Highly sensitive Fe 3 O 4 nanobeads/graphene-based molecularly imprinted electrochemical sensor for 17β-estradiol in water

Fe3O4/biochar modified with molecularly imprinted polymer as efficient persulfate activator for salicylic acid removal from wastewater: Performance and specific recognition mechanism

In this study, a novel Fe3O4-based biochar coupled surface-imprinted polymer was constructed via simple hydrothermal route for salicylic acid recognition and degradation in advanced oxidation processes. The material exhibited excellent adsorption capability, up to 118.23 mg g-1, and efficient degradation performance, 87.44% removal rate within 240 min, based on integrating the advantages of both huge specific surface area as well as abundant functional groups from biochars and specific recognition sites from imprinted cavities. Moreover, high selectivity coefficient (11.67) showed stable recognition in single and binary systems. SO4•- and •OH were confirmed as reactive oxygen species in catalytic reaction according to quenching experiments and EPR analysis. The degradation mechanism and pathway were unraveled by DFT calculations and LC-MS. Furthermore, the results of toxicity evaluation, stability and reusability demonstrated application potential in the field of water environment restoration. This study confirmed that molecular imprinting provided a promising solution to targeted removal of emerging environmental pollutants by degrading after the enrichment of pollutants to the composites surface.

A novel electrochemical sensor based on dual-functional MMIP-CuMOFs for both target recognition and signal reporting and its application for sensing bisphenol A in milk

In this work, novel magnetic molecularly imprinted CuMOFs (MMIP-CuMOFs) were synthesized and applied to construct an electrochemical bisphenol A sensor. The constructed sensor used an electrode modified with reduced graphene oxide (RGO/GCE) as the sensing platform to improve its stability and sensitivity. The Fe3O4 nanoparticles in magnetic MOFs simplified the preparation process. Moreover, the combination of CuMOFs and molecular imprinting methodology was beneficial for improving the detection specificity, and the electroactive copper hexacyanoferrate generated by the reaction of Cu2+ in CuMOFs with potassium ferricyanide was used as the signal probe. The sensor showed a good linear relationship in the range of 0.5 to 500 nmol/L, with a low detection limit of 0.18 nmol/L. In addition, the sensor had good selectivity, repeatability (RSD = 2.59 %), and a good recovery rate for actual milk sample detection (99.8-102.49 %). This technique holds great promise for the detection of detrimental substances in food.

Preparation of metal-organic framework @molecularly imprinted polymers for extracting N-nitrosamines in salted vegetables

In this paper, the novel metal-organic framework @molecularly imprinted polymers were prepared and applied in extracting N-nitrosamines from salted vegetables. The imprinted polymers were coated on the surface of MIL-101 using multi-dummy template molecules (5-nonanol, benzhydrol and N-formylpyrrolidine). The characterization and adsorbing experiments showed that the hybrid imprinted polymers presented spherical particles with typically core-shell structure, and exhibited high adsorption capacity (maximum capacity: 46.85 mg/g) and fast equilibrium rate (only 5 min) for N-nitrosamines. Various parameters (sample loading solvent, pH, washing solvent, elution solvent and elution volume) affecting solid-phase extraction were optimized. Under the optimum conditions, the solid-phase extraction process based on the hybrid polymers combined with high performance liquid chromatography-ultraviolet detection method was established and applied to analyze N-nitrosamines in different salted vegetables. The results showed that the developed method produced the linear relationship between the peak areas versus the N-nitrosamines concentrations of 0.2-10 µg/g with limit of detections from 20.6 to 76.1 ng/g. The spiked recovery of N-nitrosamines in the salted vegetable samples was in the range of 66-100.5 % with relative standard deviation from 0.1 to 3.4 %. Those results demonstrated that the established method was sensitive and efficient for directly enriching and analyzing trace N-nitrosamines in salted vegetables.

Electrochemical Determination of 17-β-Estradiol Using a Glassy Carbon Electrode Modified with α-Fe2O3 Nanoparticles Supported on Carbon Nanotubes

In this study, a novel electrochemical assay for determining 17-β-estradiol (E2) was proposed. The approach involves modifying a glassy carbon electrode (GCE) with a nanocomposite consisting of α-Fe2O3 nanoparticles supported on carbon nanotubes (CNTs)-denoted as α-Fe2O3-CNT/GCE. The synthesis of the α-Fe2O3-CNT nanocomposite was achieved through a simple and cost-effective hydrothermal process. Morphological and chemical characterization were conducted using scanning electron microscopy (SEM), Raman spectroscopy, and energy-dispersive X-ray spectroscopy (EDX). The presence of the α-Fe2O3-CNT film on the GCE surface resulted in an enhanced electrochemical response to E2, preventing electrode surface fouling and mitigating the decrease in peak current intensity during E2 oxidation. These outcomes substantiate the rationale behind the GCE modification. After the optimization of experimental conditions, E2 was determined by the square wave voltammetry technique using 0.1 mol L-1 KCl solution (pH = 7.0) with 20% ethanol as a supporting electrolyte. A linear concentration range of 5.0-100.0 nmol L-1 and a low limit of detection of 4.4 nmol L-1 were obtained. The electroanalytical method using α-Fe2O3-CNT/GCE was applied for E2 determination in pharmaceutical, lake water, and synthetic urine samples. The obtained results were attested by recovery tests and by high-performance liquid chromatography as a comparative technique at a 95% confidence level. Thus, the developed electrochemical sensor is simple and fast to obtain, presents high accuracy, and is viable for determining E2 in routine analysis.

