Novel dual-template molecular imprinted electrochemical sensor for simultaneous detection of CA and TPH based on peanut twin-like NiFe2O4/CoFe2O4/NCDs nanospheres: Fabrication, application and DFT theoretical study

Rational design of molecularly imprinted electrochemical sensor based on Nb2C-MWCNTs heterostructures for highly sensitive and selective detection of Ochratoxin a

Developing an efficient method for screening Ochratoxin A (OTA) in agriculture products is vital to ensure food safety and human health. However, the complex food matrix seriously affects the sensitivity and accuracy. To address this issue, we designed a novel molecularly imprinted polymer (MIP) electrochemical sensor based on multiwalled carbon nanotube-modified niobium carbide (Nb2C-MWCNTs) with the aid of the density functional theory (DFT). In this design, a glassy carbon electrode (GCE) was first modified by Nb2C-MWCNTs heterostructure. Afterward, the MIP layer was prepared, with ortho-toluidine as a functional monomer selected via DFT and OTA acting as a template on the surface of Nb2C-MWCNTs/GCE using in-situ electropolymerization. Electrochemical tests and physical characterization revealed that Nb2C-MWCNTs improved the sensor's active surface area and electron transmission capacity. Nb2C-MWCNTs had a good synergistic effect on MIP, endowing the sensor with high sensitivity and specific recognition of OTA in complex food matrix systems. The MIP sensor showed a wide linear range from 0.04 to 10.0 μM with a limit of detection (LOD) of 3.6 nM. Moreover, it presented good repeatability and stability for its highly antifouling effect on OTA. In real sample analysis, the recoveries, ranging from 89.77% to 103.70%, agreed well with the results obtained by HPLC methods, suggesting the sensor has good accuracy and high potential in practical applications.

Dual biomass-derived porous carbon heterogeneous functionalized mesoporous CuCo2O4 nanocomposite combined with molecularly imprinted polymers as an electrochemical sensing platform for hypersensitive and selective determination of dimetridazole contaminants

In this study, an original molecularly imprinted electrochemical sensor (MIECS) is prepared using layer-by-layer modification of sensitization nanomaterials (CuCo2O4/BPC-E) coupled with molecularly imprinted polymers (MIPs) for the ultrasensitive and rapid determination of dimetridazole (DMZ) contaminants. The biomass waste of eggshell (ES) powders subtly introduced in situ in the carbonization process of psyllium husk (PSH) substantially promotes the physicochemical properties of the resulting biomass-derived porous carbon (BPC-E). The large specific surface area and abundant pores provide a favourable surface for loading mesoporous CuCo2O4 with a spinel structure. The assembly of CuCo2O4/BPC-E on the gold electrode (GE) surface enhances the electrochemical sensing signal. The MIPs constructed using DMZ and o-phenylenediamine (oPD) as templates and functional monomers boost the targeted recognition performance of the analyte. The combined DMZ targets then undergo an electrochemical reduction reaction in situ with the transfer of four electrons and four protons. Under optimum conditions, the current response of differential pulse voltammetry (DPV) exhibits two linear ranges for DMZ detection, 0.01-10 μM and 10-200 μM. The limit of detection (LOD) is 1.8 nM (S/N = 3) with a sensitivity of 5.724 μA μM-1 cm-2. The obtained MIECS exhibits excellent selectivity, reproducibility, repeatability and stability. This electrochemical sensing system is applied to the detection of real samples (tap water, coarse fodder and swine urine), yielding satisfactory recoveries (90.6%-98.1 %), which are consistent with those obtained via HPLC. This finding verifies that the utility of MIECS for monitoring pharmaceutical and environmental contaminants and ensuring food safety.

