Comparison of pesticide sensitivity by electrochemical test based on acetylcholinesterase biosensor

Efficient Preparation of a Nonenzymatic Nanoassembly Based on Cobalt-Substituted Polyoxometalate and Polyethylene Imine-Capped Silver Nanoparticles for the Electrochemical Sensing of Carbofuran

The ever-growing exploitation of pesticides and their lethal effects on living beings have made it a dire need of the day to develop an accurate and reliable approach for their monitoring at trace levels. The designing of an enzyme-free electrocatalyst to electrochemically detect the pesticide residues is currently gaining much importance. In this study, a novel redox-sensing film was constructed successfully based on cobalt-substituted Dawson-type polyoxometalate [P₂W₁₇O₆₁ (Co²⁺·OH₂)]^7- (Co-POM) and polyethylene imine (PEI)-capped silver nanoparticles (AgNPs). A nanohybrid assembly was fabricated on a glassy carbon electrode's surface by alternately depositing Co-POM and PEI-AgNPs using the layer-by-layer self-assembly method. The surface morphology of the immobilized CoPOM/AgNP multilayer nanoassembly was analyzed through scanning electron microscopy along with energy-dispersive spectroscopy for elemental analysis. The redox properties and surface morphologies of fabricated assemblies were evaluated by cyclic voltammetry and electrochemical impedance spectroscopy. The practicability and feasibility of the proposed sensing layer was tested for the detection of a highly toxic insecticide, that is, carbofuran. The fabricated sensor exhibited a limit of detection of 0.1 mM with a sensitivity of 13.11 μA mM^-1 for carbofuran. The results depicted that the fabricated nonenzymatic hybrid film showed excellent electrocatalytic efficiency for the carbofuran oxidation. Furthermore, the obtained value of "apparent Km", that is, 0.4 mM, illustrates a good electro-oxidation activity of the sensor for the detection of carbofuran. The exceptionally stable redox activity of Co-POM, high surface area and greater conductivity of AgNPs, and the synergistic effect of all components of the film resulted in an excellent analytical performance of the proposed sensing assembly. This work provides a new direction to the progress and designing of nonenzymatic electrochemical sensors for pesticide determination in real samples.

A Nafion/AChE-cSWCNT/MWCNT/Au-based amperometric biosensor for the determination of organophosphorous compounds

In the present study, a biosensor was developed for the detection of organophosphorous compounds. Core electrode of a working electrode was obtained by depositing the paste of Gold nanoparticles and Multi-walled Carbon Nanotubes on a gold wire. The acetylcholinesterase enzyme was immobilized on carboxylated Single-walled Carbon Nanotubes and pasted onto a core of electrode followed by coating with a nafion layer to prevent enzyme leaching from the electrode. This electrode was further used as a working electrode in the sensor. This sensor worked on the AChE inhibition mechanism where the signal is inversely proportional to the amount of organophosphorous compounds. The electrocatalytic activity of this sensor was observed at a potential of +0.360 mV. The standardized conditions for this sensor were pH at 7.0, temperature at 30°C and response time at less than 10s. The linear working range of this biosensor was 0.1-130 µM with the lowest detection limit (LOD) of 1.9, 2.3, 2.2 and 2.5 nM for Methyl Parathion, Monocrotophos, Chlorpyrifos and Endosulfan, respectively. The biosensor showed excellent reusability (upto 55 times) and can be stored stably for 2 months.

