title: Evaluation of High-Yield Purification Methods on Monodisperse PEG-Grafted Iron Oxide Nanoparticles.
abstract: Fundamental research on nanoparticle (NP) interactions and development of next-generation biomedical NP applications relies on synthesis of monodisperse, functional, core-shell nanoparticles free of residual dispersants with truly homogeneous and controlled physical properties. Still, synthesis and purification of e.g. such superparamagnetic iron oxide NPs remain a challenge. Comparing the success of different methods is marred by the sensitivity of analysis methods to the purity of the product. We synthesize monodisperse, oleic acid (OA)-capped, Fe3O4 NPs in the superparamagnetic size range (3-10 nm). Ligand exchange of OA for poly(ethylene glycol) (PEG) was performed with the PEG irreversibly grafted to the NP surface by a nitrodopamine (NDA) anchor. Four different methods were investigated to remove excess ligands and residual OA: membrane centrifugation, dialysis, size exclusion chromatography, and precipitation combined with magnetic decantation. Infrared spectroscopy and thermogravimetric analysis were used to determine the purity of samples after each purification step. Importantly, only magnetic decantation yielded pure NPs at high yields with sufficient grafting density for biomedical applications (∼1 NDA-PEG(5 kDa)/nm(2), irrespective of size). The purified NPs withstand challenging tests such as temperature cycling in serum and long-term storage in biological buffers. Dynamic light scattering, transmission electron microscopy, and small-angle X-ray scattering show stability over at least 4 months also in serum. The successful synthesis and purification route is compatible with any conceivable functionalization for biomedical or biomaterial applications of PEGylated Fe3O4 NPs.
authors.affiliation: Department of Nanobiotechnology, Institute for Biologically Inspired Materials, University of Natural Resources and Life Sciences , Muthgasse 11, 1190 Vienna, Austria.
authors.forename: Andrea
authors.initials: A
authors.lastname: Lassenberger
authors.affiliation: Department of Nanobiotechnology, Institute for Biologically Inspired Materials, University of Natural Resources and Life Sciences , Muthgasse 11, 1190 Vienna, Austria.
authors.forename: Oliver
authors.initials: O
authors.lastname: Bixner
authors.affiliation: Department of Material Science and Process Engineering, Institute of Physics and Materials Science , Peter-Jordan Strasse 82, 1190 Vienna, Austria.
authors.forename: Tilman
authors.initials: T
authors.lastname: Gruenewald
authors.affiliation: Department of Material Science and Process Engineering, Institute of Physics and Materials Science , Peter-Jordan Strasse 82, 1190 Vienna, Austria.
authors.forename: Helga
authors.initials: H
authors.lastname: Lichtenegger
authors.affiliation: Department of Nanobiotechnology, Institute for Biologically Inspired Materials, University of Natural Resources and Life Sciences , Muthgasse 11, 1190 Vienna, Austria.
authors.forename: Ronald
authors.initials: R
authors.lastname: Zirbs
authors.affiliation: Department of Nanobiotechnology, Institute for Biologically Inspired Materials, University of Natural Resources and Life Sciences , Muthgasse 11, 1190 Vienna, Austria.
authors.forename: Erik
authors.initials: E
authors.lastname: Reimhult