Synthetic cinchonidine receptors obtained by cross-linking linear poly(methacrylic acid) derivatives as an alternative molecular imprinting technique

A molecular imprinting approach to construct synthetic receptors was examined, wherein a linear pre-polymer bearing functional groups for intermolecular interaction with a given molecule is cross-linked in the presence of the molecule as a template, and subsequent removal of the template from the resultant network-polymer is expected to leave a complementary binding site. Poly(methacrylic acid) (PMAA) derivatized with a vinylbenzyl group as a cross-linkable side chain was utilized as the pre-polymer for the molecular imprinting of a model template, (-)-cinchonidine. Selectivity of the imprinted polymer was evaluated by comparing the retentions of the original template, (-)-cinchonidine and its antipode (+)-cinchonine in chromatographic tests, exhibiting a selectivity factor up to 2.4. By assessment of the imprinted polymers in a batch mode, a dissociation constant at 20 degrees C for (-)-cinchonidine was estimated to be K (d) = 2.35 x 10(-6) M (the number of binding sites: 4.54 x 10(-6) mol/g-dry polymer). The displayed affinity and selectivity appeared comparable to those of an imprinted polymer prepared by a conventional monomer-based protocol, thus showing that the pre-polymer, which can be densely cross-linked, is an alternative imprinter for developing template-selective materials. (-)-Cinchonidine-imprinted polymers were prepared and assessed using the pre-polymers bearing different densities of the vinylbenzyl group and different amounts of the cross-linking agent to examine the appropriate density of the cross-linking side chain that was crucial for developing the high affinity and selectivity of the imprinted polymers.     

New biomedical devices with selective peptide recognition properties. Part 1: Characterization and cytotoxicity of molecularly imprinted polymers

Molecular imprinting is a technique for the synthesis of polymers capable to bind target molecules selectively. The imprinting of large proteins, such as cell adhesion proteins or cell receptors, opens the way to important and innovative biomedical applications. However, such molecules can incur into important conformational changes during the preparation of the imprinted polymer impairing the specificity of the recognition cavities. The "epitope approach" can overcome this limit by adopting, as template, a short peptide sequence representative of an accessible fragment of a larger protein. The resulting imprinted polymer can recognize both the template and the whole molecule thanks to the specific cavities for the epitope. In this work two molecularly imprinted polymer formulations (a macroporous monolith and nanospheres) were obtained using the protected peptide Z-Thr-Ala-Ala-OMe, as template, and Z-Thr-Ile-Leu-OMe, as analogue for the selectivity evaluation, methacrylic acid, as functional monomer, and trimethylolpropane trimethacrylate and pentaerythritol triacrylate (PETRA), as cross-linkers. Polymers were synthesized by precipitation polymerization and characterized by standard techniques. Polymerization and rebinding solutions were analyzed by high performance liquid chromatography. The highly cross-linked polymers retained about 70% of the total template amount, against (20% for the less cross-linked ones). The extracted template amount and the rebinding capacity decreased with the cross-linking degree, while the selectivity showed the opposite behaviour. The PETRA cross-linked polymers showed the best recognition (MIP 2-, alpha=1.71) and selectivity (MIP 2+, alpha'=5.58) capabilities. The cytotoxicity tests showed normal adhesion and proliferation of fibroblasts cultured in the medium that was put in contact with the imprinted polymers.     

Synthesis of molecularly imprinted polymers using a functionalized initiator for chiral-selective recognition of propranolol

We present a new concept of synthesis for preparation of molecularly imprinted polymers using a functionalized initiator to replace the traditional functional monomer. Using propranolol as a model template, a carboxyl-functionalized radical initiator was demonstrated to lead to high-selectivity polymer particles prepared in a standard precipitation polymerization system. When a single enantiomer of propranolol was used as template, the imprinted polymer particles exhibited clear chiral selectivity in an equilibrium binding experiment. Unlike the previous molecular imprinting systems where the active free radicals can be distant from the template-functional monomer complex, the method reported in this work makes sure that the actual radical polymerization takes place in the vicinity of the template-associated functional groups. The success of using functional initiator to synthesize molecularly imprinted polymers brings in new possibilities to improve the functional performance of molecularly imprinted synthetic receptors.     

