Papers by Keyword: Au Nanoparticle

Abstract: Titanium dioxide and gold nanoparticles were synthesized using an environmentally friendly method to deposit undoped and Au-doped TiO₂ thin films on silicon and glass substrates via the spray pyrolysis technique. The effect of the Au nanoparticles concentrations on structural, morphological, and hydrogen sulfide (H₂S) gas sensing characteristics of TiO₂ thin films were investigated. An X-ray diffraction pattern confirmed the polycrystalline structure of the films deposited on glass and Si substrates with a dominant rutile phase and the formation of additional mixed-phases of Ti-Au bonding. According to a Field Emission-Scanning Electron Microscopy investigation, the cluster size ranged from 20 to 180 nm depending on the concentration of AuNPs. The sensing response of the prepared films was tested against H₂S at different operating temperatures. The effect of growing a mixture of titanium-gold phases as a suitable catalyst for hydrogen sulfide sensitivity is also discussed.

Abstract: A new type of biomimetic films of bilayer lipid membrane (BLM) supported by conductive hybrid film of Au nanoparticles (Au NPs) and cellulose is developed. The facile preparation method of the conductive hybrid films and the relevant micro conducting mechanism under electrochemical redox environment are revealed. The regenerated cellulose film is prepared from the cellulose/N-methylmorpholine N-oxide monohydrate solution. After the cellulose film is regenerated by deionized water, Au NPs in the colloid react with the newborn cellulose film. Rectangular pieces of dry hybrid films with one ends clamped with copper foil are used as electrodes. The lipid solution of phospholipid and cholesterol with a ratio of 3:1 is brushed onto the surface of dry hybrid films. There are only reducing currents in the cyclic voltammetry responses of biomimetic films under the aqueous electrolyte solution of 0.1 mol/L KCl, 1 mmol/L K₃[Fe (CN)₆] and 1 mmol/L K₄[Fe (CN)₆]. It means that the anions of [Fe (CN)₆]^4- are almost impossible to be oxidized into [Fe (CN)₆]^3- by the positively charged surfaces of Au NPs under voltages below 0.3 V.

Abstract: Zinc oxide tetrapods (T-ZnO) were synthesized using thermal oxidation technique from Zn powders mixed with hydrogen per oxide (H₂O₂). Through a detailed field emission scanning electron microscopy (FE-SEM), energy dispersive spectroscopy (EDS), and x-ray diffraction (XRD) showed that the T-ZnO exhibited single crystalline hexagonal wurtzite structure. The leg tip of the T-ZnO was about 8.17±1.17 µm in length and 47.80 nm in diameter. The ethanol sensors, based on the T-ZnO and the T-ZnO doped with Au nanoparticles (Au/T-ZnO), were fabricated and investigated for the ethanol sensing properties. The ethanol sensor response of the T-ZnO and the Au/T-ZnO sensors was tested at the operating temperature of 260-360°C with the ethanol concentration of 50, 100, 500, and 1000 ppm. The results showed that the Au/T-ZnO sensors exhibited exceptionally higher sensitivity than the pure T-ZnO sensors for entire ethanol concentration with optimum temperature of 340°C and 320°C, respectively. This enhancement can be explained in terms of the electron concentration of sensor in air, n₀ and the reaction rate constant, k_Eth between the adsorbed oxygen species and the ethanol vapor due to the increase of effective surface for adsorption of ethanol on the surface. With an excellent catalytic ability, the Au nanoparticles doping on the T-ZnO sensors would result in higher reaction rate constant than the undoped T-ZnO sensors.

Abstract: The role of xanthine in the growth process of Au nanoparticles (AuNPs) was clarified by Uv-vis absorption spectra, resonance light scattering (RLS) spectra, cyclic votlammetry (CV), and differential pulse voltammetry (DPV). In a growth solution containing 0.01 M phosphate buffer solution (PBS, pH 7.4), 24.3 μM HAuCl₄, and 2 mM cetyltrimethylammonium chloride (CTAC), the AuNPs were produced by tannic acid (TA) reduction. The growth of AuNPs was inhibited by the addition of xanthine. The plasmon absorbance band of AuNPs is blue shifted, indicating that larger sized AuNPs were grown in the presence of xanthine. Both the absorbance at 555 nm and RLS intensity at 652 nm of the grown AuNPs decreased linearly with increasing concentrations of xanthine. The linear regression equation are A=1.865−0.016 C_xanthine and I=397.8−4.617C_xanthine for absorbance and RLS intensity, respectively. The results of CV and DPV reveal that the inhibition effect of xanthine on the growth of AuNPs may attribute to the formation of xanthine-Au(III) complex. The conditional stability constants of the complexes were determined to be 2.22×10⁵.

