A new turn-on fluorescence probe for Zn2+ in aqueous solution and imaging application in living cells

Abstract We designed and synthesized a new pyrazoline-based turn-on fluorescence probe for Zn 2+ by the reaction of chalcone and thiosemicarbazide. The structure of the probe was characterized by IR, NMR and HRMS spectroscopy. The probe ( L) exhibits high selectivity and sensitivity for detecting Zn 2+ in buffered EtOH/HEPES solution (EtOH/HEPES = 1/1, pH 7.2) with 80-fold fluorescence enhancement, which is superior to previous reports. Job’s plot analysis revealed 1:1 stoichiometry between probe L and Zn 2+ ions. The association constant estimated by the Benesi–Hildebrand method and the detection limit were 3.92 × 10 3  M −1 and 5.2 × 10 −7  M, respectively. A proposed binding mode was confirmed by 1 H NMR titration experiments and density functional theory (DFT) calculations. The probe is cell-permeable and stable at the physiological pH range in biological systems. Because of its fast response to Zn 2+ , the probe can monitor Zn 2+ in living cells. Moreover, the selective binding of L and Zn 2+ was reversible with the addition of EDTA in buffered EtOH/HEPES solution and Zn 2+ could be imaged in SH-SY5Y neuron cells.