Au Nanowires Research Articles

Seeded growth synthesis, reshaping, and damping of the localized surface plasmon resonance in Au@Fe2O3 nanoparticles

Core@shell Au@Fe2O3 nanoparticles with different iron oxide content were synthesized by a seeded-growth approach. The morphology and structural analysis were carried out by transmission electron microscopy (TEM and HR-TEM) and X-ray diffraction (XRD). The oxidation state of the iron was determined through cyclic voltammetry measurements. The plasmonic resonance modes were investigated by Infrared (IR) and UV–vis spectroscopy. The morphology analysis of Au nanowires (AuNW’s) shows a modification from NW’s (seeds) to faceted nanoparticles, while spectroscopic studies show a disappearance of the Propagation Surface Plasmon Resonance (PSPR) due to this change. Localized Surface Plasmon Resonance (LSPR) is damped due to the aggregation of the iron oxide layer.

Transparent Intracellular Sensing Platform with Si Needles for Simultaneous Live Imaging.

Vertically ordered Si needles are of particular interest for long-term intracellular recording owing to their capacity to infiltrate living cells with negligible damage and minimal toxicity. Such intracellular recordings could greatly benefit from simultaneous live cell imaging without disrupting their culture, contributing to an in-depth understanding of cellular function and activity. However, the use of standard live imaging techniques, such as inverted and confocal microscopy, is currently impeded by the opacity of Si wafers, typically employed for fabricating vertical Si needles. Here, we introduce a transparent intracellular sensing platform that combines vertical Si needles with a percolated network of Au-Ag nanowires on a transparent elastomeric substrate. This sensing platform meets all prerequisites for simultaneous intracellular recording and imaging, including electrochemical impedance, optical transparency, mechanical compliance, and cell viability. Proof-of-concept demonstrations of this sensing platform include monitoring electrical potentials in cardiomyocyte cells and in three-dimensionally engineered cardiovascular tissue, all while conducting live imaging with inverted and confocal microscopes. This sensing platform holds wide-ranging potential applications for intracellular research across various disciplines such as neuroscience, cardiology, muscle physiology, and drug screening.

An electrochemical metallic nanowire aptasensor for rapid and ultrasensitive detection of cardiac troponin I

Cardiac troponin I (cTnI) is regarded as a significant protein marker of cardiovascular diseases. Slight increase of blood cTnI level could reflect cardiomyocyte injury, presenting great clinical value in early diagnosis and prognostic monitoring of heart failure (HF). Here, we report for the first time, a metallic nanowire aptasensor with high sensitivity and short detection time as a promising strategy for POC detection of cTnI. We designed and fabricated a novel single Au nanowire electrode with stable anchor structure, and successfully attained immobilization of cTnI-specific aptamer probes. The metallic nanowire aptasensor exhibited high-rate mass transfer and low background current, as well as high affinity and selectivity of the aptamers that facilitated excellent detection performance such as high sensitivity (limit of detection: 13 fg/mL, S/N = 3), short detection time (≤ 15 min), high specificity and good reproducibility in serum samples. These unique properties enabled the nanowire aptasensor for POC detection of cTnI in early diagnosis and prognostic monitoring of HF. Moreover, this nanowire aptasensor was also featured with high stability and regeneration capability, which was envisioned to be further integrated into portable devices, providing potential applications in continuous monitoring of cardiomyocyte injury.

Spectral Tuning of Plasmonic Activity in 3D Nanostructures via High‐Precision Nano‐Printing

