Polymer Cookery: Influence of Polymerization Conditions on the Performance of Molecularly Imprinted Polymers

MIP-based immunoassays: A critical review

Molecularly imprinted polymers, MIPs, are man-made receptors mimicking the thermodynamic and kinetic binding behaviour of natural antibodies. Therefore, it is not surprising that many researchers have thought about MIPs as artificial receptors in immunoassay-like analytical applications, where the general machinery of the assay is maintained, but the molecular recognition is no longer assured by an antibody but by an artificial receptor. However, the number of papers devoted explicitly to applications of MIPs in the immunoassay field is quite limited if compared to the huge number of papers covering the multifaceted molecular imprinting technology. For this reason, this critical review wants to give a general view of MIP-based immunoassays, trying to highlight the critical points that have so far prevented a wider application of molecular imprinting technology in the immunoassay field and, possibly, try to suggest strategies to overcome them.

A rapid synthesis of molecularly imprinted polymer nanoparticles for the extraction of performance enhancing drugs (PIEDs)

It is becoming increasingly more significant to detect and separate hormones from water sources, with the development of synthetic recognition materials becoming an emerging field. The delicate nature of biological recognition materials such as the antibodies means the generation of robust viable synthetic alternatives has become a necessity. Molecularly imprinted nanoparticles (NanoMIPs) are an exciting class that has shown promise due the generation of high-affinity and specific materials. While nanoMIPs offer high affinity, robustness and reusability, their production can be tricky and laborious. Here we have developed a simple and rapid microwaveable suspension polymerisation technique to produce nanoMIPs for two related classes of drug targets, Selective Androgen Receptor Modulators (SARMs) and steroids. These nanoMIPs were produced using one-pot microwave synthesis with methacrylic acid (MAA) as the functional monomer and ethylene glycol dimethacrylate (EGDMA) as a suitable cross-linker, producing particles of an approximate range of 120-140 nm. With the SARMs-based nanoMIPs being able to rebind 94.08 and 94.46% of their target molecules (andarine, and RAD-140, respectively), while the steroidal-based nanoMIPs were able to rebind 96.62 and 96.80% of their target molecules (estradiol and testosterone, respectively). The affinity of nanoMIPs were investigated using Scatchard analysis, with Ka values of 6.60 × 106, 1.51 × 107, 1.04 × 107 and 1.51 × 107 M-1, for the binding of andarine, RAD-140, estradiol and testosterone, respectively. While the non-imprinted control polymer (NIP) shows a decrease in affinity with Ka values of 3.40 × 104, 1.01 × 104, 1.83 × 104, and 4.00 × 104 M-1, respectively. The nanoMIPs also demonstrated good selectivity and specificity of binding the targets from a complex matrix of river water, showing these functional materials offer multiple uses for trace compound analysis and/or sample clean-up.

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.

Recent Progress in Rapid Determination of Mycotoxins Based on Emerging Biorecognition Molecules: A Review

Mycotoxins are secondary metabolites produced by fungal species, which pose significant risk to humans and livestock. The mycotoxins which are produced from Aspergillus, Penicillium, and Fusarium are considered most important and therefore regulated in food- and feedstuffs. Analyses are predominantly performed by official laboratory methods in centralized labs by expert technicians. There is an urgent demand for new low-cost, easy-to-use, and portable analytical devices for rapid on-site determination. Most significant advances were realized in the field bioanalytical techniques based on molecular recognition. This review aims to discuss recent progress in the generation of native biomolecules and new bioinspired materials towards mycotoxins for the development of reliable bioreceptor-based analytical methods. After brief presentation of basic knowledge regarding characteristics of most important mycotoxins, the generation, benefits, and limitations of present and emerging biorecognition molecules, such as polyclonal (pAb), monoclonal (mAb), recombinant antibodies (rAb), aptamers, short peptides, and molecularly imprinted polymers (MIPs), are discussed. Hereinafter, the use of binders in different areas of application, including sample preparation, microplate- and tube-based assays, lateral flow devices, and biosensors, is highlighted. Special focus, on a global scale, is placed on commercial availability of single receptor molecules, test-kits, and biosensor platforms using multiplexed bead-based suspension assays and planar biochip arrays. Future outlook is given with special emphasis on new challenges, such as increasing use of rAb based on synthetic and naïve antibody libraries to renounce animal immunization, multiple-analyte test-kits and high-throughput multiplexing, and determination of masked mycotoxins, including stereoisomeric degradation products.

