Nanoparticle-loaded perfluorocarbon droplets for imaging and therapy

Nanoscale perfluorocarbon droplets that are in the liquid phase at physiological temperatures, but which can be converted to gas using ultrasound, offer potential as a contrast agent for the detection and therapy of solid tumours. Nanoparticles such as quantum dots can also be encapsulated within PFC droplets, enabling multi-modal imaging and controlled nanoparticle release. In this work, experiments were conducted to investigate the impact of nanoparticle incorporation on droplet conversion at low and high ultrasound frequencies. It was found that incorporation of quantum dots lowered the inertial cavitation threshold at 1 MHz by 20%. In contrast, quantum dot nanoparticles did not significantly alter the conversion threshold of perfluorohexane or perfluoropentane droplets at 18 MHz. It was also shown that perfluoropentane droplets could be converted to gas and imaged at high frequency in hepatomas in mice, using brief high pressure bursts to achieve the phase conversion. Finally, optically fluorescent quantum dots incorporated within droplets were used to demonstate the feasibility of assessing biodistribution in rabbits using fluorescence histology.