Molecularly imprinted polymer-based solid-phase extraction combined with molecularly imprinted polymer-based sensor for detection of uric acid

The development of an easy-to-use, rapid, robust and inexpensive technique is required which can measure the basal concentration of uric acid (UA) lower than 1.0 x 10(-7)M ( approximately 0.017 mgL(-1)) in biological samples to attend the problem of hypouricemia. In the present work an artificial receptor for UA, silica gel-bonded molecularly imprinted polymer (MIP), was used as a sorbent for molecularly imprinted solid-phase extraction (MISPE) in column chromatography. The use of a sensor based on a MIP-modified hanging mercury drop electrode (HMDE), as reported from our laboratory, could estimate UA with detection limit as low as 0.024 mgL(-1) under the optimized conditions of differential pulse, cathodic stripping voltammetric (DPCSV) measurement. However, in the current investigation, with the use of the combination of MISPE followed by detection with a MIP-based HMDE sensor, the minimum detectable concentration could go down to 0.0008 mgL(-1) (RSD=0.63%, S/N=3). The same MIP receptor for both MISPE and the corresponding sensor was able to enhance the preconcentration of analyte substantially so as to attain the desired level of sensitivity; and that to without any interference (cross-reactivity) from other structurally related analogues including the major interferent like ascorbic acid prevalent in the aqueous environment of biological samples.     

A molecularly imprinted polymer-based synthetic transaminase

The design, synthesis, and evaluation of a molecularly imprinted polymer transaminase mimic is described. Methacrylic acid-ethylene glycol dimethacrylate copolymers were synthesized using, as a template, a transition state analogue (TSA) for the reaction of phenylpyruvic acid and pyridoxamine to yield phenylalanine and pyridoxal. Polymer suitability was established on the basis of (1)H NMR studies of template-functional monomer interactions. Polymer recognition characteristics were examined in a series of HPLC studies using the polymers as chromatographic stationary phases. Selectivity for the TSA, relative to substrates and products, was observed in both aqueous and nonpolar media. In the latter case (chloroform/AcOH, 96:4), an enantioseparation factor (alpha) of 2.1 was obtained, and frontal chromatographic studies revealed the presence of 11.9 +/- 0.2 micromol g(-1) (dry weight) of enantioselective sites. Polymers imprinted with the l-form of the oxazine-based TSA induced a 15-fold enhancement of the apparent reaction rate (app. V(max) 2.5 x 10(-7) mol s(-1); app. K(m) 8.2 x 10(-3) M) and enantioselective production of phenylalanine (32 +/- 4% ee) for reactions conducted in an aqueous buffer system. Substrate selectivity was evident, and a turnover number (k(cat)) of 0.1 s(-)(1) was determined. This is the first example of the catalysis of sigmatropic shifts in aqueous media by molecularly imprinted polymers.     

Molecularly imprinted polymer-based electrochemical sensors for biopolymers

Electrochemical synthesis and signal generation dominate among the almost 1200 articles published annually on protein-imprinted polymers. Such polymers can be easily prepared directly on the electrode surface, and the polymer thickness can be precisely adjusted to the size of the target to enable its free exchange. In this architecture, the molecularly imprinted polymer (MIP) layer represents only one ‘separation plate’; thus, the selectivity does not reach the values of ‘bulk’ measurements. The binding of target proteins can be detected straightforwardly by their modulating effect on the diffusional permeability of a redox marker through the thin MIP films. However, this generates an ‘overall apparent’ signal, which may include nonspecific interactions in the polymer layer and at the electrode surface. Certain targets, such as enzymes or redox active proteins, enables a more specific direct quantification of their binding to MIPs by in situ determination of the enzyme activity or direct electron transfer, respectively.     

A strategy for constructing sensitive and renewable molecularly imprinted electrochemical sensors for melamine detection

A novel strategy for preparing highly sensitive and easily renewable molecularly imprinted polymer (MIP) sensors was proposed. Using melamine (MA) as the template molecule, MIP particles were synthesized and embedded in a solid paraffin carbon paste to prepare the MIP sensor. MA was indirectly determined from the competition between the reactions of MA and horseradish peroxidase-labeled MA (MA-HRP) with the vacant cavities. The detection signals were amplified because of enzymatic reaction to the H₂O₂ catalytic oxidation. Sensitivity was markedly improved. Sensor renewal was achieved by a simple mechanical polishing of the sensitive film. The linear range for MA detection was 0.005–1 μmol L⁻¹ and the detection limit was 0.7 nmol L⁻¹. The molecularly imprinted solid paraffin carbon paste sensor was used for MA detection in milk samples.     

