Photo-sensor with photo-electric conversion molecules and a modified gold nanostructured FET gate film

We have investigated a nanostructured electrode from the viewpoint of improving the performance of FETs. The nanostructured gold layer acted as a positive factor contributing to an increase in the photocurrent, while maintaining low levels of photo-voltage (photo-V_oc) of the gold electrode itself and the FET performance (photo-I_ds). Such negative effects of the nanostructured gold layer were attributed to the low-surface coverage of molecules and high interactive ability between the electrode and the electro-active species in the enlarged diffusion layer of the electrolyte solution around the nanostructured gold electrode.     

Synthesis and optical properties of dyes encapsulated in gold hollow nanoshells

Gold nanomaterials are promising objects for applications in optics and medicine because of their unique properties related to the Surface Plasmon Resonances (SPR) phenomena. It is possible to tune these properties with the control of the size and shape of the nanomaterials. Gold hollow spheres nanomaterials are an interesting concept for encapsulation of either dyes or drugs. The study of their properties and their behavior in a bio-environment still remains scarce and some phenomena are still to be explained in particular regarding local field enhancement effect or quenching of their photophysical properties. In this work we describe a process allowing inclusion of optical dyes in gold nanoshells and evaluate the optical properties.     

Photochemical synthesis of colloidal gold nanoparticles

Monodisperse gold nanoparticles protected by small organic molecules or by macromolecules with different sizes and shapes are widely used as a precursor material in various applications of gold nanotechnology. However, their preparation is still a formidable task. In this paper the use of photochemically assisted syntheses of monodisperse gold nanoparticles is summarized and some preparations by the authors’ group are introduced. These include spherical and rod-like particles, bimetallic composite nanoparticles, and syntheses using complex intramolecular photoreduction to generate the reducing agent.     

Preparation and characterization of ultra-low density porous gold foams

We present a simple approach to generate ultra-low density porous gold foams with the density as low as 0.519 gcm^-3. In our work, gold nanoparticles with small grain sizes and good solubility were prepared and used as starting building blocks; afterwards, the freeze-dry technique was employed to prepare gold compound foams. Finally the gold compound foams were sintered to obtain porous gold foams with ultra-low density. The results show that the content of gold element in the foams is close to 99.2%. Even though the density is as low as 0.519 gcm^-3 the foams still have good intensity and can be machined to simple regular shapes. The microstructure analysis results indicate that the gold foams have continuous open structure, the average pores size is about 1-2 μm, and the framework of the gold foams is piled up with gold particles of different sizes. Our approach might give a way to produce low-density gold foams with simple fabrication procedures.     

Sonochemical synthesis of gold nanoparticles on chitosan

Au nanoparticles deposited on chitosan were readily prepared from aqueous solution of NaAuCl₄ containing chitosan powder by the reaction with sonochemically formed reducing species. The average size of the formed Au particles was measured to be 22 nm with a relatively narrow size distribution, although there was no specific stabilizer for Au nanoparticles.     

Langmuir-Blodgett films of gold/silica core/shell nanorods

We report the preparation of Langmuir- and Langmuir-Blodgett films of mesoporous silica coated gold nanorods. The silica coating on the gold nanorods was found to prevent the aggregation of the plasmonic particles trapped at the air/water interface. Due to the small aspect ratio of the gold core and the presence of the silica shell, the orientational alignment of the nanorods in the Langmuir-Blodgett film is hindered. After particle deposition, no plasmon coupling was observed, which enables the design of the resulting film's optical property at the particle level. By using mesoporous silica as the shell material, the accessibility of the metal core's surface is preserved. Organic dye (Rhodamine 6G) was found to be able to penetrate into the mesoporous shell of the gold nanorods, resulting in a red shift of the longitudinal plasmon mode.     

