Single-crystalline Gold Nanoplates Research Articles

Amyloid fibrils with charge transportation facilitating the green synthesis of single-crystalline gold nanoplates for catalytic application

Peptide assemblies as the significant units in biological system play the key role in various activities i.e., charge transportation and metal ion reduction, which is rarely clarified with detailed mechanism. Herein, we determined the band gap of hIAPP20-29 to be about 2.5 eV by theoretical simulations, and peptides could self-assemble into amyloid fibrils. Further experiments confirmed the charge transport along the surface of amyloid fibril by setting electrical device. All the electroactive features of peptides combined with its capability of binding gold precursor and transferring electron to gold precursor would facilitate the reduction of gold ions to single-crystalline gold nanoplates. The obtained gold nanoplate-fibrils (Au-fibrils) hybrids were employed as catalysts in the reduction of 4-nitrophenol with good performances. We envision that amyloid fibrils with charge transportation inspired from the bio-system could be applied to manufacture peptide-metal nanomaterials in a green and precise manner for further catalytic applications.

Unveiling an unexpected potential of beetroot waste in green synthesis of single crystalline gold nanoplates: A mechanistic study

A novel green synthetic route developed toward unveiling a mechanism of formation of single crystalline gold (Au) nanoplates, with a flat surface using an aqueous extract of red beetroot waste (BRW) i.e. peel, at room temperature, the first time. The green method monitored using UV–VIS spectrophotometry, the presence of metallic gold, its structure; orientation and the responsible biomolecules; for reduction validated using EDS, XPS, XRD and FTIR spectroscopies respectively. Based on these significant characterizations, a probable three-step mechanism proposed here for nanoplate synthesis. First, the synthesis of the nanosphere, second its transformation into icosahedrons and ultimately its fragmentation into triangular nanoplates. The green synthetic mechanism for these nanoplates is investigated, validated and evidenced by both HR-TEM and XRD studies. The selected area electron diffraction (SAED) patterns and the assessment of Moire’ fringes confirmed that the nanoplates formed in this manner found single crystalline efficiently oriented in {1 1 1} lattice plane as their basal planes.

Rapid Seedless Synthesis of Gold Nanoplates with Microscaled Edge Length in a High Yield and Their Application in SERS.

We report a facile and reproducible approach toward rapid seedless synthesis of single crystalline gold nanoplates with edge length on the order of microns. The reaction is carried out by reducing gold ions with ascorbic acid in the presence of cetyltrimethylammonium bromide (CTAB). Reaction temperature and molar ratio of CTAB/Au are critical for the formation of gold nanoplates in a high yield, which are, respectively, optimized to be 85 °C and 6. The highest yield that can be achieved is 60 % at the optimized condition. The synthesis to achieve the microscaled gold nanoplates can be finished in less than 1 h under proper reaction conditions. Therefore, the reported synthesis approach is a time- and cost-effective one. The gold nanoplates were further employed as the surface-enhanced Raman scattering substrates and investigated individually. Interestingly, only those adsorbed with gold nanoparticles exhibit pronounced Raman signals of probe molecules, where a maximum enhancement factor of 1.7 × 107 was obtained. The obtained Raman enhancement can be ascribed to the plasmon coupling between the gold nanoplate and the nanoparticle adsorbed onto it.Electronic supplementary materialThe online version of this article (doi:10.1007/s40820-016-0092-6) contains supplementary material, which is available to authorized users.

Simple and rapid green synthesis of micrometer scale single crystalline gold nanoplates using chitosan as the reducing agent

A simple, rapid and green chemical method for the synthesis of single crystalline gold nanoplates of several micrometeres in size has been demonstrated. The synthesis involved the reduction of HAuCl4 in aqueous solution using low molecular weight chitosan at boiling temperature for 25min. The [Au3+]:[chitosan] molar ratio plays an important role in the formation of gold nanoplates and found that an optimized molar ratio in the range of 80 to 125 was suitable for the formation of nanoplates. The size and morphology of the nanoplates can be tuned by adjusting the molar ratio. In this process, the chitosan functions both as a reducing as well as a stabilizing agent and no other special agents were added to induce the nanoplate formation. The obtained nanoplates were single crystals with (111) planes as the basal planes with shapes of hexagonal, triangular, or truncated triangular plates.

