The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA.
Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, Berkeley, CA, 94720, USA.
Nat Commun. 2018 Aug 6;9(1):3082. doi: 10.1038/s41467-018-05577-8.
Multiphoton imaging techniques that convert low-energy excitation to higher energy emission are widely used to improve signal over background, reduce scatter, and limit photodamage. Lanthanide-doped upconverting nanoparticles (UCNPs) are among the most efficient multiphoton probes, but even UCNPs with optimized lanthanide dopant levels require laser intensities that may be problematic. Here, we develop protein-sized, alloyed UCNPs (aUCNPs) that can be imaged individually at laser intensities >300-fold lower than needed for comparably sized doped UCNPs. Using single UCNP characterization and kinetic modeling, we find that addition of inert shells changes optimal lanthanide content from Yb, Er-doped NaYF nanocrystals to fully alloyed compositions. At high levels, emitter Er ions can adopt a second role to enhance aUCNP absorption cross-section by desaturating sensitizer Yb or by absorbing photons directly. Core/shell aUCNPs 12 nm in total diameter can be imaged through deep tissue in live mice using a laser intensity of 0.1 W cm.
多光子成象技术将低能量激发转化为高能量发射，被广泛用于提高信号与背景的对比度、减少散射并限制光损伤。镧系掺杂上转换纳米粒子（UCNP）是最有效的多光子探针之一，但即使是镧系掺杂水平经过优化的 UCNP，也需要激光强度可能会造成问题。在这里，我们开发了蛋白大小的合金 UCNP（aUCNP），其可以在激光强度比同等大小的掺杂 UCNP 所需的强度低 300 多倍的情况下进行单独成象。通过单个 UCNP 特性和动力学建模，我们发现添加惰性壳可以将最佳镧系元素含量从 Yb、Er 掺杂的 NaYF 纳米晶体改变为完全合金的组成。在较高水平下，发射体 Er 离子可以通过使敏化剂 Yb 去饱和或直接吸收光子来采用第二种作用，从而增强 aUCNP 的吸收截面。总直径为 12nm 的核/壳 aUCNP 可以在活小鼠中使用 0.1W/cm 的激光强度进行深层组织成像。
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