Jidong Shi

Tactile Sensing System Based on Arrays of Graphene Woven Microfabrics: Electromechanical Behavior and Electronic Skin Application.

Nanomaterials serve as promising candidates for strain sensing due to unique electromechanical properties by appropriately assembling and tailoring their configurations. Through the crisscross interlacing of graphene microribbons in an over-and-under fashion, the obtained graphene woven fabric (GWF) indicates a good trade-off between sensitivity and stretchability compared with those in previous studies. In this work, the function of woven fabrics for highly sensitive strain sensing is investigated, although network configuration is always a strategy to retain resistance stability. The experimental and simulation results indicate that the ultrahigh mechanosensitivity with gauge factors of 500 under 2% strain is attributed to the macro-woven-fabric geometrical conformation of graphene, which induces a large interfacial resistance between the interlaced ribbons and the formation of microscale-controllable, locally oriented zigzag cracks near the crossover location, both of which have a synergistic effect on improving sensitivity. Meanwhile, the stretchability of the GWF could be tailored to as high as over 40% strain by adjusting graphene growth parameters and adopting oblique angle direction stretching simultaneously. We also demonstrate that sensors based on GWFs are applicable to human motion detection, sound signal acquisition, and spatially resolved monitoring of external stress distribution.

Structural engineering of gold thin films with channel cracks for ultrasensitive strain sensing

This work demonstrates that engineering of the connection channels in gold thin films is an effective way to alter its resistivity for improved sensitivity in strain sensors. We investigated the formation of channel cracks and explored the corresponding piezoresistive behavior. The developed strain sensor possessed GFs as high as 200 (e < 0.5%), 1000 (0.5% < e < 0.7%), and even greater than 5000 (0.7% < e < 1%), which are among the highest values reported thus far at such small deformation, and are promising in the applications of electronic skin, wearable sensors and health monitoring platforms.

Templated synthesis of TiO2 nanotube macrostructures and their photocatalytic properties

Controlled synthesis of hierarchically assembled titanium dioxide (TiO2) nanostructures is important for practical applications in environmental purification and solar energy conversion. We present here the fabrication of interconnected TiO2 nanotubes as a macroscopic bulk material by using a porous carbon nanotube (CNT) sponge as a template. The basic idea is to uniformly coat an amorphous titania layer onto the CNT surface by the infiltration of a TiO2 precursor into the sponge followed by a subsequent hydrolysis process. After calcination, the CNTs are completely removed and the titania is simultaneously crystallized, which results in a porous macrostructure composed of interconnected anatase TiO2 nanotubes. The TiO2 nanotube macrostructures show comparable photocatalytic activities to commercial products (AEROXIDE TiO2 P25) for the degradation of rhodamine B (RhB). Moreover, the TiO2 nanotube macrostructures can be settled and separated from water within 12 h after photocatalysis, whereas P25 remains suspended in solution after weeks. Thus the TiO2 nanotube macrostructures offer the advantage of easy catalyst separation and recycle and can be a promising candidate for wastewater treatment.

Recent advances in nanopore-based nucleic acid analysis and sequencing

AbstractNanopore-based sequencing platforms are transforming the field of genomic science. This review (containing 116 references) highlights some recent progress on nanopore-based nucleic acid analysis and sequencing. These studies are classified into three categories, biological, solid-state, and hybrid nanopores, according to their nanoporous materials. We begin with a brief description of the translocation-based detection mechanism of nanopores. Next, specific examples are given in nanopore-based nucleic acid analysis and sequencing, with an emphasis on identifying strategies that can improve the resolution of nanopores. This review concludes with a discussion of future research directions that will advance the practical applications of nanopore technology. Graphical AbstractA review with 116 references that highlights the progress made in nanopore-based nucleic acid analysis and sequencing, and the mechanisms operative in analytical methods based on the use of nanopores

Multifunctional Polymer-Based Graphene Foams with Buckled Structure and Negative Poisson’s Ratio

