Superparamagnetic iron oxide nanoparticlescan providemultiple benefits for biomedical applicationsin aqueous environments such asmagnetic separation ormagnetic resonance imaging. To increase the colloidalstability and allow subsequent reactions, the introductionof hydrophilic functional groups onto the particles’surface is essential. During this process, the originalcoating is exchanged by preferably covalently bondedligands such as trialkoxysilanes. The duration of thesilane exchange reaction, which commonly takes morethan 24 h, is an important drawback for this approach. Inthis paper, we present a novel method, which introducesultrasonication as an energy source to dramaticallyaccelerate this process, resulting in high-quality waterdispersible nanoparticles around 10 nmin size. To provethe generic character, different functional groups wereintroduced on the surface including polyethylene glycolchains, carboxylic acid, amine, and thiol groups. Theircolloidal stability in various aqueous buffer solutions aswell as human plasma and serum was investigated toallow implementation in biomedical and sensingapplications.
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