Molecularly imprinted TiO2-matrix-assisted laser desorption/ionization mass spectrometry for selectively detecting alpha-cyclodextrin

This study describes a new means to conduct molecular recognition-based analysis using mass spectrometry. Taking advantage of the unique characteristic of the absorption capacity of the TiO(2) sol-gel material in the UV region, a TiO(2) sol-gel-deposited thin film was employed as the sample substrate to assist in UV laser desorption/ionization of analytes. Sol-gels are polymeric materials that are easy to prepare and modify at low temperatures. Molecularly imprinted TiO(2) sol-gels were generated for molecular recognition-based analysis. alpha-Cyclodextrin (CD) was selected as the template molecule and doped into TiO(2) in a sol-gel reaction. The molecularly imprinted TiO(2) sol was spin-coated on a glass slide, and appropriate template cavities in the TiO(2) sol-gel material were formed after the template molecules were removed. We demonstrate that this modified glass slide can be used to select alpha-CD from a sample solution containing equal amounts of alpha-, beta-, and gamma-CD (50 ppb each, 18 mL); alpha-CD was directly detected from the modified glass slide by matrix-assisted laser desorption/ionization mass spectrometry without the addition of extra matrix. This approach provides a new detection method for molecular recognition-based analysis.     

Different approaches to synthesize carnosine selective imprinted polymers

Selective recognition of proteins by synthetic molecularly imprinted polymers is one of the interesting topics in biosciences. Carnosine (β-alanyl-l-histidine) and related histidine containing peptides are distributed in a wide range of tissues in vertebrate organisms. These peptides have been extensively studied because of their important physiological properties besides their metal chelation property. In this study, preparation of carnosine specific imprinted polymers (MIPs) for the recognition of imidazole containing peptides with and without copper ion is reported. Carnosine and copper–carnosine complex were employed as template molecules where 4-vinylpyridine and ethylenglycol dimethacrylate were chosen as monomer and crosslinker, respectively. The selectivity and binding studies of copper–carnosine imprinted polymer showed high selectivity toward both carnosine (template peptide) and the cupric ion. The selectivity of copper–carnosine imprinted polymer was 65% and carnosine imprinted polymer was approximately 40%. These results indicate that specific recognition of carnosine is depending on the basis of metal coordination     

Molecularly imprinted electrosynthesized polymers: new materials for biomimetic sensors

The preparation and characterization of electrosynthesized poly(o-phenylenediamine) (PPD) imprinted by glucose (iPPD) is reported as the first case of an electrosynthesized polymer molecularly imprinted by a neutral template. The material is employed as the recognition element of a QCM biomimetic sensor for glucose. Scatchard analysis of the relevant calibration curve offers information on the equilibrium and binding sites involved in glucose detection. XPS comparison of PPD and iPPD supports the occurrence of a templating effect. On this basis, molecular imprinting electropolymerization is proposed as a possible strategy for the preparation of new materials with molecular recognition properties to be applied in biomimetic sensors.     

Chemiluminescent reaction of fluorescent organic compounds with KHSO5 using cobalt(II) as catalyst and its first application to molecular imprinting