Synthesis of reticulated hollow spheres structure NiCo2S4 and its application in organophosphate pesticides biosensor

Electrode materials play a key role in the development of electrochemical sensors, particularly enzyme-based biosensors. Here, a novel NiCo₂S₄ with reticulated hollow spheres assembled from rod-like structures was prepared by a one-pot solvothermal method and its formation mechanism was discussed. Moreover, comparison of NiCo₂S₄ materials from different experiment conditions as biosensors was investigated by electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV), and the best one that was reticulated hollow spheres assembled from rod-like structures NiCo₂S₄ has been successfully employed as a matrix of AChE immobilization for the special structure, superior conductivity and rich reaction active sites. When using common two kinds of organophosphate pesticides (OPs) as model analyte, the biosensors demonstrated a wide linear range of 1.0×10^-12-1.0×10^-8gmL^-1 with the detection limit of 4.2×10^-13gmL^-1 for methyl parathion, and 1.0×10^-13-1.0×10^-10gmL^-1 with the detection limit of 3.5×10^-14gmL^-1 for paraoxon, respectively. The proposed biosensors exhibited many advantages such as acceptable stability and low cost, providing a promising tool for analysis of OPs.

A Novel Acetylcholinesterase Biosensor: Core-Shell Magnetic Nanoparticles Incorporating a Conjugated Polymer for the Detection of Organophosphorus Pesticides

To construct a sensing interface, in the present work, a conjugated polymer and core-shell magnetic nanoparticle containing biosensor was constructed for the pesticide analysis. The monomer 4,7-di(furan-2-yl)benzo[c][1,2,5]thiadiazole (FBThF) and core-shell magnetic nanoparticles were designed and synthesized for fabrication of the biosensing device. The magnetic nanoparticles were first treated with silica and then modified using carboxyl groups, which enabled binding of the biomolecules covalently. For the construction of the proposed sensor a two-step procedure was performed. First, the poly(FBThF) was electrochemically generated on the electrode surface. Then, carboxyl group modified magnetic nanoparticles (f-MNPs) and acetylcholinesterase (AChE), the model enzyme, were co-immobilized on the polymer-coated surface. Thereby, a robust and novel surface, conjugated polymer bearing magnetic nanoparticles with pendant carboxyl groups, was constructed, which was characterized using Fourier transform infrared spectrometer, cyclic voltammetry, scanning electron microscopy, and contact angle measurements. This novel architecture was then applied as an immobilization platform to detect pesticides. To the best of our knowledge, a sensor design that combines both conjugated polymer and magnetic nanoparticles was attempted for the first time, and this approach resulted in improved biosensor characteristics. Hence, this approach opens a new perspective in the field of enzyme immobilization and sensing applications. Paraoxon and trichlorfon were selected as the model toxicants. To obtain best biosensor performance, optimization studies were performed. Under optimized conditions, the biosensor in concern revealed a rapid response (5 s), a low detection limit (6.66 × 10(-3) mM), and high sensitivity (45.01 μA mM(-1) cm(-2)). The KM(app) value of poly(FBThF)/f-MNPs/AChE were determined as 0.73 mM. Furthermore, there was no considerable activity loss for 10 d for poly(FBThF)/f-MNPs/AChE biofilm.

Evaluation of Inhibition Efficiency for the Detection of Captan, 2,3,7,8-Tetrachlorodibenzodioxin, Pentachlorophenol and Carbosulfan in Water: An Electrochemical Approach

A novel bio-analytical method has been devised based on the change in catalytic activity of acetylcholinesterase (AChE) enzyme induced by captan, carbosulfan, 2,3,7,8-tetrachlorodibenzodioxin (TCDD) and pentachlorophenol (PCP) for the investigation of inhibition efficiency and sensitivity using Pt/ZnO/AChE/Chitosan bioelectrode. The inhibition curves of captan, carbosulfan, TCDD and PCP were similar to Michaelis-Menten curve. TCDD held the minimum inhibitor Michaelis-Menten constant ([Formula: see text]) value (10.2 nM) in comparison with PCP (10.9 nM), carbosulfan (14.5 nM) and captan (7.9 × 10(3) nM). The maximum inhibition of AChE enzyme by captan was about 100 %, which was much higher than that of TCDD (72.7 %), PCP (68.1 %) and carbosulfan (47.7 %). The calculated theoretical sensitivity was in the order of TCDD > PCP > carbosulfan > captan. Comparing with TCDD (35.3 %), PCP (47.8 %) and carbosulfan (20.9 %), only the inhibition efficiency of captan (55.0 %) was the maximum. The developed bioelectrode exhibited high recovery and low relative standard deviation in local tap water samples.

