Department of Biochemistry and Biophysics, Perelman School of Medicine, and Department of Chemistry, School of Arts and Sciences, University of Pennsylvania, Philadelphia, PA 19104, USA.
Martinos Center for Biomedical Imaging, Massachusetts General Hospital/Harvard Medical School, Charlestown, MA 02129, USA.
Nanoscale. 2020 Jan 28;12(4):2657-2672. doi: 10.1039/c9nr07778b. Epub 2020 Jan 15.
Lanthanide-based upconverting nanoparticles (UCNPs) are known for their remarkable ability to convert near-infrared energy into higher energy light, offering an attractive platform for construction of biological imaging probes. Here we focus on in vivo high-resolution microscopy - an application for which the opportunity to carry out excitation at low photon fluxes in non-linear regime makes UCNPs stand out among all multiphoton probes. To create biocompatible nanoparticles we employed Janus-type dendrimers as surface ligands, featuring multiple carboxylates on one 'face' of the molecule, polyethylene glycol (PEG) residues on another and Eriochrome Cyanine R dye as the core. The UCNP/Janus-dendrimers showed outstanding performance as vascular markers, allowing for depth-resolved mapping of individual capillaries in the mouse brain down to a remarkable depth of ∼1000 μm under continuous wave (CW) excitation with powers not exceeding 20 mW. Using a posteriori deconvolution, high-resolution images could be obtained even at high scanning speeds in spite of the blurring caused by the long luminescence lifetimes of the lanthanide ions. Secondly, the new UCNP/dendrimers allowed us to evaluate the feasibility of quantitative analyte imaging in vivo using a popular ratiometric UCNP-to-ligand excitation energy transfer (EET) scheme. Our results show that the ratio of UCNP emission bands, which for quantitative sensing should respond selectively to the analyte of interest, is also strongly affected by optical heterogeneities of the medium. On the other hand, the luminescence decay times of UCNPs, which are independent of the medium properties, are modulated via EET only insignificantly. As such, quantitative analyte sensing in biological tissues with UCNP-based probes still remains a challenge.
基于镧系元素的上转换纳米粒子（UCNPs）以其将近红外能量转化为更高能量光的非凡能力而闻名，为构建生物成像探针提供了一个有吸引力的平台。在这里，我们专注于体内高分辨率显微镜 - 这种应用的机会在于在非线性状态下以低光子通量进行激发，这使得 UCNPs 在所有多光子探针中脱颖而出。为了创建生物相容性纳米粒子，我们采用 Janus 型树状大分子作为表面配体，分子的一侧具有多个羧酸盐、另一侧具有聚乙二醇（PEG）残基，核心为 Eriochrome Cyanine R 染料。UCNP/Janus 树状大分子作为血管标记物表现出优异的性能，允许在连续波（CW）激发下以不超过 20 mW 的功率对小鼠大脑中的单个毛细血管进行深度分辨映射，深度可达惊人的 1000 μm。使用后验去卷积，即使在高扫描速度下，也可以获得高分辨率图像，尽管镧系离子的长荧光寿命会导致图像模糊。其次，新的 UCNP/树状大分子使我们能够评估使用流行的比率型 UCNP 到配体激发能量转移（EET）方案进行体内定量分析物成像的可行性。我们的结果表明，对于定量传感应该选择性地响应感兴趣的分析物的 UCNP 发射带的比值，也受到介质光学异质性的强烈影响。另一方面，UCNPs 的荧光衰减时间独立于介质特性，仅通过 EET 被轻微调制。因此，基于 UCNP 的探针在生物组织中的定量分析物传感仍然是一个挑战。
