Development of a voltammetric sensor based on a molecularly imprinted polymer (MIP) for caffeine measurement

A new voltammetric sensor for caffeine measurement is introduced. A caffeine-selective molecularly imprinted polymer (MIP) and a non-imprinted polymer (NIP) were synthesized and then used for carbon paste (CP) electrode preparation. The MIP, embedded in the carbon paste electrode, functioned as a selective recognition element and a pre-concentrator agent for caffeine determination. The prepared electrode was used for caffeine measurement via a three-step procedure including analyte extraction in the electrode, electrode washing and electrochemical measurement of caffeine. The MIP-CP electrode showed very high recognition ability in comparison to NIP-CP. It was shown that electrode washing after caffeine extraction led to enhanced selectivity. Differential pulse voltammetry for caffeine determination was more effective than square wave voltammetry. Some parameters affecting sensor response were optimized, and a calibration curve was then plotted. A linear range of 6 × 10⁻⁸ to 2.5 × 10⁻⁵ mol L⁻¹ was obtained. The detection limit of the sensor was calculated to be equal to 1.5 × 10⁻⁸ mol L⁻¹. This sensor was used successfully for caffeine determination in spiked beverage and tea samples.     

Promethazine determination in plasma samples by using carbon paste electrode modified with molecularly imprinted polymer (MIP): Coupling of extraction, preconcentration and electrochemical determination

A promethazine (PMZ) molecularly imprinted polymer (MIP) and a non-imprinted polymer (NIP) were synthesized by two different formulations of methacrylic acid-ethylene glycol dimethacrylate (MAA-EGDMA) and vinyl benzene-divinyl benzene (VB-DVB). Then, the MIPs were used to modify the carbon paste electrode (CP). The response difference between MIP-CP and NIP-CP electrodes, containing VB-DVB polymer, was higher than that for MIP-CP and NIP-CP modified with polymer of MAA-EGDMA, indicating the lower nonselective surface adsorption property of the VB-DVB based MIP. The MIP, incorporated in the carbon paste electrode, functioned as selectively recognition element and pre-concentrator agent for PMZ determination. The prepared electrode was used for PMZ measurement by the three steps procedure including analyte extraction in the electrode, electrode washing and electrochemical measurement of PMZ. It was shown that the electrode washing, after PMZ extraction, led to enhanced selectivity. Square wave voltammetry (SWV) for PMZ determination by proposed electrode was proved to be better than that of differential pulse voltammetry. Some parameters, effective on the electrode response, were optimized and then a calibration curve was plotted. Two dynamic linear range of 7 × 10⁻⁹ to 4 × 10⁻⁷ and 4 × 10⁻⁷ to 7 × 10⁻⁶ mol L⁻¹ were obtained. The detection limit of the method was calculated equal to 3.2 × 10⁻⁹ mol L⁻¹. This method was used successful for PMZ determination in blood serum sample.     

The influence of polymer morphology on the performance of molecularly imprinted polymers

This is the first in-depth study examining the effect of morphology on the performance of 2-aminopyridine (2-apy) imprinted polymers. A series of polymers were prepared by varying the amount of crosslinking monomer (EGDMA) whilst the other polymer components remained constant. Physical characterisation was carried out using conventional techniques, such as nitrogen sorption porosimetry and solvent swelling studies. The use of a novel thermal desorption GC-MS technique suggested higher levels of polymer degradation with prolonged exposure to elevated temperatures for those polymers formed with lower amounts of EGDMA. The thermal desorption GC-MS profiles obtained correlated with the physical characteristics of the polymers, where higher levels of polymer bleed was found to occur with larger average pore diameters. Polymer physical characteristics were also found to correlate with the binding parameters (number of binding sites and polymer-template association energy) obtained from the Langmuir-Freundlich Isotherm (L-FI) and affinity distribution spectra (AD). The flexibility of the polymers formed from lower amounts of EGDMA combined the swelling effect of the solvents on the polymers resulted in an increase in affinity, which was both specific and non-specific in nature.     

