Shape Of Gold Nanoparticles Research Articles

Light polarization properties of three fold symmetry gold nanoparticles: Model and experiments

Abstract In this study, we demonstrate that any complex nanostructure that belongs to C n , with n ≥ 3 , symmetry point group for along at least one dimension displays apolar linear response to light input when the incoming wave vector is parallel to the C n axis. Triangle and star shaped gold nanoparticles were designed and fabricated by electron beam lithography (EBL) technique. The apolar behavior of such nanostructures was experimentally confirmed by way of localized surface plasmon resonances (LSPR) properties and surface-enhanced Raman scattering (SERS) measurements.

Effects of Ag+ and Cu2+ Ions on the Shape of Triangular Gold Nanoparticles

Abstract Triangular gold nanoplates were prepared by the tartaric acid reduction of HAuCl4 in cationic surfactant solutions, in the absence and the presence of small amounts of AgNO3 and CuSO4. With increasing concentration of AgNO3, the particle shape changes from triangular to spherical. In the presence of CuSO4, triangular plates with side lengths and tips that are longer and sharper, respectively, than those of the nanoplates prepared in the absence of CuSO4, are obtained.

Green synthesis of gold nanoparticles using Citrus fruits (Citrus limon, Citrus reticulata and Citrus sinensis) aqueous extract and its characterization

This study reports the biological synthesis of gold nanoparticles by the reduction of HAuCl4 by using citrus fruits (Citrus limon, Citrus reticulata and Citrus sinensis) juice extract as the reducing and stabilizing agent. A various shape and size of gold nanoparticles were formed when the ratio of the reactants were altered with respect to 1.0mM chloroauric acid solution. The gold nanoparticles obtained were characterized by UV–visible spectra, transmission electron microscopy (TEM) and X-ray diffraction (XRD). TEM studies showed the particles to be of various shapes and sizes and particle size ranges from 15 to 80nm. Selected-area electron diffraction (SAED) pattern confirmed fcc phase and crystallinity of the particles. The X-ray diffraction analysis revealed the distinctive facets (111, 200, 220 and 222 planes) of gold nanoparticles. Dynamic light scattering (DLS) studies revealed that the average size for colloid gp3 of C. limon, C. reticulata and C. sinensis are 32.2nm, 43.4nm and 56.7nm respectively. The DLS graph showed that the particles size was larger and more polydispersed compared to the one observed by TEM due to the fact that the measured size also includes the bio-organic compounds enveloping the core of the Au NPs. Zeta potential value for gold nanoparticles obtained from colloid gp3 of C. limon, C. reticulata and C. sinensis are −45.9, −37.9 and −31.4 respectively indicating the stability of the synthesized nanoparticles. Herein we propose a novel, previously unexploited method for the biological syntheses of polymorphic gold nanoparticles with potent biological applications.

Improving the Light Trapping Efficiency of Plasmonic Polymer Solar Cells through Photon Management

In this study, we have explored how light trapping efficiency can be enhanced by using gold nanoparticles (Au NPs) of various sizes and shapes on the front of polymer solar cells (PSCs) with the active layer—blends of poly(3-hexyl thiophene) and [6,6]-phenyl-C61-butyric acid methyl ester. The light-concentrating behavior was enhanced after we had incorporated gold nanospheres or nanorods into the anodic buffer layer [based on poly(3,4-ethylenedioxythiophene):polystyrenesulfonate] to trigger various localized surface plasmon resonance (LSPR) bands. Comparison of the optical characteristics and the performance of the PSCs prepared with and without Au NPs, and we found that the UV–vis and wavelength-dependent photoluminescent spectral data corroborated with the device performance due to the photon management by considering the light scattering and LSPR effects at the active layer. The presence of Au NPs increased the power conversion efficiency to approximately 4.3% (an enhancement of 24%).

Dependence on CO adsorption of the shapes of multifaceted gold nanoparticles: A density functional theory

We present a computational study for the equilibrium shape of gold nanoparticles. By linking extensive quantum-mechanical calculations, based on Density-Functional Theory (DFT) to Wulff construction, we predict equilibrium shapes that are in good agreement with experimental observa- tions. We discuss the effect of the interactions between a nanoparticle and the encapsulating material on the equilibrium shape. As an example, we calculate adsorption of CO on several different Au(hkl) and use the results to explain the experimentally observed shape change of Au nanoparticles.

