Neem leaf-derived carbon dot-embedded chitosan-based active films: a sustainable approach to prolong the shelf life of prawns

Abstract

In response to growing environmental concerns and the demand for sustainable, functional food packaging, this study adopts a green nanotechnology approach by utilising phytochemically rich neem leaves to produce fluorescent and bioactive carbon dots (NLCDs). The NLCDs, prepared via a one-pot hydrothermal route, formed quasi-spherical nanostructures (∼8 nm) with abundant oxygen- and nitrogen-containing surface functional groups. These confer a strong electron-donating capacity, enabling the efficient scavenging of reactive oxygen species, while their quantum confinement and surface defect states underpin an excitation-dependent blue fluorescence (450 nm) and UV-vis absorption at 220 and 270 nm. When incorporated into a chitosan/polyvinyl alcohol (CP) matrix via solvent casting, the small size and uniform dispersion of NLCDs promoted strong hydrogen bonding and interfacial compatibility, as confirmed by FTIR, XRD, and SEM analyses. These reduced the polymer chain mobility, increasing the tensile strength by 66% (43.7 MPa) and enhancing the UV-blocking performance (93% attenuation at 280 nm). Antioxidant activity reached 82% (DPPH) and 77% (H₂O₂), attributable to the synergistic effects of NLCDs and the CP matrix. The films demonstrated potent antibacterial activity, with CPCD-3 inhibiting E. coli and S. aureus (15 mm and 12 mm zones) via membrane disruption and oxidative stress modulation, respectively. Biodegradation reached 94% in 100 days, and release studies showed sustained diffusion of NLCDs in food simulants. In prawn packaging trials, CPCD-3 preserved the pH (6.8–7.0), reduced the TVBN (28 mg/100 g), and maintained the microbial load (5 log CFU g⁻¹) for over 15 days at 4 °C. These findings position NLCD-embedded CP films as next-generation, multifunctional active packaging materials with a clear mechanistic basis for their performance.