Ionic liquid-based dual-mode nano-optode for ultra-sensitive detection of perchlorate ions

We introduced an orange light-emitting ionic liquid (IL), XBIL, and its dual-mode nano-optode, nXBIL, for the selective detection of perchlorate (ClO₄^-) ions. Comprehensive spectroscopic and microscopic analyses confirmed the structural integrity and morphology of both XBIL and nXBIL. In aqueous solutions, nXBIL exhibits minimal fluorescence; however, upon exposure to ClO₄^- ions, a significant fluorescence enhancement of 119-fold is observed, characterized by a 24 nm blue shift in the emission peak from 540 nm to 516 nm and a colorimetric transition from light pink to yellow. This fluorescence 'turn-on' effect is attributed to ClO₄^- ion-induced molecular deaggregation. The sensor demonstrates remarkable limits of detection (LOD) and quantification in the nanomolar range, well below the U.S. Environmental Protection Agency's regulatory limit for drinking water (15 μg L^-1). A compact fluorescence-based testing kit has been developed for rapid, on-site assessment of water quality. Its effectiveness was demonstrated through tests on environmental water samples spiked with target analytes, showcasing both high sensitivity and consistent performance. Interestingly, even the unmodified XBIL compound-without nanostructuring-showed the ability to detect ClO₄^- ions. The current work presents a facile approach to designing organo-nanofluorogenic sensors, establishing a solid foundation for identifying harmful anions in the systems.