A sensitive amperometric AChE-biosensor for organophosphate pesticides detection based on conjugated polymer and Ag-rGO-NH2 nanocomposite

MIL-88B(Fe) MOF modified screen-printed electrodes for non-enzymatic electrochemical sensing of malathion

An enzyme-free electrochemical approach for ultra-trace quantification of the organophosphate insecticide malathion is proposed in this study. It is premised on screen-printed carbon electrodes modified by the MIL-88B(Fe) metal-organic framework (MOF). A one-pot solvothermal method was used to synthesise MIL-88B(Fe). The surface modification of electrodes allowed for increased electroactive surface area and accelerated electron transport on the electrode. Inhibition in the redox signal of MIL-88B(Fe) was observed due to the affinity between metal centres of the MOF and the functional groups of malathion, leading to an accurate determination of malathion. The proposed sensor effectively quantified malathion in the wide concentration range of 1 × 10-12 M to 1 × 10-6 M. The limit of detection for malathion was 0.79 pM. The proposed sensor also possessed excellent stability, repeatability, and anti-interference characteristics. Furthermore, the proposed sensor demonstrated satisfactory malathion recovery in spiked vegetable samples.

Electrochemical Acetylcholinesterase Sensors for Anti-Alzheimer's Disease Drug Determination

Neurodegenerative diseases and Alzheimer's disease (AD), as one of the most common causes of dementia, result in progressive losses of cholinergic neurons and a reduction in the presynaptic markers of the cholinergic system. These consequences can be compensated by the inhibition of acetylcholinesterase (AChE) followed by a decrease in the rate of acetylcholine hydrolysis. For this reason, anticholinesterase drugs with reversible inhibition effects are applied for the administration of neurodegenerative diseases. Their overdosage, variation in efficiency and recommendation of an individual daily dose require simple and reliable measurement devices capable of the assessment of the drug concentration in biological fluids and medications. In this review, the performance of electrochemical biosensors utilizing immobilized cholinesterases is considered to show their advantages and drawbacks in the determination of anticholinesterase drugs. In addition, common drugs applied in treating neurodegenerative diseases are briefly characterized. The immobilization of enzymes, nature of the signal recorded and its dependence on the transducer modification are considered and the analytical characteristics of appropriate biosensors are summarized for donepezil, huperzine A, rivastigmine, eserine and galantamine as common anti-dementia drugs. Finally, the prospects for the application of AChE-based biosensors in clinical practice are discussed.

A new immunosensing platform based on conjugated Poly(ThidEp-co-EDOT) copolymer for resistin detection, a new obesity biomarker

The design of a novel electrochemical impedimetric biosensor for label-free analysis of resistin, a biomarker for obesity, is reported. For the fabrication of the immunosensor, a novel approach composed of electrochemical copolymerization of double epoxy groups-substituted thiophene (ThidEp) and 3,4-Ethylenedioxythiophene (EDOT) monomers was utilized. Anti-resistin antibodies were covalently attached to the copolymer-coated electrode. The capture of resistin antigens by anti-resistin antibodies caused significant variations in charge transfer resistance (Rct) because of the immunoreactions between these proteins. Under optimum experimental variables, the changes in impedance signals were employed for the determination of resistin antigen concentration, and the prepared immunosensor based on conjugated copolymer illustrated a wide linear range between 0.0125 and 22.5 pg/mL, a low detection limit (LOD) of 3.71 fg/mL, and a good sensitivity of 1.22 kΩ pg-1mL cm2. The excellent analytical performance of the resistin immunosensor in terms of selectivity, sensitivity, repeatability, reproducibility, storage stability, and low detection limit might be attributed to the conductive copolymer film layer generation on the disposable indium tin oxide (ITO) platform. The capability of this system for the determination of resistin in human serum and saliva samples was also tested. The immunosensor results were in accordance with the enzyme-linked immunosorbent assay (ELISA) results. The matrix effects of human serum and saliva were also investigated, and the proposed immunosensor displayed good recovery ranging from 95.91 to 106.25%. The engineered immunosensor could open new avenues for obesity monitoring.

