Morphology Of Gold Nanoparticles Research Articles

Seeded growth of gold nanoparticles in aqueous solution of cationic gemini surfactants with different spacer length: influences of molecular and aggregate structures

It is well known that surfactants play a vital role in aqueous-phase synthesis of gold nanoparticles (GNPs). However, to date, it remains challenging to fully elucidate the roles of surfactants, especially for the correlation between the molecular and aggregate structure of the employed surfactant and the structures of the resulting GNPs. In the study, the synthesis of GNPs in aqueous solution of a series of cationic gemini surfactants with different spacer length (12-s-12, s = 0, 2, 4, 6, 8, 10, and 12) has been investigated. A remarkable spacer length-dependent morphological evolution of nanorod→nanostar→nanoplate→spherical nanoparticle has been observed. The results show that the gemini surfactants can form the electrostatic complexes with AuI ions, and the complexes further self-assemble into the various aggregates of different sizes, which greatly alters the migration dynamics of AuI and eventually influences the growth kinetics of GNPs. The overall growth rate of the GNPs is determined by the combination of the monomer-AuI molecular weight, the size of aggregates, and the local concentration of AuI in the aggregates. Besides, the gemini surfactants with different spacer length could selectively anchor on various facets of GNPs, thus acting as the capping agents to direct the formation of the shaped GNPs. It is believed that the cationic gemini surfactants with different spacer length provide an excellent choice to control the growth kinetics and final morphology of GNPs, and this study provides new insights in surfactant-assisted synthesis of GNPs.

Tumor Chemo-Radiotherapy with Rod-Shaped and Spherical Gold Nano Probes: Shape and Active Targeting Both Matter.

The morphologies of gold nanoparticles (NPs) affect their tumor accumulation through enhanced permeability and retention effect. However, detailed information and mechanisms of NPs' characteristics affecting tumor accumulation are limited. The aim of this study is to evaluate the effects of shape and active targeting ligands of theranostic NPs on tumor accumulation and therapeutic efficacy, and to elucidate the underlying mechanism.Methods: αvβ3 integrin-targeted, cisplatin-loaded and radioisotope iodine-125 labeled spherical and rod-shaped gold nano theranostic probes (RGD-125IPt-AuNPs and RGD-125IPt-AuNRs) with similar sizes were fabricated and characterized. The in vivo distribution and chemo-radio therapeutic efficacy against tumors of these newly developed probes were subsequently evaluated. Moreover, a physiologically based pharmacokinetic (PBPK) model was developed to characterize the in vivo kinetics of these probes at the sub-organ level, and to reveal the mechanism of NPs' shape and active targeting ligands effects on tumor accumulation.Result: Cisplatin and iodine-125 were loaded sequentially onto the NPs through a thin polydopamine coating layer on the NPs. Both RGD-125IPt-AuNPs and RGD-125IPt-AuNRs exhibited high specificity for αvβ3 in vitro, with the rod-shaped probe being more efficient. The PBPK model revealed that rod-shaped gold NPs diffused more rapidly in tumor interstitial than the spherical ones. Tumor accumulations of non-targeted and rod-shaped RAD-125IPt-AuNRs was higher in short term (1 h post injection), but not pronounced and similar to that of non-targeted spherical RAD-125IPt-AuNPs in 24 h after intravenous injection, revealing that the NPs' shape did not have a significant impact on tumor accumulations through enhanced permeability and retention (EPR) effect in long-term. While for actively targeted NPs, in addition to a higher distribution coefficient, RGD-125IPt-AuNRs also had a much higher tumor maximum uptake rate constant than RGD-125IPt-AuNPs, indicating both the shape and active targeting ligands affected the tumor uptake of rod-shaped NPs. As a result, RGD-125IPt-AuNRs had a more effective inhibition of tumor growth than RGD-125IPt-AuNPs by chemo-radiationtherapy.Conclusion: Our study suggests that both the shape and active targeting ligands of gold NPs play important roles on tumor accumulation and chemo-radio therapeutic effect.

