Formation Of Gold Nanostructures Research Articles

Highly Controllable Fabrication of Gold Composite Nanostructures by Multiple Electroplating for High‐Performance Electrochemical and Raman Scattering Measurements

Morphology‐controlled nanostructures are important functional materials in multidisciplinary research fields, such as sensing, imaging, catalysis, and energy harvesting. However, existing nanofabrication methods have limitations in terms of controllability, diversity, cost, and efficiency. Here, a novel nanofabrication approach is proposed to construct Au nanostructures with high controllability, cost‐efficiency, and high‐performance sensing and energy harvesting. The fabrication incorporates electric field‐assisted hydrothermal growth of zinc oxide nanorods (ZnO NRs) with two‐step gold electroplating. The ZnO NRs serve as a dissolvable template during the electroplating formation of gold nanostructures for eventually synthesizing pure gold nanostructures on electrodes. The synthesized gold nanostructures take unique composite shape of nanospheres (hundreds of nanometers) covered with tinier nanostructures (tens of nanometers) like floccules, grains, lamellas, or rods, which are highly controlled by regulating electroplating parameters. The gold composite nanostructures provide high‐performance sensing and energy harvesting, such as enhanced electrochemical sensing interface (electric double‐layer impedance decrease up to 97.1%), excellent surface‐enhanced Raman scattering (SERS enhancement factor up to ), and preferable visible–near‐infrared light harvesting (absorptivity near to 90%). For the first time, the application of tumor cell photothermal therapy with nanostructured electrodes and in situ bimodal monitoring of single‐cell impedance and SERS‐based molecular expression during therapy is demonstrated.

Thermal Instability of Gold Thin Films

The disintegration of a continuous metallic thin film leads to the formation of isolated islands, which can be used for the preparation of plasmonic structures. The transformation mechanism is driven by a thermally accelerated diffusion that leads to the minimalization of surface free energy in the system. In this paper, we report the results of our study on the disintegration of gold thin film and the formation of nanoislands on silicon substrates, both pure and with native silicon dioxide film. To study the processes leading to the formation of gold nanostructures and to investigate the effect of the oxide layer on silicon diffusion, metallic film with a thickness of 3 nm was deposited by molecular beam epitaxy (MBE) technique on both pure and oxidized silicon substrates. Transformation of the thin film was observed by low-energy electron microscopy (LEEM) and a scanning electron microscope (SEM), while the nanostructures formed were observed by atomic force microscope (AFM) method. Structural investigations were performed by low-energy electron diffraction (LEED) and X-ray photoelectron spectroscopy (XPS) methods. Our experiments confirmed a strong correlation between the formation of nanoislands and the presence of native oxide on silicon substrates.

Growth Kinetics of Gold Nanoparticle Formation from Glycated Hemoglobin.

Gold nanostructures have always been a subject of interest to physicists, chemists, and material scientists. Despite the extensive research associated with gold nanoparticles, their actual formation mechanism is still debatable. The nanoscale rearrangements leading to the formation of gold nanostructures of definite size and shape are contradictory. The study presented in here details out a mechanism for gold nanoparticle formation in the presence of a biological template. The kinetics of gold nanostructure formation was studied using glycated hemoglobin as a biological template as well as the reducing agent. Particle formation was studied in a time- and temperature-dependent manner using different biophysical techniques. Here, we report for the first time spontaneous formation of gold nanoflowers which gradually dissociates to form smaller spherical particles. In addition, our experiments conclusively substantiate the existing postulations on gold nanoparticle formation from relatively larger precursor structures of gold and contradict with the popular nucleation growth mechanism.

Deposition of Gold Nanostructures into Porous SiO2∕Si Templates from the Electrolyte Based on Au(I) Sulfite Complex

Gold nanostructures were fabricated in porous SiO2/Si ion-track templates by the wet chemical deposition from a solution of Au(I) sulfite complex. Their morphological features were analyzed, and features of the deposition processes were determined. A mechanism describing the selective formation of gold nanostructures in the pores of SiO2 was proposed. The present approach allows us to control shape and size of Au nanostructures those which can be used as plasmonic active surfaces for SERS detecting of small amounts of biological and chemical substances.

