Fabrication of Enzymatic Lactate Biofuel Cells Using Direct Laser Writing Technology for Wearable Real-Time Monitoring Applications

Lactate is a key biomarker of metabolic activity, with elevated levels serving as indicators of various physiological and pathological states. Continuous monitoring of lactate is, therefore, essential for both healthcare and performance optimization, while enzymatic biofuel cells (EBFCs) provide a sustainable approach to power wearable biosensing systems. Despite lactate's abundance in biofluids and the existence of several successful examples of lactate-based EBFCs in the literature, further advancement is needed to implement these systems on scalable electrode platforms. Here, we report the first lactate/oxygen EBFC fabricated on laser-induced graphene (LIG) electrodes prepared by direct laser writing. The bioanode and biocathode were functionalized exclusively with essential components, including lactate oxidase with tetrathiafulvalene and bilirubin oxidase with ABTS, respectively. The device exhibited an open-circuit potential (OCP) of about 600 mV and a maximum power density of 48.1 mu Wcm-2 at 20 mM lactate. Importantly, the power density increased linearly with lactate concentration across the physiologically relevant sweat range (5-20 mM, slope 2.9 mu Wcm-2mM- 1, R 2 = 0.997), underscoring its suitability for sweat-based biosensing. Stable operation was maintained for over 2 h under continuous lactate flow, along with good reproducibility, with relative standard deviation (RSD) values below 5% across 10 independently fabricated devices. These findings demonstrate the viability of LIG as a sustainable and scalable electrode material and highlight the potential of simplified EBFC architectures for future integration into wearable and self-powered biosensing technologies.