Immobilization of rat brain acetylcholinesterase on porous gold-nanoparticle-CaCO₃ hybrid material modified Au electrode for detection of organophosphorous insecticides

Acetylcholinesterase biosensors for electrochemical detection of neurotoxic pesticides and acetylcholine neurotransmitter: A literature review

Neurotoxic pesticides are a group of chemicals that pose a severe threat to both human health and the environment. These molecules are also known to accumulate in the food chain and persist in the environment, which can lead to long-term exposure and adverse effects on non-target organisms. The detrimental effects of these pesticides on neurotransmitter levels and function can lead to a range of neurological and behavioral symptoms, which are closely associated with neurodegenerative diseases. Hence, the accurate and reliable detection of these neurotoxic pesticides and associated neurotransmitters is essential for clinical applications, such as diagnosis and treatment. Over the past few decades, acetylcholinesterase (AchE) biosensors have emerged as a sensitive and reliable tool for the electrochemical detection of neurotoxic pesticides and acetylcholine. These biosensors can be tailored to utilize the high specificity and sensitivity of AchE, enabling the detection of these chemicals. Additionally, enzyme immobilization and the incorporation of nanoparticles have further improved the detection capabilities of these biosensors. AchE biosensors have shown tremendous potential in various fields, including environmental monitoring, clinical diagnosis, and pesticide residue analysis. This review summarizes the advancements in AchE biosensors for electrochemical detection of neurotoxic pesticides and acetylcholine over the past two decades.

Ultrasensitive zero-background photoelectrochemical biosensor for analysis of organophosphorus pesticide based on in situ formation of DNA-templated Ag2S photoactive materials

Herein, a novel signal-on photoelectrochemical (PEC) biosensor with nearly zero background noise (ZBN) was first fabricated to determine the presence of organophosphorus pesticide based on in situ formation of DNA-templated Ag₂S photoactive materials, accompanied by hybridization chain reaction (HCR) signal amplification. The capture probe (S1) on the gold nanoparticle-modified electrode can hybridize with the aptamer molecule to generate a simple PEC biosensor. In the presence of a target molecule, the aptamer molecule is released on the double-stranded DNA (dsDNA)-modified PEC biosensor. Meanwhile, the capture probe remains on the electrode and can open the DNA hairpins (H1, H2) which are rich in cytosine, to trigger the HCR reaction. The rich "C" strands are uncovered after formation of a long dsDNA polymer strand, which can assemble multiple silver ions (Ag⁺) by means of by C-Ag⁺-C chelation. Then, a large number of Ag₂S can be generated by challenging with S^2- solution, producing a satisfactory photocurrent signal. The photoactive material is formed in situ, which eliminates the laborious operation. Moreover, the signal can be highly amplified with nearly zero background noise and HCR signal amplification. Under optimal conditions, the ZBN aptasensor exhibited high sensitivity and selectivity, with a low detection limit of 2 pg mL^-1 for malathion. Importantly, the sensing platform can also be applied to determine the presence of malathion in real samples. In this assay, a novel signal-on photoelectrochemical biosensor with nearly zero background noise was first fabricated to determine the presence of organophosphorus pesticide based on in situ formation of DNA-templated Ag₂S photoactive materials, accompanied by hybridization chain reaction signal amplification.

Enzyme inhibition methods based on Au nanomaterials for rapid detection of organophosphorus pesticides in agricultural and environmental samples: A review

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The review systematically and completely collated the enzyme inhibition method based on Au nanomaterials for organophosphorus pesticide detection method in the last 20 years.

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The significance of the optical properties of Au nanomaterials is outlined with different shapes, sizes, and surface modifiers in enzyme inhibition methods.

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The principles, classification and application of enzyme inhibition methods based on Au nanomaterials are comprehensively summarized from a new perspective in agricultural and environmental samples, including colorimetric method, fluorometric method, electrochemical biosensor method.

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Unlike traditional enzyme inhibition method, the merits of enzyme inhibition method based on Au nanomaterials were elaborated in this review.

