A solvent-dependent dual chemosensor for detecting Zn²⁺ and Hg²⁺ based on thiophene and thiourea functional groups by fluorescence turn-on

A new thiophene- and thiourea-based fluorescent chemosensor NTHC, N-(naphthalen-1-yl)-2-(thiophene-2-carbonyl)hydrazine-1-carbothioamide, was synthesized. NTHC can operate as a dual-functional chemosensor for selective sensing of Hg²⁺ and Zn²⁺ by fluorescent turn-on in different solvents, bis-tris buffer, and aqueous DMSO. According to the analysis of Job plot and ESI-mass, the complexation mode of NTHC to Zn²⁺ was determined to be a 1:1 ratio. The limits of detection of Hg²⁺ and Zn²⁺ turned out to be 4.92 μM and 3.17 μM, respectively. Interestingly, NTHC detected Hg²⁺ via the mercury-promoted desulfurization reaction of thiourea to urea. Moreover, NTHC can be applied for the bioimaging of zinc in zebrafish. The bioimaging showed fluorescence in air bladder and eyes of zebrafish. The binding mechanisms of NTHC with the two ions were identified by Job plot analysis, ESI-mass, DFT calculations, and NMR titration.