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Biomedical subjects

Shaojun Dong

Publications and source records attributed to Shaojun Dong.

At least 55 records · Page 3Linked to original sources
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

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

Direct electrochemistry of microperoxidase at Pt microelectrodes modified with carbon nanotubes.

Direct electrochemistry of microperoxidase (MP-11) was found at Pt microelectrodes modified with multi-wall carbon nanotubes (MWNTs). The MWNTs used as the immobilization matrix cooperatively promote the bioactivity of MP-11. When MP-11 was immobilized on MWNTs film-modified Pt microelectrodes, a pair of well-defined redox waves was obtained. The resulted stable microelectrode could be used to catalyze the reduction of H2O2 and O2.

Calibration↗
PubMed2005

Electrochemical functionalization of single-walled carbon nanotubes in large quantities at a room-temperature ionic liquid supported three-dimensional network electrode.

Electrochemical functionalization of single-walled carbon nanotubes (SWNTs) was one of selective, clean, and nondestructive chemical methods. But in previous studies it met difficulties in homogeneous electrografting of SWNTs in large quantities because the reaction was often localized on a very thin film (ca. 2 microm). In this report, a room-temperature ionic liquid (RTIL) supported three-dimensional network SWNT electrode was first utilized to break through this barrier. In this work, large quantities of SWNTs were considerably untangled in RTILs so as to greatly increase the effective area of the electrode. N-succinimidyl acrylate (NSA), as a model monomer, was dissolved in the supporting RTILs and was electrografted onto SWNTs (SWNTs-poly-NSA). As an application example, glucose oxidase was directly covalently anchored on the SWNTs-poly-NSA assembly, and the electrocatalytic oxidation of glucose in this assembly was investigated. RTILs opened a new path in electrochemical functionalization of SWNTs.

Journal Article↗
PubMed2005

The direct electron transfer of glucose oxidase and glucose biosensor based on carbon nanotubes/chitosan matrix.

The glucose oxidase (GOD) is entrapped in the composite of carbon nanotubes/chitosan and direct electron transfer reaction between GOD and electrode takes place. The electron transfer rate of GOD is greatly enhanced to 7.73 s(-1) in the system, which is more than one-fold higher than that of flavin adenine dinucleotide adsorbed on the carbon nanotubes (3.1 s(-1)). This maybe results from the conformational change of GOD in the microenvironment enabling the accessibility of active site for GOD to the electrode. Additionally, the bioactivity of GOD modified in the composite on electrode surface is kept. So as-prepared electrode can be used as a glucose biosensor exhibiting higher sensitivity (0.5 microA mM(-1)) and better stability. The facile procedure of immobilizing GOD will promote the developments of electrochemical research for protein, biosensors and other bioelectrochemical devices.

Adsorption↗
PubMed2005

Enhancing the electrochemiluminescence of tris(2,2'-bipyridyl)ruthenium(II) by ionic surfactants.

The dependence of the electrochemiluminescence of Ru(bpy)3(2+) (bpy = 2,2'-bipyridine) with tri-n-propylamine as co-reactant on the anionic surfactant SDS (sodium dodecyl sulfate) and the cationic surfactants CTAX (CTA = cetyltrimethylammonium cation, X = bromide, chloride and hydrogensulfate) was studied. Both SDS and CTAX, at low surfactant concentrations below the critical micelle concentrations, enhance the electrochemiluminescence at a platinum working electrode. A further enhancement of the light emission intensity by bromide ions was observed when CTAB (B = bromide) was used-an overall 30-fold increase in electrochemiluminescence efficiency was obtained at a CTAB concentration of 0.08 mM. Voltammetric data support adsorption of surfactant molecules on the electrode surface as the cause of the enhancement of electrochemiluminescence by ionic surfactants.

Animals↗
PubMed2005

Conducting polymer polypyrrole supported bilayer lipid membranes.

Electrochemically synthesized conducting polymer polypyrrole (PPy) film on gold electrode surface was used as a novel support for bilayer lipid membranes (BLMs). Investigations by surface plasmon resonance (SPR) suggest that dimyristoyl-L-alpha-phosphatidylcholine (DMPC) and dimyristoyl-L-alpha-phosphatidyl-L-serine (DMPS) can form BLMs on PPy film surface but dimyristoyl-L-alpha-phosphatidylglycerol (DMPG) and didodecyldimethylammonium bromide (DDAB) can not do so, indicating the formation of PPy supported bilayer lipid membranes (s-BLMs) is dependent on the chemical structure of the lipids used. The self-assembly of DMPC induces a smoother topography than the PPy layer with rms roughness decreasing from 4.484 to 2.914 nm convinced by atomic force microscopy (AFM). Impedance spectroscopy measurements confirm that the deposition of BLM substantially increases the resistance of the system indicating a very densely packed BLM structures. The little change of PPy film in capacitance shows that solvent and electrolyte ions still retain within the porous PPy film after BLM deposition. Therefore, the PPy supported BLM is to some extent comparable to conventional BLM with aqueous medium retaining at its two sides. As an example and preliminary application, horseradish peroxidase (HRP) reconstituted into the s-BLM shows the expected protein activity and can transfer electron from or to the underlying PPy support for its response to electrocatalytic reduction of hydrogen peroxide in solution. Thus the system maybe possesses potential applications to biomimetic membrane studies.

