Enhancement of second-harmonic generation in a 64° stacked WSe2/WS2heterobilayer with local strain.

Transition metal dichalcogenides (TMDs) are actively studied in various fields of optics and optoelectronics, including nonlinear optics of second-harmonic generation (SHG). By stacking two different TMD materials to form a heterobilyaer, unique optical properties emerge, with stronger SHG at a twist angle of 0° between TMDs and weaker SHG at a twist angle of 60°. In this work, we demonstrate the enhancement of SHG in a heterobilayer consisting of WSe2and WS2monolayers stacked at a twist angle of 64.1°, using a nanoparticle to induce local strain. The interatomic spacing of the heterobilayer is deformed by the nanoparticle, breaking the inversion symmetry, resulting in a substantial increase in the SHG of the heterobilayer at room temperature. The SHG increases depending on the polarization of the pump laser: 15-fold for linear polarization, 9-fold for right-circular polarization, and up to 100-fold for left-circular polarization. In addition, the SHG enhanced in the heterobilayer with local strain satisfies the same chiral selection rule as in the unstrained TMD region, demonstrating that the chiral selection rule of SHG is insensitive to local strain. Our findings will increase the applicability of TMD heterobilayers in nonlinear optoelectronics and valleytronics.

Therapeutic Effect of HDAC5 Binding and Cell Penetrating Peptide for the Treatment of Inflammatory Bowel Disease.

BACKGROUND: Inflammatory bowel disease (IBD) is an incurable disease that negatively influences the quality of life of patients. Current and emerging therapies target proinflammatory cytokines and/or receptors to downregulate proinflammatory responses, but insufficient remission requires other therapeutic agents. Herein, we report that the synthetic anti-inflammatory peptide 15 (SAP15) is capable of cell penetration and anti-inflammatory activity in human macrophages. METHODS: SAP15 was labeled with fluorescence and administered to human leukemia monocytic cells (THP-1) cells for cell penetration analysis. Using biolayer interferometry analysis, the binding affinity of SAP15 with histone deacetylase 5 (HDAC5) was measured. SAP15-treated THP-1 cells were analyzed by protein phosphorylation assay, flow cytometry, and enzyme-linked immunosorbent assay (ELISA). In addition, in vivo analysis of the therapeutic effect on IBD was observed in a dextran sulfate sodium (DSS)-induced model. Samples from SAP15-treated mice were analyzed at both the macroscopic and microscopic levels using ELISA, myeloperoxidase (MPO) assays, and histological evaluations. RESULTS: SAP15 was internalized within the cytosol and nucleus of THP-1 cells and bound to the HDAC5 protein. SAP15-treated macrophages were assessed for protein phosphorylation and showed inhibited phosphorylation of HDAC5 and other immune-related proteins, which led to increased M2-like macrophage markers and decreased M1-like macrophage markers and tumor necrosis factor-α and interleukin-6 cytokine levels. The SAP15 treatment on IBD model showed significant recovery of colon length. Further histological analysis of colon demonstrated the therapeutic effect of SAP15 on mucosal layer. Moreover, proinflammatory cytokine levels and MPO activity from the plasma show that SAP15 is effective in reduced proinflammatory responses. CONCLUSION: These findings suggest that SAP15 is a novel peptide with a novel cell-penetrating peptide with anti-inflammatory property that can be used as a therapeutic agent for IBD and other inflammatory diseases.

Nanograin network memory with reconfigurable percolation paths for synaptic interactions.

The development of memory devices with functions that simultaneously process and store data is required for efficient computation. To achieve this, artificial synaptic devices have been proposed because they can construct hybrid networks with biological neurons and perform neuromorphic computation. However, irreversible aging of these electrical devices causes unavoidable performance degradation. Although several photonic approaches to controlling currents have been suggested, suppression of current levels and switching of analog conductance in a simple photonic manner remain challenging. Here, we demonstrated a nanograin network memory using reconfigurable percolation paths in a single Si nanowire with solid core/porous shell and pure solid core segments. The electrical and photonic control of current percolation paths enabled the analog and reversible adjustment of the persistent current level, exhibiting memory behavior and current suppression in this single nanowire device. In addition, the synaptic behaviors of memory and erasure were demonstrated through potentiation and habituation processes. Photonic habituation was achieved using laser illumination on the porous nanowire shell, with a linear decrease in the postsynaptic current. Furthermore, synaptic elimination was emulated using two adjacent devices interconnected on a single nanowire. Therefore, electrical and photonic reconfiguration of the conductive paths in Si nanograin networks will pave the way for next-generation nanodevice technologies.