AbstractPlasmonic nanoparticles reveal unique optical properties and are increasingly incorporated into commercial products and technologies, ranging from photovoltaics to biological and chemical sensors. Shifting and tuning their plasmonic response according to the targeted application strongly depends on the ability to control the geometry in every detail and has not been reliably demonstrated for complex 3D nano‐architectures yet. Following that motivation, it herein presents how Focused Electron Beam Induced Deposition (FEBID), a highly flexible additive 3D direct‐write technology with spatial nano‐scale precision, is used for the controlled and tunable fabrication of plasmonically active 3D nanostructures that exhibit highly concentrated, well defined and predictable local plasmonic resonances. As model systems, planar Au nanowires and 3D nano‐tips of various geometries are prepared via FEBID and plasmonically characterized via scanning transmission electron microscopy based electron energy loss spectroscopy (STEM‐EELS) mapping measurements. The findings are complemented with corresponding plasmon simulations, revealing very good agreement with experimental findings. This way, on‐demand spectral tuning of the plasmonic response becomes accessible via upfront modeling and design of suitable 3D nanostructures, to achieve customized plasmonic responses, therefore paving the way for yet unrealized plasmonic applications in 3D space.

Brushed Nano‐Stirbars for Measuring Viscosity in Microscopic Systems

AbstractConventional methods for measuring viscosity rely on macroscopic device components, which are difficult to miniaturize. The magnetic nano‐stirbars are small enough to enter tiny spaces and can spin without precise installation, making them an ideal candidate for exploring new methods. It is shown that a dense layer of Au nanowires can be grown on the silica surface of the nano‐stirbars, as a means to modulate the viscous resistance during their spinning and to make them visible under an optical microscope. The uniform growth of Au nanowires and the slight fluctuation of the spinning rates are investigated. It is shown that the nano‐stirbars with the hairy layer of Au nanowires can be used to measure the viscosity in microscopic liquid systems, such as microfluidic chambers and capillary tubes, involving cell media and blood samples. It is believed that the success with the proof‐of‐concept tests will open a window for further miniaturization of the nano‐stirbars for measuring in ultrasmall systems.

In situ TEM observation of the (De)potassiation process of α-MnO2 nanowires

Based on lithium-ion batteries (LIBs), a new type of electrochemical device known as potassium-ion batteries was developed. Potassium-ion batteries potentially offer several key benefits over LIBs in Non-aqueous and several electrode materials, including steady discharge, high rate performance, cheap cost and lower charge density. Therefore, Potassium-ion batteries (PIBs) are highly likely to become the best candidate for low-cost, long-life batteries in the future, and are expected to extensively be employed in a variety of industries, including mobile devices and new energy vehicles. In recent years, research on the electrochemistry of potassium-ion batteries is still in its initial stage. Here, we use in situ transmission electron microscopy to observe the irreversible volume expansion of α-MnO2 nanowire during potassiation and depotassiation. During the first potassiation, the single crystalline α-MnO2 nanowire transformed to K1.33Mn8O16, causing a volume expansion of 35.6 %, which was unable to recover during the depotasiation process. The irreversible volume expansion suggests that most potassium ions inserted into the α-MnO2 nanowire cannot be extracted during the depotassiation process, which leads to low Coulombic efficiency in the first cycle. The cycle performance and Coulombic efficiency of α-MnO2 maybe still limited by insufficient electronic conductivity. Composite Au on the surface of α-MnO2 maybe improves its electronic conductivity. The α-MnO2 on Au (α-MnO2/Au) nanowires’ irreversible and cycle performance was better than pristine materials by the first principle calculations. Traditionally the first cycle capacity loss is attributed to the formation of the solid electrolyte interface (SEI). This research provides a new approach of the first cycle capacity loss mechanism in potassiation of α-MnO2 cathode. Also, the α-MnO2/Au improves the cycle performance and Coulombic efficiency of the K-(α-MnO2) nanobattery.

SERS-active immunoassay kit for SARS-CoV‑2 mediated by the cooperative chemical and electromagnetic effects of MXene modified with gold nanowires