Water-assisted formation of novel molecularly imprinted polymer membranes with ordered porous structure

A functional polymer, poly(styrene-stat-acrylonitrile-stat-vinyl-2,4-diamino-1,3,5-triazine) (modified SAN, mSAN) with 13.6% triazine units, was synthesized. Using mSANs as the functional polymers and poly(styrene-stat-acrylonitriles) (SANs) as the matrix polymers, the molecularly imprinted polymer (MIP) membranes with (S)-5-benzylhydantoin (S-BZH) as template and the Blank membranes without S-BZH were prepared via the water-assisted method. Scanning electron microscopy (SEM) measurement revealed an ordered porous structure on the surface and a sponge-like porous structure in the cross-section of the MIP membranes. Further, the permeation experiments of the template S-BZH and its analogues in methanol solution were carried out with MIP as well as Blank membranes; the results provided evidence for imprint effect of the ordered porous membranes.     

A novel capacitive biosensor for cholesterol assay that uses an electropolymerized molecularly imprinted polymer

A novel cholesterol biosensor based on capacitive detection has been developed using molecularly imprinted polymers. The sensitive layer was prepared by electropolymerization of 2-mercaptobenzimidazole (2-MBI) on a gold electrode in the presence of cholesterol as a template. Cyclic voltammetry and capacitive measurements were used to monitor the process of electropolymerization. Surface uncovered areas were plugged with 1-dodecanethiol to make the layer dense, and the insulating properties of the layer were studied in the presence of K₃Fe(CN)₆/K₄Fe(CN)₆ redox couples and also by the use of AC impedance measurements. The template molecules and the non-bound thiol were removed from the modified electrode surface by washing with an alkaline solution of ethanol. The sensor's linear response range was between 5 and 30 μM, with a detection limit of 0.42 μM. The proposed molecularly imprinted polymer capacitive (MIPC) sensor exhibited good selectivity for cholesterol. The reproducibility and repeatability of the MIPC senor were all found to be satisfactory. The results from sample analysis confirmed the applicability of the MIPC sensor to quantitative analysis.     

The effect of polymerisation methods on the adsorption capacity of HEMA based molecularly imprinted polymers

Molecularly imprinted polymers (MIPs) are generally synthesised either by thermal initiation or by photo polymerisation methods. Recently we used a gamma irradiation method for the preparation of MIPs. In this communication we compare three different methods for the synthesis of 2-hydroxy ethyl methacrylate (HEMA) based MIP imprinted for hydrocortisone in terms of its capacity to adsorb the print molecule. Our results show that MIP prepared by the gamma irradiation method has a better adsorption capacity than the thermally initiated polymer. It is interesting to note that its adsorption capacity is comparable or marginally better than the photo polymerised MIP.     

Preparation of molecularly imprinted polymer for sinomenine and study on its molecular recognition mechanism

A sinomenine (SIN) molecule-imprinted monolithic stationary phase (MIMSP) with specific recognition for SIN was prepared by in situ technique, utilizing methacrylic acid (MAA) as a function monomer, ethylene glycol dimethacrylate (EDMA) as a cross-linking agent, and low-polar solvents (toluene and dodecanol) as porogenic solvents. The selectivity of the polymers for SIN was evaluated by high performance liquid chromatography (HPLC). Some chromatographic conditions, such as the column temperature, the flow rate and the composition of the mobile phase, were changed in order to characterize the chromatographic procedure. SIN could be separated from some other structural analogues, including morphine, codeine, codethyline and magnoflorine, under optimized conditions. Scatchard analysis showed that two classes of binding sites existed in the SIN-imprinted polymers, with their dissociation constants estimated to be 7.257×10⁻⁵ and 3.828×10⁻³ mol l⁻¹, respectively. Compared with the SIN-imprinted polymers, the non-imprinted polymers prepared using the same method but in the absence of SIN did not exhibit the specific molecular selectivity, which suggests that the specific molecule-recognition ability of the SIN-imprinted polymers was largely ascribed to the imprinting effect.     

