Efficient immobilization of acetylcholinesterase onto amino functionalized carbon nanotubes for the fabrication of high sensitive organophosphorus pesticides biosensors

Development of integrated smartphone/resistive biosensor for on-site rapid environmental monitoring of organophosphate pesticides in food and water

Organophosphate (OP) pesticides remain a worldwide health concern due to their acute or chronic poisoning and widespread use in agriculture around the world. There is a need for robust and field-deployable tools for onsite detection of OP pesticides in food and water. Herein, we present an integrated smartphone/resistive biosensor for simple, rapid, reagentless, and sensitive monitoring of OP pesticides in food and environmental water. The biosensor leverages the hydrolytic activity of acetylcholinesterase (AChE) to its substrate, acetylcholine (ACh), and unique transport properties of polyaniline nanofibers (PAnNFs) of chitosan/AChE/PAnNF/carbon nanotube (CNT) nanocomposite film on a gold interdigitated electrode. The principle of the sensor relies on OP inhibiting AChE, thus, reducing the rate of ACh hydrolysis and consequently decreasing the rate of protons doping the PAnNFs. Such resulted decrease in conductance of PAnNF can be used to quantify OP pesticides in a sample. A mobile app for the biosensor was developed for analyzing measurement data and displaying and sharing testing results. Under optimal conditions, the biosensor demonstrated a wide linear range (1 ppt-100 ppb) with a low detection limit (0.304 ppt) and high reproducibility (RSD <5%) for Paraoxon-Methyl (PM), a model analyte. Furthermore, the biosensor was successfully applied for analyzing PM spiked food/water samples with an average recovery rate of 98.3% and provided comparable results with liquid chromatography-mass spectrometry. As such, the nanosensing platform provides a promising tool for onsite rapid and sensitive detection of OP pesticides in food and environmental water.

A retrospective screening method for carbamate toxicant exposure based on butyrylcholinesterase adducts in human plasma with ultra-high performance liquid chromatography-tandem mass spectrometry

Carbamate pesticides are extensively used in agriculture for their inhibition to acetylcholinesterase and damages to the insects' neural systems. Because of their toxicity, human poisoning incidents caused by carbamate pesticide exposure have occurred from time to time. What's more, some lethally toxic carbamate toxicants known as carbamate nerve agents (CMNAs) have been supplemented in Schedule 1 of the Annex on Chemicals in the Chemical Weapons Convention (CWC) by Organisation of the Prohibition of Chemical Weapons (OPCW) from 2020. And some other carbamates, like physostigmine, have been used in clinical treatment as anticholinergic drugs and their misuse may also cause damages to the body. Similar to organophosphorus toxicants, carbamate toxicants would react with butyrylcholinesterase (BChE) in plasma when entering the human body, resulting in the BChE adducts, based on which the exposure of carbamate toxicants could be detected retrospectively. In this study, methylcarbamyl nonapeptide and dimethylcarbamyl nonapeptide from pepsin digestion of BChE adducts were identified with ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) in product ion scan mode. Carbofuran was chosen as the target to establish the detection method of carbamate toxicant exposure based on methylcarbamyl nonapeptide digested from methylcarbamyl BChE. Procainamide-gel affinity purification, pepsin digestion and UHPLC-MS/MS analysis in multiple reaction monitoring (MRM) mode were applied. Under the optimized conditions of sample preparation and UHPLC-MS/MS MRM analysis, the limits of detection (LODs) reached 10.0 ng/mL of plasma exposed to carbofuran with satisfactory specificity. The quantitation approach was established with d₃-carbofuran-exposed plasma as the internal standard (IS) and the linearity range was 30.0-1.00 × 10³ nmol/L (R² >0.998) with the accuracy of 95.6%-107% and precision of ≤9% relative standard deviation (RSD). The applicability was also evaluated by N,N-dimethyl-carbamates with the LODs of 30.0 nmol/L for pirimicarb-exposed plasma based on dimethylcarbamyl nonapeptide. Because most of carbamate toxicants has methylcarbamyl or dimethylcarbamyl groups, this approach could be applied on the retrospective screening of carbamate toxicant exposure including CMNAs, carbamate pesticides or carbamate drugs. This study could provide an effective means in the fields of CWC verification, toxicological mechanism investigation and down-selection of potential treatment options.

A portable acetylcholinesterase-based electrochemical sensor for field detection of organophosphorus

A portable acetylcholinesterase (AChE)-based electrochemical sensor based on a screen-printed carbon electrode (SPCE) and a miniature potentiostat was constructed for the rapid field detection of organophosphorus pesticides (OPs). Graphene (GR) and gold nanoparticles (AuNPs) were successively introduced onto SPCE for surface modification. Due to the synergistic effect of the two nanomaterials, the signal of the sensor has a significant enhancement. Take isocarbophos (ICP) as a model for chemical warfare agents (CAWs) and Ops; the SPCE/GR/AuNPs/AChE/Nafion sensor shows a wider linear range (0.1-2000 μg L-1), and a lower limit of detection (0.012 μg L-1) than SPCE/AChE/Nafion and SPCE/GR/AChE/Nafion sensors. Tests in actual fruit and tap water samples also yielded satisfactory results. Therefore, the proposed method can be used as a simple and cost-effective strategy for construction of portable electrochemical sensors for OP field detection.

A Review on CNTs-Based Electrochemical Sensors and Biosensors: Unique Properties and Potential Applications

Carbon nanotubes (CNTs), are safe, biocompatible, bioactive, and biodegradable materials, and have sparked a lot of attention due to their unique characteristics in a variety of applications, including medical and dye industries, paper manufacturing and water purification. CNTs also have a strong film-forming potential, permitting them to be widely employed in constructing sensors and biosensors. This review concentrates on the application of CNT-based nanocomposites in the production of electrochemical sensors and biosensors. It emphasizes the synthesis and optimization of CNT-based sensors for a range of applications and outlines the benefits of using CNTs for biomolecule immobilization. In addition, the use of molecularly imprinted polymer (MIP)-CNTs in the production of electrochemical sensors is also discussed. The challenges faced by the current CNTs-based sensors, along with some the future perspectives and their future opportunities, are also briefly explained in this paper.

