Interactions of POPC Liposomes with Graphene Investigated by Quartz Crystal Microbalance and All-Atom Molecular Dynamics Simulations

The chemical properties of the interface between graphene and a surrounding biological environment are key to designing devices that integrate graphene in applications such as biosensing, graphene liquid cells, and biomedical devices. To this end, controlled functionalization of graphene with lipids enables the integration of a lipid-based biological sensitizing layer, which opens possibilities for sensor regeneration, as well asthe encapsulation of intact liposomes in graphene liquid cells. In this work, we developed a robust graphene-based quartz crystal microbalance sensor to study liposome-graphene interactions. Various graphene transfer protocols were investigated to obtain a clean graphene layer on the quartz crystal. Graphene with the lowest surface roughness was used to assess liposome-graphene interactions. POPC liposomes ruptured upon contact with graphene, resulting in the formation of a lipid monolayer as evidenced by the quartz crystal resonance frequency shift. The obtained lipid monolayer was stable, which was evidenced by an unchanging frequency shift after it had been rinsed with buffer. All-atom molecular dynamics simulations confirmed that it is energetically favorable for lipids to dissociate from the liposomal bilayer and adhere to graphene, resulting in the formation of a stable monolayer. The obtained QCM sensor with graphene in combination with the AAMD simulations therefore provided a powerful characterization platform to study the dynamics of graphene-liposome interactions.