Amperometric Thick-Film Strip Electrodes for Monitoring Organophosphate Nerve Agents Based on Immobilized Organophosphorus Hydrolase

Effective remediation and decontamination of organophosphorus compounds using enzymes: From rational design to potential applications

Organophosphorus compounds (OPs) have been widely used in agriculture for decades because of their high insecticidal efficiency, which maintains and increases crop yields worldwide. More importantly, OPs, as typical chemical warfare agents, are a serious concern and significant danger for military and civilian personnel. The widespread use of OPs, superfluous and unreasonable use, has caused great harm to the environment and food chain. Developing efficient and environmentally friendly solutions for the decontamination of OPs is a long-term challenge. Microbial enzymes show potential application as natural and green biocatalysts. Thus, utilizing OP-degrading enzymes for environmental decontamination presents significant advantages, as these enzymes can rapidly hydrolyze OPs; are environmentally friendly, nonflammable, and noncorrosive; and can be discarded safely and easily. Here, the properties, structure and catalytic mechanism of various typical OP-degrading enzymes are reviewed. The methods and effects utilized to improve the expression level, catalytic performance and stability of OP-degrading enzymes were systematically summarized. In addition, the immobilization of OP-degrading enzymes was explicated emphatically, and the latest progress of cascade reactions based on immobilized enzymes was discussed. Finally, the latest applications of OP-degrading enzymes were summarized, including biosensors, nanozyme mimics and medical detoxification. This review provides guidance for the future development of OP-degrading enzymes and promotes their application in the field of environmental bioremediation and medicine.

A Review of Nanocomposite-Modified Electrochemical Sensors for Water Quality Monitoring

Electrochemical sensors play a significant role in detecting chemical ions, molecules, and pathogens in water and other applications. These sensors are sensitive, portable, fast, inexpensive, and suitable for online and in-situ measurements compared to other methods. They can provide the detection for any compound that can undergo certain transformations within a potential window. It enables applications in multiple ion detection, mainly since these sensors are primarily non-specific. In this paper, we provide a survey of electrochemical sensors for the detection of water contaminants, i.e., pesticides, nitrate, nitrite, phosphorus, water hardeners, disinfectant, and other emergent contaminants (phenol, estrogen, gallic acid etc.). We focus on the influence of surface modification of the working electrodes by carbon nanomaterials, metallic nanostructures, imprinted polymers and evaluate the corresponding sensing performance. Especially for pesticides, which are challenging and need special care, we highlight biosensors, such as enzymatic sensors, immunobiosensor, aptasensors, and biomimetic sensors. We discuss the sensors' overall performance, especially concerning real-sample performance and the capability for actual field application.

Nanostructured β‐tricalcium Phosphate (Ca3(PO4)2 Based Electrochemical Sensor for Detection of Methyl Parathion and Mercury (II) Ions

In this work, we have fabricated a new electrochemical sensor based on β‐tricalcium phosphate (Ca3(PO4)2) nanoparticles (NPs) modified glassy carbon electrode (GCE) for the selective nonenzymatic determination of methyl parathion and mercury (II) ions independently. β‐tricalcium phosphate (β‐TCP) NPs were prepared by chemical precipitation method and structural and morphological properties were investigated by XRD, FTIR, and SEM. The electrochemical behavior of MP and mercury (Hg2+) ions were investigated by cyclic voltammetry (CV) and square wave voltammetry (SWV) techniques using β‐TCP/GCE. The modified electrode exhibited excellent electrocatalytic activity towards both the MP and Hg over a wide linear range from 0.15 to 141 μM and 1–381 µM with the lowest detection limits of 88 and 136.4 nM respectively. The sensor has high selectivity towards MP and Hg in the presence of major interfering compounds such as 3-nitrophenol, 4-nitrophenol, 4-aminophenol, catechol, hydroquinone and heavy metals such as lead, cadmium and arsenic. Applicability of the fabricated sensor for detection of MP and Hg (II) ions has been tested in tap water by standard addition method.

