Biomimetic piezoelectric quartz sensor for caffeine based on a molecularly imprinted polymer

A piezoelectric quartz sensor coated with molecularly imprinted polymer (MIP) for caffeine was developed. The MIP was prepared by co-polymerizing methacrylic acid (MAA) and ethylene glycol dimethacrylate (EDMA) in the presence of azobis(isobutyronitrile) as initiator, caffeine as template molecule, and chloroform as solvent. The MIP suspension in polyvinyl chloride/tetrahydrofuran (6:2:1 w/w/v) solution was spin coated onto the surface of the electrode of a 10 MHz AT-cut quartz crystal. The sensor exhibited a linear relationship between the frequency shift and caffeine concentration in the range of 1×10^–7 mg mL^–1 up to 1x10^–3 mg mL^–1 [correlation coefficient (r)=0.9935] in a stopped flow measurement mode. It has a sensitivity of about 24 Hz/ln(concentration, mg mL^–1). A steady-state response was achieved in less than 10 min. The performance characteristic of the sensor shows a promising and inexpensive alternative method of detecting caffeine. Surface studies were carried out for the reagent phase of the sensor using SEM, AFM, and XPS analysis in order to elucidate the imprinting of the caffeine molecule. The SEM micrograph, AFM image, and XPS spectra confirmed the removal of caffeine by Soxhlet extraction in the imprinting process and the rebinding of caffeine to the MIP sensing layer during measurement.     

Creatinine sensor based on a molecularly imprinted polymer-modified hanging mercury drop electrode

Molecularly imprinted polymers (MIP) have been elucidated to work as artificial receptors. In our present study, a MIP was applied as a molecular recognition element to a chemical sensor. We have constructed a creatinine sensor based on a MIP layer selective for creatinine and its differential pulse, cathodic stripping voltammetric detection (DPCSV) on a hanging mercury drop electrode (HMDE). The creatinine sensor was fabricated by the drop coating of dimethylformamide (DMF) solution of a creatinine-imprinted polymer onto the surface of HMDE. The modified-HMDE, preanodised in neutral medium at +0.4 V versus Ag/AgCl for 120 s, exhibited a marked enhancement in DPCSV current in comparison to the less anodised (≤+0.3 V) HMDE. The creatinine was preconcentrated and instantaneously oxidised in MIP layer giving DPCSV response in the concentration range of 0.0025-84.0 μg mL⁻¹ [detection limit (3σ) 1.49 ng mL⁻¹]. The sensor was found to be highly selective for creatinine without any response of interferents viz., NaCl, urea, creatine, glucose, phenylalanine, tyrosine, histidine and cytosine. The non-imprinted polymer-modified electrode did not show linear response to creatinine. The imprinting factor as high as 9.4 implies that the imprinted polymer exclusively acts as a recognition element of creatinine sensor. The proposed procedure can be used to determine creatinine in human blood serum without any preliminary treatment of the sample in an accurate, rapid and simple way.     

A 3,3′-dichlorobenzidine-imprinted polymer gel surface plasmon resonance sensor based on template-responsive shrinkage

Molecularly imprinted polymer gel film on the gold substrate of a chip was prepared with minute amount of cross-linker for the fabrication of a surface plasmon resonance (SPR) sensor sensitive to 3,3′-dichlorobenzidine. The molecularly imprinted gel film was anchored on a gold chip by a surface-bound photo-radical initiator. The sensing of 3,3′-dichlorobenzidine is based on responsive shrinkage of the imprinted polymer gel film that is triggered by target binding. This change can improve the responsiveness of the imprinted SPR sensor to 3,3′-dichlorobenzidine. The molecularly imprinted polymer gel film was characterized with contact angle measurements, electrochemical impedance spectroscopy, cyclic voltammogram, swelling measurements and atomic force microscopy. The changes of SPR spectroscopy wavenumber shifts revealed that the imprinted gel sensing film can ‘memorize’ the binding of 3,3′-dichlorobenzidine compared to non-imprinted one. The imprinted gel-SPR sensor showed a linear response in the range of 9.0 × 10⁻¹² to 5.0 × 10⁻¹⁰ mol L⁻¹ (R² = 0.9998) for the detection of 3,3′-dichlorobenzidine, and it also exhibited high selectivity to 3,3′-dichlorobenzidine compared to its structurally related analogues. We calculated the detection limits to be 0.471 ng L⁻¹ for tap water and 0.772 ng kg⁻¹ for soil based on a signal to noise ratio of 3. The method showed good recoveries and precision for the samples spiked with 3,3′-dichlorobenzidine. This suggest that the imprinted gel-SPR sensing method can be used as a promising alternative for the detection of 3,3′-dichlorobenzidine.     

