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

A Simple Colorimetric and Fluorescent Sensor to Detect Organophosphate Pesticides Based on Adenosine Triphosphate-Modified Gold Nanoparticles

A simple and dual modal (colorimetric and fluorescent) sensor for organophosphate pesticides with high sensitivity and selectivity using adenosine triphosphate (ATP)- and rhodamine B-modified gold nanoparticles (RB-AuNPs), was successfully fabricated. This detection for ethoprophos afforded colorimetric and fluorescence imaging changes visualization. The quantitative determination was linearly proportional to the amounts of ethoprophos in the range of a micromolar scale (4.0–15.0 µM). The limit of detection for ethoprophos was as low as 37.0 nM at 3σ/k. Moreover, the extent application of this simple assay was successfully demonstrated in tap water samples with high reliability and applicability, indicating remarkable application in real samples.

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.

Directed Assembly of Hybrid Nanomaterials and Nanocomposites

Hybrid nanomaterials are molecular or colloidal-level combinations of organic and inorganic materials, or otherwise strongly dissimilar materials. They are often, though not exclusively, anisotropic in shape. A canonical example is an inorganic nanorod or nanosheet sheathed in, or decorated by, a polymeric or other organic material, where both the inorganic and organic components are important for the properties of the system. Hybrid nanomaterials and nanocomposites have generated strong interest for a broad range of applications due to their functional properties. Generating macroscopic assemblies of hybrid nanomaterials and nanomaterials in nanocomposites with controlled orientation and placement by directed assembly is important for realizing such applications. Here, a survey of critical issues and themes in directed assembly of hybrid nanomaterials and nanocomposites is provided, highlighting recent efforts in this field with particular emphasis on scalable methods.

Potential Utility of Metal-Organic Framework-Based Platform for Sensing Pesticides

The progress in modern agricultural practices could not have been realized without the large-scale contribution of assorted pesticides (e.g., organophosphates and nonorganophosphates). Precise tracking of these chemicals has become very important for safeguarding the environment and food resources owing to their very high toxicity. Hence, the development of sensitive and convenient sensors for the on-site detection of pesticides is imperative to overcome practical limitations encountered in conventional methodologies, which require skilled manpower at the expense of high cost and low portability. In this regard, the role of novel, advanced functional materials such as metal-organic frameworks (MOFs) has drawn great interest as an alternative for conventional sensory systems because of their numerous advantages over other nanomaterials. This review was organized to address the recent advances in applications of MOFs for sensing various pesticides because of their tailorable optical and electrical characteristics. It also provides in-depth comparison of the performance of MOFs with other nanomaterial sensing platforms. Further, we discuss the present challenges (e.g., potential bias due to instability under certain conditions, variations in the diffusion rate of the pesticide, chemical interferences, and the precise measurement of luminesce quenching) in developing robust and sensitive sensors by using tailored porosity, functionalities, and better framework stability.

Ultrasensitive electrochemical immuno-sensing platform based on gold nanoparticles triggering chlorpyrifos detection in fruits and vegetables

Chlorpyrifos (chl) is an organophosphate pesticide extensively used in agriculture and highly toxic for human health. Fluorine doped tin-oxide (FTO) based electrochemical nanosensor was developed for chlorpyrifos detection with gold nanoparticles (AuNPs) and anti-chlorpyrifos antibodies (chl-Ab). AuNPs provides high electrical conductivity and specific resistivity, thus increases the sensitivity of immunoassay. High electrical conductivity of AuNPs reveals that it promotes the redox reaction for better cyclic voltammetry. Based on the intrinsic conductive properties of FTO-AuNPs complex, chl-Ab was immobilized onto AuNPs surface. Under optimized conditions, the proposed FTO based nanosensor exhibited high sensitivity and stable response for the detection of chlorpyrifos, ranging from 1fM to 1µM with limit of detection (LOD) up to 10fM. The FTO-AuNPs sensor was successfully employed for the detection of chlorpyrifos in standard as well in real samples up to 10nM for apple and cabbage, 50nM for pomegranate. The proposed FTO-AuNPs nanosensor can be used as a quantitative tool for rapid, on-site detection of chlorpyrifos traces in real samples when miniaturized due to its excellent stability, sensitivity, and simplicity.