Molecularly imprinted polymers by epitope imprinting: a journey from molecular interactions to the available bioinformatics resources to scout for epitope templates

The molecular imprinting of proteins is the process of forming biomimetics with entailed protein-recognition by means of a template-assisted synthesis. Protein-imprinted polymers (pMIPs) have been successfully employed in separations, assays, sensors, and imaging. From a technical point of view, imprinting a protein is both costly, for protein expression and purification, and challenging, for the preservation of the protein's structural properties. In fact, the imprinting process needs to guarantee the preservation of the same protein three-dimensional conformation that later would be recognized. So far, the captivating idea to imprint just a portion of the protein, i.e., an epitope, instead of the whole, proved successful, offering reduced costs, compatibility with many synthetic conditions (solvents, pH, temperatures), and fine-tuning of the peptide sequence so to target specific physiological and functional conditions of the protein, such as post-translational modifications. Here, protein-protein interactions and the biochemical features of the epitopes are inspected, deriving lessons to prepare more effective pMIPs. Epitopes are categorized in linear or structured, immunogenic or not, located at the protein's surface or buried in its core and the imprinting strategies are discussed. Moreover, attention is given to freely available online bioinformatics resources that might offer key tools to gain further rationale amid the selection process of suitable epitopes templates.

Evaluation of acrylamide-based molecularly imprinted polymer thin-sheets for specific protein capture-a myoglobin model

We evaluate a series of thin-sheet hydrogel molecularly imprinted polymers (MIPs), using a family of acrylamide-based monomers, selective for the target protein myoglobin (Mb). The simple production of the thin-sheet MIP offers an alternative biorecognition surface that is robust, stable and uniform, and has the potential to be adapted for biosensor applications. The MIP containing the functional monomer N-hydroxymethylacrylamide (NHMAm), produced optimal specific rebinding of the target protein (Mb) with 84.9% (± 0.7) rebinding and imprinting and selectivity factors of 1.41 and 1.55, respectively. The least optimal performing MIP contained the functional monomer N,N-dimethylacrylamide (DMAm) with 67.5% (± 0.7) rebinding and imprinting and selectivity factors of 1.11 and 1.32, respectively. Hydrogen bonding effects, within a protein-MIP complex, were investigated using computational methods and Fourier transform infrared (FTIR) spectroscopy. The quantum mechanical calculations predictions of a red shift of the monomer carbonyl peak is borne-out within FTIR spectra, with three of the MIPs, acrylamide, N-(hydroxymethyl) acrylamide, and N-(hydroxyethyl) acrylamide, showing peak downshifts of 4, 11, and 8 cm⁻¹, respectively.

Generation of High-Affinity Molecularly Imprinted Nanoparticles for Protein Recognition via a Solid-Phase Synthesis Protocol

Molecularly imprinted polymers are leading technology in the development of protein biomimetics. This chapter describes the protocol for the synthesis of protein imprinted nanoparticles. These materials exhibit exceptional affinity (into the nM/pM range) and selectivity for their target template. The nanoparticles can be developed for a wide range of targets, while exhibiting excellent robustness, solubility, and flexibility in use. They are finding use in the creation of drug delivery vectors and sensing and recognition assays.

Hybrid aptamer-molecularly imprinted polymer (AptaMIP) nanoparticles selective for the antibiotic moxifloxacin

A polymerisable aptamer incorporated into Molecularly Imprinted Polymer nanoparticles (MIPs) creates a hybrid “best-of-both-worlds” approach which outperforms individual constituent components.

Effect of polymerisation by microwave on the physical properties of molecularly imprinted polymers (MIPs) specific for caffeine

Synthesis of Molecularly Imprinted Polymers by microwave irradiation is significantly affected by applied power.

