A superstretchable and ultratough hierarchical fluorescent hydrogel with antioxidant and antimicrobial activity for simultaneous multi-tiered information encryption and real-time seafood spoilage visualization.

Product counterfeiting and Food spoilage present severe challenges to global supply chains, necessitating advanced packaging that ensures both safety and authenticity. Herein, we report a highly robust, multi-functional double-network hydrogel for advanced information encryption and real-time freshness monitoring. The hierarchical matrix integrates a covalent poly(acrylamide-co-gelatin methacrylate) network with an ionic calcium alginate network, critically reinforced by tannic acid (TA) acting as a molecular glue. This architecture endows the hydrogel with an extraordinary breaking elongation of ∼4250%, an exceptional toughness of ∼154 MJ/m3, and a high tearing energy of ∼1.7 kJ/m2. Furthermore, the controlled release of TA provides reliable, broad-spectrum tissue-level adhesiveness, alongside potent antioxidant and antimicrobial activities (near 100% bactericidal rate within 24 h). By embedding NH3-responsive carbon dots, the hydrogel exhibits distinct, reversible fluorescence shifts, enabling sophisticated, multi-tiered anticounterfeiting applications including erasable Morse code, mathematical matrices, and dynamic QR codes. Meanwhile, the fluorescent hydrogel sensor accurately mapped the real-time spoilage of tilefish at both 25 °C and 4 °C, demonstrating a near-perfect correlation (R2 ≥ 0.995) between Total Volatile Basic Nitrogen (TVB-N) accumulation and colorimetric variance (ΔE). This dual-functional hydrogel offers a highly promising platform for next-generation intelligent and active food packaging.