Nanqiang Li

Electrocatalytic Oxidation of Norepinephrine at a Glassy Carbon Electrode Modified with Single Wall Carbon Nanotubes

The voltammetric behavior of norepinephrine (NE) was studied at a glassy carbon (GC) electrode modified with single wall carbon nanotubes (SWNTs). In pH 5.72 B-R buffer solution, the SWNT-modified electrode shows high electrocatalytic activity toward NE oxidation. One well-defined reversible redox couple is obtained at scan rates lower than 0.15 V s−1. The peak current increases linearly with the concentration of NE in the range of 1.0×10−5 - 1.1×10−3 mol dm−3. The detection limit is 6.0×10−6 mol dm−3 and the diffusion coefficient (D) of NE is 8.53×10−6 cm2 s−1. The SWNT was characterized with scanning electron microscope (SEM). Furthermore, the SWNT-modified electrode has favorable electrocatalytic activity with dopamine, epinephrine, and ascorbic acid.

Electrocatalytic oxidation of 3,4-dihydroxyphenylacetic acid at a glassy carbon electrode modified with single-wall carbon nanotubes

Abstract The voltammetric behavior of 3,4-dihydroxyphenylacetic acid (DOPAC) was studied at a glassy carbon (GC) electrode modified with single-wall carbon nanotubes (SWNTs). In 0.1 M HAc–NaAc buffer solution (pH 4.4), the SWNT-modified electrode shows high electrocatalytic activity toward oxidation of DOPAC. One well-defined redox couple is obtained. The peak current increases linearly with the concentration of DOPAC in the range of 1.0×10 −6 –1.2×10 −4 M. The detection limit is 4.0×10 −7 M. The results indicate that DOPAC undergoes a two-electron oxidation to o -quinone followed by a dimerization reaction. Rate constant for this dimerization reaction was calculated to be 2.10×10 3 dm 3 mol −1 s −1 . The SWNT was characterized with scanning electron microscope (SEM). This SWNT-modified electrode can also separate the electrochemical responses of DOPAC and 5-hydroxytryptamine (5HT).

Electrochemical studies of rutin interacting with hemoglobin and determination of hemoglobin

Electrochemical investigation of the interaction of rutin (Rt) with hemoglobin (Hb) at a glassy carbon electrode is reported for the first time. With the addition of hemoglobin in a rutin solution, both the reduction and oxidation currents decrease with few changes in the peak potentials. The reaction of rutin with hemoglobin forms a nonelectroactive supramolecular complex Hb-Rt. The equilibrium constant for complex is calculated to be 3.4x10(6). A satisfactory result has been obtained for the determination of hemoglobin in clinical blood samples.

Electrochemical studies of quercetin interacting with DNA

An electrochemical investigation of the interaction between quercetin and DNA is reported for the first time. When DNA was added into quercetin solution, both the reduction and oxidation currents of quercetin decreased with few changes in the peak potentials. There was no great difference between the electrochemical parameters determined from the native quercetin solution and those from the solution mixed with DNA. We assume that quercetin interacting with DNA produces an electrochemically inactive supramolecular complex via intercalation. Comparing the phenomena motioned above with those of interaction between morin and DNA, we infer the possible active part of quercetin that interacts with DNA.

Studies of the electrochemical behavior of epinephrine at a homocysteine self-assembled electrode

The self-assembled electrode with the homocysteine monolayer (Hcy/Au) has been characterized by infrared spectroscopy and ac impedance spectroscopy in electrolyte. The Hcy/Au electrode is demonstrated to promote the electrochemical response of epinephrine (E) by cyclic voltammetry. A pair of well-defined redox waves was obtained and the calculated standard rate constant (k(s)) is 2.1x10(-2) cms(-1) at the self-assembled electrode. The reduction peak of E can be used to determine the concentration of E in presence of ascorbic acid (AA) owing to the Hcy/Au also promoting the electrochemical oxidation of AA.

