One‐Step Synthesis of Size‐Controlled Copper Oxide Nanoparticles on Laser‐Induced Graphene Sensor for L‐Cysteine Detection

Laser‐induced graphene (LIG) has emerged as a sustainable platform for electrochemical sensing due to its low‐cost, chemical‐free, and scalable fabrication. However, integrating metal or metal oxide nanoparticles into LIG remains challenging, as traditional doping strategies are constrained by complex pretreatment procedures and poor metal cation–graphene interfacial interactions, limiting performance. Therefore, simple and efficient strategies for metal‐doped LIG are highly desirable. Herein, we report a single‐step, in situ approach for synthesizing CuO‐decorated LIG using polyimide (PI) as precursor, targeting electrochemical detection of L‐cysteine (L‐Cys). Oxygen plasma pretreatment enhances PI surface hydrophilicity and promotes precursor anchoring, enabling improved nanoparticle dispersion. Subsequent laser irradiation simultaneously induces LIG formation and CuO nanoparticle synthesis. Importantly, this strategy enables control of nanoparticle size by tuning precursor concentration, yielding average diameters of ≈53 nm (50 m m ) and ≈194 nm (100 m m ), a feature rarely explored in LIG systems. Structural and compositional analyses confirm CuO incorporation into the LIG matrix while preserving high conductivity (≈20 Ω sq − 1 ). As a proof of concept, CuO–LIG electrodes exhibit enhanced electrochemical performance for L‐Cys detection, reducing oxidation overpotential to 350 mV vs Ag/AgCl (3 m KCl), achieving a limit of detection of 8.89 µ m and fast response time, only 0.23 ± 0.06 s, demonstrating a simple and effective route for LIG‐based sensors.