Fluolab【Angew.Chem.】纳米乳液助力NIR-II荧光增强，光热转化效率高达66.8%
通讯作者： Joe B. Gilroy, Gang Zheng
文章概要
本研究开发了一种新型的二氟化硼甲臜（BDF）染料，并通过纳米乳液工程技术成功克服了该类染料在水相环境中荧光淬灭的难题。研究团队利用甘油三辛酸酯构建的非极性油芯微环境，不仅有效激发了染料在第二近红外窗口（NIR-II） 的高亮度荧光，同时保持了极高的光热转化效率（66.8%）。这一成果实现了光声（PA）成像与NIR-II荧光成像的双模态引导，并在活体实验中成功实现了肿瘤的精准消融，为疏水性、极性敏感型光诊疗剂的临床转化提供了新策略。
(a) Synthesis scheme of boron difluoride formazanate 3. (b) UV–vis absorption spectra (left) and absorbance maximum as a function of dielectric constant (right) for 3 (4 µM) in various solvents. (c) Photoluminescence spectra (left) and fluorescence maximum as a function of dielectric constant (right) for 3 (4 µM) in the various solvents. Excitation wavelength: 808 nm. (d–f) Titration of 3 with nonpolar oil (glyceryl trioctanoate) in CHCl3. (d) UV–vis absorption spectra, (e) photoluminescence spectra, and (f) relative change in absorbance and fluorescence intensity as a function of oil content. (g–i) Titration of 3 with polar oil in chloroform. (g) UV–vis absorption spectra, (h) photoluminescence spectra, and (i) relative change in absorbance and fluorescence intensity as a function of oil content.
引言
在精准医疗领域，光热治疗（PTT） 因其高空间精度和低系统毒性而备受关注。为了实现更精准的治疗引导，科学家们致力于开发兼具深层组织穿透能力和高空间分辨率的成像技术。NIR-II荧光成像具有低组织自发荧光和低散射的优势，而光声成像则能提供深层解剖背景。二氟化硼甲臜（BDF）染料作为一种新兴的近红外发光材料，其独特的电子结构使其无需长链共轭即可实现长波长发射，但其在极性水溶液中极易发生荧光淬灭，限制了其在生物体内的应用。因此，如何构建一个既能保护荧光性能又能维持高效光热转换的递送平台，成为当前该领域亟待解决的核心问题。
Characterization of BDF-NE. (a) Size distribution of BDF-NE measured by dynamic light scattering at day 0, day 1, day 12, day 46, and day 100. (b) Transmission electron microscopy image of BDF-NE. Scale bar = 100 nm. (c) UV–vis absorption spectra of BDF-NE in water (red), BDF-NE in CHCl3 (red, dotted), BDF-NP in water (blue), BDF-NP in CHCl3 (blue, dotted) and 3 in CHCl3 (black) at equivalent dye concentration of 18 µM. (d) NIR-II fluorescence spectra showing enhanced emission from BDF-NE in water (red) compared to BDF-NE in CHCl3 (black) and BDF-NP in water (blue) at equivalent dye concentration of 18 µM (λex = 808 nm).
主要实验及结论
研究人员首先通过简练的三步反应合成了新型BDF染料，并通过溶剂依赖性实验证实了该染料的荧光强度对环境极性高度敏感。实验发现，只有在介电常数低于4的非极性环境中，染料才能维持高量子产率。基于此，团队设计了名为BDF-NE的油包水纳米乳液，将染料分子溶解在非极性油芯中，外部由磷脂和聚乙二醇脂质包覆以确保生物相容性。对比实验显示，不含油芯的纳米颗粒（BDF-NP）在水中完全失去荧光，而BDF-NE则展现出明亮的NIR-II荧光，绝对量子产率达到2.9%，且发射光谱延伸至1250 nm以上。
Photothermal properties of BDF-NE. (a) Temperature elevation profile of BDF-NE upon 825 nm laser irradiation (1.0 W cm−2) and subsequent cooling after laser cessation. (b) Linear fitting of time constant versus negative natural logarithm of temperature driving force for photothermal conversion efficiency calculation, yielding η = 66.8% (_R_2 = 0.9962). (c) Power density-dependent temperature rise of BDF-NE under 825 nm laser irradiation at varying power densities (0.2–1.0 W cm−2). (d) Temperature cycling profile of BDF-NE over seven ON/OFF heating-cooling cycles under 825 nm laser irradiation, demonstrating excellent photothermal stability.
