Factors Influencing the Repeated Transient Optical Droplet Vaporization Threshold and Lifetimes of Phase Change, Perfluorocarbon Nanodroplets

• Type of Material: Article
• Authors: Andrew X. Zhao, Emory University; Yiying I. Zhu, School of Electrical and Computer Engineering; Euisuk Chung, School of Electrical and Computer Engineering; Jeehyun Lee, School of Electrical and Computer Engineering; Samuel Morais, School of Electrical and Computer Engineering; Heechul Yoon, Dankook University; Stanislav Emelianov, Emory University
• Language: English
• Date: 2023-08-01
• Publisher: MDPI
• Publication Version: Final Published Version
• Copyright Statement: © 2023 by the authors.
• License: Creative Commons Attribution 4.0 International
• Final Published Version (URL): http://dx.doi.org/10.3390/nano13152238
• Title of Journal or Parent Work: Nanomaterials
• Volume: 13
• Issue: 15
• Grant/Funding Information: This work was supported by the Breast Cancer Research Foundation (BCRF-19-043) and the National Institutes of Health (NIH) (NS102860).
• Keywords: ODV; emulsion; vaporization; photoacoustic; ultrasound; perfluorocarbon nanodroplets
• Research Categories: Physics, Optics

Abstract

Perfluorocarbon nanodroplets (PFCnDs) are sub-micrometer emulsions composed of a surfactant-encased perfluorocarbon (PFC) liquid and can be formulated to transiently vaporize through optical stimulation. However, the factors governing repeated optical droplet vaporization (ODV) have not been investigated. In this study, we employ high-frame-rate ultrasound (US) to characterize the ODV thresholds of various formulations and imaging parameters and identify those that exhibit low vaporization thresholds and repeatable vaporization. We observe a phenomenon termed “preconditioning”, where initial laser pulses generate reduced US contrast that appears linked with an increase in nanodroplet size. Variation in laser pulse repetition frequency is found not to change the vaporization threshold, suggesting that “preconditioning” is not related to residual heat. Surfactants (bovine serum albumin, lipids, and zonyl) impact the vaporization threshold and imaging lifetime, with lipid shells demonstrating the best performance with relatively low thresholds (21.6 ± 3.7 mJ/cm2) and long lifetimes (t1/2 = 104 ± 21.5 pulses at 75 mJ/cm2). Physiological stiffness does not affect the ODV threshold and may enhance nanodroplet stability. Furthermore, PFC critical temperatures are found to correlate with vaporization thresholds. These observations enhance our understanding of ODV behavior and pave the way for improved nanodroplet performance in biomedical applications.