Development of a New 4-Amino-1,8-Naphthalimide Derivative as a Fluorescent Probe for Monitoring the Divalent Copper Ion

This article presents the design and synthesis of a new variant of the 4-amino-1,8-naphthalimide fluorescent probe for monitoring the divalent copper ion, Cu 2+ . The probe BRST, functionalized with two propionic carboxylic acid groups in its receptor moiety, demonstrated high selectivity and sensitivity for the detection of Cu 2+ in competitive media of various metal ions in DMSO/HEPES buffer solution (1:1; pH 7.4), with a fluorescence quenching of 75.41%. Besides its good linearity with Cu 2+ , the probe yielded commendable values of the association constant and the detection limit, 5.54 × 10 5 M –1 and 4.33 × 10 –9 M, respectively. The quenching of the fluorescence intensity of the sensor in the presence of Cu 2+ ions is attributable to the strong paramagnetic nature of the Cu 2+ ion. The fluorescence "turn off" behavior of this simple and effective probe was successfully applied for the determination of Cu 2+ levels in untreated water samples, with excellent recovery rates of 98–105.8%.