Multifunctional Chemosensors for the Simultaneous Detection of Copper and Mercury Ions: Applications in Test Strip Fabrication, Spiking Studies, and Logic Gate Formulation

Abstract

This study reports the successful synthesis of three new benzidine-based chemosensors (CRBD-1, CRBD-2, and CRBD-3). Among these, CRBD-1 and CRBD-2 exhibited exceptional selectivity and ultrafast response toward Cu2+ and Hg2+ ions, evident by a distinct naked-eye color change. The sensors demonstrated remarkable stability across a broad pH range and achieved low detection limits in the ppm range. CRBD-1 displayed a high binding constant for Cu2+ (2.42 × 108) and Hg2+ (1.45 × 107). Notably, the limit of detection (LOD) for Cu2+ (0.953 ppm) and Hg2+ (0.003 ppm) was significantly lower than the established safety thresholds set by WHO and ESEPA. The mechanism of Cu2+ sensing, involving intramolecular charge transfer (ICT), was thoroughly validated using UV-vis spectroscopy, 1H NMR, cyclic voltammetry, DFT, and Job’s plot analysis. Furthermore, reversibility studies enabled the development of logic gate operations for potential future applications. The functionality of the sensors was successfully evaluated in real-world samples like vegetable juice and water, as well as the potential of CRBD-2 as test strips for convenient, rapid, qualitative, quantitative, and naked-eye colorimetric detection of Cu2+ and Hg2+ in aqueous environments. © 2025 The Authors. Published by American Chemical Society.