Molecularly imprinted polyaniline molecular receptor–based chemical sensor for the electrochemical determination of melamine

Molecularly imprinted polymer‐modified glassy carbon electrode (GCE)‐based electrochemical sensor is prepared using the electropolymerization of aniline in the presence of melamine (MA) as a template. In this work, the advantages of molecularly imprinted conducting polymers (MICPs) and electroanalytical methods were combined to obtain an electronic device with better performances. The sensor performance was evaluated by cyclic voltammetry (CV) and square wave voltammetry (SWV) with the linear range of 0.6‐16 × 10^?9M, quantification limit of 14.9 × 10^?10M, and detection limit of 4.47 × 10^?10M (S/N = 3). The selectivity of the sensor was tested in the presence of acetoguanamine (AGA), diaminomethylatrazine (DMT), casein, histidine, and glycine interfering molecules taken at the triple concentration with MA that demonstrated too small current response compared with that of the analyte indicating high specificity of the sensor towards the template. The sensor was successfully applied to determine MA in infant formula samples with significant recovery greater than 96% and relative standard deviation (RSD) less than 4.8%. Moreover, the good repeatability, recyclability, and stability make this sensor device promising for the real‐time monitoring of MA in different food stuffs.     

Molecularly imprinted monolithic stationary phases for liquid chromatographic separation of tryptophan andN-CBZ-phenylalanine enantiomers

Monolithic molecularly imprinted columns were designed and prepared by anin-situ thermal-initiated copolymerization technique for rapid separation of tryptophan andN-CBZ-phenylalanine enantiomers. The influence of polymerization conditions and separation conditions on the specific molecular recognition ability for enantiomers and diastereomers was investigated. The specious molecular recognition was found to be dependent on the stereo structures and the arrangement of functional groups of the imprinted molecule and the cavities in the molecularly imprinted polymer (MIP). Moreover, hydrogen bonding interactions and hydrophobic interactions played an important role in the retention and separation. Compared to conventional MIP preparation procedures, the present method is very simple, and its macroporous structure has excellent separation properties.     

Molecularly imprinted polymers for drug delivery

Molecular imprinting technology has an enormous potential for creating satisfactory drug dosage forms. Although its application in this field is just at an incipient stage, the use of MIPs in the design of new drug delivery systems (DDS) and devices useful in closely related fields, such as diagnostic sensors, is receiving increasing attention. Examples of MIP-based DDS can be found for the three main approaches developed to control the moment at which delivery should begin and/or the drug release rate, i.e. rate-programmed, activation-modulated, or feedback-regulated drug delivery. The utility of these systems for administering drugs by different routes (e.g. oral, ocular or transdermal) or trapping undesired substances under in vivo conditions is discussed. This review seeks to highlight the more remarkable advantages of the imprinting technique in the development of new efficient DDS as well as pointing out some possibilities to adapt the synthesis procedures to create systems compatible with both the relative instable drug molecules, especially of peptide nature, and the sensitive physiological tissues with which MIP-based DDS would enter into contact when administered. The prospects for future development are also analysed.     

Molecularly imprinted polymer formats for capillary electrochromatography

The research aimed towards the adaptation of molecularly imprinted polymers (MIPs) to the capillary format and the use of these highly selective matrices for capillary electrochromatography (CEC) is reviewed in this article. The MIP is prepared by incorporation of a template molecule into a polymerization protocol. After polymerization and extraction of the template from the resulting polymer a highly selective material with recognition cavities complementary to the template in size, shape and chemical functionality is obtained. MIPs have been used as recognition elements in several different analytical techniques. In combination with CEC a novel separation system with a unique selectivity towards a predetermined target (the template) is achieved. The merge of molecular imprinting technology (MIT) and CEC have introduced several interesting polymer formats, due to the adaptation of the MIP to the miniaturized capillary format. The polymer formats can be classified according to their preparation protocols and appearance into three conceptually different categories, i.e. the monolith, the coating and the nanoparticles. The preparation protocols, characteristics and applications of these formats will be discussed.     