The decomposition of peroxomonosulfate (HSO5-) has been investigated by chemiluminescence (CL). A weak CL was observed during mixing the HSO5- solution with the Co2+ solution in unbuffered conditions. An appropriate amount of fluorescent organic compounds (FOCs), such as dansyl amino acids and pyrene, was added to the KHSO5/Co2+ solution, a strong CL was recorded. A possible CL mechanism, based on studies of the fluorescence, CL, and UV-visible spectra and comparison of Co3+ oxidation ability with the SO4.- radical ion, was discussed. The CL from HSO5-/Co2+ is the emission of singlet oxygen produced from the catalytic decomposition of HSO5-. It was suggested that the decomposition of HSO5- in aqueous solution with Co2+ proceeds via one-electron transfer to yield SO4.- radical ion. The FOC was attacked by SO4.- radical ion and oxidized to decompose into small molecules. During this proceeding, CL emission was given out. The present CL system has been developed as a flow injection analysis for FOCs. The detection limits (S/N = 3) were in the concentration range 10(-9)-10(-7) M for FOCs. Oxidation decomposition and CL emission of the analytes have been used in the molecular imprinting recognition. As an initial attempt, dansyl-L-phenylalanine was used as a template molecule and methacrylic acid and 2-vinylpyridine were used as functional monomers. The network copolymer imprinted with dansyl-L-phenylalanine exhibits an affinity for the template molecule. When the flowing streams of HSO5- and Co2+ solutions mixing through the molecularly imprinted polymer particles filled the flow cell, the template molecule, dansyl-L-phenylalanine reacted with the HSO5-/Co2+ solution and CL was emitted. The dansyl-L-phenylalanine was decomposed during the CL process, and the cavities of a defined shape and an arrangement of functional groups complementary to the template in the polymer were left for the next sample analysis.     

Synthesis of molecularly imprinted polymer as a sorbent for solid phase extraction of citalopram from human serum and urine

This paper describes a new method for the determination of citalopram in biological fluids using molecularly imprinted solid-phase extraction as the sample cleanup technique combined with high performance liquid chromatography. The molecularly imprinted polymers were prepared using methacrylic acid as functional monomer, ethylene glycol dimethacrylate as crosslinker, chloroform as porogen and citalopram hydrobromide as the template molecule. The novel imprinted polymer was used as a solid-phase extraction sorbent for the extraction of citalopram from human serum and urine. Effective parameters on citalopram retention were studied. The optimal conditions for molecularly imprinted solid-phase extraction consisted of conditioning with 1 mL methanol and 1 mL of deionized water at neutral pH, loading of citalopram sample (50 μg L(-1)) at pH 9.0, washing using 1 mL acetone and elution with 3 × 1 mL of 10 % (v/v) acetic acid in methanol. The MIP selectivity was evaluated by checking several substances with similar molecular structures to that of citalopram. Results from the HPLC analyses showed that the calibration curve of citalopram using MIP from human serum and urine is linear in the ranges of 1-100 and 2-120 μg L(-1) with good precisions (2.5 and 1.5 % for 10.0 μg L(-1)), and recoveries (between 82-86 and 83-85 %), respectively.     

阿司匹林表面印迹微球的制备与药物缓释性能评价

采用表面印迹技术,选取γ-氨丙基三甲氧基硅烷(APTS)和甲基丙烯酰氯修饰的硅胶为载体,以阿司匹林(Asp)为模板分子,丙烯酰胺(AM)为功能单体,乙二醇二甲基丙烯酸酯(EDGMA)为交联剂,在乙腈溶液中合成了阿司匹林表面分子印迹聚合物微球(MIPs)和非印迹聚合物微球(NIPs)。通过紫外、红外光谱、扫描电镜、透射电镜、热重分析以及吸附实验进行了表征并进行了药物扩散实验。结果表明,MIPs平衡吸附量可达164.40μmol/g,对苯甲酸(BA)和水杨酸(SA)的分离因子达到3.15和3.32,有很好的热稳定性和选择性吸附能力;MIPs持续释药时间是NIPs的2.6倍,有很好的缓释效果和应用价值。     

Rational design of a polymer specific for microcystin-LR using a computational approach

