Preparation of highly conductive, self-assembled gold/polyaniline nanocables and polyaniline nanotubes

One-dimensional gold/polyaniline (Au/PANI-CSA) coaxial nanocables with an average diameter of 5060 nm and lengths of more than 1 mu m were successfully synthesized by reacting aniline monomer with chlorauric acid (HAuCl4) through a self-assembly process in the presence Of D-camphor-10-sulfonic acid (CSA), which acts as both a dopant and surfactant. It was found that the formation probability and the size of the Au/PANI-CSA nanocables depends on the molar ratio of aniline to HAuCl4 and the concentration of CSA, respectively. A synergistic growth mechanism was proposed to interpret the formation of the Au/PANI-CSA nanocables. The directly measured conductivity of a single gold/polyaniline nanocable was found to be high (approximate to 77.2S cm(-1)). Hollow PANI-CSA nanotubes, with an average diameter of 50-60 nm, were also obtained successfully by dissolving the Au nanowire core of the Au/PANI-CSA nanocables.

Surfactantless synthesis of multiple shapes of gold nanostructures and their shape-dependent SERS spectroscopy

A useful method for the synthesis of various gold nanostructures is presented. The results demonstrated that flowerlike nanoparticle arrays, nanowire networks, nanosheets, and nanoflowers were obtained on the solid substrate under different experimental conditions. In addition, surface-enhanced Raman scattering (SERS) spectra of 4-aminothiophenol (4-ATP) on the as-prepared gold nanostructures of various shapes were measured, and their shape-dependent properties were evaluated. The intensity of the SERS signal was the smallest for the gold nanosheets, and the flowerlike nanoparticle arrays gave the strongest SERS signals.

Templated assembly of gold nanoparticles into microscale tubules and their application in surface-enhanced Raman scattering

We report a simple procedure to assemble gold nanoparticles into hollow tubular morphology with micrometer scale, wherein the citrate molecule is used not only as a reducing and capping agent, but also as an assembling template. The nanostructure and growth mechanism of microtubes are explored via SEM, TEM, FTIR spectra, and UV-vis spectra studies. The incorporation of larger gold nanoparticles by electroless plating results in an increase in the diameter of microtubes from 900 nm to about 1.2 mu m. The application of the microtubes before and after electroless plating in surface-enhanced Raman scattering (SERS) is investigated by using 4-aminothiophenol (4-ATP) as probe molecules. The results indicate that the microtubes both before and after electroless plating can be used as SERS substrates. The microtubes after electroless plating exhibit excellent enhancement ability.

Polyamidoamine dendrimers-assisted electrodeposition of gold-platinum bimetallic nanoflowers

Novel Au-Pt bimetallic flower nanostructures fabricated on a polyamidoamine dendrimers-modified surface by electrodeposition are reported. These polyamidoamine dendrimers were stable, and they assisted the formation of Au-Pt bimetallic nanoflowers during the electrodeposition process. These nanoflowers were characterized by field-emitted scanning electron microscopy (FE-SEM), energy-dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction, and electrochemical methods. FE-SEM images showed that the bimetallic nanoflower included two parts: the "light" and the "pale" part. The two parts consisted of many small bimetallic nanoparticles, which was attributed to the progressive nucleation process. Moreover, the "light" part contained more bimetallic nanoparticles. The morphologies of bimetallic nanoflowers depended on the electrodeposition time and potential and the layer number of assembled dendrimers. The average size of nanoflowers increased with the increase in electrodeposition time. The layer number of assembled dendrimers obviously affected the size and morphologies of the "pale" parts of deposited nanoflowers.

Didodecyldimethylammonium bromide lipid bilayer-protected gold nanoparticles: Synthesis, characterization, and self-assembly

Didodecyldimethylammonium bromide (DDAB) lipid bilayer-protected gold nanoparticles (AuNPs), which were stable and hydrophilic, were synthesized by in situ reduction of HAuCl4 with NaBH4 in an aqueous medium in the presence of DDAB. As-prepared nanoparticles were characterized by UV-vis spectra, transmission electron microscopy, dynamic light scattering analysis, and X-ray photoelectron spectroscopy. All these data supported the formation of AuNPs. Fourier transform infrared spectroscopy (FTIR) and differential thermal analysis/thermogravimetric analysis data revealed that DDAB existed in a bilayer structure formed on the particle surface, resulting in a positively charged particle surface. The FTIR spectra also indicated that the DDAB bilayer coated on the surface of AuNPs was probably in the ordered gel phase with some end-gauche defects. On the basis of electrostatic interactions between such AuNPs and anionic polyelectrolyte poly(sodium 4-styrenesulfonate) (PSS), we successfully fabricated (PSS/AuNP)(n) multilayers on a cationic polyelectrolyte poly(ethylenimine) coated indium tin oxide substrate via the layer-by-layer self-assembly technique and characterized as-formed multilayers with UV-vis spectra and atomic force microscopy.