Recent Advances in Rapid Detection Techniques for Pesticide Residue: A Review

As an important chemical pollutant affecting the safety of agricultural products, the on-site and efficient detection of pesticide residues has become a global trend and hotspot in research. These methodologies were developed for simplicity, high sensitivity, and multiresidue detection. This review introduces the currently available technologies based on electrochemistry, optical analysis, biotechnology, and some innovative and novel technologies for the rapid detection of pesticide residues, focusing on the characteristics, research status, and application of the most innovative and novel technologies in the past 10 years, and analyzes challenges and future development prospects. The current review could be a good reference for researchers to choose the appropriate research direction in pesticide residue detection.

Advances in Electrochemical Nano-Biosensors for Biomedical and Environmental Applications: From Current Work to Future Perspectives

Modern life quality is strongly supported by the advances made in biosensors, which has been attributed to their crucial and viable contribution in point-of-care (POC) technology developments. POC devices are exploited for the fast tracing of disease progression, rapid analysis of water, and food quality assessment. Blood glucose meters, home pregnancy strips, and COVID-19 rapid tests all represent common examples of successful biosensors. Biosensors can provide great specificity due to the incorporation of selective bio-recognition elements and portability at significantly reduced costs. Electrochemical biosensor platforms are one of the most advantageous of these platforms because they offer many merits, such as being cheap, selective, specific, rapid, and portable. Furthermore, they can be incorporated into smartphones and various analytical approaches in order to increase their sensitivity and many other properties. As a very broad and interdisciplinary area of research and development, biosensors include all disciplines and backgrounds from materials science, chemistry, physics, medicine, microbiology/biology, and engineering. Accordingly, in this state-of-the-art article, historical background alongside the long journey of biosensing construction and development, starting from the Clark oxygen electrode until reaching highly advanced wearable stretchable biosensing devices, are discussed. Consequently, selected examples among the miscellaneous applications of nanobiosensors (such as microbial detection, cancer diagnosis, toxicity analysis, food quality-control assurance, point of care, and health prognosis) are described. Eventually, future perspectives for intelligent biosensor commercialization and exploitation in real-life that is going to be supported by machine learning and artificial intelligence (AI) are stated.

Carbon nanomaterials for the detection of pesticide residues in food: A review

In agricultural fields, pesticides are widely used, but their residual presence in the environment poses a threat to humans, animals, insects, and ecosystems. The overuse of pesticides for pest control, enhancement of crop yield, etc. leaves behind a significant residual amount in the environment. Various robust, reliable, and reusable methods using a wide class of composites have been developed for the monitoring and controlling of pesticides. Researchers have discovered that carbon nanomaterials have a wide range of characteristics such as high porosity, conductivity and easy electron transfer that can be successfully used to detect pesticide residues from food. This review emphasizes the role of carbon nanomaterials in the field of pesticide residue analysis in different food matrices. The carbon nanomaterials including carbon nanotubes, carbon dots, carbon nanofibers, graphene/graphene oxides, and activated carbon fibres are discussed in the review. In addition, the review examines future prospects in this research area to help improve detection techniques for pesticides analysis.

Biocatalytic asymmetric synthesis of secondary allylic alcohols using Burkholderia cepacia lipase immobilized on multiwalled carbon nanotubes

The lipase from Burkholderia cepacia (BCL) was immobilized through physical adsorption on pristine and functionalized multiwalled carbon nanotubes (MWCNTs) with carboxyl or amine groups and used in the stereoselective acylation of (R,S)-1-octen-3-ol (1) and (R,S)-(E)-4-phenyl-3-buten-2-ol (4) with vinyl acetate. All immobilized preparations produced better results than free BCL. For (R,S)-4, 50% conversion and E > 200 were obtained in n-hexane or in solvent-free medium. For (R,S)-1, in solvent-free medium, the conversion was 38% with a slight increase in the E-value (E = 10).

Formation and Characterization of a Stable Monolayer of Active Acetylcholinesterase on Planar Gold

Enzyme activity is the basis for many biosensors where a catalytic event is used to detect the presence and amount of a biomolecule of interest. To create a practical point-of-care biosensor, these enzymes need to be removed from their native cellular environments and immobilized on an abiological surface to rapidly transduce a biochemical signal into an interpretable readout. This immobilization often leads to loss of activity due to unfolded, aggregated, or improperly oriented enzymes when compared to the native state. In this work, we characterize the formation and surface packing density of a stable monolayer of acetylcholinesterase (AChE) immobilized on a planar gold surface and quantify the extent of activity loss following immobilization. Using spectroscopic ellipsometry, we determined that the surface concentration of AChE on a saturated Au surface in a buffered solution was 2.77 ± 0.21 pmol cm^-2. By calculating the molecular volume of hydrated AChE, corresponding to a sphere of 6.19 nm diameter, divided by the total volume at the AChE-Au interface, we obtain a surface packing density of 33.4 ± 2.5% by volume. This corresponds to 45.1 ± 3.4% of the theoretical maximum monolayer coverage, assuming hexagonal packing. The true value, however, may be larger due to unfolding of enzymes to occupy a larger volume. The enzyme activity and kinetic measurements showed a 90.6 ± 1.4% decrease in specific activity following immobilization. Finally, following storage in a buffered solution for over 100 days at both room temperature and 4 °C, approximately 80% of this enzyme activity was retained. This contrasts with the native aqueous enzyme, which loses approximately 75% of its activity within 1 day and becomes entirely inactive within 6 days.