A colorimetric analytical method based on a TCPP-CuCo2O4-like peroxidase for the detection of trichlorfon

In this work, a highly sensitive colorimetric sensing platform was designed for the detection of trichlorfon based on inhibiting thiocholine (TCh)-induced redox reaction. 5,10,15,20-Tetracarboxyphenylporphyrin (TCPP) functionalized CuCo2O4 (TCPP-CuCo2O4) was synthesized to construct a colorimetric sensing platform for trichlorfon. In the presence of H2O2, TCPP-CuCo2O4 can oxidize colorless 3,3',5,5'-tetramethylbenzidine (TMB) into blue ox-TMB, accompanied by a strong absorption peak at 652 nm, while acetylcholinesterase (AChE) can specifically hydrolyze acetylthiocholine (ATCh) into TCh, which can reduce ox-TMB back into colorless TMB, resulting in a lower absorbance at 652 nm. Trichlorfon can irreversibly inhibit the activity of AChE and thus recover the absorption peak. Under the optimized conditions, detection of trichlorfon has a wide linear range of 40-4000 ng mL-1 with a linear correlation coefficient of 0.9904. The proposed method can be applied to the detection of trichlorfon in vegetables and has good application prospects.

Recent Advances in Electrochemical Biosensors for Food Control

The rapid and sensitive detection of food contaminants is becoming increasingly important for timely prevention and treatment of foodborne disease. In this review, we discuss recent developments of electrochemical biosensors as facile, rapid, sensitive, and user-friendly analytical devices and their applications in food safety analysis, owing to the analytical characteristics of electrochemical detection and to advances in the design and production of bioreceptors (antibodies, DNA, aptamers, peptides, molecular imprinted polymers, enzymes, bacteriophages, etc.). They can offer a low limit of detection required for food contaminants such as allergens, pesticides, antibiotic traces, toxins, bacteria, etc. We provide an overview of a broad range of electrochemical biosensing designs and consider future opportunities for this technology in food control.

An enzyme-free, ultrasensitive strategy for simultaneous screening of the p-nitrophenyl substituent organophosphorus pesticides

An enzyme-free, sensitive, and convenient approach was reported for the P-nitrophenyl substituent organophosphorus pesticides (NSOPs) of paraoxon-methyl (PM), paraoxon-ethyl (PE), parathion-methyl (PTM) and parathion-ethyl (PTE)) by indirectly quantification of the 4-nitrophenol (4-NP, hydrolysis product of the NSOPs). NaOH instead of hydrolase/nanozyme was applied, and temperature, pH, ultrasound was investigated to improve the NSOPs hydrolysis. Under the optimized conditions, the hydrolysis efficiencies were up to 99.9 %, 99.9 %, 99.6 %, 96.0 % for PM (10 min), PE (30 min), PTM (90 min) and PTE (120 min), based on which a low detection limits of 0.06 (PM), 0.07 (PE), 0.06 (PTM) and 0.07 (PTE) ppb were calculated with the 4-NP detection limit (0.03 ppb). Furthermore, the method exhibited good performance for the NSOPs with recoveries from 88.87 % to 100.33 % in real samples. This indirect approach offered an ultrasensitive alternative for the NSOPs detection, which holds great potential in practical application for the assessment of food safety and environmental risks.

Recent Developments in the Applications of GO/rGO-Based Biosensing Platforms for Pesticide Detection

Pesticides are often used in different applications, including agriculture, forestry, aquaculture, food industry, etc., for the purpose of controlling insect pests and weeds. The indiscriminate usage of pesticides poses a massive threat to food, environmental, and human health safety. Hence, the fabrication of a sensitive and reliable sensor for the detection of pesticide residues in agro products and environmental samples is a critical subject to be considered. Recently, the graphene family including graphene oxide (GO) and reduced graphene oxide (rGO) have been frequently employed in the construction of sensors owing to their biocompatibility, high surface-area-to-volume ratio, and excellent physiochemical, optical, and electrical properties. The integration of biorecognition molecules with GO/rGO nanomaterials offers a promising detection strategy with outstanding repeatability, signal intensity, and low background noise. This review focuses on the latest developments (2018 to 2022) in the different types of GO/rGO-based biosensors, such as surface plasmon resonance (SPR), fluorescence resonance energy transfer (FRET), and electrochemical-based techniques, among other, for pesticide analysis. The critical discussions on the advantages, limitations, and sensing mechanisms of emerging GO/rGO-based biosensors are also highlighted. Additionally, we explore the existing hurdles in GO/rGO-based biosensors, such as handling difficult biological samples, reducing the total cost, and so on. This review also outlines the research gaps and viewpoints for future innovations in GO/rGO-based biosensors for pesticide determination mainly in areas with insufficient resources.

