Development of a quantitative relationship between inhibition percentage and both incubation time and inhibitor concentration for inhibition biosensors--theoretical and practical considerations

Highly sensitive detection of environmental toxic fenitrothion in fruits and water using a porous graphene oxide nanosheets based disposable sensor

Monitoring fenitrothion (FNT) residues in food and the environment is crucial due to its high environmental toxicity. In this study, we developed a sensitive, reliable electrochemical method for detecting FNT by using screen-printed carbon electrodes (SPCE) modified with porous graphene oxide (PGO) nanosheets. PGO surface properties have been meticulously characterized using advanced spectroscopic techniques. Electrochemical impedance spectroscopy and cyclic voltammetry were used to test the electrochemical properties of the PGO-modified sensor. The PGO-modified sensor exhibited remarkable sensitivity, achieving a detection limit as low as 0.061 μM and a broad linear range of 0.02-250 μM. Enhanced performance is due to PGO's high surface area and excellent electrocatalytic properties, which greatly improved electron transfer. Square wave voltammetry was used to demonstrate the sensor's efficacy as a real-time, on-site monitoring tool for FNT residues in fruit and water. The outstanding performance of the PGO/SPCE sensor underscores its applicability in ensuring food safety and environmental protection.

Exploring the SARS-CoV-2 virus-host-drug interactome for drug repurposing

Coronavirus Disease-2019 (COVID-19) is an infectious disease caused by the SARS-CoV-2 virus. Various studies exist about the molecular mechanisms of viral infection. However, such information is spread across many publications and it is very time-consuming to integrate, and exploit. We develop CoVex, an interactive online platform for SARS-CoV-2 host interactome exploration and drug (target) identification. CoVex integrates virus-human protein interactions, human protein-protein interactions, and drug-target interactions. It allows visual exploration of the virus-host interactome and implements systems medicine algorithms for network-based prediction of drug candidates. Thus, CoVex is a resource to understand molecular mechanisms of pathogenicity and to prioritize candidate therapeutics. We investigate recent hypotheses on a systems biology level to explore mechanistic virus life cycle drivers, and to extract drug repurposing candidates. CoVex renders COVID-19 drug research systems-medicine-ready by giving the scientific community direct access to network medicine algorithms. It is available at https://exbio.wzw.tum.de/covex/.

Electrochemical micro analytical device interfaced with portable potentiostat for rapid detection of chlorpyrifos using acetylcholinesterase conjugated metal organic framework using Internet of things

An Electrochemical micro Analytical Device (EµAD) was fabricated for sensitive detection of organophosphate pesticide chlorpyrifos in the food chain. Gold microelectrode (µE) modified with Zinc based Metal Organic Framework (MOF-Basolite Z1200) and Acetylcholinesterase (AChE) enzyme served as an excellent electro-analytical transducer for the detection of chlorpyrifos. Electrochemical techniques such as Cyclic Voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS) and Differential Pulse Voltammetry (DPV) were performed for electrochemical analysis of the developed EµAD. The sensor needs only 2 µL of the analyte and it was tested within the linear range of 10 to 100 ng/L. The developed EµAD’s limit of detection (LoD) and sensitivity is 6 ng/L and 0.598 µ A/ng L⁻¹/mm² respectively. The applicability of the device for the detection of chlorpyrifos from the real vegetable sample was also tested within the range specified. The fabricated sensor showed good stability with a shelf-life of 20 days. The EµAD’s response time is of 50 s, including an incubation time of 20 s. The developed EµAD was also integrated with commercially available low-cost, handheld potentiostat (k-Stat) using Bluetooth and the results were comparable with a standard electrochemical workstation.

