Mesoporous Silica Nanoparticles and Films for Cargo Delivery

Mesoporous silica materials are well known materials that can range from films to nanoparticles. Mesoporous silica nanoparticles (MSNs) and mesoporous silica films have been of increasing interest among the scientific community for its use in cargo delivery. Silica provides ease of functionalization, a robust support and biocompatibility.Several methods have been used in order to give the mesoporous silica nanomaterials different qualities that render them a useful material with different characteristics. Among these methods is surface modification by taking advantage of the OH groups on the surface. When a molecule attached to the surface can act as a molecular machine it transforms the nanomaterial to act as delivery system that can be activated upon command. The work covered in this thesis focuses on the development and synthesis of different mesoporous silica materials for the purpose of trapping and releasing cargo molecules. Chapter 2 focuses in the photoactivation of "snap-top" stoppers over the pore openings of mesoporous silica nanoparticles that releases intact cargo molecules from the pores. The on-command release can be stimulated by either one UV photon or two coherent near-IR photons. Two-photon activation is particularly desirable for use in biological systems because it enables good tissue penetration and precise spatial control. Chapter 3 focuses on the design and synthesis of a nano-container consisting of mesoporous silica nanoparticles with the pore openings covered by "snap-top" caps that are opened by near-IR light. A photo transducer molecule that is a reducing agent in an excited electronic state is covalently attached to the system. Near IR two-photon excitation causes intermolecular electron transfer that reduces a disulfide bond holding the cap in place, thus allowing the cargo molecules to escape. The operation of the "snap-top" release mechanism by both one- and two photon is described. This system presents a proof of concept of a near-IR photoredox-induced nanoparticle delivery system that may lead to a new type of photodynamic drug release therapy. Chapter 4 focuses on the attachment of a photoacid molecule on the surface of silica nanoparticles. Upon light irradiation the pKa of the photoacid molecules decreases causing the dissociation of the proton and the acidification of the nanoparticle surface. The local nanoparticle surface acidification was probed using a pH sensitive nanovalve that was attached to MSNs next to a photoacid. The particles were loaded with a fluorescent dye that was contained by the naovalve and released upon acidification of the surrounding environment. The amount of the dye release was measure continuously by detecting its fluorescence. Chapter 5 focuses on the synthesis of materials that utilize the micropatterned structure of a mesoporous silica film to successfully load and release cargo using a thermal sensitive polymer. Films with pore sizes of ~2 and ~5 nm aligned in the pulling direction were synthesized using evaporation induced self-assembly techniques. The pores are exposed using a new method of stamping micropatterns without the use hydrofluoric acid. A well-studied temperature dependent polymer [poly(N-isopropylacrylamide-co-acrylamide)] was grafted onto the surface of these films to act as a temperature activated gatekeeper. Below the lower critical solution temperature (LCST) the polymer is erect and can block the pore openings, trapping cargo inside the pores. When the temperature is above the LCST the polymer collapses and unblocks the pores, allowing cargo to escape. The loading capacities as well as the reusability of these films were studied.