Net-1,2-Hydrogen Atom Transfer of Amidyl Radicals: Toward the Synthesis of 1,2-Diamine Derivatives.

Hydrogen atom transfer (HAT) processes are among the most useful approaches for the selective construction of C(sp3)-C(sp3) bonds. 1,5-HAT with heteroatom-centered radicals (O•, N•) have been well established and are favored relative to other 1,n-HAT processes. In comparison, net 1,2-HAT processes have been observed infrequently. Herein, the first amidyl radicalls are reported that preferentially undergo a net 1,2-HAT over 1,5-HAT. Beginning with single electron transfer from 2-azaallyl anions to N-alkyl N-aryloxy amides, the latter generate amidyl radicals. The amidyl radical undergoes a net-1,2-HAT to generate a C-centered radical that participates in an intermolecular radical-radical coupling with the 2-azaallyl radical to generate 1,2-diamine derivatives. Mechanistic and EPR experiments point to radical intermediates. Density functional theory calculations provide support for a base-assisted, stepwise-1,2-HAT process. It is proposed that the generation of amidyl radicals under basic conditions can be greatly expanded to access α-amino C-centered radicals that will serve as valuable synthetic intermediates.

Synthesis and antitumor activity of novel hybrid compounds between 1,4-benzodioxane and imidazolium salts.

A series of novel hybrid compounds between 1,4-benzodioxane and imidazolium salts was designed and prepared. The compounds were evaluated in vitro against a panel of human tumor cell lines (K562, SMMC-7721, and A-549). The structure-activity relationship results demonstrated that the 2-methyl-benzimidazole or 5,6-dimethyl-benzimidazole ring and substitution of the imidazolyl-3-position with a 4-phenylphenacyl substituent were critical for promoting cytotoxic activity. Particularly, compound 25 was found to be the most potent compound with IC50 values of 1.06-8.31 µM against the three human tumor cell lines and exhibited higher selectivity to K562 and SMMC-7721 cells with IC50 values 4.5- and 4.7-fold lower than cisplatin. Moreover, compound 25 inhibited cell proliferation by inducing the G0/G1 cell cycle arrest and apoptosis in SMMC-7721 cells.

Metal-Free Synthesis of Phenol-Aryl Selenides via Dehydrogenative C-Se Coupling of Aryl Selenoxides with Phenols.

Herein, we disclose the synthesis of diaryl selenides through an unexpected C-Se coupling between aryl benzyl selenoxides and phenols. The synthetic significance of the method is that it provides a mild, rapid, and metal-free access to organoselenides in high yields with excellent functional group tolerance. This coupling of aryl benzyl selenoxides reveals a completely new reaction possibility compared with aryl sulfoxides. We also probed the reaction mechanism of this unexpected transformation through experimental studies and revealed a special Se(IV)-Se(III)-Se(II) reaction pathway.

Bio-inspired Flexible Lateral Line Sensor Based on P(VDF-TrFE)/BTO Nanofiber Mat for Hydrodynamic Perception.

Fish and some amphibians can perform a variety of behaviors in confined and harsh environments by employing an extraordinary mechanosensory organ, the lateral line system (LLS). Inspired by the form-function of the LLS, a hydrodynamic artificial velocity sensor (HAVS) was presented in this paper. The sensors featured a polarized poly (vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)]/barium titanate (BTO) electrospinning nanofiber mat as the sensing layer, a polyimide (PI) film with arrays of circular cavities as the substrate, and a poly(methyl methacrylate) (PMMA) pillar as the cilium. The P(VDF-TrFE)/BTO electrospinning nanofiber mat demonstrated enhanced crystallinity and piezoelectricity compared with the pure P(VDF-TrFE) nanofiber mat. A dipole source was employed to characterize the sensing performance of the fabricated HAVS. The HAVS achieved a velocity detection limit of 0.23 mm/s, superior to the conventional nanofiber mat-based flow sensor. In addition, directivity was feasible for the HAVS, which was in accordance with the simulation results. The proposed bio-inspired flexible lateral line sensor with hydrodynamic perception ability shows promising applications in underwater robotics for real-time flow analysis.

Development of a Flexible Artificial Lateral Line Canal System for Hydrodynamic Pressure Detection.

