Frontiers in highly sensitive molecularly imprinted electrochemical sensors: Challenges and strategies

Mechanism of high sensitivity proton acids doped polypyrrole molecularly imprinted electrochemical sensor and its application in urea detection

Molecularly imprinted electrochemical sensor is a kind of convenient, fast, and stable analyzer, but the conductivity of electrode materials and their affinity with the analyte affect its performance. A proton acid (PSS, SA, SSA) doping method was proposed to improve the electrochemical performance of the polypyrrole molecularly imprinted polymer (PPy-MIP), which promoted the electropolymerization of pyrrole, reduced the charge transfer resistance, and increased the electrochemical surface area. In terms of both improving conductivity and affinity, the response of the proton acids doped the polypyrrole molecularly imprinted electrochemical sensors (PPy-MIECS) to urea was improved by 25-fold (PSS), 5-fold (SA), and 3-fold (SSA) over that of PPy-MIECS. In addition, the PSS-PPy-MIECS was validated for the practical application with a linear detection range from 0.1 mM to 100 mM, high selectivity (α = 39.73), reusability (RSD% = 4.54 %), reproducibility (RSD% = 0.93 %), and stability (11 days). The advantage of proton acid doping method in PSS-PEDOT-MIECS to urea and PSS-PPy-MIECS to glucose extended its application in the performance enhancement of MIECS design.

Determination of indole-3-acetic acid using disposable molecularly imprinted electrochemical sensors based on bifunctional monomers

Stainless steel sheets were coated with carbon ink to obtain disposable carbon electrodes, which were used as supports for moleculary imprinted polymer (MIP) electrochemical sensors by electropolymerizing o-phenylenediamine and o-aminophenol along with indole-3-acetic acid (IAA) as the template. After optimization, the MIP biosensors could be used for sensitive and selective detection of IAA with the limit of quantification of 0.1 µM. Our experimental results showed that stable and reproducible electrochemical responses could be achieved for the disposable MIP biosensors. This approach was successfully used for detection of IAA in different tissues of pea sprouts. This study reveals the potential of MIP electrochemical sensors in practical applications and shrinks the trench between the research and the real world.

Sensing with Molecularly Imprinted Membranes on Two-Dimensional Solid-Supported Substrates

Molecularly imprinted membranes (MIMs) have been a focal research interest since 1990, representing a breakthrough in the integration of target molecules into membrane structures for cutting-edge sensing applications. This paper traces the developmental history of MIMs, elucidating the diverse methodologies employed in their preparation and characterization on two-dimensional solid-supported substrates. We then explore the principles and diverse applications of MIMs, particularly in the context of emerging technologies encompassing electrochemistry, surface-enhanced Raman scattering (SERS), surface plasmon resonance (SPR), and the quartz crystal microbalance (QCM). Furthermore, we shed light on the unique features of ion-sensitive field-effect transistor (ISFET) biosensors that rely on MIMs, with the notable advancements and challenges of point-of-care biochemical sensors highlighted. By providing a comprehensive overview of the latest innovations and future trajectories, this paper aims to inspire further exploration and progress in the field of MIM-driven sensing technologies.

Monitoring of Medical Wastewater by Sensitive, Convenient, and Low-Cost Determination of Small Extracellular Vesicles Using a Glycosyl-Imprinted Sensor

The monitoring of small extracellular vesicles (sEVs) in medical waste is of great significance for the prevention of the spread of infectious diseases and the treatment of environmental pollutants in medical waste. Highly sensitive and selective detection methods are urgently needed due to the low content of sEVs in waste samples and the complex sample composition. Herein, a glycosyl-imprinted electrochemical sensor was constructed and a novel strategy for rapid, sensitive, and selective sEVs detection was proposed. The characteristic trisaccharide at the end of the glycosyl chain of the glycoprotein carried on the surface of the sEVs was used as the template molecule. The glycosyl-imprinted polymer films was then prepared by electropolymerization with o-phenylenediamine (o-PD) and 3-aminophenylboronic acid (m-APBA) as functional monomers. sEVs were captured by the imprinted cavities through the recognition and adsorption of glycosyl chains of glycoproteins on sEVs. The m-APBA molecule also acted as a signal probe and was then attached on the immobilized glycoprotein on the surface of sEVs by boric acid affinity. The electrochemical signal of m-APBA was amplificated due to the abundant glycoproteins on the surface of sEVs. The detection range of the sensor was 2.1 × 104 to 8.7 × 107 particles/mL, and the limit of detection was 1.7 × 104 particles/mL. The sensor was then applied to the determination of sEVs in medical wastewater and urine, which showed good selectivity, low detection cost, and good sensitivity.

