Biocompatibility and antibacterial activity of nitrogen-doped titanium dioxide nanoparticles for use in dental resin formulations

Abstract

The addition of antibacterial functionality to dental resins presents an opportunity to extend their useful lifetime by reducing secondary caries caused by bacterial recolonization. In this study, the potential efficacy of nitrogen-doped titanium dioxide nanoparticles for this purpose was determined. Nitrogen doping was carried out to extend the ultraviolet absorbance into longer wavelength blue light for increased biocompatibility. Titanium dioxide nanoparticles (approximately 20–30 nm) were synthesized with and without nitrogen doping using a sol–gel method. Ultraviolet–Visible spectroscopy indicated a band of trap states, with increasing blue light absorbance as the concentration of the nitrogen dopant increased. Electron paramagnetic resonance measurements indicated the formation of superoxide and hydroxyl radicals upon particle exposure to visible light and oxygen. The particles were significantly toxic to Escherichia coli in a dose-dependent manner after a 1-hour exposure to a blue light source (480 nm). Intracellular reactive oxygen species assay demonstrated that the particles caused a stress response in human gingival epithelial cells when exposed to 1 hour of blue light, though this did not result in detectable release of cytokines. No decrease in cell viability was observed by water-soluble tetrazolium dye assay. The results show that nitrogen-doped titanium dioxide nanoparticles have antibacterial activity when exposed to blue light, and are biocompatible at these concentrations.

Keywords:

• titanium dioxide
• antibacterial activity
• nitrogen doping

Acknowledgments

The authors wish to thank Ms Shannon Olsen for her lab managerial assistance and assay refinement efforts and Mr Duane Cox for his expert engineering skills used to construct the light box. The authors also wish to acknowledge Mr Tony Yuan and Mr Matt Morgan for their assistance with processing the confocal images. In addition, the authors thank Dr Amer Tiba for his critical feedback and thoughtful discussion.

Disclosure

The views expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the Department of the Navy, Department of Defense, or the US Government. Title 17 U.S.C. §105 provides that “Copyright protection under this title is not available for any work of the United States Government”. Title 17 U.S.C. §101 defines a US Government work as a work prepared by a military service member or employee of the US Government, as part of that person’s official duties. This work was funded by the Naval Medical Research Center’s Advanced Medical Development Program using work unit number G1405. Amber Nagy is an employee of the US Government and Andrew Zane, Ann Marie Digeorge Foushee, and Kristin Flores are contracted by the US Government. This work was prepared as part of our official duties. Ranfang Zuo was supported by Fundamental Research Funds for the Central Universities (Grant No 2652013037). The Hungarian National Research, Development and Innovation Office (NKFIH) Grant Nr. K119442 is acknowledged for support of Antal Rockenbauer.

The authors report no other conflicts of interest in this work.