A competitive immunoassay for detecting triazophos based on fluorescent catalytic hairpin self-assembly

A rapid detection method is introduced for residual trace levels of triazophos in water and agricultural products using an immunoassay based on catalytic hairpin self-assembly (CHA). The gold nanoparticle (AuNPs) surface was modified with triazophos antibody and sulfhydryl bio-barcode, and an immune competition reaction system was established between triazophos and its ovalbumin-hapten (OVA-hapten). The bio-barcode served as a catalyst to continuously induce the CHA reaction to achieve the dual signal amplification. The method does not rely on the participation of enzymes, and the addition of fluorescent materials in the last step avoids interfering factors, such as a fluorescence burst. The emitted fluorescence was detected at 489/521 nm excitation/emission wavelengths. The detection range of the developed method was 0.01-50 ng/mL for triazophos, and the limit of detection (LOD) was 0.0048 ng/mL. The developed method correlates well with the results obtained by LC-MS/MS, with satisfactory recovery and sensitivity. In sum, the designed method is reliable and provides a new approach to detect pesticide residues rapidly and quantitatively.

Nanostructured Carbons: towards Soft-Bioelectronics, Biosensing and Theraputic Applications

Recently, nanostructured carbon-based soft bioelectronics and biosensors have received tremendous attention due to their outstanding physical and chemical properties. The ultrahigh specific surface area, high flexibility, lightweight, high electrical conductivity, and biocompatibility of 1D and 2D nanocarbons, such as carbon nanotubes (CNT) and graphene, are advantageous for bioelectronics applications. These materials improve human life by delivering therapeutic advancements in gene, tumor, chemo, photothermal, immune, radio, and precision therapies. They are also utilized in biosensing platforms, including optical and electrochemical biosensors to detect cholesterol, glucose, pathogenic bacteria (e. g., coronavirus), and avian leucosis virus. This review summarizes the most recent advancements in bioelectronics and biosensors by exploiting the outstanding characteristics of nanocarbon materials. The synthesis and biocompatibility of nanocarbon materials are briefly discussed. In the following sections, applications of graphene and CNTs for different therapies and biosensing are elaborated. Finally, the key challenges and future perspectives of nanocarbon materials for biomedical applications are highlighted.

Molecular understanding of acetylcholinesterase adsorption on functionalized carbon nanotubes for enzymatic biosensors

The immobilization of acetylcholinesterase on different nanomaterials has been widely used in the field of amperometric organophosphorus pesticide (OP) biosensors. However, the molecular adsorption mechanism of acetylcholinesterase on a nanomaterial's surface is still unclear. In this work, multiscale simulations were utilized to study the adsorption behavior of acetylcholinesterase from Torpedo californica (TcAChE) on amino-functionalized carbon nanotube (CNT) (NH₂-CNT), carboxyl-functionalized CNT (COOH-CNT) and pristine CNT surfaces. The simulation results show that the active center and enzyme substrate tunnel of TcAChE are both close to and oriented toward the surface when adsorbed on the positively charged NH₂-CNT, which is beneficial to the direct electron transfer (DET) and accessibility of the substrate molecule. Meanwhile, the NH₂-CNT can also reduce the tunnel cost of the enzyme substrate of TcAChE, thereby further accelerating the transfer rate of the substrate from the surface or solution to the active center. However, for the cases of TcAChE adsorbed on COOH-CNT and pristine CNT, the active center and substrate tunnel are far away from the surface and face toward the solution, which is disadvantageous for the DET and transportation of enzyme substrate. These results indicate that NH₂-CNT is more suitable for the immobilization of TcAChE. This work provides a better molecular understanding of the adsorption mechanism of TcAChE on functionalized CNT, and also provides theoretical guidance for the ordered immobilization of TcAChE and the design, development and improvement of TcAChE-OPs biosensors based on functionalized carbon nanomaterials.

The dichotomy of nanotechnology as the cutting edge of agriculture: Nano-farming as an asset versus nanotoxicity

The unprecedented setbacks and environmental complications, faced by global agro-farming industry, have led to the advent of nanotechnology in agriculture, which has been recognized as a novel and innovative approach in development of sustainable farming practices. The agricultural regimen is the "head honcho" of the world, however presently certain approaches have been imposing grave danger to the environment and human civilization. The nano-farming paradigm has successfully elevated the growth and development of plants, parallel to the production, quality, germination/transpiration index, photosynthetic machinery, genetic progression, and so on. This has optimized the traditional farming into precision farming, utilising nano-based sensors and nanobionics, smart delivery tools, nanotech facets in plant disease management, nanofertilizers, enhancement of plant adaptive potential to external stress, role in bioenergy conservation and so on. These applications portray nanorevolution as "the big cheese" of global agriculture, mitigating the bottlenecks of conventional practices. Besides the applications of nanotechnology, the review identifies the limitations, like possible harmful impact on environment, mankind and plants, as the "Achilles heel" in agro-industry, aiming to establish its defined role in agriculture, while simultaneously considering the risks, in order to resolve them, thus abiding by "technology-yes, but safety-must". The authors aim to provide a significant opportunity to the nanotech researchers, Botanists and environmentalists, to promote judicial use of nanoparticles and establish a secure and safe environment.

