The Experts below are selected from a list of 30663 Experts worldwide ranked by ideXlab platform
Otto S Wolfbeis - One of the best experts on this subject based on the ideXlab platform.
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indicator loaded permeation selective microbeads for use in fiber optic simultaneous sensing of ph and dissolved Oxygen
Chemistry of Materials, 2006Co-Authors: Ganna Vasylevska, Sergey M Borisov, And Christian Krause, Otto S WolfbeisAbstract:New materials are described that lead to sensors capable of simultaneous sensing of pH and Oxygen via a single-fiber optic sensor. They make use of a pH Probe based on carboxyfluorescein, and of a ruthenium(II) complex acting as a Probe for dissolved Oxygen. The selectivity of the Probes was considerably improved by incorporating them into two kinds of microparticles, each of specific permeation selectivity. The pH Probe was immobilized on particles made from proton permeable amino-modified poly(hydroxyethyl methacrylate), while the Oxygen Probe was physically immobilized in beads made from an organically modified sol−gel. Both kinds of beads were then dispersed into a hydrogel matrix and placed at the distal end of an optical fiber waveguide for optical interrogation. A phase-modulated blue-green LED serves as the light source for exciting luminescence whose average decay times or phase shifts serve as the analytical information. Data are evaluated by a modified dual luminophore referencing (m-DLR) metho...
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novel Oxygen sensor material based on a ruthenium bipyridyl complex encapsulated in zeolite y dramatic differences in the efficiency of luminescence quenching by Oxygen on going from surface adsorbed to zeolite encapsulated fluorophores
Sensors and Actuators B-chemical, 1995Co-Authors: Brit Meier, Ingo Klimant, Tobias Werner, Otto S WolfbeisAbstract:Abstract Zeolite Y was ion-exchanged with ruthenium(III) chloride, and the respective ruthenium(II) bipyridyl complex (Ru 2+ (bpy) 3 ), which is an excellent fluorescent Oxygen Probe, was prepared inside the zeolite supercages. In addition, a Ru 2+ (bipy) 3 dichloride solution was used for impregnation of the zeolite surface. Both materials were characterized by X-ray diffraction and the loading with ruthenium ions determined photometrically. In order to obtain sensor materials, they were incorporated into silicone polymers and spread, as a thin layer, onto a polyester mechanical support. The resulting sensor membranes were tested with respect to luminescence intensity, quenching by molecular Oxygen, response time to Oxygen and long-term stability under various conditions. Oxygen can be measured over the 0–760 Torr range, with very good resolution between 0 and 200 Torr. Both the quenching efficiency and the long-term stability of the Stern-Volmer quenching constant are tremendously improved when compared to sensors where the fluorophore is absorbed onto the surface of either a zeolite or silica gel. When spread onto glass rather than polyester, the sensors lend themselves to operation at temperatures as high as 200 °C.
Jonathan M. White - One of the best experts on this subject based on the ideXlab platform.
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Application of the Variable Oxygen Probe to Derivatives of 2,6-Dimethyltetrahydropyran-4-ol: Evidence for Through-Bond nO–σCC–σ*CO Interactions
Australian Journal of Chemistry, 2020Co-Authors: Liam Oliver, Jonathan M. White, Somaiah Ragam, Pierre Deslongchamps, Amber N. Hancock, Samuel C. BrydonAbstract:The variable Oxygen Probe has been applied to axial and equatorial 4-pyranols 4 and 5 and their ester and ether derivatives. Plots of C–OR bond distance versus pKa (ROH) provided evidence for slightly stronger donation into the σ*C–OR antibonding orbital in the equatorial derivatives 5 than in the axial derivatives 4, which is consistent with the presence of a through-bond nO–σCC–σ*CO interaction in 5. Evidence in support of this interpretation was also provided by density functional theory (DFT) calculations and natural bond orbital (NBO) analyses of the various orbital interactions in the 4-pyranols 4 and 5, their protonated analogues 4·H2O+ and 5·H2O+, and the corresponding cyclohexane derivatives 6, 7, 6·H2O+, and 7·H2O+.
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Application of the Variable Oxygen Probe to Determine the π-Electron Donor Ability of the Alkyne Group
Australian Journal of Chemistry, 2014Co-Authors: Benjamin L. Harris, Jonathan M. WhiteAbstract:Eight ester and ether derivatives of propargyl alcohol with varying electron demand were structurally characterised using low temperature X-ray crystallography, these were combined with seven derivatives obtained from the Cambridge Structural Database. Variable Oxygen Probe analysis of these derivatives provided evidence that the ethynyl substituent is a relatively weak π-electron donor, and is a slightly less effective donor than the C–C bond of an ethyl substituent.