Morphological Growth and Theoretical Understanding of Gold and Other Noble Metal Nanoplates.

For the last decades, the chemical reduction of Au3+ to Au0 has been widely employed to produce various gold nanostructures. In comparison with the fast reduction, the slow reduction is systematically investigated in this research to provide more insights to reveal intermediary process and further disclose the underlying mechanism for growing gold nanostructures by using a series of simple ligands with aldehyde groups as weak reducing agents. The different binding energies of ligands to Aun+ (n=3, 1 and 0) exhibit variable binding affinities in starting, intermediate, and final gold species. For example, formic acid has much stronger binding affinity to Au+ than Au3+ , and thus Au+ intermediate is able to be stabilized/captured during slow reduction of Au3+ . Upon the disproportionation of Au+ to Au0 and Au3+ , formic acid has much stronger binding affinity to the newly formed Au0 than other ligands for the controlled formation of gold nanostructures. Meanwhile, the adsorption of ligands causes substantially decreased surface energies on different gold planes. There are much higher energies on {110} planes compared to the other two {111} and {100} planes with certain ratios in these energies, leading to morphological growth of gold nanosheets. In this paper, we experimentally demonstrate anisotropic growth of gold nanosheets by using various ligands with weak reducing and appropriate coordination capabilities, and further provide insights to understand their morphological growth mechanism behind. This synthetic strategy is successfully extended to prepare silver, palladium, and platinum nanoplates.

Spontaneous formation of gold nanostructures in aqueous microdroplets

The synthesis of gold nanostructures has received widespread attention owing to many important applications. We report the accelerated synthesis of gold nanoparticles (AuNPs), as well as the reducing-agent-free and template-free synthesis of gold nanoparticles and nanowires in aerosol microdroplets. At first, the AuNP synthesis are carried out by fusing two aqueous microdroplet streams containing chloroauric acid and sodium borohydride. The AuNPs (~7 nm in diameter) are produced within 60 µs at the rate of 0.24 nm µs−1. Compared to bulk solution, microdroplets enhance the size and the growth rate of AuNPs by factors of about 2.1 and 1.2 × 105, respectively. Later, we find that gold nanoparticles and nanowires (~7 nm wide and >2000 nm long) are also formed in microdroplets in the absence of any added reducing agent, template, or externally applied charge. Thus, water microdroplets not only accelerate the synthesis of AuNPs by orders of magnitude, but they also cause spontaneous formation of gold nanostructures.

Determination of mercury (II) ions based on silver-nanoparticles-assisted growth of gold nanostructures: UV–Vis and surface enhanced Raman scattering approaches

Innovative dual detection methods for mercury(II) ions (Hg(II)) have been developed based on the formation of gold nanostructures (AuNSs) following the addition of mercury-containing solution to a mixture containing an optimized amount of Au(III), H2O2, HCl, and silver nanoparticles (AgNPs). In the absence of Hg(II), the addition of Au(III), H2O2, and HCl to the AgNP solution changes the solution's color from yellow to red, and the absorption peak shifts from 400 to 526nm, indicating the dissolution of AgNPs and the formation of gold nanoparticles (AuNPs). Because of the spontaneous redox reaction of Hg(II) toward AgNPs, the change in the amount of remaining AgNP seed facilitates the generation of irregular AuNSs, resulting in changes in absorption intensity and shifting the peak within the range from 526 to 562nm depending on the concentration of Hg(II). Under optimal conditions, the limit of detection (LOD) for Hg(II) at a signal-to-noise ratio (S/N) of 3 was 0.3μM. We further observed that AgNP-assisted catalytic formation of Au nanomaterials deposited on a surface enhanced Raman scattering active substrate significantly reduced the Raman signal of 4-mercaptobenzoic acid, dependent on the Hg(II) concentration. A linear relationship was observed in the range 0.1nM–100μM with a LOD of 0.05nM (S/N 3.0). As a simple, accurate and precise method, this SERS-based assay has demonstrated its success in determining levels of Hg(II) in real water samples.