Modern Carbon-Based Materials for Adsorptive Removal of Organic and Inorganic Pollutants from Water and Wastewater

Currently, a serious threat for living organisms and human life in particular, is water contamination with persistent organic and inorganic pollutants. To date, several techniques have been adopted to remove/treat organics and toxic contaminants. Adsorption is one of the most effective and economical methods for this purpose. Generally, porous materials are considered as appropriate adsorbents for water purification. Conventional adsorbents such as activated carbons have a limited possibility of surface modification (texture and functionality), and their adsorption capacity is difficult to control. Therefore, despite the significant progress achieved in the development of the systems for water remediation, there is still a need for novel adsorptive materials with tunable functional characteristics. This review addresses the new trends in the development of new adsorbent materials. Herein, modern carbon-based materials, such as graphene, oxidized carbon, carbon nanotubes, biomass-derived carbonaceous matrices-biochars as well as their composites with metal-organic frameworks (MOFs) and MOF-derived highly-ordered carbons are considered as advanced adsorbents for removal of hazardous organics from drinking water, process water, and leachate. The review is focused on the preparation and modification of these next-generation carbon-based adsorbents and analysis of their adsorption performance including possible adsorption mechanisms. Simultaneously, some weak points of modern carbon-based adsorbents are analyzed as well as the routes to conquer them. For instance, for removal of large quantities of pollutants, the combination of adsorption and other methods, like sedimentation may be recommended. A number of efficient strategies for further enhancing the adsorption performance of the carbon-based adsorbents, in particular, integrating approaches and further rational functionalization, including composing these adsorbents (of two or even three types) can be recommended. The cost reduction and efficient regeneration must also be in the focus of future research endeavors. The targeted optimization of the discussed carbon-based adsorbents associated with detailed studies of the adsorption process, especially, for multicomponent adsorbate solution, will pave a bright avenue for efficient water remediation.

Recent advances in the applications of nano-agrochemicals for sustainable agricultural development

Modern agricultural practices have triggered the process of agricultural pollution. This process can cause the degradation of eco-systems, land, and environment owing to the modern-day by-products of agriculture. The substantial use of chemical fertilizers, pesticides, and, contaminated water for irrigation cause further damage to agriculture. The current scenario of the agriculture and food sector has therefore become unsustainable. Nanotechnology has provided innovative and resourceful frontiers to the agriculture sector by contributing practical applications in conventional agricultural ways and practices. There is a large possibility that agri-nanotechnology can have a significant impact on the sustainable agriculture and crop growth. Recent research has shown the potential of nanotechnology in improving the agriculture sector by enhancing the efficiency of agricultural inputs and providing solutions to agricultural problems for improving food productivity and security. The prospective use of nanoscale agrochemicals such as nanofertilizers, nanopesticides, nanosensors, and nanoformulations in agriculture has transformed traditional agro-practices, making them more sustainable and efficient. However, the application of these nano-products in real field situations raises concern about nanomaterial safety, exposure levels, and toxicological repercussions to the environment and human health. The present review gives an insight into recent advancements in nanotechnology-based agrochemicals that have revolutionized the agriculture sector. Further, the implementation barriers related to the nanomaterial use in agriculture, their commercialization potential, and the need for policy regulations to assess possible nano-agricultural risks are also discussed.

Preparation of a Sensor Based on Biomass Porous Carbon/Covalent-Organic Frame Composites for Pesticide Residues Detection

In this work, a covalent-organic framework with high carbon and nitrogen content microstructures (named COF-LZU1), assisted by 3D nitrogen-containing kenaf stem composites (represented as COF-LZU1/3D-KSCs), was constructed. Moreover, it was utilized for immobilizing acetylcholinesterase (AChE) for identifying trichlorfon, a commonly applied organophosphorus (OP) pesticide. The development of COF-LZU1/3D-KSC was affirmed by SEM, PXRD, and EDXS. The findings confirmed that COF-LZU1 microstructures were uniformly developed on 3D-KSC holes using a one-step synthesis approach, which can substantially enhance the effective surface area. Also, the COF-LZU1/3D-KSC composite contains not only the nitrogen element in COF-LZU1 but also the nitrogen element in 3D-KSC, which will greatly improve the biocompatibility of the material. The AChE/COF-LZU1/3D-KSC integrated electrode was fabricated by directly fixing a large amount of AChE on the composite. At the same time, the integrated electrode had good detection efficiency for trichlorfon. Improved stabilization, a wide-linear-range (0.2–19 ng/mL), and a lower detection limit (0.067 ng/mL) have been displayed by the sensor. Therefore, this sensor can be used as an important platform for the on-site detection of OP residue.

Nanoparticles in Agroindustry: Applications, Toxicity, Challenges, and Trends

Nanotechnology is a tool that in the last decade has demonstrated multiple applications in several sectors, including agroindustry. There has been an advance in the development of nanoparticulated systems to be used as fertilizers, pesticides, herbicides, sensors, and quality stimulants, among other applications. The nanoencapsulation process not only protects the active ingredient but also can affect the diffusion, interaction, and activity. It is important to evaluate the negative aspects of the use of nanoparticles (NPs) in agriculture. Given the high impact of the nanoparticulated systems in the agro-industrial field, this review aims to address the effects of various nanomaterials on the morphology, metabolomics, and genetic modification of several crops.

Development of novel oxygen carriers by coupling hemoglobin to functionalized multiwall carbon nanotubes