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Hyperconjugation involving strained carbon-carbon bonds. Application of the variable Oxygen Probe to ester and ether derivatives of cubylmethanol.
Organic & biomolecular chemistry, 2013Co-Authors: Benjamin L. Harris, G. Paul Savage, Jonathan M. WhiteAbstract:Application of the variable Oxygen Probe to derivatives of (4-methoxycarbonyl)cubylmethanol 11 demonstrated a strong response of C–OR bond distance to the electron demand of the OR substituent, consistent with an enhanced σ-donor ability of the strained C–C bonds of cubane. The extent of cubane donor ability was found to be superior to an unstrained donor 13, comparing data extracted from the Cambridge Structural Database (T. W. Cole, Ph.D. Dissertation, University of Chicago, 1966), but weaker than the previously studied cyclopropane donors. Structural evidence is also found for σCC–π*CO interactions in these structures.
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hyperconjugation involving strained carbon carbon bonds structural analysis of ester and ether derivatives and one bond 13c 13c coupling constants of α and β nopinol
Journal of Organic Chemistry, 2013Co-Authors: Shinn Dee Yeoh, Colin Skene, Jonathan M. WhiteAbstract:σC–C–σ*C–O interactions involving the strained carbon–carbon bonds of α- and β-nopinol, and their ester and ether derivatives have been demonstrated in the solid state using the variable Oxygen Probe. These hyperconjugative interactions are manifested as a strong response of the C–OR bond distance to the electron demand of the OR substituent. Although the effects upon the donor C–C bond distances are not large enough to be measurable by X-ray crystallography, they do result in systematic and measurable effects on the 13C–13C one-bond coupling constants. For the donor C–C bond, coupling constants decrease, consistent with weakening of this bond, while the intervening C–C bond coupling constants increase, consistent with bond strengthening, as the electron demand of OR increases.
Margarita Stoytcheva - One of the best experts on this subject based on the ideXlab platform.
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Microbially Induced Corrosion in the Mineral Processing Industry
Advanced Materials Research, 2010Co-Authors: Margarita Stoytcheva, Benjamin Valdez, Roumen Zlatev, Michael Schorr, Monica Carrillo, Zdravka VelkovaAbstract:A method for real time determination of microbiologically influenced corrosion (MIC) rate provoked by bacteria Thiobacillus Ferrooxidans was developed and applied on carbon steel samples. It is based on biological Oxygen demand (BOD) determination of solutions contained Thiobacillus Ferrooxidans performed by the application of a Clark type Oxygen Probe in especially designed measuring cell.
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Electrochemical sensor based on Arthrobacter globiformis for cholinesterase activity determination
Biosensors and Bioelectronics, 2006Co-Authors: Margarita Stoytcheva, Benjamin Valdez, Roumen Zlatev, Jean-pierre Magnin, Zdravka VelkovaAbstract:The sensors applied recently for determination of cholinesterase activity are mostly enzymatic amperometric sensors, in spite of their disadvantages: short life-time at ambient temperature, instability of the response, interferences, as well as passivation of the electrode surface. In the present paper a new approach for determination of cholinesterase activity was proposed, overcoming the main drawbacks of the analysis performed with amperometric enzymatic sensors. Instead of the immobilization of enzymes on a conducting electrode surface, whole cells of Arthrobacter globiformis, containing choline oxidase were fixed on a Clark type Oxygen Probe. Current proportional to bacteria respiration is registered as a sensor response. The application of whole cells of bacteria as a sensing element permits to achieve high stability of the response and long life-time of the sensor at ambient temperature, due to the conservation of the enzyme in its natural micro-environment inside the immobilized cells. The proposed sensor keeps its functionality more than 7 weeks stored in deionized water at ambient temperature. For the first 2 weeks the amplitude of the response decreases with only 10% and at the end of the studied 7 weeks period the response was 50% of the initial. The other advantages of the proposed sensor are: the dissolved Oxygen is used as a mediator which concentration can be reliably and interferences free measured by the aim of a Clark type Oxygen Probe applied as a transducer; reproducible bacterial membranes can be elaborated by filtration of resuspended bacterial culture after preliminary determination of its activity; application of membranes containing lyophilized bacteria capable to be conserved infinitely long time and activated just before their application; negligible cost compared with the sensors based on immobilized enzymes. The steady-state response of the proposed bacterial sensor to choline obtained in 200 s is linear in the investigated concentration range up to 2 × 104 mol dm3, with detection limit of 8 × 108 mol dm3 and sensitivity of 4 × 101 μA cm3 mol1, at pH 6, temperature of 25 °C and stirring rate of 300 rpm. Choline is formed as a result of the catalytic hydrolysis (depending on the cholinesterase activity) of the substrate acetylcholine. Linear calibration graph for cholinesterase activity determination was obtained in the range up to 11 mU cm3, with a slope of 1.97 × 102 μA cm3 mU1, at pH 6, temperature of 25 °C and stirring rate of 300 rpm. The tests with reconstituted lyophilized serum with known activity used as a control sample confirm the accuracy of the proposed method. The relative error of the determination was only 2.82%.