Silylated montmorillonite based molecularly imprinted polymer for the selective binding and controlled release of thiamine hydrochloride

In the present study, specific binding and controlled release of thiamine hydrochloride (THC) to and from a novel molecularly imprinted polymer (MIP) matrix namely, THC-templated-silylated montmorillonite-itaconic acid polymer was investigated. The polymer matrix was characterized by means of XRD, FTIR and SEM analyses. Optimization of various imprinting components and binding characteristics of THC by the novel MIP were examined in detail. The binding affinity of THC for MIP was found to be greater than that for non-imprinted polymer (NIP). The maximum binding was found to be at solution pH of 4.5. The Sips isotherm model was found to describe well the equilibrium binding data with maximum binding capacity of 100 mg/g for MIP. The kinetic study revealed that the binding of THC onto MIP follows pseudo-second-order kinetic model with correlation coefficient 0.999. The swelling study of MIP in distilled water showed that the maximum swelling capacity is 329.0 g/g at about 8 h. In vitro release experiments showed that MIP releases drug in intestinal fluid with a controlled manner. The release kinetics of drug from MIP was analyzed using Ritger–Peppas model. The binding specificity of MIP for THC was tested using different substrates having structural analogue to the template, THC.     

Co3O4-chitosan/biomass-derived porous carbon molecularly imprinted polymer integrated electrode for selective detection of glucose

The detection of glucose (Glu) is of great significance in medical diagnosis, food processing and biotechnology. Rapid, accurate and convenient detection technology is particularly important. Herein, the Co₃O₄-PC nanocomposite grown on biomass-derived porous carbon (PC) was prepared by hydrothermal method and subsequent air calcination. Chitosan (CS) was electrodeposited on the surface of Co₃O₄-PC by potentiostatic deposition with Glu as the template molecule. Finally, the template molecule was eluted by cyclic voltammetry to create specific recognition sites for Glu, and a highly selective and stable Glu sensor was constructed. The obtained MIP (molecularly imprinted polymer)-Glu-CS/Co₃O₄/PC nanocomposites were characterized by scanning electron microscopy, Raman spectroscopy, cyclic voltammetry, chronoamperometry and so on. The results showed that the MIP-Glu-CS/Co₃O₄-PC had great catalytic performance for Glu detection with a linear range of 12.17 μM-2.3 mM, a detection limit of 4.01 μM, and a sensitivity of 407.5 μA cm^?2 mM^?1. The sensor has excellent selectivity and stability. This work provides a guide for improving the selectivity of nanozymes.     

Preparation and characterization of monodisperse molecularly imprinted polymer microspheres by precipitation polymerization for kaempferol

A new kind of molecularly imprinted polymer (MIP) microspheres for the selective extraction of kaempferol was prepared by precipitation polymerization using 4-vinylpridine (4-VP) and ethylene glycol dimethacrylate (EDMA) as functional monomer and cross-linker respectively. The synthesis conditions, such as ratios of 4-VP/EDMA and polymerization time were discussed in detail. Results showed that the 2% was the optimal concentration of co-monomers to obtain monodisperse MIP microspheres, the best ratio of 4-VP/EDMA was 1:2, and 24 h was considered as the proper polymerization time. Compared with the MIP agglomeration or coagulum particles, monodisperse MIP microspheres showed the better adsorption capacity: the saturated adsorption capacity of monodisperse MIP microspheres was 7.47 mg g^?1, the adsorption equilibrium could be obtained in 30 min. Finally, the adsorption performances of the optimal MIP microspheres were evaluated by kinetic adsorption, adsorption isotherm, and selective adsorption experiments, which indicated that the adsorption mechanism were chemical single layer adsorption and the separation factor was up to 3.91 by comparing with the structure similar compound (quercetin). The MIP microspheres exhibit prospects in the kaempferol efficient and selective separation.     

