Facile and rapid fabrication of wearable biosensors via femtosecond laser-directed micro-patterning with large-sized reduced graphene oxide for physiological monitoring

Wearable biosensor is the most emerging field that can monitor physiological signals from the human body. Although the current biosensor demonstrates high fidelity and stability, there are still high demands to replace expensive materials and reduce complicated and time-consuming procedures. Laser-based direct micro-patterning is a promising technology owing to its fast, scalable, and cost-effective processing. In addition, large-sized reduced graphene oxide (LrGO) facilitates electron transfer through its large basal plane, leading to high electrical-conductivity as well as low cost, long-term usability/stability, and excellent biocompatibility. In this study, femtosecond (FS) laser-directed micro-patterning was adopted to realize several types of biosensors, providing various advantages, such as high-speed (∼500 mm s⁻¹), high-resolution (∼50 μm), and large-area processing (>8 in.). Moreover, the development of LrGO facilitated a solution-based process and the coating of the LrGO on the FS laser-directed micro-pattern could result in skin-mountable biosensors, so-called laser-directed micro-patterning for skin-mountable graphene sensors (LMGSs), with simplified steps. The LMGSs monitored important biological information such as skin temperature, skin hydration, and electrophysiological signals with electrocardiogram, electromyogram, and electrooculogram at the clinical level. This strategy could be established for not only the wearable biosensors but also the interconnect of stretchable electronics or inductive coils for wireless communication.