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.

Organophosphorus hydrolase-poly-β-cyclodextrin as a stable self-decontaminating bio-catalytic material for sorption and degradation of organophosphate pesticide

A region suffering from an attack of a nerve agent requires not only a highly sorptive material but also a fast-acting catalyst to decontaminate the lethal chemical present. The product should be capable of high sorptive capacity, selectivity and quick response time to neutralize the long lasting harmful effects of nerve agents. Herein, we have utilized organophosphorus hydrolase (OPH) as a non-toxic bio-catalytic material held in with the supporting matrix of poly-β-cyclodextrin (PCD) as a novel sorptive reinforced self-decontaminating material against organophosphate intoxication. OPH coated PCD (OPH-PCD) will not only be providing support for holding enzyme but also would be adsorbing methyl paraoxon (MPO) used as a simulant, in a host-guest inclusion complex formation. Sorption trend for PCD revealed preference towards the more hydrophobic MPO against para-nitrophenol (pNP). The results show sorption capacity of 1.26 mg/g of 100 μM MPO with PCD which was 1.7 times higher compared to pNP. The reaction rate with immobilized OPH-PCD was found to be 23% less compared to free enzyme. With the help of OPH-PCD, continuous hydrolysis (100%) of MPO into pNP was observed for a period of 24 h through packed bed reactor with good reproducibility and stability of enzyme. The long-term stability also confirmed its stable nature for the investigation period of 4 days where it maintained activity. Combined with its fast and reactive nature, the resulting self-decontaminating regenerating material provides a promising strategy for the neutralization of nerve agents and preserving the environment.

Printed Graphene Electrochemical Biosensors Fabricated by Inkjet Maskless Lithography for Rapid and Sensitive Detection of Organophosphates

Solution phase printing of graphene-based electrodes has recently become an attractive low-cost, scalable manufacturing technique to create in-field electrochemical biosensors. Here, we report a graphene-based electrode developed via inkjet maskless lithography (IML) for the direct and rapid monitoring of triple-O linked phosphonate organophosphates (OPs); these constitute the active compounds found in chemical warfare agents and pesticides that exhibit acute toxicity as well as long-term pollution to soils and waterways. The IML-printed graphene electrode is nano/microstructured with a 1000 mW benchtop laser engraver and electrochemically deposited platinum nanoparticles (dia. ∼25 nm) to improve its electrical conductivity (sheet resistance decreased from ∼10 000 to 100 Ω/sq), surface area, and electroactive nature for subsequent enzyme functionalization and biosensing. The enzyme phosphotriesterase (PTE) was conjugated to the electrode surface via glutaraldehyde cross-linking. The resulting biosensor was able to rapidly measure (5 s response time) the insecticide paraoxon (a model OP) with a low detection limit (3 nM), and high sensitivity (370 nA/μM) with negligible interference from similar nerve agents. Moreover, the biosensor exhibited high reusability (average of 0.3% decrease in sensitivity per sensing event), stability (90% anodic current signal retention over 1000 s), longevity (70% retained sensitivity after 8 weeks), and the ability to selectively sense OP in actual soil and water samples. Hence, this work presents a scalable printed graphene manufacturing technique that can be used to create OP biosensors that are suitable for in-field applications as well as, more generally, for low-cost biosensor test strips that could be incorporated into wearable or disposable sensing paradigms.

A novel and high performance enzyme-less sensing layer for electrochemical detection of methyl parathion based on BSA templated Au–Ag bimetallic nanoclusters

In the present manuscript, a modified glassy carbon electrode with BSA templated Au–Ag bimetallic nanoclusters (Au–Ag@BSA/GCE) was employed for the rapid, selective and sensitive determination of methyl parathion (MP) as an enzyme-less electrochemical biosensor.