Facile synthesis of single crystalline gold nanoplates and SERS investigations of 4-aminothiophenol

Single crystalline gold nanoplates with micrometer-scale sizes that are tens of nanometers in thickness were synthesized by reducing HAuCl4 with the disodium salt of ethylenediaminetetraacetic acid (Na2EDTA) in the presence of hexadecyltrimethylammonium bromide (CTAB) in aqueous solution. The results indicated that CTAB plays an important role in the formation of single crystalline gold nanoplates. The application of the as-prepared nanoplates in surface-enhanced Raman spectroscopy (SERS) was investigated by using 4-aminothiophenol (PATP) as probe molecules. As a result of the sharp corners and edges in their shape, the resultant Au nanoplates exhibit excellent Raman enhancement ability. It was found that PATP can be oxidatively transformed into 4,4′-dimercaptoazobenzene on the surface of Au nanoplates during the SERS measurement.

Structural Transitions of Octanethiol Self-Assembled Monolayers on Gold Nanoplates after Mild Thermal Annealing

Single-crystalline gold nanoplates with a thick- ness of less than 100 nm were synthesized by the reduction of HAuCl4 in water with cetyltrimethylammonium chloride, and their structures were confirmed by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction measurements. The formation and surface structures of octanethiol (OT) self-assembled monolayers (SAMs) on gold nanoplates were examined by means of atomic force microscopy and scanning tunnelling microscopy (STM). Molecularly resolved STM observation showed that OT SAMs on gold nanoplates at 25 °C for 24 h were composed of two mixed phases containing well-ordered (√3 × √3)R30° and c(4 × 2) domains and disordered domains, which are comparable to the formation of fully covered (√3 × √3)R30° or c(4 × 2) structures on conventional Au(111) films. After thermal annealing of the precovered OT SAMs on gold nanoplates at 70 °C for 30 min, we clearly observed the structural transitions of OT SAMs from the two mixed phases to the ...

Synthesis of protein–gold nanoparticle hybrid and gold nanoplates in protein aggregates

A straightforward and economically viable approach was developed to biomimetic synthesis of gold nanocrystals by using casein micelles (CMs) without additional reductant. The UV–vis, TEM, SAED, FTIR, DLS and XRD techniques were employed to systematically characterize Au nanocrystals synthesized. Isotropic gold nanoparticle (GNP) and gold nanoplates in good yields (up to 90%) with different sizes can be obtained easily by adjusting the experimental condition. Spherical nanoparticles were obtained with tunable mean sizes at higher pH and casein concentrations. The high colloidal stability of the spherical GNP is attributed to the formation of CM/GNP hybrid under some experimental condition. At lower pH, reaction temperature and casein concentrations, single-crystalline gold nanoplates in good yields (up to 90%) are obtained. The growth of these nanostructures is attributed to an interplay between the faceting tendency of the protein molecules/micelles and the growth kinetics. More importantly, the morphological evolution of large gold nanoplates at different reaction times has been followed, and compared with some earlier protein systems, different formation mechanisms in casein micelles are obtained. The results demonstrate that both the property of individual protein molecules and protein aggregates play important roles in controlling the formation of gold nanocrystals by using amphiphilic protein.

Templated biomineralization of Au nanoplates under bovine serum albumin Langmuir monolayers

Au nanoplates were generated by spontaneous reduction of chloroaurate ions (AuCl 4 −) under bovine serum albumin (BSA) Langmuir monolayers at room temperature. The structure of the resulting Au particulates was analyzed by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), selected-area electron diffraction (SAED), and high resolution transmission electron microscopy (HRTEM). The results showed that BSA provided dual functions for both reducing Au 3+ ions and directing anisotropic growth of Au particles into plate-like structure as well. Amorphous Au particulates were obtained firstly in a relatively short reaction time, and then anisotropic Au nanoparticles were generated at extended reaction durations. The triangular Au nanoplates oriented along (1 1 1) basal planes were obtained via the reduction of chloroaurate ions by BSA with a relatively longer reaction duration. The present research provides a biological route to produce single-crystalline gold nanoplates with a wide variety of applications, and it also verifies that the interaction between protein/peptide and gold ions/surface may be used advantageously for green chemical synthesis of nanogold. Hopefully, this would contribute to promote genuine green biomimetic synthesis of nanomaterials with prescribed geometrical features where rationally designed multifunctional peptides are preferred.

