A highly selective "turn-on" water-soluble fluorescent sensor for gallium ion detection

In this work, a novel sensor, (E)-N'-(3-(tert-butyl)-2-hydroxybenzylidene)thiophene-2-carbohydrazide (1), based on salicylaldehyde and thiophene hydrazide moieties was designed and synthesized. The single-crystal structure of 1 was achieved and studied for understanding its functional properties. The interaction and recognition abilities of 1 with different metal ions were investigated. Sensor 1 showed excellent "turn-on" fluorescence with highly selective and specific recognition ability in the presence of gallium ions (Ga³⁺) in an aqueous solution. The sensing behavior of 1 with Ga³⁺ was also studied by photophysical experiments, ESI-MS analysis, and ¹H NMR titration. The limit of detection (LOD) and limit of quantification (LOQ) of 1 for the detection of Ga³⁺ in an aqueous solution were calculated as 58 nM, and 192 nM, respectively. DFT calculations were carried out to optimize the configuration of 1 and 1-Ga³⁺ complexes and rationalize the photophysical experimental data. Highly selective test strips based on sensor 1 were developed for Ga³⁺ detection. Sensor 1 was also used to detect Ga³⁺ in actual water samples, and a considerable recovery rate was obtained.