Spectral Response of Interfacial Water at Different Lipid Monolayer Interfaces upon Interaction with Charged Gold Nanoparticles

Understanding the interactions of nanoparticles with cell membranes is crucial for designing materials for biomedical applications. In this paper, through the combination of vibrational sum frequency generation (VSFG) and molecular dynamics simulation techniques, the spectral responses of the interfacial water molecules due to interaction of anionic gold nanoparticles (AGNPs) and cationic gold nanoparticles (CGNPs) with three differently charged model cell membranes, namely, 1,2-dipalmitoyl-sn-glycero-3-phosphoglycerol (DPPG, negatively charged), 1,2-dipalmitoyl-3-trimethylammonium-propane (DPTAP, positively charged), and zwitterionic 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC, neutral), have been investigated. The interfacial water intensity at the DPPG–water interface decreases abruptly in the presence of CGNPs because of the significant change in Stern layer configuration, whereas it does not show any noticeable change in the presence of AGNPs, resulting in an unperturbed stern layer configuration. However, in the case of DPTAP and DPPC interfaces, the Stern layer is significantly perturbed in the presence of both the charged GNPs, resulting in a substantial change in the interfacial water intensity. This is attributed to the change in orientation and structure of interfacial water molecules in the presence of both charged GNPs. These results provide valuable insights into the solvation structure and dynamics of water molecules to exploit for designing and optimizing the delivery system for biomedical applications.