Complex coloration and antibacterial functionalization of silk fabrics based on noble metal nanoparticles

Noble metal nanoparticles and traditional dyes jointly colorate silk fabrics. Gold and silver nanoparticles were in situ synthesized on silk fabrics, and the complex coloration was realized by the integration of traditional dyes into the treated silk. The localized surface plasmon resonance properties of gold and silver nanoparticles were not affected by the coloration of dyed-on silk fabrics. The combined optical properties of nanoparticles and dyes extended the color range and enhanced the color strength (K/S) of silk fabrics. Ultraviolet–visible diffuse absorption spectroscopy and scanning electron microscopy demonstrated the in situ synthesis of gold and silver nanoparticles on silk fabrics. The coloration of traditional dyes influenced the morphologies of gold and silver nanoparticles on fiber surface slightly. The silk fabrics with complex coloration showed significant antibacterial property. The complex coloration based on particular nanoparticles and dyes provides a promising strategy to develop multifunctional textiles.

3D and Plasmonic Nanoparticle Decorated Catalytic System via Bio-inspired Polydopamine Coating: Cigar Filter Case Study

Despite the significant progress, the well-controlled deposition of nanoparticles onto the support materials having 3-D nano-morphologies for the catalytic applications is still facing challenges such as the limited accessibility of reacting molecules to catalyst surface, uncontrolled aggregation of nanoparticles, high cost and highly complicated fabrication procedures. In this study, to overcome these challenges, a simple yet versatile alternative platform is proposed to control the gold nanoparticle (AuNP) size, surface coverage and morphology onto the 3-D cigar filter surface via bio-inspired polydopamine (PDOP) coating. The effect of gold deposition time on AuNPs characteristics and their catalytic activity in the model reaction were investigated in detail. It is found that both AuNPs properties and catalytic activity can be controlled by changing deposition time. The deposition of AuNPs via functional groups of PDOP such as amine, catechol, and imine provided total conversion of 4-nitrophenol to 4-aminophenol within an hour.

Au nanoclusters in the plasmonic applications

One of the new applications of gold nanoparticles is the use of the plasmon effect, which occurs due to the interaction of an electromagnetic wave with free electrons in nanostructures. Particles of gold with a size smaller than the wavelength of a visible electromagnetic wave can strongly absorb light due to the collective oscillation of conduction electrons. Bulk gold has a high-symmetry fcc structure, but controlling the collection of metal atoms in solution can also lead to the growth of many anisotropic forms. The use of these different structures has a significant effect on the plasmonic properties, since defects at twin boundaries can serve as scattering centers of conduction electrons in a metal. Thus, on the basis of controlling the size, shape, and structure of Au nanoparticles, it is possible to control light with unprecedented accuracy, and therefore the determination of the morphology of individual gold nanoparticles is of great interest for studying their possible optical interaction.

Inhibition of retinal angiogenesis by gold nanoparticles via inducing autophagy.

To investigate the effect of gold nanoparticles on retinal angiogenesis in vitro and in vivo, and to reveal the possible mechanism. Seed growth method was used to synthesize gold nanoparticles (GNPs). The size, zeta potential, absorption spectrum and morphology of GNPs were identified using Malvern Nano-ZS, multimode reader (BioTek synergy2) and transmission electron microscope. Cell viability was analyzed using cell counting kit-8 method and cell growth was assessed with EdU kit. Transwell chamber was used to investigate cell migration. Tube formation method was used to assess the angiogenic property in vitro. Oxygen induced retinopathy (OIR) model was used to investigate the effect of GNPs on retinal angiogenesis. Confocal microscope and Western blot were used to study the possible mechanism of GNPs inhibited angiogenesis. The GNPs synthesized were uniform and well dispersed. GNPs of 10 µg/mL and 20 µg/mL were able to inhibit human umbilical vein endothelial cells proliferation (50% and 72% separately, P<0.001), migration (54% and 83% separately, P<0.001) and tube formation (52% and 90% separately, P<0.001). Further data showed that GNPs were able to improve the retinopathy in an OIR model. The possible mechanism might be that GNPs were able to induce autophagy significantly (P<0.05). The present study suggests that GNPs are able to inhibit retinal neovascularization in vitro and in vivo. GNPs might be a potential nanomedicine for the treatment of retinal angiogenesis.

