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We have developed a bienzymatic biosensor that contains acetylcholinesterase together with butyrylcholinesterase co-immobilized on the same electrode modified with a stabilized copper containing Prussian blue electrodeposited on electrodes coated with 4-aminothiophenol monolayer using diazonium chemistry and copper nanoparticles for improved sensitivity. There are organophosphorus and carbamate neurotoxic insecticides that inhibit only one of the two enzymes, e.g., pirimicarb inhibits butyrylcholinesterase at much lower concentrations than acetylcholinesterase while methomyl inhibits only acetylcholinesterase. Our system is simple and in a single measurement provides a sensitive signal for insecticides' presence based on the inhibition of the enzyme with the highest affinity for each toxic compound. The limits of detection are 50 ng/mL pirimicarb for the bienzymatic biosensor in comparison with 400 ng/mL pirimicarb for the acetylcholinesterase biosensor and 6 ng/mL methomyl for the bienzymatic biosensor, while inhibition is obtained for the butyrylcholinesterase biosensor at 700 ng/mL.

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We have developed a bienzymatic biosensor that contains acetylcholinesterase together with butyrylcholinesterase co-immobilized on the same electrode modified with a stabilized copper containing Prussian blue electrodeposited on electrodes coated with 4-aminothiophenol monolayer using diazonium chemistry and copper nanoparticles for improved sensitivity. There are organophosphorus and carbamate neurotoxic insecticides that inhibit only one of the two enzymes, e.g., pirimicarb inhibits butyrylcholinesterase at much lower concentrations than acetylcholinesterase while methomyl inhibits only acetylcholinesterase. Our system is simple and in a single measurement provides a sensitive signal for insecticides’ presence based on the inhibition of the enzyme with the highest affinity for each toxic compound. The limits of detection are 50 ng/mL pirimicarb for the bienzymatic biosensor in comparison with 400 ng/mL pirimicarb for the acetylcholinesterase biosensor and 6 ng/mL methomyl for the bienzymatic biosensor, while inhibition is obtained for the butyrylcholinesterase biosensor at 700 ng/mL. Graphical Abstract: (Figure presented.) © The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature 2024.

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Ultrasound generates cavities in liquids with high-energy behaviour due to large pressure variations, leading to (bio)chemical effects and material modification. Numerous cavity-based treatments in food processes have been reported, but the transition from research to industrial applications is hampered by specific engineering factors, such as the combination of several ultrasound sources, more powerful wave generators or tank geometry. The challenges and development of cavity-based treatments developed for the food industry are reviewed with examples limited to two representative raw materials (fruit and milk) with significantly different properties. Both active compound extraction and food processing techniques based on ultrasound are taken into consideration.

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Sensitive and stable electrodes modified with 4-aminothiophenol were developed for heavy metal detection based on coordination bonds between thiol moieties and analyte. The electrodes were modified using diazonium chemistry in one step modification protocol. The presence of 1,1-diphenyl-2-picrylhydrazyl radical (DPPH) in the electrodeposition media avoids the formation of multilayers and improves the performances due to low surface passivation and good electrochemical transfer at the interface with the solution. Electrodeposition of the organic layer on the electrode surface by chronopotentiometry allowed a good control of the electrode modification process, avoids passivation, and leads to reproducible layers with improved characteristics in comparison with modifications carried out by cyclic voltammetry or chronoamperometry. The electrode was able to detect Pb(II) by differential pulse voltammetry with a linear range of 2.5-400 mu g l(-1) and the detection limit of 1.2 mu g l(-1) and Cd(II) with the calibration line in the range of 2.5-400 mu g l(-1) and a detection limit of 1.5 mu g l(-1). Low interferences were observed and the electrodes were applied for analysis of real samples: fruits pomace and waters. (C) 2022 The Electrochemical Society (ECS). Published on behalf of ECS by IOP Publishing Limited.

