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Erkang Wang

Publications and source records attributed to Erkang Wang.

At least 37 records · Page 2Linked to original sources
PubMed2005

Microchip capillary electrophoresis with solid-state electrochemiluminescence detector.

We report microchip capillary electrophoresis (CE) coupling to a solid-state electrochemiluminescence (ECL) detector. The solid-state ECL detector was fabricated by immobilizing tris(2,2'-bipyridyl)ruthenium(II) (TBR) into an Eastman AQ55D-silica-carbon nanotube composite thin film on an indium tin oxide (ITO) electrode. After being made by a photolithographic method, the surface of the ITO electrode was coated with a thin composite film through a micromolding in capillary (MIMIC) technique using a poly(dimethylsiloxane) (PDMS) microchannel with the same pattern as an ITO electrode. Then the TBR was immobilized via ion exchange by immersing the ITO electrode containing the thin film in TBR aqueous solution. The whole system was built by reversibly sealing the TBR-modified ITO electrode plate with a PDMS layer containing electrophoresis microchannels. The results indicated that the present solid-state ECL detector displayed good durability and stability in the microchip CE-ECL system. Proline was selected to perform the microchip device with a limit of detection of 2 microM (S/N=3) and a linear range from 25 to 1000 microM. Compared with the CE-ECL of TBR in aqueous solution, while the CE microchip with solid-state ECL detector system gave the same sensitivity of analysis, a much lower TBR consumption and a high integration of the whole system were obtained. The present system was also used for medicine analysis.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed2005

Method for effective immobilization of Ru(bpy)(3)2+ on an electrode surface for solid-state electrochemiluminescene detection.

A novel method for effective immobilization of Ru(bpy)3(2+) on an electrode surface is developed. The whole process involves two steps: the electrostatic interactions between citrate-capped gold nanoparticles (AuNPs) and Ru(bpy)3Cl2 in aqueous medium were used to fabricate Ru(bpy)(3)2+-AuNP aggregates (Ru-AuNPs) first, and then the Au-S interactions between as-formed Ru-AuNPs and sulfhydryl groups were used to effectively immobilize the Ru-AuNPs on a sulfhydryl-derivated indium tin oxide (ITO) electrode surface. As-prepared ITO electrode shows excellent stability, and the ECL active species Ru(bpy)3(2+) contained therein exhibit excellent ECL behaviors.

Journal Article↗
PubMed2005

Spontaneous fractal aggregation of gold nanoparticles and controlled generation of aggregate-based fractal networks at air/water interface.

The spontaneous fractal aggregation of as-prepared cetytrimethylammonium bromide (CTAB)-capped gold nanoparticles was found to happen at the air/water interface after spreading their chloroform solution on water surfaces. Aided by Langmuir-Blodgett techniques, these fractal aggregates can be interconnected with each other to form aggregate-based fractal networks.

Journal Article↗
PubMed2005

Fabrication, characterization, and application in SERS of self-assembled polyelectrolyte-gold nanorod multilayered films.

An effective and facile approach for the preparation of multilayered nanostructure of gold nanorods (Au NRs) has been demonstrated. Linear polyethylenimine (LPEI) was selected as a polymeric adhesive layer, and an anionic polyelectrolyte poly(sodium styrenesulfonate) (PSS) was used as the linker of the positively charged Au NRs in multilayered nanostructure. They were deposited onto the LPEI-modified indium-doped tin oxide (ITO) substrate alternately using the layer-by-layer assembly technique via electrostatic interactions. The plasmonic property of the multilayered nanostructure of Au NRs is tunable by the controlled self-assembly process. FE-SEM was used to study the morphologies of the resulted substrates with Au NRs monolayer membrane and with Au NRs multilayered membrane. More importantly, it was found that the multilayered NRs films could be used as a surface-enhanced Raman spectroscopy (SERS) substrate for probing 4-aminothiophenol (4-ATP).

Journal Article↗
PubMed2005

Microfluidic chip with electrochemiluminescence detection using 2-(2-aminoethyl)-1-methylpyrrolidine labeling.

