Synthesis And Application Of Silicate-based Long Persistent Luminescence Nanomaterials For X-Ray Induced Photodynamic Therapy

Persistent luminescence nanoparticle scintillators（PLNS）have been widely explored for X-ray-induced photodynamic therapy（X-PDT）because of their persistent luminescence after ceasing radiation.This can allow less cumulative irradiation time and dose while still generating the same amount of reactive oxygen species（ROS）as conventional scintillators,making them an effective option to combat cancer cells.However,PLNS encounered various issues in this field,including visible light nanoparticles exhibit a single luminous color,poor chemical stability,poor morphology monodispersion,weak luminescence and afterglow performance,and a high X-ray dose.Silicate luminescent materials have been chosen to address these issues due to their excellent chemical stability,more kinds of matrix and luminous color diversity,a wide range of emission wavelength characteristics and favorable biocompatibility.Long persistent luminescence nanomaterials were synthesized using mesoporous silicon template method.Their afterglow performance under X-ray excitation was optimized by regulating defect engineering.Additonally,luminescence mechanism was studied.Furthermore,the research on its application in X-PDT and advanced afterglow anti-counterfeiting has been carried out,and the following contents have been studied.（1）Synthesis of Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺PLNS and its application in X-PDT.Blue Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺PLNS were synthesized using mesoporous silicon template method.In this work,the effects of synthesis temperature,nanoparticle size and Mg excess degree on the properties of PLNS were systematically studied.The application potential of the X-PDT was explored by combining with photosensitizer Ru[（bpy）₃]²⁺.When the sintering temperature was determined to be 900°C,Mg content was 160%and particle size was 110 nm,the afterglow and luminescence properties were optimized.The final optimized afterglow time was 1780 s（≥0.32mcd/m²）,which was 1.8 times higher than the un-optimized situation In addition,the material can still produce afterglow after 10 minutes of X-ray excitation.After 0.27Gy X-ray irradiation,singlet oxygen production and cytotoxic effects of composite nanoparticles(SiO₂@Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺@Ru[（bpy）₃]²⁺)connected with Ru[（bpy）₃]²⁺were successfully demonstrated in cancer cells.In vivo experiments further verified the tumor inhibition effect of the composite nanoparticles.In summary,the 600 nm emission peak of Ru[（bpy）₃]²⁺in the optimized composite nanoparticles can still be observed for 20 s after the X-ray excitation is stopped,indicating that the blue afterglow emission bands of Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺have sustained in transferring the energy to the photosensitizer,and thus singlet oxygen can be sustainably produced.Therefore,the frequency and time of X-ray irradiation can be reduced,and the radiation damage is reduced to normal cells.（2）Properties of Si-Ge solid solution long persistent luminescence materials in Zn₂SiO₄:Mn²⁺.Green Zn₄Ge_xSiO₈:Mn²⁺PLNS were synthesized using mesoporous silicon template method.The effects of Ge amount and sintering temperature on the morphology and properties of nanoparticles were systematically studied after the nanization of traditional phosphors Zn₂SiO₄:Mn²⁺.When Ge content was 0.3,the sample’s afterglow time was the longest,which could last for 1650 s（≥0.32 mcd/m²）,which was 1.3 times longer than that without Ge.When Ge content was 1.5,the luminescence of the sample was the strongest,which was nearly 20 times higher than that of the sample without Ge.However,combined with the morphological characterization,it is found that the more Ge content is,the shorter the time of the afterglow is,and the particles have poor monodispersion with serious sintering for the samples.What’s more,decreasing sintering temperature can improve the monodispersion of particles,but it is not conducive to the formation of target phase or the enhancement of luminescence.In summary,it is found that Ge can greatly improve the luminosity of Zn₂SiO₄:Mn²⁺nanoparticles,but has adverse effects on the morphology monodispersion.Considering that nanoparticles with good monodispersity are needed for biological applications,it is not suitable for further application of X-PDT.（3）Synthesis of Zn₂SiO₄:Mn²⁺,Yb³⁺,Li⁺PLNS and its application in X-PDT.Green Zn₂SiO₄:Mn²⁺,Yb³⁺,Li⁺PLNS were synthesized using mesoporous silicon template method.In this work,the effects of different Zn:Si caused by excessive Zn and the doping concentration of various ions on the properties of nanoparticles were systematically studied.The X-PDT application potential was explored by combining with Rose Bengal photosensitizers.It is determined that Zn:Si=0.868,Mn²⁺,Yb³⁺,Li⁺doping concentrations of 0.5%,1.5%,3%,respectively,could produce the best afterglow performance,and the afterglow time can reach10200 s（≥0.32 mcd/m²）,which is 6.5 times longer than Zn₂SiO₄:Mn²⁺nanoparticles.In addition,the photoluminescence and X-ray brightness increased by 7 times and more than 9 times respectively than Zn₂SiO₄:Mn²⁺nanoparticles when Li⁺doping concentration was 7%.After 0.18 Gy X-ray irradiation,singlet oxygen generation was successfully demonstrated in cancer cells by composite nanoparticles connected with photosensitizers(SiO₂@Zn₂SiO₄:Mn²⁺,Yb³⁺,Li⁺@Rose Bengal),which verified the X-PDT effect of the composite particles.In summary,the emission peak of Rose Bengal at 592 nm in the optimized composite nanoparticles was still observed 10 s after the X-ray excitation was stopped,which also indicated that the green afterglow emission bands of Zn₂SiO₄:Mn²⁺,Yb³⁺,Li⁺had sustained in transferring the energy to the photosensitizer.At the same time,the experimental results in comparison also show that improvement of the luminescence and afterglow properties of PLNS can promote the energy transfer between PLNS and photosensitizers more effectively.