Sensitive fluorescent determination of indium (III) by a thiourea–quinoline-based chemosensor

A new thiourea–quinoline-based chemosensor ATU (1-(4-acetylphenyl)-3-(quinolin-8-yl)thiourea) was developed for the determination of In3+ using the fluorescence turn-on response. ATU was able to determine In3+ in the presence of Ga3+ and Al3+. The results of a Job’s plot and electrospray ionization–mass spectrometry (ESI–MS) showed that ATU bound to In3+ in a 1:2 stoichiometry ratio. The detection limit for In3+ was 0.64 μM and the binding constant (K) was 5.0 × 1010 M−2, which is the highest value for In3+ chemosensors reported to date. Furthermore, ATU was employed in fluorescent test kits to detect In3+. Moreover, the mechanism of ATU for In3+ determination was evaluated by 1H nuclear magnetic resonance (NMR) titrations and density functional theory (DFT) calculations.