Discriminative ion detection of Hg2+ and Cu2+ and selective recognition of PO43? ions: Real time monitoring in food and water samples and molecular keypad lock integration

Abstract

A series of sensors, designated S3R1-S3R4, were designed and synthesized for the detection of PO<inf>4</inf>3? ions and toxic metals, specifically Hg2+ and Cu2+ ions. The colorimetric detection of PO<inf>4</inf>3? ions using these sensors exhibited a distinct visual color transition from yellow to purple in organo-aqueous media. The intrinsic cavity-like structure in the thiosemicarbazide-based derivative S3R4 significantly enhances the binding affinity for Hg2+ and Cu2+ ions in organic media. Utilizing UV–visible spectroscopic techniques and electrochemical investigations, the binding constants, stoichiometric ratios, limits of detection (LOD), and the electrochemical properties of the sensor-ion complexes were comprehensively characterized alongside their stability. Density Functional Theory (DFT) validation studies elucidated the binding mechanisms involved in the ion detection process. The LOD for PO<inf>4</inf>3? with S3R1 was determined to be 0.28 ppm, while the LODs for Hg2+ and Cu2+ with S3R4 were found to be 0.15 ppm and 0.15 ppm, respectively. The significant binding constants and detection limits underscore the potential of S3R1-S3R4 as real-time sensors for detecting PO<inf>4</inf>3?, Cu2+, and Hg2+ ions in environmental applications. Furthermore, the integration of molecular keypad locks and logic gate constructions highlights the applicability of these sensors in molecular communication systems. © 2025 Elsevier B.V.