Molecularly imprinted polymer nanoparticle-carbon nanotube composite electrochemical gas sensor for highly selective and sensitive detection of methanol vapour.

An electrochemical gas sensor has been fabricated using molecularly imprinted polymer nanoparticles (nanoMIPs) and multiwalled carbon nanotubes on screen-printed electrodes. Methanol vapour was chosen as the target due to its toxicity as its suitability as a model for more harmful pollutant gases. The sensor functions under ambient conditions and in the required concentration range, in contrast to all previous MIP-based gas sensors for methanol. The sensitivity of the sensor was greatly improved by the addition of multiwall carbon nanotubes, resulting in a limit of detection of approximately 10 ppm. The nanoMIPs provide an inherent selectivity for the target inherent in its design. Selectivity studies were performed with structurally analogous alcohols at various concentrations, demonstrating selectivity for methanol 12.1 times that for ethanol at 2 mmol dm-3 and 4.2 times that for ethanol at 1 mmol dm-3. Interactions with isopropanol and n-propanol were found to be non-specific, and the response to water was negligible. This demonstrates an improvement over previous methanol gas sensors based on molecularly imprinted polymers. No response was observed with carbon nanotubes alone, and no selectivity was observed with non-imprinted equivalents of the nanoMIP sensor. The resulting device is by far the most practical MIP-based instrument for methanol gas sensing thus far described in the literature, being the only example capable of functioning at the necessary methanol vapour concentrations and at the required temperature and humidity. With the selectivity and sensitivity described and the simple design, the developed device provides a substantial advance in the field of molecularly imprinted gas sensors.

Design of smart nanoparticles for the electrochemical detection of 3,4-methylenedioxymethamphetamine to allow in field screening by law enforcement officers.

A portable and highly sensitive sensor was designed for the specific detection of 3,4-methyl-enedioxy-methamphetamine (MDMA), in a range of field-testing situations. The sensor can detect MDMA in street samples, even when other controlled substances drugs, or adulterants are present. In this work, we report for the first time a sensor using electroactive molecularly imprinted polymer nanoparticles computationally designed to recognize MDMA and then produced using solid phase synthesis. A composite comprising chitosan, reduced graphene oxide, and molecularly imprinted polymer nanoparticles synthesized for MDMA for the first time was immobilized on screen-printed carbon electrodes. The sensors displayed a satisfactory sensitivity (106.8 nA × µM-1 ), limit of detection (1.6 nM; 0.31 ng/mL), and recoveries (92-99%). The accuracy of the results was confirmed through validation using Ultra-High Performance Liquid Chromatography coupled with tandem Mass Spectrometry (UPLC-MS/MS). This technology could be used in forensic analysis and make it possible to selectively detect MDMA in street samples.

A Biomimetic Polymer for the Extraction and Purification of Superior Analogues of Amphotericin B.

Amphotericin B has been an essential drug in the fight against leishmaniasis and fungal pathogens for decades, and has more recently gained attention for the very limited microbial resistance displayed against it. However, its toxicity has restricted its use to only the most severe cases of disease, and attempts to reduce these ill effects via formulation have had only minor success. Genetic engineering has allowed the development of superior amphotericin analogues, notably 16-descarboxyl-16-methyl amphotericin B (MeAmB), which shows a ten-fold reduction in toxicity in addition to a slight improvement in therapeutic activity. However, MeAmB is difficult to extract from its bacterial source and purify. Presented here is an alternative method of MeAmB purification. A biomimetic polymer with a high affinity for MeAmB was designed via computational modelling and synthesised. Prepared as a separation column, the polymer was able to retain the target MeAmB whilst allowing the removal of cell debris from the bacterial extract. Starting with a simple bacterial extract, the relatively simple process allowed the purification of an MeAmB salt complex at approximately 70% MeAmB, and likely higher purification from further extraction. The mean MeAmB recovery between the pre-purification extract sample and the final product was 81%. This is the first successful demonstration of extraction or purification of any amphotericin molecule with any polymeric material. The biomimetic polymer was additionally reusable and simple to fabricate, giving this technique significant advantages over traditional methods of extraction and purification of valuable compounds.

The effect of immediate environment on bond strength of different bond types-A valence bond study.

