Selective adsorption of L-serine functional groups on the anatase TiO₂(101) surface in benthic microbial fuel cells

To help design bacteria-friendly anodes for unmediated benthic microbial fuel cells (MFCs), we explore the role of anatase TiO₂(101) surface biocompatibility in selecting the functional groups of the levo-isomer serine (l-Ser), which contains carboxyl, hydroxyl, and amino groups in a single molecule. By performing total energy calculations and molecular dynamics simulations based on a density-functional tight-binding method, we find that at room temperature, the surface should be active for biomolecules with carboxyl/carboxylic and hydroxyl groups, but it is not sensitive to those with amino groups. The hydrogen bonding between the hydroxyl H and surface O facilitates electron transfer from the pili or the bacterial matrix to the anode surface, which improves the output power density. Thus, in combination with conductive polymers, the anatase TiO₂(101) surface can be an effective biocompatible substrate in benthic MFCs by enabling the surface O to form more hydrogen bonds with the hydroxyl H of the biomolecule.