Jie-Ke Cheng

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.

Ultrasensitive chemiluminescence detection in capillary electrophoresis

Capillary electrophoresis techniques offer high plate numbers and are highly suited for the efficient separations of a wide variety of chemical components in diverse matrices. Because of the small capillary and detection cell dimensions, together with the minute volumes of samples to be injected, sensitive detection schemes based on different physicochemical principles are being developed. One logical approach to increased sensitivity in capillary electrophoresis detection has been the development of chemiluminescence-based detectors. The development of on-line ultrasensitive chemiluminescence detection (referred to the concentration detection limit of nM order of magnitude or mass detection limit of amol order of magnitude) in capillary electrophoresis system is reviewed. The applications and limitations of the current detection methodology are briefly considered and future prospects for the development are discussed.

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.

Analysis of inorganic cations as their complexes by capillary electrophoresis

The development in the analysis of inorganic cations as their complexes by capillary electrophoresis is reviewed. Topics covered are separation strategies, approaches of derivatization, choice of complexing ligands, manipulation of sensitivity and selectivity, and applications to metal speciation analysis with emphasis on separation strategies and choice of complexing reagents. The future development was also predicted.

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.

Open tubular capillary electrochromatography in fused-silica capillaries chemically bonded with macrocyclic dioxopolyamine

Abstract In this paper, the macrocyclic dioxopolyamine compound: 1,4,7,10-tetraazacyclotridecane-11,13-dione was used as stationary phases with the aid of 3-(2-cyclooxypropoxyl)propyl-trimethoxy silane as bridge in open-tubular capillary electrochromatography (OTCEC). To increase the surface area and produce radial extensions from the surface, the capillaries were etched by aqueous sodium hydroxide before being coated. A comparison was made of the properties of capillary modified with the macrocyclic dioxopolyamine with those of the bare capillary by electroosmotic flow measurements and its dependence on pH. The direction of EOF on the capillaries modified with dioxo[13]aneN 4 is reversed at somewhat lower pH (pH

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.

Capillary electrophoresis separation and permanganate chemiluminescence on-line detection of some alkaloids with β-cyclodextrin as an additive

Capillary electrophoresis has been used in combination with on-line permanganate chemiluminescence detection for the simultaneous determination of morphine, 6-monoacetylmorphine and heroin. It was found that beta-cyclodextrins could improve the separation efficiency and enhance the chemiluminescence signal. Improved sensitivity over capillary electrophoresis with UV detection was obtained. The procedure has detection limits of 23, 66 and 115 fmol for morphine, 6-monoacetylmorphine and heroin, respectively.