Defining Rules for the Shape Evolution of Gold Nanoparticles

The roles of silver ions and halides (chloride, bromide, and iodide) in the seed-mediated synthesis of gold nanostructures have been investigated, and their influence on the growth of 10 classes of nanoparticles that differ in shape has been determined. We systematically studied the effects that each chemical component has on the particle shape, on the rate of particle formation, and on the chemical composition of the particle surface. We demonstrate that halides can be used to (1) adjust the reduction potential of the gold ion species in solution and (2) passivate the gold nanoparticle surface, both of which control the reaction kinetics and thus enable the selective synthesis of a series of different particle shapes. We also show that silver ions can be used as an underpotential deposition agent to access a different set of particle shapes by controlling growth of the resulting gold nanoparticles through surface passivation (more so than kinetic effects). Importantly, we show that the density of silver coverage can be controlled by the amount and type of halide present in solution. This behavior arises from the decreasing stability of the underpotentially deposited silver layer in the presence of larger halides due to the relative strengths of the Ag(+)/Ag(0)-halide and Au(+)/Au(0)-halide interactions, as well as the passivation effects of the halides on the gold particle surface. We summarize this work by proposing a set of design considerations for controlling the growth and final shape of gold nanoparticles prepared by seed-mediated syntheses through the judicious use of halides and silver ions.

Green synthesis of gold nanoparticles of different sizes and shapes using agar–agar water solution and femtosecond pulse laser irradiation

We report a method to create gold nanoparticles of different sizes and shapes using agar–agar water solution and irradiation with light from a xenon lamp, followed by ultrashort laser pulses. No additives, such as solvents, surfactants or reducing agents, were used in the procedure. Laser irradiation (laser ablation) was important to the reduction of the nanoparticles diameter and formation of another shapes. Distilled water was used as solvent and agar–agar (hydrophilic colloid extracted from certain seaweeds) was important for the stabilization of gold nanoparticles, avoiding their agglomeration. The formation of gold nanoparticles was confirmed with ultraviolet-visible absorption and TEM microscopy. The gold nanoparticles acquired spherical, prism, and rod shapes depending on the laser parameters. Variation of laser irradiation parameters as pulse energy, irradiation time and repetition rate was assessed. The relevant mechanisms contributing for the gold nanoparticles production are discussed.

Discovery of the DNA “Genetic Code” for Abiological Gold Nanoparticle Morphologies

DNA is in control: Different combinations of DNA nucleotides can control the shape and surface roughness of gold nanoparticles during their synthesis. These nanoparticles were synthesized in the presence of either homogenous oligonucleotides or mixed-base oligonucleotides using gold nanoprisms as seeds. The effect of the individual DNA bases and their combinations on shape control are shown in the figure.

Effect of shape and interstice on surface enhanced Raman scattering (SERS) of molecules adsorbed on gold nanoparticles in the near‐dipole and quadrupole regions

Surface enhanced Raman scattering (SERS) of adsorbed molecule on colloidal gold nanoparticles of different shapes, namely nanospheres (NSs), nanorods (NRs), and nanoprisms (NPs) as well as the three NPs arrays of different interstice prepared by NS lithography, are studied with incident wavenumbers in the near‐dipole and near‐quadrpole regions of the nanoparticles. In the colloidal gold nanoparticles, the SERS enhancement is the largest for the sharp tip followed by the truncated tip NPs, then the NRs and least enhancement for the NSs. This decreasing order of enhancement occurs although the incident wavenumber was near the dipole resonance of NSs and the quadrupole resonance for the NPs. These varied enhancements are explained in part as due to the binding energies of the nanocrystal facets, but the larger contribution results from the plasmon electromagnetic fields. A parallel finite difference time domain (FDTD) calculations were carried out, which corporate the experimental results and show agreement with ratios of the SERS enhancement for the different shapes. The normalized SERS intensity for NPs of different interstice distances show a sharp rise with the decrease of the interstice distances because of interparticle dipolar and quadrupolar coupling as evidenced also by FDTD calculations. Furthermore, these calculations show that the enhancement is polarization independent for an incident wavelength near quadrupole resonance but polarization dependent for an incident wavelength near the plasmon dipole transition. In the last case, the enhancement is larger by an order of magnitude for a polarization parallel to the NPs bisector than for polarization normal to the bisector with no hot spots for the relatively large interstice dimensions used. Copyright © 2012 John Wiley & Sons, Ltd.

