Measurements of an individual’s water metabolism dynamical information can provide us rich biological information in a noninvasive way. This concept is hindered by the trade-off between the sensitivity and responsive velocity of traditional moisture sensors. Herein, inspired by the molecular detecting system based on weak bond interactions in natural organisms, we designed a new concept of a tunable graphene-polymer heterogeneous nanosensing junction by confining a reasonable thickness sensing material into graphene nanochannels. The fundamentally new sensing mechanism based on dynamical hydrogen bonds endows the sensor with over 4 orders of magnitude sensitivity toward a wide range of relative humidity (RH) (from 0% to 97%) with unprecedented fast response (20 ms) and recovery times (17 ms) with little humidity hysteresis. The promising advantages of the sensor allow us to record humidity fluctuation information in real time during a user’s speech and breath, which can both reveal the speech feature and monitor the respiration rate accurately. Importantly, this advanced sensor provides a new opportunity for accurate and reliable physiological and psychological monitoring by detecting the subtlest RH fluctuations on human skin in a noncontact way.

upon a change in relative humidity of the surrounding air. [ 13 ] Sun et al. have demonstrated the fabrication of an energetic walking device driven by a powerful humidity responsive bilayer actuator comprising an action layer of cross-linked poly(allylamine hydrochloride)/poly(acrylic acid) (PAH/PAA) fi lms and a supporting layer of UV-cured Norland Optical Adhesive (NOA)-63. [ 8 ] Considering that graphene has many extraordinary characteristics, such as high thermal conductivity and excellent mechanical properties, it has also served as the smart water responsive actuators. [ 20 ] Ruoff et al. presented a macroscopic actuator based on graphene oxide/carbon nanotubes (GO/CNTs) bilayer fi lm to show obvious actuation that depends on variation of humidity onto water responsive materials of GO. [ 21 ] We have reported previously the asymmetric graphene/ graphene oxide (G/GO) fi ber structures obtained by positioned laser reduction of GO fi bers display well-controlled motion in a predetermined manner once exposed to moisture. [ 22 ] To realize the desired performance in a predefi ned fashion, bilayer materials or structures with different swelling behavior was necessary to mimic the strain transition among different material layers. However, as a moving component, bilayer actuators may also suffer from poor interlayer adhesion during frequent bending and complex fabrication process, etc. Moreover, concerns with respect to toughness, elasticity, and chemical/ physical stabilities also constitute a main barrier for the development of smart actuators. In this regard, from a manufacturing point of view, rational design and fabrication of actuators by refi ned control of the lateral microstructures of a solo material or even a single piece of thin fi lm might be a solution to the above-mentioned problems, but obviously, still remains big challenging. To overcome this limitation and further take advantage of the bilayer design of actuators, we present an alternative strategy in this article that a moisture gradients responsive reduced graphene oxide/polydopamine (RGO-PDA) thin fi lm, the uniform materials can serve as highly effi cient actuator driven by water absorption induced in situ formation of the bilayer structures in swelling difference. During the trigger of RGO-PDA fi lm by water with a gradient from one side, humidity-responsible hydrophilic PDA can absorb water on the surface layers of the RGO-PDA fi lm and act as soft "muscle" to active the swelling locomotion. The existing of rigid RGO sheets with relatively hydrophobic nature inside the fi lm hinders or delays the diffusion of water across the fi lm and construct the "skeleton" of the actuator which hold the PDA "muscle" to transfer the energy of water gradients to a mechanical motion.As energy transducers, actuators can provide controllable mechanical response into 2D or 3D motions upon the trigger by external stimuli, such as electric fi elds, [1][2][3][4] heat, [ 5,6 ] light, [ 7,8 ] and moisture. [ 9,10 ] Therefore, the fabrication of various actuators...

Ultra-robust carbon fibers are fabricated for purification of multi-media, including oil-in-water emulsion, dyed organic solvent and seawater via solar-thermal evaporation.