Carboxymethylcellulose/agar-based functional film incorporated with nitrogen-doped polyethylene glycol-derived carbon dots for active packaging applications

The present investigation demonstrates the role of nitrogen doping on polyethylene glycol (PEG)-derived carbon dots on optical, antibacterial, and antioxidant activity. CDs' average size and surface charge were determined using transmission electron microscopy (TEM) and a zeta sizer with 2.14 ± 0.6 nm and -20 mV, respectively. Though CDs without N-doping (PCD) did not show any significant antioxidant and antimicrobial activities, the CDs doped with nitrogen (NPCD) showed potent antioxidant (25% and 100% DPPH and ABTS radical scavenging activity) and significant antimicrobial activity against Gram-positive (1.8 cm inhibition zone) and Gram-negative (1.4 cm) bacteria. Both carbon dots were loaded into the carboxymethyl cellulose (CMC)/agar-based film with different concentrations (4 and 8%) and showed a significant increase in the physicochemical properties, and UV-blocking property was increased from 53.7 to 79.9% without sacrificing the transparency. The NPCD-loaded film also showed high antioxidant (DPPH 12.7% and ABTS 67%) and potent antibacterial activity. In particular, the CMC/agar film loaded with 8% NPCD destroyed Escherichia coli and Listeria monocytogenes completely after 6 h of incubation.