Halloysite nanotubes in analytical sciences and in drug delivery: A review

Halloysite (HNT) is a natural inorganic mineral that has many applications in manufacturing. This review (with 192 references) covers (a) the chemical properties of halloysites, (b) the effects of alkali and acid etching on the loading capacity and the release behavior of halloysites, (c) the use of halloysite nanotubes in analytical sciences and drug delivery, and (d) recent trends in the preparation of magnetic HNTs. Synthetic methods such as co-precipitation, thermal decomposition, and solvothermal method are discussed, with emphasis on optimal magnetization. In the analytical field, recent advancements are summarized in terms of applications of HNT-nanocomposites for extraction and detection of heavy metal ions, dyes, organic pollutants, and biomolecules. The review also covers methods for synthesizing molecularly imprinted polymer-modified HNTs and magnetic HNTs. With respect to drug delivery, the toxicity, techniques for drug loading and the various classes of drug-halloysite nanocomposites are discussed. This review gives a general insight on the utilization of HNT in analytical determination and drug delivery systems which may be useful for researchers to generate new ideas. Graphical abstract Schematic presentation of the structure of halloysite nanotubes, selected examples of modifications and functionalization, and represetative field of applications.

Preparation of core–shell ion imprinted nanoparticles via photoinitiated polymerization at ambient temperature for dynamic removal of cobalt in aqueous solution

In this work, novel core–shell ion imprinted polymers were firstly synthesized by photoinitiated polymerization (P-IIPs) for the selective separation of Co(ii) in aqueous solution.

Layer-by-layer assembly of low-temperature-imprinted poly(methacrylic acid)/gold nanoparticle hybrids for gaseous formaldehyde mass sensing

New gas-sensing materials capable of selectively detecting sub-ppm levels of formaldehyde with fast response and recovery kinetics are designed by layer-by-layer assembly of imprinted polymer and Au nanoparticles.

PEG-stabilized core-shell surface-imprinted nanoparticles

Here we present a simple technique to produce target-specific molecularly imprinted polymeric nanoparticles (MIP NPs) and their surface modification in order to prevent the aggregation process that is ever-present in most nanomaterial suspensions/dispersions. Specifically, we studied the influence of surface modification of MIP NPs with polymerizable poly(ethylene glycol) on their degree of stability in water, in phosphate buffer, and in the presence of serum proteins. Grafting a polymer shell on the surface of nanoparticles decreases the surface energy, enhances the polarity, and as a result improves the dispersibility, storage, and colloidal stability as compared to those of core (unmodified) particles. Because of the unique solid-phase approach used for synthesis, the binding sites of MIP NPs are protected during grafting, and the recognition properties of nanoparticles are not affected. These results are significant for developing nanomaterials with selective molecular recognition, increased biocompatibility, and stability in solution. Materials synthesized this way have the potential to be used in a variety of technological fields, including in vivo applications such as drug delivery and imaging.

Solid-Phase Synthesis of Molecularly Imprinted Polymer Nanoparticles with a Reusable Template - "Plastic Antibodies"

Molecularly Imprinted Polymers (MIPs) are generic alternatives to antibodies in sensors, diagnostics and separations. To displace biomolecules without radical changes in infrastructure in device manufacture, MIPs should share their characteristics (solubility, size, specificity and affinity, localized binding domain) whilst maintaining the advantages of MIPs (low-cost, short development time and high stability) hence the interest in MIP nanoparticles. Herein we report a reusable solid-phase template approach (fully compatible with automation) for the synthesis of MIP nanoparticles and their precise manufacture using a prototype automated UV photochemical reactor. Batches of nanoparticles (30-400 nm) with narrow size distributions imprinted with: melamine (d = 60 nm, Kd = 6.3 × 10-8 m), vancomycin (d = 250 nm, Kd = 3.4 × 10-9 m), a peptide (d = 350 nm, Kd = 4.8 × 10-8 m) and proteins have been produced. Our instrument uses a column packed with glass beads, bearing the template. Process parameters are under computer control, requiring minimal manual intervention. For the first time we demonstrate the reliable re-use of molecular templates in the synthesis of MIPs (≥ 30 batches of nanoMIPs without loss of performance). NanoMIPs are produced template-free and the solid-phase acts both as template and affinity separation medium.