A novel and simple microemulsion method for synthesis of biocompatible functionalized gold nanoparticles

Synthesize of functionalized gold nanoparticles has attracted a great deal of interest due to their favorable optical properties and broad range of biomedical applications. One challenge for biomedical application is to find a simple method in the manufacturing of biocompatible and stable water soluble gold particles with a well-controlled shape and size. In the current study, a novel methodology based on microemulsion system has been introduced to prepare biocompatible gold nanoparticles protected by a monohydroxy thioalkylated PEG ligand. The morphology and size distribution of gold nanoparticles was determined by different methods including dynamic light scattering (DLS), UV–visible spectrophotometry, Energy-dispersive X-ray analysis (EDX) and transmission electron microscopy (TEM). It is verified that the prepared water-based functionalized gold colloidal system has particles size in the range of 7–9 nm with no cytotoxicity effect to HeLa cells.

Morphological Evolution of Gold Nanoparticles into Nanodendrites Using Catechol-Grafted Polymer Templates.

Morphology, dimension, size, and surface chemistry of gold nanoparticles are critically important in determining their optical, catalytic, and photothermal properties. Although many techniques have been developed to synthesize various gold nanostructures, complicated and multistep procedures are required to generate three-dimensional, dendritic gold nanostructures. Here, we present a simple method to synthesize highly branched gold nanodendrites through the well-controlled reduction of gold ions complexed with a catechol-grafted polymer. Dextran grafted with catechols guides the morphological evolution as a polymeric ligand to generate dendritic gold structures through the interconnection of the spherical gold nanoparticles. The reduction kinetics, which is critical for morphological changes, is controllable using dimethylacetamide, which can decrease the metal–ligand dissociation and gold ion diffusivity. This study suggests that mussel-inspired polymer chemistry provides a simple one-pot synthetic route to colloidal gold nanodendrites that are potentially applicable to biosensing and catalysis.

Understanding the Effect of Iodide Ions on the Morphology of Gold Nanorods

AbstractThe presence of iodide ions during the growth of gold nanorods strongly affects the shape of the final products, which is proposed to be due to selective iodide adsorption on certain crystallographic facets. Therefore, a detailed structural and morphological characterization of the starting rods is crucial toward understanding this effect. Electron tomography is used to determine the crystallographic indices of the lateral facets of gold nanorods, as well as those present at the tips. Based on this information, density functional theory calculations are used to determine the surface and interface energies of the observed facets and provide insight into the relationship between the amount of iodide ions in the growth solution and the final morphology of anisotropic gold nanoparticles.

α-Helical Peptide-Gold Nanoparticle Hybrids: Synthesis, Characterization, and Catalytic Activity

Gold nanoparticles are promising nanomaterials for catalytic reactions, sensing/imaging systems, photonic/plasmonic devices, and electronics because of their unique physical and chemical properties. To date, significant catalytic activities of gold nanoparticles have been reported for reactions such as carbon monooxide oxidation and 4-nitrophenol reduction, and diverse gold nanoparticle morphologies such as nanospheres, wires, rods, and cubes have been achieved using a variety of capping/stabilizing organic molecules. However, there are few reports on the simultaneous assembly of peptides forming secondary structures and metallic nanoparticles into peptide-metallic particle hybrids under mild aqueous conditions and demonstration of their use as catalysts. Furthermore, the gold nanoribbon surfaces are covered with β-sheet structures, disrupting the access of substrates to the active sites, thereby possibly inhibiting their catalytic activity. The main objective of this study is design, synthesis, and characterization of peptidegold nanoparticle hybrids that are prepared by an α-helical conformation of a template and examination of the catalytic activities of the hybrids. We here report (i) the design, synthesis, and characterization of a new template peptide, RU025, that tends to form an α-helical conformation and self-assembles into network nanoarchitectures in aqueous solution through possibly hydrophobic and electrostatic interactions, (ii) the characterization of gold seed crystals synthesized by mixing RU025 and HAuCl4, (iii) the characterization of peptide-gold nanoparticle hybrids directed by crystal growth with NaBH4 and the dependence on the conditions used for nucleation, and (iv) the catalytic activities of the hybrids towards the reduction of 4-nitrophenol to 4-aminophenol in the presence of excess NaBH4. We demonstrated the design, synthesis, and characterization of a new template peptide, RU025, that tends to form an α-helical conformation and self-assembles into network nanoarchitectures in aqueous solution. Gold seed crystals were synthesized by mixing RU025 and HAuCl4 in a 1:2 molar ratio, followed by further reduction of the gold seed crystals with NaBH4. This reaction afforded worm-like gold nanoparticles embedded in the peptide self-assemblies. The peptide-gold nanoparticle hybrids exhibited catalytic activities for the Langmuir-Hinshelwood type reduction of 4-nitrophenol to 4-aminophenol in the presence of excess NaBH4, with an activation energy of 33 kJ mol-1. The size and morphology of gold nanoparticles can be tuned in the nanometer range by altering the peptide concentration relative to HAuCl4 and by changing the nucleation time. This method for constructing peptide-metallic nanoparticle hybrids, in which metallic nanoparticles are dispersed in the peptide self-assemblies, provides highly reactive catalysts.