Recent advances in biosensors based on enzyme inhibition

Enzyme inhibitors like drugs and pollutants are closely correlated to human and environmental health, thus their monitoring is of paramount importance in analytical chemistry. Enzymatic biosensors represent cost-effective, miniaturized and easy to use devices; particularly biosensors based on enzyme inhibition are useful analytical tools for fast screening and monitoring of inhibitors. The present review will highlight the research carried out in the last 9 years (2006-2014) on biosensors based on enzyme inhibition. We underpin the recent advances focused on the investigation in new theoretical approachs and in the evaluation of biosensor performances for reversible and irreversible inhibitors. The use of nanomaterials and microfluidic systems as well as the applications of the various biosensors in real samples is critically reviewed, demonstrating that such biosensors allow the development of useful devices for a fast and reliable alarm system.

Alcohol oxidase protein mediated in-situ synthesized and stabilized gold nanoparticles for developing amperometric alcohol biosensor

A simple one step method for the alcohol oxidases (AOx) protein mediated synthesis of gold nano-particles (AuNPs) in alkaline (pH 8.5) condition with simultaneous stabilization of the nanoparticles on the AOx protein surface under native environment has been developed. The formation of the AOx conjugated AuNPs was confirmed by advanced analytical and spectroscopic techniques. The significant increase in zeta potential (ζ) value of -57mV for the synthesized AOx-AuNPs conjugate from the AOx (pI 4.5) protein (ζ, -30mV) implied good stability of the in-situ synthesized nano-conjugate. The AOx-AuNPs conjugate showed steady stability in alkaline (upto pH 8.5) and NaCl (up to 10(-1)M) solutions. The efficiency (Kcat/Km) of the AuNP conjugated AOx was increased by 18% from the free enzyme confirming the activating role of the surface stabilized AuNPs for the enzyme. The AuNPs-AOx conjugate was encapsulated with polyaniline (PANI) synthesized by oxidative polymerization of aniline using H2O2 generated in-situ from the AOx catalysed oxidation of alcohol. The PANI encapsulated AuNPs-AOx assembly was stabilized on a glassy carbon electrode (GCE) by chitosan-Nafion mixture and then utilized the fabricated bioelectrode for detection of alcohol amperometrically using H2O2 as redox indicator at +0.6V. The constructed biosensor showed high operational stability (6.3% loss after 25 measurements), wide linear detection range of 10µM-4.7mM (R(2)=0.9731), high sensitivity of 68.3±0.35µAmM(-1) and low detection limit of 7±0.027µM for ethanol. The fabricated bioelectrode was successfully used for the selective determination of alcohol in beverage samples.

Screening of antidote sensitivity using an acetylcholinesterase biosensor based on a graphene–Au nanocomposite

An AChE biosensor based on graphene–Au nanocomposite was constructed for screening of the therapeutic effects of three oximes antidotes.

Biosensors containing acetylcholinesterase and butyrylcholinesterase as recognition tools for detection of various compounds

Acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) are enzymes expressed in the human body under physiological conditions. AChE is an important part of the cholinergic nerves where it hydrolyses neurotransmitter acetylcholine. Both cholinesterases are sensitive to inhibitors acting as neurotoxic compounds. In analytical applications, the enzymes can serve as a biorecognition element in biosensors as well as simple disposable sensors (dipsticks) and be used for assaying the neurotoxic compounds. In the present review, the mechanism of AChE and BChE inhibition by disparate compounds is explained and methods for assaying the enzymes activity are shown. Optical, electrochemical, and piezoelectric biosensors are described. Attention is also given to the application of sol-gel techniques and quantum dots in the biosensors’ construction. Examples of the biosensors are provided and the pros and cons are discussed.

