Beet root carbon dots cellulose sulfate film as a novel naked eye pH sensor for chromium and bacterial detection in tomatoes

This study presents the development and characterization of a novel nitrogen doped carbon dots cellulose sulfate-carboxymethyl cellulose composite film (N-CDs-CS-CMC) for multifunctional applications in tomato packaging and sensing. Density functional theory (DFT) calculations revealed a significant enhancement in polarity (29.19 Debye) and a reduced energy gap (0.019 eV) for the composite compared to CS-CMC, indicating improved molecular interactions and enhanced charge transfer. Scanning electron microscopy (SEM) showed a surface with smaller, more uniform pores (11.93-25.45 μm), increasing surface area and enhancing sensing capabilities. The N-CDs-CS-CMC film exhibited potent antimicrobial activity against Escherichia coli, Staphylococcus aureus, and Candida albicans, with inhibition zones of 20, 22, and 19 mm, respectively, and demonstrated distinct fluorescence patterns upon bacterial interaction, enabling pathogen-specific detection. Incorporating beetroot (BR) within N-CDs preparation method rendered the film pH-responsive, showing color changes from brown/reddish in alkaline to yellow in acidic environments. Tomatoes wrapped with the N-CDs-CS-CMC film exhibited a 10-day shelf life, compared to 4 days for CS-CMC. Furthermore, the film underwent rapid decolorization to yellow and increased tomato translucency upon exposure to chromium, indicating its potential for heavy metal detection. These results demonstrate the N-CDs-CS-CMC film's efficacy as a multifunctional material for enhanced food packaging, integrating antimicrobial properties, bacterial and chromium sensing, and pH monitoring for improved food safety and quality.