Determination of binary pesticide mixtures by an acetylcholinesterase–choline oxidase biosensor

Acetylcholinesterase and butyrylcholinesterase co-immobilized on a copper containing Prussian blue modified electrode for the broad screening of insecticides

We have developed a bienzymatic biosensor that contains acetylcholinesterase together with butyrylcholinesterase co-immobilized on the same electrode modified with a stabilized copper containing Prussian blue electrodeposited on electrodes coated with 4-aminothiophenol monolayer using diazonium chemistry and copper nanoparticles for improved sensitivity. There are organophosphorus and carbamate neurotoxic insecticides that inhibit only one of the two enzymes, e.g., pirimicarb inhibits butyrylcholinesterase at much lower concentrations than acetylcholinesterase while methomyl inhibits only acetylcholinesterase. Our system is simple and in a single measurement provides a sensitive signal for insecticides' presence based on the inhibition of the enzyme with the highest affinity for each toxic compound. The limits of detection are 50 ng/mL pirimicarb for the bienzymatic biosensor in comparison with 400 ng/mL pirimicarb for the acetylcholinesterase biosensor and 6 ng/mL methomyl for the bienzymatic biosensor, while inhibition is obtained for the butyrylcholinesterase biosensor at 700 ng/mL.

Ligand-protected nanoclusters and their role in agriculture, sensing and allied applications

Nano biotechnology, when coupled with green chemistry, can revolutionize human life because of the vast opportunities and benefits it can offer to the quality of human life. Luminescent metal nanoclusters (NCs) have recently developed as a potential research area with applications in different areas like medical, imaging, sensing etc. Recently these new candidates have proved to be beneficial in the food supply chain enabling controlled release of nutrients, pesticides and as nanosensors for the detection of contaminants and play roles in healthy food storage and maintaining food quality. An assortment of nanomaterials has been employed for these applications and reviews have been published on the use of nanotechnology in agriculture. Ligand-protected metal nanoclusters are a distinctive class of small organic-inorganic nanostructures that garnered immense research interest in recent years owing to their stability at specific "magic size" compositions along with tunable properties that make them promising candidates for a wide range of nanotechnology-based applications. This review tries to consolidate the recent developments in the area of ligand-protected nanoclusters in connection with the detection of pesticides, food contaminants, heavy metal ions and plant growth monitoring for healthy agricultural practices. Its antimicrobial activity to manage the microbial contamination is highlighted. The review also throws light on the various perspectives by which food production and allied areas will be transformed in future.

Assessing interactive mixture toxicity of carbamate and organophosphorus insecticides in the yabby (Cherax destructor)

Carbamate (CB) and organophosphorus (OP) pesticides are commonly detected in aquatic ecosystems and predominantly occur as mixtures of varying complexity. These pesticides inhibit the activity of total cholinesterase (ChE) and thus have the potential to interfere with behaviours that may be essential for the survival of aquatic species. Although the effects of individual ChE insecticides on aquatic species have been reported for decades, the neurotoxicity of mixtures is still poorly understood. This study examined the chronic toxicities of two OP insecticides (chlorpyrifos (CPF) and malathion (MAL)) and one carbamate insecticide (methomyl (METH)) in binary and ternary mixtures on the ChE activity of the yabby (C. destructor). Using the concentration addition approach to estimate mixture toxicity, the observed inhibition of ChE activity caused by all binary mixtures of CPF plus MAL, CPF plus METH and MAL plus METH was additive. In ternary mixtures, all combinations of CPF, MAL and METH were either additive or antagonistic depending on the relative ratios of these chemicals in the mixtures. The effect of mixtures of these three insecticides on C. destructor has not previously been assessed, and the data suggest that individual chemical risk assessments are likely to incorrectly estimate the effect of these insecticides on C. destructor in the aquatic environment where combinations of such chemicals occur.

Acetylcholinesterase biosensor for carbaryl detection based on interdigitated array microelectrodes

In this study, an acetylcholinesterase (AChE) biosensor with superior accuracy and sensitivity was successfully developed based on interdigitated array microelectrodes (IAMs). IAMs have a series of parallel microband electrodes with alternating microbands connected together. Chitosan was used as the enzyme immobilization material, and AChE was used as the model enzyme for carbaryl detection to fabricate AChE biosensor. Electrochemical impedance spectroscopy was used in conjunction with the fabricated biosensor to detect pesticide residues. Based on the inhibition of pesticides on the AChE activity, using carbaryl as model compounds, the biosensor exhibited a wide range, low detection limit, and high stability. Moreover, the biosensor can also be used as a new promising tool for pesticide residue analysis.