Optical and biomedical properties of eco-friendly metal nanostructures synthesized using Trigonella foenum-graecum leaf extract

Biogenic, eco-friendly, reliable, and cost-effective metal nanostructures were synthesized using Trigonella foenum-graecum leaf extract, which acted as reducing and stabilizing agent with no additional chemical surfactants. Nanoparticle formation was confirmed from UV–Vis absorption, XRD, and FTIR spectra. Morphology and crystallinity of spherical silver nanoparticles (Ag NPs) and gold nanoparticles (Au NTs) were further confirmed from TEM analysis. Luminescence enhancement and quenching of lanthanide ion complexes were observed and found to be dependent on metal nanostructure concentration. The factors relay on the energy transfers between nanostructures and rare-earth ions (RE). The nonlinear optical studies of Ag NPs and Au NTs were studied using Z-scan and degenerate four wave mixing (DFWM) techniques with picosecond and femtosecond lasers. The surface-enhanced Raman scattering (SERS) of the test molecule, rhodamine 6G, was studied to check the performance of Ag NPs and Au NTs in enhancing the Raman scattering signals. In vitro cytotoxic effect of the Ag NPs and Au NTs has been checked against A549 lung cancer cell lines and the efficiency of toxicity depended on the dosage. These experiments demonstrate that the nanostructures are ideal candidates for applications in optics and biology as PL based devices with appropriate concentrations of RE ions, optical switches, SERS substrates, and therapeutic agents towards cancer cell lines.

Morphological control of gold nanoparticles on exfoliated layers of layered double hydroxide: A reusable hybrid catalyst for the reduction of p -nitrophenol

Abstract We have developed a controllable method for high density of ultrafine gold nanoparticles (NP) and their uniform aggregates on exfoliated nanosheet of layered double hydroxide (LDH). The LDH nanosheet effectively supports the growth of ultrafine gold NP because the freshly exfoliated hydroxide prevents the formation of large and irregular aggregation of gold NP. We found that the reduction conditions allowed controlling the sizes and morphologies of gold NP during their growth on LDH layers. Additionally, pre-added ascorbic acid effectively induced a narrow distribution of gold NP during their reduction reactions by NaBH4 or hydrazine hydrate. This hybrid material exhibited excellent durability and catalytic activity (>99% conversion efficiency) in the reduction of p-nitrophenol. The nanoscopic nature of exfoliated LDH nanosheets affects the catalytic performances of the hybrid catalyst, such as a high positive charge for strong binding to gold NP, and a fresh hydroxide surface for a good dispersion of the hybrid catalyst in reacting solutions. Our method can be very useful to make stable and reusable Au/LDH nanohybrids for a variety of applications.

Multimode Electron Tomography as a Tool to Characterize the Internal Structure and Morphology of Gold Nanoparticles.

Three dimensional (3D) characterization of structural defects in nanoparticles by transmission electron microscopy is far from straightforward. We propose the use of a dose-efficient approach, so-called multimode tomography, during which tilt series of low and high angle annular dark field scanning transmission electron microscopy projection images are acquired simultaneously. In this manner, not only reliable information can be obtained concerning the shape of the nanoparticles, but also the twin planes can be clearly visualized in 3D. As an example, we demonstrate the application of this approach to identify the position of the seeds with respect to the twinning planes in anisotropic gold nanoparticles synthesized using a seed mediated growth approach.

Metagenomic analysis of microbial communities yields insight into impacts of nanoparticle design.

