MnO₂-Mediated Fluorescence Recovery for Selective Detection of Glutathione Using Orange-Emitting Carbon Quantum Dots

Glutathione (GSH), an essential tripeptide with antioxidant, detoxifying, and anti-inflammatory functions, requires rapid and reliable detection in biomedical fields. In this work, orange fluorescent carbon quantum dots (O-CQDs) were created using a hydrothermal method with neutral red and thiourea as precursors. These O-CQDs emit a strong orange fluorescence at 600 nm when excited by UV light, which helps reduce interference from natural fluorescence in biological samples. The fluorescence is effectively quenched by potassium permanganate (KMnO₄) through the in situ generation of manganese dioxide (MnO₂). While GSH is added, it reduces MnO₂ to Mn²⁺, restoring fluorescence via a redox-driven "off-on" mechanism. This approach provides high selectivity and resistance to interference. The O-CQDs have a high quantum yield of 37.19%. The sensor shows a linear detection range from 0 to 100 µM (with the equation F = 34.6327c + 1610.7945) and a detection limit as low as 57 nM. It was successfully used to measure GSH in rabbit serum, achieving recoveries between 93.53% and 102.77% and relative standard deviations (RSD) from 0.71% to 1.72%. This sensor offers easy synthesis, quick response, and high sensitivity, making it a reliable tool for detecting GSH.