Self-Powered Dual-Mode Hydrogel Sensors for Respiratory Monitoring via Humidity Sensing and Strain Detection

Reliance on external power sources remains a significant constraint for the practical deployment of flexible sensors. Herein, we develop a multifunctional hydrogel-based sensor that operates in two distinct modes: a self-powered mode for humidity sensing and a resistance mode for strain detection. The sensor is built around a conductive poly(vinyl alcohol)-graphene oxide/lithium bromide (PVA-GO/LiBr) hydrogel, fabricated via a straightforward one-step process. This core material exhibits a high ionic conductivity of 0.33 S·cm–1. In its self-powered humidity-sensing mode, the device leverages a metal–air redox reaction, where moisture-triggered ion mobility generates a current output with a sensitivity of 0.299 nA/s per % RH in the 70% to 90% RH range. Simultaneously, the intrinsic resistance of the very same hydrogel structure serves as a highly responsive strain gauge, capable of achieving a 6-fold increase in resistance at 400% tensile strain. Demonstrating robust performance even at −15 °C, the sensor is integrated into a respiratory monitoring platform. It successfully enables the real-time detection of abnormal breathing patterns, such as sleep apnea hypopnea syndrome (SAHS), showcasing its potential as a scalable and power-efficient solution for advanced wearable health diagnostics and telemedicine.