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 NaYF4:Yb3+/Er3+@nSiO(2)@mSiO(2) nanospheres were prepared by coating mesoporous SiO2 layers with different thicknesses on NaYF4:Yb3+/ Er3+ 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 NaYF4:Yb3+/Er3+ 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 (H-2(11/2) and S-4(3/2) -> I-4(15/2)) and fed (F-4(9/2) -> I-4(15/2)) fluorescence of Er3+ even after the loading of IBU. Interestingly, the emission intensity of Er3+ 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 Cart be easily identified, tracked, and monitored based on the change of the up-conversion luminescence. These results suggest that the core-shell structured NaYF4:Yb3+/Er3+@nSiO(2)@mSiO(2) nanospheres are a promising material for controlled drug release.