Ultrasensitive iron-based magnetic resonance contrast agent constructed with natural polyphenol tannic acid for tumor theranostics

Because of the toxicity of Gd(III) complexes and the poor T1 magnetic resonance imaging (MRI) contrast of superparamagnetic iron oxide, the development of new stable, non-toxic, and efficient contrast agents is desirable. Herein, tannic acid (TA), a large natural polyphenol, and bovine serum albumin (BSA) were used to construct non-toxic Fe(III) complexes with increased relaxivity based on a strategy slowing the molecular spin. Compared with the commercial T1 contrast agent Magnevist, TA-Fe@BSA not only exhibits comparable T1 MRI contrast enhancement under 0.5, 1 and 7 T magnetic fields both in vitro and in vivo, but also has better stability and biocompatibility. Moreover, TA-Fe@BSA with near-infrared (NIR) absorption demonstrates efficient tumor ablation via photothermal effects. These results demonstrate their strong potential as an alternative T1 MRI contrast agent and tumor theranostics agent in clinical settings.