Miniaturisation of a laser-scribed graphene electrode enables analyte detection at ultra-low concentrations

The detection of analytes at ultra-low concentrations using macroelectrodes is challenging because large capacitive currents mask faradaic currents. Reducing the sensing geometry of electrodes to the micro- or nanoscale significantly boosts the faradaic current relative to the capacitive current. Although lower-dimensional electrodes perform exceptionally well, fabricating micro-sized sensors on a large scale remains a major challenge. In this work, we introduce a simple, scalable fabrication method for creating graphene-based miniaturized electrodes (∼200 µm width) via direct laser writing using a CO₂ laser with a wavelength of 10.6 µm. The resulting LSG (laser-scribed graphene) electrode features a high specific surface area, excellent electrical conductivity, and tunable surface chemistry, making it highly suitable for electrochemical sensing applications. We evaluated the electrochemical performance of the electrode for dopamine detection over a broad dynamic concentration range from 0.167 µM to 18.634 µM. We achieved a sensitivity of ∼0.4 ± 0.013 µA µM^-1 cm^-2, a limit of detection (LOD) of 0.41 µM, and an average response time of ∼0.1 s. Given their simple and scalable fabrication process, low cost, and efficient detection capabilities, LSG-based miniaturized electrodes are highly recommended as an effective platform for the monitoring of neurotransmitters in biomedical and clinical settings.