【Adv.Mater.】华南理工吴水珠、曾钫|19.4 nm 极致半峰宽！超窄带短波红外 J-聚集体
文章标题：Formation of Ultra‐Narrowband SWIR J‐Aggregate Materials and Their Applications in Multispectral Optoacoustic Tomography Imaging
通讯作者：Fang Zeng, Shuizhu Wu
文章概要
引言
在光学成像、高精度传感以及先进光子学器件领域，具有极高光谱纯度的超窄带材料（通常指半峰宽小于 20 nm 的材料）一直备受瞩目。然而，在短波红外（SWIR，1000–2000 nm）或近红外二区波段，开发这类材料面临着巨大的物理瓶颈。为了实现低能量的红外吸收，分子必须具备广泛的 -共轭体系，这不可避免地引入了大量的软低频振动，从而导致电子跃迁信号发生严重的振动拓宽。此外，传统的短波红外发光团在水相环境中极易形成无序聚集，进一步造成光谱展宽和荧光猝灭。尽管经典的 J-聚集体可以通过激子去定域化来抑制非均匀展宽，但此前尚未有研究能在短波红外区实现真正的超窄带宽吸收或发射。为此，华南理工大学等研究团队联合攻关，通过精妙的分子结构设计，成功打破了这一长期存在的技术僵局。
Schematic illustration of the formation of highly ordered and stable SWIR J-aggregates with ultra-narrow band by cyanine IRJ1089, and its applications in multiplexed MSOT imaging in mouse models. The panel Interlocking sulfonates at the top right corner is derived from the crystallographic data of a structural analogue (IRJ1021).
主要实验及结论
研究人员首先对七甲川花菁染料的分子结构进行了系统性的工程化改造。实验结果表明，在分子侧链中引入带负电荷的磺酸基团是诱导花菁分子形成高度有序 J-聚集体的关键。为了将吸收峰进一步红移至短波红外区域，团队巧妙地在花菁主链的内消旋位置（meso-position）引入了具有较大位阻的 N-乙酰基-苄胺取代基，并在终端引入了 benzo[f]indole 杂环，从而打造出最优染料 IRJ1089。当该分子在水溶液中自组装形成 J-聚集体（IRJ1089NPs）时，溶液颜色发生显著变化，其吸收峰大幅红移至 1089 nm，摩尔吸光系数提高了 2.9 倍。令人惊叹的是，该聚集体在短波红外区的吸光/发光半峰宽（FWHM）低至 164 cm⁻¹（仅为 19.4 nm），这也是迄今为止报道的有机短波红外材料中最窄的带宽之一，充分证实了 supramolecular 结构中高度有序的激子耦合。
(a) Molecular structures of synthesized heptamethine cyanine dyes. Numeric values denote absorption peak wavelengths for monomers, and the suffix “NPs” indicates corresponding J-aggregates. (b) Absorption and normalized fluorescence spectra of IRJ1089 (DMSO, λex = 808 nm) and its J-aggregate (IRJ1089NPs, 10 mm HEPES buffered solution, λex = 1064 nm). Dye concentration: 5 µm. Inset: Photographs of solutions before and after J-aggregation. (c) Comparison of the FWHM of IRJ1089NPs and previously reported SWIR narrow-band materials with their FWHM < 100 nm (d) Hydrodynamic diameter distribution and representative TEM image (inset) of IRJ1089NPs. (e) Optoacoustic (OA) spectra and normalized absorption spectra for IRJ1089 and IRJ1089NPs at matched absorbance (0.5). (f) OA SGE at constant molarity (ICG set to 1). (g) Absorption spectra of IRJ1089NPs (2 µm) recorded in mouse blood over 5 days.
