Antibacterial mechanisms of a novel type picosecond laser-generated silver-titanium nanoparticles and their toxicity to human cells

In this study, we explored the antibacterial mechanisms for a novel type of Ag-TiO(2) compound nanoparticles (NPs) produced from an Ag-TiO(2) alloy using a picosecond laser and evaluated the toxicity of the Ag-TiO(2) NPs to a range of human cell types. Transmission electron microscopy was used to determine the morphology, shapes, and size distribution of the laser-generated Ag-TiO(2) NPs. UV-visible spectrometer was used to confirm the shift of light absorbance of the NPs toward visible light wavelength. Results showed that the laser-generated Ag-TiO(2) NPs had significant antibacterial activities against both Gram-negative and Gram-positive bacterial strains, including Escherichia coli, Pseudomonas aeruginosa, and the methicillin-resistant Staphylococcus aureus. Increased level of reactive oxygen species was produced by E. coli after exposure to the Ag-TiO(2) NPs, which was accompanied with lipid peroxidation, glutathione depletion, disintegration of cell membrane and protein leakage, leading to the cell death. Five types of human cells originated from lung (A549), liver (HePG2), kidney (HEK293), endothelium cells (human coronary artery endothelial cells [hCAECs]), and skin (human dermal fibroblast cells [HDFc]) were used to evaluate the cytotoxicity of the laser-generated Ag-TiO(2) NPs. A weak but statistically significant decrease in cell proliferation was observed for hCAECs, A549 and HDFc cells when co-cultured with 2.5 µg/mL or 20 µg/mL of the laser-generated Ag-TiO(2) NPs for 48 hours. However, this effect was no longer apparent when a higher concentration of NPs (20 µg/mL) was used after 72 hours of co-culture with human cells, suggesting a possible adaptive process in the cells had occurred. We conclude that picosecond laser-generated Ag-TiO(2) NPs have a broad spectrum of antibacterial effect, including against the drug-resistant strain, with multiple underlying molecular mechanisms and low human cell toxicity. The antimicrobial properties of the new type of picoseconds laser-generated Ag-TiO(2) compound NPs could have potential biomedical applications.