Heteroatom-Doped carbon dots as ’On-Off-On’ fluorescent sensors for Fe3+ and L-cysteine detection with applications in real samples and Colon cancer cell imaging

• Published in: Inorganic chemistry communications 2025-02, Vol.172, p.113662, Article 113662
• Main Authors: Tamizhselvi, Ramamoorthi, Velu, Kuppu Sakthi, Napoleon, Ayyakannu Arumugam, Akhtar, Muhammad Saeed, Ahmad, Naushad, Palanisamy, Subramanian, You, SangGuan, Mohandoss, Sonaimuthu, Kim, Seong-Cheol
• Format: Article
• Language: English
• Subjects: Carbon dots; Colon cancer cells; Heteroatoms; Iron; L-cysteine; Real samples
• ISSN: 1387-7003
• DOI: 10.1016/j.inoche.2024.113662

[Display omitted] •One-pot synthesis of N,S-doped carbon dots using ribavirin and thiourea.•N,S-CDs show blue emission fluorescence at 456 nm with a 23.7 % quantum yield.•Spherical, well-dispersed N,S-CDs with an average size of 3.2 ± 0.2 nm.•High selectivity for Fe3+ ions and CYS with detection limits of 187 nM and 87.1 nM.•N,S-CDs are low toxicity for successful use in intracellular imaging in HCT-116 cells. A straightforward and fast approach has been established for detecting iron ions (Fe3+) and L-cysteine (CYS) using fluorescent carbon dots doped with nitrogen and sulfur (N,S-CDs), synthesized from ribavirin and thiourea as precursor materials. The resulting N,S-CDs exhibit strong water solubility, stable blue fluorescence, and a notable quantum yield of 23.7 %, with fluorescence properties independent of excitation wavelength. These N,S-CDs were further characterized via FTIR, XRD, TEM, and XPS analyses to evaluate their surface functionalities, structural features, and elemental composition. Morphological analysis reveals spherical particles averaging 3.2 ± 0.2 nm in diameter, decorated with hydroxyl, carbonyl, thiol, and amino functional groups on the surface. The N,S-CDs displayed highly selective and sensitive fluorescence quenching (turn-off) in response to Fe3+ ions, with a detection threshold of 187 nM and a linear response range of 0–50 µM. Remarkably, the quenched N,S-CDs/Fe3+ fluorescence was reactivated by the addition of CYS, enabling CYS detection at a limit of 87.1 nM and within a linear range of 0–100 µM. The fluorescence switching between off and on states was consistently achievable for over 10 cycles by alternately adding Fe3+ and CYS, demonstrating excellent reversibility. The high selectivity and sensitivity of the N,S-CDs enabled their application as “on-off-on” fluorescent switches, successfully used for Fe3+ detection in real water samples, supporting environmental monitoring and safety. Additionally, cytotoxicity tests indicate low toxicity, allowing for successful use in intracellular imaging of N,S-CDs/Fe3+ and N,S-CDs/Fe3+ with CYS in HCT-116 cells. Thus, these fluorescent N,S-CDs represent a promising sensing platform for label-free detection of metal ions and biomolecules.