LuAG:Pr 3+ -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 nanocomposite, was successfully prepared by a three step process: photo-induced precipitation of the Lu3 Al5 O12 :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 1 O2 inhibitor, also confirm the presence of 1 O2 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.