Evolution of size and shape in the colloidal crystallization of gold nanoparticles

The addition of dodecanethiol to a solution of oleylamine-stabilized gold nanoparticles in chloroform leads to aggregation of nanoparticles and formation of colloidal crystals. Based on results from dynamic light scattering and scanning electron microscopy we identify three different growth mechanisms: direct nanoparticle aggregation, cluster aggregation, and heterogeneous aggregation. These mechanisms produce amorphous, single-crystalline, polycrystalline, and core-shell type clusters. In the latter, gold nanoparticles encapsulate an impurity nucleus. All crystalline structures exhibit fcc or icosahedral packing and are terminated by (100) and (111) planes, which leads to truncated tetrahedral, octahedral, and icosahedral shapes. Importantly, most clusters in this system grow by aggregation of 60-80 nm structurally nonrigid clusters that form in the first 60 s of the experiment. The aggregation mechanism is discussed in terms of classical and other nucleation theories.     

Green synthesis of well-dispersed gold nanoparticles using Macrotyloma uniflorum

The synthesis of metal nanoparticles of different sizes, shapes, chemical composition and controlled monodispersity is an important area of research in nanotechnology because of their interesting physical properties and technological applications. Present work describes an eco-friendly method for the synthesis of spherical gold nanoparticles using aqueous extract of Macrotyloma uniflorum. The effects of quantity of extract, temperature and pH on the formation of nanoparticles are studied. The nanoparticles are characterized by UV-visible spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD) and FTIR analysis. The high crystallinity of nanoparticles with fcc phase is evident from HRTEM images, SAED and XRD patterns. Synthesized nanoparticles have size in the range 14-17nm. FTIR spectrum indicates the presence of different functional groups present in the bio-molecule capping the nanoparticles. The possible mechanism leading to the formation of gold nanoparticles is suggested.     

Biosynthesis of Au nanoparticles using olive leaf extract: 1st Nano Updates

The biological synthesis of gold nanoparticles (AuNPs) of various shapes (triangle, hexagonal, and spherical) using hot water olive leaf extracts as reducing agent is reported. The size and the shape of Au nanoparticles are modulated by varying the ratio of metal salt and extract in the reaction medium. Only 20 min were required for the conversion into gold nanoparticles at room temperature, suggesting a reaction rate higher or comparable to those of nanoparticles synthesis by chemical methods. The variation of the pH of the reaction medium gives AuNPs nanoparticles of different shapes. The nanoparticles obtained are characterized by UV–Vis spectroscopy, photoluminescence, transmission electron microscopy (TEM), X-ray diffraction (XRD), FTIR spectroscopy and thermogravimetric analysis. The TEM images showed that a mixture of shapes (triangular, hexagonal and spherical) structures was formed at lower leaf broth concentration and high pH, while smaller spherical shapes were obtained at higher leaf broth concentration and low pH.     

Facile electrocatalytic redox of hemoglobin by flower-like gold nanoparticles on boron-doped diamond surface

The flower-like gold nanoparticles together with spherical and convex polyhedron gold nanoparticles were fabricated on boron-doped diamond (BDD) surface by one-step and simple electrochemical method through easily controlling the applied potential and the concentration of HAuCl(4). The recorded X-ray diffraction (XRD) patterns confirmed that these three shapes of gold nanoparticles were dominated by different crystal facets. The cyclic voltammetric results indicated that the morphology of gold nanoparticles plays big role in their electrochemical behaviors. The direct electrochemistry of hemoglobin (Hb) was realized on all the three different shapes of nanogold-attached BDD surface without the aid of any electron mediator. In pH 4.5 acetate buffer solutions (ABS), Hb showed a pair of well defined and quasi-reversible redox peaks. However, the results obtained demonstrated that the redox peak potential, the average surface concentration of electroactive heme, and the electron transfer rates of Hb are greatly dependent upon the surface morphology of gold nanoparticles. The electron transfer rate constant of hemoglobin over flower-like nanogold/BDD electrode was more than two times higher than that over spherical and convex polyhedron nanogold. The observed differences may be ascribed to the difference in gold particle characteristics including surface roughness, exposed surface area, and crystal structure.     

