Voltammetric sensor for theophylline using sol–gel immobilized molecularly imprinted polymer particles

Boosting Electrochemical Sensing Performances Using Molecularly Imprinted Nanoparticles

Nanoparticles of molecularly imprinted polymers (nanoMIPs) combine the excellent recognition ability of imprinted polymers with specific properties related to the nanosize, such as a high surface-to-volume ratio, resulting in highly performing recognition elements with surface-exposed binding sites that promote the interaction with the target and, in turn, binding kinetics. Different synthetic strategies are currently available to produce nanoMIPs, with the possibility to select specific conditions in relation to the nature of monomers/templates and, importantly, to tune the nanoparticle size. The excellent sensing properties, combined with the size, tunability, and flexibility of synthetic protocols applicable to different targets, have enabled the widespread use of nanoMIPs in several applications, including sensors, imaging, and drug delivery. The present review summarizes nanoMIPs applications in sensors, specifically focusing on electrochemical detection, for which nanoMIPs have been mostly applied. After a general survey of the most widely adopted nanoMIP synthetic approaches, the integration of imprinted nanoparticles with electrochemical transducers will be discussed, representing a key step for enabling a reliable and stable sensor response. The mechanisms for electrochemical signal generation will also be compared, followed by an illustration of nanoMIP-based electrochemical sensor employment in several application fields. The high potentialities of nanoMIP-based electrochemical sensors are presented, and possible reasons that still limit their commercialization and issues to be resolved for coupling electrochemical sensing and nanoMIPs in an increasingly widespread daily-use technology are discussed.

Emerging trends in sensors based on molecular imprinting technology: Harnessing smartphones for portable detection and recognition

Molecular imprinting technology (MIT) has become a promising recognition technology in various fields due to its specificity, high efficiency, stability and eco-friendliness in the recognition of target. Molecularly imprinted polymers (MIPs), known as 'artificial receptors', are shown similar properties to natural receptors as a biomimetic material. The selectivity of recognition for targets can be greatly improved when MIPs are introduced into sensors, as known that MIPs, are suitable for the pretreatment and analysis of trace substances in complex matrix samples. At present, various sensors has been developed by the combination with MIPs for detecting and identifying trace compounds, biological macromolecules or other substances, such as optical, electrochemical and piezoelectric sensors. Smart phones, with their built-in sensors and powerful digital imaging capabilities, provide a unique platform for the needs of portability and instant detection. MIP sensors based on smart phones are expected to become a new research direction in the future. This review discusses the latest applications of MIP sensors in the field of detection and recognition in recent years, summarizes the frontier progress of MIP sensor research based on smart phones in the past two years, and points out the challenges, limitations and future development prospects.

Recent Progress, Challenges, and Trends in Polymer-Based Sensors: A Review

Polymers are long-chain, highly molecular weight molecules containing large numbers of repeating units within their backbone derived from the product of polymerization of monomeric units. The materials exhibit unique properties based on the types of bonds that exist within their structures. Among these, some behave as rubbers because of their excellent bending ability, lightweight nature, and shape memory. Moreover, their tunable chemical, structural, and electrical properties make them promising candidates for their use as sensing materials. Polymer-based sensors are highly utilized in the current scenario in the public health sector and environment control due to their rapid detection, small size, high sensitivity, and suitability in atmospheric conditions. Therefore, the aim of this review article is to highlight the current progress in polymer-based sensors. More importantly, this review provides general trends and challenges in sensor technology based on polymer materials.

Molecularly imprinted polymers - towards electrochemical sensors and electronic tongues

Molecularly imprinted polymers (MIPs) are artificially synthesized materials to mimic the molecular recognition process of biological macromolecules such as substrate-enzyme or antigen-antibody. The combination of these biomimetic materials with electrochemical techniques has allowed the development of advanced sensing devices, which significantly improve the performance of bare or catalyst-modified sensors, being able to unleash new applications. However, despite the high selectivity that MIPs exhibit, those can still show some cross-response towards other compounds, especially with chemically analogous (bio)molecules. Thus, the combination of MIPs with chemometric methods opens the room for the development of what could be considered a new type of electronic tongues, i.e. sensor array systems,  based on its usage. In this direction, this review provides an overview of the more common synthetic approaches, as well as the strategies that can be used to achieve the integration of MIPs and electrochemical sensors, followed by some recent examples over different areas in order to illustrate the potential of such combination in very diverse applications.

