An approach for fabricating self-assembled monolayer of Ag nanoparticles on gold as the SERS-active substrate

In this paper, an approach for fabricating an active surface-enhanced Raman scattering (SERS) substrate is adopted. This approach is based on the assembling of silver nanoparticles film on gold substrate. Rhodamine 6G (R6G) and p-aminothiophenol (P-ATP) were used as probe molecules for SERS experiments, showing that this new active substrate has sensitivity to SERS response. Tapping-mode atomic force microscopy (AFM) was also used to investigate the surface morphology following the fabricating process of the active SERS substrate, which showed that large quantities of silver nanoparticles were uniformly coated on the substrate.

Fabrication of silver nanoparticles ring templated by plasmid DNA

Silver nanoparticles ring was successfully fabricated by electrostatic assembling 4-aminothiophenol (4-ATP) capped silver nanoparticles on predefined extended circular plasmid pBR322 DNA. The silver nanoparticles ring which was about 1.5 mu m in length, and about 2.2 nm in height can be obtained by adjusting the reaction time. The normal Raman scattering spectra reveal that the 4-ATP has contacted with the silver nanoparticles by forming a strong Ag-S bond. The AFM data show that the assembly of 4-ATP capped silver nanoparticles on DNA is ordered.

Electrostatic assembly of Cu2O nanoparticles on DNA templates

In this paper, a method for highly ordered assembly of cuprous oxide (Cu2O) nanoparticles (NPs) by DNA templates was reported. Cetyltrimethylammonium bromide (CTAB)-capped Cu2O NPs were adsorbed onto well-aligned lambda-DNA chains to form necklace-like one-dimensional (1D) nanostructures. UV-vis, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) were used to characterize the nanostructure. The Cu2O nanostructures fabricated with the method are both highly ordered and quite straight.

One-step polyelectrolyte-based route to well-dispersed gold nanoparticles: Synthesis and insight

Polyelectrolytes have been widely used as building blocks for the creation of thickness-controllable multilayer thin films in a layer-by-layer fashion, and also been used as flocculants or stabilizer of colloids. This paper reports novel finding that a kind of polyelectrolyte, polyamines, can facilely induce HAuCl4 to spontaneously form well-stabilized gold nanoparticles without the additional step of introducing a reducing reagent during the elevation of temperature, even at room temperature in some cases. The polymer chain-confined microenvironment and the acid-induced evolution of amide of such kind of polyelectrolyte solution play an important role in the nucleation and growth of gold nanoparticles. This method would not only be helpful to gain an insight into the formation of gold nanoparticles in polyelectrolyte systems, but also provide a novel and facile one-step polyelectrolyte-based synthetic route to polyelectrolyte protected gold nanoparticles in aqueous media for potential applications. More importantly, this strategy will be general to the preparation of other nanoparticles.

Synthesis and fluorescence properties of Eu2+-doped KMgF3 nanoparticles

The phase diagram of a cetyltrimethyl ammonium bromide( CTAB)/n-butanol/n-octane/KNO3-Mg( NO3)(2) system was drawn. Nanoparticles of Eu2+-doped KMgF3 were prepared from the quaternary microemulsions of cetyltrimethyl ammonium bromide(CTAB), n-butanol, n-octane and water. The X-ray diffraction(XRD) patterns were indexed to a pure KMgF3 cubic phase. The environmental scanning electron microscopic (ESEM) images show the presence of spherical Eu2+-doped KMgF3 nanoparticles with a diameter of ca. 20 nm. The emission of KMgF3: Eu2+ nanoparticles peaks at 360 mn. The excitation band was observed at 250 nm with a blue shift of ca. 70 nm compared with that of KMgF3: Eu2+ single crystal. The preparation method of nano-KMgF3: Eu2+/PMMA composite films was inquired into.

Preparation, characterization and quantized capacitance of 3-mercapto-1,2-propanediol monolayer protected gold nanoparticles

Monolayer protected gold nanoparticles (MPCs) are the focus of recent research for their stability and are deemed as the building blocks of bottom-up strategies. In this Letter, 3-mercapto-1,2-propanediol monolayer protected gold nanoparticles (MPD-MPCs) were synthesized and characterized by transmission electron microscopy, UV/Vis spectroscopy, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The value of quantized double-layer capacitance (1.13 aF) of MPD-MPCs in aqueous media was obtained by differential pulse voltammograms.

