N,S-Co-Doped Carbon Dot-Reinforced Biopolymer Films with Enhanced Barrier, Antioxidant, and Antimicrobial Performance for Active Food Packaging

The development of sustainable active food packaging materials with multifunctional protective capabilities is highly desirable for improving food safety and extending shelf life. In this study, sulfur- and nitrogen-rich carbon dots (GLCDs) were synthesized from glycine and lipoic acid through a facile hydrothermal approach and subsequently incorporated into chitosan/poly(vinyl alcohol) (PVA) matrices to fabricate multifunctional nanocomposite films. Structural and physicochemical characterization suggested the successful incorporation of GLCDs within the polymer network and suggested favorable interactions between the nanofillers and the chitosan/PVA matrix. The GLCD-incorporated films exhibited enhanced mechanical strength, improved thermal stability, reduced water vapor permeability, and superior UV-shielding performance compared with pristine chitosan/PVA films. Furthermore, the nanocomposite films demonstrated significantly enhanced antioxidant activity, achieving approximately 60% DPPH and 90% ABTS radical scavenging efficiency at higher GLCD loading. The films also exhibited strong antibacterial activity and demonstrated preservation potential based on qualitative observations during storage by reducing visible spoilage and maintaining structural integrity. In addition, the developed films showed excellent cytocompatibility toward NIH-3T3 fibroblast cells with high cell viability after 5 days of culture. The synergistic combination of GLCDs and chitosan/PVA matrices provides an effective strategy for developing biodegradable, multifunctional, and cytocompatible active packaging materials with potential food-packaging applications.