3D Flower-Like Gadolinium Molybdate Catalyst for Efficient Detection and Degradation of Organophosphate Pesticide (Fenitrothion)

Three-dimensional (3D) nanostructured materials have received enormous attention in energy and environment remediation applications. Herein, we developed a novel 3D flower-like gadolinium molybdate (Gd₂MoO₆; GdM) and used as a bifunctional catalyst for the electrochemical detection and photocatalytic degradation of organophosphate pesticide fenitrothion (FNT). The flower-like GdM catalyst was prepared via a simple sol-gel technique with the assistance of urea and ethylene glycol. The properties of GdM were confirmed by various spectroscopic and analytical techniques. The GdM catalyst played a significant role in electrochemical reduction of FNT and results in a very low detection limit (5 nM), wide linear ranges (0.02-123; 173-1823 μM), and good sensitivity (1.36 μA μM^-1 cm^-2). Interestingly, the GdM electrocatalyst had good recoveries to FNT in soil and water sample analysis. In addition to trace level detection, the flower-like GdM was used as the photocatalyst which portrayed an excellent photocatalytic degradation behavior to eliminate the FNT in the aqueous system. The GdM photocatalyst could degrade above 99% of FNT under UV light irradiation with good stability even after five cycles.

Progress in enzyme inhibition based detection of pesticides

The previous few decades have seen the development of biosensors and their use in monitoring of pesticides in food and environmental samples. Although inhibition-based biosensors have been subject of several recent research works, their performance characteristics greatly depend on the type of immobilization and the presence of interfering compounds in the samples. Moreover, sensitivity, detection limits, and rapidity of the response are few of the other major features that need to be investigated further if they are to become operationally user-friendly. This review will highlight research carried out in the past on biosensors that are based on enzyme inhibition for determination of organophosphorus compounds and carbamate pesticides.

Environmentally-friendly in situ plated bismuth-film electrode for the quantification of the endocrine disruptor parathion in skimmed milk

An in situ bismuth-film electrode (BiFE) together with square-wave cathodic voltammetry (SWCV) was used to determine the concentration of the endocrine disruptor parathion in skimmed milk. The experimental conditions (deposition time, deposition potential and Bi (III) concentration) were optimized for the preparation of the BiFE. A glassy carbon electrode was used as the substrate. The selection of the chemical composition of the supporting electrolyte and the solution pH was aimed at improving the reduction of parathion at the BiFE surface. In addition, the parameters of the square-wave cathodic voltammetry were adjusted to improve the sensor performance. A cathodic current identified at -0.523 V increased linearly with the parathion concentration in the range of 0.2-2.0 μmol L(-1) (R=0.999). The sensitivity of the calibration curve obtained was 4.09 μA L μmol(-1), and the limits of detection (LOD) and quantification (LOQ) were 55.7 nmol L(-1) and 169.0 nmol L(-1), respectively. The performance of the sensor was tested using a sample of skimmed milk with parathion added. The same determination was carried out by UV-vis spectroscopy and the results obtained were used for the statistical evaluation of the data obtained.

Electrochemical sensor based on gold nanoparticles/ethylenediamine-reduced graphene oxide for trace determination of fenitrothion in water

AuNP/en-rGO/SPE electrochemical sensor for sensitive determination of fenitrothion in natural waters.

Optical detection of paraoxon using single-walled carbon nanotube films with attached organophosphorus hydrolase-expressed Escherichia coli

In whole-cell based biosensors, spectrophotometry is one of the most commonly used methods for detecting organophosphates due to its simplicity and reliability. The sensor performance is directly affected by the cell immobilization method because it determines the amount of cells, the mass transfer rate, and the stability. In this study, we demonstrated that our previously-reported microbe immobilization method, a microbe-attached single-walled carbon nanotube film, can be applied to whole-cell-based organophosphate sensors. This method has many advantages over other whole-cell organophosphate sensors, including high specific activity, quick cell immobilization, and excellent stability. A device with circular electrodes was fabricated for an enlarged cell-immobilization area. Escherichia coli expressing organophosphorus hydrolase in the periplasmic space and single-walled carbon nanotubes were attached to the device by our method. Paraoxon was hydrolyzed using this device, and detected by measuring the concentration of the enzymatic reaction product, p-nitrophenol. The specific activity of our device was calculated, and was shown to be over 2.5 times that reported previously for other whole-cell organophosphate sensors. Thus, this method for generation of whole-cell-based OP biosensors might be optimal, as it overcomes many of the caveats that prevent the widespread use of other such devices.

