Lanqun Mao

Electrochemical Nitric Oxide Sensors Based on Electropolymerized Film of M(salen) with Central Ions of Fe, Co, Cu, and Mn

Electropolymerized film of metal ethylenebis(salicylideneiminate) [(M(salen), M=Co, Fe, Cu and Mn] was utilized as material for development of an electrochemical sensor for the determination of NO in solution. The sensors based on polymeric M(salen) were prepared by a means of electropolymerization with cyclic voltammetry (CV) in acetonitrile solution containing M(salen) for optimized cycles. Nafion was used as a second coating to the sensors and differential pulse amperometry (DPA) was used as a subsequent determination technique. The resulted sensors were found to display good activity toward the oxidation of NO with low detection limits and a good linear relationship between the current and NO concentration. The mechanism of the polymeric M(salen) modified sensor was preliminarily studied by using a technique of quantum chemistry and proposed to be a three-dimensional catalytic pattern by conjugation of the electron of the NO molecule and the polymeric M(salen).

Determination of nitric oxide with ultramicrosensors based on electropolymerized films of metal tetraaminophthalocyanines

Preparation and electrochemical responses to nitric oxide (NO) of the electropolymerized films of metal tetraaminophthalocyanines (MTAPc, M=Co, Ni, Cu) are studied to test them as molecular devices for design and construction of amperometric ultramicrosensors for selective and sensitive determination of NO. The ultramicrosensors based on electropolymerized films of MTAPc and Nafion, are found to show a low detection limit, high selectivity and sensitivity to NO determination. The potential interference from some endogenous electroactive substances in biological tissues, such as catecholamines and their metabolites, ascorbic acid (AA), uric acid (UA), and nitrite (NO(2)(-)), the metabolite of NO at the concentrations higher than those in biological systems could be eliminated by using a technique of DPV or DPA and further coating the modified ultramicrosensors with a layer of Nafion.

Glucose and choline on-line biosensors based on electropolymerized Meldola's blue

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 (H(2)O(2)) 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 H(2)O(2) at a potential of -0.30 V (versus AgCl/Ag). The H(2)O(2) sensing system was applied to construct glucose and choline on-line sensors by wiring H(2)O(2) 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.

Amperometric Biosensor for Glutathione Based on Osmium‐Polyvinylpyridine Gel Polymer and Glutathione Sulfhydryl Oxidase

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, 3M 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.

Electrochemical Microsensor for In Vivo Measurements of Oxygen Based on Nafion and Methylviologen Modified Carbon Fiber Microelectrode

An electrochemical microsensor based on carbon fiber microelectrode (CFME) chemically modified with the perfluorinated cation-exchange polymer, Nafion and methylviologen (MV) and its application for in vivo voltammetric measurements of oxygen (O2) are described. The microsensor shows a high catalytic activity for the reduction of O2 with a good reproducibility, high sensitivity and selectivity and significant ability against electrode fouling. The current is linear with the concentration of O2in a range from 9.0×10–6to 2.0×10–4 mol/L with a calculated detection limit, at a signal-to-noise ratio of 3 to 1, of 5.0×10–6 mol/L and correlation coefficient of 0.9985. The relative standard deviation for 2.0×10–4 mol/L O2 is 1.7% (n = 2). Some compounds common to biological fluids such as glucose, ascorbic acid, uric acid, catecholamine, glutamate, glutathione, Mg2+, Ca2+, Na+, K+and Cl–are tested in vitro and show no interferences with the voltammetric responses to O2. In vivo performance of the O2 microsensors is demonstrated by measurements of local changes in O2 in the brain of anesthetized rat before and during transient ischemia.

A novel thin-layer amperometric detector based on chemically modified ring-disc electrode and its application for simultaneous measurements of nitric oxide and nitrite in rat brain combined with in vivo microdialysis.