A novel nanometer-scale "gold electrode-molecular wires-silver" junction: An efficient test bed for electrochemical investigation of electron transportation through molecular wires in self-assembled monolayers

A novel "gold electrode-molecular wires-silver" junction was facilely fabricated for electrochemical study on the electron transportation through molecular wires. Rapid electron transportation through this sandwich-like structure was indeed observed by cyclic voltammograms and ac impedance measurements. Since rather reproducible and reliable results are easily available by electrochemical techniques, it would be an efficient and reliable test bed for electrochemical investigation of charge transportation through molecular wires in self-assembled monolayers on electrodes.

Surface-enhanced Raman scattering of silver-gold bimetallic nanostructures with hollow interiors

Surface-enhanced Raman scattering (SERS) activity of silver-gold bimetallic nanostructures (a mean diameter of similar to 100 nm) with hollow interiors was checked using p-aminothiophenol (p-ATP) as a probe molecule at both visible light (514.5 nm) and near-infrared (1064 nm) excitation. Evident Raman peaks of p-ATP were clearly observed, indicating the enhancement Raman scattering activity of the hollow nanostructure to p-ATP. The enhancement factors (EF) at the hollow nanostructures were obtained to be as large as (0.8 +/- 0.3)x10(6) and (2.7 +/- 0.5)x10(8) for 7a and 19b (b(2)) vibration mode, respectively, which was 30-40 times larger than that at silver nanoparticles with solid interiors at 514.5 nm excitation. EF values were also obtained at 1064 nm excitation for 7a and b(2)-type vibration mode, which were estimated to be as large as (1.0 +/- 0.3)x10(6) and (0.9 +/- 0.2)x10(7), respectively. The additional EF values by a factor of similar to 10 for b(2)-type band were assumed to be due to the chemical effect. Large electromagnetic EF values were presumed to derive from a strong localized plasmas electromagnetic field existed at the hollow nanostructures.

Seed-mediated synthesis of branched gold nanoparticles with the assistance of citrate and their surface-enhanced Raman scattering properties

We report an easy synthesis of highly branched gold particles through a seed-mediated growth approach in the presence of citrate. The addition of citrate in the growth solution is found to be crucial for the formation of these branched gold particles. Their size can be varied from 47 to 185 nm. The length of the thumb-like branch is estimated to be between about 5 and 20 nm, and changes slightly as the particle size increases. Owing to these obtuse and short branches, their surface plasmon resonance displays a marked red-shift with respect to the normal spherical particles. These branched gold particles exhibit stronger SERS activity than the non-branched ones, which is most likely related to these unique branching features.

Synthesis of highly faceted multiply twinned gold nanocrystals stabilized by polyoxometalates

A novel and facile chemical synthesis of highly faceted multiply twinned gold nanocrystals is reported. The gold nanocrystals are hexagonal in transmission electron microscopy and icosahedral in scanning electron microscopy. Phosphotungstic acid (PTA), which was previously reduced, serves as a reductant and stabilizer for the synthesis of gold nanocrystals. The PTA-gold nanocomposites are quite stable in aqueous solutions, and electrochemically active towards the hydrogen evolution reaction.

One-step synthesis of 3D dendritic gold/polypyrrole nanocomposites via a self-assembly method

Novel spherical three-dimensional (3D) dendritic gold-polypyrrole nanocomposites were successfully prepared in the presence of an amphiphilic p-toluene sulfonic acid (TSA) as dopant and surfactant via a self-assembly process which is based on the oxidation of pyrrole (Py) and the reduction of the chloroaurate ions, yielding PPy and Au(0) simultaneously. It was found that the probability of obtaining dendritic Au@PPy/TSA nanostructures depended on the concentration of TSA and the rate of addition of the oxidant (HAuCl4), It was also proposed that the supramolecular micelles formed by Py and TSA play the role of a 'soft template' to produce the dendritic Au@PPy/TSA nanocomposites.

Self-assembly of cinnamic acid-capped gold nanoparticles

In this work, a new capping agent, cinnamic acid ( CA) was used to synthesize Au nanoparticles (NPs) under ambient conditions. The size of the NPs can be controlled by adjusting the concentration of reductant ( in our experiment sodium borohydride was used) or CA. The CA-stabilized Au NPs can self-assemble into 'nanowire-like' or 'pearl-necklace-like' nanostructures by adjusting the molar ratio of CA to HAuCl4 or by tuning the pH value of the Au colloidal solution. The process of Au NPs self-assembly was investigated by UV - vis spectroscopy and transmission electron microscopy. The results reveal that the induced dipole - dipole interaction is the driving force of Au NP linear assemblies.