Single-Crystalline Gold Nanoplates from a Commercial Gold Plating Solution

A novel route was proposed to synthesize gold nanoplates using a commercial gold plating solution as the reactant. Single-crystalline gold nanoplates can be successfully synthesized by reacting gold plating solution with HCl. The as-prepared nanoplates are from several micrometers to tens of micrometers in size. The effects of reactant concentration and temperature on the morphology of the gold products were investigated. The size of the gold nanoplate increases with the decrease of the amount of gold plating solution, while irregular gold nanoparticles are formed as the HCl concentration becomes low. When the reaction temperature is as low as room temperature, nanoplates with a concavity form. Specifically, it is found that the Cl- plays an important role for the formation of these gold nanoplates. The formation mechanism of the gold nanoplates is studied in detail.

Block Copolymer-Mediated Synthesis of Size-Tunable Gold Nanospheres and Nanoplates

We have successfully controlled the size and shape of isotropic and anisotropic gold nanocrystals through a one-step reaction by using amphiphilic polyethylene oxide-polystyrene oxide block copolymers as both reductant and stabilizing agents in water solution. Spherical or quasispherical nanoparticles were obtained at room temperature with tunable mean sizes and polydispersities depending on reaction conditions, that is, on copolymer block length, and copolymer and gold salt concentrations. By moderate increases of reaction temperature up to 65 degrees C, progressive formation of single-crystalline gold nanoplates in good yields takes place (up to 70%) without the necessity of additional reactants or growing solutions. These nanoplates are characterized by lateral mean sizes between 0.1-1.2 microm depending on copolymer concentration and reaction temperature, with mainly truncated or rounded triangular shapes with {111} planes as two basal surfaces. This allows us to tune the surface plasmon band of the nanoplates from ca. 850 nm to more than 1100 nm, well inside the near-infrared region (NIR), which enables the use of these type of nanostructures as a very promsing materials in applications such as optical coatings, SERS, and cancer cell hyperthermia. We proposed that the growth of these nanostructures can stem from a decrease in the reaction rate as temperature increases due to an enhanced copolymer hydrophobicity, which gives rise to a structure of interacting micelles formed from the fluid via a percolation transition (known as "soft gel") at elevated temperatures. In this way, reduction becomes slow enough to allow kinetic control of the reaction, and preferential adsorption of the copolymer molecules/micelles on certain crystallographic planes can favor the growth of certain nanocrystal facets to give the final structure. This alternative water-based system provides a more convenient and environmentally benign route to the synthesis of shape-controlled noble-metal nanocrystals in high yield because it does not involve toxic organic solvents or reagents and serves as a bridge between two frontline discipline: the block copolymeric science and anisotropic nanoparticles.

Synthesis of gold nanoplates in lamellar liquid crystal

Single-crystalline gold nanoplates have been synthesized in a lamellar lyotropic liquid crystal (LLC) composed of a nonionic surfactant, C 12E 4 (tetraethylene glycol monododecyl ether) and the chloroauric acid (HAuCl 4) solution. The sizes of gold nanoplates can be varied from several hundreds of nanometers to a few microns in width by changing reaction conditions. The factors which influence the product morphology, like LLC composition, capping agent and reaction temperature are studied by small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The mechanism analysis indicates that the LLC plays an important role for the consequent growth of single-crystal anisotropic plates by providing an ordered reaction medium and a limited growth space.

Synthesis of Single-Crystalline Gold Nanoplates in Aqueous Solutions through Biomineralization by Serum Albumin Protein

In this work, single-crystalline gold nanoplates were produced by reacting an aqueous solution of chloroauric acid with one serum albumin protein (BSA) at the physiological temperature, where BSA provided the dual function of Au(III) reduction and directing the anisotropic growth of Au(0) into plate-like structures. Structural characterizations by FESEM, TEM, HRTEM, and SAED showed that the nanoplates were oriented with {111} planes as their basal planes. The effects of environmental factors such as temperature and pH were investigated, which showed low temperature and acidic pH favoring the anisotropic growth of gold nanoparticles. More interestingly, the kinetics of chloroauric acid reduction in BSA solutions could be manipulated through the addition of a trace amount of Ag+ ions, and plates with lateral size ranging from a few micrometers to tens of nanometers could be produced. The growth of gold nanoplates in BSA solution with time was monitored by electron microscopy, allowing the detection of sever...