Portable, intelligent MIECL sensing platform for ciprofloxacin detection using a fast convolutional neural networks-assisted Tb@Lu2O3 nanoemitter

Environmental pollution caused by ciprofloxacin is a major problem of global public health. A machine learning-assisted portable smartphone-based visualized molecularly imprinted electrochemiluminescence (MIECL) sensor was developed for the highly selective and sensitive detection of ciprofloxacin (CFX) in food. To boost the efficiency of electrochemiluminescence (ECL), oxygen vacancies (OVs) enrichment was introduced into the flower-like Tb@Lu2O3 nanoemitter. With the specific recognition reaction between MIP as capture probes and CFX as detection target, the ECL signal significantly decreased. According to, CFX analysis was determined by traditional ECL analyzer detector in the concentration range from 5 × 10-4 to 5 × 102 μmol L-1 with the detection limit (LOD) of 0.095 nmol L-1 (S/N = 3). Analysis of luminescence images using fast electrochemiluminescence judgment network (FEJ-Net) models, achieving portable and intelligent quick analysis of CFX. The proposed MIECL sensor was used for CFX analysis in real meat samples and satisfactory results, as well as efficient selectivity and good stability.

A novel molecularly imprinted electrochemical sensor from poly (3, 4-ethylenedioxythiophene)/chitosan for selective and sensitive detection of levofloxacin

The improper usage of levofloxacin (LEV) endangers both environmental safety and human public health. Therefore, trace analysis and detection of LEV have extraordinary significance. In this paper, a novel molecularly imprinted polymer (MIP) electrochemical sensor was developed for the specific determination of LEV by electrochemical polymerization of o-phenylenediamine (o-PD) using poly(3,4-ethylenedioxythiophene)/chitosan (PEDOT/CS) with a porous structure and rich functional groups as a carrier and LEV as a template molecule. The morphology, structure and properties of the modified materials were analyzed and studied. The result showed that the electron transfer rate and the electroactive strength of the electrode surface are greatly improved by the interconnection of PEDOT and CS. Meanwhile, PEDOT/CS was assembled by imprinting with o-PD through non-covalent bonding, which offered more specific recognition sites and a larger surface area for the detection of LEV and effectively attracted LEV through intermolecular association. Under the optimized conditions, MIP/PEDOT/CS/GCE showed good detection performance for LEV in a wide linear range of 0.0019- 1000 μM, with a limit of detection (LOD, S/N = 3) of 0.4 nM. Furthermore, the sensor has good stability and selectivity, and exhibits excellent capabilities in the microanalysis of various real samples.

Dual-channel MIRECL portable devices with impedance effect coupled smartphone and machine learning system for tyramine identification and quantification

We designed a novel, portable, and visual dual-potential molecularly imprinted ratiometric electrochemiluminescence (MIRECL) sensor for tyramine (TYM) detection based on smartphone and deep learning-assisted optical devices. Molecularly imprinted polymer-Ce2Sn2O7 (MIP-Ce2Sn2O7) layers were fabricated by in-situ electropolymerization method as the capture and signal amplification probe. Oxygen vacancies in Ce2Sn2O7 not only enhance the electrochemical redox capability but also accelerate the energy transfer, thereby enhancing the luminescence of cathode ECL. Under optimal conditions, the ECL signals of MIP-Ce2Sn2O7 at the cathode and the anode response of Ru(bpy)32+ was reduced, thus a wide linear range from 0.01 μM to 1000 μM with the detection limit as low as 0.005 μM. Interestingly, combined with an artificial intelligence image recognition algorithm and the principle of optical signal reading by smartphone, the developed MIRECL sensor has been applied to the portable and visual determination of TYM in aquatic samples, and its practicability has been satisfactorily verified.

Novel electrochemical sensing platform basing on di-functional stimuli-responsive imprinted polymers for simultaneous extraction and determination of metronidazole