Molecularly imprinted micro and nanospheres for the selective recognition of 17beta-estradiol

A one-step precipitation polymerization procedure for the synthesis of molecularly imprinted polymers selective for 17beta-estradiol yielding imprinted micro and nanospheres was developed in this study and compared to templated materials obtained by conventional bulk polymerization. The polymer particles prepared by precipitation polymerization exhibited a regular spherical shape at the micro and nanoscale with a high degree of monodispersity. Moreover, the influence of the polymerization temperature, and the ratio of functional monomer to cross-linker on the size of the obtained particles was investigated. The selectivity of the imprinted micro and nanospheres was evaluated by HPLC analysis and via radioligand binding assays. HPLC separation experiments revealed that the imprinted microspheres provide higher or similar affinity to the template in contrast to imprinted polymers prepared by conventional bulk polymerization or synthesized by multi-step swelling/polymerization methods. The dimensions of the imprinted nanospheres facilitate suspension in solution rendering them ideal for binding assay applications. Results from saturation and displacement assays prove that the imprinted nanospheres exhibit superior specific affinity to the target molecule in contrast to control materials. The binding properties of the nanospheres including binding isotherms and affinity distribution were studied via Freundlich isotherm affinity distribution (FIAD) analysis. Moreover, release experiments show that 70% of rebound 17beta-estradiol was released from the imprinted nanospheres within the first 2 h, while more intimately bound 17beta-estradiol molecules (approx. 16%) were released in the following 42 h. Fitting Brunnauer-Emmet-Teller (BET) multi-point adsorption isotherms to the obtained results indicated that the micro and nanospheres are characterized by a comparatively homogenous and narrow distribution of mesopores in contrast to the corresponding bulk polymers.     

Synthesis and evaluation of a selective molecularly imprinted polymer for the contraceptive drug levonorgestrel

A molecularly imprinted polymer (MIP) has been prepared using levonorgestrel (LEV) as template. The polymer was synthesised in a non-covalent approach using methacrylic acid (MAA) as functional monomer and ethylene glycol dimethacrylate (EGDMA) as cross-linking monomer via a free radical polymerization. An equivalent blank polymer was also synthesised in the absence of the template compound. Batch adsorption experiments were used to evaluate the binding affinity of the imprinted polymer. After packing MIP into a stainless steel column (150 mm x 4.6 mm i.d.), retention and elution of the template and related compounds were evaluated by high-performance liquid chromatography (HPLC). This LEV imprinted polymer was further applied for selective solid phase extraction (SPE) of LEV from human serum. It was confirmed that the binding ability of the prepared MIP for LEV was essentially sufficient in the presence of other compounds coexisting in serum sample. Therefore, as a selective and efficient solid phase material, LEV imprinted polymer has a high potential application in analysis of this steroidal hormone in clinical purposes.     

An innovative approach to molecularly imprinted capillaries for polar templates by grafting polymerization

Molecularly imprinted polymers have been successfully used as selective stationary phases in capillary electrophoresis. Notwithstanding, this technique suffers from several drawbacks as the loss of molecular recognition properties in aqueous media and the lack of feasibility for imprinted systems directed towards highly polar templates soluble in aqueous environments only. Thus, the preparation of imprinted polymers for highly polar, water-soluble analytes, represents a challenge. In this work, we present an innovative approach to overcome these drawbacks. It is based on a surface molecular imprinting technique that uses preformed macromonomers as both functional recognition elements and cross-linking agents. A poly-2-hydroxyethyl-co-methacrylic acid linear polymer was grafted from the surface of silica capillaries. The grafted polymer was exhaustively esterified with methacrylic anhydride to obtain polyethylendimethacrylate-co-methacrylic acid linear chains. Then, as a proof of concept, an adequate amount of a very polar template like penicillin V was added in a hydro-organic mixture, and a thin layer of imprinted polymer was obtained by cross-linking the polymer linear chains. The binding behaviour of the imprinted and non-imprinted capillaries was evaluated in different separation conditions in order to assess the presence of template selectivity and molecular recognition effects. The experimental results clearly show that this innovative kind of imprinted material can be easily obtained in very polar polymerization environments and that it is characterized by enhanced molecular recognition properties in aqueous buffers and good selectivity towards the template and strictly related molecules.     

