Co-assembly of zwitterionic surfactant-like peptides with fatty acids at the solid-liquid interface of magnetic nanoparticles improves their water dispersibility, morphology, and size distribution

The potential of Fe3O4 nanoparticles (NPs) can only be fully realized when highly stable water-dispersible particles with narrow particle size distribution and uniform morphology are produced in a simple sustainable and scalable process. Fatty acids have been successfully utilized as surfactants in the coprecipitation process to produce hydrophobic Fe3O4 NPs with desirable properties, which need additional processing to render them hydrophilic. In this study, an innovative single-step process was introduced for coating Fe3O4 NPs using two surfactant-like peptides, AC-A6K +/- and NH2-A6K +/- (+/-; refers to the coexisting positive and negative charge at the C-terminal of the peptides). This simplified process involves a single-step co-assembly of these peptides with aliphatic chains of palmitic acid (PA) at the surface of the Fe3O4 NPs. The impact of these modifications on the physicochemical properties of Fe3O4 NPs was thoroughly investigated, revealing that the peptide-coated particles exhibited enhanced dispersibility in aqueous environments, a more uniform morphology, nearly neutral zeta potential, and reduced aggregation, resulting in smaller and more uniform particles, when compared to lipid-stabilized NPs (Fe3O4PA). Furthermore, the Fe3O4PA NPs that were coated with AC-A6K +/- peptide (Fe3O4PA/AC-A6K +/-) demonstrated superior coating efficiency and a more favorable particle size distribution than those coated with A6K +/- (Fe3O4PA/A6K +/-). Notably, the crystal structure and magnetic saturation of the Fe3O4PA NPs were preserved even after being assembled with AC-A6K +/- peptide. Our observations suggest that coating fatty acid-stabilized Fe3O4 NPs with surfactant-like peptides by a one-step co-assembly process is feasible and can produce magnetic nanoparticles (MNPs) with potential clinical application.