Identification of Active Biomolecules in the High‐Yield Synthesis of Single‐Crystalline Gold Nanoplates in Algal Solutions

In this work, single-crystalline gold nanoplates were produced by treating an aqueous solution of chloroauric acid with the extract of the unicellular green alga Chlorella vulgaris at room temperature. The results suggest proteins as the primary biomolecules involved in providing the dual function of Au(III) reduction and the size- and shape-controlled synthesis of the nanogold crystals. A protein with a molecular weight of approximately 28 kDa was isolated and purified by reversed-phase HPLC; this protein tested positive for the reduction of chloroauric acid in aqueous solution. The isolated protein (named gold shape-directing protein, or GSP for convenience) was then used to produce gold nanoplates with distinctive triangular and hexagonal shapes in high yields (approximately 90 %). The kinetics of the reduction reaction could be manipulated through changes in the GSP concentration to produce plates with lateral sizes ranging from nanometers to micrometers. The growth of gold nanoplates in the GSP solution with time was monitored by microscopic and spectroscopic techniques, thereby allowing the detection of several key intermediates in the growth process.

Large-scale preparation of single-crystalline gold nanoplates

A thermal process has been demonstrated for the large-scale preparation of single-crystalline gold nanoplates with several micrometers in size, carried out by heating a salicylic acid–HAuCl 4 aqueous solution at 100 °C in the presence of poly(diallyldimethylammonium chloride) (PDDA). It is found that such nanoplates are single-crystalline gold with a preferential growth direction along the {111} plane and PDDA is crucial to the formation of such nanoplates. The possible formation mechanism of gold nanoplate is also discussed.

Controlled formation of gold nanoplates and nanobelts in lyotropic liquid crystal phases with imidazolium cations

Single-crystalline gold nanoplates and also nanobelts, with {1 1 1} crystallographic facets and size length longer than 20 μm, are synthesized in large scale by reduction of HAuCl 4 in lyotropic liquid crystal phases. Such flat products can be obtained from different systems including hexagonal or lamellar phases made of P123 (EO 20PO 70EO 20) where different ionic liquid like additives play the crucial roles in the product formation. The results demonstrate that the product sizes and morphologies strongly depend on the balance among forces between different components and the adsorption of imidazolium cations on gold through controlling the reduction rates by their molar ratios.

Synthesis of microsized gold nanoplates by a self-seeding method in ethanol solution

Single-crystalline gold nanoplates with microsized edges have been synthesized by a simple self-seeding method with the assistance of aniline in an ethanol solution. The as-synthesized gold nanoplates showed strong absorption in near infrared region (NIR). Investigation suggests the amount of aniline added to the reaction solution plays a key role in the generation of nanoplates. A possible formation mechanism for these gold nanoplates is also proposed.

Optimization of High‐Yield Biological Synthesis of Single‐Crystalline Gold Nanoplates.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Size-Controlled Synthesis of Machinable Single Crystalline Gold Nanoplates

Monodispersive size-controlled gold nanoplates were synthesized with high purity from the reduction of hydrogen tetrachloroaurate by reduced amount of sodium citrate, which kinetically controls the reaction pathway, in the presence of poly(vinyl pyrrolidone) (PVP). With the insufficient addition of the reductant, the molar ratio of sodium citrate and PVP relative to hydrogen tetrachloroaurate played an important role in determining the geometric shape and size of the product. These nanoplates were single crystals with planar width of 80−500 nm and thickness of 10−40 nm, exhibiting strong surface plasmon absorption in the near-infrared (NIR) region of 700−2000 nm. The gold nanoplates were used as the synthetically provided nanoblocks to fabricate single-crystalline nanocomponents, such as a nanoscaled gear or a nanoscaled letter.

Optimization of High-Yield Biological Synthesis of Single-Crystalline Gold Nanoplates

In this work, single-crystalline gold nanoplates were obtained by reducing aqueous chloroauric acid solution with the extract of Sargassum sp. (brown seaweed) at room temperature. The gold nanoplates so obtained were characterized by UV-vis spectroscopy, X-ray diffraction, atomic force microscopy, and transmission electron microscopy. The formation of gold nanoplates was found to depend on a number of environmental factors, such as the time taken to age the seaweed extract, pH of the reaction medium, reaction temperature, reaction time, and initial reactant concentrations. The size of the gold nanoplates could be controlled to between 200 and 800 nm by manipulating the initial reactant concentrations. The yield of the flat gold nanocrystals relative to the total number of nanoparticles formed was as high as approximately 80-90%.

High-Yield Synthesis of Large Single-Crystalline Gold Nanoplates through a Polyamine Process

A polyamine process has been demonstrated for the high-yield preparation of single-crystalline gold nanoplates with several 10 microm in size, carried out by heating a concentrated aqueous solution of linear polyethylenimine and HAuCl4 at 100 degrees C. It suggests that the concentration of reactants is crucial to the formation of nanoplates.