Au Nanoframes Research Articles

Stable Au–Ag nanoframes based on Au nanorods: construction and plasmon-enhanced catalytic performance

Au NR@Ag–Au nanoframes not only exhibit highly tunable SPR properties, but also show excellent structural stability and catalytic activity.

Template-directed growth of Ag nanostructures: soft templates versus hard templates.

Hard template-directed growth methods present a compelling route for the synthesis of Ag nanostructures with precise size control. Meanwhile, soft template methods are effective and flexible for the synthesis of Ag nanostructures with various morphologies. However, the role of the soft template is ambiguous and obviously neglected in hard template-directed growth processes due to the strong confinement effect of the hard template, limiting the diversity of Ag nanostructures that can be obtained. Herein, we design Au nanoframes with deformable head structures as a hard template while using cetyltrimethylammonium chloride as a soft template, to direct the growth of Ag atoms on Au nanobipyramid seeds. When using the Au nanoframes with a closed head, the longitudinal growth of the Ag atoms is clearly limited by the hard template, leading to the formation of thick Ag nanorods with a five-fold twinned structure. The soft template starts to influence the growth process when the head structure of the Au nanoframes becomes hollow. In particular, the confinement effect of the hard template can be completely broken by selectively strengthening the role of the soft template, promoting the production of slender Ag nanorods similar to the results obtained in the absence of the hard template. Our results indicate that the morphology of the Ag nanostructures depends on the competition between the qualitatively confined energies of the hard and soft templates during the template-directed growth process. Moreover, this confined growth mechanism is also verified by the successful construction of various Ag nanostructures. The understanding of the collaborative competition mechanism between the soft and hard templates presents a great opportunity to construct novel Ag nanostructures through a template-directed method.

Designer Gold‐Framed Palladium Nanocubes for Plasmon‐Enhanced Electrocatalytic Oxidation of Ethanol

Surface plasmon of coinage metal nanostructures has been employed as a powerful route in boosting the performances in heterogenous catalysis. Development of efficient plasmonic nanocatalysts with high catalytic performance and efficient light harvesting properties is of vital importance. Herein, we rationally designed and synthesized a plasmonic nanocatalyst composed of Au-framed Pd nanocubes by an Ag(I)-assisted seed-mediated growth method. In the synthesis, the incorporation of Ag(I) suppresses the reduction of Au on the {100} surface of cubic Pd seeds and leads to the formation of Au nanoframes on the Pd nanocubes. The unique Au-framed Pd nanocubes can integrate the superior electrocatalytic of Pd and the outstanding plasmonic properties of Au. Thus, these nanostructures were employed as plasmonic nanocatalysts for plasmon-enhanced electrocatalytic oxidation of ethanol with improved stability.

Synthesis of Pd nanorod arrays on Au nanoframes for excellent ethanol electrooxidation.

Au-Pd hollow nanostructures have attracted a lot of attention because of their excellent ethanol electrooxidation performance. Herein, we report a facile preparation of Au nanoframe@Pd array electrocatalysts in the presence of cetylpyridinium chloride. The reduced Pd atoms were directed to mainly deposit on the surface of the Au nanoframes in the form of rods, leading to the formation of Au nanoframe@Pd arrays with a super-large specific surface area. The red shift and damping of the plasmon peak were ascribed to the deposition of the Pd arrays on the surface of the Au nanoframes and nanobipyramids, which was verified by electrodynamic simulations. Surfactants, temperature and reaction time determine the growth process and thereby the architecture of the obtained Au-Pd hollow nanostructures. Compared with the Au nanoframe@Pd nanostructures and Au nanobipyramid@Pd arrays, the Au nanoframe@Pd arrays exhibit an enhanced electrocatalytic performance towards ethanol electrooxidation due to an abundance of catalytic active sites. The Au NF@Pd arrays display 4.1 times higher specific activity and 13.7 times higher mass activity than the commercial Pd/C electrocatalyst. Moreover, the nanostructure shows improved stability towards the ethanol oxidation reaction. This study enriches the manufacturing technology to increase the active sites of noble metal nanocatalysts and promotes the development of direct ethanol fuel cells.

