title: Functional PEG-PAMAM-tetraphosphonate capped NaLnF₄ nanoparticles and their colloidal stability in phosphate buffer.
abstract: 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 (NH2-PAMAM-4P) as a multidentate ligand for these NPs has been synthesized and characterized as a ligand for the surface of NaGdF4 and NaTbF4 nanoparticles. A two-step ligand exchange protocol was developed for introduction of the NH2-PAMAM-4P ligand on oleate-capped NaLnF4 NPs. The NPs were first treated with methoxy-poly(ethylene glycol)-monophosphoric acid (M(n) = 750) in tetrahydrofuran. The mPEG750-OPO3-capped NPs were stable colloidal solutions in water, where they could be ligand-exchanged with NH2-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. NaGdF4 and NaTbF4 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 NaTbF4 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.
authors.affiliation: Department of Chemistry, University of Toronto , 80 St. George Street, Toronto, Ontario, Canada M5S 3H6.
authors.forename: Guangyao
authors.initials: G
authors.lastname: Zhao
authors.forename: Lemuel
authors.initials: L
authors.lastname: Tong
authors.forename: Pengpeng
authors.initials: P
authors.lastname: Cao
authors.forename: Mark
authors.initials: M
authors.lastname: Nitz
authors.forename: Mitchell A
authors.initials: MA
authors.lastname: Winnik
mesh_terms: D003102:Colloids / Q000737:chemistry*; D050091:Dendrimers / Q000737:chemistry*; D053758:Nanoparticles / Q000737:chemistry*; D010710:Phosphates / Q000737:chemistry*; D011092:Polyethylene Glycols / Q000737:chemistry*
chemical_list: D003102:Colloids; D050091:Dendrimers; C522249:PEG-PAMAM; D010710:Phosphates; D011092:Polyethylene Glycols