A novel “turn-on” fluorescent probe based on naphthalimide for the tracking of lysosomal Cu2+ in living cells

A novel fluorescent probe CuNI was synthesized and exhibited highly effective fluorescence detection ability for Cu2+ in aqueous solution (HOAc–NaOAc buffer, 10 mM, pH 5.0). CuNI was obtained by a simple condensation reaction between the aldehyde (MFNI, bearing the naphthalimide fluorescence group) and the 2-picolinyl hydrazide, which bears the Cu2+ recognized group. Under acidic conditions, CuNI showed turn-on fluorescence recognition of Cu2+ which could be readily distinguished with the naked eye under a 365 nm UV lamp and the detection limit is as low as 19.40 nM. It has been further demonstrated that CuNI was hydrolyzed under the action of Cu2+ and the significant increase of fluorescence is due to the obvious AIE effect of the hydrolysate MFNI. The application of the probe CuNI in imaging lysosomal Cu2+ in HepG2 cells has also been demonstrated.