Molecular recognition meets microcontroller: calixarene-based fluorescent sensors for selective detection of...

Fluorescent supramolecular materials have emerged as versatile tools for detecting nitroaromatic compounds (NACs), which are key components of explosives and persistent environmental pollutants. Among these analytes, 2-nitrobenzaldehyde (2-NBZ) warrants particular attention due to its high toxicity, environmental persistence, and industrial relevance. 2-NBZ exhibits ecotoxicity (GHS H412 Harmful to aquatic life with long-lasting effects) and is classified by the US EPA as a priority pollutant because of its persistence and aquatic toxicity. However, selective and sensitive detection of 2-NBZ in complex environmental matrices remains challenging. This study reports a series of 2,6-dihydroxyacetophenone[4]arene based derivatives (DAP-AAQ: S_3.1-S_3.4). All sensors operate efficiently in aqueous solution at neutral pH and exhibit a selective "turn-on" fluorescence response toward 2-NBZ; among them, S_3.1 demonstrated the strongest binding constant (K_a = 2.0 × 10⁵ M^-1) and the lowest detection limit (LOD = 0.25 µM), while showing negligible response to other common nitroaromatics. HR-MS titration and density functional theory (DFT) calculations reveal the formation of a 1 : 1 host-guest complex stabilized by hydrogen bonding and dipole-dipole interactions, driving an interamolecular charge-transfer quenching mechanism. Furthermore, the optimized fluorescent sensor was successfully integrated with a microcontroller (Arduino) RGB detection platform. The developed device demonstrated good analytical performance in water samples, with recovery values of 93.5-96.5%, % RSD below 1.5%, while maintaining relative errors below 6% compared to a standard fluorescence spectrometer. Overall, the proposed approach presents a simple, cost-effective, and reliable platform for on-site 2-NBZ detection.