Energy-Looping Nanoparticles: Harnessing Excited-State Absorption for Deep-Tissue Imaging

作者：Elizabeth S. Levy, Cheryl Tajon, Thomas S. Bischof, Jillian Iafrati, Ángel Fernández-Bravo, David J. Garfield, Maysamreza Chamanzar, Michel M. Maharbiz, Vikaas S. Sohal, P. James Schuck, Bruce E. Cohen, Emory M. Chan · 发表于：ACS Nano · 年份：2016 · DOI：10.1021/acsnano.6b03288 · 被引用次数：169 · 研究领域：Nanoplatforms for cancer theranostics、Luminescence Properties of Advanced Materials、Luminescence and Fluorescent Materials

Near infrared (NIR) microscopy enables noninvasive imaging in tissue, particularly in the NIR-II spectral range (1000-1400 nm) where attenuation due to tissue scattering and absorption is minimized. Lanthanide-doped upconverting nanocrystals are promising deep-tissue imaging probes due to their photostable emission in the visible and NIR, but these materials are not efficiently excited at NIR-II wavelengths due to the dearth of lanthanide ground-state absorption transitions in this window. Here, we develop a class of lanthanide-doped imaging probes that harness an energy-looping mechanism that facilitates excitation at NIR-II wavelengths, such as 1064 nm, that are resonant with excited-state absorption transitions but not ground-state absorption. Using computational methods and combinatorial screening, we have identified Tm(3+)-doped NaYF4 nanoparticles as efficient looping systems that emit at 800 nm under continuous-wave excitation at 1064 nm. Using this benign excitation with standard confocal microscopy, energy-looping nanoparticles (ELNPs) are imaged in cultured mammalian cells and through brain tissue without autofluorescence. The 1 mm imaging depths and 2 μm feature sizes are comparable to those demonstrated by state-of-the-art multiphoton techniques, illustrating that ELNPs are a promising class of NIR probes for high-fidelity visualization in cells and tissue.