Detection of vapor-phase organophosphate threats using wearable conformable integrated epidermal and textile wireless biosensor systems

Flexible epidermal tattoo and textile-based electrochemical biosensors have been developed for vapor-phase detection of organophosphorus (OP) nerve agents. These new wearable sensors, based on stretchable organophosphorus hydrolase (OPH) enzyme electrodes, are coupled with a fully integrated conformal flexible electronic interface that offers rapid and selective square-wave voltammetric detection of OP vapor threats and wireless data transmission to a mobile device. The epidermal tattoo and textile sensors display a good reproducibility (with RSD of 2.5% and 4.2%, respectively), along with good discrimination against potential interferences and linearity over the 90-300mg/L range, with a sensitivity of 10.7µA∙cm³∙mg^-1 (R² = 0.983) and detection limit of 12mg/L in terms of OP air density. Stress-enduring inks, used for printing the electrode transducers, ensure resilience against mechanical deformations associated with textile and skin-based on-body sensing operations. Theoretical simulations are used to estimate the OP air density over the sensor surface. These fully integrated wearable wireless tattoo and textile-based nerve-agent vapor biosensor systems offer considerable promise for rapid warning regarding personal exposure to OP nerve-agent vapors in variety of decentralized security applications.

A microneedle biosensor for minimally-invasive transdermal detection of nerve agents

A microneedle array based biosensor for minimally invasive electrochemical monitoring of organophosphate (OP) nerve agents under the skin.

Recent approaches to improving selectivity and sensitivity of enzyme-based biosensors for organophosphorus pesticides: A review

Pesticide determination has attracted great attention due to the fact that they exhibit high acute toxicity and can cause long-term damage to the environment and human lives even at trace levels. Although classical analytical methods (including gas chromatography, high performance liquid chromatography, capillary electrophoresis and mass spectrometry) have been effectively used for analysis of pesticides in contaminated samples, they present certain limitations such as time-consuming sample preparation, complexity, and the requirement of expensive instrumentation and highly skilled personnel. For these reasons, there is an expanding need for analytical methods able to provide simple, rapid, sensitive, selective, low cost and reliable detection of pesticides at trace levels. Over the past decades, acetylcholinesterase (AChE) biosensors have emerged as simple, rapid and ultra-sensitive tools for toxicity detection of pesticides in the environment and food. 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. With the recent engineering of more sensitive AChE enzymes, the development of more reliable immobilization matrices and the progress in the area of microelectronics, AChE biosensors could become competitive for multi-analyte screening and soon be used for the development of portable instrumentation for rapid toxicity testing of samples. The enzymes organophosphorus hydrolase (OPH) and organophosphorus acid anhydrolase (OPAA) have also shown considerable potential in OP biosensor applications and they have been used for direct detection of OPs. This review presents the recent advances in the fabrication of enzyme biosensors for organophosphorus pesticides (OPs) and their possible applications for toxicity monitoring of organophosphorus pesticide residues in real samples. The focus will be on the different strategies for the biosensor construction, the analytical performance of the biosensors and the advantages and disadvantages of these biosensor methods. The recent works done to improve the analytical performance, sensitivity and selectivity of these biosensors will also be discussed.

A potentiometric biosensing system based on an isolated degrading bacterium Klebsiella sp. MP-6 for the determination of methyl parathion

A potentiometric system for methyl parathion using bacterial cells as bioreceptors and an anion-sensitive electrode as a transducer is described.

Preparation of electrochemical biosensor for detection of organophosphorus pesticides

Polyvinyl chloride (PVC) can be used to develop reaction beaker which acts as electrochemical cell for the measurement of OP pesticides. Being chemically inert, corrosion resistant, and easy in molding to various shapes and size, PVC can be used for the immobilization of enzyme. Organophosphorus hydrolase was immobilized covalently onto the chemically activated inner surface of PVC beaker by using glutaraldehyde as a coupling agent. The carbon nanotubes paste working electrode was constructed for amperometric measurement at a potential of +0.8 V. The biosensor showed optimum response at pH 8.0 with incubation temperature of 40°C. K_m and I_max for substrate (methyl parathion) were 322.58 µM and 1.1 µA, respectively. Evaluation study showed a correlation of 0.985, which was in agreement with the standard method. The OPH biosensor lost 50% of its initial activity after its regular use for 25 times over a period of 50 days when stored in 0.1 M sodium phosphate buffer, pH 8.0 at 4°C. No interference was observed by interfering species.