In this study, we report the polymer-based graphene foams through combination of bottom-up assembly and simple triaxially buckled structure design. The resulting polymer-based graphene foams not only effectively transfer the functional properties of graphene, but also exhibit novel negative Poisson’s ratio (NPR) behaviors due to the presence of buckled structure. Our results show that after the introduction of buckled structure, improvement in stretchability, toughness, flexibility, energy absorbing ability, hydrophobicity, conductivity, piezoresistive sensitivity and crack resistance could be achieved simultaneously. The combination of mechanical properties, multifunctional performance and unusual deformation behavior would lead to the use of our polymer-based graphene foams for a variety of novel applications in future such as stretchable capacitors or conductors, sensors and oil/water separators and so on.

Multiscale Hierarchical Design of a Flexible Piezoresistive Pressure Sensor with High Sensitivity and Wide Linearity Range

Flexible piezoresistive pressure sensors have been attracting wide attention for applications in health monitoring and human-machine interfaces because of their simple device structure and easy-readout signals. For practical applications, flexible pressure sensors with both high sensitivity and wide linearity range are highly desirable. Herein, a simple and low-cost method for the fabrication of a flexible piezoresistive pressure sensor with a hierarchical structure over large areas is presented. The piezoresistive pressure sensor consists of arrays of microscale papillae with nanoscale roughness produced by replicating the lotus leafs surface and spray-coating of graphene ink. Finite element analysis (FEA) shows that the hierarchical structure governs the deformation behavior and pressure distribution at the contact interface, leading to a quick and steady increase in contact area with loads. As a result, the piezoresistive pressure sensor demonstrates a high sensitivity of 1.2 kPa-1 and a wide linearity range from 0 to 25 kPa. The flexible pressure sensor is applied for sensitive monitoring of small vibrations, including wrist pulse and acoustic waves. Moreover, a piezoresistive pressure sensor array is fabricated for mapping the spatial distribution of pressure. These results highlight the potential applications of the flexible piezoresistive pressure sensor for health monitoring and electronic skin.

Flexible and biocompatible nanopaper-based electrode arrays for neural activity recording

Advances in neural electrode technologies can have a significant impact on both fundamental and applied neuroscience. Here, we report the development of flexible and biocompatible neural electrode arrays based on a nanopaper substrate. Nanopaper has important advantages with respect to polymers such as hydrophilicity and water wettability, which result in significantly enhanced biocompatibility, as confirmed by both in vitro viability assays and in vivo histological analysis. In addition, nanopaper exhibits high flexibility and good shape stability. Hence, nanopaper-based neural electrode arrays can conform to the convoluted cortical surface of a rat brain and allow stable multisite recording of epileptiform activity in vivo. Our results show that nanopaper-based electrode arrays represent promising candidates for the flexible and biocompatible recording of the neural activity.

Simultaneous surface and depth neural activity recording with graphene transistor-based dual-modality probes

Subdural surface and penetrating depth probes are widely applied to record neural activities from the cortical surface and intracortical locations of the brain, respectively. Simultaneous surface and depth neural activity recording is essential to understand the linkage between the two modalities. Here, we develop flexible dual-modality neural probes based on graphene transistors. The neural probes exhibit stable electrical performance even under 90° bending because of the excellent mechanical properties of graphene, and thus allow multi-site recording from the subdural surface of rat cortex. In addition, finite element analysis was carried out to investigate the mechanical interactions between probe and cortex tissue during intracortical implantation. Based on the simulation results, a sharp tip angle of π/6 was chosen to facilitate tissue penetration of the neural probes. Accordingly, the graphene transistor-based dual-modality neural probes have been successfully applied for simultaneous surface and depth recording of epileptiform activity of rat brain in vivo. Our results show that graphene transistor-based dual-modality neural probes can serve as a facile and versatile tool to study tempo-spatial patterns of neural activities.