Peroxidase-mimicking Nanozymes for redox monitoring and regulation in Cancer Theranostics.

Cancer progression is closely associated with dysregulated redox homeostasis, including altered hydrogen peroxide (H₂O₂) metabolism and adaptive antioxidant responses within the tumour microenvironment (TME). These biochemical changes provide opportunities for redox-responsive cancer diagnosis and therapeutic intervention. Peroxidase-mimicking nanozymes have emerged as engineered catalytic materials capable of exploiting H₂O₂-dependent reactions for signal amplification and modulation of oxidative stress. This review critically examines their catalytic mechanisms, structural determinants, and applications in cancer theranostics, with particular emphasis on the relationship between interfacial redox chemistry and biological function. Unlike natural peroxidases with structurally defined catalytic sites, many nanozymes mediate peroxide-dependent reactions through surface-associated redox centres involving electron transfer and reactive intermediate formation. Their tunable composition, morphology, and surface chemistry offer opportunities to tailor catalytic performance for diagnostic and therapeutic applications. By exploiting tumour-associated H₂O₂ availability and local acidity, appropriately designed nanozyme systems may facilitate preferential catalytic activation and amplified diagnostic signals. Therapeutically, peroxidase-like activity can promote oxidative damage in cancer cells, while multifunctional nanozyme platforms may incorporate complementary mechanisms to modulate hypoxia, antioxidant defences, and tumour-associated immune responses. However, catalytic performance and tumour selectivity are strongly influenced by biological matrix effects, tumour heterogeneity, catalyst stability, and potential contributions from dissolved metal species. Distinguishing sustained heterogeneous catalysis from consumptive redox reactions, together with establishing in vivo efficacy, safety, and reproducibility, remains essential for clinical translation. Future developments should therefore prioritise mechanistically validated nanozyme platforms that integrate reliable redox monitoring with controllable therapeutic activity, supporting the development of more effective cancer theranostic strategies.