Characterization of gold nanoparticle pentacene memory device with polymer dielectric layer

We report on the electrical behavior of gold nanoparticles (Au NPs) intervened metal-pentacene-insulator-semiconductor structures. The structure adopts polyvinyl alcohol (PVA) and pentacene as gate insulator and semiconductor, respectively. On the PVA (250 nm) film which was spin-coated and UV cross-linked, 3-aminopropyl triethoxysilane was functionalized for self assembling of the Au NPs monolayer. The devices exhibited clockwise hysteresis in their capacitance-voltage characteristics, with a memory window depending on the range of the voltage sweep. A relatively large memory window of about 4.7 V, which was deduced from control devices, was achieved with voltage sweep of (−/+)7 V. Formation of the monolayered Au NPs was confirmed by field effect scanning electron microscopy and atomic force microscopy.     

纳米金/单壁碳纳米管复合物的制备、表征及其多相催化的潜力

制备了一种单壁碳纳米管担载金纳米颗粒复合材料,利用X射线衍射、扫描透射显微镜、能量色散X射线分析、比表面积分析、激光拉曼光谱和紫外-可见分光光度计等对其结构进行了表征.结果表明:纳米金粒为微晶体,其平均直径为7nm且直径分布范围较窄.研究了该单壁碳纳米管担载金颗粒对仲醇的无溶剂氧化的活性和选择性,发现其转化效率可达95％.     

Preparation of thermosensitive gold nanoparticles by plasma pretreatment and UV grafted polymerization

This work is to develop an easy method of plasma treatment and graft polymerization to prepare thermosensitive gold nanoparticles. Gold nanoparticles (Nano-Au) were reduced by trisodium citrate combined with hydrogen tetrachloroaurate(III) tetrahydrate (chloroauric acid) and modified with 11-mercaptoundecanoic acid (MUA) by the self-assembly monolayers (SAM). The surface graft polymerization of N-isopropylacrylamide (NIPAAm) was carried out by two steps, using O₂ plasma pretreatment of the surface on MUA SAM modified Nano-Au to form the peroxide groups on Nano-Au(MUA), and then subsequently using UV light to induce grafting with thermosensitive polymer. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used to direct investigation of the particle size and morphology in situ. The diameters of the gold nanoparticles measured from the TEM images are in good agreement with data measured at room temperature which is about 15 nm. The thermosensitive gold nanoparticles were characterized by chemical structure of surface (ESCA) and Fourier-transform infrared spectroscopy (FTIR). ESCA result suggests that plasma treatments can be employed to generate peroxides on the Nano-Au(MUA) for the subsequent UV graft polymerization of PNIPAAm.     

Coriander leaf mediated biosynthesis of gold nanoparticles

Extracellular biological synthesis of gold nanoparticles was achieved by a simple biological procedure using coriander extract as the reducing agent. The aqueous gold ions when exposed to coriander leaf extract are reduced and resulted in the biosynthesis of gold nanoparticles in the size range from 6.75-57.91 nm. The gold nanoparticles were characterized by UV-Vis spectroscopy, X-ray diffraction (XRD), energy dispersive X-ray analysis (EDAX), fourier transform infra-red spectroscopy (FT-IR) and transmission electron microscopy (TEM). This eco-friendly approach for the synthesis of nanoparticles is simple, amenable for large scale commercial production and technical applications.     

Optical properties of suspensions of gold half-shells

Suspensions of mesoscale gold half-shells of controlled size were produced by microsphere-templated vapour deposition and their optical properties were studied. The transmission spectra of the particles exhibited an extinction peak that could be tuned from 530 to over 2000 nm by variation of the diameter of the template used. In this respect the optical properties of these reduced-symmetry particles are similar to those of full nanoshells, however they may be more convenient to prepare.     

