Synthesis and conjugation of Sr₂MgSi₂O₇:Eu²⁺, Dy³⁺ water soluble afterglow nanoparticles for photodynamic activation

The applications of afterglow particles for photodynamic activation and biological imaging have become a topical research area. For these applications, it is critical to have water soluble nanoparticles. However, the synthesis of water soluble afterglow nanoparticles like Sr₂MgSi₂O₇:Eu²⁺, Dy³⁺ is a challenging issue because most afterglow materials are very complicated in composition that cannot be synthesized by simple chemical routes. Here, for the first time, Sr₂MgSi₂O₇:Eu²⁺, Dy³⁺ water soluble and stable nanoparticles are synthesize using a modified Sol-Gel method followed by the grinding and coating with APTES. The surface coating of the afterglow with APTES and the conjugation with PpIX and folic acid not only improve their water solubility but also enhance the PpIX luminescence by 10 times. More importantly, these strategies make it possible to produce singlet oxygen under X-ray irradiation, which is a very important result for deep cancer treatment. In addition, the surface coating and conjugation largely increase the cell uptake and greatly reduce their dark cytotoxicity. All these results indicate the methods reported here for afterglow nanoparticle synthesis, coating and conjugation are successful, and consequently, the prepared Sr₂MgSi₂O₇:Eu²⁺, Dy³⁺/PPIX/Folic acid nano-conjugates are promising for X-ray induced photodynamic therapy on cancer treatment.