Preparation of stable and effective artificial oxygen carriers (AOCs) is a promising strategy to temporarily replace transfused blood and solve tissue hypoxia. Developing hemoglobin (Hb) loaded particles is one of the main ways to prepare suitable AOCs. Particles with a hierarchical micro/nanostructure can be loaded with plenty of proteins and have attracted great attention. Therefore, multiwall carbon nanotubes (MWCNTs) were chosen to fabricate AOCs. To improve the Hb-loading capacity of MWCNTs, functionalized MWCNTs, including carboxyl-functionalized MWCNTs (MWCNT-COOH), amino-functionalized MWCNTs (MWCNT-NH2), and heparin-conjugated MWCNTs (MWCNT-Hep), were prepared. Then, in this study, Hb was coupled to the functionalized MWCNTs to fabricate the AOCs. The functionalized MWCNTs and the AOCs were characterized by FTIR, SEM, TEM, and zeta potential analysis. The oxygen/Hb-loading capacity of the AOCs was also measured. The adverse effects of the AOCs on human umbilical vein endothelial cells (HUVECs) and human red blood cells (RBCs) were evaluated. The results showed that (1) the functional groups were grafted on the surface of the MWCNTs, and Hb was bound to the functionalized MWCNTs, thus the AOCs were successfully prepared; (2) MWCNT-Hep-Hb had the most stable dispersibility (i.e., the most negative zeta potential) in 0.9 wt% NaCl solution (MWCNT-Hep-Hb < MWCNT-COOH-Hb < MWCNT-Hb < MWCNT-NH2-Hb < 0); (3) MWCNT-Hep had the best Hb-loading capability, which was three times that of purified MWCNTs; (4) with concentrations increased up to 400 μg mL-1, MWCNT-Hep-Hb still had the highest cell viability (97.63% > 80%, ISO 10993-5:2009) and excellent blood biocompatibility. Therefore, MWCNT-Hep-Hb might be a satisfactory candidate as a blood substitute.

Electrostatic Effect of Functional Surfaces on the Activity of Adsorbed Enzymes: Simulations and Experiments

The efficient immobilization of haloalkane dehalogenase (DhaA) on carriers with retaining of its catalytic activity is essential for its application in environmental remediation. In this work, adsorption orientation and conformation of DhaA on different functional surfaces were investigated by computer simulations; meanwhile, the mechanism of varying the catalytic activity was also probed. The corresponding experiments were then carried out to verify the simulation results. (The simulations of DhaA on SAMs provided parallel insights into DhaA adsorption in carriers. Then, the theory-guided experiments were carried out to screen the best surface functional groups for DhaA immobilization.) The electrostatic interaction was considered as the main impact factor for the regulation of enzyme orientation, conformation, and enzyme bioactivity during DhaA adsorption. The synergy of overall conformation, enzyme substrate tunnel structural parameters, and distance between catalytic active sites and surfaces codetermined the catalytic activity of DhaA. Specifically, it was found that the positively charged surface with suitable surface charge density was helpful for the adsorption of DhaA and retaining its conformation and catalytic activity and was favorable for higher enzymatic catalysis efficiency in haloalkane decomposition and environmental remediation. The neutral, negatively charged surfaces and positively charged surfaces with high surface charge density always caused relatively larger DhaA conformation change and decreased catalytic activity. This study develops a strategy using a combination of simulation and experiment, which can be essential for guiding the rational design of the functionalization of carriers for enzyme adsorption, and provides a practical tool to rationally screen functional groups for the optimization of adsorbed enzyme functions on carriers. More importantly, the strategy is general and can be applied to control behaviors of different enzymes on functional carrier materials.

Fluorescence sensor for organophosphorus pesticide detection based on the alkaline phosphatase-triggered reaction

The threat of organophosphorus pesticide (OPP) residue to food safety and human health has caused widespread concern. In this paper, a sensitive fluorescence sensor for OPP detection was constructed based on the alkaline phosphatase (ALP) -triggered in situ reaction. In this method, ALP catalyses the dephosphorylation of the substrate l-ascorbic acid 2-phosphate sesquimagnesium salt hydrate (AAP) to generate l-ascorbic acid (AA). AA instantly combines with o-phenylenediamine (OPD) to form 3-(1,2-dihydroxyethyl)furo[3,4-b]quinoxalin-1(3H)-one (DFQ), which contains a quinoxaline core skeleton fluorophore and emits a strong fluorescence intensity at 425 nm. The existence of OPPs inhibits the activity of ALP and the production of AA and DFQ. As a result, the fluorescence intensity obviously decreases. Under optimal conditions, the fluorescence intensity linearly depends on the logarithm of chlorpyrifos concentration over a wide range of 20 pg/mL ∼1000 ng/mL with a detection limit of 15.03 pg/mL (S/N = 3), which is lower than the previously reported values. The sensor with its satisfactory accuracy and precision has been successfully applied to the detection of chlorpyrifos in leeks and celery samples with recoveries of 94.5-106.7% and an inter-assay relative standard deviation (RSD) below 11.51%. OPPs can be semiquantitatively determined by the colour changes in ultraviolet light. The superiority of the sensor is due to its visual simplicity without complex fluorescence labelling procedures and costly instruments.

Acetylcholinesterase electrochemical biosensors with graphene-transition metal carbides nanocomposites modified for detection of organophosphate pesticides

An acetylcholinesterase biosensor modified with graphene and transition metal carbides was prepared to detect organophosphorus pesticides. Cyclic voltammetry, differential pulse voltammetry, and electrochemical impedance spectroscopy were used to characterize the electrochemical catalysis of the biosensor: acetylcholinesterase/chitosan-transition metal carbides/graphene/glassy carbon electrode. With the joint modification of graphene and transition metal carbides, the biosensor has a good performance in detecting dichlorvos with a linear relationship from 11.31 μM to 22.6 nM and the limit of detection was 14.45 nM. Under the premise of parameter optimization, the biosensor showed a good catalytic performance for acetylcholine. Compared to the biosensors without modification, it expressed a better catalytic performance due to the excellent electrical properties, biocompatibility and high specific surface area of graphene, transition metal carbides. Finally, the biosensor exhibits good stability, which can be stored at room temperature for one month without significant performance degradation, and has practical potential for sample testing.

