A three-mode biosensor for hypoxanthine assay in aquatic products under various storage conditions

Establishing a rapid and accurate method for monitoring the freshness of aquatic products is of great importance. Hypoxanthine has been considered an essential indicator of aquatic products' freshness. Here, a novel smartphone colorimetric / inductively coupled plasma mass spectrometry (ICP-MS) / photothermal three-mode sensing strategy was established for monitoring hypoxanthine. Hypoxanthine can be catalyzed by xanthine oxidase to H₂O₂ and uric acid, which can simultaneously degrade MnO₂ nanosheets (NSs) to Mn²⁺. After filter-assisted separation, the smartphone and ICP-MS were performed by monitoring the color of the membrane and the Mn²⁺ in the filtrate. Additionally, MnO₂ NSs can facilitate the oxidation of dopamine to form polydopamine nanoparticles, which exhibit strong photothermal efficiency. The approach successfully monitored the deterioration of aquatic products under various storage conditions through portable thermometers and smartphones with low limits of detection (LODs), providing a potential application for in-situ evaluation of the freshness of aquatic products.