Self-assembly of inorganic nanoparticle amphiphiles for biomedical applications
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Ensembles of interacting nanoparticles (NPs) can exhibit novel collective properties ─ arising from the coupling between NPs ─ that can be radically different from individuals. Realizing the enormous potential of NPs in biomedical applications requires the organization of NPs into hierarchically ordered structures. My dissertation is focused on the design of NP amphiphiles (NPAMs) and the use of NPAMs as building blocks to construct polymer-inorganic hybrid materials. The NPAMs are made from NPs surface-grafted with amphiphilic block copolymers (BCPs). In this way, the NPAMs synergistically combine the properties of both inorganic NPs and grafted BCPs, such as optical and magnetic properties of NPs, and flexibility of BCPs. First, we demonstrated that NPAMs with relatively low polymer ligand densities (~0.03 chain/nm2) self-assembled into vesicular nanostructures composed of a single layer of NP chains in the membrane. The decrease in the interparticle distance between NPAMs in the chain vesicles led to strong plasmon coupling of NPs and hence enhanced efficiency in photoacoustic imaging. Second, we fabricated hybrid vesicles with well-defined shapes and surface patterns by co-assembling amphiphilic BCPs and NPAMs, which include Janus-like vesicles (JVs) with different shapes, patchy vesicles, and homogeneous vesicles. Third, we prepared magneto-plasmonic hybrid vesicles with various structures through concurrent self-assembly of NPAMs, free BCPs, and hydrophobic magnetic NPs. The hybrid vesicles were demonstrated for both light-triggered release of payload and magnetic resonance imaging. Particularly, the magnetic manipulation of vesicles to specific location can be used to enhance the photothermal effect of the vesicles in cancer imaging and therapy. Finally, we reported that the use of a microfluidic flow-focusing device for the self-assembly of JVs that can act as vesicular motors. The vesicles can be used to encapsulate active compounds, and the release of this payload can be effected using near-infrared light. This systematic study will help us gain deeper understanding of the self-assembly of NPAMs into controllable nanostructures and control the collective properties of NP ensembles for various applications. This research will also provide new insights into the fundamental questions that must be overcome before the hybrid materials can be utilized in effective cancer imaging and treatment.