Structure-property relationships in saccharide-derived carbon dots: Tuning oxygen functionalities and sp(2) domains for antioxidant performance.

Excessive reactive oxygen species (ROS) drive oxidative stress and disease progression, yet the structural determinants of antioxidant activity in carbon dots (CDs) remain unclear. In this study, the influence of oxygenated surface functional groups and carbon hybridization states on the performance of saccharide-derived CDs was elucidated. CDs were synthesized from five saccharide precursors via hydrothermal carbonization, and synthesis parameters were systematically optimized using response surface methodology combined with central composite design (200-240 °C, 6-12 h). Among the tested precursors, xylose yielded CDs (X-CDs) with the smallest size (2.17-4.38 nm), the strongest blue emission (427-450 nm), the highest negative surface charge (-38.5 to -84.6 mV), and the highest quantum yield (0.80-2.81%). Spectroscopic analyses revealed enriched oxygen functionalities (O/C ratio up to 0.32) and graphitic sp domains with reduced sp content, correlating with enhanced electronic delocalization. Optimized X-CDs exhibited potent radical scavenging activity EC₅₀ = 0.047 mg/mL for DPPH; 0.008 mg/mL for ABTS while showing low cytotoxicity toward normal and cancer cells. These findings establish a mechanistic framework linking oxygenated groups and sp hybridization to enhanced antioxidant properties and provide a green, tunable strategy for designing high-performance CDs from renewable precursors for biomedical, nutraceutical, and environmental applications.