Fabrication of Size-Controlled Carbon Dots with Biofilm-Disrupting Activity for Antibacterial Applications

Carbon dots (CDs) have demonstrated broad-spectrum biological activity, with particle size considered a key determinant of their biological efficacy. However, the interrelationships among size, structure, and function remain unclear. To address this, we synthesized CDs under identical hydrothermal protocols and separated them into four size fractions (NPDCDs₁-NPDCDs₄), to directly investigate how particle size influences physicochemical and antibacterial properties. The four fractions exhibited distinct optical and structural properties: NPDCDs₁ (3.2 nm) emitted at 510 nm with the highest C-O content; NPDCDs₂ (2.2 nm) emitted at 510 nm with high C-C/C=C content; NPDCDs₃ (2.1 nm) showed red-shifted emission at 570 nm and the highest C=C ratio; NPDCDs₄ (1.9 nm) displayed the most red-shifted emission at 580 nm (λex = 380 nm) with the highest C=O content. Notably, NPDCDs₁ demonstrated excellent biocompatibility and potent antibacterial activity, primarily through efficient disruption of bacterial biofilms, possibly due to its high C-O content and appropriate particle size. Thus, particle size modulated biological function via corresponding changes in structural and surface chemical properties. These findings clarify that particle size critically influences both the physicochemical properties and antibacterial activity of CDs, providing an empirical foundation for the rational design of highly efficient and low-toxicity carbon-based antimicrobial materials.