A novel magnetic-controlled electrochemical sensor has been fabricated by combined photo-responsive surface molecular imprinted polymers (P-SMIPs) and electrochemical sensor. In particular, the P-SMIPs were obtained by living radical polymerization of photo-responsive functional monomer onto the magnetic Fe₃O₄ modified multi-walled carbon nanotubes nanocomposites. The magnetic glassy carbon electrode was introduced to make the anchoring and removal of P-SMIPs onto the magnetic-controlled glassy carbon electrode easy to manipulate. Driven by UV/vis light, the platform performs releasing and absorption of metronidazole basing on conformational variations of the photo-responsive monomer at the receptor sites part in the P-SMIPs. This process can be tested by the photo-responsive variations of metronidazole electrochemical signal. As the consequence, extracting of P-SMIPs sensor can be conveniently triggered by the controllable UV light intervention measure, leading to effectively improve in both analytes mass transfer rate to the receiving media and extraction efficiency. The experimental result indicated that the excellent recoveries of metronidazole were varied between 77.9% and 89.9% with RSDs ≤4.87% in the biological samples. Therefore, the P-SMIPs sensor shows satisfactory potential in reusable extractions that can be recycled several times with no significant loss of activity, and this utilization strategy can be extended to other analytes, achieving manifold applications of pharmaceutical and environmental.

Ultrasensitive Luteolin Electrochemical Sensor Based on Novel Lamellar CuZn@ Nitrogen-Containing Carbon Nanosheets

The Cu/Zn-zeolitic imidazolate framework (Cu/Zn-ZIF) was synthesized using the traditional hydrothermal method, and its surface morphology was controlled by adding polyvinylpyrrolidone (PVP) during its synthesis. It was then calcined at 800 °C to form the nitrogen-containing carbon material CuZn@NC, which improved the electron transfer rate. Scanning electron microscopy (SEM), X-ray crystal diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were used to investigate the surface morphology and structure. Finally, the electrochemical sensing platform for luteolin was effectively constructed by changing the metal-ion ratio during synthesis to achieve the most suitable electrode material. The sensor platform detects luteolin well, with an operating curve equation of Ip (A) = 0.0571C (nM) - 1.2913 and a minimum detection limit of 15 nM, and the platform has been successfully employed for luteolin detection in real samples.

Highly selective molecularly imprinted-electrochemiluminescence sensor based on perovskite/Ru(bpy)32+ for simazine detection in aquatic products

A novel molecularly imprinted electrochemiluminescence (MIECL) sensor based on the luminescence of molecularly imprinted polymer-perovskite (MIP-CsPbBr₃) layer and Ru(bpy)₃²⁺ was fabricated for simazine detection. MIP-CsPbBr₃ layers were immobilized onto the surface of glassy carbon electrode as the capture and signal amplification probe, and Ru(bpy)₃²⁺ and co-reactant tripropylamine exhibited stronger electrochemiluminescence (ECL) emission. Under optimal conditions, the ECL signal of the MIECL sensor was linearly quenched, with the logarithm of simazine concentration ranging from 0.1 μg/L to 500.0 μg/L, correlation coefficient of 0.9947, and limit of detection of 0.06 μg/L. The practicality of the developed MIECL sensor method for simazine determination in aquatic samples was validated. Excellent recoveries of 86.5 %-103.9 % with relative standard deviation below 1.6 % were obtained for fish and shrimp samples at three different spiked concentrations. The MIECL sensor exhibited excellent selectivity, sensitivity, reproducibility, accuracy, and precision for simazine determination in actual aquatic samples.

Design of a Novel Nanosensors Based on Green Synthesized CoFe2O4/Ca-Alginate Nanocomposite-Coated QCM for Rapid Detection of Pb(II) Ions

