All-Organic Pectin-Nitroxide Nanoconjugates as Biocompatible and Metal-Free Magnetic Resonance Imaging Contrast Agents

Because it is noninvasive and radiation-free, magnetic resonance imaging (MRI) is a commonly used imaging method that is very helpful for the early detection and monitoring of malignant growths. The development of alternative imaging probes is essential to reducing the toxicity of contrast agents (CAs) based on metals, such as gadolinium (Gd), which are used in clinical settings. Our goal is to create innovative MRI contrast agents that do not require metallic components and have great stability and relaxivity while still exhibiting excellent efficacy. In this work, the esterification reaction and ring-opening polymerization methods used to successfully synthesize pectin-nitroxide nanoconjugates are demonstrated, and their effective use as a CA for MRI is established. For each radical, the nanoconjugates have a favorable longitudinal water ¹H relaxivity of 0.23 and 0.41 mM^-1 s^-1 for the pectin-TEMPO (PT) and pectin-PGTEMPO (PPGT). The PPGT exhibits notable characteristics like nontoxicity in vivo and resistance to quenching. For longer than 3 h, the PPGT in Wistar female rats shows increased MRI contrast. Comparable contrast enhancement is achieved with PPGT at 3.85 times lower (0.026 mmol/kg) than the standard dose (0.1 mmol/kg). Consequently, the PPGT shows promise as a workable metal-free MRI CA.