Metal-free and biocompatible TEMPO-containing nanoparticles for safe magnetic resonance imaging and stimuli-triggered drug release.

Magnetic resonance imaging (MRI) is a cornerstone of modern diagnostic imaging. In clinical MRI diagnosis, MRI contrast agents are routinely employed to enhance the image contrast of specific areas in the body. However, conventional metal-based contrast agents pose potential toxicity risks, driving the development of safer metal-free alternatives. Nowadays, nitroxide radical contrast agents have emerged as a promising substitute, offering comparable efficiency without metallic components. In this study, we report three different nitroxide radical (TEMPO)-containing amphiphilic polymers that can self-assemble into spherical nanoparticles in aqueous solution. These nanoparticles exhibit increased longitudinal relaxivities (ranging from 0.58 to 0.88 mM s), improved stability, and excellent biocompatibility. Following intravenous injection into mice, the nanoparticles produce significant MRI contrast enhancement in the urinary system for at least 1 h. Additionally, the synthesized polymers can function as effective carriers for anticancer drugs. Under reductive conditions, the drug-loaded nanoparticles undergo rapid release, achieving a final cumulative drug release of 62 %. Furthermore, the drug-loaded nanoparticles also show inhibitory effect on Hela cells. Overall, these TEMPO-containing polymer nanoparticles hold significant promise for applications in MRI and stimuli-triggered drug release.