A computational approach for the design of a molecularly imprinted polymer (MIP) specific for Cyanobacterial toxin microcystin-LR is presented. By using molecular modeling software, a virtual library of functional monomers was designed and screened against the target toxin, employed as a template. The monomers giving the highest binding energy were selected and used in a simulated annealing (molecular dynamics) process to investigate their interaction with the template. The stoichiometric ratio observed from the simulated annealing study was used in MIP preparation for microcystin-LR. The monomers were copolymerized with a cross-linker in the presence of the template. A control (blank) polymer was prepared under the same conditions but in the absence of template. A competitive assay with microcystin-horseradish peroxidase conjugate was optimized and used to evaluate the affinity and cross-reactivity of the polymer. The performance of the artificial receptor was compared to the performance of monoclonal and polyclonal antibodies raised against the toxin. The results indicate that imprinted polymer has affinity and sensitivity comparable to those of polyclonal antibodies (the detection limit for microcystin-LR using the MIP-based assay was found to be 0.1 microg L-1), while superior chemical and thermal stabilities were obtained. Moreover, cross-reactivity to other toxin analogues was very low for the imprinted polymer, in contrast to the results achieved for antibodies. It is anticipated that the polymer designed could be used in assays, sensors, and solid-phase extraction.     

Controlled fabrication of theophylline imprinted polymers on multiwalled carbon nanotubes via atom transfer radical polymerization

Theophylline imprinted polymers were synthesized on the surface of multiwalled carbon nanotubes via atom transfer radical polymerization using brominated multiwalled carbon nanotubes as an initiator. The nanotube-based initiator was prepared by directly reacting acyl chloride-modified multiwalled carbon nanotubes with 2-hydroxylethyl-2'-bromoisobutyrate. The grafting copolymerization of 2-hydroxyethyl-2-methyl-2-propenoate and ethylene glycol dimethacrylate in the presence of template theophylline led to thin molecularly imprinted polymer films coating multiwalled carbon nanotubes. The thickness of molecularly imprinted polymer films prepared in this study was about 5 nm as determined by transmission electron microscopy. Fourier-transform infrared spectroscopy was utilized to follow the introduction of initiator groups as well as polymers on the carbon nanotube surfaces. Thermogravimetric analysis indicated that the molecularly imprinted polymers were successfully grown from the carbon nanotube surfaces, with the final products having a polymer weight percentage of ca. 50 wt%. The adsorption properties, such as adsorption dynamics, special binding and selective recognition capacity, of the as-prepared molecularly imprinted polymer films were evaluated. The results demonstrated that the composite of molecularly imprinted polymers and multiwalled carbon nanotubes not only possessed a rapid dynamics but also exhibited a good selectivity toward theophylline, compared to caffeine.     

Probing the recognition of molecularly imprinted polymer beads

A facile, robust and cost-effective suspension polymerisation methodology for the generation of ibuprofen molecularly imprinted polymers in bead formats was evaluated. Mineral oil was employed as the continuous phase whereby microdroplets of the pre-polymerisation mixture were formed through vigorous agitation, followed by photo-polymerisation resulting in formation of imprinted beads. For comparison purposes, irregular particles were also prepared from monolith polymers. Physical characteristics of the imprinted polymers were investigated using scanning electron microscope, particle size distribution, nitrogen sorption porosimetry and solvent swelling ratios, with subsequent correlation of these parameters to analyte rebinding performance. Overall, an increase in affinity was observed with decreasing the degree of cross-linking, however, specific rebinding was compromised. An inverse relationship between polymer affinity for the template and surface area was identified, while solvent swelling ratios were directly related to polymer affinity. Correlation between pre-polymerisation studies and polymer binding performance highlighted the significance of employing the polymerisation solvent in template rebinding in order to achieve superior recognition capabilities. Additionally, shape selectivity of binding sites was demonstrated by the decreased binding performance of template structural analogues to the imprinted polymer.     

Exploiting β-cyclodextrin as functional monomer in molecular imprinting for achieving recognition in aqueous media

A series of molecularly imprinted polymers (MIPs) for 4,4′-(1,4-phenylenediisopropylidene)bisphenol (BPP) were prepared by using β-cyclodextrin (β-CD) as functional monomer, toluene 2,4-diisocyanate (TDI) or 4,4′-Diphenylmethane diisocyanate (DDI) as the cross-linker. The results of binding experiments showed that the MIPs can bind the template selectively in aqueous media. The binding specificity mechanism of the polymers was investigated in detail. The template molecule is too large and cannot be included in the cavity of one β-CD molecule. The mutual orientation of β-CD molecules in the imprinted polymers is regulated by molecular imprinting, so that they can cooperatively bind the template molecule. It is suggested that the major contribution to the recognition ability of the imprinted polymer was the stereo-shape effect inherent in the MIPs. The study indicated that hydrophobic effects play an important role in the recognition process.     