Pb(II) is a significant contaminant that is known to have negative effects on both humans and animals. Recent industrial operations have exacerbated these consequences, and their release of several contaminants, including lead ions, has drawn attention to the potential effects on human health. Therefore, there is a lot of interest in the rapid, accurate, and selective detection of lead ions in various environmental samples. Sensors-based nanomaterials are a significant class among the many tools and methods developed and applied for such purposes. Therefore, a novel green synthesized cobalt ferrite (CoFe₂O₄) nanoparticles and functionalized CoFe₂O₄/Ca-alginate nanocomposite was designed and successfully synthesized for the fabrication of nanoparticles and nanocomposite-coated quartz crystal microbalance (QCM) nanosensors to detect the low concentrations of Pb(II) ions in the aqueous solutions at different temperatures. The structural and morphological properties of synthesized nanoparticles and nanocomposite were characterized using different tools such as X-ray diffraction (XRD), N₂ adsorption-desorption isotherm, dynamic light scattering (DLS), zeta potential analyzer (ζ-potential), atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDX). The QCM results revealed that the green synthesized CoFe₂O₄ nanoparticles and functionalized CoFe₂O₄/Ca-alginate nanocomposite-coated QCM nanosensors exhibited high sensitivity, stability, and rapid detection of Pb(II) ions in the aqueous solutions at different temperature. The lowest detection limit for Pb(II) ions in the aqueous solutions could reach 125 ng, which resulted in a frequency shift of 27.49 ± 0.81, 23.63 ± 0.90, and 19.57 ± 0.86 Hz (Δf) for the QCM detector coated with green synthesized CoFe₂O₄ nanoparticles thin films, and 25.85 ± 0.85, 33.87 ± 0.73, and 6.87 ± 0.08 Hz (Δf) for the QCM detector coated with CoFe₂O₄/Ca-Alg nanocomposite thin films in a real-time of about 11, 13, and 13 min at 25 °C, 35 °C, and 45 °C, respectively. In addition, the resonance frequency change results showed the superiority of functionalized CoFe₂O₄/Ca-alginate nanocomposite coated QCM nanosensor over CoFe₂O₄ nanoparticles towards Pb(II) ions detecting, which attributed to the beneficial properties of alginate biopolymer.

Simple immunosensor for ultrasensitive electrochemical determination of biomarker of the bone metabolism in human serum

Ultrasensitive and selective determination of biomarkers of the bone metabolism in serum is crucial for early screening, timely treatment, and monitoring of the curative effect of osteoporosis, which is a silent disease with serious health threats. Immunoassay with a simple sensing interface and ultrahigh sensitivity is highly desirable. Herein, a simple electrochemical immunosensor is demonstrated based on gold nanoparticles (AuNPs) electrodeposited on chitosan-reduced graphene oxide (CS-G) composite modified electrode, which can achieve sensitive determination of the important biomarker of bone metabolism, bone gamma-carboxyglutamate protein (BGP). To overcome the agglomeration of graphene and introduce a biocompatible matrix with functional amino groups, CS-G is prepared and modified on the supporting glassy carbon electrode (GCE). Then, AuNPs are electrodeposited on CS-G through their interaction between amine groups of CS. The immobilized AuNPs provide numerous binding sites to immobilize anti-BGP antibodies (Ab_BGP). The specific recognition between BGP and Ab_BGP results in a reduction in the mass transfer of the electrochemical probe (Fe(CN)₆^3-/4-) in solution, leading to a reduced electrochemical signal. Based on this mechanism, fast and ultrasensitive electrochemical detection of BGP is achieved when the concentration of BGP ranges from 100 ag ml⁻¹ to 10 μg mL⁻¹ with a limit of detection (LOD) of 20 ag ml⁻¹ (S/N = 3). The determination of BGP in human serum is also realized with high reliability.

Design of imprinting matrix for dual template sensing via electropolymerized polythiophene films

This work presents the design of 3-thiophene acetic acid (3-TAA) polymer matrix based molecularly imprinted polymer (MIP)/reduced graphene oxide (RGO) composite for sensitive and selective detection of antipyrine (AnP) and ethionamide (ETH) simultaneously. Dual drug embedded molecularly imprinted polymer (MIP) based electrochemical sensor was developed via electropolymerization of 3-TAA. AnP and ETH were embedded inside a polymer matrix based on their 3-D orientation and interaction(s) with functional monomer(s). Their extraction from polymeric matrix generates cavities complimentary to shape and size of AnP and ETH. The extraction of templates was confirmed by differential pulse voltammetry (DPV) as well as high-performance liquid chromatography (HPLC). The designed sensor selectively captures and produces the electrochemical signal for imprinted drugs. The electrochemical behaviour of AnP and ETH was investigated by DPV technique. The sensitivity for both drug molecules was commendable on a single polymeric composite with RGO on GC electrode (LOD of 0.117 μM for AnP and 0.15 μM for ETH). Also, the sensor exhibited excellent selectivity towards AnP and ETH in the presence of other analogous interferent molecules. Thus, the designed sensor showed high sensitivity as well as high selectivity for imprinted dual drug molecules on a single platform.