Bio-inspired anchoring of amino-functionalized multi-wall carbon nanotubes (N-MWCNTs) onto PES membrane using polydopamine for oily wastewater treatment

The major problem that limits the utilization of PES membranes in treatment of oily wastewater is the drastic irreversible membrane fouling due to the attachment of oil droplets onto the membrane surface. The goal of this study was to develop a novel, fast and facile post-functionalization of polydopamine (PDA) coated membranes using pre-synthesized nanoparticles for fabrication of novel organic-inorganic hybrid recoverable membranes with high hydrophilicity and underwater oleophobicity. Here, bio-inspired technique was studied because the membrane technology could separate small oil droplets (even <10 µm) with high performance if faced little fouling phenomena during the treatment process. The amino-functionalized multi-wall carbon nanotubes (N-MWCNTs) were anchored onto the PDA coated PES membranes. The membranes characteristics, with specific focus on surface morphology and wettability were investigated. The newly developed PES/PDA/N-MWCNTs membranes showed an enhanced flux (~1086%) compared to the unmodified PES membrane. This enhancement was attributed to the high hydrophilic and underwater oleophobic properties, which were found to alleviate the effect of fouling. The total fouling ratio (R_t) of the PES/PDA/N-MWCNTs membrane was 22.35%, which was far lower than that of the unmodified PES membrane (98.38%). Meanwhile, most of the fouling was reversible for the former with the remaining (irreversible fouling) of 18.08%. It was concluded that cake filtration is the dominant fouling mechanism of the PES/PDA/N-MWCNTs membranes due to their average pore diameter. The modified membranes showed high oil rejection (>99%) so that the obtained clean water with oil concentration lower than 5 ppm met the wastewater discharge standard recommendations. Also, evaluation of the PES/PDA/N-MWCNT membrane in cross-flow filtration showed its antifouling properties in the long-term application (16 h).

Simulated revelation of the adsorption behaviours of acetylcholinesterase on charged self-assembled monolayers

An acetylcholinesterase (AChE)-based electrochemical biosensor, as a promising alternative to detect organophosphates (OPs) and carbamate pesticides, has gained considerable attention in recent years, due to the advantages of simplicity, rapidity, reliability and low cost. The bio-activity of AChE immobilized on the surface and the direct electron transfer (DET) rate between an enzyme and an electrode directly determined the analytical performances of the AChE-based biosensor, and experimental studies have shown that the charged surfaces have a strong impact on the detectability of the AChE-based biosensor. Therefore, it is very important to reveal the behaviour of AChE in bulk solution and on charged surfaces at the molecular level. In this work, the adsorption orientation and conformation of AChE from Torpedo californica (TcAChE) on oppositely charged self-assembled monolayers (SAMs), COOH-SAM and NH₂-SAM with different surface charge densities, were investigated by parallel tempering Monte Carlo (PTMC) and all-atom molecular dynamics simulations (AAMD). Simulation results show that TcAChE could spontaneously and stably adsorb on two oppositely charged surfaces by the synergy of an electric dipole and charged residue patch, and opposite orientations were observed. The active-site gorge of TcAChE is oriented toward the surface with the "end-on" orientation and the active sites are close to the surface when it is adsorbed on the positively charged surface and the tunnel cost for the substrate is lower than that on the negatively charged surface and in bulk solution, while for TcAChE adsorbed on the negatively charged surface, the active site of TcAChE is far away from the surface and the active-site gorge is oriented toward the solution with a "back-on" orientation. It suggests that the positively charged surface could provide a better microenvironment for the efficient bio-catalytic reaction and quick DET between TcAChE and the electrode surface. Moreover, the RMSD, RMSF, dipole moment, gyration radius, eccentricity and superimposed structures show that only a slight conformational change occurred on the relatively flexible structure of TcAChE during simulations, and the native conformation is well preserved after adsorption. This work helps us better comprehend the adsorption mechanism of TcAChE on charged surfaces and might provide some guidelines for the development of new TcAChE-based amperometric biosensors for the detection of organophosphorus pesticides.

A new [Co21(H2O)4(OH)12]30+ unit-incorporating polyoxotungstate for sensitive detection of dichlorvos

A new [Co₂₁(H₂O)₄(OH)₁₂]³⁰⁺ unit-incorporating polyoxotungstate (denoted as Co25Si6W60) has been hydrothermally synthesized and fully characterized. The unique Co25Si6W60-based biosensing system offers an environmentally-friendly route for detecting dichlorvos.

A critical review on organic micropollutants contamination in wastewater and removal through carbon nanotubes

The prevalence of organic micropollutants (OMPs) in various environmental compartments is posing a serious health risks to all kinds of lives on the planet. The levels of OMPs such as polyaromatic hydrocarbons, antibiotics, pesticides, contraceptive medicines, and personal care products in water bodies are increasing with each passing day. It is an urgent need of time to limit the release of OMPs into the environment, and to remove the prevailing OMPs for sustainable environmental management. The majority of the conventional means of water decontamination are either inefficient or expensive. However, due to nanosize, high surface area, and hollow and layered structure, carbon nanotubes (CNTs) serve as excellent sorbents for the removal of a diverse range of OMPs. The occurrence of emerging OMPs and their detrimental effects on human and animal health are collected and discussed in this review. The characteristics and efficacy of various CNTs (pristine and modified) for the efficient removal of different OMPs, and the removal mechanisms have been reviewed and discussed. The literature demonstrated that adsorption of OMPs onto CNTs is very complicated and rely on multiple factors including the properties of adsorbent and the adsorbate as well as solution chemistry. It was found that H-bonding, electrostatic interactions, van der Waals forces, hydrophobic interactions, H-π bongs, and π-π interactions were the major mechanisms responsible for the adsorption of OMPs onto various kinds of CNTs. Despite of higher affinities for OMPs, hydrophobicity and higher costs restrain the practical application of CNTs for wastewater treatment on large scale. However, continuous production may lead to the development of cost-effective, efficient and eco-friendly CTNs technology for wastewater treatments in future.