Development of fructosyl valine binding polymers by covalent imprinting

Molecularly imprinted polymers (MIPs) against fructosyl valine (Fru-Val), the N-terminal constituent of hemoglobin A1c β-chains, were prepared by cross-linking of β-d-Fru-Val-O-bis(4-vinylphenylboronate) with an excess of ethylene glycol dimethacrylate (EDMA) or trimethylolpropane trimethacrylate (TRIM). Control MIPs were prepared in analogy by cross-linking the corresponding vinylphenylboronate esters of fructose and pinacol. After template extraction batch rebinding studies were performed using different pH values and buffer compositions. The Fru-Val imprinted TRIM cross-linked polymer binds about 1.4 times more Fru-Val than the fructose imprinted polymer and 2.7 times more Fru-Val than pinacol imprinted polymer. The highest imprinting effect was obtained in 100 mM sodium carbonate/10% methanol (pH 11.4). The TRIM cross-linked Fru-Val imprinted polymer showed a better specificity than the EDMA cross-linked polymer. The binding of valine was very low. Thermo gravimetric analysis indicated that the generated Fru-Val imprinted polymer has high thermo stability. No change in binding was observed after incubation of the polymers in buffer at 80 °C for 36 h. Since the functional group of the polymers (phenyl boronic acid) targets the sugar part of Fru-Val the imprint technique used should also be applicable for the development of MIPs against other glycated amino acids and peptides.     

Molecular imprinted polymer with cloned bacterial protein template enriches authentic target in cell extract

Here we describe a new method for preparing a protein-imprinted polymer with a cloned bacterial protein template, which recognizes/adsorbs authentic target protein present at a relatively low level in cell extract. In this work, cloned pig cyclophilin 18 (pCyP18) was used as a template. The template protein was selectively assembled with memory molecules from their library, which consists of numerous limited length polymer chains with randomly distributed recognition sites and immobilizing sites. These assemblies of protein and memory molecules were adsorbed by porous polymeric beads and immobilized by cross-linking polymerization. After removing the template, binding sites that were complementary to the target protein in size, shape and the position of recognition groups were exposed, and their confirmation was preserved by the cross-linked structure. The synthesized imprinted polymer was used to adsorb authentic pCyP18 from cell extract, and its proportional content was enriched 300 times.     

Preparation of molecularly imprinted polymers using nitroxide-mediated living radical polymerization

The use of molecularly imprinted polymers (MIPs) in chemical and bioanalytical applications has been gaining in interest in recent years. Compared to their biological receptor counterparts, MIPs are easy to prepare, have long shelf stability and can be used under a variety of harsh conditions. The majority of MIPs currently used are produced by traditional free radical polymerization. One drawback with the use of standard free radical initiators is that little control can be exerted over the chemical processes that form the final imprinted cavities. In this study we set out to investigate the application of controlled (living) free radical polymerization to the preparation of MIPs. This was exemplified by the synthesis of cholesterol-imprinted bulk polymers by nitroxide-mediated polymerization (NMP). A sacrificial covalent bond was employed to maintain imprinting fidelity at elevated temperature. Selective uptake of cholesterol from solutions in hexane was studied with imprinted polymers prepared under different conditions. The imprinted hydrolyzed MIP prepared by NMP displayed higher selective cholesterol binding than that prepared by a traditional radical polymerization.     

Chiral separation using molecularly imprinted heteroaromatic polymers

Novel molecularly imprinted polymer systems utilizing 4-vinylpyridine and 1-vinylimidazole as functional monomers have been developed for enantioselective recognition of carboxylic and N-protected amino acids. Non-covalent interactions between the functional monomers and the template molecules were the source of the subsequent recognition sites in the resultant polymers. The capacity of the polymers for molecular recognition was investigated by using them as stationary phases in the HPLC mode. Polymers prepared with 4-vinylpyridine were found to be more efficient in racemic resolution than those prepared with 1-vinylimidazole. When applying a racemic mixture of the template molecule, the polymers showed highest affinity for the enantiomer used as template. Imprints of a racemic template molecule, as expected, did not exhibit enantioselectivity. The optimal molar ratio of 4-vinylpyridine to the template Cbz-L -Asp-OH in the polymerization mixture was determined to be 12:1. In addition to enantioselectivity, the investigated polymers demonstrated ‘ligand selectivity’ e.g., a Cbz-L -Asp-OH-imprinted polymer was able to separate Cbz-D ,L -Asp-OH, but was unable to separate Cbz-D ,L -Glu-OH.     

