Graphene/Metal-Oxide Sensors with Highly Tunable Responses Enabled by Direct Laser

Flexible and wearable devices play a pivotal role in the realm of smart portable electronics due to their diverse applications in healthcare monitoring, soft robotics, human-machine interfaces, and artificial intelligence. Nonetheless, the extensive employment of intelligent wearable sensors faces challenges within a resource-limited environment, necessitating low-cost manufacturing, high reliability, stability, and multifunctionality. In this study, a cost-effective fiber laser direct writing method (fLDW) was illustrated to create highly responsive and robust flexible sensors. These sensors integrate laser-induced graphene oxide (LrGO) with mixed metal oxides on a flexible polyimide film. fLDW simplifies the synthesis of reduced graphene oxide, functionalization of carbon structures, and deposition of metal-oxide nanoparticles within a single laser writing setup. The preparation and surface modification of dense oxygenated graphene networks and semiconducting metal oxide nanoparticles (CuO_x, ZnO­_x, FeO_x) enables rapid fabrication of LrGO/MO_x composite sensors with the ability to detect and differentiate various stimuli, including visible light, UV light, temperature, humidity, and magnetic fluxes. Further, this in-situ customizability of fLDW-produced sensors allows for tunable sensitivity, response time, recovery time, and selectivity. The normalized current gain of resistive LrGO/MO_x sensors can be controlled between -2.7 to 3.5, response times ranging from 0.02 to 15 s, and recovery times from 0.04 to 6 s. Collectively, these LrGO/MO_x sensors stand as a testament to the effectiveness of fLDW in economically mass-producing flexible and wearable electronic devices to meet the explicit demands of the Internet of Things.