Zong-Li Wang

Modification of glassy carbon and gold electrodes with DNA

The modification of glassy carbon and gold electrodes with DNA by adsorption or covalent immobilization in a mono- or submonolayer has been investigated using the couple Co(bpy)3+2+3 as an indicator. It has been found that when the solution containing double stranded or single stranded DNA is evaporated to dryness, dehydrated DNA molecules can be irreversibly adsorbed on the surfaces of glassy carbon electrodes, in an amount close to that of the saturated adsorptive monolayer. The DNA-adsorbed layer on glassy carbon electrodes is unstable to bases, but stable to 1 M HCl solution. The adsorption of DNA on the electrodes can be evaluated from the increase in the peak current, the decrease in the value of ΔEp, and the negative shift in the value of Eo′ for the Co(bpy)3+2+3 couple. DNA is very strongly adsorbed on the oxidized surfaces of glassy carbon electrodes, and the adsorptive layer is very stable towards heating. The covalent immobilization of DNA directly onto the electrode surfaces is impossible due to considerable steric hindrance; but if the active groups (sites) on the electrode surfaces are elongated with other suitable molecules, the covalent immobilization of DNA becomes possible on the electrode surfaces. The quantity of covalently immobilized DNA at the electrodes reported in the paper is about 31% of the saturated monolayer.

Recent advances in single-cell analysis using capillary electrophoresis and microfluidic devices.

Cells are the fundamental unit of life, and studies on cell contribute to reveal the mystery of life. However, since variability exists between individual cells even in the same kind of cells, increased emphasis has been put on the analysis of individual cells for getting better understanding on the organism functions. During the past two decades, various techniques have been developed for single-cell analysis. Capillary electrophoresis is an excellent technique for identifying and quantifying the contents of single cells. The microfluidic devices afford a versatile platform for single-cell analysis owing to their unique characteristics. This article provides a review on recent advances in single-cell analysis using capillary electrophoresis and microfluidic devices; focus areas to be covered include sampling techniques, detection methods and main applications in capillary electrophoresis, and cell culture, cell manipulation, chemical cytometry and cellular physiology on microfluidic devices.

DNA-modified electrodes; part 4: optimization of covalent immobilization of DNA on self-assembled monolayers.

The covalent immobilization of DNA onto self-assembled monolayer (SAM) modified gold electrodes (SAM/Au) was studied by X-ray photoelectron spectrometry and electrochemical method so as to optimize its covalent immobilization on SAMs. Three types of SAMs with hydroxyl, amino, and carboxyl terminal groups, respectively, were examined. Results obtained by both X-ray photoelectron spectrometry and cyclic voltammetry show that the largest covalent immobilization amount of dsDNA could be gained on hydroxyl-terminated SAM/Au. The ratio of amount of dsDNA immobilized on hydroxyl-terminated SAMs to that on carboxyl-terminated SAMs and to that on amino-terminated SAMs is (3-3.5): (1-1.5): 1. The dsDNA immobilized covalently on hydroxyl-terminated SAMs accounts for 82.8-87.6% of its total surface amount (including small amount of dsDNA adsorbed). So the hydroxyl-terminated SAM is a good substrate for the covalent immobilization of dsDNA on gold surfaces.

DNA-modified electrodes. Part 2. Electrochemical characterization of gold electrodes modified with DNA

Abstract Gold electrodes were modified with DNA by adsorption. The DNA-modified electrodes were electrochemically characterized with Co(bpy) 3 3+ , a electroactive DNA-binding complex, as an indicator. It is interesting that the pair of redox peaks of Co(bpy) 3 3+ split into two pairs at dsDNA-modified gold electrodes. One pair of peaks shifts negative, and the peak current increases notably; another pair of peaks shifts positive. These suggest that dsDNA has been immobilized onto gold electrode surfaces and the layer of dsDNA on the surfaces can bind Co(bpy) 3 3+ in two different ways. Gold electrodes can be modified also with ssDNA by adsorption but only one pair of peaks of Co(bpy) 3 3+ appears at ssDNA-modified gold electrodes. The amount of Co(bpy) 3 3+ enriched by the layers of dsDNA or ssDNA adsorbed at gold electrodes was estimated from the peak charge of Co(bpy) 3 3+ reduction at the electrodes obtained by CV. The stability of the DNA-modified electrodes was investigated. The DNA modification layer on gold surfaces is unstable to alkali and to heat, but stable to acid solutions and very stable in long stock in a dry state. A comparison of modifications of gold, platinum and glassy carbon with DNA was carried out.

Determination of dopamine in single rat pheochromocytoma cell by capillary electrophoresis with amperometric detection

A method is described for the direct identification of dopamine in single cultured rat pheochromocytoma cell by capillary electrophoresis (CE) with amperometric detection. The separation and detection conditions were optimized. The dopamine in single cell analysis was identified based on the migration time of standard dopamine and internal standard (epinephrine). The amount of dopamine in a single cell ranged from 0.29 to 1.28 fmol.

Real-time monitoring of NO release from single cells using carbon fiber microdisk electrodes modified with single-walled carbon nanotubes.