Binding site characteristics of 17beta-estradiol imprinted polymers

The variety of applications utilizing molecularly imprinted polymers (MIPs) requires synthetic strategies yielding different MIP formats including films, irregular particles, or spheres, along with precise knowledge on the specific material characteristics, such as binding capacity and binding efficiency of these materials. In response to this demand, MIPs are prepared in different formats by variation of the polymerization methodology. It is commonly agreed that micro- and sub-microspheres are particularly advantageous MIP formats, due to their monodispersity and facile synthesis procedures in contrast to conventional imprinted polymers prepared by bulk polymerization. However, the differences in actual rebinding characteristics of different MIP formats based on molecular interactions under a variety of binding/rebinding conditions have not been studied in detail to date. Consequently, the present work details an analytical strategy generically applicable to MIP systems for rebinding studies including equilibrium binding, non-equilibrium binding, and release experiments enabling more profound understanding on the molecular interactions between the imprinted materials and the template molecules. In this study, three MIP formats were considered for the same template molecule, 17beta-estradiol: irregularly shaped particulate polymers prepared by bulk polymerization and grinding, microspheres, and sub-microspheres. The latter two formats were synthesized via precipitation polymerization using different processing strategies. The morphologies and porosities of the resulting imprinted materials were characterized by scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) analysis, respectively. The obtained results indicate that microspheres prepared by precipitation polymerization provide superior rebinding properties during equilibrium binding in contrast to bulk polymers and sub-microspheres, and that the rebinding properties are different during equilibrium binding versus non-equilibrium binding. The median binding affinity constant determined during non-equilibrium rebinding is higher than the values obtained from equilibrium rebinding. Furthermore, the binding site distribution appears more homogeneous thief derived from non-equilibrium rebinding, as reflected in a heterogeneity index of m=0.725. Moreover, it is hypothesized that the specific interactions between template and monomers are related to the porosity of the imprinted polymers, which implies that the amount of binding sites and the pore sized distribution of the imprinted materials are a critical factor in achieving the desired MIP performance in various analytical applications. The BET results indicate that particles prepared with lower cross-linker-to-template ratio have a reduced surface area. Furthermore, it can be expected that there are less specific binding sites available at particles with reduced surface area and pore volume given similar distribution of the binding sites, as confirmed by the equilibrium binding isotherm studies. The pore size distribution results reveal that control of the pore size in the range of 100-180 A is essential to obtain the desired retention properties and Gaussian peak shape during HPLC analysis of small molecules.     

Probing the limits of molecular imprinting: strategies with a template of limited size and functionality

A series of polymers molecularly imprinted with the general anaesthetic propofol were synthesized using both semi- and non-covalent approaches. The polymers were evaluated with respect to template rebinding in both aqueous and organic media. In aqueous media, the observed propofol binding in these polymer systems was largely hydrophobic and non-specific in nature. In non-polar solvents such as hexane, electrostatic (hydrogen bonding) interactions dominate resulting in some selectivity. The implication of these results, in conjunction with those obtained using structures of similar size in other studies, is that propofol, a template possessing limited functionality and size, appears to define the lower limit for template size and degree of functionalization that can be used for the creation of ligand-selective recognition sites in molecularly imprinted polymers. Furthermore, studies with alternative ligands indicate that the steric crowding of a ligand's functionality to the polymer contributes to the extent of polymer-ligand recognition.     

Comparative study of the molecularly imprinted polymers prepared by reversible addition–fragmentation chain transfer “bulk” polymerization and traditional radical “bulk” polymerization

Bisphenol A (BPA) and propranolol‐imprinted polymers have been prepared via both reversible addition–fragmentation chain transfer “bulk” polymerization (RAFTBP) and traditional radical “bulk” polymerization (TRBP) under similar reaction conditions, and their equilibrium binding properties were compared in detail for the first time. The chemical compositions, specific surface areas, equilibrium bindings, and selectivity of the obtained molecularly imprinted polymers (MIPs) were systematically characterized. The experimental results showed that the MIPs with molecular imprinting effects and quite fast binding kinetics could be readily prepared via RAFTBP, but they did not show improved template binding properties in comparison with those prepared via TRBP, which is in sharp contrast to many previous reports. This could be attributed to the heavily interrupted equilibrium between the dormant species and active radicals in the RAFT mechanism because of the occurrence of fast gelation during RAFTBP. The findings presented here strongly demonstrates that the application of controlled radical polymerizations (CRPs) in molecular imprinting does not always benefit the binding properties of the resultant MIPs, which is of significant importance for the rational use of CRPs in generating MIPs with improved properties. Copyright © 2013 John Wiley & Sons, Ltd.     