Synthesis of MRGO@ZIF-7-Based Molecular Imprinted Polymer by Surface Polymerization for the Fast and Selective Removal of Phenolic Endocrine-Disrupting Chemicals from Aqueous Environments

In this study, Zn(NO3)2·6H2O was selected as the metal source, and ZIF-7-modified magnetic graphene-based matrix materials (MRGO@ZIF-7) were prepared by in situ growth. ZIF-7 modified magnetic graphene-based molecular imprinting complexes (MRGO@ZIF7-MIP) were successfully synthesized by a surface molecular imprinting technique using bisphenol A (BPA) as the template molecule. The obtained experimental materials were characterized by X-ray diffraction (XRD), Brunner–Emmet–Teller (BET) analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM), vibrating sample magnetometry (VSM), and X-ray photoelectron spectroscopy (XPS). The proper adsorption and selective recognition ability of the MRGO@ZIF7-MIP were studied by an equilibrium adsorption method. The obtained MRGO@ZIF7-MIP showed significant molecular recognition of bisphenol A (BPA) and good selectivity and reproducibility for BPA in different aqueous environments such as drinking water, river water, and lake water. These properties make this material potentially applicable for the efficient removal of phenolic endocrine disruptors in real water environments.

Development of a Chemically Modified Electrode with Magnetic Molecularly Imprinted Polymer (MagMIP) for 17-β-Estradiol Determination in Water Samples

The present work consisted of the development of an electrode based on carbon paste modified with magnetic molecularly imprinted polymer (CPE-MagMIP) for 17-β-estradiol (E2) detection. The incorporation of magnetic material (MagMIP) improved sensor performance, an increase of over 317%. The proposed method resulted in a linear response range from 0.5 to 14.0 μM, and the detection limit (LOD) and quantification limit (LOQ) were equal to 0.13 and 0.44 μM, respectively. Under optimized conditions, the developed sensor obtained satisfactory parameters in E2 determination in water samples, demonstrating selectivity, accuracy, and precision, making it a promising method for monitoring E2 in environmental samples.

A review on carbon-based molecularly-imprinted polymers (CBMIP) for detection of hazardous pollutants in aqueous solutions

This article discusses the unique properties and performance of carbon-based molecularly-imprinted polymers (MIPs) for detecting hazardous pollutants in aqueous solutions. Although MIPs have several advantages such as specific recognition sites, selectivity, and stability, they suffer from a series of drawbacks, including loss of conductivity, electrocatalytic activity, and cost, which limit their use in various fields. Carbon-based MIPs, which utilize carbon electrodes, carbon nanoparticles, carbon dots, carbon nanotubes, and graphene substrates, have been the focus of research in recent years to enhance their properties and remove their weaknesses as much as possible. These carbon-based nanomaterials have excellent sensitivity and specificity for molecular identification. As a result, they have been widely used in various applications, such as assessing the environmental, biological, and food samples. This article examines the growth of carbon-based MIPs and their environmental applications.

Wearable Sensors for Healthcare: Fabrication to Application

This paper presents a substantial review of the deployment of wearable sensors for healthcare applications. Wearable sensors hold a pivotal position in the microelectronics industry due to their role in monitoring physiological movements and signals. Sensors designed and developed using a wide range of fabrication techniques have been integrated with communication modules for transceiving signals. This paper highlights the entire chronology of wearable sensors in the biomedical sector, starting from their fabrication in a controlled environment to their integration with signal-conditioning circuits for application purposes. It also highlights sensing products that are currently available on the market for a comparative study of their performances. The conjugation of the sensing prototypes with the Internet of Things (IoT) for forming fully functioning sensorized systems is also shown here. Finally, some of the challenges existing within the current wearable systems are shown, along with possible remedies.

Novel Surfactant-Induced MWCNTs/PDMS-Based Nanocomposites for Tactile Sensing Applications

The paper presents the use of surfactant-induced MWCNTs/PDMS-based nanocomposites for tactile sensing applications. The significance of nanocomposites-based sensors has constantly been growing due to their enhanced electromechanical characteristics. As a result of the simplified customization for their target applications, research is ongoing to determine the quality and quantity of the precursor materials that are involved in the fabrication of nanocomposites. Although a significant amount of work has been done to develop a wide range of nanocomposite-based prototypes, they still require optimization when mixed with polydimethylsiloxane (PDMS) matrices. Multi-Walled Carbon Nanotubes (MWCNTs) are one of the pioneering materials used in multifunctional sensing applications due to their high yield, excellent electrical conductivity and mechanical properties, and high structural integrity. Among the other carbon allotropes used to form nanocomposites, MWCNTs have been widely studied due to their enhanced bonding with the polymer matrix, highly densified sampling, and even surfacing throughout the composites. This paper highlights the development, characterization and implementation of surfactant-added MWCNTs/PDMS-based nanocomposites. The prototypes consisted of an optimized amount of sodium dodecyl sulfonate (SDS) and MWCNTs mixed as nanofillers in the PDMS matrix. The results have been promising in terms of their mechanical behaviour as they responded well to a maximum strain of 40%. Stable and repeatable output was obtained with a response time of 1 millisecond. The Young’s Modulus of the sensors was 2.06 MPa. The utilization of the prototypes for low-pressure tactile sensing applications is also shown here.

