The Experts below are selected from a list of 255 Experts worldwide ranked by ideXlab platform
Quansheng Chen - One of the best experts on this subject based on the ideXlab platform.
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a system composed of polyethylenimine capped upconversion nanoparticles copper ii hydrogen peroxide and 3 3 5 5 Tetramethylbenzidine for colorimetric and fluorometric determination of glyphosate
Mikrochimica Acta, 2019Co-Authors: Lan Yang, Arumugam Selva Sharma, Min Chen, Quansheng ChenAbstract:A dual (colorimetric and fluorometric) method is described for sensitive and selective determination of the herbicide glyphosate. It is based on the use of a system composed of polyethylenimine-capped NaGdF4:Yb,Er upconversion nanoparticles (UCNPs), copper(II) ions, hydrogen peroxide and 3,3′,5,5′-Tetramethylbenzidine. The physicochemical and photophysical properties of the polyethylenimine-capped UCNPs were characterized by various spectroscopic and microscopic techniques. The fluorescence of the UCNPs (with main emission peaks at 548 and 660 nm under 980 nm excitation) is reduced in the presence of Cu(II) because of the formation of a blue oxidation product of 3,3′,5,5′-Tetramethylbenzidine as a result of the peroxidase mimicking activity of Cu(II). In the presence of glyphosate, its strong affinity for Cu(II) leads to the formation of N-(phosphonomethyl)glycine copper(II) complexes. This inhibits the quenching ability and catalysis activity of Cu(II). Hence, fluorescence is increasingly less reduced. Fluorescence at 660 nm increases linearly in the 0.05 to 125 μg·mL−1 glyphosate concentration range and the detection limit is found 9.8 ng·mL−1. The colorimetric assay (performed at 652 nm) has a detection ranges from 5 to 125 μg·mL−1, and the limit of detection is 1 μg·mL−1.
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A system composed of polyethylenimine-capped upconversion nanoparticles, copper(II), hydrogen peroxide and 3,3′,5,5′-Tetramethylbenzidine for colorimetric and fluorometric determination of glyphosate
Mikrochimica Acta, 2019Co-Authors: Lan Yang, Arumugam Selva Sharma, Min Chen, Quansheng ChenAbstract:A dual (colorimetric and fluorometric) method is described for sensitive and selective determination of the herbicide glyphosate. It is based on the use of a system composed of polyethylenimine-capped NaGdF4:Yb,Er upconversion nanoparticles (UCNPs), copper(II) ions, hydrogen peroxide and 3,3′,5,5′-Tetramethylbenzidine. The physicochemical and photophysical properties of the polyethylenimine-capped UCNPs were characterized by various spectroscopic and microscopic techniques. The fluorescence of the UCNPs (with main emission peaks at 548 and 660 nm under 980 nm excitation) is reduced in the presence of Cu(II) because of the formation of a blue oxidation product of 3,3′,5,5′-Tetramethylbenzidine as a result of the peroxidase mimicking activity of Cu(II). In the presence of glyphosate, its strong affinity for Cu(II) leads to the formation of N-(phosphonomethyl)glycine copper(II) complexes. This inhibits the quenching ability and catalysis activity of Cu(II). Hence, fluorescence is increasingly less reduced. Fluorescence at 660 nm increases linearly in the 0.05 to 125 μg·mL−1 glyphosate concentration range and the detection limit is found 9.8 ng·mL−1. The colorimetric assay (performed at 652 nm) has a detection ranges from 5 to 125 μg·mL−1, and the limit of detection is 1 μg·mL−1.
Zhengbo Chen - One of the best experts on this subject based on the ideXlab platform.
