A Flexible Multimodal Sensor That Detects Strain, Humidity, Temperature, and Pressure with Carbon Black and Reduced Graphene Oxide Hierarchical Composite on Paper

Flexible sensors (FSs) are the key components of intelligent equipment and wearable devices, thus attracting increasing research interests in recent years. However, the preparation of multifunctional FS with good degradability in a natural environment is still challenging. In this work, we fabricated a flexible multimodal sensor that can detect multiple stimuli with only one device by spraying the mixture of carbon black (CB) and reduced graphene oxide (rGO) on a paper substrate. Scanning electron microscopy visualization indicated the CB particles absorbed on the surface of rGO, which then overlayered together, constructing a hierarchical structure. Benefiting from this unique structure, the obtained FS was demonstrated to have good sensitivity for strain, humidity, temperature, and pressure as well as multiple stimuli and was used to monitor human respirations as well as body motions, such as finger and elbow bending and head nodding. Besides, the sensor can be easily degraded in water being free of electronic pollution, but it also can be reused after the soaking-drying process, implying its reliability. This degradable and multimodal FS may find great potential in flexible electronics.