High-performance electrochemical enzyme sensor for organophosphate pesticide detection using modified metal-organic framework sensing platforms

A practical electrochemical biosensor with high sensitivity was developed for detecting organophosphorus (OP). Initially, Ce metal was introduced into an UiO-66-template to form Ce/UiO-66. Later, graphene oxide (GO), carbon black (CB) and multi-walled carbon nanotubes (MWCNTs) were separately added to Ce/UiO-66 to compare the effect of different carbon-based material types on the performance of the biosensor. Exclusively, Ce/UiO-66/MWCNTs with a Ce (7%) and MWCNT (30%) matrix was found to not only load more acetylcholinesterase (AChE) onto vacant sites but also increase electron transfer and decrease the number of diffusion pathways between the thiocholine and electrode surface. Moreover, the appropriate oxophilicity of Ce coupled with the high surface area and good conductivity of MWCNTs in the UiO-66 structure revealed a high affinity to acetylthiocholine chloride (ATCl) and possible catalysis of the hydrolysis of ATCl with a Michaelis-Menten constant of 0.258 mM. This biosensor, under optimal conditions, demonstrated a rapid and sensitive detection of paraoxon over a wide linear range of 0.01-150 nM, with a low detection limit of 0.004 nM. As a result, the AChE/Ce/UiO-66/MWCNTs/GCE biosensor can be employed in laboratory and field experiments to determine paraoxon levels.

Monocrotophos detection with a bienzyme biosensor based on ionic-liquid-modified carbon nanotubes

Acetylcholinesterase (AChE) biosensor technology is widely applied in the detection of organophosphate pesticides in agricultural production via the inhibition of AChE activity by organophosphates. However, the AChE electrode has some drawbacks, such as low stability and high overpotential. Combining the advantages of multiwalled carbon nanotubes (MWCNTs) and ionic liquids, we constructed a novel bienzyme electrode [Cl/iron porphyrin (FePP)-modified MWCNTs/AChE/glassy carbon electrode], which included AChE and mimetic oxidase FePP. In this electrode, FePP is covalently bound to the AChE carrier via ionic liquid for increased electrode sensitivity and stability. Under optimal conditions, this novel biosensor has a monocrotophos detection limit of 3.2 × 10-11 mol/L and good recovery of 89-104%. After 5 weeks of storage at 4 °C, the oxidation current was 97.8% of its original value. The biosensor has high stability and sensitivity for monocrotophos detection and is a promising device for monitoring food safety. Graphical abstract The complete synthesis process of Cl/FePP-MWCNTs/AChE/GCE.

Polydopamine-Capped Bimetallic AuPt Hydrogels Enable Robust Biosensor for Organophosphorus Pesticide Detection

Noble metal hydrogels/aerogels with macroscopic nanoassemblies characterized by ultralow density, profuse continuous porosity, and extremely large surface area have gained abundant interest due to not only their tunable physicochemical properties, but also promising applications in catalysis and sensing. Coupling the increased reaction temperature with dopamine-induced effect, herein, a one-step synthetic approach with accelerated gelation kinetics is reported for the synthesis of polydopamine-capped bimetallic AuPt hydrogels. 3D porous nanowire networks with surface functionalization of polydopamine make them a promising biocompatible microenvironment for immobilizing acetylcholinesterase (AChE) and constructing enzyme-based biosensors for sensitive detection of organophosphorus compounds. Taking advantage of their favorable structure and composition, the optimized product exhibits superior electrochemical activity toward thiocholine produced by AChE-catalyzed hydrolysis of acetylthiocholine. Based on the inhibition of organophosphorus pesticide on the enzymatic activity of AChE, the inhibition mode for the detection of paraoxon-ethyl is established, displaying linear regions over the range of 0.5-1000 ng L^-1 with a low detection limit of 0.185 ng L^-1 .

Amorphous metal boride as a novel platform for acetylcholinesterase biosensor development and detection of organophosphate pesticides

The exploration of new materials for modifying electrodes is important to advance electrochemical biosensors. Herein, we demonstrated that amorphous bimetallic boride material (Co-2Ni-B) prepared by a simple and facile aqueous reaction is an efficient matrix to immobilize acetylcholinesterase (AChE) to construct a biosensor for the determination of organophosphate pesticides. The effects of different composition and crystallinity on its electrochemical performance are investigated, and the optimization studies of the biological transducer were also discussed. Under optimal conditions, the fabricated sensor showed good analytical performance for the determination of chlorpyrifos with a low limit of detection (2.83 pM) and a wide linear range (3 pM-300 nM). The proposed biosensor also demonstrated high reproducibility, stability and accuracy. The impressive performance was due to the excellent conductivity and the unique amorphous bimetal-metalloid complex nanostructure. These results introduce a new class of promising materials as a robust platform for biosensor applications.

Carbon Nanotube Chemical Sensors

Carbon nanotubes (CNTs) promise to advance a number of real-world technologies. Of these applications, they are particularly attractive for uses in chemical sensors for environmental and health monitoring. However, chemical sensors based on CNTs are often lacking in selectivity, and the elucidation of their sensing mechanisms remains challenging. This review is a comprehensive description of the parameters that give rise to the sensing capabilities of CNT-based sensors and the application of CNT-based devices in chemical sensing. This review begins with the discussion of the sensing mechanisms in CNT-based devices, the chemical methods of CNT functionalization, architectures of sensors, performance parameters, and theoretical models used to describe CNT sensors. It then discusses the expansive applications of CNT-based sensors to multiple areas including environmental monitoring, food and agriculture applications, biological sensors, and national security. The discussion of each analyte focuses on the strategies used to impart selectivity and the molecular interactions between the selector and the analyte. Finally, the review concludes with a brief outlook over future developments in the field of chemical sensors and their prospects for commercialization.