Next-generation DNA sequencing and metagenomic analysis provide powerful tools for the environmentally friendly design of nanoparticles. Herein we demonstrate this approach using a model community of environmental microbes (that is, wastewater-activated sludge) dosed with gold nanoparticles of varying surface coatings and morphologies. Metagenomic analysis was highly sensitive in detecting the microbial community response to gold nanospheres and nanorods with either cetyltrimethylammonium bromide or polyacrylic acid surface coatings. We observed that the gold-nanoparticle morphology imposes a stronger force in shaping the microbial community structure than does the surface coating. Trends were consistent in terms of the compositions of both taxonomic and functional genes, which include antibiotic resistance genes, metal resistance genes and gene-transfer elements associated with cell stress that are relevant to public health. Given that nanoparticle morphology remained constant, the potential influence of gold dissolution was minimal. Surface coating governed the nanoparticle partitioning between the bioparticulate and aqueous phases.

Structural and Optical Properties Correlated with the Morphology of Gold Nanoparticles Embedded in Synthetic Sapphire: A Microscopy Study.

This work reports on the electron microscopy analysis of the structure and morphology of gold nanoparticles produced by ion implantation as well as their relationship to their optical properties. Metalic nanoparticles by ion implantation are usually spherical and formed beneath the surface of a dielectric matrix. In this experiment, the matrix was sapphire. After high-energy Si ion irradiation, the gold nanoparticles were elongated into prolate spheroids. Since the nanoparticles are embedded in a dielectric matrix, secondary electron imaging in a JEOL JSM-7800F at low voltage did not allow their analysis. This work proposes an analysis using backscattered electron imaging in a field emission scanning electron microscopy at higher voltages (20 kV) to explore the morphology of the embedded nanoparticles. The samples were observed by cross-sectional view as well as a top view of the surface of the sapphire matrix for exploration and recognition of their morphology, dimensions, distribution, and composition. The analysis was extended by means of Rutherford backscattering spectrometry, X-ray diffraction, and optical extinction spectroscopy. The nanoparticles exhibited structural and optical properties correlated directly to the morphology observed by microscopy. The beam interaction with the sample and the used parameters was simulated in the CASINO code, from which the depth of exploration with distinct parameters used in microscopy analysis was estimated.

Evaluation of size, morphology, concentration, and surface effect of gold nanoparticles on X-ray attenuation in computed tomography

Increasing attention has been focused on the use of nanostructures as contrast enhancement agents in medical imaging, especially in computed tomography (CT). To date, gold nanoparticles (GNPs) have been demonstrated to have great potential as contrast agents for CT imaging. This study was designed to evaluate any effect on X-ray attenuation that might result from employing GNPs with a variety of shapes, sizes, surface chemistries, and concentrations. Gold nanorods (GNRs) and spherical GNPs were synthesized for this application. X-ray attenuation was quantified by Hounsfield unit (HU) in CT. Our findings indicated that smaller spherical GNPs (13 nm) had higher X-ray attenuation than larger ones (60 nm) and GNRs with larger aspect ratio exhibited great effect on X-ray attenuation. Moreover, poly ethylene glycol (PEG) coating on GNRs declined X-ray attenuation as a result of limiting the aggregation of GNRs. We observed X-ray attenuation increased when mass concentration of GNPs was elevated. Overall, smaller spherical GNPs can be suggested as a better alternative to Omnipaque, a good contrast agent for CT imaging. This data can be also considered for the application of gold nanostructures in radiation dose enhancement where nanoparticles with high X-ray attenuation are applied.

Study on dependence of dose enhancement on cluster morphology of gold nanoparticles in radiation therapy using a body-centred cubic model

