A hybrid lipid membrane coating “shape-locks” silver nanoparticles to prevent surface oxidation and silver ion dissolution

Abstract

The controlled synthesis of stable silver nanoparticles (AgNPs), that do not undergo surface oxidation and Ag⁺ ion dissolution, continues to be a major challenge. Here the synthesis of robust hybrid lipid-coated AgNPs, comprised of L-α-phosphatidylcholine (PC) membranes anchored by a stoichiometric amount of long-chained hydrophobic thiols and sodium oleate (SOA) as hydrophobic binding partners, that do not undergo surface oxidation and Ag⁺ ion dissolution, is described. UV-Visible (UV-Vis) spectroscopy, transmission electron microscopy (TEM), and inductively coupled plasma mass spectrometry (ICP-MS) demonstrate that in the presence of strong oxidants, such as potassium cyanide (KCN), the hybrid lipid-coated AgNPs are stable and do not undergo surface oxidation even in the presence of membrane destabilizing surfactants. UV-Vis studies show that the stability of hybrid lipid-coated AgNPs of various sizes and shapes is dependent on the length of the thiol hydrocarbon chain and can be ranked in the order of increasing stability as follows: propanethiol (PT) < hexanethiol (HT) ≤ decanethiol (DT). UV-Vis and ICP-MS studies show that the hybrid lipid-coated AgNPs do not change in size or shape confirming that the AgNPs do not undergo surface oxidation and Ag⁺ ion dissolution when placed in the presence of strong oxidants, chlorides, thiols, and low pH. Long-term stability studies, over 21 days, show that the hybrid lipid-coated AgNPs do not release Ag⁺ ions and are more stable. Overall, these studies demonstrate hybrid membrane encapsulation of nanomaterials is a viable method for stabilizing AgNPs in a “shape-locked” form that is unable to undergo surface oxidation, Ag⁺ ion release, aging, or shape conversion. More importantly, this design strategy is a simple approach to the synthesis and stabilization of AgNPs for a variety of biomedical and commercial applications where Ag⁺ ion release and toxicity is a concern. With robust and shielded AgNPs, investigators can now evaluate and correlate how the physical features of AgNPs influence toxicity without the confounding factor of Ag⁺ ions present in samples. This design strategy also provides an opportunity where the membrane composition can be tuned to control the release rate of Ag⁺ ions for optimizing antimicrobial activity.