A Novel Electrochemical Biosensor Based on Polyaniline-Embedded Copper Oxide Nanoparticles for High-Sensitive Paraoxon-Ethyl (PE) Detection

This paper proposes a fabrication of a hyper-sensitive amperometric biosensor for paraoxon-ethyl (PE) detection. In this developed biosensor, polyaniline (PANI) and copper oxide (CuO)-based nanocomposite is used as a sensing platform. The homogeneous distribution of CuO onto the PANI matrix enhances the surface area and conductivity of the nanocomposite. Additionally, the PANI produces a compatible environment for enzyme immobilization, which further enhances the rate of electron transfer. For biosensor fabrication, the nanocomposite is deposited electrophoretically onto the ITO glass substrate and immobilization of acetylcholinesterase (AChE) enzyme is conducted onto the fabricated electrode surface. The results validate good reproducibility, good stability, and high selectivity of the fabricated biosensor (AChE/PANI@CuO/ITO). The inhibition rate of paraoxon-ethyl (PE) is recorded in the concentration range of 1-200 nM with a low limit of detection of 0.096 nM or 96 pM. The sensitivity of the developed biosensor is found to be 49.86 µA(nM)^-1. The developed biosensor is further successfully accomplished for the detection of PE in real samples like rice and pulse.

A Paper-Based Electrochemical Sensor Based on PtNP/COFTFPB-DHzDS@rGO for Sensitive Detection of Furazolidone

Herein, a paper-based electrochemical sensor based on PtNP/COF_TFPB-DHzDS@rGO was developed for the sensitive detection of furazolidone. A cluster-like covalent organic framework (COF_TFPB-DHzDS) was successfully grown on the surface of amino-functional reduced graphene oxide (rGO-NH₂) to avoid serious self-aggregation, which was further loaded with platinum nanoparticles (PtNPs) with high catalytic activity as nanozyme to obtain PtNP/COF_TFPB-DHzDS@rGO nanocomposites. The morphology of PtNP/COF_TFPB-DHzDS@rGO nanocomposites was characterized, and the results showed that the smooth rGO surface became extremely rough after the modification of COF_TFPB-DHzDS. Meanwhile, ultra-small PtNPs with sizes of around 1 nm were precisely anchored on COF_TFPB-DHzDS to maintain their excellent catalytic activity. The conventional electrodes were used to detect furazolidone and showed a detection limit as low as 5 nM and a linear range from 15 nM to 110 μM. In contrast, the detection limit for the paper-based electrode was 0.23 μM, and the linear range was 0.69-110 μM. The results showed that the paper-based electrode can be used to detect furazolidone. This sensor is a potential candidate for the detection of furazolidone residue in human serum and fish samples.

Recent Advancements in Nanobiosensors: Current Trends, Challenges, Applications, and Future Scope

In recent years, there has been immense advancement in the development of nanobiosensors as these are a fundamental need of the hour that act as a potential candidate integrated with point-of-care-testing for several applications, such as healthcare, the environment, energy harvesting, electronics, and the food industry. Nanomaterials have an important part in efficiently sensing bioreceptors such as cells, enzymes, and antibodies to develop biosensors with high selectivity, peculiarity, and sensibility. It is virtually impossible in science and technology to perform any application without nanomaterials. Nanomaterials are distinguished from fine particles used for numerous applications as a result of being unique in properties such as electrical, thermal, chemical, optical, mechanical, and physical. The combination of nanostructured materials and biosensors is generally known as nanobiosensor technology. These miniaturized nanobiosensors are revolutionizing the healthcare domain for sensing, monitoring, and diagnosing pathogens, viruses, and bacteria. However, the conventional approach is time-consuming, expensive, laborious, and requires sophisticated instruments with skilled operators. Further, automating and integrating is quite a challenging process. Thus, there is a considerable demand for the development of nanobiosensors that can be used along with the POCT module for testing real samples. Additionally, with the advent of nano/biotechnology and the impact on designing portable ultrasensitive devices, it can be stated that it is probably one of the most capable ways of overcoming the aforementioned problems concerning the cumulative requirement for the development of a rapid, economical, and highly sensible device for analyzing applications within biomedical diagnostics, energy harvesting, the environment, food and water, agriculture, and the pharmaceutical industry.

