Triangular Au Nanoplates Research Articles

Plasmonic gold nanoplates-decorated ZnO branched nanorods@TiO2 nanorods heterostructure photoanode for efficient photoelectrochemical water splitting

Transition metal-oxide semiconductors have shown great potential in the renewable energy harvesting and conversion, e.g., photoelectrochemical (PEC) water splitting. However, the existing disadvantages of semiconductors, such as insufficient solar light utilization and fast charge recombination, are urgently needed to be addressed to realize an efficient PEC device. In this work, we synthesized a well-defined ZnO branched nanorods (b-NRs) attached to TiO2 nanorod (NR) arrays on FTO substrate using atomic layer deposition (ALD) and hydrothermal method. Meanwhile, Au triangular nanoplates (TNPs) were also incorporated with ZnO@TiO2 heterostructure by immersing the structure in Au TNPs solution. The ZnO b-NRs@TiO2 NRs and Au TNPs@ZnO b-NRs@TiO2 NRs exhibited the photocurrent densities of 0.490 mA/cm2 and 0.733 mA/cm2 at 1.23 V vs. reversible hydrogen electrode which were 2.8 and 4.2 times of pure TiO2 NR arrays (0.176 mA/cm2), respectively. Incident photon-to-current conversion efficiency measurements showed enhanced photoactivity after Au TNPs decoration. Moreover, the electrochemical impedance spectroscopy and Mott-Schottky analysis provided further evidence that the separation of photogenerated carriers and the transfer kinetics of charge carriers at the semiconductor/electrolyte interface were greatly improved by the ZnO b-NRs modification and Au TNPs decoration. It was concluded that the significantly enhanced PEC water splitting performance was attributed to the synergistic effect of the three-dimensional ZnO@TiO2 composites heterostructure and the localized surface plasmon resonance resulting from Au TNPs. This study reported a facile combination of ALD and hydrothermal method for fabricating ZnO branched heterostructure and decorating Au TNPs to improve the PEC water splitting performance of TiO2.

Site-Selective Chiral Growth of Anisotropic Au Triangular Nanoplates for Tuning the Optical Chirality.

Site-selective chiral growth of anisotropic nanoparticles is of great importance to realize the plasmonic nanostructures with delicate geometry and desired optical chirality; however, it remains largely unexplored. This work demonstrates a controlled site-selective chiral growth system based on the seed-mediated growth of anisotropic Au triangular nanoplates. The site-selective chiral growth involves two distinct underlying pathways, faceted growth and island growth, which are interswitchable upon maneuvering the interplay of chiral molecules, surfactants, and reducing agents. The pathway switch governs the geometric and chirality evolution of Au triangular nanoplates, giving rise to tailorable circular dichroism spectra. The ability to tune the optical chirality in a controlled manner by manipulating the site-selective chiral growth pathway opens up a promising strategy for exploiting chiral metamaterials with increasing architectural complexity in chiroptical applications.

Visualizing the Spatial Heterogeneity of Electron Transfer on a Metallic Nanoplate Prism.

The involvement between electron transfer (ET) and catalytic reaction at the electrocatalyst surface makes the electrochemical process challenging to understand and control. Even ET process, a primary step, is still ambiguous because it is unclear how the ET process is related to the nanostructured electrocatalyst. Herein, locally enhanced ET current dominated by mass transport effect at corner and edge sites bounded by {111} facets on single Au triangular nanoplates was clearly imaged. After decoupling mass transport effect, the ET rate constant of corner sites was measured to be about 2-fold that of basal {111} plane. Further, we demonstrated that spatial heterogeneity of local inner potential differences of Au nanoplates/solution interfaces plays a key role in the ET process, supported by the linear correlation between the logarithm of rate constants and the potential differences of different sites. These results provide direct images for heterogeneous ET, which helps to understand and control the nanoscopic electrochemical process and electrode design.

