Fig. 4

Oxygen vacancy of CeO₂NPs contributes to the NOS-like activity. (A) The UV-Vis spectra of both CeO₂NPs and CeO₂NPs mixed with L-Arg (concentration of CeO₂NPs is 1 mM and that of L-Arg is 0.29 mg/mL, the concentration used below is the same as here) in PBS buffer before and after nitrogen blowing are provided. (B) Dissolved oxygen concentration is detected by dissolved oxygen electrode, where CeO₂NPs is added when the concentration of dissolved oxygen in L-Arg solution drops to equilibrium. (C) NO level is measured by Griess Reagents, and oxygen blowing is operated into PBS solution to increase dissolved oxygen level and nitrogen blowing to remove dissolved oxygen, both for 60 min (n = 7). (D) Another type of CeO₂NPs is prepared according to the conditions detailed in Materials section. Post-synthesis, the synthesized CeO₂NPs is baked at 100℃ for a total of 48 h. The XPS data obtained from the dried powder of CeO₂NPs were classified into peaks to illustrate the spectrum of the O element (D) and the Ce element (E), in addition to the proportions of Ce³⁺/Ce⁴⁺ and the proportions of lattice oxygen (Lo) and vacancy oxygen (Vo). (F) The dynamic process of NO generation induced by CeO₂NPs with different Vo ratio. (G) A possible mechanism to interpret the NOS-like activity of CeO₂NPs