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 (HO) dependence, noble metal costs, and poor antioxidant discrimination. To address these challenges, we engineered a dual-regulated Ni-doped CeO (Ni-CeO) 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 = 0.10 μM/s) compared to undoped CeO. Leveraging this HO-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.