The ability to design catalysis largely depends on our understanding of the electrostatic effect of the surrounding on the bonds participating in the reaction. Here, we used a simplistic model of point charges (PCs) to determine a set of rules guiding how to construct PC-bond arrangement that can strengthen or weaken different chemical bonds. Using valence bond theory to calculate the in situ bond energies, we show that the effect of the PC mainly depends on the bond's dipole moment irrespective of its type (being covalent or charge shift). That is, polar bonds are getting stronger or weaker depending on the sign and location of the PC, whereas non- or weakly polar bonds become stronger or weaker depending only on the location of the PC and to a smaller extent compared with polar bonds. We also show that for polar bonds, the maximal bond strengthening and weakening effect can be achieved when the PC is placed along the bond axis, as close as possible to the more and less polarizable atom/fragment, respectively. Finally, due to the stabilizing effects of polarizability, we show that, overall, it is easier to cause bond strengthening compared with bond weakening. Particularly, for polar bonds, bond strengthening is larger than bond weakening obtained by an oppositely signed PC. These rules should be useful in the future design of catalysis in, e.g., enzyme active sites.

Nanoparticle-induced enhancement of cholinesterase activity in the presence of malathion: A potential nerve agent therapeutic.

Organophosphate nerve agents are associated with assassination, terrorism and chemical warfare, but there has been slow progress in developing a broad-spectrum response to poisoning. For some nerve agents the oxime component of the therapy may not be effective, limiting the effectiveness of emergency treatment that is desperately needed. An alternative therapy may be possible based on accelerating enzyme (acetylcholinesterase) catalysis in unaffected adjacent enzymes. Herein we demonstrate a restoration of acetylcholinesterase activity in malathion-inhibited cell membrane preparations by the administration of functional nanoparticles. The molecularly imprinted polymer nanoparticles were designed to bind selectively to designated enzyme epitopes. Enzyme activity of membrane-bound acetylcholinesterase was measured in the presence of the organophosphate malathion and the selected nanoparticles. Enzymatic acceleration of the cholinesterase was observed at 162 ± 17 % the rate of erythrocyte ghosts without bound nanoparticles. This may restore sufficient acetylcholine hydrolysis to mitigate the effects of poisoning, offsetting the acetylcholine accumulation resulting from enzyme inhibition.

Template Imprinting Versus Porogen Imprinting of Small Molecules: A Review of Molecularly Imprinted Polymers in Gas Sensing.

The selective sensing of gaseous target molecules is a challenge to analytical chemistry. Selectivity may be achieved in liquids by several different methods, but many of these are not suitable for gas-phase analysis. In this review, we will focus on molecular imprinting and its application in selective binding of volatile organic compounds and atmospheric pollutants in the gas phase. The vast majority of indexed publications describing molecularly imprinted polymers for gas sensors and vapour monitors have been analysed and categorised. Specific attention was then given to sensitivity, selectivity, and the challenges of imprinting these small volatile compounds. A distinction was made between porogen (solvent) imprinting and template imprinting for the discussion of different synthetic techniques, and the suitability of each to different applications. We conclude that porogen imprinting, synthesis in an excess of template, has great potential in gas capture technology and possibly in tandem with more typical template imprinting, but that the latter generally remains preferable for selective and sensitive detection of gaseous molecules. More generally, it is concluded that gas-phase applications of MIPs are an established science, capable of great selectivity and parts-per-trillion sensitivity. Improvements in the fields are likely to emerge by deviating from standards developed for MIP in liquids, but original methodologies generating exceptional results are already present in the literature.

Design and fabrication of a smart sensor using in silico epitope mapping and electro-responsive imprinted polymer nanoparticles for determination of insulin levels in human plasma.

A robust and highly specific sensor based on electroactive molecularly imprinted polymer nanoparticles (nanoMIP) was developed. The nanoMIP tagged with a redox probe, combines both recognition and reporting capabilities. The developed nanoMIP replaces enzyme-mediator pairs used in traditional biosensors thus, offering enhanced molecular recognition for insulin, improving performance in complex biological samples, and yielding high stability. Also, most of existing sensors show poor performance after storage. To improve costs of the logistics and avoid the need of cold storage in the chain supply, we developed an alternative to biorecognition system that relies on nanoMIP. NanoMIP were computationally designed using "in-silico" insulin epitope mapping and synthesized by solid phase polymerisation. The characterisation of the polymer nanoparticles was performed by transmission electron microscopy (TEM), dynamic light scattering (DLS), Fourier-transform Infrared (FT-IR) and surface plasmon resonance (SPR). The electrochemical sensor was developed by chemical immobilisation of the nanoMIP on screen printed platinum electrodes. The insulin sensor displayed satisfactory performances and reproducible results (RSD = 4.2%; n = 30) using differential pulse voltammetry (DPV) in the clinically relevant concentration range from 50 to 2000 pM. The developed nanoMIP offers the advantage of large number of specific recognition sites with tailored geometry, as the resultant, the sensor showed high sensitivity and selectivity to insulin with a limit of detection (LOD) of 26 and 81 fM in buffer and human plasma, respectively, confirming the practical application for point of care monitoring. Moreover, the nanoMIP showed adequate storage stability of 168 days, demonstrating the robustness of sensor for several rounds of insulin analysis.