Layered Nanocomposites from Gold Nanoparticles for Neural Prosthetic Devices

Treatments of neurological diseases, diagnostics of brain malfunctions, and the realization of brain-computer interfaces require ultrasmall electrodes that are "invisible" to resident immune cells. Functional electrodes smaller than 50 μm are impossible to produce with traditional materials due to high interfacial impedance at the characteristic frequency of neural activity and insufficient charge storage capacity. The problem can be resolved by using gold nanoparticle nanocomposites. Careful comparison indicates that layer-by-layer assembled films from Au NPs provide more than 3-fold improvement in interfacial impedance and 1 order of magnitude increase in charge storage capacity. Prototypes of microelectrodes could be made using traditional photolithography. Integration of unique nanocomposite materials with microfabrication techniques opens the door for practical realization of the ultrasmall implantable electrodes. Further improvement of electrical properties is expected when using special shapes of gold nanoparticles.

Map of the Structural and Optical Properties of Gold Nanoparticles at Thermal Equilibrium

The remarkable relationship among the size, shape, and optical properties of gold nanoparticles is proving to be very useful in a range of high-performance applications. Considerable effort and investment is focused on delivering gold nanoparticles with precise morphologies. However, the reliability of these particles is contingent upon the morphological stability, particularly against variations in the thermodynamic environment, such as changes in temperature. Presented here are results from a combination of computational and theoretical techniques showing how the optical properties of gold nanoparticles respond to changes in the size, shape, or temperature, obtained by sampling the optical spectrum over large configuration space, in accordance with the nanoscale phase diagram. We find that spectrum from morphologies expected at small sizes is robust against temperature fluctuations, unless the concentration is very high. At larger sizes, the color will likely change with temperature, due to the accompan...

Tunability and stability of gold nanoparticles obtained from chloroauric acid and sodium thiosulfate reaction

In the quest for producing an effective, clinically relevant therapeutic agent, scalability, repeatability, and stability are paramount. In this paper, gold nanoparticles (GNPs) with precisely controlled near-infrared (NIR) absorption are synthesized by a single-step reaction of HAuCl4 and Na2S2O3 without assistance of additional templates, capping reagents, or seeds. The anisotropy in the shape of gold nanoparticles offers high NIR absorption, making it therapeutically relevant. The synthesized products consist of GNPs with different shapes and sizes, including small spherical colloid gold particles and non-spherical gold crystals. The NIR absorption wavelengths and particle size increase with increasing molar ratio of HAuCl4/Na2S2O3. Non-spherical gold particles can be further purified and separated by centrifugation to improve the NIR-absorbing fraction of particles. In-depth studies reveal that GNPs with good structural and optical stability only form in a certain range of the HAuCl4/Na2S2O3 molar ratio, whereas higher molar ratios result in unstable GNPs, which lose their NIR absorption peak due to decomposition and reassembly via Ostwald ripening. Tuning the optical absorption of the gold nanoparticles in the NIR regime via a robust and repeatable method will improve many applications requiring large quantities of desired NIR-absorbing nanoparticles.

Effects of different shaped gold nanoparticles on the photoelectrode of dye-sensitized solar cells

In this study, we prepared different shapes of gold nanoparticles by the seed-mediated growth method to apply on the photoelectrode of dye-sensitized solar cells. Analyses of field emission scanning electron microscopy and ultraviolet–visible absorption spectra show that the average diameter of spherical gold nanoparticles is 66 nm and gold nanorods in aspect ratio is 2. The best conversion efficiencies of dye-sensitized solar cell with spherical gold nanoparticles and gold nanorods added in are 6.77 and 7.08%, and are higher than that without gold nanoparticles. These results indicate that the effect of gold nanoparticles on the photoelectrode can increase the conductivity and reduce the recombination of charges in the photoelectrode, resulting in the increase of conversion efficiency for dye-sensitized solar cells. Futhermore, gold nanorods have stronger surface plasmon resonance intensity than spherical gold nanoparticles at long wavelength. This may be the reason why conversion efficiency of dye-sensitized solar cells with gold nanorods is higher than that of spherical gold nanoparticles.

