A Highly Selective Fluorescent Sensor for Cu²⁺ Based on a Covalently Immobilized Naphthalimide Derivative

Abstract

In this paper, we describe the fabrication and analytical characteristics of fluorescence-based copper ion-sensing glass slides. To construct the sensor, a naphthalimide derivative N-allyl-4-(bis(pyridin-2-ylmethyl)amino)ethylamino-1,8-naphthalimide (1) with a terminal double bond was synthesized and photo-copolymerized with 2-hydroxyethyl methacrylate (HEMA) on a glass surface treated with a silanizing agent. In the presence of Cu²⁺ at pH 7.24, the resulting optical sensor undergoes fluorescence quenching. Thus, the proposed sensor with visible excitation can behave as a fluorescent sensor for the selective detection of Cu²⁺. In addition, the sensor exhibits satisfactory selectivity, reproducibility and response time. The sensing membrane possesses a relatively long lifetime of at least 2 months. The linear response range covers a concentration range of Cu²⁺ from 4.0 × 10⁻⁷ to 6.0 × 10⁻⁴ mol/L and the detection limit is 2.0 × 10⁻⁷ mol/L. The determination of Cu²⁺ in river water samples shows satisfactory results.