Integration of Different Graphene Nanostructures with PDMS to Form Wearable Sensors

This paper presents a substantial review of the fabrication and implementation of graphene-PDMS-based composites for wearable sensing applications. Graphene is a pivotal nanomaterial which is increasingly being used to develop multifunctional sensors due to their enhanced electrical, mechanical, and thermal characteristics. It has been able to generate devices with excellent performances in terms of sensitivity and longevity. Among the polymers, polydimethylsiloxane (PDMS) has been one of the most common ones that has been used in biomedical applications. Certain attributes, such as biocompatibility and the hydrophobic nature of PDMS, have led the researchers to conjugate it in graphene sensors as substrates or a polymer matrix. The use of these graphene/PDMS-based sensors for wearable sensing applications has been highlighted here. Different kinds of electrochemical and strain-sensing applications have been carried out to detect the physiological signals and parameters of the human body. These prototypes have been classified based on the physical nature of graphene used to formulate the sensors. Finally, the current challenges and future perspectives of these graphene/PDMS-based wearable sensors are explained in the final part of the paper.

A signal-off photoelectrochemical aptasensor for ultrasensitive 17β-estradiol detection based on rose-like CdS@C nanostructure and enzymatic amplification

Carbon-coated cadmium sulfide rose-like nanostructures (CdS@C NRs) were prepared via a facile solvothermal approach and used as the photoelectrochemical (PEC) sensing platform for the integration of functional biomolecules. Based on this, a novel "signal-off" PEC aptasensor mediated by enzymatic amplification was proposed for the sensitive and selective detection of 17β-estradiol (E2). In the presence of E2, alkaline phosphatase-modified aptamer (ALP-apta) were released from the electrode surface through the specific recognition with E2, which caused the negative effect on PEC response due to the decrease of ascorbic acid (AA) produced by the ALP in situ enzymatic catalysis. The developed PEC aptasensor for detection of E2 exhibited a wide linear range of 1.0-250 nM, with the low detection limit of 0.37 nM. This work provides novel insight into the design of potential phoelectroactive materials and the application of signal amplification strategy in environmental analysis field.

Graphitic carbon nitride and APTES modified advanced electrochemical biosensor for detection of 17β-estradiol in spiked food samples

This work demonstrates a simple and inexpensive electrochemical biosensing pathway for selective and sensitive recognition of 17β-estradiol (E2) in environmental and food samples. The biosensing system is based on graphitic carbon nitride (g-C₃N₄) and a conductive polymer 3-aminopropyltriethoxysilane (APTES). The proposed biosensor shows the ability to detect E2 in attomolar levels within a wide linear logarithm concentration range of 1 × 10⁻⁶ to 1 × 10⁻¹⁸ mol L⁻¹ with a limit of detection (LOD) of 9.9 × 10⁻¹⁹ mol L⁻¹. The selectivity of the developed biosensor was confirmed by conducting the DPV of similarly structured hormones and naturally occurring substances. The proposed biosensor is highly stable and applicable to detect E2 in the presence of spiked food and environmental samples with satisfactory recoveries ranging from 95.1 to 104.8%. So, the designed electrochemical biosensor might be an effective alternative tool for the detection of E2 and other endogenous substances to attain food safety.

This work demonstrates a simple and inexpensive electrochemical biosensing pathway for selective and sensitive recognition of 17β-estradiol (E2) in environmental and food samples.

Magnetic-molecularly imprinted polymers in electrochemical sensors and biosensors

Magnetic particles, as well as molecularly imprinted polymers, have revolutionized separation and bioanalytical methodologies in the 1980s due to their wide range of applications. Today, biologically modified magnetic particles are used in many scientific and technological applications and are integrated in more than 50,000 diagnostic instruments for the detection of a huge range of analytes. However, the main drawback of this material is their stability and high cost. In this work, we review recent advances in the synthesis and characterization of hybrid molecularly imprinted polymers with magnetic properties, as a cheaper and robust alternative for the well-known biologically modified magnetic particles. The main advantages of these materials are, besides the magnetic properties, the possibility to be stored at room temperature without any loss in the activity. Among all the applications, this work reviews the direct detection of electroactive analytes based on the preconcentration by using magnetic-MIP integrated on magneto-actuated electrodes, including food safety, environmental monitoring, and clinical and pharmaceutical analysis. The main features of these electrochemical sensors, including their analytical performance, are summarized. This simple and rapid method will open the way to incorporate this material in different magneto-actuated devices with no need for extensive sample pretreatment and sophisticated instruments.