Controlled formation of gold nanostructures on biopolymer films upon electromagnetic radiation

The localized formation of gold nanostructures with controlled size and shape on chitosan films doped with gold precursor upon electromagnetic irradiation of various types is demonstrated here. Such controlled formation is achieved by tuning the wavelength, the energy and the interaction time of the radiation with the composite films. In particular, the use of a single UV nanosecond laser pulse results in the formation of gold sub-micron platelets with specific crystal structure, while increasing the number of pulses, further precursor reduction and photofragmentation induce the formation of gold nanoparticles. Using x-ray radiation as an alternative energy source, the reduction of the gold precursor and the subsequent formation of particles follow a different pathway. Specifically, x-ray-induced photo-reduction triggers the selective formation of gold sub-micron platelets with a very well defined {111} crystal phase. In this case, the density of crystal platelets increases by increasing the irradiation time of the films, while no photofragmentation process is observed. The gold structures pre-formed by x-ray radiation can be fragmented by subsequent pulsed UV laser irradiation forming nanoparticles with much narrower size distribution compared to that obtained via exclusive UV irradiation. Thanks to the perfect coupling between the natural polymeric matrix and gold nanostructures, the bionanocomposite systems developed could find various applications in biomaterial science and in biosensors field.

Dendrimer–Dye Assemblies as Templates for the Formation of Gold Nanostructures

Dendrimer–dye assemblies are used as novel supramolecular nanoreactors for the formation of various gold nanostructures. The organic–inorganic hybrid systems are investigated with dynamic light scattering, UV–vis spectroscopy, and transmission electron microscopy (TEM) as well as cryo-TEM and high-resolution TEM (HRTEM). We show that the shape of the hybrid assemblies is determined by the choice and the ratio of the building blocks. Shape and size of the gold nanoparticles within the assemblies are controlled by the reducing agent. The accessible range of gold morphologies extends from small and spherical, over ellipsoidal, faceted, and large to highly anisotropic. The approach may open the way to new hybrid systems with applications in catalysis or in the biomedical field.

Formation of different gold nanostructures by silk nanofibrils

Metal nanostructures that have unique size- and shape-dependent electronic, optical and chemical properties gain more and more attention in modern science and technology. In this article, we show the possibility that we are able to obtain different gold nanostructures simply with the help of silk nanofibrils. We demonstrate that only by varying the pH of the reaction solution, we get gold nanoparticles, nano-icosahedrons, nanocubes, and even microplates. Particularly, we develop a practical method for the preparation of gold microplates in acid condition in the presence of silk nanofibrils, which is impossible by using other forms of silk protein. We attribute the role of silk nanofibrils in the formation of gold nanostructure to their reduction ability from several specific amino acid residues, and the suitable structural anisotropic features to sustain the crystal growth after the reduction process. Although the main purpose of this article is to demonstrate that silk nanofibrils are able to mediate the formation of different gold nanostructure, we show the potential applications of these resulting gold nanostructures, such as surface-enhanced Raman scattering (SERS) and photothermal transformation effect, as same as those produced by other methods. In conclusion, we present in this communication a facile and green synthesis route to prepare various gold nanostructures with silk nanofibrils by simply varying pH in the reaction system, which has remarkable advantages in future biomedical applications.

Formation of gold nanostructures on copier paper surface for cost effective SERS active substrate – Effect of halide additives

In this study, we report the simple fabrication of an active substrate assisted by gold nanostructures (AuNS) for application in surface-enhanced Raman scattering (SERS) using copier paper, which is a biodegradable and cost-effective material. As cellulose is the main component of paper, it can behave as a reducing agent and as a capping molecule for the synthesis of AuNS on the paper substrate. AuNS can be directly generated on the surface of the copier paper by addition of halides. The AuNS thus synthesized were characterized by ultraviolet–visible spectroscopy, SEM, XRD, and XPS. In addition, the SERS effect of the AuNS–paper substrates synthesized by using various halides was investigated by using rhodamine 6G and melamine as probe molecules.

