Lanthanide-doped NaScF4 nanoprobes: crystal structure, optical spectroscopy and biodetection

Abstract

Trivalent lanthanide ions (Ln³⁺)-doped inorganic nanoparticles (NPs) as potential luminescent bioprobes have been attracting tremendous interest because of their unique upconversion (UC) and downconversion (DC) luminescence properties. NaScF₄, as an important host material, has been rarely reported and its crystal structure remains unclear. Herein, based on the single crystal X-ray diffraction, the space group of NaScF₄ crystals was determined to be P3₁ containing multiple sites of Sc³⁺ with crystallographic site symmetry of C₁, which was verified by high-resolution photoluminescence spectroscopy of Eu³⁺ at low temperature (10 K). Furthermore, monodisperse and size-controllable NaScF₄:Ln³⁺ NPs were synthesized via a facile thermal decomposition method. The biotinylated NaScF₄:Er³⁺/Yb³⁺ NPs were demonstrated for their applications as a heterogeneous UC luminescence bioprobe to detect avidin with a detection limit of 180 pM. After bioconjugation with amino-terminal fragment (ATF) of urokinase plasminogen activator (uPA), NaScF₄:Ln³⁺ NPs also exhibited specific recognition of cancer cells overexpressed with uPA receptor (uPAR, an important marker of tumor biology and metastasis), showing great potentials in tumor-targeted bioimaging.