Optimizing the NIR Fluence Threshold for Nanobubble Generation by Controlled Synthesis of 10-40 nm Hollow Gold Nanoshells

The laser fluence to trigger nanobubbles around hollow gold nanoshells (HGN) with near infrared light is examined through systematic modification of HGN size, localized surface plasmon resonance (LSPR), HGN concentration, and surface coverage. Improved temperature control during silver template synthesis provides monodisperse, silver templates as small as 9 nm. 10 nm HGN with <2 nm shell thickness are prepared from these templates with a range of surface plasmon resonances from 600 to 900 nm. The fluence of picosecond near infrared (NIR) pulses to induce transient vapor nanobubbles decreases with HGN size at a fixed LSPR wavelength, unlike solid gold nanoparticles of similar dimensions that require an increased fluence with decreasing size. Nanobubble generation causes the HGN to melt with a blue shift of the LSPR. The nanobubble threshold fluence increases as the irradiation wavelength moves off the nanoshell LSPR. Surface treatment does not influence the threshold fluence. The threshold fluence increases with decreasing HGN concentration, suggesting that light localization through multiple scattering plays a role. The nanobubble threshold to rupture liposomes is four times smaller for 10 nm than for 40 nm HGN at a given LSPR, allowing us to use HGN size, LSPR, laser wavelength and fluence to control nanobubble generation.