Carboranethiol-modified gold surfaces. A study and comparison of modified cluster and flat surfaces

Four different carboranethiol derivatives were used to modify the surfaces of gold nanoparticles and flat gold films. The novel materials engendered from these modifications are extraordinarily stable species with surfaces that support self-assembled monolayers of 1-(HS)-1,2-C2B10H11, 1,2-(HS)2-1,2-C2B10H10, 1,12-(HS)2-1,12-C2B10H10, and 9,12-(HS)2-1,2-C2B10H10, respectively. Surprisingly, characterization of these materials revealed that a number of molecules of the carboranethiol derivatives are incorporated inside the nanoparticles. This structural feature was studied using a number of techniques, including X-ray photoelectron spectroscopy (XPS), UV-vis, and IR spectroscopies. Thermal desorption experiments show that carborane molecules detach and leave the nanoparticle surface mostly as 1,2-C2B10H10 isotopic clusters, leaving sulfur atoms bound to the gold surface. The surfaces of both the gold nanoparticles and the flat gold films are densely packed with carboranethiolate units. One carborane cluster molecule occupies an area of six to seven surface gold atoms of the nanoparticle and eight surface gold atoms of the flat film. XPS data showed that molecules of 1,12-(HS)2-1,12-C2B10H10 bind to the flat gold surface with only half of the thiol groups due to the steric demands of the icosahedral carborane skeleton. Electrochemical measurements indicate complete coverage of the modified gold surfaces with the carboranethiol molecules.     

Biological Synthesis of Gold Nanoparticles by Fungus <Emphasis Type="Italic">Epicoccum</Emphasis><Emphasis Type="Italic">nigrum</Emphasis>

Gold nanoparticles exhibit unique optical, thermal, chemical and physical properties. The microorganisms have high potential for production of nanoparticles with wide applications. Application of fungi to produce nanoparticles is potentially exciting because of their ability to secrete large amounts of enzymes. In this study, we investigated biosynthesis of gold nanoparticles by the fungus Epicoccum nigrum isolated from Andalian gold mine in north-west of Iran. The gold nanoparticles were produced intra and extracellular by reaction of an aqueous solution of chloroauric acid with the biomass of fungus E. nigrum. The produced gold nanoparticles were in the size range of 5–50 nm in spherical and rod shapes. This is the first report on the biosynthesis of gold nanoparticles by the fungus E. nigrum.     

Effect of hydrophobicity inside PEO-PPO-PEO block copolymer micelles on the stabilization of gold nanoparticles: experiments

In this paper we present the effect of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymer micelles and their hydrophobicity on the stabilization of gold nanoparticles. Gold nanoparticles were prepared by a method developed by Sakai et al. (Sakai, T.; Alexandridis, P. Langmuir 2004, 20, 8426). An absorption centered at 300-400 nm in time-dependent UV spectra provided evidence that the very first step of the synthesis was to form primary gold clusters. Then the gold clusters grew in size and were stabilized by block copolymer micelles. The stabilization capacities of the micelles were modulated by tuning the block copolymer concentration and composition and by adding salts. With good stabilization, gold particles were spherical and uniform in size with a diameter of 5-10 nm. Otherwise they were aggregates with irregular shapes such as triangular, hexagonal, and rodlike. The presence of a small amount of NaF significantly increased the stabilization capacity of the micelles and consequently modified the quality of the gold particles. Using FTIR and 1H NMR spectroscopy, micellization of the block copolymers and hydrophobicity of the micelles were proven very important for the stabilization. A higher hydrophobicity of the micelle cores was expected to favor the entrapment of primary gold clusters and the stabilization of gold nanoparticles.     