A novel potentiometric sensor for l-ascorbic acid based on molecularly imprinted polypyrrole

A polymeric membrane-based ion-selective electrode (ISE) for the determination of l-ascorbic acid (l-AA) was developed. The sensor was fabricated by modifying glassy carbon electrodes with molecularly imprinted polypyrrole (PPy) synthesized by electropolymerization of the monomer in the presence of ascorbate. A comparison between the non-imprinted modified electrode (PPy-NIP) and the molecularly imprinted polymer (PPy-MIP) is reported. The molecularly imprinted polymer improves the performances of the sensor, especially if the PPy film has been submitted to an oxidation treatment. The PPy-MIPox electrode shows near-Nernstian response (approx. −57 mV/decade) to the ascorbate over the concentration range between 5 × 10⁻⁶ M and 2 × 10⁻³ M and it can be used for more than 3 weeks without any considerable change in the measured response. The potentiometric sensor has been successfully applied to the determination of ascorbate in food and pharmaceutical samples (recoveries of about 100%).     

Effect of the mimic structure on the molecular recognition properties of molecularly imprinted polymers for ochratoxin A prepared by a fragmental approach

In this work the fragmental approach was used to prepare several molecularly imprinted ethylene dimethacrylate-co-methacrylic acid polymers with molecular recognition towards the mycotoxin ochratoxin A, with the aim of searching for simpler mimic templates than the well-known N-(4-chloro-1-hydroxy-2-naphthoylamido)-(l)-phenylalanine. The screening for binding of two different kinds of ochratoxin-related molecules was performed by HPLC analysis. Ochratoxin A and the mimic templates were eluted in acetonitrile–acetic acid (0.1% v/v) and the imprinting factor was measured for all the ligands on all the columns packed with the imprinted polymers. The experimental results show that changes to the amino acidic sub-structure or the presence/absence of a chlorine atom in position 4 on the naphthalene ring system does not affect the molecular recognition of ochratoxin A by the resulting imprinted polymer. On the contrary, the presence of the bulky naphthalene ring system in the mimic template seems to be necessary to preserve the molecular recognition of ochratoxin. This binding behavior was found to be compatible with in silico simulations of the complexation between some of the mimic templates and molecules of methacrylic acid. The use of the mimic template N-(1-hydroxy-2-naphthoylamido)-(L)-phenylalanine seems to represent a synthetically simple approach to the preparation of imprinted polymers with molecular recognition properties towards ochratoxin A.     

Design of molecularly imprinted polymer grafts with embedded gold nanoparticles through the interfacial chemistry of aryl diazonium salts

A novel strategy is described for the preparation of highly sensitive molecularly imprinted (MIPs) sensors for dopamine. It combines mercaptobenzene diazonium salt as a coupling agent for immobilizing gold nanoparticles to gold electrodes and benzoyl benzene diazonium salt as photoinitiator of radical polymerization at the said gold nanoparticle-decorated gold electrodes. The MIP films were prepared by surface-initiated photopolymerization (SIPP) of methacrylic acid (MAA) as functional monomer (F) for dopamine (DA) the template molecule (T), and ethylene glycol dimethacrylate (EGDMA), the crosslinker (C). Dimethylaniline was employed as a hydrogen donor. The specificity and selectivity were demonstrated by square wave voltammetry (SWV). The detection limit was 0.35 nmol L^-1 (0.054 ng mL⁻¹). The sensor layers are stable and adherent to the surface through aryl layers. The originality and advantage of the process lie in the use of aryl diazonium salt as coupling agents for anchroring nanoparticles and MIP layers to the electrode surface in a simple and efficient way which ensures high sensing performance together with good surface-MIP adhesion. The same strategy can be extended to a broad range of templates.     

