Shape Of Gold Nanoparticles Research Articles

Size‐ and Shape‐Dependent Fluorescence Quenching of Gold Nanoparticles on Perylene Dye

Organo‐soluble decane thiol monolayer‐protected gold nanoparticles of different shapes and sizes are homogenously mixed with strong fluorescent perylene diimide (PDI) dye molecules in both solution and solid states. The effect of the doped gold nanoparticles on PDI is investigated by UV–vis, fluorescence, transmission electron microscopy, scanning electron microscopy, and Raman experiments. The gold nanoparticles are found to modify the strong fluorescence properties of PDI depending on particle size and shape. The smallest spherical gold nanoparticles (2.6 nm) exhibit the strongest quenching effect. When the smallest spherical gold nanoparticles are cast on the PDI soaked paper followed by drying and/or sealing in a polydimethylsiloxane film, the area with gold nanoparticles shows significant quenching effects under a UV light but appears visually identical to the surrounding area under daylight. This demonstrates the potential to introduce gold nanoparticles into practical applications such as antifraud technologies.

Organogels from Dimeric Bile Acid Esters: In Situ Formation of Gold Nanoparticles

A new class of steroid dimers (bile acid derivatives) linked through ester functionalities were synthesized, which gelled various aromatic solvents. The organogels formed by the three dimeric ester molecules showed birefringent textures and fibrous nature by polarizing optical microscopy and scanning electron microscopy, respectively. A detailed rheological study was performed to estimate the mechanical strengths of two sets of organogels. In these systems, the storage modulus varied in the range of 0.8-3.5 × 10(4) at 1% w/v of the organogelators. The exponents of scaling of the storage modulus and yield stress of the two systems agreed well with those expected for viscoelastic soft colloidal gels with fibrillar flocs. The nanofibers in the organogel were utilized to engineer gold nanoparticles of different sizes and shapes and generate new gel-nanoparticle hybrid materials.

Tunable gold nanoparticles shape and size in reductive and structuring media containing protic ionic liquids

Herein, a facile method was developed for preparing high concentration of monodispersed gold nanoparticles (NPs) at room temperature from gold(III) chloride by using different media based on N,N-dimethylformamide or water solutions containing a protic ionic liquid (PIL), namely, the octylammonium formate or the bis(2-ethyl-hexyl)ammonium formate, based on which both PILs were used as redox-active structuring media. The formation of gold NPs in these systems was then characterized using UV–visible spectroscopy, transmission electron microscopy, and dynamic light scattering. From these investigations, it appears that the structure and aggregation pathway of PILs in selected solvents affect strongly the formation, growth, the shape, and the size of gold NPs. In fact, by using this approach, the shape-/ size-controlled gold NPs (branched and spherical) can be generated under mild condition. This approach suggests also a wealth of potential for these designer nanomaterials within the biomedical, materials, and catalysis communities by using designer and safer media based on PILs.

Cancer cell sensing and therapy using affinity tag-conjugated gold nanorods.

Through the developments in controlling the shape of gold nanoparticles, synthesis of gold nanorods (AuNRs) can be considered as a milestone discovery in the area of nanomaterial-based cancer treatments. Besides having tuneable absorption maxima at near infrared (NIR) range, AuNRs have superior absorption cross section at NIR frequencies compared with other gold nanoparticles. When this unique optical property is combined with the specificity against cancer cells used by affinity tag conjugations, AuNRs become one of the most important nanoparticles used in both cancer cell sensing and in therapy. In this review, the impact of size and shape control of nanoparticles, especially AuNRs, on cancer cell treatments and a range of aptamer-conjugated AuNR applications in this regard are reviewed.