A Molecularly Imprinted Sol-Gel Electrochemical Sensor for Naloxone Determination

A molecularly imprinted sol-gel is reported for selective and sensitive electrochemical determination of the drug naloxone (NLX). The sensor was developed by combining molecular imprinting and sol-gel techniques and electrochemically grafting the sol solution onto a functionalized multiwall carbon nanotube modified indium-tin oxide (ITO) electrode. The sol-gel layer was obtained from acid catalyzed hydrolysis and condensation of a solution composed of triethoxyphenylsilane (TEPS) and tetraethoxysilane (TES). The fabrication, structure and properties of the sensing material were characterized via scanning electron microscopy, spectroscopy and electrochemical techniques. Parameters affecting the sensor's performance were evaluated and optimized. A sensor fabricated under the optimized conditions responded linearly between 0.0 µM and 12 µM NLX, with a detection limit of 0.02 µM. The sensor also showed good run-to-run repeatability and batch-to-batch performance reproducibility with relative standard deviations (RSD) of 2.5-7.8% (n = 3) and 9.2% (n = 4), respectively. The developed sensor displayed excellent selectivity towards NLX compared to structurally similar compounds (codeine, fentanyl, naltrexone and noroxymorphone), and was successfully used to measure NLX in synthetic urine samples yielding recoveries greater than 88%.

Fluorescent nanomaterials combined with molecular imprinting polymer: synthesis, analytical applications, and challenges

Fluorescent nanomaterials (FNMs) and molecular imprinted polymers (MIPs) have been widely used in analytical chemistry for determination. However, low selectivity of FNMs and low sensitivity of MIPs hinder their applications. Combining the merits of FNMs and MIPs, FNMs coated with MIPs (FNMs@MIPs) were proposed to solve those problems. Carbon dots, semiconductor quantum dots, noble metal nanoparticles, silica nanoparticles, and covalent-organic frameworks have been reported to be coated with MIPs. In order to overcome challenges for FNMs@MIPs, such as the lack of handy synthesis routes, incompatibility with aqueous solutions, heterogeneous size of particles, leakage of template molecules, the biocompatibility of FNMs@MIPs, and the inference between FNMs and MIPs, scientists proposed some solutions in recent years. We comprehensively review the newest advances of the FNMs@MIPs, and predict the direction of the future development. Graphical abstract.

Computational aided acetaminophen - phthalic acid molecularly imprinted polymer design for analytical determination of known and new developed recreational drugs

In recent times, abuse drug consumption rates have been increasing. In addition, authorities have detected a trend in the development of new substances expressly created to avoid legislation. These novel psychoactive substances (NPS) are non-registered formulations, closely chemically related to outlawed ones to maintain the same psychotropic effects while circumventing legal restrictions. This issue arises enormous social, sanitary, and road safety problems since there is no way to detect nor quantify these non-registered substances. The aim of this work is the development of a high selective material able to pre-concentrate and detect NPS. On that account, molecularly imprinted polymers (MIPs) designed with an imprinted cavity that matches the cathinones structural shape were proposed to detect both conventional and new cathinone derived recreational drugs. The increasing number of illicit drug modifications that is being reported requires developing a receptor valid for not only known molecules but also for incoming ones; thus, a virtual procedure must be carried out to take a step forward towards future modifications. Accordingly, a computational MIP design is proposed as the most appropriated method to effectively design this receptor. By means of molecular dynamics and molecular docking, several combinations are studied regarding their pre-polymerization complex stability but also their rebinding capacity against the proposed analytes. Hence, a phthalic acid - acetaminophen MIP is selected as the most well-suited receptor, valid for current and forthcoming cathinone recreational drugs.

