Development of fluorinated dyes for deeper tissue photoacoustic imaging with phase changing nanodroplets

抽象的。光声成像（派）是一种有前途的非电离、低成本、高分辨率的成像方式。 在适合高通量临床前应用的平台中进行对比度和高时空分辨率成像 用于特定的临床应用。然而，分子派的广泛使用受到以下因素的严重限制： 有效造影剂的可用性。目前可用的造影剂要么不具有足够的 派所需的脉冲光照下的光稳定性，缺乏足够的PAI信号产生能力 对于深度成像，或者它们的吸收光谱与血红蛋白的吸收光谱显著重叠， 成像灵敏度为了解决这些局限性，提出了一类新的派造影剂， 基于相变全氟化碳（PFC）纳米液滴（ND）。这些药剂是基于一种液体 PFC核心和染料或纳米颗粒形式的光吸收“保险丝”。这些ND的照明， 脉冲激光触发PFC核心的液体到气体的转变，PFC核心被光吸收发色团加热， 有很强的派信号因此，这些药剂通常被称为激光激活ND（LAND）。 此外，在激光激发后，PFC微泡可以重新凝结回到它们的液体纳米液滴形式， 其可以允许多个激励以及动态成像对比度和超分辨率派的可能性。 然而，多个研究小组对这种令人兴奋的造影剂设计进行的评估显示， 局限性-通常使用的染料分子或纳米颗粒不溶于全氟化碳或与全氟化碳混合。 因此，当前的LAND包含它们的“熔断器”（即，染料吸收剂），具有负载效率， 根据LAND涂层和染料化学品的具体情况，染料的分布高度可变 结构重要的是，除了与不可再现性和LAND的拍摄保质期相关的限制外， 由于染料分子从LAND的外壳中泄漏，最近对相变ND的研究表明， 这是从堆芯内部加热LAND的优点，以实现有效的液体到气体的转变。这些数据表明， ND核心内部加热对于激活LAND的重要性，这是无法有效实现的， 位于外周的发色团。在这里，我们建议通过开发 在第一和第二近红外组织窗口（NIR-I和NIR-II）中具有吸收率的氟化染料。我们 假设氟化染料将可溶于PFC核内，因此导致高度可再现， 稳定的LAND配方，大大提高了激光活化效率。为了反映土地的这些进步， 在配制中，我们将掺杂有氟化染料的PFC ND称为增强的LAND（eLAND）。我们将其视为 PFC核内均匀分布的氟化染料浓度的增加将显著改善 eLAND激活的功效。我们的估计表明，这种激活功效的增加可能与以下因素有关： 使用eLAND的派的深度敏感性的高度显著（厘米量级）增加;这种增加 在临床前和临床环境中，深度渗透可能是分子派的游戏规则改变者。

Abstract. Photoacoustic imaging (PAI) is a promising modality that is non-ionizing, low-cost, and offers high- contrast and high-spatiotemporal-resolution imaging in a platform that is amenable for high-throughput preclinical use and for specific clinical applications. However, widespread use of molecular PAI is severely limited by availability of validated contrast agents. Currently available contrast agents either do not have adequate photostability under the pulsed illumination that is required for PAI, lack sufficient PAI-signal-generation ability for deep imaging, or their absorbance spectra significantly overlap with those of hemoglobin, which reduces imaging sensitivity. In order to address these limitations, a new class of PAI contrast agents was proposed that is based on phase-changing perfluorocarbon (PFC) nanodroplets (NDs). These agents are based on a liquid PFC core and a light-absorbing “fuse” in the form of a dye or a nanoparticle. Illumination of these NDs with a pulsed laser triggers liquid-to-gas transition of the PFC core heated by light-absorbing chromophores that results in a very strong PAI signal. Therefore, these agents are often referred to as Laser-Activated NDs (LANDs). Furthermore, after laser excitation PFC microbubbles can re-condense back into their liquid nanodroplet form, which can allow multiple excitations and the possibility for dynamic imaging contrast and super-resolution PAI. However, evaluation of this exciting contrast agent design by multiple research groups revealed one critical limitation – commonly used dye molecules or nanoparticles are not soluble or mixable with perfluorocarbons. Therefore, current LANDs contain their “fuses” (i.e., dye absorbers) in the shell with a loading efficiency and distribution of the dyes that is highly variable depending on specifics of a LAND's coating and a dye's chemical structure. Importantly, in addition to the limitations associated with irreproducibility and a shot shelf-life of LANDs due to leakage of dye molecules from a LAND's shell, recent studies of phase-changing NDs showed the advantage of heating LANDs from within the core for an effective liquid-to-gas transition. These data underline the importance of heating inside an ND's core for activation of LANDs that cannot be effectively achieved with peripherally located chromophores. Here we propose to address weaknesses of the prior research by developing fluorinated dyes with absorbance in the first and second near-infrared tissue windows (NIR-I and NIR-II). Our hypothesis is that the fluorinated dyes will be soluble inside the PFC core, thus resulting in highly reproducible, stable LAND formulations with greatly improved laser activation efficacy. To reflect these advancements in LAND formulation, we refer to PFC NDs doped with fluorinated dyes as enhanced LANDs (eLANDs). We posit that an increase in concentration of uniformly distributed fluorinated dyes inside the PFC core will dramatically improve efficacy of eLAND's activation. Our estimates show that this gain in activation efficacy could be associated with a highly significant (on the order of centimeters) increase in depth sensitivity of PAI with eLANDs; such increase in depth penetration could be a game changer in molecular PAI in pre-clinical and clinical settings.