Au Nanowires Research Articles

Tuning Catalytic Activity in Ultrathin Bimetallic Nanowires Via Surface Segregation: Application in Electrochemical Methanol Oxidation

The reaction kinetics and efficiency in any catalytic process is controlled by the adsorption and desorption of reactant and intermediates on the surface of catalyst. As a consequence, the surface properties, composition and geometry of the catalyst dictates the mechanism of reactions. The surface electronic structure is modulated by variations in surface and subsurface atomic configurations, e.g., ordering and surface segregation, which in turn can vividly affects catalytic properties.1,2 A great deal of efforts are being devoted to develop efficient heterogenous catalyst by critically controlling the surface structure and chemistry. Here, I would like to present results on two different strategies for controlling the surface composition in ultrathin bimetallic AuPd nanowires. Au nanowire template-based method was used to grow AuPd wires by gradually increasing the amount of Pd.3 Percentage of composition of Au and Pd in AuPd nanowires gave either alloy nanowires with Au-rich compositions or core-shell structure at higher Pd compositions with Au-rich core and Pd-rich shell. Surface morphology of alloyed nanowires were induced through segregation of Pd to the surface by annealing under controlled CO atmosphere. High resolution microscopic imaging was possible due to the fact of substantial difference in the atomic number between Au and Pd. Electrocatalytic methanol oxidation reaction (MOR) in alkaline medium is important for energy conversion and was selected to study the catalytic activity of AuPd nanowires. A nearly monotonic increase of MOR potential was observed with increase in Pd content. Interestingly, a typical volcano type behavior of the specific activity was observed with different composition and with 40 and 50% Pd samples showed the optimum values in terms of current, potential and If/Ib values. Owing to a higher Pd content of CO-annealed nanowires, a lowering of potential was observed though the specific activity was maintained. These findings provide clear strategies to independently control the reaction potential and the activities of nanocatalysts with smaller amounts of the expensive active metal. The compositional effects on the electronic structure of the AuPd nanowires (catalyst surface) as well as binding energy of intermediates involved in the MOR was investigated using DFT calculations. d-band center analysis was employed to check interaction of CO* which a major intermediate of MOR with the catalyst surface. The theoretical investigation align well with the experimental results where it was found that the MOR potential increases with increasing amount of Pd and for the Au rich case the reaction does not reach up to CO2 but yields HCHO as a product at lower potentials. From our experimental finding it was evident that it is possible to lower the MOR potential to attain comparable or better activity through enrichment with the precious metal on the surface while essentially dropping the real quantity used.

Theoretical simulation of DNA hybridization based on cascaded plasmonic V-shaped channel biosensor

A compact biosensor based on specially designed Cascaded V-shaped Channels (CVSChs) for the analysis and detection of Deoxyribonucleic Acid (DNA) hybridization is presented in this paper. The proposed biosensor employs a Gold (Au) nanowire in then CVSChs sensing region and provides more flexibility as far as tailoring the detection range and sensitivity as compared to the single V-shaped channel (VSC). It has been numerically demonstrated that the detection sensitivity of DNA hybridization is significantly dependent on the number of the V shaped channels. A two – dimensional Finite Difference Time Domain (FDTD) analysis with Perfectly Matched Layers (PMLs) is employed to evaluate the sensor performance with different structural parameters. Simulation results indicate that the proposed biosensor can achieve a high sensitivity of 2541 nm / RIU by optimizing the structural parameters. We demonstrate a proof-of-concept hybrid biosensor by monitoring the resonance shift due to the hybridization event. The proposed biosensor will have great impact on early stage detection of infected cells.

Single gold nanowire-based nanosensor for adenosine triphosphate sensing by using in-situ surface-enhanced Raman scattering technique

Development of new hot spots for surface enhanced Raman scattering (SERS) technique is of great significance recently. Herein, we developed a single Au nanowire (NW)-based nanosensor for adenosine triphosphate (ATP) sensing by using in-situ SERS technique. Single Au NWs, fabricated by laser-assisted pulling method and hydrofluoric acid (HF) etching process, were linked with single-stranded HS-terminated DNA. After that, gold-silver bimetallic nanoparticles (Au/Ag NPs), attached with thiol-containing Raman dyes and ATP aptamer, were immobilized on DNA-modified single AuNW due to the designed affinity between ATP aptamer and single-stranded DNA. This single AuNW-based device exhibited strong SERS signals. In the presence of adenosine triphosphate (ATP), due to the strong specific affinity between the aptamer and the target, the Au/Ag NPs will be separated from the AuNW, resulting in the obvious decrease of the Raman signals, which can be used for ATP sensing with high sensitivity, selectivity and stability. This nanosensor can be used as an ideal platform for real applications, especially at some confined-space samples, such as trace detection, single cell and in vivo analysis.

