Mesoporous silica nanoparticles for applications in drug delivery and catalysis
Mesoporous silica materials, discovered in 1992 by the Mobile Oil Corporation, have received considerable attention due to their superior textual properties such as high surface area, large pore volume, tunable pore diameter, and narrow pore size distribution. A general overview of recent developments of organofunctionalized hybrid mesoporous silica nanoparticles (MSNs) materials is presented, focusing on the use of MSNs as biocompatible, stimuli-responsive drug delivery devices and a description of the sophisticated systems with novel capping agents and controlled release mechanisms.
The potential of employing MSNs for drug delivery was further studied on the biological behaviors of these nanoparticles in blood vessels. The research demonstrated the size and surface effects on the interaction of MSNs with human red blood cell membranes, and proposed that appropriate surface modification of nanoparticles can improve their biocompatibility and diminish their dangerous side effects on red blood cells.
MSN materials have also been extensively applied in the field of catalysis. We have tethered a Pt(II) bipyridine catalyst onto MSNs in order to enhance its thermal stability and product selectivity. A detailed investigation on the catalytic activity showed that the catalytic performance was similar between the homogeneous and heterogeneous systems. However, the homogeneous system exhibited appreciable degradation after 16 hr at 100 °C. Instead, using MSNs as scaffolds, this catalyst system retained its activity after 72 hr at 150 °C, demonstrating an increased thermal stability.
We also explored the feasibility of introducing a biocatalyst to function synergically with MSN supported inorganic catalyst. Supported Au-nanoparticle catalyst employed for direct alcohol oxidative esterification usually suffers from a slow alcohol oxidation rate. We designed a co-catalyst system by combining a biocatalyst, alcohol dehydrogenase enzyme and an inorganic catalyst, mesoporous silica nanoparticles supported Au nanoparticle to accelerate reaction tandemly. We identified several factors that affect the catalytic performance of the co-catalyst system. We then examined the catalytic capability of this co-catalyst system on the one-pot transformation of allyl alcohol into allyl acrylate ester. We expect that this system could lead to the development of a variety of catalyst pairs for a great scope of reactions.
We further explored the possibility of the intracellular co-delivery of a biocatalyst and its substrate using MSNs. We designed a gold nanoparticle-capped MSNs platform and demonstrated its ability to release luciferin from the interior pores of MSNs upon gold nanoparticle uncapping in response to disulfide-reducing antioxidants, and co-deliver bioactive luciferase from the PEGylated exterior surface of MSNs into Hela cells. The effectiveness of intracellular catalytical reactions was evaluated by measuring luminescence emission signals. We envision that our co-delivery systems could play a significant role in intracellular controlled catalysis and tumor imaging.
The research presented in this dissertation would provide MSNs with a great potential for various biomedical and catalytic applications.