A sensitive "turn-on" Schiff-base fluorescent probe for the selective detection of Fe³⁺ and bio-imaging

A novel Schiff-base fluorescent probe, 4-(N-(2- hydroxyl-1-naphthalymethylimino)-ethylamino) -7-nitro-1,2,3-benzoxadiazole (HENB) was synthesized and utilized for spectral sensing of Fe³⁺ ions at neutral pH. The binding of Fe³⁺ to HENB in C₂H₅OH-HEPES buffer (1:1 v/ v, 25 mM, pH 7.2) resulted in a pronounced emission enhancement at 530 nm, which is possibly due to the inhibition of photo-induced electron transfer (PET) process as well as the chelation enhanced fluorescence (CHEF) effect. HENB shows good selectivity and sensitivity toward Fe³⁺ with the detection limit as low as 4.51 nM. Test strips made of HENB was used for rapid "naked-eye" detection of Fe³⁺ ions in aqueous medium. Moreover, HENB was successfully applied in fluorescence imaging of exogenous and endogenous Fe³⁺ in live Hela cells as well as zebrafish. Importantly, HENB is capable of effectively monitoring the variations of Fe³⁺ in living cells during ferroptosis process.