Towards the development of molecularly imprinted polymer based screen-printed sensors for metabolites of PAHs.

This paper describes the fabrication of a sensor for 1-hydroxypyrene (1-OHP) based on a screen-printed carbon electrode (SPCE) modified with a molecularly imprinted polymer (MIP); 1-OHP was chosen as a model metabolite of polyaromatic hydrocarbons (PAHs). It was shown that 1-OHP could be readily oxidised at a plain SPCE and the electrochemical mechanism was found to involve an ECE (electron transfer-chemical reaction-electron transfer) process. The MIP for 1-OHP was prepared using only divinylbenzene (DVB) and styrene as monomers and the binding was only based on hydrophobic interactions. Batch binding studies revealed that optimum uptake of 1-OHP by the MIP occurred from solutions containing 35% water in methanol. Selectivity of the binding sites in the MIP was examined by performing uptake studies in the same solution containing either phenol or 1-naphthol; the specific binding of 1-OHP was twenty times greater than the former and five times greater than the latter. Preliminary calibration studies were performed with the MIP-SPCE using a two-step approach; accumulation was carried out in 35% water in methanol followed by measurement in 50% methanol-0.025 mol dm(-3) phosphate buffer pH 12. This two-step non-competitive affinity assay gave encouraging results and indicated potential for use in pollution studies.     

Selective piezoelectric odor sensors using molecularly imprinted polymers

Molecular imprinting technique has been used to create sensors with a predetermined selectivity for molecules in the gas phase. Piezoelectric quartz crystals coated with a 2-methylisoborneol (MIB) imprinted polymer gave responses which were consistently 5–10 Hz (1.1–1.3 times) higher than those of sensors coated with a non-imprinted polymer. Geosmin, another tertiary alcohol odorant with an earthy odor resembling, and often accompanying MIB, produced almost equal responses on either imprinted- or non-imprinted sensors. A number of other odorants were examined and their responses to the non-imprinted sensors were found to be similar to or greater than their responses to the imprinted sensors. The responses of MIB to the imprinted sensors were always the highest, while other odorants produced equal or higher responses using the non-imprinted sensor. The sensor has a detection limit of ca. 5 mg l⁻¹ and a dynamic range of at least 1000 mg l^−l. When the time taken for the sensor to stabilize is used as the response, instead of the frequency change, the detection limit is lowered to ca. 200 μg l^−l.     

基于磁性分子印迹聚合物的电化学传感器的研究进展

分子印迹聚合物与磁性纳米材料结合,制备成磁性分子印迹纳米敏感膜,这样做不仅可以发挥分子印迹聚合材料的优势,而且磁性纳米粒子可有效提高电化学传感器的灵敏度、稳定性以及生物相容性等.近年来将磁性分子印迹纳米敏感膜应用于电化学传感器制备成的磁性分子印迹电化学传感器得到了较快的发展.本文就近5年来磁性分子印迹电化学传感器敏感膜...     

4-氨基吡啶印迹聚合物毛细管整体柱的电色谱识别机理

在石英毛细管中原位聚合制备了4-氨基吡啶印迹聚合物毛细管整体柱，通过考察流动相中乙腈比例对4-氨基吡啶、2-氨基吡啶和硫脲在分子印迹聚合物毛细管整体柱、空白聚合物毛细管整体柱和硅烷化衍生的开管柱上迁移时间和分离情况的影响，研究了4-氨基吡啶分子印迹聚合物毛细管整体柱的CEC识别机理。发现有机添加剂的含量对印迹聚合物的印迹识别能力影响很大，甚至能改变混合物的流出顺序。根据随乙腈含量改变混合物迁移时间和流出顺序的变化规律，可以推测：随着乙腈含量的提高，色谱保留对迁移的影响越来越大；随着乙腈含量的降低，电泳对迁移的影响越来越大。     

