Gold Nanoparticles Of Different Shapes Research Articles

In situ tuning and investigating the growth process of size controllable gold nanoparticles and statistical size prediction analysis

A critical understanding of the formation and growth process of gold nanoparticles (GNPs) is crucial, in order to synthesize monodisperse gold nanocrystals of controllable size and shape in a predictable way. GNPs of different shapes and sizes can be produced by altering different physicochemical reaction conditions, such as pH, temperature, and the ratio of reactants. The significant variations in the morphological features of GNPs can be monitored in situ in a time-dependent manner by using UV–visible spectroscopy. In this study, we have synthesized seedless GNPs by reduction of HAuCl4 by using various molar ratios of HEPES and Na2HPO4. The shape and the geometry of the gold nanostructures were optimized by varying the pH (5, 7, and 9) of the HEPES, molar concentrations of disodium phosphate to HAuCl4, and reaction temperatures (20 °C, 40 °C, and 60 °C). The changes in the color of the reaction mixtures over time were recorded in situ in terms of the absorbance of the UV–visible light to tune and investigate the growth process of gold nanostructures. Transmission electron microscopic (TEM) images indicated that the gold nanostructures are anisotropic, stable, and exist in the size range of < 1–100 nm. The present study also confirms that the change in the color of nanostructure reaction mixtures is a function of the surface plasmon resonance bands under the influence of physicochemical reaction conditions and corroborates with the size and shape of nano-gold. Physicochemical parameters such as temperature, pH, and the molar concentration of the reactants act synergistically to influence the growth, molecular mechanics, and reaction thermodynamics that aid to affect the particle size, shape, and surface corona of the GNPs. By tracking the growth process, we can confirm that the nucleation, growth process, size, and shape of the gold nanostructures depend on the HEPES free radicals and phosphate ions which cluster to form polymeric chains on the gold nanocore. The present study's findings explain the growth process of the GNPs of various colors that can be observed by the naked eye and have promising applications, for example in the development of the biosensing rapid lateral flow immunoassays (LFIA) for the detection of mycotoxins in food samples.

Analysis of Brownian motion trajectories of non-spherical nanoparticles using deep learning

As nanoparticles are being put to practical use as useful materials in the medical, pharmaceutical, and industrial fields, the importance of technologies that can evaluate not only nanoparticle populations of homogeneous size and density but also those of rich diversity is increasing. Nano-tracking analysis (NTA) has been commercialized and widely used as a method to measure individual nanoparticles in liquids and evaluate their size distribution by analyzing Brownian motion. We have combined deep learning (DL) for NTA to extract more property information and explored a methodology to achieve an evaluation for individual particles to understand their diversity. Practical NTA always assumes spherical shape when quantifying particle size using the Stokes–Einstein equation, but it is not possible to verify whether the measured particles are truly spherical. We developed a DL model that predicts the shape of nanoparticles using time series trajectory data of BM obtained from NTA measurements to address this problem. As a result, we were able to discriminate with ∼80% accuracy between spherical and rod-shaped gold nanoparticles of different shapes, which are evaluated to have nearly equal particle size without any discrimination by conventional NTA. Furthermore, we demonstrated that the mixing ratio of spherical and rod-shaped nanoparticles can be quantitatively estimated from measured data of mixed samples of nanoparticles. This result suggests that it is possible to evaluate particle shape by applying DL analysis to NTA measurements, which was previously considered impossible, and opens the way to further value-added NTA.

Solvent-Dispersible Nanostructured MIMI: An Experimental and Computational Study

A MIMI (metal–insulator-metal–insulator) nanoparticle was conceived and synthesized. It consists of a core of gold nanoparticles of different shapes, covered by a silica shell in turn covered by a layer of gold and finally by another silica shell. This hybrid nano-matryoshka, completely dispersed in water, was characterized by UV–Vis and TEM spectroscopy, comparing the architecture and photophysical properties of each synthetic step. Through a numerical simulation, it was possible to study in depth the absorption and extinction cross sections, determining the role of the various layers. This is an example of architecture used in the construction of metamaterials, the first in the form of a water-dispersed nanoparticles.

Evaluating EM-field enhancement of different shapes of metallic nanoparticles using COMSOL multiphysics for SERS-based sensors

Surface-enhanced Raman spectroscopy (SERS) plays a significant role in the detection of chemicals/ biochemicals in very low concentration levels. Most metals exhibit plasmonic properties, therefore, can be used in SERS substrates. In the present computational study, gold nanoparticles of different shapes are modelled to study the electromagnetic (EM) field enhancement using finite element methods (FEM) in COMSOL Multiphysics. Simulation results show the electric field distribution and Raman enhancement for different shapes of Gold nanoparticles. This study would be helpful for designing SERS-based sensors with a high electromagnetic enhancement factor.

