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

Abstract

Hydrazine (N₂H₄) and hydrogen sulfide (H₂S) 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 H₂S are highly beneficial. With this objective, we synthesized a pyrene-based fluorophore, 2-(pyren-1-ylmethylene)malononitrile (PMM), to detect and differentiate hydrazine and H₂S 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 H₂S in solution and human blood serum. The addition of H₂S 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, Cu²⁺, and H₂S. This detection utilizes the affinity of Py-Az for Cu²⁺ and the subsequent demetallation of the Py-Az-Cu complex facilitated by H₂S. Overall, PMM generated a ratiometric response to hydrazine, a turn-on response to Cu²⁺, and a turn-off response to H₂S. Given that PMM exhibited a ratiometric response to H₂S, PMM-coated filter paper strips were also employed to assess the freshness of protein-rich foods such as fish and meat.