NIR II Light-Response Au Nanoframes: Amplification of a Pressure- and Temperature-Sensing Strategy for Portable Detection and Photothermal Therapy of Cancer Cells.

Quantitative detection of cancer cells using portable devices is promising for the development of simple, fast, and point-of-care cancer diagnostic techniques. However, how to further amplify the detection signal to improve the sensitivity and accuracy of detecting cancer cells by portable devices remains a challenge. To solve the problem, we, for the first time, synthesized folic-acid-conjugated Au nanoframes (FA-Au NFs) with amplification of pressure and temperature signals for highly sensitive and accurate detection of cancer cells by portable pressure meters and thermometers. The resulting Au NFs exhibit excellent near-infrared (NIR) photothermal performance and catalase activity, which can promote the decomposition of NH4HCO3 and H2O2 to generate corresponding gases (CO2, NH3, and O2), thereby synergistically amplifying pressure signals in a closed reaction vessel. At the same time, Au NFs with excellent peroxidase-like activity can catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to produce TMB oxide (oxTMB) with a strong photothermal effect, thereby cooperating with Au NFs to amplify the photothermal signal. In the presence of cancer cells with overexpressing folate receptors (FRs), the molecular recognition signals between FA and FR can be converted into amplified pressure and temperature signals, which can be easily read by portable pressure meters and thermometers, respectively. The detection limits for cancer cells using pressure meters and thermometers are 6 and 5 cells/mL, respectively, which are better than other reported methods. Moreover, such Au NFs can improve tumor hypoxia by catalyzing the decomposition of H2O2 to produce O2 and perform photothermal therapy of cancer. Together, our work provides new insight into the application of Au NFs to develop a dual-signal sensing platform with amplification of pressure and temperature signals for portable and ultrasensitive detection of cancer cells as well as personalized cancer therapy.

One-Pot Self-Templated Growth of Gold Nanoframes for Enhanced Surface-Enhanced Raman Scattering Performance.

As one of the representative metallic hollow nanostructures, Au nanoframes have shown fascinating properties such as strong localized surface plasmon resonance associated with emerging applications such as surface-enhanced Raman scattering (SERS) sensors. In this study, for the first time, a facile one-pot synthetic approach for hollow Au nanoframes is demonstrated by directly etching Au nanoplates, that is, the so-called self-templates. A novel growth mechanism has been revealed that involves a synergistic function of Ag and Br ions. The presence of Ag+ leads to the observation of self-limiting Au film thickness, whereas Au{111} facets are preferentially attacked by the presence of Br- in the reaction ambient. More importantly, graphene is introduced to prevent/minimize aggregation during the formation of Au nanoframes. The combined simulation and experimental studies show that the hybrid platform made of graphene/Au nanoframes is capable of detecting analytes at concentration levels down to 10-9 M by using the SERS technique.

Quantitative Surface-Enhanced Raman Spectroscopy Analysis through 3D Superlattice Arrays of Au Nanoframes with Attomolar Detection.

This paper reports a methodology for synthesizing and ordering gold nanoframes into three-dimensional (3D) arrays with a controlled thickness, leading to homogeneous plasmonic superstructures, with which quantitative analysis via surface-enhanced Raman spectroscopy (SERS) has been successfully demonstrated. Because this preparation method allows for systematic control of nanoframe film thickness and the resulting 3D plasmonic superstructure, which exhibits a unique nanoporous network of hot-spots, detection limits down to 10-18 M, corresponding to ≈6000 molecules, have been measured. Compared to analogous solid nanoparticle superstructures, the nanoframe superstructures with their unique nanoporous architecture effectively dissipate the heat inevitably generated by laser excitation during measurement, effectively suppressing the formation of carbonaceous materials and therefore their accompanying fluorescence interference, especially important for low concentration detection.