Acetylcholinesterase biosensor based on a gold nanoparticle-polypyrrole-reduced graphene oxide nanocomposite modified electrode for the amperometric detection of organophosphorus pesticides

A nanohybrid of gold nanoparticles, polypyrrole, and reduced graphene oxide sheets (named as Au-PPy-rGO) was achieved by electrochemical deposition of reduced graphene oxide with pyrrole and the introduction of gold nanoparticles. Acetylcholinesterase (AChE) was further encapsulated in a silica matrix and immobilized on the Au-PPy-rGO nanocomposite by co-deposition with (NH4)2SiF6. The presence of PPy helped to avoid the aggregation of rGO caused by van der Waals interactions between individual sheets and significantly increased the surface area of the modified electrode. The obtained Au-PPy-rGO nanocomposite not only showed excellent conductivity but also exhibited a high electrocatalytic activity and specific affinity for thiocholine, the hydrolysis product of the enzyme, and thus an improved detection sensitivity. Since AChE molecules were protected by the circumambient silica matrix, which provided a biocompatible environment and facilitated mass transport, the fabricated AChE biosensor displayed high stability and excellent activity together with a fast response to organophosphorus pesticides. Under optimum conditions, the biosensor led to the rapid and sensitive detection of paraoxon-ethyl from 1.0 nM to 5 μM with a detection limit of 0.5 nM.

Acetylcholinesterase biosensors for electrochemical detection of organophosphorus compounds: a review

The exponentially growing population, with limited resources, has exerted an intense pressure on the agriculture sector. In order to achieve high productivity the use of pesticide has increased up to many folds. These pesticides contain organophosphorus (OP) toxic compounds which interfere with the proper functioning of enzyme acetylcholinesterase (AChE) and finally affect the central nervous system (CNS). So, there is a need for routine, continuous, on spot detection of OP compounds which are the main limitations associated with conventional analytical methods. AChE based enzymatic biosensors have been reported by researchers as the most promising tool for analysis of pesticide level to control toxicity and for environment conservation. The present review summarises AChE based biosensors by discussing their characteristic features in terms of fabrication, detection limit, linearity range, time of incubation, and storage stability. Use of nanoparticles in recently reported fabrication strategies has improved the efficiency of biosensors to a great extent making them more reliable and robust.

Self-assembly of acetylcholinesterase on gold nanoparticles electrodeposited on graphite

The immobilisation of AChE enzyme through chemisorption on Au-modified graphite was examined with view of its prospective application in the design of membraneless electrochemical biosensors for the assay of enzyme inhibitors. The developed immobilisation protocol has been based on a two-stage procedure, comprising i) electrodeposition of gold nanostructures on spectroscopic graphite; followed by ii) chemisorption of the enzyme onto gold nanoparticles. Both the coverage of the electrode surface with Au nanostructures and the conditions for enzyme immobilisation were optimised. The proposed electrode architecture together with the specific type of enzyme immobilisation allow for a long-term retaining of the enzyme catalytic activity. The extent of inhibition of the immobilised acetylcholinesterase enzyme by the organophosphorous compound monocrotophos has been found to depend linearly on its concentration over the range from 50 to 400 nmol mL−1 with sensitivity 77.2% inhibition per 1 µmol mL−1 of monocrotophos.

Acetylcholinesterase inhibition-based biosensors for pesticide determination: a review

Pesticides released intentionally into the environment and through various processes contaminate the environment. Although pesticides are associated with many health hazards, there is a lack of monitoring of these contaminants. Traditional chromatographic methods-high-performance liquid chromatography, capillary electrophoresis, and mass spectrometry-are effective for the analysis of pesticides in the environment but have certain limitations such as complexity, time-consuming sample preparation, and the requirement of expensive apparatus and trained persons to operate. Over the past decades, acetylcholinesterase (AChE) inhibition-based biosensors have emerged as simple, rapid, and ultra-sensitive tools for pesticide analysis in environmental monitoring, food safety, and quality control. These biosensors have the potential to complement or replace the classical analytical methods by simplifying or eliminating sample preparation and making field-testing easier and faster with significant decrease in cost per analysis. This article reviews the recent developments in AChE inhibition-based biosensors, which include various immobilization methods, different strategies for biosensor construction, the advantages and roles of various matrices used, analytical performance, and application methods for constructing AChE biosensors. These AChE biosensors exhibited detection limits and linearity in the ranges of 1.0×10(-11) to 42.19 μM (detection limits) and 1.0×10(-11)-1.0×10(-2) to 74.5-9.9×10(3)μM (linearity). These biosensors were stable for a period of 2 to 120days. The future prospects for the development of better AChE biosensing systems are also discussed.

