Covalent functionalization of graphene oxide with polyglycerol and their use as templates for anchoring magnetic nanoparticles

An efficient strategy for the preparation of water-dispersible hybrid material containing graphene oxide and polyglycerol for the first time is demonstrated. Pristine graphite was firstly oxidized to obtain graphene oxide with hydroxyl functional groups. Then, the covalent grafting of polyglycerol onto the surface of graphene oxide was carried out based on in situ ring-opening polymerization of glycidol. For the construction of novel hybrid nanostructure, Fe-core/Au-shell nanoparticles were prepared and further functionalized using 4-mercaptophenylboronic acid through the well-developed Au–S chemistry. Subsequently, magnetic nanoparticles were anchored on the surface of polyglycerol-grafted graphene nanosheets via boroester bonds. The resulting hybrid materials were characterized using a range of analytical techniques. Fourier transform infrared spectroscopy (FT-IR) was employed to investigate the initial changes in surface functionalities. While X-ray diffraction (XRD) was used to confirm the structure of graphene oxide nanosheets, high resolution transmission electron microscopy (HR-TEM), and field emission scanning electronic microscopy (FE-SEM) equipped with an energy dispersive X-ray (EDX) spectrometer were used to study the morphologies and distribution of magnetic nanoparticles onto the surface of polyglycerol-grafted graphene. Thermogravimetric analysis (TGA) was used to study the weight loss of the samples on heating. Superconducting quantum interference device magnetometer (SQUID) was employed to the magnetic property of magnetic nanoparticles. The digital images provided a vivid observation on the high dispersion stability of the prepared novel hybrid materials in distilled water.     

Surface functionalization of single-walled carbon nanombes using metal nanoparticles

Surface functionalization of suspended single-walled carbon nanotubes (SWNTs) using metal (Au) nanoparticles (NPs) is reported. SWNTs are grown on three-dimensionally patterned substrates by thermal chemical vapor deposition and successfully functionalized with Au NPs. Ethylendiamine is mainly used to functionalize SWNTs surface with amino groups before introducing Au NPs. From Raman scattering spectroscopy of the Au-functionalized suspended SWNTs, enhanced Raman scattering properties are obtained. The results suggest that the attached Au NPs may contribute to the enhancement of resonant phenomena. By measuring the electric properties after each functionalization process, it is found that Au NPs act as electron acceptor to the amine functionalized SWNTs.     

Microbial production of gold nanoparticles

The development of techniques for the synthesis of nanoparticles of well-defined size, shape and composition is a challenge and an important area of research in nanotechnology. Many microorganisms have the ability to produce inorganic nanostructures and metal nanoparticles with properties similar to chemically-synthesised materials, while exercising control over the size, shape and composition of the particles. This alternative approach to chemical synthesis procedures uses microbial systems for the production of nanosized materials. Intracellular synthesis of gold nanoparticles, as well as extracellular formation of nanoparticles in the presence of fungal cell extract has been successfully demonstrated. The possibility to manipulate the size and shape of gold nanoparticles by altering key growth parameters was investigated and the results have provided some understanding as to which parameters may have an effect on the formation of gold nanoparticles.     

Synthesis of non-spherical gold nanoparticles

Non-spherical gold nanoparticles such as rods (short, long) (1,2), wires, cubes (3), nanocages (4), (multi-)concentric shells (5), triangular prisms (6–7), as well as other more exotic structures such as hollow tubes, capsules (6), even branched nanocrystals (8–9) have garnered significant research attention in the past few years. They exhibit unique and fine-tuned properties which either strongly differ or are more pronounced from those of symmetric, spherical gold nanoparticles. Their unusual optical and electronic properties, improved mechanical properties and specific surface-enhanced spectroscopies make them ideal structures for emerging applications in photonics, electronics, optical sensing and imaging, biomedical labelling and sensing, catalysis and electronic devices among others (10,11,12,13,14,15,16,17,18). Furthermore, some of these anisotropic nanoparticles enable elucidation of the particle growth mechanism, which in turn makes it possible to predict and systematically manipulate the final nanocrystal morphology (8,19-20). Finally, these anisotropic gold nanomaterials provide templates for further generation of novel materials (21,22).     