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Combined with the research progress of enzyme inhibition method, this review predicts the future research direction of enzyme inhibition method, providing a theoretical reference for researchers.

Background

Organophosphorus pesticides (OPs), as insecticides or acaricides, are widely used in agricultural products to ensure agricultural production. However, widespread use of OPs leads to environmental contamination and significant negative consequences on biodiversity, food security, and water resources. Therefore, developing a sensitive and rapid method to determine OPs residues in different matrices is necessary. Originally, the enzyme inhibition methods are often used as preliminary screens of OPs in crops. Many studies on the characteristic of Au nanomaterials have constantly been emerging in the past decade. Combined with anisotropic Au nanomaterials, enzyme inhibition methods have the advantages of high sensitivity, durability, and high stability.

Aim of Review

This review aims to summarize the principles and strategies of gold (Au) nanomaterials in enzyme inhibition methods, including colorimetric (dispersion, particle size of Au nanomaterials) and fluorometric (fluorescence energy transfer, internal filtration effect) detection, and electrochemical sensing system (shape of Au nanomaterials, Au nanomaterials combined with other nanomaterials). The application of enzyme inhibition in agricultural products and research progress was also outlined. Next, this review illustrates the advantages of Au nanomaterial-based enzyme inhibition methods compared with conventional enzyme inhibition methods. The detection limits and linear range of colorimetric and fluorometric detection and electrochemical biosensors have also been provided. At last, key perspectives, trends, gaps, and future research directions are proposed.

Key Scientific Concepts of Review

Herein, we introduced the technology of enzyme inhibition method based on Au nanomaterials for onsite and infield rapid detection of organophosphorus pesticide.

A stable biosensor for organophosphorus pesticide detection based on chitosan modified graphene

An acetylcholinesterase (AChE) biosensor was successfully fabricated with a stable structure and high detection accuracy. Graphene (Gra) nanofragments modified with chitosan (CS) and AChE were successively drip coated on the surface of a glassy carbon electrode via a layer-by-layer assembly method. The concentration range of the sensor to detect dichlorvos was 0.1-100,000 nM, and the limit of detection was 54 pM. CS was used to modify Gra for the first time, which enhanced the mechanical flexibility of these Gra nanostructures, significantly improving the stability and detection accuracy of this sensor.

Nanomaterial-Enabled Sensors and Therapeutic Platforms for Reactive Organophosphates

Unintended exposure to harmful reactive organophosphates (OP), which comprise a group of nerve agents and agricultural pesticides, continues to pose a serious threat to human health and ecosystems due to their toxicity and prolonged stability. This underscores an unmet need for developing technologies that will allow sensitive OP detection, rapid decontamination and effective treatment of OP intoxication. Here, this article aims to review the status and prospect of emerging nanotechnologies and multifunctional nanomaterials that have shown considerable potential in advancing detection methods and treatment modalities. It begins with a brief introduction to OP types and their biochemical basis of toxicity followed by nanomaterial applications in two topical areas of primary interest. One topic relates to nanomaterial-based sensors which are applicable for OP detection and quantitative analysis by electrochemical, fluorescent, luminescent and spectrophotometric methods. The other topic is directed on nanotherapeutic platforms developed as OP remedies, which comprise nanocarriers for antidote drug delivery and nanoscavengers for OP inactivation and decontamination. In summary, this article addresses OP-responsive nanomaterials, their design concepts and growing impact on advancing our capability in the development of OP sensors, decontaminants and therapies.

Development of enzymatic electrochemical biosensors for organophosphorus pesticide detection

The enzymatic electrochemical biosensor has the advantages of simple operation, speed, and integration in the detection of organophosphorus pesticide (OPs) residues. It has the potential to become the best alternative to the traditional OP detection technology. This article introduces the OP identification principle of different enzymes, the OP detection mechanism of several common sensors, and the enzyme assembly method. In addition, the article discusses application of nanomaterials in sensor preparation and sensor performance parameters in the past decade. The related content of early sensors is outside the scope of this article.

