Imprinting of nucleotide and monosaccharide recognition sites in acrylamidephenylboronic acid-acrylamide copolymer membranes associated with electronic transducers

Molecularly Imprinted Polymer-Based Biomimetic Systems for Sensing Environmental Contaminants, Biomarkers, and Bioimaging Applications

Molecularly imprinted polymers (MIPs), a biomimetic artificial receptor system inspired by the human body's antibody-antigen reactions, have gained significant attraction in the area of sensor development applications, especially in the areas of medical, pharmaceutical, food quality control, and the environment. MIPs are found to enhance the sensitivity and specificity of typical optical and electrochemical sensors severalfold with their precise binding to the analytes of choice. In this review, different polymerization chemistries, strategies used in the synthesis of MIPs, and various factors influencing the imprinting parameters to achieve high-performing MIPs are explained in depth. This review also highlights the recent developments in the field, such as MIP-based nanocomposites through nanoscale imprinting, MIP-based thin layers through surface imprinting, and other latest advancements in the sensor field. Furthermore, the role of MIPs in enhancing the sensitivity and specificity of sensors, especially optical and electrochemical sensors, is elaborated. In the later part of the review, applications of MIP-based optical and electrochemical sensors for the detection of biomarkers, enzymes, bacteria, viruses, and various emerging micropollutants like pharmaceutical drugs, pesticides, and heavy metal ions are discussed in detail. Finally, MIP's role in bioimaging applications is elucidated with a critical assessment of the future research directions for MIP-based biomimetic systems.

Phenylboronic Acid-polymers for Biomedical Applications

Background:

Phenylboronic acid-polymers (PBA-polymers) have attracted tremendous attention as potential stimuli-responsive materials with applications in drug-delivery depots, scaffolds for tissue engineering, HIV barriers, and biomolecule-detecting/sensing platforms. The unique aspect of PBA-polymers is their interactions with diols, which result in reversible, covalent bond formation. This very nature of reversible bonding between boronic acids and diols has been fundamental to their applications in the biomedical area.

Methods:

We have searched peer-reviewed articles including reviews from Scopus, PubMed, and Google Scholar with a focus on the 1) chemistry of PBA, 2) synthesis of PBA-polymers, and 3) their biomedical applications.

Results:

We have summarized approximately 179 papers in this review. Most of the applications described in this review are focused on the unique ability of PBA molecules to interact with diol molecules and the dynamic nature of the resulting boronate esters. The strong sensitivity of boronate ester groups towards the surrounding pH also makes these molecules stimuli-responsive. In addition, we also discuss how the re-arrangement of the dynamic boronate ester bonds renders PBA-based materials with other unique features such as self-healing and shear thinning.

Conclusion:

The presence of PBA in the polymer chain can render it with diverse functions/ relativities without changing their intrinsic properties. In this review, we discuss the development of PBA polymers with diverse functions and their biomedical applications with a specific focus on the dynamic nature of boronate ester groups.

Molecularly Imprinted Sites Translate into Macroscopic Shape-Memory Properties of Hydrogels

The polymerization of acrylamide, dopamine methacrylamide, and bis-acrylamide in the presence of one of the electron acceptors, N,N'-dimethyl-4,4'-bipyridinium, (1), N,N'-dimethylbipyridinium-4,4'-ethylene, (2), or bipyridinium dithienylethene, (3), yields hydrogel matrices of high stiffness that are cooperatively cross-linked by bis-acrylamide and electron donor (dopamine)-acceptor complexes. Washing off the diffusional electron acceptor units yields molecularly imprinted matrices of lower stiffness, stabilized only by the bis-acrylamide bridges that include specific binding sites for the selective association of the electron acceptor (1), (2), or (3). These imprinted hydrogel matrices show selective recovery of the stiff properties upon binding the respective electron acceptor units to the imprinted sites. The control over the stiffness properties enables the development of shape-memory, molecularly imprinted hydrogels and stiffness-based sensors. The results show how molecularly imprinted sites translate into macroscopic shape-memory properties of hydrogels.

