Selective fluorescent probe for Tl³⁺ ions through metal-induced hydrolysis and its application for direct assay of artificial urine

In this research, we report a simple fluorescent probe designed to detect thallium(iii) ions (Tl³⁺) in artificial urine samples. The Tl³⁺ signaling probe (TP-1) was readily prepared from 2-acetyl-6-methoxynaphthalene and hydrazine. In a pH 4.8 acetate buffer solution containing 1% (v/v) N,N-dimethylformamide as a solubilizer, probe TP-1 exhibited turn-on fluorescence signaling behavior in the presence of Tl³⁺. Other metal ions, anions, and major urine components such as uric acid, urea, and creatinine did not produce any noticeable fluorescence changes. The Tl³⁺ signaling of TP-1 was attributed to the hydrolysis of the hydrazone moiety, yielding the parent fluorophore 2-acetyl-6-methoxynaphthalene. The detection limit of TP-1 for Tl³⁺ sensing was 19 nM, and the signaling was completed within 2 min. Additionally, to further optimize the Tl³⁺ signaling of the hydrazone derivatives, we compared the effect of structural variations between the closely related ketone-hydrazone (TP-1) and aldehyde-hydrazone (TP-2) derivatives. We confirmed that the ketone-hydrazone (TP-1) demonstrated rapid and stable Tl³⁺ signaling behavior with satisfactory stability under the measurement conditions. Finally, as a practical application, a Tl³⁺ assay in artificial urine samples was performed using a smartphone as a portable signaling measurement and data analysis device.