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 poorT(1)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 commercialT(1)contrast agent Magnevist, TA-Fe@BSA not only exhibits comparable T-1 MRI contrast enhancement under 0.5, 1 and 7 T magnetic fields bothin vitroandin vivo, but also has better stability and biocompatibility. Moreover, TA-Fe@BSA with near-infrared (NIR) absorption demonstrates efficient tumor ablationviaphotothermal effects. These results demonstrate their strong potential as an alternative T-1 MRI contrast agent and tumor theranostics agent in clinical settings.