Biosensing Techniques↗
PubMed2005

Alternate assemblies of platinum nanoparticles and metalloporphyrins as tunable electrocatalysts for dioxygen reduction.

Through electrostatic layer-by-layer (LBL) assembly, negatively charged citrate-stabilized platinum nanoparticles (PtNPs) and positively charged [tetrakis(N-methylpyridyl)porphyrinato] cobalt were alternately deposited on a 4-aminobenzoic acid-modified glassy carbon electrode and also on indium tin oxide substrates, directly forming the three-dimensional nanostructured materials. Thus-prepared multilayer films were characterized by UV--visible spectroscopy, surface plasmon resonance (SPR) spectroscopy, atomic force microscopy (AFM), and cyclic voltammetry. Regular growth of the multilayer films is monitored by UV--visible spectroscopy and SPR spectroscopy. AFM provides the morphology of the multilayer films. The PtNPs containing multilayer films exhibit high electrocatalytic activity for the reduction of dioxygen with high stability. Rotating disk electrode voltammetry and rotating ring-disk electrode voltammetry demonstrate that the PtNP-containing multilayer films can catalyze an almost four-electron reduction of O(2) to H(2)O in an air-saturated 0.5 M H(2)SO(4) solution. Furthermore, the electrocatalytic activity of the films could be further tailored by simply choosing different cycles in the LBL process or more specifically the amount of the assembly components in the films. The high electrocatalytic activity and good stability for dioxygen reduction make the PtNP-containing multilayer films potential candidates for the efficient cathode material in fuel cells.

Metalloporphyrins↗
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↗
PubMed2004

Electrogenerated chemiluminescence biosensor with alcohol dehydrogenase and tris(2,2'-bipyridyl)ruthenium (II) immobilized in sol-gel hybrid material.

An ethanol biosensor based on electrogenerated chemiluminescence detection was developed. Electrogenerated chemiluminescence reagent tris(2,2'-bipyridyl)ruthenium (II) and alcohol dehydrogenase were immobilized in the same sol-gel hybrid film. The copolymer poly(vinyl alcohol) with 4-vinylpyridine and cation exchanger Nafion were incorporated into sol-gel film to provide the microenvironment for retaining the activity of enzyme and immobilize tris(2,2'-bipyridyl)ruthenium (II). The design was simpler than the previous two-layer format. The experimental conditions, such as scan rate, pH and concentration of the cofactor were investigated. The intensity of electrogenerated chemiluminescence increased linearly with ethanol concentration from 2.5x10(-5) to 5.0x10(-2) M and detection limit was 1.0x10(-5) M. The prepared biosensor exhibited high sensitivity, wide linear range and good stability.

2,2'-Dipyridyl↗
PubMed2004

Attachment of gold nanoparticles to glassy carbon electrode and its application for the direct electrochemistry and electrocatalytic behavior of hemoglobin.

Gold nanoparticles have been attached onto glassy carbon electrode surface through sulfhydryl-terminated monolayer and characterized by X-ray photoelectron spectroscopy, atomic force microscopy, electrochemical impedance spectroscopy and cyclic voltammetry. The gold nanoparticles-attached glassy carbon electrodes have been applied to the immobilization/adsorption of hemoglobin, with a monolayer surface coverage of about 2.1 x 10(-10) mol cm(-2), and consequently obtained the direct electrochemistry of hemoglobin. Gold nanoparticles, acting as a bridge of electron transfer, can greatly promote the direct electron transfer between hemoglobin and the modified glassy carbon electrode without the aid of any electron mediator. In phosphate buffer solution with pH 6.8, hemoglobin shows a pair of well-defined redox waves with formal potential (E0') of about -0.085 V (versus Ag/AgCl/saturated KCl). The immobilized hemoglobin maintained its biological activity, showing a surface controlled electrode process with the apparent heterogeneous electron transfer rate constant (ks) of 1.05 s(-1) and charge-transfer coefficient (a) of 0.46, and displays the features of a peroxidase in the electrocatalytic reduction of hydrogen peroxide. A potential application of the hemoglobin-immobilized gold nanoparticles modified glassy carbon electrode as a biosensor to monitor hydrogen peroxide has been investigated. The steady-state current response increases linearly with hydrogen peroxide concentration from 2.0 x 10(-6) to 2.4 x 10(-4) M. The detection limit (3sigma) for hydrogen peroxide is 9.1 x 10(-7) M.

