Showing papers by "Sheng Xu published in 2019"

Wearable thermoelectrics for personalized thermoregulation

Abstract: Thermoregulation has substantial implications for energy consumption and human comfort and health. However, cooling technology has remained largely unchanged for more than a century and still relies on cooling the entire space regardless of the number of occupants. Personalized thermoregulation by thermoelectric devices (TEDs) can markedly reduce the cooling volume and meet individual cooling needs but has yet to be realized because of the lack of flexible TEDs with sustainable high cooling performance. Here, we demonstrate a wearable TED that can deliver more than 10°C cooling effect with a high coefficient of performance (COP > 1.5). Our TED is the first to achieve long-term active cooling with high flexibility, due to a novel design of double elastomer layers and high-ZT rigid TE pillars. Thermoregulation based on these devices may enable a shift from centralized cooling toward personalized cooling with the benefits of substantially lower energy consumption and improved human comfort.

Biomembrane-Modified Field Effect Transistors for Sensitive and Quantitative Detection of Biological Toxins and Pathogens.

Abstract: The efforts of detecting bioactive targets with complex, dynamic, and unknown molecular profiles have inspired the development of various biosensor platforms. Herein, we report a cell-membrane-modified field effect transistor (FET) as a function-based nanosensor for the detection and quantitative measurement of numerous toxins and biological samples. By coating carbon nanotube FETs with natural red blood cell membranes, the resulting biomimetic nanosensor can selectively interact with and absorb broad-spectrum hemolytic toxins regardless of their molecular structures. Toxin–biomembrane interactions alter the local charge distribution at the FET surface in an ultrasensitive and concentration-dependent manner, resulting in a detection limit down to the femtomolar (fM) range. Accurate and quantitative measurements are enabled via a built-in calibration mechanism of the sensor, which overcomes batch-to-batch fabrication variations, and are demonstrated using three distinct toxins and various complex bacterial...

Stretchable and Flexible Buckypaper-Based Lactate Biofuel Cell for Wearable Electronics

Abstract: This work demonstrates a stretchable and flexible lactate/O2 biofuel cell (BFC) using buckypaper (BP) composed of multi-walled carbon nanotubes as the electrode material. Free-standing BP, functionalized with a pyrenepolynorbornene homopolymer, is fabricated as the immobilization matrix for lactate oxidase (LOx) at the anode and bilirubin oxidase at the cathode. This biofuel cell delivers an open circuit voltage of 0.74 V and a high-power density of 520 μW cm−2. The functionalized BP electrodes are assembled onto a stretchable screen-printed current collector with an “island–bridge” configuration, which ensures conformal contact between the wearable BFC and the human body and endows the BFC with excellent performance stability under stretching condition. When applied to the arm of the volunteer, the BFC can generate a maximum power of 450 μW. When connected with a voltage booster, the on-body BFC is able to power a light emitting diode under both pulse discharge and continuous discharge modes during exercise. This demonstrates the promising potential of the flexible BP-based BFC as a self-sustained power source for next-generation wearable electronics.

Stretchable Ultrasonic Transducer Arrays for Three-Dimensional Imaging on Complex Surfaces

Abstract: Ultrasonic imaging technology has been widely implemented in the fields of medical imaging, non-destructive evaluation, and structural health monitoring. Tradition- ally, rigid and semi-flexible ultrasound probes in current bulky packages can detect the sub-surface defects of a component with a flat surface, but neither is suitable for the accurate defect inspection with three-dimensional curvatures, which significantly constrains the universality and practicability of ultrasonic imaging technology. This study reports the development of flexible and stretchable ultrasound two-dimensional (2D) array probe that exploits an ’island-bridge’ structured interconnection and multi-layer electrodes to integrate miniature ultrasound transducer elements with thin, low modulus silicone elastomeric polymer matrix. The achieved soft device, owning dense transducer distribution, excellent piezoelectric performance, bare internal cross-talk, and over 60% stretchability, is capable of long-time seamlessly conforming on almost any curved com- ponents, and reconstructing the object images with high resolution. With the designed probe, mono-view 2D images of internal defects in a specimen with a convex surface are collected. The entire geometries of two internal defects are reconstructed in threedimensional space. The proposed flexible and stretchable ultrasonic device along with the imaging reconstruction algorithm provides an effective, accurate, and straightforward solution for ultrasonic imaging of complex-shaped structure components.

