Application of a Custom-Synthesized Molecularly Imprinted Polymer for the Selective Isolation of Total Glucose and Fructose from 100% Fruit Juice Samples Prior to Instrumental Analysis

This article presents a novel sample preparation strategy that employed a custom-synthesized glucose - fructose (G-F) specific molecularly imprinted polymer (MIP) powder as an adsorbent for the simultaneous and selective extraction, isolation and pre-concentration of total glucose and fructose from the complex and `dirty` sample matrix of ‘100%’ fruit juices purchased from retail shops in Palapye, Botswana. The prepared G-F MIP powder demonstrated high selectivity, effective extraction and isolation for glucose and fructose from real samples of `100%` fruit juice samples as evidenced by the calculated high extraction efficiencies (EEs) of over 90%, with low percentage relative standard deviations (%RSD) of below 7% for n=6, for both glucose and fructose when compared to the low EEs of below 25% by the non-imprinted polymer (NIP), regarded as the control. Furthermore, the G-F MIP showed lower selectivity towards the analogous molecules; maltose and lactose as supported by the low EEs of below 31%. With the high affinity for glucose and fructose, the selective sample preparation strategy proposed herein presented itself as a potential procedure to be employed to improve the accurate analysis of adulterated artificial sugar sweeteners that are usually illegally added to the so-called `100%` fruit juices by producers to improve their taste.

Development of an aflatoxin B1 specific molecularly imprinted solid phase extraction sorbent for the selective pre-concentration of toxic aflatoxin B1 from child weaning food, Tsabana

This paper presents the synthesis, optimization and application of a molecularly imprinted polymer (MIP) sorbent for the selective extraction and pre-concentration of the potent toxin, aflatoxin B1 (AFB1), from the child weaning food, Tsabana (manufactured in Serowe, Botswana). As a food safety regulatory measure, Tsabana must be cleared of hazardous aflatoxins, especially AFB1, before consumption. This is because AFB1 is the most common and potent of the aflatoxins commonly found in cereals. Accurate analysis of AFB1 is challenging because it exists in very low concentrations in complex, ‘dirty’ matrices such as food, making it difficult to detect using analytical instruments, even if these analytical techniques have sensitivities at the femto level. The MIP extraction sorbent synthesized in this paper deals with these challenges by selectively pre-concentrating AFB1 from real Tsabana samples, successfully achieving a pre-concentration factor of 5 and therefore significantly increasing ABF1 signal intensity for easier detection. Further advantages of this system include the short time (25.0 minutes) and reasonable optimal MIP dose (20.0 mg) needed for maximum AFB1 extraction by the sorbent. Scanning electron microscopy revealed that the prepared AFB1 powder particles have spherical geometries and reasonably small sizes (800 nm), two advantageous physical characteristics that are associated with excellent sorbent materials.

Molecular imprinted photonic crystal for sensing of biomolecules

Molecularly imprinted polymers (MIPs) are highly cross-linked polymers with high binding capacity and selectivity to the target molecules. MIPs become increasingly important because of the potential applications in drug delivery, purification and separation. In spite of the tremendous progress that has been made in the molecular imprinting field, many challenges remain to be addressed, especially in transforming the binding event into a detectable optical signal. The combination of photonic crystal and molecular imprinting technique is becoming a popular research idea. Compared to the conventional MIPs, the molecularly imprinted photonic crystal sensors (MIPCB) have the advantage of directly convert the molecule recognition process into optical signal. This review comprehensively summarizes various MIPCB, including the principle of molecular imprinted photonic crystal sensors, recent development, some challenges and effective strategies for MIPCB.