Combinatorial screening of polymer precursors for preparation of benzo[α] pyrene imprinted polymer: an ab initio computational approach

A combinatorial screening procedure was used for the selection of polymer precursors in the preparation of molecularly imprinted polymer (MIP), which is useful in the detection of the air pollution marker molecule benzo[a]pyrene (BAP). Molecular imprinting is a technique for the preparation of polymer materials with specific molecular recognition receptors. The preparation of imprinted polymers requires polymer precursors such as functional monomer, cross-linking monomer, solvent, an initiator of polymerization and thermal or UV radiation. A virtual library of functional monomers was prepared based on interaction binding scores computed using HyperChem Release 8.0 software. Initially, the possible minimum energy conformation of the monomers and BAP were optimized using the semi-empirical (PM3) quantum method. The binding energy between the functional monomer and the template (BAP) was computed using the Hartree-Fock (HF) method with 6-31 G basis set, which is an ab initio approach based on Moller-Plesset second order perturbation theory (MP2). From the computations, methacrylic acid (MAA) and ethylene glycol dimethacrylate (EGDMA) were selected for preparation of BAP imprinted polymer. The larger interaction energy (ΔE) represents possibility of more affinity binding sites formation in the polymer, which provides high binding capacity. The theoretical predictions were complimented through adsorption experiments. There is a good agreement between experimental binding results and theoretical computations, which provides further evidence of the validity of the usefulness of computational screening procedures in the selection of appropriate MIP precursors in an experiment-free way.     

Room temperature synthesis and binding studies of solution‐processable histamine‐imprinted microspheres

Accurate quantification of histamine levels in food and in biological samples is important for monitoring the quality of food products and for the detection of pathophysiological conditions. In this study, solution processable histamine‐imprinted microspheres were synthesized at 30°C via dilute free radical phototochemical polymerization technique using ethylene glycol dimethacrylate (EGDMA) as the crosslinker and methacrylic acid (MAA) as the monomer. The processability of the resulting polymer is dictated by the monomer feed concentration (eg, 4 wt% 80:20 EGDMA:MAA formulation) and solvent (acetonitrile). Whereas, the particle size is influenced by the monomer feed concentration, the presence of template molecule, and independent of the crosslinker content. Evaluation of the binding performance of the photochemically imprinted polymers (PCP) with different crosslinker content (80 and 90 wt%) indicated that the selective binding capacity was notably higher in PCP‐80 (N= 16.0 μmol/g) compared to PCP‐90 (N= 10.1 μmol/g) when analyzed via frontal analysis capillary electrophoresis (FACE) using Freundlich isotherm. In addition, PCP‐80 microspheres are more selective toward histamine than conventional thermal polymers (CTP‐80) prepared at 60°C in the presence of structural analogs such as histidine, imidazole, and tryptamine under cross‐rebinding and competitive conditions. These results demonstrated that histamine‐selective imprinted polymers can be obtained readily using room temperature photochemical polymerization where these materials can be subsequently used as recognition element for optical‐based histamine sensing.     

Insight into molecular imprinting in precipitation polymerization systems using solution NMR and dynamic light scattering

Molecular imprinting is a powerful synthetic technique for generating template-defined binding sites in cross-linked polymers. One scientific challenge in molecular imprinting research is to understand the intermolecular interactions leading to molecular complexation and the process of binding site formation during polymerization. In this work, we present a novel method for studying the molecular imprinting process in precipitation polymerization systems. This method employs solution (1) H NMR and dynamic light scattering (DLS) to investigate the association of template molecules with colloidal particles and the dynamic process of particle growth. Under precipitation polymerization conditions, the colloidal particles formed did not interfere with NMR signals from the soluble components, allowing unreacted monomers and free template to be easily quantified. To examine the process of particle nucleation and growth, DLS was used to measure the hydrodynamic particle size at different reaction times. To corroborate the interpretation of the NMR and DLS results, imprinted nanoparticles were collected at different reaction times and their binding characteristics were evaluated using radioligand-binding analysis. Our experimental results provide new insights into the molecular imprinting process that will be useful in the development of new imprinted nanoparticles.     

Controlling size and uniformity of molecularly imprinted nanoparticles using auxiliary template

Molecularly imprinted nanomaterials are gaining substantial importance. As a simple and efficient synthetic method, precipitation polymerization has been used to prepare uniform molecularly imprinted microspheres for numerous template compounds. Despite of its general applicability, the difficulty of obtaining uniform particles for some difficult templates by precipitation polymerization has been reported. In this work, we attempted to produce uniform atrazine-imprinted nanoparticles using propranolol as an auxiliary template under standard precipitation polymerization condition. When propranolol was added in the prepolymerization mixture for atrazine imprinting, it displayed a significant effect on particle size and size distribution of atrazine-imprinted polymers. The molecular binding characteristics of the molecularly imprinted polymer (MIP) nanoparticles were found to be dependent on the relative ratios of the two templates. Under an optimal template propranolol-atrazine ratio of 1:3 mol/mol, very uniform imprinted nanoparticles (d(H) =?106?nm) with a polydispersity index of 0.07 were obtained. The loading of the auxiliary template (propranolol) could be reduced to as low as 5% without sacrificing the uniformity of the MIP nanoparticles. The uniform MIP nanoparticles could be easily encapsulated into polyethylene terephthalate nanofibers using a simple electrospinning technique. The composite nanofibers containing the MIP nanoparticles maintained specific molecular binding capability for both atrazine and propranolol.     

