University of North Florida
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Contact Info

Stuart Chalk, Ph.D.
Department of Chemistry
University of North Florida
Phone: 1-904-620-1938
Fax: 1-904-620-3535
Email: schalk@unf.edu
Website: @unf

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Lan Qun Mao

Abbrev:
Mao, L.Q.
Other Names:
Lanqun Mao, Lan-qun Mao
Address:
Department of Research and Development, Bioanalytical Systems Inc., 1-36-6, Oshiage, Sumida-ku, Tokyo 131-0045, Japan
Phone:
+86-10-62646525
Fax:
+86-10-62559373

Citations 5

"Glucose And Choline On-line Biosensors Based On Electropolymerized Meldolas Blue"
Talanta 2000 Volume 51, Issue 1 Pages 187-195
Lanqun Mao and Katsunobu Yamamoto

Abstract: Electropolymerized film of Meldolas blue (MB) was prepared and demonstrated as electron shuttle between the immobilized horse peroxidase (HRP) and glassy carbon electrode (GCE) for sensing hydrogen peroxide (H2O2) produced by enzyme catalytical reactions. Electrochemical polymerization of Meldolas blue was carried out by cyclic voltammetry (CV) in a phosphate buffer solution (pH 7.00) in a potential window from - 0.60 to + 1.30 V. The pH of the electropolymerization solution was found to be closely related to the resulted polymeric MB and the best polymeric film was obtained in a pH 7.00 phosphate buffer. The polymeric MB was demonstrated to shuttle the electron transfer between the immobilized HRP and GCE and utilized as a mediator for HRP immobilized biosensor for biocatalytical reduction of H2O2 at a potential of - 0.30 V (versus AgCl/Ag). The H2O2 sensing system was applied to construct glucose and choline on-line sensors by wiring H2O2 produced by enzyme oxidase catalytical reaction. The possibility of these sensors as on-line detectors for on-line and continuous measurement was explored off-line. The operating potential, interference, and lifetime of these sensors were also examined.
Glucose Choline Voltammetry Electrode Amperometry Sensor Interferences Indirect Apparatus

"Amperometric Biosensor For Glutathione Based On Osmium-polyvinylpyridine Gel Polymer And Glutathione Sulfhydryl Oxidase"
Electroanalysis 2000 Volume 12, Issue 8 Pages 577-582
Lanqun Mao, Katsunobu Yamamoto

Abstract: A new amperometric biosensor based on glutathione sulfhydryl oxidase (GSH-SOx) and osmium-polyvinylpyridine gel polymer (Os-gel-HRP) bilayer film modified glassy carbon (GC) electrode was demonstrated for glutathione (GSH) and glutathione disulfide (GSSG). Os-gel-HRP was applied at glassy carbon (GC) electrode with a surface coverage of 7.1 µL/cm2 to sense hydrogen peroxide based on horseradish peroxide (HRP) catalytic reaction mediated by osmium. GSH-SOx was immobilized at Os-gel-HRP cast coated GC electrode with an approximate surface coverage of 7 U/cm2 by cross-linking with BAS-GSH-SOx in glutaraldehyde vapor for 5 min. The resultant bienzyme-based sensor was tested toward GSH and GSSG with techniques of cyclic voltammetry (CV), flow cell amperometry and flow injection analysis (FIA). The sensor was polarized at 0.0 V (versus Ag/AgCl, 3 M KCl) electrode for the detection of GSH and GSSG in a flow system at a flow rate of 6 µL/min. Linear response to GSH and GSSG in a concentration range from 1 µM to 200 µM and 2 µM to 120 µM was obtained at the sensor with a sensitivity of 1.195 nA/µM and 0.60 nA/µM for GSH and GSSG, respectively. The dependence of current response on pH value of the buffer and operating potential was also tested and optimized.
Derivatization

"Novel Electrochemical Method For Sensitive Determination Of Homocysteine With Carbon Nanotube-based Electrodes"
Biosens. Bioelectron. 2004 Volume 20, Issue 2 Pages 253-259
Kuanping Gong, Yu Dong, Shaoxiang Xiong, Yi Chen and Lanqun Mao

