(616a) Tunable Hollow Gold Nanoshell Structures of Varying Morphology Formed Using Soft Core-Shell Templates
Hollow gold nanoshells are typically formed using hard, solid particle templates that must be removed prior to loading and use. The rigid nature of the hard template surface also means that it plays a passive role in nanoshell formation. As an alternative approach, we employ soft, self-assembled templates that respond dynamically during nanoshell formation and remain an integral part of the final hollow structure. The templates are comprised of lipid bilayer vesicles with a thin coating of cationic polylysine, referred to as layersomes, on the outermost surface to enrich the template interface in soluble gold ion prior to reduction. After surface enrichment, ascorbic acid is used as the reducing agent and subsequent functionalization of the gold surfaces is achieved using thiolated ligands. The nanoshells exhibit rough, jagged or "spiky" surface structures with large specific surface areas and high degrees of near infrared (NIR) absorption and NIR laser heating. The surface roughness of the nanoshells can be further controlled by manipulating the synthesis conditions; for example, surface roughnesses decreases with increasing gold concentration or by using small gold seeds to direct nanoshell formation. Comparatively, gold nanoshells formed on silica nanoparticle templates of the same size coated with polylysine formed only smooth nanoshell surfaces with lower near infrared activity. By co-encapsulating superparamagnetic iron oxide nanoparticles and hydrophilic cargo, the layersome nanoshells are responsive to dual external electromagnetic triggers for release and/or hyperthermia applications. This work suggests that additional parameters beyond those associated with the chemical reaction, such as template flexibility and its ability to restructure, can be explored as a means to create multifunctional gold and gold-iron oxide nanostructures.