Highly selective dual-responsive chemosensor for S^2- in pure water and its application to environmental samples such as beverage, zebrafish and food spoilage

A new dual-responsive chemosensor NOP (4-(7-nitrobenzo[c][1,2,5]oxadiazol-4-yl)piperazin-1-yl)(pyrazin-2-yl)methanone) was synthesized. Chemosensor NOP selectively probed S^2- via fluorescent turn-off and colorimetric change from yellow to pink in pure water. The detection limit of NOP for S^2- was determined to be 1.22 μM (fluorescence) and 1.05 μM (colorimetry), which were much below the WHO standard (14.8 μM). The detection mechanism of S^2- was illustrated to be thiolysis reaction of NBD-amine moiety by ¹H NMR titrations, ESI-mass, and DFT calculations, producing the cleavage product (NBD-S^-). NOP could successfully quantify S^2- in water, beverage samples, and zebrafish. Practically, NOP-coated strips could be employed for easy and rapid recognition of S^2- in real-field and for monitoring food spoilage by dual-response. Therefore, NOP assured an auspicious approach for reliable S^2- detection in real-field and food systems.