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Few biosensors are reported for usage in combination with the organic solvent due to their negative impact on the enzymes. The usage of ternary water-organic solvent mixtures in combination with acetylcholinesterase biosensors allows to increase the useable total content of organic solvents with minimum negative effects to a higher content in comparison with a single organic solvent in water. The combination of acetonitrile/ethanol/ water has a smaller negative effect on both enzyme activity and inhibition by insecticides in comparison with acetonitrile/methanol/water mixtures. The insecticides were eluted from solid-phase extraction (SPE) columns with a binary mixture of organic solvents acetonitrile/ethanol in 1/3 ratio and subsequently analysed with an acetylcholinesterase biosensor and the optimum total content of organic solvents of 12%. The analytical method allows the analysis of complex samples with improved selectivity and at improved limits of detection for chlorpyrifos-oxon and carbofuran analysis in river waters and soil samples. The usage of mixtures of organic solvents in combination with enzymes is an interesting approach that allows working with a higher total content of organic solvents than each individual solvent.

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Few biosensors are reported for usage in combination with the organic solvent due to their negative impact on the enzymes. The usage of ternary water–organic solvent mixtures in combination with acetylcholinesterase biosensors allows to increase the useable total content of organic solvents with minimum negative effects to a higher content in comparison with a single organic solvent in water. The combination of acetonitrile/ethanol/water has a smaller negative effect on both enzyme activity and inhibition by insecticides in comparison with acetonitrile/methanol/water mixtures. The insecticides were eluted from solid-phase extraction (SPE) columns with a binary mixture of organic solvents acetonitrile/ethanol in 1/3 ratio and subsequently analysed with an acetylcholinesterase biosensor and the optimum total content of organic solvents of 12%. The analytical method allows the analysis of complex samples with improved selectivity and at improved limits of detection for chlorpyrifos-oxon and carbofuran analysis in river waters and soil samples. The usage of mixtures of organic solvents in combination with enzymes is an interesting approach that allows working with a higher total content of organic solvents than each individual solvent. © 2022 Elsevier Inc.

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A rapid, simple, and precise electrochemical method was developed for the determination of the total content of antibiotics containing a 5-nitrofuran ring with antibacterial activity including furazolidone, nitrofurazone, nitrofurantoin, and furaltadone in several samples. Boron-doped diamond electrode was used as the working electrode. The electrochemical properties of these compounds were evaluated by cyclic voltammetry. A differential pulse voltammetric method based on the cathodic reduction at high potentials was used for the determination of the total nitrofuran content in a mixture at pH 6.47. The voltammetric measurements showed that the proposed electrochemical method was able to identify the nitrofurazone from a mixture of antibiotics based on its anodic oxidation in alkaline medium (pH 10.6). This method presented good accuracy (between 94.5 and 102.5%) and precision (less than 3.94%), with calibration graphs starting from 50 nmol L-1. The method was applied with success for the determination of total content of compounds with 5-nitrofuran ring and for the selective determination of nitrofurazone in pharmaceutical tablets and food products (milk and honey) without pretreatment of the samples.

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A stable and reproducible layer of Prussian blue (PB) modified with copper was electrodeposited on carbon paper electrodes for the multiple detection of ester flavorants with a bienzymatic biosensor. Carbon fiber composite paper was investigated as high-surface, low-cost substrate for biosensor development. The pre-activation of the electrode surface by cyclic voltammetry was necessary to improve the electrochemical properties before the electrochemical deposition of Prussian blue-copper film (PB-Cu). The stability and the reproducibility of the obtained PB-Cu carbon paper electrode was demonstrated at pH 7.4, optimum for biosensor development. The developed biosensor is based on the immobilization of two enzymes (carboxyl esterase and alcohol oxidase) by cross-linking with glutaraldehyde onto PB-Cu carbon paper electrode. A mixture of key aroma ester compounds (methyl butyrate, ethyl butyrate, methyl cinnamate and ethyl cinnamate) was detected in several food samples with low interferences.