Approaches to the rational design of molecularly imprinted polymers

In our experience the efficient design of molecularly imprinted polymer (MIPs) for novel templates has proved difficult. Following commonly used imprinting protocols, MIPs designed against one template show both a lack of capacity and poor specificity for rebinding either the template or structurally similar analytes. Optimisation methods that involve changing one factor at a time can be laborious.A novel approach for the optimisation of MIPs using chemometrics is described. Sulfonamides, common drug residues in foodstuffs, were used as the model analytes with a methacrylic acid/ethylene glycol dimethacrylate MIP. To avoid the inaccuracies in measurement caused by template bleed a multi-analyte competition rebind assay was developed to select suitable sulfonamides to be used as the template for the MIP, and for the rebind analyte in the chemometric optimisation study. The rebinding efficiencies were monitored by HPLC. The template sulfonamide was selected as sulfamethazine (SMZ), and the rebind analyte as sulfadimethoxine (SDIM). The template:monomer:cross-linker (T:M:X) ratio of the SMZ block MIP was then optimised using a three-level full factorial design to predict a MIP with the highest rebind capacity. On synthesis this was 38.8% for SDIM in a solid phase extraction (SPE) application agreeing with the predication. The factorial design was further utilised to predict an optimum T:M:X ratio for the production of a class specific MIP, capable of binding a range of sulfonamides simultaneously. The predicted optimum T:M:X ratios of (1:10:55) and (1:10:10) were found to be different to commonly used ratios from the MIP literature.     

Development of a selective molecularly imprinted polymer-based solid-phase extraction for indomethacin from water samples

A selective molecularly imprinted solid-phase extraction (MISPE) for indomethacin (IDM) from water samples was developed. Using IDM as template molecule, acrylamide (AM) or methacrylic acid (MAA) as functional monomer, ethylene dimethacrylate (EDMA) as crosslinker, and bulk or suspension polymerization as the synthetic method, three molecularly imprinted polymers (MIPs) were synthesized and characterized with a rebinding experiment. It was found that the MIP of AM-EDMA produced by bulk polymerization showed the highest binding capacity for IDM, and so it was chosen for subsequent experiments, such as those testing the selectivity and recognition binding sites. Scatchard analysis revealed that at least two kinds of binding sites formed in the MIP, with the dissociation constants of 7.8 μmol L⁻¹ and 127.2 μmol L⁻¹, respectively. Besides IDM, three structurally related compounds — acemetacin, oxaprozin and ibuprofen — were employed for selectivity tests. It was observed that the MIP exhibited the highest selective rebinding to IDM. Accordingly, the MIP was used as a solid-phase extraction sorbent for the extraction and enrichment of IDM in water samples. The extraction conditions of the MISPE column for IDM were optimized to be: chloroform or water as loading solvent, chloroform with 20% acetonitrile as washing solution, and methanol as eluting solvent. Water samples with or without spiking were extracted by the MISPE column and analyzed by HPLC. No detectable IDM was observed in tap water and the content of IDM in a river water sample was found to be 1.8 ng mL⁻¹. The extraction efficiencies of the MISPE column for IDM in spiked tap and river water were acceptable (87.2% and 83.5%, respectively), demonstrating the feasibility of the prepared MIP for IDM extraction. Figure Molecularly imprinted polymer-based solid-phase extraction for indomethacin     

Optical interrogation of molecularly imprinted polymers and development of MIP sensors: a review

This article reviews the progress and developments achieved in the past five years (2000–2005) in the application of optical analytical techniques to the evaluation of molecularly imprinted polymer (MIP) characteristics. The MIP binding efficiency, recognition processes and selectivity have been intensively studied by optical means due to the general high sensitivity and simplicity of the utilisation of optical techniques. In addition, recent progress in the covalent linkage of MIPs to optical transducers has allowed for the realisation of highly efficient and robust optical MIP-based molecular recognition sensors. The review provides insight into the various approaches to the optical interrogation of MIPs, and is organised according to the type of optical technique employed (fluorescence, UV/Vis and infrared spectroscopy, surface plasmon resonance, chemiluminescence, refractive interference spectroscopy and Raman scattering) and the detailed strategies applied. The review also covers the recent progress achieved in the area of optical sensors based on MIPs.     

