Synthesis ofpolyethylenimine/NaYF4 nanoparticles with upconversion fluorescence

Abstract

Upconverting materials, which can be efficiently excited by near infrared light and emitstrong visible light through a process termed ‘upconversion fluorescence’, have shown greatpotential for use in biological labelling and imaging. Some upconverting nanoparticles such asNaYF4 doped with lanthanide ions have been synthesized; however, these nanoparticles are notsoluble in water, not biocompatible and do not have functional chemical groups forconjugation of biomolecules, and as a result their bioapplications are very limited unlesssome surface modifications are performed. Here we report a method for one-pot synthesis ofpolyethylenimine/NaYF4 nanoparticles doped with lanthanide ions, which are water soluble andbiocompatible. The amino groups of polyethylenimine existing on the nanoparticlescan be used for attachment of biomolecules. The nanoparticles showed aspherical shape with an average size of about 50 nm. Different lanthanide ions(Yb3+,Er3+ and Tm3+) were doped into the nanoparticles, which showed strong upconversion fluorescence ofdifferent colours in aqueous solutions under excitation at 980 nm.