A pyrene-based fluorescent sensor for the discrimination and estimation of hydrazine and hydrogen sulfide and its application in assessing food spoilage.

Hydrazine (NH) and hydrogen sulfide (HS) are environmental contaminants that adversely affect human health. Fluorescence-based detection methods for these analytes utilize their nucleophilicity and reducing ability. Therefore, fluorescent sensors capable of detecting and distinguishing hydrazine and HS are highly beneficial. With this objective, we synthesized a pyrene-based fluorophore, 2-(pyren-1-ylmethylene)malononitrile (PMM), to detect and differentiate hydrazine and HS in various media and real samples. Using colorimetric and fluorimetric techniques, we examined the reaction of PMM with these analytes. Although they underwent 1,4-addition with PMM to generate a ratiometric response, the reactions followed different pathways, leading to two different products with distinct emission profiles. The reaction of PMM with hydrazine yielded the corresponding azine Py-Az, resulting in a ratiometric fluorescence response characterized by the emergence of a new peak at 458 nm and a simultaneous reduction in emission intensity at 540 nm. PMM was able to detect hydrazine in soil and water as well as its vapors. Likewise, PMM successfully detected and quantified HS in solution and human blood serum. The addition of HS to PMM solution resulted in a ratiometric response characterized by an increase in the intensity of pyrene monomer emission, accompanied by a concurrent decrease in emission at 540 nm. Using PMM, we also demonstrated the sequential detection of hydrazine, Cu, and HS. This detection utilizes the affinity of Py-Az for Cu and the subsequent demetallation of the Py-Az-Cu complex facilitated by HS. Overall, PMM generated a ratiometric response to hydrazine, a turn-on response to Cu, and a turn-off response to HS. Given that PMM exhibited a ratiometric response to HS, PMM-coated filter paper strips were also employed to assess the freshness of protein-rich foods such as fish and meat.