Self-Assembly of Nanoparticle Surfactants and Their Use As Theranostic Agents

Controlling the assembly of nanoparticle building blocks is of great interest because ‘emergent’ properties arise that can enable new applications in energy, imaging and medicine. Self-assembly has long been demonstrated a viable approach to drive button-up organization in amphiphilic systems including molecular surfactants and block-copolymers. We have recently synthesized nanoparticle surfactants that also self-assemble and cluster into ‘colloidal-molecules’ with controllable morphology. A scalable synthesis method was developed by tuning steric stabilization imparted by grafted hydrophilic polymers and short-ranged attractive interactions from small molecule ligands. The phase behavior of nanoparticle surfactants has been explored in detail and found to mimic that of molecular surfactants. Cluster formation is analogous to micelle formation and nanoparticle surfactants also stabilize oil-water and air-water interfaces by adsorbing strongly. The close arrangement of metallic particles in clusters and emulsions induce changes in optical absorption and local electric fields due to surface plasmon resonance. Specifically, near infrared (NIR) absorption is greatly enhanced in nano-Pickering emulsions. This enables the use of these materials as powerful non-linear contrast agents for photoacoustic imaging and for mechanical thrombolysis. Self-assembly of surfactant nanoparticles represents a powerful platform to form diverse nanostructures and colloidal materials with novel properties.