Enhanced upconversion fluorescent probe of single NaYF4:Yb3+/Er3+/Zn2+ nanoparticles for copper ion detection

Surface modified NaYF4:Yb3+/Er3+/Zn2+ upconversion nanoparticles were obtained by using branched polyethylenimine (PEI). Strong fluorescence emission was observed and the influence of copper ions on the fluorescence emission of the PEI-modified NaYF4:Yb3+/Er3+/Zn2+ nanoparticles was investigated. It was found that the fluorescence emission can be quenched through luminescence resonance energy transfer from the particle to the copper ions. The results show that the PEI modified NaYF4:Yb3+/Er3+/Zn2+ nanoparticle can be used as a fluorescent probe for highly sensitive and selective detection of copper ions.