Electrochemical study of 4-ferrocene thiophenol monolayers assembled on gold nanoparticles

In this paper, 4-ferrocene thiophenol was employed as a novel capping agent to synthesize electroactive gold nanoparticles. Transmission electron microscopy showed an average core diameter of 2.5 nm. The optical and electrochemical properties of the 4-ferrocene thiophenol capped gold nanoparticles were characterized by UV-Vis spectroscopy and cyclic voltammograms. Surface plasmon absorbance was detected at 522 nm. Cyclic voltammograms revealed the adsorbed layer reaction controlled electrode process, and the formal potential of electroactive ferrocene centers shifted anodically compared with ferrocene in solution, which could be attributed to the electron-withdrawing phenyl moiety linked to ferrocene.

Self-assembly of 4-ferrocene thiophenol capped electroactive gold nanoparticles onto gold electrode

Gold nanoparticles capped by 4-ferrocene thiophenol with an average core size of 2.5 nm and surface plasmon absorbance at 522 nm were place-exchanged with 1,8-octanedithiol, and then self-assembled onto the gold electrode via tail SH group. The self-assembly was characterized by X-ray photoelectron spectroscopy. Cyclic voltammograms examined the coverage fraction of the self-assembled monolayers of the electroactive gold nanoparticles and the formal potential of the indicated SAMs. Further experiments exhibited that the electrode process was controlled by surface confined faradic reactions.

Electroactive gold nanoparticles protected by 4-ferrocene thiophenol monolayer

Numerous reports have focused on ferrocene-terminated electroactive self-assembled monolayers (SAMs) on a flat An surface but only a few on ferrocene SAMs on An colloid. In this paper, we employ 4-ferrocene thiophenol as a novel capping agent to produce electroactive gold nanoparticles in consideration of the peculiar pi-conjugated structure. Transmission electron microscopy shows the narrow-dispersed gold core with an average core diameter of ca. 2.5 nm. UV/vis spectra examine the pi-conjugated structure of 4-ferrocene thiophenol and surface plasmon absorbance of the indicated gold nanoparticles. X-ray photoelectron spectroscopy reveals electronic properties of the An core and thiol ligands. Electrochemical measurement shows that the oxidation peak current is proportional to the scan rate, indicating the electrode process is controlled by adsorbed layer reaction. The formal potential of the Fc-MPCs is compared with that of free ferrocene in MeCN solution and the Fc-SAMs. The shifts are attributed to the phenyl moiety in the 4-ferrocene thiophenol and dielectric constant of the solvation environment.

Preparation of multilayer films containing pt nanoparticles on a glassy carbon electrode and application as an electrocatalyst for dioxygen reduction

In this paper, a simple route for the preparation of Pt nanoparticles is described. PtCl62- and [tetrakis-(N-methylpyridyl)porphyrinato] cobalt (CoTMPyP) were assembled on a 4-aminobenzoic acid modified glassy carbon electrode through the layer-by-layer method. The three-dimensional Pt nanoparticle films are directly formed on an electrode surface by electrochemical reduction of PtCl62- sandwiched between CoTMPyP layers. Regular growth of the multilayer films is monitored by UV-vis spectroscopy. X-ray photoelectron spectroscopy verifies the constant composition of the multilayer films containing Pt nanoparticles. Atomic force microscopy proves that the as-prepared Pt nanoparticles are uniformily distributed with average particle diameters of 6-10 nm. The resulting multilayer films containing Pt nanoparticles on the modified electrode possess catalytic activity for the reduction of dissolved oxygen. Rotating disk electrode voltammetry and rotating ring-disk electrode voltammetry confirm that Pt nanoparticle containing films can catalyze an almost four-electron reduction of O-2 to water in 0.5 M H2SO4 solution.