Synthesis of near-infrared absorbing triangular Au nanoplates using biomineralisation peptides

Triangular Au nanoplates (TrAuNPls) possessing strong plasmonic properties can be used as photothermal agents in cancer therapy. However, the controlled preparation of such morphologies typically requires harsh synthetic conditions. Biomolecules offer an alternative route to developing biocompatible synthetic protocols. In particular, peptides offer a novel route for inorganic synthesis under ambient conditions. Herein, using the previously isolated peptide, ASHQWAWKWE, for Au nanoparticle (AuNP) synthesis, the conditions for preparing TrAuNPls via a one-pot synthetic process of mixing HAuCl4 and peptides at room temperature were investigated to effectively obtain particles possessing near-infrared absorbance for non-invasive optical diagnosis and phototherapy. By adjusting the peptide concentration, the size and property of TrAuNPls were controlled under neutral pH conditions. The synthesised particles showed potential as photothermal therapeutic agents in vitro. In addition, peptide characterisation using B3 derivatives revealed the importance of the third amino acid histidine in morphological regulation and potential circular Au nanoplates (AuNPl) synthesis with ASEQWAWKWE and ASAQWAWKWE peptides. These findings provide not only an easy and green synthetic method for TrAuNPls and circular AuNPls, but also some insight to help elucidate the regulation of peptide-based nanoparticle synthesis for use in cancer therapy. Statement of significanceBiological molecules have received increasing attention as a vehicle to synthesise inorganic materials with specific properties under ambient conditions; particularly, short peptides have the potential to control the synthesis of nanoscale materials with tailored functions. Here, the application of a previously isolated peptide was assessed in synthesising Au nanoparticles containing decahedral and triangular nanoplates with near-infrared absorbance. The size and absorbance peaks of the triangular nanoplates observed were peptide concentration-dependent. In addition, these fine-tuned triangular nanoplates exhibited potential as a phototherapeutic agent. Moreover, the peptide derivatives indicated the possibility of synthesising circular nanoplates. These findings may offer insight into development of new techniques for synthesising functional nanoparticles having biological applications using non-toxic molecules under mild conditions stituted in the original B3 peptide is underlined.

Symmetric and asymmetric epitaxial growth of metals (Ag, Pd, and Pt) onto Au nanotriangles: effects of reductants and plasmonic properties.

The surface plasmon resonance of noble metals can be tuned by morphology and composition, offering interesting opportunities for applications in biomedicine, optoelectronics, photocatalysis, photovoltaics, and sensing. Here, we present the results of the symmetrical and asymmetrical overgrowth of metals (Ag, Pd, and Pt) onto triangular Au nanoplates using l-ascorbic acid (AA) and/or salicylic acid (SA) as reductants. By varying the reaction conditions, various types of Au nanotriangle-metal (Au NT-M) hetero-nanostructures were easily prepared. The plasmonic properties of as-synthesized nanoparticles were investigated by a combination of optical absorbance measurements and Finite-Difference Time-Domain (FDTD) simulations. We show that specific use of these reductants enables controlled growth of different metals on Au NTs, yielding different morphologies and allowing manipulation and tuning of the plasmonic properties of bimetallic Au NT-M (Ag, Pd, and Pt) structures.

Spectral dependence of third-order susceptibility of Au triangular nanoplates

We experimentally investigated the spectral dependence of the third-order susceptibility chi^{left( 3 right)} of Au triangular nanoplates in a broad wavelength region (400–1,000 nm). Complex shaped plasmonic nanoparticles provide a promising route to achieve control of their optical properties at the nanoscale. However, little is known about the effects of geometrical parameters to the optical nonlinearities and underlying mechanisms of the plasmon modes. Here, we obtained the chi^{left( 3 right)} of Au triangular nanoplates featuring a narrow plasmon resonance that is tunable in the visible and near-IR regions. This work demonstrates that the plasmonic triangular nanoplates simultaneously shows self-focusing and -defocusing, and saturable and reverse-saturable absorption properties at specific wavelength regions. Maximum amplitudes of real and imaginary components are − 6.8 × 10−18 m2/V2 at 668 nm and − 6.7 × 10−18 m2/V2 at 646 nm, respectively. Spectral dependence of the quantity chi^{left( 3 right)} enables comparison between different shaped plasmonic NPs to boost active plasmonic applications performance.