The structure and morphology of gold nanoparticles produced in cationic gemini surfactant systems

Potential applications of gold nanoparticles (GNP) are strictly connected with their size and shape. The influence of different dicationic (gemini) surfactants, alkyloxymethylimidazolium derivatives derivatives, on the structure and morphology of GNP was studied. The synthesis of nanoparticles was performed in the presence of various gemini surfactants—dodecyloxymethylimidazolium nitrate (IMI_NO3_C4_C12), propionate (IMI_PROP_C4_C12) and 3,3'-[1,9-(2,8-dioxanonane)]bis-(1-nonyloxymethylimidazolium) chloride (IMI_Cl_oxyC7_C9), used as stabilizers and templates for obtaining different size and shape of gold nanoparticles. The samples obtained were examined using transmission electron microscopy (TEM), small angle scattering of synchrotron radiation (SAXS), UV–vis spectroscopy and NMR PFG spectroscopy. For the obtained solutions of nanoparticles the plasmon resonance was observed at the wavelengths corresponding to the presence of gold nanoparticles of sizes ranging from 5–100nm, with a significant shift towards higher wavelength for the samples prepared with addition of dicationic surfactants. TEM images evidence the presence of gold nanoparticles with tetrahedral and spherical morphology in solutions prepared with the surfactants IMI_PROP_C4_C12, IMI_NO3_C4_C12, and those of spherical morphology, but strongly aggregated, in the solution with the cationic surfactant IMI_Cl_oxyC7_C9.

Gold Nanoparticles as a Vaccine Platform: Influence of Size and Shape on Immunological Responses in Vitro and in Vivo

This paper demonstrates how the shape and size of gold nanoparticles (AuNPs) affect immunological responses in vivo and in vitro for the production of antibodies for West Nile virus (WNV). We prepared spherical (20 and 40 nm in diameter), rod (40 × 10 nm), and cubic (40 × 40 × 40 nm) AuNPs as adjuvants and coated them with WNV envelope (E) protein. We measured anti-WNVE antibodies after inoculation of these WNVE-coated AuNPs (AuNP-Es) into mice. The 40 nm spherical AuNP-Es (Sphere40-Es) induced the highest level of WNVE-specific antibodies, while rod AuNP-Es (Rod-Es) induced only 50% of that of Sphere40-E. To examine the mechanisms of the shape-dependent WNVE antibody production, we next measured the efficiency of cellular uptake of AuNP-Es into RAW264.7 macrophage cells and bone-marrow-derived dendritic cells (BMDCs) and the subsequent cytokine secretion from BMDCs. The uptake of Rod-Es into the cells proceeded more efficiently than those of Sphere-Es or cubic WNVE-coated AuNPs (Cube-Es), suggesting that antibody production was not dependent on the uptake efficiency of the different AuNP-Es. Cytokine production from BMDCs treated with the AuNP-Es revealed that only Rod-E-treated cells produced significant levels of interleukin-1β (IL-1β) and interleukin-18 (IL-18), indicating that Rod-Es activated inflammasome-dependent cytokine secretion. Meanwhile, Sphere40-Es and Cube-Es both significantly induced inflammatory cytokine production, including tumor necrosis factor-α (TNF-α), IL-6, IL-12, and granulocyte macrophage colony-stimulating factor (GM-CSF). These results suggested that AuNPs are effective vaccine adjuvants and enhance the immune response via different cytokine pathways depending on their sizes and shapes.

Shape control technology during electrochemical synthesis of gold nanoparticles

Gold nanoparticles with different shapes and sizes were prepared by adding gold precursor (HAuCl4) to an electrolyzed aqueous solution of poly(N-vinylpyrrolidone) (PVP) and KNO3, which indicates the good reducing capacity of the PVP-containing solution after being treated by electrolysis. Using a catholyte and an anolyte as the reducing agents for HAuCl4, respectively, most gold nanoparticles were spherical particles in the former case but plate-like particles in the latter case. The change in the pH value of electrolytes caused by the electrolysis of water would be the origin of the differences in shape and morphology of gold nanoparticles. A hypothesis of the H+ or OH− catalyzed PVP degradation mechanism was proposed to interpret why the pH value played a key role in determining the shape or morphology of gold nanoparticles. These experiments open up a new method for effectively controlling the shape and morphology of metal nanoparticles by using electrochemical methods.

