Controlled Synthesis and Single-Particle Imaging of Bright, Sub-10 nm Lanthanide-Doped Upconverting Nanocrystals

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• 作者：Alexis D. Ostrowski ; Emory M. Chan ; Daniel J. Gargas ; Elan M. Katz ; Gang Han ; P. James Schuck ; Delia J. Milliron ; Bruce E. Cohen
• 刊名：ACS Nano
• 出版年：2012
• 出版时间：March 27, 2012
• 年：2012
• 卷：6
• 期：3
• 页码：2686-2692
• 全文大小：906K
• 年卷期：v.6,no.3(March 27, 2012)
• ISSN：1936-086X

文摘

Phosphorescent nanocrystals that upconvert near-infrared light to emit at higher energies in the visible have shown promise as photostable, nonblinking, and background-free probes for biological imaging. However, synthetic control over upconverting nanocrystal size has been difficult, particularly for the brightest system, Ybp>3+p>- and Erp>3+p>-doped 尾-phase NaYF₄, for which there have been no reports of methods capable of producing sub-10 nm nanocrystals. Here we describe conditions for the controlled synthesis of protein-sized 尾-phase NaYF₄: 20% Ybp>3+p>, 2% Erp>3+p> nanocrystals, from 4.5 to 15 nm in diameter. The size of the nanocrystals was modulated by varying the concentration of basic surfactants, Yp>3+p>:Fp>鈥?/sup> ratio, and reaction temperature, variables that also affected their crystalline phase. Increased reaction times favor formation of the desired 尾-phase nanocrystals while having only a modest effect on nanocrystal size. Core/shell 尾-phase NaYF₄: 20% Ybp>3+p>, 2% Erp>3+p>/NaYF₄ nanoparticles less than 10 nm in total diameter exhibit higher luminescence quantum yields than comparable >25 nm diameter core nanoparticles. Single-particle imaging of 9 nm core/shell nanoparticles also demonstrates that they exhibit no measurable photobleaching or blinking. These results establish that small lanthanide-doped upconverting nanoparticles can be synthesized without sacrificing brightness or stability, and these sub-10 nm nanoparticles are ideally suited for single-particle imaging.

Keywords:

upconverting nanoparticles; lanthanides; phosphorescence; nanocrystal synthesis