High-harmonic generation from a subwavelength dielectric resonator.

Higher-order optical harmonics entered the realm of nanostructured solids being observed recently in optical gratings and metasurfaces with a subwavelength thickness. Structuring materials at the subwavelength scale allows us toresonantly enhance the efficiency of nonlinear processes and reduce the size of high-harmonic sources. We report the observation of up to a seventh harmonic generated from a single subwavelength resonator made of AlGaAs material. This process is enabled by careful engineering of the resonator geometry for supporting an optical mode associated with a quasi-bound state in the continuum in the mid-infrared spectral range at around λ = 3.7 µm pump wavelength. The resonator volume measures ~0.1 λ3. The resonant modes are excited with an azimuthally polarized tightly focused beam. We evaluate the contributions of perturbative and nonperturbative nonlinearities to the harmonic generation process. Our work proves the possibility to miniaturize solid-state sources of high harmonics to the subwavelength volumes.

Enhanced Five-Photon Photoluminescence in Subwavelength AlGaAs Resonators.

Multiphoton processes of absorption photoluminescence have enabled a wide range of applications including three-dimensional microfabrication, data storage, and biological imaging. While the applications of two-photon and three-photon absorption and luminescence have matured considerably, higher-order photoluminescence processes remain more challenging to study due to their lower efficiency, particularly in subwavelength systems. Here, we report the observation of five-photon luminescence from a single subwavelength nanoantenna at room temperature enabled by the Mie resonances. We excite an AlGaAs resonator at around 3.6 µm and observe photoluminescence at around 740 nm. We show that the interplay of the Mie multipolar modes at the subwavelength scale can enhance the efficiency of the five-photon luminescence by at least 4 orders of magnitude, being limited only by sensitivity of our detector. Our work paves the way toward applications of higher-order multiphoton processes at the subwavelength scales enabled by the physics of Mie resonances.

Electrically driven strain-induced deterministic single-photon emitters in a van der Waals heterostructure.

Quantum confinement in transition metal dichalcogenides (TMDCs) enables the realization of deterministic single-photon emitters. The position and polarization control of single photons have been achieved via local strain engineering using nanostructures. However, most existing TMDC-based emitters are operated by optical pumping, while the emission sites in electrically pumped emitters are uncontrolled. Here, we demonstrate electrically driven single-photon emitters located at the positions where strains are induced by atomic force microscope indentation on a van der Waals heterostructure consisting of graphene, hexagonal boron nitride, and tungsten diselenide. The optical, electrical, and mechanical properties induced by the local strain gradient were systematically analyzed. The emission at the indentation sites exhibits photon antibunching behavior with a g(2)(0) value of ~0.3, intensity saturation, and a linearly cross-polarized doublet, at 4 kelvin. This robust spatial control of electrically driven single-photon emitters will pave the way for the practical implementation of integrated quantum light sources.

Ultralow-threshold laser using super-bound states in the continuum.

Wavelength-scale lasers provide promising applications through low power consumption requiring for optical cavities with increased quality factors. Cavity radiative losses can be suppressed strongly in the regime of optical bound states in the continuum; however, a finite size of the resonator limits the performance of bound states in the continuum as cavity modes for active nanophotonic devices. Here, we employ the concept of a supercavity mode created by merging symmetry-protected and accidental bound states in the continuum in the momentum space, and realize an efficient laser based on a finite-size cavity with a small footprint. We trace the evolution of lasing properties before and after the merging point by varying the lattice spacing, and we reveal this laser demonstrates the significantly reduced threshold, substantially increased quality factor, and shrunken far-field images. Our results provide a route for nanolasers with reduced out-of-plane losses in finite-size active nanodevices and improved lasing characteristics.

Recent advances in nanocavities and their applications.

High quality factor and small mode volume in nanocavities enable the demonstration of efficient nanophotonic devices with low power consumption, strong nonlinearity, and high modulation speed, due to the strong light-matter interaction. In this review, we focus on recent state-of-the-art nanocavities and their applications. We introduce single nanocavities including semiconductor nanowires, plasmonic cavities, and nanostructures based on quasi-bound states in the continuum (quasi-BIC), for laser, photovoltaic, and nonlinear applications. In addition, nanocavity arrays with unique feedback mechanisms, including BIC cavities, parity-time symmetry coupled cavities, and photonic topological cavities, are introduced for laser applications. These various cavity designs and underlying physics in single and array nanocavities are useful for the practical implementation of promising nanophotonic devices.