Molecular recognition by synthetic receptors: Application in field-effect transistor based chemosensing

Molecular recognition, i.e., ability of one molecule to recognize another through weak bonding interactions, is one of the bases of life. It is often implemented to sensing systems of high merits. Preferential recognition of the analyte (guest) by the receptor (host) induces changes in physicochemical properties of the sensing system. These changes are measured by using suitable signal transducers. Because of possibility of miniaturization, fast response, and high sensitivity, field-effect transistors (FETs) are more frequently being used for that purpose. A FET combined with a biological material offers the potential to overcome many challenges approached in sensing. However, low stability of biological materials under measurement conditions is a serious problem. To circumvent this problem, synthetic receptors were integrated with the gate surface of FETs to provide robust performance. In the present critical review, the approach utilized to devise chemosensors integrating synthetic receptors and FET transduction is discussed in detail. The progress in this field was summarized and important outcome was provided.

Synthesis and Applications of Boronate Affinity Materials: From Class Selectivity to Biomimetic Specificity

Due to the complexity of biological systems and samples, specific capture and targeting of certain biomolecules is critical in much biological research and many applications. cis-Diol-containing biomolecules, a large family of important compounds including glycoproteins, saccharides, nucleosides, nucleotides, and so on, play essential roles in biological systems. As boronic acids can reversibly bind with cis-diols, boronate affinity materials (BAMs) have gained increasing attention in recent years. However, real-world applications of BAMs are often severely hampered by three bottleneck issues, including nonbiocompatible binding pH, weak affinity, and difficulty in selectivity manipulation. Therefore, solutions to these issues and knowledge about the factors that influence the binding properties are of significant importance. These issues have been well solved by our group in past years. Our solutions started from the synthesis and screening of boronic acid ligands with chemical moieties favorable for binding at neutral and acidic pH. To avoid tedious synthesis routes, we proposed a straightforward strategy called teamed boronate affinity, which permitted facile preparation of BAMs with strong binding at neutral pH. To enhance the affinity, we confirmed that multivalent binding could significantly enhance the affinity toward glycoproteins. More interestingly, we observed that molecular interactions could be significantly enhanced by confinement within nanoscale spaces. To improve the selectivity, we investigated interactions that govern the selectivity and their interplays. We then proposed a set of strategies for selectivity manipulation, which proved to be useful guidelines for not only the design of new BAMs but also the selection of binding conditions. Applications in metabolomic analysis, glycoproteomic analysis, and aptamer selection well demonstrated the great potential of the prepared BAMs. Molecular imprinting is an important methodology for creating affinity materials with antibody-like binding properties. Boronate affinity-based covalent imprinting is a pioneering approach in molecular imprinting, but only a few cases of successful imprinting of glycoproteins by this method were reported. With sound understanding of boronate affinity, we developed two facile and generally applicable boronate affinity-based molecular imprinting approaches. The resulting boronate affinity molecularly imprinted polymers (MIPs) exhibited dramatically improved binding properties, including biocompatible binding pH range, enhanced affinity, improved specificity, and superb tolerance to interference. In terms of nanoconfinement effect, we explained why the binding pH range was widened and why the affinity was enhanced. The excellent binding properties made boronate affinity MIPs appealing alternatives to antibodies in promising applications such as disease diagnosis, cancer-cell targeting, and single-cell analysis. In this Account, we survey the key aspects of BAMs, the efforts we made to solve these issues, and the connections between imprinted and nonimprinted BAMs. Through this survey, we wish to pave a sound fundamental basis of the dependence of binding properties of BAMs on the nature and structure of the ligands and the supporting materials, which can facilitate the development and applications of BAMs. We also briefly sketch remaining challenges and directions for future development.

