Role of Mn(2+) Doping in the Preparation of Core-Shell Structured Fe(3)O(4)@upconversion Nanoparticles and Their Applications in T(1)/T(2)-Weighted Magnetic Resonance Imaging, Upconversion Luminescent Imaging and Near-Infrared Activated Photodynamic Therapy

Core-shell (C/S) structured upconversion coated Fe(3)O(4) nanoparticles (NPs) are of great interest due to their potential as magnetic resonance imaging (MRI) and upconversion luminescent (UCL) imaging agents, as well as near-infrared activated photodynamic therapy (PDT) platforms. When C/S structured Fe(3)O(4)@Mn(2+)-doped NaYF(4):Yb/Er NPs were prepared previously, well-defined C/S-NPs could not be formed without the doping of Mn(2+) during synthesis. Here, the role of Mn(2+) doping on the synthesis of core-shell structured magnetic-upconversion nanoparticles (MUCNPs) is investigated in detail. Core-shell-shell nanoparticles (C/S/S-MUCNPs) with Fe(3)O(4) as the core, an inert layer of Mn(2+)-doped NaYF(4) and an outer shell consisting of Mn(2+)-doped NaYF(4):Yb/Er were prepared. To further develop C/S/S-MUCNPs applications in the biological field, amphiphilic poly(maleic anhydride-alt-1-octadecene) (C(18)PMH) modified with amine functionalized methoxy poly(ethylene glycol) (C(18)PMH-mPEG) was used as a capping ligand to modify the surface of C/S/S-MUCNPs to improve biocompatibility. UCL imaging, T(1)-weighted MRI ascribed to the Mn(2+) ions and T(2)-weighted MRI ascribed to the Fe(3)O(4) core of C/S/S-MUCNPs were then evaluated. Finally, chlorine e6 (Ce6) was loaded on the C/S/S-MUCNPs and the PDT performance of these NPs was explored. Mn(2+) doping is an effective method to control the formation of core-shell structured MUCNPs, which would be potential candidate as multifunctional nanoprobes for future T(1)/T(2)-weighted MR/UCL imaging and PDT platforms.