Surface Of Au Nanoparticles Research Articles

Preparation and electrochemical properties of MnO2nanosheets attached to Au nanoparticles on carbon nanotubes

A wet chemical route for the preparation of MnO(2) nanosheet/Au nanoparticle/MWNT hybrid materials is developed. The Au nanoparticles are prepared by reducing AuCl(4)(-) with citrate and attached to thiol-modified MWNTs. Owing to the reducing property and the binding ability to Mn-containing species of capping agents surrounded the Au nanoparticles, the MnO(2) nanosheets are formed on the surface of Au nanoparticles. The ternary nanocomposites of MnO(2)/Au/MWNT have been characterized by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and FT-IR spectroscopy. The affiliation of MnO(2) nanosheets into the hybrids remarkably enhances the electrocatalytic performance of Au nanoparticle/MWNT towards the oxygen reduction reaction. The specific capacitance of the ternary hybrids is also increased dramatically comparing with that of Au/MWNT.

Heterostructured CIGS–Au nanoparticles: from Au–CIGS side-by-side structure to Au-core/CIGS-shell configuration

Heterostructured Au-Copper Indium Gallium Selenide (CIGS) nanoparticles (nps) with Au-CIGS side-by-side and Au-core/CIGS-shell configurations have been synthesized in a controllable manner using seed mediated growth. Detailed microstructure analysis reveals that (112) planes in the tetragonal chalcopyrite CIGS serve as the predominant termination surfaces during single phase CIGS nanoparticle growth. Preferential nucleation of Au on such planes determines the Au-CIGS side-by-side configuration when the pre-synthesized CIGS nps are used as the seeds for further Au growth. Reversing the growth sequence by employing Au nano-seeds results in Au-core/CIGS-shell configuration, as determined by the non-preferential nucleation of CIGS on the spherical Au nanoparticle surface. The different morphological configurations of the heterostructures are found to modify the surface plasmon resonance of Au in the corresponding samples.

Electrochemical sensing the genotoxicity of Cu2O nanocubes activated by hydrogen peroxide electro-generated on the surface of Au nanoparticles

In order to investigate the genotoxicity of Cu2O nanocubes, a novel electrochemical biosensor was constructed by incorporating the mixture of Cu2O nanocubes and Au nanoparticles (AuNPs) into a multi-membrane containing natural ds-DNA. The ds-DNA was damaged in situ in the membrane and the DNA damage was monitored by DPV with two electrochemical indicators, Co(phen)33+ and Ru(NH3)63+. The mechanism studies showed that the nanoCu2O and AuNPs had synergistic effects on DNA damage and the DNA damage reagent (OH) was generated via electro-Fenton (E-Fenton) reactions on the surface of Cu2O nanocubes and Au nanoparticles. This method was very suitable to study the genotoxicity mechanisms of nanomaterials and it had potential application in studying some chemicals anti-oxidation property.

Design of a peptide linker group to increase the surface enhanced Raman spectroscopy signal intensity of a rhodamine-nanoparticle system

The surface enhanced resonance Raman spectra of three modified carboxy-x-rhodamine dyes were recorded using Au nanoparticles and an excitation laser operating at 670 nm. The dyes were modified with a linker group designed both to increase the surface enhanced Raman spectroscopy signal and to couple the dye to the Au nanoparticles surface. The maximum signal intensity was recorded for a Cys-Gly linker with Cys thiol group acting as the coupling point to the Au surface and Gly-NH2 group used to attach the carboxy-x-rhodamine dye. This gave a signal intensity in the 1503 cm−1 Raman peak that was more than 20 times greater than for the unmodified dye. The Au nanoparticles used had a diameter of 49.8 ± 1.2 nm and were synthesised by the citrate reduction method.

Preparation of a nonleaching, recoverable and recyclable palladium-complex catalyst for Heck coupling reactions by immobilization on Au nanoparticles

The loading of a palladium complex immobilized on the surface of Au nanoparticles (NPs) was controlled through coordination to a supported spacer ligand (SL = S(CH 2) 11NHP(O)(2-py) 2) to yield catalyst particles of the composition (RS) x Au(SL) y (SL–PdCl 2) z (SR = S(CH 2) 7CH 3; x: y: z = (0.31–2.3):1:(0.45–3.3)) with diameters of 3.1–4.9 nm. A fraction of the supported spacer ligands (23–69%) was left uncapped to capture any soluble Pd species resulting from leaching. These surface-bound Pd(II)-complex catalysts were highly effective for Heck reactions of iodobenzene and alkylacrylates, yielding a maximum turnover frequency (TOF) of 4.87 × 10 4 h 1. Their catalytic activity was three- to tenfold higher than that of their unbound counterparts. These hybrid catalysts could be dissolved and precipitated. They could be quantitatively recovered and effectively recycled 15 times without significant loss of reactivity. The recovered Au NP-supported palladium could be also dissolved, precipitated and isolated. Various spectroscopic analyses were performed to determine a surface-structure composition of (RS) x Au(SL) 1(SL–Pd 0) 0.53.

