Regulation of multifunctional mesoporous core–shell nanoparticles with luminescence and magnetic properties for biomedical applications

Abstract

Gd³⁺-based/mesoporous silica-coated multifunctional core–shell (Y,Gd)₂O₃:Eu³⁺@nSiO₂@mSiO₂ nanoparticles (YGO-Bmnc NPs) with red luminescence, paramagnetic and mesoporous properties are developed as a novel nanomedical platform for combined multimodal diagnosis and therapy. 40 nm sized (Y,Gd)₂O₃:Eu³⁺ (YGO-Ac) nanocore is synthesized by a labor-saving solvothermal method, 20 nm sized perpendicularly aligned mesoporous silica shell is then successfully coated onto the nanocore through two-step sol–gel process and a highly efficient surfactant removal method (NH₄NO₃–EtOH). The surface area of nanocore can be increased from 24 m² g⁻¹ to 562 m² g⁻¹ after coating mesoporous silica shell without any core-free silica NPs. Light-emitting Eu³⁺ ion is chosen as a model to study the solvothermal mechanism and downconversion/upconversion luminescence properties of nanocore; Y³⁺ is doped into matrix to enhance energy transfer from Gd³⁺ to the doped Eu³⁺. Further investigation of luminescence property of YGO-Bmnc NPs shows that they are good red phosphors with millisecond-lever fluorescence lifetime (τ = 2.54 ms, 612 nm, ⁵D₀–⁷F₂). MTT assay reveals low cytotoxicity of the system with IC₅₀ ([Gd]) > 1000 µg mL⁻¹ (6.36 mM). The possibility of using YGO-Bmnc NPs for optical imaging in vitro has been demonstrated. Magnetic resonance imaging (MRI) in vitro exhibits a high r₁ relaxivity of 5.05 mM⁻¹ s⁻¹ and low r₂/r₁ ratio of 1.216 (3.0 T) which is much lower than other existing Gd³⁺-based nanoscale contrast agents, manifesting that YGO-Bmnc NPs can be efficient T₁ contrast agents. In light of their good performance in optical-MR imaging and highly ordered mesoporous structure, it is anticipated that they are suitable for combined multimodal diagnosis and therapy, they can load other imaging agents or drugs to provide complementary information from each imaging modality and guide individual treatment. What's more, the mesoporous silica shell can provide a large venue for the effective modification of various functional groups and biotargets with selectivity and specificity.