Silane Ligand Exchange to Make Hydrophobic Superparamagnetic Nanoparticles Water-Dispersible

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.

The design and utility of polymer-stabilized iron-oxide nanoparticles for nanomedicine applications

“…Silane can be covalently attached onto IONP surfaces by reaction of the surface Fe-OH group with the Si-OCH 3 moiety [11]. Further cross-linking events produce a thin inorganic silica layer around the particles [12]. However, during this cross-linking process, the irreversible formation of aggregates can be observed, limiting the use of the resultant IONPs.…”

“…However, during this cross-linking process, the irreversible formation of aggregates can be observed, limiting the use of the resultant IONPs. Th e functionalization of IONPs using silane chemistry is versatile, involving the use of many functional silanes available commercially, such as alcohol, amine and thiol, which are useful for further biofunctionalization using small biocompounds [12] and carbohydrates [13].…”

Role of polymeric surfactants on the growth of manganese ferrite nanoparticles

“…In this method the magnetic nanoparticles are heated to 800°C under N 2 and recorded the changes in mass due to the loss of organic material from the synthesized nanoparticles. Generally, the organic materials with strong bond to the particles can be desorbed at higher temperatures [44].…”

Modification of Thermoplastics with Reactive Silanes and Siloxanes

“…Instead of (trialkoxy)propylsilanes containing different carbofunctional groups: amine, aldehyde, acrylate, isocyanate, thiol, ether, triacetoxydiamine, and trialkoxysilanes containing aldehyde and nitrile groups attached to a longer alkylene "connector" were grafted on the surface of cobalt ferrite CoFe 2 O 4 . They were utilized for the preparation of water dispersions of nanoparticles with supermagnetic properties (de Palma et al, 2007).…”