Mesoporous silicate materials as substrates for molecular machines and drug delivery

Mesoporous silica thin films and nanoparticles prepared by surfactant-templated sol–gel techniques are versatile substrates that can be easily derivatized with active molecules to create functional materials. By exploiting the chemical and physical differences that exist in different regions of the mesostructure, active molecules can be deliberately placed using one-pot techniques, or they can be tethered to the exposed surfaces post-synthetically. The methods available for functionalization have been used to design operational machines including nanoimpellers based on the dynamic photoisomerization of azobenzene, and nanovalves based on the switchable motion of supramolecular rotaxanes and pseudorotaxanes. The ability of nanoimpellers and nanovalves to control the release of molecules from the pores of mesoporous silica materials is demonstrated using luminescence spectroscopy. These machines can be designed to operate under a range of external stimuli, including light, electrical (redox) or chemical (pH, competitive binding) energy, making them useful systems for a variety of controlled release applications. Mesoporous silica nanoparticles not functionalized with molecular machines are capable of delivering water-insoluble anticancer drugs to cancer cells. Carefully designed nanoimpellers and nanovalves supported on mesoporous silica nanoparticles offer the ability to develop sophisticated drug delivery vehicles for a wide range of drug molecules.