Assembly of graphene oxide vs. reduced graphene oxide in a phospholipid monolayer at air–water interfaces

Abstract

Graphene and its derivatives, such as graphene oxide (GO) and reduced graphene oxide (rGO), havepropelled advancements in biosensor research owing to their unique physicochemical and electroniccharacteristics. To ensure their safe and effective utilization in biological environments, it is crucial tounderstand how these graphene-based nanomaterials (GNMs) interact with a biological milieu. Thepresent study depicts GNM-induced structural changes in a self-assembled phospholipid monolayerformed at an air–water interface that can be considered to represent one of the leaflets of a cellularmembrane. Surface pressure–area isotherm and electrostatic surface potential measurements, alongwith advanced X-ray scattering techniques, have been utilized in this study. Experimental findingsdemonstrate a strong interaction between negatively charged GO flakes and a positively chargedmonolayer, primarily dictated by electrostatic forces. These GO flakes assemble horizontally beneath thehead groups of the monolayer. In contrast, rGO flakes permeate the zwitterionic lipid layer throughdominant hydrophobic interaction. This organization of GNMs alters the in-plane elasticity of the lipidfilm, exhibiting a drop in the electrostatic potential of the surface according to the extent of oxygencontaininggroups. These results provide a solid groundwork for designing devices and sensors aimed ataugmenting the biomedical applications of GNMs.