Assessment of the Antioxidant Activity of Catechin in Nutraceuticals: Comparison between a Newly Developed Electrochemical Method and Spectrophotometric Methods

The analysis of antioxidants in different foodstuffs has become an active area of research, which has led to many recently developed antioxidant assays. Many antioxidants exhibit inherent electroactivity, and, therefore, the use of electrochemical methods could be a viable approach for evaluating the overall antioxidant activity of a matrix of nutraceuticals without the need for adding reactive species. Green tea is believed to be a healthy beverage due to a number of therapeutic benefits. Catechin, one of its constituents, is an important antioxidant and possesses free radical scavenging abilities. The present paper describes the electrochemical properties of three screen-printed electrodes (SPEs), the first one based on carbon nanotubes (CNTs), the second one based on gold nanoparticles (GNPs) and the third one based on carbon nanotubes and gold nanoparticles (CNTs-GNPs). All three electrodes were modified with the laccase (Lac) enzyme, using glutaraldehyde as a cross-linking agent between the amino groups on the laccase and aldehyde groups of the reticulation agent. As this enzyme is a thermostable catalyst, the performance of the biosensors has been greatly improved. Electro-oxidative properties of catechin were investigated using cyclic voltammetry (CV) and differential pulse voltammetry (DPV), and these demonstrated that the association of CNTs with GNPs significantly improved the sensitivity and selectivity of the biosensor. The corresponding limit of detection (LOD) was estimated to be 5.6 × 10⁻⁸ M catechin at the CNT-Lac/SPE, 1.3 × 10⁻⁷ M at the GNP-Lac/SPE and 4.9 × 10⁻⁸ M at the CNT-GNP-Lac/SPE. The biosensors were subjected to nutraceutical formulations containing green tea in order to study their catechin content, using CNT-GNP-Lac/SPE, through DPV. Using a paired t-test, the catechin content estimated was in agreement with the manufacturer’s specification. In addition, the relationship between the CNT-GNP-Lac/SPE response at a specific potential and the antioxidant activity of nutraceuticals, as determined by conventional spectrophotometric methods (DPPH, galvinoxyl and ABTS), is discussed in the context of developing a fast biosensor for the relative antioxidant activity quantification.

Tuning nanozyme property of Co@NC via V doping to construct colorimetric sensor array for quantifying and discriminating antioxidant phenolic compounds

Through V₂O₅ etching of ZIF-67 and subsequent pyrolysis in an argon flow, the V doped Co@NC (V/Co@NC) with mixed-valence Co(II)/Co(III) and V(III)/V(IV) was successfully obtained. V doping plays an important role in regulating the enzyme-like activity of Co@NC. Specifically, the Co@NC has both oxidase-like activity and peroxidase-mimic activity, while the V/Co@NC possesses the specific oxidase-like activity. Benefiting from the elevated Co²⁺ level due to electrons transfer from the reduced V(III) to Co³⁺ and recyclable redox reactions between the Co(III)/Co(II) and V(IV)/V(III) couples, the V/Co@NC displays 4-fold increase in the oxidase-like activity, smaller K_m (0.18 mM) and larger V_max (4.01 × 10^-8 M s^-1) toward TMB relative to Co@NC. The origin of V/Co@NC as oxidase mimic is likely attributed to the generation of ¹O₂ and •OH. Different phenolic compounds (PC), like gallic acid, kaempferol, caffeic acid, quercetin, and catechin, have distinct antioxidant capacity, showing a differential inhibiting effect on the V/Co@NC-TMB system. The different PC antioxidants in the V/Co@NC-TMB system lead to unique decrease in the absorbance at 652 nm (A₆₅₂), resulting in a unique absorbance signal response mode. By choosing different combinations of A₆₅₂ signals at various time points, multichannel information can be extracted from a single nanozyme for pattern recognition. Based on this, a colorimetric array sensing platform for the identification of PC is established successfully. Furthermore, the constructed sensor array can be used for quantifying and discriminating multiple PC antioxidants.