Biosensors based on enzyme inhibition

The present chapter describes the use of biosensors based on enzyme inhibition as analytical tools. The parameters that affect biosensor sensitivity, such as the amount of immobilized enzyme, incubation time, and immobilization type, were critically evaluated, highlighting how the knowledge of enzymatic kinetics can help researchers optimize the biosensor in an easy and fast manner. The applications of these biosensors demonstrating their wide application have been reported. The objective of this survey is to give a critical description of biosensors based on enzyme inhibition, of their assembly, and their application in the environmental, food, and pharmaceutical fields.

Design and Development of Biosensors for the Detection of Heavy Metal Toxicity

Many compounds (including heavy metals, HMs) used in different fields of industry and/or agriculture act as inhibitors of enzymes, which, as consequence, are unable to bind the substrate. Even if it is not so sensitive, the method for detecting heavy metal traces using biosensors has a dynamic trend and is largely applied for improving the “life quality”, because of biosensor's sensitivity, selectivity, and simplicity. In the last years, they also become more and more a synergetic combination between biotechnology and microelectronics. Dedicated biosensors were developed for offline and online analysis, and also, their extent and diversity could be called a real “biosensor revolution”. A panel of examples of biosensors: enzyme-, DNA-, imuno-, whole-cell-based biosensors were systematised depending on the reaction type, transduction signal, or analytical performances. The mechanism of enzyme-based biosensor and the kinetic of detection process are described and compared. In this context, is explainable why bioelectronics, nanotechnology, miniaturization, and bioengineering will compete for developing sensitive and selective biosensors able to determine multiple analytes simultaneously and/or integrated in wireless communications systems.

Immobilization of acetylcholineesterase-choline oxidase on a gold-platinum bimetallic nanoparticles modified glassy carbon electrode for the sensitive detection of organophosphate pesticides, carbamates and nerve agents

A novel, highly sensitive amperometric biosensor, based on electrodeposition of gold-platinum bimetallic nanoparticles onto 3-aminopropyltriethoxy silane modified glassy carbon electrode for the detection of paraoxon ethyl, aldicarb, and sarin has been developed. The biosensor consists of acetylcholineesterase (AChE)/choline oxidase (ChOx) immobilized by cross-linking with glutaraldehyde on a modified electrode. The properties of nanoparticles modified electrodes are characterized by scanning electron microscopy (SEM), energy dispersive X-ray (EDX), cyclic voltammograms (CVs) and electrochemical impedance spectroscopy (EIS). The synergistic action of Au and Pt nanoparticles showed excellent electrocatalytic activity with low applied potential for the detection of hydrogen peroxide (H(2)O(2)). The IC(50) and inhibition rate constant (K(i)) values were determined for the inhibitors using immobilized enzymes on modified electrode and the data were compared by spectrophotometric determination of these kinetic parameters using free enzymes in solution. Paraoxon ethyl, sarin, and aldicarb could be detected up to 150-200nM, 40-50nM, and 40-60 microM respectively at 30-40% inhibition level of AChE enzyme and followed linearity in wide range concentration.

Nanoparticle-based electrochemical immunosensor for the detection of phosphorylated acetylcholinesterase: an exposure biomarker of organophosphate pesticides and nerve agents

A nanoparticle-based electrochemical immunosensor has been developed for the detection of phosphorylated acetylcholinesterase (AChE), which is a potential biomarker of exposure to organophosphate (OP) pesticides and chemical warfare nerve agents. Zirconia nanoparticles (ZrO(2) NPs) were used as selective sorbents to capture the phosphorylated AChE adduct, and quantum dots (ZnS@CdS, QDs) were used as tags to label monoclonal anti-AChE antibody to quantify the immunorecognition events. The sandwich-like immunoreactions were performed among the ZrO(2) NPs, which were pre-coated on a screen printed electrode (SPE) by electrodeposition, phosphorylated AChE and QD-anti-AChE. The captured QD tags were determined on the SPE by electrochemical stripping analysis of its metallic component (cadmium) after an acid-dissolution step. Paraoxon was used as the model OP insecticide to prepare the phosphorylated AChE adducts to demonstrate proof of principle for the sensor. The phosphorylated AChE adduct was characterized by Fourier transform infrared spectroscopy (FTIR) and mass spectroscopy. The binding affinity of anti-AChE to the phosphorylated AChE was validated with an enzyme-linked immunosorbent assay. The parameters (e.g., amount of ZrO(2) NP, QD-anti-AChE concentration,) that govern the electrochemical response of immunosensors were optimized. The voltammetric response of the immunosensor is highly linear over the range of 10 pM to 4 nM phosphorylated AChE, and the limit of detection is estimated to be 8.0 pM. The immunosensor also successfully detected phosphorylated AChE in human plasma. This new nanoparticle-based electrochemical immunosensor provides an opportunity to develop field-deployable, sensitive, and quantitative biosensors for monitoring exposure to a variety of OP pesticides and nerve agents.