Synthetic receptors for selectively detecting erythrocyte ABO subgroups

Surface imprinting techniques with erythrocytes as templates yield polymer coatings with selective recognition sites towards red blood cells. The resulting cavities in the respective surface exhibit selectivity between blood subgroups as shown by Quartz Crystal Microbalance (QCM) measurements. Mass sensitive effects in the kilohertz range could be observed for concentrations down to 0.5 × 10⁸ cells/mL. Frequency response as well as recovery of the sensor took place within a few minutes, indicating that no covalent binding is involved. Linear concentration dependence over a defined region provides ideal conditions for cross selectivity measurements. A₁ imprinted sensor coatings resulted in an effect of 40 kHz when exposed to the template blood group, while A₂ erythrocytes yielded just 11% of that value on the same layer. Furthermore, A₂ imprinted coatings incorporated only one third the amount of A₁ erythrocytes as compared to A₂ ones. Therefore, imprinted materials depict the entire cell surface and utilize it for recognition, whereas natural antibodies bind on the defined antigen position and thus usually cannot distinguish between cells carrying different amounts of them.     

Swellable molecularly imprinted polyN-(N-propyl)acrylamide particles for detection of emerging organic contaminants using surface plasmon resonance spectroscopy

Lightly crosslinked theophylline imprinted polyN-(N-propyl)acrylamide particles (ca. 300 nm in diameter) that are designed to swell and shrink as a function of analyte concentration in aqueous media were spin coated onto a gold surface. The nanospheres responded selectively to the targeted analyte due to molecular imprinting. Chemical sensing was based on changes in the refractive index of the imprinted particles that accompanied swelling due to binding of the targeted analyte, which was detected using surface plasmon resonance (SPR) spectroscopy. Because swelling leads to an increase in the percentage of water in the polymer, the refractive index of the polymer nanospheres decreased as the particles swelled. In the presence of aqueous theophylline at concentrations as low as 10⁻⁶ M, particle swelling is both pronounced and readily detectable. The full scale response of the imprinted particles to template occurs in less than 10 min. Swelling is also reversible and independent of the ionic strength of the solution in contact with the polymer. Replicate precision is less than 10⁻⁴ RI units. By comparison, there is no response to caffeine which is similar in structure to theophylline at concentrations as high as 1 × 10⁻² M. Changes in the refractive index of the imprinted polymer particles, as low as 10⁻⁴ RI units could be readily detected. A unique aspect of the prepared particles is the use of light crosslinking rather than heavy crosslinking. This is a significant development as it indicates that heavy crosslinking is not entirely necessary for selectivity in molecular imprinting with polyacrylamides.     

Piezoelectric quartz crystal sensor for rapid analysis of pirimicarb residues using molecularly imprinted polymers as recognition elements

A new piezoelectric quartz crystal (PQC) sensor using molecularly imprinted polymer (MIP) as sensing material has been developed for fast and onsite determination of pirimicarb in contaminated vegetables. Three MIPs particles have been prepared by conventional bulk polymerization (MIP-B) and precipitation polymerization in either acetonitrile (MIP-P1) or chloroform (MIP-P2). MIP-P2, with uniform spherical shape and mean diameter at about 50 nm, has shown the best performance as the sensing material for PQC sensor. The sensor fabricated with MIP-P2 can achieve a steady-state response within 5 min, a very short response time as compared to MIPs-coated PQC sensor reported in the literature. The sensor developed exhibits good selectivity (low response to those pesticides with similar structures to pirimicarb, such as atrazine, carbaryl, carbofuran and aldicarb) and high sensitivity to pirimicarb with a linear working range from 5.0 × 10⁻⁶ to 4.7 × 10⁻³ mol L⁻¹ (following a regression equation (r = 0.9988) of −ΔF = 0.552 + 1.79 × 10⁶ C), a repeatability (R.S.D., n = 5) of 4.3% and a detection limit (S/N = 3, n = 5) of 5 × 10⁻⁷ mol L⁻¹. The MIP-coated PQC sensor developed is shown to provide a sensitive and fast method for onsite determination of pirimicarb in aqueous extract from contaminated vegetables with satisfactory recoveries from 96 to 103% and repeatability (R.S.D., n = 5) from 4.6 to 7.1% at pirimicarb concentrations ranging from 8.0 × 10⁻⁶ to 2.0 × 10⁻⁴ mol L⁻¹.     