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Bacterial sensors based on Acidithiobacillus ferrooxidans Part II. Cr(VI) determination
Biosensors and Bioelectronics, 2006Co-Authors: Roumen Zlatev, Jean-pierre Magnin, Patrick Ozil, Margarita StoytchevaAbstract:The aerobic acidophilic bacterium Acidithiobacillus ferrooxidans oxidizes Fe2+ and S2O32 ions by consuming Oxygen. An amperometric biosensor was designed including an Oxygen Probe as transducer and a recognition element immobilized by a suitable home-made membrane. This biosensor was used for the indirect amperometric determination of Cr2O72 ions owing to methods based on a mediator (Fe2+) or titration. Using the mediator, the biosensor response versus Cr2O72 was linear up to 0.4 mmol L1, with a response time of, respectively, 51 s (2 × 105 mol L1 Cr2O72) and 61 s (6 × 105 mol L1 Cr2O72). The method sensitivity was 816 μA L mol1. Response time and measurement sensitivity depended on membrane material and technique for biomass immobilization. For example, their values were 90 s200 μA L mol1 when using a glass-felt membrane and 540 s4.95 μA L mol1 with a carbon felt one to determine a concentration of 2 × 105 mol L1 Cr2O72. For the titration method, the biosensor is used to determine the equivalence point. The relative error of quantitative analysis was lower than 5%.
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Bacterial sensors based on Acidithiobacillus ferrooxidans Part I. Fe2+ and S2O32 determination
Biosensors and Bioelectronics, 2006Co-Authors: Roumen Zlatev, Jean-pierre Magnin, Patrick Ozil, Margarita StoytchevaAbstract:An amperometric bacterial sensor with current response to Fe2+ and S2O32– ions has been designed by immobilizing an acidophilic biomass of Acidithiobacillus ferrooxidans on a multi disk flat-front Oxygen Probe. The bacterial layer was located between the Oxygen Probe and a membrane of cellulose. A filtration technique was used to yield the bacterial membranes having reproducible activity. The decrease of O2 flow across the bacterial layer is proportional to the concentration of the dosed species. The dynamic range appeared to be linear for the Fe2+ ions up to 2.5 mmol L–1 with a detection limit of 9 × 10–7 mol L–1 and a sensitivity of 0.25 A L mol–1. The response of the biosensor is 84 s for a determination of 2 × 10–4 mol L–1 Fe2+. Optimizing the Fe2+ determination by A. ferrooxidans sensor was carried out owing to Design of Experiments (DOE) methodology and empirical modelling. The optimal response was thus obtained for a pH of 3.4, at 35 °C under 290 rpm solution stirring. S2O32– concentration was determined at pH 4.7, so avoiding its decomposition. The concentration range was linear up to 0.6 mmol L–1. Sensitivity was 0.20 A L mol–1 with a response time of 207 s for a 2 × 10–4 mol L–1 S2O32– concentration.
Erhan Dinçkaya - One of the best experts on this subject based on the ideXlab platform.
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Urate oxidase electrode based on dissolved Oxygen Probe for urine uric acid determination.
Indian journal of biochemistry & biophysics, 2000Co-Authors: Erhan Dinçkaya, Erol Akyilmaz, Sinan AkgölAbstract:A biosensor for the specific determination of uric acid in urine was developed using urate oxidase (EC 1.7.3.3) in combination with a dissolved Oxygen Probe. Urate oxidase was immobilized with gelatin by means of glutaraldehyde and fixed on a pretreated teflon membrane to serve as enzyme electrode. The electrode response was maximum when 50 mM glycine buffer was used at pH 9.2 and 35 degrees C. The enzyme electrode response depends linearly on uric acid concentration between 5-40 microM with a response time of 5 min. The enzyme electrode is stable for more than 2 weeks and during this period over 35 assays were performed.
