP detection. The developed sensor was successfully employed for the detection of MP in real samples.