Non-Enzymatic Electrochemical Sensing of Malathion Pesticide in Tomato and Apple Samples Based on Gold Nanoparticles-Chitosan-Ionic Liquid Hybrid Nanocomposite

Malathion (MLT) is an organophosphorous type pesticide and having seriously high toxicity and electrochemical platforms for rapid, simple, inexpensive and sensitive determination of pesticides is still a special concern. This paper describes a simple preparation of a composite film consisting of ionic liquid (IL), chitosan (CS) and electrochemically synthesized gold nanoparticles (AuNPs) on single use pencil graphite electrodes (PGEs). The microscopic and electrochemical characterization of AuNP-CS-IL/PGE was studied using scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy. This fabricated surface was then explored for the first time as a sensing matrix for the non-enzymatic electrochemical sensing of malathion by cyclic voltammetry and square wave voltammetry measurements. The proposed AuNP-CS-IL/PGE showed excellent characteristics and possessed remarkable affinity for malathion. The voltammetric current response exhibited two linear dynamic ranges, 0.89–5.94 nM and 5.94–44.6 nM reflecting two binding sites, with a detection limit of 0.68 nM. The method was applied in real sample analysis of apple and tomato. The results demonstrate the feasibility of AuNP-CS-IL-modified electrodes for simple, fast, ultrasensitive and inexpensive detection of MLT.

Ultrasensitive Determination of Malathion Using Acetylcholinesterase Immobilized on Chitosan-Functionalized Magnetic Iron Nanoparticles

A renewable, disposable, low cost, and sensitive sensor for the detection of organophosphorus pesticides was constructed by immobilizing the acetylcholinesterase enzyme (AChE), via glutaraldehyde, on magnetic iron nanoparticles (Fe₃O₄) previously synthesized and functionalized with chitosan (CS). The sensor was denoted AChE/CS/Fe₃O₄. The magnetic nanoparticles were characterized by Fourier transform infrared spectroscopy and transmission electron microscopy. Acetylthiocholine (ATCh) was incubated with AChE/CS/Fe₃O₄ and attached to a screen-printed electrode using a magnet. The oxidation of thiocholine (from ATCh hydrolysis) was monitored at an applied potential of +0.5 V vs. Ag/AgCl(KCl_sat) in 0.1 mol L⁻¹ phosphate buffer solution (pH 7.5) as the supporting electrolyte. A mixture of the pesticide malathion and ATCh was investigated using the same procedure, and the results were compared and expressed as inhibition percentages. For determination of malathion, the proposed sensor presented a linear response in the range from 0.5 to 20 nmol L⁻¹ (R = 0.9942). The limits of detection (LOD) and quantification (LOQ) were 0.3 and 0.8 nmol L⁻¹, respectively. Real samples were also investigated, with recovery values of 96.0% and 108.3% obtained for tomato and pond water samples, respectively. The proposed sensor is a feasible option for malathion detection, offering a linear response, good sensitivity, and a low detection limit.

Palladium-copper nanowires-based biosensor for the ultrasensitive detection of organophosphate pesticides

A highly sensitive acetylcholinesterase (AChE) electrochemical biosensor for the quantitative determination of organophosphate pesticides (OPs) in vegetables and fruits based on palladium-copper nanowires (Pd-Cu NWs) was reported. AChE immobilized on the modified electrode could catalyze hydrolysis of acetylthiocholine chloride (ATCl), generating an irreversible oxidation peak. When exposed to the OPs, the activity of the AChE was inhibited and the current significantly decreased. The detection mechanism is based on the inhibition of AChE. The Pd-Cu NWs not only provide a large active surface area (0.268 ± 0.01) cm² for the immobilization of AChE, which was approximately 3.8 times higher than the bare glass carbon electrode, but also exhibit excellent electro-catalytic activity and remarkable electron mobility. The biosensor modified with Pd-Cu NWs displayed a good affinity to ATCl and catalyzed hydrolysis of ATCl, with a low Michaelis-Menten constant (K_M) of 50.56 μM. Under optimized conditions, the AChE-Cs/Pd-Cu NWs/GCE biosensor detected malathion with wide linear ranges of 5-1000 ppt and 500-3000 ppb, and the low detection limit was 1.5 ppt (4.5 pM). In addition, the OPs biosensor has been applied to the analysis of malathion in commercial vegetable and fruit samples, with excellent recoveries in the range of 98.5%-113.5%. This work provides a simple, sensitive and effective platform for biosensors and exhibits future potential in practical application for the OPs assay.