Investigation of the NaBH4-Induced Aggregation of Au Nanoparticles

Colloidal Au nanoparticles (AuNPs) with a diameter of 17 nm were prepared by the reduction of HAuCl(4) with citrate trisodium. The addition of NaBH(4) to the prepared citrate-stabilized AuNP solutions not only induced a blue shift in the surface plasmon resonance peak (lambda(max)) because of the increased number of electrons in the NPs injected by NaBH(4) but also affected the stability of citrate adsorbed on AuNPs. The zeta potential of AuNPs after the addition of 6 mM NaBH(4) decreased (67%) but was restored (88%) after the discharge of the injected electrons. The effect of NaBH(4) treatment on the stability of citrate ions on AuNPs was investigated by X-ray photoelectron spectroscopy (XPS). The XPS data showed that citrate ions partially desorbed from the surfaces of AuNPs (67%) after NaBH(4) treatment but readsorbed onto the AuNPs (80%) after the discharge of the NPs; this result agrees well with the zeta potential data. The partial removal of citrate ions from AuNPs results in an anisotropic charge distribution around the AuNPs. By increasing the amount of NaBH(4) and the electrolyte concentration of the solution, non-close-packed aggregates of AuNPs can be formed, from monomers to small aggregates containing a few AuNPs and 3D network aggregates.

Solvothermal syntheses of hollow carbon microspheres modified with –NH 2 and –OH groups in one-step process

Homogeneous and monodisperse hollow carbon microspheres (HCMS) functionalized with amino and hydroxyl groups are synthesized by decomposing 2,4,6-tribromophenol/ferrocene mixture in the presence of ammonia via a one-step solvothermal process at 250 °C for 24 h. The effect of experimental conditions on the morphology of carbon microspheres has been investigated systematically. The surface of the HCMS is modified with amino and hydroxyl groups through the synthesis process as confirmed by infra-red spectroscopy and X-ray photoelectron spectroscopy. The pore-size distribution and the specific area of macropores are measured by nitrogen adsorption–desorption and mercury intrusion porosimetry. The as-synthesized HCMS has the high Brunauer–Emmett–Teller surface area of 289 m 2/g and macropores whose diameter is mostly larger than 100 nm. To investigate the chemical reactivity of functionalized groups on the surface of HCMS, Au and Ag nanoparticles are successfully loaded onto HCMS by direct reduction of HAuCl 4 or AgNO 3 without adding any reducing agent.

Self-Assembled Heterosupramolecular Visible Light Photocatalyst Consisting of Gold Nanoparticle-Loaded Titanium(IV) Dioxide and Surfactant

Au nanoparticle surface plasmon resonance-induced photocatalytic chemoselective oxidation of alcohols to carbonyl compounds has been investigated. The heterosupramolecular system consisting of Au nanoparticle-loaded titanium(IV) dioxide and surfactant molecular assembly dramatically enhances the reaction. This system should evolve the photocatalyst to intelligent nanodevices.

Understanding the Mechanism of Amino Acid-Based Au Nanoparticle Chain Formation

Understanding the surface orientation and interactions between biomolecules and nanoparticles is important in order to determine their effects on the final structure and activity. At present, limited analytical techniques are available to probe these interactions, especially for materials dispersed in solution. We recently demonstrated that arginine, a simple amino acid, is able to bind to the surface of Au nanoparticles in a segregated pattern, which produces an electronic dipole across the structure. As a result, the formation of linear chains of Au nanoparticles occurred that was dependent upon of the concentration of arginine. Here, we present new information concerning the mechanism of assembly and demonstrate unique reaction conditions that can be used to directly control the assembly rate, and thus the size of the final superstructure that is produced. The assembly process was modulated by the arginine/Au nanoparticle ratio, the temperature of the system, the dielectric of the solvent, and the solution ionic strength, all of which can be used in combination to control the process. These effects were monitored using UV-vis spectroscopy, transmission electron microscopy, and dynamic light scattering. From these results, it is suggested that the second step of the assembly process, which is the formation of nanoparticle chains mediated by Brownian motion, controls the overall assembly rate and thus the size and orientation of the final superstructure produced. Furthermore, the reaction kinetics of the system have been studied from which rate constants and activity energies have been extracted for electrostatic-based nanoparticle assembly. This analysis indicates that the assembly/organization step is likely broken into two substeps with the formation of nanoparticle dimers occurring in solution first, followed by the oligomerization of the dimers to form the linear and branched chains. The dimerization step follows traditional second-order kinetics and is relatively fast, while the oligomerization process is quite complex and is anticipated to be slower than the dimerization step. These results are important, as they lay the basis for the subsequent use of this technique for the possible fabrication of electronic device components or as sensitive assays to probe the surface structure of nanomaterials.

