An Ultra-broadband Metallic Plasmonic Antenna for Ultrasensitive Molecular Fingerprint Identification.

Near-field enhanced mid-infrared light-matter interactions via metallic plasmonic antennae (PA) have attracted much attention but are inevitably limited by the detuning between their narrow band and the broad applied spectral range. Here, we develop a new low-temperature incubation synthetic method to acquire uniform Ag microparticles (MPs) with numerous hotspots. Their plasmonic band is remarkably extended by the plasmonic coupling of numerous hotspots and covers the entire mid-infrared range (400-4000 cm-1). Hence, the almost complete molecular fingerprint of 4-mercaptobenzonitrile was successfully probed for the first time via resonant surface-enhanced infrared absorption (rSEIRA), and the rSEIRA spectra of different essential amino acids were further detected and exhibit a high spectral identification degree assisted by machine learning. This work changes the inertia perception of "narrow band and large size but small hotspot area" of mid-infrared metallic PA and paves the way for the ultrasensitive mid-infrared optical sensing.

Self-Confined Dewetting Mechanism in Wafer-Scale Patterning of Gold Nanoparticle Arrays with Strong Surface Lattice Resonance for Plasmonic Sensing.

A self-confined solid-state dewetting mechanism is reported that can fundamentally reduce the use of sophisticated nanofabrication techniques, enabling efficient wafer-scale patterning of non-closely packed (ncp) gold nanoparticle arrays. When combined with a soft lithography process, this approach can address the reproducibility challenges associated with colloidal crystal self-assembly, allowing for the batch fabrication of ncp gold arrays with consistent ordering and even optical properties. The resulting dewetted ncp gold nanoparticle arrays exhibit strong surface lattice resonance properties when excited in inhomogeneous environments under normal white-light incidence. With these SLR properties, the sensitive plasmonic sensing of molecular interactions is achieved using a simple transmission setup. This study will advance the development of miniaturized and portable devices.

Rapid controllable synthesis of branched Au superparticles: formation mechanism of toggling the growth mode and their applications in optical broadband absorption.

We develop a tunable, ultrafast (5 seconds), and mass-producible seed-mediated synthesis method to prepare branched Au superparticles consisting of multiple small Au island-like nanoparticles by a wet chemical route. We reveal and confirm the toggling formation mechanism of Au superparticles between the Frank-van der Merwe (FM) growth mode and the Volmer-Weber (VW) growth mode. The key factor of this special structure is the frequent toggling between the FM (layer by layer) growth mode and the VW (island) growth mode induced by 3-aminophenol, which is continuously absorbed on the surface of newborn Au nanoparticles, leading to a relatively high surface energy during the overall synthesis process, thus achieving an island on island growth. Such Au superparticles demonstrate broadband absorption from visible to near-infrared regions due to their multiple plasmonic coupling and hence they have important applications in sensors, photothermal conversion and therapy, etc. We also exhibit the excellent properties of Au superparticles with different morphologies, such as NIR-II photothermal conversion and therapy and SERS detection. The photothermal conversion efficiency under 1064 nm laser irradiation was calculated to be as high as 62.6% and they exhibit robust photothermal therapy efficiency. This work provides insight into the growth mechanism of plasmonic superparticles and develops a broadband absorption material for highly efficient optical applications.

Mass-determining role in the electrophoretic separation of colloidal plasmonic nanoparticle oligomers.

Gel electrophoresis techniques have been commonly applied in sieving plasmonic nanoparticle oligomers, while the intrinsic role in determining their phoresis velocity differences through the gel remains debatable. In this work, we explore the components and yield in each gel band after bundling two rationally designed types of nanoparticles in a system for electrophoretic separation. All results indicate that the mass property of plasmonic oligomers plays an essential role in determining their phoresis velocity divergences during separation. Further theoretical simulations reveal that the grounds for the mass-determining role stemmed from the random inelastic collisions among the oligomers and the gel-network microchannel. Moreover, under the guidance of such a mass-determining role, it is easy to achieve the direct electrophoretic separation of hetero-structured plasmonic dimers with high purity and high yield. This work will not only facilitate the precise nano-engineering of complex plasmonic oligomers with unique optical properties, but also might remove the obstacles toward their industrial manufacture with high purity.