In Vivo Quantitative Photoacoustic Diagnosis of Gastric and Intestinal Dysfunctions with a Broad pH-Responsive Sensor

Gastrointestinal diseases affect many people in the world and significantly impair life quality and burden the healthcare system. The functional parameters of the gastrointestinal tract such as motility and pH can effectively reflect the changes of gastrointestinal activity in physiological and pathological conditions. Thus, a noninvasive method for real-time and quantitative measurement of gastrointestinal functional parameters in vivo is highly desired. At present, there are many strategies widely used for the diagnosis of gastrointestinal diseases in clinic, including X-ray barium meal examination, ultrasound imaging, radionuclide examination, endoscopy, etc. However, these methods are limited in determining the gastrointestinal status and cannot provide comprehensive quantitative information. Photoacoustic imaging (PAI) is a rapid noninvasive real-time imaging technique in which multiple types of functional and quantitative information can be simultaneously obtained. Unfortunately, very few ratiometric PAI contrast agents have been reported for quantification of gastrointestinal functional parameters in vivo. In this work, a broad, pH-responsive ratiometric sensor based on polyaniline and Au triangular nanoplates was developed. Utilizing the sensor as a contrast agent, PAI served as an all-in-one technique, accurately measuring the gastrointestinal functional parameters in a single test. Notably, this sensor was examined to be ultrasensitive with pH responses as fast as 0.6 s and durability as long as 24 h, and was repeatable and reversible for longitudinal monitoring. The quantitative results demonstrated a significant disorder in motility and decrease in pH for gastric and duodenal ulcers. Collectively, the combination of PAI and this broad pH-responsive sensor might be a promising candidate for quantitative diagnosis of gastrointestinal diseases.

Sensitive and Highly Selective Biosensor Based on Triangular Au Nanoplates for Detection of Uric Acid in Human Serum

Herein a uric acid (UA) biosensor based on triangular Au nanoplates–uricase was presented. In the presence of uricase and oxygen, UA was oxidized to produce H2O2. H2O2 etched the active “tips” area of the triangular Au nanoplates, eventually, it results in great increase in ultraviolet absorbance strength of triangular Au nanoplates. Under the optimized conditions, a linear relationship between the absorbance of triangular Au nanoplates and UA concentration ranged from 0.0027 to 0.5333 μM (R2 = 0.9959) with the detection limit of UA for 0.0013 μM (S/N = 3). Some of the interfering substances (e.g., histidine, glycine, valine and tryptophan) in human serum have no effect on the experiment. Serum samples could be detected directly with the sensing system and the obtained results are in agreement with the biochemistry analyzer test results with the average relative error for 3.9%. These results suggest that the proposed UA sensor has great potential in applications for clinical diagnosis.

Au@AuAg yolk-shell triangular nanoplates with controlled interior gap for the improved surface-enhanced Raman scattering of rhodamine 6G

In this work, a combined seed mediated and galvanic replacement strategy has been proposed to design and fabricate two unique nanostructures, including Au@AuAg yolk-shell nanostructures with tunable interior gap and Au multi-spiky nanostructures with tunable spike length. The interior gap of the Au@AuAg yolk-shell nanostructures can be controlled by varying either the amount of AgNO3 in the first step or the amount of HAuCl4 in the second step. The SERS activity of Au@AuAg yolk-shell nanostructures was found to increase with increase in the interior gap. Owing to the build-in electromagnetic hot spots induced by plasmonic coupling effect of the Au triangular nanoplate core and AuAg shell especially the intensive coupling between the three sharp tips of the core and the concave of the inner wall of the shell, Au@AuAg yolk-shell nanostructures exhibit significantly higher SERS enhancement compared to their original Au triangular nanoplates. The best enhancement has been achieved when the interior gap of Au@AuAg yolk-shell nanostructures is 10 nm with the enhancement factor of 3.2 × 106 for rhodamine 6G, making them promising candidates for SERS-based detection.

Ag-Hybridized plasmonic Au-triangular nanoplates: highly sensitive photoacoustic/Raman evaluation and improved antibacterial/photothermal combination therapy.