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Acrylamide (AA) is a toxic compound formed in thermally prepared foods by Maillard reaction. Besides foods, AA may be found in cosmetic products as an impurity of the widely-used non-toxic polyacrylamide. We present a novel, fast and selective detection method based on the amperometric monitoring of the coupling reaction between reduced glutathione (GSH) and AA catalyzed by glutathione S-transferase (GST) to produce an electrochemically inactive compound. We have used electrodes modified with cobalt-phthalocyanine to monitor the decrease of GHS concentration at +300 mV. Our system is simple, does not require supplementary substrates such as 1-chloro-2,4-dinitrobenzene (CDNB) nor have disadvantageous competitive kinetics characteristic to inhibition like signals. Using the optimum concentration of 100 M GSH we have obtained a linear calibration graph from 7 to 50 M AA and a limit of detection of 5 M AA. The method is not affected by interfering compounds usually found in foods and was applied for real sample analysis.

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Acrylamide (AA) is a toxic compound formed in thermally prepared foods by Maillard reaction. Besides foods, AA may be found in cosmetic products as an impurity of the widely-used non-toxic polyacrylamide. We present a novel, fast and selective detection method based on the amperometric monitoring of the coupling reaction between reduced glutathione (GSH) and AA catalyzed by glutathione S-transferase (GST) to produce an electrochemically inactive compound. We have used electrodes modified with cobalt-phthalocyanine to monitor the decrease of GHS concentration at +300 mV. Our system is simple, does not require supplementary substrates such as 1-chloro-2,4-dinitrobenzene (CDNB) nor have disadvantageous competitive kinetics characteristic to inhibition like signals. Using the optimum concentration of 100 μM GSH we have obtained a linear calibration graph from 7 to 50 μM AA and a limit of detection of 5 μM AA. The method is not affected by interfering compounds usually found in foods and was applied for real sample analysis. © 2018 The Royal Society of Chemistry.

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A Sense and Control Circuit (SCC) developed for amperometric concentration evaluation is redesigned, based on preliminary experimental investigations. This cost-effective circuit comprises a potentiostat for three-electrode electrochemical cell (biosensor) control and a transimpedance amplifier for cell current sensing. Stability, noise robustness and response time are improved, as demonstrated by experiments and simulations. SCC performances are evaluated in comparison with a professional system, by H2O2 concentration measurements.

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Novel molecularly imprinted polymers (MIPs) designated for the solid-phase extraction of antibiotics containing a 5-nitrofuran ring (nitrofurantoin and furaltadone) are reported. The synthesis of these MIPs was based on commercial monomers and cross-linking agents capable of forming hydrogen bonds with the template molecules. Thus, the designed MIPs should involve acceptable costs and easier accessibility. Their retention properties were studied by solid-phase extraction (SPE) procedures and the breakthrough curves were evaluated for both imprinted and non-imprinted polymers (NIPs). Due to the presence of adsorption sites created in polymers by imprinting, the MIPs showed a significant difference in the retention property in comparison to NIPs. The MIPs were also immobilized onto a gold electrode surface by entrapment into a silane sol-gel matrix for the development of a sensor based on electrochemical impedance measurements. The good mechanical adherence of the sol-gel matrix on the gold electrode surface was achieved by formation of a self-assembled monolayer using 3-mercaptopropyl trimethoxisilane that acts as an anchoring bridge.

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A low-interferences enzymatic sensor for evaluating the antioxidant capacity was developed. Xanthine oxidase was used to produce superoxide radicals that spontaneously dismutate to hydrogen peroxide. Low xanthine concentrations were used to minimize the rapid dismutation of the superoxide radical before its fast reaction with antioxidants. The sensor operates in the reduction mode, and evaluations with low interferences of the antioxidant capacity are based on the detection of remaining hydrogen peroxide using Prussian blue electrodes at low potentials. The linear calibration graph is between 2 - 10 mu M ascorbic acid. No interferences were observed from easily oxidisable substances including uric acid, which is produced in the enzymatic reaction or other substances usually found in foods. The method was used to evaluate the antioxidant capacity in different real juice samples.

