Covalent Functionalization of Graphene with PAMAM Dendrimer and Its Implications on Graphene’s Dispersion and Cytotoxicity

Abstract

Functionalizing graphene with polymers is an important area of research, owing to the potential applications of graphene in biomedicine and nanotechnology. In this paper, we investigate the covalent functionalization of graphene with a G2 poly(amidoamine) (PAMAM) dendrimer using all atom molecular dynamics simulations. Specifically, we study the dependence of the grafting approach (grafting-from and grafting-to) and the binding location of the PAMAM dendrimer to graphene (top, edge, and top-edge), on the functionalization. The instantaneous snapshots and the thickness profiles of the equilibrated dendrimer-graphene complexes reveal that the thickness of the adsorbed dendrimer is more in the grafting-to case. We have also observed that the edge-binding dendrimers of grafting-from approach can coat the graphene on either of its sides, whereas the top-binding dendrimers adsorb mostly on the side of their binding. In addition to the grafting approach and the binding location, we find that the dimension of the graphene sheet also determines the extent of surface coverage by the dendrimer. From the radii of gyration analysis and the thickness profiles of the dendrimers, we illustrate that an increase in the sheet dimensions gives rise to smoother surface coverage, whereas increasing the grafting density results in rough surface coverage. We also find that the percentage of surface coverage is higher in the grafting-to approach when compared with the grafting-from method, for a given binding condition and sheet dimensions. Our results on the dispersion of the functionalized graphene in water suggest that the dispersion of graphene depends on its surface coverage and is more probable with the grafting-from approach. Furthermore, our results on the interaction of functionalized graphene with a dimyristoylphosphatidylcholine (DMPC) lipid membrane demonstrate no bilayer disruption, hence illustrating the noncytotoxicity of the graphene–dendrimer complex.