A hollow visible-light-responsive surface molecularly imprinted polymer for the detection of chlorpyrifos in vegetables and fruits

A visible-light-responsive azobenzene derivative, 3,5-dichloro-4-((2,6-dichloro-4-(methacryloyloxy)phenyl)diazenyl)benzoic acid, was synthesized and used as the functional monomer to fabricate a visible-light-responsive core-shell structured surface molecularly imprinted polymer (PS-co-PMAA@VSMIP). After removal of the sacrificial PS-co-PMAA core, a hollow structured surface molecularly imprinted polymer (HVSMIP) was obtained. Both the PS-co-PMAA@VSMIP and HVSMIP were used for the detection of chlorpyrifos, a moderately toxic organophosphate pesticide. They exhibited good visible-light-responsive properties (550 nm for trans→cis and 440 nm for cis→trans isomerization for an azobenzene chromophore) in ethanol/water (9:1, v/v). Compared with the PS-co-PMAA@VSMIP, the HVSMIP had a larger surface area, pore volume, binding capacity, imprinting effect, maximum chemical binding capacity, dissociation constant, and photo-isomerization rate. The HVSMIP was applied to detect trace chlorpyrifos in fruit and vegetable samples. This was achieved by measuring the trans→cis rate constant of the HVSMIP in the sample solution, with good recoveries, low relative standard deviations, and a low detection limit.

Nanomaterial-based electrochemical sensors and biosensors for the detection of pharmaceutical compounds

The surging growth of the pharmaceutical industry is a result of the rapidly increasing human population, which has inevitably led to new biomedical and environmental issues. Aside from the quality control of pharmaceutical production and drug delivery, there is an urgent need for precise, sensitive, portable, and cost-effective technologies to track patient overdosing and to monitor ambient water sources and wastewater for pharmaceutical pollutants. The development of advanced nanomaterial-based electrochemical sensors and biosensors for the detection of pharmaceutical compounds has garnered immense attention due to their advantages, such as high sensitivity and selectivity, real-time monitoring, and ease of use. This review article surveys state-of-the-art nanomaterials-based electrochemical sensors and biosensors for the detection and quantification of six classes of significant pharmaceutical compounds, including anti-inflammatory, anti-depressant, anti-bacterial, anti-viral, anti-fungal, and anti-cancer drugs. Important factors such as sensor/analyte interactions, design rationale, fabrication, characterization, sensitivity, and selectivity are discussed. Strategies for the development of high-performance electrochemical sensors and biosensors tailored toward specific pharmaceuticals are highlighted to provide readers and scientists with an extensive toolbox for the detection of a wide range of pharmaceuticals. Our aims are two-fold: (i) to inspire readers by further elucidating the properties and functionalities of existing nanomaterials for the detection of pharmaceuticals; and (ii) to provide examples of the potential opportunities that these devices have for the advanced sensing of pharmaceutical compounds toward safeguarding human health and ecosystems on a global scale.

Study on the fluorescence of double-emission carbon quantum dots by improved intercept method

The fluorescence mechanism of dual-emission carbon quantum dots (DCQDs) is investigated by the improved intercept method, of which the DCQDs with high quantum yield are synthesized by hydrothermal method by using the precursor of sulfadiazine. The research of the morphology, chemical properties and fluorescence properties on DCQDs, shows that DCQDs have graphene-like structure and well-resolved lattice fringes, and that DCQDs fluorescence emission as well intensity has reversibility between acid and alkaline. Based on the ultraviolet absorption spectrum (UV-vis) of the DCQDs, the band gap of DCQDs is estimated by the improved intercept method. Then, the change law of DCQDs emission wavelength at different excitation wavelengths is studied by using the estimated band gap. It is found that the improved intercept method is well consisted with the emission change law of DCQDs at different excitation wavelengths. In addition, the influence of different concentration of Fe3+ on the estimated band gap of DCQDs shows that the Fe3+ has big influence on the band gap of 3.99 eV and 3.06 eV but almost no effect on band gap of 4.93 eV and 3.67 eV. It indicates that the quenching of Fe3+ to DCQDs may be due to the band gap caused by surface defect is changed by Fe3+. Also, DCQDs are used as probe to detect Fe3+ and used as spray ink. Thereby, the improved intercept method may provide a new direction for researching the fluorescence mechanism of carbon quantum dots.

Truncated affinity-improved aptamers for 17β-estradiol determination by AuNPs-based colorimetric aptasensor

17β-estradiol (E2) residues could enrich in organisms via food chain and lead to harmful biological effects for human body. To ascertain the binding domain of original E2 aptamer (E00) with long-sequence (76-mer), we developed novel truncated aptamers from E00, through rationally designed truncation by intercepting a single ring or a combination of rings (containing hairpin loop, interior loop or multiloop) at different sites and retaining appropriate double helix regions. Through comparison, 15-mer E09 presented improved affinity and higher specificity, indicating the hairpin loop near to 3' end of E00 served on the binding domain to E2. E09 was used for gold nanoparticles (AuNPs)-based colorimetric determination of E2, achieved the detection limit of 0.02 μg/mL. The truncated aptamer (only 15-mer) first proposed in this study has great application potential in E2 determination, and this work provides proof-of-concept study for truncation of other long-sequence aptamers.