Surface-enhanced Raman scattering (SERS) technique with high sensitivity, reliable specificity, and rapid recognition ability exhibits attractive promise for the effective fast-monitoring of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Herein, a novel SERS-active immunoassay kit for SARS-CoV-2 nucleocapsid (N) protein was prepared by in-situ growing gold (Au) nanowire forests (NFs) onto Ti3C2Tx, which was then modified onto polymethyl methacrylate (PMMA) matrix and encapsulated into kit. It was noted that the Au nanowires with fibrous structures which vertically anchored on Ti3C2Tx served as perfect channels to promote photo-induced charge transfer. The synergistic action of electromagnetic and chemical effects resulted in an enhancement factor (EF) of 1.27 × 107. Furthermore, the unreliable fluctuation of the enhanced signal was eliminated by using the intrinsic Raman signal of the flexible PMMA platform, achieving an improved correlation coefficient (R2) value from 0.950 to 0.990. Moreover, the as-designed immunoassay kit with both high sensitivity and remedied quantitative ability rendered by the Ti3C2Tx@Au NFs-PMMA composite exhibited a powerful performance in the practical detection of N-protein with concentration low to 5.0 × 10−8 mg/mL.

An atomistic study on the strain rate and temperature dependences of the plastic deformation Cu–Au core–shell nanowires: On the role of dislocations

Abstract Recently, Cu–Au core–shell nanowires have been extensively used as conductors, nanocatalysts, and aerospace instruments due to their excellent thermal and electrical conductivity. In experimental studies, various methods have been presented for producing, characterizing, and strengthening these structures. However, the mechanical behavior and plastic deformation mechanisms of these materials have not been investigated at the atomic scale. Consequently, in the present study, we carried out uniaxial tensile tests on Cu–Au nanowires at various tension rates and temperatures by means of the molecular dynamics approach. The Cu–Au interface was found to be the main site for nucleation of perfect dislocations, Shockley partials, and stacking faults due to the stress concentration and high potential energy arising from the atomic mismatch between shell and core layers. It was observed that an increase in the strain rate from 108 to 1,011 s−1 shortened the time required for the nucleation of dislocations, decreasing the dislocation density. This emphasizes that dislocation nucleation and slip mechanisms are time-dependent. Moreover, it was found that the interaction of Shockley partials can lead to the creation of lock dislocations, such as Hirth, Frank, and Stair-rod dislocations, imposing obstacles for the slip of other dislocations. However, as the tension temperature rose from 300 to 600 K, opposite-sign dislocations removed each other due to thermally activated mechanisms such as dislocation climb and dislocation recovery. Furthermore, the combination of Shockley partial dislocations decreased the stacking fault density, facilitating the plastic deformation of these structures. The yield strength and elastic modulus of the samples increased with the strain rate and substantially decreased as the temperature rose.

Au/Pt Bimetallic Nanowires with Stepped Pt Sites for Enhanced C-C Cleavage in C2+ Alcohol Electro-oxidation Reactions.

Efficient C-C bond cleavage and oxidation of alcohols to CO2 is the key to developing highly efficient alcohol fuel cells for renewable energy applications. In this work, we report the synthesis of core/shell Au/Pt nanowires (NWs) with stepped Pt clusters deposited along the ultrathin (2.3 nm) stepped Au NWs as an active catalyst to effectively oxidize alcohols to CO2. The catalytic oxidation reaction is dependent on the Au/Pt ratios, and the Au1.0/Pt0.2 NWs have the largest percentage (∼75%) of stepped Au/Pt sites and show the highest activity for ethanol electro-oxidation, reaching an unprecedented 196.9 A/mgPt (32.5 A/mgPt+Au). This NW catalyst is also active in catalyzing the oxidation of other primary alcohols, such as methanol, n-propanol, and ethylene glycol. In situ X-ray absorption spectroscopy and infrared spectroscopy are used to characterize the catalyst structure and to identify key reaction intermediates, providing concrete evidence that the synergy between the low-coordinated Pt sites and the stepped Au NWs is essential to catalyze the alcohol oxidation reaction, which is further supported by DFT calculations that the C-C bond cleavage is indeed enhanced on the undercoordinated Pt-Au surface. Our study provides important evidence that a core/shell structure with stepped core/shell sites is essential to enhance electrochemical oxidation of alcohols and will also be central to understanding electro-oxidation reactions and to the future development of highly efficient direct alcohol fuel cells for renewable energy applications.

