Improving Magnetic Resonance Imaging and Chemodynamic Therapy Properties via Tuning the Fe(II)/Fe(III) Ratio in Hydrophilic Single-Atom Nanobowls.

We developed an intrinsic hydrophilic single-atom iron nanobowl (Fe-SANB) for magnetic resonance imaging (MRI)-guided tumor microenvironment-triggered cancer therapy. Benefiting from the sufficient exposure of Fe single atoms and the intrinsic hydrophilicity of the bowl-shaped structure, the Fe-SANBs exhibited a superior performance for T 1 -weighted MRI with an r 1 value of 11.48 mM-1 s-1 , which is 3-fold higher than that of the commercial Gd-DTPA ( r 1 = 3.72 mM-1 s-1 ). After further coembedding Gd single atoms in the nanobowls, the r 1 value can be greatly improved to 19.54 mM-1 s-1 . In tumor microenvironment (TME), the Fe-SANBs can trigger pH-induced Fenton-like activity to generate highly toxic hydroxyl radicals for high-efficiency chemodynamic therapy (CDT). Both the MRI and CDT efficiency of these nanobowls can be optimized by tuning the ratio of Fe(II)/Fe(III) in the Fe-SANBs via controlling the calcination temperature. Furthermore, the generation of •OH at the tumor site can be accelerated via the photothermal effect of Fe-SANBs, thus promoting CDT efficacy. Both in vitro and in vivo results confirmed that our nanoplatform exhibited high T 1 -weighted MRI contrast, robust biocompatibility, and satisfactory tumor treatment, providing a potential nanoplatform for MRI-guided TME-triggered precise cancer therapy.