Pressure sensors have attracted much attention for their potential applications in health monitoring, wearable devices, electronic skin and smart robots, etc. With the rapid development of Internet of Things, considering...

Wearable sweat sensors can analyze the abundant composition of solutes and metabolites in sweat to reflect the health state of the wearers in real time. The realization of active motion control for sweat droplets is significant for a multifunctional sweat monitoring device with several analysis chambers. Here, a wearable droplet-based human sweat monitoring platform (WSMP), by combining an electrowetting on dielectrics (EWOD) device and a triboelectric nanogenerator (TENG), is demonstrated. It allows to collect and transport sweat droplets in different chambers by dielectric wetting effect and eventually merge and react with a pH indicator. The mechanical and electrical model of WSMP is introduced to describe the relationship between the open-circuit voltage of the TENG and the voltage applied on the EWOD device. The highvoltage electrical field generated by the TENG can change the wettability of solid-liquid interfaces and realize the controlling of droplet motion. The contact angle of electrolyte droplets changes over 30% with the triboelectric voltage of 5 kV. The driving, merging, and color reaction can be realized by actively controlling the motion of droplets. Finally, a wearable WSMP worn on the shank successfully demonstrates the preliminary detection of the pH level of human sweat.

No abstract

Traditional triboelectric tactile sensors based on solid–solid interface have illustrated promising application prospects through optimization approach. However, the poor sensitivity and reliability caused by hard contact-electrification still poses challenges for the practical applications. In this work, a liquid–solid interface ferrofluid-based triboelectric tactile sensor (FTTS) with ultrahigh sensitivity is proposed. Relying on the fluidity and magnetism of ferrofluid, the topography of microstructure can be flexibly adjusted by directly employing ferrofluid as triboelectric material and controlling the position of outward magnet. To date, an ultrahigh sensitivity of 21.48 kPa−1 for the triboelectric sensors can be achieved due to the high spike microstructure, low Young’s modulus of ferrofluid and efficient solid–liquid interface contact-electrification. The detection limit of FTTS of 1.25 Pa with a wide detection range to 390 kPa was also obtained. In addition, the oleophobic property between ferrofluid and poly-tetra-fluoro-ethylene triboelectric layer can greatly reduce the wear and tear, resulting in the great improvement of stability. Finally, a strategy for personalized password lock with high security level has been demonstrated, illustrating a great perspective for practical application in smart home, artificial intelligence, Internet of things, etc.

No abstract