Molecularly-mediated assembly of gold nanoparticles

The understanding of the interparticle interactions and reactivities is essential to the exploitation of the unique optical, electronic, and chemical or biological properties of gold nanoparticles in many areas of nanotechnology. This paper describes findings of a comparison of optical properties of molecularlymediated assemblies of gold nanoparticles where the interparticle interactions and spatial properties are defined by molecular mediators and templates. The changes of the surface plasmon resonance band of the assemblies of gold nanoparticles mediated by several different types of molecular mediators, including multidendate methylthiosilane thioether, homocysteine, 1-(4-methyl)-piperazinyl fullerene, and indolenine cyanine dye, are compared. In the assembly process, the size of individual Au nanoparticles and the volume fraction of gold nanoparticles in the solution should remain largely constant, whereas the interparticle distance changes, which leads to changes in the interparticle dielectric medium constant or refractive index. The changes in the SP band in relation to the change in effective refractive index are discussed, along with their implications to assembly sizes, interparticle interactions, and potential applications in designing electrical and optical sensors.     

Electrochemical behaviour of carbon steel in acid chloride solution in the presence of dodecyl cysteine hydrochloride self-assembled on gold nanoparticles

In this work, the dodecyl cysteine hydrochloride surfactant was synthesized. The surface properties of this surfactant were studied using surface tension technique. The nanostructure of this surfactant with the prepared gold nanoparticles was investigated using TEM technique. The synthesized surfactant and its nanostructure with the prepared gold nanoparticles were examined as non-toxic corrosion inhibitors for carbon steel in 2 M HCl solution using potentiodynamic polarization and electrochemical impedance spectroscopy techniques. The results show that the percentage inhibition efficiency (η%) for each inhibitor increases with increasing concentration until critical micelle concentration (CMC) is reached. The maximum inhibition efficiency approached 76.6% in the presence of 175 ppm of dodecyl cysteine and 90.8% in the presence of the same concentration of dodecyl cysteine hydrochloride self-assembled on gold nanoparticles. Polarization data indicate that the selected additives act as mixed type inhibitors. The slopes of the cathodic and anodic Tafel lines (β_c and β_a) are approximately constant and independent of the inhibitor concentration. Analysis of the impedance spectra indicates that the charge transfer process mainly controls the corrosion process of carbon steel in 2 M HCl solution both in the absence and presence of the inhibitors. Adsorption of these inhibitors on carbon steel surface is found to obey the Langmuir adsorption isotherm. From the adsorption isotherms the values of adsorption equilibrium constants (K_ads) were calculated. The relatively high value of (K_ads) in case of dodecyl cysteine hydrochloride self-assembled on gold nanoparticles reveals a strong interaction between the inhibitor molecules and the metal surface.     

Room-temperature synthesis of gold nanoparticles — Size-control by slow addition

We report a simple and rapid process for the roomtemperature synthesis of gold nanoparticles using tannic acid, a green reagent, as both the reducing and stabilising agent. We systematically investigated the effect of pH on the size distribution of nanoparticles synthesized. Based on induction time and σ-potential measurements, we show that particle size distribution is controlled by a fine balance between the rates of reduction (determined by the initial pH of reactants) and coalescence (determined by the pH of the reaction mixture) in the initial period of growth. This insight led to the optimal batch process for size-controlled synthesis of 2–10 nm gold nanoparticles — slow addition (within 10 minutes) of chloroauric acid into tannic acid.     