沉淀聚合法制备咖啡因分子印迹聚合物微球

以咖啡因为印迹分子,甲基丙烯酸为功能单体,乙二醇二甲基丙烯酸酯为交联剂,偶氮二异丁腈为引发剂,采用沉淀聚合法在乙腈溶液中制备了针对咖啡因的分子印迹聚合物微球。对沉淀聚合中单体、引发剂、溶剂用量的比例关系进行探索,并利用平衡结合实验研究了聚合物对印迹分子的吸附性能,结果表明该印迹聚合物微球呈现出较好的结合能力。     

Optimisation of the synthesis of vancomycin-selective molecularly imprinted polymer nanoparticles using automatic photoreactor

A novel optimized protocol for solid-state synthesis of molecularly imprinted polymer nanoparticles (nanoMIPs) with specificity for antibiotic vancomycin is described. The experimental objective was optimization of the synthesis parameters (factors) affecting the yield of obtained nanoparticles which have been synthesized using the first prototype of an automated solid-phase synthesizer. Applications of experimental design (or design of experiments) in optimization of nanoMIP yield were carried out using MODDE 9.0 software. The factors chosen in the model were the amount of functional monomers in the polymerization mixture, irradiation time, temperature during polymerization, and elution temperature. In general, it could be concluded that the irradiation time is the most important and the temperature was the least important factor which influences the yield of nanoparticles. Overall, the response surface methodology proved to be an effective tool in reducing time required for optimization of complex experimental conditions.     

Chloride selective potentiometric sensor based on a newly synthesized hydrogen bonding anion receptor

A new potentiometric chloride sensor based on the use of anion receptor 2-(1-H-imidazo [4,5-f][1,10]phenanthroline-2-yl)-6methoxyphenol (HIPM) in poly(vinyl chloride) (PVC) matrix is reported. Effect of various plasticizers: 2-nitrophenyloctylether (o-NPOE), di-n-butylphthalate (DBP), diethyl phthalate (DEP), dioctylpthalate (DOP), tri-n-butyl phosphates (TBP), chloronapthalene (CN) and cation excluder, cetryltrimethylammoniumbromide (CTAB) was studied. The best performance was obtained with a membrane composition of PVC: o-NPOE:HIPM: CTAB ratio (w/w, %) of 31:60:7:3. The sensor exhibits significantly enhanced selectivity towards chloride over the concentration range 5.0 × 10⁻⁸ to 1.0 × 10⁻¹ M with a lower detection limit of 1.0 × 10⁻⁸ M and a Nernstian slope of 59.8 mV decade⁻¹ of activity. Influence of the membrane composition and possible interfering ions was investigated on the response properties of the electrode. Fast and stable response, good reproducibility and long-term stability are demonstrated. The sensor shows response time of <10 s and can be used for about 3 months without any considerable divergence in their potential response. Selectivity coefficients determined with matched potential method (MPM) indicate high selectivity for chloride. The proposed electrode shows fairly good discrimination of chloride from anions. It was successfully applied to determination of chloride ion in packed drinking water. The electrode can be used in the pH range of 6.5-8.0 and mixtures containing up to 20% (v/v) non-aqueous content. It was used as an indicator electrode in potentiometric titration of chloride ion against silver nitrate.     

Preparation of the molecularly imprinted polymers-based capacitive sensor specific for tegafur and its characterization by electrochemical impedance and piezoelectric quartz crystal microbalance

Molecularly imprinted polymers (MIPs)-based capacitive sensor specific for tegafur was constructed by electropolymerization of m-aminophenol onto the surface of gold electrode and the Au-coated quartz crystal electrodes. Electrochemical impedance (EI) and quartz crystal microbalance (QCM) were employed to characterize the modified gold electrodes and the modified Au-coated quartz crystals, respectively. Unlike the capacitive sensors reported in the previous literatures, the present sensors were not treated with alkanethiol after electropolymerization and show even more satisfactory performance. QCM measurements also confirmed the imprinting effect of the polymer layers.     

