Carbon Dot Biopolymer-Based Flexible Functional Films for Antioxidant and Food Monitoring Applications

Heteroatom-doped carbon dot (CD)-reinforced flexible, antioxidant, and UV-resistant polymeric thin films have been fabricated by a facile physical compounding strategy associated with the 'cast and peel' technique. The prepared CDs were found to be stable in aqueous media because of their zeta potential value (-5.85 mV). There was no significant change in the zeta potential values during 7 days of storage, indicating the long-term stability of CPCDs. CD-reinforced thermoplastic starch (TPS)/κ-carrageenan hybrid films have been developed as antioxidants to improve the shelf-life of agro-products. Besides this, they also qualified for mechanical strength (>40 MPa), transparency (∼77%), nondeteriorative dimensional integrity at a high relative humidity (∼97%), and UV-resistant properties. For assessing the food preservation behavior, the leaching of CDs also has been studied by time-dependent sustained release in different food simulant media, where it showed a gradual alteration of entrapment efficacy in high-polarity gradient environments. The mechanism of CD release has been obtained from the non-Fickian fittings of the initial preplateaued kinetic data. Surprisingly, when these nanodots were arrested inside the polymer matrix, the film also showed excellent water vapor impermeability, low moisture retention, sufficient toughness, and superficial compliance to external flexing and stretching. Also, CD-based TPS/κ-carrageenan films exhibited strong antioxidant activity, as determined by 1,1-diphenyl-2-picrylhydrazyl (>85%) and 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid assays (>90%). Thus, these hybrid films could be promoted as ideal alternatives for food packaging with their thin, flexible, tough, antioxidant, and moisture-impermeable properties.