Chromatographic characterisation, under highly aqueous conditions, of a molecularly imprinted polymer binding the herbicide 2,4-dichlorophenoxyacetic acid

The affinity of a 2,4-dichlorophenoxyacetic acid (2,4-D) molecularly imprinted polymer (MIP), which was synthesised directly in an aqueous organic solvent, for its template (2,4-D) was studied and compared with the affinity exhibited by two other reference (control) polymers, NIPA and NIPB, for the same analyte. Zonal chromatography was performed to establish the optimal selectivity, expressed as imprinting factor (IF), under chromatographic conditions more aqueous than those described so far in the literature. Frontal analysis (FA) was performed on columns packed with these polymers, using an optimized mobile phase composed of methanol/phosphate buffer (50/50, v/v), to extract adsorption isotherm data and retrieve binding parameters from the best isotherm model. Surprisingly, the template had comparable and strong affinity for both MIP (K = 3.8 × 10⁴ M⁻¹) and NIPA (K = 1.9 × 10⁴ M⁻¹), although there was a marked difference in the saturation capacities of selective and non-selective sites, as one would expect for an imprinted polymer. NIPB acts as a true control polymer in the sense that it has relatively low affinity for the template (K = 8.0 × 10² M⁻¹). This work provides the first frontal chromatographic characterization of such a polymer in a water-rich environment over a wide concentration range. The significance of this work stems from the fact that the chromatographic approach used is generic and can be applied readily to other analytes, but also because there is an increasing demand for well-characterised imprinted materials that function effectively in aqueous media and are thus well-suited for analytical science applications involving, for example, biofluids and environmental water samples.     

Electrochemical determination of L-phenylalanine at polyaniline modified carbon electrode based on β-cyclodextrin incorporated carbon nanotube composite material and imprinted sol-gel film

A sensitive and selective electrochemical sensor based on a polyaniline modified carbon electrode for the determination of l-phenylalanine has been proposed by utilizing β-cyclodextrin (β-CD) incorporated multi-walled carbon nanotube (MWNT) and imprinted sol-gel film. The electrochemical behavior of the sensor towards l-phenylalanine was investigated by cyclic voltammetry (CV), differential pulse voltammetry (DPV), and amperometric i-t curve. The surface morphologies of layer-by-layer assembly electrodes were displayed by scanning electron microscope (SEM). The response mechanism of the imprinted sensor for l-phenylalanine was based on the inclusion interaction of β-CD and molecular recognition capacity of the imprinted film for l-phenylalanine. A linear calibration plot was obtained covering the concentration range from 5.0 × 10⁻⁷ to 1.0 × 10⁻⁴ mol L⁻¹ with a detection limit of 1.0 × 10⁻⁹ mol L⁻¹. With excellent sensitivity, selectivity, stability, reproducibility and recovery, the electrochemical imprinted sensor was used to detect l-phenylalanine in blood plasma samples successfully.     

Enatioselective quantitative separation of d- and l-thyroxine by molecularly imprinted micro-solid phase extraction silver fiber coupled with complementary molecularly imprinted polymer-sensor

Thyroxine is a known disease biomarker which demands a highly sensitive and selective technique to measure ultratrace level with enantiodifferentiation of its optical isomers (d- and l-), in real samples. In this work, an approach of hyphenation between molecularly imprinted micro-solid phase extraction and a complementary molecularly imprinted polymer-sensor was adopted for enantioseparation, preconcentration, and analysis of d- and l-thyroxine. In both techniques, the same imprinted polymer, coated on a vinyl functionalized self-assembled monolayer modified silver wire, was used as the respective extraction fiber as well as sensor material. This combination enabled enhanced preconcentration of test analyte substantially so as to achieve the stringent limit [limit of detection: 0.0084 ng mL⁻¹, RSD = 0.81%, S/N = 3 (d-thyroxine); 0.0087 ng mL⁻¹, RSD = 0.63%, S/N = 3 (l-thyroxine)] of clinical detection of thyroid-related diseases, without any problems of non-specific false-positive contribution and cross-reactivity.     

