The development of highly sensitive, selective, and low-cost chemical sensors that can detect trace amounts of volatile organic compounds (VOCs) is essential for environmental sustainability and human health monitoring. Here,...
Exfoliated and aligned continuous graphene nanoplatelet channels with enhanced mechanical properties and superior electrical conductivity.
portable chemiresistive devices based on the resistance change of metal oxide semiconductors upon absorbing VOCs. [8-14] In particular, when nanostructured, their detection capabilities to analytes could reach down to a few parts per billion (ppb) and with good response time. [15] Thus, they are ideal for important biological applications, such as breath and respiratory diagnostics. [16] Their high sensitivities are nevertheless coupled with elevated operating temperatures, usually several hundred degrees Celsius as well as low thermal stability under various environments. [17-19] This limits their application in multifunctional devices, especially due to the low survivability of the rigid metaloxide devices under complex dynamic or fatigue conditions. On the other hand, conductive polymer nanoparticle composites have demonstrated stable performances under extreme conditions, [20] can be scalably manufactured, [21-23] and meet compliance requirements of wearable electronics. [24,25] Their gas sensing functionalities, based on the Flory-Huggins interaction parameters between solvents and polymers, have also been investigated with various polymer matrices and nanoparticles. [26-30] Currently, the main performance-limiting factor is their low sensitivity, usually in the range of several parts per thousand to a few hundred parts per million (ppm). Increasing the surface area is one of the most efficient methods to increase sensitivity, such as in macroscale helical structure, [31] microscale scaffolds, [32] and nanoscale nanofibers. [33] Notably, nature provides inspirations that have unparalleled advantages in material design and fabrication. [34-37] Herein, we introduce a multilayered, porous, and hollow fiber sensor with enhanced functionalities mimicking the metaxylem structure of vascular plants (Figure 1a). Vascular plants utilize metaxylem conduits for the transpiration and transport of water and minerals from the ground to the leaves. In the presence of nutrient scarcity, transpiration efficiency is enhanced as pits on the cell wall facilitate the horizontal diffusion of water and minerals into adjacent cells. [38] Inspired by this highly ordered pit structure, we developed a multilayered polymer nanoparticle sensor with a self-induced hollow core that increases the surface area in macro-and microscales, with VOC sensitivity up to 15 ppm for xylene, There are advantages to polymer/nanoparticle composite-based volatile organic compounds (VOCs) sensors, such as high chemical and physical stability, operability under extreme conditions, flexible use in manufacturing, and low cost. Nevertheless, their lower limit of detection due to thickness-dependent diffusion has constrained their application. Inspired by the metaxylem in vascular plants and its vertical conduits and horizontal pits that enable efficient transpiration, a polymer/nanoparticle compositebased sensor is fabricated with a controllable, spontaneously formed, hollow core for inline VOCs transportation, and porous microstructure for radial direction d...
Honeycomb is one of nature's best engineered structures. Even though it has inspired several modern engineering structures, an understanding of the process by which the hexagonal cells are formed in 3D space is lacking. Previous studies on the structure of the honeycomb are based on either 2D microscopy or by direct visual observations. As a result, several critical features of its microstructure and the precise mechanisms of its growth are not well understood. Using 4D X‐ray microscopy, this study shows how individual and groups of honeycomb cells are formed. Cells grow additively from a corrugated central spine in a dynamic manner. The previously undocumented, corrugated spine contributes significantly to the comb's robust mechanical properties in all three dimensions. As cells grow, honey bees create a “coping,” which this study shows to be the location where new wax material is deposited behind where compaction and densification take place. This is exemplified by pores in the wax observed at the coping and alternating rear junctions between the comb cells that arise from the additive building technique and the highly efficient cell packing methodology, respectively. Additional mechanisms for growth and formation are discussed and described.
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