Preparation and antibacterial properties of ZnFe₂O₄@polydopamine@Ag nanocomposites

With the improvement of life quality, antibiotics have become indispensable drugs for human beings. However, the prevalence of multiple super pathogenic bacteria in environments are induced by the extensive use of antibiotics, which poses a serious threat to social health. It has become extremely urgent to develop new, effective and durable antibacterial agents in response to a rising publichealth demand. In this paper, magnetic zinc ferrite (ZnFe₂O₄) was prepared by one-pot method using FeCl₃, NaAc and ZnCl₂ as raw materials. Secondly, ZnFe₂O₄@PDA nanospheres were formed by coating polydopamine (PDA) on the surface of ZnFe₂O₄. Finally, silver nanoparticles (Ag NPs) with particle size of 2-16 nm prepared by chemical reduction method were adsorbed on the surface of ZnFe₂O₄@PDA nanospheres to form ZnFe₂O₄@PDA@Ag nanocomposites. The prepared nanocomposite was characterized by TEM, XRD, XPS, UV-Vis, FTIR and Zeta potential. The antimicrobial activity and mechanism of ZnFe₂O₄@PDA@Ag were studied with gram-negative bacteria P. eruginosa, gram-positive bacteria S. aureus and drug-resistant bacteria T-Salmonella. Compared with the same concentration of Ag NPs (loading 0.39%), the antibacterial rate of the material against P. aeruginosa was increased by 57.1%, and that against S. aureus and T-Salmonella was increased by 61.7% and 39.2%, respectively. When tested bacterial were treated for 60 min in 200 μg/mL ZnFe₂O₄@PDA@Ag, the inhibition rates of the material to the three test bacteria reached 99.9%. The results of bacteriostasis mechanism showed that ZnFe₂O₄@PDA@Ag could interact with cell wall surface proteins to destroy cell wall, enter the interior of bacterial and interact with intracellular proteins and related enzymes to hinder cell respiration, damage DNA structure, and inhibit its replication process, thus affecting physiological and biochemical processes such as bacterial respiration and cell division, and eventually lead to bacterial death. With magnetic ZnFe₂O₄ as the core, the nanocomposite is of repeatable utilization, high ratio performance and price, no second pollution. And the coating of PDA layer makes the nanocomposite has good biocompatibility. Importantly, the ZnFe₂O₄@PDA@Ag not only solves the problem of Ag NPs being easy to agglomerate, but also has high antibacterial activity because small particles of Ag NPs can directly enter bacteria through ion channels. This study provides a theoretical basis for research and development of new and intelligent antibiotic materials.