Covalently assembled NIR nanoplatform for simultaneous fluorescence imaging and photodynamic therapy of cancer cells

A highly efficient multifunctional nanoplatform for simultaneous upconversion luminescence (UCL) imaging and photodynamic therapy has been developed on the basis of selective energy transfer from multicolor luminescent NaYF4:Yb3+,Er3+ upconversion nanoparticles (UCNPs) to photosensitizers (PS). Different from popular approaches based on electrostatic or hydrophobic interactions, over 100 photosensitizing molecules were covalently bonded to every 20 nm UCNP, which significantly strengthened the UCNP-PS linkage and reduced the probability of leakage/desorption of the PS. Over 80% UCL was transferred to PS, and the singlet oxygen production was readily detected by its feature emission at 1270 nm. Tests performed on JAR choriocarcinoma and NIH 3T3 fibroblast cells verified the efficient endocytosis and photodynamic effect of the nanoplatform with 980 nm irradiation specific to JAR cancer cells. Our work highlights the promise of using UCNPs for potential image-guided cancer photodynamic therapy.