Modification of ZnO nanorods through Au nanoparticles surface coating for dye-sensitized solar cells applications

Dye-sensitized solar cells (DSSC) based on ZnO nanorods were fabricated and modified through the addition of Au nanoparticles. The as-synthesized ZnO nanorods were well-dispersed and of high crystallinity quality leading to a high cell efficiency of 5.2%. On the other hand, thick layer of Au nanoparticles aggregation may have led to distortion of plasmonic effect. Also, the addition of Au nanoparticles have effectively decreased the surface area of ZnO nanorods with direct contact to the dye molecules, resulting in a lower amount of adhered dye molecules to convert sunlight. The electrons generated by the photo-absorption through thick aggregated Au nanoparticles layer may have a lower injection rate to ZnO nanorods as compared to those absorbed by the dye.

Luminescent gold–poly(thiophene) nanoaggregates prepared by one-step oxidative polymerization

We report the facile synthesis, formation mechanism, and photoluminescent (PL) properties of gold–poly(thiophene) (Au–PTh) nanoaggregates. They were prepared by one-step oxidative polymerization, in which Au3+ ion was utilized as an oxidizing agent for the polymerization of thiophene. Transmission electron microscopy (TEM) and high-resolution TEM (HR-TEM) analyses demonstrated that the ‘raspberry-like’ Au–PTh nanoaggregates consist of individual Au NPs covered by PTh and stabilized by Tween 80. For Au–PTh nanoaggregates, a clear red shift in the SP peak was observed in the UV absorption spectra as compared with pristine Au nanoparticles (NPs). This red shift of the SP band is a consequence of the location of π-conjugated PTh on the surface of Au NPs, resulted from a strong binding between sulfur atoms of PTh and the Au NPs (sulfur–gold interaction). The strong interaction between the gold and sulfur atoms of PTh in the Au–PTh nanoaggregates was observed by X-ray photoelectron spectroscopy (XPS) analysis. The SP effect contributes to the PL intensity enhancement of the Au–PTh nanoaggregates and was confirmed by confocal laser scanning microscopy (CLSM).

Effect of atom and molecule adhesion on surface magnetism of Au nanoparticle

ab initio calculations are carried out on the magnetism of the Au surface where ionic bonded molecules such as HCl and KCl are put on the Au thin layer surface or Au nanoparticle surface. The reason why the ionic molecules are introduced in the model is that the anion contacting with the Au attracts electrons and the charge transfer from the Au atom to anion may be expected to cause the lowering the Fermi level, resulting in the d band crossing the Fermi level. As for the layer structure models, the calculations revealed that the d electron of the Au is still below the Fermi level (≈ 2 eV) and that the ferromagnetism should not be the ground state. On the other hand, for the particle model the d band is expected to be crossing the Fermi level. The result of the calculations suggests that the Au surface has a potential to be ferromagnetic (the magnetic moment of 0.1μB is expected), but the KCl molecule does not have significant effect on the occurrence of the magnetic moment.

Electromagnetic field enhancement in the gap between two Au nanoparticles: the size of hot site probed by surface-enhanced Raman scattering