Chiral Transcription from Chiral Au Nanowires to Self-Assembled Monolayers of Achiral Azobenzene Derivatives

Abstract Chiral transcription from chiral inorganic nanoobjects to achiral organic molecules is a fascinating topic. In this study, chiral transcription was demonstrated using helically controlled Au nanowires (NWs) and achiral azobenzene derivatives with thiol moieties as the terminal group. The azobenzene derivatives mAZonSH can form a self-assembled monolayer on helical Au NWs through thiol-Au bonding. UV-Vis spectroscopy revealed that mAZonSH in the self-assembled monolayer forms H-aggregates. The self-assembled monolayers on the right- and left-handed Au NWs showed opposing circular dichroism (CD) signals derived from the azobenzene chromophore. This result indicates that chiral transcription from the helical Au NWs to the azobenzene derivatives was successfully accomplished by the self-assembly of achiral mAZonSH. Furthermore, we demonstrated that the CD responses of mAZonSH are independent of the tail (m) and spacer (n) alkyl lengths.

Ultrafast-response and broad-spectrum polarization sensitive photodetector based on Bi1.85In0.15S3 nanowire

Alloying of semiconductors is a good strategy to manipulate their electronic band structures, which can broaden the photoresponse range of the corresponding optoelectronic devices. In addition, building a Schottky diode and improving the crystal quality of the channel semiconductor can improve the photoresponse speed of the optoelectronic device. Here, we report the design and preparation of Bi1.85In0.15S3 nanowires by a facile chemical vapor transport method. The individual Bi1.85In0.15S3 nanowire photodetectors realize excellent photoresponse in a broadband range from solar-blind deep ultraviolet (266 nm) to near-infrared (830 nm), and the obtained maximum external photoresponsivity of 95.99 A/W and detectivity of about 3.52×1011 Jones at 638 nm. Furthermore, the photodetectors also exhibit the ultrafast photoresponse speed with the rise time of 190 ns and the fall time of 180 ns, owing to the high crystal quality and the Schottky contacts between the Au electrodes and nanowires. In addition, the photoresponse of photodetectors is polarization angle sensitive in a broadband range from 266 to 808 nm, and the obtained maximum dichroic ratio is 3.54 at 808 nm, which results from the structural anisotropy of the Bi1.85In0.15S3 crystal. These performances are superior to the reported Bi2S3, In2S3, and other Bi or In sulfide nanowire photodetectors. The results render (BixIn1−x)2S3 photodetectors have significant application potentials in multifunctional optoelectronics and electronics.

Gold Nanowires Array-Based Closed Bipolar Nanoelectrode System for Electrochemiluminescence Detection of α-Fetoprotein on Cell Surface.

Inspired by the promising applications of a closed bipolar electrodes (c-BPEs) system in electrochemiluminescence (ECL) detection of cell adhesion and disease-related biomarkers, here, a gold nanowires array-based c-BPEs system was constructed for cell surface protein detection. Regular and uniform gold nanowires array were prepared by intermittent potentiostatic deposition. Then, two poly(dimethylsiloxane) (PDMS) chips with a hole diameter of 2 mm as a reservoir were placed at both sides of Au nanowires array to construct c-BPEs system. Thionine-functionalized silicon dioxide nanoparticles conjugated to antibody (Ab2-Th@SiO2) were used as the electrochemical probe, while [Ru(bpy)3]2+-wrapped SiO2 nanoparticles (Ru(II)@SiO2) were employed as the ECL signal readout. Taking α-fetoprotein (AFP) as model, the gold nanowires array-based c-BPEs system allowed sensitive detection of AFP at a linear range from 0.002 to 50.0 ng/mL and at least 6 living cells ascribing to the synergetic amplification effect at both sensing and reporting chambers. Besides, the amount of AFP expressed by HepG2 cells was calculated to be 6.71 pg/cell. The presented strategy with high sensitivity provided a promising and universal platform for the detection of other cancer cells and disease-related biomarkers (such as proteins, glycan, miRNA).

