Tunable photoluminescence of biomass-derived amine-functionalized fluorescent CQD nanotrackers and biocompatible imaging capabilities for zebrafish embryogenesis.

The synthesis of Carbon Quantum Dots (CQDs) from agro-waste supports United Nations Sustainable Development Goals 3, 9, 12, and 13, offering a sustainable approach to environmental and healthcare challenges. Dried coconut leaves (DCL), abundant agro-waste from the Kongu region of Coimbatore, Tamil Nadu, India, serve as a carbon-rich precursor for CQD synthesis. The DCL is carbonized at 300 °C for 2 h, producing spherical, semi-crystalline CQDs with an average particle size of 15.3 nm, confirmed by HR-TEM. UV-Vis analysis shows peaks at 260 nm and 295 nm, and FT-IR spectra confirm NH, OH, and CN groups. XRD patterns display semi-crystalline structures with graphitic peaks at 22°, 28°, and 43°, while Raman spectra show a D band at 1369 cm-1 and a G band at 1582 cm-1, supporting partial graphitization. Amine functionalization quenches photoluminescence due to disruption of surface states and enhanced non-radiative energy transfer. XPS confirms functionalization with peaks at 284.4 eV (C 1 s) and 399-400 eV (N 1 s), indicating stable incorporation of nitrogen and oxygen. Photoluminescence stability is maintained under pH variation, UV exposure, NaCl, and H2O2. Functionalized and pristine DCL-CQDs show antibacterial activity at 175 µg/mL against MDR clinical pathogens including Escherichia coli, Klebsiella pneumoniae, and MRSA, and antifungal activity at 125 µg/mL against Candida auris and Aspergillus niger. Zebrafish embryogenesis studies confirm high biocompatibility and bright fluorescence at 2 ng/mL, demonstrating potential for biomedical and antimicrobial applications.