Lipase immobilized on nanostructured cerium oxide thin film coated on transparent conducting oxide electrode for butyrin sensing

Nanostructured cerium oxide (CeO₂) thin films were deposited on transparent conducting oxide (TCO) substrate using spray pyrolysis technique with cerium nitrate salt, Ce(NO₃)₃·6H₂O as precursor. Fluorine doped cadmium oxide (CdO:F) thin film prepared using spray pyrolysis technique acts as the TCO film and hence the bare electrode. The structural, morphological and elemental characterizations of the films were carried out using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray analysis (EDX) respectively. The diffraction peak positions in XRD confirmed the formation of highly crystalline ceria with cubic structure and FE-SEM images showed uniform adherent films with granular morphology. The band gaps of CeO₂ and TCO were found to be 3.2 eV and 2.6 eV respectively. Lipase enzyme was physisorbed on the surface of CeO₂/TCO film to form the lipase/nano-CeO₂/TCO bioelectrode. Sensing studies were carried out using cyclic voltammetry and amperometry, with lipase/nano-CeO₂/TCO as working electrode and tributyrin as substrate. The mediator-free biosensor with nanointerface exhibited excellent linearity (0.33–1.98 mM) with a lowest detection limit of 2 μM with sharp response time of 5 s and a shelf life of about 6 weeks.     

Preparation of carbon nanotube/chitosan/gold nanoparticle composite microspheres

The electrostatic layer-by-layer (LbL) assembly of acid-modified multi-walled carbon nanotubes (MWNTs) and biopolymer chitosan (CHIT) is realized on planar substrates and polystyrene (PS) microsphere templates, respectively. The successful stepwise growing process of the composite films on planar substrates is investigated and confirmed by scanning electron microscopy and UV-vis spectroscopy. The transfer of the LbL assembly of MWNTs and CHIT to spherical PS microspheres leads to novel (MWNT/CHIT)PS core-shell structure, on which the gold nanoparticles (GNPs) are deposited to fabricate GNP(MWNT/CHIT)PS composite microspheres. The glass carbon electrodes modified with such (MWNT/CHIT)PS or GNP(MWNT/CHIT)PS composites exhibit satisfactory electrocatalytic activities for biomolecule dopamine.     

One-pot sonochemical synthesis of dendron-stabilized gold nanoparticles as promising nano-hybrid with potential impact in biological application

Dihydroxy fatty acid-based (DF) dendron-stabilized gold nanoparticles (AuNps) were synthesized without adding any external reducing or stabilizing agent. Each DHA base dendron (G1, G2, or G3) possesses a single thiol at the focal point and free -OH groups at the other terminal and as a result can be used to reduce AuCl₄⁻ to Au⁰ and stabilize the nascent AuNps by the thiol group. The size and distribution of the AuNp produced can also be correlated with the rate of Au (III) reduction. TEM images vividly demonstrate the specific morphology of gold nanoparticles with different sizes and shapes obtained by using different generations of DF dendrons.     

Annealing effect on the structural and optical properties of embedded Au nanoparticles in silicon suboxide films

Au/SiO_x nanocomposite films have been fabricated by co-sputtering Au wires and SiO₂ target using an RF magnetron co-sputtering system before the thermal annealing process at different temperatures. The structural and optical properties of the samples were characterized using X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), optical transmission, and reflection spectroscopy. XPS analysis confirms that the as-prepared SiO_x films are silicon-rich suboxide films. FESEM images reveal that with an increase in annealing temperature, the embedded Au NPs tend to diffuse toward the surface of the SiO_x films. In IR spectra, the intensity of the Si-O-Si absorption band increases with the annealing temperature. Optical spectra reveal that the position and intensity of the surface plasmon resonance (SPR) peak are dominated by the effect of the inter-particle distance and size of the Au NPs embedded in the SiO_x films, respectively. The SPR absorption peak shows the blue-shift from 672 to 600 nm with an increase in annealing temperature. The growth of silica nanowires (SiO_x NWs) is observed in the film prepared on a c-Si substrate instead of a quartz substrate and annealed at temperatures of 1000 °C.     

