On the mechanism of graphene quantum dot encapsulation by chitosan: A molecular dynamics study

The safe and effective encapsulation and scavenging of carbon nanomaterials is of great importance in bionanotechnology. Chitosan has been extensively studied as a scavenger due to its superior biocompatibility, biodegradability, and strong adsorption capacity. In this work, molecular dynamics simulation was employed to systematically investigate the interactions between chitosan and GQDs at the molecular level. Our simulation demonstrates that chitosan chains in a highly basic solution can rapidly aggregate due to intermolecular hydrophobic interaction and encapsulate GQDs more efficiently, while chitosan chains in a highly acidic solution are relatively rigid and aggregate with difficulty due to repulsive electrostatic interaction, leading to a lower GQD capture efficiency. Moreover, with an increase in pH from 5.9 to 7.1, the hydrophobic segment of a chitosan chain increases and encourages the transition of the chitosan chain from a dispersed state to a self-aggregated state; thus, GQDs can be better encapsulated in the network of aggregated chitosan clusters. These results suggest that the behavior and mechanism of GQD encapsulation is mainly affected by the GQD-chitosan interaction and chitosan self-aggregation.