(701a) Gold-Layersome Nanoshells: Preparation and Characterization for Photothermal Therapy

Gold nanoshells have attracted great attention in medicine due to their surface plasmon resonance (SPR) bands, nontoxic properties and ease of surface functionalization. A unique property of gold nanoshells is the ability to tune the optical resonances within the near-infrared (NIR) region. The high absorption efficiency of gold nanoshells and their ability to efficiently convert absorbed light into heat has enabled them to be an effective candidate for photothermal therapy for cancer treatment. In this work we present a new approach to synthesize gold nanoshells with variable shell morphologies using soft hollow templates; anionic liposomes coated with the cationic polyelectrolyte poly-l-lysine (PLL) (ca. 100 nm hydrodynamic diameter). PLL was used to enrich the template surface by adsorbing negatively-charged gold species in solution.

Two different approaches to create gold nanoshells were compared. In both approaches the nanoshells were characterized by transmission electron microscopy, field-emission scanning electron microscopy and UV-vis/NIR spectroscopy. The first method was in situ reduction of chloroauric acid in presence of layersomes, which has been reported for gold nanoshell formation on liposomes. This approach led to a packed structure of gold nanoparticles on the layersome surface with little control over nanoparticle or shell morphology. To gain this control and achieve a more continuous gold shell, a second approach based on a seeded growth method was used. Small gold nanoparticles (1-3 nm diameter) were synthesized and anchored onto the surfaces of layersome via electrostatic interactions to nucleate the growth of the gold overlayer. The resulting gold nanoshells exhibited controllable shell thickness by adjusting the gold ions concentration. Upon changing the shell thickness, the absorption wavelength corresponding to these plasmonic layersomes could be tuned to the biologically safe near-infrared wavelength. Changing chloroauric acid concentration also led to gold nanoshells with rough structures (branched, star or flake-like) that may have been due to the shape directing effect of PLL. It is hypothesized that the key role of PLL as a structure directing agent is originated from the electrostatic interaction between positive amine groups in PLL and the negatively charged AuNPs. The prepared gold nanoshells have the potential to be used for photothermal therapy and photothermal mediated drug delivery.