One-step graphene exfoliation and biofunctionalization 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. While previous studies have examined graphene exfoliation using green solvents, an understanding of how solvent polarity modulates surfactant behaviour, such as PLs conformation and its subsequent interaction with graphene, remains largely unexplored. The interaction between alcohols and PLs regulates their fluidity, conformation, orientation, and species formations. These properties emerge as key experimental parameters leading to enhanced dispersibility, higher exfoliation yield, and distinct lipid fingerprints on the graphene surface. Among the tested solvents, ethanol provided superior graphene dispersibility and stability over an 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 that the bare surface of nanomaterials, such as graphene, can trigger the formation of a slowly exchanging interfacial molecular layer. This process depends on the physiochemical state of the biomolecule in the surrounding medium and provides new insights into controlling interfacial behavior for targeted applications. This work establishes a framework for employing environmentally friendly solvents and biomolecules in graphene exfoliation, offering a versatile platform for the direct integration of biomimetic structures and biomolecules onto 2D materials.