In situ decorating of ultrasmall Ag2Se on upconversion nanoparticles as novel nanotheranostic agent for multimodal imaging-guided cancer photothermal therapy

A novel multifunctional theranostic nanoplatform was fabricated via in situ growth of ultrasmall Ag 2 Se nanodots on the surface of chitosan (CS) coated NaYF 4 :Yb/Er@NaLuF 4 :Nd/Yb@NaLuF 4 upconversion nanoparticles (UCNPs). NaYF 4 :Yb/Er@NaLuF 4 :Nd/Yb@NaLuF 4 @CS@Ag 2 Se (labeled as UCNPs@CS@Ag 2 Se) nanocomposites can provide downshifting (DS) and upconversion (UC) luminescence in NIR biological window I and II under 808-nm continuous-wave laser excitation simultaneously. Meanwhile, the attached Ag 2 Se nanodots could produce hyperthermia and photoacoustic energy upon 808-nm laser irradiation due to its strong near-infrared (NIR) absorbance. Together with the X-ray absorbance feature of lanthanide components, the nanocomposites with excellent luminescent properties, high X-ray attenuation coefficient and strong NIR absorbance could be utilized as a smart contrast agent for upconversion luminescence (UCL)/downshifting luminescence (DSL)/computer tomography (CT)/photoacoustic (PA) multimodal imaging in vitro and in vivo . Furthermore, the as-synthesized nanocomposites possess superior photothermal performance, good biocompatibility, and negligible toxicity, showing great potential as an ideal photothermal therapy (PTT) agent. These outstanding properties revealed that UCNPs@CS@Ag 2 Se nanocomposites are promising theranostic agents for tetra-modal imaging-guided PTT of cancer.