Acetylcholinesterase Biosensor Based On Mesoporous Hollow Carbon Spheres/Core-Shell Magnetic Nanoparticles-Modified Electrode for the Detection of Organophosphorus Pesticides

The present study investigated the synthesis of mesoporous hollow carbon spheres (MHCS) and magnetic mesoporous hollow carbon spheres with core-shell structures (Fe₃O₄@MHCS). Two acetylcholinesterase sensors (acetylcholinesterase/mesoporous hollow carbon spheres/glassy carbon electrode (AChE/MHCS/GCE) and acetylcholinesterase/core-shell magnetic mesoporous hollow carbon spheres/glassy carbon electrode (AChE/Fe₃O₄@MHCS/GCE) based on mesoporous carbon materials were prepared. Under the optimum conditions, using Malathion as the model compound, the developed biosensors showed a wide detection range, low detection limit, good reproducibility, and high stability. The AChE/MHCS/GCE electrochemical sensor response exhibited two good linear ranges at the incubation time of 10 min at the Malathion concentration ranges of 0.01 to 100 ppb and 100 to 600 ppb, with a detection limit of 0.0148 ppb (S/N = 3). The AChE/Fe₃O₄@MHCS/GCE electrochemical sensor that was operated with an incubation time of 12 min at the malathion concentration ranges between 0.01–50 ppb and 50–600 ppb had a detection limit of 0.0182 ppb (S/N = 3). Moreover, the AChE/MHCS/GCE and AChE/Fe₃O₄@MHCS/GCE biosensors were effective for the detection of real samples, and were demonstrated to be suitable for the field-testing of organophosphorus pesticide (OP) residues.

Voltammetric Biosensor Based on Nitrogen-doped Ordered Mesoporous Carbon for Detection of Organophosphorus Pesticides in Vegetables

Background:

Pesticides residues in agricultural products have posed a serious threat to food safety and human health, so it is necessary to develop a rapid and accurate method to detect pesticide in the environment. N-OMC with excellent electroconductivity, high biocompatibility and the functional amino group that can be covalently attached to the enzyme can be applied to construct a sensitive and stable acetylcholinesterase biosensor for rapid and accurate detection of organophosphorus pesticides with the help of L-cysteine self-assembled monolayer and AuNPs.

Methods:

Transmission electron microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy and nitrogen adsorption measurements are used to characterize materials. Electrochemical impedance spectroscopy and cyclic voltammetry are used to study the surface features of modified electrodes. Differential pulse voltammetric is used to measure the peak current of modified electrodes. GC-MS is applied to verify the reliability of the prepared biosensor for organophosphorus pesticides detection.

Results:

N-OMC was synthesized and applied to constructed stable and sensitive acetylcholinesterase biosensors. The combination of N-OMC, L-cysteine self-assembled monolayer and AuNPs to modify the electrode surface has greatly improved the conductivity of biosensor and provided a stable platform for acetylcholinesterase immobilization. The linear detection range of paraoxon was from 3 to 24 nM with a lower detection limit of 0.02 nM.

Conclusion:

The biosensor exhibited satisfactory reproducibility, repeatability and stability, and was successfully employed to determine the paraoxon in vegetables as well as tap water samples, providing a promising tool for rapid and sensitive detection of organophosphorus pesticides in agricultural products.

Nanomaterial enabled sensors for environmental contaminants

The need and desire to understand the environment, especially the quality of one's local water and air, has continued to expand with the emergence of the digital age. The bottleneck in understanding the environment has switched from being able to store all of the data collected to collecting enough data on a broad range of contaminants of environmental concern. Nanomaterial enabled sensors represent a suite of technologies developed over the last 15 years for the highly specific and sensitive detection of environmental contaminants. With the promise of facile, low cost, field-deployable technology, the ability to quantitatively understand nature in a systematic way will soon be a reality. In this review, we first introduce nanosensor design before exploring the application of nanosensors for the detection of three classes of environmental contaminants: pesticides, heavy metals, and pathogens.

N-Carbamoylmaleimide-treated carbon dots: stabilizing the electrochemical intermediate and extending it for the ultrasensitive detection of organophosphate pesticides

To date, numerous methods have been reported for the detection of organophosphorus pesticides (OP) due to their severe potential hazard to the environment, public health and national security. However, very few works have ever found that the signal loss of thiocholine (TCh) during electrochemical processing is a key factor leading to the low sensitivity of acetylcholinesterase (AChE)-based OP electrochemical sensing platforms. Herein, we propose an ultrasensitive detection method for multiple OPs including parathion-methyl, paraoxon, dimethoate and O,O-dimethyl-O-2,2-dichlorovinyl-phosphate using N-carbamoylmaleimide-functionalized carbon dots (N-MAL-CDs) as a nano-stabilizer. For the first time, Michael addition is introduced into an AChE-based OP electrochemical sensing platform to enrich the electrochemical intermediate TCh. The Michael addition between TCh and N-MAL-CDs is demonstrated via XRD, FTIR, SEM and EDS elemental mapping experiments. Due to the stabilization and enhancement of TCh with N-MAL-CDs, the as prepared OP sensing platform achieves ultrahigh sensitivity by detecting the initial electrochemical signals of TCh without signal loss, showing a wide linear range of 3.8 × 10^-15-3.8 × 10^-10 M for parathion-methyl and 1.8 × 10^-14-3.6 × 10^-10 M for paraoxon, with a limit of detection of 1.4 × 10^-15 M for parathion-methyl and 4.8 × 10^-15 M for paraoxon.

Nanosensors for water quality monitoring

Nanomaterial-enabled sensors are being designed for high-efficiency, multiplex-functionality and high-flexibility sensing applications. Many existing nanosensors have the inherent capacity to achieve such goals; however, they require further development into consumer- and operator-friendly tools with the ability to detect analytes in previously inaccessible locations, as well as at a greater scale than heretofore possible. Here, I discuss how nanotechnology-enabled sensors have great, as yet unmet, promise to provide widespread and potentially low-cost monitoring of chemicals, microbes and other analytes in drinking water.