Self-assembling into nanostructure of Cu-Ag NPs with both enhanced antimicrobial activity and cytocompatibility

The germ-killing functions of silver and copper nanoparticles (NPs) were worthy of biomedical applications, but as heavy metals, NPs need to be more antimicrobial at lower doses to minimize hazards to human health, which requires more explorations on the new structures resulting from the compositing between two metals. In this study, self-assembled Cu-Ag bimetallic NPs were synthesized using a two-step reduction method. Results showed that both the Cu and Ag in Cu-Ag NPs existed as pure phases, the nanoparticles comprised ∼5 nm primary particles that self-assembled into ∼50 nm secondary particles surrounded with carbon-chain coatings. The larger secondary particles provided Cu-Ag with good particle dispersibility and chemical stability against deeper oxidation above ∼360 °C, while the smaller primary particles facilitated their suspensions in achieving a maximum inhibition ring of 10.01±0.25 mm and a minimum optical density (OD) of 0.11±0.01. Cu-Ag NPs demonstrated superior antimicrobial performance against all target strains, exhibiting synergistic enhancement through released active ions and reactive oxygen species (ROS). Cell viability ranged from 74.4 % to 95.4 % after co-culturing for 24 h, confirming that all synthesized nanometals were non-toxic to L929 cells at most concentrations. Increasing the suspension concentration enhanced antimicrobial activity while reducing cell viability. This conflict established an optimal Cu/Ag ratio of 10:4 and a concentration of 4 μg/mL, allowing Cu-Ag NPs to perform both broad-spectrum bactericidal activity and cell safety.