Interpenetrating Self‐Supporting Networks from Anisotropic Semiconductor Nanoparticles and Noble Metal Nanowires

In this work, a new type of multicomponent nanostructures is introduced by forming interpenetrating networks of two different nanomaterials. In detail, gel networks from semiconductor nanorods are interpenetrated by Au nanowires. Two different types of gelling agents, namely S2− and Yb3+, are employed to trigger the network formation. The structural and electrochemical properties of the resulting materials are discussed. (Photo)electrochemical measurements are performed on the structures to compare the materials in terms of their conductivity as well as their efficiency in converting photonic energy to electrical energy. The new type of CdSe/CdS:Au nanostructure gelled with S2− shows one order of magnitude higher photocurrent than the system gelled with Yb3+. Moreover, the introduction of Au nanowires exhibit a photocurrent which is two orders of magnitudes higher than in samples without Au nanowires.

Chiral Excitation of Exchange Spin Waves Using Gold Nanowire Grating

We propose an experimental method for the unidirectional excitation of spin waves. By structuring Au nanowire arrays within a coplanar waveguide onto a thin yttrium iron garnet (YIG) film, we observe a chiral coupling between the excitation field geometry of the nanowire grating and several well-resolved propagating magnon modes. We report a propagating spin wave spectroscopy study with unprecedented spectral definition, wavelengths down to 130 nm and attenuation lengths well above 100 μm over the 20 GHz frequency band. The proposed experiment paves the way for future non-reciprocal magnonic devices.

In Situ Observation of High Bending Strain Recoverability in Au Nanowires

Metallic nanowires (NW) usually exhibit unique physical, mechanical, and chemical properties compared to their bulk counterparts. Despite extensive research on their mechanical behavior, the atomic-scale deformation mechanisms of metallic nanowires remain incompletely understood. In this study, we investigate the deformation behavior of Au nanowires embedded with a longitudinal twin boundary (TB) under different loading rates using in situ nanomechanical testing integrated with atomistic simulations. The Au nanowires exhibit a recoverable bending strain of up to 27.5% with the presence of TBs. At low loading rates, the recoverable bending is attributed to the motion of stacking faults (SFs) and their interactions with TBs. At higher loading rates, the formation of high-angle grain boundaries and their reversible migration become dominant in Au nanowires. These findings enhance our understanding of the bending behavior of metallic nanowires, which could inspire the design of nanodevices with improved fatigue resistance and a large recoverable strain capacity.

Mechanism of Au nanowire growth by Au evaporation on Si substrates irradiated with Ar ions

This study aims to clarify the mechanism of site-selective Au-nanowire (NW) growth on Si substrates irradiated with Ar ions. Au NWs are grown by Au evaporation at specific regions in the boundary zones between the ion-irradiated and unirradiated areas of Si substrates. The NW growth area are restricted by placing a grid mesh with a certain hole size within the boundary zone to limit the irradiation area. The length and diameter of the NWs can be controlled by controlling the hole size. Cross-sectional microscopic analyses reveal the presence of a thin Si-oxide layer as well as an Au–Si buried layer beneath the NWs. A site-selective Au NW growth model is developed by modifying the already-existence model. By fitting the Au NW length calculated using our model to the experimental data, the surface diffusion length of Au adatoms (λs) is estimated to be approximately 7 μm, close to the radius of the irradiated area Rw (6 μm). This validates our model that assumes that the NWs are grown at the bottom from the Au adatoms migrating onto the substrate. The Au-NW growth mechanism is discussed along with the role of the oxide layer and surface diffusion of Au adatoms.

Tuning of Plasmonic Response in High Aspect-Ratio Au Nanowires through Laser Irradiation: A TEM-EELS Study.

Tuning of Plasmonic Response in High Aspect-Ratio Au Nanowires through Laser Irradiation: A TEM-EELS Study.

