Sensitive “On–Off” Sensing Platform for Phosphate and Total Antioxidant Capacity Based on Phosphate-Mediated Cerium Oxide Laccase Nanozymes

The determination of phosphate levels and total antioxidant capacity (TAC) is of great significance in evaluating food quality, nutritional value, and oxidative stability. However, developing simple and efficient methods for their sequential detection remains a challenge. Herein, we present a phosphate-mediated strategy to enhance the laccase-like activity of cerium oxide (CeO 2 ) nanomaterials. Phosphate modulates the valence state of CeO 2 nanosheets and induces the formation of cerium-based nanowires, synergistically boosting the nanozyme activity. Conversely, reducing substances such as ascorbic acid (AA) and reduced glutathione (GSH) inhibit this enhancement, enabling the quantitative detection of these reductants. Based on this “activation-inhibition” dual-modulation mechanism, a novel sensing platform was developed for sequential detection of phosphate and TAC. Ingeniously utilizing the opposing regulatory effects of phosphate (activator) and reducing substances (inhibitor) on the laccase-like activity of the CeO 2 nanozyme, this approach enables the sequential detection of two distinct targets on a single platform. The method demonstrates high sensitivity, selectivity, and robustness in complex food matrices. This work not only provides a practical tool for food quality monitoring but also offers new insights into the design of copper-free laccase-like nanozymes, highlighting the importance of structural and electronic modulation in enhancing catalytic performance.