Structured silicon for revealing transient and integrated signal transductions in microbial systems.

Bacterial response to transient physical stress is critical to their homeostasis and survival in the dynamic natural environment. Because of the lack of biophysical tools capable of delivering precise and localized physical perturbations to a bacterial community, the underlying mechanism of microbial signal transduction has remained unexplored. Here, we developed multiscale and structured silicon (Si) materials as nongenetic optical transducers capable of modulating the activities of both single bacterial cells and biofilms at high spatiotemporal resolution. Upon optical stimulation, we capture a previously unidentified form of rapid, photothermal gradient-dependent, intercellular calcium signaling within the biofilm. We also found an unexpected coupling between calcium dynamics and biofilm mechanics, which could be of importance for biofilm resistance. Our results suggest that functional integration of Si materials and bacteria, and associated control of signal transduction, may lead to hybrid living matter toward future synthetic biology and adaptable materials.

Unique Scattering Properties of Silicon Nanowires Embedded with Porous Segments.

The development of advanced imaging tools is important for the investigation of the fundamental properties of nanostructures composed of single or multiple nanomaterials. However, complicated preparation processes and irreversible alterations of the samples to be examined are inevitable in most current imaging techniques. In this work, we developed a simple method based on polarization-resolved light scattering measurements to characterize the structural and optical properties of complex nanomaterials. In particular, we examined a single Si nanowire embedded with porous Si segments, in which the porous Si could not be easily distinguished from solid Si by scanning electron microscopy. The dark-field optical images and polarization-resolved scattering spectra showed unique optical features of porous and solid Si. In particular, the porosity, diameter, and number of porous Si segments in the single Si nanowire were identified from the scattering measurements. In addition, we performed systematic optical simulations based on the effective medium model in individual porous and solid Si nanowires. A good agreement between the simulation and measurement results enabled the estimation of the structural parameters of the nanowires, such as diameter and porosity. We believe that our method will be useful for analyzing the structural and optical properties of nanomaterials prior to using complicated and uneconomical imaging tools.

Photon-Triggered Current Generation in Chemically-Synthesized Silicon Nanowires.

A porous Si segment in a Si nanowire (NW), when exposed to light, generates a current with a high on/off ratio. This unique feature has been recently used to demonstrate photon-triggered NW devices including transistors, logic gates, and photodetection systems. Here, we develop a reliable and simple procedure to fabricate porous Si segments in chemically synthesized Si NWs for photon-triggered current generation. To achieve this, we employ 100 nm-diameter chemical-vapor-deposition grown Si NWs that possess an n-type high doping level and extremely smooth surface. The NW regions uncovered by electron-beam resist become selectively porous through metal-assisted chemical etching, using Ag nanoparticles as a catalyst. The contact electrodes are then fabricated on both ends of such NWs, and the generated current is measured when the laser is focused on the porous Si segment. The current level is changed by controlling the power of the incident laser and bias voltage. The on/off ratio is measured up to 1.5 × 104 at a forward bias of 5 V. In addition, we investigate the porous-length-dependent responsivity of the NW device with the porous Si segment. The responsivity is observed to decrease for porous segment lengths beyond 360 nm. Furthermore, we fabricate nine porous Si segments in a single Si NW and measure the identical photon-triggered current from each porous segment; this single NW device can function as a high-resolution photodetection system. Therefore, our fabrication method to precisely control the position and length of the porous Si segments opens up new possibilities for the practical implementation of programmable logic gates and ultrasensitive photodetectors.

Photon-triggered nanowire transistors.

Photon-triggered electronic circuits have been a long-standing goal of photonics. Recent demonstrations include either all-optical transistors in which photons control other photons or phototransistors with the gate response tuned or enhanced by photons. However, only a few studies report on devices in which electronic currents are optically switched and amplified without an electrical gate. Here we show photon-triggered nanowire (NW) transistors, photon-triggered NW logic gates and a single NW photodetection system. NWs are synthesized with long crystalline silicon (CSi) segments connected by short porous silicon (PSi) segments. In a fabricated device, the electrical contacts on both ends of the NW are connected to a single PSi segment in the middle. Exposing the PSi segment to light triggers a current in the NW with a high on/off ratio of >8 × 106. A device that contains two PSi segments along the NW can be triggered using two independent optical input signals. Using localized pump lasers, we demonstrate photon-triggered logic gates including AND, OR and NAND gates. A photon-triggered NW transistor of diameter 25 nm with a single 100 nm PSi segment requires less than 300 pW of power. Furthermore, we take advantage of the high photosensitivity and fabricate a submicrometre-resolution photodetection system. Photon-triggered transistors offer a new venue towards multifunctional device applications such as programmable logic elements and ultrasensitive photodetectors.