One-step Synthesis of Shape-controllable Gold Nanoparticles and Their Application in Surface-enhanced Raman Scattering

Gold nanoparticles (NPs) of various shapes were synthesized by a one-step method at ambient temperature in the presence of NaCl. 2-mercaptosuccinic acid (MSA) was used as both reducing agent and stabilizing agent. The shapes of gold NPs were controllable by simply tuning S/Au ratio (S is from MSA molecule, and S/Au ratio is controlled by tuning the volume of added MSA solution), and triangle, polygonal and spherical nanoparticles were obtained. This result suggested a new way to consider the effects of MSA on the growth of nanoparticles, which showed that MSA is a strong capping agent and facilitates more uniform growth of nanoparticles in every dimension. And other important factors on nanoparticles growth including NaCl and temperature were discussed. Furthermore, a typical probe molecule, 4-aminothiophenol (4-ATP) was used to test the surface-enhanced Raman scattering (SERS) activity of these gold NPs and the results indicated good Raman activity on these substrates. And the enhancement factor (EF) at 1078 cm−1 (a1) was estimated to be as large as 6.3 × 104 and 5.5 × 104 for triangular plates and truncated particles, respectively.

Seedless Initiation as an Efficient, Sustainable Route to Anisotropic Gold Nanoparticles

Seedless initiation has been used as a simple and sustainable alternative to seed-mediated production of two canonical anisotropic gold nanoparticles: nanorods and nanoprisms. The concentration of reducing agent during the nucleation event was found to influence the resulting product morphology, producing nanorods with lengths from 30 to 630 nm and triangular or hexagonal prisms with vertex-to-vertex lengths ranging from 120 to over 700 nm. The seedless approach is then used to eliminate several chemical reagents and reactions steps from classic particle preparations while achieving almost identical nanoparticle products and product yields. Our results shed light on factors that influence (or do not influence) the evolution of gold nanoparticle shape and present a dramatically more efficient route to obtaining these architectures. Specifically, using these methods reduces the total amount of reagent needed to produce nanorods and nanoprisms by as much as 90 wt % and, to the best of our knowledge, has yielded the first report of spectroscopically discernible, colloidal gold nanoplates synthesized using a seedless methodology.

Thiolate adsorption on Au(${\bm {hkl}}$hkl) and equilibrium shape of large thiolate-covered gold nanoparticles

The adsorption of thiolates on Au surfaces employing density-functional-theory calculations has been studied. The dissociative chemisorption of dimethyl disulfide (CH(3)S-SCH(3)) on 14 different Au(hkl) is used as a model system. We discuss trends on adsorption energies, bond lengths, and bond angles as the surface structure changes, considering every possible Au(hkl) with h, k, l ≤ 3 plus the kinked Au(421). Methanethiolate (CH(3)S-) prefers adsorption on bridge sites on all surfaces considered; hollow and on top sites are highly unfavourable. The interface tensions for Au(hkl)-thiolate interfaces is determined at low coverage. Using the interface tensions in a Wulff construction method, we construct atomistic models for the equilibrium shape of large thiolate-covered gold nanoparticles. Gold atoms in a nanoparticle change their equilibrium positions upon adsorption of thiolates towards shapes of higher sphericity and higher concentration of step-edge atoms.

Self-Assembly of Two-Dimensional Hexagon Shaped Gold Nanoparticle Film Using Solvent Evaporation Method

Self-Assembly of Two-Dimensional Hexagon Shaped Gold Nanoparticle Film Using Solvent Evaporation Method

Evolution of size and shape of gold nanoparticles during long-time aging

The evolution of size and shape of gold nanoparticles was studied during long-time aging. The initial particle size of 2–5 nm increased to about 25 nm in one year of storage. It was revealed that the main mechanism of particle growth is Ostwald ripening, however, fusion of particles was also observed. Additionally, while the initial particles have spherical morphology, the grown particles show various shapes such as sphere, bipyramid, decahedron, deca-tetrahedron, triangular plate and rod. Twin boundaries with large frequency of ∼5% were detected inside the particles which have an important effect on the evolution of morphology. This study suggests that aging may be a new way of tuning size and shape of gold nanoparticles.

