Green functionalization of nanodiamonds by ultrasonication: Surface chemistry-driven antibacterial and antioxidant activities

Green chemistry approaches are increasingly relevant for the sustainable development of functional nanomaterials with biomedical potential. In this work, nanodiamonds (NDs) were functionalized through an environmentally friendly ultrasonication-assisted method using (3-aminopropyl)triethoxysilane, di-tert-butyl peroxide, hydrogen peroxide, and ascorbic acid, avoiding harsh conditions and toxic reagents. Comprehensive physicochemical characterization confirmed successful surface modification for all functionalized nanodiamonds (FNDs). The biological performance of the resulting nanosystems was evaluated through antibacterial assays against Staphylococcus aureus and Escherichia coli , as well as antioxidant and cytoprotective tests. Amino- and peroxide-functionalized NDs exhibited selective antibacterial activity, with significant reductions in viable S. aureus counts in the concentration range between 100–500 μg/mL, whereas antibacterial effects against E. coli were limited and surface-chemistry dependent. In contrast, ascorbic acid–functionalized nanodiamonds (ND-AA) displayed pronounced antioxidant behavior, with a DPPH radical scavenging EC 50 of 17 ± 3 μg/mL and a Trolox equivalent antioxidant capacity of 759 ± 45 μmol TE/g. Notably, ND-AA provided strong protection against oxidative hemolysis in human erythrocytes, achieving an IC 50 of 8.2 ± 0.3 μg/mL, markedly outperforming free ascorbic acid. These results demonstrate that green ultrasonication-driven surface functionalization influences the bioactivity of nanodiamonds, allowing the selective design of antibacterial or antioxidant nanoplatforms. The proposed strategy highlights nanodiamonds as sustainable and versatile nanomaterials for advanced biomedical applications within a green chemistry framework.