An Electrochemiluminescent Sensor Based on Glycosyl Imprinting and Aptamer for the Detection of Cancer-Related Extracellular Vesicles

Cancer-related extracellular vesicles (EVs) are considered important biomarkers for cancer diagnosis because they can convey a large amount of information about tumor cells. In order to detect cancer-related EVs efficiently, an electrochemiluminescence (ECL) sensor for the specific identification and highly sensitive detection of EVs in the plasma of cancer patients was constructed based on dual recognitions by glycosyl-imprinted polymer (GIP) and aptamer. The characteristic glycosyl Neu5Ac-α-(2,6)-Gal-β-(1-4)-GlcNAc trisaccharide on the surface of EVs was used as a template molecule and 3-aminophenylboronic acid as a functional monomer to form a glycosyl-imprinted polymer by electropolymerization. After glycosyl elution, the imprinted film specifically recognized and adsorbed the EVs in the sample, and then the CD63 aptamer-bipyridine ruthenium (Aptamer-Ru(bpy)) was added to combine with the CD63 glycoprotein on the extracellular vesicle's surface, thus providing secondary recognition of the EVs. Finally, the EVs were quantitatively detected according to the ECL signal produced by the labeled bipyridine ruthenium. When more EVs were captured by the imprinted film, more probes were obtained after incubation, and the ECL signal was stronger. Under the optimized conditions, the ECL signal showed a good linear relationship with the concentration of EVs in the range of 9.5 × 102 to 9.5 × 107 particles/mL, and the limit of detection was 641 particles/mL. The GIP sensor can discriminate between the EV contents of cancer patients and healthy controls with high accuracy. Because of its affordability, high sensitivity, and ease of use, it is anticipated to be employed for cancer early detection and diagnosis.

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.

A molecularly imprinted sensor for single-molecule detection of pesticide metabolite at the amol/L level sensitized by water-soluble luminol derivative encapsulated liposome via click reaction

A novel luminol derivative, 4-[(1,4-dioxo-1,2,3,4-tetrahydrophthalazin-5-yl)amino]-4-oxobut-2-enoic acid (ALD) with electrochemiluminescence intensity and stability characteristics similar to luminol, but higher solubility in near neutral solution, was designed and synthesized in this study. Using this derivative, a molecular imprinted electrochemiluminescence sensor (MIECLS) was prepared for the sensitive and selective determination of 2-amino-5-mercapto-1,3,4-thiadiazole (AMT), a metabolite of bismerthiazol, thiediazole copper, thiazole zinc, and other pesticides. The ALD probes encapsulated in liposomes are immobilized on the molecularly imprinted film by light-triggered click reaction, and the concurrent release of multiple probes allows for highly sensitive detection. In the AMT concentration range of 1.00 × 10-18 - 5.00 × 10-13 mol/L, the relation between ECL response and log AMT concentration is linear. With a detection limit of 5.25 × 10-19 mol/L (about 4 - 6 molecules in 10 μL of the sample), the sensor allows for high sensitivity analysis of ultra-trace amounts of small organic compounds. In general, the ECL-based single-molecule detection technique proposed herein might be a promising alternative to fluorescence single-molecule detection.

Exploring the potential of molecularly imprinted polymers and metal/metal oxide nanoparticles in sensors: recent advancements and prospects

Metal/metal oxide nanoparticles have gained increasing attention in recent years due to their outstanding features, including optical and catalytic properties, as well as their excellent conductivity. The implementation of metal/metal oxide nanoparticles, combined with molecularly imprinted polymers (MIPs) has paved the way for a new generation of building blocks to engineer and enhance the fascinating features of advanced sensors. This review critically evaluates the impact of combining metal/metal oxide nanoparticles with MIPs in sensors. It covers synthesis strategies, advantages of coupling these materials with MIPs, and addresses questions about the selectivity of these hybrid materials. In the end, the current challenges and future perspectives of this field are discussed, with a particular focus on the potential applications of these hybrid composites in the sensor field. This review highlights the exciting opportunities of using metal/metal oxide nanoparticles along with MIPs for the development of next-generation sensors.

Research progress of sensors based on molecularly imprinted polymers in analytical and biomedical analysis

Molecularly imprinted polymers (MIPs) have had tremendous impact on biomimetic recognition due to their precise specificity and high affinity comparable to that of antibodies, which has shown the great advantages of easy preparation, good stability and low cost. The combination of MIPs with other analytical technologies can not only achieve rapid extraction and sensitive detection of target compounds, improving the level of analysis, but also achieve precise targeted delivery, in-vivo imaging and other applications. Among them, the recognition mechanism plays a vital role in chemical and biological sensing, while the improvement of the recognition element, such as the addition of new nanomaterials, can greatly improve the analytical performance of the sensor, especially in terms of selectivity. Currently, due to the need for rapid diagnosis and improved sensing properties (such as selectivity, stability, and cost-effectiveness), researchers are investigating new recognition elements and their combinations to improve the recognition capabilities of chemical sensing and bio-sensing. Therefore, this review mainly discusses the design strategies of optical sensors, electrochemical sensors and photoelectric sensors with molecular imprinting technology and their applications in environmental systems, food fields, drug detection and biology including bacteria and viruses.