Luminescent Self-Assembled Monolayer on Gold Nanoparticles: Tuning of Emission According to the Surface Curvature

Until now, the ability to form a self-assembled monolayer (SAM) on a surface has been investigated according to deposition techniques, which in turn depend on surface-coater interactions. In this paper, we pursued two goals: to form a SAM on a gold nanosurface and to correlate its formation to the nanosurface curvature. To achieve these objectives, gold nanoparticles of different shapes (spheres, rods, and triangles) were functionalized with a luminescent thiolated bipyridine (Bpy-SH), and the SAM formation was studied by investigating the photo-physics of Bpy-SH. We have shown that emission wavelength and excited-state lifetime of Bpy-SH are strongly correlated to the formation of specific aggregates within SAMs, the nature of these aggregates being in close correlation to the shape of the nanoparticles. Micro-Raman spectroscopy investigation was used to test the SERS effect of gold nanoparticles on thiolated bipyridine forming SAMs.

Manipulation of the quantum dots photostability using gold nanoparticles

The effect of plasmonic films containing gold nanoparticles of different shape (nanospheres and nanorods) on the photostability of InP/ZnSe/ZnSeS/ZnS and CdSe/ZnCdS/ZnS quantum dots with core/shell structure has been determined. Gold nanospheres increase the photostability of InP/ZnSe/ZnSeS/ZnS quantum dots when excited by blue LED radiation when reducing the average lifetime of the excited state of quantum dots and, accordingly, when reducing the probability of Auger processes. An increase in the average lifetime of the excited state of CdSe/ZnCdS/ZnS quantum dots in complexes with gold nanorods leads to a decrease in the photostability upon excitation at 449 and 532 nm.

Simulation of Gold Nanoparticle Transport during MHD Electroosmotic Flow in a Peristaltic Micro-Channel for Biomedical Treatment.

The study of gold nanoparticles (AuNPs) in the blood flow has emerged as an area of interest for numerous researchers, due to its many biomedical applications, such as cancer radiotherapy, DNA and antigens, drug and gene delivery, in vitro evaluation, optical bioimaging, radio sensitization and laser phototherapy of cancer cells and tumors. Gold nanoparticles can be amalgamated in various shapes and sizes. Due to this reason, gold nanoparticles can be diffused efficiently, target the diseased cells and destroy them. The current work studies the effect of gold nanoparticles of different shapes on the electro-magneto-hydrodynamic (EMHD) peristaltic propulsion of blood in a micro-channel under various effects, such as activation energy, bioconvection, radiation and gyrotactic microorganisms. Four kinds of nanoparticle shapes, namely bricks, cylinders and platelets, are considered. The governing equations are simplified under the approximations of low Reynolds number (LRN), long wavelength (LWL) and Debye–Hückel linearization (DHL). The numerical solutions for the non-dimensional equations are solved using the computational software MATLAB with the help of the bvp4c function. The influences of different physical parameters on the flow and thermal characteristics are computed through pictorial interpretations.

Single-particle studies on plasmon enhanced photoluminescence of monolayer MoS2 by gold nanoparticles of different shapes.

Plasmon-exciton interactions between noble metal nanostructures and two-dimensional transition metal dichalcogenides have drawn great interest due to their significantly enhanced optical properties. Plasmon resonance of noble metal nanoparticles and plasmon-exciton interactions are strongly dependent on the particle morphology. Single-particle spectroscopic studies can overcome the ensemble average effects of sample inhomogeneity to unambiguously reveal the effects of the particle morphology. In this work, plasmon modulated emission of MoS2 in various plasmon-MoS2 hybrid structures has been studied on the single-particle level. Gold (Au) nanoantennas of different shapes including nanosphere, nanorod, nanocube, and nanotriangle with similar overall dimensions, which have different sharp tips and contact areas with MoS2, have been chosen to explore the particle shape effects. Different extent of enhancement in photoluminescence (PL) of MoS2 was observed for Au nanoantennas of different shapes. It was found that Au nanotriangles gave the highest enhancement factor, while Au nanospheres gave the lowest enhancement factor. The numerical simulation results show that the dominant contribution arises from an increased quantum yield, while enhanced excitation efficiency just plays a minor role. The quantum yield enhancement is affected by both the sharp tips and contact mode of the Au nanoantenna with MoS2. Polarization of the MoS2 emission was also found to be modulated by the plasmon mode of the Au nanoantenna. These single-particle spectroscopic studies allow us to unambiguously reveal the effects of the particle morphology on plasmon enhanced PL in these nanohybrids to provide a better understanding of the plasmon-exciton interactions.