Method for synthesis and screening of large groups of molecularly imprinted polymers

A technique for the synthesis of molecularly imprinted polymers (MIPs) in small scale (～55 mg) coupled with direct in situ processing and batch rebinding evaluation is reported. The primary assessment is based on quantification by HPLC or UV absorbance measurement of the amount of template released from the polymer in a given solvent. This method allows a rapid screening of the parameters of importance to reach a desired level of binding affinity capacity and selectivity for a given target molecule. This was demonstrated for the triazine herbicide terbutylazine, where an initial screening was performed for the type of functional monomer used in the MIP preparation. Thus among the six functional monomers tested, methyl methacrylate, 4-vinylpyridine, and N-vinyl-α-pyrrolidone led to rapid and quantitative extraction whereas methacrylic acid and (trifluoromethyl)acrylic acid led to polymers that retained the template the most. After having established useful functional monomers, a secondary screening for selectivity was performed. In this, nonimprinted blank polymers were prepared and a normal batch rebinding evaluation was performed. The polymer showing the highest selectivity was the one prepared using methacrylic acid as functional monomer. This polymer was shown to strongly retain chlorotriazines including atrazine when a normal-scale batch of the polymer was evaluated in chromatography.     

Quartz crystal microbalance sensor for organic vapor detection based on molecularly imprinted polymers

Molecularly imprinted polymers on quartz crystal microbalances (QCM) are examined for their ability to detect vapors of small organic molecules with greater sensitivity and selectivity than the traditional amorphous polymer coatings. Hydroquinone and phenol serve as noncovalently bound templates that generate shape-selective cavities in a poly(acrylic) or poly(methacrylic) polymer matrix. The imprinted polymers are immobilized on the piezoelectric crystal surface via a precoated poly(isobutylene) layer. The behavior of the imprinted polymer films is characterized by the dynamic and steady-state response of the QCM frequency to pulses of organic vapors in dry air. The apparent partition coefficients are determined for imprinted and nonimprinted polymers prepared by two synthetic methods and for varying mole ratios of template to monomer. The hydroquinone-imprinted polymers and, to a lesser extent, the phenol-imprinted polymers exhibit greater sensitivity and higher selectivity than the nonimprinted polymers toward organic vapors that are structurally related to the templates. These results indicate that molecularly imprinted polymers are promising for the development of selective piezoelectric sensors for organic vapor detection.     

Determination of theophylline in serum by molecularly imprinted solid-phase extraction with pulsed elution

The technique of molecular imprinting is used to produce an extensively cross-linked poly(methacrylic acid-co-ethylene dimethacrylate) material that contains theophylline as a print molecule. After Soxhlet extraction of the theophylline, binding sites are formed in the polymer with complementary size, shape, and positioning of chemical functionalities. The molecularly imprinted polymer's (MIP) high theophylline selectivity, chemical stability, and physically robust nature make it an ideal stationary-phase material in columns for HPLC separation of theophylline from other structurally related drug compounds. Mobile-phase tests confirm that a retention mechanism typical of normal-phase chromatography governs the separation, and selectivity of the MIP column can be controlled by a combination of the mobile phase and the sample solvent. Under optimal conditions, the MIP column functions like a solid-phase sorbent for theophylline extraction. Rapid elution of the bound theophylline can be accomplished in a pulsed format through injection of 20 μL of a solvent that has the proper polarity and protic nature to disrupt the electrostatic interactions and hydrogen bonding between theophylline and binding sites. A concentration detection limit of 120 ng/mL is obtained using direct UV absorption detection at 270 nm, which corresponds to a mass detection limit of 2.4 ng. This new technique, molecularly imprinted solid-phase extraction with pulsed elution (MISPE-PE), permits on-line preconcentration of theophylline from a large volume of dilute sample solution. Using a sample volume of 300 μL, a 40 ng/mL standard solution produces a detectable peak signal. Application of MISPE-PE in serum analysis further demonstrates the high capability of the MIP column to selectively isolate theophylline from other matrix components for fast, accurate determination.     

