A facile and effective method to prepare long-persistent phosphorescent nanospheres and its potential application for in vivo imaging

Abstract

In order to prepare new promising optical nanoprobes, long afterglow nanospheres with a narrow size distribution were successfully synthesized using mesoporous silica nanospheres (MSNs) both as morphology-controlling templates and the silicon source of long afterglow silicate. In our experiments, metal ions (Sr²⁺, Mg²⁺, Eu³⁺, Dy³⁺) were impregnated into the pores of mesoporous silica nanospheres followed by high temperature calcination. The X-ray powder diffraction results show that SrMgSi₂O₆ crystalline phase can be formed after calcination at 900 °C for 3 h in a weakly reducing atmosphere and the as-prepared afterglow nanospheres have a nominal composition of SiO₂/SrMgSi₂O₆:Eu_0.01, Dy_0.02. The field emission scanning electron microscopy results indicate that the as-prepared long afterglow silicate nanoparticles have spherical morphology with a narrow size distribution and their size can be tuned between 50 nm and 500 nm. Approximately 10 nm pores can be formed in the as-prepared nanospheres, certified by the transmission electron microscopy and BET analysis results. Long afterglow properties, ranging from 400 nm to 550 nm, peaking at 467 nm, can be observed from the as-prepared nanospheres. After the surface was modified with amino groups, grafted by PEG–COOH and irradiated with 365 nm UV light for 10 min, the afterglow signal could be observed in real time for more than 1 h in a live mouse after peritoneal injection.