New analytical strategies Amplified with 2D carbon nanomaterials for electrochemical sensing of food pollutants in water and soils sources

Pharmaceutical and food pollutants have threatened global health. Pharmacotherapy has left a positive impression in the field of health and life of people and animals. However, the many unresolved problems brought along with residues of pharmaceuticals in the environmental and food. Consumption of the world's freshwater resources, toxic chemicals, air pollution, plastic waste directly affects water and soil resources. Pesticides have a wide role in pollutants. Therefore, the determination of pesticides is significant to eliminate their negative effects on living things. Nowadays, there are many analytical methods available. However, new analysis methods are still being researched due to certain limitations of traditional methods. Electrochemical sensors have drawn attention because of their superior properties, such as short analysis time, affordability, high sensitivity, and selectivity. The development of new analytical strategies for assessing risks from pharmaceutical to food pollutants in water and soil sources is important for the measurement of different pollutants. Moreover, the 2D-carbon nanomaterials used in the development of electrochemical sensors are widely utilized to enlarge the surface area, increase porosity, and make easy immobilization. Graphene (graphene derivations) and carbon nanotubes integrated nanosensors are widely used for the determination of pesticides. 2D-carbon nanomaterials can be tailored according to the purpose of the study. The characterization and synthesis methods of 2D-carbon nanomaterials are widely explained. Furthermore, enzyme nanobiosensors, especially Acetylcholinesterase (AChE), are widely used to determine pesticides. The three main topics are focused on in this review: 2D-carbon nanomaterials, pesticides that threaten life, and the application of 2D-carbon nanomaterials-based electrochemical sensors. The various developed 2D-carbon nanomaterials-based electrochemical sensors were applied in pharmaceutical forms, fruits, tap/lake water, beverages, and soils sources. This work aims to indicate the recently published paper related to pesticide analysis and highlight the importance of 2D-nanomaterials on sensors.

Progress in Nanomaterials-Based Enzyme and Aptamer Biosensor for the Detection of Organophosphorus Pesticides

With the improvement of people's safety awareness, the requirement of pesticide detection is gradually increasing, and many new detection methods toward Organophosphorus pesticide (OPs) has been further developed and applied. Nanomaterials-based biosensors have played an important role in the trace detection of OPs. This article mainly introduces the detection principle of enzymes and aptamers as the identification element of biosensors. Various nanomaterials (i.e., metals and metal oxides, carbon nanotubes, graphene and graphene oxide, quantum dots, metal organic frameworks, molecular imprinted polymers, etc.) possess their unique properties and play different roles in the enzyme and aptamer-based biosensors toward OPs: (a) to produce the optical or electrochemical signal; (b) as a carrier to load the enzyme or aptamer; (c) to enhance the signal response. Besides, the intelligent portable devices provide the possibility to realize the onsite and real-time detection. The limitations of some nanomaterials and the future development are discussed. Finally, the future of enzyme and aptamer-based biosensors has prospected.

Highly sensitive visual colorimetric sensor for trichlorfon detection based on the inhibition of metallization of gold nanorods

In this study, a highly sensitive visual colorimetric sensor was designed for the detection of trichlorfon based on inhibiting ascorbate oxidase (AAO)-induced metallization of gold nanorods (Au NRs). Ascorbic acid (AA) can reduce silver ion (Ag⁺) to metal silver (Ag) that will be deposited on the surface of Au NRs, which results in the blue shift of longitudinal localized surface plasmon resonance (LSPR) peak of Au NRs, accompanying by perceptible color changes from red to cyan to red to yellow. In the presence of trichlorfon, the activity of AAO will be inhibited, resulting in less AA is hydrolyzed to dehydroascorbic acid (DHA), and therefore more Ag⁺ is reduced to Ag by AA. Under the optimized conditions, detection of trichlorfon has a wide linear range of 27.8-11111.1 μg/L with a limit of detection as low as 132.6 ng/L. Moreover, the sensor has a good sample spiked recovery (84.7-96.8%) for the determination of trichlorfon in lake water samples. The proposed method can achieve rapid analysis (about 10 min) of trichlorfon with simple operation when there are no other types of organophosphorus pesticides in the real samples.