Pesticide analysis using nanoceria-coated paper-based devices as a detection platform

We report the first use of a paper-based device coated with nanoceria as a simple, low-cost and rapid detection platform for the analysis of organophosphate (OP) pesticides using an enzyme inhibition assay with acetylcholinesterase (AChE) and choline oxidase (ChOX). In the presence of acetylcholine, AChE and ChOX catalyze the formation of H2O2, which is detected colorimetrically by a nanoceria-coated device resulting in the formation of a yellow color. After incubation with OP pesticides, the AChE activity was inhibited, producing less H2O2, and a reduction in the yellow intensity. The assay is able to analyze OP pesticides without the use of sophisticated instruments and gives detection limits of 18 ng mL(-1) and 5.3 ng mL(-1) for methyl-paraoxon and chlorpyrifos-oxon, respectively. The developed method was successfully applied to detect methyl-paraoxon in spiked vegetables (cabbage) and a dried seafood product (dried green mussel), obtaining ∼95% recovery values for both sample types. The spiked samples were also analyzed using LC-MS/MS as a comparison to the developed method and similar values were obtained, indicating that the developed method gives accurate results and is suitable for OP analysis in real samples.

Glycated hemoglobin biosensing integration formed on Au nanoparticle-dotted tubular TiO2 nanoarray

Excessive glucose present in the blood of diabetic patients binds with the hemoglobin of red blood cells resulting in the formation of glycated hemoglobin (HbA_1c). Measurement of HbA_1c levels may help in identifying the efficacy of the ongoing treatment and hence provide a better control over the disease. In the present study, we have synthesized a sensitive and stable scaffold, which consists of Au nanoparticles (GNPs)-dotted tubular TiO₂, for the construction of an electrochemical HbA_1c biosensor. 12-phosphotungstic acid has been used as a reducer after depositing well-dispersed GNPs on TiO₂ nanotubes (TiO₂ NTs) and an electron mediator by accelerating the electron transfer between the conductor and protein. The fabricated electrode was characterized using scanning electron microscopy (SEM), cyclic voltammetry (CV), Fourier transform infrared spectroscopy (FTIR) and electrochemical impedance spectroscopic analysis (EIS). Biosensor exhibited low detection limit (0.5 μM), fast response time (3 s) and wide linearity (from 0.5 to 2000 μM). The working electrode was used 100 times over 4 months, when stored at 4 °C. The HbA1c biosensor was then effectively used to measure the % of HbA_1c in the blood of apparently healthy persons and diabetic patients.

Plant Esterase-Chitosan/Gold Nanoparticles-Graphene Nanosheet Composite-Based Biosensor for the Ultrasensitive Detection of Organophosphate Pesticides

As broad-spectrum pesticides, organophosphates (OPs) are widely used in agriculture all over the world. However, due to their neurotoxicity in humans and their increasing occurrence in the environment, there is growing interest in their sensitive and selective detection. This paper reports a new cost-effective plant esterase-chitosan/gold nanoparticles-graphene nanosheet (PLaE-CS/AuNPs-GNs) biosensor for the sensitive detection of methyl parathion and malathion. Highly pure plant esterase is produced from plants at low cost and shares the same inhibition mechanism with OPs as acetylcholinesterase, and then it was used to prepare PLaE-CS/AuNPs-GNs nanocomposites, which were systematically characterized using SEM, TEM, and UV-vis. The PLaE-CS/AuNPs-GNs composite-based biosensor measured as low as 50 ppt (0.19 nM) of methyl parathion and 0.5 ppb (1.51 nM) of malathion (S/N = 3) with a calibration curve up to 200 ppb (760 nM) and 500 ppb (1513.5 nM) for methyl parathion and malathion, respectively. There is also no interference observed from most of common species such as metal ions, inorganic ions, glucose, and citric acid. In addition, its applicability to OPs-contaminated real samples (carrot and apple) was also demonstrated with excellent response recovery. The developed simple, sensitive, and reliable PLaE-CS/AuNPs-GNs composite-based biosensor holds great potential in OPs detection for food and environmental safety.