Direct patterning of molecularly imprinted microdot arrays for sensors and biochips

We have used fountain pen microlithography to deposit arrays of molecularly imprinted polymer microdots on flat substrates. We visualize analyte binding to the dots by fluorescence microscopy with the aid of fluorescein as a model analyte. Elution and readsorption of the analyte to the MIP dots were possible if the porosity of the dots was improved by a sacrificial polymeric porogen. The imprinting effect was confirmed by using compounds structurally related to fluorescein. In addition, we show with another MIP specific to 2,4-D that, apart from the direct measurement of the binding of fluorescent compounds, a competitive immunoassay-type format can also be used to transduce the binding. We believe that this technique has a strong potential for the fabrication of biomimetic microchips and other types of integrated biosensors.     

Molecular imprinted polymer-based chemiluminescence imaging sensor for the detection of trans-resveratrol

Sensitive, rapid and inexpensive chemiluminescence (CL) imaging has been developed based on molecular imprinted polymer (MIP) sensing elements. Imprinted uniform microspheres were synthesized by precipitation polymerization. Microtiter plates (96 wells) were coated with polymer microspheres imprinted with trans-resveratrol, which were fixed in place using poly(vinyl alcohol) (PVA) as glue. The amount of polymer-bound trans-resveratrol was quantified using imidazole (IMZ)-catalyzed peroxyoxalate chemiluminescence (PO-CL) reaction. The light produced was then measured with a high-resolution CCD camera. Calibration curve corresponding to analyte concentration ranging from 0.3 to 25 μg mL⁻¹ was obtained with a limit of detection 0.1 μg mL⁻¹. These results showed that the MIP-based CL imaging sensor can become a useful analytical tool for quick simultaneous detection of trans-resveratrol in a large number of real samples.     

Optical sensors with molecularly imprinted nanospheres: a promising approach for robust and label-free detection of small molecules

Molecularly imprinted nanospheres obtained by miniemulsion polymerization have been applied as the sensitive layer for label-free direct optical sensing of small molecules. Using these particles as the sensitive layer allowed for improving response times in comparison to sensors using MIP layers. As a model compound, well-characterized nanospheres imprinted against l-Boc-phenylalanine anilide (l-BFA) were chosen. For immobilization, a simple concept based on electrostatic adsorption was used, showing its applicability to different types of surfaces, leading to a good surface coverage. The sensor showed short response times, good selectivity, and high reversibility with a limit of detection down to 60 μM and a limit of quantitation of 94 μM. Furthermore, reproducibility, selectivity, and long-term stability of the sensitive layers were tested. The best results were achieved with an adsorption on aminopropylsilane layers, showing a chip-to-chip reproducibility of 22%. Furthermore, the sensors showed no loss in signal after a storage time of 1 year.     

A novel molecularly imprinted electrochemiluminescence sensor for isoniazid detection

Based on Ru(bpy)(3)(2+)-Au nanoparticles decorated multi-walled carbon nanotubes composites and a molecularly imprinted polymer (MIP), we propose a novel molecularly imprinted electrochemiluminescence (ECL) sensor to selectively determine isoniazid (INH). The MIP is synthesized through electrochemical copolymerization of acrylamide and N,N'-methylene diacrylamide in the presence of INH template molecules. The enhanced ECL intensity is linear in the range of 0.1 to 110 μg cm(-3) and the detection limit is 0.08 μg cm(-3) (3σ) INH with relative standard deviation 3.8% (n = 6) for 8 μg cm(-3). As a result, the sensor has been successfully applied to the determination of INH in human urine and pharmaceutical samples. Moreover, the possible ECL mechanism is discussed.     

Molecularly imprinted polymer-based electrochemical sensor for the sensitive detection of glyphosate herbicide

A sensitive electrochemical molecularly imprinted sensor was developed for the detection of glyphosate (Gly), by electropolymerisation of p-aminothiophenol-functionalised gold nanoparticles in the presence of Gly as template molecule. The extraction of the template leads to the formation of cavities that are able to specifically recognise and bind Gly through hydrogen bonds between Gly molecules and aniline moieties. The performance of the developed sensor for the detection of Gly was investigated by linear sweep voltammetry using a hexacyanoferrate/hexacyanoferrite solution as redox probe, the electron transfer rate increasing when concentration of Gly increases, due to a p-doping effect. The molecularly imprinted sensor exhibits a broad linear range, between 1 pg/L and 1 µg/L and a quantification limit of 0.8 pg/L. The selectivity of the proposed sensor was investigated towards the binding of Gly metabolite, aminomethylphosphonic acid, revealing excellent selectivity towards Gly. The developed sensor was successfully applied to detect Gly in tap water samples.     