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Prussian blue modified with copper was electrodeposited on a platinum microelectrode for the amperometric determination of hydrogen peroxide at -50 mV. The Prussian blue-copper layer was stable for 2 h at pH 7.4 and a storage period of 2 months. The Prussian blue-copper modified microelectrodes were used to develop oxidase based microbiosensors for ethanol and lactate. Lactate and alcohol oxidases were immobilized by cross-linking with glutaraldehyde. No interferences were observed from possible interfering compounds up to a concentration of 0.5 mM. The calibration plot of the lactate microbiosensor was linear between 0.005 and 0.2 mM with a limit of detection of 0.0035 mM lactate. The linear dynamic range of the alcohol microbiosensor was between 0.05 and 2 mM and the limit of detection was 0.02 mM ethanol. The developed microbiosensors were used for the analysis of pickled cucumber juice, yogurt, and wine.

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beta-Carbolines are inhibitors of monoamine oxidases (MAO-A and MAO-B) and can be found in foods, hallucinogenic plant or various drugs. We have developed a fast analysis method for beta-carbolines based on the inhibition of MAO. The enzymes were immobilized on screen-printed electrodes modified with a stabilized film of Prussian blue that contain also copper. We have used benzylamine as substrate for the enzymatic reaction and the hydrogen peroxide was measured amperometrically at -50 mV. The detection limits obtained were 5.0 mu M for harmane and 2.5 mu M for both harmaline and norharmane. The MAO-A is inhibited by all three tested beta-carbolines (harmane, norharmane, and harmaline) while MAO-B is inhibited only by norharmane. The presence of norharmane in mixtures of beta-carbolines can be identified based on the difference between the cumulative inhibition of MAO-A by all beta-carbolines and MAO-B inhibition. The developed biosensors were used for food analysis. (C) 2015 Elsevier B.V. All rights reserved.

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β-Carbolines are inhibitors of monoamine oxidases (MAO-A and MAO-B) and can be found in foods, hallucinogenic plant or various drugs. We have developed a fast analysis method for β-carbolines based on the inhibition of MAO. The enzymes were immobilized on screen-printed electrodes modified with a stabilized film of Prussian blue that contain also copper. We have used benzylamine as substrate for the enzymatic reaction and the hydrogen peroxide was measured amperometrically at -50 mV. The detection limits obtained were 5.0 μM for harmane and 2.5 μM for both harmaline and norharmane. The MAO-A is inhibited by all three tested β-carbolines (harmane, norharmane, and harmaline) while MAO-B is inhibited only by norharmane. The presence of norharmane in mixtures of β-carbolines can be identified based on the difference between the cumulative inhibition of MAO-A by all β-carbolines and MAO-B inhibition. The developed biosensors were used for food analysis. © 2015 Elsevier B.V. All rights reserved.

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A rapid, simple and stable biosensor for aspartame detection was developed. Alcohol oxidase (AOX), carboxyl esterase (CaE) and bovine serum albumin (BSA) were immobilised with glutaraldehyde (GA) onto screen-printed electrodes modified with cobalt-phthalocyanine (CoPC). The biosensor response was fast. The sample throughput using a flow injection analysis (FIA) system was 40 h(-1) with an RSD of 2.7%. The detection limits for both batch and FIA measurements were 0.1 mu M for methanol and 0.2 mu M for aspartame, respectively. The enzymatic biosensor was successfully applied for aspartame determination in different sample matrices/commercial products (liquid and solid samples) without any pre-treatment step prior to measurement.

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The anticholinesterase activity of four biochemical pesticides: spinosad, pyrethrum, neem bark extract and veratrine was tested against one acetylcholinesterase extracted from Electrophorus electricus and two from Drosophila melanogaster. Pyrethrum, neem bark extract, and veratrine induced a dose-related inhibition of a variable type. Electric eel cholinesterase was inhibited uncompetitively by neem bark extract, the inhibition of the wilde-type fruit fly enzyme by pyrethrum was competitive, and the other enzyme-biochemical pesticide inhibitions were non-competitive. The sensitivity of each enzyme toward biochemical pesticides was variable. (C) Pesticide Science Society of Japan