Towards the fabrication of a label-free amperometric immunosensor using SWNTs for direct detection of paraoxon

A label-free immunosensor based on SWNTs modified GC electrodes has been developed for the direct detection of paraoxon. Based on aryldiazonium salt chemistry, forest of SWNTs can be vertically aligned on mixed monolayers of aryldiazonium salt modified GC electrodes by C-C bonding, which provides an interface showing efficient electron transfer between biomolecules. PEG molecules were introduced to the interface to resist non-specific protein adsorption. Ferrocenedimethylamine (FDMA) was subsequently attached to the ends of SWNTs through the amide bonding followed by the attachment of epitope i.e., paraoxon hapten to which a paraoxon antibody would bind. This immunosensor shows good selectivity and high specificity to paraoxon, and is functional for the detection of paraoxon in both laboratory and field by a displacement assay. There is a linear relationship between electrochemical signal of FDMA and the concentration of paraoxon over the range of 2-2500 ppb with a lowest detected limit of 2 ppb in 0.1 M phosphate buffer at pH 7.0. The SWNTs based amperometric immunosensor provides an opportunity to develop the sensing system for on-site sensitive detection of a spectrum of insecticides.

Development of a novel optical biosensor for detection of organophosphorus pesticides based on methyl parathion hydrolase immobilized by metal-chelate affinity

We have developed a novel optical biosensor device using recombinant methyl parathion hydrolase (MPH) enzyme immobilized on agarose by metal-chelate affinity to detect organophosphorus (OP) compounds with a nitrophenyl group. The biosensor principle is based on the optical measurement of the product of OP catalysis by MPH (p-nitrophenol). Briefly, MPH containing six sequential histidines (6× His tag) at its N-terminal was bound to nitrilotriacetic acid (NTA) agarose with Ni ions, resulting in the flexible immobilization of the bio-reaction platform. The optical biosensing system consisted of two light-emitting diodes (LEDs) and one photodiode. The LED that emitted light at the wavelength of the maximum absorption for p-nitrophenol served as the signal light, while the other LED that showed no absorbance served as the reference light. The optical sensing system detected absorbance that was linearly correlated to methyl parathion (MP) concentration and the detection limit was estimated to be 4 μM. Sensor hysteresis was investigated and the results showed that at lower concentration range of MP the difference got from the opposite process curves was very small. With its easy immobilization of enzymes and simple design in structure, the system has the potential for development into a practical portable detector for field applications.

Site-specific immobilization of gold binding polypeptide on gold nanoparticle-coated graphene sheet for biosensor application

The effective and strong immobilization of enzymes on solid surfaces is required for current biological applications, such as microchips, biofuel cells, and biosensors. Gold-binding polypeptide (GBP), a genetically designed peptide, possesses unique and specific interactions with a gold surface, resulting in improved enzyme stability and activity. Herein we demonstrated an immobilization method for biosensor applications through site-specific interactions between GBP-fused organophosphorus hydrolase (GBP-OPH) and gold nanoparticle-coated chemically modified graphene (Au-CMG), showing enhanced sensing capability. A flow injection biosensor was fabricated by using GBP-OPH/Au-CMG to detect paraoxons, a model pesticide, showing higher sensitivity, lower detection limit and better operating stability compared that of OPH/Au-CMG. This strategy, which integrates biotic and abiotic moieties through site-specific interactions, has a great potential for use in biosensing and bioconversion process.

