Highly sensitive and flexible pressure sensors were developed based on dielectric membranes composed of insulating microbeads contained within polyvinylidene fluoride (PVDF) nanofibers. The membrane is fabricated using a simple electrospinning process. The presence of the microbeads enhances porosity, which in turn enhances the sensitivity (1.12 kPa −1 for the range of 0−1 kPa) of the membrane when used as a pressure sensor. The microbeads are fixed in position and uniformly distributed throughout the nanofibers, resulting in a wide dynamic range (up to 40 kPa) without any sensitivity loss. The fluffy and nonsticky PVDF nanofiber features low hysteresis and ultrafast response times (∼10 ms). The sensor has also demonstrated reliable pressure detection over 10 000 loading cycles and 250 bending cycles at a 13 mm bending radius. These pressure sensors were successfully applied to detect heart rate and respiratory signals, and an array of sensors was fabricated and used to recognize spatial pressure distribution. The sensors described herein are ultrathin and ultralight, with a total thickness of less than 100 μm, including the electrodes. All of the materials comprising the sensors are flexible, making them suitable for on-body applications such as tactile sensors, electronic skins, and wearable healthcare devices.

It has long been puzzling regarding the trends and physical origins of the size-effect on the elasticity of ZnO nanostructures. An extension of the atomic “coordination-radius” correlation premise of Pauling and Goldschmidt to energy domain has enabled us to clarify that the elastic modulus is intrinsically proportional to the sum of bond energy per unit volume and that the size-induced elastic stiffening arises from (i) the broken-bond-induced local strain and skin-depth energy pinning and (ii) the tunable fraction of bonds between the undercoordinated atoms, and therefore, the elastic modulus of ZnO nanostructures should increase with the inverse of feature size.

Multilayer films of negatively charged single-wall carbon nanotubes (SWCNTs) and positively charged cetylpyridinium bromide (CPB) have been deposited on a glassy carbon electrode (GCE) using layer-by-layer (LBL) technique. The assembled multilayer films have been investigated by scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), and quartz crystal microbalance (QCM) measurements. The voltammetric signal of dopamine (DA), uric acid (UA), and ascorbic acid (AA) could be observed well-separated with the assembled SWCNTs/CPB multilayer films in pH 7.0 PBS. The oxidation peak potentials of DA, UA, and AA are centered at about 169 mV, 292 mV and À 10 mV on differential pulse voltammograms (DPVs), respectively. The peakto-peak potential separation was 123 mV, 179 mV, and 302 mV for DA-UA, DA-AA, and UA-AA in DPVs, respectively. This permits the simultaneous detection of DA and UA in the presence of AA.

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