Oxadiazole-based 'on-off' fluorescence chemosensor for rapid recognition and detection of Fe2+ and Fe3+ in aqueous solution and in living cells

An oxadiazole-based chemosensor (sensor 1) for Fe3+/Fe2+ was successfully designed and synthesized. Sensor 1 displayed fluorescence quenching response towards both Fe3+ and Fe2+ in THF:H2O (4:1, v/v) solvent with high selectivity and sensitivity over all other competitive metal ions. Job's plot, mass spectra, DFT calculation and fluorescence titration disclosed that fluorescence quenching was caused by forming 1:1 complex between sensor 1 and iron ions. Sensor 1 presented high sensitive fluorescence response at the pH value of human body and its fluorescence intensity showed linear relationship with the concentration of iron ion. Sensor 1 also presented fast fluorescence response towards iron ions and the lower detection limit, 7.78 mu M for Fe2+ ion and 6.95 mu M for Fe3+ ion, respectively. Sensor 1 can be used as test strips to detect iron ions in water samples. Fluorescence cell imaging also demonstrated sensor 1 can recognize iron ions in living cells.