Non-enzymatic electrochemical platform for parathion pesticide sensing based on nanometer-sized nickel oxide modified screen-printed electrodes

Graphene oxide@Ce-doped TiO2 nanoparticles as electrocatalyst materials for voltammetric detection of hazardous methyl parathion

A sensitive voltammetric sensor has been developed for hazardous methyl parathion detection (MP) using graphene oxide@Ce-doped TiO₂ nanoparticle (GO@Ce-doped TiO₂ NP) electrocatalyst. The GO@Ce-doped TiO₂ NPs were prepared through the sol-gel method and characterized by various physicochemical and electrochemical techniques. The GO@Ce-doped TiO₂ NP-modified glassy carbon electrode (GCE) addresses excellent electrocatalytic activity towards MP detection for environmental safety and protection. The developed strategy of GO@Ce-doped TiO₂ NPs at GCE surfaces for MP detection achieved excellent sensitivity (2.359 μA μM^-1 cm^-2) and a low detection limit (LOD) 0.0016 μM with a wide linear range (0.002 to 48.327 μM). Moreover, the fabricated sensor shows high selectivity and long-term stability towards MP detection; this significant electrode further paves the way for real-time monitoring of environmental quantitative samples with satisfying recoveries.

Recent developments in non-enzymatic (bio)sensors for detection of pesticide residues: Focusing on antibody, aptamer and molecularly imprinted polymer

The utilization of pesticides has been increased in recent years due to population growth and increasing urbanization. The constant use of pesticides has resulted in contamination of the environment and agricultural products with serious human health concerns associated with their use. Therefore, detection and quantification of pesticides by sensitive and selective methods is highly required in food safety management. Traditional detection methods cannot realize highly sensitive, selective and on-site detection, which limits their application. (Bio)sensors and (bio)assays are emerging tools with unique properties such as rapid, sensitive, efficient and portable detection. Among them, enzyme-based biosensors have been widely developed and some have even been commercialized. However, they suffer from some limitations such as instability and low reproducibility that originate from the nature of enzyme. Non-enzymatic (bio)sensors overcome the current limitations of enzyme-based detection methods and provide great potential for efficient, highly sensitive and low-cost detection assays using smart and miniaturized devices. In this study, we provide an overview of recent advances and new trends in optical and electrochemical non-enzymatic (bio)sensors for the detection of pesticides by focusing on antibody, aptamer and molecularly imprinted polymer (MIP) as recognition elements. Performance, advantages and drawbacks of the developed (bio)sensors are discussed well. The main advantage these recognition elements is their stability over an extended period of time compared to the enzymes. Furthermore, the combination of nanomaterials in these (bio)sensors can significantly improve their performance.

A dual-signal sensor for the analysis of parathion-methyl using silver nanoparticles modified with graphitic carbon nitride

A highly sensitive and selective method was developed for both UV-vis spectrophotometric and fluorimetric determination of organophosphorus pesticides (OPs). This method used silver nanoparticles (AgNPs) modified with graphitic carbon nitride (g-C3N4). The AgNPs reduced the fluorescence intensity of g-C3N4. Acetylthiocholine (ATCh) could be catalytically hydrolyzed by acetylcholinesterase (AChE) to form thiocholine, which induces aggregation of the AgNPs. This aggregation led to the recovery of the blue fluorescence of g-C3N4, with excitation/emission peaks at 310/460 nm. This fluorescence intensity could be reduced again in the presence of OPs because of the inhibitory effect of OPs on the activity of AChE. The degree of reduction was found to be proportional to the concentration of OPs, and the limit of fluorometric detection was 0.0324 μg/L (S/N = 3). In addition, the absorption of the g-C3N4/AgNPs at 390 nm decreased because of the aggregation of the AgNPs, but was recovered in presence of OPs because of the inhibition of enzyme activity by OPs. This method was successfully applied to the analysis of parathion-methyl in real samples.