Molecularly imprinted nanoparticles-based assay (MINA) - detection of leukotrienes and insulin.

A novel molecularly imprinted polymer nanoparticle-based assay (MINA) performed in magnetic microplates was developed as an improved high-quality alternative to existing antibody-based immunoassays. MINA is a generic technology that can be adapted for biomarker detection in biological samples. Herein, we demonstrate the applicability of the MINA assay for the detection of leukotrienes and insulin in biological samples. MINA, used in a competition format, has allowed the detection of LTE4 in urine in a concentration range from 0.45 to 364 pM, with a LOD of 0.73 pM. MINA, used in a competition format, has allowed the detection of insulin in plasma in a concentration range from 25 to 2500 pM, with a LOD of 27 pM. This assay has shown comparable performance for LTE4 and insulin detection to existing chromatographic techniques (LC-MS/MS) and immunoassays in clinically relevant concentrations. The main advantages of this assay are the efficient and low cost fabrication, preparation of synthetic binders without the use of animals, and fewer steps used in the assay protocol as compared to traditional immunoassays.

Probing Peptide Sequences on Their Ability to Generate Affinity Sites in Molecularly Imprinted Polymers.

An array of 4000 defined and addressable tripeptides on a polymer-coated glass slide is used to synthesize molecularly imprinted polymer (MIP) nanoparticles. This work is undertaken to systematically probe the impact of the peptide sequence on the ability to generate affinity MIPs. The polymer affinity is assessed by measuring the fluorescence of bound MIP nanoparticles at each peptide spot on the surface after washing the array to remove any low-affinity polymer. The generic composition commonly used in the preparation of MIPs against proteins seems to be equally suitable for imprinting hydrophobic and hydrophilic tripeptides. The amino acids frequently contributing to the formation of high-affinity MIPs include T, F, D, N, Y, W, and P. The amino acids that rarely contribute to the formation of high-affinity interactions with MIPs are G, V, A, L, I, and M. These observations are confirmed by computational modeling. The basic technique proposed here may be applicable in optimizing polymer compositions for the production of high-affinity MIPs or, more specifically, for the selection of appropriate amino acid sequences when peptide epitopes are used instead of whole protein imprinting.

Electrochemical sensing of cocaine in real samples based on electrodeposited biomimetic affinity ligands.

A selective electrochemical sensor for direct detection of cocaine was developed based on molecularly imprinted polymers electropolymerized onto graphene-modified electrodes. Palladium nanoparticles were integrated in the sensing layer for the benefit of enhancing the communication between the imprinted sites and the electrode and improving their homogeneous distribution. The molecularly imprinted polymer was synthesized by cyclic voltammetry using p-aminobenzoic acid as a high affinity monomer selected by computational modeling, and cocaine as a template molecule. Experimental parameters related to the electrochemical deposition of palladium nanoparticles, pH, composition of the electropolymerization mixture, extraction and rebinding conditions were studied and optimized. Under optimized conditions, the oxidation peak current varied linearly with cocaine concentration in the range of 100-500 µM, with a detection limit of 50 µM (RSD 0.71%, n = 3). The molecularly imprinted sensor was able to detect cocaine in saliva and river water with good recoveries after sample pretreatment and was successfully applied for screening real street samples for cocaine.

Highly Efficient Abiotic Assay Formats for Methyl Parathion: Molecularly Imprinted Polymer Nanoparticle Assay as an Alternative to Enzyme-Linked Immunosorbent Assay.

Enzyme-linked immunosorbent assay (ELISA) is a widely used standard method for sensitive detection of analytes of environmental, clinical, or biotechnological interest. However, ELISA has clear drawbacks related to the use of relatively unstable antibodies and enzyme conjugates and the need for several steps such as washing of nonbound conjugates and addition of dye reagents. Herein, we introduce a new completely abiotic assay where antibodies and enzymes are replaced with fluorescent molecularly imprinted polymer nanoparticles (nanoMIPs) and target-conjugated magnetic nanoparticles, which acted as both reporter probes and binding agents. The components of the molecularly imprinted polymer nanoparticle assay (MINA) are assembled in microtiter plates fitted with magnetic inserts. We have compared the performance of a new magnetic assay with molecularly imprinted polymer (MIP)-based ELISA for the detection of methyl parathion (MP). Both assays have shown high sensitivity toward allowing detection of MP at picomolar concentrations without any cross-reactivity against chlorpyriphos and fenthion. The fully abiotic assays were also proven to detect analyte in real samples such as tap water and milk. Unlike ELISA-based systems, the novel assay required no washing steps or addition of enzyme substrates, making it more user-friendly and suitable for high throughput screening.

