PubMed Health⌕ Search

Biomedical subjects

Shaowei Chen

Publications and source records attributed to Shaowei Chen.

15 recordsLinked to original sources
PubMed2007

Electrochemical quartz crystal microbalance studies of the rectified quantized charging of gold nanoparticle multilayers.

Electrochemical quartz crystal microbalance (EQCM) was employed to investigate the dynamics of rectified quantized charging of gold nanoparticle multilayers by in situ monitoring of the interfacial mass changes in aqueous solutions with varied electrolytes. EQCM measurements showed that interfacial mass changes only occurred at potentials more positive than the potential of zero charge (PZC), where nanoparticle quantized charging was well-defined, whereas in the negative potential regime where only featureless voltammetric responses were observed, the QCM frequency remained virtually invariant. This was ascribed to the fact that nanoparticle quantized charging was induced by the formation of ion-pairs between hydrophobic electrolyte anions (PF6-, ClO4-, BF4-, and NO3-) and positively charged gold nanoparticles. Based on the total frequency changes and the number of electrolyte anions adsorbed onto the particle layers, the number of water molecules that were involved in the ion-pairing processes was then quantitatively estimated at varied particle charge states, which was found to increase with increasing hydrophobicity of the anions. Additionally, the electron-transfer dynamics of the gold particle multilayers were also evaluated by electrochemical impedance measurements. It was found that the particle electron-transfer rate was about an order of magnitude slower than that of the ion diffusion and binding.

Journal Article↗
PubMed2006

Synthesis and characterization of ultrathin WO3 nanodisks utilizing long-chain poly(ethylene glycol).

Metal oxide nanostructures hold great potential for photovoltaic (PV), photoelectrochemical (PEC), and photocatalytic applications. Whereas thin films of various materials of both nanoparticle and nanorod morphologies have been widely investigated, there have been few inquiries into nanodisk structures. Here, we report the synthesis of ultrathin WO3 nanodisks using a wet chemical route with poly(ethylene glycol) (PEG) as a surface modulator. The reported nanodisk structure is based on the interaction of the nonionic 10000 g/mol PEG molecules with tungsten oxoanion precursors. The WO3 nanostructures formed are dominated by very thin disks with dimensions on the nanometer to micrometer scale. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images reveal the structures to have dimensions on the order of 350-1000 nm in length, 200-750 nm in width, and 7-18 nm in thickness and possessing textured single-crystalline features. A number of analytical techniques were used to characterize the WO3 nanodisks, including selected-area electron diffraction (SAED), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM), Raman scattering spectroscopy, UV-visible spectrophotometry, and cyclic voltammetry (CV). The growth of the WO3 nanodisks was inhibited in the [010] crystal direction, leading to ultrathin morphologies in the monoclinic crystal phase. The large flat surface area and high aspect ratio of the WO3 nanodisks are potentially useful in PEC cells for hydrogen production via direct water splitting, as has been demonstrated in a preliminary experiment with external bias.

Electrochemistry↗
PubMed2006

Dithiocarbamate-capped silver nanoparticles.

Nanometer-sized silver particles were synthesized by using didecylamine dithiocarbamates as the protecting ligands. With control of the initial ligand-metal feed ratios, the core diameter of the resulting particles was found to vary from about 5 to 2.5 nm, as determined by transmission electron microscopic measurements. The core size dispersity was also found to decrease with increasing feed ratio. In UV-visible spectroscopic studies, the particle surface plasmon resonance peak diminished in intensity as the particle core size decreased, whereas in electrochemical measurements, smaller sized particles gave rise to well-defined quantized charging voltammetric features, in contrast to the featureless responses with the larger particles. Such single electron-transfer behaviors were consistent with those observed in STM measurements involving individual nanoparticles. Overall, this study provides an effective approach to the synthesis of stable nanometer-sized silver nanoparticles with interesting electronic and electrochemical properties.

Journal Article↗
PubMed2006

Electro-oxidation of formic acid catalyzed by FePt nanoparticles.

