Nanomaterials based on TiO2 have been attracting much attention due to their diverse applications in the biomedical or engineering fields. The ability of TiO2 nanotubes to suppress proliferation of microbes bodes well for bone implants, dental devices, and so on[1],[2]. However, the inactivation effectiveness relies on the presence of light and fades away in darkness[3]. Recent studies have shown that TiO2 modified with gold nanoparticles can inactivate bacteria in the absence of light (4) making the materials more attractive clinically. Nevertheless, the bacteria inactivation mechanism is still not fully understood. It has been suggested that reactive oxygen species (ROS) play a key role in the inactivation process and others have indicated that electron disturbance of the bacteria membrane (charge transfer) is the dominant mechanism[4] similar to that observed from graphene[5] and fullerene[6]. In most cases, the mechanistic studies focus on the materials but few direct evidences have been presented from the perspective of the bacteria.
In this study, TiO2 nanotubes with a diameter of 100 nm are incorporated with different amounts of Au nanoparticles by magnetron sputtering and different concentrations of the bacteria Staphylococcus aureus (S. aureus) are incubated on the modified TiO2 nanotubes. The inactivation effects are evaluated by CFU investigation and the ROS concentration is determined by flow cytometry and confocal laser scanning microscopy. In addition, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) are performed to monitor the morphological changes on the bacteria. An inactivation rate of 90% is observed from the 40s-Au nanoparticle modified TiO2 sample in the absence of light after 24 h and the efficacy is in fact significantly higher than that in the presence of light as well as the 120s-Au sample without light (Fig. 1). Flow cytometry shows that the ROS signals of both the experimental and control groups have the same level (Fig. 2). Our results suggest that the dominant inactivation mechanism is charge transfer and ROS only plays a relatively minor role in the suppression process.
Figure 1. Survival rate of different sputtering time-Au nanoparticles modified TiO2 nanotubes (D means in dark and L means with light)
Figure 2. Reactive Oxygen Species signal detection result by flow cytometry.
References:
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[2] Yoshinari M, Matsuzaka K, Inoue T, Oda Y, Shimono M. Bio-Functionalization of Titanium Surfaces for Dental Implants. Materials transactions. 2002;43(10):2494-501.
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