Effect of TiO₂ Nanoparticles Defect Structure on their ROS Scavenging Ability

Titanium dioxide nanoparticles ($\mathrm{TiO}_{2} \mathbf{N P s}$) have attracted significant interest for their ability to modulate reactive oxygen species (ROS) levels within cells. These nanoparticles have shown promise in drug delivery, sonodynamic, photodynamic, photothermal, and ionizing radiation-based anti-cancer therapies, as well as antimicrobial and antioxidant applications. In this study, we analyzed the effects of $\mathbf{T i O}_{2}$ NP defect structures—specifically the presence of stoichiometric ($\mathrm{Ti}^{\mathbf{4}}$) and non-stoichiometric ($\mathrm{Ti}^{3+}$ and $\mathbf{T i}^{\mathbf{2 +}}$) titaniumions within the crystal lattice—and the aggregation state of TiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> NPs on their ROS scavenging capabilities in both cell-free conditions and H<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>O<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>-treated $\mathbf{L 9 2 9}$ cells. Two types of $\mathrm{TiO}_{2} \mathbf{N P s}$ with varying concentrations of $\mathrm{Ti}^{3+}$ and $\mathrm{Ti}^{2+}$ ions were synthesized and characterized using XRD, TEM, SAXS, and XPS techniques. The antioxidant properties of these $\mathbf{T i O}_{2}$ NPs were assessed through chemiluminescence and optical spectroscopy using ROS sensors. Results from chemiluminescence and total antioxidant capacity assays indicated that the synthesized TiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> NPs possess radical scavenging abilities, with $\mathrm{TiO}_{2} \mathbf{N P s}(1)$, containing a higher amount of non-stoichiometric titanium ions, demonstrating a stronger effect. Concentrations of up to $40 \mathrm{mg} / \mathrm{L}$ of TiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> NPs showed no impact on $\mathrm{L929}$ cell viability or cell death. Moreover, $\mathrm{TiO}_{2} \mathbf{N P s}(1)$ exhibited a tendency to reduce $\mathbf{H}_{2} \mathrm{O}_{2}$ induced oxidative stress in $\mathbf{L 9 2 9}$ cells, while $\mathrm{TiO}_{2} \mathbf{N P s}(2)$ had the opposite effect, likely due to their propensity for aggregation in the cell medium. Our findings suggest that the synthesized TiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> NPs have potential as agents for modulating intracellular ROS levels at concentrations that do not compromise cell viability.