Flexible Prussian Blue‐Au Fibers as Robust Peroxidase – Like Nanozymes for Wearable Hydrogen Peroxide and Uric Acid Monitoring

AbstractFiber‐based electronics technology has been making significant strides towards applicable emergence into many fields. One such field is the use of fiber‐based electronics in the development of smart textiles. Here, we report the use of stretchable styrene‐ethylene‐butylene‐styrene (SEBS) fibers as a conductive substrate to simultaneously load Au nanowire and Prussian blue (PB) as biosensing interfaces. Accordingly, due to the synergistic catalytic effect between Au nanowire and Prussian blue, the as‐obtained flexible PB/Au fibers can not only show the potential as wearable biosensors but also serve as high‐performance peroxidase‐like nanozymes. The functional fibers can be used for colorimetric detection of H2O2 and uric acid, exhibiting satisfactory sensitivity and selectivity in serum sample analysis. The flexible PB/Au fibers represent a new form of Peroxidase‐like nanozymes, which could open doors to various wearable biosensing applications.

Dynamics of Quasi-One-Dimensional Structures under Roughening Transition Stimulated by External Irradiation.

We studied the striking effect of external irradiation of nanowires on the dynamics of their surface morphology at elevated temperatures that do not destroy their crystal lattice. Numerical experiments performed on the basis of the Monte Carlo model revealed new possibilities for controlled periodic modulation of the cross-section of quasi-one-dimensional nanostructures for opto- and nanoelectronic elements. These are related to the fact that external irradiation stimulates the surface diffusion of atoms. On the one hand, such stimulation should accelerate the development of the well-known spontaneous thermal instability of nanowires (Rayleigh instability), which leads to their disintegration into nanoclusters. On the other hand, this leads to the forced development of the well-known roughening transition (RT) effect. Under normal circumstances, this manifests itself on selected crystal faces at a temperature above the critical one. The artificial stimulation of this effect on the lateral surface of quasi-one-dimensional structures determines many unpredictable scenarios of their surface dynamics, which essentially depend on the orientation of the nanowire axis relative to its internal crystal structure. In particular, the long-wave Rayleigh breakup observed in absence of external irradiation transforms into strongly pronounced short-wave metastable modulations of the cross-section (a chain of unduloids). The effect of the self-consistent relationship between the Rayleigh instability and RT is dimensional and can be observed only at relatively small nanowire radii. The fact is analyzed that, for the manifestation of this effect, it is very important to prevent significant heating of the nanowire when surface diffusion is stimulated. A number of developed theoretical concepts have already found confirmation in real experiments with Au and Ag nanowires irradiated by electrons and Ag+ ions, respectively.

Molecular dynamics simulation of nanofilament breakage in neuromorphic nanoparticle networks

Neuromorphic computing systems may be the future of computing and cluster-based networks are a promising architecture for the realization of these systems. The creation and dissolution of synapses between the clusters are of great importance for their function. In this work, we model the thermal breakage of a gold nanofilament located between two gold nanoparticles via molecular dynamics simulations to study on the mechanisms of neuromorphic nanoparticle-based devices. We employ simulations of Au nanowires of different lengths (20–80 Å), widths (4–8 Å) and shapes connecting two Au1415 nanoparticles (NPs) and monitor the evolution of the system via a detailed structural identification analysis. We found that atoms of the nanofilament gradually aggregate towards the clusters, causing the middle of wire to gradually thin and then break. Most of the system remains crystalline during this process but the center is molten. The terminal NPs increase the melting point of the NWs by fixing the middle wire and act as recrystallization areas. We report a strong dependence on the width of the NWs, but also their length and structure. These results may serve as guidelines for the realization of cluster-based neuromorphic computing systems.

Ultra-high strength yet superplasticity in a hetero-grain-sized nanocrystalline Au nanowire

