| Upconversion nanoparticles?UCNPs?are becoming promising materials for widely biomedical applications due to their unique optical and chemical properties.Particularly for photodynamic therapy?PDT?,UCNPs can convert near-infrared?NIR?excitation to visible/UV emission,and the fluorescence can activate the photosensitizers?PS?via the process of F?rster resonance energy transfer?FRET?to generate cytotoxic singlet oxygen?1O2?.Thus,the PDT effect closely related to the upconversion luminescence?UCL?intensity.With the aim to enhance the UCL intensity,much attention was paid to control the thickness of shell or construct various kinds of multilayer UCNPs.However,the synthetic process was too complex and difficult to control,and the thick shell of UCNPs is not favourable for effective FRET.In this paper,an effective and facile method was applied to prepare UCNPs by optimizing the composition to largely enhance the red emission?at 660 nm?for efficient generation of 1O2.In detail,the concentrations of Nd3+ions and Yb3+ions doped in the sensitizing shell were systematically researched to balance the energy back-transfer and the light harvest ability.The optimal emission and a relatively high Red/Green?R/G?ratio of NaYF4:Yb,Er,Nd@NaYF4:Yb0.1Nd0.2 UCNPs were obtained simultaneously.Furthermore,the emission firstly demonstrated the energy back-transfer from Er3+to Yb3+ions was also notable under the 980 nm excitation.Then,UCNPs were encapsulated into mesoporous silica shell,and the photosensitizer Chlorin e6?Ce6?was covalently conjugated to form a non-leaking nanoplatform.The efficiency of 1O2 generation obviously increased with the enhanced emission of UCNPs.To further optimize the structure and UCL intensity of UCNPs,we prepared a dumbbell-like UCNPs to prevent the energy back trsnsfer and do not increase the distance of FRET.In addition,the strongest UCL intensity was obtained by controlling the Yb3+doping concentration in transition layer. |
PDF Full Text Request