Brian G. Prevo, Shelley Esakoff, and Joseph A. Zasadzinski. University of California, Santa Barbara, Santa Barbara, CA
Near infrared (NIR) light is especially useful for in vivo applications as physiological media are relatively transparent to these wavelengths. Nanoscopic hollow shells of gold possess a strong NIR plasmon absorption. Recently, many researchers have demonstrated an array of different imaging and therapeutic applications taking advantage of these phenomena. Galvanic replacement chemistry (GRC) offers a facile and scalable ‘one pot' route to metal nanoshell synthesis, providing a distinct advantage over conventional layer by layer nanoshell fabrication techniques. Using GRC, template metallic nanoparticles (e.g. silver) act as reductants, nucleating the desired metal nanoshell (e.g. gold) around them provided that the template metal has a lower standard reduction potential. The resulting aqueous core/metal shell particles are formed in minutes, and can be tunably varied from ~ 20 – 75 nm shells with varying thickness (depending on reagent ratios). The use of pulsed NIR laser irradiation for inducing plasmonic heating effects minimizes the temperature rise in the surrounding media due to the fast relaxation times (~ ps) of the metal particles. The kinetics of the laser attenuation by the particles correlates well with the corresponding UV/Vis/NIR spectroscopy, TEM, experimental calorimetry, and heat transfer calculations. We are currently exploring these particles as remote photothermal actuators within submicron liposomes. While bilayer compartments are quite deformable, they pop like balloons if stretched too far (in excess of approximately 5-10%). This could give both spatial and temporal control of drug delivery from liposomes without the need for specialized liposome compositions or large scale heating of the tissue itself.