Core–Shell Structured Up-Conversion Luminescent and Mesoporous NaYF4:Yb3+/Er3+@nSiO2@mSiO2 Nanospheres as Carriers for Drug Delivery

Core–shell structured up-conversion luminescent and mesoporous NaYF 4:Yb 3+ /Er 3+ @ n SiO 2 @ m SiO 2 nanospheres were prepared by coating mesoporous SiO 2 layers with different thicknesses on NaYF 4:Yb 3+ /Er 3+ nanoparticles via a simple two-step sol–gel process. The obtained sample shows a typical mesoporous structure and well-dispersed spherical morphology with a narrow size distribution. The nanospheres exhibit little cytotoxicity (via MTT assay), and ibuprofen (IBU) was used as a model drug to access the release properties of the system in detail. The amount of IBU adsorbed in mesoporous channels increases with the thickness of the ordered mesoporous silica shell coated on the NaYF 4:Yb 3+ /Er 3+ nanoparticles. The in vitro release study of IBU reveals a release profile in two steps: an initial diffusion-controlled release, followed by a slower release rate. Furthermore, upon excitation by a 980 nm near-infrared laser, the nanospheres emit green ( 2 H 11/2 and 4 S 3/2 → 4 I 15/2 ) and red ( 4 F 9/2 → 4 I 15/2 ) fluorescence of Er 3+ even after the loading of IBU. Interestingly, the emission intensity of Er 3+ in the bifunctional (mesoporous and luminescence) drug carrier increases with an increase of the cumulative released amount of the model drug (IBU). Thus, the extent of drug release can be easily identified, tracked, and monitored based on the change of the up-conversion luminescence. These results suggest that the core–shell structured NaYF 4:Yb 3+ /Er 3+ @ n SiO 2 @ m SiO 2 nanospheres are a promising material for controlled drug release.