Hydrogel Based Sensors for Biomedical Applications: An Updated Review

Biosensors that detect and convert biological reactions to a measurable signal have gained much attention in recent years. Between 1950 and 2017, more than 150,000 papers have been published addressing the applications of biosensors in different industries, but to the best of our knowledge and through careful screening, critical reviews that describe hydrogel based biosensors for biomedical applications are rare. This review discusses the biomedical application of hydrogel based biosensors, based on a search performed through Web of Science Core, PubMed (NLM), and Science Direct online databases for the years 2000⁻2017. In this review, we consider bioreceptors to be immobilized on hydrogel based biosensors, their advantages and disadvantages, and immobilization techniques. We identify the hydrogels that are most favored for this type of biosensor, as well as the predominant transduction strategies. We explain biomedical applications of hydrogel based biosensors including cell metabolite and pathogen detection, tissue engineering, wound healing, and cancer monitoring, and strategies for small biomolecules such as glucose, lactate, urea, and cholesterol detection are identified.

Role of Mechanical Factors in Applications of Stimuli-Responsive Polymer Gels - Status and Prospects

Due to their unique characteristics such as multifold change of volume in response to minute change in the environment, resemblance of soft biological tissues, ability to operate in wet environments, and chemical tailorability, stimuli responsive gels represent a versatile and very promising class of materials for sensors, muscle-type actuators, biomedical applications, and autonomous intelligent structures. Success of these materials in practical applications largely depends on their ability to fulfill application-specific mechanical requirements. This article provides an overview of recent application-driven development of covalent polymer gels with special emphasis on the relevant mechanical factors and properties. A short account of mechanisms of gel swelling and mechanical characteristics of importance to stimuli-responsive gels is presented. The review highlights major barriers for wider application of these materials and discusses latest advances and potential future directions toward overcoming these barriers, including interpenetrating networks, homogeneous networks, nanocomposites, and nanofilamentary gels.

3D hydrogel scaffold doped with 2D graphene materials for biosensors and bioelectronics

Hydrogels consisting of three-dimensional (3D) polymeric networks have found a wide range of applications in biotechnology due to their large water capacity, high biocompatibility, and facile functional versatility. The hydrogels with stimulus-responsive swelling properties have been particularly instrumental to realizing signal transduction in biosensors and bioelectronics. Graphenes are two-dimensional (2D) nanomaterials with unprecedented physical, optical, and electronic properties and have also found many applications in biosensors and bioelectronics. These two classes of materials present complementary strengths and limitations which, when effectively coupled, can result in significant synergism in their electrical, mechanical, and biocompatible properties. This report reviews recent advances made with hydrogel and graphene materials for the development of high-performance bioelectronics devices. The report focuses on the interesting intersection of these materials wherein 2D graphenes are hybridized with 3D hydrogels to develop the next generation biosensors and bioelectronics.

A novel sensor based on bifunctional monomer molecularly imprinted film at graphene modified glassy carbon electrode for detecting traces of moxifloxacin

A novel selective and sensitive electrochemical sensor for moxifloxacin (MFLX) detection based on bifunctional monomer molecularly imprinted polymer (MIP) membranes on a glassy carbon electrode (GCE) modified with graphene was constructed.

Molecular imprinting: perspectives and applications

This critical review presents a survey of recent developments in technologies and strategies for the preparation of MIPs, followed by the application of MIPs in sample pretreatment, chromatographic separation and chemical sensing.

Boronate affinity materials for separation and molecular recognition: structure, properties and applications

Boronate affinity materials, as unique sorbents, have emerged as important media for the selective separation and molecular recognition of cis-diol-containing compounds. With the introduction of boronic acid functionality, boronate affinity materials exhibit several significant advantages, including broad-spectrum selectivity, reversible covalent binding, pH-controlled capture/release, fast association/desorption kinetics, and good compatibility with mass spectrometry. Because cis-diol-containing biomolecules, including nucleosides, saccharides, glycans, glycoproteins and so on, are the important targets in current research frontiers such as metabolomics, glycomics and proteomics, boronate affinity materials have gained rapid development and found increasing applications in the last decade. In this review, we critically survey recent advances in boronate affinity materials. We focus on fundamental considerations as well as important progress and new boronate affinity materials reported in the last decade. We particularly discuss on the effects of the structure of boronate ligands and supporting materials on the properties of boronate affinity materials, such as binding pH, affinity, selectivity, binding capacity, tolerance for interference and so on. A variety of promising applications, including affinity separation, proteomics, metabolomics, disease diagnostics and aptamer selection, are introduced with main emphasis on how boronate affinity materials can solve the issues in the applications and what merits boronate affinity materials can provide.