Development of protein-recognition SPR devices by combination of SI-ATRP with biomolecular imprinting using protein ligands

Molecularly imprinted polymer brush layers and gel layers with both a lectin (ConA) and an antibody-IgG as biomolecular ligands for a target protein were formed on surface plasmon resonance (SPR) sensor chips via surface-initiated atom transfer radical polymerization (SIATRP) without and with a crosslinker, respectively. While the IgG-imprinted brush layers chip had almost the same affinity constant for target IgG as the nonimprinted brush layer chip, the affinity constant of the IgG-imprinted gel layer chip was approximately twice than that of the nonimprinted gel layer chip. These indicate that chemical crosslinks are very important factor to create distinct molecular recognition sites by molecular imprinting. Thus, biomolecular imprinting that uses biomolecular ligands and crosslinkers enables us to design polymer layer chips with distinct molecular recognition sites with a strong affinity for a target biomolecule. The molecularly imprinted gel layers chips with lectin and antibody ligands are promising candidates for fabricating SPR sensor systems to monitor target biomolecules such as proteins.

Stabilized sensing of heparin in whole blood using the ‘gate effect’ of heparin-imprinted polymer grafted onto an electrode

A real-time heparin monitor is required to optimize the dosage of heparin and its antidote, protamine sulfate, during extracorporeal circulation procedures. The gate effect of molecularly imprinted polymer (MIP) is a potential tool for the rapid and selective sensing of heparin. We here present a method to stabilize the measurement of heparin concentration in whole blood using an MIP-grafted electrode. An initiator of radical polymerization, the diethyldithiocarbamicbenzyl group, was introduced onto the surface of an indium-tin oxide (ITO) electrode. Heparin sodium, methacryloxethyltrimethoxysilane, and acrylamide were dissolved in water, and methylenebisacrylamide was dissolved in dimethylformamide. A mixture of the two solutions was introduced into the 50 μm gap between the surfaces of a quartz crystal plate and the treated ITO electrode. Ultraviolet light was irradiated onto the surface of the ITO to graft the copolymer of the monomers, then the ITO was washed with a 1 M sodium chloride aqueous solution to remove the heparin template and obtain the MIP-grafted electrode. Cyclic voltammetry was performed with the MIP-grafted electrode in physiological saline or bovine whole blood containing 0-8 units/ mL heparin and 5 mM ferrocyanide as a redox marker, and the relationship between the current intensity and the heparin concentration was analyzed. The current intensity decreased as the heparin concentration in either saline or whole blood increased, and the sensitivity of the electrode to heparin in blood was approximately 52% of its sensitivity to heparin in saline. The grafted-electrode was washed with a protease-containing detergent (Sterizyme® S, Maruishi Pharmaceutical) between measurements in blood. The heparin-sensitivity of the washed electrode in blood was 77% of that in saline. No sensitivity to chondroitin sulfate C was observed but sensitivity to low molecular weight heparin was demonstrated. We thus conclude that selective and stable sensing of heparin can be achieved using an electrode grafted with heparinimprinted polymer.

Analysis of cooperative interactions in molecularly imprinted polymer nanoparticles

Cooperative binding is commonly observed in biological receptor systems. This study investigates whether it is possible to prepare nano-sized molecularly imprinted polymers (nanoMIPs) that show cooperative binding. NanoMIPs which exhibit cooperative binding would have increased affinity for immobilised template molecules making them useful for advanced applications in diagnostics and sensors. The use of a templatederivatised solid support provides a facile route to prepare nanoMIPs with surface imprints, and the method is ideally suited to study this topic. Although not observed during the course of this study, positive interbinding site cooperativity was hypothesised by way of an increase in the number of binding sites imprinted on the nanoMIPs, by increasing template density on the solid support surface. After synthesis, the affinity of nanoMIPs was analysed using surface plasmon resonance (SPR) technique. Under the conditions investigated, a ten fold increase in binding affinity was measured as template density was increased. SPR results could be explained by an increase in cooperative binding; however calculations showed that the increase in affinity was not significant enough to prove cooperative binding interactions. The main conclusion obtained was that MIP nanoparticles contain only one “high-affinity” binding site that interacts with immobilised template in an SPR assay.