In situ synthesis of molecularly imprinted nanoparticles in porous support membranes using high-viscosity polymerization solvents

There is a growing need in membrane separations for novel membrane materials providing selective retention. Molecularly imprinted polymers (MIPs) are promising candidates for membrane functionalization. In this work, a novel approach is described to prepare composite membrane adsorbers incorporating molecularly imprinted microparticles or nanoparticles into commercially available macroporous filtration membranes. The polymerization is carried out in highly viscous polymerization solvents, and the particles are formed in situ in the pores of the support membrane. MIP particle composite membranes selective for terbutylazine were prepared and characterized by scanning electron microscopy and N? porosimetry. By varying the polymerization solvent microparticles or nanoparticles with diameters ranging from several hundred nanometers to 1 μm could be embedded into the support. The permeability of the membranes was in the range of 1000 to 20,000 Lm?2 hr?1 bar?1. The imprinted composite membranes showed high MIP/NIP (nonimprinted polymer) selectivity for the template in organic media both in equilibrium-rebinding measurements and in filtration experiments. The solid phase extraction of a mixture of the template, its analogs, and a nonrelated compound demonstrated MIP/NIP selectivity and substance selectivity of the new molecularly imprinted membrane. The synthesis technique offers a potential for the cost-effective production of selective membrane adsorbers with high capacity and high throughput.     

Electrochemical sensor for dopamine based on a novel graphene-molecular imprinted polymers composite recognition element

A novel composite of graphene sheets/Congo red-molecular imprinted polymers (GSCR-MIPs) was synthesized through free radical polymerization (FRP) and applied as a molecular recognition element to construct dopamine (DA) electrochemical sensor. The template molecules (DA) were firstly absorbed at the GSCR surface due to their excellent affinity, and subsequently, selective copolymerization of methacrylic acid (MAA) and ethylene glycol dimethacrylate (EGDMA) was further achieved at the GSCR surface. Potential scanning was presented to extract DA molecules from the imprinted polymers film, and as a result, DA could be rapidly and completely removed by this way. With regard to the traditional MIPs, the GSCR-MIPs not only possessed a faster desorption and adsorption dynamics, but also exhibited a higher selectivity and binding capacity toward DA molecule. As a consequence, an electrochemical sensor for highly sensitive and selective detection of DA was successfully constructed as demonstration based on the synthesized GSCR-MIPs nanocomposites. Under experimental conditions, selective detection of DA in a linear concentration range of 1.0 × 10(-7)-8.3 × 10(-4)M was obtained, which revealed a lower limit of detection and wider linear response compared to some previously reported DA electrochemical MIPs sensors. The new DA electrochemical sensor based on GSCR-MIPs composites also exhibited excellent repeatability, which expressed as relative standard deviation (RSD) was about 2.50% for 30 repeated analyses of 20 μM DA.     

Optimization of virus imprinting methods to improve selectivity and reduce nonspecific binding

Molecular imprinting is a technique that creates synthetic materials containing highly specific receptor sites that have an affinity for a target molecule. When large particles such as viruses are imprinted, special consideration must be taken to ensure the formation of complementary cavities. Factors that influence imprint formation, include uniformity of the precross-linked mixture and release of the virus template after cross-linking. In this study, tobacco mosaic virus (TMV) was used as a model virus. Polymer-virus aggregates formed when poly(allylamine hydrochloride) (PAA) was mixed with TMV at low polymer concentrations (<0.0001% w/v), but such aggregates were prevented at high polymer concentrations (>25% w/v). Various wash protocols were compared for their ability to remove the virus template from the cross-linked molecularly imprinted polymer (MIP), with sodium hydroxide (1 M) exhibiting the best performance. On the basis of these results, optimized MIPs targeted for TMV virus were synthesized, exhibiting a high affinity to TMV (imprinting factor of 2.3) and low affinity to tobacco necrosis virus, the nontarget virus.