Dihydroxycoumarins as highly selective fluorescent probes for the fast detection of 4-hydroxy-TEMPO in aqueous solution
Due to the biological significance of 4-hydroxy-TEMPO, its detection in biological systems such as blood serum is of great importance in both research and clinical applications. The following paper reports a novel fluorimetric method for the detection and quantitative determination of 4-hydroxy-TEMPO radicals in an aqueous solution using dihydroxycoumarins as fluorescent probes. Among the 17 coumarin derivatives studied, only some dihydroxycoumarins show high sensitivity, specificity and selectivity for 4-hydroxy-TEMPO. Among them, 6,7-dihydroxycoumarin (esculetin) exhibits the strongest fluorescence enhancement under the action of 4-hydroxy-TEMPO. In this assay, esculetin reacts with 4-hydroxy-TEMPO to exclusively yield a dimer. 6,7-Dihydroxycoumarin responds to 4-hydroxy-TEMPO quickly and shows a 2.5-fold fluorescence enhancement with an estimated detection limit of 285 μM.