Molecularly imprinted polymer films for reflectometric interference spectroscopic sensors

Reflectometric interference spectroscopic measurements were performed on molecularly imprinted polymer (MIP) films with the herbicide atrazine as the template molecule. A conventional imprinting protocol was used relying on non-covalent interactions between the functional monomers and the template. The MIPs were deposited on glass transducers by two different methods: spin-coating followed by in situ polymerization of thin films of monomers containing a sacrificial polymeric porogen, and autoassembly of MIP nanoparticles with the aid of an associative linear polymer. Reproducible results were obtained upon measurements of atrazine solutions in toluene with both films. Atrazine concentrations as low as 1.7 ppm could be detected with the autoassembled particle film. No or very little analyte adsorption was observed onto non-imprinted control films made by spin-coating and by particle assembly, respectively. We believe that these MIP layers in combination with the general reflectrometric transduction scheme could be a versatile sensing tool for the detection of environmentally important and other analytes.     

Molecularly imprinted cryogel for L-glutamic acid separation

A molecular recognition based L-glutamic acid (L-GLU) imprinted cryogel was prepared for L-GLU separation via chromatographic applications. The novel functional monomer N-methacryloyl-(L)-glutamic acid-Fe(3+) (MAGA-Fe(3+) ) was synthesized to be complex with L-GLU. The L-GLU imprinted cryogel was prepared by free radical polymerization under semifrozen conditions in the presence of a monomer-template complex MAGA-Fe(3+) -L-GLU. The binding mechanism of MAGA-Fe(3+) and L-GLU was characterized by Fourier transform infrared (FTIR) spectroscopy in detail. FTIR analyses on the synthesized MAGA-Fe(3+) -GLU complex reveals bridging bidentate and monodentate binding modes of Fe(3+) in complex with the carboxylate groups of the glutamate residues. The template L-GLU could be reversibly detached from the cryogel to form the template cavities using a 100 mM solution of HNO(3) . The amount of adsorbed L-GLU was detected using the phenyl isothiocyanate method. The L-GLU adsorption capacity of the cryogel decreased drastically from 11.3 to 6.4 μmol g(-1) as the flow rate increased from 0.5 to 4.0 mL min(-1) . The adsorption onto the L-GLU imprinted cryogel was highly pH dependent due to electrostatic interaction between the L-GLU and MAGA-Fe(3+) . The PHEMAGA-Fe(3+) -GLU cryogel exhibited high selectivity to the corresponding guest amino acids (i.e., D-GLU, L-ASN, L-GLN, L-, and D-ASP). Finally, the L-GLU imprinted cryogel was recovered and reused many times, with no significant decrease in their adsorption capacities.     

Molecularly imprinted hollow sphere array for the sensing of proteins

Mono‐dispersed molecularly imprinted hollow spheres (MIHSs) for hemoglobin (Hb) were prepared by employing silica nanospheres as the sacrificial templates. The obtained hollow spheres with uniform particle size of 360 nm in diameter were characterized by transmission electron microscopy. The outstanding affinities of these MIHSs to the target protein were confirmed by adsorption experiment in aqueous solution. Adsorption equilibrium was achieved within 10 min while the binding capacity (Q_max) of Hb was 8.84 µmol g^–1 at pH7.0. Furthermore, the MIHSs were successfully assembled into a closely‐packed 3D colloidal array. The molecularly imprinted hollow sphere array (MIHSA) can selectively recognize Hb. As the concentration of Hb increased, the structure color of the MIHSA changed from blue to green, and turn to white finally with maximum red shift for 43 nm. The MIHSA showed promising potential for the naked‐eye detection of target Hb.

