Comparative Evaluation of Chemically and Green-synthesized Carbon Quantum Dots for Aquatic Applications

Carbon Quantum Dots (CQDs) are fluorescent carbon-based nanoparticles with a dimension smaller than 10 nanometers. They exhibit enhanced characteristics, including good compatibility, solubility, negligible toxicity, robust inert behavior, high resistance to photo-bleaching, facile modification, electrochemical luminescence, and have potential applications in catalysts, biosensors, imaging, drug delivery, and bio-molecules. Carbon quantum dots were chemically and biologically synthesised from citric acid and unripe lemon as precursors, respectively, through hydrothermal treatment. They were characterized using UV-Vis spectroscopy, UV-Vis transilluminator, SEM, EDAX, and FT-IR. Four Gram-negative fish pathogens, Aeromonas salmonicida, Pseudomonas fluorescens, Pseudomonas aeruginosa, and Stenotrophomonas maltophilia, and four Gram-positive fish pathogens, Staphylococcus aureus, Micrococcus luteus, Bacillus cereus, and Enterococcus faecalis, were used for the present study. The antibacterial activity was studied by the agar well variant method, and the antioxidant potential using the DPPH assay. Chemically synthesized CQDs showed a larger zone of inhibition against Pseudomonas fluorescens, indicating their strong antibacterial activity. The antioxidant activity of CQDs is less than that of standard ascorbic acid.