Mesoporous silica nanoparticles are useful nanomaterials that have demonstrated the ability to contain and release cargos with mediation by gatekeepers. Magnetic nanocrystals have the ability to exhibit hyperthermic effects when placed in an oscillating magnetic field. In a system combining these two materials and a thermally sensitive gatekeeper, a unique drug delivery system can be produced. A novel material that incorporates zinc-doped iron oxide nanocrystals within a mesoporous silica framework that has been surface-modified with pseudorotaxanes is described. Upon application of an AC magnetic field, the nanocrystals generate local internal heating, causing the molecular machines to disassemble and allowing the cargos (drugs) to be released. When breast cancer cells (MDA-MB-231) were treated with doxorubicin-loaded particles and exposed to an AC field, cell death occurred. This material promises to be a noninvasive, externally controlled drug delivery system with cancer-killing properties.

Conspectus Nanotechnology has been cited as a response to the most challenging issues facing society as a whole today. With nanoscale assemblies promising to improve on previously established therapeutic and diagnostic motifs, medicine stands to benefit significantly from advances in nanotechnology. To this end, the use of delivery platforms has attracted attention during the past decade, with researchers shifting their focus towards devising ways to deliver therapeutic and / or diagnostic agents, and away from developing new drug candidates. Metaphorically, the use of delivery platforms in medicine can be viewed as the “bow-and-arrow” approach, where the drugs are the arrows and the delivery vehicles are the bows. Even if one possesses the best arrows that money can buy, the arrows are not going to be useful if one does not have the appropriate bow to deliver the arrows to a desired location. The same can be said of drugs. Currently, a variety of strategies for delivering bioactive agents within living tissue exists. Dendrimers, polymers, micelles, vesicles, and nanoparticles have all been investigated for their use as possible delivery vehicles. With the growth of nanomedicine, one can then envisage the possibility in theranostic medicine of fabricating a vector that is capable of releasing simultaneously powerful therapeutics and diagnostic markers selectively to diseased tissue. In our design of new theranostic delivery systems, we have focused our attention on using mesoporous silica nanoparticles (SNPs). It is possible to store a payload of “cargo” molecules within such a robust platform that is stable to a wide range of chemical conditions. This stability allows SNPs to be functionalized with responsive mechanically interlocked molecules (MIMs) in the shape of bistable rotaxanes and psuedorotaxanes to yield mechanized silica nanoparticles (MSNPs). These MIMs can be designed in such a way that they either change shape or shed off some of their parts in response to a specific stimulus, allowing a theranostic payload to be released from the nanopores to a precise location at the most ideal time. In this Account, we chronicle the evolution of various MSNPs which came about as a result of our decade-long collaboration, and discuss advances that have been made in synthesizing novel hybrid mesoporous silica nanoparticles, and the various MIMs which have been attached to their surfaces. Recognizing the theranostics of the future, we aim to start moving out of the chemical domain and into the biological one, with some MSNPs already being subjected to biological testing.