Gold nanoparticles immobilized on lipoic acid functionalized SBA-15: Synthesis, characterization and catalytic applications

Gold nanoparticles immobilized on lipoic acid functionalized SBA-15 (SBA-LAG) catalyst was synthesized via functionalization of SBA-15 with propylamine followed by tethering of lipoic acid and immobilization of gold nanoparticles. The structural and texctural characteristics of the catalyst have been determined by N2 adsorption–desorption and low-angle XRD. The successive attachment of spacers has been characterized by 13C CP-MAS NMR, FT-IR and TG-DTA. The size, shape, surface composition and oxidation state of gold nanoparticles have been determined by XRD, TEM and XPS techniques. SBA-LAG catalyst is found to be an efficient solid catalyst for producing good to excellent yields of propargylamines by condensing three-components such as (i) amine, (ii) aldehyde and (iii) alkyne in one-pot under solvent-free conditions.

PH Dependence of the Size and Shape of the Gold Nanoparticles Prepared by Macromolecules

The effect of the pH of the preparing solution on the size and shape of gold nanoparticles was studied in the solution containing soybean peptides or β-cyclodextrin (β-CD) as reducing agent. The resulting gold nanostructures were characterized by transmission electron microscopy (TEM), XRD and UV-vis spectra. Different shape of gold nanoparticles such as nanoplates, networked nanowires and spheres were prepared by changing the pH of solution. Electron diffraction pattern showed that the shape changes from plate or network to sphere as the pH of solution is increasing.

Model of Multi-Source Nanonetworks for the Detection of BRCA1 DNA Alterations Based on LSPR Phenomenon

In this paper, we present a multi-source nanonetwork model for biomedical diagnosis applications, based on the Localized Surface Plasmon Resonance by different shape gold nanoparticles (i.e., cylinder, cube, and rod). We present the process of multi-source emission, diffusion, and reception of nanoparticles, based on the ligand/receptor binding. Then, a multi-detection process of DNA alterations is accomplished when nanoparticles are captured at the receiver. The colloidal particles are selectively functionalized with specific splice junctions of gene sequences to reveal simultaneously different alteration that could be associated to an early disease condition. Particularly, full-wave simulations have been carried out for the multi-detection of alternative splice junctions of breast cancer susceptibility gene 1. The proposed application is verified through numerical results and expressed in terms of Extinction-Cross Section, in the case of synchronous and asynchronous nanoparticles detection. We show that the proposed approach is able to detect DNA alterations, based on a selective nanoparticle reception process.

A Simple, Rapid, and Green Synthesis of Capped Gold Nanospheres and Nanorods Using Aqueous Extract of Azolla

In the last few decades, an increasing commercial demand for metal nanoparticles is found due to their numerous applications in various fields such as electronics, catalysis in organic synthesis, material chemistry, energy, and medicine. Metallic nanoparticles are traditionally synthesized by wet chemical techniques, wherein the chemicals used are quite harmful and flammable. Herein, we reported a cheap and environment-friendly procedure for the synthesis of capped gold nanoparticles of different shapes from aqueous solution of tetrachloroauric acid (HAuCl4) using aqueous extract of Azolla pinnata, blue-green algae used as a reducing as well as capping agent. The so-prepared gold nanoparticles were well characterized by UV-visible spectroscopy, transmission electron microscopy (TEM), and quasi-elastic light scattering (QELS) techniques. The TEM showed nearly uniform distribution of the particles in water, which is again confirmed by QELS. This is for the first time that aqueous extract of A. pinnata was used for the synthesis of gold nanoparticles.

