(765d) Synthesis and Characterization of Plasmon-Resonant Hollow Gold Nanoshells

Spatio-temporal controlled delivery of siRNA, proteins, and small molecules is the main goal of new drug delivery systems. Activation by highly penetrating, physiologically friendly, near infrared (NIR) light can provide sub-millisecond initiation of delivery with sub-micron spatial control. We have developed new synthesis routes to produce monodisperse plasmon-resonant, hollow gold nanoshells (HGN) with strong optical adsorption from 700 – 950 nm. This covers the near-infrared window over which physiological material has minimal adsorption. We have made HGN as small as 10 nm, with < 2 nm thick gold shells as well as larger HGN with cubic and spheroidal shapes. The adsorption maxima can be tuned by controlling the ratio of shell thickness to shell diameter to make HGN of a given size with a range of NIR adsorption maxima.

Adsorption of picosecond NIR light pulses induces large, transient temperature increases in the HGN, which in turn generate transient vapor nanobubbles, similar to the cavitation bubbles generated by ultrasound. The nanobubbles can be used to rupture endosomes, liposomes and even entire cells. We show that the threshold laser fluence needed to initiate nanobubbles increases linearly with HGN radius at a given wavelength for HGN with similar adsorption maxima. Higher fluence is required for NIR wavelengths off resonance, which allows us to differentiate HGN with different adsorption maxima using a combination of NIR wavelength and laser fluence to initiate nanobubble formation. When continuous NIR irradiation is used we find that the temperature difference between the nanoparticle and the surroundings is minimal and there is little difference in performance between HGN of different sizes and shapes and differentiating between various HGN based on wavelength or fluence is difficult.