A novel molecularly imprinting polypyrrole electrochemiluminescence sensor based on MIL-101-g-C3N4 for supersensitive determination of ciprofloxacin

Ciprofloxacin (CIP), a quinolone antibiotic, was rapidly and sensitively detected by integrating the molecularly imprinted polymer (MIP) with an ultra-sensitive electrochemiluminescence (ECL) method. g-C3N4, a typical polymer semiconductor, exhibited outstanding ECL efficiency and excellent ECL stability after combining with an iron-based metal-organic framework (MIL-101). Subsequently, the molecularly imprinted polypyrrole was electropolymerized on the composites of MIL-101-g-C3N4 modified glassy carbon electrode (GCE). The specific sites that could target rebinding the CIP molecules were formed on the surface of MIP after extracting the CIP templates. The determination of specific concentrations of CIP could be realized according to the difference in ECL intensity (△ECL) between the eluting and rebinding of the CIP. Under optimal conditions, a good linear response of △ECL and the logarithm of CIP concentrations was obtained in the range 1.0 × 10-9 ~ 1.0 × 10-5 mol/L, with a detection limit of 4.5 × 10-10 mol/L (S/N = 3) (the working potential was -1.8 ~ 0 V). The RSD of all points in the calibration plot was less than 5.0% and the real samples recovery was between 98.0 and 104%. This paper displays satisfactory selectivity and sensitivity, providing a rapid, convenient, and cheap method for the determination of CIP in real samples.

A novel smartphone-integrated binary-emission molecularly imprinted fluorescence sensor embedded with MIL-101(Cr) for sensitive and real-time detection of protein

Aiming for precise, real-time, and on-site analysis of proteins, an innovative binary-emission fluorescence imprinted polymer was designed by sol-gel method after mixing MIL-101(Cr), green CdTe (g-CdTe) and red CdTe (r-CdTe) for detection of protein. In this proposal, MIL-101(Cr), as a favorable supporter, provided high surface area and porosity for imprinting sites, which ameliorated the transfer rate and the sensitivity of the nanosensor. And g-CdTe and r-CdTe were served as signal transduction for dual-emission response. Based on strengthened recognition reaction between high-affinity imprinting sites and protein, the fluorescence intensities of g-CdTe and r-CdTe yielded conspicuous two responses at 528 nm and 634 nm for protein under the excitation of 350 nm. The cytochrome c (Cyt c) and trypsin were served as model proteins to verify the generality of strategy. Given prominent merits of MIL-101(Cr), g-CdTe/r-CdTe@MIL-101(Cr)@MIP exhibited good linear range of 1-30 μM for Cyt c and 0.15-4 μM for trypsin, and the limit of detection were 0.13 μM and 0.014 μM, respectively. Significantly, an unsophisticated smartphone-based sensing device was developed by integrating g-CdTe/r-CdTe@MIL-101(Cr)@MIP with a 3D printing portable device to obtain precise on-site results. As expected, this portable platform was successfully applied for monitoring Cyt c and trypsin with a detection limit of 0.71 μM and 0.026 μM, respectively. These results indicated this dual-response molecularly imprinted fluorescence senor based on smartphone provided promising perspectives on futural on-site protein analysis.

Determination of ribavirin by molecularly imprinted electrochemical sensors using pyrro-1-propionyl-alaninoyl-chitooligosaccharide and pyrrole as bifunctional monomers on Prussian blue-gold nanocomposite films

Herein, we developed a highly sensitive imprinted electrochemical sensor for the trace detection of ribavirin (RBV) using pyrrole (PYR) and pyrro-1-propionyl-alaninoyl-chitooligosaccharides (PPACO) as bifunctional monomers on Prussian blue-gold nanocomposite films. PPACO had strong molecular effect on RBV molecule and was selected by quantitative calculations. After the deposition of the Prussian blue-gold nanocomposite on a glassy carbon electrode (GCE) surface, a 4-aminothiophenol layer successfully self-assembled on the surface. Subsequently, the molecularly imprinted membrane (MIM) was subjected to electrochemical polymerization on the electrode surface using RBV as the template and PPACO and PYR as the two monomers. After eluting the RBV molecules from the MIM, the fabricated RBV-MIM/Fn-Au-PB/GCE exhibited the specific adsorption of RBV. Under optimal conditions, differential pulse voltammetry (DPV) was used to measure the performance of the synthesized sensor, which exhibited a linear relationship between the decreasing peak current and RBV concentration from 0.015 to 3.5 μM with a low detection limit of 3 nM (S/N = 3). As a proof of concept, RBV-MIM/Fn-Au-PB/GCE was also applied to monitor the RBV content in RBV granules. It showed a satisfactory recovery (96.5-99.2%) with a relative standard deviation of less than 3.5% (n = 5), and thus, we believe it has potential for practical applications.

MIP-on-a-chip: Artificial receptors on microfluidic platforms for biomedical applications

Lab-on-a-chip (LOC) as an alternative biosensing approach concerning cost efficiency, parallelization, ergonomics, diagnostic speed, and sensitivity integrates the techniques of various laboratory operations such as biochemical analysis, chemical synthesis, or DNA sequencing, etc. on miniaturized microfluidic single chips. Meanwhile, LOC tools based on molecularly imprinted biosensing approach permit their applications in various fields such as medical diagnostics, pharmaceuticals, etc., which are user-, and eco-friendly sensing platforms for not only alternative to the commercial competitor but also on-site detection like point-of-care measurements. In this review, we focused our attention on compiling recent pioneer studies that utilized those intriguing methodologies, the microfluidic Lab-on-a-chip and molecularly imprinting approach, and their biomedical applications.