Emerging vistas on pesticides detection based on electrochemical biosensors - An update

Organophosphates and carbamates pesticides are widely used to increase crop production globally causing a threat to human health and the environment. A variety of pesticides are applied during different stages of vegetable production. Therefore, monitoring the presence of pesticide residues in food and soil has great relevance to sensitive pesticide detection through distinct determination methods that are urgently required. Conventional techniques for the detection of pesticides have several limitations that can be overcome by the development of highly sensitive, fast, reliable and easy-to-use electrochemical biosensors. Herein, we describe the types of biosensors with the main focus on electrochemical biosensors fabricated for the detection of OPPs and carbamates pesticides. An overview of conventional techniques employed for pesticide detection is also discussed. This review aims to provide a glance of recently developed biosensors for some common pesticides like chlorpyrifos, malathion, parathion, paraoxon, and carbaryl which are present in food and environment samples.

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.

A 3D printable adapter for solid-state fluorescence measurements: the case of an immobilized enzymatic bioreceptor for organophosphate pesticides detection

The widespread use of pesticides in the last decades and their accumulation into the environment gave rise to major environmental and human health concerns. To address this topic, the scientific community pointed out the need to develop methodologies to detect and measure the presence of pesticides in different matrices. Biosensors have been recently explored as fast, easy, and sensitive methods for direct organophosphate pesticides monitoring. Thus, the present work aimed at designing and testing a 3D printed adapter useful on different equipment, and a membrane support to immobilize the esterase-2 from Alicyclobacillus acidocaldarius (EST2) bioreceptor. The latter is labelled with the IAEDANS, a bright fluorescent probe. EST2 was selected since it shows a high specificity toward paraoxon. Our results showed good stability and replicability, with an increasing linear fluorescent intensity recorded from 15 to 150 pmol of labelled EST2. Linearity of data was also observed when using the immobilized labelled EST2 to detect increasing amounts of paraoxon, with a limit of detection (LOD) of 0.09 pmol. This LOD value reveals the high sensitivity of our membrane support when mounted on the 3D adapter, comparable to modern methods using robotic workstations. Notably, the use of an independent support significantly simplified the manipulation of the membrane during experimental procedures and enabled it to match the specificities of different systems. In sum, this work emphasizes the advantages of using 3D printed accessories adapted to respond to the newest research needs.

Omics technologies used in pesticide residue detection and mitigation in crop

In agriculture, the convenience and efficacy of chemical pesticides have become inevitable to manage cultivated crop production. Here, we review the worldwide use of pesticides based on their categories, mode of actions and toxicity. Excessive use of pesticides may lead to hazardous pesticide residues in crops, causing adverse effects on human health and the environment. A wide range of high-tech-analytical methods are available to analyse pesticide residues. However, they are mostly time-consuming and inconvenient for on-site detection, calling for the development of biosensors that detect cellular changes in crops. Such new detection methods that combine biological and physicochemical knowledge may overcome the shortage in current farming to develop sustainable systems that support environmental and human health. This review also comprehensively compiles domestic pesticide residues removal tips from vegetables and fruits. Synthetic pesticide alternatives such as biopesticide and nanopesticide are greener to the environment. However, its safety assessment for large-scale application needs careful evaluation. Lastly, we strongly call for reversions of pesticide application trends based on the changing climate, which is lacking in the current scenario.

Recent advancements in the detection of organophosphate pesticides: a review

Organophosphorus pesticides (OPPs) are generally utilized for the protection of crops from pests. Because the use of OPPs in various agricultural operations has expanded dramatically, precise monitoring of their concentration levels has become the critical issue, which will help in the protection of ecological systems and food supply. However, the World Health Organization (WHO) has classified them as extremely dangerous chemical compounds. Taking their immense use and toxicity into consideration, the development of easy, rapid and highly sensitive techniques is necessary. Despite the fact that there are numerous conventional ways for detecting OPPs, the development of portable sensors is required to make routine analysis considerably more convenient. Some of these advanced techniques include colorimetric sensors, fluorescence sensors, molecular imprinted polymer-based sensors, and surface plasmon resonance-based sensors. This review article specifically focuses on the colorimetric, fluorescence and electrochemical sensors. In this article, the sensing strategies of these developed sensors, analytical conditions and their respective limit of detection are compiled.

