Au Nanoplates Research Articles

Photocatalytic Synthesis of Au Nanoplates

Photocatalytic Synthesis of Au Nanoplates

Boring holes in Au nanoplates by active surface etching

Boring holes in Au nanoplates by active surface etching

Seedless synthesis of Au nanoplates with tunable plasmonic peaks

Au nanoplates with tunable in-plane dipolar localized surface plasmon resonance peaks in a broad range from the visible to near-infrared region were obtained in high yield using a seedless wet chemical growth method after purification. Cetyltrimethylammonium chloride was used as a surfactant, while hydrogen peroxide and sodium borohydride were used as the weak and strong reducing agents, respectively. The edge length and in-plane dipolar localized surface plasmon resonance peak of the Au nanoplates could be adjusted by varying the amounts of hydrogen peroxide and sodium borohydride. The Au nanoplates were further used as the saturable absorber to generate pulsed laser output in a passively Q-switched solid-state laser at approximately 2 µm. Our study offers a new method for obtaining Au nanoplates with tunable plasmonic peaks over a broad range.

A simple approach for effectively improving the resolution of scanning electrochemical cell microscopy

The high-resolution scanning electrochemical cell microscopy (SECCM) is a powerful tool that can directly explore the structure-property correlation of materials at nanometer scale. However, so far, the attainable maximum resolution is still restricted by the diameter of the droplet probe. Here, we report a simple and effective approach that can highly reduce the effective size of a nanopipette probe in SECCM. The effective working size was reduced to tens of nanometers by using the conventional droplet probe with an opening size of ∼129 nm through one-step oil coating. Furthermore, both the topographical and electrochemical activity of the Au nanoplate were simultaneously recorded successfully at the pixel size of sub-10 nm in the x-axis direction, meaning the potential to achieve a sub-10 nm resolution. Finally, the modified probe displays excellent applicability with acidic, neutral and alkaline electrolytes. The method retains the advantages of the droplet probe and breaks the limitation of its opening size on the SECCM imaging resolution, opening a broad avenue for both further rapid commercialization and broad applications of SECCM.

Corrigendum: Correction to “Hybrid Integration of Au Nanoplates and Ag Nanoparticles with Controlled Nanogaps via Cu2O‐mediated Galvanic Replacement Reaction: Plasmonic Catalysis and Photothermal Conversion”

Corrigendum: Correction to “Hybrid Integration of Au Nanoplates and Ag Nanoparticles with Controlled Nanogaps via Cu2O‐mediated Galvanic Replacement Reaction: Plasmonic Catalysis and Photothermal Conversion”

(Invited) To Prepare 2D Au Nanoplates and Its Controlled Molecular Self-Assembly (MS) Mechanism

It is very important to prepare 2D noble-metal nanomaterials, but very little is known about their chemical synthesis at molecular level. In this paper, we found the classic citric (CA) reduction method can prepare 2D Au nanoplates with a large range for 2D size (3-150nm). Furthermore, these 2D Au nanoplates exhibit thin thickness (8-20nm), along with two kinds of single crystal structure as 2D Au (110) –dominated and Au (111) –dominated nanoplates. To explore their preparation, we adjusted the CA reduction kinetic as CA additive→ acetone dicarboxylic acid (DCA) →acetone, revealing the intermediate species of DCA is crucial for nanoplate formation. Our DFT (Density-Functional-Theory) model further clarifies that the DCA has molecular interaction, preferentially transferring 2D clusters (Au3-Au7) towards Au(111) facets though accompanying with some Au (100) facets. These soft-hard interaction help us establish two kinds of controlled MS mechanisms towards (111) –dominated nanoplates and Au (110) –dominated nanoplates, revealing the cluster origination and its essential 2D growth process in nucleation-growth process. Consequently, our preparation for 2D Au nanoplates and controlled MS mechanisms open a gate towards nucleation-growth process, thus having great significance and broad impact for future studies.

Vibrational Anharmonicity and Energy Relaxation in Nanoscale Acoustic Resonators.

The fundamental and n = 3 overtones of Au nanoplate thickness vibrations have been studied by transient absorption microscopy. The frequencies of the n = 3 overtone are less than 3× the frequency of the fundamental. This anharmonicity is explained through a continuum mechanics model that includes organic layers on top of the nanoplate and between the nanoplate and the glass substrate. In this model, anharmonicity arises from coupling between the vibrations of the nanoplate and the organic layers, which creates avoided crossings that reduce the overtone frequencies compared to the fundamental. Comparison of the experimental and calculated quality factors shows that coupling occurs to the top organic layer. Good agreement between the measured and calculated quality factors is obtained by introducing internal damping for the nanoplate. These results show that engineering layers of soft material around metal nanostructures can be used to control the vibrational lifetimes.