Reflection spectra of the MIHSA in response to different Hb concentrations (0.075–15 µmol L^–1)     

Molecularly imprinted polymers in pseudoimmunoassay

Immunoassays are a class of analytical techniques based on the selective affinity of a biological antibody for its antigen. Competitive binding assays, of which the radioimmunoassay (RIA) was the first example, are based on the competition between analyte and a labelled probe for a limited number of binding sites. Molecularly imprinted polymers (MIPs) have been shown to be suitable replacements for biological antibodies in such techniques. Molecularly imprinted sorbent assays (MIAs) similar to RIA have been developed for a range of analytes of clinical and environmental interest. Limits of detection and selectivities of such assays are often similar to those using biological antibodies. Some assays have been used for measurements directly in biological fluids. The field is reviewed and it is shown that some perceived disadvantages of MIPs do not hinder their application in competitive binding assays: many MIAs have been demonstrated in aqueous solvents, and it has been shown that the quantity of template required to prepare imprinted polymers can be drastically reduced, and that binding site heterogeneity is not a problem as long as the sites which bind the probe most strongly are selective. Finally, recent developments including assays in microtitre plates, the use of enzyme-labelled probes, flow-injection assays and a scintillation proximity MIA are discussed.     

Thermochemical study of amino acid imprinted polymer films

Molecularly imprinted polymers provide an alternative to traditional methods of amino acid analysis. The imprinted polymers are more robust and significantly less expensive than, for example, ELISA analysis. Amino acid imprinted nylon‐6 thin films were studied by differential scanning calorimetry and scanning electron microscopy. Endothermic peaks were observed for imprinted films at temperatures higher than that for pure nylon, indicating the formation of a more‐ordered, hydrogen bonded polymer. Removal of the amino acid from the imprinted film resulted in reversion to the peak observed for pure nylon‐6. Additives, β‐cyclodextrin and multiwalled carbon nanotubes, were added to the imprinted polymer solutions as a means to increase the porosity of the films. These studies resulted in alternative morphologies and calorimetric results that provide additional functionalities and applications for imprinted polymers. Copyright © 2015 John Wiley & Sons, Ltd.     

Molecularly imprinted polymer using-p-hydroxybenzoic acid, p-hydroxyphenylacetic acid and p-hydroxyphenylpropionic acid as templates.

Molecularly imprinted polymers (MIPs) using p-hydroxybenzoic acid (p-HB), p-hydroxyphenylacetic acid (p-HPA) and p-hydroxyphenylpropionic acid (p-HPPA) as templates were synthesized. The performance of the templates and their analogues on polymer-based high performance liquid chromatography (HPLC) columns was studied. The imprinting effect of the MIP using p-HB as template is more obvious than that of MIP using either p-HPA or p-HPPA as template, and the mixture of p-HB and p-HPA can be well separated on the MIP using p-HB as template, but not on the blank. Interestingly, the recognition of MIP (p-HB as the template) to p-HB showed a synergistic effect. The retention factor of p-HB is not the sum of those of phenol and benzoic acid. We also found that the imprinting effect decreased when increasing the concentration of acetic acid in mobile phase. The possible reason is that acetic acid molecules occupied the binding sites of the polymer, thereby decreasing the concentration of binding sites. Furthermore, polymers, which showed specificity to 3,4-dihydroxybenzoic acid, can be prepared with p-HB as template. It is thus possible to synthesize a specific polymer for a compound that is either expensive or unstable by using a structurally similar compound as template.     

分子印迹技术应用于血清中地高辛的快速检测

应用分子印迹的方法制备对地高辛有特异性吸附性能的印迹聚合物颗粒,再将颗粒与琼脂糖混合并固定于玻碳电极上制备成地高辛分子印迹聚合膜传感器,传感器可以特异性地结合模板分子地高辛且其电化学信号与模板浓度相关,再用它来检测血清中地高辛的含量。结果表明:分子印迹传感器具有制作简便、成本低、检测快速、特异性高、稳定性好等优点,检测下限为1.28 nmol/L,检测时间为5 min。     