Application of Nanostructured Carbon-Based Electrochemical (Bio)Sensors for Screening of Emerging Pharmaceutical Pollutants in Waters and Aquatic Species: A Review

Pharmaceuticals, as a contaminant of emergent concern, are being released uncontrollably into the environment potentially causing hazardous effects to aquatic ecosystems and consequently to human health. In the absence of well-established monitoring programs, one can only imagine the full extent of this problem and so there is an urgent need for the development of extremely sensitive, portable, and low-cost devices to perform analysis. Carbon-based nanomaterials are the most used nanostructures in (bio)sensors construction attributed to their facile and well-characterized production methods, commercial availability, reduced cost, high chemical stability, and low toxicity. However, most importantly, their relatively good conductivity enabling appropriate electron transfer rates-as well as their high surface area yielding attachment and extraordinary loading capacity for biomolecules-have been relevant and desirable features, justifying the key role that they have been playing, and will continue to play, in electrochemical (bio)sensor development. The present review outlines the contribution of carbon nanomaterials (carbon nanotubes, graphene, fullerene, carbon nanofibers, carbon black, carbon nanopowder, biochar nanoparticles, and graphite oxide), used alone or combined with other (nano)materials, to the field of environmental (bio)sensing, and more specifically, to pharmaceutical pollutants analysis in waters and aquatic species. The main trends of this field of research are also addressed.

Magnetic molecularly imprinted electrochemical sensors: A review

The preparation and practical applications of molecularly imprinted electrochemical sensors (MIECSs) remain challenging due to issues involving electrode surface renewal modes, low adsorption capacities, and sample preparation speeds. To solve these issues, magnetic molecularly imprinted electrochemical sensors (MMIECSs) have been extensively explored by various groups. Recently, MMIECSs fabricated based on diverse strategies have yielded insight into the development of MIECSs, and they have provided effective paths for sample preparation, immobilization and renewal of molecularly imprinted polymers (MIPs) on the electrode surface, leading to promising performances of MIECSs. This review comprehensively describes the research advances for various types of MMIECSs and their applications in the fields of food safety, environmental monitoring, and clinical and pharmaceutical analysis. Based on our understanding of MMIECSs, the literature in this field is thoroughly explored and classified in this review. The challenges existing in this research area and some potential strategies for the rational design of high-performance MMIECS are also outlined.

Voltammetric sensor based on cobalt-poly(methionine)-modified glassy carbon electrode for determination of estriol hormone in pharmaceuticals and urine

A voltammetric sensor based on the electropolymerization of cobalt-poly(methionine) (Co-poly(Met)) on a glassy carbon electrode (GCE) was developed and applied for the determination of estriol by differential pulse voltammetry (DPV) for the first time. The electrochemical properties of the Co-poly(Met)/GCE were analysed by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used to characterize the polymers on the GCE surface. The deposition of the Co-poly(Met) film on the GCE surface enhanced the sensor electronic transfer. CV studies revealed that estriol exhibits an irreversible oxidation peak at +0.58 V for the Co-poly(Met)/GCE (vs. Ag/AgCl reference electrode) in 0.10 mol/L Britton-Robinson buffer solution (pH = 7.0). Different voltammetric scan rates (10–200 mV/s) suggested that the estriol oxidation on the Co-poly(Met)/GCE surface is controlled by adsorption and diffusion processes. Based on the optimized DPV conditions, the linear responses for estriol quantification were from 0.596 μmol/L to 4.76 μmol/L (R² = 0.996) and from 5.66 μmol/L to 9.90 μmol/L (R² = 0.994) with a limit of detection (LOD) of 0.0340 μmol/L and a limit of quantification (LOQ) of 0.113 μmol/L. The DPV-Co-poly(Met)/GCE method provided good intra-day and inter-day repeatability with RSD values lower than 5%. Also, no interference of real sample matrices was observed on the estriol voltammetric response, making the DPV-Co-poly(Met)/GCE highly selective for estriol. The accuracy test showed that the estriol recovery was in the ranges 96.7%–103% and 98.7%–102% for pharmaceutical tablets and human urine, respectively. The estriol quantification in pharmaceutical tablets performed by the Co-poly(Met)/GCE-assisted DPV method was comparable to the official analytical protocols.

Doping of transition metal dichalcogenides in molecularly imprinted conductive polymers for the ultrasensitive determination of 17β-estradiol in eel serum

Molecularly imprinted polymers (MIPs) have been developed to replace antibodies for the recognition of target molecules (such as antigens), and have been integrated into electrochemical sensing approaches by polymerization onto an electrode. Electrochemical sensing is inexpensive and flexible, and has demonstrated utility in point-of-care devices. In this work, several 2D (conductive) materials were employed to improve the performance of MIP sensors. Screen-printed electrodes were coated by the electropolymerization of aniline and metanilic acid, commingled with target molecules and various 2D materials. Tungsten disulfide (WS₂) with an average particle size of 2 μm was found to increase the sensitivity of detection of molecularly imprinted conductive polymer-coated electrodes to 17β-estradiol. As estradiol concentrations are important to eel aquaculture, we screened eel serum samples to determine their 17β-estradiol concentrations, which were found to be in the range 28.2 ± 3.6 to 73.0 ± 11.6 pg/mL after dilution. These results were in agreement with measurements using commercial immunoanalysis.