Core-shell metal nanostructures with versatile functions have attracted extensive attention and are highly desirable for imaging and therapeutic purposes. Among them, gold and silver nanomaterials are widely explored for biological applications due to their unique properties. Despite a wide range of applications, limited enhancement ability and insufficient photothermal performance have hampered their further development. In this work, a novel multifunctional nanoprobe, a Au@Ag nanoplate (NP), is fabricated with a biocompatible surface in the aqueous phase. The as-obtained nanocomposite possesses a unique core-shell triangular configuration, sharp apexes, and a large specific surface area, exhibiting strong absorption at 780 nm. PEG-Au@Ag NPs depict highly sensitive photoacoustic imaging (PAI) capacity and extraordinary photothermal conversion efficiency (η = 73%) under 808 nm laser irradiation. Raman signals are multiplied benefitting from the enhanced surface plasma resonance contributed by the silver layer and sharp spears. PAI provides deeper pathological information while Raman detection presents superficial optical properties. Their union forms comprehensive scale coverage for disease imaging and localization. Outstanding photothermal therapy and antibacterial efficacy are observed on animal disease models. This novel multifunctional nanocomposite not only holds great potential as an excellent contrast agent for the combination of PAI and Raman evaluation, but also allows tumor and infection therapy as well as the corresponding therapeutic monitoring.

Green Synthesis of Triangular Au Nanoplates: Role of Small Molecules Present in Bael Gum

The green and selective synthesis of triangular nanoplates (NPs) is shown to arise out of the slow rate of reduction and generation of Au(0) from HAuCl4. Toward this purpose, the small molecules present along with the polysaccharide in bael gum (BG) are separated; their structures are identified, and their role in the reduction of HAuCl4 in aqueous solution as well as their possible role in shape direction are studied. The observations suggest that in all the cases studied the slow rate of reduction could be the primary reason for shape selectivity toward formation of NPs, and the role of small molecules is possibly limited to that of a reducing agent. This was further confirmed by carrying out the reduction reaction in some detail by using imperatorin oxide (one of the molecules isolated from BG) at different concentrations. At higher concentrations of imperatorin oxide, the formation of pseudospherical and rodlike particles (instead of smaller NPs) in solution further confirmed the hypothesis. The forma...

A Novel Photochemical Method for the Synthesis of Au Triangular Nanoplates inside Nanocavity of Mesoporous Silica Shells

We report a new photochemical method for tuning the shapes of gold nanoparticles inside nanocavity of mesoporous silica shells (mHSS) using Ag+ ions without using any convential organic capping ligands. mHSS acts as a nanocontainer and is used for entrapping the chloroauric acid molecules along with Ag+ ions. The shape of gold nanoparticles is tuned from spheres to triangular nanoplates inside mHSS by varying the molar ratio of [AuCl4–]/[Ag+] in the reaction. The results confirm that the presence of Ag+ ions promotes the growth of Au triangular nanoplates inside mHSS. The Au triangular nanoplates demonstrate superior catalytic activity than spherical Au nanoparticles.

Green, Selective, Seedless and One-Pot Synthesis of Triangular Au Nanoplates of Controlled Size Using Bael Gum and Mechanistic Study

A seedless, one pot, green and selective synthesis of triangular gold nanoplates (NPs) by the reduction of chloroauric acid using Aegle marmelos gum (bael fruit derived gum; BG), with control over size is reported. The size of the NPs is found to be dependent critically on the concentration of the BG with triangular, triangular with truncation at the apex and hexagonal plates being the predominant shapes over a wide concentration range, at room temperature. At very high concentration of BG and at room temperature, the shape of the particles is spherical. A fine-tuning of the temperature, at a particular concentration of BG, results in the formation of perfect triangular NPs. Increasing the temperature of reduction to 90 °C and especially above a particular BG concentration, Au nanoparticles that are elongated spheres are obtained as the major product. The possible mechanism for the Au NPs formation is investigated using techniques such as HR-TEM, SEM, XRD and UV–visible spectroscopy. The formation of sing...

Close-packed assemblies of discrete tiny silver nanoparticles on triangular gold nanoplates as a high performance SERS probe

An island like array of tiny Ag nanoparticles bounded on triangular Au nanoplates was synthesized as surface-enhanced Raman spectroscopy substrate.

High-yield seedless synthesis of triangular gold nanoplates through oxidative etching.

We demonstrate that monodispersed triangular gold nanoplates with high morphological yield (>90%) can be synthesized through a rapid one-pot seedless growth process. The edge length of triangular Au nanoplates can be readily tuned between 40 and 120 nm by varying the reaction parameters. Systematic studies reveal that distinct from previous hypothesis that the formation of nanoplates is mainly determined by the selective binding of iodide ions, our results show that iodide ions could have dual functions: it can selectively bind to the Au {111} facets and also selectively remove other less stable shape impurities through oxidative etching by forming tri-iodide ions (I(3)(-)), thus facilitating the formation of nuclei with dominant planar structure. This new synthetic route will not only help to better understand the growth mechanism of triangular gold nanoplates but also promote the research in anisotropic noble metal nanostructures.

