Multicolor core/shell-structured upconversion fluorescent nanoparticles

Abstract

The core/shell-structured pure-hexagonal-phase NaYF4:Yb,Er/Tm nanospheres with very thin and uniform silica coatings was prepared. These nanoparticles were usually synthesized in organic solvents or at high temperatures, where ethylenediamine tetraacetic acid (EDTA) was used as a chelating agent to control the growth of NaYf4 nanocrystal. These nanoparticles have advantages such as minimum photo damage to living organisms, weak background fluorescence, high detection sensitivity, and high light-penetration depth in tissues. Some inorganic materials, as semiconductor quantum dots (QDs) and metal nanospheres or nanorods, were also developed and used for two-photon imaging of cells. The results shows that the nanospheres were used as fluorescent probes in cell imaging. The multicolor upconversion nanosphere, produced by encapsulating organic dyes or QDs into the silica shell, would prove very useful for in vitro multiplexed bioassays and in vivo studies.