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highly sensitive colorimetric detection of glucose through glucose oxidase and cu2 catalyzed 3 3 5 5 Tetramethylbenzidine oxidation
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2019Co-Authors: Xin Li, Zhengbo ChenAbstract:Abstract We develop a glucose oxidase (GOx)-mediated strategy for detecting glucose based on oxidized 3,3′,5,5′-Tetramethylbenzidine (oxTMB), which is generated from Cu2+-catalyzed 3,3′,5,5′-Tetramethylbenzidine (TMB)-H2O2 reaction, as colorimetric readout. The sensing system involves two processes: generation of H2O2 from GOx-catalyzed oxidation of glucose, and H2O2-induced the oxidization of TMB via the catalysis of Cu2+. The H2O2 formed by GOx-catalyzed oxidation of glucose oxidizes colorless TMB to blue oxTMB, thus enhancing the absorbance intensity at 670 nm. Therefore, we draw a conclusion that the enhancement in colorimetric signal relies directly on H2O2 concentration, which, in turn, depends on glucose concentration. This color change can be used not only for visual detection of glucose by naked eyes but for reliable glucose quantification in the range from 1 to 100 nM with a detection limit of 0.21 nM. The method possesses the following advantages: simple design, low experimental cost, and no any additional experimental equipment for heating, illuminating, or bubbling.
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Highly sensitive colorimetric detection of glucose through glucose oxidase and Cu2+-catalyzed 3,3′,5,5′-Tetramethylbenzidine oxidation
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2019Co-Authors: Xin Li, Zhengbo ChenAbstract:Abstract We develop a glucose oxidase (GOx)-mediated strategy for detecting glucose based on oxidized 3,3′,5,5′-Tetramethylbenzidine (oxTMB), which is generated from Cu2+-catalyzed 3,3′,5,5′-Tetramethylbenzidine (TMB)-H2O2 reaction, as colorimetric readout. The sensing system involves two processes: generation of H2O2 from GOx-catalyzed oxidation of glucose, and H2O2-induced the oxidization of TMB via the catalysis of Cu2+. The H2O2 formed by GOx-catalyzed oxidation of glucose oxidizes colorless TMB to blue oxTMB, thus enhancing the absorbance intensity at 670 nm. Therefore, we draw a conclusion that the enhancement in colorimetric signal relies directly on H2O2 concentration, which, in turn, depends on glucose concentration. This color change can be used not only for visual detection of glucose by naked eyes but for reliable glucose quantification in the range from 1 to 100 nM with a detection limit of 0.21 nM. The method possesses the following advantages: simple design, low experimental cost, and no any additional experimental equipment for heating, illuminating, or bubbling.
Dario Compagnone - One of the best experts on this subject based on the ideXlab platform.
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sub micromolar detection of hydrogen peroxide at a peroxidase Tetramethylbenzidine solid carbon paste electrode
Analytical Letters, 1998Co-Authors: Dario Compagnone, P Schweicher, J M Kauffman, George G GuilbaultAbstract:Abstract Horseradish peroxidase and the substrate 3,3′,5,5′-Tetramethylbenzidine have been incorporated into a solid carbon paste electrode for the development of a H2O2 probe. The electrode exhibited a detection limit of 10−8 mol/L H2O2 and a linearity extended over three orders of magnitude. Glucose oxidase was then used in the paste or covalently immobilized onto a preactivated membrane for the detection of glucose. Using both immobilization procedures the measurement of glucose in the micromolar range and an extended linearity was achieved.
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Sub-micromolar detection of hydrogen peroxide at a peroxidase/Tetramethylbenzidine solid carbon paste electrode
Analytical Letters, 1998Co-Authors: Dario Compagnone, P Schweicher, J M Kauffman, George G GuilbaultAbstract:Abstract Horseradish peroxidase and the substrate 3,3′,5,5′-Tetramethylbenzidine have been incorporated into a solid carbon paste electrode for the development of a H2O2 probe. The electrode exhibited a detection limit of 10−8 mol/L H2O2 and a linearity extended over three orders of magnitude. Glucose oxidase was then used in the paste or covalently immobilized onto a preactivated membrane for the detection of glucose. Using both immobilization procedures the measurement of glucose in the micromolar range and an extended linearity was achieved.