Bioelectronic tongue: Current status and perspectives

In the course of evolution, nature has endowed humans with systems for the recognition of a wide range of tastes with a sensitivity and selectivity which are indispensable for the evaluation of edibility and flavour attributes. Inspiration by a biological sense of taste has become a basis for the design of instruments, operation principles and parameters enabling to mimic the unique properties of their biological precursors. In response to the demand for fast, sensitive and selective techniques of flavouring analysis, devices belonging to the group of bioelectronic tongues (B-ETs) have been designed. They combine achievements of chemometric analysis employed for many years in electronic tongues (ETs), with unique properties of bio-inspired materials, such as natural taste receptors (TRs) regarding receptor/ligand affinity. Investigations of the efficiency of the prototype devices create new application possibilities and suggest successful implementation in real applications. With advances in the field of biotechnology, microfluidics and nanotechnologies, many exciting developments have been made in the design of B-ETs in the last five years or so. The presented characteristics of the recent design solutions, application possibilities, critical evaluation of potentialities and limitations as well as the outline of further development prospects related to B-ETs should contribute to the systematisation and expansion of our knowledge.

Integrating molecularly imprinted polymer beads in graphite-epoxy electrodes for the voltammetric biosensing of histamine in wines

This manuscript presents a voltammetric biosensing study with use of molecularly imprinted polymers to detect histamine in wine. Polymer beads were synthesized by standard precipitation polymerization method and implemented on the electrode surface via sol-gel immobilization. Scanning and confocal microscopy examinations permitted characterizing the material. Adsorptive stripping voltammetry in differential mode was the technique chosen for final application, selecting an enrichment time of 5 min. These conditions permitted a limit of detection of 0.19 μg mL^-1 (1.0 μM), with a linear response range from 0.5 to 6.0 μg mL^-1 (2.71-32.4 μM). The repeatability of the measurements was 4.6% relative standard deviation (n = 12). Principal component analysis showed the ability of the prepared receptor for discriminating other biogenic amines and potential interfering species. A final application, illustrating the determination of histamine, was completed to show agreement of results between the fluorimetric reference method and the proposed electrochemical approach.

Preparation of magnetic molecularly imprinted polymers for the rapid detection of diethylstilbestrol in milk samples

BACKGROUND

Diethylstilbestrol (DES) residues are harmful to human health because of their potential carcinogenic properties. Therefore, it is important to develop a fast and efficient pretreatment method to prevent their harmful effects on human health and the environment.

RESULTS

In this paper, two types of magnetic molecularly imprinted polymers (MMIPs) of DES were prepared by bulk polymerization and the sol-gel method, respectively. The synthetic materials were characterized using Fourier transform infrared spectroscopy, scanning electron microscopy and thermogravimetric analysis. Adsorption capacities of the bulk and sol-gel MMIPs were investigated. A rapid detection method was developed using the two types of MMIPs as sorbents, coupled to high-performance liquid chromatography, for the determination of DES residues in milk samples. Under optimized conditions, the limit of detection (S/N = 3) of both methods for DES was 2.0 μg L^-1 ; and the linear response range to DES was 0.1-500 mg L^-1 . The milk samples were analyzed according to this method with good recoveries of 88.3-97.6 and 90.5-103.5% for the two types of MMIPs, respectively.

CONCLUSIONS

The method described had high sensitivity and high selectivity, and could prove to be a new method for the rapid determination of DES residues in milk samples. © 2019 Society of Chemical Industry.

Molecularly Imprinted Materials for Selective Biological Recognition

Molecular imprinting is an approach of generating imprinting cavities in polymer structures that are compatible with the target molecules. The cavities have memory for shape and chemical recognition, similar to the recognition mechanism of antigen-antibody in organisms. Their structures are also called biomimetic receptors or synthetic receptors. Owing to the excellent selectivity and unique structural predictability of molecularly imprinted materials (MIMs), practical MIMs have become a rapidly evolving research area providing key factors for understanding separation, recognition, and regenerative properties toward biological small molecules to biomacromolecules, even cell and microorganism. In this review, the characteristics, morphologies, and applicability of currently popular carrier materials for molecular imprinting, especially the fundamental role of hydrogels, porous materials, hierarchical nanoparticles, and 2D materials in the separation and recognition of biological templates are discussed. Moreover, through a series of case studies, emphasis is given on introducing imprinting strategies for biological templates with different molecular scales. In particular, the differences and connections between small molecular imprinting (bulk imprinting, "dummy" template imprinting, etc.), large molecular imprinting (surface imprinting, interfacial imprinting, etc.), and cell imprinting strategies are demonstrated in detail. Finally, future research directions are provided.

