UV-Mediated Enzyme-Like Activity Reversal Strategy To Regulate Nanozymes for Detection and Elimination of Bacteria

Nanozyme-based biosensing has gained a great deal of attention in various fields. However, most peroxidase-like (POD-like) nanozymes exhibit excellent enzyme-like activity, relying heavily on acidic environments, and their activity decays sharply in neutral or alkaline scenarios, posing a substantive challenge in more extensive applications. Herein, we propose an ultraviolet (UV)-mediated enzyme-like activity reversal strategy to regulate Fe₃O₄/CDs nanozyme, greatly recovering the enzyme-like activity of nanozymes in neutral/weakly alkaline environments. Specifically, UV irradiation of the nanozyme induces the transition of valence band electrons to the conduction band under neutral/weakly alkaline conditions. The conduction band electrons activate the Fenton-like cycle to generate hydroxyl radicals (·OH), while valence band holes (h⁺) oxidize H₂O₂ to also produce ·OH. Moreover, CDs act as electron channels to accelerate electron transfer, thereby further strengthening the ·OH generation capacity of the two aforementioned pathways. Therefore, these factors endow the Fe₃O₄/CDs nanozyme with excellent POD-like activity at neutral/weakly alkaline pH. As proof of concept, a chemiluminescence (CL) imaging biosensing platform was constructed to detect <i>E. coli</i>, with a linear range of 1.5 × 10¹-1.5 × 10⁷ CFU/mL. Furthermore, the generated abundant ·OH by the proposed strategy can effectively eliminate bacteria. This study offers an innovative approach to break the pH-related bottleneck of nanozymes in the catalytic process for biosensing and antibacterial applications.