Development of an eco-friendly sensor manufactured from reused milk cartons and graphene-based conductive ink as substrates

This work presents the development of an innovative, disposable, and eco-friendly electrochemical sensor based on a post-consumer milk carton substrate and graphene-based conductive ink. The sensor was fabricated through a simple and cost-effective process, promoting sustainable reuse of urban solid waste while maintaining excellent electrochemical performance. Cyclic voltammetry and square wave voltammetry revealed a reversible redox profile and efficient electron transfer properties, demonstrating the viability of the device for analytical applications. The sensor was applied to the detection of two analytes of high clinical and environmental relevance: L-cysteine (L-Cys), a key biomarker involved in redox balance under pathological conditions, and paraquat (PQ), a highly toxic herbicide widely used in agriculture. For L-Cys, the device showed a linear response in the range of 50.0 to 700.0 µmol L^-1 with a detection limit of 14.6 µmol L^-1, suitable for physiological levels in human serum. For PQ, a linear response was observed in the range of 5.0 to 300.0 µmol L^-1, with a detection limit of 0.21 µmol L^-1, meeting the safety standards established by U.S. regulations for drinking water. The sensor also demonstrated good selectivity in the presence of common interfering species and was successfully applied in real sample analyses, including serum, tap water, and fruit juice. These results highlight the potential of this low-cost and sustainable platform for decentralized and real-time monitoring in clinical diagnostics and environmental safety, aligning with global sustainability goals and promoting circular economy principles.