A location- and sharpness-specific tactile electronic skin based on staircase-like nanowire patches

We report a new tactile electronic skin sensor based on staircase-like vertically aligned gold nanowires (V-AuNWs). With the back-to-back linear or spiral assembly of two antiparallel staircase structures into a single sensor, we are able to recognize pressure in a highly location-specific manner for both non-stretched and stretched states (up to 50% strain). With a concentric design on the fingertip, we can identify the sharpness of an external object in a similar way to human skin for the first time. Note that only location-specific pressure sensing under a non-stretched state has been demonstrated with existing unpixellated pressure sensors. Other important functions of human tactile sensing, such as the ability to discriminate sharp/blunt objects and location-specific sensing under stretched states, have not yet been achieved in the literature. We believe that our methodologies open up a new route to low-cost stretchable smart tactile sensors with potential facile integration and high location resolution into future wearable electronics, such as stretchable touch-on displays, soft robotics and prosthetic skins. The staircase structures and location-specific sensitivity could be extended to other novel nanomaterials and designs to form heterogeneous multifunctional optoelectronic devices, indicating broad application potentiality in next-generation skin-like electronics.

Single glucose molecule transport process revealed by force tracing and molecular dynamics simulations

Molecular transports across cell membranes are essential activities of cellular systems. How fast can nutrients, such as single glucose and amino acids, be transported into a living cell? What is the effort the cells need to pay for transporting such molecules? These questions are quite fundamental in cell biology, but have never been revealed at the single molecule level. To address these critical questions, we use the atomic force microscopy (AFM)-based force-tracing technique to monitor the process of single-glucose transport, inspired by a “fishing” concept. We demonstrate that the force-tracing technique enables the single molecule transport process to be followed at a high temporal-spatial resolution. The forces to transport a single molecule of d-glucose across cell membranes and the corresponding transport interval were recorded. Combining with theoretical simulation, the transporting mechanism of glucose is further revealed at an atomic level, which was confirmed by the biological experiments. Our approach leads to the first unambiguous description of the kinetics of the transport process in living cells at the single molecule level, which is significant for understanding how a membrane transporter works. This study provides a new concept of investigating the dynamic function of cell membranes.

Efficient hole transfer from monolayer WS2 to ultrathin amorphous black phosphorus

We introduce an amorphous semiconductor to the material library for constructing van der Waals heterostructures. Since 2014, van der Waals heterostructures have been one of the most dynamic research topics in nanoscience and nanotechnology. Previous efforts have mostly been focused on combining two materials with similar lattices, such as different types of transition metal dichalcogenides. However, heterostructures combining materials with different lattice structures can potentially allow integration of vastly different properties. Here we explore an extreme example by combining a crystalline monolayer with an amorphous ultrathin film. We fabricate heterostructures composed of a 2 nm amorphous black phosphorus layer and a monolayer of WS2. Time-integrated photoluminescence and time-resolved transient absorption measurements both revealed that holes excited in WS2 can efficiently transfer to amorphous black phosphorus on an ultrafast time scale. Furthermore, we show that a hexagonal BN bilayer can effectively control the hole transfer process. These results establish amorphous black phosphorus as a building block for van der Waals heterostructures, provide new information for understanding interlayer charge transfer, and allow electrical connections to amorphous materials by van der Waals interfaces.