Organophosphorus insecticides extraction and heterogeneous oxidation on column for analysis with an acetylcholinesterase (AChE) biosensor

This paper presents an analysis method for organophosphorus insecticides based on AChE biosensors coupled with a preconcentration and oxidation on a solid phase column. Three organic solvents, acetonitrile (ACN), ethanol and methanol were tested for their influence on AChE activity, insecticide inhibition and their ability to elute the adsorbed insecticides. Our results showed that ACN in a concentration of 5% (v/v) had the less negative effect on biosensor analysis and was the most appropriate organic solvent for the column elution. The presence of the organic solvent in the incubation media of the biosensor was found to induce a reduction of the inhibition percentages. The inhibition of the biosensors was performed in phosphate buffer with 5% (v/v) ACN, while the initial and remaining response of the biosensors were measured in PBS. In these conditions, the LODs of paraoxon and dichlorvos were measured with or without a preconcentration step. The LODs of the AChE biosensor without sample preconcentration were 8 x 10(-8) M for paraoxon and 1 x 10(-7) M dichlorvos and the LOD obtained after the preconcentration step were 2.5 x 10(-8) M for paraoxon and 2.5 x 10(-8) M for dichlorvos. Moreover, the use of the column allowed the heterogeneous oxidation of organophosphorus insecticides for improved LOD.

Tyrosinase inhibition organic phase biosensor for triazinic and benzotriazinic pesticide analysis (part two)

Several triazine pesticides, such as atrazine, are much more soluble in several organic solvents, such as chloroform, than in water. Our recent research was aimed at analyzing this class of pesticides using tyrosinase OPEE (organic phase enzyme electrodes), exploiting their inhibiting action on the tyrosinase enzyme when operating in water-saturated chloroform medium. In this work we studied the response of a tyrosinase inhibition enzyme sensor to several triazinic (simazine, propazine, terbuthylazine) and benzotriazinic (azinphos-ethyl and azinphos-methyl) pesticides (LOD=0.5x10(-9) mol l(-1)). Recovery trials were also performed in vegetal matrixes (corn, barley, lentils). Lastly, the effect of the solvent (chloroform or water) on the inhibition process was investigated via Hill's equation and the diffusion of analyte from the solvent to the enzyme membrane.

Effects of paraoxon and ethylparathion on choline oxidase from Alcaligenes species: Inhibition and denaturation

The kinetics and thermodynamics of the effects of paraoxon (POX) and ethylparathion (EPA) on choline oxidase (ChOx) were studied. Lineweaver-Burk plots of initial velocity data showed a parallel pattern indicating uncompetitive inhibition versus choline. The inhibition constant (K(I)) obtained from the secondary plots for POX and EPA were 0.14+/-0.01 and 0.48+/-0.05 mM, respectively, suggesting that POX is a more potent inhibitor of ChOx than EPA. UV absorption was used to monitor the denaturation of ChOx by POX and EPA. A decrease in FAD fluorescence associated with the interaction of POX and EPA with ChOx suggested a tertiary structural change. Interaction of the enzyme molecule with POX or EPA resulted in inhibition and subsequently denaturation of the enzyme. The results indicate that inhibition and denaturation of the enzyme by POX and EPA are linked, but not parallel events, with inhibition occurring at lower concentrations with respect to denaturation. This suggests that the loss of initial velocity of the enzyme is an active site specific effect and not due to global conformational changes induced by the inhibitors.

