In situ UV-laser-induced forward transfer of carbon nanosphere/graphene composites on siloxane-polyurethane substrates for human health monitoring

In this study, we developed UV-laser-induced carbon nanosphere/graphene (UV-LICNG) composites using a single-step ablation technique. This method employs UV-laser-induced forward transfer (UV-LIFT) to directly fabricate line-patterned UV-LICNG composites on silane-terminated polyurethane (S-PU) substrates with excellent mechanical properties. The unique structure of UV-LICNG, comprising conjugated carbon nanospheres and graphene with a large surface area, enables outstanding strain and humidity sensing performance. Owing to a separation-based sensing mechanism, the UV-LICNG-based strain sensor exhibits highly sensitive strain detection in the low-strain regime, achieving a high gauge factor (GF ≈ 146.5 within the 0–2% strain range), along with excellent linearity (R² ≈ 0.9906), rapid response and recovery times (29 ms and 31 ms, respectively), and exceptional durability over 3,000 stretching cycles at 0.2% strain. These attributes enable precise detection of subtle human motions and vocalization-induced strain signals. In addition, the intrinsic nano–micro porous graphitic structure of UV-LICNG imparts excellent humidity-sensing performance, characterized by fast response and recovery times (4.2 and 4.8 s, respectively), thereby facilitating reliable respiration monitoring and non-contact skin humidity sensing. The combined strain and humidity sensing capabilities, together with the simplicity and scalability of the UV-LIFT process, highlight the strong potential of UV-LICNG-based wearable electronics for continuous human health monitoring and multifunctional wearable sensing applications.