In this paper, a novel NO electrochemical microsensor, which is fabricated by modifying the surface of a carbon fiber microdisk electrode (CFMDE, diameter: 5-7 microm) with single-walled carbon nanotubes (SWNTs) and Nafion membrane, is reported for the first time. The modification of SWNTs dramatically improves the sensitivity of CFMDEs, and the detection limit for NO is 4.3 nM that is nearly 10 times lower than that from the bare one and lower than most NO electrochemical sensors reported before. The Nafion membrane offers a good barrier to some interferents such as nitrite and ascorbic acid without losing response speed to NO. The sensor has been successfully applied to the measurement of NO release from single isolated human umbilical vein endothelial cells (HUVECs). Real-time amperometric data show that the addition of l-arginine (l-arg) or acetylcholine (ACh) can cause a quick increase in NO production with a maximum concentration of 232+/-44 nM (n=5) and 159+/-29 nM (n=5), respectively.

DNA-modified electrodes - Part 3: spectroscopic characterization of DNA-modified gold electrodes

DNA-modified gold electrodes were characterized by scanning tunneling microscopy (STM), Raman spectroscopy, in situ UV/Vis reflection spectroscopy, X-ray photoelectron spectroscopy (XPS) and alternating current (AC) impedance. It has been found that dsDNA adsorbed firmly on gold surfaces lies strand-on in an ordered saturated monolayer, and ssDNA strands exist in a honeycomb-like form on the surfaces. The bases and phosphate groups of DNA backbone interacting with gold electrode surfaces play an important role in DNA immobilization onto gold electrode surfaces.

Electrocatalysis of metalloporphyrins: Part 9. Catalytic electroreduction of cystine using water-soluble cobalt porphyrins

Abstract The electrocatalytic reduction of cystine with water-soluble cobalt(II) tetrakis(4-trimethylammoniumphenyl)porphyrin (CoTTAPP) and cobalt(II) tetrakis(4-sulphophenyl)porphyrin (CoTSPP) in 0.2 M H 2 SO 4 solution was investigated. The experimental results of cyclic voltammetry and the rotating disc electrode technique indicated that both CoTTAPP and CoTSPP obviously exhibit catalytic activity for cystine reduction in 0.2 M H 2 SC 4 solution. Cystine reduction at a glassy carbon electrode in 0.2 M H 2 SO 4 solution containing CoTTAPP or CoTSPP is an irreversible, simple charge-transfer reaction. The number of electrons involved in the rate-determining step is 1. The rate constants of cystine reduction in these systems were calculated to be 2.9 × 10 −3 −7.3 × 10 −3 cm s −1 in the potential range of −0.80 to −0.90 V (vs. SCE). It is demonstrated that Co(II) complexing in the N 4 internal ring of porphyrin plays the main role in the electrocatalytic reduction of cystine. The reaction mechanism of cystine reduction electrocatalysed by CoTTAPP or CoTSPP in 0.2 M H 2 SO 4 solution is discussed.

Monitoring of vesicular exocytosis from single cells using micrometer and nanometer-sized electrochemical sensors

AbstractCommunication between cells by release of specific chemical messengers via exocytosis plays crucial roles in biological process. Electrochemical detection based on ultramicroelectrodes (UMEs) has become one of the most powerful techniques in real-time monitoring of an extremely small number of released molecules during very short time scales, owing to its intrinsic advantages such as fast response, excellent sensitivity, and high spatiotemporal resolution. Great successes have been achieved in the use of UME methods to obtain quantitative and kinetic information about released chemical messengers and to reveal the molecular mechanism in vesicular exocytosis. In this paper, we review recent developments in monitoring exocytosis by use of UMEs-electrochemical-based techniques including electrochemical detection using micrometer and nanometer-sized sensors, scanning electrochemical microscopy (SECM), and UMEs implemented in lab-on-a-chip (LOC) microsystems. These advances are of great significance in obtaining a better understanding of vesicular exocytosis and chemical communications between cells, and will facilitate developments in many fields, including analytical chemistry, biological science, and medicine. Furthermore, future developments in electrochemical probing of exocytosis are also proposed. FigureIn this paper, we review recent developments in monitoring the exocytosis by use of UMEs-electrochemical-based techniques including electrochemical detection using micrometer and nanometer-sized sensors, Scanning Electrochemical Microscopy (SECM) and UMEs implemented in lab-on-a-chip (LOC) microsystems. These advances are of great significance in obtaining a better understanding of vesicular exocytosis and chemical communications between cells, and will facilitate developments in many fields including analytical chemistry, biological science and medicine. Furthermore, future developments in electrochemical probing of exocytosis are proposed.

Electrocatalysis of metalloporphyrins: Part 13. Electrocatalysis of several water-soluble porphyrins for the oxidation of some small molecules

Abstract The electrocatalysis of three water-soluble porphyrins (tetrakis (4-trimethylammoniumphenyl) porphyrin (H 2 TMAP) and its cobalt complex (CoTMAP) and cobalt tetrakis (4-sulfonatophenyl) porphyrin (CoTSPP)) for the electro-oxidation of some small molecules is reported. The relationship between the electrocatalytic properties of the water-soluble porphyrins and their electrochemical behavior is discussed. The catalysis of the porphyrin ring is related to its reversible transport of electrons. An adduct of H 2 TMAP or CoTMAP with the substrate was observed using the in-situ UV-visible spectroelectrochemical method.