Grating-Integrated Gold Nanograsses Encapsulated with ZIF-8: A Quantitative and Ultrasensitive Surface-Enhanced Raman Scattering Substrate.

We proposed and demonstrated highly sensitive hybrid surface-enhanced Raman scattering (SERS) substrates, which are grating-integrated gold nanograsses (GIGN) that are tip-selectively encapsulated by ZIF-8 nanospheres (GIGN/tip-ZIF). This unique structure is realized through the tip-selective modification of GIGN by polyvinylpyrrolidone (PVP), and then, the tips of the GIGN were encapsulated by ZIF-8 nanospheres. The ZIF-8 nanospheres can adsorb analyte molecules, resulting in the spatial overlap between the analyte molecules and the "hotspots" on the tips of GIGN.

Transfer-Printing Hydrogel-Based Platform for Moisture-Driven Dynamic Display and Optical Anti-Counterfeiting.

Humidity-responsive materials offer a promising approach to achieving tunable metasurface systems due to their fast and reversible swelling responses to moisture, which enables many important applications, such as real-time humidity sensing, optical switches, dynamic displays, and optical information encryption. However, the humidity-responsive structural coloration generally cannot provide a high spatial resolution and requires a complex patterning process. Here, we present a scalable moisture-driven color-changing Fabry-Pérot (FP)-like cavity composed of a polyvinyl alcohol layer sandwiched between an upper gold nanoparticles assembly and a bottom gold mirror.

Fabricating 3D freestanding metamaterials on elastic substrates the shadow metal-sputtering and plastic deformation.

3D metamaterials have gained considerable attention owing to their extraordinary optical properties and promising applications beyond natural materials. However, fabricating 3D metamaterials with high resolution and reliable controllability is still a significant challenge. Here, a novel approach to manufacturing various 3D freestanding plasmonic nanostructures on elastic substrates is demonstrated using the shadow metal-sputtering and plastic deformations.

Tunable Fabry-Pérot Resonator with Dynamic Structural Color: A Visual and Ultrasensitive Hydrogen Sensor.

Hydrogen detection is crucial for the forthcoming hydrogen economy. Here, we present a visual, ultrasensitive, optical hydrogen sensor based on a tunable Fabry-Pérot (FP) resonator, which can fully release the volume expansion of palladium during hydrogenation and transfer this volume expansion into an optical signal. The FP resonator consists of a suspended polymethylmethacrylate/palladium (PMMA/Pd) bilayer on a gold (Au) square-hole array.

A flexible optical gas pressure sensor as the signal readout for point-of-care immunoassay.

Gas generation-based immunoassay is considered an attractive biosensing platform for the detection of biomarkers by incorporating the target recognition event with a catalyzed gas-generating reaction. Herein, an optical gas pressure sensor based on a silver/polydimethylsiloxane (Ag/PDMS) bilayer system was designed as a signal transducer to read the concentration of the detection target alpha-fetoprotein (AFP) quantitatively. In this proposed pressure-based assay, silicon dioxide (SiO) nanospheres decorated with platinum (Pt) nanoparticles were coupled to detect antibodies by covalent linkage, and the captured antibodies were conjugated with magnetic beads streptavidin-biotin interaction, simultaneously.

Wide-Field Visualization of Palladium Hydrogenation.

Visualizing hydrogenation processes in palladium (Pd) in real-time is important to various hydrogen-involved applications. However, observing hydrogen diffusion of Pd was limited by its small permittivity variation, and the kinetics of lateral diffusion of hydrogen in Pd film was not reported. Here, we proposed an optical microscopy-based visualization of Pd hydrogenation from the diffusion surface to the interior by introducing a fast-response mechanical platform that transforms the hydrogen diffusion into self-organized ordered wrinkles with sharp optical contrast.

Suspended Palladium/Polymer Bilayer for High-Contrast and Fast Hydrogen Sensors.

Hydrogen sensing is extremely essential for hydrogen-related applications due to the explosibility of hydrogen gas (H). Here, we first present a high-contrast and fast optical hydrogen sensor, which is a partially suspended Pd/PMMA bilayer on a PDMS substrate with a microgroove array on the surface. The suspended structure reduces constraints from the substrate on the Pd film, leading to a large wrinkling amplitude and fast response rate during hydrogenation.

Polarization-insensitive graphene photodetectors enhanced by a broadband metamaterial absorber.

Graphene, combined with plasmonic nanostructures, shows great promise for achieving desirable photodetection properties and functionalities. Here, we theoretically proposed and experimentally demonstrated a graphene photodetector based on the metamaterial absorber in the visible and near-infrared wavebands. The experimental results show that the metamaterial-based graphene photodetector (MGPD) has achieved up to 3751% of photocurrent enhancement relative to an antennasless graphene device at zero external bias.