Ultrasensitive immunoassay of proteins based on in-situ enzymatic formation of quantum dots and microliter-droplet anodic stripping voltammetry

We report an ultrasensitive sandwich-type electrochemical immunoassay of proteins, on the basis of in situ enzymatic formation of CdS quantum dots (QDs), simultaneous chemical dissolution of CdS and cathodic preconcentration of Cd, and microliter-droplet anodic stripping voltammetry (ASV) detection directly on the immunoelectrode. The antibody 2 labeled with alkaline phosphatase (ALP) and Au nanoframes (Ab2-ALP-AuNFs) can catalyze hydrolysis of ascorbic acid 2-phosphate to form ascorbic acid and inorganic phosphate, and the latter can stabilize the formation of CdS QDs on the immunoelectrode through Cd2+-S2− reaction. A beforehand “potential control” and then an injection of 7 μL 0.1 M aqueous HNO3 lead to dissolution of the CdS QDs for simultaneous electrodeposition of metallic Cd, and ASV directly on the immunoelectrode is then conducted to quantify the antigen analyte. The use of AuNFs can increase the enzyme load and activity for improved signaling. Under optimized conditions, this method is used for ultrasensitive analysis of human immunoglobulin G (IgG) and human cardiopathy biomarker cardiac troponin I (cTnI), giving limits of detection (LODs, S/N = 3) of 1.2 fg mL−1 for IgG and of 1.1 fg mL−1 for cTnI (equivalent to 173 molecules in the 6 μL sample employed for cTnI analysis). The LOD of IgG is ca. 3 orders of magnitude lower than that of the fluorescent method by experimentally recording the emission spectrum of the CdS QDs at λex = 290 nm and λem = 500 nm.

Gold nanorings synthesized via a stress-driven collapse and etching mechanism

Toroidal Au or Ag nanostructures are of particular interest due to their unique optical responses and superior catalytic applications. However, the fabrication of ring-like Au or Ag nanostructures is limited to either electron beam lithography or template techniques, thus hampering their applications. Here, we present a new stress-driven structure collapse and etching mechanism to synthesize Au nanorings via a direct one-pot solution-based chemical reaction. The nanoparticle-mediated recrystallization process contributes to the formation of Au nanoframes, which contain unusual stress, thus promoting the breakup of the nanoframes and finally converting them into Au nanorings. The Au nanorings with tunable hole sizes exhibit interesting localized surface plasmon features owing to the coupling of bonding and antibonding modes on the inner and outer surfaces of the nanorings. This facile approach may open the door for the preparation of toroidal nanostructures in other compositions for numerous applications. A new strategy for synthesizing gold nanorings that employs stress-driven structure collapse and etching has been demonstrated. Gold nanorings exhibit unique optical and catalytic properties and are used in a wide range of applications, but the synthesizing ways suffer from significant limitations. Now, Jixiang Fang of Xi'an Jiaotong University in China and co-workers in China and Singapore have exploited a simple way to fabricate gold nanorings that involves the formation of frame structures by recrystallization mediated by nanoparticles. The unusual stress distribution in these frames causes them to collapse into nanoring structures. The size of the central hole of the nanorings can be tuned from hundreds to tens of nanometres, allowing the nanorings' optical properties (in particular, their plasmonic properties) to be tailored. A new stress-driven structural collapse and etching mechanism for the synthesis of Au nanorings via a direct one-pot solution-based chemical reaction is presented. The nanoparticle-mediated recrystallization process contributes to the formation of Au nanoframes that contain unusual stress, which promotes the breakup of the nanoframes and conversion into Au nanorings. The Au nanorings have tunable hole sizes and exhibit interesting localized surface plasmon features owing to the coupling of bonding and antibonding modes on the inner and outer surfaces of the nanorings.

