Antimicrobial peptide-functionalized magnetic nanoparticles for rapid capture and removal of pathogenic bacteria

•Novel antimicrobial peptide-based magnetic nanoparticles are synthesized.•Ultrarapid and magnetic separation of pathogenic bacteria is achieved.•Capture efficiency is greater than 97% with incubation time of 5 s.•AMP-MNPs do not have bactericidal effect, but a strong capture ability.•MNPs can capture and separate bacteria from potable and recreational water. A method that can rapidly and effectively capture and separate pathogenic bacteria, which remain viable even after capture for subsequent analysis, is potential future tool for medicine, water and food safety. In this study, novel antimicrobial peptide-based magnetic nanoparticles with neutralized bactericidal effects are developed for rapid and efficient capture and removal of pathogenic bacteria in water samples. The antimicrobial peptide-functionalized magnetic nanoparticles (AMP-MNPs) consist of magnetic core (Fe3O4), polydopamine (PDA) as an intermediate layer and antimicrobial peptide (Magainin I) as an outer layer (PDA@Fe3O4-AMP). The unique structure of AMP-MNPs allows retaining their capture ability via strong electrostatic interactions, while eliminating their bactericidal actions during interactions with bacteria’s outer membrane. The results of fluorescent microscopy indicate that the AMP-MNPs has no bactericidal effect, but only the binding ability towards bacteria. Factors such as concentration of AMP-MNPs, pH of the medium and ionic strength are crucial in mediating rapid and efficient bacterial capture. Higher concentration of AMP-MNPs (0.5 mg/mL) results in a high sensitive capture effect on 5 × 106–5 × 101 cfu/mL E. coli O157:H7, and a broad spectrum of capture ability towards various bacterial strains (1.5 × 107 cfu/mL) and allow rapid and efficient capture and magnetic-separation of pathogenic bacteria from tap and recreational water samples with capture efficiency greater than 97% and incubation time as short as 5 s. Whereas semi-selective capture of pathogenic and Gram-negative bacteria is achieved at lower concentration of AMP-MNPs (0.1 mg/mL). The developed AMP-MNPs may find great potential in microbiological applications and water quality analyses.