Novel ammonia-responsive imidazole/carboxylate functionalized - MOF multifunctional films for shrimp freshness monitoring driven by synergistic effect of ligand-to-metal charge transfer and proton transfer

Biopolymer films responsive to ammonia have gained attention as intelligent packaging for seafood freshness tracking. Yet, balancing strong antibacterial effects with reliable visual spoilage indicators is still a key hurdle. In this study, imidazole/carboxylate-functionalized cobalt-based metal-organic frameworks (Co-MOFs) with ammonia sensitivity and antibacterial properties were synthesized and incorporated into a gelatin/agar (GA) matrix to fabricate intelligent active films with superior multifunctionality. The addition of Co-MOF nanofillers to GA films resulted in a multifunctional nanocomposite with superior chemical and mechanical properties. The Co-MOF-based fluorescent indicator demonstrated excellent ammonia-responsive behavior, driven by the synergistic effects of ligand-to-metal charge transfer (LMCT) and proton transfer between ammonia and the Co-MOFs. Additionally, the composite films displayed strong antibacterial effects, highlighting their potential for real-time food freshness monitoring. The GA/Co-MOF nanocomposite films were effectively employed for on-site monitoring of shrimp spoilage. By integrating a portable digital sensing system, an online platform utilizing smartphones is developed for monitoring shrimp freshness, significantly enhancing the precision and convenience of intelligent packaging. The combined mechanical, antibacterial, and ammonia-sensing properties make this nanocomposite a promising candidate for advanced food preservation and monitoring technologies.