Au Polyhedron Array with Tunable Crystal Facets by PVP-Assisted Thermodynamic Control and Its Sharp Shape As Well As High-Energy Exposed Planes Co-Boosted SERS Activity.

A route is developed for directly growing 2D Au polyhedron arrays with controllable exposed facets of polyhedron by utilizing the substrate-supported 2D Au quasi-spherical nanoparticle arrays as the Au seed arrays, which cannot be realized by traditional lithography. In the reaction system, polyvinyl pyrrolidone (PVP) plays a vital role in guiding the reduced Au atoms and stabilizing the substrate-supported Au seeds. More importantly, by thermodynamic control, PVP as a capping agent can further direct the formation of {111} facets. The key to guarantee the integrity and periodicity of array is a proper reduction of Au ions and low growth rate of crystal. Benefiting from the higher electric field intensity near the sharp vertexes and edges of Au polyhedra and the exposed {110} facets with high energy, the Au polyhedron array with {110} facets encasing polyhedron exhibits good, stable surface enhanced Raman scattering activity toward 4-aminothiophenol among the involved arrays. The proposed fabrication approach tremendously enriches the structural diversity of Au nanoarrays on substrates and greatly overcomes the shortcoming of traditional lithography.

A universal route with fine kinetic control to a family of penta-twinned gold nanocrystals.

Some of the major difficulties hindering the synthesis of different types of colloidal nanocrystals are their complex synthetic methods and the lack of a universal growth mechanism in one system. Herein, we propose a general strategy of kinetically controlled seed-mediated growth to synthesize a family of penta-twinned gold nanocrystals. Specifically, different kinds of penta-twinned nanocrystals (truncated penta-twinned decahedra, truncated bipyramids, bipyramids, truncated bipyramids with tips, star-like penta-twinned nanocrystals, decahedra with concave edges, and decahedra) with tunable sizes and high purity were readily achieved in one system solely by tailoring the deposition kinetics of adatoms on different sites of decahedral seeds. The controllable deposition kinetics can be realized by changing the ratio of reductant/gold precursors (R), which dictates whether horizontal or vertical features along the 5-fold axis direction of Au decahedral seeds are produced. Additionally, the selective growth of a second metal (silver) on penta-twinned gold seeds can be reached through minor modification of R, which opens a new avenue for mechanistic investigation by visualizing the seed localization within the final particles. The present work demonstrates a general paradigm for the kinetic growth of penta-twinned crystals and would be extended to the synthesis of other families of nanocrystals.

Janus Evaporators with Self-Recovering Hydrophobicity for Salt-Rejecting Interfacial Solar Desalination.

The recent advancements in interfacial evaporation of salty water using renewable solar energy provide one of the promising pathways to solve worldwide water scarcity. Pursuing a stable evaporation rate of water has been the central focus of this field, as it is directly related to the throughput, while salt deposition on the evaporator becomes a critical issue. Although Janus-structured evaporators with an upper hydrophobic layer and a bottom hydrophilic layer have been demonstrated as an effective way to suppress the salt precipitation, the hydrophobic upper layer, achieved usually by some special organic groups, suffers from a photochemical oxidation when exposed to oxidative chemicals in water and high-energy light, resulting in a deteriorated surface hydrophobicity. Here, we report our design of an efficient salt-rejecting Janus evaporator by taking advantage of the self-recovering surface hydrophobicity of poly(dimethylsiloxane) (PDMS) against photochemical damages, which ensures a long-term surface hydrophobicity. With its upper layer partially covered with PDMS, the Janus evaporator demonstrates an excellent salt rejection capability and exhibits a stable evaporation rate of 1.38 kg·m-2·h-1 under 1 sun illumination for 400 min of continuous operation, or 90 d of intermittent work. By combining the advantages of high structural integration, long-term salt-rejection, and efficient evaporation, our Janus evaporator holds great promise for the stable production of clean water from seawater.