Analysis of the activation of acetylcholinesterase by carbon nanoparticles using a monolithic immobilized enzyme microreactor: role of the water molecules in the active site gorge

A biochromatographic system was used to study the direct effect of carbon nanoparticles (CNPs) on the acetylcholinesterase (AChE) activity. The AChE enzyme was covalently immobilized on a monolithic CIM-disk via its NH2 residues. Our results showed an increase in the AChE activity in presence of CNPs. The catalytic constant (k(cat)) was increased while the Michaelis constant (K(m)) was slightly decreased. This indicated an increase in the enzyme efficiency with increase of the substrate affinity to the active site. The thermodynamic data of the activation mechanism of the enzyme, i.e. ΔH* and ΔS*, showed no change in the substrate interaction mechanism with the anionic binding site. The increase of the enthalpy (ΔH*) and the entropy (ΔS*) with decrease in the free energy of activation (Ea) was related to structural conformation change in the active site gorge. This affected the stability of water molecules in the active site gorge and facilitated water displacement by substrate for entering to the active site of the enzyme.

The effect of mixtures of organophosphate and carbamate pesticides on acetylcholinesterase and application of chemometrics to identify pesticides in mixtures

Organophosphate (OP) and carbamate (CP) pesticides act by the inhibition of acetylcholinesterase (AChE). This enables the use of this enzyme for the detection of these pesticides in the environment. While many studies have looked at the effect of single pesticides on AChE, the effect of mixtures of pesticides still requires extensive investigation. This is important to evaluate the cumulative risk in the case of simultaneous exposure to multiple pesticides. Therefore we examined the effect of five different pesticides (carbaryl, carbofuran, parathion, demeton-S-methyl, and aldicarb) on AChE activity to determine whether combinations had an additive, synergistic, or antagonistic inhibitory effect. Results indicated that the mixtures had an additive inhibitory effect on AChE activity. The data from the assays of the mixtures were used to develop and train an artificial neural network (ANN) which was then utilised successfully for the identification of pesticides and their concentrations in mixtures. This study is significant because it evaluated mixtures of OPs and CPs where previous studies focused on either OPs or CPs. Previous studies have only examined up to three pesticides while this study evaluated mixtures of five pesticides simultaneously. This is also the first study where an ANN was able to utilise data from the inhibition of a single enzyme to differentiate five different pesticides and their concentrations from mixtures.

Biosensors based on enzyme inhibition

The present chapter describes the use of biosensors based on enzyme inhibition as analytical tools. The parameters that affect biosensor sensitivity, such as the amount of immobilized enzyme, incubation time, and immobilization type, were critically evaluated, highlighting how the knowledge of enzymatic kinetics can help researchers optimize the biosensor in an easy and fast manner. The applications of these biosensors demonstrating their wide application have been reported. The objective of this survey is to give a critical description of biosensors based on enzyme inhibition, of their assembly, and their application in the environmental, food, and pharmaceutical fields.

Impact of chemical proportions on the acute neurotoxicity of a mixture of seven carbamates in preweanling and adult rats

Statistical design and environmental relevance are important aspects of studies of chemical mixtures, such as pesticides. We used a dose-additivity model to test experimentally the default assumptions of dose additivity for two mixtures of seven N-methylcarbamates (carbaryl, carbofuran, formetanate, methomyl, methiocarb, oxamyl, and propoxur). The best-fitting models were selected for the single-chemical dose-response data and used to develop a combined prediction model, which was then compared with the experimental mixture data. We evaluated behavioral (motor activity) and cholinesterase (ChE)-inhibitory (brain, red blood cells) outcomes at the time of peak acute effects following oral gavage in adult and preweanling (17 days old) Long-Evans male rats. The mixtures varied only in their mixing ratios. In the relative potency mixture, proportions of each carbamate were set at equitoxic component doses. A California environmental mixture was based on the 2005 sales of each carbamate in California. In adult rats, the relative potency mixture showed dose additivity for red blood cell ChE and motor activity, and brain ChE inhibition showed a modest greater-than additive (synergistic) response, but only at a middle dose. In rat pups, the relative potency mixture was either dose-additive (brain ChE inhibition, motor activity) or slightly less-than additive (red blood cell ChE inhibition). On the other hand, at both ages, the environmental mixture showed greater-than additive responses on all three endpoints, with significant deviations from predicted at most to all doses tested. Thus, we observed different interactive properties for different mixing ratios of these chemicals. These approaches for studying pesticide mixtures can improve evaluations of potential toxicity under varying experimental conditions that may mimic human exposures.