Polyethylene glycol functionalized gold nanoparticles: the influence of capping density on stability in various media

Thiol-terminated polyethylene glycol (PEG) is commonly used to functionalize the surface of gold nanoparticles (AuNPs) in order to improve their in vivo stability and to avoid uptake by the reticular endothelial system. Although it has been reported that AuNPs functionalized with tethered PEG are stable in biological media, the influence of chain density remains unclear. This study investigates the influence of PEG capping density on the stability of washed and dried AuNPs in: water, phosphate-buffered saline solution (PBS), phosphate-buffered saline solution containing bovine serum albumin (PBS/BSA), and dichloromethane (DCM). PEG coating had a dramatic effect on stability enabling stable suspensions to be produced in all the media studied. A linear relationship was observed between capping density and stability in water and DCM with a somewhat lower stability observed in PBS and PBS/BSA. A maximum PEG loading level of ∼14 wt.% was achieved, equivalent to a PEG surface density of ∼1.13 chains/nm².     

Gas sensing properties of SnO2 nanoparticles mixed with gold nanoparticles

SnO₂ nanoparticles mixed with different amounts of gold nanoparticles (GNPs) were synthesized and their CO sensing properties were investigated. The sol–gel method was employed to prepare the initial solution. SEM, TEM, XRD, DLS and spectrophotometry were used to characterize the nanoparticles. The pure sensors showed a response of about 4 to 12.8 for (20–80)×10^?6 CO at operating temperature of 340 °C. The response and recovery time at 50×10^?6 Co is about 10 and 14 s, respectively. The amount of GNPs optimized was used to create high performance GNP-SnO₂ sensors (m(Au)/m(Sn)=3.7663×10^?4) and optimal operating temperature was about 260 °C and the response at concentrations of (20–80)×10^?6 was 8.3 to 29.5, respectively.     

Fullerene non-linear excited state absorption induced by gold nanoparticles light harvesting

Au nanoparticles can be synthesized in solution by a laser ablation methodology which allows to obtain funtionalized metal nanoparticles with a disulfide fullerene derivative in a simple one step process. The supramolecular system is shown to be an efficient non-linear absorbers of 532 nm nanosecond laser pulses. The mechanism of the non-linear absorption is shown to proceed through a light harvesting step by the metal nanoparticles and an efficient energy transfer to the fullerene moieties which absorb in a non-linear regime through their triplet states.     

Tunable infrared absorption by metal nanoparticles: The case for gold rods and shells

Nanoparticles of elements such as Au, Al or Ag have optical extinction cross-sections that considerably surpass their geometric cross-sections at certain wavelengths of light. While the absorption and scattering maxima for nanospheres of these elements are relatively insensitive to particle diameter, the surface plasmon resonance of Au nanoshells and nanorods can be readily tuned from the visible into the infrared by changing the shape of the particle. Here we compare nanoshells and nanorods in terms of their ease of synthesis, their optical properties, and their longer term technological prospects as tunable “plasmonic absorbers”. While both particle types are now routinely prepared by wet chemistry, we submit that it is more convenient to prepare rods. Furthermore, the plasmon resonance and peak absorption efficiency in nanorods may be readily tuned into the infrared by an increase of their aspect ratio, whereas in nanoshells such tuning may require a decrease in shell thickness to problematic dimensions.     

Selective entrance of gold nanoparticles into cancer cells

We report that Au(0) nanoparticles, stabilized by 5-aminovaleric acid, selectively penetrate into K562 cancer cells in a short time. These experiments were carried out in order to verify the specific recognition of gold sol by abnormal cells. The observed selectivity towards gold nanoparticles by K562 makes the metallic system attractive for cancer therapy.     