Direct extraction of penicillin G and derivatives from aqueous samples using a stoichiometrically imprinted polymer

A molecularly imprinted polymer (MIP) prepared using penicillin G procaine salt as the template (PENGp) and a stoichiometric quantity of urea-based functional monomer to target the single oxyanionic species in the template molecule has been applied to the development of a molecularly imprinted solid-phase extraction (MISPE) procedure for the selective preconcentration of beta-lactam antibiotics (BLAs) from environmental water samples. Various parameters affecting the extraction efficiency of the polymer have been evaluated to achieve the selective preconcentration of the antibiotics from aqueous samples and to reduce nonspecific interactions. This resulted in an MISPE-HPLC method allowing the direct extraction of the analytes from the sample matrix with a selective wash using just 10% (v/v) organic solvent. On the basis of UV detection only, the method showed good recoveries and precision, ranging between 93% and 100% (RSD 3.8-8.9%, n = 3) for tap water and between 90% and 100% (RSD 4.2-9.1%, n = 3) for river water fortified with 30 or 60 microg L-1 (50 mL samples) penicillin G, penicillin V, nafcillin, oxacillin, cloxacillin, and dicloxacillin, suggesting that this MIP can be successfully applied to the direct preconcentration of BLAs in environmental water samples.     

Data on the structure and recognition properties of the template-selective binding sites in semi-IPN-based molecularly imprinted polymer membranes

Data on the structure and recognition properties of the template-selective binding sites in molecularly imprinted polymer membranes are presented. Porous molecularly imprinted polymer membranes based on semi-interpenetrating polymer networks (semi-IPN) were synthesized using the method of molecular imprinting in a combination with the method of computational modeling. Methacrylic acid, itaconic acid, and acrylamide were identified as optimal functional monomers for a model template — atrazine. Optimal ratios between atrazine and functional monomers as well as their binding energies were determined using the method of computational modeling and compared with the experimental data on the adsorbtion capability of porous molecularly imprinted polymer membranes. The factors influencing quality of the template-binding sites in MIP membranes (binding energy template-functional monomer and the number of functional groups taking part in the recognition of the template molecule) were revealed. The computational atrazine-selective membranes were capable of highly-selective and effective adsorbtion of atrazine from its 10^− 9–10^− 4 M aqueous solutions, and were characterized by high stability during prolonged storage. The apparent structure of the synthetic mimics of biological receptors to triazine herbicides was compared with the structure of their natural counterparts.     

单一结合位点分子印迹聚合物的合成及性能

采用分子自组装印迹技术在光引发条件下制备了以(S)-布洛芬为模板分子,α-甲基丙烯酸为功能单体的分子印迹聚合物。通过红外对聚合物的结构进行了表征。透射电镜结果表明,交联剂用量对印迹聚合物的形貌特征具有显著的影响。同时结合Scatchard分析研究了印迹聚合物的吸附性能及选择性识别能力,表明印迹聚合物特异性吸附容量为41μmol/g,印迹指数为2.28,对(S)-布洛芬形成单一结合位点,且表现出明显的吸附选择性。     

