Self-triggered “Core-Shell” hydrogel sensor integrated with copper nano-aggregates for aquatic product freshness monitoring and preservation

Aquatic products are susceptible to spoilage throughout the supply chain, creating an urgent demand for techniques that synchronize freshness monitoring and preservation. To bridge this technological gap, a "core-shell" hydrogel sensor was developed. Copper nano-aggregates incorporated in the hydrogel's outer layer responded to total volatile basic nitrogen (TVB-N) by undergoing structural collapse. This process orchestrated a dual-action mechanism: the collapse directly induced fluorescence quenching for real-time freshness indication while simultaneously triggering rapid release of encapsulated eugenol for active preservation. Optimization of the polymer composition significantly enhanced the mechanical properties of hydrogels, achieving a 20-fold increase in compressive stress compared with polyacrylic acid hydrogels, alongside improved thermal stability. The sensor enabled freshness monitoring through TVB-N-correlated color transitions, and extended the shelf life of blackfish by three days (4 °C) via the triggered release of eugenol.