A Sensitive and Reversible Fluorescent Probe for Selective Detection of Hg²⁺ and Au³⁺ Ions

The rapid and reliable detection of toxic heavy metals in environmental water sources is crucial due to the significant health risks they pose to humans. This study presents the design and development of a novel xanthene-based fluorescent probe, XH-HDZ, which is functionalized with a 2-pyridylhydrazone recognition unit. The probe initially exhibits strong fluorescence, which is quickly quenched (< 1 min) upon interacting with Hg²⁺ or Au³⁺ ions. The quenching process follows a reversible 2:1 binding mechanism, as confirmed by Job's Plot analysis and ¹H NMR titration studies. The limits of detection (LOD) for the probe were determined to be 268 nM for Hg²⁺ and 425 nM for Au³⁺, indicating high sensitivity. Furthermore, the probe was able to detect target metal ions in real water samples, including drinking water and tap water, highlighting its potential for environmental monitoring. Additionally, TLC strips were prepared and successfully used for the visual detection of Hg²⁺ and Au³⁺ ions under both daylight and UV illumination.