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Surface Modification of Gadolinium Oxide Thin Films and Nanoparticles using Poly(ethylene glycol)-Phosphate

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journal contribution
posted on 10.01.2012, 00:00 by Andrée-Anne Guay-Bégin, Pascale Chevallier, Luc Faucher, Stéphane Turgeon, Marc-André Fortin
The performance of nanomaterials for biomedical applications is highly dependent on the nature and the quality of surface coatings. In particular, the development of functionalized nanoparticles for magnetic resonance imaging (MRI) requires the grafting of hydrophilic, nonimmunogenic, and biocompatible polymers such as poly(ethylene glycol) (PEG). Attached at the surface of nanoparticles, this polymer enhances the steric repulsion and therefore the stability of the colloids. In this study, phosphate molecules were used as an alternative to silanes or carboxylic acids, to graft PEG at the surface of ultrasmall gadolinium oxide nanoparticles (US-Gd2O3, 2–3 nm diameter). This emerging, high-sensitivity “positive” contrast agent is used for signal enhancement in T1-weighted molecular and cellular MRI. Comparative grafting assays were performed on Gd2O3 thin films, which demonstrated the strong reaction of phosphate with Gd2O3 compared to silane and carboxyl groups. Therefore, PEG-phosphate was preferentially used to coat US-Gd2O3 nanoparticles. The grafting of this polymer on the particles was confirmed by XPS and FTIR. These analyses also demonstrated the strong attachment of PEG-phosphate at the surface of Gd2O3, forming a protective layer on the nanoparticles. The stability in aqueous solution, the relaxometric properties, and the MRI signal of PEG-phosphate-covered Gd2O3 particles were also better than those from non-PEGylated nanoparticles. As a result, reacting PEG-phosphate with Gd2O3 particles is a promising, rapid, one-step procedure to PEGylate US-Gd2O3 nanoparticles, an emerging “positive” contrast agent for preclinical molecular and cellular applications.