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a new enzyme electrode based on ascorbate oxidase immobilized in gelatin for specific determination of l ascorbic acid
Talanta, 1999Co-Authors: Erol Akyilmaz, Erhan DinçkayaAbstract:Abstract A biosensor for the specific determination of l -ascorbic acid in fruit juices and vitamin C tablets was developed using ascorbate oxidase (EC 1.10.3.3) from cucumber (Cucumis sativus L.) in combination with a dissolved Oxygen Probe. Ascorbate oxidase immobilized with gelatin using glutaraldehyde and fixed on pretreated teflon membrane served as an enzyme electrode. The phosphate buffer (50 mM, pH 7.5) and 35°C were established as providing the optimum conditions. The biosensor response depends linearly on l -ascorbic acid concentration between 5.0×10−5 and 1.2×10−3 M with a response time 45 s. The biosensor is stable for more than 2 months, while more than 200 assays were performed. The results obtained for fruit juices and tablets were compared with DCIP (2,6 dichlorophenolindophenol) method.
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A novel biosensor for specific determination of hydrogen peroxide: catalase enzyme electrode based on dissolved Oxygen Probe
Talanta, 1999Co-Authors: Sinan Akgöl, Erhan DinçkayaAbstract:Abstract A biosensor for the specific determination of hydrogen peroxide was developed using catalase (EC 1.11.1.6) in combination with a dissolved Oxygen Probe. Catalase was immobilized with gelatin by means of glutaraldehyde and fixed on a pretreated teflon membrane served as enzyme electrode. The electrode response was maximum when 50 mM phosphate buffer was used at pH 7.0 and at 35°C. The biosensor response depends linearly on hydrogen peroxide concentration between 1.0×10−5 and 3.0×10−3 M with a response time of 30 s. The sensor is stable for >3 months so in this period >400 assays can be performed.
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A Novel Catechol Oxidase Enzyme Electrode for the Specific Determination of Catechol
Bioscience Biotechnology and Biochemistry, 1998Co-Authors: Erhan Dinçkaya, Erol Akyilmaz, Sinan Akgöl, Seçil Önal, Figen Zihnioglu, Azmi TelefoncuAbstract:An enzyme electrode for the specific determination of catechol was developed by using catechol oxidase (EC 1.10.3.1) from eggplant (Solanum melangena L.) in combination with a dissolved Oxygen Probe. Optimization studies of the prepared catechol oxidase enzyme electrode established a phosphate buffer 50 mM at pH 7.0 and 35°C to provide the optimum conditions for affirmative electrode response. The enzyme electrode response depended linearly on a catechol concentration range of 5•10-7-30•10-5 M with a response time of 25 sec and substrate specificity of the catechol oxidase electrode of 100%. The biosensor retained its enzyme activity for at least 70 days.
Roumen Zlatev - One of the best experts on this subject based on the ideXlab platform.
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Microbially Induced Corrosion in the Mineral Processing Industry
Advanced Materials Research, 2010Co-Authors: Margarita Stoytcheva, Benjamin Valdez, Roumen Zlatev, Michael Schorr, Monica Carrillo, Zdravka VelkovaAbstract:A method for real time determination of microbiologically influenced corrosion (MIC) rate provoked by bacteria Thiobacillus Ferrooxidans was developed and applied on carbon steel samples. It is based on biological Oxygen demand (BOD) determination of solutions contained Thiobacillus Ferrooxidans performed by the application of a Clark type Oxygen Probe in especially designed measuring cell.
