Fig. 4.

Increased or decreased surface defects correlate with ROS generation and oxidative stress. (A) XPS of untreated (red), plasma-treated (blue), and surface passivated (black) TiO₂ NPs was used to monitor changes in oxygen vacancies in response to surface modification. Binding energies and peak areas are listed in Table S1.^† (B) EPR spectra of control and surface-modified TiO₂ NPs (10 mg mL⁻¹) with DMPO (0.02 M). The TiO₂ NP spectrum is replotted from Fig. 1 for comparison. (C) Fluorescence spectra of H₂DCF (5 μM) in response to ROS. All TiO₂ NPs (400 μg mL⁻¹) were incubated with H₂DCF in the dark (1 h, RT). Auto-oxidation of H₂DCF (5 μM, green) results in a small positive signal. (D) Western blots were used to quantify changes in cellular oxidative stress as a function of surface modification of TiO₂ NPs. The control shows cells incubated with standard cell culture media (MEM + 10% FBS). Experiments were carried out in triplicate. A representative western blot is shown in Fig. S5A.^†