ICG-Sensitized NaYF4:Er Nanostructure for Theranostics

Here lanthanide-doped luminescent nanoparticles (LNPs) NaYF4:Er conjugated to the indocyanine green dye (ICG) are introduced for theranostics applications in trimodal imaging as well as in photothermal therapy. ICG as a donor with high absorption cross-section at 808 nm increases excitation efficiency of Er3+ through the energy transfer mechanism and, therefore, significantly enhances both upconverted and Stokes emissions from Er3+ ions in LNPs. Enhanced Stokes emission is used at 1.5 mu m for bioimaging in the second near-infrared wavelength window, which allows deeper penetration in biological media due to reduced scattering. A part of the ICG excitation decays by the competing nonradiating relaxation to produce local heating, which is utilized for photoacoustic imaging as well as for local thermal imaging. All these modalities are demonstrated by in vivo imaging of subcutaneous pancreatic tumor-bearing nude mice. Furthermore, in the thermal imaging as well as in vitro photocytotoxicity studies, it is shown that the local temperature rise is high enough to be used for highly effective photothermal therapy. Cytotoxicity study on cells using the MTT assay shows the biocompatibility feature of this nanoconstruct. The obtained results demonstrate the potential of ICG-NaYF4:Er nanoconjugates for multimodal theranostics.