Biodegradable, spectrally tunable plasmon resonant nanocapsules are created via the deposition of gold onto the surface of 100 nm diameter thermosensitive liposomes. These nanocapsules demonstrate selective release of encapsulated contents upon illumination with light of a wavelength matching their distinct resonance bands, which correspond to 760 and 1210 nm in this study. Spectrally selective release is accomplished through the use of multiple, low intensity laser pulses delivered over a period of less than four minutes, ensuring that illumination affects only the gold-coated liposomes and avoids heating the surrounding media. The result of this illumination scheme for selective release using multiple wavelengths of light is a biologically safe mechanism for realizing drug delivery, microfluidic, and sensor applications.

We recently demonstrated that liposome-supported plasmon resonant gold nanoshells are degradable into components of a size compatible with renal clearance, potentially enabling their use as multifunctional agents in applications in nanomedicine, including imaging, diagnostics, therapy, and drug delivery (Troutman et al., Adv. Mater. 2008, 20, 2604-2608. When illuminated with laser light at the wavelength matching their plasmon resonance band, gold-coated liposomes rapidly release their encapsulated substances, which can include therapeutic and diagnostic agents. The present research demonstrates that release of encapsulated agents from gold-coated liposomes can be spectrally controlled by varying the location of the plasmon resonance band; this spectral tuning is accomplished by varying the concentration of gold deposited on the surface of liposomes. Furthermore, the amount of laser energy required for release is qualitatively explained using the concept of thermal confinement (Jacques, Appl. Opt. 1993, 32(3), 2447-2454). Overlapping thermal confinement zones can be avoided by minimizing the laser pulse width, resulting in lower energy requirements for liposomal content release and less global heating of the sample. Control of heating is especially important in drug delivery applications, where it enables spatial and spectral control of delivery and prevents thermal damage to tissue.

We have recently introduced liposome-supported plasmon resonant gold nanoshells (Troutman et al., Adv. Mater. 2008, 20, 2604–2608). These plasmon resonant gold-coated liposomes are degradable into components of a size compatible with renal clearance, potentially enabling their use as multifunctional agents in applications in nanomedicine, including imaging, diagnostics, therapy, and drug delivery. The present research demonstrates that laser illumination at the wavelength matching the plasmon resonance band of a gold-coated liposome leads to the rapid release of encapsulated substances, which can include therapeutic and diagnostic agents. Leakage of encapsulated contents is monitored through the release of self-quenched fluorescein, which provides an increase in fluorescence emission upon release. Moreover, the resonant peak of these gold-coated liposomes is spectrally tunable in the near infrared range by varying the concentration of gold deposited on the surface of liposomes. Varying the plasmon resonant wavelengths of gold-coated liposomes can provide a method for spectrally-coding their light-mediated content release, so that the release event is initiated by the specific wavelength of light used to illuminate the liposomes. The development of spectrally-coded release can find applications in controlled delivery of multiple agents to support complex diagnostic tests and therapeutic interventions.

Biodegradable, spectrally tunable plasmon resonant nanocapsules are created via the deposition of gold onto the surface of 100 nm diameter thermosensitive liposomes. These nanocapsules exhibit selective release of encapsulated contents upon illumination with light of a wavelength matching their distinct resonance bands. In this study, 760 and 1210 nm laser illumination elicits complete release from gold‐coated liposomes with a corresponding resonance, while causing minimal release from liposomes with an unmatching resonance. Spectrally selective release is accomplished through the use of multiple, low‐intensity laser pulses delivered over a period of minutes, ensuring that illumination affects the gold‐coated liposomes without heating the surrounding media. The use of pulsed illumination to achieve spectral selectivity is validated experimentally and through modeling of the heat equation. The result of this illumination scheme for selective release using multiple wavelengths of light is a biologically safe mechanism for realizing drug delivery, microfluidic, and sensor applications.