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3 3 5 5 Tetramethylbenzidine as electrochemical substrate for horseradish peroxidase based enzyme immunoassays a comparative study
Analyst, 1998Co-Authors: G Volpe, R Draisci, G Palleschi, Dario CompagnoneAbstract:The use of 3,3′,5,5′-Tetramethylbenzidine (TMB) as an electrochemical substrate for horseradish peroxidase (HRP) was investigated. HRP activity has been detected using flow injection analysis at a glassy carbon working electrode polarised at +100 mV versus Ag/AgCl in 0.1 mol l–1 citrate–phosphate buffer (pH 5.0). The optimum concentrations were 2 × 10–4 mol l–1 TMB and 10–3 mol l–1 H2O2. The detection limit obtained after 15 min of incubation was 8.5 × 10–14 mol l–1 HRP with the amperometric method. This limit was lower than that obtained using hydroquinone as HRP substrate and comparable to that with the p-aminophenyl phosphate–alkaline phosphatase system. Better performance was achieved with amperometric than spectrophotometric detection using TMB in a competitive ELISA for rabbit immunoglobulin G as a model analyte.
Lan Yang - One of the best experts on this subject based on the ideXlab platform.
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a system composed of polyethylenimine capped upconversion nanoparticles copper ii hydrogen peroxide and 3 3 5 5 Tetramethylbenzidine for colorimetric and fluorometric determination of glyphosate
Mikrochimica Acta, 2019Co-Authors: Lan Yang, Arumugam Selva Sharma, Min Chen, Quansheng ChenAbstract:A dual (colorimetric and fluorometric) method is described for sensitive and selective determination of the herbicide glyphosate. It is based on the use of a system composed of polyethylenimine-capped NaGdF4:Yb,Er upconversion nanoparticles (UCNPs), copper(II) ions, hydrogen peroxide and 3,3′,5,5′-Tetramethylbenzidine. The physicochemical and photophysical properties of the polyethylenimine-capped UCNPs were characterized by various spectroscopic and microscopic techniques. The fluorescence of the UCNPs (with main emission peaks at 548 and 660 nm under 980 nm excitation) is reduced in the presence of Cu(II) because of the formation of a blue oxidation product of 3,3′,5,5′-Tetramethylbenzidine as a result of the peroxidase mimicking activity of Cu(II). In the presence of glyphosate, its strong affinity for Cu(II) leads to the formation of N-(phosphonomethyl)glycine copper(II) complexes. This inhibits the quenching ability and catalysis activity of Cu(II). Hence, fluorescence is increasingly less reduced. Fluorescence at 660 nm increases linearly in the 0.05 to 125 μg·mL−1 glyphosate concentration range and the detection limit is found 9.8 ng·mL−1. The colorimetric assay (performed at 652 nm) has a detection ranges from 5 to 125 μg·mL−1, and the limit of detection is 1 μg·mL−1.
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A system composed of polyethylenimine-capped upconversion nanoparticles, copper(II), hydrogen peroxide and 3,3′,5,5′-Tetramethylbenzidine for colorimetric and fluorometric determination of glyphosate
Mikrochimica Acta, 2019Co-Authors: Lan Yang, Arumugam Selva Sharma, Min Chen, Quansheng ChenAbstract:A dual (colorimetric and fluorometric) method is described for sensitive and selective determination of the herbicide glyphosate. It is based on the use of a system composed of polyethylenimine-capped NaGdF4:Yb,Er upconversion nanoparticles (UCNPs), copper(II) ions, hydrogen peroxide and 3,3′,5,5′-Tetramethylbenzidine. The physicochemical and photophysical properties of the polyethylenimine-capped UCNPs were characterized by various spectroscopic and microscopic techniques. The fluorescence of the UCNPs (with main emission peaks at 548 and 660 nm under 980 nm excitation) is reduced in the presence of Cu(II) because of the formation of a blue oxidation product of 3,3′,5,5′-Tetramethylbenzidine as a result of the peroxidase mimicking activity of Cu(II). In the presence of glyphosate, its strong affinity for Cu(II) leads to the formation of N-(phosphonomethyl)glycine copper(II) complexes. This inhibits the quenching ability and catalysis activity of Cu(II). Hence, fluorescence is increasingly less reduced. Fluorescence at 660 nm increases linearly in the 0.05 to 125 μg·mL−1 glyphosate concentration range and the detection limit is found 9.8 ng·mL−1. The colorimetric assay (performed at 652 nm) has a detection ranges from 5 to 125 μg·mL−1, and the limit of detection is 1 μg·mL−1.