A tertiary amine derivative, 2-(2-aminoethyl)-1-methylpyrrolidine (AEMP) was successfully developed as electrochemiluminescence (ECL) probe within microfluidic chip using ECL detection in this paper. The system was characterized by the interaction between biotin and avidin. In principle, tertiary amine derivatives containing active group can be used as a potential alternative of traditional tris(2,2'-bipyridine)ruthenium(II) [Ru(bpy)3(2+)] label. Firstly, The ECL efficiency of AEMP was characterized via comparing with that of two coreactants enhancing Ru(bpy)3(2+) ECL, TPA and proline. At same condition, AEMP has a similar ECL efficiency to TPA, and much higher than proline. After AEMP reacted with NHS-LC-biotin (succinimidyl-6-(biotinamido) hexanoate), the products and their ECL were analyzed by directly injecting it in the microfluidic chip. A 4.5 cm microchannel was used to separate the mixture of AEMP and biotinylated AEMP. The present works indicated that AEMP has a good reactivity to the analytes containing carboxyl group with a similar ECL efficiency to TPA. Under optimal condition, the detection limits (based on 3 S/N) of AEMP was 2.7 microM. The system was also validated by the reaction between biotin and avidin. The calculated binding ratio between avidin and biotin based on the present method was 4.4.

Aminocaproates↗
PubMed2005

Rapid preparation and characterization of uniform, large, spherical Ag particles through a simple wet-chemical route.

In this article we report the rapid preparation of uniform, large, spherical Ag particles through a simple wet-chemical route. The formation of Ag particles with about 750 nm in diameter occurs in a single process, carried out by direct mix of AgNO3 aqueous solution and ortho-phenylenediamine N-methyl-2-pyrrolidone solution at room temperature, producing a relatively low-polydispersity product. It is also found that raising the temperature results in larger particles. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectra have been used to characterize the resulting product.

Particle Size↗
PubMed2005

Coordination-induced formation of submicrometer-scale, monodisperse, spherical colloids of organic-inorganic hybrid materials at room temperature.

In this communication, we demonstrate a novel coordination-based strategy to the fabrication of submicrometer-scale, monodisperse, spherical colloids of organic-inorganic hybrid materials, carried out by mixing H2PtCl6 and p-phenylenediamine (PPD) aqueous solutions at room temperature. The particle size and polydispersity can be controlled by the molar ratio and concentration of reactants, and the optimum experimental parameters for the production of monodisperse colloids are also given.

Colloids↗
PubMed2005

Designed nanostructured pt film for electrocatalytic activities by underpotential deposition combined chemical replacement techniques.

Multiple-deposited Pt overlayer modified Pt nanoparticle (MD-Pt overlayer/PtNPs) films were deliberately constructed on glassy carbon electrodes through alternately multiple underpotential deposition (UPD) of Ag followed redox replacement reaction by Pt (II) cations. The linear and regular growth of the films characterized by cyclic voltammetry was observed. Atomic force spectroscopy (AFM) provides the surface morphology of the nanostructured Pt films. Rotating disk electrode (RDE) voltammetry and rotating ring-disk electrode (RRDE) voltammetry demonstrate that the MD-Pt overlayer/PtNPs films can catalyze an almost four-electron reduction of O(2) to H(2)O in air-saturated 0.1 M H(2)SO(4). Thus-prepared Pt films behave as novel nanostructured electrocatalysts for dioxygen reduction and hydrogen evolution reaction (HER) with enhanced electrocatalytic activities, in terms of both reduction peak potential and peak current, when compared to that of the bulk polycrystalline Pt electrode. Additionally, it is noted that after multiple replacement cycles, the electrocatalytic activities improved remarkably, although the increased amount of Pt is very low in comparison to that of pre-modified PtNPs due to the intrinsic feature of the UPD-redox replacement technique. In other words, the electrocatalytic activities could be improved markedly without using very much Pt by the technique of tailoring the catalytic surface. These features may provide an interesting way to produce Pt catalysts with a reliable catalytic performance as well as a reduction in cost.

Journal Article↗
PubMed2005

Fabrication of a poly(dimethylsiloxane)-based electrochemiluminescence detection cell for capillary electrophoresis.