The electrocatalytic oxidation of formic acid at a gold electrode functionalized with FePt nanoparticles was studied by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in a mixed solution of 0.1 M HCOOH and 0.1 M HClO4. The FePt bimetallic nanoparticles, with a mean diameter of 3 nm, were prepared by a chemical reduction method. The Au/FePt nanostructured electrode was prepared firstly by the deposition of FePt nanoparticles onto a clean Au electrode surface, followed by ultraviolet ozone treatment to remove the organic coating. In CV measurements, two well-defined anodic peaks were observed at +0.20 and +0.51 V (vs. a Ag/AgCl quasi-reference). The anodic peak at +0.20 V was attributed to the oxidation of HCOOH to CO2 on surface unblocked by CO, whereas the peak at +0.51 V was ascribed to the oxidation of surface-adsorbed CO (an intermediate product of HCOOH oxidation) and further oxidation of bulk HCOOH. From the onset potential and current density of the electro-oxidation of HCOOH, FePt nanoparticles exhibit excellent electrocatalytic activities as compared to Pt and other metal alloys. EIS measurements were carried out to further examine the reaction kinetics involved in the HCOOH electro-oxidation. The EIS responses were found to be strongly dependent on electrode potentials. At potentials more positive than -0.25 V (vs. Ag/AgCl), pseudo-inductive behavior was typically observed. At potentials between +0.3 and +0.5 V, the impedance response was found to reverse from the first quadrant to the second quadrant; such negative Faradaic impedance was indicative of the presence of an inductive component due to the oxidation of surface-adsorbed CO. The impedance responses returned to normal behavior at more positive potentials (+0.6 to +0.9 V). The mechanistic variation was attributed to the formation of different intermediates (CO or oxygen containing species) on the electrode surface in different potential regions. Two equivalent circuits were proposed to model these impedance behaviors.

Catalysis↗
PubMed2006

Silica-coated CdTe quantum dots functionalized with thiols for bioconjugation to IgG proteins.

Quantum dots (QDs) have been increasingly used in biolabeling recently as their advantages over molecular fluorophores have become clear. For bioapplications QDs must be water-soluble and buffer stable, making their synthesis challenging and time-consuming. A simple aqueous synthesis of silica-capped, highly fluorescent CdTe quantum dots has been developed. CdTe QDs are advantageous as the emission can be tuned to the near-infrared where tissue absorption is at a minimum, while the silica shell can prevent the leakage of toxic Cd(2+) and provide a surface for easy conjugation to biomolecules such as proteins. The presence of a silica shell of 2-5 nm in thickness has been confirmed by transmission electron microscopy and atomic force microscopy measurements. Photoluminescence studies show that the silica shell results in greatly increased photostability in Tris-borate-ethylenediaminetetraacetate and phosphate-buffered saline buffers. To further improve their biocompatibility, the silica-capped QDs have been functionalized with poly(ethylene glycol) and thiol-terminated biolinkers. Through the use of these linkers, antibody proteins were successfully conjugated as confirmed by agarose gel electrophoresis. Streptavidin-maleimide and biotinylated polystyrene microbeads confirmed the bioactivity and conjugation specificity of the thiolated QDs. These functionalized, silica-capped QDs are ideal labels, easily synthesized, robust, safe, and readily conjugated to biomolecules while maintaining bioactivity. They are potentially useful for a number of applications in biolabeling and imaging.

Biotinylation↗
PubMed2006

Photo-gated charge transfer of organized assemblies of CdSe quantum dots.

The electronic conductivity of tri-n-octylphosphineoxide (TOPO)-protected CdSe quantum dots (QDs) was studied at the air-water interface using the Langmuir technique within the context of photochemical and photophysical excitation. It was found that, upon photoirradiation with photon energies higher than that of the absorption threshold, the voltammetric currents increased rather substantially with a pair of voltammetric peaks at positive potentials. However, the photoconductivity profiles exhibited a dynamic transition, which was ascribed to the strong affinity of oxygen onto the CdSe surface and the consequent trapping of the photogenerated electrons. The resulting excess of holes led to photocorrosion of the particle cores. The oxygen adsorption and photoetching processes were found to be reversible upon cessation of the photoexcitation. In contrast, only featureless voltammetric responses were observed when the particle monolayers were deposited onto the electrode surface and the film conductance was measured in a vacuum (the overall profiles were analogous to that of a Coulomb blockade). A comparative study was also carried out with a CdSe dropcast thick film immersed in acetonitrile, where the photoconductivity profiles were reversible and almost linear. The latter was attributed to the separation of photogenerated electrons and holes which were subsequently collected at the electrodes under voltammetric control. In the dropcast system, the oxygen effects were minimal which was ascribed to the acetontrile medium that limited the access to oxygen and thus the particles were chemically intact. These studies suggest that chemical environment plays an important role in the determination of the chemical stability and electronic conductivity of CdSe QD thin films.