We have estimated the apparent size of the 'hot' site for surface-enhanced Raman scattering (SERS) located within the gap between two spherical Au nanoparticles. Initially, 55-nm sized Au nanoparticles are laid on a thiol-group terminated silane film, and then 1,4-phenylenediisocyanide (1,4-PDI) molecules are self-assembled onto the Au nanoparticles. 1,4-PDI is bonded to Au by forming one Au-CN bond, with another isocyanide group being pendent with respect to the Au surface. Up to this point, no Raman scattering is detected at all for 1,4-PDI. Upon attaching new Au nanoparticles onto the pendent isocyanide groups of 1,4-PDI, a Raman signal is distinctly observed. In agreement with the finite-difference time-domain (FDTD) calculation, this is understood in terms of the electromagnetic hot sites formed at the gaps between two Au nanoparticles. The Raman signal does not increase further, however, even after the adsorption of additional 1,4-PDI onto the vacant surfaces of the second Au nanoparticles. To a rough estimate, about 400 molecules residing only within a 10-nm diameter area of the center of the gap, adsorbed in the first stage, are then conjectured to have contributed most of the measured Raman signal of 1,4-PDI. This apparently indicates that the size of 'hot' site is very limited.

Bifunctional polyacrylamide based polymers for the specific binding of hexahistidine tagged proteins on gold surfaces

We describe a modified bifunctional analogue of polyacrylamide that spontaneously forms self-assembled polymeric thin films on Au surfaces. The film is engineered to specifically bind histidine tagged proteins (6His), while simultaneously remaining inherently resistant to the non-specific adsorption of proteins in solution. The backbone of a polyacrylamide-co-n-acryloxysuccinimide copolymer is functionalized via tandem active ester (NHS) couplings with 3-(methylthio)propylamine (MTP) and nitrilotriacetic acid (NTA). The resulting functionalized polymers form stable and exceptionally hydrophilic thin films that are approximately 2-5 nm thick, a mass coverage that varies with the MTP graft density. These films are characterized using a variety of techniques (X-ray photoelectron spectroscopy (XPS), reflection absorption infrared spectroscopy (RAIRS), ellipsometry, surface plasmon resonance (SPR), and matrix assisted laser desorption ionization (MALDI)) to establish their structure and function. The protein resistance of the films, as demonstrated by their exposure to solutions of bovine serum albumin (BSA), can be modulated by the amount of MTP grafted to the polymer, which in turn, affects their mass coverage. We show that it is possible to specifically capture hexahistidine tagged proteins with low incidences of nonspecific adsorption using these materials, a discrimination quantified using surface plasmon resonance (SPR) at concentrations down to approximately 20 nM. These polymers also bind strongly to the surfaces of Au nanoparticles, stabilizing them against aggregation, providing them with a similar capacity to selectively bind 6His tagged proteins that can then be speciated using MALDI.

Ultrasensitive chemiluminescence quantification of single-nucleotide polymorphisms by using monobase-modified Au and CuS nanoparticles

An ultrasensitive chemiluminescence method based on the Au nanoparticles amplification for the quantitative detection of single-nucleotide polymorphisms (SNPs) in genomic DNA was accomplished by the DNA polymerase I (Klenow fragment)-induced coupling of the nucleotide-modified nanoparticle probe to the mutant sites of duplex DNA under the Watson–Crick base-pairing rule. The concentration of the one-base mutant DNA was determined by chemiluminescence (CL) detection of the cupric ions dissolved from the CuS nanoparticles (NPs) modified on the Au NPs. The incorporation of Au NPs in this method significantly enhanced the sensitivity because a single Au NP can be loaded with 77 CuS NPs through the link-age of an amidization reaction between mercaptoacetic acid on the surface of Au NPs and aminoethanethiol on the surface of CuS NPs. A preconcentration process of cupric ions performed by anodic stripping voltammetric (ASV) technology further increased the sensitivity of the design for about 10-fold. As a result of these two combined effects, this method could detect as low as 19 aM SNPs and the linear range for SNPs was from 8.0 × 10 −17 to 1.0 × 10 −14 M.

Delivery and Efficacy of a Cancer Drug as a Function of the Bond to the Gold Nanoparticle Surface

In this feature article, gold nanoparticle conjugates loaded with phthalocyanine-based PDT drugs are prepared and tested for delivery efficiency and PDT efficacy on HeLa cancer cells. It could be shown that the delivery and PDT outcome are strongly affected by the bond that links the drug load to the nanoparticle surface. Whereas labile amino adsorption to the Au nanoparticle surface allows for efficient drug release into the cancer cells and for efficient PDT, a covalent thiol bond to the Au nanoparticle leads to the delivery of the drug into cell vesicles, and no PDT effect is observed. This work highlights the importance of carefully choosing the interaction between drug molecules and the nanoparticle surface.