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.

Voltammetric detection of anti-HIV replication drug based on novel nanocomposite gold-nanoparticle-CaCO3 hybrid material

A novel bionanocomposite, horse radish peroxidase- gold-nanoparticle-Calcium carbonate (HRP-AuNPs-CaCO3), hybrid material was encapsulated by silica sol on a glassy carbon electrode (GCE). The fabricated modified electrode was used as a novel voltammetric sensor for electrochemical sensing of anti-HIV replication drug i.e. deferiprone. The surface morphology of the modified electrode was characterized by scanning electron microscopy (SEM). Results obtained from the voltammetric measurements show that HRP-AuNPs-CaCO3 modified GCE offers a selective and sensitive electrochemical sensor for the determination of deferiprone. Under experimental conditions, the proposed voltammetric sensor has a linear response range from 0.01 to 10,000 μM with a detection limit of 0.01 μM. Furthermore, the fabricated sensor was successfully applied to determine deferiprone level in spiked urine and serum samples.

Coimmobilization of acetylcholinesterase and choline oxidase on gold nanoparticles: stoichiometry, activity, and reaction efficiency

Hybrid structures constructed from biomolecules and nanomaterials have been used in catalysis and bioanalytical applications. In the design of many chemically selective biosensors, enzymes conjugated to nanoparticles or carbon nanotubes have been used in functionalization of the sensor surface for enhancement of the biosensor functionality and sensitivity. The conditions for the enzyme:nanomaterial conjugation should be optimized to retain maximal enzyme activity, and biosensor effectiveness. This is important as the tertiary structure of the enzyme is often altered when immobilized and can significantly alter the enzyme catalytic activity. Here we show that characterization of a two-enzyme:gold nanoparticle (AuNP) conjugate stoichiometry and activity can be used to gauge the effectiveness of acetylcholine detection by acetylcholine esterase (AChE) and choline oxidase (ChO). This was done by using an analytical approach to quantify the number of enzymes bound per AuNP and monitor the retained enzyme activity after the enzyme:AuNP synthesis. We found that the amount of immobilized enzymes differs from what would be expected from bulk solution chemistry. This analysis was further used to determine the optimal ratio of AChE:ChO added at synthesis to achieve optimum sequential enzyme activity for the enzyme:AuNP conjugates, and reaction efficiencies of greater than 70%. We here show that the knowledge of the conjugate stoichiometry and retained enzyme activity can lead to more efficient detection of acetylcholine by controlling the AChE:ChO ratio bound to the gold nanoparticle material. This approach of optimizing enzyme gold nanoparticle conjugates should be of great importance in the architecture of enzyme nanoparticle based biosensors to retain optimal sensor sensitivity.

GOLD NANOPARTICLES-BASED BIOSENSORS FOR BIOMEDICAL APPLICATION

Gold nanoparticles are the most extensively studied nanomaterials for biomedical application due to their unique properties, such as rapid and simple synthesis, large surface area, strong adsorption ability and facile conjugation to various biomolecules. The remarkable photophysical properties of gold nanoparticles have provided plenty of opportunities for the preparation of gold nanoparticles-based optical biosensors, while the excellent biocompatibility, conductivity, catalytic properties and large surface-to-volume ratio have facilitated the application of gold nanoparticles in the construction of electrochemical biosensors. In this review, we mainly detail the gold nanoparticles-based optical and electrochemical biosensors for biomedical application in the recent two years, which have exhibited greatly enhanced analytical performances in the detection of DNA, proteins and some important small molecules.