Biomedical subjects

Xiaohu Qu

Publications and source records attributed to Xiaohu Qu.

13 recordsLinked to original sources

PubMed2006

Noncovalent functionalization of multiwalled carbon nanotubes: application in hybrid nanostructures.

We developed a reproducible, noncovalent strategy to functionalize multiwalled carbon nanotubes (MWNTs) via embedding nanotubes in polysiloxane shells. (3-Aminopropyl)triethoxysilane molecules adsorbed to the nanotube surfaces via hydrophobic interactions are polymerized simply by acid catalysis and form a thin polysiloxane layer. On the basis of the embedded MWNTs, negatively charged gold nanoparticles are anchored to the nanotube surfaces via electrostatic interactions between the protonated amino groups and the gold nanoparticles. Furthermore, these gold nanoparticles can further grow and magnify along the nanotubes through heating in HAuCl4 aqueous solution at 100 degrees C; as a result these nanoparticles are joined to form continuous gold nanowires with MWNTs acting as templates.

Journal Article↗

PubMed2006

In situ synthesis and characterization of multiwalled carbon nanotube/Au nanoparticle composite materials.

An effective and facile in situ reduction approach for the fabrication of carbon nanotube-supported Au nanoparticle (CNT/Au NP) composite nanomaterials is demonstrated in this article. Linear polyethyleneimine (PEI) is ingeniously used as both a functionalizing agent for the multiwalled carbon nanotubes (MWNTs) and a reducing agent for the formation of Au NPs. This method involves a simple mixing process followed by a mild heating process. This approach does not need the exhaustive surface oxidation process of CNTs. The coverage of Au NPs on CNTs is tunable by varying the experimental parameters, such as the initial molar ratio of PEI to HAuCl4, the relative concentration of PEI and HAuCl4 to MWNTs, and the temperature and duration of the heat treatment. More importantly, even the heterogeneous CNT/Au composite nanowires are obtainable through this method. TEM, XPS, and XRD are all used to characterize the CNT/Au composite materials. In addition, the optical and electrocatalytic properties are investigated.

Journal Article↗

PubMed2006

Surface-enhanced resonance Raman spectroscopy and spectroscopy study of redox-induced conformational equilibrium of cytochrome c adsorbed on DNA-modified metal electrode.

The redox-induced conformational equilibrium of cytochrome c (cyt c) adsorbed on DNA-modified metal electrode and the interaction mechanism of DNA with cyt c have been studied by electrochemical, spectroscopic and spectroelectrochemical techniques. The results indicate that the external electric field induces potential-dependent coordination equilibrium of the adsorbed cyt c between its oxidized state (with native six-coordinate low-spin and non-native five-coordinate high-spin heme configuration) and its reduced state (with native six-coordinate low-spin heme configuration) on DNA-modified metal electrode. The strong interactions between DNA and cyt c induce the self-aggregation of cyt c adsorbed on DNA. The orientational distribution of cyt c adsorbed on DNA-modified metal electrode is potential-dependent, which results in the deviation from an ideal Nernstian behavior of the adsorbed cyt c at high electrode potentials. The electric-field-induced increase in the activation barrier of proton-transfer steps attributed to the rearrangement of the hydrogen bond network and the self-aggregation of cyt c upon adsorption on DNA-modified electrode strongly decrease the interfacial electron transfer rate. In addition, the strongly Coulombic interactions between DNA and cyt c only disturb the microenvironment of the heme, and do not affect the states of heme ligation and spin. The secondary structure of the adsorbed cyt c is retained, while the conformation of DNA is changed from the B form DNA to A form DNA.

Adsorption↗

PubMed2005

Facile preparation of amperometric laccase biosensor with multifunction based on the matrix of carbon nanotubes-chitosan composite.

The carbon nanotubes-chitosan (CNTs-CS) composite provides a suitable biosensing matrix due to its good conductivity, high stability, and good biocompatibility. Enzymes can be firmly incorporated into the matrix without the aid of other cross-linking reagents. The composite is easy to form insoluble film in solution above pH 6.3. Based on this, a facilely fabricated amperometric biosensor by entrapping laccase into the CNTs-CS composite film has been developed. At pH 6.0, the fungi laccase incorporated into the composite film remains better catalytic activity than that dissolved in solution. The system is in favor of the accessibility of substrate to the active site of laccase, thus the affinity to substrates is improved greatly, such as 2,2'-azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid) diammonium salt (ABTS), catechol, and O2 with Km values of 19.86 microM, 9.43 microM, and 3.22 mM, respectively. The major advantages of the as-prepared biosensor are: detecting different substrates (ABTS, catechol, and O2), possessing high affinity and sensitivity, durable long-term stability, and facile preparation procedure. On the other hand, the system can be applied in fabrication of biofuel cells as the cathodic catalysts based on its good electrocatalysis for oxygen reduction. It can be extended to immobilize other enzymes and biomolecules, which will greatly facilitate the development of biosensors, biofuel cells, and other bioelectrochemical devices.

