Spectrally-Selective Light-Induced Release from Gold-Coated Liposomes

In the interest of creating functional nanostructures to address unmet medical needs for controlled delivery and release, we recently presented liposome-supported plasmon resonant gold nanoshells (Troutman et al., Adv. Mater. 2008, 20, 2604-2608). These composite structures are degradable into components of a size compatible with renal clearance, potentially enabling their use as multifunctional agents in imaging, diagnostic, therapeutic, and drug delivery applications. The liposome allows for the encapsulation of substances, including diagnostic and therapeutic agents, while the plasmon resonant structure facilitates the rapid release of encapsulated contents upon laser light illumination using a wavelength corresponding to the resonance band. Furthermore, the resonance of these gold-coated liposomes is tunable in the near-infrared range. Using this tunability, we achieved spectrally selective content release using two laser wavelengths, in which full content release occurs for liposomes spectrally matched with the illumination source and minimal release occurs for liposomes not matched with the source. Also, spectrally selective release is accomplished through the use of multiple, low intensity laser pulses, ensuring that illumination affects only the gold-coated liposomes and avoids heating the surrounding media; this observation is supported experimentally and through modeling of the heat equation. Within the context of biological and medical applications, gold-coated liposomes may enable the spectral, spatial, and temporal control of release of multiple agents from liposome carriers by means of a physiologically safe light-delivery method.