Gold Nanostars with Reduced Fouling Facilitate Small Molecule Detection in the Presence of Protein.

Gold nanoparticles have the potential to be used in biomedical applications from diagnostics to drug delivery. However, interactions of gold nanoparticles with different biomolecules in the cellular environment result in the formation of a “protein corona”—a layer of protein formed around a nanoparticle, which induces changes in the properties of nanoparticles. In this work we developed methods to reproducibly synthesize spheroidal and star-shaped gold nanoparticles, and carried out a physico-chemical characterization of synthesized anionic gold nanospheroids and gold nanostars through transmission electron microscopy (TEM), dynamic light scattering (DLS), zeta potential (ZP), nanoparticles tracking analysis (NTA), ultraviolet-visible (UV–Vis) spectroscopy and estimates of surface-enhanced Raman spectroscopy (SERS) signal enhancement ability. We analyzed how they interact with proteins after pre-incubation with bovine serum albumin (BSA) via UV–Vis, DLS, ZP, NTA, SERS, cryogenic TEM (cryo-TEM) and circular dichroism (CD) spectroscopy. The tests demonstrated that the protein adsorption on the particles’ surfaces was different for spheroidal and star shaped particles. In our experiments, star shaped particles limited the protein corona formation at SERS “hot spots”. This benefits the small-molecule sensing of nanostars in biological media. This work adds more understanding about protein corona formation on gold nanoparticles of different shapes in biological media, and therefore guides design of particles for studies in vitro and in vivo.

Subpercent Local Strains Due to the Shapes of Gold Nanorods Revealed by Data-Driven Analysis.

Analysis of subpercent local strain is important for a deeper understanding of nanomaterials, whose properties often depend on the strain. Conventional strain analysis has been performed by measuring interatomic distances from scanning transmission electron microscopy (STEM) images. However, measuring subpercent strain remains a challenge because the peak positions in STEM images do not precisely correspond to the real atomic positions due to disturbing influences, such as random noise and image distortion. Here, we utilized an advanced data-driven analysis method, Gaussian process regression, to predict the true strain distribution by reconstructing the true atomic positions. As a result, a precision of 0.2% was achieved in strain measurement at the atomic scale. The method was applied to gold nanoparticles of different shapes to reveal the shape dependence of the strain distribution. A spherical gold nanoparticle showed a symmetric strain distribution with a contraction of ∼1% near the surface owing to surface relaxation. By contrast, a gold nanorod, which is a cylinder terminated by hemispherical caps on both sides, showed nonuniform strain distributions with lattice expansions of ∼0.5% along the longitudinal axis around the caps except for the contraction at the surface. Our results indicate that the strain distribution depends on the shape of the nanomaterials. The proposed data-driven analysis is a convenient and powerful tool to measure the strain distribution with high precision at the atomic scale.

Optical and tomography studies of water-soluble gold nanoparticles on bacterial exopolysaccharides

Gold nanoparticles of different shapes (spherical, rods, and prisms) aggregate when deposited onto Lactobacillus fermentum's exopolysaccharide (EPS), a set of polysaccharides excreted by the bacteria. Transmission electron microscopy studies revealed that gold nanoparticles have high affinity for EPS. UV-vis spectra of aggregated gold nanoparticles showed additional absorbance peaks at lower energies in comparison with isolated nanoparticles. In the case of gold nanoprisms, the aggregation leads to a new absorption at a very low energy centered at 1100 nm. Moreover, the EPS of L. fermentum itself produces gold aggregates from a Au(III) solution. Surface-enhanced Raman spectroscopy performances for the detection of rhodamine B of gold aggregates were drastically different. A tomography study on all samples revealed clear differences in the extension of the EPS coating on the gold nanoparticles. Only the gold aggregate in which gold interparticle surfaces were exposed to RhB showed a drastic increase (two orders of magnitude) of intensity in the Raman spectrum of RhB.

Universal Method for Producing Reduced Graphene Oxide/Gold Nanoparticles Composites with Controlled Density of Grafting and Long-Term Stability.

