Synthesis and antibacterial activity of magnetic Fe3O4-loaded silver nanocomposites

The problem of drug-resistant bacteria arising from antibiotic misuse is a growing global health concern. Therefore, there is an urgent need to develop effective antimicrobial agents. In this study, Fe3O4 nanospheres with superparamagnetic properties were first prepared by the "solvothermal method" and then coated with dopamine. The coordination principle was then utilized for the adsorption of ultra-small Ag nanocomposites (Ag NPs) on the surface of Fe3O4@PDA nanocomposite (FPN). The material morphology and crystallinity of the prepared composites were characterized using TEM, XRD, XPS, UV-vis, and FT-IR analysis techniques. The performance and mechanism of inhibition of Gram-negative Escherichia coli (E. coli), Gram-positive Bacillus subtilis (B. subtilis), and drug-resistant Salmonella typhi (S. typhi) by Fe3O4@PDA@Ag nanocomposite (FAN) were also studied. The results showed that FAN with an inhibitory concentration of 200 μg/mL achieved 99.9% inhibition against E. coli, B. subtilis, and S. typhi at 60 min. Zeta potential, PI staining, ion leakage, bacterial growth curves, cytoplasmic leakage, and biocompatibility experiments were used further to explore the probable bacterial inhibition mechanisms of the composites. The results of the experiments done to determine the inhibition mechanism suggest that the composite material disrupts the negative environment of the bacterial cell wall, altering membrane permeability and ultimately leading to rupture and death. The findings of this study demonstrate that FAN possess excellent antibacterial properties and have a promising future in wastewater treatment and biomedical applications.