Department of Chemistry , Texas A&M University , College Station , Texas 77843-3255 , United States.
Department of Chemistry & State Key Laboratory of Molecular Engineering of Polymers , Fudan University , Shanghai 200433 , PR China.
J Am Chem Soc. 2018 Apr 25;140(16):5493-5499. doi: 10.1021/jacs.8b01613. Epub 2018 Apr 17.
Triplet-triplet annihilation upconversion (TTA-UC) has gained increasing attention because it allows for harvesting of low-energy photons in the solar spectrum with high efficiency in relevant applications including solar cells and bioimaging. However, the utilization of conventional TTA-UC systems for low-power bioapplications is significantly hampered by their general incompatibility and low efficiency in aqueous media. Herein we report a metal-organic framework (MOF) as a biocompatible nanoplatform for TTA-UC to realize low-power in vivo imaging. Our MOF consists of a porphyrinic sensitizer in an anthracene-based Zr-MOF as a TTA-UC platform. In particular, closely aligned chromophores in the MOF facilitate a long-range 3D triplet diffusion of 1.6 μm allowing efficient energy migration in water. The tunable ratio between sensitizer and annihilator by our synthetic method also allows an optimization of the system for maximized TTA-UC efficiency in water at a very low excitation power density. Consequently, the low-power imaging of lymph node in a live mouse was successfully demonstrated with an excellent signal-to-noise ratio (SNR > 30 at 5 mW cm).
三重态-三重态湮灭上转换（TTA-UC）引起了越来越多的关注，因为它可以在包括太阳能电池和生物成像在内的相关应用中高效地利用太阳能光谱中的低能光子。然而，传统的 TTA-UC 系统在低功率生物应用中的应用受到严重阻碍，因为它们在水介质中普遍不兼容且效率低下。在此，我们报告了一种金属-有机骨架（MOF）作为 TTA-UC 的生物相容性纳米平台，以实现低功率体内成像。我们的 MOF 由卟啉敏化剂和基于蒽的 Zr-MOF 组成，作为 TTA-UC 平台。特别是，MOF 中紧密排列的发色团促进了长程 3D 三重态扩散，扩散距离可达 1.6μm，从而允许在水中进行有效的能量迁移。通过我们的合成方法，可以调节敏化剂和猝灭剂的比例，从而优化系统在低激发功率密度下在水中的 TTA-UC 效率。因此，成功地在活鼠的淋巴结中进行了低功率成像，信噪比（SNR > 30，在 5 mW cm 下）非常高。
