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.