A turn-on Schiff base fluorescent probe for the exogenous and endogenous Fe3+ ion sensing and bioimaging of living cells

A Schiff base fluorescent probe, namely naphthalic anhydride - (2-pyridine) hydrazone (NAH), has been synthesized and developed for the highly selective and sensitive monitoring of Fe3+ ions in an aqueous solution and living cells. The enhanced fluorescence emission intensity of NAH has been observed upon the introduction of Fe3+ with a large Stokes shift of 100 nm, and the trace levels of Fe3+ at 38.3 nM can be monitored with no interference from other existing metal ions. Moreover, the recognition mechanism of NAH with Fe3+ has been discussed via ESI-MS, H-1 NMR and FT-IR techniques. The binding mode of NAH with Fe3+ is found to be 1 : 1 complex with the binding constants (K-a) of 1.77 x 10(6) M-1. In addition, NAH has been demonstrated to be nontoxic by cytotoxicity experiments and successfully proved to be a good probe for exogenous and endogenous Fe3+ sensing in living cells.