One-step preparation and characterization of PDDA-protected gold nanoparticles

Poly(diallyl dimethylammonium) chloride (PDDA), an ordinary and watersoluble, cationic polyelectrolyte, was investigated for its ability to generate and stabilize gold colloids from a chloroauric acid precursor. In this reaction, PDDA acted as both reducing and stabilizing agents for gold nanoparticles (AuNPs). More importantly, PDDA is a quaternary ammonium polyelectrolyte, which shows that the scope of the reducing and stabilizing agents for metal nanoparticles can be extended from the amine-containing molecules to quaternary ammonium polyelectrolytes or salts. UV-vis spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS) and Fourier transform infrared (FTIR) were used to characterize the synthetic AuNPs. The PDDA-protected AuNPs obtained are very stable and have relative narrow size distribution.

Self-assembling gold nanoparticles on thiol-functionalized poly(styrene-co-acrylic acid) nanospheres for fabrication of a mediatorless biosensor

A novel strategy to construct a sensitive mediatorless sensor of H2O2 was described. At first, a cleaned gold electrode was immersed in thiol-functionalized poly(styrene-co-acrylic acid) (St-co-AA) nanosphere latex prepared by emulsifier-free emulsion polymerization St with AA and function with dithioglycol to assemble the nanospheres, then gold nanoparticles were chemisorbed onto the thiol groups and formed monolayers on the surface of poly(St-co-AA) nanospheres. Finally, horseradish peroxidase (HRP) was immobilized on the surface of the gold nanoparticles. The sensor displayed an excellent electrocatalytical response to reduction of H2O2 without the aid of an electron mediator. The biosensor showed a linear range of 8.0 mu mol L-1-7.0 mmol L-1 with a detection limit of 4.0 mu mol L-1. The biosensor retained more than 97.8% of its original activity after 60 days' storage. Moreover, the studied biosensor exhibited good current reproducibility and good fabrication reproducibility.

Application of electrochemical impedance spectroscopy for monitoring allergen-antibody reactions using gold nanoparticle-based biomolecular immobilization method

Gold nanoparticles were used to enhance the immobilization amount and retain the immunoactivity of recombinant dust mite allergen Der f2 immobilized on a glassy carbon electrode (GCE). The interaction between allergen and antibody was studied by electrochemical impedance spectroscopy (EIS). Self-assembled Au colloid layer (Phi = 16 nm) deposited on (3-mercaptopropyl)trimethoxysilane (MPTS)-modified GCE offered a basis to control the immobilization of allergen Der f2. The impedance measurements were based on the charge transfer kinetics of the [Fe(CN)(6)](3-/4-) redox pair, compared with bare GCE, the immobilization of allergen Der f2 and the allergen-antibody interaction that occurred on the electrode surface altered the interfacial electron transfer resistance and thereby slowed down the charge transfer kinetics by reducing the active area of the electrode or by preventing the redox species in electrolyte solution from approaching the electrode. The interactions of allergen with various concentrations of monoclonal antibody were also monitored through the change of impedance response. The results showed that the electron transfer resistance increased with increasing concentrations of monoclonal antibody.

A novel hydrogen peroxide sensor based on horseradish peroxidase immobilized in DNA films on a gold electrode

A novel third-generation hydrogen peroxide (H2O2) biosensor was developed by immobilizing horseradish peroxidase (HRP) on a biocompatible gold electrode modified with a well-ordered, self-assembled DNA film. Cysteamine was first self-assembled on a gold electrode to provide an interface for the assembly of DNA molecules. Then DNA was chemisorbed onto the self-assembled monolayers (SAMs) of cysteamine to form a network by controlling DNA concentration. The DNA-network film obtained provided a biocompatible microenvironment for enzyme molecules, greatly amplified the coverage of HRP molecules on the electrode surface, and most importantly could act as a charge carrier which facilitated the electron transfer between HRP and the electrode. Finally, HRP was adsorbed on the DNA-network film. The process of the biosensor construction was followed by atomic force microscopy (AFM). Voltammetric and time-based amperometric techniques were employed to characterize the properties of the biosensor derived. The enzyme electrode achieved 95% of the steady-state current within 2 s and had a 0.5 mu mol l(-1) detection limit of H2O2. Furthermore, the biosensor showed high sensitivity, good reproducibility, and excellent long-term stability.