Engineering Single-Atom Iron Nanozymes with Radiation-Enhanced Self-Cascade Catalysis and Self-Supplied H 2 O 2 for Radio-enzymatic Therapy.

Single-atom nanozymes (SAzymes), with individually isolated metal atom as active sites, have shown tremendous potential as enzyme-based drugs for enzymatic therapy. However, using SAzymes in tumor theranostics remains challenging because of deficient enzymatic activity and insufficient endogenous H 2 O 2 . We develop an external-field-enhanced catalysis by an atom-level engineered FeN 4 -centered nanozyme (FeN 4 -SAzyme) for radio-enzymatic therapy. This FeN 4 -SAzyme exhibits peroxidase-like activity capable of catalyzing H 2 O 2 into hydroxyl radicals and converting single-site Fe II species to Fe III for subsequent glutathione oxidase-like activity. Density functional theory calculations are used to rationalize the origin of the single-site self-cascade enzymatic activity. Importantly, using X-rays can improve the overall single-site cascade enzymatic reaction process via promoting the conversion frequency of Fe II /Fe III . As a H 2 O 2 producer, natural glucose oxidase is further decorated onto the surface of FeN 4 -SAzyme to yield the final construct GOD@FeN 4 -SAzyme. The resulting GOD@FeN 4 -SAzyme not only supplies in situ H 2 O 2 to continuously produce highly toxic hydroxyl radicals but also induces the localized deposition of radiation dose, subsequently inducing intensive apoptosis and ferroptosis in vitro. Such a synergistic effect of radiotherapy and self-cascade enzymatic therapy allows for improved tumor growth inhibition with minimal side effects in vivo. Collectively, this work demonstrates the introduction of external fields to enhance enzyme-like performance of nanozymes without changing their properties and highlights a robust therapeutic capable of self-supplying H 2 O 2 and amplifying self-cascade reactions to address the limitations of enzymatic treatment.