Molecularly imprinted polymer with salicylaldehyde-Cu(OAc)2 as template

In the report molecularly imprinted polymer (MIP) with salicylaldehyde-Cu(OAc)(2) as the template was synthesized and characterized by SEM, porosity and elemental analysis. Copper acetate was introduced since salicylaldehyde alone cannot display imprinting effect for its intramolecular hydrogen bond. The strong coordination interaction between salicylaldehyde and copper acetate made the complex have high retention on the HPLC column based on the SAD-Cu(OAc)(2) imprinted polymer. Several structural analogues such as salicylaldoxime, sulfosalicylic acid, p-hydroxybenzaldehyde and their complexes with copper acetate were chosen to study the selectivity of the MIPs. The influence of acetic acid and H(2)O in methanol mobile phase was studied. The experimental results showed that small amount of either acetic acid or H(2)O in mobile phase would weaken the interaction between the complex and the polymer, therefore, the retention of the complex was lowered to a large extent, but that of salicylaldehyde remained almost unchanged. The polymer imprinted with the complex showed high selectivity to both the acetate and copper (II). In addition, the MIP showed an enhanced selectivity to its template compared with the polymer prepared without copper acetate.     

Molecularly imprinted polymer-based optical immunosensors

Molecularly imprinted polymers (MIPs) are artificial antibodies for a target molecule. The review focuses mainly on mechanistic steps involved in forming MIPs and the role of co-monomers and porogen. In addition, the electronic transition between different energy levels is explained with the help of the Jablonski diagram. Diverse receptor and target molecules for anchoring artificial MIPs are discussed, accentuating the synergetic effects obtained. The binding efficiency, selectivity, and sensitivity of various optical sensors are discussed intensively. In addition to this, we focused on synthesis, physical forms, characterization techniques, and microorganism detection of imprinted polymers. A brief investigation on the use of MIPs in cancer diagnosis is also included, and attention is extended to the important challenges faced in using imprinted polymers.     

Design and evaluation of thin and flexible theophylline imprinted polymer membrane materials

The aim of this work was to produce a thin, flexible and diffusion able molecularly imprinted polymeric matrix with good template accessibility. Membranes were prepared using a non‐covalent molecular imprinting approach and their physical characteristics and binding capabilities investigated. Two materials were used, a poly(tri‐ethyleneglycol dimethyacrylate‐co‐methyl methacrylate‐co‐methacrylic acid) copolymer containing 14% cross‐linker and a monomer (g) to porogen (ml) ratio of 1:0.5 (A), and a blend of poly(TEGMA‐co‐MAA) and polyurethane (B). The polyurethane was added to improve membrane flexiblity and stability. The polymers were characterized using AFM, SEM and nitrogen adsorption, whilst binding was evaluated using batch‐rebinding studies. For all membranes the specific surface area was low (<10 m²/g). MIP (A) films were shown to bind specifically at low concentrations but specific binding was masked by non‐specific interactions at elevated concentrations. Selectivity studies confirmed specificity at low concentrations. K_D approximations confirmed a difference in the population of binding sites within NIP and MIP films. The data also indicated that at low concentrations the ligand‐occupied binding site population approached homogeneity. Scanning electron microscopy images of membrane (B) revealed a complex multi‐layered system, however these membranes did not demonstrate specificity for the template. The results described here demonstrate how the fundamental parameters of a non‐covalent molecularly imprinted system can be successfully modified in order to generate flexible and physically tolerant molecularly imprinted thin films. Copyright © 2009 John Wiley & Sons, Ltd.     

Molecularly imprinted polymers: synthesis and characterisation

This short review aims to present, in clear English, a summary of the principal synthetic considerations pertaining to good practice in the polymerisation aspects of molecular imprinting, and is primarily aimed at researchers familiar with molecular imprinting methods but with little or no prior experience in polymer synthesis. It is our hope that this will facilitate researchers to plan their own syntheses of molecular imprints in a more logical and structured fashion, and to begin to appreciate the limitations of the present synthetic approaches in this molecularly complex area, as well as the scope for rationally designing improved imprinted materials in the future.     

