One step graphene exfoliation and biofunctionalizaton using phospholipids for sustainable bioelectronics

Abstract

Liquid phase exfoliation of graphene is a sustainable and versatile approach for graphene processing. Mild solvents are commonly preferred for their lower toxicity, ease of handling, and environmental compatibility however they are not as effective at matching the surface energy of graphene, compromising exfoliation yield and stability. Here we introduce phospholipids (PLs) to reduce the energy barrier for exfoliation owing to their amphiphilic nature. The PL driven liquid phase exfoliation resulting in few-layer graphene (FLG) dispersions, is investigated in organic (green) solvents of varying polarities to elucidate the effect of polarity on the resulting structures and dispersion. The interaction between alcohols and PLs regulates the fluidity, conformation, orientation, and species formations of the PLs. These properties emerge as key experimental parameters resulting in superior dispersibility, exfoliation yield, and distinct lipid fingerprints on the resulting graphene surface. Among the tested solvents, ethanol provided superior graphene dispersibility and stability over extended period compared to methanol and isopropanol. As proof of concept, the resulting dispersion was used as a conducting ink to coat a hydrogel-based adhesive highlighting its excellent film-forming properties and wettability, and was used to record electrocardiogram signals from the skin surface. Our findings reveal that alcohol interactions can modify PL properties, and highlights how the bare surface of nanomaterials like graphene can trigger the formation of a slowly exchanging layer of surrounding molecules depending on the physiochemical state of a biomolecule in media, offering new insights into controlling these processes for specific applications. This work establishes a framework in the use of environmentalfriendly solvents and biomolecules for graphene exfoliation as a versatile platform for introducing biomimetic structures and biomolecules directly on graphene by rationally selecting PLs with varying end-groups.