First-principles study of L-cysteine adsorption on vacancy graphene and Ag-doped graphene

The understanding of interactions between graphene and biomolecules is of fundamental relevance to the area of nanobiotechnology. Herein, taking L-cys as the probe molecule, its adsorptions on single-vacancy graphene (SV), double-vacancy graphene (DV), Ag doped single-vacancy graphene (AgSV) and Ag doped double-vacancy graphene (AgDV) were investigated using first-principles calculations. SV and AgSV exhibit exothermical chemisorptions while AgDV exhibits endothermical chemisorptions towards L-cys, regardless of the end type. DV shows exothermical chemisorption towards S-end L-cys and endothermical physisorption towards O-end and N-end L-cys. Two-step energy barrier related to initial symmetry broken and structural reorganization leads to differences in adsorption types and adsorption energies. Site-specific immobilization was also revealed. Calculations at 298.15 K and 1 atm reveal that L-cys adsorptions on SV, AgSV, the S-end, O-end adsorptions on DV are thermodynamically favourable. The results could provide guidance for further choice of graphene in bionanotechnological applications.