Preparation and applications of electrochemical chemosensors based on carbon-nanomaterial-modified molecularly imprinted polymers

The past few decades have witnessed a rapid development in electrochemical chemosensors (ECCSs). The integration of carbon nanomaterials (CNMs) and molecularly imprinted polymers (MIPs) has endowed ECCSs with high selectivity and sensitivity toward target detection. Due to the integrated merits of MIPs and CNMs, CNM-modified MIPs as ECCSs have been widely reported and have excellent detection applications. This review systematically summarized the general categories, preparation strategies, and applications of ECCSs based on CNM-modified MIPs. The categories include CNM-modified MIPs often hybridized with various materials and CNM-encapsulated or CNM-combined imprinting silica and polymers on working electrodes or other substrates. The preparation strategies include the polymerization of MIPs on CNM-modified substrates, co-polymerization of MIPs and CNMs on substrates, drop-casting of MIPs on CNM-modified substrates, self-assembly of CNMs/MIP complexes on substrates, and so forth. We discussed the in situ polymerization, electro-polymerization, and engineering structures of CNM-modified MIPs. With regard to potential applications, we elaborated the detection mechanisms, signal transducer modes, target types, and electrochemical sensing of targets in real samples. In addition, this review discussed the present status, challenges, and prospects of CNM-modified MIP-based ECCSs. This comprehensive review is desirable for scientists from broad research fields and can promote the further development of MIP-based functional materials, CNM-based hybrid materials, advanced composites, and hybrid materials.

A promising voltammetric biosensor based on glutamate dehydrogenase/Fe3O4/graphene/chitosan nanobiocomposite for sensitive ammonium determination in PM2.5

A novel NH₄⁺ voltammetric electrochemical biosensor was constructed by immobilizing glutamate dehydrogenase (GLDH)/Fe₃O₄/graphene (GR)/chitosan (CS) nanobiocomposite onto a glassy carbon electrode (GCE). On the GLDH/Fe₃O₄/GR/CS/GCE, GLDH catalyzed the reversible reaction, i.e., the reductive amination of α-ketoglutaric acid and the oxidative deamination of L-glutamate. The electrons produced in the enzymatic reactions were transferred to the surface of the electrode via the [Fe(CN)₆]^3-/4- couple, which helped for the amplification of the electrochemical signal. The electrochemical detection of NH₄⁺ was based on the fact that the enhanced response current was proportional to the NH₄⁺ concentration. Owing to the combination of the advantages of the synergistic effects of Fe₃O₄ nanospheres, GR and CS, a promising platform for NH₄⁺ sensing was provided. Under optimum conditions, the introduced biosensor had a linear range of 0.4-2.0 μM for NH₄⁺ with the detection and quantification limits of 0.08 and 0.27 μM, respectively. Moreover, the biosensor exhibited good sensitivity and excellent reproducibility. It could retain 91.8% of its original response after two weeks of storage at 4 °C, suggesting satisfactory stability. Additionally, the proposed biosensor was successfully applied to detect NH₄⁺ levels in PM_2.5 samples, indicating its feasibility for application in NH₄⁺monitoring in the environmental fields.

An Electrochemical Sensor for Diphenylamine Detection Based on Reduced Graphene Oxide/Fe₃O₄-Molecularly Imprinted Polymer with 1,4-Butanediyl-3,3'-bis-l-vinylimidazolium Dihexafluorophosphate Ionic Liquid as Cross-Linker

In this paper, we report a new composite of reduced graphene oxide/Fe₃O₄-ionic liquid based molecularly imprinted polymer (RGO/Fe₃O₄-IL-MIP) fabricated for diphenylamine (DPA) detection. RGO/Fe₃O₄-IL-MIP was prepared with RGO/Fe₃O₄ as supporter, ionic liquid 1-vinyl-3-butylimidazolium hexafluorophosphate ([VC₄mim][PF₆]) as functional monomer, ionic liquid 1,4-butanediyl-3,3'-bis-l-vinylimidazolium dihexafluorophosphate ([V₂C₄(mim)₂][(PF₆)₂]) as cross-linker, and diphenylamine (DPA) as template molecule. Fourier transform infrared spectroscopy, thermal gravimetric analysis, scanning electron microscopy, and vibrating sample magnetometer were employed to characterize the RGO/Fe₃O₄-IL-MIP composite. RGO/Fe₃O₄-IL-MIP was then drop-cast onto a glassy carbon electrode to construct an electrochemical sensor for DPA. The differential pulse voltammetry (DPV) peak current response for 20 μM DPA of RGO/Fe₃O₄-IL-MIP modified glassy carbon electrode (GCE) was 3.24 and 1.68 times that of RGO/Fe₃O₄-IL-NIP and RGO/Fe₃O₄-EGDMA-MIP modified GCEs, respectively, indicating the advantage of RGO/Fe₃O₄-IL-MIP based on ionic liquid (IL) as a cross-linker. The RGO/Fe₃O₄-IL-MIP sensor demonstrated good recognition for DPA. Under the optimized conditions, the RGO/Fe₃O₄-IL-MIP sensor exhibited a DPA detection limit of 0.05 μM (S/N = 3) with a linear range of 0.1⁻30 μM. Moreover, the new RGO/Fe₃O₄-IL-MIP based sensor detected DPA in real samples with satisfactory results.

