Energy level engineering of graphene-functional graphene quantum dot for highly sensitive and selective electrochemical detection of uric acid in human sweat.

Pristine graphene lacks a bandgap, which prevents energy-selective electron transfer and results in a poor selectivity among analytes with similar oxidation potentials, along with high background currents. To address this intrinsic limitation, we hybridize graphene with quantum-confined graphene quantum dots (GQDs) to create an energy-level gating interface for electrochemical sensing. The mixture of citric acid, arginine, boric acid and phosphoric acid was heated at 180 °C and then protonated with hydrochloric acid, yielding a positively charged, arginine-functionalized B,P-co-doped GQD (RBP-GQD⁺). Dropwise addition of RBP-GQD⁺ to a graphene oxide dispersion drives rapid electrostatic self-assembly, followed by thermal reduction under N₂ to form a G/RBP-GQD composite. The composite exhibits enhanced electrocatalytic activity and selectivity from three synergistic effects: enlarged electroactive area, Schottky heterojunction formation, and energy-level gating interface. The catalytic behavior depends critically on GQD structure, which governs energy-level alignment and thus selectivity. Using this platform, an electrochemical sensor for uric acid achieves linear range of 0.1-200 µM, a detection limit of 0.031 µM, and reliable operation in human sweat. More generally, this work establishes a mesoscopic electronic-state engineering strategy that extends to other zero-bandgap materials through functionalization with tailored quantum dots-opening avenues for catalysis, diagnostics, and environmental sensing.