Effects of dichlorvos and carbaryl on the activity of free and immobilized acetylcholinesterase

Acetylcholinesterase (AChE) is responsible for the rapid hydrolytic degradation of the neurotransmitter acetylcholine into inactive products choline and acetic acid. The purpose of this study was to examine the effect of carbaryl and dichlorvos on the activity of AChE. In this experimental study, 60 samples of free and immobilized form of AChE were prepared. Determination of AChE activity followed the Ellman’s method with modifications. Briefly, 200 µl of the enzyme solution was combined with 400 µl of 25 mM phosphate-buffered saline, 200 µl of DTNB [5,5′-dithio-bis(2-nitrobenzoic acid)], and 200 µl of 300 μM acetylthiocholine iodide. Triplicate (1000 µl) samples were transferred to clean 1.5-ml centrifuge tubes, mixed, and held on ice until analysed and the change in absorbance was measured. For inhibition studies, substrate solutions were pre-incubated with dichlorvos and/or carbaryl. Dichlorvos and carbaryl were used at the concentrations of 100 and 500 μM. The activity was evaluated at 412 nm using Ceceil, CE 1020 spectrophotometer. Phosphate buffer (pH 7.35) was used for blanks. AChE activity was quantified as mM/ml/min. AChE activity of free form is more affected by Dichlorvos (0.09 ± 0.03 mM/ml/min) than immobilized form (0.19 ± 0.02 mM/ml/min). AChE activity of free form is more affected by carbaryl (0.11 ± 0.01 mM/ml/min) than immobilized form (0.1 ± 0.04 mM/ml/min). Comparison of mean AChE activity showed that the activity of the enzyme in presence of dichlorvos and carbaryl was significantly lower compared to controls. To calculate the significance of the difference, the t-test for paired values was applied. The results of our study indicate that dichlorvos and carbaryl cause decrease in AChE activity for both free and immobilization form of enzyme. It is therefore concluded that measuring AChE activity is a way to evaluate poisoning with carbaryl and dichlorvos.

Evaluation of acetylcholinesterase biosensor based on carbon nanotube paste in the determination of chlorphenvinphos

An amperometric biosensor for chlorphenvinphos (organophosphorus pesticide) based on carbon nanotube paste and acetylcholinesterase enzyme (CNTs-AChE biosensor) is described herein. This CNTs-AChE biosensor was characterized by scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). The SEM result shows the presence of CNTs and small lumps, due to the enzyme AChE, which has a type of cauliflower formation. From EIS analysis is possible to observe increased R(tc) for CNTs-AChE biosensor when compared to the carbon nanotube paste electrode for the reaction [Fe(CN)(6)](4-/3-). Using a chronoamperometric procedure, a linear analytical curve was observed in the 4.90 × 10(-7)-7.46 × 10(-6) M range with limit of detection of 1.15 × 10(-7) M. The determination of chlorphenvinphos in the insecticide sample proved to be in agreement with the standard spectrophotometric method, with a 95% confidence level and with a relative error lower than 3%. In this way, the CNTs-AChE biosensor presented easy preparation, fast response, sensitivity, durability, good repeatability, and reproducibility.