Synthesis and evaluation of new propazine-imprinted polymer formats for use as stationary phases in liquid chromatography

Silica particles have been used as supports for the preparation of three different propazine-imprinted polymer formats. First format refers to grafting of thin films of molecularly imprinted polymers (MIPs) using an immobilised iniferter-type initiator (inif-MIP). The other two new formats were obtained by complete filling of the silica pores with the appropriate polymerisation mixture leading to a silica-MIP composite material (c-MIP) followed by the dissolution of the silica matrix resulting in spherical MIP beads (dis-MIP). These techniques offer a mean of fine-tuning the particle morphology of the resulting MIP particles leading to enhanced capacity in chromatographic applications. Porous silica (specific surface area S = 380 m² g⁻¹, particle size p_s = 10 μm, pore volume V_p = 1.083 ml g⁻¹ and pore diameter d_p = 10.5 nm), methacrylic acid and ethylenglycol dimethacrylate were used for the preparation of the materials. All the MIP formats imprinted with propazine have been characterised by elemental analysis, FT-IR spectroscopy, nitrogen adsorption and scanning electron microscopy. Further, the materials were assessed as stationary phases in HPLC. Capacity factors, imprinting factors and theoretical plate numbers were calculated for propazine and other related triazines in order to compare the chromatographic properties of the three different stationary phases. For the inif-MIPs the column efficiency depended strongly on the amount of grafted polymer. Thus, only the polymers grafted as thin films of ca. 1.3 nm average thickness show imprinting effects and the highest column efficiency giving plate numbers (N) of 1600 m⁻¹ for the imprinted propazine. The performance of the c-MIP stationary phase decreases as result of the complete pore filling after polymerisation and increases again after the removal of the silica matrix due to a better mass transfer in the porous mirror-image resulting polymer. From this study can be concluded that the inif-MIP shows the best efficiency for use as stationary phase in HPLC for the separation of triazinic herbicides.     

Synthesis and application of a carbamazepine-imprinted polymer for solid-phase extraction from urine and wastewater

A molecularly imprinted polymer (MIP) designed to enable the selective extraction of carbamazepine (CBZ) from effluent wastewater and urine samples has been synthesised using a non-covalent molecular imprinting approach. The MIP was evaluated chromatographically in the first instance and its affinity for CBZ also confirmed by solid-phase extraction (SPE). The optimal conditions for SPE consisted of conditioning of the cartridge using acidified water purified from a Milli-Q system, loading of the sample under basic aqueous conditions, clean-up using acetonitrile and elution with methanol. The attractive molecular recognition properties of the MIP gave rise to good CBZ recoveries (80%) when 100 mL of effluent water spiked with 1 μg L⁻¹ was percolated through the polymer. For urine samples, 2 mL samples spiked with 2.5 μg L⁻¹ CBZ were extracted with a recovery of 65%. For urine, the linear range was 0.05-24 mg L⁻¹, the limit of detection was 25 μg L⁻¹ and precision, expressed as relative standard deviation at 0.5 mg L⁻¹ (n = 3), was 3.1% and 12.6% for repeatability and reproducibility between days, respectively.     

Imprinting unique motifs formed from protein-protein associations

Lysozyme and cytochrome c were imprinted in aqueous media, both as individual proteins and in combination, together with the functional monomer 3-aminophenylboronic acid (APBA) using ammonium persulphate as the initiator. The polymers were formed as films on the gold surfaces of quartz crystal microbalance (QCM) electrodes. It was shown that the lysozyme imprinted polymer was capable of selective template recognition. Micro-calorimetry measurements were used to determine the ratio of lysozyme and cytochrome c giving rise to the maximum enthalpy change when combined in the presence of the functional monomer. Using this procedure a maximum enthalpic change was found when the two proteins were present in an equimolar ratio. A polymer, formed by jointly imprinting the proteins in this ratio, exhibited minimal recognition for the individual template proteins, but was however able to recognise them in combination, suggesting that the proteins when imprinted together interact to form a ‘new’ imprintable motif.The introduction of a series of protein solutions, comprising the imprint proteins in various ratios, to the lysozyme/cytochrome c imprinted films, showed that the films exhibit maximum affinity towards the proteins when they are presented in approximately the same mole ratio (57% cytochrome c and 43% lysozyme) as was used to form the original imprint (equimolar ratio).Frequency response profiles of the QCM electrodes carrying the films, as a function of time, showed the establishment of a new stable baseline (−4.3 Hz) after the electrode was challenged with template protein (1.39 × 10⁻⁹ mol) in less than 3 min.     