• Nanocrystalline nanowire always exhibits strength-ductility trade-off. Here, we provide in situ atomic-scale evidence that hetero-grain-sized nanocrystalline nanowires are simultaneously ultra-strong and ductile, with no strength-ductility trade-off. • The hetero-grain-sized nanocrystalline nanowire exhibits a super uniform elongation of ∼ 236% and high strength of ∼ 2.34 gigapascals at room temperature. • The in situ atomic-scale observations revealed that the dislocation activities, grain boundary plasticity, and surface atoms diffusion all contribute to the super elongation ability of hetero-grain-sized nanocrystalline nanowire. Nanocrystalline metals often display a high strength up to the gigapascal level, yet they suffer from poor plasticity. Previous studies have shown that the development of hetero-sized grains can efficiently overcome the strength-ductility trade-off of nanocrystalline metals. However, whether this strategy can lead to the fabrication of nanocrystalline nanowires exhibiting both high strength and superplasticity is unclear, similar to the atomistic deformation mechanism. In this paper, we show that ultra-small nanocrystalline Au nanowires comprising grains in both the Hall–Petch and inverse Hall–Petch grain-size regions can exhibit extremely high uniform elongation (236%) and high strength (2.34 gigapascals) at room temperature. In situ atomic-scale observations revealed that the plastic deformation underwent two stages. In the first stage, the super-elongation ability originated from the intergrain plasticity of small grains via mechanisms such as grain boundary migration and grain rotation. This intergrain plasticity caused the grains in the heterogeneous-structured nanowires to grow very large. In the second stage, the super-elongation ability originated from intragrain plasticity accompanied by the diffusion of surface atoms. Our results show that the hetero-grain-sized nanocrystalline nanowires, comprising grains with sizes both in the strongest Hall–Petch effect region and the inverse Hall–Petch effect region, were simultaneously ultra-strong and ductile. They displayed neither a strength-ductility trade-off nor plastic instability.

Tuning Catalytic Activity in Ultrathin Bimetallic Nanowires via Surface Segregation: Some Insights.

The efficiency of heterogeneous catalysts critically depends on the nature of the surface. We present results on controlling the composition in ultrathin bimetallic AuPd. AuPd wires were grown using Au nanowire templates; the surface composition could be tuned by increasing the amount of Pd. Further, segregation of Pd to the surface could be induced in alloyed nanowires by annealing under a controlled CO atmosphere. Electrocatalytic activity of these bimetallic systems is assessed for the methanol oxidation reaction (MOR). While the MOR potential shows a monotonic increase with Pd content, the specific activity displays a typical volcano-type behavior. The CO-annealed nanowires show a lowering of potential owing to a higher Pd content on the surface while still maintaining the specific activity. These findings provide clear strategies to independently control the reaction potential and the activities of nanocatalysts. The experimental findings are well supported by the theoretical investigations using density functional theory (DFT) calculations.

Near-UV-to-Near-IR Hyperbolic Photonic Dispersion in Epitaxial (Hf,Zr)N/ScN Metal/Dielectric Superlattices

Hyperbolic metamaterials (HMMs) with extreme dielectric anisotropy have shown great promise in nanophotonic applications such as superlensing, enhancement of spontaneous emission, negative refraction, and the diverging photonic density of states. Noble metal-based metal/dielectric multilayers (e.g., Au/SiO2 and Ag/TiO2) and metallic (Au and Ag) nanowires embedded inside a dielectric matrix have been traditionally used to demonstrate HMM properties and for implementations into devices. Noble metals are, however, unstable at high temperatures, complementary metal oxide semiconductor incompatible, and difficult to deposit in thin-film form due to their high surface energies that limit their potential applications. TiN has emerged as an alternative plasmonic material to Au in recent years, and epitaxial TiN/Al0.72Sc0.28N metal/semiconductor superlattices were developed that exhibit excellent HMM properties. As TiN exhibits ε-near-zero (ENZ) at ∼500 nm, TiN/Al0.72Sc0.28N HMM also operates from ∼500 nm to long-wavelength regions. However, for several energy-conversion-related applications as well as for fundamental studies, it is desirable to achieve HMM wavelengths from the near-UV to the near-IR region of the spectrum. In this article, we demonstrate hyperbolic photonic dispersion in (Hf,Zr)N/ScN, a class of metal/semiconducting superlattice metamaterial that covers the near-UV to the near-IR spectral range. Epitaxial HfN/ScN, ZrN/ScN, and Hf0.5Zr0.5N/ScN superlattices are deposited on (001) MgO substrates and characterized with synchrotron-radiation X-ray diffraction as well as high-resolution electron microscopy techniques. Superlattices grow with cube-on-cube epitaxy and with sharp interfaces. Optical characterization reveals both type-I and type-II hyperbolic photonic dispersions as well as low losses and high figures-of-merit. Along with its high-temperature thermal stability, demonstration of HMM properties in (Hf,Zr)N/ScN metal/dielectric superlattices makes them potential candidates for HMM devices.

Water-phase synthesis of Au and Au-Ag nanowires and their SERS activity.

