A Xanthene-Scaffold Fluorescent Probe for Dual-Mode Fluorescence-Colorimetric Detection of Hydrazine and its Application in Environmental Analysis.

Hydrazine (N2H4) is recognized as a hazardous substance with severe implications for human health, ecological balance, and food security. To address this, we present HCA-IN, a novel xanthene-derived fluorescent probe engineered for the highly sensitive and specific recognition of N2H4. HCA-IN was constructed through a Knoevenagel condensation reaction between a xanthene aldehyde derived from 4-(diethylamino)salicylaldehyde and 1,3-indanedione. Mechanistically, the recognition relies on a N2H4-induced Michael addition followed by a specific cleavage event, which dynamically alters the intramolecular charge-transfer (ICT) pathway, eliciting both a remarkable fluorescence amplification and a distinct naked-eye color shift. In a THF/10 mM PBS system (8:2, v/v; pH 7.0), HCA-IN exhibited a rapid response to hydrazine, reaching equilibrium within 120 s, and delivered a broad linear working range (1-50 µM) alongside an exceptionally low limit of detection (LOD) of 6.31 nM. The probe showed excellent selectivity against prevalent metal ions, amino acids, various amines, and biological small molecules. Standard-addition experiments in lake water gave recoveries of 97.2-106.8% with relative standard deviations below 4.22%, indicating good accuracy and reproducibility. In addition, smartphone-assisted RGB analysis enabled portable quantitative detection of hydrazine, demonstrating excellent linearity (0-60 µM, R2 = 0.99666) for ΔRGB against N2H4 levels. This study provides an efficient and convenient fluorescence sensing platform for trace hydrazine detection in environmental analysis.