Abstract: An electrochemical method has been successfully demonstrated for sensitive determination of homocysteine (HcySH) with carbon nanotube (CNT)-modified glassy carbon (GC) electrodes. Cyclic voltammetric results clearly show that carbon nanotubes, especially those pretreated with nitric acid, possess an excellent electrocatalytic activity toward the oxidation of HcySH at a low potential (0.0 V versus Ag/AgCl). The remarkable catalytic property of the acid-pretreated CNTs, which is essentially associated with oxygen-containing moieties introduced on the tube surface, has been further exploited as a sensitive determination scheme for HcySH. Continuous-flow amperometric results suggest that the CNT-based electrodes (p-CNT/Nafion/GC), which were prepared by using Nafion to solubilize and further immobilize CNTs on GC electrodes, show striking analytical properties of good stability and reproducibility and strong ability against electrode fouling. Such analytical properties, along with the low operation potential, substantially enable a reliable and sensitive determination of HcySH with a good dynamic linearity up to 60 µM and a detection limit of 0.06 µM (S/N=3). The catalytic mechanism and the possible application of the as-prepared p-CNT/Nafion/GC electrodes for the study of the auto-oxidation of HcySH are also demonstrated and discussed.

"Amperometric On-line Sensor For Continuous Measurement Of Hypoxanthine Based On Osmium-polyvinylpyridine Gel Polymer And Xanthine Oxidase Bienzyme Modified Glassy Carbon Electrode"
Anal. Chim. Acta 2000 Volume 415, Issue 1-2 Pages 143-150
Lanqun Mao and Katsunobu Yamamoto

Abstract: Osmium-polyvinylpyridine gel polymer (Os-gel-horseradish peroxide (HRP)) and xanthine oxidase (XOD) bienzyme-based amperometric biosensor was developed for use in a thin-layer radial flow cell for on-line measurement of hypoxanthine. Glassy carbon electrodes (GCEs) were initially cast-coated with Os-gel-HRP with a surface coverage of 7.1 µl/cm(2) to sense hydrogen peroxide produced from XOD catalytic enzyme reaction based on HRP catalytic reduction mediated by osmium, Then, bovine serum albumin (BSA)/XOD was cross-linked to the Os-gel-HRP-coated glassy carbon electrodes (GCEs) with glutaraldehyde vapor for the measurement of hypoxanthine at 0.0 mV (versus Ag/AgCl). The resultant HRP and XOD bienzyme-based sensors (Os-gel-HRP/XOD/GCEs) were tested with techniques of cyclic voltammetry (CV), on-line amperometry in a flow system and flow injection analysis (FIA). In continuous-flow amperometric experiments, the Os-gel-HRP/XOD/GCEs were quick to stabilize background current and show linear and sensitive response towards hypoxanthine in a concentration range from 0.5 to 80 µM with a detection limit of 0.2 µM (S/N=3). The specificity against ascorbic acid was enhanced by negatively shifting the operating potential to -200 mV versus Ag/AgCl and was demonstrated to be acceptable for on-line performance. The interference from higher than physiological levels of dopamine (DA), norepinephrine (NE), serotonin, their principal metabolites and uric acid was minimal. The dependency of sensor response on pH value of the buffer and operating potential was also tested and optimized.
Hypoxanthine Amperometry Electrode Electrode Detector Optimization Interferences

"Miniaturized Amperometric Biosensor Based On Xanthine Oxidase For Monitoring Hypoxanthine In Cell Culture Media"
Anal. Biochem. 2001 Volume 292, Issue 1 Pages 94-101
Lanqun Mao, Fang Xu, Qi Xu and Litong Jin

Abstract: Fabrication and characterization of miniaturized amperometric hypoxanthine biosensors are described and demonstrated for monitoring hypoxanthine in myocardial cell culture media. The sensors are based on xanthine oxidase (XO) immobilized on carbon fiber microelectrodes (CFMEs) using a composite film of Nafion and electropolymerized phenol (PPh), Nafion was used for XO immobilization because of its film hydrophobicity, enzyme-favored environment., and electrostatic interaction with XO, which was dispersed in Nafion film by immersing the Nafion-coated CFMEs in XO solution for 5 h, PPh film was formed as an overlay on Nafion and XO-modified CFMEs via electropolymerization. Hypoxanthine was measured with the sensor by the oxidation of enzymatic reaction products, hydrogen peroxide (H2O2), and uric acid (UA) at +0.60 V (vs Ag/AgCl). The use of Nafion and PPh as a matrix for XO immobilization yields enhanced specificity, sensitivity, and linearity toward hypoxanthine. A dynamic linear range of 5.0 muM to 1.8 mM was achieved with a calculated detection limit of 1.5 muM (S/N = 3) and a sensitivity of 3.144 nA/mM. In addition, the measurement was virtually interference-free from easily oxidizable species such as UA, ascorbic acid, physiological levels of neurotransmitters, and their principal metabolites. The biosensor was used to monitor hypoxanthine accumulation in myocardial cell culture media, in which the level of extracellular hypoxanthine was found to increase with ischemic tolerance, (C) 2001 Academic Press.
Selectivity Membrane