Silane Ligand Exchange to Make Hydrophobic Superparamagnetic Nanoparticles Water-Dispersible

TLDR

The MNPs were prepared by thermal decomposition, a widely used method for producing monodisperse nanoparticles with controllable size. The study aims to develop a ligand‑exchange method to render ferrite magnetic nanoparticles water‑dispersible for biological applications. The authors functionalized ferrite MNPs by exchanging hydrophobic surfactant ligands with silanes bearing various endgroups and characterized the ligand exchange using SQUID, TEM, XPS, DLS, TGA, FTIR, UV–vis, and zeta potential. Amino, carboxylic acid, and PEG‑terminated silanes produced highly stable, water‑dispersible MNPs with electrostatic/steric protection and resistance to mild acid/alkaline, demonstrating a generic strategy for biological applications.

Abstract

Ferrite magnetic nanoparticles (MNPs) were functionalized with a variety of silanes bearing different functional endgroups to render them stable with respect to aggregation and keep them well-dispersed in aqueous media. The MNPs were prepared by the thermal decomposition method, widely used for the synthesis of monodisperse nanoparticles with controllable size. This method makes use of a hydrophobic surfactant to passivate the surface, which results in nanoparticles that are solely dispersible in nonpolar solvents. For use in biological applications, these nanoparticles need to be made water-dispersible. Therefore, a new procedure was developed on the basis of the exchange of the hydrophobic surface ligands with silanes bearing different endgroups to decorate ferrite magnetic nanoparticles with diverse functionalities . By this means, we could easily determine the influence of the endgroup on the nanoparticle stability and water-dispersibility. Amino-, carboxylic acid- and poly(ethylene glycol)-terminated silanes were found to render the MNPs highly stable and water-dispersible because of electrostatic and/or steric repulsion. The silane molecules were also found to form a protective layer against mild acid and alkaline environments. The ligand exchange on the nanoparticle surface was thoroughly characterized using SQUID, TEM, XPS, DLS, TGA, FTIR, UV−vis, and zeta potential measurements. The presented approach provides a generic strategy to functionalize magnetic ferrite nanoparticles and to form stable dispersions in aqueous media, which facilitates the use of these magnetic nanoparticles in biological applications.