A novel pyrazoline-based fluorescence probe armed by pyrene and naphthol system for the selective detection of Cu2+ and its biological application

A photo-induced electron transfer cationic fluorescence probe L1 based on pyrene-naphthol system was designed to detect the change of Cu2+ with fluorescence. The probe L1 was found to selectively recognize Cu2+ in aqueous ethanol solution [10.0 mmol/L HEPES, pH 7.4, EtOH–H2O = 1:1 (v/v)] without interference from other coexisting metal ions. The response of the sensor to Cu2+ is transient and reversible, and anions generally have no impact on the selectivity of Cu2+. Probe L1 forms complex with Cu2+ in 1:1 ratio as supported by Job’s plot analysis. The binding constants of Cu2+ was calculated to be 6.322 × 104 L/mol using a nonlinear curve-fitting method. The detection limit of Cu2+ was determined to be 1.620 × 10–7 mol/L. The energy gap between HOMO and LUMO in L1 and L1–Cu2+ was calculated by density functional theory as 3.76 eV and 2.71 eV, respectively. In addition, the probe L1 has extremely low cytotoxicity and can be used for living cell imaging studies.