为了揭示这一超窄带特性背后的微观机理，研究团队利用结构类似物 IRJ1021 成功生长出单晶，并结合密度泛函理论（DFT）计算进行了深入剖析。晶体衍射数据表明，在单个分子堆叠内部，染料分子以特定的平行“头对尾”滑移几何方式紧密排列，完全符合经典 J-聚集体的特征。而在相邻的分子堆叠之间，带负电的磺酸基团尾部与带正电的 -共轭骨架之间产生了强烈的静电互锁作用，驱动四个分子堆叠共同构筑出一种独特的管状 supramolecular 结构。计算结果进一步证实，IRJ1089 拥有更长且更平整的共轭平面，其 benzo[f]indole 单元之间的二面角仅为 3.5°，这种极佳的平面性极大地增强了激子耦合。正是这种精妙的电荷互补与位阻平衡，赋予了 IRJ1089NPs 极其优异的生理环境稳定性、抗光漂白性以及高达 45.8 nM 的极低临界聚集浓度，使其无需任何表面活性剂或胶囊包裹即可直接用于生物体内。
(a) Crystal structure of IRJ1021 with the thermal ellipsoids drawn at the 50% probability. (b) Crystal packing diagram of IRJ1021. (c,d) Molecular interactions of two adjacent molecules within the same stack (c) and between adjacent stacks (d). (e,f) Electrostatic potential (ESP) maps (e) and optimized geometries (f) of IRJ1021 and IRJ1089, both calculated at the B3LYP-D3(BJ)/6-311G(d,p) level. (g) Molecular orbitals of IRJ1021 and its dimer were calculated at the B3LYP/6-311G(d,p) level, and the derived energy gap (Egap), with the dimer geometry extracted from the crystal packing of IRJ1021.
凭借极其敏锐的光谱特性和极高的光声信号生成效率（其摩尔光声效率高达临床常用印氰绿 ICG 的 10.3 倍），IRJ1089NPs 展现出了无与伦比的多光谱光声断层扫描（MSOT）成像性能。在活体小鼠实验中，外源性的 IRJ1089NPs 注入后，MSOT 能够以极高的空间分辨率逆向清晰显影位于脊髓下方、深达 1.2 厘米以上的下腔静脉、门静脉及主动脉等深层血管和肝实质结构。利用这一优势，研究团队成功在自发性高血压大鼠模型中，实时、非侵入性地监测了抗高血压药物 Isoket 诱导的主动脉血管扩张动力学过程，光声信号测得的血管扩张半峰宽变化与大鼠收缩压的下降呈现出完美的光学线性对应关系，为心血管药物的药效体内评估开辟了新途径。
(a) Normalized absorption spectra of endogenous chromophores and exogenous contrast agents. (b) Schematic illustration and experimental timeline of optoacoustic imaging in the liver region in mice. (c) Representative cross-sectional MSOT images of a mouse at different time points after intravenous injection of IRJ1089NPs (0.5 mg/kg) or ICG (2 mg/kg). Background signals were derived from single-wavelength (800 nm) OA signals. (d) Cryosection image of a female mouse corresponding to the same cross-section in (c). (e) Schematic illustration and experimental timeline of optoacoustic imaging of Isoket-induced aortic expansion in rats. (f) Representative cross-sectional MSOT images of a rat at different time points after injection of IRJ1089NPs (1 mg/kg), followed by Isoket or saline administration 2 min later. Inset: MSOT signal profile along the aortic region (ROI) and the corresponding FWHM derived from the profile. (g) Enlarged MSOT images of the aortic region in (f). (h) Temporal changes in the FWHM of the MSOT signal quantified within the aortic region (ROI) depicted in (f). (i) Temporal changes in systolic blood pressure (SBP) of the rat corresponding to (h). Abbreviations: Hb: deoxyhemoglobin; HbO2: oxyhemoglobin; SC: spinal cord; LU: lung; IVC: inferior vena cava; AA: abdominal aorta; PV: portal vein; LV: liver; GB: gallbladder. For (h) and (i), the data are presented as the mean ± s.d. (n = 3).
