Cellulose nanofiber-based pH indicator integrated with resazurin-modified carbon dots for real-time monitoring of food freshness

Modified carbon dots with resazurin (R-CD) were prepared using a hydrothermal method to fabricate a CNF-based pH-responsive indicator for real-time food freshness monitoring. FE-SEM and FTIR results confirmed that the R-CD was uniformly distributed in the CNF matrix. The thermal stability of the CNF/R-CD indicator film was increased, and the water contact angle of the film was slightly lower than that of the neat CNF film. The CNF/R-CD film showed excellent UV-barrier properties, with ∼98.3% and 87.7% blocking the UV-B and UV-A light. The indicator film showed excellent color stability even after 2 months of storage at 25 °C and responded rapidly to alkaline pH and NH3 through a color change from yellow to brownish-red. The CNF/R-CD indicator films exhibited distinct color changes during shrimp packaging depending on pH and TVB-N concentration. Therefore, the CNF/R-CD indicator can be used as a promising pH-sensitive color-changing intelligent packaging application for freshness monitoring.