Palladium atomic layers coated on ultrafine gold nanowires boost oxygen reduction reaction

Palladium-based nanocatalysts play an important role in catalyzing the cathode oxygen reduction reaction (ORR) for fuel cells working under alkaline conditions, but the performance still needs to be improved to meet the requirements for large-scale applications. Herein, Au@Pd core–shell nanowires have been developed by coating Pd atomic layers on ultrafine gold nanowires and display outstanding electrocatalytic performance towards alkaline ORR. It is found that Pd overlayers with atomic thickness can be coated on 3 nm Au nanowires under CO atmosphere and completely cover the surfaces. The obtained ultrafine Au@Pd nanowires exhibit an electrochemical active area (ECSA) of 68.5 m2/g and a mass activity of 0.91 A/mg (at 0.9 V vs. RHE), which is around 3.1 and 15.2 times higher than that of commercial Pd/C. The activity loss of the ultrafine Au@Pd nanowire after 10,000 cycles of accelerated degradation tests is only ∼20 %, demonstrating its much better stability compared to commercial Pd/C. Further characterizations combined with density functional theory (DFT) calculations demonstrate that the electronic interactions between Pd atomic layers and underlying Au can increase the electronic density of Pd and promote the efficient activation of oxygen, thus leading to the improved ORR performance.

A D-Shaped SPR-Based PCF Sensor with an Extremely High-Amplitude Sensitivity for Measuring the Refractive Index.

In this work, a new D-shaped photonic crystal fibre sensor structure based on surface plasmon resonance (SPR) is purposed for measurement of analyte refractive index (RI). In this design, a silica cylinder is polished into a D-shaped silica material structure with a flattened surface where two Au nanowires are coated. Some air holes are omitted to form the core mode region. With the implementation of gold nanowires and a core region for the exciting SPR effect with variate physical values, analyte RI can be measured with a wavelength coverage from 850 to 1350nm. The numerical simulation shows the maximum wavelength sensitivity of the purposed design achieves 19,600nm/RIU with an RI coverage from 1.37 to 1.42. Moreover, the sensor has a tremendous amplitude sensitivity and the maximum absolute value is about 2300RIU-1. Benefiting from these outstanding performance, the purposed structure can be given priority when it is applied in biomedical detecting and environmental assessment science.

Nanowires-Based Stretchable Strain Sensor for Wearable Applications

Flexible, stretchable strain sensors are needed to measure physiological parameters or joint angles in wearable systems and robotics, respectively. This letter presents the stretchable strain sensor that is directly fabricated on environment-friendly Ecoflux substrate. The sensor uses stretchable serpentine-shaped Au interconnects and Ag nanowires (NWs) as the strain-sensitive active channel. The sensor structure has been evaluated under stretching conditions that provided insights about the material integrity during device operation. The device characteristics show good linearity under low strain range (<40%), average gauge factor of 5.8, cyclic stability for more than 5000 cycles, and response time of 200 ms. Finally, the sensor was placed on human finger, as a proof of concept, and measurements were taken to understand the bending strain during finger movements and potential application in smart glove and robotics.

Selective Electrocatalytic CO2 Reduction into CO Using Au-Coated Dendritic Silica Nanoparticle Arrays

Highly selective electrocatalytic CO2 reduction for CO production has attracted tremendous attention for achieving the forthcoming goals of carbon neutrality and widespread industrial utilization and recycling of carbon. Among various approaches, the structural control of the catalyst is particularly interesting because of the facile control of CO2 reduction conditions, such as reaction media and reaction pathways. Thus far, a wide range of nanostructured catalysts, including Au needle tips, Au nanowires, and Au wrinkles, have been used for the enhancement of the selectivity of CO production. In this study, an electrocatalyst with a hierarchical nanostructure for the highly selective production of CO is reported. This hierarchical structure is fabricated by the deposition of Au via e-beam evaporation on a dendritic fibrous nanosilica (KCC-1) template, which is a spherical silica particle consisting of uniformly distributed center-radial fibers. The conversion efficiency of this catalyst is strongly affected by the thickness of the Au deposited on the KCC-1 template, and the highest CO selectivity of ∼98% (at −0.5 V vs. RHE) is obtained at an optimum Au thickness of 50 nm. According to the CO2 electrocatalytic reduction results obtained from KCC-1 with dendritic fibers and a conventional spherical particle without the fibers under various electrolyte conditions, such selectivity enhancement of Au on the KCC-1 template is attributed to the increase in the local pH near the hierarchical catalyst surface. This work provides potential promising templates that exhibit a unique nanostructure for efficient electrocatalysis.