Magnetic Cu-MOFs embedded within graphene oxide nanocomposites for enhanced preconcentration of benzenoid-containing insecticides

Hybrid magnetic nanocomposites based on Cu-MOFs, graphene oxide (GO), and Fe₃O₄ nanoparticles (NPs) were prepared via chemical bonding approach, which GO were used as platforms to load nanostructured Cu-MOFs and Fe₃O₄ NPs. The composite features both magnetic separation characteristics and high MOFs porosity, making it an excellent adsorbent for magnetic solid-phase extraction (MSPE). The as-synthesized nanocomposites are characterized by XRD, TGA, SEM, TEM, nitrogen adsorption-desorption analysis and FT-IR spectroscopy. The composites are used in MSPE of six aromatic insecticides from various real samples prior to their quantification by HPLC. Amount of adsorbent, extraction times, extraction temperature, desorption times and oscillation rate are optimized. Under the optimal conditions, the method has a relative standard deviations (RSDs) of 1.9-2.7%, and good linearity (correlation coefficients higher than 0.9931). The low LOD and LOQ for six insecticides are found to be 0.30-1.58μgL^-1 and 1.0-5.2μgL^-1, respectively. The RSDs of within batch extraction are 1.6-9.5% and 3.9-12% for batch to batch extraction. The experimental results suggest that the nanocomposites have potential application for removal of hazardous pollutants from effluents.

High-Capacitance Hybrid Supercapacitor Based on Multi-Colored Fluorescent Carbon-Dots

Multi-colored, water soluble fluorescent carbon nanodots (C-Dots) with quantum yield changing from 4.6 to 18.3% were synthesized in multi-gram using dated cola beverage through a simple thermal synthesis method and implemented as conductive and ion donating supercapacitor component. Various properties of C-Dots, including size, crystal structure, morphology and surface properties along with their Raman and electron paramagnetic resonance spectra were analyzed and compared by means of their fluorescence and electronic properties. α-Manganese Oxide-Polypyrrole (PPy) nanorods decorated with C-Dots were further conducted as anode materials in a supercapacitor. Reduced graphene oxide was used as cathode along with the dicationic bis-imidazolium based ionic liquid in order to enhance the charge transfer and wetting capacity of electrode surfaces. For this purpose, we used octyl-bis(3-methylimidazolium)diiodide (C8H16BImI) synthesized by N-alkylation reaction as liquid ionic membrane electrolyte. Paramagnetic resonance and impedance spectroscopy have been undertaken in order to understand the origin of the performance of hybrid capacitor in more depth. In particular, we obtained high capacitance value (C = 17.3 μF/cm2) which is exceptionally related not only the quality of synthesis but also the choice of electrode and electrolyte materials. Moreover, each component used in the construction of the hybrid supercapacitor is also played a key role to achieve high capacitance value.

Nanotechnology: The new perspective in precision agriculture

Nanotechnology is an interdisciplinary research field. In recent past efforts have been made to improve agricultural yield through exhaustive research in nanotechnology. The green revolution resulted in blind usage of pesticides and chemical fertilizers which caused loss of soil biodiversity and developed resistance against pathogens and pests as well. Nanoparticle-mediated material delivery to plants and advanced biosensors for precision farming are possible only by nanoparticles or nanochips. Nanoencapsulated conventional fertilizers, pesticides and herbicides helps in slow and sustained release of nutrients and agrochemicals resulting in precise dosage to the plants. Nanotechnology based plant viral disease detection kits are also becoming popular and are useful in speedy and early detection of viral diseases. In this article, the potential uses and benefits of nanotechnology in precision agriculture are discussed. The modern nanotechnology based tools and techniques have the potential to address the various problems of conventional agriculture and can revolutionize this sector.

Two-Dimensional 1T-Phase Transition Metal Dichalcogenides as Nanocarriers To Enhance and Stabilize Enzyme Activity for Electrochemical Pesticide Detection

Single or few layers lithium-exfoliated transition metal dichalcogenides (TMDs) are found to exist predominantly in the conducting metallic 1T-polymorph, which makes it desirable for numerous applications due to its large surface area, good electrical conductivity, and enhanced electrocatalytic capabilities. We demonstrated the use of tert-butyllithium exfoliated TMDs (MoS₂, MoSe₂, WS₂, WSe₂) as a platform for the indirect electrochemical detection of an organophosphate pesticide, fenitrothion, via enzymatic inhibition pathway. All four reported materials enhanced the response of the enzymatic biosensor in comparison to the corresponding biosensor in the absence of TMDs. 1T-Phase WS₂ outperforms all other TMD materials, and we proved that it serves as an excellent transducer for enhancing electron transfer in a robust model enzyme-based inhibition assay system using cross-linking immobilization with glutaraldehyde. The reported system showed a broad fenitrothion concentration range (1-1000 nM) with an excellent linearity (r = 0.987). Moreover, the system displayed high sensitivity with low limit of detection (2.86 nM) obtained, which far exceeds the required limit set by Food and Agriculture Organisation (FAO) of the United Nations (UN). The feasibility of the proposed system in real samples was demonstrated in apple juice samples with good recoveries of 80.2% and 80.3% obtained at 10 and 1000 nM fenitrothion, respectively.

