Functional PEG?PAMAM-Tetraphosphonate Capped NaLnF_4 Nanoparticles and their Colloidal Stability in Phosphate Buffer

摘要

Developing surface coatings for NaLnF4 nanoparticles (NPs) that provide long-term stability in solutions containing competitive ions such as phosphate remains challenging. An amine-functional polyamidoamine tetraphosphonate (NH_2-PAMAM-4P) as a multidentate ligand for these NPs has been synthesized and characterized as a ligand for the surface of NaGdF_4 and NaTbF_4 nanoparticles. A two-step ligand exchange protocol was developed for introduction of the NH_2- PAMAM-4P ligand on oleate-capped NaLnF_4 NPs. The NPs were first treated with methoxy-poly(ethylene glycol)-monophosphoric acid (M_n = 750) in tetrahydrofuran. The mPEG750- OPO_3-capped NPs were stable colloidal solutions in water, where they could be ligand-exchanged with NH_2-PAMAM-4P. The surface amine groups on the NPs were available for derivatization to attach methoxy-PEG (M_n = 2000) and biotin-terminated PEG (M_n = 2000) chains. The surface coverage of ligands on the NPs was examined by thermal gravimetric analysis, and by a HABA analysis for biotin-containing NPs. Colloidal stability of the NPs was examined by dynamic light scattering. NaGdF_4 and NaTbF_4 NPs capped with mPEG2000?PAMAM-4P showed colloidal stability in DI water and in phosphate buffer (10 mM, pH 7.4). A direct comparison with NaTbF_4 NPs capped with a mPEG2000-lysine-based tetradentate ligand that we reported previously (Langmuir 2012, 28, 12861?12870) showed that both ligands provided long-term stability in phosphate buffer, but that the lysine-based ligand provided better stability in phosphate-buffered saline.