An electrochemical sensing platform with a molecularly imprinted polymer based on chitosan-stabilized metal@metal-organic frameworks for topotecan detection

The present study aims to develop an electroanalytical method to determine one of the most significant antineoplastic agents, topotecan (TPT), using a novel and selective molecular imprinted polymer (MIP) method for the first time. The MIP was synthesized using the electropolymerization method using TPT as a template molecule and pyrrole (Pyr) as the functional monomer on a metal-organic framework decorated with chitosan-stabilized gold nanoparticles (Au-CH@MOF-5). The materials' morphological and physical characteristics were characterized using various physical techniques. The analytical characteristics of the obtained sensors were examined by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV). After all characterizations and optimizing the experimental conditions, MIP-Au-CH@MOF-5 and NIP-Au-CH@MOF-5 were evaluated on the glassy carbon electrode (GCE). MIP-Au-CH@MOF-5/GCE indicated a wide linear response of 0.4-70.0 nM and a low detection limit (LOD) of 0.298 nM. The developed sensor also showed excellent recovery in human plasma and nasal samples with recoveries of 94.41-106.16 % and 95.1-107.0 %, respectively, confirming its potential for future on-site monitoring of TPT in real samples. This methodology offers a different approach to electroanalytical procedures using MIP methods. Moreover, the high sensitivity and selectivity of the developed sensor were illustrated by the ability to recognize TPT over potentially interfering agents. Hence, it can be speculated that the fabricated MIP-Au-CH@MOF-5/GCE may be utilized in a multitude of areas, including public health and food quality.

Recent advances in electrochemical-based sensors amplified with carbon-based nanomaterials (CNMs) for sensing pharmaceutical and food pollutants

Foodborne-related infections due to additives and pollutants pose a considerable task for food processing enterprises. Therefore, the competent, cost-effective, and quick investigation of nutrition additives and contaminants is essential to reduce the threat of public fitness problems. The electrochemical sensor (ECS) shows facile and potent analytical approaches desirable for food protection and quality inspection over traditional methods. The consequence of a broad display of nanomaterials has paved the path for their relevance in designing high-performance ECSs appliances for medical diagnostics and conditions and food protection. This review article has discussed the importance of electrochemical-based sensors amplified with carbon-based nanomaterials (CNMs). Initially, we have demonstrated the types of pharmaceutical and food/agriculture pollutants (such as pesticides, heavy metals, antibiotics and other medical drugs) present in water. Subsequently, we have compiled the information on electrochemical techniques (such as voltammetric and electrochemical impedance spectroscopy) and their crucial parameters for detecting pollutants. Further, the applications of CNMs for sensing pharmaceutical and food pollutants have been demonstrated in detail. Finally, the topic has been concluded with existing challenges and future prospects.

Electropolymerized Molecularly Imprinted Polymer Synthesis Guided by an Integrated Data-Driven Framework for Cortisol Detection

Molecularly imprinted polymers (MIPs), often called "synthetic antibodies", are highly attractive as artificial receptors with tailored biomolecular recognition to construct biosensors. Electropolymerization is a fast and facile method to directly synthesize MIP sensing elements in situ on the working electrode, enabling ultra-low-cost and easy-to-manufacture electrochemical biosensors. However, due to the high dimensional design space of electropolymerized MIPs (e-MIPs), the development of e-MIPs is challenging and lengthy based on trial and error without proper guidelines. Leveraging machine learning techniques in building the quantitative relationship between synthesis parameters and corresponding sensing performance, e-MIPs' development and optimization can be facilitated. We herein demonstrate a case study on the synthesis of cortisol-imprinted polypyrrole for cortisol detection, where e-MIPs are fabricated with 72 sets of synthesis parameters with replicates. Their sensing performances are measured using a 12-channel potentiostat to construct the subsequent data-driven framework. The Gaussian process (GP) is employed as the mainstay of the integrated framework, which can account for various uncertainties in the synthesis and measurements. The Sobol index-based global sensitivity is then performed upon the GP surrogate model to elucidate the impact of e-MIPs' synthesis parameters on sensing performance and interrelations among parameters. Based on the prediction of the established GP model and local sensitivity analysis, synthesis parameters are optimized and validated by experiment, which leads to remarkable sensing performance enhancement (1.5-fold increase in sensitivity). The proposed framework is novel in biosensor development, which is expandable and also generally applicable to the development of other sensing materials.

A Disposable Sensor Chip Using a Paste Electrode with Surface-Imprinted Graphite Particles for Rapid and Reagentless Monitoring of Theophylline

This work focuses on a carbon-based imprinted polymer composite, employed as a molecular recognition and sensing interface in fabricating a disposable electrochemical sensor. The carbon-paste electrode was made of a molecularly imprinted polymer comprising a copolymer of methacrylic acid as the functional monomer and blended crosslinking monomers of N,N'-methylenebisacrylamide, and ethylene glycol dimethacrylate, with theophylline as the template. The analytical properties of the proposed theophylline sensor were investigated, and the findings revealed an increase in differential pulse voltammetric current compared to the non-imprinted electrode. Under optimized conditions, the sensor has shown high sensitivity, high selectivity, lower detection limit (2.5 µg/mL), and satisfactory long-term stability. Further, the sensor was tested in whole bovine blood and validated without any matrix effect and cross-reactivity. Additionally, chronoamperometry of the sensor chip supported a rapid determination of THO with a short response time of 3 s. This carbon-paste electrode is highly specific for theophylline and may be applied as a drug sensor for clinical use.

