Hexanedioic acid mediated surface–ligand-exchange process for transferring NaYF4:Yb/Er (or Yb/Tm) up-converting nanoparticles from hydrophobic to hydrophilic

Water-soluble and carboxyl-functionalized up-converting rare-earth nanoparticles (UCNPs) are obtained via an efficient surface–ligand-exchange procedure. Hexanedioic acid molecules are employed to replace the original hydrophobic ligands in diethylene glycol solvent at high temperature. Various characterizations indicate the ligand-exchange process has negligible adverse effect on the quality of the UCNPs. The resulting hydrophilic UCNPs show small size, strong up-converting emission and high water stability. The specific molecular recognition capacity of avidin-modified hydrophilic UCNPs confirms that hydrophilic UCNPs are suitable for potential biological labeling.

Graphical abstractHexanedioic acid is used to replace the original hydrophobic ligands on the surface of up-converting rare-earth nanoparticles via an efficient ligand-exchange approach, the resulting carboxyl-functionalized UCNPs are suitable for biological applications.Figure optionsDownload full-size imageDownload as PowerPoint slide