Synthesis and self-assembly of cetyltrimethylammonium bromide-capped gold nanoparticles

In this article, cetyltrimethylammonium bromide (CTAB)-capped gold nanoparticles were synthesized successfully by using CTAB as a phase-transfer catalyst and stabilizer simultaneously in a two-phase toluene/water system. The as-prepared gold nanoparticles were characterized and analyzed by virtue of X-ray photoelectron spectroscopy, UV-visible absorbance spectroscopy, and infrared spectroscopy. The particle size information and collective self-assembling properties of the CTAB-capped gold nanoparticles on carbon-coated copper grid and mica were evaluated by transmission electron microscopy and atomic force microscopy, respectively. As a result it is demonstrated that the 3-D CTAB monolayers on a gold cluster are in the disordered liquid state. The interparticle spacing can be controlled either physically by the inherent particle-to-particle interactions or chemically by molecular linker. The assembly of both nanoparticles and linker-bridged nanonetworks on mica follows a hydrophobic interaction mechanism.

Simple preparation method of Pd nanoparticles on an Au electrode and its catalysis for dioxygen reduction

A simple method for the fabrication of Pd nanoparticles is described. The three-dimensional Pd nanoparticle films are directly formed on a gold electrode surface by simple electrodeposition at -200 mV from a solution of 1 M H2SO4+0.01 mM K2PdCl4. X-Ray photoelectron spectroscopy verifies the constant composition of the Pd nanoparticle films. Atomic force microscopy proves that the as-prepared Pd nanoparticles are uniformly distributed with an average particle diameter of 45-60 nm. It is confirmed that the morphology of the Pd nanoparticle films are correlated with the electrodeposition time and the state of the Au substrate. The resulting Pd-nanoparticle-film-modified electrode possesses high catalytic activity for the reduction of dissolved oxygen in 0.1 M KCl solution. Freshly prepared Pd nanoparticles can catalyze the reduction of O-2 by a 4-electron process at -200 mV in 0.1 M KCl, but this system is not very stable. The cathodic peaks corresponding to the reduction of O-2 gradually decrease with potential cycling and at last reach a steady state. Then two well-defined reduction peaks are observed at -390 and -600 mV vs. Ag/AgCl/KCl (sat.). Those two peaks correspond to a 2-step process for the 4-electron reduction pathway of O-2 in this neutral medium.

Electrochemical behavior of alpha-Keggin-type nanoparticles, Co(en)(3)(PMo12O40), in polyethylene glycol

The electrochemical behavior of alpha-Keggin-type nanoparticles, Co(en)(3)(PMo12O40) (abbreviated as PMo12-Co), have been studied in poly(ethylene glycol) for four different molecular weights (PEG, average MW 400, 600, 1000, and 2000 g mol(-1)) and containing LiClO4 (O/Li=100/1) supporting electrolyte. The diffusion coefficients of the PMo12-Co nanoparticles were determined using a microelectrode by chronoamperometry for PEG of different molecular weights that were used to describe the diffusion behavior of PMo12-Co nanoparticles in different phase states. Moreover, the conductivity of the composite system increases upon addition of PMo12-Co nanoparticles, which was measured by an a.c. impedance technique. FT-IR spectra and DSC were used to follow the interactions of PEG-LiClO4-PMo12-Co, and well described the reason that the PMo12-Co nanoparticles could promote the conductivity of the PEG-LiClO4-PMo12-Co system.

Preparation of gold nanoparticles protected with polyelectrolyte

Gold nanoparticles were synthesized through the reduction of tetrachlorauric acid (HAuCl4) by NaBH4, with polyethyleneimine(PEI) as stabilizer. The nanoparticles were characterized by LTV-vis spectroscopy and atomic. force microscopy(AFM).

One-step synthesis and size control of dendrimer-protected gold nanoparticles: A heat-treatment-based strategy

Dendrimer-protected gold nanoparticles have been facilely obtained by heating an aqueous solution containing third generation poly(propyleneimine) dendrimers and HAuCl4 without the additional step of introducing other reducing agents. Transmission electron microscopy (TEM) and UV vis data indicate the size the nucleation and growth kinetics of gold nanoparticles thus formed which can be tuned by changing the initial molar ratio of dendrimer to gold.