In this study, laser-induced graphene oxide (LIGO) was synthesized through a facile liquid-based process involving the introduction of deionized (DI) water onto polyimide (PI) film and subsequent direct laser irradiation using a CO2 laser (λ = 10.6 μm). The synthesized LIGO was then evaluated as a sensing material for monitoring changes in humidity levels. The synthesis conditions were optimized by precisely controlling the laser scribing speed, leading to the synthesis of LIGO with different structural characteristics and varying oxygen contents. The increased number of oxygen-containing functional groups contributed to the hydrophilic properties of LIGO, resulting in a superior humidity sensing capabilities compared with laser-induced graphene (LIG). The LIGO-based sensors outperformed LIG-based sensors, demonstrating approximately tenfold higher sensing responsivity when detecting changes at each humidity level, along with 1.25 to 1.75 times faster response/recovery times, making LIGO-based sensors more promising for humidity-monitoring applications. This study demonstrated laser ablation in a renewable and natural precursor as an eco-friendly and energy-efficient approach to directly synthesize LIGO with controllable oxidation levels.

Facile synthesis of laser-induced graphene oxide and its humidity sensing properties
    Abstract
        Graphical abstract
    1 Introduction
    2 Materials and methods
        2.1 Preparation of LIG and LIGO
        2.2 Fabrication of resistive humidity sensors based on LIG and LIGO
        2.3 Humidity sensing measurements
        2.4 Characterization
    3 Results and discussion
    4 Conclusions
    Acknowledgements 
    References

• Jin Woo An(School of Materials Science and Engineering, Pusan National University, Busan 46241, Republic of Korea)
• Seok‑Ki Hyeong(Functional Composite Materials Research Center, Korea Institute of Science and Technology, Wanju, Jeonbuk 55324, Republic of Korea)
• Kang Min Kim(Functional Composite Materials Research Center, Korea Institute of Science and Technology, Wanju, Jeonbuk 55324, Republic of Korea)
• Hee Ra Lee(School of Materials Science and Engineering, Pusan National University, Busan 46241, Republic of Korea)
• Ji‑won Park(R & D Center of JB Lab Corporation, Seoul 08788, Republic of Korea)
• Tae‑Wook Kim(Department of Flexible and Printable Electronics, Jeonbuk National University, Jeonju, Jeonbuk 54896, Republic of Korea, Department of JBNU, KIST Industry-Academia Convergence Research, Jeonbuk National University, Jeonju, Jeonbuk 54896, Republic of Korea)
• Sukang Bae(Functional Composite Materials Research Center, Korea Institute of Science and Technology, Wanju, Jeonbuk 55324, Republic of Korea, Department of JBNU, KIST Industry-Academia Convergence Research, Jeonbuk National University, Jeonju, Jeonbuk 54896, Republic of Korea)
• Seoung‑Ki Lee(School of Materials Science and Engineering, Pusan National University, Busan 46241, Republic of Korea) Corresponding author