三硝基甲苯分子印迹电化学传感器的制备和应用

以三硝基甲苯（TNT）为模板分子,甲基丙烯酸（MAA）为功能单体,采用乳液聚合法制备TNT的分子印迹聚合物（MIPs）。将制备的MIPs分散在溶剂中,通过表面涂覆法制备出检测TNT的分子印迹电化学传感器。紫外光谱表明TNT与MAA之间存在相互作用力,有助于形成结构稳定、亲和性强的MIPs。利用扫描电镜观测不同制备条件下印迹聚合物的表观形貌,发现溶剂用量为30mL、乳化剂用量为12mg时制备的聚合物形貌较优异。吸附实验表明MIPs对TNT的吸附量随着TNT初始浓度的增加而增加,140min后达到最大吸附量的95%。MIPs对TNT的分离常数远大于RDX和DNT,对RDX和DNT的选择性系数均达到4.4以上,说明MIPs对TNT有较好的选择性吸附能力。铁氰化钾探针实验和对TNT的响应曲线验证了电化学传感器的成功制备,该传感器富集3min就达到了最大电流值的94%,5min内达到吸附平衡。TNT浓度在0.1~5mg/mL的范围内与峰电流有良好的线性关系,检出限为0.06mg/mL。MIPs传感器对TNT的电流响应分别为DNT和RDX的3.13倍、3.27倍,说明其对TNT分子具有很强的特异性识别能力。     

Electrochemical tolazoline sensor based on gold nanoparticles and imprinted poly-o-aminothiophenol film

Amperometric detection of tolazoline (TL) was carried out on a gold nanoparticles (AuNPs)/poly-o-aminothiophenol (PoAT)-modified electrode by a molecular imprinting technique and electropolymerization method. The modification procedure was characterized via electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The recognition between the imprinted sensor and target molecule was observed by measuring the variation of amperometric response of the oxidation-reduction probe, K₃Fe(CN)₆ on electrode. Under the optimal experimental conditions, the peak currents were proportional to the concentrations of tolazoline in two ranges of 0.05-5.0 μg mL⁻¹ and 5.0-240 μg mL⁻¹ with the detection limit of 0.016 μg mL⁻¹. Meanwhile the prepared sensor showed sensitive and selective binding sites for tolazoline. The enhancement of sensitivity was attributed to the presence of AuNPs which decreased the electron-transfer impedance.     

Selective molecularly imprinted polymer nanofiber sorbent for the extraction of bisphenol A in a water sample

Novel molecularly imprinted polymer nanofibers (MIP‐NFs) were prepared for the adsorption of bisphenol A (BPA) in a water sample using the sol–gel process and the electrospinning technique. The effects of a number of synthesis parameters on the adsorption efficiency were investigated. The successful removal of BPA from MIP‐NFs was studied using UV–visible spectroscopy. The prepared MIP‐NFs were characterized by Fourier transform infrared, field emission SEM, TEM and energy dispersive X‐ray analysis. The results showed that the required molar ratio of 3‐aminopropyltriethoxysilane (APTES) to BPA was 15:1, which indicates a good performance in the rebinding test. Likewise, the molar ratio of APTES:acid:water was 1:2:9. The nylon 6 polymer solution, with a concentration of 12 wt%, showed a maximum adsorption capacity for BPA due to a decrease in the nanofiber diameter and an increase in the accessible sites. Furthermore, the maximum adsorption capacity of BPA was achieved at pH 7. Concerning the binding of BPA on MIP‐NFs, the experimental data matched well with the pseudo‐second‐order kinetics data and the Sips isotherm model. The saturated binding capacity for MIP‐NFs was predicted to be 115.1 mg g^?1, which was more than twice as high as that for non‐imprinted polymer nanofibers (46.82 mg g^?1). The results obtained in this study confirmed that the prepared MIP‐NFs showed considerable binding specificity for BPA in comparison with similar structural compounds such as phenol, naphthol and Naphthol AS, in aqueous solution. The binding capacity of MIP‐NFs remained almost constant after five cycles of reuse. The real sample analysis indicated that MIP‐NFs could be utilized as a useful sorbent material for the extraction of BPA from a water sample.