Surface modification of upconversion nanoparticles with amphiphilic chitosan for cancer cell imaging

Abstract

Upconversion nanoparticles (UCNPs) as a new kind of biological luminescence materials have many advantages comparing with organic fluorescence probes and semi-conductive quantum dots, such as sharp fluorescence emission, long emission lifetimes, high optical and chemical stability and low toxicity, especially low auto-fluorescence background and deep tissue penetration under near-infrared (NIR) light excitation for bioimaging. Herein, we demonstrate a facile approach to transfer UCNPs from hydrophobic to hydrophilic and the use of these UCNPs for cell imaging. Oleic acid-capped UCNPs based on NaYF₄ were synthesized and modified with amphiphilic chitosan derivative through hydrophobic interaction. The as-prepared chitosan coated UCNPs with an average diameter of 35 nm were mono-dispersed in aqueous solution and possess good optical properties upon NIR light excitation. Cell viability assays indicated the low cytotoxicity and good biocompatibility of chitosan-coated UCNPs. Cell imaging results demonstrated that chitosan-coated UCNPs had great potential for bioimaing and biolabeling. Our work suggests a feasible method to modify OA-UCNPs with amphiphilic polymer and the promise of chitosan-based UCNPs for bioimaging application.