Biosensing Techniques↗
PubMed2004

Loosely packed self-assembled monolayer of N-hexadecyl-3,6-di(p-mercaptophenylacetylene)carbazole on gold and its application in biomimetic membrane research.

Dithiols of N-hexadecyl-3,6-di(p-mercaptophenylacetylene)carbazole (HDMC) have been synthesized and employed to form self-assembled monolayers (SAMs) on gold. One characteristic of the HDMC molecule is its peculiar molecular structure consisting of a large and rigid headgroup and a small and flexible alkyl-chain tail. HDMC adsorbates can attach to gold substrates by a strong Au-S bond with weak van der Waals interactions between the alkyl-chain tails, leading to a loosely packed hydrophobic SAM. In this way we can couple hybrid bilayer membranes (HBMs) to gold surfaces with more likeness to a cell bilayer than the conventional HBMs based on densely packed long-chain alkanethiol SAMs. The insulating properties and stability of the HDMC monolayer as well as the HDMC/lipid bilayer on gold have been investigated by electrochemical techniques including cyclic voltammetry and impedance spectroscopy. To test whether the quality of the bilayer is sufficiently high for biomimetic research, we incorporated the pore-forming protein alpha-hemolysin) and the horseradish peroxidase into the bilayers, respectively. Experimental results demonstrated that this type of loosely packed hydrophobic SAM has great potential in biomimetic bilayer research and biosensor application.

Biomimetic Materials↗
PubMed2004

Single-wall carbon nanotube-based voltammetric sensor and biosensor.

The pH-sensitive property of the single-wall carbon nanotube modified electrode based on the electroactive group on the single-wall carbon nanotube was explored by differential pulse voltammetry technique. In pH range 1-13 investigated in Britton-Robinson (B-R) buffer, the anodic peak shifted negatively along with the increase of pH exhibiting a reversible Nernstian response. Experiments were carried out to investigate the response of the single-wall carbon nanotube (SWNT) modified electrode to analytes associated with pH change. The response behavior of the modified electrode to ammonia was studied as an example. The potential response could reach equilibrium within 5 min. The modified electrode had good operational stability. Voltammetric urease and acetylcholinesterase biosensors were constructed by immobilizing the enzymes with sol-gel hybrid material. The maximum potential shift could reach 0.130 and 0.220 V for urea and acetylthiocholine, respectively. The methods for preparing sensor and biosensor were simple and reproducible and the range of analytes could be extended to substrates of other hydrolyases and esterases. This broadened the biosensor application of carbon nanotube in electrochemical area.

Acetylcholine↗
PubMed2004

Electrochemical and bioelectrochemistry properties of room-temperature ionic liquids and carbon composite materials.

Room-temperature ionic liquids (RTILs) are liquids at room temperature and represent a new class of nonaqueous but polar solvents with high ionic conductivity. The conductivity property of carbon nanotubes/RTILs and carbon microbeads/RTILs composite materials has been studied using ac impedance technology. Enzyme coated by RTILs-modified gold and glassy carbon electrodes allow efficient electron transfer between the electrode and the protein and also catalyze the reduction of O2 and H2O2.

Biochemistry↗
PubMed2004

pH-dependent conformational changes of ferricytochrome c induced by electrode surface microstructure.

pH-dependent processes of bovine heart ferricytochrome c have been investigated by electronic absorption and circular dichroism (CD) spectra at functionalized single-wall carbon nanotubes (SWNTs) modified glass carbon electrode (SWNTs/GCE) using a long optical path thin layer cell. These methods enabled the pH-dependent conformational changes arising from the heme structure change to be monitored. The spectra obtained at functionalized SWNTs/GCE reflect electrode surface microstructure-dependent changes for pH-induced protein conformation, pK(a) of alkaline transition and structural microenvironment of the ferricytochrome c heme. pH-dependent conformational distribution curves of ferricytochrome c obtained by analysis of in situ CD spectra using singular value decomposition least square (SVDLS) method show that the functionalized SWNTs can retain native conformational stability of ferricytochrome c during alkaline transition.

Animals↗