Hybrid Integration of Au Nanoplates and Ag Nanoparticles with Controlled Nanogaps via Cu2O‐mediated Galvanic Replacement Reaction: Plasmonic Catalysis and Photothermal Conversion

AbstractRational assembling of different noble metal nanocrystals with controlled nanogaps in one entity allows the efficient coupling of electromagnetic fields of each component and versatile manipulation over the overall physiochemical properties. In the present study, we report a stepwise synthetic strategy to hybridlike assemble Au nanoplate and Ag nanoparticles without direct physical contact. Particularly, the success of current work relies on the conformal coating of Cu2O over the Au nanoplate as an intermediate layer, followed by the in situ formation of Ag nanoparticles via the galvanic replacement reaction between Cu2O and Ag+. With the anchoring of Ag nanoparticles over the Cu2O‐wrapped Au nanoplate, the resulting hybrid nanostructures exhibit noticeable multiple plasmonic absorptions across the UV‐vis‐NIR region. The potential use as the plasmonic catalyst for current Au@Cu2O‐Ag hybrid products is validated using reduction of 4‐nitrophenol as the model reaction, where the catalytic performance is greatly improved by the UV‐vis light irradiation. They also exhibit satisfactory photothermal conversion performance under the irradiation of Xe lamp. The current work provides a niche strategy to create noble‐metal hybrid nanostructures with controlled interparticle distance and tunable plasmonic properties, could be extended to other noble metal or alloys.

Fabrication of flexible electrospinning nano-fiber membrane for detection of respiratory tract transmission virus based on SERS

The application of flexible sensors in the biomedical field is deepening. It is of great significance to develop flexible wearable sensors which are more in line with the needs of the public. A flexible polylactic acid membrane fabric was prepared by electrospinning method. The membrane was used as SERS active substrate by screen printing capture probe which combine Au nanoplates with antibodies to the target substance. Thioglycolic acid-labeled silver nanoparticles coupled with antibodies as SERS nanotags. The target substance can be fixed between the capture probe and SERS nanotags. Due to the high specific surface area between the spinning, the adhesion rate of the capture probe is higher than that of the rigid substrate, and the enrichment and hypersensitivity detection of the object to be tested could be realized. The membranes prepared are flexible, wearable, portable, highly biocompatible, and can be mass-produced for high-throughput detection. We then applied the sensor to the detection of SARS-CoV-2 with detection limits as low as 10 TU/mL. This membrane as a SERS substrate can offer a fast and non-invasive reference for the early diagnosis of respiratory infectious diseases similar to COVID-19.

Chiral Active Surface Growth via Glutathione Control

AbstractIt is shown that the chiral ligand glutathione can induce active surface growth in the deposition of Au on Au nanoplates, forming nano‐badges with complex surface patterns. The special feature of the growth mode is that the growth materials are diverted to a few active sites, causing deep valleys and high standing walls. The circular dichroism signal depends on the tilting degree of the walls, which likely arises from the different packing of the chiral ligands on the two pro‐chiral slopes. As a characteristic sign of the Active Surface Growth mode, low seed concentration is used to promote the rate of deposition, which expands the ridge–valley competition favoring growth at the active sites. The understanding and rational control of the chiral ridges will advance the synthetic control for chiral nanostructures.

Regio-selective growth of plates on Au nanorods

Morphological control is extremely difficult during the second-stage growth on existing nanoparticles. Here, we show that it is possible to combine nanorod and nanoplate morphologies by using partially encapsulated polystyrene-block-poly(acrylic acid) shells as the mask. Au nanoplates were grown selectively from the exposed surface of the Au nanorod, with consistent orientation for each nanorod. As such, we achieve three levels of synthetic control simultaneously: 1) the polymer mask focuses the Au deposition onto a few sites, so that the nanoplates could extend out prominently; 2) the longitudinal extension of the nanorod could be shifted to the traverse growth of nanoplates by using iodide ions as the inhibitor; 3) the nanoplates grow from only one of the twin planes because of the dynamic competition via the depletion sphere mechanism.

Seed-Mediated Synthesis of Thin Gold Nanoplates with Tunable Edge Lengths and Optical Properties

Thin Au nanoplates show intriguing localized surface plasmon resonance (LSPR) properties with potential applications in various fields. The conventional synthesis of Au nanoplates usually involves the formation of spherical nanoparticles or produces nanoplates with large thicknesses. Herein, we demonstrate a synthesis of uniform thin Au nanoplates by using Au-Ag alloy nanoframes obtained by the galvanic replacement of Ag nanoplates with HAuCl4 as the seeds and a sulfite (SO32-) as a ligand. The SO32- ligand not only complexes with the Au salt for the controlled reduction kinetics but also strongly adsorbs on Au {111} facets for effectively constraining the crystal growth on both basal sides of the Au nanoplates for controlled shape and reduced thicknesses. This seed-mediated synthesis affords Au nanoplates with a thickness of only 7.5 nm, although the thickness increases with the edge length. The edge length can be customizable in a range of 48-167 nm, leading to tunable LSPR bands in the range of 600-1000 nm. These thin Au nanoplates are applicable not only to surface-enhanced Raman spectroscopy with enhanced sensitivity and reliability but also to a broader range of LSPR-based applications.

Improving the efficiency of the concentrating solar power plants using heat transfer nanofluids with gold nanoplates: An analysis from laboratory to industrial scale

We report about the remarkable changes in the thermophysical properties of the heat transfer fluid used in concentrating solar power plants with parabolic-trough collectors (Dowtherm A, a mixture of diphenyl oxide and biphenyl) by addition of Au nanoplates in mass fractions around 10−2 wt%. The resulting nanofluids are stable for weeks, and their enhanced physical properties make them good candidates for the application. Particularly, with 4.8·10−2 wt% of Au nanoplates, specific heat increases by 12.0 ± 1.2 % at 523 K and thermal conductivity increases by 24.9 ± 6.1 % at 373 K, with no measurable changes in density or dynamic viscosity. This set of physical properties allows to make a realistic estimation of the performance of a prototypical concentrating solar power plant using these nanofluids for solar-to-thermal energy conversion. We determine, using computational cost-free numerical models available in literature, that the performance of a concentrating solar power plant could increase up to 35.1 %, compared to the predicted 24.7 % with the conventional heat transfer fluid, with neither rheological penalties nor economically prohibitive structural changes. The findings here reported may contribute to encourage the application of heat transfer nanofluids in order to improve the efficiency of concentrating solar power plants, and to consolidate a working scheme that positively promotes the transition from laboratory scale to industrial scale.

Gold nanohexagrams via active surface growth under sole CTAB control.

The synthesis of homochiral nanostructures involves not only the chiral ligand, but also CTAB. The latter is often treated as a weak ligand unable to compete with the thiol-based chiral ligand. Here, we show that CTAB alone is able to induce Active Surface Growth on Au nanoplates, giving curved tips and steep ridges in the resulting nano-hexagrams. The growth materials (Au0) are diverted to a few active sites, whereas the rest of the Au surfaces are inhibited. Modulation of the growth rate by the ratio of ascorbic acid to Au precursor gives a continuous change of the growth modes, explaining the main trends of shape evolution and the inequivalent growth of the equivalent surfaces. With only CTAB as the ligand, the fact that ridges and spikes could be formed in defiance of facet control suggests that the role of CTAB cannot be ignored in the chiral synthesis and that the precise modulation of the Active Surface Growth could be the key to rational synthetic controls.

Long-Range SERS Detection of the SARS-CoV-2 Antigen on a Well-Ordered Gold Hexagonal Nanoplate Film.

The development of an effective method for identifying severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) via direct viral protein detection is significant but challenging in combatting the COVID-19 epidemic. As a promising approach for direct detection, viral protein detection using surface-enhanced Raman scattering (SERS) is limited by the larger viral protein size compared to the effective electromagnetic field (E-field) range because only the analyte remaining within the E-field can achieve high detection sensitivity. In this study, we designed and fabricated a novel long-range SERS (LR-SERS) substrate with an Au nanoplate film/MgF2/Au mirror/glass configuration to boost the LR-SERS resulting from the extended E-field. On applying the LR-SERS to detect the SARS-CoV-2 spike protein (S protein), reagent-free detection achieved a low detection limit of 9.8 × 10-11 g mL-1 and clear discrimination from the SARS-CoV S protein. The developed technique also allows testing of the S protein in saliva with 98% sensitivity and 100% specificity.

Substrate-Free Fabrication of Single-Crystal Two-Dimensional Gold Nanoplates for Catalytic Application.

Two-dimensional (2D) gold nanoplates (AuNPLs) have shown potential in catalysis, photonics, electronics, sensing, and biomedicine fields due to their high aspect ratio, fascinating surface chemistry, and quantum-size effect. Therefore, the synthesis of substrate-free, size-controlled single-crystal gold (Au) nanoplates is highly desirable for the development of catalysis and optical near-field enhancement applications. EDTA and hydroxide anions were used in this study to stimulate the formation of microscale single-crystal gold nanoplates under hydrothermal conditions. The reaction temperature, amount of EDTA, and hydroxyl anions all have a significant effect on the morphologies and size distributions of the gold nanoplates. The gold nanoplates had an average side length of between 3 and 11 μm. The application of the microscale single-crystal gold nanoplates as a nanocatalyst proved their excellent catalytic activity and recyclability for the catalysis of 4-nitrophenol to 4-aminophenol, implying that the large-size gold nanoplates were promising in heterogeneous catalysis applications.

