Metal-free thiadiazole–triazine porous polymer modified planar electrodes for electrochemical Hg(II) detection in water

The detection and monitoring of mercury ions (Hg²⁺) in water have become increasingly critical due to their extreme toxicity, bioaccumulation potential, and regulatory significance under international frameworks such as the Minamata Convention. Persistent mercury contamination continues to affect water systems in both developed and developing nations, including India and the United Kingdom. As a step towards detecting mercury (Hg²⁺) in water samples, we have developed miniaturized point-of-analysis electrochemical sensor based on a new metal-free, thiadiazole (TDA) and triazine (Trz) linked porous organic polymer (TDA-Trz-POP). Unlike conventional sensors that rely on metal-based recognition elements, our heteroatom-rich POP enables highly selective Hg²⁺ capture via synergistic sulphur and nitrogen coordination. The resulting sensors exhibit a lower limit-of-detection (LoD) as 1.5 nM (≈ 0.4 ppb, below the WHO Limit of 6 ppb) and a Linear range of 5-100 nM (1.4 to 27 ppb). The selective and sensitive detection of Hg²⁺ attributed to the nitrogen- and sulphur-rich surface functionalities of the TDA-Trz-POP-modified electrode, with the underlying binding mechanism is discussed in detail. Using square wave anodic stripping voltammetry (SWASV), we demonstrate real-sample applicability in water, offering a robust, low-cost, and scalable solution for on-site mercury detection in groundwater. The present work is among the first demonstrations of a metal-free porous organic polymer (POP) integrated into SPEs for point-of-analysis mercury sensing with huge potential for public health in developing nations.