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

We designed and synthesized a new pyrazoline-based turn-on fluorescence probe for Zn2+ 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 Zn2+ 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 Zn2+ ions. The association constant estimated by the Benesi-Hildebrand method and the detection limit were 3.92 x 10(3) M (1) and 5.2 x 10 (7) M, respectively. A proposed binding mode was confirmed by 1H 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 Zn2+, the probe can monitor Zn2+ in living cells. Moreover, the selective binding of L and Zn2+ was reversible with the addition of EDTA in buffered EtOH/HEPES solution and Zn2+ could be imaged in SH-SY5Y neuron cells. (c) 2014 Elsevier B.V. All rights reserved.