Bioinspired Dual-Mode Self-Powered Paper Sensor for Sustainable Wearable Health Monitoring via Synergistic Humidity Gradient and Triboelectric Effects.

Wearable sensors are becoming increasingly important in human health detection. However, existing sensors face severe challenges in achieving self-sustained multimodal sensing and environmentally friendly and low-cost manufacturing. Here, we report a dual self-powered paper-based humidity-difference/triboelectric sensor. This sensor integrates humidity and triboelectric self-powered detection functions through the synergistic effect of the ion gradient effect and triboelectric contact electrification. A carbon nanotube composite salt solution is used to modify the fibrous paper substrate, and bionic graphite fingerprint electrodes are drawn with a pencil on the cellulose paper. Relying on the noncontact humidity detection driven by the ion gradient inside the paper, a humidity open-circuit voltage is generated, and the humidity detection range is 11%-90% RH with a high linearity of R2 = 0.97. At the same time, a friction self-powered triboelectric sensing device is prepared with paper as the substrate. Through the principle of charge difference and contact mode, a triboelectric sensor is integrated, enabling triboelectric and humidity dual-mode sensing without an external power source. This work provides a sustainable and low-cost strategy for constructing paper-based self-powered dual-mode sensors. Moreover, we apply the prepared sensors to various human body detections and tests in other application environments.