Abstract: A novel technique to covalently immobilize indicator dyes with terminal amino groups for preparing optical sensors is investigated. Au nanoparticles are used as bridges and carriers for anchoring indicator dyes on the surface of a quartz glass slide. 1-Aminopyrene (AP) was employed as an example of indicator dyes and covalently immobilized onto the outmost surface of the glass slide. First, the glass slide was functionalized by (3-mercaptopropyl) trimethoxysilane (MPS) to form a thiol-terminated self-assembled monolayer, where Au nanoparticles were strongly anchored via covalent link. Then, 16-mercaptohexadecanoic acid (MHDA) was self-assembled to bring carboxylic groups onto the surfaces of Au nanoparticles. A further activation by using 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) converted the carboxylic group into succinimide ester. Finally, the active succinimide ester was reacted with 1-aminopyrene (AP). Thus, AP was covalently immobilized to the glass slide and an AP-immobilized sensor was obtained. The resulting sensor was used to determine rutin based on fluorescence quenching. It showed a linear response toward rutin (R) from 5.0 × 10^-7 to 6.0 × 10^-4 mol L^-1 with a detection limit of 2.0× 10^-7 mol L^-1. This AP-immobilized sensor has very satisfactory reproducibility, reversibility, rapid response and no dye-leaching.

Abstract: AgCl@polypyrrole(PPy) nanocomposites were synthesized through in situ chemical oxidation polymerization by using poly(vinylpyrrolidane) (PVP) as dispersant, and some Au colloid were prepared by using KBH4 as reductant and sodium citrate as stabilizer, then the Au nanoparticles-AgCl@PPy hybrid material was formed by physical chemical reaction. Fourier transform infrared spectrometer (FTIR) and electron dispersive spectrometer (EDS) data suggested that the hybrid material were composed of Au, AgCl and PPy. An amperometric glucose biosensor was fabricated by adsorbing glucose oxidase (GOx) to an Au nanoparticles-AgCl@PPy hybrid material modified platinum electrode. The biosensor exhibited a super highly sensitive response to H2O2.

Abstract: In order to prepare the enzyme electrode for sensing of chemical molecules, the Au was coated on the surface of PP film by sputter coater. Polyaniline (PANI) was polymerized on the surface of the coated Au film by electrochemical polymerization of aniline in order to use working electrode. Subsequently, horseradish peroxide (HRP) was immobilized on PANI electrode as follows: Method I. The HRP was immobilized on the surface of PANI electrode by using Au nanoparticle as linker (physical adsorption). Method II. The HRP was immobilized on the surface of PANI electrode by using 2-aminothiophenol and Au nanoparticle as linker (Self-assembling immobilization). Method III. HRP was directly immobilized with PANI electrode by using glutaric dialdehyde as linker (covalent bonding). The sensing efficiency of the prepared HRP-PANI electrode was also examined. The sensing efficiency of the HRP-PANI electrode for H2O2 was as following order; Method I > Method III > Method II..

Abstract: In situ ultrahigh vacuum transmission electron microscope (TEM) is a powerful tool to investigate the dynamic changes of nanostructures on silicon. By observing growth and phase transitions in situ, understanding of their mechanisms can be used to model relevant processes. With the precise knowledge of the changes occurred on an atomic level, accurate control of the growth process can be achieved. The dynamical changes occurred on the nano scale are often unexpected, which also underscores the importance of the approach. In this presentation, we highlight two examples to demonstrate the unique capability of in situ TEM to study the dynamical changes. The examples include collective movement of Au nanoparticles and directed movement of Au-Si droplets on Si bi-crystal.

Abstract: A citrate-stabilizing Au nanoparticles aqueous solution was prepared at near 0 oC by reducing tetracholoaurate(III) ions with sodium borohydride. Combining with Pluronic block copolymers, the citrate-stabilizing Au nanoparticles was nearly completely embedded in the mesoporous silica channels via fast silicification with silicate solution at near neutral pH. After calcination for removing organic templates, Au nanoparticles@mesoporous silicas of high surface area and pore volume were obtained. With different block copolymer, the pore size of the mesoporous silica can be tuned. The Au nanoparticles@SBA-15 mesoporous silica exhibits high catalytic activity to CO oxidation reaction.