Lowering Impedance and Improving Sensitivity in Laser-Induced Graphene Biosensors via Speed-Dependent Sequential Irradiation.

Abstract

Laser-induced graphene (LIG) is a promising material platform for flexible bioelectronic devices, but further lowering its electrochemical impedance, without additives or postprocessing, is essential for scalable, implant-grade microelectrodes. Here, we introduce a speed-dependent sequential irradiation strategy that decouples the kinetically limited carbonization of the first lase from the higher-temperature graphitization induced during the second lase. We show that two passes at 49 mm/s reduce the electrochemical impedance by an order of magnitude compared to a single pass at 105 mm/s. Complementary structural and chemical characterization (Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy) reveals that relasing increases graphitic crystallinity, decreases heteroatom content, and generates a high-surface-area cratered morphology. Finite-element moving-heat-source simulations confirm that the second lasing pass produces markedly higher peak temperatures due to enhanced absorptance and reduced thermal diffusivity of the preformed LINC layer, providing quantitative thermodynamic support for the observed graphitization and controlled ablation. These combined effects enable robust, low-impedance microelectrodes capable of detecting dopamine concentrations below 25 nM using square-wave voltammetry. Importantly, this performance is not achievable using single-pass LIG. We further demonstrate seamless spatial control of the morphology on the same substrate, underscoring the versatility of the approach. Sequential CO₂-laser irradiation therefore offers a scalable, additive-free pathway toward high-performance carbon microelectrode arrays for next-generation neural sensing and stimulation technologies.