Growth of gold nanostructures on a Si wafer by concerted mechanisms of photoreduction and galvanic displacement

The development of a facile growth method of gold nanocrystals with a controlled shape is of crucial importance to expand the potential applications of gold nanoarchitectures which have various unique and useful physicochemical properties. Here, we report the site-preferential formation of gold nanostructures with various shapes on Si substrates. When a Si wafer covered with cetyltrimethylammonium bromide (CTAB, an organic salt) is immersed in Au(OH)4− aqueous solution and immediately photoirradiated, dendritic gold nanostructures grow on the surface of the Si wafer. Interestingly, the gold nanodendrites preferentially grow on scratched portions drawn by using a pen-type diamond glass cutter on the Si wafer. The shape of gold nanocrystals depends on the structure of both quaternary alkylammonium cations and halide anions, which are components of the organic salt film, and gold nanostructures with various shapes are successfully obtained at the scratched portions. It is revealed that concerted mechanisms of photoreduction of Au3+ ions and a new type of galvanic displacement reaction between Si and Au(OH)4− cause the site-preferential growth of gold nanoarchitectures.

The Kirkendall Effect in Binary Alloys: Trapping Gold in Copper Oxide Nanoshells

In this work, we report on the Kirkendall-induced hollowing process occurring upon thermal oxidation of gold–copper (Au–Cu) alloy nanowires and nanodots. Contrary to elemental metals, the oxidation reaction results in the formation of gold nanostructures trapped inside hollow copper oxide nanoshells. We particularly focus on the thermally activated reshaping mechanism of the gold phase forming the core. Using scanning transmission electron microscopy coupled to energy dispersive X-ray spectroscopy mapping, we show that such a reshaping is a consequence to the reorganization of gold at the atomic level. The gold nanostructures forming the core were found to be strongly dependent on the chemical composition of the alloy and the oxidation temperature. By selecting the appropriate annealing conditions (i.e., duration, temperature), one can easily synthesize various heteronanostructures: wire-in-tube, yolk–shell, oxide nanotubes embedding or decorated by Au nanospheres. The advanced understanding of the Kirken...

Biogenic Preparation of Gold Nanostructures Reduced from Piper longum Leaf Broth and Their Electrochemical Studies.

Exploitation of green chemical procedures for the synthesis of metal nanoparticles by biological process has received great attention in the field of nanotechnology. To demonstrate a biogenic method that involves the reduction of aqueous gold ions by the extract of Piper longum leaves leading to the formation of different morphological gold nanoparticles (AuNPs). The formation of gold nano-structures has been characterized by UV-Vis absorption spectroscopy. The X-ray diffraction (XRD) and selected area electron diffraction (SAED) patterns indicates the AuNPs are highly crystalline nature with the face-centered cubic (111), (200), (220) and (311) facets, respectively. The AuNPs have different sizes and morphologies that are identified by TEM studies. The involvement of water soluble bio-molecules such as carboxylic acids, flavonoids, proteins and terpenoids were identified by Fourier transform infrared (FT-IR) and Raman spectrum. The responsible mechanism of improving acidic nature and the process of encapsulation of gold nanoparticles by Piper longum extract was discussed. Additionally, we have demonstrated the modified carbon paste electrode using gold nanoparticles by means of cyclic voltammetry in a solution of 1 M KCI and 1 mM [Fe(CN)6]3-/4-. The analysis of cyclic voltammetry shows electronic transmission rate between modified Au-CPE and Bare-CPE electrode increased.

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

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

Controlling Interparticle Gaps in Self-Organizing Gold Nanostructures on Templates Made by a Modified Hard Anodization Technique

In this article, we demonstrate how the formation of large-area self-organizing gold nanostructures formed on porous alumina templates can be grown with interparticle gaps that can be tuned both by appropriate choice of anodization technique and by the amount of deposited gold. The gold nanostructures reported in this work are formed by sputter-coating the porous alumina templates made with a hard anodization technique in oxalic acid, and the interparticle gap size is reproducibly controlled simply by adjusting the amount of sputter-coated gold. To make a change from mild and into hard anodization regimes in oxalic acid, several stages are used in the anodization procedure, including the use of a protective porous oxide layer initially created under mild anodization conditions. This simple stepwise anodization technique, which only uses electrolyte cooling, can facilitate burn-free anodization at even higher voltages during hard anodization processing in oxalic acid. The formation of the gold nanostructures is studied with scanning electron microscopy, and the influence of the morphology on the optical properties of the nanostructures is investigated by optical reflectance spectroscopy. Tunability of the localized surface plasmon resonances is demonstrated, and it can be optimized and exploited with a special view to surface enhanced molecular sensing techniques.