Recent advances in biofluid detection with micro/nanostructured bioelectronic devices

Most biofluids contain a wide variety of biochemical components that are closely related to human health. Analyzing biofluids, such as sweat and tears, may deepen our understanding in pathophysiologic conditions associated with human body, while providing a variety of useful information for the diagnosis and treatment of disorders and disease. Emerging classes of micro/nanostructured bioelectronic devices for biofluid detection represent a recent breakthrough development of critical importance in this context, including traditional biosensors (TBS) and micro/nanostructured biosensors (MNBS). Related biosensors are not restricted to flexible and wearable devices; solid devices are also involved here. This article is a timely overview of recent technical advances in this field, with an emphasis on the new insights of constituent materials, design architectures and detection methods of MNBS that support the necessary levels of biocompatibility, device functionality, and stable operation for component analysis. An additional section discusses and analyzes the existing challenges, possible solutions and future development of MNBS for detecting biofluids.

Cloud-point extraction associated with voltammetry: preconcentration and elimination of the sample matrix for trace determination of methyl parathion in honey

This work presents the association of cloud point extraction (CPE) and electroanalysis for the selective and sensitive determination of methyl parathion (MP) in honey. The CPE step provided the pre-concentration of MP from a complex sample, in which the optimized extraction parameters (Triton X-100 concentration of 0.75% w/v, NaCl concentration of 1.0% w/v and heating time of 30 min) were investigated using a factorial design (23). The detection of MP was performed using a cathodically pre-treated boron-doped diamond (BDD) working electrode and square wave voltammetry (SWV), after a suitable dilution of the CPE extract in Britton-Robinson buffer pH 6.0 as the supporting electrolyte. MP presented three electrochemical processes over the BDD surface, but only the reduction peak at around -0.7 V was monitored for the MP determination (higher detectability). Improved reproducibility was reached by applying an in situ cleaning step (+2.0 V for 15 s) followed by a re-activation process (-2.0 V for 15 s) between measurements. Using the optimized variables, a linear range between 0.1 and 2.0 μmol L-1 was obtained for MP with a limit of detection of 0.006 μmol L-1, a 6-fold lower value when compared with the value attained without the CPE step. The experimental enrichment factor of MP was 6.1. Also, the optimized CPE allowed the determination of MP in honey samples with good accuracy (recovery between 94 and 106%), which was not possible using direct detection (without CPE) due to the matrix interference. This is the first paper that demonstrates the combination of CPE and electroanalysis for the determination of an organic compound.

Sensitive, simple and fast voltammetric determination of pesticides in juice samples by novel BODIPY-phthalocyanine-SWCNT hybrid platform

The present work describes the first synthesis of novel asymmetric zinc (II) phthalocyanine (ZnPc) including three boron dipyrromethene (BODIPY) and one ethyloxy azido moieties. Moreover, single walled carbon nanotube (SWCNT) surface was functionalized by this ZnPc containing BODIPY; using the azide-alkyne Huisgen cycloaddition (Click) reaction to obtain SWCNT-ZnPc hybrid material. Structural, thermal and morphological characterizations of both ZnPc and SWCNT-ZnPc hybrid were carried out in-depth by spectroscopic, thermal and microscopic techniques. In this study, the synthesized SWCNT-ZnPc material was decorated on composite glassy carbon electrode (GCE) by means of an easy and a practical drop cast method. The modified electrode was tested as a non-enzymatic electrochemical sensor in various common pesticides such as methyl parathion, deltamethrin, chlorpyrifos and spinosad. Electrochemical behavior of non-enzymatic electrode (GCE/SWCNT-ZnPc) was determined via cyclic voltammetry and differential pulse voltammetry. The non-enzymatic sensor demonstrated high selectivity for methyl parathion in a wide linear range (2.45 nM-4.0 × 10^-8 M), low limit of detection value (1.49 nM) and high sensitivity (0.1847 μA nM^-1). Also, the developing non-enzymatic sensor exhibited good repeatability (RSD = 2.3% for 10 electrodes) and stability (85.30% for 30 days). Validation guidelines by HPLC and statistical analysis showed that the proposed voltammetric method were precise, accurate, sensitive, and can be used for the routine quality control of methyl parathion determination in juice samples.

