Small-sized Gold Nanoparticles Research Articles

Tuning the Observability of Surface Plasmon in Silica–Gold Raspberry Shaped Nanoparticles Using Cuprous Oxide Shell

A raspberry shaped silica-gold nanoparticle system has been coated with a cuprous oxide shell using a simple wet chemical approach. The optical properties of such particles depend on thin dielectric shell material, and we calculate far-field scattering and extinction of cuprous oxide coated silica-gold composite. In accordance with our theoretical findings, for ultrasmall gold nanoparticles (AuNPs < 5 nm) attached over silica, the localized surface plasmon resonance (LSPR) peak is completely suppressed after Cu2O coating. The cloaking (nonobservability) of the LSPR peak in extinction spectra has been explained via calculation of contribution from absorbance (<10%) and scattering (>90%) in the composite nanostructure. For larger particles (>5 nm), the traditional red-shift of the plasmon peak (from 532 to 588 nm) is still significant due to the large dielectric constant (approx. 8.0 @ 600 nm) of cuprous oxide (Cu2O) coating. A complete and controlled suppression of LSPR in small sized gold nanoparticles due to high dielectric refractory oxide shell could play a significant role in plasmon derived applications.

In‐situ Formation and Assembly of Gold Nanoparticles by Gum Arabic as Efficient Photothermal Agent for Killing Cancer Cells

Gold nanoparticles (AuNPs) have been established to sufficiently eradicate tumors by means of heat production for photothermal therapy. However, the translation of the AuNPs from bench to the clinic still remains to be solved until realizing high bioclearance after treatment. Herein, we developed a simple strategy for simultaneous formation and assembly of small-size gold nanoparticles (Au-SNPs) to form a novel nanocomposite in the presence of gum arabic (GA) by synchrotron X-ray irradiation in an aqueous solution within 5 min. GA, a porous polysaccharide, can not only provide a confined space in which to produce uniform Au-SNPs (1.6 ± 0.7 nm in diameter), but can also facilitate the formation of Au-SNPs@GA (diameter ≈ 40 nm) after irradiating synchrotron X-rays. Specifically, the Au-SNPs@GA possesses high thermal stability and a strong photothermal effect for killing cancer cells. Importantly, a bioclearance study demonstrated that the Au-SNPs@GA can be gradually excreted by the renal and hepatobiliary system, which might be due to the breakdown and oxidation of GA under irradiating synchrotron X-rays. Thus, the novel gold nanocomposite can be promising photothermal agents for cancer treatment at the therapeutic level, minimizing toxicity concerns regarding long-term accumulation in vivo.

Rapid Synthesis and Structural Characterization of Well-Defined Gold Clusters by Solution Plasma Sputtering

Ultrafine metal nanoparticles of a few nanometers in diameter exhibit size-dependent photonic and electric properties that are of interest for applications such as biosensors, catalysts, optics, and electronics. Chemical approaches and vacuum metal-vapor-condensation physical techniques were used to successfully synthesize gold nanoparticles. While it is difficult to obtain monodisperse and small sized gold nanoparticles without any reductant and polymer stabilizer or under vacuum conditions, in the present study, multiply twinned and near monodisperse gold clusters of diameter less than 2.0 nm were successfully fabricated for the first time by solution plasma sputtering in liquid nitrogen (LN2) without any chemical additions (such as reductant and polymer stabilizer). Gold clusters formed in several microseconds simultaneously with solution plasma sputtering in an open system under atmospheric pressure. Gold clusters are identified to be well crystalline and multitwin-particles (MTPs) by high-resolution transmission electron microscopy. No surface plasmon resonance band was detected in the gold cluster aqueous solutions. Such MTPs with special corners and edges would be beneficial for tailoring catalytic properties at the nanoscale. The solution plasma sputtering method will have potential application in the future in the design and mass preparation of various multifunctional metal clusters.

Gold nanoparticle-templated assembly of oligothiophenes: preparation and film properties

Terthiophene-appended gold nanoparticles were prepared by the reduction of AuCl 4 −(C 8H 17) 4N + with NaBH 4 in the presence of bis[2,5-di(3-hexylthiophen-2-yl)thiophene-3-carboxyloxyhexanyl]disulfide. A hexagonal self-assembly of particles with gold core diameters (1.9±0.1 nm) was detected by high-angle annular dark-field scanning transmission electron microscopy. The electric conductivity of the iodine-doped film was 9.1×10 −6 S cm −1, which was ascribable to the terthiophene-based inter-ligand π–π interactions. The Au/terthiophene hybrid spin-coated film consisted of a highly three-dimensional assembled structure of terthiophenes, as inferred from grazing-incidence small-angle X-ray scattering, indicating that such monodispersed and small-sized gold nanoparticles can serve as a template for this organization. In this study, a gold nanoparticle-templated assembly of oligothiophenes has been fabricated for proposing a method to develop tailor-made organizations of π-conjugated oligomers.