Electrochemical Sensor for Determination of Parathion Based on Electropolymerization Poly(Safranine) Film Electrode

Parathion has been determined with voltammetric technique based on a novel sensor fabricated by electropolymerization of safranine on a glassy carbon electrode (GCE). The electrochemical behavior of poly(safranine) film electrode and its electrocatalytic activity toward parathion were studied in detail by cyclic voltammetry (CV) and linear sweep voltammetry (LSV). All experimental parameters were optimized, and LSV was proposed for its determination. In optimal working conditions, the reduction current of parathion at this poly(safranine)-modified electrode exhibited a good linear relationship with parathion concentration in the range of3.43×10−8to3.43×10−5 molL−1. The detection limit was1.0×10−8 molL−1. The high sensitivity and selectivity of the sensor were demonstrated by its practical application for the determination of trace amounts of parathion in fruit samples.

Solution chemistry of self-assembled graphene nanohybrids for high-performance flexible biosensors

We report the preparation of free-standing flexible conductive reduced graphene oxide/Nafion (RGON) hybrid films by a solution chemistry that utilizes self-assembly and directional convective-assembly. The hydrophobic backbone of Nafion provided well-defined integrated structures, on micro- and macroscales, for the construction of hybrid materials through self-assembly, while the hydrophilic sulfonate groups enabled highly stable dispersibility ( approximately 0.5 mg/mL) and long-term stability (2 months) for graphene. The geometrically interlocked morphology of RGON produced a high degree of mechanical integrity in the hybrid films, while the interpenetrating network constructed favorable conduction pathways for charge transport. Importantly, the synergistic electrochemical characteristics of RGON were attributed to high conductivity (1176 S/m), facilitated electron transfer (ET), and low interfacial resistance. Consequently, RGON films obtained the excellent figure of merit as electrochemical biosensing platforms for organophosphate (OP) detection, that is, a sensitivity of 10.7 nA/microM, detection limit of 1.37 x 10(-7) M, and response time of <3 s. In addition, the reliability of RGON biosensors was confirmed by a fatigue test of 100 bending cycles. The strategy described here provides insight into the fabrication of graphene and hybrid nanomaterials from a material perspective, as well as the design of biosensor platforms for practical device applications.

Covalent coupling of organophosphorus hydrolase loaded quantum dots to carbon nanotube/Au nanocomposite for enhanced detection of methyl parathion

An amperometric biosensor for highly selective and sensitive determination of methyl parathion (MP) was developed based on dual-signal amplification: (1) a large amount of introduced enzyme on the electrode surface and (2) synergistic effects of nanoparticles towards enzymatic catalysis. The fabrication process includes (1) electrochemical deposition of gold nanoparticles by a multi-potential step technique at multiwalled carbon nanotube (MWCNT) film pre-cast on a glassy carbon electrode and (2) immobilization of methyl parathion degrading enzyme (MPDE) onto a modified electrode through CdTe quantum dots (CdTe QDs) covalent attachment. The introduced MWCNT and gold nanoparticles significantly increased the surface area and exhibited synergistic effects towards enzymatic catalysis. CdTe QDs are further used as carriers to load a large amount of enzyme. As a result of these two important enhancement factors, the proposed biosensor exhibited extremely sensitive, perfectly selective, and rapid response to methyl parathion in the absence of a mediator. The detection limit was 1.0 ng/mL. Moreover, since MPDE hydrolyzes pesticides containing the P-S bond, it showed high selectivity for detecting MP and many interfering compounds, such as carbamate pesticides. Other organophosphorous pesticides and oxygen-containing inorganic ions (SO(4)(2-), NO(3)(-)) did not interfere with the determination. The proposed MPDE biosensor presents good reproducibility and stability, and the MPDE is not poisoned by organophosphate pesticides. Unlike cholinesterase-based biosensor, the MPDE biosensor can be potentially reused and is suitable for continuous monitoring.