Use of sub-10 nm Diameter Upconversion Nanophosphors as Bio-labels
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0950-D01-04
Use of sub-10 nm Diameter Upconversion Nanophosphors as Bio-Labels Shuang Fang Lim1,2, Robert Riehn1,2, Chih-Kuan Tung2, David Tank2, William S. Ryu3, Nan Yao4, and Robert H. Austin2 1 Physics, North Carolina State University, Campus Box 8202, Raleigh, NC, 27695 2 Physics, Princeton University, Jadwin Hall, Princeton, NJ, 08544 3 Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ, 08544 4 PRISM, Princeton University, Princeton, NJ, 08544
ABSTRACT
We have synthesized rare-earth doped sub-10 nm diameter upconverting yttrium oxide based nanophosphors by flame spray pyrolysis. We have investigated the emitted visible fluorescence of the sub-10nm nanophosphors under both infrared excitation and electron excitation, and observed comparable narrow band emission spectra. The viability of the nanoparticles for biological imaging was confirmed by imaging the digestive system of the nematode worm C. elegans in the upconversion mode. We have surface functionalized the nanophosphors making them suitable for bio labeling. INTRODUCTION
UCPs show promise in imaging applications such as the lack of autofluorescence by the specimen, absence of bleaching, multicolor imaging and high resolution cathodoluminescent imaging in a SEM [1]. In order to target organisms at the sub-cellular level, UCPs in the sub-10 nm range are required. Because of the high degree of crystallinity [2] required for upconversion, attempts to synthesize smaller oxide-based upconverting particles were hindered by the need for post-synthesis annealing at a temperature above 500 oC, which often leads to undesired sintering of particles. Upconverting nanoparticles around 10-17 nm and even smaller based on NaYF4 and LaF3 have recently been synthesized by sol-gel chemistry approaches [3-6]. However, as yet, the as-synthesized phosphors are not water-soluble, and the toxicity is undetermined. We report on the synthesis of low aggregating, upconverting, yttrium oxide based phosphors which are sub-10 nm in size. We show that these nanophosphors, when coated with a PEG functionalized layer to enhance water dispersibility and stability, can be imaged by detection of the upconverted fluorescence in a biological sample. Finally, we describe the surface functionalization and immobilization of the UCPs onto thiolated gold substrates.
EXPERIMENT
Nanophosphors were synthesized using a custom-built supersonic flame-spray pyrolysis apparatus. For the precursor in the synthesis of sub-10 nm UCPs, 9.6 g of Y(NO3)3.6H2O was dissolved in 50 ml of ethanol and 11.9 ml of 2- ethylhexanoic acid (2-EHA) (99 %, SigmaAldrich) was added, [7] followed by heating at 60 C to dissolve. Separately, 11.2 g of Yb(NO3)3.5H2O was dissolved in 50 ml of ethanol with 11.9 ml of 2-ethylhexanoic acid added. The same procedure was performed with 11.1 g of Er(NO3)3.5H2O dissolved in 50 ml of ethanol and 11.9 ml of 2-ethylhexanoic acid. Before use, a 60 ml precursor mixture consisting of 0.1M Yttrium 2-ethylnexanoate (Y(2-EHA)3) solution in ethanol was prep
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