Differential pulse voltammetric determination of methyl parathion based on multiwalled carbon nanotubes-poly(acrylamide) nanocomposite film modified electrode

A sensitive electrochemical differential pulse voltammetry method was developed for detecting methyl parathion based on multiwalled carbon nanotubes-poly(acrylamide) (MWCNTs-PAAM) nanocomposite film modified glassy carbon electrode. The novel MWCNTs-PAAM nanocomposite, containing high content of amide groups, was synthesized by PAAM polymerizing at the vinyl group functionalized MWCNTs surface using free radical polymerization. The MWCNTs-PAAM nanocomposite was characterized by Fourier transform infrared spectroscopy, thermal gravimetric analysis and scanning electron microscopy. Electrochemical behavior and interference studies of MWCNTs-PAAM/GCE for methyl parathion were investigated. The experimental results demonstrated that the MWCNTs-PAAM/GCE exhibited a high adsorption and strong affinity toward methyl parathion compared with some metal ions and nitroaromatic compounds, which exist in environmental samples. The adsorbed amount of methyl parathion on the MWCNTs-PAAM/GCE approached the equilibrium value upon 5 min adsorption time. A linear calibration curve for methyl parathion was obtained in the concentration range from 5.0×10(-9) to 1.0×10(-5) mol L(-1), with a detection limit of 2.0×10(-9) mol L(-1). The MWCNTs-PAAM/GCE was proved to be a suitable sensing tool for the fast, sensitive and selective determination of methyl parathion in environmental water samples.

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.

Highly-sensitive organophosphorous pesticide biosensors based on nanostructured films of acetylcholinesterase and CdTe quantum dots

The optical transducer of CdTe semiconductor quantum dots (QDs) has been integrated with acetylcholinesterase enzyme (AChE) by the layer-by-layer (LbL) assembly technique, resulting in a highly sensitive biosensor for detection of organophosphorus pesticides (OPs) in vegetables and fruits based on enzyme inhibition mechanism. The detection limits of the proposed biosensors are as low as 1.05 × 10(-11) M for paraoxon and 4.47 × 10(-12) M for parathion, which are significantly better than those of the conventional GC/MS methods or amperometric biosensors (0.5 nM). These biosensors are used for quick determination of low concentrations of OPs in real vegetable and fruit samples and exhibit satisfactory reproducibility and accuracy. Moreover, the stock stability of the biosensors are very good due to the stabilizing environment for the enzyme in the nanostructures made by LbL technique. Many advantages provided by these biosensors, like fluorescent change recognized by naked eyes and mass production with low cost, will facilitate future development of rapid and high-throughput screening of OPs.

A high-throughput enzyme assay for organophosphate residues in milk

A rapid, high-sensitivity, chemiluminescence (CL) enzyme assay for the determination of organophosphate (OP) residues in milk is presented. The assay for quantification of OP residues in milk is based on the inhibition of enzyme butyrylcholinesterase (BuChE). BuChE was stabilized and preloaded in 384 well plates at 30 °C. The assay permits rapid determination of OPs in milk within 12 min including an incubation step. The enzyme assay was tested for individual and mixtures of OPs such as methyl paraoxon (MPOx), methyl parathion (MP) and malathion (MT) in milk to evaluate their synergistic effect on BuChE inhibition. Good linearity was obtained in the range 0.005–50 μg·L⁻¹ for MPOx and 0.5–1,000 μg·L⁻¹ for MP as well as MT in milk. Mean recovery of 93.2%–98.6% was obtained for MPOx spiked milk samples with 0.99%–1.67% reproducibility (RSD). The proposed method facilitated rapid screening of milk samples in 384 well plate formats with further miniaturization presented in 1,536 well plates.

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.

Recent biosensing developments in environmental security

Environmental security is one of the fundamental requirements of our well being. However, it still remains a major global challenge. Therefore, in addition to reducing and/or eliminating the amounts of toxic discharges into the environment, there is need to develop techniques that can detect and monitor these environmental pollutants in a sensitive and selective manner to enable effective remediation. Because of their integrated nature, biosensors are ideal for environmental monitoring and detection as they can be portable and provide selective and sensitive rapid responses in real time. In this review we discuss the main concepts behind the development of biosensors that have most relevant applications in the field of environmental monitoring and detection. We also review and document recent trends and challenges in biosensor research and development particularly in the detection of species of environmental significance such as organophosphate nerve agents, heavy metals, organic contaminants, pathogenic microorganisms and their toxins. Special focus will be given to the trends that have the most promising applications in environmental security. We conclude by highlighting the directions towards which future biosensors research in environmental security sector might proceed.

