Measurement of Uptake and Release Capacities of Mesoporous Silica Nanoparticles Enabled by Nanovalve Gates

The uptake and release capacities of mesoporous silica particles are measured on nanovalve-gated stimulated release systems, using a water-soluble biological stain, Hoechst 33342, as the cargo model. Five different types of mesoporous silica nanoparticles, 2D-hexagonal MCM-41, swollen pore MCM-41, rodlike MCM-41, hollow mesoporous nanoparticles, and radial mesoporous nanoparticles, are studied and compared. Solid silica nanoparticles are used as the control. Because of the presence of the nanovalves, the loaded and capped particles can be washed thoroughly without losing the content of the mesopores. The quantities of Hoechst 33342 molecules trapped within the nanoparticles and released upon opening the nanovalves are systematically studied for the first time. The loading conditions are optimized by varying the Hoechst concentration in the loading solutions. Surprisingly, increasing the Hoechst concentration in the loading solution does not always result in a larger amount of Hoechst being trapped and released. Among the five types of mesoporous silica nanoparticles, the radial mesoporous nanoparticles and the swollen pore MCM-41 particles show the highest and lowest release capacity, respectively. The uptake capacities are correlated with the specific surface area of the materials rather than their internal volume. The uptake and release behaviors are also affected by charge and spatial factors.