Abstract

Nanohybrids fabricated with upconversion nanoparticles (UCNPs) and gold nanoparticles (NPs) hold great promise for near infrared photothermal therapy (NIR-PTT) and upconversion fluorescence imaging. However, the obstacle of poor solubility in water and finite hydrophilic modification method about UCNPs limited its application in biological field. Herein, we reported a novel UCNP@Al(OH)3/Au nanohybrids mediated by high hydrophilic and biocompatible Al(OH)3 layer to realize a synergistic targeted PTT and fluorescence imaging capability to U87MG tumor-bearing mice under NIR light irradiation. The modification of Al(OH)3 layers can improve the water solubility of UCNPs. And the cytotoxicity assays and hemolysis assay showed that the modificiation of Al(OH)3 layers makes UCNPs have low cytotoxicity and good biocompatibility. In addition, the Al(OH)3 layers are thin enough to allow the fluorescence resonance energy transfer (FRET) between UCNP and gold nanoparticles occur, making the nanoparticles have good PTT effect for tumor-bearing mice. Meanwhile, as the pH-sensitive Al(OH)3 layer decomposed in the acidic tumor microenvironments with Au NPs detached from their surface, the FRET effect no longer existed subsequently, leading to the fluorescence intensity of naked UCNPs recovered for good imaging effects. The study suggests that Al(OH)3 mediated layer as promising hydrophilic nanoplatform can potentially be used for the preparation of superior hydrophilic nanoparticles and pH-stimulative drug release carrier for theranostic application in vivo.