Facile Synthesis of Ultrasmall and Hexagonal NaGdF4: Yb3+, Er3+ Nanoparticles with Magnetic and Upconversion Imaging Properties

Synthesis of nanomaterials with multi-imaging modality is of great importance in clinical molecular imaging and diagnostics. This work reports novel synthetic strategy to create ultrasmall and hexagonal upconversion nanoparticles (UCNPs), beta-NaGdF4: Yb3+, Er3+, and beta-NaGdF4: Yb3+, Tm3+, with inherent magnetic and efficient upconversion properties. The use of new combination of lanthanide chloride and sodium TFA as the precursors for UCNPs gave the best results in terms of size (10-40 nm), crystallinity and morphology, and proved to be cost-and time-saving. Water solubilization of both NaGdF4: Yb3+, Er3+, and beta-NaGdF4: Yb3+ Tm3+ UCNPs was achieved by homogeneous polymer coating using amphiphilic poly(acrylic acid) derivatives. The strong upconversion and magnetic properties were maintained after extensive polymer coating process. To see the potential of the UCNPs for biological applications, the surface of NaGdF4: Yb3+, Er3+ UCNPs were functionalized with Ni-nitrilotriacetate (NiNTA) moiety. The remarkable specificity of these NiNTA-UCNPs for the oligohistidine peptide was clearly shown by both magnetic resonance and optical imaging. Finally, the cellular uptake of these UCNPs was investigated by fluorescence microscope using spectral imaging technique.