Laser-Induced Graphene for Electrochemical Sensing: From Process Development to Real-World Applications

Graphene-based electrodes offers a promising solution for developing effective electrochemical sensors due to their high surface area (2630 m²g^-1), mechanical strength (Young’s Modulus ~1100 GPa), electrical conductivity (~64 mS cm^-1), chemical stability, biocompatibility, and tunable properties. Among graphene-based electrodes, laser-induced graphene (LIG) has emerged as a cost-effective, scalable alternative by directly converting sp³ carbon found in carbon-rich substrates, such as polyimide into conductive sp²-hybridized carbon found in graphene through a laser scribing technique. We have demonstrated that the surface area and wettability of the LIG can be tuned to greatly improve the sensitivity of electrochemical enzymatic biosensors (detection limits down to the picomolar range) and reduce the water layer buildup between the ion-selective membrane and the electrode, which improves the accuracy of the sensor readings and its longevity. We have systematically characterized LIG formation and how the quality of graphene can be improved by varying the laser power, focus, DPI (dots per inch), and the number of repeat runs. We demonstrated that initial defocused lasing followed by focused lasing improves the quality of graphene produced, the surface wettability, and the resulting electrochemical sensors. The LIG electrodes have been used in a wide variety of electrochemical sensing applications including in food safety, environmental (soil and water) monitoring, wearable health sensors, and even for urinary potassium and ammonium, and salivary lactate and potassium sensing. All these electrochemical sensors have been validated in real-world samples and demonstrated to have limits of detection and linear sensing ranges that are relevant to their sensing applications. Additionally, we have demonstrated the ability to fabricate LIG electrodes using biodegradable substrates (i.e.; paper and cork) as a more sustainable approach to electrochemical sensing. The responses of the LIG-based ion-selective electrodes from cork and paper exhibited similarities to those made from the standard material, polyimide. In these studies, we show how high-quality, sensitive LIG electrodes can be systematically fabricated and integrated into electrochemical analytical devices for point-of-service and in-field applications.