Facile one-pot synthesis of gold nanoparticles using tannic acid and its application in catalysis

The paper reports a simple and efficient method for the synthesis of stable, nearly spherical gold nanoparticles using tannic acid as both the reducing and stabilizing agent. The nanoparticles are characterized by UV–visible spectroscopy, transmission electron microscopy (TEM), EDX and X-ray diffraction (XRD) analysis. The influence of tannic acid on the control of size and shape of gold nanoparticles is reported. Upon an increase in the concentration of tannic acid, there is a shift in the shape of nanoparticles as evidenced by the change in bandwidth and peak position of the surface plasmon resonance (SPR) band. Also, it is found that tannic acid ceases to act as a reducing agent beyond the limit of 10mL (6×10−3M) for 30mL of HAuCl4 (1.3×10−3M). On increasing the quantity of tannic acid, nucleation is favored in the initial stages and thereafter growth supersedes nucleation. The stable colloids obtained by this method are found to consist of nanoparticles with average size 8 and 12nm. The crystallinity of the sample with fcc phase is observed from TEM, SAED and XRD pattern. Involvement of carboxylic acid group in capping of gold nanoparticles is evident from the FTIR spectrum. The application of the synthesized nanoparticles as catalyst in the reduction of 4-Nitrophenol to 4-Aminophenol is also reported.

Biosynthesis of Controllable Size and Shape Gold Nanoparticles by Black Seed (Nigella Sativa) Extract

We report on the use of black seed (Nigella sativa) extract, previously not exploited, in synthesis of gold nanoparticles. On treating aqueous chloroauric acid solution with black seed extract, the antioxidant activities critical roles of the various phytochemicals is observed leading to the formation of crystalline and poly shaped gold nanoparticles. In this research work, we developed a rapid and non-toxic method for the preparation of biocompatible gold nanoparticles by two different synthetic routes: microwave irradiation and thermo-induced procedures. The nanoparticles were characterized and investigated by ultraviolet-visible (UV-Vis) spectrophotometry, transmission electron microscopy (TEM), energy-dispersive X-ray (EDX) spectroscopy, and X-ray diffraction (XRD).The size and shape of the nanoparticles were found to be very sensitive to the quantity of the extract. As the amount of extract is increased, the stronger the interaction between the extract biomolecules and nascent nanoparticles, thus the yield of nanoparticles increased as shown by surface plasmon resonance bands in the UV-vis-NIR spectra. The reaction temperature has a significant role in production of gold nanoparticles with different shapes. The XRD studies reflect an interesting feature indicates that gold nanocrystals are highly anisotropic in nature, mainly triangular and hexagonal shapes, and that the particles are (111) oriented. The observed characteristics suggest the application of the biocompatible gold nanoparticles to future in vivo imaging and therapy.

Nanoparticle-Enhanced Surface Plasmon Resonance Detection of Proteins at Attomolar Concentrations: Comparing Different Nanoparticle Shapes and Sizes

The application of biofunctionalized nanoparticles possessing various shapes and sizes for the enhanced surface plasmon resonance (SPR) detection of a protein biomarker at attomolar concentrations is described. Three different gold nanoparticle shapes (cubic cages, rods and quasi-spherical) with each possessing at least one dimension in the 40-50 nm range were systematically compared. Each nanoparticle (NP) was covalently functionalized with an antibody (anti-thrombin) and used as part of a sandwich assay in conjunction with a Au SPR chip modified with a DNA-aptamer probe specific to thrombin. The concentration of each NP-antibody conjugate solution was first optimized prior to establishing that the quasi-spherical nanoparticles resulted in the greatest enhancement in sensitivity with the detection of thrombin at concentrations as low as 1 aM. When nanorod and nanocage antibody conjugates were instead used, the minimum target concentrations detected were 10 aM (rods) and 1 fM (cages). This is a significant improvement (>10(3)) on previous NP-enhanced SPR studies utilizing smaller (~15 nm) gold NP conjugates and is attributed to the functionalization of both the NP and chip surfaces resulting in low nonspecific adsorption as well as a combination of density increases and plasmonic coupling inducing large shifts in the local refractive index at the chip surface upon nanoparticle adsorption.

