Highly Sensitive and Waterproof Flexible Sensor Based on Liquid Metal/Laser-Induced Graphene Multilayer Structure for Human Signal Detection.

Laser-induced graphene (LIG) is widely utilized in flexible sensors because of its simple fabrication and low cost. However, transferring LIG to PDMS results in insufficient conductivity and high overall device resistance, which limits its application in high-sensitivity signal detection. Liquid metal (LM), characterized by high conductivity and low resistance, offers a promising pathway to enhance the sensing performance of LIG. This study proposes a hierarchical composite structure that adopts the liquid metal/polydimethylsiloxane (LP) composite strategy to prepare liquid metal graphene flexible sensors (LM-LIGFS). By adopting this composite strategy, the resistance of the pure LIG flexible sensor has been reduced by approximately 50%, significantly enhancing sensitivity. Furthermore, the composite sensor demonstrates excellent dynamic response capabilities under various pressures, frequencies, and grip strengths, featuring both rapid response times (loading: 0.138 s/unloading: 0.234 s) and high stability (over 9000 s of repetitive bending). Additionally, the sensor possesses superior waterproof properties and generates distinct responses at different underwater depths. Finally, the potential of the LM-LIG flexible sensor in correcting human breaststroke movements was demonstrated. These attributes make the LM-LIG sensor a low-cost and green solution for wearable electronics.