Highly Sensitive and Durable Sea-Urchin-Shaped Silver Nanoparticles Strain Sensors for Human-Activity Monitoring.

High-performance strain sensors, composed of various artificial sensing materials on/in stretchable substrates, show great promise for applications in flexible electronic devices. Here, we demonstrated a highly sensitive and durable strain sensor consisting of a ribbon of close-packed sea-urchin-shaped silver nanoparticles (SUSNs) sandwiched between two layers of poly(dimethylsiloxane) (PDMS). Each of SUSNs possesses high-density and spherically distributed sharp spines over the body, which promotes electron transduction and further improves signal detection.

High-Contrast Dynamic Reflecting System Based on Pneumatic Micro/Nanoscale Surface Morphing.

Cephalopods offer a fascinating dynamic reflecting system to create desired colors and patterns through contracting and releasing their soft skins in response to environmental stimuli. Inspired by this natural display strategy, we designed a novel dynamic reflecting system based on pneumatic micro/nanoscale surface morphing. This system consists of a thin metal skin/elastomer bilayer modulated by a microfluidic-based gas injector.

Surface-enhanced Raman scattering induced by the coupling of the guided mode with localized surface plasmon resonances.

Surface-enhanced Raman spectroscopy (SERS) is considered to be a powerful analysis tool for the detection of molecules due to its ultra-high sensitivity and non-destructive nature. Here, we introduce a new type of hybrid SERS substrate, where gold nanorods are assembled on a structured support containing a top dielectric grating, dielectric spacer and gold mirror. Compared with the conventional metal nanoparticle assemblies on a flat support, our hybrid substrate shows an approximately 30-fold enhancement in the SERS signal.

Flexible plasmonic modulators induced by the thermomechanical effect.

Reconfigurable plasmon-based flexible devices, composed of artificial plasmonic nanostructures on stretchable substrates, show great promise for dynamic functionalities such as tunability, switching and modulation of electromagnetic waves. Here, we theoretically proposed and experimentally demonstrated a simple and efficient flexible plasmonic modulator based on an array of gold nanostructures on a poly(dimethylsiloxane) (PDMS) substrate. Arising from the current-induced local Joule heat, the local expansion of the PDMS substrate widens the gap distances between the neighboring gold wires, which results in a spectral shift of the plasmon resonance.

Layer-by-Layer Assembly of Three-Dimensional Optical Functional Nanostructures.

Nanotransfer printing (nTP) technology can generate highly functional three-dimensional (3D) nanostructures in a low-cost and high-throughput fashion. Nevertheless, the fabrication yield and quality of the transferred nanostructures are often limited by the merging of the surface patterns of replica stamps during transfer printing. Here, an nTP technology was developed to fabricate large-area and crack-free 3D multilayer nanostructures.

Pd films on soft substrates: a visual, high-contrast and low-cost optical hydrogen sensor.

For the rapid development of the hydrogen economy, a reliable and low-cost hydrogen sensor appears to be extremely important. Here, we first show that a palladium film deposited on polydimethylsiloxane (PDMS) can obtain an exceedingly high-reflectance contrast of 25.78 over the entire visible band upon exposure to 4 vol% hydrogen gas (H) mixed with nitrogen gas.

Metal-Assisted Transfer Strategy for Construction of 2D and 3D Nanostructures on an Elastic Substrate.

Compared with conventional rigid devices, the elastic substrates integrated with functional components offer various advantages, such as flexibility, dynamic tunability, and biocompatibility. However, the reliable formations of 2D nanoparticles, nanogaps, and 3D nanostructures on elastic substrates are still challenging. The conventional transfer method plays an important role in the fabrication of microstructures on elastic substrates; however, it could not fabricate structures with feature size less than a few micrometers.

Low-loss integrated electrical surface plasmon source with ultra-smooth metal film fabricated by polymethyl methacrylate 'bond and peel' method.

External light sources are mostly employed to functionalize the plasmonic components, resulting in a bulky footprint. Electrically driven integrated plasmonic devices, combining ultra-compact critical feature sizes with extremely high transmission speeds and low power consumption, can link plasmonics with the present-day electronic world. In an effort to achieve this prospect, suppressing the losses in the plasmonic devices becomes a pressing issue.

White-light emission from a single heavy atom-free molecule with room temperature phosphorescence, mechanochromism and thermochromism.