DNA‐Encoded Tuning of Geometric and Plasmonic Properties of Nanoparticles Growing from Gold Nanorod Seeds

Systematically controlling the morphology of nanoparticles, especially those growing from gold nanorod (AuNR) seeds, are underexplored; however, the AuNR and its related morphologies have shown promises in many applications. Herein we report the use of programmable DNA sequences to control AuNR overgrowth, resulting in gold nanoparticles varying from nanodumbbell to nanooctahedron, as well as shapes in between, with high yield and reproducibility. Kinetic studies revealed two representative pathways for the shape control evolving into distinct nanostructures. Furthermore, the geometric and plasmonic properties of the gold nanoparticles could be precisely controlled by adjusting the base compositions of DNA sequences or by introducing phosphorothioate modifications in the DNA. As a result, the surface plasmon resonance (SPR) peaks of the nanoparticles can be fine‐tuned in a wide range, from visible to second near‐infrared (NIR‐II) region beyond 1000 nm.     

Rapid green synthesis of gold nanoparticles using Rosa hybrida petal extract at room temperature

This study reports a green method for the synthesis of gold nanoparticles using the aqueous extract of rose petals. The effects of gold salt concentration, extract concentration and extract quantity were investigated on nanoparticles synthesis. Gold nanoparticles were characterized with different techniques such as UV-vis spectroscopy, FT-IR spectroscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, dynamic light scattering and transmission electron microscopy. Transmission electron microscopy experiments showed that these nanoparticles are formed with various shapes. FT-IR spectroscopy revealed that gold nanoparticles were functionalized with biomolecules that have primary amine group (-NH2), carbonyl group, -OH groups and other stabilizing functional groups. X-ray diffraction pattern showed high purity and face centered cubic structure of gold nanoparticles. Dynamic light scattering technique was used for particle size measurement, and it was found to be about 10nm. The rate of the reaction was high and it was completed within 5 min.     

Synthesis of uniform gold nanoparticles using non-pathogenic bio-control agent: evolution of morphology from nano-spheres to triangular nanoprisms

Green synthesis of gold nanospheres with uniform diameter and triangular nanoprisms with optically flat surface was carried out using a non-pathogenic bio-control agent Trichoderma asperellum for reduction of HAuCl(4). Kinetics of the reaction was monitored by UV-Vis absorption spectroscopy. No additional capping/complexing agent was used for stabilizing the gold nanoparticles. Evolution of morphology from pseudospherical nanoparticles to triangular nanoprisms was studied by transmission electron microscopy (TEM). It revealed that three or more pseudospheres fused to form nanoprisms of different shapes and sizes. Slow rate of reduction of HAuCl(4) by constituents of cell-free fungal extract was instrumental in producing such exotic morphologies. Isolation of gold nanotriangles from the reacting masses was achieved by differential centrifugation.     

Octahedral and Cubic Gold Nanoframes with Platinum Framework

Herein, we report a general synthetic pathway to various shapes of three‐dimensional (3D) gold nanoframes (NFs) embedded with a Pt skeleton for structural rigidity. The synthetic route comprises three steps: site‐specific (edge and vertex) deposition of Pt, etching of inner Au, and regrowth of Au on the Pt framework. Site‐specific reduction of Pt on Au nanoparticles (NPs) led to the high‐quality of 3D Au NFs with good structural rigidity, which allowed the detailed characterization of the corresponding 3D metal NFs. The synthetic method described here will open new avenues toward many new kinds of 3D metal NFs.     

Sonochemical Synthesis of Gold Nanoparticles by Using High Intensity Focused Ultrasound

The sonochemical synthesis of gold nanoparticles (GNPs) with different shapes and size distributions by using high‐intensity focused ultrasound (HIFU) operating at 463 kHz is reported. GNP formation proceeds through the reduction of Au³⁺ to Au⁰ by radicals generated by acoustic cavitation. TEM images reveal that GNPs show irregular shapes at 30 W, are primarily icosahedral at 50 W and form a significant amount of nanorods at 70 W. The size of GNPs decreases with increasing acoustic power with a narrower size distribution. Sonochemiluminescence images help in the understanding of the effect of HIFU in controlling the size and shapes of GNPs. The number of radicals that form and the mechanical forces that are generated control the shape and size of the GNPs. UV/Vis spectra and TEM images are used to propose a possible mechanism for the observed effects. The results presented demonstrate, for the first time, that the HIFU system can be used to synthesise size‐ and shape‐controlled metal nanoparticles.     