Integrated Evaporator for Efficient Solar-Driven Interfacial Steam Generation.

Solar-driven interfacial steam generation is a promising technique for clean water production because it can minimize thermal loss by localizing solar-to-heat conversion at the air/liquid interface. Here we report an integrated solar evaporator by partially growing 2D polypyrrole microsheets within a melamine foam through chemical vapor polymerization. These microsheets can induce multiple light reflections within the foam, enable omnidirectional light absorption, provide abundant surfaces to promote heat transfer, and achieve spatially defined hydrophobicity to facilitate vapor escape. Meanwhile, the inherent hydrophilicity of the bottom part of the foam promotes spontaneous upward water transport and suppresses heat loss. The composite foam exhibits an excellent apparent evaporation rate of ∼2 kg/(m2·h) and solar-to-vapor efficiency of ∼91%. The combined advantages of large surface area, high efficiency, low cost, all-weather application, excellent durability, and scalable manufacturing make our integrated design promising for fabricating large-scale solar steam generation systems that are suitable for practical clean water production.

Flexible vanadium-doped Ni2P nanosheet arrays grown on carbon cloth for an efficient hydrogen evolution reaction.

Tuning the electronic structure, morphology, and structure of electrocatalysts is of great significance to achieve a highly active and stable hydrogen evolution reaction (HER). Herein, combining hydrothermal and low temperature phosphidation methods, V-doped Ni2P nanosheet arrays grown on carbon cloth (V-Ni2P NSAs/CC) were successfully prepared for the HER. It is found that the prepared V-Ni2P NSAs/CC exhibits preeminent performance for the HER. Specifically, it only requires an overpotential of 85 mV to achieve a current density of 10 mA cm-2 in 1.0 M KOH solution. Moreover, the V-Ni2P NSAs/CC shows superior electrochemical stability, maintaining its HER performance up to 3000 cyclic voltammetry cycles. This work affords a guiding strategy for the synthesis of a high-performance and stable electrocatalyst for the HER.

Nanosecond-Laser-Based Charge Transfer Plasmon Engineering of Solution-Assembled Nanodimers.

The ability to re-engineer self-assembled functional structures with nanometer accuracy through solution-processing techniques represents a big challenge in nanotechnology. Herein we demonstrate that Ag+-soldered nanodimers with a steric confinement coating of silica can be harnessed to realize an in-solution nanosecond laser reshaping to form interparticle conductive pathway with finely controlled conductance. The high structural purity of the nanodimers, the rigid silica coating, and the uniform (but still adjustable) sub-1-nm interparticle gap together determine the success of the laser reshaping process. This method is applicable to DNA-assembled nanodimers, and thus promises DNA-based programming toward higher structural complexity. The resulting structures exhibit highly tunable charge transfer plasmons at visible and near-infrared frequencies dictated by the fluence of the laser pulses. Our work provides an in-solution, rapid, and nonperturbative route to realize charge transfer plasmonic coupling along prescribed paths defined by self-assembly, conferring great opportunities for functional metamaterials in the context of chemical, biological, and nanophotonic applications. The ability to continuously control a subnm interparticle gap and the nanomeric width of a conductive junction also provides a platform to investigate modern plasmonic theories involving quantum and nonlocal effects.

Mn doped porous cobalt nitride nanowires with high activity for water oxidation under both alkaline and neutral conditions.

We report the successful synthesis of Mn doped CoN nanowires on a carbon fiber cloth substrate (CFC) by a two-step strategy, which can be used as an efficient and stable OER electrocatalyst under both alkaline and neutral conditions. Benefiting from enhanced electronic interaction, high active area and electrical conductivity, the Mn doped CoN nanowires/CFC exhibits enhanced kinetics and improved cycling stability for the OER under both alkaline and neutral conditions. To achieve a current density of 10 mA cm-2, the Mn doped CoN nanowires/CFC requires an overpotential of 265 mV in alkaline solution and 285 mV in neutral solution.