PtRu-Modified Au Nanoparticles as Electrocatalysts for Direct Methanol Fuel Cells

PtRu-modified Au nanoparticles on a carbon support were prepared using a polyol reduction process with various Pt/Ru ratios. The prepared nanoparticles were characterized using transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, cyclic voltammetry, and chronoamperometry. The surfaces of most Au nanoparticles were covered with bimetallic PtRu overlayers with a thickness of 1–2 monolayers. The thin PtRu overlayers represented distinct CO stripping characteristics, which may be attributable to the unique surface structures of the PtRu overlayers on the Au nanoparticles. PtRu utilization was enhanced by as much as two times compared to that of PtRu/C, which can be attributed to the PtRu overlayers that were deposited only on the surface of the Au nanoparticles. The distinct CO stripping characteristics and the enhanced PtRu utilization affected the electrocatalytic activities of methanol oxidation. overlayers exhibited the highest CO tolerance and the highest methanol oxidation activity. The unique electrocatalytic characteristics of the PtRu overlayer structures on the Au nanoparticles are expected to provide methods for reducing the use of active elements.

Facile Synthesis and One-Dimensional Assembly of Cyclodextrin-Capped Gold Nanoparticles and Their Applications in Catalysis and Surface-Enhanced Raman Scattering

Controlled synthesis of Au nanoparticles with adjustable sizes (10−50 nm) and narrow size distributions (<10% in standard deviation) was realized by reducing hydrochloroauric acid with α-cyclodextrin (α-CD) in an alkaline aqueous solution, which was very simple and “green”. It was revealed that a proper pH was essential to the formation of stable dispersions of nonaggregated Au nanoparticles and a higher pH would lead to the welding of the Au nanoparticles into one-dimensional (1D) wires or three-dimensional (3D) aggregates. Moreover, 1D assembly of α-CD-capped Au nanoparticles into nanochains was readily induced by partial removal of the organic stabilization shell, which resulted from the host−guest interactions between α-CDs capped on Au nanoparticle surfaces and toluene molecules. Finally, the as-prepared Au nanoparticles were found to serve as effective catalyst to activate the reduction of 4-nitrophenol in the presence of NaBH4, and the application of the assembled Au nanoparticle thin film as a substrate for surface-enhanced Raman scattering (SERS) was also demonstrated.

Experimental Studies on the Interactions between Au Nanoparticles and Amino Acids: Bio-Based Formation of Branched Linear Chains

Biomacromolecules represent new structures employed for the fabrication, assembly, and subsequent use of nanomaterials for a variety of applications. By genetically selecting for the binding abilities of these bio-based molecules, the generation of materials with enhanced and environmentally sound properties is possible. Unfortunately, the level of understanding as to how the biomolecules bind and arrange on the nanomaterial surface is incomplete. Recent experimental and theoretical results suggest that the binding is dependent upon the peptide composition, sequence, and structure; however, these results were obtained for two-dimensional surfaces of the targeted inorganic material. Changing of the sample from two-dimensional targets to in solution three-dimensional nanomaterials presents a challenge because the level of analytical characterization for the latter system is minimal. Here we present our recent studies on the interactions between Au nanoparticles and the amino acid arginine. In our experimental design, the introduction of increasing concentrations of arginine to citrate-capped Au nanoparticles resulted in the formation of branched linear chains of the spherical nanomaterials. This assembly process was able to be monitored using UV-vis spectroscopy, transmission electron microscopy, and dynamic light scattering. The final results suggest that incomplete substitution of the original citrate surface passivant with the amino acid occurs, resulting in surface segregation of the two species. The segregation effect produces a dipole across the Au nanoparticle surface to drive the linear assembly of the materials in solution. Such results can possibly be exploited in understanding binding motifs and modes for biomolecules on the surface of functional nanomaterials.

PtRu overlayers on Au nanoparticles for methanol electro-oxidation

PtRu overlayer structures were deposited on the surface of carbon-supported Au nanoparticles with atomic-scale thicknesses and their activity for methanol electro-oxidation was examined. The results of transmission electron microscopy, X-ray diffraction, and cyclic voltammetry demonstrated that the PtRu deposited uniformly on Au nanoparticles. The peak potential in CO stripping analysis shifted to higher potentials with decreasing amounts of PtRu, indicating stronger Pt–CO and Ru–CO bonding. PtRu utilization was enhanced with decreasing PtRu, which might be attributed to the overlayer structures on Au substrates. In methanol electro-oxidation, a negative effect of the strengthened Pt–CO and Ru–CO bonding on surface specific activity and a positive effect of PtRu utilization on mass specific activity might contribute competitively to overall activity for methanol electro-oxidation.