Catalytic properties of supported gold nanoparticles in organic syntheses

Gold nanoparticles exhibit unique properties due to their ability to form aggregates of atoms of diverse morphology shapes and sizes of which depend, to a considerable extent, on specific features of the nearest environment. The nature of gold nanoparticles varies in a wide range: from the particles with pronounced Lewis acidic properties to the negatively charged particles bearing a formal zero-valence charge. The most examples of new reactions catalyzed by gold nanoparticles include unsaturated compounds and strong nucleophiles (such as amines) as substrates. This short review provides a digest of the catalytic properties of gold nanoparticles. The main attention is paid to the possible role of certain forms of the metal in catalytic reactions. Of special interest are reactions in which effects of synergism of gold and other active species or second metals present in the catalyst are revealed or a size effect is established.     

Predicting the shape and structure of face-centered cubic gold nanocrystals smaller than 3 nm.

Although a number of computational studies have examined the relative stability of icosahedral and decahedral gold clusters from 1 to 3 nm in size, few studies have focussed on the variety of face-centered cubic (fcc) nanoparticles in this size regime. In most cases small fcc gold particles are assumed to adopt the truncated octahedral shape, but in light of the fact that the shape and structure of gold nanoparticles is known to vary, the relative stability of fcc polyhedra may change with size. Presented here are results of first-principles calculations investigating the preferred shape of gold particles less than 3 nm in size. Our results indicate that the equilibrium shape of fcc gold nanoparticles less than 1 nm is the cuboctahedron, but this shape rapidly becomes energetically unstable with respect to the truncated octahedron, octahedron and truncated cube shapes as the size increases.     

Measuring the number concentration of arbitrarily-shaped gold nanoparticles with surface plasmon resonance microscopy

Molar concentration of gold nanoparticles is one of the most critical parameters of gold colloids in order to develop their applications in sensing, diagnostics and nanomedicine. Previous methods often stand just for gold nanoparticles with regular shape and narrow size distribution. In the present work, we proposed an absolute quantification method that determined the molar concentration of gold nanoparticles with arbitrary shapes and polydisperse sizes. This approach involved the real time monitoring and counting of individual nanoparticles collision events, from which the quantification of molar concentration was achieved using a theoretical model consisting of Fick’s laws of diffusion and Stokes-Einstein equation. The determination of spherical gold nanoparticles concentration resulted in excellent agreement with traditional spectrometry method. It was further demonstrated that the present approach can be expanded to determine the molar concentration of gold nanoparticles with arbitrary shapes and poly-diversed distributions.     

基于离心加速耗散作用的纳米金三角片高效分离方法研究

纳米金三角片由于制备和纯化困难,获得较纯、较好形貌的产物一直是个挑战。本文提出利用离心加速的耗散作用,采用十六烷基三甲基氯化铵(CTAC)作为絮凝剂,对纳米金三角片粗产物进行纯化,从而快速获得尺寸形貌均一且顶角保持尖锐的不同尺寸的三角形金纳米颗粒。通过紫外可见分光光度计对比了用不同浓度絮凝剂获得的胶体上清液与沉淀的颜色以及消光光谱,从而确定分离不同尺寸的金三角纳米颗粒所需的最佳絮凝剂浓度。通过透射电子显微镜(TEM)对比纯化前后颗粒形貌的变化,发现已有的静置纯化方法存在较大局限性,即耗时较长且对颗粒的形貌有明显影响;而辅助以离心加速的分离方法,不仅可实现对不同尺寸纳米金三角片的快速高效分离,且有效减小了纯化过程中纳米颗粒的尖端损失。特别是对小尺寸(边长小于50 nm)的三角纳米颗粒,经离心加速的耗散力诱导的凝聚作用分离所得的颗粒,其尖端仍能保持尖锐。此方法简便高效地实现了纳米金三角片的分离,并有望推广到其它成分、非球形、低对称性形貌的纳米颗粒的纯化。     

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.     

