Cooperative aggregation of gold nanoparticles on phospholipid vesicles is electrostatically driven

Gold nanoparticles (AuNP) are known to aggregate on the surface of lipid vesicles, yet the molecular mechanism behind this phenomenom remains unclear. In this work, we have investigated the binding behaviour of AuNPs, synthesized with pulsed laser ablation, to phospholipid vesicles under varying conditions of ionic strength (KCl concentration) and NP to vesicle ratios. Our observations reveal a strong influence of electrolyte concentration on AuNP aggregation mediated by vesicles. Notably, cluster formation is observed even at less than one AuNP per vesicle ratio at low enough ionic strengths. These results evidence a binding mechanism governed by electrostatic attraction with a distinct cooperative behaviour at very low salt concentrations, resulting in a significant increase in nanoparticle clustering. This behaviour is quantitatively analysed through a model that incorporates the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, considering the electrical double layer attraction between dissimilar, non-oppositely charged objects. This study not only provides insight into the fundamental understanding of nanoparticle-vesicle interactions but also suggests potential strategies for controlling nanoparticle assembly in biological and synthetic systems by tuning the ionic strength.