Molecularly imprinted polypyrrole based sensor for the detection of SARS-CoV-2 spike glycoprotein

This study describes the application of a polypyrrole-based sensor for the determination of SARS-CoV-2-S spike glycoprotein. The SARS-CoV-2-S spike glycoprotein is a spike protein of the coronavirus SARS-CoV-2 that recently caused the worldwide spread of COVID-19 disease. This study is dedicated to the development of an electrochemical determination method based on the application of molecularly imprinted polymer technology. The electrochemical sensor was designed by molecular imprinting of polypyrrole (Ppy) with SARS-CoV-2-S spike glycoprotein (MIP-Ppy). The electrochemical sensors with MIP-Ppy and with polypyrrole without imprints (NIP-Ppy) layers were electrochemically deposited on a platinum electrode surface by a sequence of potential pulses. The performance of polymer layers was evaluated by pulsed amperometric detection. According to the obtained results, a sensor based on MIP-Ppy is more sensitive to the SARS-CoV-2-S spike glycoprotein than a sensor based on NIP-Ppy. Also, the results demonstrate that the MIP-Ppy layer is more selectively interacting with SARS-CoV-2-S glycoprotein than with bovine serum albumin. This proves that molecularly imprinted MIP-Ppy-based sensors can be applied for the detection of SARS-CoV-2 virus proteins.

Selective detection of enrofloxacin in biological and environmental samples using a molecularly imprinted electrochemiluminescence sensor based on functionalized copper nanoclusters

Enrofloxacin (ENR) is a broad-spectrum fungicide that has been largely applied in pharmacy and animal-specific medicine. In this paper, a simple, novel and highly sensitive molecularly imprinted electrochemiluminescence (MIP-ECL) sensor based on mercaptopropionic acid-functionalized copper nanoclusters (MPA-Cu NCs) was developed to selectively detect enrofloxacin (ENR). MPA-Cu NCs prepared by a one-step method were used to modify the glassy carbon electrode. A molecularly imprinted polymer film containing the cavity was constructed after electropolymerization and elution. Under optimized conditions, the MIP-ECL sensor could detect ENR in the range of 0.1 nM-1 μM (R² = 0.9863) with a low limit of detection of 27 pM, and the recovery rates of ENR in biological and lake water samples were 88.20-105.0%. The MIP-ECL sensor provided path to improve the stability issues of Cu NCs, which might open promising avenues to develop new ECL systems for biological analysis and environmental water monitoring.

A versatile and ultrasensitive molecularly imprinted electrochemiluminescence sensor with HRP-encapsulated liposome labeled by light-triggered click reaction for pesticide residues

A novel approach for trace detection of fipronil with a molecularly imprinted electrochemiluminescence sensor (MIECLS) is proposed. The sensitivity is significantly improved via signal amplification of the enzymatic reaction of horseradish peroxidase (HRP) released from encapsulated liposomes which linked onto the template molecules after rebinding. The molecularly imprinted polymer membrane was prepared through the electropolymerization of monomers with fipronil as a template. After the elution of the template molecules, the analyte fipronil was reabsorbed into the cavities. HRP-encapsulated liposomes were linked to the target molecules by light-triggered click reaction. The higher the concentration of the target was, the more HRP-encapsulated liposomes were present on the molecularly imprinted polymer (MIP) sensor. Then, HRP was liberated from liposomes, and the catalytic degradation of hydrogen peroxide (H₂O₂) by HRP occurs, which changed the electrochemiluminescence intensity of luminol significantly. The change of the ∆ECL intensity was linearly proportional to the logarithm of the fipronil concentration ranging from 1.00 × 10^-14 to 1.00 × 10^-9 mol/L, and the detection limit was 7.77 × 10^-16 mol/L. The recoveries obtained ranged from 95.7 to 105.8% with RSD < 5%. The sensitivity of the detection was significantly improved, and the analysis process was simplified in that the incubation step required in the conventional method was avoided. The sensor proposed provides a feasible platform for ultra-trace amount determination.

Extremely Sensitive Molecularly Imprinted ECL Sensor with Multiple Probes Released from Liposomes Immobilized by a Light-Triggered Click Reaction

A molecularly imprinted electrochemiluminescence sensor was prepared for sensitive and selective determination of aminotriazole via a novel strategy of multiple Ru(bpy)₃Cl₂ probes released from liposomes immobilized by a light-triggered click reaction. This sensing strategy provides a platform for trace detection of amino-containing pesticides. The target on the molecularly imprinted membrane connected to the Ru(bpy)₃Cl₂-encapsulated liposomes via the click reaction. After the destabilizing agent Triton X-100 was added, numerous Ru(bpy)₃Cl₂ molecules were released by liposomes on the molecularly imprinted polymer electrode. The ECL response of the sensor was linearly proportional to the logarithm of the aminotriazole concentration ranging from 5.00 × 10^-18 to 1.00 × 10^-12 mol/L, and the detection limit was 1.15 × 10^-18 mol/L. The sensitivity of the detection was significantly improved, and the analysis process was simplified.

