Deposition−Separation First, Then Response: A Bifunctional Magnetic Nanozyme Enables Anti-Interference Uranyl Sensing

Abstract Although nanozymes have been demonstrated as a promising sensing element to achieve sensitive detection of uranyl (UO22+) thanks to their catalytic signal amplification feature, it is still challenging to achieve a reliable analysis of the target in real complex matrices because some coexisting constituents can perturb nanozyme catalysis, consume reactive species, or directly alter catalytic products. To address this deficiency, here, we proposed a “deposition−separation first, then response” strategy for anti-interference uranyl sensing via designing a bifunctional magnetic Fe3O4/CoOx nanozyme that coupled target conversion, matrix cleanup, and catalytic response together. In the presence of H2O2, UO22+ was first converted into uranyl peroxide hydrate that deposited on the surface of Fe3O4/CoOx. Structural and spectroscopic analyses indicated that this deposition could enrich oxygen vacancy sites to promote H2O2 activation and accelerate the production of hydroxyl radicals for enhanced oxidation of 3,3′,5,5′-tetramethylbenzidine. The UO22+-deposited Fe3O4/CoOx was then collected magnetically and resuspended before nanozyme response; thus, potential interference from coexisting species in samples was avoided, with no appreciable compromise of the uranyl-dependent signal. Consequently, the proposed strategy enabled the sensitive detection of uranyl in the range of 0.1−20 μM, demonstrating excellent resistance to matrix effects during real water analysis. By isolating unknown backgrounds from chromogenic transduction while retaining the analyte-activated catalytic interface, our work offers a reliable route for uranyl sensing in diverse matrices.