Superparamagnetic iron oxide nanoparticles stabilized by a poly(amidoamine)-rhenium complex as potential theranostic probe

Three-component nanocomposites, constituted by a superparamagnetic iron oxide core coated with apolymeric surfactant bearing tightly bound Re(CO)3 moieties, were prepared and fully characterized. Thewater soluble and biocompatible surfactant was a linear poly(amidoamine) copolymer (PAA), containingcysteamine pendants in the minority part (ISA23SH), able to coordinate Re(CO)3 fragments. For thesynthesis of the nanocomposites two methods were compared, involving either (i) peptization of baremagnetite nanoparticles by interaction with the preformed ISA23SH-Re(CO)3 complex, or (ii) "one-pot"synthesis of iron oxide nanoparticles in the presence of the ISA23SH copolymer, followed by complexationof Re to the SPIO@ISA23SH nanocomposite. Full characterization by TEM, DLS, TGA, SQUID, andrelaxometry showed that the second method gave better results. The magnetic cores had a roundishshape, with low dispersion (mean diameter ca. 6 nm) and a tendency to form larger aggregates (detectedboth by TEM and DLS), arising from multiple interactions of the polymeric coils. Aggregation did notaffect the stability of the nano-suspension, found to be stable for many months without precipitateformation. The SPIO@PAA-Re nanoparticles (NPs) showed superparamagnetic behaviour and nuclearrelaxivities similar or superior to commercial MRI contrast agents (CAs), which make them promising asMRI "negative" CAs. The possibility to encapsulate 186/188Re isotopes (? and ? emitters) gives these novelNPs the potential to behave as bimodal nanostructures devoted to theranostic applications.