不仅如此，研究团队利用光谱完全分离的两种超窄带 J-聚集体（IRJ1021NPs 和 IRJ1089NPs），首次在动物深层组织中实现了无信号串扰的多重短波红外光声多器官标记，成功清晰分辨了小鼠的膀胱、直肠、肺部和胃部等缺乏内源性血红蛋白信号的器官。在此基础上，针对临床上致死率极高的结直肠癌（CRC）引起肠梗阻的诊断难题，团队进一步将靶向环肽 cRGD 修饰到包裹染料的脂质体上，构建了靶向纳米探针。在原位结直肠癌小鼠模型中，结合直肠内灌注非靶向探针，多重 MSOT 成像不仅精准定位了肿瘤边界，还清晰揭示了肿瘤由早期压迫演变为占据五分之四管腔、导致严重肠道狭窄的完整病理演变过程，为非侵入性诊断结直肠癌并发肠梗阻提供了强有力的影像学证据。
Utilization of encapsulation-free J-aggregates in multiple organ labeling via MSOT imaging. (a) Normalized absorption spectra of IRJ1021NPs and IRJ1089NPs. (b) Schematic illustration of OA imaging after subcutaneous injection of contrast agents at different dorsal locations in a mouse. (c) 3D MIP MSOT images (x-z plane) corresponding to (b). Inset: MSOT signal profile across the selected ROI. (d) Schematic illustration of SWIR multiplexed OA imaging for bladder and rectum, and a female mouse cryosection at the corresponding imaging plane. (e) Orthogonal MIP MSOT images of a mouse after intravesical instillation of IRJ1021NPs and intrarectal administration of IRJ1089NPs. (f,g) Normalized MSOT signal intensity in ROI 1 (f) and ROI 2 (g) at dashed lines in (e). (h) Schematic of SWIR multiplexed OA imaging for lungs and stomach, and a female mouse cryosections at the corresponding imaging plane. (i) Orthogonal MIP MSOT images of a mouse after oral gavage of IRJ1021NPs and intratracheal instillation of IRJ1089NPs. (j,k) Normalized MSOT signal intensity in ROI 3 (j) and ROI 4 (k) at dashed lines in (i). Abbreviations: SC: spinal cord; RT: rectum; BL: bladder; STO: stomach; LU: lung.
(a) Schematic illustration of the preparation of IRJ1089NPs-cRGD nanoparticles. (b) Hydrodynamic diameter distribution and representative TEM image (inset) of IRJ1089NPs-cRGD. (c) Normalized absorption spectra of different contrast agents. (d) Schematic of NIR-II OA imaging for a tumor in a CRC mouse model. (e) Representative MSOT images of a mouse with a CRC model, acquired at different time points after intravenous injection of IRJ1089NPs-cRGD (1.5 mg/kg). (f) Mean MSOT intensity in the tumor region corresponding to (e). Statistical comparisons between groups were made using a two-tailed Student’s t-test. (g) Cryosection image at the rectal position of a female mouse. (h) Representative bioluminescence image of the major organs isolated from a CRC model mouse. (i) Schematic and timeline of NIR-II multiplexed OA imaging for orthotopic colorectal tumor. (j) Representative MSOT images after intravenous injection of IRJ1089NPs-cRGD and intrarectal administration of IRJ1021NPs at different stages of CRC development. (k) Normalized MSOT signal intensity in ROI 1 and ROI 2 at dashed lines in (j). (l) Percentage of contrast-labeled rectal lumen area corresponding to (j). Abbreviations: SC: spinal cord; RT: rectum. For (f, l), the data are expressed as the mean ± s.d. (n = 3).
总结及展望
本研究通过侧链磺酸基介导的静电互锁、内消旋位阻调控以及终端共轭面优化等多维策略，成功开发出了具有无包裹水相高稳定性和 19.4 nm 极致窄带宽的短波红外 J-聚集体材料。该材料不仅在深层大血管显影、血管活性药物精准评估方面表现优异，更攻克了活体多重光声成像缺乏窄带交叉无串扰探针的行业瓶颈，实现了癌症诊断与器官病变的高精度实时监控。这一创新成果不仅显著提升了多光谱光声断层扫描的成像深度和多路复用检测能力，也为未来开发高纯度红外发光显示、先进光电探测传感以及量子光子学器件等前沿领域提供了全新的分子构筑蓝图。