Gold Nanoparticles Reshaped by Ultrafast Laser Irradiation Inside a Silica-Based Glass, Studied Through Optical Properties

Quasi-spherical or quasi-rod gold nanoparticles with an average diameter of 3.8 nm are randomly precipitated in a silica-based glass by a heat-treatment method. After ultrafast laser irradiation at 400 and 620 nm, optical absorption, birefringence, and dichroism measurements are performed to investigate the modification of gold nanoparticles shape. Theoretical simulations have been carried out to interpret the experimental results. We suggest that a small fraction of gold nanospheres are transformed mainly into nanodisks but also into nanorods oriented along the laser polarization for both fs laser wavelength. Absorption simulation suggests that they have an aspect ratio of 1.8 and 0.5, respectively, for fs laser irradiation at 400 nm. For 620 nm, the aspect ratio of the nanorods increases and the one of the nanodisks decreases. In such a way, we demonstrate that reshaping of gold nanoparticles, i.e. a property that was previously found for silver nanoparticles in multicomponent glass is also possible. By imaging the distribution of the birefringence according to the probe wavelength, we show that nanoparticles are aligned into nanorods mainly out of irradiated volume and into nanopellets mainly in the irradiated volume.

Synthesis and Characterization of Poly(N-tert-amylacrylamide-co-Acrylamide/Sodium acrylate) Gold Nanocomposite Hydrogels

In the present study, a series of Poly (N-tert-amylacrylamide –co –acrylamide / Sodium acrylate) gold nanocomposite hydrogels were synthesized by free-radical copolymerization in Water/Methanol medium using Ammonium persulfate (APS) as the initiator and N,N’-methylenebisacrylamide (MBA) as a crosslinker. The amount of N-tert-amylacrylamide (NTA) and Acrylamide (AM) monomers are fixed (50:50) and the amount of Sodium Acrylate (AcNa) ionic monomer was varied from 0.1g to 0.5g. The swelling ehaviour of Nanocomposite Hydrogels studied by Gravimetric method and degree of swelling was increased by increasing the amount of Sodium acrylate. The surface morphology was studied by SEM analysis and it indicates the formation spherical shaped gold nanoparticle in the polymer matrix.

Growth and branching of gold nanoparticles through mesoporous silica thin films

Composite materials made of mesoporous oxide thin films containing metallic nanoparticles are of high interest in various fields, including catalysis, biosensing and non-linear optics. We demonstrate in this work the fabrication of such composite materials containing a sub-monolayer of gold nanoparticles (GNPs) of various shapes covered with mesoporous silica thin films. Additionally, the shape of the GNPs (and thus their optical properties) can be modified in situ through seeded growth and branching. Such growth proceeds upon wetting with HAuCl(4) solution, a surfactant (cetyltrimethylammonium bromide, CTAB) and a mild reducing agent (ascorbic acid, AA). The effect of varying several reaction parameters (time and CTAB and AA concentrations) was evaluated, showing that more anisotropic particles are obtained at longer reaction times, lower CTAB concentration and higher AA concentration. The final shape of the GNPs was also found to depend on their initial shape and size, as well as the pore size of the mesoporous film covering them. Because the growth proceeds through the pores of the film, it may lead to shapes that are not easily obtained in solution, such as particles with branches on one side only. Finally, we have confirmed that no damage was induced to the mesoporous silica structure during the growth process and thus the final particles remain well covered by the thin film, which can eventually be used as a filter between the GNPs and the outer medium.

Synthesis of gold nanoparticles of variable morphologies using aqueous leaf extracts of Cocculus hirsutus

Spherical, triangular (prismatic) and square plate shaped gold nanoparticles have been synthesised from HAuCl4 · 3H2O solution using the aqueous leaf extract of Cocculus hirsutus. Nanoparticles are characterised using higher resolution transmission electron microscope, X-ray diffraction and UV–Vis absorption spectroscopic study. FT-IR analysis reveals that the gold nanostructures are mostly stabilised by the carbonyl and amide groups present in the active component of C. hirsutus leaf extract. Formation of gold nanostructures of variable morphologies has been explained due to slow reduction of gold ions by the mild reducing ascorbic acid present within the extract and this controlled reduction assists the preferential deposition of Au atom on different lesser-protected faces of initially grown gold nanostructure.