Near‐Infrared‐Light‐Induced Fast Drug Release Platform: Mesoporous Silica‐Coated Gold Nanoframes for Thermochemotherapy

Development of advanced theranostics for personalized medicine is of great interest. Herein, a multifunctional mesoporous silica‐based drug delivery carrier has been developed for efficient chemo/photothermal therapy. The unique Au nanoframes@mSiO2 spheres are elaborately prepared by utilizing Ag@mSiO2 yolk–shell spheres as the template through spatially confined galvanic replacement method. Compared with the Ag@mSiO2 yolk–shell spheres, the resultant Au nanoframes@mSiO2 spheres show a strong and broad near‐infrared (NIR) absorbance in the 550–1100 nm region, high surface areas, and good biocompatibility. When irradiated with a NIR laser with a power intensity of 1 W cm−2 at 808 nm, they can become highly localized heat sources through the photothermal effect. Moreover, the photothermal effect of the Au nanoframes can significantly promote the fast release of doxorubicin. The in vitro studies show obvious synergistic effects combining photothermal therapy and chemotherapy in the Au nanoframes@mSiO2 spheres against Hela cells. It is believed that the as‐obtained multifunctional vehicles provide a promising platform for the combination of hyperthermia and chemotherapy for cancer treatment application.

Plasmonic Nanoframes for Photothermal Energy Conversion

We study the photothermal behavior of laser-pulsed colloidal metallic nanoframe structures using three-dimensional (3D) photonic and thermofluidic computational models. The models predict the optical response of the nanoframe, photothermal transduction at plasmon resonance, heat transfer to the surrounding fluid, and the dynamics of nanobubble generation under conditions of superheating. We quantify for the first time the photothermal transduction of Au nanoframes as a function of their orientation with respect to the polarization of the incident field and, also, cooperative heating effects as a function of nanoframe spacing. We further demonstrate that laser illumination parameters and nanoframe properties can be tuned to control spatiotemporal heating and nanobubble dynamics.

Gold Nanoframes by Nonepitaxial Growth of Au on AgI Nanocrystals for Surface-Enhanced Raman Spectroscopy.

Plasmonic noble metal nanoparticles with defined interior nanogaps are of great significance to surface-enhanced Raman spectroscopy (SERS) applications owing to the presence of intraparticle hotspots. In this contribution, we discovered site-selective nonepitaxial growth of Au on nonmetallic AgI nanocrystals, and on the basis of this observation, we designed an unconventional route to synthesize monometallic Au nanoframes that possess ∼7 nm of interior nanogaps and ∼23 nm of overall size by templating of small AgI nanocrystals. Chemical bonding between Au and the iodide-rich surface of the AgI nanocrystals was proposed to play a critical role in the nonepitaxial growth of the Au nanoframes against the AgI nanocrystals. The Au nanoframes obtained from this synthesis showed superior SERS activity in detecting molecules of interest in low concentrations owing to the presence of intraparticle hotspots in additional to the interparticle ones, benchmarking against Au nanospheres. This intriguing synthesis may open up new opportunities toward a variety of noble metal/semiconductor nanoconjugates for a broad range of applications such as synergistic catalysis.

Octahedral and Cubic Gold Nanoframes with Platinum Framework.

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

Following Charge Separation on the Nanoscale in Cu2O–Au Nanoframe Hollow Nanoparticles

Cu(2)O-Au nanoframes with different nanolayer thicknesses of Cu(2)O were prepared, and their photocatalytic properties in aqueous solutions were studied. Cu(2)O semiconductor excitation leads to electron-hole separation. In aqueous solution, the hole is known to oxidize water to produce hydroxyl radicals whose concentration (and that of the holes) can be monitored by the rate of the degradation of dissolved methylene blue dye. The exciton lifetime is determined by femtosecond techniques and is determined by electron-hole recombination which depends on the rates of a number of competing processes such as, electron or hole transfer to an acceptor such as a gold nanoframe and/or the electron or hole trapping processes at the Cu(2)O-Au nanoframe interface. We measured the exciton lifetime as a function of the average Cu(2)O-Au layer separation. A good correlation was found between the rate of the photocatalytic degradation of methylene blue and the exciton lifetime. The exciton lifetime is found to increase as the Cu(2)O thickness is increased. This leads to an increase in the electron-hole separation time and thus an increase in the hole (and so the hydroxyl radical) concentration leading to an observed enhanced rate of the dye degradation.