Highly stable Ag–Au nanoplates and nanoframes for two-photon luminescence

Highly stable Ag–Au triangular nanoplates and nanoframes were fabricated through well controlled galvanic reaction, which showed tunable localized surface plasmon resonance (LSPR) and efficient two-photon luminescence with the guarantee of high stability under both strong near infrared laser and tough ion-contained environments. The two-photon absorption cross section (6.34 × 104 GM) could reach double that of Au nanorods. As revealed by excitation wavelength dependent TPL spectra and the simulation of the localized electric field of the nanostructures, the TPL performance of the Ag–Au TNFs was possibly mainly determined by the matched LSPR absorbance and the Ag–Au alloys composition. The high stability and the strong TPL make the Ag–Au TNFs promising candidates for various nonlinear optical applications and further the understanding of the two-photon behavior of noble metals.

A novel high efficiency composite catalyst: single crystal triangular Au nanoplates supported by functional reduced graphene oxide.

To improve the utilization efficiency of Au catalyst, triangular Au nanoplates on functional reduced graphene oxide were prepared by a facile method. The products with ultra-low trace amounts of Au afforded high catalytic efficiency for the reduction of 4-nitro phenol. The morphology of the products was controlled by tuning the addition of HAuCl4.

High-yield synthesis of triangular gold nanoplates with improved shape uniformity, tunable edge length and thickness.

We report the synthesis of uniform triangular gold nanoplates by a modified seeded growth method. The concentration of cetyltrimethylammonium bromide (CTAB) in the growth solution and the time interval between multiple steps of growth were important factors which determined the formation of uniform triangular Au nanoplates. In addition, by further isotropic overgrowth, the thickness of triangular Au nanoplates can be finely tuned within a wide range of 10-80 nm, which at present remains a challenge using conventional seeded growth.

Single-Molecule Catalysis Mapping Quantifies Site-Specific Activity and Uncovers Radial Activity Gradient on Single 2D Nanocrystals

Shape-controlled metal nanocrystals are a new generation of nanoscale catalysts. Depending on their shapes, these nanocrystals exhibit various surface facets, and the assignments of their surface facets have routinely been used to rationalize or predict their catalytic activity in a variety of chemical transformations. Recently we discovered that for 1-dimensional (1D) nanocrystals (Au nanorods), the catalytic activity is not constant along the same side facets of single nanorods but rather differs significantly and further shows a gradient along its length, which we attributed to an underlying gradient of surface defect density resulting from their linear decay in growth rate during synthesis (Nat. Nanotechnol.2012, 7, 237-241). Here we report that this behavior also extends to 2D nanocrystals, even for a different catalytic reaction. By using super-resolution fluorescence microscopy to map out the locations of catalytic events within individual triangular and hexagonal Au nanoplates in correlation with scanning electron microscopy, we find that the catalytic activity within the flat {111} surface facet of a Au nanoplate exhibits a 2D radial gradient from the center toward the edges. We propose that this activity gradient results from a growth-dependent surface defect distribution. We also quantify the site-specific activity at different regions within a nanoplate: The corner regions have the highest activity, followed by the edge regions and then the flat surface facets. These discoveries highlight the spatial complexity of catalytic activity at the nanoscale as well as the interplay amid nanocrystal growth, morphology, and surface defects in determining nanocatalyst properties.

Shape-controlled synthesis of Pt nanoframes

Plate-like Pt nanoframes were synthesized using Au nanoplates as a template, followed by formation of a Ag layer coating on the Au template, and selective chemical etching of Au and Ag leaving the Pt structure intact. Circular, triangular, and hexagonal Au nanoplates successfully served as templates for fabrication of various Pt nanoframe shapes, which resembled the original Au nanoplate shape. A thin Ag layer was found to play a critical role as an electron-transfer mediator in the galvanic replacement reaction between the thin Ag layer on Au nanoplates and Pt precursors. During the replacement reaction, the Pt layer grew faster at the {112} edges than at the {111} terraces of Au nanoplates. The thicker periphery of the nanoplates survived the chemical etching step, while the thinner center was etched, leading to formation of Pt nanoframes in high yield and good homogeneity.