Plasmonic Photocatalytic Antimicrobial Effect of TiO₂ Nanotubes With Various RGOs

Objectives: This study aimed to evaluate the visible light-based plasmonic photocatalytic antibacterial effects of various reduced graphene oxides coated titania nanotubes (rGO-TiO₂ NTs) and to determine which functional group of rGO exhibits the best visible light-mediated antibacterial activity.
Methods: The rGO powders with three different functional groups ((1) None, (2) -COOH, and (3) -NH₂; Sigma-Aldrich Inc., USA) dispersed in DI water were electrochemically (60V, 1min) coated onto the surface of anodized TiO₂ nanotubes (Φ=100nm). We performed the surface characterizations of rGO-TiO₂ NTs using FE-SEM and diffuse UV-Vis-NIR spectrophotometer. Antibacterial activity was evaluated by the colony-forming-unit (CFU) test, catalase (CAT) activity assay, and superoxide dismutase (SOD) activity assay of P. aeruginosa and S. aureus for the 470 nm LED visible light irradiation (Power density:60mW/cm², Period:15min). MTT assay was performed to evaluate the biocompatibility of the rGO-TiO₂ NTs under visible light irradiation (Statistical analysis: one-way ANOVA, Tukey, p<0.05).
Results: FE-SEM observation and diffuse UV-Vis-NIR spectra showed that all rGO powders were uniformly coated on TiO₂ nanotubes, and all groups showed the highest absorption value around the 470 nm region. The CFU test, CAT assay, and SOD assay resulted that amine-functionalized (NH₂-) rGO-TiO₂ NTs showed the highest visible light-promoting antibacterial activity among all groups in P. aeruginosa and S. aureus (p<0.05). MTT assay results showed excellent biocompatibility of the NH₂-rGO-TiO₂ NTs.
Conclusions: The NH₂-rGO-TiO₂ NTs showing the feature of plasmonic photocatalytic effect at visible light region have enhanced visible light-mediated antibacterial activity and biocompatibility. Therefore, the NH₂-rGO-TiO₂ NTs will be expected to facilitate the development of novel fusion technologies in the surface treatment of implant materials without antibacterial drugs.