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

Dendronization-induced phase-transfer, stabilization and self-assembly of large colloidal Au nanoparticles

The phase-transfer of CTAB-coated aqueous, spherical gold nanoparticles, with metallic core diameters ranging from ca. 27 to 54 nm, into organic solvents by exchanging the primitive polar bilayer with lipophilic, disulfide dendritic ligands is reported. The presence of such a thick nonpolar organic shell around these large nanoparticles enhances their stabilization against aggregation, in addition to enabling their transfer into a variety of solvents such as chloroform, toluene or tetrahydrofuran. Upon the slow evaporation of a chloroform suspension deposited on a solid support, the dendronized hybrids were found to self-assemble into ring structures of various diameters. Moreover, their self-assembly at the liquid-air interface affords the formation of fairly long-range ordered monolayers, over large areas, that can then be entirely transferred onto solid substrates.

Active and Stable Platinum/Ionic Liquid/Carbon Nanotube Electrocatalysts for Oxidation of Methanol

Platinum (Pt) nanoparticles (NPs) on carbon nanotubes (CNTs) from PtCl62– ions through a facile ionic liquid (IL)-assisted method has been developed and used for methanol oxidation. 1-Butyl-3-methylimidazolium (BMIM) with four different counter ions (PF6–, Cl–, Br–, and I–) have been tested for the preparation of Pt/IL/CNT nanohybrids, showing the counter ions of ILs play an important role in the formation of small sizes of Pt NPs. Only [BMIM][PF6] and [BMIM][Cl] allow reproducible preparation of Pt/IL/CNT nanohybrids. The electroactive surface areas of Pt/[BMIM][PF6]/CNT, Pt/[BMIM][Cl]/CNT, Pt/CNT, and commercial Pt/C electrodes are 62.8, 101.5, 78.3, and 87.4 m2 g-1, respectively. The Pt/[BMIM][Cl]/CNT nanohybrid-modified electrodes provide higher catalytic activity (251.0 A g–1) at a negative onset potential of -0.60 V than commercial Pt/C-modified ones do (133.5 A g–1) at -0.46 V. The Pt/[BMIM][Cl]/CNT electrode provides the highest ratio (4.52) of forward/reverse oxidation current peak, revealing a little accumulation of carbonaceous residues.

Voltammetry and redox charge storage capacity of ferrocene-functionalized silica nanoparticles

We describe the electrochemistry of 15 nm diameter silica nanoparticles densely functionalized with ferrocene (FcSiO(2)) through siloxane couplings. Each nanoparticle bears approximately 600 Fc sites, as measured by potentiometric titration (590 Fc) and diffusion-controlled voltammetry (585 Fc) and estimated by XPS (630 Fc). The nanoparticle ferrocene coverage amounts to ca. a complete monolayer of ferrocene sites, which react electrochemically without mutual interactions and which are apparently fully accessible for diffusion-controlled electrode reactions. Diffusion-controlled voltammetry of the FcSiO(2) nanoparticles was observed in dilute methanol dispersions and in more concentrated slurry phases formed in methanol/acetonitrile mixtures. Electrochemical studies reveal interesting behavior in the dilute and more concentrated solutions. Because of the large nanoparticle surface area/volume ratio, the ferrocene-coated silica nanoparticles are capable of storing up to 5 x 10(7) C/m(3) of redox charge as dry phases and 6 x 10(5) C/m(3) in the concentrated slurries.

Investigation of the electrochemical and electrocatalytic behavior of positively charged gold nanoparticle and l-cysteine film on an Au electrode

Positively charged gold nanoparticle (positively charged nano-Au), which was prepared, characterized by xi-potential and transmission electron microscopy (TEM) was used in combination with L-cysteine to fabricate a modified electrode for electrocatalytic reaction of biomolecules. Compared with electrodes modified by negatively charged gold nanoparticle/L-cysteine, or L-cysteine alone, the electrode modified by the positively charged gold nanoparticle/L-cysteine exhibited excellent electrochemical behavior toward the oxidation of biomolecules such as ascorbic acid, dopamine and hydrogen peroxide. Moreover, the proposed mechanism for electrocatalytic response of positively charged gold nanoparticle was discussed. The immunosensor showed a specific to ascorbic acid in the range 5.1x10(-7)-6.7x10(-4) M and a low detection limit of 1.5x10(-7) M. The experimental results demonstrate that positively charged gold nanoparticle have more efficient electrocatalytic reaction than negatively charged gold nanoparticle, which opens up new approach for fabricating sensor.

Photofragmentation of Phase-Transferred Gold Nanoparticles by Intense Pulsed Laser Light

Gold nanoparticles with an average diameter of approximately 20 nm were prepared in an aqueous solution by a wet chemistry method. The parent gold nanoparticles were then capped with a 4-aminothiophenol protecting layer and transferred into toluene by tuning the surface charge of the modified nanoparticles. Gold nanoparticles before and after phase transfer were subjected to photofragmentation by a pulsed 532 nm laser. The effects of solvent properties and surface chemistry on the photofragmentation of the gold nanoparticles have been investigated. Fast photofragmentation has been observed in the organic solvent in which the dielectric constant, heat capacity, and thermal conductivity are lower. The results suggest new approaches for the preparation of very small gold clusters from gold nanoparticles.

Influence of intense pulsed laser irradiation on optical and morphological properties of gold nanoparticle aggregates produced by surface acid-base reactions

Gold nanoparticles were surface modified with an ionizable and pH-sensitive monolayer of thiobarbituric acid (TBA). By variation of the pH value of the solution, nanoparticle aggregates can be produced in a controlled way. The aggregates thus prepared were irradiated with an intense pulsed laser at 532 nm. The products in solution were examined by transmission electron microscopy (TEM) and optical absorption spectroscopy. The TEM images of the products revealed that the nanoparticle aggregates dissociate upon laser irradiation and form much smaller gold nanoparticles. The optical absorption spectra measured simultaneously show the gradual disappearance of the absorbance band of the aggregates at around 680 nm. Additionally, a blue shift (from 534 to 524 nm) of the resonance absorbance corresponding to isolated nanoparticles has been observed. All the observations suggest that the colloidal solution becomes more stable after laser irradiation. Both the reduced nanoparticle size and the stabilizing TBA ligands present on the particle surface contribute to the acquired stability of the colloidal solutions.

Loosely packed self-assembled monolayer of N-hexadecyl-3,6-di(p-mercaptophenylacetylene)carbazole on gold and its application in biomimetic membrane research

Dithiols of N-hexadecyl-3,6-di(p-mercaptophenylacetylene)carbazole (HDMC) have been synthesized and employed to form self-assembled monolayers (SAMs) on gold. One characteristic of the HDMC molecule is its peculiar molecular structure consisting of a large and rigid headgroup and a small and flexible alkyl-chain tail. HDMC adsorbates can attach to gold substrates by a strong Au-S bond with weak van der Waals interactions between the alkyl-chain tails, leading to a loosely packed hydrophobic SAM. In this way we can couple hybrid bilayer membranes (HBMs) to gold surfaces with more likeness to a cell bilayer than the conventional HBMs based on densely packed long-chain alkanethiol SAMs. The insulating properties and stability of the HDMC monolayer as well as the HDMC/lipid bilayer on gold have been investigated by electrochemical techniques including cyclic voltammetry and impedance spectroscopy. To test whether the quality of the bilayer is sufficiently high for biomimetic research, we incorporated the pore-forming protein alpha-hemolysin) and the horseradish peroxidase into the bilayers, respectively. Experimental results demonstrated that this type of loosely packed hydrophobic SAM has great potential in biomimetic bilayer research and biosensor application.