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We have modified a glassy carbon electrode (GCE) with nanoparticles composed of a 4,4'-bipyridinesilver coordination polymer (CP) and showed that this CP can be applied to the sensitive differential pulse voltammetric analysis of the ions Hg(II), Cu(II) and Pb(II). The coordination polymer was prepared by mixing a solution of silver nitrate and 4,4'-bipyridine at room temperature. The surface of the GCE was modified with an organic layer of synthesized 1-[(4-nitrophenyl)methyl]-4,4'-bipyridinium and silver ions, which caused the binding of the added Ag-bipy CP. Anodic (oxidative) peaks of the electrode were at +300 mV for Hg(II), -70 mV for Cu(II), and at -540 mV for Pb(II) [versus Ag/AgCl]. Under optimal conditions, calibration graphs were linear in concentration ranges from 0.2 to 10 mu g L-1 for Hg(II), from 1.3 to 6.4 mu g L-1 for Cu(II), and from 4.1 to 20.7 mu g L-1 for Pb(II). The respective detection limits were 0.09 mu g L-1 Hg(II), 0.71 mu g L-1 Cu(II) and 2.3 mu g L-1 Pb(II). Relative standard deviation was 3.2% at a level of 4 mu g L of Hg(II) for n = 10. The modified electrode was applied to the analysis of Hg(II) in spiked fish samples, and of Cu(II), Pb(II), and Hg(II) in spiked plant samples, and recoveries ranged from 90 to 108%. This is the first paper that presents the use of 4,4'-bipyridine-silver coordination polymer for heavy metal electrochemical detection.

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Numerous amperometric biosensors have been developed for the fast analysis of neurotoxic insecticides based on inhibition of cholinesterase (AChE). The analytical signal is quantified by the oxidation of the thiocholine that is produced enzymatically by the hydrolysis of the acetylthiocholine pseudosubstrate. The pseudosubstrate is a cation and it is associated with chloride or iodide as corresponding anion to form a salt. The iodide salt is cheaper, but it is electrochemically active and consequently more difficult to use in electrochemical analytical devices. We investigate the possibility of using acetylthiocholine iodide as pseudosubstrate for amperometric detection. Our investigation demonstrates that operational conditions for any amperometric biosensor that use acetylthiocholine iodide must be thoroughly optimized to avoid false analytical signals or a reduced sensitivity. The working overpotential determined for different screen-printed electrodes was: carbon-nanotubes (360 mV), platinum (560 mV), gold (370 mV, based on a catalytic effect of iodide) or cobalt phthalocyanine (110 mV, but with a significant reduced sensitivity in the presence of iodide anions).

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A new modified glassy carbon electrode (GCE) based on a synthesized N-(2-aminoethyl)-4,4'-bipyridine (ABP) was developed for the determination of Ag(I) by differential pulse voltammetry (DPV). ABP was covalently immobilized on GC electrodes surface using 4-nitrobenzendiazonium (4-NBD) and glutaraldehyde (GA). The Ag(I) ions were preconcentrated by chemical interaction with bipyridine under a negative potential (-0.6 V); then the reduced ions were oxidized by differential pulse voltammetry and a peak was observed at 0.34 V. The calibration curve was linear in the concentration range from 0.05 μM to 1 μM Ag(I) with a detection limit of 0.025 μM and RSD = 3.6%, for 0.4 μM Ag(I). The presence of several common ions in more than 125-fold excess had no effect on the determination of Ag(I). The developed sensor was applied to the determination of Ag(I) in water samples using a standard addition method. © 2010 by the authors.

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A new modified glassy carbon electrode (GCE) based on a synthesized N-(2-aminoethyl)-4,4'-bipyridine (ABP) was developed for the determination of Ag(I) by differential pulse voltammetry (DPV). ABP was covalently immobilized on GC electrodes surface using 4-nitrobenzendiazonium (4-NBD) and glutaraldehyde (GA). The Ag(I) ions were preconcentrated by chemical interaction with bipyridine under a negative potential (-0.6 V); then the reduced ions were oxidized by differential pulse voltammetry and a peak was observed at 0.34 V. The calibration curve was linear in the concentration range from 0.05 mu M to 1 mu M Ag(I) with a detection limit of 0.025 mu M and RSD = 3.6%, for 0.4 mu M Ag(I). The presence of several common ions in more than 125-fold excess had no effect on the determination of Ag(I). The developed sensor was applied to the determination of Ag(I) in water samples using a standard addition method.