Reduced graphene oxide/silk fibroin/cellulose nanocrystal-based wearable sensors with high efficiency and durability for physiological monitoring

Monitoring the physiological signals of people by using wearable sensors attached to the skin while they go about their daily routine is a practical approach to prevent diseases and monitor people’s health status. However, conventional monitoring devices are bulky, their signals are corrupted by the noise generated by external sources, and they are prone to mechanical failure, which hinder their practical use. Herein, a mechanically durable biomaterial-based arterial pulse thin-film sensor is developed for real-time monitoring of cyclic physiological signals. A hierarchical layered material (rGO/SF/CNC) comprising reduced graphene oxide (rGO), silk fibroin (SF), and cellulose nanocrystals (CNCs) is fabricated using the spin-assisted layer-by-layer (SA-LbL) technique and thermal reduction. Thermal reduction is performed to tailor the defects in rGO, which significantly enhances its mechanical robustness and bending properties, as well as in-plane stress sensitivity, owing to a change in conductivity. The thin-film (thickness: 40.9 nm) sensor has a rapid response time (69 ms) and excellent durability exceeding 8000 cycles. Moreover, it is insensitive to strain in the orthogonal direction, which significantly reduces the noise level and dramatically increases its sensitivity. The sensor’s suitability for practical use as an arterial pulse sensor for monitoring physiological signals is demonstrated. The developed thin-film flexible stress sensor has the potential to contribute toward the improvement of wearable healthcare monitoring devices and human–machine interaction. Graphical abstract