Immobilization of acetylcholinesterase on gold nanoparticles embedded in sol–gel film for amperometric detection of organophosphorous insecticide

A simple method to immobilize acetylcholinesterase (AChE) on silica sol-gel (SiSG) film assembling gold nanoparticles (AuNPs) was proposed, thus a sensitive, fast and stable amperometric sensor for quantitative determination of organophosphorous insecticide was developed. The large quantities of hydroxyl groups in the sol-gel composite provided a biocompatible microenvironment around enzyme molecule and stabilized its biological activity to a large extent. The immobilized AChE could catalyze the hydrolysis of acetylthiocholine chloride (ATCl) with a Kmapp value of 450 microM to form thiocholine, which was then oxidized to produce detectable single with a linear range of 10-1000 microM. AuNPs catalyzed the electro-oxidation of thiocholine, thus increasing detection sensitivity. Based on the inhibition of organophosphorous insecticide on the enzymatic activity of AChE, using monocrotophos as a model compound, the conditions for detection of the insecticide were optimized. The inhibition of monocrotophos was proportional to its concentration ranging from 0.001 to 1 microg/ml and 2 to 15 microg/ml, with the correlation coefficients of 0.9930 and 0.9985, respectively. The detection limit was 0.6 ng/ml at a 10% inhibition. The developed biosensor exhibited good reproducibility and acceptable stability, thus providing a new promising tool for analysis of enzyme inhibitors.

Determination of carbaryl pesticide using amperometric acetylcholinesterase sensor formed by electrochemically deposited chitosan

A sensitive, fast and cheap sensor for quantitative determination of carbaryl pesticide using amperometric acetylcholinesterase (AChE) sensor based on electrochemically deposited chitosan was reported. From a mildly acidic chitosan solution, a chitosan film is electrochemically deposited on Au electrode surface via a negative voltage bias, leading to a stable AChE sensor. The characteristics of the deposited layer were observed to be dependent upon the deposition time, pH, and the chitosan concentration. Fourier-transform infrared spectra proved that the immobilized enzyme could preserve their native structure due to the excellent biocompatibility and non-toxicity of chitosan. Under the optimal experimental conditions, the carbaryl inhibition on AChE-CHIT/Au was proportional to its concentration in two ranges, from 0.005 to 0.1 microg/ml and 0.5 to 5 microg/ml, with the correlation coefficients of 0.9966 and 0.9982, respectively. The detection limit was 0.003 microg/ml taken as the concentration equivalent to a 10% decrease in signal. The determination of carbaryl in garlic samples obtained from export of farm base showed acceptable accuracy. The developed sensor exhibited good fabrication reproducibility and acceptable stability, which provided a new promising tool for pesticide analysis.

Use of Biosensors for Detecting Organophosphorus Agents

The present paper reviews the use of electrochemical biosensors for detecting organophosphorus pesticides and nerve agents. Acetylcholine esterase (AChE)-immobilized electrodes have been used for detecting AChE inhibitors including organophosphorus and carbamate pesticides. The sensors are composed of AChE and choline oxidase (ChOx) for converting the AChE-generated choline into betaine and hydrogen peroxide (H(2)O(2)), which is electrochemically oxidized at the electrode surface to produce the output signal of the sensor. In the presence of AChE inhibitors, the suppressed output signal of the sensor can be observed. If the sensors are operated in the presence of acetylthiocholine as a substrate of AChE, one can eliminate ChOx from the sensor design because enzymatically generated thiocholine is electrochemically active and thus directly oxidized at the electrode without using ChOx. Electron-transfer mediators such as tetracyanoquinodimethane have often been used for catalytically oxidizing thiocholine at the electrode set at less positive potential, which is effective in circumventing possible interference arising from oxidizing compounds in the sample solution. One of the drawbacks of the AChE-based biosensors in detecting organophosphorus pesticides and nerve agents arises from the fact that the sensors indirectly detect the signal based on the inhibition of the AChE-catalyzed reaction. On the other hand, for directly obtaining the output signal, organophosphorus hydrolase (OPH) is immobilized on the electrode surface to prepare amperometric biosensors. OPH catalyzes the hydrolysis reaction of organophosphorus compounds to produce electrochemically active compounds such as p-nitrophenol and thiols from parathion and VX, respectively. Thus OPH-based sensors can be used for detecting these compounds directly. These biosensors would be useful for in-site measurements of organophosphorus pesticides and nerve agents because portable-type biosensors are easily fabricated at relatively low cost.

