Vacancy-Enhanced Photothermal Killing of Bacteria Mediated by Graphene Oxide

With the emergence of antibiotic resistance, the development of efficient antimicrobial agents has become increasingly important. Graphene oxide (GO) has been used as an antibacterial agent, but how to realize and improve the antibacterial properties of GO is still required critically. Herein, we prepared two GO samples, abbreviated as GO-V11 and GO-V9. Positron annihilation spectra showed that they possessed predominantly V (V11C) and V (V9C) carbon vacancies, respectively. Their photothermal antibacterial properties were measured against Gram-negative Escherichia coli (E. coli) and Gram-positive Bacillus subtilis (B. subtilis) by using colony-forming unit and liquid optical density assays. GO-V9 displayed a higher photothermal antibacterial efficiency toward the two bacteria than GO-V11 because GO-V9 had a higher photothermal conversion efficiency (PTCE) (57.3%) than GO-V11 (42.5%). To reveal the difference in their PTCEs and antibacterial efficiencies, their energy band structures were tested with density functional theory calculations. The different vacancies changed the energy band structure from the indirect band gap of GO-V11 to the quasi-metallic band gap of GO-V9. The quasi-metallic band gap showed the higher PTCE, so we revealed the importance of the band gap of GO for its antibacterial mechanism. Tuning the vacancy properties is promising for improving the photothermal antibacterial efficiency.