An easy but effective technique is described here for quick fabrication of low-cost electrochemiluminescence detection cells for capillary electrophoresis. The technique is based on molding of poly(dimethylsiloxane) (PDMS) with a capillary column inserted into a pipet tip. Two access holes are left in the PDMS slab; they provide neat accommodations for the separation capillary and the working electrode made with the same type of tip. Since the access holes are well-aligned, the electrode and the capillary are automatically aligned; thus, end-column detection is easily obtained. Fabrication of the detection cell is straightforward; no micromechanical operation is included. Also the principle for the procedure makes it possible to efficiently batch production detection cells with good reproducibility. Because of the end-column scheme, the cell can be adopted for electrophoresis with electrochemical detection as well.

Journal Article↗
PubMed2005

A colloidal Au monolayer modulates the conformation and orientation of a protein at the electrode/solution interface.

The orientation and conformation of adsorbed cytochrome c (cyt c) at the interface between an electrode modified with colloidal Au and a solution were studied by electrochemical, spectroscopic, and spectroelectrochemical techniques. The results indicate that the colloidal Au monolayer formed via preformation of an organic self-assembled monolayer (SAM) can increase the electronic coupling between the SAM and cyt c in the same manner as bifunctional molecular bridges, one functional group of which is bound to the electrode surface while the other interacts with the protein surface. The approach of cyt c to the modified electrode/solution interface can be assisted by strong interactions of the intrinsic charge of colloidal particles with cyt c, while the heme pocket remains almost unchanged due to the screening effect of the negatively charged field created by the intrinsic charge. The conformational changes of cyt c induced by its adsorption at a bare glassy carbon electrode/solution interface and the effect of the electric field on the ligation state of the heme can be avoided at the colloidal-Au-modified electrode/solution interface. Finally, a possible model for the adsorption orientation of cyt c at the colloidal-Au-modified electrode/solution interface is proposed.

Electrochemistry↗
PubMed2005

One-step preparation of highly concentrated well-stable gold colloids by direct mix of polyelectrolyte and HAuCl4 aqueous solutions at room temperature.

Highly concentrated, well-stable gold colloids can be prepared directly from an amine-bearing polyelectrolyte-HAuCl4 aqueous solution at room temperature. It is found that increasing molar ratio of polyelectrolyte to gold leads to increasing particle size. UV-vis spectra, transmission electron microscopy (TEM), and X-ray photoelectron spectra (XPS) were used to characterize the products thus formed.

Journal Article↗
PubMed2005

Quantifying kinetic paths of protein folding.

We propose a new approach to activated protein folding dynamics via a diffusive path integral framework. The important issues of kinetic paths in this situation can be directly addressed. This leads to the identification of the kinetic paths of the activated folding process, and provides a direct tool and language for the theoretical and experimental community to understand the problem better. The kinetic paths giving the dominant contributions to the long-time folding activation dynamics can be quantitatively determined. These are shown to be the instanton paths. The contributions of these instanton paths to the kinetics lead to the "bell-like" shape folding rate dependence on temperature, which is in good agreement with folding kinetic experiments and simulations. The connections to other approaches as well as the experiments of the protein folding kinetics are discussed.

Algorithms↗
PubMed2005

4-(Dimethylamino)butyric acid labeling for electrochemiluminescence detection of biological substances by increasing sensitivity with gold nanoparticle amplification.

4-(Dimethylamino)butyric acid (DMBA) labeling combined with gold nanoparticle amplification for electrochemiluminescence (ECL) determination of a biological substance (bovine serum albumin (BSA) and immunoglobulin G (IgG) as models) was presented. After DMBA, an analogue of tripropylamine, was tagged on the (anti)analytes, an ECL signal related to the content of the analytes was generated when the analyte tagged with DMBA was in contact with tris(2,2'-bipyridine)ruthenium (Ru(bpy)(3)2+) solution and a potential was applied. To improve the adsorption capacity, a gold nanoparticle layer was first combined into the surface of the 2-mm-diameter gold electrode. For the determination of BSA, avidin was covalently conjugated to a self-assembled monolayer of 3-mercaptopropanoic acid on the gold nanoparticle layer. Biotinylated BSA-DMBA was then immobilized on the gold nanoparticle layer of the gold electrode via the avidin-biotin reaction. IgG was tested via a typical sandwich-type immobilization method. ECL signals were generated from the electrodes immobilized with BSA or IgG by immersing them in a 1 mmol L-1 Ru(bpy)(3)2+ solution and scanning from 0.5 to 1.3 V versus Ag/AgCl. With gold nanoparticle amplification, the ECL peak intensity was proportional to the concentration over the range 1-80 and 5-100 microg/mL for BSA and IgG consuming 50 microL of sample, respectively. A 10- and 6-fold sensitivity enhancement was obtained for BSA and IgG over their direct immobilization on an electrode using DMBA labeling. The relative standard deviations of five replicate determinations of 10 microg/mL BSA and 20 microg/mL IgG were 8.4 and 10.2%, respectively. High biocompatibility and low cost were the main advantages of the present DMBA labeling technique over the traditional Ru(bpy)(3)2+ labeling.