Review on the use of enzymes for the detection of organochlorine, organophosphate and carbamate pesticides in the environment

Pesticides are released intentionally into the environment and, through various processes, contaminate the environment. Three of the main classes of pesticides that pose a serious problem are organochlorines, organophosphates and carbamates. While pesticides are associated with many health effects, there is a lack of monitoring data on these contaminants. Traditional chromatographic methods are effective for the analysis of pesticides in the environment, but have limitations and prevent adequate monitoring. Enzymatic methods have been promoted for many years as an alternative method of detection of these pesticides. The main enzymes that have been utilised in this regard have been acetylcholinesterase, butyrylcholinesterase, alkaline phosphatase, organophosphorus hydrolase and tyrosinase. The enzymatic methods are based on the activation or inhibition of the enzyme by a pesticide which is proportional to the concentration of the pesticide. Research on enzymatic methods of detection, as well as some of the problems and challenges associated with these methods, is extensively discussed in this review. These methods can serve as a tool for screening large samples which can be followed up with the more traditional chromatographic methods of analysis.

Biomonitoring of organophosphorus agent exposure by reactivation of cholinesterase enzyme based on carbon nanotube-enhanced flow-injection amperometric detection

A portable, rapid, and sensitive assessment of subclinical organophosphorus (OP) agent exposure based on reactivation of cholinesterase (ChE) from OP-inhibited ChE using rat saliva (in vitro) was developed using an electrochemical sensor coupled with a microflow-injection system. The sensor was based on a carbon nanotube (CNT)-modified screen printed carbon electrode (SPE), which was integrated into a flow cell. Because of the extent of interindividual ChE activity variability, ChE biomonitoring often requires an initial baseline determination (noninhibited) of enzyme activity which is then directly compared with activity after OP exposure. This manuscript describes an alternative strategy where reactivation of the phosphorylated enzyme was exploited to enable measurement of both inhibited and baseline ChE activity (after reactivation by an oxime, i.e., pralidoxime iodide) in the same sample. The use of CNT makes the electrochemical detection of the products from enzymatic reactions more feasible with extremely high sensitivity (5% ChE inhibition) and selectivity. Paraoxon was selected as a model OP compound for in vitro inhibition studies. Some experimental parameters, e.g., inhibition and reactivation time, have been optimized such that 92-95% of ChE reactivation can be achieved over a broad range of ChE inhibition (5-94%) with paraoxon. The extent of enzyme inhibition using this electrochemical sensor correlates well with conventional enzyme activity measurements. On the basis of the double determinations of enzyme activity, this flow-injection device has been successfully used to detect paraoxon inhibition efficiency in saliva samples (95% of ChE activity is due to butyrylcholinesterase), which demonstrated its promise as a sensitive monitor of OP exposure in biological fluids. Since it excludes inter- or intraindividual variation in the normal levels of ChE, this new CNT-based electrochemical sensor thus provides a sensitive and quantitative tool for point-of-care assessment and noninvasive biomonitoring of the exposure to OP pesticides and chemical nerve agents.

Electrochemical biosensor for pesticides based on acetylcholinesterase immobilized on polyaniline deposited on vertically assembled carbon nanotubes wrapped with ssDNA

An electrochemical biosensor for the determination of pesticides: methyl parathion and chlorpyrifos, two of the most commonly used organophosphorous insecticides in vegetable crops, is described. The self-assembled monolayers (SAMs) of single walled carbon nanotubes (SWCNT) wrapped by thiol terminated single strand oligonucleotide (ssDNA) on gold was utilized to prepare nano size polyaniline matrix for acetylcholinesterase (AChE) enzyme immobilization. The key step of this biosensor was AChE-acetylcholine enzymatic reaction which causes the small changes of local pH in the vicinity of an electrode surface. The pesticides were determined through inhibition of enzyme reaction. The dynamic range for the determination of methyl parathion and chlorpyrifos was found to be in between 1.0x10(-11) and 1.0x10(-6) M (0.6<SD<3.5) with good reproducibility and stability. The detection limit of the biosensor for both pesticides was found to be 1x10(-12) M. The biosensor has been applied for the determination of methyl parathion and chlorpyrifos in spiked river water samples.