Two heavy atom-free luminophores (SHBt and SDBt) with simple molecular structures have been synthesized Suzuki coupling reactions in which both display white-light emission with prompt fluorescence and room temperature phosphorescence (RTP) in the solid state. The impressive RTP of the luminophores is produced by a synergistic effect of the strong intermolecular hydrogen bonding in addition to the spin-orbit coupling of the sulfonyl oxygen atoms and the moderate singlet-triplet energy gaps (Δ). These factors facilitate the intersystem crossing (ISC) process to generate triplet excitons in which the molecular conformations become immobilized to effectively suppress radiationless decay.

Mechanically tunable sub-10 nm metal gap by stretching PDMS substrate.

Manipulating light in sub-10 nm or subnanometer metal nanogaps is crucial to study the strong interaction between electromagnetic waves and matters. However, the fabrication of metallic nanogaps with precisely controlled size and high-throughput still remains a challenge. Here, we developed an approach to actively control the gap distance between adjacent metal nanoparticles from 140 nm to sub-10 nm or even 0 nm via mechanical stretching process.

Slanted gold mushroom array: a switchable bi/tridirectional surface plasmon polariton splitter.

Surface plasmon polaritons (SPPs) show great promise in providing an ultracompact platform for integrated photonic circuits. However, challenges remain in easily and efficiently coupling light into and subsequently routing SPPs. Here, we theoretically propose and experimentally demonstrate a switchable bi/tridirectional beam splitter which can simultaneously perform both tasks.

Achieving very bright mechanoluminescence from purely organic luminophores with aggregation-induced emission by crystal design.

Although bright organic mechanoluminescence (ML) has been observed for a few luminophores with aggregation-induced emission (AIE), details of the positive effect of AIE on ML performance remain unclear and a feasible design principle for AIE-ML compounds has not yet been presented. Herein, an effective strategy for the molecular design of efficient AIE-ML materials is demonstrated, based on tetraphenylethene (TPE) building blocks with formyl substituents, which yield non-centrosymmetric crystal structures with prominent piezoelectric properties for molecular excitation combined with AIE features for intense emission. Following this approach, three AIE-active compounds have been developed and are found to show unique ML characteristics.

Highly sensitive and uniform surface-enhanced Raman spectroscopy from grating-integrated plasmonic nanograss.

Surface-enhanced Raman scattering (SERS) spectroscopy has found a wide range of applications in biomedicine, food safety and environmental monitoring. However, to date, it is difficult for most SERS substrates to provide an extremely sensitive and highly uniform Raman response simultaneously. Here, we developed a sensitive and uniform SERS sensing strategy based on grating-integrated gold nanograsses (GIGNs), which can amplify the SERS signal up to 10-fold compared to the nanograss without grating (namely on the flat substrate) experimentally.

Nonreciprocal spin wave elementary excitation in dislocated dimerized Heisenberg chains.

A mechanism for realizing nonreciprocal elementary excitation of spin wave (SW) is proposed. We study a reference model which describes a magnonic crystal (MC) formed by two Heisenberg chains with a lateral displacement (dislocation) and a longitudinal spacer, and derive a criterion to judge whether the elementary excitation spectra are reciprocal in this ferromagnetic lattice. An analytical method based on the spin precession equation is used to solve the elementary excitation spectra.

Achieving remarkable mechanochromism and white-light emission with thermally activated delayed fluorescence through the molecular heredity principle.

Achieving high contrast mechanochromism (Δ > 100 nm) and white-light emission under mild conditions from a single compound with a simple structure is a great challenge. Herein, we report a novel dual-emissive compound, namely SCP, with an asymmetric molecular structure that fully inherits the photophysical properties of the parent molecules SC and SP. SCP shows high contrast, linearly tunable mechanochromism and bright white-light emission arising from a combination of traditional fluorescence and thermally activated delayed fluorescence (TADF).

Double-layered metal grating for high-performance refractive index sensing.

The detection of minuscule changes in the local refractive index by localized surface plasmon resonances (LSPRs), carried by metal nanostructures, has been used successfully in applications such as real-time and label-free detection of molecular binding events. However, localized plasmons demonstrate 1-2 orders of magnitude lower figure of merit (FOM) compared with their propagating counterparts. Here, we propose and experimentally demonstrate a high-performance refractive index sensor based on a structure of double-layered metal grating (DMG) with an FOM and FOM* reaching 38 and 40 respectively under normal incidence.

Very bright mechanoluminescence and remarkable mechanochromism using a tetraphenylethene derivative with aggregation-induced emission.

Organic materials exhibiting mechanoluminescence (ML) are promising for usage in displays, lighting and sensing. However, the mechanism for ML generation remains unclear, and the light-emitting performance of organic ML materials in the solid state has been severely limited by an aggregation-caused quenching (ACQ) effect. Herein, we present two strongly photoluminescent polymorphs (, C and C) with distinctly different ML activities based on a tetraphenylethene derivative PTA.