Hierarchical nanoarchitecture of zirconium phosphate/graphene oxide: Robust electrochemical platform for detection of fenitrothion

We report the rational design of nanocomposite with zirconium phosphate encapsulated on graphene oxide (ZrP/GO) for the highly sensitive and selective analysis of fenitrothion (FT). The characteristics of ZrP/GO nanocomposite are systematically analyzed by various in-depth electron microscopic, spectroscopic and analytical techniques. The ZrP/GO nanocomposite modified electrodes show better electrochemical response towards FT than other electrodes. The improved electrochemical activity of nanocomposite is attributed to large surface area, high conductivity, numerous active surface sites, GO nanosheets served as the conductivity matrix while preventing ZrP from agglomeration and the synergistic effect of ZrP and GO. Benefitting from the unique features, our fabricated sensor exhibits the superior performance in terms of wide working range (0.008-26 μM), appropriate peak potential (-0.61 V), low limit of detection (0.001 µM), high sensitivity (6 µA µM^-1 cm^-2) with the regression coefficient of 0.999. Additionally, the electrochemical sensor also displays good selectivity, excellent stability (99.6%), reproducibility (4.9%) and reusability (6.1%). The practical applicability of ZrP/GO sensor is shown by performing the detection of FT in water samples. These results clearly suggest that the ZrP/GO nanocomposite is an efficient electrode material for the future real-time environmental monitoring of FT.

An ultrasensitive disposable sandwich-configuration electrochemical immunosensor based on OMC@AuNPs composites and AuPt-MB for alpha-fetoprotein detection

Early finding and diagnosis are critical for prevention and treatment of hepatocellular carcinoma (HCC). Alpha-fetoprotein (AFP) is a typical biomarker of HCC. Since AFP level can reflect the severity of HCC, it is essential to ensure the accurate detection of AFP. In this study, through a combination of the advantages exhibited by ordered mesoporous carbon (OMC)@gold nanoparticles (AuNPs) composites and AuPt-methylene blue (AuPt-MB), a disposable ultrasensitive sandwich-configuration electrochemical immunosensor for determination of AFP was designed. Characterized by excellent conductivity, highly ordered pore distribution and great surface area, OMC can be effective in promoting electron transfer and loading a large number of AuNPs. In the meantime, AuNPs can also immobilize AFP-Ab₁ through Au-N bonds. As a new redox-active species, rod-like AuPt-MB demonstrates high conductivity, uniform morphology and excellent biocompatibility, which makes it capable not only to fix AFP-Ab₂, but also to release electrochemical signals. A wide linearity of 10 fg mL^-1-100 ng mL^-1 and a low detection limit of 3.33 fg mL^-1 (S/N = 3) were obtained. Moreover, the proposed immunosensor exhibited acceptable selectivity, high stability and reproducibility. The excellent performance in detecting serum samples endows the proposed immunosensor with broad prospects of extensive application in the detection of disease biomarkers.

Development of ESAT-6 Based Immunosensor for the Detection of Mycobacterium tuberculosis

Early secreted antigenic target of 6 kDa (ESAT-6) has recently been identified as a biomarker for the rapid diagnosis of tuberculosis. We propose a stable and reusable immunosensor for the early diagnosis of tuberculosis based on the detection and quantification of ESAT-6 via cyclic voltammetry (CV). The immunosensor was synthesized by polymerizing aniline dispersed with the reduced graphene oxide (rGO) and Ni nanoparticles, followed by surface modification of the electroconductive polyaniline (PANI) film with anti-ESAT-6 antibody. Physicochemical characterization of the prepared materials was performed by several analytical techniques, including FE-SEM, EDX, XRD, FT-IR, Raman, TGA, TPR, and BET surface area analysis. The antibody-modified Ni-rGO-PANI electrode exhibited an approximately linear response (R2 = 0.988) towards ESAT-6 during CV measurements over the potential range of -1 to +1 V. The lower detection limit for ESAT-6 was approximately 1.0 ng mL-1. The novelty of this study includes the development of the reusable Ni-rGO-PANI-based electrochemical immunosensor for the early diagnosis of tuberculosis. Furthermore, this study successfully demonstrates that electro-conductive PANI may be used as a polymeric substrate for Ni nanoparticles and rGO.

