Journal of Materials Science

, Volume 43, Issue 15, pp 5325–5330 | Cite as

Improvement of dispersion stability and characterization of upconversion nanophosphors covalently modified with PEG as a fluorescence bioimaging probe

  • Tamotsu ZakoEmail author
  • Hiroyasu Nagata
  • Naofumi Terada
  • Masafumi Sakono
  • Kohei SogaEmail author
  • Mizuo Maeda


Upconverting (UC) phosphors (UCPs) are ceramic materials doped with rare earth ions. These materials can absorb and upconvert infrared (IR) radiation to emit visible light by the stepwise excitation among discrete energy levels of the rare earth ions. UCPs are potentially useful reagents for use in bioimaging since the use of low energy photons avoids photo-toxicity. The use of UCP nanoparticles as bioimaging probes requires surface modifications in an effort to improve dispersion stability in aqueous milieu. In this study, we covalently attached poly(ethylene glycol) (PEG) to the surface of Er-doped Y2O3 nanoparticles and firstly demonstrated that PEG covalently bound to the Y2O3 surface markedly improved dispersion stability in water. UC emission of PEG-modified Er–Y2O3 nanoparticles excited with IR light was successfully observed. We also showed that PEG-modified Er–Y2O3 nanoparticles exhibit no cell-toxicity. These observations lend strong support to the potential use of PEG-modified UCP nanoparticles as bioimaging tools.


Y2O3 Dispersion Stability Yttrium Oxide Upconversion Emission Discrete Energy Level 



The authors thank Prof. Y. Nagasaki (Univ. of Tsukuba, Ibaraki, Japan) for his advice and discussion on the PEG modification of the particles. This work is financially supported by RIKEN and the Ministry of Education, Science, Sports, Culture, and Technology (MEXT) of Japan. K.S. was financially supported by “Development of upconversion nano-particles for bio-nano-photonics” from New Energy and Industrial Technology Development Organization (NEDO) of Japan.

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This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.


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Copyright information

© The Author(s) 2008

Open AccessThis is an open access article distributed under the terms of the Creative Commons Attribution Noncommercial License (, which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.

Authors and Affiliations

  1. 1.Bioengineering LaboratoryRIKEN InstituteWakoJapan
  2. 2.Department of Materials Science and TechnologyTokyo University of ScienceNodaJapan

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