Sustainable synthesis of corncob-derived graphene quantum dots for versatile electrochemical detection of metabolic biomarkers via SPCE/GQDs@Nafion platform

This study reports the green, sustainable hydrothermal synthesis of graphene quantum dots (GQDs) from corncob agricultural waste and their integration into a screen-printed carbon electrode (SPCE) platform, modified with Nafion binder (SPCE/GQDs@Nafion), for multi-analyte electrochemical biosensing. The synthesized GQDs exhibited a spherical morphology with an average diameter of 6.21 nm, composed of 64.7 wt% carbon and 25.48 wt% oxygen, with characteristic UV absorption at 208 nm (π–π* C C transition) and 250 nm (n–π* C O transition), and a green fluorescence emission under 254 nm UV irradiation. Electrochemical characterization using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) demonstrated enhanced signal response from GQD-modified SPCE compared to bare SPCE. The SPCE/GQDs@Nafion sensor successfully detected four analytes: AC (LOD: 0.378 μM, linear range: 1–2000 μM), AA (LOD: 3.968 μM, linear range: 0–2000 μM), UA (LOD: 2.546 μM, linear range: 0–2000 μM), and DA (LOD: 0.298 μM, linear range: 0–50 μM). Real sample analyses confirmed effective detection of AA, UA, and AC across multiple biofluids, while DA detection was selectively validated in urine. Multi-analyte testing revealed signal interference between analytes with close oxidation potentials, identifying a key direction for future optimization. This work demonstrates a cost-effective, eco-friendly approach to biosensor fabrication with strong translational potential for point-of-care clinical diagnostics.