Antibacterial activity of multi-metallic (Ag-Cu-Li) nanorods with different metallic combination ratios against Staphylococcus aureus.

Objective: Because of the need to extensively study the synergistic activity of metallic nanoparticles, this study aimed to evaluate the antibacterial activity of mixed metallic nanoparticles, made by differing the weight mixing ratio. We prepared multi-metallic nanorods (NRs) by chemical reduction method, with different ratio combinations of silver Ag and copper Cu, two main batches of nanorods were produced: bimetallic mix made only of Ag-Cu, and trimetallic mix made of Ag-Cu and lithium Li, AgCu NRs and AgCuLi NRs respectively. NaOH was used in the synthesis for the co-reduction of salt precursors. Ag percentage was varied from 10 to 90% in bimetallic NRs but in the trimetallic NRs, which has a fixed ratio of Li (10%), the percentage of silver precursor was from 10 to 80%. The presence of metals was confirmed by energy dispersive X-rays (EDX) analysis. Ion release was detected using inductively coupled plasma spectrometer (ICP) and the values showed that NRs are effective source for ion supply for up to 24 h. The antibacterial activity of metallic NRs was tested against Staphylococcus aureus using Bauer Kirby method.

Results: The bi-synergistic mix of Ag and Cu generates more ions than the tri-synergistic mix of Ag, Cu, and Li. Nevertheless, the later was more efficient and showed higher antibacterial activity at lower concentrations. This effect is less likely to be attributed to modality of ion release. Indeed, the results of our work suggest that besides ion release, alloyed nanorods themselves are toxic and the trimetallic mix exhibited more biocidal activity, specifically at Ag salt concentrations of 30%, 50% and 70%.