Cross-linked magnetic nanoparticles with a biocompatible amide bond for cancer-targeted dual optical/magnetic resonance imaging

A poly(succinimide) (PSI) graft copolymer was designed and synthesized as a cross-linkable precursor polymer to fabricate biocompatible and biodegradable cross-linked magnetic nanoparticles (CMNPs) with excellent structural stability in vivo and multifunctionality, including specific cancer-targeting and dual imaging modalities. After coating the magnetic nanoparticles with amphiphilic PSI grafted with folate-conjugated PEG and alkyl chains, the succinimide units on the inner shell of the nanoparticles were cross-linked and converted into a biocompatible and biodegradable structure consisting of amide bonds and further used to bear free amine groups on the surface of the CMNPs. Finally, the CMNPs were directly conjugated with the near-infrared (NIR) fluorescent dye Cy5.5 for use in specific cancer-targeted magnetic resonance (MR)/optical imaging applications. The resulting Cy5.5- and folate-conjugated CMNPs (CMNPs-Cy5.5-fol) were approximately 45 nm in diameter, showed excellent biocompatibility and had a high T₂ relaxivity coefficient. Our in vitro and in vivo study demonstrates the potential utility of CMNPs-Cy5.5-fol as dual imaging probes for specific cancer-targeted MR/NIR imaging applications.