Polymer platforms for selective detection of cocaine in street samples adulterated with levamisole.

Accurate drug detection is of utmost importance for fighting against drug abuse. With a high number of cutting agents and adulterants being added to cut or mask drugs in street powders the number of false results is increasing. We demonstrate for the first time the usefulness of employing polymers readily synthesized by electrodeposition to selectively detect cocaine in the presence of the commonly used adulterant levamisole. The polymers were selected by computational modelling to exhibit high binding affinity towards cocaine and deposited directly on the surface of graphene-modified electrodes via electropolymerization. The resulting platforms allowed a distinct electrochemical signal for cocaine, which is otherwise suppressed by levamisole. Square wave voltammetry was used to quantify cocaine alone and in the presence of levamisole. The usefulness of the platforms was demonstrated in the screening of real street samples.

Modulation of Quorum Sensing in a Gram-Positive Pathogen by Linear Molecularly Imprinted Polymers with Anti-infective Properties.

We describe the development, characterization, and biological testing of a new type of linear molecularly imprinted polymer (LMIP) designed to act as an anti-infective by blocking the quorum sensing (QS) mechanism and so abrogating the virulence of the pathogen Streptococcus pneumoniae. The LMIP is prepared (polymerized) in presence of a template molecule, but unlike in traditional molecular imprinting approaches, no cross-linker is used. This results in soluble low-molecular-weight oligomers that can act as a therapeutic agent in vitro and in vivo. The LMIP was characterized by mass spectrometry to determine its monomer composition. Fragments identified were then aligned along the peptide template by computer modeling to predict the possible monomer sequence of the LMIP. These findings provide a proof of principle that LMIPs can be used to block QS, thus setting the stage for the development of LMIPs a novel drug-discovery platform and class of materials to target Gram-positive pathogens.

In Silico Synthesis of Synthetic Receptors: A Polymerization Algorithm.

Molecularly imprinted polymer (MIP) synthetic receptors have proposed and applied applications in chemical extraction, sensors, assays, catalysis, targeted drug delivery, and direct inhibition of harmful chemicals and pathogens. However, they rely heavily on effective design for success. An algorithm has been written which mimics radical polymerization atomistically, accounting for chemical and spatial discrimination, hybridization, and geometric optimization. Synthetic ephedrine receptors were synthesized in silico to demonstrate the accuracy of the algorithm in reproducing polymers structures at the atomic level. Comparative analysis in the design of a synthetic ephedrine receptor demonstrates that the new method can effectively identify affinity trends and binding site selectivities where commonly used alternative methods cannot. This new method is believed to generate the most realistic models of MIPs thus produced. This suggests that the algorithm could be a powerful new tool in the design and analysis of various polymers, including MIPs, with significant implications in areas of biotechnology, biomimetics, and the materials sciences more generally.

Computational approaches in the design of synthetic receptors - A review.

The rational design of molecularly imprinted polymers (MIPs) has been a major contributor to their reputation as "plastic antibodies" - high affinity robust synthetic receptors which can be optimally designed, and produced for a much reduced cost than their biological equivalents. Computational design has become a routine procedure in the production of MIPs, and has led to major advances in functional monomer screening, selection of cross-linker and solvent, optimisation of monomer(s)-template ratio and selectivity analysis. In this review the various computational methods will be discussed with reference to all the published relevant literature since the end of 2013, with each article described by the target molecule, the computational approach applied (whether molecular mechanics/molecular dynamics, semi-empirical quantum mechanics, ab initio quantum mechanics (Hartree-Fock, Møller-Plesset, etc.) or DFT) and the purpose for which they were used. Detailed analysis is given to novel techniques including analysis of polymer binding sites, the use of novel screening programs and simulations of MIP polymerisation reaction. The further advances in molecular modelling and computational design of synthetic receptors in particular will have serious impact on the future of nanotechnology and biotechnology, permitting the further translation of MIPs into the realms of analytics and medical technology.