LuAG:Pr3+-porphyrin based nanohybrid system for singlet oxygen production: Toward the next generation of PDTX drugs

A highly prospective drug for the X-ray induced photodynamic therapy (PDTX), LuAG:Pr3+@SiO2-PpIX nano composite, was successfully prepared by a three step process: photo-induced precipitation of Lu3Al5O12:Pr3+ (LuAG:Pr3+) core, sol gel technique for amorphous silica coating, and a biofunctionalization by attaching the protoporphyrin IX (PpIX) molecules. The synthesis procedure provides three-layer nanocomposite with uniform shells covering an intensely luminescent core. Room temperature radioluminescence (RT RL) spectra as well as photoluminescence (RT PL) steady-state and time resolved spectra of the material confirm the non-radiative energy transfer from the core Pr3+ ions to the PpIX outer layer. First, excitation of Pr3+ ions results in the red luminescence of PpIX. Second, the decay measurements exhibit clear evidence of mentioned non-radiative energy transfer (ET). The singlet oxygen generation in the system was demonstrated by the 3'-(p-aminophenyl) fluorescein (APF) chemical probe sensitive to the singlet oxygen presence. The RT PL spectra of an X-ray irradiated material with the APF probe manifest the formation of singlet oxygen due to which enhanced luminescence around 530 nm is observed. Quenching studies, using NaN3 as an O-1(2) inhibitor, also confirm the presence of O-1(2) in the system and rule out the parasitic reaction with OH radicals. To summarize, presented features of LuAG:Pr3+@SiO2-PpIX nanocomposite indicate its considerable potential for PDTX application.