Gold nanoparticles (GNPs) injected in a body for dose enhancement in radiation therapy are known to form clusters. We investigated the dependence of dose enhancement on the GNP morphology using Monte-Carlo simulations and compared the model predictions with experimental data. The cluster morphology was approximated as a body-centred cubic (BCC) structure by placing GNPs at the 8 corners and the centre of a cube with an edge length of 0.22–1.03 µm in a 4 × 4 × 4 µm3 water-filled phantom. We computed the dose enhancement ratio (DER) for 50 and 260 kVp photons as a function of the distance from the cube centre for 12 different cube sizes. A 10 nm-wide concentric shell shaped detector was placed up to 100 nm away from a GNP at the cube centre. For model validation, simulations based on BCC and nanoparticle random distribution (NRD) models were performed using parameters that corresponded to the experimental conditions, which measured increases in the relative biological effect due to GNPs. We employed the linear quadratic model to compute cell surviving fraction (SF) and sensitizer enhancement ratio (SER). The DER is inversely proportional to the distance to the GNPs. The largest DERs were 1.97 and 1.80 for 50 kVp and 260 kVp photons, respectively. The SF predicted by the BCC model agreed with the experimental value within 10%, up to a 5 Gy dose, while the NRD model showed a deviation larger than 10%. The SERs were 1.21 ± 0.13, 1.16 ± 0.11, and 1.08 ± 0.11 according to the experiment, BCC, and NRD models, respectively. We most accurately predicted the GNP radiosensitization effect using the BCC approximation and suggest that the BCC model is effective for use in nanoparticle dosimetry.

Evaluation of morphology, aggregation pattern and size-dependent drug-loading efficiency of gold nanoparticles stabilised with poly (2-vinyl pyridine)

Presence of basic nitrogen throughout the chain of poly(2-vinylpyridine) make them alluring candidate for applications requiring chelation of heavy metals. In this study, we report the use of poly (2-vinylpyridine) (P2VP) homopolymers of varying molar masses for the stabilization of gold nanoparticles for the first time. A study based on AFM, DLS and UV-visible spectroscopy was conducted to establish a correlation of the molar mass of P2VP with the size and distribution of the gold nanoparticles. Systematic and gradual change in the absorbance intensity and shift in SPR band of gold nanoparticles were also observed upon variations in treatment temperature, concentration of polymer, residence time, pH, and electrolyte concentration. The results obtained by UV-visible spectroscopy, AFM and DLS are complementary. The size of the P2VP-stabilised AuNPs was found to be in the range of 20–130 nms. At last, the effect of the size of P2VP-stabilised AuNPs (directly related to the molar mass of P2VP) on the drug-loading efficiency is evaluated.

The effects of gold nanoparticles functionalized with ß-amyloid specific peptides on an in vitro model of blood–brain barrier

We studied the effect of gold nanoparticle (AuNP) size, surface charge, concentration and morphology on the integrity of the blood–brain barrier (BBB) in a well-established in vitro model set-up. We focused on the effect of peptide functionalized hollow gold nanospheres and gold nanorods, which selectively bind to amyloidogenic β-amyloid structures. These AuNP conjugates have already been successfully tested as photothermal absorbers for potential application in Alzheimer's disease (AD) therapy in an in vitro set-up, but may exhibit a low passage through the BBB due to their overall negative charge. Our results show that: (i) small (1.4 nm) AuNPs strongly affects the BBB integrity, (ii) negative surface charge impedes BBB passage, and (iii) this charge effect caused by the peptide is compensated by covalent coupling to a polyethylene glycol ligand stabilizing the particles in diluted manner.

WITHDRAWN: Microscopy study, structural and optical properties correlated with the morphology of metallic nanoparticles embedded in synthetic sapphire

Abstract This work reports on the electron microscopy analysis of the structure and morphology of gold nanoparticles produced by ion implantation, as well as their relationship to their optical properties. Gold nanoparticles are usually spherical and formed beneath the surface of a dielectric matrix. In this experiment, the matrix was sapphire. After high-energy Si ion irradiation, the gold nanoparticles were elongated into prolate spheroids. Since the nanoparticles are embedded in a dielectric matrix, secondary electron imaging in a JEOL JSM-7800F at low voltage did not allow their analysis. This work proposes an analysis using backscattered electron imaging in a field emission scanning electron microscope at higher voltages (20 kV) in order to explore the morphology of the embedded nanoparticles. The samples were observed by cross-sectional view as well as a top view of the surface of the sapphire matrix for exploration and recognition of their morphology, dimensions, distribution, and composition. The analysis was extended with Rutherford backscattering spectrometry, X-ray diffraction, and optical extinction spectroscopy. The nanoparticles exhibited structural and optical properties correlated directly to the morphology observed by microscopy. The beam interaction with the sample and the conditions used were simulated in the CASINO code, from which the depth of exploration with the conditions used in field emission scanning electron microscopy were estimated.