Electrochemical behavior of reduced graphene oxide/cyclodextrins sensors for ultrasensitive detection of imidacloprid in brown rice

Various pesticides employed in modern agriculture result in large amounts of pesticide residues in agricultural production, greatly threatening human health. Herein, we report a facile approach to fabricate a reduced graphene oxide/cyclodextrin modified glassy carbon electrode (rGO/CD/GCE) for the sensitive electrochemical sensing of imidacloprid (IDP). Three different modified electrodes using CDs (α-, β-, γ-CD) were fabricated, and their electrochemical performance was further studied. The results demonstrate that α-CD possesses the best signal amplification for IDP. Compared with wet-chemical synthesis of rGO/CDs (W-rGO/CDs), the electrochemical synthesis of rGO/CDs (E-rGO/CDs) produced sensors that showed better performance for IDP sensing. Taking advantage of prepared E-rGO/α-CD nanocomposite, the fabricated sensor offered a low detection limit (0.02 μM) with a wider linear range (0.5-40 μM) and long-term stability. The new sensor was successfully applied for the detection of IDP in brown rice, providing a new technique for efficient and convenient monitoring of pesticide residues in food.

A novel, biocompatible and electrocatalytic stearic acid/nanosilver modified glassy carbon electrode for the sensing of paraoxon pesticide in food samples and commercial formulations

A simple, biocompatible and an enzyme-free sensing platform was developed for detection of paraoxon. The surface of a glassy carbon electrode was modified with an electrodeposition of stearic acid/nanosilver composite at -0.7 V for 40 s. The paraoxon undergoes electro-reduction at -550 mV on the modified electrode, and the limits of detection (LOD) was calculated as 0.1 nM (S/N = 3) using differential pulse voltammetry which is lower than that of the existing materials reported. The high stability observed with the modified electrode for prolonging period indicated that the sensitivity of the electrode remains active for several runs of the analysis. The developed analytical strategy was implemented for onion and paddy grain samples and good recovery rates were observed. Also, it was applied for analyzing the purity of the commercial paraoxon sample. The reliability of the developed strategy was confirmed by comparing the results of electrochemical approach with that of HPLC technique.

Impedimetric aptasensor based on highly porous gold for sensitive detection of acetamiprid in fruits and vegetables

A novel electrochemical aptasensor modified with highly porous gold and aptamer was prepared for the determination of acetamiprid in fruits and vegetables. Highly porous gold was synthesized by electroreduction at -4 V in an electrolyte containing 2.5 mol/L NH₄Cl and 10 mmol/L HAuCl₄. Acetamiprid-binding aptamer was immobilized on highly porous gold by self-assembly. Acetamiprid could be captured by aptamer on the sensing interface, resulting in an increment of electron transfer resistance. Thanks to the large specific surface area of highly porous gold and the high affinity of aptamer, the aptasensor exhibited a highly sensitive impedance response for acetamiprid. Under optimal condition, the aptasensor displayed a linear response for acetamiprid in the concentration range of 0.5-300 nmol/L, and the detection limit was 0.34 nmol/L. Furthermore, the aptasensor showed high selectivity, good reproducibility and stability. Finally, the aptasensor was applied for the determination of acetamiprid in fruits and vegetables with satisfactory results.

Electrochemical (Bio)Sensors for Pesticides Detection Using Screen-Printed Electrodes

Pesticides are among the most important contaminants in food, leading to important global health problems. While conventional techniques such as high-performance liquid chromatography (HPLC) and mass spectrometry (MS) have traditionally been utilized for the detection of such food contaminants, they are relatively expensive, time-consuming and labor intensive, limiting their use for point-of-care (POC) applications. Electrochemical (bio)sensors are emerging devices meeting such expectations, since they represent reliable, simple, cheap, portable, selective and easy to use analytical tools that can be used outside the laboratories by non-specialized personnel. Screen-printed electrodes (SPEs) stand out from the variety of transducers used in electrochemical (bio)sensing because of their small size, high integration, low cost and ability to measure in few microliters of sample. In this context, in this review article, we summarize and discuss about the use of SPEs as analytical tools in the development of (bio)sensors for pesticides of interest for food control. Finally, aspects related to the analytical performance of the developed (bio)sensors together with prospects for future improvements are discussed.

