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

Abstract

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, ¹H 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 × 10⁶ 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.