Engineering optically triggered droplets for photoacoustic imaging and therapy

Abstract

Liquid perfluorocarbon (PFC) droplets incorporating optical absorbers can be vaporized through photothermal heating using a pulsed laser source. Here, we report on the effect of droplet core material on the optical fluence required to produce droplet vaporization. We fabricate gold nanoparticle templated microbubbles filled with various PFC gases (C 3 F 8 , C 4 F 10, and C 5 F 12 ) and apply pressure to condense them into droplets. The core material is found to have a strong effect on the threshold optical fluence, with lower boiling point droplets allowing for vaporization at lower laser fluence. The impact of droplet size on vaporization threshold is discussed, as well as a proposed mechanism for the relatively broad distribution of vaporization thresholds observed within a droplet population with the same core material. We propose that the control of optical vaporization threshold enabled by engineering the droplet core may find application in contrast enhanced photoacoustic imaging and therapy.

Polypyrrole-Coated Perfluorocarbon Nanoemulsions as a Sono-Photoacoustic Contrast Agent

“…Several studies have confirmed that the ADV threshold can be as high as 5 MPa, while several PA droplet formulations require up to a 400 mJ/cm 2 laser fluence for activation 14,18,27,28,36–39 . In many cases, the pressures and optical fluences required to initiate droplet vaporization approach exceed FDA and ANSI limits for diagnostic purposes.…”

A Laser-Activated Biocompatible Theranostic Nanoagent for Targeted Multimodal Imaging and Photothermal Therapy

“…As the area is continually irradiated, more nanoparticles are vaporized, creating a cascading effect of tumor destruction and deeper penetration. Combining laser and ultrasound irradiation can also be used to facilitate PFC droplet vaporization, enhancing the tissue penetration of the nanoparticles [63][64][65]. The therapeutic effects of PTT here are amplified due to enhanced distribution of SPIO and DIR throughout the tumor compared to existing nanomedicine therapies that rely on the EPR effect alone.…”

Laser-driven resonance of dye-doped oil-coated microbubbles: A theoretical and numerical study

“…It has recently been proposed that even greater contrast enhancement in photoacoustic imaging could be achieved through the use of volatile droplets whose vaporization is triggered by light. 2,8,9 However, the necessary phase change consumes energy under the form of latent heat, that cannot then participate in the acoustic generation, which makes the use of the available energy inherently suboptimal. Stable microbubbles modified with the addition of an optically absorbing coating have been proposed as a potential solution to this problem.…”