Electrochemical sensors based on molecularly imprinted polymers on Fe3O4/graphene modified by gold nanoparticles for highly selective and sensitive detection of trace ractopamine in water

A novel molecular imprinting polymer (MIP)-based electrochemical senor, consisting of Fe3O4 nanobeads and gold nanoparticles on a reduced graphene oxide (RGO) substrate, was fabricated to detect ractopamine (RAC) in water using the reversible addition fragmentation chain transfer (RAFT) polymerization technique. The Au nanoparticles widely dispersed on RGO can significantly increase the response current for RAC detection in water, which is confirmed by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and theoretical calculations. By means of the differential pulse voltammetry technique, the as-prepared MIP-based electrode shows a dynamic linear range of 0.002 to 0.1 μM with a correlation coefficient of 0.992 and a remarkably low detection limit of 0.02 nM (S/N = 3). Additionally, the sensor exhibits high binding affinity and selectivity towards RAC with excellent reproducibility. Our study demonstrates the potential for the proposed electrochemical sensors in monitoring organic pollutants in water.

Double strand DNA functionalized Au@Ag Nps for ultrasensitive detection of 17β-estradiol using surface-enhanced raman spectroscopy

A detection method for 17β-estradiol (E2) using surface-enhanced Raman scattering (SERS)-based aptamer sensor was presented. Raman reporter molecule Cy3 labeled E2-aptamer and DNA functionalized gold-silver core-shell nanoparticles (Au@Ag CS NPs) offered SERS with high sensitivity and selectivity. Based on the fabricated double strand DNA-immobilized gold-silver core-shell nanoparticles (Au@Ag NPs), SERS signal intensity of Raman reporter changed with the number of Cy3-labeled aptamer attached to the core-shell nanoparticles due to the strong binding affinity between the aptamers and E2 with different concentrations. A wide linear range from 1.0 × 10^-13 to 1.0 × 10^-9 was obtained for the detection of E2, with a low detection limit of 2.75 fM. This proposed method showed highly sensitive and selective for detecting E2, and could be used to determine E2 in actual samples.

Design of an enhanced SAT using the graphene-MAR mixture for the removal of 17β-E2 at a demonstration site of Qianjin farm in China

An adsorption-enhanced soil aquifer treatment (SAT) system was designed to reduce the level of estrogens below the threshold stipulated by the standards. The 17β-E2 adsorption by graphene and MARs (H103) was investigated and an optimum amount of graphene and MARs in the mixture was determined using the linear programming. The kinetics and isotherm characteristics of both adsorbents were well described by the Lagergren pseudo-second order and the Freundlich model, respectively. The 17β-E2 adsorption on graphene and H103 was 88% and 70.37%, and the high temperature was beneficial to the 17β-E2 adsorption on graphene while the thermodynamic behaviors of H103 were in direct contrast to that of graphene. The study found that the maximum economic benefits could be achieved when the mass of graphene and H103 in the mixture is 2.79 g and 13.20 kg, respectively.

A novel electrochemical sensor based on Fe3O4-doped nanoporous carbon for simultaneous determination of diethylstilbestrol and 17β-estradiol in toner

In this paper, Fe₃O₄-doped nanoporous carbon (Fe₃O₄-NC) was synthesized through the carbonization of Fe-porous coordination polymer (Fe-PCP), which are also known as metal-organic framework (MOF), and fabricated into an electrochemical sensor for simultaneous analysis of diethylstilbestrol (DES) and 17β-estradiol (E2) in toner. Fe₃O₄-NC was characterized by scanning electron microscope (SEM), powder X-ray diffraction (pXRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, N₂ adsorption-desorption and so on. It is of great practical significance to achieve the simultaneous determination of the two estrogens because estrogens are co-existing in many real samples. The simultaneous determination of two common estrogens, DES and E2, was achieved through electro-catalytically oxidization at a Fe₃O₄-NC modified glassy carbon electrode (Fe₃O₄-NC/GCE). The peak currents of DES and E2 increased linearly as their concentrations increasing from 0.01 to 12 μmol/L and from 0.01 to 20 μmol/L, with detection limits of 4.6 nmol/L and 4.9 nmol/L (S/N = 3), respectively. This work was focused on the simultaneous determination of the two estrogens in toner. Furthermore, the recoveries of DES and E2 were 91.2-110%, in actual toner samples. The experimental results manifest that the sensor with a stronger anti-interference ability can be used for the simultaneous detection of DES and E2 in the actual toner sample.

Imprinted Oxide and MIP/Oxide Hybrid Nanomaterials for Chemical Sensors †

The oxides of transition, post-transition and rare-earth metals have a long history of robust and fast responsive recognition elements for electronic, optical, and gravimetric devices. A wide range of applications successfully utilized pristine or doped metal oxides and polymer-oxide hybrids as nanostructured recognition elements for the detection of biologically relevant molecules, harmful organic substances, and drugs as well as for the investigative process control applications. An overview of the selected recognition applications of molecularly imprinted sol-gel phases, metal oxides and hybrid nanomaterials composed of molecularly imprinted polymers (MIP) and metal oxides is presented herein. The formation and fabrication processes for imprinted sol-gel layers, metal oxides, MIP-coated oxide nanoparticles and other MIP/oxide nanohybrids are discussed along with their applications in monitoring bioorganic analytes and processes. The sensor characteristics such as dynamic detection range and limit of detection are compared as the performance criterion and the miniaturization and commercialization possibilities are critically discussed.

Molecularly imprinted polymers for the detection of illegal drugs and additives: a review

This review (with 154 refs.) describes the current status of using molecularly imprinted polymers in the extraction and quantitation of illicit drugs and additives. The review starts with an introduction into some synthesis methods (lump MIPs, spherical MIPs, surface imprinting) of MIPs using illicit drugs and additives as templates. The next section covers applications, with subsections on the detection of illegal additives in food, of doping in sports, and of illicit addictive drugs. A particular focus is directed towards current limitations and challenges, on the optimization of methods for preparation of MIPs, their applicability to aqueous samples, the leakage of template molecules, and the identification of the best balance between adsorption capacity and selectivity factor. At last, the need for convincing characterization methods, the lack of uniform parameters for defining selectivity, and the merits and demerits of MIPs prepared using nanomaterials are addressed. Strategies are suggested to solve existing problems, and future developments are discussed with respect to a more widespread use in relevant fields. Graphical abstract This review gives a comprehensive overview of the advances made in molecularly imprinting of polymers for use in the extraction and quantitation of illicit drugs and additives. Methods for syntheses, highlighted applications, limitations and current challenges are specifically addressed.

Gold nanrods plasmon-enhanced photoelectrochemical aptasensing based on hematite/N-doped graphene films for ultrasensitive analysis of 17β-estradiol

It remains a vital task to establish ultrasensitive sensing interfaces for detection of target analytes to meet the demands of modern analysis. Herein, a highly sensitive turn-on photoelectrochemical (PEC) platform for trace 17β-estradiol (E2) assay was developed based on Au nanrods (AuNRs) with surface plasmon resonance (SPR) properties induced signal amplification. Specifically, a ternary hybrid was prepared by integrating hematite (α-Fe₂O₃) nanocrystals and N-doped graphene (NG) with AuNRs, which further served as highly efficient photoactive species. Subsequently, a PEC sensing platform was fabricated based on the specific binding of E2 and its aptamer. On such a sensor, the capture of E2 molecules by aptamers led to increased photocurrent. This was attributed to that the specific recognition reaction between E2 and aptamer resulted in the conformational change of the aptamers and complete dissociation of some aptamers on the PEC sensing interface. It can be confirmed by the electrochemical impedance spectroscopy (EIS) results. This process decreased the steric hindrances between the electrode surface and solution and thus increased the photocurrent response. Under the optimal conditions, the as-prepared PEC aptasensor exhibited superb analytical performances for detection of E2 in the range from 1×10^-15M to 1×10^-9M with a detection limit of 3.3×10^-16M. The aptasensor manifested outstanding selectivity towards E2 when other endocrine disrupting compounds with similar structure coexisted. Furthermore, the aptasensor was successfully applied for the determination of E2 in milk powder. The present strategy provides a potential way to boost the activity of photoactive materials and improve the sensitivity of PEC biosensor.

Electrochemical sensors based on magnetic molecularly imprinted polymers: A review

Participation of magnetic component in molecularly imprinted polymers (MIPs) has facilitated enormously the incorporation of these polymeric materials on electrode surfaces allowing the design of electrochemical sensors with very attractive analytical characteristics in terms of simplicity, reproducibility, low fabrication cost, high sensitivity and selectivity and rapid assay time. The magnetically susceptible resultant MIPs (MMIPs) allowed a simple and fast elution of the template molecules from MMIPs, are easily and faster collected without filtration, centrifugation or other complex operations and are also faster assembled and removed from the electrode surface by simply using an external magnetic field. A wide range of different (nano)materials such as gold nanoparticles (AuNPs), graphene oxide, single-walled and multi-walled carbon nanotubes (SWCNTs and MWCNTs) as well as different electrode modifiers (ionic liquids (ILs) and surfactants/dispersants) have been incorporated into the MMIPs to improve the analytical performance of the resulting electrochemical sensors which have demonstrated great promise for determination of relevant analytes in environmental, food and clinical analyses.

Acetylene black paste electrode modified with molecularly imprinted polymers/graphene for the determination of bisphenol A

A novel nanocomposite of molecularly imprinted polymers and graphene sheets was fabricated and used to obtain a highly conductive acetylene black paste electrode with high conductivity for the detection of bisphenol A. The two-dimensional structure and the chemical functionality of graphene provide an excellent surface for the enhancement of the sensitivity of the electrochemical sensor and the specificity of molecularly imprinted polymers to improve detection of bisphenol A. The synergistic effect between graphene and molecularly imprinted polymers confers the nanocomposite with superior conductivity, broadened effective surface area and outstanding electrochemical performance. Factors affecting the performance of the imprinted sensor such as molecularly imprinted polymers concentration, foster time and scan rate are discussed. The sensor successfully detects bisphenol A with a wide linear range of 3.21 × 10^-10 to 2.8 × 10^-1 g/L (R = 0.995) and a detection limit of 9.63 × 10^-11 g/L. The fabricated sensor also possessed high selectivity and stability and exhibits potential for environmental detection of contaminants and food safety inspection.