Sensitive Detection and Cell Imaging of Ca²⁺ Based on a "Turn-On" Schiff Base Fluorescent Probe

Ca²⁺ ion as a second messenger in signaling pathway plays many vital roles in many biological phenomena. Thus, it is of significance for developing effective probes to detect Ca²⁺ ion specifically. Herein, a new Schiff base fluorescent probe FPH, fluorescein monoaldehyde (2-aminomethylpyridine) hydrazone, was designed and synthesized to identify Ca²⁺ in DMSO aqueous solution. The probe FPH revealed significant responses to Ca²⁺ with a fluorescence enhancement at 540 nm, exhibiting an evident fluorescence change from ultraweak luminescence to bright green. Otherwise, the FPH displayed a good linear range of 0.67 × 10^-6 to 3.33 × 10^-6 mol/L with a lower detection limit at 7.02 × 10^-8 mol/L. The probe FPH were further successfully utilized to detect Ca²⁺ in living cells by an increased bright green fluorescence.