Research and Application of Highly Selective Molecular Imprinting Technology in Chiral Separation Analysis

Since residual chiral pollutants in the environment and toxic or ineffective chiral components in drugs can threat human health, there is an urgent need for methods to separation and analyze chiral molecules. Molecular imprinting technology (MIT) is a biomimetic technique for specific recognition of analytes with high potential for application in the field of chiral separation and analysis. However, since MIT has some disadvantages when used for chiral recognition, such as poor rigidity of imprinted materials, a single type of recognition site, and poor stereoselectivity, reducing the interference of conformationally and structurally similar substances to increase the efficiency of chiral recognition is difficult. Therefore, improving the rigidity of imprinted materials, increasing the types of imprinted cavity recognition sites, and constructing an imprinted microenvironment for highly selective chiral recognition are necessary for the accurate identification of chiral substances. In this article, the principle of chiral imprinting recognition is introduced, and various strategies that improve the selectivity of chiral imprinting, using derivative functional monomers, supramolecular compounds, chiral assembly materials, and biomolecules, are reviewed in the past 10 years.

Biomimetic electrochemical sensors: New horizons and challenges in biosensing applications

The urge to meet the ever-growing needs of sensing technology has spurred research to look for new alternatives to traditional analytical methods. In this scenario, the glucometer is the flagship of commercial electrochemical sensing platforms, combining selectivity, reliability and portability. However, other types of enzyme-based biosensors seldom achieve the market, in spite of the large and increasing number of publications. The reasons behind their commercial limitations concern enzyme denaturation, and the high costs associated with procedures for their extraction and purification. In this sense, biomimetic materials that seek to imitate the desired properties of natural enzymes and biological systems have come out as an appealing path for robust and sensitive electrochemical biosensors. We herein portray the historical background of these biomimicking materials, covering from their beginnings until the most impactful applications in the field of electrochemical sensing platforms. Throughout the discussion, we present and critically appraise the major benefits and the most significant drawbacks offered by the bioinspired systems categorized as Nanozymes, Synzymes, Molecularly Imprinted Polymers (MIPs), Nanochannels, and Metal Complexes. Innovative strategies of fabrication and challenging applications are further reviewed and evaluated. In the end, we ponder over the prospects of this emerging field, assessing the most critical issues that shall be faced in the coming decade.

Recent Advances in Solid-Phase Extraction (SPE) Based on Molecularly Imprinted Polymers (MIPs) for Analysis of Hormones

Steroid hormones are active substances that are necessary in the normal functioning of all physiological activities in the body, such as sexual characteristics, metabolism, and mood control. They are also widely used as exogenous chemicals in medical and pharmaceutical applications as treatments and at times growth promoters in animal farming. The vast application of steroid hormones has resulted in them being found in different matrices, such as food, environmental, and biological samples. The presence of hormones in such matrices means that they can easily come into contact with humans and animals as exogenous compounds, resulting in abnormal concentrations that can lead to endocrine disruption. This makes their determination in different matrices a vital part of pollutant management and control. Although advances in analytical instruments are constant, it has been determined that these instruments still require some sample preparation steps to be able to determine the occurrence of pollutants in the complex matrices in which they occur. Advances are still being made in sample preparation to ensure easier, selective, and sensitive analysis of complex matrices. Molecularly imprinted polymers (MIPs) have been termed as advanced solid-phase (SPE) materials for the selective extraction and preconcentration of hormones in complex matrices. This review explores the preparation and application of MIPs for the determination of steroid hormones in different sample types.

Molecular Imprinting Technology for Determination of Uric Acid

The review focuses on the overview of electrochemical sensors based on molecularly imprinted polymers (MIPs) for the determination of uric acid. The importance of robust and precise determination of uric acid is highlighted, a short description of the principles of molecular imprinting technology is presented, and advantages over the others affinity-based analytical methods are discussed. The review is mainly concerned with the electro-analytical methods like cyclic voltammetry, electrochemical impedance spectroscopy, amperometry, etc. Moreover, there are some scattered notes to the other electrochemistry-related analytical methods, which are capable of providing additional information and to solve some challenges that are not achievable using standard electrochemical methods. The significance of these overviewed methods is highlighted. The overview of the research that is employing MIPs imprinted with uric acid is mainly targeted to address these topics: (i) type of polymers, which are used to design uric acid imprint structures; (ii) types of working electrodes and/or other parts of signal transducing systems applied for the registration of analytical signal; (iii) the description of the uric acid extraction procedures applied for the design of final MIP-structure; (iv) advantages and disadvantages of electrochemical methods and other signal transducing methods used for the registration of the analytical signal; (vi) overview of types of interfering molecules, which were analyzed to evaluate the selectivity; (vi) comparison of analytical characteristics such as linear range, limits of detection and quantification, reusability, reproducibility, repeatability, and stability. Some insights in future development of uric acid sensors are discussed in this review.