The application of methacrylate-based polymers to enzyme biosensors

Enzyme electrodes based on methacrylates have received significant attention in the development of biosensors. This article reviews the use and application of methacrylate and its derivatives as an immobilization system for the preparation of enzyme electrodes. Resent examples, extracted from the literature, illustrate the superior performance of such materials in the fabrication of biosensors and bioreactors.

Twenty years research in cholinesterase biosensors: From basic research to practical applications

Over the last decades, cholinesterase (ChE) biosensors have emerged as an ultra sensitive and rapid technique for toxicity analysis in environmental monitoring, food and quality control. These systems have the potential to complement or replace the classical analytical methods by simplifying or eliminating sample preparation protocols and making field testing easier and faster with significant decrease in costs per analysis. Over the years, engineering of more sensitive ChE enzymes, development of more reliable immobilization protocols and progress in the area of microelectronics could allow ChE biosensors to be competitive for field analysis and extend their applications to multianalyte screening, development of small, portable instrumentations for rapid toxicity testing, and detectors in chromatographic systems. In this paper, we will review the research efforts over the last 20 years in fabricating AChE biosensors and the recent trends and challenges encounter once the sensor is used outside research laboratory for in situ real sample applications. The review will discuss the generations of cholinesterase sensors with their advantages and limitations, the existing electrode configurations and fabrication techniques and their applications for toxicity monitoring. We will focus on low-cost electrochemical sensors and the approaches used for enzyme immobilization. Recent works for achieving high sensitivity and selectivity are also discussed.

Enzyme inhibition-based biosensors for food safety and environmental monitoring

Analytical technology based on sensors is an extremely broad field which impacts on many major industrial sectors such as the pharmaceutical, healthcare, food, and agriculture industries as well as environmental monitoring. This review will highlight the research carried out during the last 5 years on biosensors that are based on enzyme inhibition for determination of pollutants and toxic compounds in a wide range of samples. Here the different enzymes implicated in the inhibition, different transducers forming the sensing devices, and the different contaminants analyzed are considered. The general application of the various biosensors developed, with emphasis on food and environmental applications, is reviewed as well as the general approaches that have been used for enzyme immobilization, the enzyme catalysis, and the inhibition mechanism.

A fluorescent glucose biosensor based on immobilized glucose oxidase on bamboo inner shell membrane

A fluorescent glucose biosensor was constructed by immobilizing glucose oxidase on a bamboo inner shell membrane with glutaraldehyde as a cross-linker. The detection scheme was based on the depletion of dissolved oxygen content upon exposure to glucose solution with a concomitant increase in the fluorescence intensity of an oxygen transducer, tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(Pi) ditetrakis(4-chlorophenyl)borate. The enzyme immobilization, effect of pH, temperature and ionic strength have been studied in detail. The biosensor exhibited repeatable response to a 2.0 mM glucose solution with a relative standard deviation of 3.0% (n = 10). It showed good storage stability and maintained 95% of its initial response after it had been kept at 4 degrees C for 8 months. The biosensor has a linear response range of 0.0-0.6 mM glucose with a detection limit of 58 microM (S/N = 3). Common potential interferants in samples do not pose any significant interference on the response of the glucose biosensor. It was successfully applied to the determination of glucose content in some commercial wines and medical glucose injections.

Tyrosinase inhibition organic phase biosensor for triazinic and benzotriazinic pesticide analysis (part two)

Several triazine pesticides, such as atrazine, are much more soluble in several organic solvents, such as chloroform, than in water. Our recent research was aimed at analyzing this class of pesticides using tyrosinase OPEE (organic phase enzyme electrodes), exploiting their inhibiting action on the tyrosinase enzyme when operating in water-saturated chloroform medium. In this work we studied the response of a tyrosinase inhibition enzyme sensor to several triazinic (simazine, propazine, terbuthylazine) and benzotriazinic (azinphos-ethyl and azinphos-methyl) pesticides (LOD=0.5x10(-9) mol l(-1)). Recovery trials were also performed in vegetal matrixes (corn, barley, lentils). Lastly, the effect of the solvent (chloroform or water) on the inhibition process was investigated via Hill's equation and the diffusion of analyte from the solvent to the enzyme membrane.