In this study, we report a universal approach allowing the non-covalent deposition of gold nanoparticles on reduced graphene oxide surface in a controlled fashion. We used a modified Hummers method to obtain graphene oxide, which then underwent surficial functionalization with carboxyl moieties coupled with simultaneous reduction. Nanoparticles were synthesized ex-situ and capped with a thiolated poly-ethylene glycol (PEG) ligand. The interactions between the surface of modified graphene oxide and nanoparticle ligands enabled the formation of stable hybrid graphene-nanoparticles materials in the aqueous phase. Using this technique, we were able to cover the surface of graphene with gold nanoparticles of different shapes (spheres, rods, triangles, stars, and bipyramids), broad range of sizes (from 5 nm to 100 nm) and controlled grafting densities. Moreover, materials obtained with this strategy exhibited long-term stability, which coupled with the versatility and facility of preparation, makes our technique appealing in the light of increasing demand for new graphene-based hybrid nanostructures.

Shape dependent catalytic activity of unsupported gold nanostructures for the fast reduction of 4-nitroaniline

A one step seed mediated strategy is adopted here for synthesizing spherical, dog bone and rod shaped gold nanoparticles. Usually noble metals decorated by supporting materials are used for chemical catalysis. Here, a variety of unsupported gold nanoparticles (spherical, dog bone and rod shaped) originating from the same growth procedure are used for the catalytic reduction of para-nitroaniline (4-NA). The product obtained, para-phenylenediamine, is an important material, especially in the field of dye industry. The reaction kinetic values were analyzed based on to the Langmuir–Hinshelwood (LH) mechanism. A comparison of the rate constants obtained for gold nanoparticles of different shapes with almost similar volume pointy that gold nanorods are superior to that of spherical and dog bone like nanoparticles. The turnover frequency obtained here is high compared to other reported results and is found to be sensitive to the shape of the nanoparticles.

Gold nanoparticles of different shape for bicolor lateral flow test

Spherical gold nanoparticles are the most commonly used marker in lateral flow assays. However, the widespread practice of using identical coloration for the test and control zones of test strips can lead to erroneous interpretations of the assay's results. We propose an immunochromatographic test strip with lines of different colors. For this purpose, gold nanoparticles of different shapes were used, namely blue nanoflowers in the test zone and red gold nanospheres in the control zone. A detailed synthesis procedure for nanoparticles and their conjugates is considered and design parameters for optimal results are described. For the first time, nanoparticles of different shapes have been combined in the test strip with indirect labeling of specific antibodies (via their interaction with labeled secondary antibodies). Using the T-2 toxin (T2T) as an example, an instrumental detection limit of 30 pg/ml and a working range 0.06–0.9 ng/mL were achieved in an analysis of water-organic corn extracts.

Synthesis and pH-dependent assembly of isotropic and anisotropic gold nanoparticles functionalized with hydroxyl-bearing amino acids

In recent years, the synthesis of gold nanostructures of controllable shapes and dimensions has become a subject of intensive and interesting studies. Especially, anisotropic gold nanostructures such as nanoplates, nanoribbons, nanoprisms and nanorods have attracted much attention due to their striking optical properties and promising applications in electronics, photonics, sensing and biomedicine. Keeping this in mind, in the present report, an unprecedented, facile and one pot synthesis of isotropic (spherical) and anisotropic (triangular, pentagonal, hexagonal, rod shaped) gold nanomaterials via pH controlled shape modulation using hydroxyl moeity containing α-amino acids (Serine, Threonine, Tyrosine) as both reducing and capping agents is reported. The synthesized nanostructures have been further characterized by UV–Vis spectroscopy and transmission electron microscopy. It was deduced from these studies that pH played a key role in the anisotropic growth of gold nanostructures. These gold nanoparticles can be further used for applications in biosensing, plasmonics, and electrocatalysis and others involving surface enhanced raman scattering. This study is therefore, important from the point of view of using amino acids for the synthesis of gold nanoparticles of different shapes and sizes leading towards the development of inventive biosensors and biocompatible nanoconstructs.

Analysis of Photothermal Release of Oligonucleotides from Hollow Gold Nanospheres by Surface-Enhanced Raman Scattering

The photothermal release of single-stranded DNA (ssDNA) from the surface of gold nanoparticles of different shapes and sizes is a promising mode of delivering DNA for gene-therapy applications. Here, we demonstrate the first targeted photothermal release of ssDNA from hollow gold nanospheres (HGNs) and analyze the release of the ssDNA using quantitative surface-enhanced Raman scattering (SERS). The HGNs used demonstrate a tunable localized surface plasmon resonance (LSPR) frequency while maintaining size consistency, allowing for selective ssDNA release based on matching the excitation frequency to the plasmon resonance. It is shown that HGNs with resonances at 760 and 670 nm release significant amounts of ssDNA when excited via 785 and 640 nm lasers, respectively. When excited with a wavelength far from the LSPR of the particles, the ssDNA release is negligible. This is the first demonstration of SERS to analyze the amount of ssDNA photothermally released from the surface of HGNs. In contrast to traditio...