Surface mounted 'smart skin' can enhance the situational and environmental awareness of marine vehicles, which requires flexible, reliable, and light-weight hydrodynamic pressure sensors. Inspired by the lateral line canal system in fish, we developed an artificial lateral line (ALL) canal system by integrating cantilevered flow-sensing elements in a polydimethylsiloxane (PDMS) canal. Polypropylene and polyvinylidene fluoride (PVDF) layers were laminated together to form the cantilevered flow-sensing elements. Both the ALL canal system and its superficial counterpart were characterized using a dipole vibration source. Experimental results showed that the peak frequencies of both the canal and superficial sensors were approximately 110 Hz, which was estimated to be the resonance frequency of the cantilevered flow-sensing element. The proposed ALL canal system demonstrated high-pass filtering capabilities to attenuate low-frequency stimulus and a pressure gradient detection limit of approximately 11 Pa/m at a frequency of 115 ± 1 Hz. Because of its structural flexibility and noise immunity, the proposed ALL canal system shows significant potential for underwater robotics applications.

Fabrication of All-SiC Fiber-Optic Pressure Sensors for High-Temperature Applications.

Single-crystal silicon carbide (SiC)-based pressure sensors can be used in harsh environments, as they exhibit stable mechanical and electrical properties at elevated temperatures. A fiber-optic pressure sensor with an all-SiC sensor head was fabricated and is herein proposed. SiC sensor diaphragms were fabricated via an ultrasonic vibration mill-grinding (UVMG) method, which resulted in a small grinding force and low surface roughness. The sensor head was formed by hermetically bonding two layers of SiC using a nickel diffusion bonding method. The pressure sensor illustrated a good linearity in the range of 0.1-0.9 MPa, with a resolution of 0.27% F.S. (full scale) at room temperature.

[Optical Properties of Ag-Al Nanosphere Heterodimer].

Metal nanostructure material has attracted great attention due to its surface plasmon resonance. The optical properties of heterodimer metallic nanostructure materials are different compared with that of homogeneous nanostructure materials because their symmetry structure is broken. The symmetry of the original structures will be changed, and the interaction between the two particles will produce Fano resonance. The Fano resonances are the result of the double or more surface plasmon resonances coupling, and be controlled by properly controlling the nanostructures. The electric field enhancement and the radiation characteristics of the nanostructure are further optimized for the Fano resonance controlled. Aluminum nanostructure materials have become the best choice of the surface plasmon resonance in the UV region, because gold, silver and other noble metals have inter-band transition effects. In this work, we study the local field and absorption spectra of heterodimer composed of a silver nanosphere and an aluminum nanosphere by the Finite-Difference Time-Domain (FDTD) theory. Firstly, the effects of the incident polarization, the geometric like, nanospheres separation, nanosphere radius and physical dielectric media on the optical response of silver-aluminum nanospheres heterodimer are analyzed. Secondly, the near field distributions of heterodimer are given in-depth discussion. Due to the destruction of the symmetry of dimer material, heterodimeric optical character is significantly different from homodimer. Fano resonances are produced in UV and visible light in the heterodimer respectively when silver-aluminum nanospheres heterodimer is illuminated by the Y-polarized light. More favorable Fano resonance effects can be obtained by regulating the spacing and size of heterodimer in the given dielectric environment which is also an effect factor certainly. Finally, the absorption of the heterodimer contributed from each nanosphere structure is also analyzed. In this way, the result which is a general and complete description of the optical properties of silver-aluminum nanospheres heterodimer nanostructure in the paper, leads to the suppression and enhancement of the surface plasmon resonance in different frequency bands and may be valuable for the design and development of plasmonic devices and optical tools in UV-visible light and could serve as the basis of the future experimental analysis of surface enhanced spectroscopy, molecular detection and biosensor etc.

A Highly Sensitive Deep-Sea Hydrodynamic Pressure Sensor Inspired by Fish Lateral Line.

Hydrodynamic pressure sensors offer an auxiliary approach for ocean exploration by unmanned underwater vehicles (UUVs). However, existing hydrodynamic pressure sensors often lack the ability to monitor subtle hydrodynamic stimuli in deep-sea environments. In this study, we present the development of a deep-sea hydrodynamic pressure sensor (DSHPS) capable of operating over a wide range of water depths while maintaining exceptional hydrodynamic sensing performance. The DSHPS device was systematically optimized by considering factors such as piezoelectric polyvinylidene fluoride-trifluoroethylene/barium titanate [P(VDF-TrFE)/BTO] nanofibers, electrode configurations, sensing element dimensions, integrated circuits, and packaging strategies. The optimized DSHPS exhibited a remarkable pressure gradient response, achieving a minimum pressure difference detection capability of approximately 0.11 Pa. Additionally, the DSHPS demonstrated outstanding performance in the spatial positioning of dipole sources, which was elucidated through theoretical charge modeling and fluid-structure interaction (FSI) simulations. Furthermore, the integration of a high Young's modulus packaging strategy inspired by fish skull morphology ensured reliable sensing capabilities of the DSHPS even at depths of 1000 m in the deep sea. The DSHPS also exhibited consistent and reproducible positioning performance for subtle hydrodynamic stimulus sources across this wide range of water depths. We envision that the development of the DSHPS not only enhances our understanding of the evolutionary aspects of deep-sea canal lateral lines but also paves the way for the advancement of artificial hydrodynamic pressure sensors.

