Figure 3.

Schematic diagram of the drug loading and releasing processes in mesoporous silica nanoparticles (NPs) (a) or nonporous silica NPs (b, c). (a) Mesoporous silica NPs are loaded with cargo molecules entrapped in the interior of the nanochannels (meso pores). The inner surface can be modified to control the binding affinity with cargos. Gatekeepers (e.g., gold NPs) are attached to mesoporous silica NP surface for capping to prevent premature release. Cargo release can be facilitated by detaching the gatekeeper with stimuli. (b) Cargos could be encapsulated inside nonporous silica NPs and are released when the silica matrix is degraded. (c) Cargos could also be conjugated with nonporous silica NPs through various chemical linkers. The release profile of cargos is controlled by the responsive degradation of the chemical linkers.