Weaving phosphorus-doped Co₃O₄ nanozyme: a colorimetric detection platform for total antioxidant capacity

Although nanozymes are promising substitutes for natural enzymes due to their exceptional stability, low cost, and activity tunability, peroxidase (POD)-mimicking metal oxides like Co₃O₄ are often limited by its moderate intrinsic activity. In this study, phosphorus-doped Co₃O₄ nanofibers (P-Co₃O₄ NFs) are synthesized via electrospinning and calcination. Optimizing the P incorporation level yields 21% P-Co₃O₄ NFs with significantly enhanced peroxidase-like activity. Experimental and theoretical results reveal that P incorporation modulates the local electronic structure of Co sites, promoting H₂O₂ adsorption, interfacial electron transfer, and Co²⁺/Co³⁺ redox cycling, while the nanofibrous morphology ensures abundant accessible surfaces. A dual-mode colorimetric platform is constructed for ascorbic acid (AA) detection, yielding detection limits of 0.57 μM for solution-based assays and 1.66 μM for paper-based formats. Accurate total antioxidant capacity (TAC) determination in real samples (vitamin C tablets, fruits, beverages) is also demonstrated, with excellent recovery rates and assay time of only 140 s (solution) or 2 min (paper). This work provides mechanistic insights into heteroatom-doped nanozymes and offers a rapid, reliable sensing strategy for food quality monitoring.