Efficient construction of functionalized pyrroloindolines through cascade radical cyclization/intermolecular coupling.

Pyrroloindolines are important structural units in nature and the pharmaceutical industry, however, most approaches to such structures involve transition-metal or photoredox catalysts. Herein, we describe the first tandem SET/radical cyclization/intermolecular coupling between 2-azaallyl anions and indole acetamides. This method enables the transition-metal-free synthesis of C3a-substituted pyrroloindolines under mild and convenient conditions. The synthetic utility of this transformation is demonstrated by the construction of an array of C3a-methylamine pyrroloindolines with good functional group tolerance and yields. Gram-scale sequential one-pot synthesis and hydrolysis reactions demonstrate the potential synthetic utility and scalability of this approach.

Flexible calorimetric flow sensor with unprecedented sensitivity and directional resolution for multiple flight parameter detection.

The accurate perception of multiple flight parameters, such as the angle of attack, angle of sideslip, and airflow velocity, is essential for the flight control of micro air vehicles, which conventionally rely on arrays of pressure or airflow velocity sensors. Here, we present the estimation of multiple flight parameters using a single flexible calorimetric flow sensor featuring a sophisticated structural design with a suspended array of highly sensitive vanadium oxide thermistors. The proposed sensor achieves an unprecedented velocity resolution of 0.11 mm·s-1 and angular resolution of 0.1°. By attaching the sensor to a wing model, the angles of attack and slip were estimated simultaneously. The triaxial flight velocities and wing vibrations can also be estimated by sensing the relative airflow velocity due to its high sensitivity and fast response. Overall, the proposed sensor has many promising applications in weak airflow sensing and flight control of micro air vehicles.

Preparation of biosilica structures from frustules of diatoms and their applications: current state and perspectives.

Frustules, the silica shells of diatoms, have unique porous architectures with good mechanical strength. In recent years, biologists have learned more about the mechanism of biosilica shells formation; meanwhile, physicists have revealed their optical and microfluidic properties, and chemists have identified ways to modify them into various materials while maintaining their hierarchical structures. These efforts have provided more opportunities to use biosilica structures in microsystems and other commercial products. This review focuses on the preparation of biosilica structures and their applications, especially in the development of microdevices. We discuss existing methods of extracting biosilica from diatomite and diatoms, introduce methods of separating biosilica structures by shape and sizes, and summarize recent studies on diatom-based devices used for biosensing, drug delivery, and energy applications. In addition, we introduce some new findings on diatoms, such as the elastic deformable characteristics of biosilica structures, and offer perspectives on planting diatom biosilica in microsystems.

Artificial Whisker Sensor with Undulated Morphology and Self-Spread Piezoresistors for Diverse Flow Analyses.

Harbor seal whiskers possess an undulated surface morphology that can effectively modify the vortex street behind the whiskers and suppress vortex-induced vibrations (VIVs). In this study, we propose a novel piezoresistive flow sensor that mimics the function of seal whiskers. The sensor consists of a bionic whisker with an undulated morphology and integrated out-of-plane piezoresistors. The piezoresistors are formed using a novel directional liquid spreading method to deliver a conductive nanocomposite ink into four Ω-shaped microchannels. Steady flow experiments indicate that the undulated morphology of the artificial whisker significantly reduces the drag forces and VIVs of the whisker at an angle of attack of 0°. Moreover, the whisker sensor can measure the oscillatory flow, which reaches a threshold detection limit of 8 mm/s. In addition, we demonstrate the function of the artificial whisker sensor to distinguish various wakes induced by upstream cylinders. Therefore, the facile fabrication and preliminary experiments of the artificial whisker sensor demonstrate its potential application in diverse flow analyses.

Bionic Aerogel with a Lotus Leaf-like Structure for Efficient Oil-Water Separation and Electromagnetic Interference Shielding.