Spectrophotometric detection of fenthion in foods after extraction by magnetic zirconia

A magnetic material, Fe₃O₄@ZrO₂, was used to enrich an organophosphorus pesticide, fenthion. After enrichment the Fe₃O₄@ZrO₂ was treated with NaOH to elute and hydrolyze fenthion. The hydrolysis products, orthophosphate ions, combine to molybdate ions to yield molybdophosphoric acid, which was further reduced with SnCl₂ to obtain a blue phosphatemolybdate. The content of orthophosphate ions as well as fenthion can be determined through the spectrophotometric method. Adsorption and elution conditions were optimized to obtain an enrichment factor of 12.5. The proposed composite method was successfully used to analyze the fenthion residues on the skin of cucumber and apple samples. The limit of detection was as low as 0.037 mg/Kg, which was close to that of the gas chromatography-mass spectrometer method. The method was simple, rapid, and economic, suitable for the rapid screen of fenthion and the other organophosphorus pesticide in mass samples.

Metal oxide heterojunctions using a printable nickel oxide ink

Wide band gap metal oxides are ideally suited for inorganic optoelectronic devices. While zinc oxide is a commonly used n-type material, there is still a lot of ongoing work for finding suitable p-type oxides. In this work, we describe a two-step route to formulate a stable and conducting p-type nickel oxide (NiO) nanofluid. NiO nanoparticles were synthesised using a bottom-up wet chemical approach and dispersed in ethylene glycol to form a nanofluid. The viscosity and surface tension of the nanofluid were optimised for printing. The printing was done using an extrusion-based direct writer. The NiO nanofluid was printed onto an aluminum-doped zinc oxide layer and annealed at different temperatures. Electrical characterisation of the junction was used to extract the junction barrier for carriers across the interface. The resulting heterojunction was found to exhibit rectifying behaviour, with the highest rectification ratio occurring at an annealing temperature of 250 °C. This annealing temperature also resulted in the lowest junction barrier height, and was in excellent agreement with theoretically predicted values. The development of a printed p-type ink will help in the realisation of oxide-based printed electronic devices.

Fabrication of magnetic iron oxide-supported copper oxide nanoparticles (Fe3O4/CuO): modified screen-printed electrode for electrochemical studies and detection of desipramine

The present investigation examines a sensitive electrochemical technique to detect desipramine through Fe₃O₄/CuO nanoparticles (NPs). Fe₃O₄/CuO NPs were synthesized via a coprecipitation procedure, and the products were characterized via energy disperse spectroscopy, X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and vibrating sample magnetometer. The voltage–current curve and differential pulse voltammetry examinations of Fe₃O₄/CuO-modified screen-printed electrode (Fe₃O₄/CuO/SPE) were followed by the determination of electro-catalytic activities toward desipramine oxidation in a phosphate buffer solution (pH = 7.0). In addition, the value of diffusion coefficient (D = 3.0 × 10⁻⁶ cm² s⁻¹) for desipramine was calculated. Then, based on the optimum conditions, it was observed that the currents of the oxidation peak were linearly proportionate to the concentration of desipramine in the broad range between 0.08 and 400.0 μM and LOD of 0.03 μM (S/N = 3). Finally, our new sensor was successfully utilized to detect desipramine in the real samples, with reasonable recovery in the range of 97.2% to 102.7%.

The present investigation examines a sensitive electrochemical technique to detect desipramine through Fe₃O₄/CuO nanoparticles.

Direct competitive immunosensor for Imidacloprid pesticide detection on gold nanoparticle-modified electrodes

