Perfluorocarbon bubbles as photoacoustic signal amplifiers for cancer theranostics

Phase change nanoemulsions have been proposed as theranostic agents, using light to induce vaporization into bubbles (also called optical droplet vaporization). The current work uses perfluorohexane nanoemulsions (PFH-NEs) stabilized by a highly biocompatible and optically absorbing fluorosurfactant shell. Once vaporized, the bubbles can be used for contrast enhanced ultrasound (CEUS) imaging but also to enhance photoacoustic (PA) signals due to the presence of bubbles and optical absorbing shell material. The formation and expansion of these gas filled bubbles leads to increasing photoacoustic signals for imaging. Compared to other contrast agents which may not give stable signals due to photo-degradation, these contrast agents are shown to be stable up to 24 hours. The source of PA signal enhancement is through the presence of long lasting perfluorohexane (PFH) bubbles resulting from the optical vaporization. These bubbles generated from the PFH-NEs directly generate photoacoustic signals due to the optical absorption from the fluorosurfactant shell, but also secondary signals from the subsequent scattering of the photoacoustic waves from the PFH bubbles. In addition, the pressures generated from vaporization of NEs and ability to load chemotherapeutic agents enable these nanoparticles to also be used for cancer therapy by contributing to drug delivery and transport. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement