Nanofibrous Matrix Mediated Ultrasensitive Flexible Strain Sensor for Subtle Human Motion Monitoring

Flexible strain sensors have attracted extensive research interest in health monitoring and early diagnosis owing to their superiority in continuous measurement of physiological signals. However, the design of flexible sensors with high sensitivity for subtle strain measurement coupled with biocompatibility, breathability, and eco-friendly properties is still challenging. In this study, a facile and universal approach was developed for the preparation of highly sensitive, biocompatible, and eco-friendly flexible strain sensors in reduced graphene oxide (rGO)/silk composites. The microcrack structures generated in rGO functional layers were achieved by vacuum filtration of GO onto silk nanofibrous matrices followed by a reduction process. The optimized flexible sensor exhibited high sensitivity with a gauge factor (GF) of 436 and 204 at a stretching strain of 8-8.7% and a bending strain of 0.12%, respectively. The sensor also revealed a superfast response of 8.8 ms, excellent durability for over 2000 cycles of bending, and waterproof ability up to 80 °C after 9 cycles. The degradability of the silk substrates enables the recycling of conductive materials, leading to eco-friendly sensor materials. The optimized rGO/silk sensor was able to sensitively and stably detect physiological signals with subtle strain changes (voices, pulse, and airflow), demonstrating great potential for use in flexible strain sensing of human health monitoring and medical diagnostics.