Abstract
Superparamagnetic iron oxide nanoparticles can provide multiple benefits for biomedical applications in aqueous environments such as magnetic separation or magnetic resonance imaging. To increase the colloidal stability and allow subsequent reactions, the introduction of hydrophilic functional groups onto the particles’ surface is essential. During this process, the original coating is exchanged by preferably covalently bonded ligands such as trialkoxysilanes. The duration of the silane exchange reaction, which commonly takes more than 24 h, is an important drawback for this approach. In this paper, we present a novel method, which introduces ultrasonication as an energy source to dramatically accelerate this process, resulting in high-quality water-dispersible nanoparticles around 10 nm in size. To prove the generic character, different functional groups were introduced on the surface including polyethylene glycol chains, carboxylic acid, amine, and thiol groups. Their colloidal stability in various aqueous buffer solutions as well as human plasma and serum was investigated to allow implementation in biomedical and sensing applications.Electronic supplementary materialThe online version of this article (doi:10.1007/s11051-012-1100-5) contains supplementary material, which is available to authorized users.
Highlights
IntroductionIron oxide nanoparticles have been the subject of intensive research
For many years, iron oxide nanoparticles have been the subject of intensive research
For biomedical applications in aqueous environments, this hydrophobic coating has to be replaced with a hydrophilic coating
Summary
Iron oxide nanoparticles have been the subject of intensive research. A similar method reported by Park et al (2004) uses iron-oleate as a precursor and oleic acid as a capping agent This results in nanoparticles with a hydrophobic coating since the polar end groups are attached to the surface. Capping agents such as oleic acid are often used because they form a protective monolayer, which is strongly bonded. Kohler et al (2004) managed to introduce silanes, but pretreated the oleic acid coating with a mixture of 1 M ammonium hydroxide in 1-butanol These methods have serious drawbacks, e.g., the extensive reaction time (24–72 h) or pre-treatment procedure
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