Multimodal‐Luminescence Core–Shell Nanocomposites for Targeted Imaging of Tumor Cells

Abstract

Light on target: Silica-coated upconverting nanophosphor (UCNP) nanocomposites have been synthesized with organic dye (fluorescein isothiocyanate, FITC) incorporated in the silica shell. The nanocomposites are well dispersed and have good photostability and biocompatibility. These nanocomposites readily conjugated with folic acid for targeted multimodal bioimaging (see schematic representation). Uniform silica-coated NaYF₄: 20 mol % Yb, 2 mol % Er nanocomposites with good dispersibility, containing organic dye incorporated in the silica shell and folic acid conjugated on the surface of the shell, were prepared and characterized. The core–shell nanocomposites are 20–22 nm in size, water soluble, and buffer stable, with good photostability and biocompatibility. Folic acid (FA) offers a means of targeting human cells that greatly overexpress the folate receptor (FR). By the use of confocal microscopy and quantitative flow cytometry analysis, we demonstrate the receptor-mediated delivery of FA-conjugated nanocomposites targeting FR-positive cell lines, such as KB cells. The receptor-mediated targeting was confirmed by a comparison with the uptake of these nanocomposites in FR-negative cell lines, such as MCF-7. These results show that the silica-coated upconverting nanophosphor (UCNP) nanocomposites prepared by our strategy can potentially be useful as multimodal bioimaging agents.