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 (C3F8, C4F10, and C5F12) 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.
Highlights
Phase change droplets composed of low boiling point perfluorocarbons (PFCs) have received widespread interest from the ultrasound imaging community for diagnostic and molecular imaging applications, and for potential use as therapeutic agents [1,2]
ODV based contrast agents have several advantages over photoacoustic contrast agents that rely solely on photothermal heating to produce acoustic waves in that a) the vaporization event produces an exceptionally strong photoacoustic response, exceeding that from the thermoelastic expansion and allowing for improved photoacoustic imaging contrast, b) the microbubbles created through ODV can provide ultrasound contrast in dual mode imaging scenarios and c) the light absorbing species incorporated into the droplets remain after vaporization and can be used to provide lasting enhanced photoacoustic contrast [7,8,9]
We study the effect of droplet core material on the ODV threshold with an aim towards reducing the threshold laser fluence at which ODV can be achieved
Summary
Phase change droplets composed of low boiling point perfluorocarbons (PFCs) have received widespread interest from the ultrasound imaging community for diagnostic and molecular imaging applications, and for potential use as therapeutic agents [1,2]. Under sufficiently high laser fluence, a phase transition is induced; a process termed optical droplet vaporization (ODV). ODV based contrast agents have several advantages over photoacoustic contrast agents that rely solely on photothermal heating to produce acoustic waves in that a) the vaporization event produces an exceptionally strong photoacoustic response, exceeding that from the thermoelastic expansion and allowing for improved photoacoustic imaging contrast, b) the microbubbles created through ODV can provide ultrasound contrast in dual mode imaging scenarios and c) the light absorbing species incorporated into the droplets remain after vaporization and can be used to provide lasting enhanced photoacoustic contrast [7,8,9]. The core material is found to have a profound effect on ODV, with more volatile PFC droplets vaporizing at a lower laser fluence. The effects of droplet size on vaporization threshold are 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
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