Selective triggering in-plane and out-of-plane dipolar modes of hexagonal Au nanoplate with the polarization of excitation beam

The dipolar responses of a single hexagonal Au nanoplate are investigated under the illuminations of linearly polarized beam and tightly focused radially polarized beam (RPB). It is found from the scattering spectra that the in-plane and out-of-plane electric dipole modes can be selectively triggered with a linearly polarized beam and tightly focused RPB, respectively. The features of these two dipolar modes are further confirmed in terms of electrical field and charge maps by the finite-difference time-domain simulation. Additionally, using the multipole expansion method, the existence of the out-of-plane dipole mode is further verified by the fact that the z-component of electric dipole response has a dominant contribution to the scattered power. Moreover, by combining the back focal plane imaging technique with the simulation, the appearance of in-plane and out-of-plane dipoles in the scattering pattern are clearly discerned. Our results provide an efficient method for selectively exciting the in-plane and out-of-plane dipolar modes of the nanoplate. We envision that the ease of tuning the dipolar momentum may facilitate the enhancement of the interaction between the plasmon and emitters at single-particle level.

Interface chemistry effects in nanofluids: Experimental and computational study of oil-based nanofluids with gold nanoplates

The chemistry of interfaces and its relation with energy storage at and transport through solid–liquid interfaces in heat transfer nanofluids is a very unexplored terrain. Here we discuss how the magnitude of the changes in specific heat and thermal conductivity of the base fluid, upon dispersion of a nanomaterial, depends on the surface chemistry of that nanomaterial. We focus on nanofluids with Au nanoplates from an integrated experimental and theoretical perspective, and compared our findings with those previously reported for nanofluids with Pd nanoplates in the same base fluid. Pd and Au are known to have different surface chemistry, and so are the structures of the solid–liquid interfaces and the thermal properties of these nanofluids. It was experimentally found that for mass fractions in the order of 0.01 wt%, Pd and Au nanoplates provide enhancements of 5.9% and 1.6% in specific heat, and enhancements of 12.5% and 17.9% in thermal conductivity, at 373 K. It was verified using density functional theory and classical molecular dynamics simulations that base fluid molecules can chemisorb on Pd surfaces, but not on Au surfaces. This work suggests that the stronger interactions between species at solid–liquid interfaces, the higher the specific heat enhancements and the lower the thermal conductivity enhancements at high temperature.

Anisotropic growth of gold nanocrystals induced by concerted adsorption using a photochemical approach

Photochemical reduction of noble metal ions in the presence of stabilizers that selectively adsorb on different crystal planes is a fascinating method for synthesizing shape-controlled metal nanocrystals (NCs). In this study, we demonstrate the photoreduction of Au3+ ions in the presence of polyvinylpyrrolidone (PVP) and Br− ions, that are classified into different categories of protective agents. Au nanoplates with atomically flat surfaces are obtained by the photoirradiation of an aqueous solution containing Au3+, PVP and Br−. Notably, PVP preferentially adsorbs along the perimeter, while Br− ions tend to adsorb on the flat top and bottom (111) faces. The selective adsorption of these structurally distinct stabilizers promotes two-dimensional growth of the Au nanoplates. PVP serves not only as a protective agent but also as a reduction agent in the photoreduction process. At high concentrations of Br− ions, the adsorption of the Br− ions also occurs at the perimeter, which kinetically traps the side growth of the nanoplates and leads to the formation of polygonal Au nanoplates. In other words, competitive adsorption of PVP and Br− at the facets and their density kinetically affect the shape of the formed Au NCs. This concept was successfully applied to control the photoreduction of Au3+ ions into icosahedral Au nanoparticles.

Unveiling radial breathing mode in a particle-on-mirror plasmonic nanocavity

Abstract Plasmonic radial breathing mode (RBM), featured with radially oscillating charge density, arises from the surface plasmon waves confined in the flat nanoparticles. The zero net dipole moment endows the RBM with an extremely low radiation yet a remarkable intense local field. On the other hand, owing to the dark mode nature, the RBMs routinely escape from the optical measurements, severely preventing their applications in optoelectronics and nanophotonics. Here, we experimentally demonstrate the existence of RBM in a hexagonal Au nanoplate-on-mirror nanocavity using a far-field linear-polarized light source. The polarization-resolved scattering measurements cooperated with the full-wave simulations elucidate that the RBM originates from the standing plasmon waves residing in the Au nanoplate. Further numerical analysis shows the RBM possesses the remarkable capability of local field enhancement over the other dark modes in the same nanocavity. Moreover, the RBM is sensitive to the gap and nanoplate size of the nanocavity, providing a straightforward way to tailor the wavelength of RBM from the visible to near-infrared region. Our approach provides a facile optical path to access to the plasmonic RBMs and may open up a new route to explore the intriguing applications of RBM, including surface-enhanced Raman scattering, enhanced nonlinear effects, nanolasers, biological and chemical sensing.