Geometrical Confinement of Gadolinium Oxide Nanoparticles in Poly(ethylene glycol)/Arginylglycylaspartic Acid-Modified Mesoporous Carbon Nanospheres as an Enhanced T₁ Magnetic Resonance Imaging Contrast Agent

A new strategy for designing contrast agents (CAs) based on geometrical confinement will become a competent way to improve the relaxivity of CAs. Herein, a magnetic resonance imaging (MRI) nanoconstruct is fabricated through loading Gd₂O₃ nanoparticles into mesoporous carbon nanospheres, followed by conjugation of poly­(ethylene glycol) (PEG) and the c­(RGDyK) peptide (Gd₂O₃@OMCN-PEG-RGD), which could prolong the blood circulation half-life as well as improve the tumor-targeting ability. As a result, the Gd₂O₃@OMCN-PEG-RGD exhibits an outstandingly high relaxivity (r₁ = 68.02 mM^–1 s^–1), which is ∼5.3 times higher than that of Gd₂O₃ nanoparticles (r₁ = 12.74 mM^–1 s^–1). Afterward, both the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide test and H&E staining show that the Gd₂O₃@OMCN-PEG-RGD has wonderful biocompatibility in vitro and in vivo. Moreover, the in vivo MR images indicate that the Gd₂O₃@OMCN-PEG-RGD could accumulate in the tumor region more rapidly than Gd₂O₃@OMCN-PEG. This study presents a facile method to fabricate an MRI CA with excellent T₁ contrast ability based on geometrical confinement and excellent biocompatibility, which could act as an optimal contender for sensitive in vivo tumor imaging with outstanding targeting ability.