Recent Advances in Quartz Crystal Microbalance Biosensors Based on the Molecular Imprinting Technique for Disease-Related Biomarkers

The molecular imprinting technique is a quickly developing field of interest regarding the synthesis of artificial recognition elements that enable the specific determination of target molecule/analyte from a matrix. Recently, these smart materials can be successfully applied to biomolecule detection in biomimetic biosensors. These biosensors contain a biorecognition element (a bioreceptor) and a transducer, like their biosensor analogs. Here, the basic difference is that molecular imprinting-based biosensors use a synthetic recognition element. Molecular imprinting polymers used as the artificial recognition elements in biosensor platforms are complementary in shape, size, specific binding sites, and functionality to their template analytes. Recent progress in biomolecular recognition has supplied extra diagnostic and treatment methods for various diseases. Cost-effective, more robust, and high-throughput assays are needed for monitoring biomarkers in clinical settings. Quartz crystal microbalance (QCM) biosensors are promising tools for the real-time and quick detection of biomolecules in the past two decades A quick, simple-to-use, and cheap biomarkers detection technology based on biosensors has been developed. This critical review presents current applications in molecular imprinting-based quartz crystal microbalance biosensors for the quantification of biomarkers for disease monitoring and diagnostic results.

Carbon fiber microelectrode array loaded with the diazonium salt-single-walled carbon nanotubes composites for the simultaneous monitoring of dopamine and serotonin in vivo

Carbon fiber microelectrode arrays based on diazonium salt and single-walled carbon nanotubes composites (DS-SWCNT/CFMEA) have been fabricated, and it developed for the simultaneous monitoring of dopamine (DA) and serotonin (5-HT) with differential pulse voltammary (DPV). The diazonium salt can improve the water-solubility of single-walled carbon nanotubes and show good selectivity to DA, thus DS-SWCNT/CFMEA exhibits enhanced electrocatalytic activity for the oxidation of DA and 5-HT, and well antifouling ability to the other biomolecules. Moreover, DS-SWCNT/CFMEA shows the wider liner range, and the good performance of precision, reproducibility and biocompatibility. The excellent characteristics of the prepared microsensor array make it to be used to monitor the release of DA and 5-HT in the mouse brain striatum of different group over time. Meanwhile, the results of in vivo on line assay further confirmed the pharmacological effects of Uncaria alkaloid extract solution on DA and 5-HT. This research may provide a new method for monitoring the release of neurobiomolecules, and the microsensor array are expected to be a tool for the study of pharmacological and physiological processes on line in vivo.

MXene/carbon nanohorns decorated with conductive molecularly imprinted poly(hydroxymethyl-3,4-ethylenedioxythiophene) for voltammetric detection of adrenaline

A novel molecularly imprinted sensor was developed for the voltammetric determination of adrenaline (AD). MXene/carbon nanohorn (MXene/CNH) composite with good electric conductivity and enormous accessible active sites was firstly introduced as catalytic substrate. Subsequently, molecularly imprinted polymer (MIP) film was fabricated in mixed solutions containing hydroxymethyl-3,4-ethylenedioxythiophene (functional monomer) and AD (template) through electro-polymerization process. A molecularly imprinted sensor was formed after removing the template. The morphology and elemental composition of the prepared composites were studied by scanning electron microscopy and X-ray photoelectron spectroscopy. Cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS) were used to investigate the electrochemical performance of the molecularly imprinted sensors. Under optimized conditions, the designed sensor displays a wide linear range from 1.0 nM to 60.0 μM and a low limit of detection of 0.3 nM. The developed sensor also presents good selectivity, reproducibility and long-term stability, and satisfactory feasibility in practical sample analysis. MXene/carbon nanohorns decorated with conductive molecularly imprinted poly(hydroxymethyl-3,4-ethylenedioxythiophene) was proposed for highly sensitive and selective detection of adrenaline.