Aqueous monitoring of toxic mercury through a rhodamine-based fluorescent sensor

Mercury is a toxic heavy element, which contaminates air, land, and water, thus posing environment and human health-related threats to the ecological system. Considering the adverse ecological effects, there is an urgent need to design and develop strategic tools to detect a broader spectrum of toxic elements in different environments. The development of point-of-care tools, e.g., sensor-based devices offers a noteworthy solution to detect and monitor real-time generation or release of environmentally-related toxic elements from different sectors, even with or without partial treatments. For a first-hand estimate, a qualitative method (colorimetric) for detection of mercury could suffice. Benefiting from the colorimetric recognition methodology, herein, we developed a new system (2-(5-bromothiazol-2-yl)-3',6'-bis(diethylamino)spiro[isoindoline-1,9' xanthen]-3-one) for the detection of mercury ions. The newly developed chemical sensor is composed of a fluorescent part (rhodamine b) and a binding site (2-amino-5-bromothiazole). A highly selective and sensitive response accompanied by visual color change (colorless to pink) towards Hg2+ was observed among miscellaneous metal cations. This colorimetric change confirmed that the coordination complex exists as spirocyclic ring opened derivative of rhodamine moiety. Furthermore, the binding affinity and detection limit was also calculated from the absorbance and emission data. The calculated values are in the order of 4.72 × 10⁴ M^-1 and 6.9 μM, respectively. In addition, the results reveal that the complex between the chemical sensor (S) and Hg²⁺ is reversible in the presence of ethylenediaminetetraacetate (EDTA^2-). Finally, the newly developed sensor S was employed to detect Hg²⁺ in the wastewater. The fluorescence intensity was measured at 583 nm with S followed by spiking with Hg²⁺ at different concentrations and related linearly. In summary, taken together all the properties suggest that the newly developed sensor might display great potential in the field of environmental monitoring of toxic elements.