Absorption↗
PubMed2005

Self-assembled multilayers of gold nanoparticles: nitrate-induced rectification of quantized capacitance charging and effects of alkaline (earth) ions in aqueous solutions.

Gold nanoparticle multilayers were self-assembled onto an electrode surface by using a dipping method. The particle assemblies exhibited quantized capacitance charging characteristics in aqueous media that were rectified by hydrophobic anions such as PF6-, BF4- and ClO4-, similar to the behavior with the monolayer counterparts. More interestingly, even in the presence of less hydrophobic anions such as NO3-, very well-defined single electron transfers were observed voltammetrically with these particle multilayers, a response unseen previously with particle monolayers. This was ascribed, in part, to the enhanced interactions between the particle multilayers and the electrolyte anions as well as the minimization of the structural defects within the particle thin films as compared to the monolayer counterparts. Further studies showed that with particles functionalized with oligo(ethylene oxide) moieties, the particle charge transfer properties were also found to be affected by electrolyte cations, reflected by the variation of the particle molecular capacitance and formal potentials with the nature of the alkaline (earth) metal ions.

Electric Capacitance↗
PubMed2004

Fullerene-functionalized gold nanoparticles: electrochemical and spectroscopic properties.

Fullerene (C(60))-tethered gold nanoparticles were synthesized by the coupling of the fullerene molecules with peripheral amine moieties on the particle surface. The particle composition was determined by thermogravimetric analysis and FT-IR spectroscopy. The resulting particles exhibited unique optical and electrochemical properties. UV-visible measurements showed that the C(60) characteristic absorption remained practically invariant whereas the fluorescence demonstrated rather drastic enhancement of emission efficiency as compared to the behaviors of C(60) monomers. Tethering of C(60) on the particle surface has virtually no effect on the particle molecular capacitance when C(60) is in neutral state, whereas when C60 is electroreduced, the particle effective capacitance increases drastically, reflected in the quantized capacitance charging measurements. The strong affinity of C(60) to amine moieties was also exploited to assemble multilayers of C(60) and gold particle nanocomposite structures. Quartz crystal microbalance measurements showed quite efficient adsorption of C(60) and particles up to two repeated cycles. However, the voltammetric responses of the surface-confined C(60) and gold particle composite structures were found to be complicated by the inaccessibility of electrolyte counterions due to the compact nature of the surface assemblies.

Journal Article↗
PubMed2004

Lateral quantized charge transfer across nanoparticle monolayers at the air/water interface.

Lateral quantized charge transfer was observed with gold nanoparticle monolayers at the air/water interface. The electronic conductivity was measured by using an interdigitated arrays (IDA) electrode perpendicularly aligned at the air/water interface where a particle ensemble was trapped between the IDA fingers. The overall voltammetric responses were analogous to that of the Coulomb blockade with a relatively flat central gap. This gap was found to shrink with increasing surface pressure. Differential pulse voltammetry revealed a series of well-defined voltammetric peaks within this central gap, which are ascribed to the single electron transfer of the particle ensemble. This observation was interpreted on the basis of relatively weak electronic coupling between neighboring particles where the particles behave more individually.

Journal Article↗
PubMed2003

Fabrication of self-supported patterns of aligned beta-FeOOH nanowires by a low-temperature solution reaction.

Self-supported patterns of oriented alignment of beta-FeOOH nanowires are fabricated through a simple solution reaction from the complex [Fe(phen)(3)](2+) at 60 degrees C. The alignment of nanowires with a diameter of 40 nm and length of 6 mum is relatively uniform. HRTEM studies show that the growing direction of beta-FeOOH nanowires is perpendicular to the orientation plane of self-formed beta-FeOOH flake-like substrates. In the reaction and crystal growth process, the precursor [Fe(phen)(3)](2+) is undoubtedly vital to the formation of nanowire alignment. In detail, the formation of aligned nanowires is thought to be realized by controlling two competing reactions. Electrochemical and UV-visible measurements suggest that the product might have potential applications in lithium batteries and semiconductor electronics. This synthetic process is simple, mild, clean, reproducible, and free of any template; it provides a novel pathway for the low-temperature growth of nanowires and their simultaneous oriented alignment.