Electrochemical Sensor for Organophosphate Pesticides and Nerve Agents Using Zirconia Nanoparticles as Selective Sorbents

An electrochemical sensor for detection of organophosphate (OP) pesticides and nerve agents using zirconia (ZrO2) nanoparticles as selective sorbents is presented. Zirconia nanoparticles were electrodynamically deposited onto the polycrystalline gold electrode by cyclic voltammetry. Because of the strong affinity of zirconia for the phosphoric group, nitroaromatic OPs strongly bind to the ZrO2 nanoparticle surface. The electrochemical characterization and anodic stripping voltammetric performance of bound OPs were evaluated using cyclic voltammetric and square-wave voltammetric (SWV) analysis. SWV was used to monitor the amount of bound OPs and provide simple, fast, and facile quantitative methods for nitroaromatic OP compounds. The sensor surface can be regenerated by successively running SWV scanning. Operational parameters, including the amount of nanoparticles, adsorption time, and pH of the reaction medium have been optimized. The stripping voltammetric response is highly linear over the 5-100 ng/mL (ppb) methyl parathion range examined (2-min adsorption), with a detection limit of 3 ng/mL and good precision (RSD = 5.3%, n = 10). The detection limit was improved to 1 ng/mL by using 10-min adsorption time. The promising stripping voltammetric performances open new opportunities for fast, simple, and sensitive analysis of OPs in environmental and biological samples. These findings can lead to a widespread use of electrochemical sensors to detect OP contaminates.

A rapid and simple respirometric biosensor with immobilized cells of Nitrosomonas europaea for detecting inhibitors of ammonia oxidation

As obligate chemolithotrophs, ammonia-oxidizing bacteria (AOB) grow very slowly and are known to be extremely sensitive to a wide variety of inhibitors. Since it is generally accepted that inhibition of ammonia oxidation by AOB results in a total failure of nitrogen removal, it is necessary to develop a method to detect inhibitors of ammonia oxidation in wastewater. Since ammonia oxidation accompanies oxygen consumption, ammonia oxidation can be easily evaluated by measuring oxygen consumption rate using a dissolved oxygen (DO) probe. In this study, a rapid and simple respirometric biosensor using the pure culture of Nitrosomonas europaea was developed. N. europaea was cultivated in a continuous fermentor operating at the dilution rate of 0.008 h(-1) to obtain physiologically constant cells and was immobilized onto the dialysis membrane through filtration. DO, determined by the biosensor, started to increase 30 s later after ammonia oxidation inhibitor was fed, and a new steady-state DO was obtained in 10-30 min. For this DO profile, steady-state kinetics was applied to evaluate ammonia oxidation efficiency. The concentration of a toxic compound causing 50% decrease of oxygen-consumption activity (EC50) was determined for different chemicals. The EC50 values obtained with the biosensor (0.018 mg l(-1) for allylthiourea, 0.027 mg l(-1) for thioacetamide, 1.10 mg l(-1) for phenol and 0.0 1mg l(-1) for thiourea) indicated that the developed biosensor was highly sensitive to a variety of the inhibitors. It was also shown that the biosensor is applicable for on-line real time monitoring.

Characterization of platinum nanoparticle-embedded carbon film electrode and its detection of hydrogen peroxide

A method for the highly sensitive determination of acetylcholine (ACh) and choline (Ch) that employs a graphite-like carbon film electrode containing 6.5% platinum (Pt) nanoparticles was developed for use as a detector in microbore liquid chromatography (LC) with a postcolumn enzyme reactor. The film electrode was prepared by RF cosputtering carbon and Pt, which requires only a one-step formation process. This method can control the Pt content of the film at a relatively low deposition temperature (below 200 degrees C). The average size of the Pt nanoparticles was 2.5 nm. The film electrode showed excellent electrocatalytic activity, high sensitivity, and negligible baseline drift when detecting hydrogen peroxide. The electrode was modified with glucose oxidase and responded rapidly to glucose with a much more stable baseline current than at a Pt bulk electrode based sensor. Therefore, it is appropriate to employ the electrode to detect trace amounts of biomolecules, such as neurotransmitters and hormones combined with various oxidase enzymes. We used the electrode as a detector for microbore LC and observed a low detection limit of 2.5 and 2.3 fmol (10-microL injection) for ACh and Ch, respectively, which is approximately 1 order of magnitude lower than that of a Pt bulk electrode.