Eco-friendly synthesis and evaluation of carbon dots from kitchen waste for potential antibacterial applications.

This study presents a comparative analysis of carbon dots (CDs) synthesized from four kitchen waste sources-potato peels, banana peels, tea residues, and lemon peels-under a sustainable "waste-to-wealth" approach to identify the most suitable precursor for theranostic applications. The synthesized CDs exhibited distinct physicochemical and optical properties depending on the precursor material. Among all samples, tea-derived CDs showed the highest quantum yield (22.69%), followed by lemon (15.38%), banana (7.62%), and potato-derived CDs (5.11%). Fluorescence emission intensity followed a similar trend, with maxima observed at 458 nm (tea), 435 nm (lemon), 471 nm (banana), and 398 nm (potato). HR-TEM analysis revealed spherical morphology with particle sizes ranging from  2.3 nm (tea) to  4.5 nm (potato). Tea-derived CDs exhibited superior photostability (94% retention under UV irradiation) and excellent long-term stability (97% over 6 months), whereas potato-derived CDs showed the lowest stability (12%). Antibacterial studies revealed that tea-derived CDs exhibited the highest activity, with MIC values decreasing from 128 to 64 µg/mL against E. coli and from 64 to 32 µg/mL against S. aureus under UV irradiation. In contrast, banana-derived CDs showed the lowest activity, with MIC values reduced from 1024 to 512 µg/mL and 512 to 256 µg/mL, respectively, highlighting a significant enhancement in antibacterial efficacy upon UV exposure. All CDs displayed excellent biocompatibility, with  96% cell viability observed in MTT assays after 72 h. Overall, tea residue emerged as the most promising precursor for the synthesis of highly stable, photoluminescent, and biocompatible carbon dots, highlighting its potential for advanced biomedical and theranostic applications.