Metal nanowires (NWs) with a diameter of a few nanometers have attracted considerable attention as a promising one-dimensional nanomaterial due to their inherent flexibility and conductive properties and their weak plasmon absorption in the visible region. In a previous paper, we reported the synthesis of ultrathin 1.8 nm-diameter Au NWs using toluene-solubilized aqueous solutions of a long-chain amidoamine derivative (C18AA). This study investigates the effect of different organic solvents solubilized in C18AA aqueous solutions on the morphology of the Au products and demonstrates that solubilizing methylcyclohexane yields thick 2.7 nm-diameter Au NWs and 3.3 nm-diameter Au-Ag alloy NWs. Further, the surface-enhanced Raman scattering sensitivity of ultrathin Au NWs, thick Au NWs, and thick Au-Ag alloy NWs were assessed using 4-mercaptopyridine and found that their enhancement factors are 104-105 and the order is Au-Ag NWs > thick Au NWs > ultrathin Au NWs.

Facile and robust fabrication of hierarchical Au nanorods/Ag nanowire SERS substrates for the sensitive detection of dyes and pesticides.

Surface enhanced Raman spectroscopy (SERS) has emerged as a promising tool for the rapid and ultrasensitive recognition of trace amounts of environmental pollutants. Hierarchical SERS substrates usually show superior performance to single-component substrates but require complicated preparation protocols. Herein, a facile, robust and low-cost route for the fabrication of hierarchical SERS substrates has been reported, in which no complicated laborious protocols or sophisticated equipment is needed. In the hierarchical SERS substrate, Au nanorods were distributed onto the network of Ag nanowires through evaporation induced self-assembly. The density of the Au nanorods and Ag nanowires could be easily tailored by tuning the number of droplets of gold nanorod solution and the concentration of silver nanowire solution. The nanogaps formed between Au nanorods and Ag nanowires were able to induce a rich enhanced electromagnetic field area via localized surface plasmon resonances and surface plasmon polaritons to achieve amplification of the Raman signal. The as-prepared substrate showed high uniformity and was capable of identifying 10-12 M rhodamine 6G, 10-10 M thiram and 10-10 M crystal violet, with correlation coefficients (R2) all higher than 0.98. This approach can be employed for the detection of trace dyes, pesticides or other environmental pollutants with high sensitivity and uniformity.

Restructuring of 4H phase Au nanowires and its catalytic behavior toward CO electro-oxidation

Au nanowires in 4H crystalline phase (4H Au NWs) are synthesized by colloid solution methods. The crystalline phase and surface structure as well as its performance toward electrochemical oxidation of CO before and after removing adsorbed oleylamine molecules (OAs) introduced from its synthesis are evaluated by high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), underpotential deposition of Pb (Pb-upd) and cyclic voltammetry. Different methods, i.e. acetic acid cleaning, electrochemical oxidation cleaning, and diethylamine replacement, have been tried to remove the adsorbed OAs. For all methods, upon the removal of the adsorbed OAs, the morphology of 4H gold nanoparticles is found to gradually change from nanowires to large dumbbell-shaped nanoparticles, accompanying with a transition from the 4H phase to the face-centered cubic phase. On the other hand, the Pb-upd results show that the sample surfaces have almost the same facet composition before and after removal of the adsorbed OAs. After electrochemical cleaning with continuous potential scans up to 1.3 V, CO electro-oxidation activity of the 4H Au sample is significantly improved. The CO electro-oxidation activity is compared with results on the three basel Au single crystalline surfaces reported in the literature, possible origins for its enhancement are discussed.

Flexible and transparent electrodes imprinted from Au nanowires: stability and ageing.

We study the stability of flexible transparent electrodes (FTEs) that were self-assembled from ultra-thin gold nanowires (AuNW) by direct nanoimprinting of inks with different particle concentrations (1 to 10 mg mL−1). The resulting lines were less than 3 μm wide and contained bundles of AuNW with oleylamine (OAm) ligand shells. Small-angle X-ray scattering confirmed a concentration-independent bundle structure. Plasma sintering converted the wire assemblies into lines with a thin metal shell that contributes most to electrical conductivity and covers a hybrid core. We studied the relative change in sheet resistance and the morphology of the FTEs with time. The sheet resistance increased at all concentrations, but at different rates. The metal shell aged by de-wetting and pore formation. The hybrid core de-mixed and densified, which led to a partial collapse of the shell. Residual organics migrated through the shell via its pores. Lines formed at low concentration (cAu = 2 to 3 mg mL−1) contained less residual organics and aged slower than those formed at high cAu ≥ 5 mg mL−1. We passivated the conductive shell with thin, adsorbed layers of PEDOT:PSS and found that it decelerated degradation by slowing surface diffusion and hindering further rupture of the shell. Thick capping layers prevented degradation entirely and stopped pore formation.

