A supertough zwitterionic hydrogel with reversible fluorescence for dual-mode food spoilage visualization and information encryption.

Food spoilage and counterfeiting pose significant threats, but a single solution addressing both is lacking. This work reports a supertough zwitterionic hydrogel that integrates anticounterfeiting and freshness monitoring. The hydrogel, formed by a poly(acrylamide-co-2-hydroxyethyl methacrylate-co-sulfobetaine methacrylate) network crosslinked with alginate-Ca2+, exhibited impressive 2200% elongation and 492.6 kJ/m3 toughness. It also demonstrated excellent fatigue resistance and tear strength with a tearing energy of 1136 J/m2. The zwitterionic chemistry provided strong, repeatable adhesion to various substrates. When doped with curcumin-ZnO carbon dots, the hydrogel showed reversible dual-emission fluorescence, enabling rewritable anticounterfeiting features like pattern printing, ASCII codes, and QR codes. This same mechanism also allowed accurate real-time monitoring of grass carp freshness at 25 °C and 4 °C, with an R2 > 0.986 between Total Volatile Basic Nitrogen (TVB-N) and ΔE. This dual-function hydrogel offers promising potential for next-generation intelligent packaging in food safety and authenticity.