Controlled-access hollow mechanized silica nanocontainers.

A new category of mechanized nanoparticles, consisting of a hollow mesoporous silica spherical framework controlled by a supramolecular system containing the alpha-cyclodextrin (alpha-CD) ring on a stalk that is tethered to the pore openings on the nanosphere, is synthesized and tested. Construction of the nanovalve relies on the hydrogen-bonding interaction between alpha-CD and the stalk. The stalk is bonded to the nanoparticle chemically and contains an anilino group that is located on the end of the linker molecule that is closest to the pore entrance. When the alpha-CD ring is complexed with the stalk at neutral pH, the bulky cyclic component is located near the pore openings, thereby blocking departure of cargo molecules that were loaded in the nanopores and hollow interior of the particle. Protonation of the nitrogen atoms at lower pH causes the binding affinity to decrease, releasing the alpha-CD and allowing the cargo molecules to escape. The properties of this newly designed pH-responsive nanovalve are compared to those of conventional mesoporous silica nanoparticles. The on-command pH-activated release is measured using luminescence spectroscopy. The effect of different stalk lengths and pH conditions on the release of fluorescent dye cargo molecules is measured.