掺杂无机纳米粒子的阿魏酸分子印迹复合膜的制备

分子印迹膜是一种兼具分子印迹技术与膜分离技术双重优点的新兴技术,但由于有机膜的力学强度较小,在分离过程中容易使印迹孔穴的空间变形和互补官能团位置的失稳,使得其分离效率大大降低。文中使用紫外光引发原位聚合的方法,以聚偏氟乙烯(PVDF)作为支撑膜,将无机纳米材料和铸膜液共混制备了含有无机纳米材料的阿魏酸分子印迹复合膜。利用红外光谱和扫描电镜测试了膜的结构和表面形貌,发现纳米粒子是以纯物理方式共混的,且都分散在孔的周围,有利于维持膜的孔穴结构。通过平板超滤装置对改性膜的分离性能、水通量和承压能力进行了研究,结果表明,添加质量分数0.5%18 nm TiO_2的改性膜性能最好,承压能力在0.4 MPa以上,分离因子在3.4左右,水通量为6696 L/(m~2·h)。     

Patterning Nanostructured,Synthetic, Polymeric Receptors by Simultaneous Projection Photolithography,Nanomolding, and Molecular Imprinting

Microscope projection photolithography is combined with nanomolding and molecular imprinting for the fast microfabrication of molecularly imprinted polymer (MIP) arrays in the form of micrometric islands of nanofilaments. Dot diameters from 70–90 μm are easily obtained using a 10× objective and a photomask carrying the desired pattern. The dots are composed of parallel nanofilaments of a high aspect ratio, 150 nm in diameter and several micrometers in length, which are obtained through a nanomolding procedure on porous alumina. The arrays are molecularly imprinted with the small molecule fluorescein or with the protein myoglobin. The fluorescein MIP arrays are able to specifically recognize their target, as demonstrated by fluorescence microscopy. A four‐fold increase in binding capacity and imprinting factor (IF = 13) is obtained compared to non‐nanostructured porous dots. Imprinting of the nanofilament arrays with the protein myoglobin as the template is also possible and allows for a high imprinting factor of 4.3. Such nanostructured microarrays of synthetic receptors obtained by projection photolithography have great potential in biosensor and biochip development.     

Electropolymerized molecularly imprinted polymer films of a bis-terthiophene dendron: folic acid quartz crystal microbalance sensing

A folic acid sensor was prepared via an electropolymerized molecularly imprinted polymer (E-MIP) film of a bis-terthiophene dendron on a quartz crystal microbalance (QCM). The cyclic voltammetry (CV) electrodeposition of the imprinted polymer film was monitored by electrochemical QCM or E-QCM, enabling in situ monitoring and characterization of E-MIP film formation and the viscoelastic behavior of the film. A key component of the E-MIP process is the use of a bifunctional monomer design to precomplex with the template and function as a cross-linker. The complex was electropolymerized and cross-linked by CV to form a polythiophene matrix. Stable cavities were formed that specifically fit the size and shape of the folic acid template. The same substrate surface was used for folic acid sensing. The predicted geometry of the 1:2 folic acid/terthiophene complex was obtained through semiempirical AM1 quantum calculations. The analytical performance, expressed through the figures of merit, of the sensor in aqueous solutions of the analyte was investigated. A relatively good linearity, R(2) = 0.985, was obtained within the concentration range 0-100 μM folic acid. The detection limit was found to be equal to 15.4 μM (6.8 μg). The relative cross selectivity of the folic acid imprinted polymer against the three molecules follows this trend: pteroic acid (= 50%) > caffeine (= 41%) > theophylline (= 6%). The potential and limitations of the E-MIP method were also discussed.     

Protein recognition via surface molecularly imprinted polymer nanowires

In this paper, we present a technique for the preparation of polymer nanowires with the protein molecule imprinted and binding sites at surface. These surface imprinting nanowires exhibit highly selective recognition for a variety of template proteins, including albumin, hemoglobin, and cytochrome c. This recognition may be through a multistep adsorption, with the specificity conferred by hydrogen bonding and shape selectivity. Due to the protein imprinted sites are located at, or close to, the surface; these imprinted nanowires have a good site accessibility toward the target protein molecules. Furthermore, the large surface area of the nanowires results in large protein molecule binding capacity of the imprinted nanowires.