Design and modelling of nano-channel based plasmonic sensor for refractive index and pressure sensing in mid – IR range

A groove incorporated two-dimensional silver (Ag) nanostructure having a polymer-based sensing channel is proposed for pressure/refractive index (RI) sensing. The plasmonic device exploits the strong correlation of surface plasmon resonance (SPR) with material parameters of the surrounding medium, and the optical sensing properties of the device under different pressure conditions are analyzed numerically. The whole design and performance evaluation are carried out using the 2D finite element method (FEM). A high RI sensitivity of 3227 nm/RIU across the mid-infrared region with excellent sensor parameters (figure of merit = 44.19 RIU−1, Q-factor = 43.20) is observed from the proposed device. Further, a sensor performance enhancement with a tunability in the operational electromagnetic (EM) wavelength range is achieved by introducing Au/Ag/Cu/Ti/GaAs nanowire in the sensing grooves. The 48.66 % enhancement in RI sensitivity obtained from the structure with an Au nanowire (NW) of a thickness (tw) 5 nm is promising for optical devices in bio and chemical sensors. Additional performance optimization is also achieved from the material parameter of the nanowire used. An optimized maximum sensitivity of 2251.14 nm/MPa observed from Ag NW introduced grove integrated pressure sensor (GIPS) structure makes it an excellent candidate across nano-SPR pressure sensors.

Ultra-stable self-standing Au nanowires/TiO2 nanoporous membrane system for high-performance photoelectrochemical water splitting cells.

We introduce for the first time a core-shell structure composed of nanostructured self-standing titania nanotubes (TNT, light absorber) filled with Au nanowire (AuNW) array (electrons collector) applied to the photoelectrocatalytic water splitting. Its activity is four times higher than that of reference TNT-Ti obtained with the same anodizing conditions. The composite photoanode brings a distinct photocurrent generation (8 mA cm-2 at 1.65 V vs. RHE), and a high incident photon to current efficiency of 35% obtained under UV light illumination. Moreover, the full system concept of selected constitutional materials, based on Au noble metal and the very stable semiconductor TiO2, ensures a stable performance over a long-time range with no photocurrent loss during 100 on-off cycles of light illumination, after 12 h constant illumination and after one-month storage in air. We provide experimental evidence by photoelectron spectroscopy measurements, confirming that the electronic structure of TNT-AuNW is rectifying for electrons and ohmic for holes, while the electrochemical characterization confirms that the specific architecture of the photoanode supports electron separation due to the presence of a Schottky type contact and fast electron transport through the Au nanowires. Although the composite material shows an unchanged electrochemical band gap, typical for plain TiO2, we find this material to be an innovative platform for efficient photoelectrochemical water splitting under UV light illumination, with significant potential for further modifications, for example extension into the visible light regime.

Synthesis of substrate-bound seaweed-like Au nanowires with amino silane coupling agents.

A seedless method has been developed to synthesize seaweed-like Au nanowires on a Au substrate. The amino silane coupling agent 3-aminopropyltriethoxysilane was employed to form the active surfaces that facilitate the one dimensional growth. The growth mechanism and controlling parameters were investigated. Furthermore, the compatibility of this synthesis with a colloidal Au substrate was also demonstrated.

Designing anisotropic inorganic nanocapsules via self-assembly of polymer-like ultrathin Au nanowires.

Anisotropic assembly of nanomaterials into hollow structures is an attractive technique in biomedicine and biosensing. Commonly used polymer materials are easy to assemble yet it is hard to form anisotropic morphologies. Here in this work, we successfully prepared a novel gold nanocapsule with an anisotropic ellipsoidal shape and cavity structure by the self-assembly of ultrathin Au nanowires. The assembly mechanism is further studied by tuning the assembly conditions such as nanowire concentration, solvent composition, and temperature. It is found that the controlling forces of the nanowire assembly process are mainly the symmetric interfacial tension and the asymmetric nanowire deformation potential, which contribute together to result in anisotropic nanocapsules. Finally, the obtained Au nanocapsules were used as nanocarriers to load pyrene as a model drug, showing great drug loading ability and pH-responsive drug release behavior. We believe that this unique anisotropic assembly product will bring new insights into nanostructure design and soft matter research.