Dependence of carbon nanotubes dispersion kinetics on surfactants

Carbon nanotubes (CNTs) have been the subject of many studies due to their unique structure and desirable properties. However, the ability to solubilize and separate single CNTs from the bundles they form is still a challenge that needs to be overcome in order to extend their applications in the field of Nanotechnology. Covalent interactions are designed to modify CNTs surface and so prevent agglomeration. Though, this method alters the structures and intrinsic properties of CNTs. In the present work, noncovalent approaches to functionalize and solubilize CNTs are studied in detail. A dispersion kinetic study was performed to characterize the ability of different type of surfactants (non-ionic, anionic, cationic and biopolymer) to unzip CNT bundles. The dispersion kinetic study performed depicts the distinct CNTs bundles unzipping behavior of the different type of surfactants and the results elucidate specific wavelengths in relation with the degree of CNT clustering, which provides new tools for a deeper understanding and characterization of CNTs. Small angle x-ray scattering and transmission electron microscopy results are in agreement with UV-vis-NIR observations, revealing perfectly monodispersed CNTs for the biopolymer and cationic surfactant.

An on–off–on gold nanocluster-based fluorescent probe for sensitive detection of organophosphorus pesticides

In this study, a highly sensitive fluorescent probe based on bovine serum protein-protected gold nanoclusters (BSA-AuNCs) was developed for the determination of organophosphorus pesticides (OPs).

Facile colorimetric detection of 6-benzylaminopurine based on p-aminobenzenethiol functionalized silver nanoparticles

A simple colorimetric assay has been developed to detect 6-benzylaminopurine (6-BA) in a complex environment by using the novel probe p-aminobenzenethiol functionalized silver nanoparticles (ABT-AgNPs).

Strong base pre-treatment for colorimetric sensor array detection and identification of N-methyl carbamate pesticides

A strategy of strong base pre-treatment was developed and employed to the colorimetric sensor array detection and differentiation of N-methyl carbamate pesticides.

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.

Colorimetric sensor array for detection and identification of organophosphorus and carbamate pesticides

Due to relatively low persistence and high effectiveness for insect and pest eradication, organophosphates (OPs) and carbamates are the two major classes of pesticides that broadly used in agriculture. Hence, the sensitive and selective detection of OPs and carbamates is highly significant. In this current study, a colorimetric sensor array comprising five inexpensive and commercially available thiocholine and H2O2 sensitive indicators for the simultaneous detection and identification of OPs and carbamates is developed. The sensing mechanism of this array is based on the irreversible inhibition capability of OPs and carbamates to the activity of acetylcholinesterase (AChE), preventing production of thiocholine and H2O2 from S-acetylthiocholine and acetylcholine and thus resulting in decreased or no color reactions to thiocholine and H2O2 sensitive indicators. Through recognition patterns and standard statistical methods (i.e., hierarchical clustering analysis and principal component analysis), the as-developed array demonstrates not only discrimination of OPs and carbamates from other kinds of pesticides but, more interestingly, identification of them exactly from each other. Moreover, this array is experimentally confirmed to have high selectivity and sensitivity, good anti-interference capability, and potential applications in real samples for OPs and carbamates.