Aqueous-organic phase transfer of gold nanoparticles and gold nanorods using an ionic liquid

The water-immiscible ionic liquid, [C4MIM][PF6], is a solvent medium that allows complete transfer of gold nanoparticles from an aqueous phase into an organic phase. Both spherical and rod-shaped gold nanoparticles are efficiently transferred from an aqueous solution into the organic phase without requiring the use of thiols. The sizes and shapes of the gold nanoparticles were preserved during the phase-transfer process when a surfactant was added to the ionic liquid. This process offers a simple approach for obtaining solutions of differently sized and shaped gold nanoparticles in ionic liquids.     

Highly sensitive biomolecule detection on a quartz crystal microbalance using gold nanoparticles as signal amplification probes.

We report here a novel strategy for the high-sensitive detection of target biomolecules with very low concentrations on a quartz crystal microbalance (QCM) device using gold nanoparticles as signal enhancement probes. By employing a streptavidin-biotin interaction as a model system, we could prepare biotin-conjugated gold nanoparticles maintaining good dispersion and long-term stability by controlling the biotin density on the surface of gold nanoparticles that have been investigated by UV-vis spectra and AFM images. These results showed that 10 microM N-(6-[biotinamido]hexyl)-3'-(2'-pyridyldithio)propionamide (biotin-HPDP) was the critical concentration to prevent the nonspecific aggregation of gold nanoparticles in this system. For sensing streptavidin target molecules by QCM, biotinylated BSA was absorbed on the Au surface of the QCM electrode and subsequent coupling of the target streptavidin to the biotin in the sensing interface followed. Amplification of the sensing process was performed by the interaction of the target streptavidin on the sensing surface with gold nanoparticles modified with 10 microM biotin-HPDP. The biotinylated gold nanoparticles were used as signal amplification probes to improve the detection limit, which was 50 ng/ml, of the streptavidin detection system without signal enhancement, and the calibration curve determined for the net frequency changes showed good linearity over a wide range from 1 ng/ml to 10 microg/ml for the quantitative streptavidin target molecule analysis. In addition, the measured dissipation changes suggested that the layer of biotin-BSA adsorbed on the Au electrode and the streptavidin layer assembled on the biotin-BSA surface were highly compact and rigid. On the other hand, the structure formed by the biotinylated gold nanoparticles on the streptavidin layer was flexible and dissipative, being elongated outward from the sensing surface.     

A study on the sizes and concentrations of gold nanoparticles by spectra of absorption, resonance Rayleigh scattering and resonance non-linear scattering

Liquid phase gold nanoparticles with different diameters and colors can be prepared using sodium citrate reduction method by controlling the amounts of sodium citrate. The mean diameters of gold nanoparticles are measured by transmission electron microscope (TEM). Gold nanoparticles with different sizes have specific absorption spectra. When the diameters of nanoparticles is between 12 and 41 nm, the maximum absorption peaks locate at 520-530 nm and there are red shifts gradually with the increase of diameters of gold nanoparticles. And when the size of gold nanoparticle is constant, the absorbance is proportional to the concentration of gold. Obvious resonance Rayleigh scattering (RRS) and the resonance non-linear scattering such as second-order scattering (SOS) and frequency-doubling scattering (FDS) appear at the same time as well, and the maximum scattering peaks are located at 286 nm (RRS), 480 nm (SOS) and 310 nm (FDS), respectively. When the concentration of gold is constant, absorbance and the intensities of RRS, SOS and FDS (I(RRS), I(SOS) and I(FDS)) have linear relationships with the diameters of gold nanoparticles. When the diameter of gold nanoparticle is constant, the absorbance and I(RRS), I(SOS), I(FDS) are directly proportional to the concentrations of gold nanoparticles. Therefore, it is very useful for studying the liquid phase gold nanoparticles by investigating the absorption, RRS, SOS and FDS spectra.