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 of1was achieved and studied for understanding its functional properties. The interaction and recognition abilities of1with different metal ions were investigated. Sensor1showed 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 of1with Ga³⁺was also studied by photophysical experiments, ESI-MS analysis, and¹H NMR titration. The limit of detection (LOD) and limit of quantification (LOQ) of1for 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 of1and1-Ga³⁺complexes and rationalize the photophysical experimental data. Highly selective test strips based on sensor1were developed for Ga³⁺detection. Sensor1was also used to detect Ga³⁺in actual water samples, and a considerable recovery rate was obtained.