Electrochemical and <Emphasis Type="Italic">in situ</Emphasis> spectroelectrochemical studies of gold nanoparticles immobilized Nafion matrix modified electrode

Electrochemical and in situ spectroelectrochemical behaviours of phenosafranine (PS⁺) were studied at the gold nanoparticles (Au_Nps) immobilized Nafion (Nf) film coated glassy carbon (GC) and indium tin oxide (ITO) electrodes. Cyclic voltammetric studies showed that the PS⁺ molecules strongly interact with the Au_Nps immobilized in the Nf matrix through the electrostatic interaction. The presence of Au_Nps in the Nf film improved the electrochemical characteristics of the incorporated dye molecules. The emission spectra of Nf-Au_Nps-PS⁺ films showed that the incorporated PS⁺ was quenched by Au_Nps and it could be explained based on the electronic interaction between the Au_Nps and PS⁺ molecules. The in situ spectroelectrochemical study showed an improved electrochemical characteristic of the incorporated PS⁺ molecules at the ITO/Nf-Au_Nps electrode when compared to the ITO/Nf electrode.     

Optical and photoelectrical studies of gold nanoparticle-decorated C60 films

Optical and photoelectrical studies were performed on octane-1,8-dithiol cross-linked fullerene films, with supported gold nanoparticles (C₆₀-DT-Au). According to high-resolution transmission electron microscopy observations, the average size of obtained gold nanoparticles was about 5 nm, and the shape was spherical. The comparative investigation of optical properties of pristine and cross-linked with octane-1,8-dithiol C₆₀ films, decorated with gold nanoparticles, found the difference in the extinction coefficient spectra, which was observed also in the photocurrent spectra of barrier heterostructure Au/C₆₀/Si. The analysis of dark current-voltage characteristics for Au/C₆₀/Si heterostructures showed that the model for them includes the barrier at the C₆₀/Si interface and internal barriers in the C₆₀ layer, caused by the trapping centers. The hopping mechanism of the current transport in the C₆₀ layer was supplemented with the Poole-Frenkel emission process on these centers, with the barrier height greater for the fullerene C₆₀ film cross-linked with octane-1,8-dithiol.     

Synthesis,optical properties and self-assembly of gold nanorods

Noble metal nanostructures of different aspect ratios were synthesised and optically characterised at individual nanorod level. Rayleigh scattering spectroscopy/scanning electron microscopy measurements were performed to uniquely correlate optical signatures with nanorod size and shape. Scattering spectra of nanorods were dominated by the intense longitudinal surface plasmon resonance (SPR) band in the near-infrared part of the spectrum. This band was found to be highly shape and size dependent. Droplet evaporation techniques and application of dielectrophoretic forces have been used to organise nanorod dispersions into ordered arrays. Depending on the technique and nanoparticle size used, nanorods were found to form one, two or three dimensional (1D, 2D and 3D) superstructures. Within these superstructures nanorods organised themselves into end-to-end lines (1D), side-to-side fashion (2D) or hexagonal arrangements (3D).     

Gold nanoparticles incorporated mesoporous silica thin films of varied gold contents and their well-tuned third-order optical nonlinearities

Gold nanoparticles (NPs) incorporated mesoporous silica thin films (MSTFs) of varied gold contents from 4.64 to 29.15 wt.% were synthesized through a refined chemical modification to the mesopore surface using different amounts of silane with amino end group. The microstructures of the composite thin films were characterized and the off-resonant third-order optical nonlinearities of the composite thin films were investigated by Z-scan technique at 1064 nm. The resultant composite thin films showed increased third-order optical nonlinear susceptibility (χ⁽³⁾) from 4.26 × 10⁻¹¹ to 9.24 × 10⁻¹⁰ esu at increased gold contents. The dependence of χ⁽³⁾ on gold content have been discussed, which can be described by an exponent function y = y₀ + Ae^−x/t when the gold contents of the composite thin films were below 30 wt.%.     

Synthesis and optical properties of cubic gold nanoframes

This paper describes a facile method of preparing cubic Au nanoframes with open structures via the galvanic replacement reaction between Ag nanocubes and AuCl₂ ⁻. A mechanistic study of the reaction revealed that the formation of Au nanoframes relies on the diffusion of both Au and Ag atoms. The effect of the edge length and ridge thickness of the nanoframes on the localized surface plasmon resonance peak was explored by a combination of discrete dipole approximation calculations and single nanoparticle spectroscopy. With their hollow and open structures, the Au nanoframes represent a novel class of substrates for applications including surface plasmonics and surface-enhanced Raman scattering.