A Covalently Anchored Biobased Nanofiber Label for Self-Reporting Fish Spoilage with High Stability and Radiometric Visibility

The development of efficient and reliable strategies for real-time monitoring of seafood freshness is crucial for ensuring food safety and reducing waste. Herein, a novel biobased colorimetric film was designed and fabricated for visual and intelligent detection of fish spoilage. A pH-responsive chromogenic monomer (TGI) was first synthesized from tributyl citrate and then covalently incorporated into polyester-based polyurethane (PCCU) to prevent dye leaching and enhance stability. Experiments demonstrate that TGI enhances the spinnability of PCCU. The resulting PCCU-TGI nanofiber membrane exhibits a high specific surface area (SSA = 12.65 m2/g) and porous structure (Vtotal = 24.28 cm3/g), enabling rapid gas permeation and responsiveness. The mechanistic studies indicate that under the influence of total volatile organic compounds (TVB-N), the alkaline hydrolysis reaction of TGI ester groups expands the π-conjugated system and reduces the bandgap of excited electrons. This enables the colorimetric film to undergo a color change linearly correlated with the degree of spoilage under natural light through intrinsic means. The optimized film (PCCU-9%TGI) exhibited a highly linear correlation (R2 > 0.93) between the color difference (ΔE) and the TVB-N content of cod fillets during storage at both 25 and 4 °C. Furthermore, an electronic eye system was integrated for real-time color capture and data processing, which successfully demonstrated remote, quantitative spoilage monitoring and alert capabilities. This work provides a robust and feasible platform combining smart material design with intelligent sensing technology for next-generation food packaging applications.