A novel thin-layer amperometric detector (TLAD) based on chemically modified ring-disc electrode and its application for simultaneous measurements of nitric oxide (NO) and nitrite (NO(2)(-)) in rat brain were demonstrated in this work. The ring-disc electrode was simultaneously sensitive to nitric oxide (NO) and nitrite (NO(2)(-)) by modifying its inner disc with electropolymerized film of cobalt(II) tetraaminophthalocyanine (polyCoTAPc)/Nafion and its outer ring with poly(vinylpyridine) (PVP), respectively. The ring-disc electrode was used to constitute a novel TLAD in radial flow cell for simultaneous measurements of NO and NO(2)(-) in rat brain combined with techniques of high performance liquid chromatography (HPLC) and in vivo microdialysis. It was found that the basal concentration of NO in the caudate nucleus of rat brain is lower than 1.0x10(-7) mol l(-1), NO(2)(-) concentration is 5.0x10(-7) mol l(-1) and NO exists in brain maybe mainly in the form of its decomposed product.

A New Ultramicrosensor for Nitric Oxide Based on Electropolymerized Film of Nickel Salen

Abstract A new amperometric ultramicrosensor for the determination of nitric oxide (NO) is described. The ultramicrosensor, which is based on an electropolymerized film of ethylenebis(salicylideneiminate) nickel [Ni(salen)] and Nafion, shows a low detection limit, high selectivity and sensitivity to NO determination. The oxidation current (measured by a differential pulse amperometric method) is linear with NO concentration ranging from 1.0x10−8 to 4.0x10−6 mol/L with a calculated detection limit, at a signal to noise ratio of three, equal to 5.0x10−9 mol/L. Some endogenous electroactive substances in biological tissues, such as dopamine, 5-HT and nitrite do not interfere with NO determination at the concentrations higher than those in biological systems. The ultramicrosensor could be employed for in vivo measurements of NO. The mechanism of the response of the ultramicrosensor to NO is also studied.

A Novel Electrochemical Microsensor for Nitric Oxide Based on Electropolymerized Film ofo‐Aminobenzaldehyde‐ethylene‐diamine Nickel

A novel electrochemical microsensor for nitric oxide (NO) is described. The microsensor, which is based on an electropolymerized film ofo-aminobenzaldehyde-ethylene-diamine nickel [Ni(ABED)] and Nafion, shows a low detection limit, high selectivity and sensitivity to NO determination. The oxidation current (measured by differential pulse amperometric method) is linear with NO concentration ranging from 1.0×10−8to 1.0×10−6mol/L with a calculated detection limit, at a signal-to-noise ratio of three, equal to 5.0×10−9mol/L and a linear coefficient of 0.9921. Some endogenous electroactive substances in biological tissues, such as ascorbate, dopamine, 5-hydroxytryptamine, cysteine and nitrite do not interfere with NO determination at the concentrations higher than those in biological systems. The microsensor should be promising for in vivo measurement of NO. The mechanism of the response of the microsensor to NO is preliminary studied.

Measurement of dioxygen by electrocatalytic reduction on microelectrodes modified with Nafion and methyl viologen

Nafion/methyl viologen (MV) has been chemically modified on a gold disk microelectrode (GDME). The electrochemistry of the Nafion/MV modified GDME is investigated by cyclic voltammetry (CV). Linear sweep voltammetry (LSV) and differential pulse amperometry (DPA) show that the Nafion/MV modified GDME exhibits very high electrocatalytic activity toward dioxygen reduction with good reproducibility and high sensitivity. The electrocatalytic peak current is found to be linear with the dioxygen concentration in the range of 3.44x10(-7) to 2.59x10(-4) mol l(-1) (at 25 degrees C), with a correlation coefficient of 0.9978. The detection limit (signal/noise=3) is calculated to be 0.19 mumol l(-1). The response time of the microsensor for dioxygen measurement is less than 15 s. For ten parallel measurements for 8.50 mumol l(-1) dioxygen, the relative standard deviation (RSD) is found to be 2.7%. The sensitivity of the microsensor is 0.17 nA mumol(-1) l(-1). This microsensor has been successfully employed to measure the concentration of dioxygen in real samples. The quantity of dioxygen, released from the three kinds of chloroplasts of plant leaves under different illumination, is monitored by the Nafion/MV modified gold microsensor. In order to survey the dioxygen concentration in vivo, a Nafion/MV modified carbon fiber microelectrode (CFME) is fabricated by a modification procedure similar to that of the Nafion/MV GDME. As a preliminary test, the dioxygen levels in the different areas of rat brain are determined by the Nafion/MV modified carbon fiber microsensors. The mechanism of the catalytic reaction is also addressed.