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

Abstract

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 (Fe₃O₄ ^PA). Furthermore, the Fe₃O₄ ^PA NPs that were coated with AC-A6K^± peptide (Fe₃O₄ ^{PA/AC−A6K±}) demonstrated superior coating efficiency and a more favorable particle size distribution than those coated with A6K^± (Fe₃O₄ ^PA/A6K±). Notably, the crystal structure and magnetic saturation of the Fe₃O₄ ^PA 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.

Graphical abstract