Fe₃O₄ nanoparticles modified by CD-containing star polymer for MRI and drug delivery

Fe₃O₄ nanoparticles with ultrasmall sizes show good T₁ or T₁+T₂ contrast abilities, and have attracted considerable interest in the field of magnetic resonance imaging (MRI) contrast agents. For effective biomedical applications, the colloidal stability and biocompatibility of the Fe₃O₄ nanoparticles need to be improved without reducing MRI relaxivity. In this paper, star polymers were used as coating materials to modify Fe₃O₄ nanoparticles in view of their dense molecular architecture with moderate flexibility. The star polymer was composed of a β-cyclodextrin (β-CD) core and poly(2-(dimethylamino) ethyl methacrylate) (PDMAEMA) arms. Meanwhile, reduced glutathione (GSH), as a model drug, was also associated with the star polymer. Thus, a new platform for simultaneous diagnosis and treatment was achieved. Compared to the Fe₃O₄ nanoparticles coated with linear polymers, the Fe₃O₄ nanoparticles coated with star polymers (Fe₃O₄@GCP) possessed higher GSH association capacity and better stability in serum-containing solution. GSH could be released from Fe₃O₄@GCP nanoparticles in response to pH value of the solution. Since the sulfhydryl group on GSH is able to combine free radicals, Fe₃O₄@GCP nanoparticles exhibited less cytotoxicity compared to the Fe₃O₄ nanoparticles without including GSH. Furthermore, the nanoparticles could also serve as good T₁ MRI contrast agent, and the MRI relaxivity of Fe₃O₄@GCP nanoparticles did not decrease after coated with the star polymer. These results indicate that the precisely designed Fe₃O₄@GCP nanoparticles could be used as a versatile promising theranostic nano-platform.