A Carbon Dots-Cobalt Oxyhydroxide-Based Dual Optical\nNanosensor for ppb-Level Detection of Sulfide Ions and H<sub>2</sub>S in Aqueous Media and Alginate Beads

Sulfide\nions cause considerable health risks such as loss of olfactory\nresponse, organ toxicity, and potentially malignant disorders. In\nthis report, we present the design and synthesis of a reaction-driven\nnanosensing assembly based on carbon dots (CDs), cobalt oxyhydroxide\nnanoflakes (CoOOH NF), and 1,2-bis(4-nitrobenzyl) oxy)benzene (<b>DNBC</b>) to detect sulfide ions in aqueous media. The sensing\nmechanism relies on the formation of a CDs-CoOOH nanoconjugate resulting\nin the quenching of the inherent fluorescence of CDs by CoOOH NF via\nthe inner filter effect (IFE). In this three-component nanosensor,\nthe protected form of catechol, <b>DNBC</b> acts as a pseudochemodosimeter.\nUpon the addition of S<sup>2–</sup>, it reacts with <b>DNBC</b> and leads to the in situ generation of catechol and the fluorescence\nis revived due to the catechol-mediated reductive disintegration of\nthe CoOOH framework to release fluorescent CDs, and thus, the sensing\nassembly can be used for the fast and selective assay of sulfide ions.\nThis CD-CoOOH-DNBC-based nanosensor displayed a nominal response toward\ncations, anions, small molecules, and several other reducing agents\nand offered a low limit of detection of 0.77 ppb (24 nM). The nanosensor\nworks effectively for the detection of dissolved H<sub>2</sub>S gas\nin water providing a linear response. The practical applicability\nof the sensing assembly was tested by determining the spiked sulfide\nions in real water samples with good recovery. Solid-phase detection\nof S<sup>2–</sup> ions was demonstrated using sodium alginate\nbeads to establish the ability of this cost-effective nanosensor for\nonsite detection.