Cu2O microcrystals: a versatile class of self-templates for the synthesis of porous Au nanocages with various morphologies

Design and synthesis of Au nanocages is one of the basic interests in the fabrication of nanoscale structures due to their attractive potentials in catalysis, medical science and so on. In most cases, spherical or cubic Au nanocages were fabricated using silica nanoparticles or Ag nanocubes as templates. In this article, another kind of versatile template, Cu2O microcrystals, has been employed to synthesize Au nanocages with various morphologies, such as cube, sphere, octahedron, truncated octahedron, cuboctahedron and concave cube morphologies. Surface modification of the templates, which is a necessary procedure in the synthesis of cage-shaped structures using a template-based strategy is avoided by this method because AuCl4− can be reduced spontaneously on the surfaces of the Cu2O microcrystals at room temperature. When the Cu2O microcrystals possess only one type of exposed planes, Au nanoparticles (NPs) are deposited homogeneously on the supports, etching out Cu2O portions in the as-prepared nanocomposites, with porous Au nanocages produced. However, if the Cu2O microcrystals have two kinds of exposed planes, such as (111) and (100), selective deposition of Au NPs was observed. Based on this phenomenon, cuboctahedral and truncated octahedral Au nanoframes were synthesized. Due to the porous structure of the as-prepared Au nanocages, the catalytic activity of cubic Au nanocages in the reduction of 4-nitrophenol by sodium borohydride is much higher than that of reported spongy Au nanocrystals.

Fabrication of Nanoframe Structures by Site-selective Assembly of Gold Nanoparticles on Silver Cubes in an Ionic Liquid

Abstract Gold nanoparticles (Au-NPs) prepared by sputter deposition of Au in an ionic liquid were selectively assembled at the edges and vertices of Ag nanocubes, the surfaces of which were modified with a self-assembled monolayer of 1-octadecanethiol and 4-amino-2-mercaptopyrimidine. Chemical etching of Ag from the resulting Au–Ag binary nanocomposites resulted in the formation of Au nanoframes.

Simulating Synthesis of Metal Nanorods, Nanoplates, and Nanoframes by Self-Assembly of Nanoparticle Building Blocks

A general synthesis strategy to prepare metal nanostructures by self-assembly was proposed by molecular dynamics (MD) simulation. In this simulating synthesis strategy, the metal nanostructures were generated by the self-assembly of the amorphous nanoparticles with the attractive forces of the nanoparticle−nanoparticle interactions by the annealing MD method at high temperatures, and finally, the resulting amorphous metal nanostructures were cooled to 10 K, which could resemble the nanoparticle self-assembly in experiment. By using the simulating synthesis, we obtained the full atomistic models of the shape-controlled metal nanostructures, including Au, Ag−Au, and beaded Ag−Cu nanorods, triangular and hexagonal Ag nanoplates, triangular Ag−Au and hexagonal Au, cubic hollow Fe, and Ag−Au nanoframes. It is found that these models are in good agreement with the experimental results. Moreover, we predicted a new metal nanostructure, Au nanoporous framework architecture, which has not been reported in experime...

Electrochemical deposition of gold frame structure on silver nanocubes

Au-framed Ag nanocubes were prepared by site-selective electrochemical deposition of Au onto the edges and vertices of Ag nanocubes modified with a self-assembled monolayer (SAM) of 1-octanethiol, and further chemical etching of the Ag cubes used as a template produced Au nanoframes.

Synthesis and optical properties of cubic gold nanoframes

This paper describes a facile method of preparing cubic Au nanoframes with open structures via the galvanic replacement reaction between Ag nanocubes and AuCl(2) (-). A mechanistic study of the reaction revealed that the formation of Au nanoframes relies on the diffusion of both Au and Ag atoms. The effect of the edge length and ridge thickness of the nanoframes on the localized surface plasmon resonance peak was explored by a combination of discrete dipole approximation calculations and single nanoparticle spectroscopy. With their hollow and open structures, the Au nanoframes represent a novel class of substrates for applications including surface plasmonics and surface-enhanced Raman scattering.