Takafumi Aizawa - One of the best experts on this subject based on the ideXlab platform.
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local density augmentation around acetophenone n n n n Tetramethylbenzidine exciplex in supercritical water
Chemical Physics Letters, 2004Co-Authors: Takafumi Aizawa, Yutaka Ikushima, Mitsuhiro Kanakubo, Richard L Smith, Tohru Saitoh, Nobuhiro SugimotoAbstract:Abstract Local density augmentation around exciplex between acetophenone and N,N, N ′ , N ′ -Tetramethylbenzidine (TMB) in supercritical water was measured by peak shift of transient absorption spectrum at 380 °C and at pressures from 6 to 37 MPa. Large local density augmentation was observed at lower densities. The excess density, defined by the difference between local density and bulk density, exhibited a maximum at approximately 0.15 g cm −3 . Our results show that the degree of local density augmentation that exists in supercritical water is comparable to that observed in supercritical carbon dioxide in some system.
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Local density augmentation around acetophenone N,N,N′,N′-Tetramethylbenzidine exciplex in supercritical water
Chemical Physics Letters, 2004Co-Authors: Takafumi Aizawa, Yutaka Ikushima, Mitsuhiro Kanakubo, Richard L Smith, Tohru Saitoh, Nobuhiro SugimotoAbstract:Abstract Local density augmentation around exciplex between acetophenone and N,N, N ′ , N ′ -Tetramethylbenzidine (TMB) in supercritical water was measured by peak shift of transient absorption spectrum at 380 °C and at pressures from 6 to 37 MPa. Large local density augmentation was observed at lower densities. The excess density, defined by the difference between local density and bulk density, exhibited a maximum at approximately 0.15 g cm −3 . Our results show that the degree of local density augmentation that exists in supercritical water is comparable to that observed in supercritical carbon dioxide in some system.
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pressure dependence of acetophenone n n n n Tetramethylbenzidine exciplex in supercritical carbon dioxide
Chemical Physics Letters, 2002Co-Authors: Takafumi Aizawa, Siriporn Janttarakeeree, Yutaka Ikushima, Norio SaitohAbstract:Abstract The pressure dependence of the formation and decay processes of exciplex between two neutral species acetophenone (AP) and N , N , N ′ , N ′ -Tetramethylbenzidine (TMB) in supercritical carbon dioxide was investigated by a transient absorption technique at 40 °C and at pressures from 9.0 to 14.7 MPa. The exciplex formation rate constant could be described by the Stokes–Einstein/Debye (SE/D) equation. The trend of the exciplex decay rate constant showed local density augmentation around the exciplex in the low-pressure region.
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Pressure dependence of acetophenone N,N,N′,N′-Tetramethylbenzidine exciplex in supercritical carbon dioxide
Chemical Physics Letters, 2002Co-Authors: Takafumi Aizawa, Siriporn Janttarakeeree, Yutaka Ikushima, Norio SaitohAbstract:Abstract The pressure dependence of the formation and decay processes of exciplex between two neutral species acetophenone (AP) and N , N , N ′ , N ′ -Tetramethylbenzidine (TMB) in supercritical carbon dioxide was investigated by a transient absorption technique at 40 °C and at pressures from 9.0 to 14.7 MPa. The exciplex formation rate constant could be described by the Stokes–Einstein/Debye (SE/D) equation. The trend of the exciplex decay rate constant showed local density augmentation around the exciplex in the low-pressure region.
