One stone two birds: Multifunctional flavonol nanocrystals enable food packaging to both preserve freshness and visually monitor freshness

Food packaging with both active and intelligent components is critical for reducing food waste and ensuring food safety. However, concerns about the toxicity of components or detecting results prevent their commercialization. Herein, we report three flavonol nanocrystals with aggregation-induced emission characteristics that have been individually composited with a flexible film to form three multifunctional food packaging systems. The nanocrystals are derived from quercetin, myricetin, and kaempferol, respectively; they all exhibit antibacterial properties, antioxidant abilities, and alkaline pH sensitivities in both colorimetric and fluorescent modes. Among them, myricetin nanocrystals with more phenolic hydroxyl groups are the most sensitive to alkalinity. Hemolysis and acute oral toxicity tests ensure their biocompatibility in vitro and in vivo. Just incorporating any one of the prepared nanocrystals into packaging can simultaneously extend the shelf life of bananas and provide dual-mode monitoring of shrimp freshness. Moreover, the addition of these nanocrystals can improve the mechanical, water vapor barrier, and thermal performances of packaging. This work demonstrates that the design of natural-derived nanocrystals as both active and intelligent components offers an opportunity to construct multifunctional packaging systems toward simultaneously food preservation and freshness monitoring.