Effects of gold nanoparticle shape on the aggregation and fluorescence behaviour of water soluble zinc phthalocyanines

The absorption and fluorescence response as well as the fluorescence quantum yields and lifetimes of sulfonated phthalocyanines and alkyl carboxylic acid substituted zinc phthalocyanines in the presence of differently shaped water soluble gold nanoparticles were studied. The respective phthalocyanines are known to be highly aggregated in water, which is reported to markedly reduce the excited state lifetimes. This paper shows that in the presence of star shaped gold nanoparticles, the degree of phthalocyanine aggregation in water is greatly reduced, but the aggregation status of the phthalocyanines does not change for spherical Au nanoparticles. Since gold nanoparticles have already proven to be useful in numerous nanomedicinal and nanomedical applications, the disaggregation of phthalocyanines is an added advantage.

Preparation of Narrow Dispersity Gold Nanorods by Asymmetrical Flow Field-Flow Fractionation and Investigation of Surface Plasmon Resonance

The development of an asymmetrical field-flow fractionation (AsFlFFF) method for separating gold nanorods (GNR) is reported. Collected fractions containing GNR subpopulations with aspect ratios, sizes, and shapes which are more narrowly dispersed than the original population were further characterized by UV-vis spectroscopy and transmission electron microscopy. This ability to obtain different sizes and shapes of nanoparticles enabled the evaluation of a new approach to estimating the retention time and hydrodynamic size of nanorods and the investigation of GNR optical properties at a previously unattainable level of detail. Experimental results demonstrate that the longitudinal surface plasmon absorption maximum of GNRs is correlated with the effective particle radius in addition to the aspect ratio. This may account for some of the variabilities reported in published empirical data from different research groups and supports reports of simulated absorption spectra of GNRs of different physical dimensions. The use of AsFlFFF with dual UV-vis detection to rapidly assess relative changes in GNR subpopulations was demonstrated for irregularly shaped gold nanoparticles formed at different synthesis temperatures.

Spheres vs. rods: The shape of gold nanoparticles influences aggregation and deposition behavior

The influence of shape on nanomaterial aggregation and deposition was systematically studied with poly-acrylic acid (PAA) coated uniform-sized gold nanospheres (AuNSs) and nanorods (AuNRs). Time resolved dynamic light scattering was employed to study their aggregation kinetics in a wide range of mono- and di-valent electrolyte conditions. Results indicated that PAA coated AuNSs have higher aggregation propensity compared to anisotropic PAA coated AuNRs, as observed through critical coagulation concentration (CCC). The CCC values were estimated as 50mM NaCl and 1.8mM CaCl2 for AuNS, which showed substantial increase to 250mM NaCl and 7mM CaCl2 for anisotropic AuNRs. Though electrokinetic behavior showed similar surface potential for the spherical and rod-shaped materials, the geometric differences between the samples have likely resulted in unique conformation of the PAA coatings, leading to different magnitudes of steric hindrances and hence yielding the observed aggregation behavior. The deposition kinetics was monitored using the quartz crystal microbalance with dissipation technique. AuNRs showed relatively slower deposition compared to AuNSs for low electrolytes concentrations. With the increase in electrolyte concentration, the differences in deposition rates between spheres and rods diminished. The results from this study showed that the shape of nanomaterials can influence interfacial properties and result in unique aggregation and deposition behavior under typical aquatic conditions.

Pattern formation of gold-PVA nanomix spin coated on different substrates

The patterns arising from the interplay of colloidal gold nanoparticles solutions containing polyvinyl alcohol spin coated on different substrates have been investigated. High Resolution Transmission Electron Microscope results show chain-like assemblies and direct attachment of spherical shape gold nanoparticles with different size in the polyvinyl alcohol matrix. X-ray photoelectron spectroscopy analysis of the C 1s peak shows three different Au-polyvinyl alcohol bands (CH2, COH and CO) which accounts for the effect of the Au particle size in the gold-PVA films. Dewetting of indium tin oxide substrates by 6nm Au nanoparticles/polyvinyl alcohol colloidal solution induces concentration dependent cellular structures and fingering instability patterns which were duly reproduced using Monte Carlo simulations. Our results ascertain the importance of nanoparticle size, substrate type, oriantation and surface roughness on the pattern formation. In addition, we demonstrate that pattern formation on different substrates takes two different routes based on nanoparticle mobility rate, evoparation chemical potential and nanoparticle density.