PEG-modified upconversion nanoparticles for in vivo optical imaging of tumors

A novel surface modification approach of brightly luminescent upconversion nanoparticles (UCNPs) is reported. Inorganic core@shell UCNPs (core - NaYF4 co-doped with Yb3+ and Tm3+ ions, shell - NaYF4) were modified by intercalation with amphiphilic copolymer poly(maleic anhydride-alt-1-octadecene) followed by cross-linking with poly(ethylene glycol) diglycidyl ether (PEG-DGE). The proposed approach enables preparation of UCNPs with an outmost PEG-containing layer, which provides steric stabilization and low non-specific protein adsorption. Intravenous injection of PEG-functionalized UCNPs into the mice results in extension of the UCNP blood circulation time up to 1 hour. In vivo epi-luminescence imaging of the mouse model with Lewis lung carcinoma is ensured by the high quantum yield of the modified UCNPs and passive targeting associated with efficient UCNP accumulation in solid tumors.