Surface-modified multifunctional MIP nanoparticles

The synthesis of core-shell molecularly imprinted polymer nanoparticles (MIP NPs) has been performed using a novel solid-phase approach on immobilised templates. The same solid phase also acts as a protective functionality for high affinity binding sites during subsequent derivatisation/shell formation. This procedure allows for the rapid synthesis, controlled separation and purification of high-affinity materials, with each production cycle taking just 2 hours. The aim of this approach is to synthesise uniformly sized imprinted materials at the nanoscale which can be readily grafted with various polymers without affecting their affinity and specificity. For demonstration purposes we grafted anti-melamine MIP NPs with coatings which introduce the following surface characteristics: high polarity (PEG methacrylate); electro-activity (vinylferrocene); fluorescence (eosin acrylate); thiol groups (pentaerythritol tetrakis(3-mercaptopropionate)). The method has broad applicability and can be used to produce multifunctional imprinted nanoparticles with potential for further application in the biosensors, diagnostics and biomedical fields and as an alternative to natural receptors.

Enantioseparations by high-performance liquid chromatography using molecularly imprinted polymers

Molecularly imprinted polymers (MIPs) are becoming increasingly useful as chromatographic adsorbents for molecular separations, especially chiral separations, because they can be tailored to specifically recognize the target molecule including its stereochemistry. Traditionally formed MIPs (as described here) are stable under ambient conditions for years, take only days to make, and use relatively inexpensive components, with the possible exception of the template in some cases which can be reused after it is removed from the polymer to keep costs down. In addition to providing experimental details for typical synthetic methods to fabricate MIPs and pack them into HPLC columns, this chapter also gives an overview of the concepts of molecular imprinting method and discusses important factors for designing an effective imprinted polymer.

Preparation and evaluation of a molecularly imprinted polymer for the selective recognition of testosterone--application to molecularly imprinted sorbent assays

Biomimetic testosterone receptors were synthesized via molecular imprinting for use as antibody mimics in immunoassays. As evaluated by radioligand binding assays, imprinted polymers prepared in acetonitrile were very specific for testosterone because the nonimprinted control polymers bound virtually no radiolabeled testosterone. The polymers present an appreciable affinity, with association constants of K(a) = 3.3 x 10(7) M(- 1) (high-affinity binding sites). The binding characteristics of the polymers were also evaluated in aqueous environment to study their viabilities as alternatives to antibodies in molecularly imprinted sorbent assays. Compared with the testosterone-specific antibodies present in commercial kits, our molecularly imprinted polymers are somewhat less sensitive but show a high selectivity.

A path to soluble molecularly imprinted polymers

Molecular imprinting is a technique for making a selective binding site for a specific chemical. The technique involves building a polymeric scaffold of molecular complements containing the target molecule. Subsequent removal of the target leaves a cavity with a structural “memory” of the target. Molecularly imprinted polymers (MIPs) can be employed as selective adsorbents of specific molecules or molecular functional groups. In addition, sensors for specific molecules can be made using optical transduction through lumiphores residing in the imprinted site. We have found that the use of metal ions as chromophores can improve selectivity due to selective complex formation. The combination of molecular imprinting and spectroscopic selectivity can result in sensors that are highly sensitive and nearly immune to interferences. A weakness of conventional MIPs with regard to processing is the insolubility of crosslinked polymers. Traditional MIPs are prepared either as monoliths and ground into powders or are prepared in situ on a support. This limits the applicability of MIPs by imposing tedious or difficult processes for their inclusion in devices. The size of the particles hinders diffusion and slows response. These weaknesses could be avoided if a means were found to prepare individual macromolecules with crosslinked binding sites with soluble linear polymeric arms. This process has been made possible by controlled free radical polymerization techniques that can form pseudo-living polymers. Modern techniques of controlled free radical polymerization allow the preparation of block copolymers with potentially crosslinkable substituents in specific locations. The inclusion of crosslinkable mers proximate to the binding complex in the core of a star polymer allows the formation of molecularly imprinted macromolecules that are soluble and processable. Due to the much shorter distance for diffusion, the polymers exhibit rapid responses. This paper reviews the methods that have been employed for the trace determination of organophosphates in real world samples using MIPs.