Biosensing Techniques↗

PubMed2005

Parallel alignment of carbon nanotubes induced with inorganic molecules.

In this work, a new strategy is presented to form ordered multiwalled carbon nanotube (MWNT) arrays. The MWNTs are aligned horizontally and parallel in (3-aminopropyl)triethoxysilane (3-APTES) sol films on the surface of mica and glassy carbon (GC). 3-APTES is ready to form charged rodlike micelles, which play a key role in fabricating orderly MWNT arrays. Moreover, we prepare MWNT arrays on the surfaces of solid electrodes and detect the electrochemical response of the microarray electrodes for the Fe(CN)(6)3-/Fe(CN)6(4-) couple.

Journal Article↗

PubMed2005

Small molecules as cross-linkers: fabrication of carbon nanotubes/thionine self-assembled multilayers on amino functionalized surfaces.

Electroactive and photoactive thionine molecules have been selected as cross-linkers to construct self-assembled multilayers containing carbon nanotubes (CNTs)via the alternate layer deposition technique. The resulting multilayer system can electrocatalyze the oxidation of NADH and offer potential applications in other fields such as biosenors and photovoltaic devices.

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

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

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

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↗

PubMed2004

Surface charge influence on the surface plasmon absorbance of electroactive thiol-protected gold nanoparticles.

Gold nanoparticles (3.1-5.0 nm in size) surface-derivatized with both electroactive and nonelectroactive self-assembled monolayers were synthesized. The surface-derivatized electroactive particles can be easily oxidized/reduced at an electrode surface based on the diffusion-controlled current-voltage curve observed in cyclic voltammetry measurements. Spectroelectrochemical investigation demonstrated that the maximum absorbance of the nanoparticles in their oxidized state red-shifted compared with their reduced state to a different extent according to their size distribution. In the case of the particles surface-derivatized with nonelectroactive monolayers, much less shift was observed. This study showed that surface plasmon absorbance of gold nanoparticles was not only related to core charge states but was also influenced by surface charge states as well.

Electrochemistry↗

PubMed2004

Immobilization of the nanoparticle monolayer onto self-assembled monolayers by combined sterically enhanced hydrophobic and electrophoretic forces.

The immobilization of surface-derivatized gold nanoparticles onto methyl-terminated self-assembled monolayers (SAMs) on gold surface was achieved by the cooperation of hydrophobic and electrophoretic forces. Electrochemical and scanning probe microscopy techniques were utilized to explore the influence of the SAM's structure and properties of the nanoparticle/SAM/gold system. SAMs prepared from 1-decanethiol (DT) and 2-mercapto-3-n-octylthiophene (MOT) were used as hydrophobic substrates. The DT SAM is a closely packed and organized monolayer, which can effectively block the underlying gold and inhibit a variety of solution species including organic and inorganic molecules from penetrating, whereas the MOT monolayer is poorly packed or disorganized (because of a large difference in dimension between the thiophene head and the alkylchain tail) and permeable to many organic probes in aqueous solution but not to inorganic probes. Thus, the MOT monolayer provides a more energetically favorable hydrophobic surface for the penetration and adsorption of organic species than the DT monolayer. This hypothesis is supported by experiments in which the density of hydrophobically immobilized nanoparticles on the MOT SAM is much larger than that on the DT SAM. The results also suggest new approaches for modification of macroscopic surfaces with nanoscopic particles.

Electrochemistry↗

PubMed2003

Preparation of hybrid thin film modified carbon nanotubes on glassy carbon electrode and its electrocatalysis for oxygen reduction.

A hybrid thin film containing Pt nanoparticles and [tetrakis(N-methylpyridyl)porphyrinato]cobalt (CoTMPyP) modified multi-walled carbon nanotubes (MWNTs) on a glassy carbon (GC) electrode surface was fabricated. This hybrid film electrode exhibited remarkable electrocatalytic activity for oxygen reduction and high stability with promising applications in fuel cells.

Journal Article↗