Biosensor technology for pesticides--a review

Pesticides, due to their lucrative outcomes, are majorly implicated in agricultural fields for crop production enhancement. Due to their pest removal properties, pesticides of various classes have been designed to persist in the environment over a longer duration after their application to achieve maximum effectiveness. Apart from their recalcitrant structure and agricultural benefits, pesticides also impose acute toxicological effects onto the other various life forms. Their accumulation in the living system may prove to be detrimental if established in higher concentrations. Thus, their prompt and accurate analysis is a crucial matter of concern. Conventional techniques like chromatographic techniques (HPLC, GC, etc.) used for pesticides detection are associated with various limitations like stumpy sensitivity and efficiency, time consumption, laboriousity, requirement of expensive equipments and highly trained technicians, and many more. So there is a need to recruit the methods which can detect these neurotoxic compounds sensitively, selectively, rapidly, and easily in the field. Present work is a brief review of the pesticide effects, their current usage scenario, permissible limits in various food stuffs and 21st century advancements of biosensor technology for pesticide detection. Due to their exceptional performance capabilities, easiness in operation and on-site working, numerous biosensors have been developed for bio-monitoring of various environmental samples for pesticide evaluation immensely throughout the globe. Till date, based on sensing element (enzyme based, antibody based, etc.) and type of detection method used (Electrochemical, optical, and piezoelectric, etc.), a number of biosensors have been developed for pesticide detection. In present communication, authors have summarized 21st century's approaches of biosensor technology for pesticide detection such as enzyme-based biosensors, immunosensors, aptamers, molecularly imprinted polymers, and biochips technology. Also, the major technological advancements of nanotechnology in the field of biosensor technology are discussed. Various biosensors mentioned in manuscript are found to exhibit storage stability of biocomponent ranging from 30-60 days, detection limit of 10(-6) - 10(-16) M, response time of 1-20 min and applications of developed biosensors in environmental samples (water, food, vegetables, milk, and juice samples, etc.) are also discussed. Researchers all over the globe are working towards the development of different biosensing techniques based on contrast approaches for the detection of pesticides in various environmental samples.

A polyaniline–zeolite nanocomposite material based acetylcholinesterase biosensor for the sensitive detection of acetylcholine and organophosphates

A nanoporous polyaniline film formed on high surface area Nano-ZSM-5 is responsible for excellent bio-sensing ability.

Upconversion nanoparticle-based fluorescence resonance energy transfer assay for organophosphorus pesticides

This paper reports a novel nanosensor for organophosphorus pesticides based on the fluorescence resonance energy transfer (FRET) between NaYF4:Yb,Er upconversion nanoparticles (UCNPs) and gold nanoparticles (AuNPs). The detection mechanism is based on the facts that AuNPs quench the fluorescence of UCNPs and organophosphorus pesticides (OPs) inhibit the activity of acetylcholinesterase (AChE) which catalyzes the hydrolysis of acetylthiocholine (ATC) into thiocholine. Under the optimized conditions, the logarithm of the pesticides concentration was proportional to the inhibition efficiency. The detection limits of parathion-methyl, monocrotophos and dimethoate reached 0.67, 23, and 67 ng/L, respectively. Meanwhile, the biosensor shows good sensitivity, stability, and could be successfully applied to detection of OPs in real food samples, suggesting the biosensor has potentially extensive application clinic diagnoses assays.

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.

Electrochemical biosensor for carbofuran pesticide based on esterases from Eupenicillium shearii FREI-39 endophytic fungus

In this work, a biosensor was constructed by physical adsorption of the isolated endophytic fungus Eupenicillium shearii FREI-39 esterase on halloysite, using graphite powder, multi-walled carbon nanotubes and mineral oil for the determination of carbofuran pesticide by inhibition of the esterase using square-wave voltammetry (SWV). Specific esterase activities were determined each 2 days over a period of 15 days of growth in four different inoculation media. The highest specific activity was found on 6th day, with 33.08 U on PDA broth. The best performance of the proposed biosensor was obtained using 0.5 U esterase activity. The carbofuran concentration response was linear in the range from 5.0 to 100.0 µg L(-1) (r=0.9986) with detection and quantification limits of 1.69 µg L(-1) and 5.13 µg L(-1), respectively. A recovery study of carbofuran in spiked water samples showed values ranging from 103.8±6.7% to 106.7±9.7%. The biosensor showed good repeatability and reproducibility and remained stable for a period of 20 weeks. The determination of carbofuran in spiked water samples using the proposed biosensor was satisfactory when compared to the chromatographic reference method. The results showed no significant difference at the 95% confidence level with t-test statistics. The application of enzymes from endophytic fungi in constructing biosensors broadens the biotechnological importance of these microorganisms.

Iridium oxide nanoparticle induced dual catalytic/inhibition based detection of phenol and pesticide compounds

We report a tyrosinase biosensor based on iridium oxide nanoparticles for induced dual catalytic/inhibition for detection of phenol and pesticides.

Acetylcholinesterase biosensors for electrochemical detection of organophosphorus compounds: a review

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