Recent Progress in Fluorescent Probes for Hydrazine Detection with Double-Bond Structural Features

Hydrazine (N₂H₄) is widely used in industrial and academic fields, yet its high toxicity poses serious risks to environmental safety and human health. Reliable and sensitive quantification of trace N₂H₄ in environmental and biological systems is therefore of great importance. To meet this demand, a wide variety of fluorescent probes have been developed in recent years. Among them, probes employing hydrazine-responsive functional groups as recognition units are particularly common. Despite significant advances in this field, no systematic review currently exists that focuses exclusively on fluorescent probes containing double bonds as a structural feature. In this review, we have summarized recently reported fluorescent probes for detecting N₂H₄. These fluorescent probes classified by double bond type include carbon-oxygen double bonds (forming aldehyde motifs) and carbon-carbon double bonds (malononitrile, benzothiazole-2-acetonitrile, barbituric acid, 1,3-indanedione and 2,2-Dimethyl-1,3-dioxane-4,6-dione motifs). All these double bonds react with hydrazine to form hydrazine derivatives as the final products. Furthermore, the comments for improving probe performance are proposed. This review aims to provide valuable insights for the rational design of novel fluorescent probes for N₂H₄ detection.