Thin-film electrochemical sensor for diphenylamine detection using molecularly imprinted polymers

This work reports on the development of a new voltammetric sensor for diphenylamine based on the use of a miniaturized gold electrode modified with a molecularly imprinted polymer recognition element. Molecularly imprinted particles were synthesized ex situ and further entrapped into a poly(3,4-ethylenedioxythiophene) polymer membrane, which was electropolymerized on the surface of the gold electrode. The thickness of the polymer layer was optimized in order to get an adequate diffusion of the target analyte and in turn to achieve an adequate charge transfer at the electrode surface. The resulting modified electrodes showed a selective response to diphenylamine and a high sensitivity compared with the bare gold electrode and the electrode modified with poly(3,4-ethylenedioxythiophene) and non-imprinted polymer particles. The sensor showed a linear range from 4.95 to 115 μM diphenylamine, a limit of detection of 3.9 μM and a good selectivity in the presence of other structurally related molecules. This sensor was successfully applied to the quantification of diphenylamine in spiked apple juice samples.     

Capturing molecules with templated materials--analysis and rational design of molecularly imprinted polymers

The creation of synthetic tailor-made receptors capable of recognizing desired molecular targets with high affinity and selectivity is a persistent long-term goal for researchers in the fields of chemical, biological, and pharmaceutical research. Compared to biomacromolecular receptors, these synthetic receptors promise simplified production and processing, less costs, and more robust receptor architectures. During recent decades, molecularly imprinted polymers (MIPs) are widely considered mimics of natural molecular receptors suitable for a diversity of applications ranging from biomimetic sensors, to separations and biocatalysis.A remaining challenge for the next generation of MIPs is the synthesis of deliberately designed and highly efficient receptor architectures suitable for recognizing biologically relevant molecules, for which natural receptors are either not prevalent, or difficult to isolate and utilize. Hence, this review discusses recent advances in synthetic receptor technology for biomolecules (e.g. drugs, amino acids, steroids, proteins, entire cells, etc.) via molecular imprinting techniques. Surface imprinting methods and epitope imprinting approaches have been introduced for protein recognition at imprinted surfaces. Imprinting techniques in aqueous solution or organic-water co-solvents have been introduced avoiding denaturation of biomolecules during MIP synthesis. In addition, improved bioreactivity of entire enzyme or active site mimics generated by molecular imprinting will be highlighted. Finally, the emerging importance of molecular modeling and molecular dynamics studies detailing the intermolecular interactions between the template species, the porogenic solvent molecules, and the involved monomer and cross-linker in the pre-polymerization solution will be addressed yielding a rational approach toward next-generation MIP technology.     

A highly selective molecularly imprinted electrochemiluminescence sensor for ultra-trace beryllium detection

A new molecularly imprinted electrochemiluminescence (ECL) sensor was proposed for highly sensitive and selective determination of ultratrace Be²⁺ determination. The complex of Be²⁺ with 4-(2-pyridylazo)-resorcinol (PAR) was chosen as the template molecule for the molecularly imprinted polymer (MIP). In this assay, the complex molecule could be eluted from the MIP, and the cavities formed could then selectively recognize the complex molecules. The cavities formed could also work as the tunnel for the transfer of probe molecules to produce sound responsive signal. The determination was based on the intensity of the signal, which was proportional to the concentrations of the complex molecule in the sample solution, and the Be²⁺ concentration could then be determined indirectly. The results showed that in the range of 7 × 10⁻¹¹ mol L⁻¹ to 8.0 × 10⁻⁹ mol L⁻¹, the ECL intensity had a linear relationship with the Be²⁺ concentrations, with the limit of detection of 2.35 × 10⁻¹¹ mol L⁻¹. This method was successfully used to detect Be²⁺ in real water samples.     

Ultrathin molecularly imprinted polymer sensors employing enhanced transmission surface plasmon resonance spectroscopy

An ultrathin novel nanosensor (31.5 +/- 4.1 nm thick in the absence of analytes), employing a molecularly imprinted polymer as a recognition element for cholesterol and gold nanoparticle enhanced transmission surface plasmon resonance spectroscopy for detection, was constructed.