2,2'-Dipyridyl↗
PubMed2005

Simultaneous electrochemical and electrochemiluminescence detection for microchip and conventional capillary electrophoresis.

A simultaneous electrochemical (EC) and electrochemiluminescence (ECL) detection scheme was introduced to both microchip and conventional capillary electrophoresis (CE). In this dual detection scheme, tris(2,2'-bipyridyl)ruthenium(II) (Ru(bpy)3(2+)) was used as an ECL reagent as well as a catalyst (in the formation of Ru(bpy)3(3+)) for the EC detection. In the Ru(bpy)3(2+)-ECL process, Ru(bpy)3(3+) was generated and then reacted with analytes resulting in an ECL emission and a great current enhancement in EC detection due to the catalysis of Ru(bpy)3(3+). The current response and ECL signals were monitored simultaneously. In the experiments, dopamine and three kinds of pharmaceuticals, anisodamine, ofloxacin, and lidocaine, were selected to validate this dual detection strategy. Typically, for the EC detection of dopamine with the presence of Ru(bpy)3(2+), a approximately 5 times higher signal-to-noise ratio (S/N) can be achieved than that without Ru(bpy)3(2+), during the simultaneous EC and ECL detection of a mixture of dopamine and lidocaine using CE separation. The results indicated that this dual EC and ECL detection strategy could provide a simple and convenient detection method for analysis of more kinds of analytes in CE separation than the single EC or ECL detection alone, and more information of analytes could be achieved in analytical applications simultaneously.

Electrochemistry↗
PubMed2005

Electrochemiluminescence quenching as an indirect method for detection of dopamine and epinephrine with capillary electrophoresis.

An electrochemiluminescence (ECL) inhibition method was developed as an indirect detection method for the determination of dopamine and epinephrine separated by capillary electrophoresis (CE). When the concentration of Ru(bpy)(3) (2+) was 50 muM diluted by 50 mM phosphate (pH 8.5) in the cell and 0.5 M tripropylamine (TPA) was added to the running buffer (10 mM phosphate, pH 9.0), an inhibition of ECL of the Ru(bpy)(3) (2+)/TPA system by the analytes was observed. Under the optimized conditions, the relative standard deviations of migration time and negative peak area were less than 1% and 3%, respectively, for 1 microM dopamine or 1 microM epinephrine (n = 10). Linear ranges of 0.1-10 microM for both analytes and the detection limits (signal-to-noise ratio S/N = 3) of 10 nM for dopamine and 30 nM for epinephrine were obtained.

Dopamine↗
PubMed2005

Effect of electrode surface microstructure on electron transfer induced conformation changes in cytochrome c monitored by in situ UV and CD spectroelectrochemistry.

Electrochemical redox processes of bovine heart cytochrome c were investigated by in situ UV-vis and CD spectroelectrochemistry at bare glassy carbon electrode (GCE) and single-wall carbon nanotubes (SWNTs) modified glassy carbon electrode (SWNTs/GCE) using a long optical path thin layer cell. The spectra obtained at GCE and SWNTs/GCE reflect electrode surface microstructure-dependent changes in protein conformation during redox transition. Potential-dependent conformational distribution curves of cytochrome c obtained by analysis of in situ circular dichroism (CD) spectra using singular value decomposition least square (SVDLS) method show that SWNTs can retain conformation of cytochrome c. Some parameters of the electrochemical reduction process, i.e. the product of electron transfer coefficient and number of electrons (alpha n = 0.3), apparent formal potential (E0' = 0.04 V), were obtained by double logarithmic analysis and standard heterogeneous electron transfer rate constant k0 was obtained by electrochemistry and double logarithmic analysis, respectively.

Animals↗