ATP‐Triggered Ultrafine Iron Oxide Nanowires for Self‐Monitoring Tumor Therapy by T ₁ ‐Magnetic Resonance Imaging‐Guided •OH Generation

Abstract Theranostic probes that integrate diagnosis and treatment together are considered as effective tools for individual therapy. However, the separation of detection and treatment components limits precise assessment of therapeutic efficacy. Herein, a novel self‐monitoring probe that sensitively responds to adenosine triphosphate (ATP) was developed by ultrafine iron oxide nanowires (UIONWs) through an oleyl amine‐assisted way. The UIONWs, with a diameter of 1.5 nm and length of 75 nm, are surface‐coordinated with oleyl amine. UIONWs can be decomposed in ATP‐containing solution and expose the shielded iron ions. Consequently, it can boost the peroxidase (POD) activity and activate the T 1 ‐magnetic resonance imaging (MRI) signal by ATP. In addition, UIONWs can be rapidly engulfed into cells due to the high aspect ratio. The improved ATP and hydrogen peroxide (H 2 O 2 ) within tumor cells leads to higher hydroxyl radicals (OH) generation for effective tumor inhibition.In contrast, normal cells exhibit lower ATP and H 2 O 2 levels, reducing cytotoxicity and ensuring safety. Since both the illumination of T 1 ‐MRI and OH generation are ATP‐controlled, this work raised a potential way to self‐monitor tumor therapy with timely feedback on therapeutic effects.