A modular approach to fluorescent probes: Extending the scope of beta-carboline scaffold to selective fluoride sensing and its application in the visualisation of fluoride-induced ROS

Given the diverse role fluoride ions play and their detrimental effects both in excess and in deficiency, the main focus of this work was to develop a selective fluoride probe based on bioactive tryptamine core. The devised probe (TrySy) was prepared from tryptamine and salicylaldehyde. It displayed selective fluoride sensing with a LOD of 1.3 x 10-7 M and a binding ratio of 2:1 (TrySy: F-). The probe is effective even in the presence of known interfering ion acetate, despite the lack of silyl protection of the phenolic hydroxyl moiety. Modifying the structure of TrySy with 3-hydroxyphenyl/4-hydroxyphenyl substituents failed to show any selectivity towards fluoride ions. The plausible mechanism of fluoride detection was identified as the inhibition of ESIPT based on excitation experiments and pH studies. Probe TrySy shows the capability of fluoride detection in a wide tem-perature range along with the reversible binding of fluoride. The TrySy could also monitor fluoride-induced oxidative damage to the eukaryotic cell nucleus. It could be applied to obtain the fluoride content of a commercially available toothpaste.