Development of trichloroacetic acid sensor based on molecularly imprinted polymer membrane for the screening of complex mixture of haloacetic acids in drinking water

This work shows developing conductometric sensor based on molecularly imprinted polymer (MIP) for the screening of complex mixture of haloacetic acids (HAAs) in drinking water. The recognition of the HAAs was achieved by trichloroacetic acid (TCAA)-imprinted polymers synthesised from the copolymerization of 4-vinylpyridine (4-VPD) and ethylene glycol dimethacrylate (EDMA) in the presence of the TCAA template in acetonitrile, either by bulk polymerization (BP) method or by a multi-step swelling polymerization (MSP) method. TCAA-imprinted polymer of both methods was tested for re-binding with the template and its analogs. It was found that these polymers could bind selectively to the template molecule and HAA derivatives. HAA measurements were carried out by the application of the polyvinyl chloride membrane fabricated with TCAA-imprinted polymer on conductometric sensors. The technological parameters (operating frequency, membrane composition, ionic strength and medium pH) for the sensors were identified and optimised in respect to the response to TCAA, using sensor fabricating with BP-based MIP as a model. The selectivity of the sensors constructed with MIPs made by either that of the two imprinting methods was also investigated, which the influence of the method of imprinting on the binding strength and selectivity of the recognition element embedded in sensor was observed. The sensors showed high sensitivity and selectivity for the response toward TCAA, the sensor modified with MSP-based MIP being better. In addition, the sensors, particularly when was constructed with MSP-based MIP exhibited good cross-reactivities with a wide range of HAAs, which is useful for the screening of the group of HAA usually present in chlorinated water in complex mixtures. Thus, the sensor modified with MSP-based MIP was chosen for analytical application. The calibration of this sensor was determined, showing the good linear graphs (R²>0.970) for HAAs over the concentration range of 25-1000 μg/l and the detection limit of each HAA in the range 0.2-5.0 μg/l. Moreover, the results in real analysis of the sensor indicate the simplicity and reliability of the method. The present work demonstrated that the sensor based on TCAA-imprinted polymer is a fast and sensitive screening method of HAAs in drinking water.     

Construction of a novel molecularly imprinted sensor for the determination of O,O-dimethyl-(2,4-dichlorophenoxyacetoxyl)(3′-nitrophenyl)methinephosphonate

A novel voltammetric sensor for O,O-dimethyl-(2,4-dichlorophenoxyacetoxyl)(3′-nitrophenyl)methinephosphonate (Phi-NO₂) based on molecularly imprinted polymer (MIP) film electrode is constructed by using sol-gel technology. The sensor responds linearly to Phi-NO₂ over the concentration range of 2.0 × 10⁻⁵ to 1.0 × 10⁻⁸ mol L⁻¹ and the detection limit is 1.0 × 10⁻⁹ mol L⁻¹ (S/N = 3). This sensor provides an efficient way for eliminating interferences from coexisting substances in the solution. The high sensitivity, selectivity and stability of the sensor demonstrates its practical application for a simple and rapid determination of Phi-NO₂ in cabbage samples.     

以马来松香丙烯酸乙二醇酯为交联剂的咖啡因分子印迹电化学传感器

以咖啡因为模板分子, 含菲环骨架的马来松香丙烯酸乙二醇酯为交联剂, 甲基丙烯酸为功能单体, 在玻碳电极表面以自由基热聚合的方式制备分子印迹聚合物敏感膜, 构建了测定咖啡因的新型分子印迹膜电化学传感器. 通过循环伏安法、 差分脉冲伏安法及电化学交流阻抗法研究了传感器对咖啡因的响应特性. 结果表明, 在最佳的实验条件下, 传感器的峰电流与咖啡因浓度在3.00×10^-3~2.73 mmol/L范围内呈现良好的线性关系, 检出限(S/N=3)为1.12×10^-4 mmol/L. 传感器具有良好的选择性和重现性. 将该传感器用于可口可乐饮料中咖啡因含量的测定, 平均回收率为98.7%.     

Electrochemical sensor based on chlorohemin modified molecularly imprinted microgel for determination of 2,4-dichlorophenol

A newly designed molecularly imprinted polymer (MIP) was synthesized and successfully utilized as a recognition element of an amperometric sensor for 2,4-dichlorophenol (2,4-DCP) detection. The MIP with a well-defined structure could imitate the dehalogenative function of the natural enzyme chloroperoxidase for 2,4-DCP. Imprinted sensor was fabricated in situ on a glassy carbon electrode surface by drop-coating the 2,4-DCP imprinted microgel suspension and chitosan/Nafion mixture. Under optimized conditions, the sensor showed a linear response in the range of 5.0–100 μmol L⁻¹ with a detection limit of 1.6 μmol L⁻¹. Additionally, the imprinted sensor demonstrated higher affinity to target 2,4-DCP over competitive chlorophenolic compounds than non-imprinted sensor. It also exhibited good stability and acceptable repeatability. The proposed sensor could be used for the determination of 2,4-DCP in water samples with the recoveries of 96.2–111.8%, showing a promising potential in practical application.     

