A naphthalimide-derived chemosensor for ratiometric detection of sulphide ions: insights into the S2−-driven reduction cascade, real-time applications and live cell imaging of bacterial cells†

Hydrogen sulphide (H₂S) is an unpleasant, harmful gas commonly found in the environment, released from geothermal vents, and produced as a byproduct in industries such as oil refining and wastewater treatment. Because of its extreme toxicity, there is growing concern about its presence, necessitating timely detection to ensure human welfare. However, detecting H₂S in various environments, including air and water, remains a significant challenge. To develop a probe for sulphide ion detection, herein, we report the synthesis of a highly selective, sensitive, and colorimetric chemosensor (NATRP) for the detection of sulphide ions (S²⁻) in a 50% aqueous medium. NATRP demonstrates exceptional sensitivity and selectivity for S²⁻ ions relative to other ions, with a limit of quantification of 26 nM and a detection limit of 7.9 nM. It shows aggregation-induced emission quenching, which upon the addition of S²⁻ ions, disaggregates with enhancement in fluorescence intensity. This enables NATRP to detect S²⁻ ions within 15 seconds and it demonstrates good pH stability, suggesting that NATRP can detect sulphide ions across a broad pH range. The mechanism underlying the detection involves the reduction of azide groups to amine groups in the presence of S²⁻ ions, confirmed by NMR titrations and HRMS analysis. Furthermore, NATRP successfully detects S²⁻ ions in water, serum and solid samples, as well as in live cell imaging in bacterial cells. Moreover, UV-visible and fluorescence data have been employed to construct 1-to-2 decoders.