Peptide-induced functionalization of superparamagnetic silver-conjugated iron oxide nanocomposites for enhancing antibacterial activity

Abstract

The integration of antimicrobial peptides and nanomaterials exhibited synergistic antibacterial effects. The peptides as ligands have been used to construct ideal antibacterial agents, attracting great attention. Herein, peptide-modified silver-conjugated iron oxide nanocomposites were successfully prepared according to the procedures as below. The formed Fe3O4 core with sufficient magnetic properties via co-precipitation was coated by polydopamine (PDA) intermediate layer to form Fe3O4@PDA. Due to the groups binding and reducing silver ions in Fe3O4@PDA, Ag nanoshell with high bacteriostatic activity was deposited on the surface of Fe3O4@PDA to form Fe3O4@PDA-Ag. The synthetic peptide (CA2R5) was beneficial for binding with bacterial surface through electrostatic interactions, and they were used to modify Fe3O4@PDA-Ag to form Fe3O4@PDA-Ag-CA2R5 nanocomposites. Fe3O4@PDA-Ag-CA2R5 nanocomposites produced higher antibacterial activity than Fe3O4@PDA-Ag nanocomposites, confirming their synergistic antibacterial effect. The minimum bactericidal concentration (MBC) of Fe3O4@PDA-Ag-CA2R5 nanocomposites against Staphylococcus aureus or Escherichia coli was 0.6 μg/mL Ag. Fe3O4@PDA-Ag-CA2R5 nanocomposites with the same MBC also killed another four bacteria (Listeria monocytogenes, Shigella Castellani, Salmonella typhimurium, and Pseudomonas aeruginosa). The bactericidal activity of Fe3O4@PDA-Ag-CA2R5 nanocomposites against S. aureus remained above 80% after five recycle of antibacterial action and magnetic separation. The antibacterial activity of Fe₃O₄@PDA-Ag-CA₂R₅ nanocomposites was almost not disturbed by pH environment (4, 7.4, and 9) and store time (within 30 days). In the presence of external H2O2, Fe3O4@PDA-Ag-CA2R5 nanocomposites with the high peroxidase (POD)-like activity showed better bactericidal performance due to production of ·OH. The death of the bacterial was attributed to disrupted integrity of the bacterial cell. Fe₃O₄@PDA-Ag-CA₂R₅ with 6-fold MBC did not have toxicity to living organisms. The synthesized Fe3O4@PDA-Ag-CA2R5 nanocomposites in our work possessed strong bactericidal ability, broad antibacterial spectrum, good recyclability, high stability, high POD-like activity, and excellent biocompatibility, providing a promising strategy for building robust antibacterial agents.