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Electrochemical sensor based on Arthrobacter globiformis for cholinesterase activity determination
Biosensors and Bioelectronics, 2006Co-Authors: Margarita Stoytcheva, Benjamin Valdez, Roumen Zlatev, Jean-pierre Magnin, Zdravka VelkovaAbstract:The sensors applied recently for determination of cholinesterase activity are mostly enzymatic amperometric sensors, in spite of their disadvantages: short life-time at ambient temperature, instability of the response, interferences, as well as passivation of the electrode surface. In the present paper a new approach for determination of cholinesterase activity was proposed, overcoming the main drawbacks of the analysis performed with amperometric enzymatic sensors. Instead of the immobilization of enzymes on a conducting electrode surface, whole cells of Arthrobacter globiformis, containing choline oxidase were fixed on a Clark type Oxygen Probe. Current proportional to bacteria respiration is registered as a sensor response. The application of whole cells of bacteria as a sensing element permits to achieve high stability of the response and long life-time of the sensor at ambient temperature, due to the conservation of the enzyme in its natural micro-environment inside the immobilized cells. The proposed sensor keeps its functionality more than 7 weeks stored in deionized water at ambient temperature. For the first 2 weeks the amplitude of the response decreases with only 10% and at the end of the studied 7 weeks period the response was 50% of the initial. The other advantages of the proposed sensor are: the dissolved Oxygen is used as a mediator which concentration can be reliably and interferences free measured by the aim of a Clark type Oxygen Probe applied as a transducer; reproducible bacterial membranes can be elaborated by filtration of resuspended bacterial culture after preliminary determination of its activity; application of membranes containing lyophilized bacteria capable to be conserved infinitely long time and activated just before their application; negligible cost compared with the sensors based on immobilized enzymes. The steady-state response of the proposed bacterial sensor to choline obtained in 200 s is linear in the investigated concentration range up to 2 × 104 mol dm3, with detection limit of 8 × 108 mol dm3 and sensitivity of 4 × 101 μA cm3 mol1, at pH 6, temperature of 25 °C and stirring rate of 300 rpm. Choline is formed as a result of the catalytic hydrolysis (depending on the cholinesterase activity) of the substrate acetylcholine. Linear calibration graph for cholinesterase activity determination was obtained in the range up to 11 mU cm3, with a slope of 1.97 × 102 μA cm3 mU1, at pH 6, temperature of 25 °C and stirring rate of 300 rpm. The tests with reconstituted lyophilized serum with known activity used as a control sample confirm the accuracy of the proposed method. The relative error of the determination was only 2.82%.
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Bacterial sensors based on Acidithiobacillus ferrooxidans Part II. Cr(VI) determination
Biosensors and Bioelectronics, 2006Co-Authors: Roumen Zlatev, Jean-pierre Magnin, Patrick Ozil, Margarita StoytchevaAbstract:The aerobic acidophilic bacterium Acidithiobacillus ferrooxidans oxidizes Fe2+ and S2O32 ions by consuming Oxygen. An amperometric biosensor was designed including an Oxygen Probe as transducer and a recognition element immobilized by a suitable home-made membrane. This biosensor was used for the indirect amperometric determination of Cr2O72 ions owing to methods based on a mediator (Fe2+) or titration. Using the mediator, the biosensor response versus Cr2O72 was linear up to 0.4 mmol L1, with a response time of, respectively, 51 s (2 × 105 mol L1 Cr2O72) and 61 s (6 × 105 mol L1 Cr2O72). The method sensitivity was 816 μA L mol1. Response time and measurement sensitivity depended on membrane material and technique for biomass immobilization. For example, their values were 90 s200 μA L mol1 when using a glass-felt membrane and 540 s4.95 μA L mol1 with a carbon felt one to determine a concentration of 2 × 105 mol L1 Cr2O72. For the titration method, the biosensor is used to determine the equivalence point. The relative error of quantitative analysis was lower than 5%.
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Bacterial sensors based on Acidithiobacillus ferrooxidans Part I. Fe2+ and S2O32 determination
Biosensors and Bioelectronics, 2006Co-Authors: Roumen Zlatev, Jean-pierre Magnin, Patrick Ozil, Margarita StoytchevaAbstract:An amperometric bacterial sensor with current response to Fe2+ and S2O32– ions has been designed by immobilizing an acidophilic biomass of Acidithiobacillus ferrooxidans on a multi disk flat-front Oxygen Probe. The bacterial layer was located between the Oxygen Probe and a membrane of cellulose. A filtration technique was used to yield the bacterial membranes having reproducible activity. The decrease of O2 flow across the bacterial layer is proportional to the concentration of the dosed species. The dynamic range appeared to be linear for the Fe2+ ions up to 2.5 mmol L–1 with a detection limit of 9 × 10–7 mol L–1 and a sensitivity of 0.25 A L mol–1. The response of the biosensor is 84 s for a determination of 2 × 10–4 mol L–1 Fe2+. Optimizing the Fe2+ determination by A. ferrooxidans sensor was carried out owing to Design of Experiments (DOE) methodology and empirical modelling. The optimal response was thus obtained for a pH of 3.4, at 35 °C under 290 rpm solution stirring. S2O32– concentration was determined at pH 4.7, so avoiding its decomposition. The concentration range was linear up to 0.6 mmol L–1. Sensitivity was 0.20 A L mol–1 with a response time of 207 s for a 2 × 10–4 mol L–1 S2O32– concentration.
