Search for: All records

Abstract Silver nanowires (AgNWs) hold great promise for applications in wearable electronics, flexible solar cells, chemical and biological sensors, photonic/plasmonic circuits, and scanning probe microscopy (SPM) due to their unique plasmonic, mechanical, and electronic properties. However, the lifetime, reliability, and operating conditions of AgNW-based devices are significantly restricted by their poor chemical stability, limiting their commercial potentials. Therefore, it is crucial to create a reliable oxidation barrier on AgNWs that provides long-term chemical stability to various optical, electrical, and mechanical devices while maintaining their high performance. Here we report a room-temperature solution-phase approach to grow an ultra-thin, epitaxial gold coating on AgNWs to effectively shield the Ag surface from environmental oxidation. The Ag@Au core-shell nanowires (Ag@Au NWs) remain stable in air for over six months, under elevated temperature and humidity (80 °C and 100% humidity) for twelve weeks, in physiological buffer solutions for three weeks, and can survive overnight treatment of an oxidative solution (2% H 2 O 2 ). The Ag@Au core-shell NWs demonstrated comparable performance as pristine AgNWs in various electronic, optical, and mechanical devices, such as transparent mesh electrodes, surface-enhanced Raman spectroscopy (SERS) substrates, plasmonic waveguides, plasmonic nanofocusing probes, and high-aspect-ratio, high-resolution atomic force microscopy (AFM) probes. These Au@Ag core-shell NWs offer a universal solution towards chemically-stable AgNW-based devices without compromising material property or device performance. 

Ionic liquids (ILs) exhibit unique properties of good ionic conductivity, electrochemical and thermal stability, and nonflammability, which make them promising candidates for biomedical applications. The limitations of their cytocompatibility are enhanced by using bioionic liquids (BILs) derived from biological molecules such as amines, sugars, and organic acids. BILs can be synthesized using tailorable chemistries that enable their immobilization onto biopolymers. For example, the cholinium ion and its derivatives have found significant interest in tissue engineering and drug delivery systems. Ion‐doped BIL‐functionalized polymers and their composites can also be used to design pH and electrical responsive actuators and sensors. The cytocompatibility and low immunogenicity of BIL‐functionalized polymers enable the possibilities of their use for power storage devices as well as implantable devices. These devices are gaining recognition and importance in nucleic acid delivery and molecular medicine. This review focuses on the recent advances of BILs in biomedical applications. Specifically, the review explores BILs as agents for biopolymer functionalization and highlights BILs as solvents for supermolecular ionic networks.

 

Chemically-synthesized single-crystalline silver nanowire (AgNW) probes can combine the scanning tunneling microscopy (STM) technique with tip-enhanced Raman scattering spectroscopy (TERS) for complementary morphological and chemical information with nanoscale spatial resolution. However, its performance has been limited by the blunt nanowire tip geometry, the insulating surfactant layer coating AgNW surfaces, and the thermal-induced mechanical vibrations. Here, we report a reproducible fabrication method for the preparation of sharp-tip AgNW-based TERS probes. By removing the polyvinylpyrrolidone (PVP) surfactant molecules from the AgNW surfaces for stable electrical conductivity and controlling the protruding length with μm-level accuracy for improved mechanical stability, we demonstrate atomic-resolution STM imaging with the sharp-tip AgNW probe. Furthermore, the sharp-tip AgNW has an excellent TER enhancement (∼1.1 × 10 6 ), which is about 66 folds of that achieved by regular AgNWs. Our experiments demonstrate that AgNWs with clean interfaces and the proper tip geometry can provide reliable and reproducible STM and TER characterizations, which remove the hurdles preventing the implementation of AgNW in STM-based near-field optical applications for a broad community. 

Wearable piezoresistive sensors are being developed as electronic skins (E‐skin) for broad applications in human physiological monitoring and soft robotics. Tactile sensors with sufficient sensitivities, durability, and large dynamic ranges are required to replicate this critical component of the somatosensory system. Multiple micro/nanostructures, materials, and sensing modalities have been reported to address this need. However, a trade‐off arises between device performance and device complexity. Inspired by the microstructure of the spinosum at the dermo epidermal junction in skin, a low‐cost, scalable, and high‐performance piezoresistive sensor is developed with high sensitivity (0.144 kPa^‐1), extensive sensing range ( 0.1–15 kPa), fast response time (less than 150 ms), and excellent long‐term stability (over 1000 cycles). Furthermore, the piezoresistive functionality of the device is realized via a flexible transparent electrode (FTE) using a highly stable reduced graphene oxide self‐wrapped copper nanowire network. The developed nanowire‐based spinosum microstructured FTEs are amenable to wearable electronics applications.