A “two-in-one” pyrrolopyrrole cyanine fluorescent probe for discriminative detection of hydrazine and hydrogen sulfide in real samples

Abstract

Hydrazine (N₂H₄) and hydrogen sulfide (H₂S) play important roles in industrial, agricultural and pharmaceutical fields. However, their high toxicity and carcinogenic effects as environmental pollutants cannot not be neglected when their concentrations are higher than their threshold limit. Therefore, it is urgent and challenging to develop a highly sensitive method for determining N₂H₄ and H₂S to assess environmental risks and protect human health. In this work, by utilizing a “two-in-one” strategy in which the pyrrolopyrrole cyanine (PPCy) core acts as both a recognition group and a fluorophore, an efficient dual-responsive fluorescent probe was designed and synthesized to simultaneously monitor N₂H₄ and H₂S with high sensitivity. PPCy as an electron-accepting unit and triphenylamine (TPA) as an electron-donating unit were linked by a phenyl bridge. The resulting D–A–D type probe (PPCy-Ph-BF2) was non-fluorescent. The merits of PPCy-Ph-BF2 include excellent selectivity, rapid response, low limits of detection (2.38 nM for N₂H₄ and 0.64 nM for H₂S), visual colorimetric changes and discriminative fluorescence “turn on” dual signals. The sensing mechanism revealed that when the probe encountered N₂H₄ or H₂S featuring distinct nucleophilic abilities, it undergoes different additional nucleophilic reactions to break the PPCy core, producing diverse reaction compounds. Moreover, the probe was successfully employed for quantitative detection of N₂H₄ and H₂S in solution or in the gas phase by combining a smartphone-based color app with a polyamide thin film or a sponge-based platform, meeting the requirements for household use. The release of H₂S gas from garlic and detection of N₂H₄ in soil were clearly demonstrated by a fluorescence “turn on” response visible to the naked eye. Good recovery in real samples (water, soil, red wine, beer, flour, and corn flour) showcased its broad potential for multiple applications. This work provides a new approach for dual detection of N₂H₄ and H₂S in environmental monitoring and food freshness detection more conveniently.