Investigation of the electrocatalytic behavior of single-wall carbon nanotube films on an Au electrode

Abstract The voltammetric behavior of uric acid (UA) was studied with an Au electrode modified with single-wall carbon nanotubes (SWNTs). In 0.1 M HAc–NaAc buffer solution (pH 5.0), the SWNT-modified electrode shows high electrocatalytic activity toward UA oxidation. The electro-oxidation of UA is an irreversible diffusion-controlled process with a diffusion coefficient (D) of 8.85×10−6 cm2 s−1. The peak current increases linearly with the concentration of UA in the range of 4.0×10−6–7.0×10−4 M. The detection limit is 1.0×10−6 M. The SWNT was characterized with scanning electron microscopy (SEM). Furthermore, the SWNT-modified electrode has favorable electrocatalytic activity toward dopamine and norepinephrine. This SWNT-modified electrode can also separate the electrochemical responses of uric acid, norepinephrine and ascorbic acid.

Electrochemical studies of NiTMpyP and interaction with DNA.

In this paper, cyclic voltammetry, linear sweep voltammetry and chronocoulometry in connection with the hang mercury drop electrode were used to study NiTMpyP and its mixture with DNA. The reduction of NiTMpyP in our experimental conditions involves in 4e reduction of TMpyP. NiTMpyP interacting with DNA forms electrochemically non-active complex DNA-2NiTMpyP, which can not be reduced on the Hg electrode. The peak potential of NiTMpyP does not shift and its electrochemical kinetic parameters indicate no significant change in the presence of DNA. However, the reduction current of NiTMpyP decreases obviously due to the formation of DNA-2NiTMpyP, which implies its equilibrium concentration decreases when DNA was mixed. The decrease of peak current is proportional to DNA concentration, which can be applied to estimate DNA concentration.

Electrocatalytic response of dopamine at a dl-homocysteine self-assembled gold electrode

Abstract The gold electrode self-assembled with the homocysteine monolayer (Hcy/Au) is demonstrated to catalyze the electrochemical response of dopamine (DA) by cyclic voltammetry. A pair of well-defined redox waves was obtained and the calculated standard rate constant ( k s ) is 2.1×10 −2 cm/s at the self-assembled electrode. The reduction peak of DA can be used to determine the concentration of DA in presence of ascorbic acid (AA) owing to the Hcy/Au also catalyzing the electrochemical oxidation of AA.

Electrocatalytic response of dopamine at a thiolactic acid self-assembled gold electrode

Abstract The thiolactic acid (TLA) self-assembled monolayer modified gold electrode (TLA/Au) is demonstrated to catalyze the electrochemical response of dopamine (DA) by cyclic voltammetry. A pair of well-defined redox waves were obtained and the calculated standard rate constant ( k s ) is 0.525 cm/s at the self-assembled electrode. The electrode reaction is a reversible process. The oxidation peak of DA can be used to determine the concentration of DA. The peak current and the concentration of DA have a linear relationship in the range of 4.0×10 −5 –8.0×10 −4 mol/l. The detection limit is 3.0×10 −6 mol/l. The TLA-SAM was characterized with X-ray photoelectron spectroscopy (XPS) and a contact angle goniometer.

Electrocatalytic oxidation of norepinephrine at a reduced C60-[dimethyl-(β-cyclodextrin)]2 and Nafion chemically modified electrode

Abstract The reduced C 60 -[dimethyl-(β-cyclodextrin)] 2 /Nafion chemically modified electrode is demonstrated to catalyze the electrochemical response of norepinephrine (NE) by cyclic voltammetry. A pair of well-defined redox waves were obtained and the calculated standard rate constant ( k s ) is 4.4×10 −3 cm s −1 at this reduced CME, indicating that the reduced C 60 -[dimethyl-(β-cyclodextrin)] 2 can act as promoter to the electron transfer of NE.