Dual-template docking oriented molecular imprinting: a facile strategy for highly efficient imprinting within mesoporous materials

Molecular imprinting within mesoporous materials is a challenging task. Herein, we present a new strategy, called dual-template docking oriented molecular imprinting (DTD-OMI), for facile and highly efficient imprinting within mesoporous materials.

Bio-mimetic sensors based on molecularly imprinted membranes

An important challenge for scientific research is the production of artificial systems able to mimic the recognition mechanisms occurring at the molecular level in living systems. A valid contribution in this direction resulted from the development of molecular imprinting. By means of this technology, selective molecular recognition sites are introduced in a polymer, thus conferring it bio-mimetic properties. The potential applications of these systems include affinity separations, medical diagnostics, drug delivery, catalysis, etc. Recently, bio-sensing systems using molecularly imprinted membranes, a special form of imprinted polymers, have received the attention of scientists in various fields. In these systems imprinted membranes are used as bio-mimetic recognition elements which are integrated with a transducer component. The direct and rapid determination of an interaction between the recognition element and the target analyte (template) was an encouraging factor for the development of such systems as alternatives to traditional bio-assay methods. Due to their high stability, sensitivity and specificity, bio-mimetic sensors-based membranes are used for environmental, food, and clinical uses. This review deals with the development of molecularly imprinted polymers and their different preparation methods. Referring to the last decades, the application of these membranes as bio-mimetic sensor devices will be also reported.

Covalent molecular imprinting made easy: a case study of mannose imprinted polymer

Covalent mannose imprinted polymers were synthesized by a one-pot method in aqueous medium.

Determination of ATP using a double-receptor sandwich method based on molecularly imprinted membrane and fluorescence-labeled uranyl-salophen complex

A double-receptor sandwich method for the fluorescence determination of adenosine triphosphate (ATP) is proposed in this paper. The solid phase receptor on the surface of glass slides is a molecularly imprinted membrane (MIM) containing an artificial nanocavity. It is constructed by a molecular imprinting technique using adenosine monophosphate (AMP) as a template molecule. The labeled receptor is a uranyl-salophen complex containing a fluorescent group or uranyl-salophen-fluorescein (USF). It is synthesized with salophen, 5-aminofluorescein, and uranyl. In a procedure of determining ATP, ATP in sample solution is first adsorbed on the surface of the glass slide through the combination of the AMP group in ATP with the nanocavity in MIM. Then, the adsorbed ATP binds USF through the coordination reaction of the phosphate group in ATP with uranyl in USF to form a sandwich-type structure of MIM-ATP-USF. The amount of ATP is detected through the fluorescence determination of USF bound on the slide. Under optimal conditions, the linear range for the determination of ATP is 0.3 to 4.8 nmol/mL with a detection limit of 0.041 nmol/mL. The proposed method has been successfully employed for the determination of ATP in real samples with the recoveries of 98.5 to 102.5 %.

Molecularly imprinted membranes

Although the roots of molecularly imprinted polymers lie in the beginning of 1930s in the past century, they have had an exponential growth only 40-50 years later by the works of Wulff and especially by Mosbach. More recently, it was also proved that molecular imprinted membranes (i.e., polymer thin films) that show recognition properties at molecular level of the template molecule are used in their formation. Different procedures and potential application in separation processes and catalysis are reported. The influences of different parameters on the discrimination abilities are also discussed.