Increasing pollution from industrial wastewater containing oils or organic solvents poses a serious threat to both the environment and human health. Compared to complex chemical modifications, bionic aerogels with intrinsic hydrophobic properties exhibit better durability and are considered as ideal adsorbents for oil-water separation. However, the construction of biomimetic three-dimensional (3D) structures by simple methods is still a great challenge. Here, we prepared biomimetic superhydrophobic aerogels with lotus leaf-like structures by growing carbon coatings on Al2O3 nanorod-carbon nanotube hybrid backbones. Thanks to its multicomponent synergy and unique structure, this fascinating aerogel can be directly obtained through a simple conventional sol-gel and carbonization process. The aerogels exhibit excellent oil-water separation (22 g·g-1), recyclability (over 10 cycles) and dye adsorption properties (186.2 mg·g-1 for methylene blue). In addition, benefiting from the conductive porous structure, the aerogels also demonstrate outstanding electromagnetic interference (EMI) shielding capabilities (~40 dB in X-band). This work presents fresh insights for the preparation of multifunctional biomimetic aerogels.

Ultralight elastic Al2O3 nanorod-graphene aerogel for pressure sensing and thermal superinsulation.

Novel nanorod aerogels have gained tremendous attention owing to their unique structure. However, the intrinsic brittleness of ceramics still severely limits their further functionalization and application. Here, based on the self-assembly between one-dimensional (1D) Al2O3 nanorods and two-dimensional (2D) graphene sheets, lamellar binary Al2O3 nanorod-graphene aerogels (ANGAs) were prepared by the bidirectional freeze-drying technique. Thanks to the synergistic effect of rigid Al2O3 nanorods and high specific extinction coefficient elastic graphene, the ANGAs not only exhibit robust structure and variable resistance under pressure, but also possess superior thermal insulation properties compared to pure Al2O3 nanorod aerogels. Therefore, a series of fascinating features such as ultra-low density (3.13-8.26 mg cm-3), enhanced compressive strength (6 times higher than graphene aerogel), excellent pressure sensing durability (500 cycles at 40% strain) and ultra-low thermal conductivity (0.0196 W m-1 K-1 at 25 °C and 0.0702 W m-1 K-1 at 1000 °C) are integrated in ANGAs. The present work provides fresh insight into the fabrication of ultralight thermal superinsulating aerogels and the functionalization of ceramic aerogels.

Ultra-Sensitive and Wide Sensing-Range Flexible Pressure Sensors Based on the Carbon Nanotube Film/Stress-Induced Square Frustum Structure.

Flexible pressure sensors have attracted much attention due to their significant potentials in E-skin, artificial intelligence, and medical health monitoring. However, it still remains challenging to achieve high sensitivity and wide sensing range simultaneously, which greatly limit practical applications for flexible sensors. Inspired by the surface stress-induced structure of mimosa, we propose a novel flexible sensor based on the carbon nanotube paper film (CNTF) and stress-induced square frustum structure (SSFS) and demonstrated their excellent sensing performances. Based on interdigital electrodes and uniform CNTF consisting of fibers with large specific surface area, rich conductive paths are formed for enhanced resistance variation. Besides, both experiments and modeling are conducted to verify the synergistic effect of substrates with diverse stiffnesses and SSFS. The SSFS of polydimethylsiloxane transfer small pressure to the CNTF, resulting in sensitive responses with a broad resistance variation. The sensor achieves an ultrahigh sensitivity (2027.5 kPa-1) and a wide pressure range (0.0003-200 kPa). Therefore, it can not only detect human signals such as pulse, vocal cord vibration, wrist flexion, and foot pressure but also be integrated onto car tires to monitor vehicle statuses. These fascinating features endow the sensors with great potentials for future health monitoring, human-computer interaction, and virtual reality.

Ultralight Ceramic Fiber Aerogel for High-Temperature Thermal Superinsulation.

Emerging fiber aerogels with excellent mechanical properties are considered as promising thermal insulation materials. However, their applications in extreme environments are hindered by unsatisfactory high-temperature thermal insulation properties resulting from severely increased radiative heat transfer. Here, numerical simulations are innovatively employed for structural design of fiber aerogels, demonstrating that adding SiC opacifiers to directionally arranged ZrO2 fiber aerogels (SZFAs) can substantially reduce high-temperature thermal conductivity. As expected, SZFAs obtained by directional freeze-drying technique demonstrate far superior high-temperature thermal insulation performance over existing ZrO2-based fiber aerogels, with a thermal conductivity of only 0.0663 W·m-1·K-1 at 1000 °C. Furthermore, SZFAs also exhibit excellent comprehensive properties, including ultralow density (6.24-37.25 mg·cm-3), superior elasticity (500 compression cycles at 60% strain) and outstanding heat resistance (up to 1200 °C). The birth of SZFAs provides theoretical guidance and simple construction methods for the fabrication of fiber aerogels with excellent high-temperature thermal insulation properties used for extreme conditions.