A novel signal amplified electrochemiluminescence biosensor based on MIL-53(Al)@CdS QDs and SiO2@AuNPs for trichlorfon detection

An ultrasensitive electrochemiluminescence (ECL) biosensor was developed based on MIL-53(Al)@CdS QDs and SiO₂@AuNPs for trichlorfon detection. Metal-organic frameworks (MOFs) were used as a loading platform that provided a large surface area to load targets and modified materials onto the electrode. At the same time, SiO₂@AuNPs loaded plenty of AuNPs which effectively increased the ECL resonance energy transfer between the CdS QDs, so that the ECL signal was strongly quenched and resulted in an amplified response. In the range of 10^-11-10^-4 M, the ECL response showed a linear relationship with the concentration (logarithm) of trichlorfon, and the detection limit was 5.1 × 10^-12 M (S/N = 3). When the biosensor was applied to detect trichlorfon in lettuce, broccoli, cucumber, and chives, the recoveries obtained from the spiked samples were 97%-105%, 102%-104%, 100%-104%, and 98%-104%, respectively. Thus, this novel ECL biosensor has potential applications for the analysis of trichlorfon in food samples.

An ultra-sensitive and selective AChE based colorimetric detection of malathion using silver nanoparticle-graphene oxide (Ag-GO) nanocomposite

Herein, we propose rapid, precise acetylcholinesterase (AChE) inhibition-based sensing strategy for malathion detection in the presence of Ag-GO and acetylthiocholine (ATCh). The biosensing method was developed with a nanocomposite of citrate stabilized AgNPs anchored on the GO sheets (Ag-GO). The physical and chemical properties of the prepared Ag-GO composite were analyzed with various characterization techniques, including XRD, FT-IR, XPS, UV-Visible spectroscopy, and HR-TEM. The positively charged thiocholine (TCh) produced by enzyme hydrolysis triggers the AgNPs aggregation on GO sheets, which ultimately decreases the intensity of the corresponding SPR absorption peak. While the addition of malathion into the sensing system hindered the AChE activity and limited the TCh production, and thus inhibits the decrease in the SPR band intensity. The designed sensing system displayed linearity in the broad range of malathion concentrations (0.01 pM-1000 pM) with a limit of detection and the limit of quantification values of 0.01 pM, and 0.035 pM, respectively. The application of the designed biosensing system was extended to determine the malathion in actual samples namely, tap water, agricultural runoff water, lake water, and grape extract, which resulted in almost 100% recovery rates in all the spiked samples.

An insect acetylcholinesterase biosensor utilizing WO3/g-C3N4 nanocomposite modified pencil graphite electrode for phosmet detection in stored grains

This study was undertaken to assess the potential of Tribolium castaneum (Red flour beetle) acetylcholinesterase (Tc-AChE) based electrochemical biosensor integrating WO₃/g-C₃N₄ nanocomposite modified Pencil graphite electrode to detect an organophosphate insecticide, Phosmet. The WO₃/g-C₃N₄ nanocomposite provides a non-toxic, biocompatible surface for binding the enzyme on the electrode surface, attributed to its large surface area, high conductivity, and low ohmic resistance. The proposed biosensor shows a very good analytical performance with LOD 3.6 nM for Phosmet and effectively determined Phosmet in wheat with a 99% recovery rate. Furthermore, molecular docking deciphers the binding interactions of Phosmet with Tc-AChE using a modified AutoDock LGA algorithm and an AMBER03 force field in YASARA. The kinetic parameters strongly suggest the high potency of inhibitor with the enzyme. This study presents an adaptable, rapid, and straightforward approach that opens ways towards real progress in developing commercial biosensors for pesticide detection.

A treatise on Organophosphate pesticide pollution: Current strategies and advancements in their environmental degradation and elimination

Pesticides have been used in the field of agriculture ever since their role in protection of crops from pests which include four different categories namely insects, mites, rodents and animals has been identified. Organophosphate pesticides are one of the most extensively applied insecticides in the field of agriculture such that around 40% of all the pesticides that are produced and used commercially belong to this category. The main toxicological effect of these pesticides when exposed to a living being encompasses the irremediable inhibition of the acetylcholinesterase (AChE) enzyme which is involved in the neurotransmission of signals and hence its inhibition causes impairment of the respiratory tract and neuromuscular transmission. Apart from being used as a pesticide, organophosphates have also been applied as herbicides to some extent. The residues of these highly toxic chemicals have found route into the underground water system by seeping into the ground, in rivers where the agricultural run off water is disposed, and in the air when sprayed on the crops hence posing a threat to all the living strata exposed to these chemicals in various ways which are discussed further. Many significant studies have been carried out in order to evaluate the health risks associated with these pesticides which commonly include acute neurological disorders. This review emphasizes on the toxicological effects of organophosphate pesticides and the recent methods of detection that are used to identify trace amounts of organophosphate pesticides along with strategies which are used for their degradation.

