Controllable synthesis of bifunctional NaYF4:Yb3+/Ho3+@SiO2/Au nanoparticles with upconversion luminescence and high X-ray attenuation

A novel type of bifunctional water-soluble NaYF4:Yb3+/Ho3+@SiO2/Au nanocomposite is fabricated by a facile layer-by-layer technology in which the mercapto-silica shell is used as the functional layer coating on the central NaYF4:Yb3+/Ho3+ nanocrystals. Then by adjusting the mole ratio of the Au nanoparticles to the NaYF4:Yb3+/Ho3+@SiO2 nanoparticles, control of the gold loading on the upconversion nanocrystal surface is achieved. The fabricated nanocomposites inherit the excellent physical and chemical properties from their building blocks, simultaneously exhibiting upconversion luminescence and high X-ray attenuation and as well are easily modified with various molecules. These properties render the synthesized NaYF4:Yb3+/Ho3+@SiO2/Au nanocomposite not only useful as a multimodality contrast agent to increase the efficiency of molecular imaging but also has the potential of in situ curing of diseases. (C) 2011 Elsevier B. V. All rights reserved.