Phenothiazine-thiophene-benzimidazole-based fluorescent probes for selective detection of Au3+, Ag+ and Hg2+ ions in aqueous solution and construction of molecular logic gates

Abstract

Metal ions are ubiquitous in biological and environmental systems, and their sensing and monitoring are crucial due to their significant biological roles and the need for precise concentration regulation. We synthesized three phenothiazine-thiophene-benzimidazole-based probes (1–3) for metal ion sensing. These probes possess two potential metal ion coordination sites, exhibited distinctive and sensitive sensing of Au3+, Ag+, and Hg2+ among various metal ions based on changes in luminescence/fluorescence color or intensity. The presence of Au3+ and Ag+ caused a fluorescence color change of the solution containing probe 1, shifting from bright green to orange and greenish-yellow, respectively. In contrast, the addition of Hg2+ completely quenched the fluorescence emission of the probe. The calculated limit of detection (LOD) of probe 1 was 0.003 pM for Au3+ detection, while the LODs for Hg2+ and Ag+ detection were 0.011 and 0.005 pM, respectively. Among the three probes, probe 1 was found to be the most suitable for detecting metal ions in tap water, lake drainage water, and food/beverage samples. Solid surfaces such as silica gels and cotton buds were used for the detection of Au3+, Ag+ and Hg2+ after being coated with probe 1. In addition, the [1-Au3+] and [1-Ag+] − complexes were selective for the sensing of SCN− and I−, respectively, exhibiting an OFF-ON fluorescence behavior, whereas the [1-Hg2+] complex did not respond to any anion. The fluorescence responses of probe 1 to the presence of Au3+, Ag+ and Hg2+, as well as the [1-Au3+] and [1-Ag+] complexes with SCN− and I−, enabled the construction of ‘NOR-YES-INHIBIT’ molecular logic gates. The sensing behaviors of the probes were fully characterized by various techniques including fluorescence spectroscopy, NMR, DFT calculations, FE-SEM, and DLS. © 2025 Elsevier B.V.