Sulfur Quantum Dots as Fillers in Gelatin/Agar-Based Functional Food Packaging Films

The present work is the first attempt to study the applicability of sulfur quantum dots (SQDs) as functional fillers for food packaging biopolymer films. SQDs were prepared via hydrothermal synthesis using sublimated sulfur powder. The SQDs were 8.7 nm in size and consisted of an elemental sulfur core stabilized by PEG-400 confirmed by TEM, FTIR, and XPS characterization. The SQDs exhibited a high surface charge of -13.9 mV, indicating good dispersion in aqueous suspensions. In addition, the SQDs showed high antioxidant and antimicrobial activities with almost negligible toxicity toward L929 cells even at prolonged exposure of 72 h. The addition of SQDs to the gelatin/agar blend films increased the UV-barrier property without compromising color and transparency. The composite film showed excellent antioxidant activity, a moderate bactericidal effect on Listeria monocytogenes, and an inhibitory effect on Escherichia coli. The SQDs are likely to be value-added, low-cost, safe, and multifunctional nanofillers for preparing functional films in active packaging applications.