Dual-Modal Bimetallic\nNanozyme-Based Sensing Platform\nCombining Colorimetric and Photothermal Signal Cascade Catalytic Enhancement\nfor Detection of Hypoxanthine to Judge Meat Freshness

Abstract

Considering the enormous demand for meat in people’s\ndaily\nlives, the development of efficient meat freshness assays is of great\nsignificance for safeguarding food safety. Here, a novel bimetallic\nnanozyme Fe@CeO₂ with high peroxidase-like activity was\nfirst synthesized by embedding ferrocenecarboxylic acid (Fc) into\nhollow CeO₂ nanospheres, which combined with xanthine oxidase\n(XOD) to develop a self-supplying H₂O₂-facilitated\nenzymatic cascade catalytic system of XOD + Fe@CeO₂, yielding\na meat freshness indicator hypoxanthine (Hx)-responsive colorimetric\nand photothermal dual-mode analytical platform for judging meat freshness\nupon the assistance of 3,3′,5,5′-tetramethylbenzidine\n(TMB). Owing to the catalytic activity of XOD to convert Hx into H₂O₂, Fe@CeO₂ rapidly dissociated it into ^•OH via a peroxidase activity-triggered Fenton-like\nreaction, emerging a typical enzymatic cascade catalytic reaction.\nAs a result, the colorless TMB was oxidized to be the product of dark-blue\noxTMB by ^•OH, with a chromogenic reaction-driven\nabsorption enhancement at 652 nm, which endowed it with a significant\nphotothermal effect under 660 nm laser irradiation. On this basis,\nan Hx concentration-dependent colorimetric and photothermal dual-mode\nsignal cascade catalytic enhancement sensing platform was proposed\nby integrating with a Color Picker App-installed smartphone and a\n660 nm laser-equipped handheld thermal imager, achieving the onsite\nquantitative, reliable, and visual detection of Hx in real meat samples\nfor judging meat freshness with acceptable results. Notably, the colorimetric\nand photothermal dual-mode signal cascade catalytic enhancement improved\nnot only the reliability but also the sensitivity of the assay, which\nprovided new insights for efficient onsite visual monitoring of meat\nfreshness to safeguard food safety.