Optical sensing properties of Au nanoparticle/hydrogel composite microbeads using droplet microfluidics.

Uniform Au nanoparticle (NP)/poly (acrylamide-co-acrylic acid) [P(AAm-co-AA)] hydrogel microbeads were successfully prepared using droplet microfluidics technology. The microbeads exhibited a good stimuli-responsive behavior to pH value. Particularly in the pH value ranging from pH 2-pH 9, the composite microbead sizes gradually increased along with the increase of pH value. The homogeneous Au NPs, which were encapsulated in the P(AAm-co-AA) hydrogel microbeads, could transform the volume changes of hydrogel into optical signals by a tested single microbead with a microspectrometre system. The glucose was translated into gluconic acid by glucose oxidase. Thus, the Au NP/P(AAm-co-AA) hydrogel microbeads were used for detecting glucose based on pH effects on the composite microbeads. For this, the single Au NP/P(AAm-co-AA) hydrogel microbead could act as a good pH- or glucose-visualizing sensor.

Surface enhanced Raman scattering properties of dynamically tunable nanogaps between Au nanoparticles self-assembled on hydrogel microspheres controlled by pH.

We developed an interesting route for preparing a poly (acrylamide-co-acrylic acid) (P(AAm-co-AA)) hydrogel microsphere with a coating of Au nanospheres (hydrogel microsphere @ Au nanospheres) through self-assembly based on electrostatic interaction. The fabricated composites could be used as highly sensitive enhanced Raman scattering substrates. The nanogaps between adjacent Au nanospheres were dynamically tuned by volume changes in the hydrogel microspheres in the semiwet state under different pH conditions. At pH 6, the hydrogel microsphere @ Au nanospheres demonstrated highly sensitive SERS with an enhancement factor of 109. The product could detect very low concentrations of analytes up to 10-12M 4-aminothiophenol (4-ATP) molecules. This paper proposes a new method for detecting trace amounts of environmental organic pollutants by dynamically tuning the SERS enhancement in the semiwet testing state.

Effective SERS-active substrates composed of hierarchical micro/nanostructured arrays based on reactive ion etching and colloidal masks.

A facile route has been proposed for the fabrication of morphology-controlled periodic SiO2 hierarchical micro/nanostructured arrays by reactive ion etching (RIE) using monolayer colloidal crystals as masks. By effectively controlling the experimental conditions of RIE, the morphology of a periodic SiO2 hierarchical micro/nanostructured array could be tuned from a dome-shaped one to a circular truncated cone, and finally to a circular cone. After coating a silver thin layer, these periodic micro/nanostructured arrays were used as surface-enhanced Raman scattering (SERS)-active substrates and demonstrated obvious SERS signals of 4-Aminothiophenol (4-ATP). In addition, the circular cone arrays displayed better SERS enhancement than those of the dome-shaped and circular truncated cone arrays due to the rougher surface caused by physical bombardment. After optimization of the circular cone arrays with different periodicities, an array with the periodicity of 350 nm exhibits much stronger SERS enhancement and possesses a low detection limit of 10(-10) M 4-ATP. This offers a practical platform to conveniently prepare SERS-active substrates.

Complete Au@ZnO core-shell nanoparticles with enhanced plasmonic absorption enabling significantly improved photocatalysis.

