Plasmonic Fe-MoO_3–<i>x</i> Nanozyme for Dual-Mode Sensing of Hypoxanthine in Meat to Judge Freshness

Given the high demand for meat in daily diets, developing effective methods to assess meat freshness is crucial for ensuring food safety. Here, a ratiometric colorimetric/photothermal dual-mode sensing platform was proposed for the detection of hypoxanthine (Hx) to assess meat freshness based on the Fe-doped oxygen-deficient molybdenum trioxide (Fe-MoO3–x) nanodots. The as-prepared Fe-MoO3–x nanodots exhibited a localized surface plasmon resonance (LSPR) effect and peroxidase-like (POD-like) activity. On the one hand, the Fe-MoO3–x nanodots with POD-like activity could effectively catalyze colorless o-phenylenediamine (OPD) into yellow 2,3-diaminophenazine (DAP) with significant absorption at 450 nm in the presence of H2O2 that was produced from the enzymatic reaction between xanthine oxidase (XOD) and Hx. On the other hand, following the reaction between H2O2 and Fe-MoO3–x, the structure and surface state of Fe-MoO3–x underwent changes, leading to a gradual decrease in its LSPR absorption peak at 770 nm and accompanied by a diminishing LSPR-induced photothermal effect. Based on this, the newly developed dual-mode sensing platform was effectively employed for the detection of Hx in shrimp, pork, and fish samples. Unlike conventional correlated signals, the decoupled ratiometric colorimetric/photothermal channels enabled cross-validation, enhancing the accuracy and reliability. This dual-mode sensing platform offered a powerful solution for meat freshness assessment in food supply chains.