Hydrophilic/Hydrophobic functionalization of HFBI-Graphene composite using intensity and direction of external electric field: In silico study

Graphene surfaces were selectively functionalized with hydrophobic or hydrophilic properties by aligning Hydrophobin I (HFBI) proteins under an external electric field (EF). By modulating the intensity and direction of the EF, HFBI proteins were precisely aligned and adsorbed onto the graphene surface. Molecular dynamics (MD) simulations revealed EF's influence on the interaction between HFBI and graphene, with a focus on the protein's electric and hydrophobic dipole moments. An EF of 0.05 V/nm maintained the structural stability of HFBI proteins, enabling effective adsorption onto the graphene surface. We verified that the hydrophobic dipole and helix patch orientation of HFBI proteins were significantly rotated when an optimal EF was applied along the Z-axis. Selective functionalization of the graphene surface was achieved by orienting the dipole moments of randomly distributed HFBI proteins (in up, side, or down positions) using an optimal EF (0.05 V/nm) along the Z-axis in either the Z-positive or Z-negative direction. Under a Z-positive EF, hydrophilic functionalization of the HFBI-Graphene composite was observed. Conversely, a Z-negative EF induced hydrophobic functionalization for HFBI proteins in the side and down positions, though not for those in the up position. We attributed this variation in hydrophilic/hydrophobic functionalization to the electrostatic interactions of charged amino acids. Furthermore, by employing HFBI protein mutants with charged amino acids, we successfully achieved hydrophobic functionalization of HFBI-Graphene composite. This study highlights the potential of EF-mediated functionalizing strategies to advance the development of high-performance graphene-based bioelectrodes for biomedical applications.