Multifunctional N-Doped Carbon Dots Derived from Glucono-d-lactone and Histidine for Fe ³⁺ /Ce ⁴⁺ Ion Detection, Tryptophan Sensing, Antioxidant Activity, and Bioimaging

Development of sustainable and multifunctional nanomaterials is essential for advancing environmentally benign technologies in sensing and biomedical applications. Herein, hydrothermal-based one-pot synthesis of carbon dots (GH-CDs) using glucono-d-lactone (GDL) and L-histidine is reported. The GH-CDs exhibit cyan-blue fluorescence and excellent aqueous dispersibility with abundant surface functionalities, as confirmed using UV–vis, fluorescence spectroscopy, HR-TEM, SAED, pXRD, XPS, FT-IR, TGA, and zeta potential measurements. These natural-source-derived CDs exhibited selective detection of Fe 3+ and Ce 4+ ions mainly due to static interaction and surface complexation, which was confirmed using fluorescence quenching mechanistic analysis. Specifically, GH-CDs demonstrated excellent LOD values of 0.0514 and 0.034 μM for Fe 3+ and Ce 4+ ions, respectively. The real-time validation of this selective metal ion detection was performed in real water samples, which confirmed the operational robustness and interference resistance of GH-CDs. Additionally, the GH-CDs demonstrated exceptionally high specificity for tryptophan compared to all other natural amino acids. Further, the multifunctional nanoprobe analysis of GH-CDs was extended for evaluating their antioxidant activity using a DPPH assay. This analysis revealed a concentration-dependent radical scavenging efficiency of GH-CDs with 73.2% inhibition at 500 μg/mL and an IC 5 0 value of 86.6 μg/mL. The cytotoxicity analysis followed by cellular imaging studies using the normal HEK cell line further demonstrated the high biocompatibility and fluorescence imaging potential of GH-CDs. The reported versatile applications of GH-CDs make them a sustainable, cost-effective, and efficient nanoprobe material for future use.