A pyrene-containing Schiff base fluorescent ratiometric probe for the detection of Cu2+ in aqueous solutions and in cells

A highly selective and sensitive fluorescent ratiometric probe (1) based on pyrene-containing Schiff base for the dection of Cu2+ was synthesized. In acetonitrile-HEPES buffer solution (20.0 mM HEPES, 8:2, v/v, pH 7.4), only Cu2+, out of tested common cations, could induce the aggregation of probe 1. Fluorescence analysis showed that the excimer emission band of pyrene groups of probe 1 appeared and gradually increased with the addition of Cu2+. The fluorescent intensity ratio of excimer and monomer (I-470/I-409) of probe 1 increased 27.8-fold upon the addition of one equiv. of Cu2+ with a detection limit of 20.2 nM (1.28 ppb). The addition of Cu2+ also induced obvious color change and the characteristic peaks of pyrene excimer in UV-vis spectrometra of the relutant solution. Results from the Job plot, metal-binding fluorescent titration, mass spectra experiments and density functional theory calculations indicated a binding ratio of 2:1 (probe 1: Cu2+). In addition, probe 1 showed good potential as a fluorescent visualizing probe for the detection of Cu2+ in living GS cells of epinepheluscoioides.