Facile imprinted polymer for label-free highly selective potentiometric sensing of proteins: case of recombinant human erythropoietin

In the current study, a molecularly imprinted polymer (MIP)-based potentiometric sensor was fabricated for a label-free determination of recombinant human erythropoietin (rhEPO). The MIP sensor was operated under zero current conditions using tetra-butyl ammonium bromide as a marker ion. A highly ordered rhEPO surface imprinted layer was prepared using 3-aminopropyl triethoxysilane and tetraethoxysilane as a monomer and cross-linker, respectively, under mild reaction conditions. A two-fold increase in the signal output was obtained by polymeric surface minimization (0.5 mm) that allowed more pronounced molecular recognition (imprinting factor = 20.1). The proportion of cross-reactivity was examined using different interfering biomolecules. Results confirmed sensor specificity for both structurally related and unrelated proteins. An ~40% decrease in the response was obtained for rhEPO-β compared to rhEPO-α. The imprinted polymeric surface was evaluated using scanning electron microscopy and Fourier transform infrared spectroscopy. Under the optimal measurement conditions, a linear range of 10.00-1000.00 ng mL^-1 (10^-10 - 10^-8 M) was obtained. The sensor was employed for the determination of rhEPO in different biopharmaceutical formulations. Results were validated against standard immunoassay. Spiked human serum samples were analyzed and the assay was validated. The presence of non-specific proteins did not significantly affect (~8%) the results of our assay. A concentration-dependent linear response was produced in an identical range with detection limit as low as 6.50 ng mL^-1 (2.14 × 10^-10 M). The facile fabricated MIP sensor offers a cost-effective, portable, and easy to use alternative for biosimilarity assessment and clinical application.

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%.

A MIP-based low-cost electrochemical sensor for 2-furaldehyde detection in beverages

There is an increasing interest in determining the concentration of furanic compounds naturally formed in food aqueous matrices, by in situ, fast and low-cost methods. A sensor presenting such characteristics is here proposed, and characterized. It is based on a molecularly imprinted polymer (MIP) as a receptor with electrochemical transduction on a screen printed cell (SPC). The molecularly imprinted polymer has been developed for a particular furanic derivative, 2-furaldehyde (2-FAL). The detection bases on the reduction of 2-FAL selectively adsorbed on the polymer layer in contact with the working electrode. The polymer layer is simply formed by in situ polymerization, directly over the SPC and it was characterized by IR, SEM and electrochemical methods. Even if based on an easy and fast preparation procedure, the layer sufficiently adheres to the cell surface giving a reusable sensor. Square wave voltammetry (SWV) was applied as the signal acquisition method. The sensor performance in aqueous solution (NaCl 0.1 M) was tested, obtaining that the dose-response curve is fitted by the Langmuir adsorption isotherm. The sensitivity, and so the limit of detection, were noticeably improved by a chemometric approach based on the Design of experiment method. (optimized conditions: E_step = 0.03 V, E_pulse = 0.066 V, f = 31 s^-1). In water solution at pH around neutrality the dynamic range was from about 50 μM to 20 mM. Similar results were obtained for a white wine containing 12% ethanol, which has been considered as a typical example of beverage possibly containing furhaldehydes. The higher limit of quantification can be modulated by the amount of MIP deposited, while the lower detection limit by the conditions of the electrochemical measurement.

Gut microbiota derived trimethylamine N-oxide (TMAO) detection through molecularly imprinted polymer based sensor

Trimethylamine N-oxide (TMAO), a microbiota-derived metabolite has been implicated in human health and disease. Its early detection in body fluids has been presumed to be significant in understanding the pathogenesis and treatment of many diseases. Hence, the development of reliable and rapid technologies for TMAO detection may augment our understanding of pathogenesis and diagnosis of diseases that TMAO has implicated. The present work is the first report on the development of a molecularly imprinted polymer (MIP) based electrochemical sensor for sensitive and selective detection of TMAO in body fluids. The MIP developed was based on the polypyrrole (PPy), which was synthesized via chemical oxidation polymerization method, with and without the presence of TMAO. The MIP, NIP and the non-sonicated polymer (PPy-TMAO) were separately deposited electrophoretically onto the hydrolyzed indium tin oxide (ITO) coated glasses. The chemical, morphological, and electrochemical behavior of MIP, non-imprinted polymer (NIP), and PPy-TMAO were characterized using Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and electrochemical techniques. The detection response was recorded using differential pulse voltammetry (DPV), which revealed a decrease in the peak current with the increase in concentration of TMAO. The MIP sensor showed a dynamic detection range of 1-15 ppm with a sensitivity of 2.47 µA mL ppm^-1 cm^-2. The developed sensor is easy to construct and operate and is also highly selective to detect TMAO in body fluids such as urine. The present research provides a basis for innovative strategies to develop sensors based on MIP to detect other metabolites derived from gut microbiota that are implicated in human health and diseases.