Electrochemically synthesized polymers in molecular imprinting for chemical sensing

This critical review describes a class of polymers prepared by electrochemical polymerization that employs the concept of molecular imprinting for chemical sensing. The principal focus is on both conducting and nonconducting polymers prepared by electropolymerization of electroactive functional monomers, such as pristine and derivatized pyrrole, aminophenylboronic acid, thiophene, porphyrin, aniline, phenylenediamine, phenol, and thiophenol. A critical evaluation of the literature on electrosynthesized molecularly imprinted polymers (MIPs) applied as recognition elements of chemical sensors is presented. The aim of this review is to highlight recent achievements in analytical applications of these MIPs, including present strategies of determination of different analytes as well as identification and solutions for problems encountered.

Paper-based electrochemiluminescent 3D immunodevice for lab-on-paper, specific, and sensitive point-of-care testing

Recent research on microfluidic paper-based analytical devices (μPADs) has shown that paper has great potential for the fabrication of low-cost diagnostic devices for healthcare and environmental monitoring applications. Herein, electrochemiluminescence (ECL) was introduced for the first time into μPADs that were based on screen-printed paper-electrodes. To further perform high-specificity, high-performance, and high-sensitivity ECL on μPADs for point-of-care testing (POCT), ECL immunoassay capabilities were introduced into a wax-patterned 3D paper-based ECL device, which was characterized by SEM, contact-angle measurement, and electrochemical impedance spectroscopy. With the aid of a home-made device-holder, the ECL reaction was triggered at room temperature. By using a typical tris(bipyridine)ruthenium-tri-n-propylamine ECL system, this paper-based ECL 3D immunodevice was applied to the diagnosis of carcinoembryonic antigens in real clinical serum samples. This contribution further expands the number of sensitive and specific detection modes of μPADs.

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.

Detection of 2,4-dinitrotoluene (DNT) as a model system for nitroaromatic compounds via molecularly imprinted short-alkyl-chain SAMs

A 2-D molecularly imprinted monolayer (2-D MIM) approach was used to prepare a simple and robust sensor for nitroaromatic compounds with 2,4-dinitrotoluene (DNT) as the model compound, which is a precursor and analog for explosive 2,4,6-trinitrotoluene (TNT). In contrast to studies utilizing long-chain hexadecylmercaptan self-assembled monolayers (SAM)s for sensing, a shorter-chain alkylthiol (i.e., butanethiol SAM) was utilized for DNT detection. The role of the chain length of the coadsorbed alkylthiol was emphasized with a matched template during solution adsorption. Semiempirical PM3 quantum calculations were used to determine the molecular conformation and complexation of the adsorbates. A switching mechanism was invoked on the basis of the ability of the template analyte to alter the packing arrangement of the alkylthiol SAMs near defect sites as influenced by the DNT-ethanol solvent complex. A 2-D MIM was formed on the Au surface electrode of a quartz crystal microbalance (QCM), which was then used to sense various concentrations of the analyte. Interestingly, the 2-D MIM QCM also enabled the selective detection of DNT even in a mixed solution of competing molecules, demonstrating the selectivity figure of merit. Likewise, electrochemical impedance spectroscopy (EIS) data at different concentrations of DNT confirmed the 2-D MIM effectiveness for sensing based on the interfacial conformation and electron-transport properties of the imprinted butanethiol SAM.

Stimuli-responsive porous hydrogels at interfaces for molecular filtration, separation, controlled release, and gating in capsules and membranes

A continuously growing area of controlled and tunable transport and separation of biomolecules and drugs has recently attracted attention to the structures which can be referred to as stimuli-responsive porous hydrogel thin films. Because of spatial constraints, swelling/shrinking of the hydrogel films results in closing/opening (or vice versa) of the film's pores. Such responsive systems can be used in the configuration of plane films or capsules. The combination of a low thickness (translating into a low hydrodynamic flow resistance and rapid response) with well-defined size and shape of pores (translating into better control of transport and separation), which can be closed, opened, or tuned by an external signal (allowing a large amplitude of changes in diffusivity of solutes in the thin film and a precise control of the pore size), makes these materials very attractive for a range of applications, such as molecular filtration, separation, drug delivery, sensors, and actuators.