Journal Article↗
PubMed2003

[The effects of nm23-H1 on metastases ability and chemo-sensitivity in Tca8113 cell lines].

OBJECTIVE: The purpose of this study was to establish a stable, high-efficient and low-toxic way of transfecting nm23-H1 into Tca8113 line cells, and then to find out whether nm23-H1 could affect the invasion and metastases ability of Tca8113 line cells. METHODS: nm23-H1 was transfected into Tca8113 line cells with Lipofect. The different expressions of nm23-H1 between transfected and non-transfected line cells were detected by the method of immunohistochemistry. The difference of the invasion and metastases ability between transfected and non-transfected line cells was detected by transwell-room and wash techniques. The change of chemo-sensitivity was evaluated by MTT. RESULTS: Using pCMV-NEO-BAM system to keep stable expression of nm23-H1, the significant difference of NDPKA expression between transfected and non-transfected Tca8113 line cells was discovered; The metastases ability of transfected Tca8113 line cells decreased significantly; The chemo-sensitivity of transfected Tca8113 line cells to CDDP increased significantly. CONCLUSION: nm23-H1 can inhibit the metastases of Tca8113 line cells and increase the chemo-sensitivity to CDDP significantly.

Antineoplastic Agents↗
PubMed2003

[In vitro study of the effect of nm23-H1 on metastasis ability and chemo-sensitivity of Acc-M cell lines].

OBJECTIVE: To transfect nm23-H1 into the Acc-M cell lines in a safe, high-efficiency and low-toxicity way, and then to find out whether nm23-H1 affects the metastasis ability and chemo-sensitivity of Acc-M cell lines. METHODS: Lipofect was used to transfect nm23-H1 into Acc-M cell lines. The difference in expression of nm23-H1 between the transfected and non-transfected cell lines was detected by immunohistochemistry. Then by use of transwell-room and wash way, the difference in invasion and metastasis ability between the transfected and non-transfected cell lines was tested. MTT method was adopted in finding the change of chemo-sensitivity. RESULTS: Using pCMV-Neo-Bam system, we observed the stable expression of nm23-H1 and the significant difference in Nucleoside Diphosphate kinase-A, expression between the transfected and non-transfected Acc-M cell lines. The metastasis ability of transfected Acc-M cell lines decreased significantly. The chemo-sensitivity of transfected Acc-M cell line to cis-diamminedichloroplatin (C-DDP) increased significantly. CONCLUSION: nm23-H1 can inhibit the metastases of Acc-M cell lines significantly and can increase the chemo-sensitivity to C-DDP significantly.

Animals↗
PubMed2003

[Behavior of bone formation around the porous-hollow cylindrical titanium implant composed of bone morphogenetic protein].

OBJECTIVE: The purpose of this study was to observe the behavior of bone formation around the titanium-hollow porous cylinder implant composed of bovine bone morphogentic protein(bBMP). METHODS: Porous-hollow cylinder titanium implant composed of bBMP was implanted into mandibule of dogs. Multiple fluorescent was labeled at different times and then LSCM was used to observe the newly formed bone around the complex implant. RESULTS: The newly formed bone around the complex implant in experimental group was more obvious than that in other groups. CONCLUSION: Earlier, longer and more new-bone formation can be induced by porous-hollow cylinder titanium implant composed of bBMP, and LSCM is an effective method to observe new bone formation around implant.

Animals↗
PubMed2002

Magnetoelectrochemistry of gold nanoparticle quantized capacitance charging.

Magnetoelectrochemical studies of gold nanoparticle quantized capacitance charging were carried out at ambient conditions. The single electron transfer responses were found to be sensitive to external magnetic fields, reflected in the enhancement of voltammetric peak currents and shifts of peak formal potentials with increasing magnetic field intensities. Additionally, splittings of voltammetric peaks were also observed upon the application of an external magnetic field. These phenomena might be partly attributed to the paramagnetic characters (electron parity) of nanosized gold particles which are contingent upon their charge states. These novel observations suggest that the nanoparticle electronic energy structures can be varied by magnetic fields, leading to molecular manipulations of the nanoscale charge-transfer chemistry.

Journal Article↗