Strong Ligand Control for Noble Metal Nanostructures.

ConspectusNanosynthesis is the art of creating nanostructures, with on-demand synthesis as the ultimate goal. Noble metal nanoparticles have wide applications, but the available synthetic methods are still limited, often giving nanospheres and symmetrical nanocrystals. The fundamental reason is that the conventional weak ligands are too labile to influence the materials deposition, so the equivalent facets always grow equivalently. Considering that the ligands are the main synthetic handles in colloidal synthesis, our group has been exploring strong ligands for new growth modes, giving a variety of sophisticated nanostructures. The model studies often involve metal deposition on seeds functionalized with a certain strong ligand, so that the uneven distribution of the surface ligands could guide the subsequent deposition.In this Account, we focus on the design principles underlying the new growth modes, summarizing our efforts in this area along with relevant literature works. The basics of ligand control are first revisited. Then, the four major growth modes are summarized as follows: (1) The curvature effects would divert the materials deposition away from the high-curvature tips when the ligands are insufficient. With ligands fully covering the seeds, the sparser ligand packing at the tips would then promote the initial nucleation thereon. (2) The strong ligands may get trapped under the incoming metal layer, thus modulating the interfacial energy of the core-shell interface. The evidence for embedded ligands is discussed, along with examples of Janus nanostructures arising from the synthetic control, including metal-metal, metal-semiconductor, and metal-C60 systems using a variety of ligands. (3) Active surface growth is an unusual mode with divergent growth rates, so that part of the emerging surface is inhibited, and the growth is focused onto a few active sites. With seeds attached to oxide substrates, the selective deposition at the metal-substrate interface produces ultrathin nanowires. The synthesis can be generally applied to grow Au, Ag, Pd, Pt, and hybrid nanowires, with straight, spiral, or helical structures, and even rapid alteration of segments via electrochemical methods. In contrast, active surface growth for colloidal nanoparticles has to be more carefully controlled. The rich growth phenomena are discussed, highlighting the role of strong ligands, the control of deposition rates, the chiral induction, and the evidence for the active sites. (4) An active site with sparse ligands could also be exploited in etching, where the freshly exposed surface would promote further etching. The result is an unusual sharpening etching mode, in contrast to the conventional rounding mode for minimized surface energy.Colloidal nanosynthesis holds great promise for scalable on-demand synthesis, providing the crucial nanomaterials for future explorations. The strong ligands have delivered powerful synthetic controls, which could be further enhanced with in-depth studies on growth mechanisms and synthetic strategies, as well as functions and properties.

3D Plasmonic Nanostructure-Based Polarized ECL Sensor for Exosome Detection in Tumor Microenvironment.

Exosomes of cancer cells play an important role in the proliferation, adhesion, and migration of tumors. Especially, exosomes in the tumor microenvironment can reflect the proliferation of tumors directly, thus serving as ideal referenced markers of the possibility and grade of malignancy in neoplasms. However, the sensitive and accurate detection of exosomes remains challenging. In this work, a novel three-dimensional (3D) plasmonic nanostructure was constructed for exosomal miRNA detection. It combined the advantages of Au nanostar monolayer and Ag nanowire monolayer to provide multiple hot spots. Moreover, Au nanostar monolayer changed the isotropic electrochemiluminescence (ECL) into polarized emission. The Ag nanowire monolayer worked as waveguides for the light direction. As a result, the polarized resolution and intensity of ECL signal were improved. The polarized ECL emission was significantly increased by 47.1 times. This high-resolution polarized ECL sensor was used for detecting exosomal miRNA-146b-5p in the thyroid tumor microenvironment. This sensor showed the linear range from 1 fM to 1 nM with a detection limit of 0.3 fM. The satisfactory results indicated the developed 3D plasmonic nanostructure-based ECL sensor had great potential in biosensing and clinical diagnosis.