Intelligent chiral sensing based on supramolecular and interfacial concepts

Of the known intelligently-operating systems, the majority can undoubtedly be classed as being of biological origin. One of the notable differences between biological and artificial systems is the important fact that biological materials consist mostly of chiral molecules. While most biochemical processes routinely discriminate chiral molecules, differentiation between chiral molecules in artificial systems is currently one of the challenging subjects in the field of molecular recognition. Therefore, one of the important challenges for intelligent man-made sensors is to prepare a sensing system that can discriminate chiral molecules. Because intermolecular interactions and detection at surfaces are respectively parts of supramolecular chemistry and interfacial science, chiral sensing based on supramolecular and interfacial concepts is a significant topic. In this review, we briefly summarize recent advances in these fields, including supramolecular hosts for color detection on chiral sensing, indicator-displacement assays, kinetic resolution in supramolecular reactions with analyses by mass spectrometry, use of chiral shape-defined polymers, such as dynamic helical polymers, molecular imprinting, thin films on surfaces of devices such as QCM, functional electrodes, FET, and SPR, the combined technique of magnetic resonance imaging and immunoassay, and chiral detection using scanning tunneling microscopy and cantilever technology. In addition, we will discuss novel concepts in recent research including the use of achiral reagents for chiral sensing with NMR, and mechanical control of chiral sensing. The importance of integration of chiral sensing systems with rapidly developing nanotechnology and nanomaterials is also emphasized.

Surface plasmon resonance analysis of antibiotics using imprinted boronic acid-functionalized Au nanoparticle composites

Au nanoparticles (NPs) are functionalized with thioaniline electropolymerizable groups and (mercaptophenyl)boronic acid. The antibiotic substrates neomycin (NE), kanamycin (KA), and streptomycin (ST) include vicinal diol functionalities and, thus, bind to the boronic acid ligands. The electropolymerization of the functionalized Au NPs in the presence of NE, KA, or ST onto Au surfaces yields bisaniline-cross-linked Au NP composites that, after removal of the ligated antibiotics, provide molecularly imprinted matrixes which reveal high sensitivities toward the sensing of the imprinted antibiotic analytes (detection limits for analyzing NE, KA, and ST correspond to 2.00 +/- 0.21 pM, 1.00 +/- 0.10 pM, and 200 +/- 30 fM, respectively). The antibiotics are sensed by surface plasmon resonance (SPR) spectroscopy, where the coupling between the localized plasmon of the NPs and the surface plasmon wave associated with the Au surface is implemented to amplify the SPR responses. The imprinted Au NP composites are, then, used to analyze the antibiotics in milk samples.

Responsive hydrogels for label-free signal transduction within biosensors

Hydrogels have found wide application in biosensors due to their versatile nature. This family of materials is applied in biosensing either to increase the loading capacity compared to two-dimensional surfaces, or to support biospecific hydrogel swelling occurring subsequent to specific recognition of an analyte. This review focuses on various principles underpinning the design of biospecific hydrogels acting through various molecular mechanisms in transducing the recognition event of label-free analytes. Towards this end, we describe several promising hydrogel systems that when combined with the appropriate readout platform and quantitative approach could lead to future real-life applications.

Self-Limiting Robust Surface-Grafted Organic Nanofilms

Robust surface-bound insulating polymer films with controlled thickness in <5 nm range are important for technological advances in diverse disciplines such as electrochemical sensors, molecular electronics, separations and anti-corrosive coatings. Creating these films by simple methods from readily available materials has been a significant challenge. Here we report a newly synthesized molecule combining a styrene and thiol moieties, joined via a short linker, that binds to the gold surface, polymerizes and crosslinks polymer chains to form robust films with uniform and controlled thickness and complete surface coverage. Additional layers can be deposited. These films that bridge two- and three-dimensional materials show excellent stability and insulating properties.