Dual-engineered strategy of Ni-CeO_v nanozyme with enhanced oxidase activity for sensitive colorimetric detection of...

Antioxidants are crucial in the fight against reactive oxygen species and thus in maintaining organismal health, so it is particularly important to realize a rapid and quantitative assay for common antioxidants in life. Current nanozyme-based total antioxidant capacity (TAC) assays face limitations: hydrogen peroxide (H₂O₂) dependence, noble metal costs, and poor antioxidant discrimination. To address these challenges, we engineered a dual-regulated Ni-doped CeO₂ (Ni-CeO_v) nanozyme through oxygen vacancy engineering and 3d-2p-4f orbital coupling. Density functional theory (DFT) calculations revealed that Ni doping synergistically affects the spontaneous formation of oxygen vacancies and enhances electron transfer through gradient orbital hybridization, resulting in a 2-fold increase in oxidase-like activity (V_max = 0.10 μM/s) compared to undoped CeO₂. Leveraging this H₂O₂-independent nanozyme, we developed a portable colorimetric platform capable of both ultra-sensitive detection and antioxidant discrimination through distinct inhibition kinetics. Integration with smartphone-based paper sensors enabled on-site TAC quantification in commercial beverages and cosmetics within 5 min, achieving recovery rates of 98.35-104.41 %, at a cost of only $0.2/assay. This work establishes a paradigm for developing low-cost, field-deployable nanozyme sensors for the detection of TAC.