在光热性能评价中，BDF-NE表现出色，其光热转化效率高达66.8%，优于大多数已报道的同类材料。在连续七个循环的加热-冷却实验中，该纳米乳液展现了卓越的光稳定性，未见明显的降解或性能衰减。随后，研究团队利用其强大的光声响应性能，在荷瘤小鼠模型中清晰地观察到药物在注射后6至9小时达到肿瘤部位的峰值富集，这为后续治疗方案的选择提供了精确的时间窗口。
Photoacoustic (PA) imaging performance of BDF-NE in phantom and in vivo. (a) Ultrasound (top) and PA image at 780 nm (bottom) of BDF-NE solutions at concentrations ranging from 20 to 100 µM in thin tube phantoms. (b) Wavelength-dependent PA signal intensity of BDF-NE at various concentrations, showing maximum signal near 780 nm. (c) Linear correlation between PA signal intensity at 780 nm and BDF-NE concentration (_R_2 > 0.99). (d) Time-resolved PA imaging of KB tumor-bearing mice following intravenous injection of BDF-NE, with grayscale ultrasound overlaid with PA signal (red). (e) Quantification of PA signal intensity at 780 nm in tumor regions at different time points post-injection, demonstrating peak accumulation at 6–9 h.
In vivo photothermal therapeutic efficacy of BDF-NE in KB tumor-bearing mice. (a) Infrared thermal images of tumor-bearing mice during 825 nm laser irradiation (1.0 W cm−2, 4 min). Top row: laser only control; bottom row: BDF-NE + laser (PTT group). (b) Temperature elevation profiles at tumor sites monitored by thermocouple for PTT group (red) and laser only control (black). Dotted lines represent standard deviation; solid lines represent mean values. (c) Tumor growth curves monitored over 90 days for all treatment groups (n = 5 per group). (d) Kaplan-Meier survival curves for mice in different treatment groups. (e) Body weight changes during the 16-day observation period, showing no significant differences among groups. (f) Representative photographs of tumor-bearing mice at days 0, 2, and 14 post-treatment for four groups: no treatment (NT), laser only, injection only (BDF-NE without laser), and PTT (BDF-NE + laser). Red circles indicate tumor locations. (g) Histological analysis of tumor tissues harvested 2 days post-treatment. Top row: H&E staining; middle row: Ki-67 staining; bottom row: TUNEL staining. Scale bars: 50 µm.
在活体治疗实验中，研究团队将BDF-NE注射入KB肿瘤模型小鼠体内，并进行825 nm激光照射。结果表明，治疗组小鼠的肿瘤内部温度迅速升至54°C，足以引发肿瘤细胞发生大规模的坏死与凋亡。经过单次治疗，部分小鼠实现了肿瘤的完全消融，且在长达90天的观察期内未见复发。组织学分析进一步证实，该疗法对主要脏器无明显毒副作用，安全性表现优异。此外，高分辨率的血管成像实验再次证明了其在深层组织成像方面的潜力，1250 nm长通滤波下的信噪比高达1.75。
NIR-II fluorescence imaging performance of BDF-NE. (a) NIR-II fluorescence images (left) and quantified average intensities from ROI (right) of (A) BDF-NE in water, (B) 3 in water, and (C) 3 in CHCl3 at equivalent chromophore concentrations. Images were acquired using a small animal imaging system with 785 nm excitation and 800 nm long-pass filter. (b) NIR-II fluorescence images of BDF-NE (50 µM) and CF770 (50 µM) solutions captured through 800 nm, 1000 nm, and 1250 nm longpass (LP) filters. (c) High-resolution NIR-II fluorescence imaging of hindlimb vasculature in mice 5 min post-injection of BDF-NE, acquired through 850, 1000, and 1250 nm LP. Bottom panels show normalized fluorescence intensity profiles across vessels (marked by red lines). (d) Time-resolved whole-body NIR-II fluorescence imaging of KB tumor-bearing mice following intravenous injection of BDF-NE (1250 nm LP filter). White dashed circles indicate tumor region. Right panel shows ex vivo fluorescence imaging of dissected organs at 24 h post-injection. (e) Quantification of tumor fluorescence intensity over time. Tumor fluorescence intensity at all time points was significantly higher than pre-injection baseline (***p < 0.0001, one-way ANOVA with Dunnett's test, n = 5) (f) Quantitative analysis of ex vivo organ fluorescence at 24 h post-injection.
总结及展望
本研究成功证明了通过纳米乳液微环境工程，可以同时最大化疏水性染料的荧光性能与光热效能。这种将染料分子单分散在非极性油芯中的策略，巧妙地解决了发光与产热之间的能量竞争平衡问题。BDF-NE作为首个此类纳米乳液平台，不仅实现了高性能的双模态影像引导治疗，还为其他高性能疏水性光诊疗试剂的开发提供了普适性的技术范式。未来，该平台有望在更多复杂疾病的精准诊断与治疗中发挥关键作用。