Ultrasensitive and\nStretchable Strain Sensors Based\non Laser-Induced Graphene With ZnO Nanoparticles

Laser-induced graphene (LIG) has attracted considerable\nattention\nfor its use in flexible and stretchable sensors, owing to its electrical/mechanical\nproperties and scalable fabrication processes. Although laser scanning\nfacilitates the formation of LIG and its strain sensor, the strain-sensing\nsensitivity enhancement of LIG remains limited by the material’s\nproperties and structural design. In this study, we demonstrate a\nsubstantial improvement in sensitivity that was achieved by fabricating\na LIG using ZnO nanoparticle (NP)-assisted photothermal enhancement.\nThe results show that ZnO NPs selectively reduce the threshold fluence\nneeded to convert polyimide (PI) into LIG. By transferring the LIG\nformed on PI to poly(dimethylsiloxane), we fabricate a stretchable\nstrain sensor with ultrahigh sensitivity and a gauge factor of 1214\nat 10% strain, which is approximately 60 times higher than the gauge\nfactor without ZnO NPs. Using the selective graphenization properties\nof LIG, a flexible, dual-sided integrated sensor sheet that is equipped\nwith flexible strain and ultraviolet (UV) sensors is demonstrated.\nThis sheet enables simultaneous monitoring of UV intensity and joint\nbending angles of sports wearable devices. We validated the developed\nsensors by attaching them to a runner’s body to monitor and\nsimulate forefoot and heel strikes, demonstrating the sensor’s\nultrahigh sensitivity and long-term stability without the need for\na camera. These findings highlight the potential of the proposed method\nfor developing multifunctional sensor applications with ultrahigh\nsensitivity and stability.