Chameleon-inspired ratiometric fluorescent hydrogel for on-site monitoring of food freshness through multi-color response

Abstract

The assessment of food freshness is crucial for ensuring food safety and quality, as spoilage biomarkers such as cadaverine (Cad) pose severe health risks. Inspired by the chameleon's dynamic color-adaptation mechanism, a novel ratiometric pyrene-based fluorescence probe PDCN was developed by featuring dicyanovinyl group for specific Cad recognition. PDCN enabled rapid (<35 s) and selective detection of Cad through nucleophilic addition-induced fluorescence ratiometric shifts (I402/I465), achieving an ultra-low detection limit of 31 nM with a broad linear range (0–200 μM). Initial integration of PDCN into paper strips achieved visual Cad detection, yet sensitivity constraints motivated the design of an enhanced hydrogel platform. Mimicking chromatophore-driven skin color transitions, PDCN was engineered into sodium alginate hydrogel to construct a portable sensing platform. The bioinspired sensory hydrogel exhibited Cad vapor concentration-dependent multiple fluorescence color transitions (red→yellow→blue), facilitated by the matrix's hierarchical pores for vapor adsorption/amplification. The platform demonstrated on-site monitoring of shrimp and beef freshness under room temperature (25 °C), refrigerated (0 °C) and frozen (−25 °C) conditions, showing strong correlations with TVBN value profiles (R2 > 0.97). Integrated into packaging films as smart labels, the non-cytotoxic hydrogel achieved effectively predicting food spoilage before visible decay. The chameleon-inspired sensing strategy offers an instrument-free spoilage alert system for intelligent food packaging and supply chain management. © 2025