A Biomimetic Soft Lens Controlled by Electrooculographic Signal

Abstract: Thanks to many unique features, soft robots or soft machines have been recently explored intensively to work collaboratively with human beings. Most of the previously developed soft robots are either controlled manually or by prewritten programs. In the current work, a novel human–machine interface is developed to use electrooculographic signals generated by eye movements to control the motions and the change of focal length of a biomimetic soft lens. The motion and deformation of the soft lens are achieved by the actuation of different areas of dielectric elastomer films, mimicking the working mechanisms of the eyes of human and most mammals. The system developed in the current study has the potential to be used in visual prostheses, adjustable glasses, and remotely operated robotics in the future.

Array atomic force microscopy for real-time multiparametric analysis.

Abstract: Nanoscale multipoint structure-function analysis is essential for deciphering the complexity of multiscale biological and physical systems. Atomic force microscopy (AFM) allows nanoscale structure-function imaging in various operating environments and can be integrated seamlessly with disparate probe-based sensing and manipulation technologies. Conventional AFMs only permit sequential single-point analysis; widespread adoption of array AFMs for simultaneous multipoint study is challenging owing to the intrinsic limitations of existing technological approaches. Here, we describe a prototype dispersive optics-based array AFM capable of simultaneously monitoring multiple probe-sample interactions. A single supercontinuum laser beam is utilized to spatially and spectrally map multiple cantilevers, to isolate and record beam deflection from individual cantilevers using distinct wavelength selection. This design provides a remarkably simplified yet effective solution to overcome the optical cross-talk while maintaining subnanometer sensitivity and compatibility with probe-based sensors. We demonstrate the versatility and robustness of our system on parallel multiparametric imaging at multiscale levels ranging from surface morphology to hydrophobicity and electric potential mapping in both air and liquid, mechanical wave propagation in polymeric films, and the dynamics of living cells. This multiparametric, multiscale approach provides opportunities for studying the emergent properties of atomic-scale mechanical and physicochemical interactions in a wide range of physical and biological networks.

Soft sensors form a network

Abstract: A wearable wireless sensor network for personalized healthcare can be created through the indirect integration of soft on-skin sensors and rigid in-clothes circuits.

Discovery of Ionic Impact Ionization (I3) in Perovskites Triggered by a Single Photon

Abstract: Organic-inorganic metal halide perovskite devices have generated significant interest for LED, photodetector, and solar cell applications due to their attractive optoelectronic properties and substrate-choice flexibility1-4. These devices exhibit slow time-scale response, which have been explained by point defect migration5-6. In this work, we report the discovery of a room temperature intrinsic amplification process in methylammonium lead iodide perovskite (MAPbI3) that can be triggered by few photons, down to a single photon. The electrical properties of the material, by way of photoresponse, are modified by an input energy as small as 0.19 attojoules, the energy of a single photon. These observations cannot be explained by photo-excited electronic band-to-band transitions or prevailing model of photo-excited point defect migration since none of the above can explain the observed macroscopic property change by absorption of single or few photons. The results suggest the existence of an avalanche-like collective motion of iodides and their accumulation near the anode, which we will call ionic impact ionization (I3 mechanism). The proposed I3 process is the ionic analog of the electronic impact ionization, and has been considered impossible before because conventionally it takes far more energy to move ions out of their equilibrium position than electrons. We have performed first principle calculations to show that in MAPbI3 the activation energy for the I3 mechanism is appreciably lower than the literature value of the activation energy for the electronic impact ionization. The discovery of I3 process in perovskite material opens up possibilities for new classes of devices for photonic and electronic applications.