Nanostructured ZnO exhibits high chemical stability and unique optical properties, representing a promising candidate among photocatalysts in the field of environmental remediation and solar energy conversion. However, ZnO only absorbs the UV light, which accounts for less than 5% of total solar irradiation, significantly limiting its applications. In this article, we report a facile and efficient approach to overcome the poor wettability between ZnO and Au by carefully modulating the surface charge density on Au nanoparticles (NPs), enabling rapid synthesis of Au@ZnO core-shell NPs at room temperature. The resulting Au@ZnO core-shell NPs exhibit a significantly enhanced plasmonic absorption in the visible range due to the Au NP cores. They also show a significantly improved photocatalytic performance in comparison with their single-component counterparts, i.e., the Au NPs and ZnO NPs. Moreover, the high catalytic activity of the as-synthesized Au@ZnO core-shell NPs can be maintained even after many cycles of photocatalytic reaction. Our results shed light on the fact that the Au@ZnO core-shell NPs represent a promising class of candidates for applications in plasmonics, surface-enhanced spectroscopy, light harvest devices, solar energy conversion, and degradation of organic pollutants.

Black Gold: Plasmonic Colloidosomes with Broadband Absorption Self-Assembled from Monodispersed Gold Nanospheres by Using a Reverse Emulsion System.

A facile approach for the fabrication of novel black plasmonic colloidosomes assembled from Au nanospheres is developed by an emulsion-templating strategy. This self-assembly process is based on a new reverse water-in-1-butanol emulsion system, in which the water emulsion droplets can dissolve into 1-butanol (oil) phase at an appropriate rate. These Au colloidosomes possess hexagonal close-packed multilayer shells and show a low reflectivity and intense broadband absorption owing to the strong interparticle plasmonic coupling, which is further investigated by a finite-difference time-domain method. This method is universal and is suitable for self-assembly of different noble-metal nanoparticles into different colloidosomes. These colloidosomes have important applications in photothermal therapy, biosensors, and drug delivery.

Rapid synthesis of monodisperse Au nanospheres through a laser irradiation-induced shape conversion, self-assembly and their electromagnetic coupling SERS enhancement.

We develop a facile and effective strategy to prepare monodispersed Au spherical nanoparticles by two steps. Large-scale monocrystalline Au nanooctahedra with uniform size were synthesized by a polyol-route and subsequently Au nanoparticles were transformed from octahedron to spherical shape in a liquid under ambient atmosphere by non-focused laser irradiation in very short time. High monodispersed, ultra-smooth gold nanospheres can be obtained by simply optimizing the laser fluence and irradiation time. Photothermal melting-evaporation model was employed to get a better understanding of the morphology transformation for the system of nanosecond pulsed-laser excitation. These Au nanoparticles were fabricated into periodic monolayer arrays by self-assembly utilizing their high monodispersity and perfect spherical shape. Importantly, such Au nanospheres arrays demonstrated very good SERS enhancement related to their periodic structure due to existence of many SERS hot spots between neighboring Au nanospheres caused by the electromagnetic coupling in an array. These gold nanospheres and their self-assembled arrays possess distinct physical and chemical properties. It will make them as an excellent and promising candidate for applying in sensing and spectroscopic enhancement, catalysis, energy, and biology.

Physical deposition improved SERS stability of morphology controlled periodic micro/nanostructured arrays based on colloidal templates.

An effective and inexpensive method is developed to fabricate periodic arrays by sacrificial colloidal monolayer template route by chemical deposition and further physical deposition. By a colloidal template induced precursor solution dipping strategy, different periodic arrays of semi-hollow sphere array, inverse opal with monolayer pore arrays and hole arrays are obtained under different conditions. After magnetron sputtering deposition, their morphologies are changed to novel micro/nanostructured arrays of honeycomb-shaped arrays, hollow cavity arrays, and regular network arrays due to multiple direction deposition of sputtering deposition and shadow effect. After coating a gold thin layer, these periodic micro/nanostructured arrays are used as SERS active substrates and demonstrate a very stable SERS performance compared with periodic arrays achieved by direct colloidal template-induced chemical deposition. Additionally, a honeycomb-shaped array displays better SERS enhancement than that of a hollow cavity array or a regular network array. After optimization of honeycomb-shaped arrays with different periodicities, an array with periodicity of 350 nm demonstrates much stronger SERS enhancement and possesses a low detection limit of 10(-11) M R6G. Such stable SERS performance is useful for practical application in portable Raman detecting devices to detect organic molecules.