Generation of size-selected gold nanoparticles by spark discharge — for growth of epitaxial nanowires

One-dimensional semiconductor nanowires are a promising candidate for future electronic devices. The epitaxial growth of nanowires is often mediated by metal seed particles, usually gold particles. In this paper the setup of a simple and robust technique to generate nanometer-sized aerosol gold particles by spark discharge is described. Furthermore we demonstrate for the first time that particles generated by spark discharge can be used to design advanced nanoelectronic structures, namely nanowires. In order to obtain compact, spherical particles suitable for nanowire growth, the sparkgenerated agglomerate particles were reshaped in a special compaction furnace. The reshaped particles were used to seed the growth of epitaxial GaP and InP nanowires, by metal organic vapor phase epitaxy, which was shown to be a reliable and reproducible method. This work indicates the possibility of using spark-discharge generated gold particles for the creation of new electronic devices even at large scale processing.     

A facile and completely green route for synthesizing gold nanoparticles by the use of drink additives

A facile and completely green route to synthesize Au nanoparticles by mixing the Au(III) ions-dissolved rice wine and soda at a slightly elevated temperature in the absence of extra protective agents was developed. Rice wine was used as a solvent and a reducing agent. Also, soda not only functioned as a protective agent but also played a role of base catalyst. No extra protective agents are needed. From the analyses of UV/VIS absorption spectra, TEM, and XRD patterns, the formation of Au nanoparticles was recognized. The appropriate pH and temperature were around 6.5 and 25–55°C, respectively. The resultant solution was quite stable. No precipitation occurred even after several months. In addition, rice wine and soda are often used as the additives of drinks or foods, and are easily obtained in our daily life. So, it becomes possible that people can easily make the Au nanoparticles at home by the route proposed in this work.     

Structural stability of multiply twinned FePt nanoparticles

The structural stability of FePt nanoparticles in multiply twinned and single crystalline morphologies is investigated by means of molecular statics calculations based on a recently developed analytic bond-order potential. The results obtained from the atomistic calculations are used for validating a continuum model which allows the contributions of elastic strain, surface and twin boundary energies to be assessed separately. The static model calculations predict a strong energetic preference for single crystalline morphologies in the ordered L1₀ and disordered A1 phases. If estimates of vibrational entropy contributions are taken into account, however, icosahedral particles can become thermodynamically stable at elevated temperatures.     

The fine structure of plasmon bands in gold nanoparticles

The correlation between the electronic configurations of Au atom in the ground and excited electronic states and the E _pl plasmon energies of gold nanoparticles is studied in the many-electron approximation, taking into account 5d, 6s, and 6p valence electrons. Relativistic effects are found to result in the E _pl splitting in the visible and ultraviolet spectral ranges, and the splitting energies are predicted. The origin of low-energy plasmons with E _pl = 1.14, 2.7, and 6.4 eV is determined by 5d ⁹6s ²(² D _5/2), 5d ⁹6s ²(² D _3/2), and 5d _5/2 ⁹ 6s _1/26p _1/2 excited electronic configurations of Au atom. The bulk plasmon energy E _pl = 25.4 eV is assigned to the mixed oxidation states of Au ions in the nanoparticle cores.     

Equilibrium and stability of phase-separating Au–Pt nanoparticles

We report on a theoretical and experimental investigation of Au–Pt nanoparticles (NPs). The Au–Pt miscibility gap is theoretically reevaluated for NPs of various sizes. The model includes a composition-dependent surface energy evaluated by considering surface segregation. Using precise quantitative energy-dispersive X-ray spectroscopy (EDXS) and high-resolution electron microscopy (HREM), the structural evolution of ∼20 nm Au(core)–Pt(shell) NPs upon annealing at various temperatures (300–800 °C) is studied. At low temperatures, only interdiffusion occurs between the core and the shell, while above ∼600 °C, the NPs evolve into Au- and Pt-rich crystals, separated by an interface. At these temperatures, the Au solubility in the Pt-rich phase is found to be 5–10% higher than the bulk phase diagram and agrees qualitatively with the theoretical model. Based on the EDXS and HREM results, the nature of the interface separating the Au- and Pt-rich phases within a NP is discussed and an estimate of its energy is obtained.