Ultrathin hierarchical hydrogel-carbon nanocomposite for highly stretchable fast-response water-proof wearable humidity sensors

Wearable humidity sensors play an important role in human health monitoring. However, challenges persist in realizing high performance wearable humidity sensors with fast response and good stretchability and durability. Here we report wearable humidity sensors employing an ultrathin micro-nano hierarchical hydrogel-carbon nanocomposite. The nanocomposite is synthesized on polydimethylsiloxane (PDMS) films via a facile two-step solvent-free approach, which creates a hierarchical architecture consisting of periodic microscale wrinkles and vapor-deposited nanoporous hydrogel-candle-soot nanocoating. The hierarchical surface topography results in a significantly enlarged specific surface area (4107 times that of planar hydrogel), which along with the ultrathin hydrogel endow the sensor with high sensitivity and a fast response/ recovery (13/0.48 s) over a wide humidity range (11-96%). Owing to the wrinkle structure and interpenetrating network between the hydrogel and PDMS, the sensor is stable and durable against repeated 1808 bending, 100% strain, and even scratching. Furthermore, encapsulation of the sensor imparts excellent resistance to water, sweat, and bacteria without influencing its performance. The sensor is then successfully used to monitor different human respiratory behaviors and skin humidity in real time. The reported method is convenient and cost-effective, which could bring exciting new opportunities in the fabrication of next-generation wearable humidity sensors.

Automated summary

Wearable humidity sensors are crucial for human health monitoring, but realizing high-performance sensors with fast response and durability remains a challenge. In this study, we present a wearable humidity sensor based on an ultrathin micro-nano hierarchical hydrogel-carbon nanocomposite. The sensor exhibits high sensitivity and a fast response/recovery over a wide humidity range due to its unique hierarchical structure. Additionally, the sensor is stable and durable against bending, strain, and scratching, and shows excellent resistance to water, sweat, and bacteria without affecting its performance. The sensor is successfully used for real-time monitoring of human respiratory behaviors and skin humidity. This convenient and cost-effective method opens up exciting opportunities for the fabrication of next-generation wearable humidity sensors.