Comparison of pyrimethanil-imprinted beads and bulk polymer as stationary phase by non-linear chromatography

A pyrimethanil-imprinted polymer (P1) was prepared by iniferter-mediated photografting a mixture of methacrylic acid and ethylene dimethacrylate onto homemade near-monodispersed chloromethylated polydivinylbenzene beads. The chromatographic behaviour of a column packed with these imprinted beads was compared with another column packed with irregular particles obtained by grinding a bulk pyrimethanil-imprinted polymer (P2). The comparison was made using the kinetic model of non-linear chromatography, studying the elution of the template and of two related substances, cyprodinil and mepanipyrim. Extension of the region of linearity, capacity factors for the template and the related substances, column selectivity, binding site heterogeneity, apparent affinity constant (K) and lumped kinetic association (k_a) and dissociation rate constant (k_d) were studied during a large interval of solute concentration, ranging between 1 and 2000 μg/ml. From the experimental results obtained, in the linearity region of solute concentration column selectivity and binding site heterogeneity remained essentially the same for the two columns, while column capacity (at 20 μg/ml, P1 = 23.1, P2 = 11.5), K (at 20 μg/ml, P1 = 8.3 × 10⁶ M⁻¹, P2 = 2.5 × 10⁶ M⁻¹) and k_a (at 20 μg/ml, P1 = 3.5 μM⁻¹ s⁻¹, P2 = 0.47 μM⁻¹ s⁻¹) significantly increased and k_d (at 20 μg/ml, P1 = 0.42 s⁻¹, P2 = 0.67 s⁻¹) decreased for the column packed with the imprinted beads. These results are consistent with an influence of the polymerisation method on the morphology of the resulting polymer and not on the molecular recognition properties due to the molecular imprinting process.     

Selective adenosine-5'-monophosphate uptake by water-compatible molecularly imprinted polymer

Molecularly imprinted polymers (MIPs) were prepared for adenosine-5′-monophosphate (AMP), a substrate of AMP-activated protein kinase. The template molecule was formed by the vinylphenylboronate diester of adenosine on which 5′-free hydroxide was protected by tert-butyldimethylsilyl group in order to mimic the steric hindrance of the phosphate moiety of AMP. Molecular imprinting was performed by complexing acrylamide and the template in a highly cross-linked polymer. MIPs were tested in batch experiments with aqueous samples of nucleotides and a number of parameters were investigated. The use of tetrabutylammonium hydroxide (TBAH) was necessary to obtain a rebinding of nucleotides on MIP. The adsorption of AMP was optimal in 5 mM ammonium acetate buffer solution pH 9.5 for 30 min, with 30 mM of TBAH. The imprinted polymer was selective for AMP towards others nucleotides or deoxi analogues.     

Synthetic approaches to parabens molecularly imprinted polymers and their applications to the solid-phase extraction of river water samples

In this paper we describe the synthesis, characterisation and use of two distinct molecularly imprinted polymers (MIPs) prepared using esters of p-hydroxybenzoic acid (parabens) as templates: one MIP was synthesised by precipitation polymerisation using a semi-covalent molecularly imprinting strategy with methyl paraben as the template/target (MIP 1); the second MIP was prepared in monolithic form through a conventional non-covalent molecular imprinting strategy, with butyl paraben as the template (MIP 2). MIP 1 recognized methyl paraben, showed cross-selectivity for other parabens analytes used in the study and higher affinity towards these compounds than did a non-imprinted control polymer. Similarly, MIP 2 demonstrated higher affinity towards paraben analytes than a non-imprinted control polymer.For the analysis of environmental water samples, a solid-phase extraction (SPE) protocol was developed using MIP 2 as sorbent, and results were compared to a SPE using a commercial sorbent (Oasis HLB). With MIP 2 as sorbent and butyl paraben as target, when percolating 500 mL of river water spiked at 1 μg L⁻¹ through the SPE cartridge, and using 1 mL of isopropanol as cleaning solvent, a higher recovery of butyl 4-hydroxybenzoate (butyl paraben) and a cleaner chromatogram where achievable when using the MIP compared to the commercial sorbent.     

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

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