Biogenic carbon dots (CDs) have emerged as promising nanomaterials for biomedical applications due to their tunable photoluminescence, biocompatibility, and facile synthesis. Additionally, the presence of abundant oxygen-containing functional groups, including carbonyl, carboxyl, and hydroxyl groups, enhances their water solubility and facilitates functionalization. As a result, CDs have shown significant potential in applications such as sensing, bioimaging, light-emitting diodes, and therapeutic interventions.
In this study, highly fluorescent CDs were synthesised via a microwave-assisted approach using natural amino acids, L-tryptophan and L-glutamic acid, as precursors. CDs derived from the combined amino acid system exhibited enhanced optical properties, showing strong blue emission at 450 nm with a quantum yield of 31.3% and excellent stability across a broad pH range. Structural investigations revealed a crystalline graphitic core primarily originating from the aromatic moiety of L-tryptophan, while L-glutamic acid contributed surface-bound polar functional groups that improved water dispersibility and functionality. The synthesised CDs demonstrated high sensitivity and selectivity toward cysteamine detection, with minimal interference from competing metal ions, anions, and other thiol-containing molecules. In vitro cytotoxicity studies using MCF-7 and fibroblast cells confirmed excellent biocompatibility, even at higher concentrations. Furthermore, efficient cellular uptake of the CDs enabled clear fluorescence imaging of live cells. This work highlights a sustainable strategy for designing multifunctional biogenic CDs with strong luminescent properties, offering significant potential for applications in biomolecular sensing and cellular imaging.