Biocompatible starch based smart active packaging film engineered with a novel CuNa-MOF colorimetric ammonia sensing agent based on crystal-to-crystal transformation

Colorimetric ammonia-sensing smart packaging materials that enables real-time visual detection of food freshness play an important role in ensuring food safety. This work involved the construction of a novel Cu/Na-metal organic framework (CuNa-MOF) colorimetric ammonia sensing agent and its subsequent exploitation as functional reinforcing filler of potato starch (PS) substrate to boost the fabrication of high-performance smart packaging materials. Based on single crystal data analysis, a new mechanism of crystal-to-crystal phase transformation was proposed for the colorimetric ammonia-sensing action of CuNa-MOF. This new mechanism involved only minor changes in CuNa-MOF crystal structure (with the coordinated water replaced by ammonia), indicating its unique structural integrity and stability, thus contributing to superior ammonia sensing ability. The results also demonstrated that the introduction of CuNa-MOF (2–6 wt%) within PS substrate resulted in the formation of compatible and tight nanocomposite films. When the content of CuNa-MOF increased from 0 to 6 wt%, the tensile strength, water vapor barrier, and oxygen barrier capability was respectively increased by 11.6 %, 16.4 %, and 18.2 %, and the UV-shielding efficacy was increased from 36.8 % to 96.1 %. Furthermore, the fabricated PS/CuNa-MOF film presented good biocompatibility and long-term colour stability, while combining remarkable colour-changing ammonia sensing function with high antibacterial efficiency (100 %) against Escherichia coli and Staphylococcus aureus . Additionally, the PS/CuNa-MOF film allowed for real-time visual monitoring of prawn freshness decay by discernible coloration changes. This work offers a new strategy in the design of high-performance colorimetric ammonia-sensing materials for smart packaging application.