Iron(II) phthalocyanine-modified carbon-paste electrode for potentiometric detection of ascorbic acid

A chemically modified electrode constructed by incorporating iron(II) phthalocyanine [Fe(II)Pc] into carbon-paste matrix was used as a sensitive potentiometric sensor for detection of ascorbic acid. The resulting electrode exhibits catalytic properties for the electrooxidation of ascorbic acid, and lowers the overpotential for the oxidation of this compound. The faster rate of electron transfer results in a near-Nernstian behavior of the modified electrode, and makes it a suitable potentiometric sensor for detection of ascorbic acid. A linear response in concentration range from 10(-6) to 10(-2) M (0.18--1800 microg ml(-1)) was obtained with a detection limit of 5 x 10(-7) M for the potentiometric detection of ascorbic acid. The modified electrode was used for the determination of ascorbic acid in vitamin preparations. The recovery was 97.2--102.4% for the vitamin added to the preparations with a relative standard deviation of less than 5%. The modified electrode exhibited a fast response time (<10 s),had good stability, and had an extended lifetime.     

Molecularly imprinted polymeric membranes

Molecularly imprinted polymeric membranes have been emerged since 1990. Among various kinds of molecular imprinting studies, the application of molecular imprinting to membrane separation is still a novel investigation. In the present review paper, molecularly imprinted polymeric membranes are summarized and examined. The application of molecular imprinting to membrane separation shortly leads to high performance separation membranes.     

Molecularly imprinted hydroxyapatite thin film for bilirubin recognition

A novel piezoelectric sensor has been developed for bilirubin (BR) detection, based on the modification of molecularly imprinted hydroxyapatite (HAP) film onto a quartz crystal by molecular imprinting and surface sol-gel technique. The performance of the developed BR biosensor was evaluated and the results indicated that a sensitive BR biosensor could be fabricated. The obtained BR biosensor presents high-selectivity monitoring of BR, better reproducibility, shorter response time (37 min), wider linear range (0.05-80μM) and lower detection limit (0.01μM). The analytical application of the BR biosensor confirms the feasibility of BR detection in serum sample.     

Molecularly imprinted composite cryogels for hemoglobin depletion from human blood

A molecularly imprinted composite cryogel (MICC) was prepared for depletion of hemoglobin from human blood prior to use in proteome applications. Poly(hydroxyethyl methacrylate) based MICC was prepared with high gel fraction yields up to 90%, and characterized by Fourier transform infrared spectrophotometer, scanning electron microscopy, swelling studies, flow dynamics and surface area measurements. MICC exhibited a high binding capacity and selectivity for hemoglobin in the presence of immunoglobulin G, albumin and myoglobin. MICC column was successfully applied in fast protein liquid chromatography system for selective depletion of hemoglobin for human blood. The depletion ratio was highly increased by embedding microspheres into the cryogel (93.2%). Finally, MICC can be reused many times with no apparent decrease in hemoglobin adsorption capacity. Copyright © 2014 John Wiley & Sons, Ltd.     

Development of a quantum dot molecularly imprinted polymer sensor for fluorescence detection of atrazine

Atrazine is a common agricultural pesticide which has been reported to occur widely in surface drinking water, making it an environmental pollutant of concern. In the quest for developing sensitive detection methods for pesticides, the use of quantum dots (QDs) as sensitive fluorescence probes has gained momentum in recent years. QDs have attractive and unique optical properties whilst coupling of QDs to molecularly imprinted polymers (MIPs) has been shown to offer excellent selectivity. Thus, the development of QD@MIPs based fluorescence sensors could provide an alternative for monitoring herbicides like atrazine in water. In this work, highly fluorescent CdSeTe/ZnS QDs were fabricated using the conventional organometallic synthesis approach and were then encapsulated with MIPs. The CdSeTe/ZnS@MIP sensor was characterized and applied for selective detection of atrazine. The sensor showed a fast response time (5 min) upon interaction with atrazine and the fluorescence intensity was linearly quenched within the 2–20 mol L^?1 atrazine range. The detection limit of 0.80 × 10^?7 mol L^?1 is comparable to reported environmental levels. Lastly, the sensor was applied in real water samples and showed satisfactory recoveries (92–118%) in spiked samples, hence it is a promising candidate for use in water monitoring.