Functionalization of nano-graphenes by chimeric peptide engineering

Abstract

Here, we report the non-covalent functionalization of reduced graphene oxide (rGO) nanosheets using chimeric peptides engineered to have a biologically functional sequence, a spacer sequence, and an rGO-binding sequence. As a model peptide with biological activity, the cell-penetrating peptide buforin IIb (Bu) was used. A stretch of seven consecutive phenylalanine residues (7F) was used as the rGO-binding sequence. The various effects of tetraglycine (4G) and tetra-aspartate (4D) as spacers between the biologically active Bu and the rGO-binding 7F sequences were compared. All the chimeric peptides had α-helical structures at the carboxyl-terminal sequence, showing a structural similarity to the α-helical structure of Bu alone. Free chimeric peptides composed of 7F-Bu, 7F4G-Bu, or 7F4D-Bu in solution exhibited cell-penetrating abilities similar to that of Bu alone. However, following attachment onto rGO nanosheets, the compositions of the chimeric peptides affected the biological activity of Bu. Following modification, the 7F4D-Bu chimeric peptide yielded a higher cellular uptake of the rGO nanosheets than the other chimeric peptides. The levels of cellular uptake of the rGO nanosheets modified with the chimeric peptides were further evaluated by measuring the photothermal effect after near-infrared laser irradiation. The cells treated with 7F4D-Bu-modified rGO showed the greatest increase in temperature upon irradiation, with the temperature reaching 58.3 °C. The 7F4D-Bu-modified rGO also exhibited the highest photothermal cell-killing activity upon near-infrared laser irradiation. Our results demonstrate the utility of chimeric peptide engineering for simple and facile one-step non-covalent modification of rGO. The chimeric peptide composed of 7F4D can be further used to tether various functional peptides onto rGO nanosheets.