Beyond the staple motif: a new order at the thiolate-gold interface.

Staple motifs in the form of -RS(AuSR)x- (x = 1, 2, 3, etc.) are the most common structural feature at the interface of the thiolate-protected gold nanoclusters, Aun(SR)m. However, the recently solved structure of Au92(SR)44, in which the facets of the Au84 core are protected mainly by the bridging thiolates, challenges the staple hypothesis. Herein, we explore the surface sensitivity of the thiolate-gold interface from first principles density functional theory. We find that the interfacial structures of thiolates on gold are surface sensitive: while a staple motif (such as -RS-Au-SR-) is preferred on Au(111), a bridging motif (-RS-) is preferred on Au(100) and Au(110). We show that this surface sensitivity is closely related to the coordination number of the surface Au atom on the different surfaces. We further confirm the preference of the bridging motif for self-assembled monolayers of two different ligands (methylthiolate and 4-tert-butylbenzenethiolate) on Au(100). With this surface sensitivity, we categorize the structure-known Aun(SR)m clusters into three groups: (1) no bridging; (2) ambiguous bridging; (3) distinct bridging. We further employ the surface sensitivity of the thiolate-Au interface to predict the protecting motifs of face-centered cubic (fcc) gold nanoparticles of different shapes. Our study provides a unifying view of the Aun(SR)m structures with guidelines for structure predictions for larger Aun(SR)m clusters of a fcc core.

Nanovaccines for malaria using Plasmodium falciparum antigen Pfs25 attached gold nanoparticles

Malaria transmission-blocking vaccines (TBV) targeting sexual stages of the parasite represent an ideal intervention to reduce the burden of the disease and eventual elimination at the population level in endemic regions. Immune responses against sexual stage antigens impair the development of parasite inside the mosquitoes. Target antigens identified in Plasmodium falciparum include surface proteins Pfs230 and Pfs48/45 in male and female gametocytes and Pfs25 expressed in zygotes and ookinetes. The latter has undergone extensive evaluation in pre-clinical and phase I clinical trials and remains one of the leading target antigens for the development of TBV. Pfs25 has a complex tertiary structure characterized by four EGF-like repeat motifs formed by 11 disulfide bonds, and it has been rather difficult to obtain Pfs25 as a homogenous product in native conformation in any heterologous expression system. Recently, we have reported expression of codon-harmonized recombinant Pfs25 in Escherichia coli (CHrPfs25) and which elicited highly potent malaria transmission-blocking antibodies in mice. In the current study, we investigated CHrPfs25 along with gold nanoparticles of different shapes, size and physicochemical properties as adjuvants for induction of transmission blocking immunity. The results revealed that CHrPfs25 delivered with various gold nanoparticles elicited strong transmission blocking antibodies and suggested that gold nanoparticles based formulations can be developed as nanovaccines to enhance the immunogenicity of vaccine antigens.

Thermal Stability and Hot Carrier Dynamics of Gold Nanoparticles of Different Shapes

Anisotropic shapes of gold nanoparticles are prepared using a modified seed method in the presence of silver ions or clusters in order to study the thermal stability and the dynamics of the hot carriers induced by femtosecond laser pulses. Although gold nanospheres are stable towards thermal treatment, the decomposition of the gold nanorods into spherical nanoparticle aggregates upon thermal treatment is mechanistically different from the case of nanoprisms. Great enhancement of thermal stability is achieved by modifying the surface of the nanoparticles by adding specific amounts of polyvinyl pyrrolidone (PVP) after preparation of gold particles of different shapes capped with cetyltrimethylammonium bromide (CTAB). The surface plasmon resonance spectra of the gold nanostructures are used to monitor their morphological changes. In regards to the hot carrier dynamics, it is found that the phonon-phonon (ph-ph) coupling is much slower in dots than in rods and prisms while electron-phonon (e-ph) coupling is almost the same in these particles.

Gold Nanoparticles: Synthesis, Stability Test, and Application for the Rice Growth

In today’s science, with the use of nanotechnology, nanomaterials, which behave very differently from the bulk solid, can be made. One of the capable uses of nanomaterials is bioapplications which make good use of the specific properties of nanoparticles. However, since the nanoparticles will be used both in-vivo and in-vitro, their stability is an important issue to the scientists, concern. In this dissertation, we are going to test the stability of gold nanoparticles in a number of media including the biocompatible medium and their behaviors will be illustrated in terms of optical properties change and aggregation degree. Herein, we report the synthesis of gold nanoparticles of different shapes and applications for the rice growth with significant difference. The gold nanoparticles can inhibit the elongation of rice root without inhibiting the germination of rice seeds.