Chiral molecular imprinted sensor for highly selective determination of D-carnitine in enantiomers via dsDNA-assisted conformation immobilization

In this paper, a novel approach was established on the basis of a molecularly imprinted technique with the aid of double-stranded deoxyribonucleic acid (dsDNA) embedded in a molecularly imprinted polymer (MIP) membrane as a new functional unit with chiral recognition for highly specific chiral recognition. The chiral molecules were immobilized and anchored in the cavities of the MIP membrane on the basis of the three-dimensional structure of a molecule determined by the functional groups, spatial characterization of the cavities of MIPs, and the spatial orientation with dsDNA embedded in MIPs. D-carnitine was selected as an example of a chiral molecular template, which intercalated into dsDNA immobilized on the gold electrode surface to form dsDNA-D-carnitine complex, and then the complex was embedded in the MIP during electropolymerization. After elution, the stereo-selective cavities were obtained. Our findings have shown that AAAA-TTTT base sequence had high affinity for D-carnitine intercalation. Combined with the electrochemical detection method, MIP sensor was prepared. The selectivity of the MIP sensor to ultratrace D-carnitine was significantly improved; the sensor had remarkable stereo-selectivity and highly chiral specific recognition to D-carnitine, and L-carnitine with a concentration of 10,000 times D-carnitine did not interfere with the detection of D-carnitine in the assay of raceme. The sensor also exhibited high sensitivity to ultratrace D-carnitine determination with a linear response to the concentration of D-carnitine in the range of 3.0 × 10^-16 mol/L to 4.0 × 10^-13 mol/L, with a detection limit of 2.24 × 10^-16 mol/L. The mechanism of chiral recognition was studied, and result showed that apart from the recognition effect of imprinted cavities, dsDNA provided chiral selectivity to the spatial orientation of chiral molecules via the intercalation of chiral molecules with dsDNA and electrostatic interaction with groups of DNA base.

A "Single-Use" Ceramic-Based Electrochemical Sensor Chip Using Molecularly Imprinted Carbon Paste Electrode

An inexpensive disposable electrochemical drug sensor for the detection of drugs (vancomycin, meropenem, theophylline, and phenobarbital) is described. Molecularly imprinted polymer (MIP) templated with the target drugs was immobilized on the surface of graphite particles using a simple radical polymerization method and packed into the working electrode of a three-electrode ceramic-based chip sensor. Differential pulse voltammetry (DPV) was used to determine the relationship between the response current and the concentration of the targeted drug while using one sensor chip for one single operation. The time required for each DPV measurement was less than 2 min. Concentrations corresponding to the therapeutic range of these drugs in plasma were taken into account while performing DPV. In all the cases, the single-used MIP sensor showed higher sensitivity and linearity than non-imprinted polymer. The selectivity test in drugs with a structure similar to that of the target drugs was performed, and it was found that MIP-based sensors were more selective than the untreated ones. Additionally, the test in whole blood showed that the presence of interfering species had an insignificant effect on the diagnostic responses of the sensor. These results demonstrate that the disposable MIP-sensor is promising for quick and straightforward therapeutic drug monitoring to prevent the toxic side effects and the insufficient therapeutic effect due to the overdose and underdose, respectively.

Microsphere Polymers in Molecular Imprinting: Current and Future Perspectives

Molecularly imprinted polymers (MIPs) are specific crosslinked polymers that exhibit binding sites for template molecules. MIPs have been developed in various application areas of biology and chemistry; however, MIPs have some problems, including an irregular material shape. In recent years, studies have been conducted to overcome this drawback, with the synthesis of uniform microsphere MIPs or molecularly imprinted microspheres (MIMs). The polymer microsphere is limited to a minimum size of 5 nm and a molecular weight of 10,000 Da. This review describes the methods used to produce MIMs, such as precipitation polymerisation, controlled/'Living' radical precipitation polymerisation (CRPP), Pickering emulsion polymerisation and suspension polymerisation. In addition, some green chemistry aspects and future perspectives will also be given.

The molecular imprinting effect of propranolol and dibenzylamine as model templates: Binding strength and selectivity

Recent studies have shown anomalies with the most studied non-covalent molecularly imprinted polymer, the propranolol imprinted one. This imprinted polymer, like many others, binds more template than the non-imprinted control polymer, but its selectivity in template adsorption is only slightly or not at all improved by imprinting, depending on the compound compared. The reasons for this anomaly are discovered here. Simple experiments show that acid homoassociation in the prepolymerisation complex is the likely cause of the anomaly. The specific conductivity of prepolymerization mixtures at different functional monomer to template ratios follows a pattern observed in homoassociating systems. Analysis of the optimal prepolymerization mixture shows that on average two molecules of the functional monomer are complexed to the basic template, even if the template lacks any other hydrogen bonding functional group than the amino group. Molecular modeling calculations provide the structure and stability of the homoassociated prepolymerization complexes. These results lead to a plausible interpretation of the anomaly, which may not be unique for the propranolol imprinted polymer, but may affect all imprinted polymers made for basic templates by using acidic functional monomers. The analytical applications of the new imprinting model are demonstrated.