LAUSR

An off–on colorimetric and fluorescent probe N1, N4-bis (2-(3′, 6′-bis(diethylamino)-3-oxospiro[isoindoline-1,9′-xanthen]-2-yl) ethyl) terephthalamide (Rp) for Fe3+ was designed and synthesized, which could selectively and sensitively respond to Fe3+ among other tested metal cations in THF–H2O solution (v/v = 4/6, pH = 7.2) accompanied with a remarkable fluorescence enhancement and an obvious color change visible to “naked-eye”. The fluorescence intensity of the probe Rp showed a good linearity with the concentration of Fe3+ covering from 0.1 to 26 μM and the detection limit was 0.0231 μM. Meanwhile, the binding mode between Rp and Fe3+ was found to be a 1:2 stoichiometric formation. Moreover, the complexation of Rp–Fe3+ could be broken by carbonate, so this system might be utilized as a carbonate probe in the future. Most importantly, the probe Rp was not only applied to monitor Fe3+ level in human blood serum and water samples, but also was used for fluorescence imaging of Fe3+ in living cell.Graphical abstract