Improved molecularly imprinted polymer grafted to porous polyethylene frits for the solid-phase extraction of thiabendazole from citrus sample extracts

In this paper, the improvement over a novel format for selective solid-phase extraction based on a molecularly imprinted polymer (MIP) is described. A small amount of MIP has been synthesized within the superficial pores of commercial polyethylene (PE) frits and attached to its surface using benzophenone (BP), a photo-initiator capable to start the polymerization from the surface of the support material. Key properties affecting the obtainment of a proper polymeric layer, such as polymerization time and kind of cross-linker were optimized. Prepared composite material was applied to the SPE of TBZ in real samples extracts, showing an impressive clean-up ability. Calibrations showed good linearity in the concentration range of 0.05–5.00 μg g-1, referred to the original solid sample, and the regression coefficients obtained were greater than 0.998. The calculated detection limit was 0.01 μg g-1, low enough to satisfactory analysis of TBZ in real samples. Mean recoveries were about 70 % at different concentration levels with RSDs always ranged below 15% in all the cases.

Recent Advances in Macromolecularly Imprinted Polymers by Controlled Radical Polymerization Techniques

Molecularly imprinted polymers (MIPs) are synthetic receptors with tailor-made recognition sites for the target molecules. Their high molecular recognition ability, good stability, easy preparation, and low cost make them highly promising substitutes for biological receptors. Recent years have witnessed rapidly increasing interest in the imprinting of biomacromolecules and especially proteins because of the great potential of these MIPs in such applications as proteome analysis, clinical diagnostics, and biomedicine. So far, some useful strategies have been developed for the imprinting of proteins and controlled radical polymerization techniques have proven highly versatile for such purpose. This mini-review describes recent developments in the controlled preparation of proteins-imprinted polymers via such advanced polymerization techniques.

ATP-binding peptide-hydrogel composite synthesized by molecular imprinting on beads

Molecular imprinting has been recognized as a useful technique to produce synthetic mimics of functional proteins, such as antibodies and enzymes. However, only a few studies have examined peptides as starting materials for synthesizing molecularly imprinted polymers in spite of the expectation that peptides would be suitable materials for realizing water-compatibility and proteinlike functions. In this study, molecular imprinting was performed using a vinyl-end-capped on-beads-peptide as functional monomer to produce an on-beads-peptide hydrogel composite selective for ATP; the on-beadspeptide peptide, of which sequence was designed to possess both an adenine-recognition site and phosphate recognition site, was co-polymerized with NIPAM and BIS in the presence of ATP as a template species. The resultant ATP-imprinted composite showed 14-times higher affinity and an enhanced selectivity towards ATP, suggesting that the peptide conformation, i.e. a mutual orientation of the two binding sites, was pre-organized and immobilized in a manner where the ATP binding is more favored.

Molecular imprinting in particle-stabilized emulsions: enlarging template size from small molecules to proteins and cells

Molecular imprinting of small organic compounds is now a standard procedure for preparation of tailor-designed affinity materials. Molecularly imprinted polymers (MIPs) have outstanding stability and can be prepared in a large quantity, therefore are useful replacements for biological receptors for a number of applications including product purification, analytical separation, chemical sensing and controlled delivery and biomineralization. Although preparation of MIPs, in particular using the non-covalent imprinting strategy, has become a routine practice in many research laboratories, new synthetic methods continued to be invented, which contribute to new MIPs with unprecedented functional performances. As the size of the template increases from small organic compounds to biomacromolecules to large virus particles and cells, the traditional methods of imprinting often fail to give useful MIP products. Another important aspect is the shift from organic solvents to water for MIPs designed for treatment or analysis of biological samples. The demand on water-compatibility and recognition of larger entities for MIPs call for new and efficient synthetic methods. This mini review will summarize the recent progress of molecular imprinting using particle-stabilized emulsion as a general synthetic platform to furnish the new MIPs with the desired functions.