A Sustainable Deep Eutectic Solvent-Assisted Approach for the Synthesis of Ascorbic Acid-Derived Carbon Dots toward Dual Fluorescence Sensing of Manganese(VII) and Glutathione

Abstract

In this thesis, blue-emissive carbon dots (AA-CDs) was synthesized via a sustainable hydrothermal approach using L-ascorbic acid as the carbon precursor and a choline chloride/urea (1:2) deep eutectic solvent (DES) as a green reaction medium. The synthetic strategy emphasizes environmentally benign chemistry by employing renewable, low-cost, and readily available precursors while avoiding hazardous reagents. The as-prepared AA-CDs exhibited excitation-dependent photoluminescence with a maximum emission centered at 416 nm under 330 nm excitation. Comprehensive investigations of pH, ionic strength, temperature, and continuous UV irradiation demonstrated their excellent photostability and environmental robustness, highlighting their suitability for fluorescence sensing under diverse operating conditions. The AA-CDs displayed high selectivity toward multiple metal ions, with exceptional sensitivity for permanganate (Mn(VII) ions), achieving a detection limit of 307.25 nM. Furthermore, fluorescence quenching induced by Mn(VII) was selectively restored in the presence of glutathione (GSH), enabling its determination with a detection limit of 35.27 μM. The fluorescence recovery originates from the redox reaction between GSH and Mn(VII), which effectively eliminates the quenching species and restores the emissive state of the AACDs. This sequential fluorescence "turn-off/turn-on" sensing platform provides a simple, rapid, and highly selective strategy for the dual detection of Mn(VII) and GSH. The combination of green synthesis, excellent photostability, and sensitive dual-analyte detection underscores the potential of DES-derived carbon dots as versatile fluorescent nanoprobes for environmental monitoring and bioanalytical applications.