Surface Nano-patterning of Polymers for Mass-Sensitive Biodetection

The crafting of sensor material of desired features has always remained a challenging task in the field of material designing and predominantly becomes more interesting when analyte belongs to biospecies. Label-free detection of different bioanalytes such as enzymes, viruses, microorganisms, and blood groups through mass-sensitive transducers has gained considerable importance in the development of modern biosensors. Analyte molecules interact with the surface of sensitive layer coated on these devices and as a result of this interaction, the frequency change is determined, which provides quantitative information about the mass of analyte. One of the most vital elements of these detection systems is to design selective sensor coatings through control surface structuring at nanoscale. Molecular imprinting has proven to be a highly suitable technique to generate selective surfaces that are capable of detecting different analytes, quantitatively and qualitatively as well. The tailor-made synthetic antibody cavities are rigid and stable, which are not immediately collapsed upon analyte interaction; moreover, the different bioanalytes do not undergo any phase change and maintain their original identity during analysis. This chapter will discuss the contribution of imprinting methods to design optimized surfaces for mass-sensitive detection of diverse biological species.

Advances in the manufacture of MIP nanoparticles

Molecularly imprinted polymers (MIPs) are prepared by creating a three-dimensional polymeric matrix around a template molecule. After the matrix is removed, complementary cavities with respect to shape and functional groups remain. MIPs have been produced for applications in in vitro diagnostics, therapeutics and separations. However, this promising technology still lacks widespread application because of issues related to large-scale production and optimization of the synthesis. Recent developments in the area of MIP nanoparticles might offer solutions to several problems associated with performance and application. This review discusses various approaches used in the preparation of MIP nanoparticles, focusing in particular on the issues associated with large-scale manufacture and implications for the performance of synthesized nanomaterials.

Development of the custom polymeric materials specific for aflatoxin B1 and ochratoxin A for application with the ToxiQuant T1 sensor tool

Two polymers were computationally designed with affinity to two of the most abundant mycotoxins aflatoxin B1 (AFB1) and ochratoxin A (OTA) for application in the ToxiQuant T1 System. The principle of quantification of AFB1 and OTA using the ToxiQuant T1 instrument comprised of a fluorimetric analysis of mycotoxins adsorbed on the polymer upon exposure to UV light. High affinity of the developed resins allowed the adsorption of both toxins as discrete bands on the top of the cartridge with detection limit as low as 1ng quantity of mycotoxins.

Selection of imprinted nanoparticles by affinity chromatography

Soluble molecularly imprinted nanoparticles were synthesised via iniferter initiated polymerisation and separated by size via gel permeation chromatography. Subsequent fractionation of these particles by affinity chromatography allowed the separation of high affinity fractions from the mixture of nanoparticles. Fractions selected this way possess affinity similar to that of natural antibodies (K(d) 6.6x10(-8)) M and were also able to discriminate between related functional analogues of the template.

Imprinted polymers for chiral resolution of (+/-)-ephedrine. Part 3: NMR predictions and HPLC results with alternative functional monomers

The monomers trifluoromethacrylic acid (TFMAA), 2-hydroxyethylmethacrylate (HEMA) and itaconic acid (IA) have been compared for the molecular imprinting of (-)-ephedrine. Data from NMR titrations were fitted using the program HypNMR to obtain association constants for monomer-template (M-T) complexes of different stoichiometries. These were used to predict the speciation in imprinting mixtures with porogen and cross-linker, and molecularly imprinted polymers (MIPs) were fabricated and their ability to bind (-)-ephedrine and its enantiomer were assessed by high performance liquid chromatography (HPLC). TFMAA and IA interact more strongly with ephedrine than does MAA, yet MIPs made with each of these monomers perform worse. With TFMAA, covalent monomer-template adducts and TFMAA oligomers, present in the polymerisation mixture, may detract from the MIP recognition properties. With IA, the relative flexibility of the monomer may be an issue. HEMA interacts more weakly with ephedrine, and HEMA-based MIPs exhibit much worse retention, and poorer recognition, than those based on MAA. It may be useful to use a higher ratio of M : T in the case of HEMA because the monomer interacts with the cross-linker EDMA.

Molecularly imprinted cavities template the macrocyclization of tetrapeptides

Cavities formed using cyclic tetrapeptides (CTPs) or heat-induced conformers act as templates for cyclization; the cavities bind to linear tetrapeptides and enforce turn conformations to enhance cyclization to constrained CTPs.