A direct competitive immunosensor for the electrochemical determination of Imidacloprid (IMD) pesticide on gold nanoparticle-modified screen-printed carbon electrodes (AuNP-SPCE) is here reported for the first time. Self-obtained specific monoclonal antibodies are immobilized on the AuNP-SPCE taking advantage of the AuNPs biofunctionalization abilities. In our biosensor design, free IMD in the sample competes with IMD conjugated with horseradish peroxidase (IMD-HRP) for the recognition by the antibodies. After that, 3,3',5,5'-Tetramethylbenzidine (TMB) is enzymatically oxidized by HRP, followed by the oxidized TMB reduction back at the surface of the SPCE. This process gives an associated catalytic current (analytical signal) that is inversely proportional to the IMD amount. The main parameters affecting the analytical signal have been optimized, reaching a good precision (repeatability with a RSD of 6%), accuracy (relative error of 6%), stability (up to one month), selectivity and an excellent limit of detection (LOD of 22 pmol L^-1), below the maximum levels allowed by the legislation, with a wide response range (50-10000 pmol L^-1). The detection through antibodies also allows to have an excellent selectivity against other pesticides potentially present in real samples. Low matrix effects were found when analysing IMD in tap water and watermelon samples. The electrochemical immunosensor was also validated with HPLC-MS/MS, the reference method used in official laboratories for IMD analysis, through statistical tests. Our findings make the electrochemical immunosensor as an outstanding method for the rapid and sensitive determination of IMD at the point-of-use.

Development of Nanozymes for Food Quality and Safety Detection: Principles and Recent Applications

The public concerns about agrifood safety call for innovative and reformative analytical techniques to meet the inspection requirements of high sensitivity, specificity, and reproducibility. Enzyme-mimetic nanomaterials or nanozymes, which combine enzyme-like properties with nanoscale features, emerge as an excellent tool for quality and safety detection in the agrifood sector, due to not only their robust capacity in detection but also their attraction in future-oriented exploitations. However, in-depth understanding about the fundamental principles of nanozymes for food quality and safety detection remains limited, which makes their applications largely empirical. This review provides a comprehensive overview of the principles, designs, and applications of nanozyme-based detection technique in the agrifood industry. The discussion mainly involves three mimicking types, that is, peroxidase, oxidase, and catalase-like nanozymes, capable of detecting major agrifood analytes. The current principles and strategies are classified and then discussed in details through discriminating the roles of nanozymes in diverse detection platforms. Thereafter, recent applications of nanozymes in detecting various endogenous ingredients and exogenous contaminants in foods are reviewed, and the outlook of profound developments are explained. Evidenced by the increasing publications, nanozyme-based detection techniques are narrowing the gap to practical-oriented food analytical methods, while some challenges in optimization of nanozymes, diversification of recognition-to-signal manners, and sustainability of methodology need to conquer in the future.

A review of the advanced developments of electrochemical sensors for the detection of toxic and bioactive molecules

The recent developments made regarding the novel, cost-effective, and environmentally friendly nanocatalysts for the electrochemical sensing of biomolecules, pesticides, nitro compounds and heavy metal ions are discussed in this review article.

Peroxidase-like activity of acetylcholine-based colorimetric detection of acetylcholinesterase activity and an organophosphorus inhibitor

Colorimetric detection of acetylcholinesterase (AChE) and its inhibitor organophosphates (OPs) is attractive for its convenience, but the addition of exogenous catalyst to produce a chromogenic agent may result in complexity and interference. Herein, we first found that acetylcholine (ATCh) itself mimicked peroxidase's activity, based on which a simple and reliable colorimetric system containing ATCh- 3,3',5,5'-tetramethylbenzidine (TMB)-H₂O₂ was developed for the sensitive and selective assay of AChE activity and its inhibitor OPs. Due to the AChE-catalyzed hydrolysis of acetylcholine, the peroxidase-like activity was affected, which was used for highly sensitive detection of AChE activity with a low limit of detection (LOD) of 0.5 mU mL^-1 and a linear detection range from 2.0 to 14 mU mL^-1. Furthermore, due to the inhibition of OPs on AChE, OPs were also detected with the present ATCh regulated colorimetric system with LOD of 4.0 ng mL^-1 and a linear dynamic range from 10 to 10 000 µg L^-1. This strategy was also demonstrated to be applicable for pesticide detection in real samples. Meanwhile, the sensing platform can also be implemented on test strips for rapid and visual monitoring of OPs. Thus, this extremely simple colorimetric strategy without the addition of other exogenous catalysts holds great promise for on-site pesticide detection and can be further exploited for sensing applications in the environmental and food safety fields.