Multimodal/Multifunctional Nanomaterials in (Bio)electrochemistry: Now and in the Coming Decade

Multifunctional nanomaterials, defined as those able to achieve a combined effect or more than one function through their multiple functionalization or combination with other materials, are gaining increasing attention in the last years in many relevant fields, including cargo targeted delivery, tissue engineering, in vitro and/or in vivo diseases imaging and therapy, as well as in the development of electrochemical (bio)sensors and (bio)sensing strategies with improved performance. This review article aims to provide an updated overview of the important advances and future opportunities exhibited by electrochemical biosensing in connection to multifunctional nanomaterials. Accordingly, representative aspects of recent approaches involving metal, carbon, and silica-based multifunctional nanomaterials are selected and critically discussed, as they are the most widely used multifunctional nanomaterials imparting unique capabilities in (bio)electroanalysis. A brief overview of the main remaining challenges and future perspectives in the field is also provided.

Development of enzymatic electrochemical biosensors for organophosphorus pesticide detection

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

Facile and Low-Cost SPE Modification Towards Ultra-Sensitive Organophosphorus and Carbamate Pesticide Detection in Olive Oil

Despite the fact that a considerable amount of effort has been invested in the development of biosensors for the detection of pesticides, there is still a lack of a simple and low-cost platform that can reliably and sensitively detect their presence in real samples. Herein, an enzyme-based biosensor for the determination of both carbamate and organophosphorus pesticides is presented that is based on acetylcholinesterase (AChE) immobilized on commercially available screen-printed carbon electrodes (SPEs) modified with carbon black (CB), as a means to enhance their conductivity. Most interestingly, two different methodologies to deposit the enzyme onto the sensor surfaces were followed; strikingly different results were obtained depending on the family of pesticides under investigation. Furthermore, and towards the uniform application of the functionalization layer onto the SPEs’ surfaces, the laser induced forward transfer (LIFT) technique was employed in conjunction with CB functionalization, which allowed a considerable improvement of the sensor’s performance. Under the optimized conditions, the fabricated sensors can effectively detect carbofuran in a linear range from 1.1 × 10⁻⁹ to 2.3 × 10⁻⁸ mol/L, with a limit of detection equal to 0.6 × 10⁻⁹ mol/L and chlorpyrifos in a linear range from 0.7 × 10⁻⁹ up to 1.4 × 10⁻⁸ mol/L and a limit of detection 0.4 × 10⁻⁹ mol/L in buffer. The developed biosensor was also interrogated with olive oil samples, and was able to detect both pesticides at concentrations below 10 ppb, which is the maximum residue limit permitted by the European Food Safety Authority.

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.

Novel electrochemical aptasensor with dual signal amplification strategy for detection of acetamiprid

In this work, a novel dual signal amplification strategy for aptasensor employing reduced graphene with silver nanoparticles and prussian blue-gold nanocomposites was developed for detection of acetamiprid. To improve the sensitivity of aptasensors, reduced graphene oxide-silver nanoparticles (rGo-AgNPs) were modified on a bare glassy carbon electrode surface, which provided a large specific surface area for subsequent material immobilization and amplified current signal. The electrical signal output and sensitivity of the aptasensor was significantly improved after the immobilization of prussian blue-gold nanoparticles (PB-AuNPs) as a catalyst for the redox reaction. The analysis experiment exhibited that it had super-high sensitivity with a detection limit of 0.30 pM (S/N = 3), which met the requirements of the vast majority of daily leaf vegetable testing. Under optimized conditions, the proposed aptasensor showed a wide linear detection range from 1 pM to 1 μM. This aptasensor also had good stability and high selectivity for acetamiprid detection without an interfering effect of some other pesticides. The proposed aptasensor displayed good recovery rates in real samples, which proposed a new method for constructing electrochemical sensors and provided a novel tool for rapid, sensitive analysis of pesticides with low cost.

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.