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Size-Tailored Biocompatible FePt Nanoparticles for Dual T1/T2 MRI Contrast Enhancement.

The development of new contrast agents (CAs) for magnetic resonance imaging (MRI) is of high interest especially due to the increased concerns of patient safety and quick clearance of clinically used gadolinium and iron oxide based CAs, respectively. Here, a two-step synthesis of superparamagnetic water soluble iron platinum (FePt) nanoparticles (NPs) with core sizes between 2 nm and 8 nm for use as CAs in MRI is reported. Firstly, wet-chemical organometallic NPs are synthesized by thermal decomposition in presence of stabilizing oleic acid and oleylamine. Secondly, the hydrophobic NPs are coated with an amphiphilic polymer and transferred into aqueous media. Their magnetization values and relaxation rates exceed those published for contrast agents already used for clinical application. Their saturation magnetization increases with the core size to approximately 82 Am2/kgFe. For 8 nm NPs the T2 relaxivity of approximately 221 (mM·s)-1 is 5 times larger than for the ferumoxides, and for 6 nm NPs the T1 relaxivity of approximately 12 (mM·s)-1 is slightly higher than that of ultra-small gadolinium oxide nanoparticles. The 6 nm FePt NPs are identified as excellent contrast agents for both T1 and T2 imaging. Most importantly, due to their coating significantly low cytotoxicity is achieved. FePt NPs prove to be a promising alternative to gadolinium and iron oxide nanoparticles showing high quality CAs characteristics for both T1- and T2-weighted images.