Solvent-dependent fluorescence sensing of Cu2+, Hg2+, and CN− based on a thiosemicarbazone-functionalized pillar[5]arene and its applications in actual water samples and molecular logic gates

Abstract

A novel solvent-dependent fluorescent probe (P5T) based on a pillar[5]arene containing a thiosemicarbazone unit has been synthesized. P5T acted as a fluorescent probe for the selective detection of Cu²⁺, Hg²⁺, and CN⁻ ions in mixed solvent systems of acetonitrile (AN) and dimethyl sulfoxide (DMSO) with water. A significant fluorescence enhancement was observed following the addition of Cu²⁺ to the AN/H₂O (v/v = 7 : 3) solution of P5T. The Job's plot method and the spectrometric titrations indicated a 1 : 1 stoichiometric ratio between Cu²⁺ and the P5T probe, with a detection limit as low as 2.70 × 10⁻⁷ M. Obvious fluorescence quenching occurred when Cu²⁺, Hg²⁺, or CN⁻ was added to the DMSO/H₂O (v/v = 7 : 3) solution of P5T. The stoichiometric ratios for P5T with Cu²⁺, Hg²⁺ and CN⁻ are 1 : 1, 2 : 1, and 1 : 1, with detection limits of 3.70 × 10⁻⁷ M, 1.20 × 10⁻⁷ M and 3.32 × 10⁻⁷ M, respectively. Notably, an INHIBIT logic gate was constructed using the fluorescence turn-on phenomenon of S₂O₃²⁻ and glycine for P5T/Hg²⁺ and P5T/CN⁻, respectively, thus facilitating the rapid and efficient detection of multiple ions. P5T provides high sensitivity and strong anti-interference capability for analyzing Cu²⁺, Hg²⁺, and CN⁻ in natural water samples, yielding a relative standard deviation (RSD) of less than 5%. Thus, the solvent-dependent selective recognition capabilities and molecular logic gate functionalities of the P5T probe provide a novel approach for the analytical detection of multiple ions.