A Carbon Dots-Cobalt Oxyhydroxide-Based Dual Optical Nanosensor for ppb-Level Detection of Sulfide Ions and H₂S in Aqueous Media and Alginate Beads

Sulfide ions cause considerable health risks such as loss of olfactory response, organ toxicity, and potentially malignant disorders. In this report, we present the design and synthesis of a reaction-driven nanosensing assembly based on carbon dots (CDs), cobalt oxyhydroxide nanoflakes (CoOOH NF), and 1,2-bis(4-nitrobenzyl) oxy)benzene (DNBC) to detect sulfide ions in aqueous media. The sensing mechanism relies on the formation of a CDs-CoOOH nanoconjugate resulting in the quenching of the inherent fluorescence of CDs by CoOOH NF via the inner filter effect (IFE). In this three-component nanosensor, the protected form of catechol, DNBC acts as a pseudochemodosimeter. Upon the addition of S2–, it reacts with DNBC and leads to the in situ generation of catechol and the fluorescence is revived due to the catechol-mediated reductive disintegration of the CoOOH framework to release fluorescent CDs, and thus, the sensing assembly can be used for the fast and selective assay of sulfide ions. This CD-CoOOH-DNBC-based nanosensor displayed a nominal response toward cations, anions, small molecules, and several other reducing agents and offered a low limit of detection of 0.77 ppb (24 nM). The nanosensor works effectively for the detection of dissolved H2S gas in water providing a linear response. The practical applicability of the sensing assembly was tested by determining the spiked sulfide ions in real water samples with good recovery. Solid-phase detection of S2– ions was demonstrated using sodium alginate beads to establish the ability of this cost-effective nanosensor for onsite detection.