Three-dimensional grating nanowires for enhanced light trapping.

We propose rationally designed 3D grating nanowires for boosting light-matter interactions. Full-vectorial simulations show that grating nanowires sustain high-amplitude waveguide modes and induce a strong optical antenna effect, which leads to an enhancement in nanowire absorption at specific or broadband wavelengths. Analyses of mode profiles and scattering spectra verify that periodic shells convert a normal plane wave into trapped waveguide modes, thus giving rise to scattering dips. A 200 nm diameter crystalline Si nanowire with designed periodic shells yields an enormously large current density of ∼28 mA/cm2 together with an absorption efficiency exceeding unity at infrared wavelengths. The grating nanowires studied herein will provide an extremely efficient absorption platform for photovoltaic devices and color-sensitive photodetectors.

Assessment of C-phycocyanin effect on astrocytes-mediated neuroprotection against oxidative brain injury using 2D and 3D astrocyte tissue model.

Drugs are currently being developed to attenuate oxidative stress as a treatment for brain injuries. C-phycocyanin (C-Pc) is an antioxidant protein of green microalgae known to exert neuroprotective effects against oxidative brain injury. Astrocytes, which compose many portions of the brain, exert various functions to overcome oxidative stress; however, little is known about how C-Pc mediates the antioxidative effects of astrocytes. In this study, we revealed that C-Pc intranasal administration to the middle cerebral artery occlusion (MCAO) rats ensures neuroprotection of ischemic brain by reducing infarct size and improving behavioral deficits. C-Pc also enhanced viability and proliferation but attenuated apoptosis and reactive oxygen species (ROS) of oxidized astrocytes, without cytotoxicity to normal astrocytes and neurons. To elucidate how C-Pc leads astrocytes to enhance neuroprotection and repair of ischemia brain, we firstly developed 3D oxidized astrocyte model. C-Pc had astrocytes upregulate antioxidant enzymes such as SOD and catalase and neurotrophic factors BDNF and NGF, while alleviating inflammatory factors IL-6 and IL-1ß and glial scar. Additionally, C-Pc improved viability of 3D oxidized neurons. In summary, C-Pc was concluded to activate oxidized astrocytes to protect and repair the ischemic brain with the combinatorial effects of improved antioxidative, neurotrophic, and anti-inflammatory mechanisms.

Chitosan nanoparticle/PCL nanofiber composite for wound dressing and drug delivery.

Many investigations of wound dressings equipped with drug delivery systems have recently been conducted. Chitosan is widely used not only as a material for wound dressing by the efficacy of its own, but also as a nanoparticle for drug delivery. In this study, an electrospun polycaprolactone nanofiber composite with chitosan nanoparticles (ChiNP-PCLNF) was fabricated and then evaluated for its drug release and biocompatibility to skin fibroblasts. ChiNP-PCLNF complexes showed no cytotoxicity and nanoparticles adsorbed by van der Waals force were released into aquatic environments and then penetrated into rat primary fibroblasts. Our studies demonstrate the potential for application of ChiNP-PCLNF as a wound dressing system with drug delivery for skin wound healing without side effects.

Development of a complex bone tissue culture system based on cellulose nanowhisker mechanical strain.

In bone tissue engineering, scaffolds have been investigated for their ability to support osteoblast growth and differentiation for recovery of damaged bones. Tunicate cellulose nanowhisker (CNW) film and mechanical strain were assessed for their suitability for osteoblasts. In this study, sulfuric acid hydrolysis extraction of tunicates integuments was conducted to obtain CNWs, which were found to be acceptable for adhering, growing, and differentiating osteoblasts without cytotoxicity. Mechanical stress enhanced osteoblast differentiation, and cell survival rate was recovered at around day 3, although there was a slight increase in cell death at day 1 after stimulation. We also found that intracellular flux of calcium ion was related to increased differentiation of CNWs under mechanical stress. Overall, we demonstrated the suitability of tunicate CNWs as a scaffold for bone tissue engineering and developed a complex system based on CNW for osteoblast growth and differentiation that will be useful for bone substitute fabrication.