Noise-Free Dual-Wavelength Difference Imaging of Plasmonic Resonant Nanoparticles in Living Cells

Herein, we demonstrated a new optical microscopy method to selectively image small-size gold nanoparticles (GNPs) inside noisy living cells through determination of the difference image between the probe beam (illuminated at the resonance wavelength of GNPs, 532 nm) and the reference beam (illuminated at 473 nm). From computer simulation and single-particle imaging experiments, we demonstrated that GNPs with a diameter of 45 nm could be selectively imaged in the GNPs/cell lysates mixture and inside living cells by dual-wavelength difference (DWD) imaging. The diffusion dynamics of nucleic acids functionalized GNPs on cell membranes and the internalization kinetics of these GNPs by living cells were explored with this method. Our real-time tracking experiments showed that statistically 80% of GNPs were under restricted diffusion on the cell membrane. The cell cytoskeleton fence effect, as observed in the single-particle tracking experiments, may be one of the main factors for the restricted diffusion mode.

Dithiolate-Appended Iridium(III) Complex with Dual Functions of Reducing and Capping Agent for the Design of Small-Sized Gold Nanoparticles

The unprecedented combined reduction of chloroauric acid and capping of the resulting gold nanoparticles in the absence of an external reducing agent are demonstrated using a novel heteroleptic Ir(III) complex incorporating a 4,5-diazafluorenedithiolate ligand. The reduction process in basic medium results from a cascade mechanism involving oxidation of the ligand, reduction of the gold salt, and stabilization and functionalization of the gold nanoparticles.

Layer-by-layer assembly of electro-active gold nanoparticle/cytochrome c multilayers

In this study we have tested the use of modified gold nanoparticles (GNPs) for introduction into cytochrome c (CytC) multilayer assemblies, constructed by the layer-by-layer deposition technique. For this purpose gold nanoparticles of different size are synthesized and the GNPs modified with mercaptopropionic acid (MPA). The particles are characterized by UV–vis-spectroscopy and transmission electron microscopy (TEM). The modified particles have been studied with respect to their binding capability on a CytC layer by SPR. The negatively charged particles exhibit rather fast adsorption kinetics on CytC. We can also show that CytC binds to MPA-modified gold nanoparticles.For the construction of electro-active CytC multilayers a negatively charged polyelectrolyte can be used. We demonstrated that the polyelectrolyte can be replaced by small-sized GNPs (5nm) in the multilayer assemblies, but assemblies consisting only of GNPs and CytC can be formed too. When these arrangements are prepared on gold electrodes, full electro-activity of the redox protein in the multiple layers can be obtained. CytC exhibits a formal potential of −24±12mV vs. Ag/AgCl. The electrochemical response is linearly increasing with the number of layers deposited, reaching a CytC surface concentration of 100pmol/cm2 with 6 layers. The electron transfer mechanism through the layer system and the particle size influence are discussed.

Extracellular biosynthesis of monodispersed gold nanoparticles by a SAM capping route

Monodispersed gold nanoparticles capped with a self-assembled monolayer of dodecanethiol were biosynthesized extracellularly by an efficient, simple, and environmental friendly procedure, which involved the use of Bacillus megatherium D01 as the reducing agent and the use of dodecanethiol as the capping ligand at 26 °C. The kinetics of gold nanoparticle formation was followed by transmission electron microscope (TEM) and UV-vis spectroscopy. It was shown that reaction time was an important parameter in controlling the morphology of gold nanoparticles. The effect of thiol on the shape, size, and dispersity of gold nanoparticles was also studied. The results showed that the presence of thiol during the biosynthesis could induce the formation of small size gold nanoparticles (<2.5 nm), hold the shape of spherical nanoparticles, and promote the monodispersity of nanoparticles. Through the modulation of reaction time and the use of thiol, monodispersed spherical gold nanoparticles capped with thiol of 1.9 ± 0.8 nm size were formed by using Bacillus megatherium D01.

Shape-controlled synthesis of highly monodisperse and small size gold nanoparticles

We describe here that fine control of nanoparticle shape and size can be achieved by systematic variation of experimental parameters in the seeded growth procedure in aqueous solution. Cubic and spherical gold nanoparticles are obtained respectively. In particularly, the Au cubes are highly monodisperse in 33±2 nm diameter. The experimental methods involve the preparation of Au seed particles and the subsequent addition of an appropriate quantity of Au seed solution to the aqueous growth solutions containing desired quantities of CTAB and ascorbic acid (AA). Here, AA is a weak reducing agent and CTAB is not only a stable agent for nanoparticles but also an inductive agent for leading increase in the face of nanoparticle. Ultraviolet visible spectroscopy (UV-vis), X-ray diffraction (XRD), transmission electron microscopy (TEM) are used to characterize the nanoparticles. The results show that the different size gold nanoparticles displayed high size homogenous distribution and formed mono-membrane at the air/solid interface.