Water-Responsive Fluorescence and Room-Temperature Phosphorescence Carbon Dots for Trace Water Detection in Ethylene Glycol and Multimodal Anticounterfeiting

Identifying trace water in ethylene glycol is essential for maintaining stringent quality control in chemical processes and ensuring product purity. However, the development of highly sensitive detection methods for aqueous impurities within this viscous solvent presents significant challenges, primarily arising from the strong intermolecular hydrogen bonding network within ethylene glycol, which not only masks the presence of water but also interferes with conventional analytical techniques. This work introduces a novel fluorescence-based detection method that combines simplicity, efficiency, and rapid response by leveraging water-responsive carbon dots (CDs). Specifically, we synthesized water-responsive carbon dots (WCDs) that exhibit enhanced fluorescence in anhydrous ethylene glycol. Notably, the introduction of water induces a concentration-dependent fluorescence enhancement at 394 nm, establishing a linear correlation within the 0-0.284% (v/v) water content range (detection limit: 0.017%, 3σ/S) with a remarkably low. By exploiting the hydrogen bonding between WCDs and cellulose paper matrices, the triplet excited states are effectively stabilized, thereby enabling green room-temperature phosphorescence (RTP) emission. This enables precise modulation of the WCDs' aggregation-dispersion states through controlled water/ethanol addition, a mechanism that drives stimulus-responsive transitions between fluorescence and RTP. These tunable optical properties not only validate the detection mechanism but also create new opportunities for developing dual-mode dynamic anticounterfeiting technologies.