Polymer-based recyclable solid-phase optical sensor to quantify Hg²⁺ in aqueous samples

In this work, we engineered a facile and portable solid-state sensor for the selective colorimetric detection of toxic Hg²⁺. The sensor architecture was based on a hierarchically organized macro/mesoporous polymeric monolith, which provided a highly ordered porous framework and substantial surface area features that significantly enhanced the immobilization efficiency of the chromoionophoric probe and facilitated the capture of trace-level analytes in the sub-ppb concentration range. The chromoionophore, DPQD, was synthetically tailored and subsequently integrated into a poly(acrylic acid-co-trimethylolpropane triacrylate) [poly(AA-co-TMPTA)] monolithic matrix via a robust physisorptive method. The morphological and physicochemical characteristics of the functionalized monolith were elucidated using a suite of analytical techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), ultraviolet-visible spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). Upon interaction with Hg²⁺, the spatially confined DPQD moieties form a stable 2:1 charge-transfer complex, eliciting a pronounced chromogenic transition from light yellow to deep orange. The resultant poly(AA-co-TMPTA)DPQD sensor demonstrated exceptional selectivity for Hg²⁺ over a broad array of potentially interfering metal ions, achieving a low detection threshold of 0.23 ppb and a linear response range spanning 0.02-100 ppb. The sensor also exhibited commendable operational durability, retaining over 90 % of its initial sensing efficacy after seven consecutive reuse cycles. Validation studies conducted using environmental water samples, simulated industrial wastewater, and tobacco extract matrices confirmed the sensor's practical applicability, yielding high recovery rates and excellent reproducibility, thereby underscoring its utility for real-time, in situ monitoring of mercury contamination in complex sample environments.