Polymer Membrane Stabilized Gold Nanostructures Modified Electrode and Its Application in Nitric Oxide Detection

Nafion polymer/gold nanostructures film that can be utilized as a proficient electrochemical sensor for nitric oxide was prepared by an electrochemical process, forming the gold nanostructures (Aunano) through infiltration into a Nafion (Nf) matrix preassembled on an electrode. The formation of gold nanostructures was monitored by the in situ spectroelectrochemical method. The in situ absorption spectra of Aunano showed systematic and uniform formation of gold nanostructures at the Nafion (Nf−Aunano)-modified electrode. The electrochemically formed Nf−Aunano was characterized by UV−visible spectroscopy, X-ray diffraction, scanning electron microscope, transmission electron microscope, and electrochemical techniques. The surface plasmon absorption spectra recorded for the wet and dry Nf−Aunano composite film showed the interaction between the gold nanostructures and the swelled polymer matrix. The longitudinal surface plasmon band and the TEM images observed for the Nf−Aunano showed the formation of nanorod-like and Y-shaped gold nanostructures in the Nafion matrix. In addition to the nanoparticles, the edge-to-edge interactions lead to the formation of 1D assembly. The electrical communication between the gold nanostructures embedded in the Nafion film improved the electrocatalytic properties of the modified electrode toward NO detection. The Nf−Aunano electrode showed excellent sensitivity for NO detection with the experimental detection limit of 1 nM. The present Nf−Aunano electrode is very simple to fabricate and is stable, sensitive, and reproducible.

Optical Enhancing Properties of Anisotropic Gold Nanoplates Prepared with Different Fractions of a Natural Humic Substance

The results of this work demonstrate the properties of suspensions of humic substances (HS) used as reducing and templating agent for the formation of gold nanostructures. It is further established that a considerable degree of control over the size and shape of the nanoparticles can be achieved by selecting the appropriate humic fraction and adjusting the pH of the working suspension. These gold nanostructures can sustain surface plasmon resonances and exhibit optical enhancing properties that make them suitable for plasmonic applications and optical enhancement such as surface-enhanced Raman scattering (SERS). The efficiency of the nanostructures as a SERS substrate is illustrated enhancing the Raman spectrum of 2-mercaptobenzothiazole (MBT), a common organic pollutant.

Core-Controlled Formation of Micellar Cubic Assemblies of Supramolecular Dendrimers: From Their Mechanism to Formation of Gold Nanostructures

We prepared gold nanostructures from a taper-shaped supramolecular material (1-COOH) containing a carboxylic acid (−COOH) core, rigid biphenylene group, and three perfluorinated (−CF3) tails. The carboxylic core of the supramolecule serves as the site for reaction with the metal ions. We show that the self-assembling behavior of the material is strongly affected by substituting the carboxylic core of the supramolecule with a Na+ ion, followed by ion transfer of AuIII and subsequent reduction of AuIII with UV irradiation. Synchrotron X-ray diffraction (XRD) results show that the structure of 1-COOH solution (THF) and [1-COO-−Na+] complex is disordered. However, the [1-COO-−AuIIICl3]- complex before UV irradiation exhibits liquid crystalline order with micellar cubic assemblies. This order and spacing are preserved during reduction of the metal salt with UV irradiation, although the intensities of the peaks increase. UV−visible spectra and transmission electron microscopy (TEM) images show the generation of the gold arrays in the presence of the supramolecular building block. Moreover, the size and shape of gold nanocrystals are controllable depending on UV irradiation time. These types of perfluorinated supramolecular templates have enhanced mesophase stability on account of the existence of strong intermolecular interactions, although many of these molecules are not traditional amphiphiles.

Pit-Templated Synthesis and Oxygen Adsorption Properties of Gold Nanostructures on Highly Oriented Pyrolytic Graphite

Etch pits on highly oriented pyrolytic graphite (HOPG) were used as templates for the formation of gold nanostructures, which were characterized using STM (scanning tunneling microscopy), AFM (atom...