Antibacterial Activity of Polyvinyl Alcohol/WO3 Films Assisted by Near-Infrared Light and Its Application in Freshness Monitoring

Nowadays, films with antibacterial activity and applied for freshness monitoring by colorimetric response have been drawing growing attention in food packaging. However, the development of versatile antibacterial and colorimetric agents is still highly desirable. Herein, WO3 nanorods are incorporated in a polyvinyl alcohol (PVA) matrix to develop a novel composite film with photothermal antibacterial activity and freshness monitoring faculty. The interaction between WO3 nanorods and PVA is due to hydrogen bonds. Compared with the PVA film, the presence of WO3 nanorods can significantly enhance the mechanical and barrier properties; typically, the target film (WO3/PVA)4 shows an increase in tensile strength by 52.7% and Young's modulus by 400.0% and a decrease in oxygen permeability by 72.4% and water vapor permeability by 66.9%. The films demonstrate a WO3 content-dependent antibacterial activity. Under irradiation of near-infrared light (NIR808), the synergistic effect of physical damage, oxidative stress, and temperature increase markedly improves the antibacterial activity of (WO3/PVA)4, showing an antibacterial efficiency of ∼90% against Escherichia coli or beyond 90% against Staphylococcus aureus. The incorporated WO3 nanorods demonstrate lower cytotoxicity toward the model cells of human colon cancer cell line HT-29. The (WO3/PVA)4 film exhibits colorimetric response to H2S and can also be used for pork freshness monitoring as an indicator.