Nanofiber embedded bioinspired strong wet friction surface.

Robust and reversible wet attachments are important for medical engineering and wearable electronics. Although ultrastrong capillarity from interfacial nano-thick liquid bridges creates tree frog's strong wet friction, its unstable nano-liquid characteristic challenges further wet friction enhancement. Here, unique hierarchical micro-nano fibrous pillars have been discovered on Chinese bush crickets exhibiting a robust wet friction ~3.8 times higher than tree frog's bulk pillar. By introducing a nano-fibrous pillar array covered with thin films (NFPF), the pillar's separation position switches from the rear to front side compared with bulk pillars, indicating the interfacial contact stress shifting from compressing to stretching. This largely decreases the interfacial separation stress to form more stable and larger nano-liquid bridges. The NFPF array with self-splitting of interfacial liquid and contact stress further guards such interfacial stress shifting to ensure a ~1.9 times friction enhancement. Last, the theories are established, and the applications on wearable electronics are validated.

Microfabrication of functional polyimide films and microstructures for flexible MEMS applications.

Polyimides are widely used in the MEMS and flexible electronics fields due to their combined physicochemical properties, including high thermal stability, mechanical strength, and chemical resistance values. In the past decade, rapid progress has been made in the microfabrication of polyimides. However, enabling technologies, such as laser-induced graphene on polyimide, photosensitive polyimide micropatterning, and 3D polyimide microstructure assembly, have not been reviewed from the perspective of polyimide microfabrication. The aims of this review are to systematically discuss polyimide microfabrication techniques, which cover film formation, material conversion, micropatterning, 3D microfabrication, and their applications. With an emphasis on polyimide-based flexible MEMS devices, we discuss the remaining technological challenges in polyimide fabrication and possible technological innovations in this field.

Single-Atom and Hierarchical-Pore Aerogel Confinement Strategy for Low-Platinum Fuel Cells.

Achieving high catalytic performance through the lowest possible content of platinum (Pt) is the key to cost reduction of proton-exchange-membrane fuel cells (PEMFCs). However, lowering the Pt loading in PEMFCs leads to the high mass-transport resistance of oxygen originating from the limited active sites, and causes less stability of the catalysts due to Pt size growth after long-time operation. Herein, Pt-metal/metal-N-C aerogel catalysts are designed that substantially reduce oxygen-related mass transport resistance and have long-term durability. The tailoring of the Fe-N-C aerogel support with hierarchical and interconnecting pores enable a low local oxygen transport resistance (0.18 s cm-1 ) for PEMFCs with ultralow Pt loading (50 ± 5 µgPt cm- 2 ). Chemical confinement of Fe─N sites ensures high stability of the loaded-Pt both in the processes of synthesis up to 1000 °C and practical application in PEMFCs. The ultralow Pt PEMFC displays a low voltage loss of 8 mV at 0.80 A cm- 2 and unchanged electrochemical surface area after 60 000 cycles of accelerated durability testing. The allying of the hierarchical pores, the aerogel, and the single atoms can fully reflect their structural advantages and expand the understanding for the synthesis of advanced fuel cell PEMFCs catalysts.

Fish-Wearable Piezoelectric Nanogenerator for Dual-Modal Energy Scavenging from Fish-Tailing.

Aiming to develop a self-powered bioelectric tag for fish behavioral studies, here we present a fish-wearable piezoelectric nanogenerator (FWPNG) that can simultaneously harvest the strain energy and the flow impact energy caused by fish-tailing. The FWPNG is fabricated by transferring a 2 µm-thick Nb0.02-Pb(Zr0.6Ti0.4)O3 (PZT) layer from a silicon substrate to a spin-coated polyimide film via a novel zinc oxide (ZnO) release process. The open-circuit voltage of the strain energy harvester reaches 2.3 V under a strain of 1% at an ultra-low frequency of 1 Hz, and output voltage of the impact energy harvester reaches a 0.3 V under a pressure of 82.6 kPa at 1 Hz, which is in good agreement with our theoretical analysis. As a proof-of-concept demonstration, an event-driven underwater acoustic transmitter is developed by utilizing the FWPNG as a trigger switch. Acoustic transmission occurs when the amplitude of fish-tailing is larger than a preset threshold. The dual-modal FWPNG device shows the potential application in self-powered biotags for animal behavioral studies and ocean explorations.