Molecularly Imprinted Polymers in Electrochemical and Optical Sensors

Molecular imprinting is the process of template-induced formation of specific recognition sites in a polymer. Synthetic receptors prepared using molecular imprinting possess a unique combination of properties such as robustness, high affinity, specificity, and low-cost production, which makes them attractive alternatives to natural receptors. Improvements in polymer science and nanotechnology have contributed to enhanced performance of molecularly imprinted polymer (MIP) sensors. Encouragingly, recent years have seen an increase in high-quality publications describing MIP sensors for the determination of biomolecules, drugs of abuse, and explosives, driving toward applications of this technology in medical and forensic diagnostics. This review aims to provide a focused overview of the latest achievements made in MIP-based sensor technology, with emphasis on research toward real-life applications.

Selective extraction of theophylline from plasma by copper-doped magnetic microspheres prior to its quantification by HPLC

The authors describe the preparation of copper-doped magnetic microspheres (Cu-Fe₃O₄) by a solvothermal method. Due to their good magnetic property and high affinity for compounds containing an imidazole moiety (containing N-H), they are excellent adsorbents for such compounds as tested by eighteen compounds. Specifically, a method has been developed for magnetic solid-phase extraction (MSPE) of theophylline (TP) from plasma. The method enables selective enrichment of TP over many potential interferents that can occur in plasma. Following elution with alkaline methanol, TP was quantified by HPLC-UV at a detection wavelength of 272 nm. Under the optimized conditions, a linear response is found for the 0.02 to 20 μg·mL^-1 concentration range, and the limit of detection is as low as 3 ng·mL^-1. Recoveries from spiked samples range from 91.2 to 100.4%, and the repeatabilities are between 2.9 and 12% (for n = 6). The method was successfully applied to the determination of TP in rabbit and rat plasma. Graphical abstract Copper-doped magnetic microspheres are described that show good magnetic property and high affinity for compounds containing an imidazole moiety (containing an N-H group). They were successfully applied to the selective extraction of theophylline in plasma.

Molecularly imprinted poly(4-amino-5-hydroxy-2,7-naphthalenedisulfonic acid) modified glassy carbon electrode as an electrochemical theophylline sensor

Theophylline is an inexpensive drug employed in asthma and chronic obstructive pulmonary disorder medications and is toxic at higher concentration. The development of a molecularly imprinted polymer based theophylline electrochemical sensor on glassy carbon electrode by the electropolymerization of 4-amino-5-hydroxy-2,7-naphthalenedisulfonic acid is being discussed in this work. The MIP modification enhances the theophylline recognition ability and the electron transfer kinetics of the bare electrode. The parameters, controlling the performance of the imprinted polymer based sensor, like number of electropolymerization cycles, composition of the pre-polymerization mixture, pH and immersion time were investigated and optimized. The interaction energy and the most stable conformation of the template-monomer complex in the pre-polymerization mixture were determined computationally using ab initio calculations based on density functional theory. The amperometric measurements showed that the developed sensor has a method detection limit of 0.32μM for the dynamic range of 0.4 to 17μM, at optimized conditions. The transducer possesses appreciable selectivity in the presence of structurally similar interferents such as theobromine, caffeine and doxofylline. The developed sensor showed remarkable stability and reproducibility and was also successfully employed in theophylline detection from commercially available tablets.

Preparation of a novel molecularly imprinted polymer by the sol–gel process for solid phase extraction of vitamin D3

A novel molecularly imprinted polymer (MIP) as an artificial receptor for vitamin D3 is prepared and used.

From imprinting to microcontact imprinting-A new tool to increase selectivity in analytical devices

Molecular imprinting technology has been successfully applied to small molecular templates but a slow progress has been made in macromolecular imprinting owing to the challenges in natural properties of macromolecules, especially proteins. In this review, the macromolecular imprinting approaches are discussed with examples from recent publications. A new molecular imprinting strategy, microcontact imprinting is highlighted with its recent applications.